Symposium Organizers
Xiaobo Chen Lawrence Berkeley National Laboratory
Michael Graetzel Ecole Polytechnique Federale de Lausanne
Can Li Chinese Academy of Sciences
P.Davide Cozzoli Universita del Salento - Facolta di Ingneria Industriale
and Nanoscience Institute of CNR -
National Nanotechnology Laboratory
GG5: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
GG1: Synthesis
Session Chairs
Tuesday PM, April 26, 2011
Room 3020 (Moscone West)
9:15 AM - GG1.1
Sol-peptization-gel Derived Nanostructured Titania: Influence of Critical-nuclei-size, Initial Particle Size and Packing on the Phase Stability of Anatase.
Rino Mukti 1 2 , Suminto Winardi 1 6 , Krishnankutty-Nair Kumar 3 4 , Junzheng Wang 1 , Wilfried Wunderlich 5 , Tatsuya Okubo 1
1 Department of Chemical System Engineering, The University of Tokyo, Tokyo, Tokyo, Japan, 2 Division of Inorganic and Physical Chemistry, Institut Teknologi Bandung, Bandung, West Java, Indonesia, 6 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 3 Department of Material Science and Engineering, The University of Texas at Dallas, Richardson, Texas, United States, 4 , Institute for Research in Management and Advanced Technology (IRMAT), Trivandrum India, 5 Department of Material Sciences, Tokai University, Hiratsuka, Kanagawa, Japan
Show AbstractTitania exists in a number of polymorphic forms with anatase and rutile being the most common ones. The metastable anatase is usually considered to be photocatalytically more active than rutile but the transformation to stable rutile occurs irreversibly upon heat treatment. A thorough understanding of anatase-to-rutile phase transformation behavior is not only important for designing titania based nanostructures but also for gaining a fundamental understanding on metastable-to-stable nucleation-growth based transformations. It is well known that there are several factors such as primary particle size, solution pH, hydrolysis, physical nature of precursor, reaction condition, washing and drying temperature, which can influence anatase-to-rutile transformation. Also there are several studies clearly demonstrating the importance of critical nuclei size in this transformation. However, very few studies have focused on the degree of packing of the primary particles and almost no studies have reported the influence of the initial primary particle size. In this study we focused primarily on the influence of primary paricle size and packing on the phase transformation behavior. Dried anatase gels with different degrees of particle packing in which the well-packed titania was prepared via peptization–induced by the electrostatic repulsion of primary particles in the sol (sol-peptization-gel) whereas loosely-packed titania was prepared without peptization in the sol (sol-gel). To see the effect of initial anatase primary particle size, all samples were precalcined prior to the anatase-to-rutile phase transformation that occurred during the final calcination. In the case of well-packed titania, the initial size of anatase primary particles does not influence the phase transformation behavior whereas loosely packed titania shows a strong initial anatase primary particle size dependence on the phase-transformation behavior. This concludes that the initial particle size of anatase is an important parameter emphasizing the importance of critical nuclei size in nucleation-growth type transformations in general and phase stability of nanostructured anatase in particular.
9:30 AM - **GG1.2
Controlling the Nano-Morphology of Porous Titania through Fusion of Ultrasmall Nanocrystals.
Thomas Bein 1
1 Chemistry, University of Munich (LMU), Munich Germany
Show AbstractGaining control over the nanoscale morphology of porous titanium dioxide is of enormous importance to fully exploit the great potential of this versatile material in numerous applications such as photovoltaics or charge storage. We have recently developed a highly flexible new preparation strategy for the formation of various nano-morphologies, based on fusing novel preformed ultrasmall titania nanocrystals with surfactant-templated sol-gel titania acting as a structure-directing matrix and as a chemical glue. In this "brick and mortar" approach, the “mortar” acts as a reactive precursor for the further growth of the crystalline phase seeded by the nanocrystalline “bricks”. This synergy leads to a significantly lowered temperature needed for crystallization and the preservation of the mesoporous structure. It also allows us to build various hierarchical structures such as titania inverse opals penetrated by titania mesopores, because we can significantly reduce shrinkage effects. The resulting thin films were investigated using X-ray scattering and HRTEM measurements to monitor and visualize the seeding effect, crystal growth and mesostructure development during calcination, respectively. Coatings with a broad variety of periodic mesostructures can be tuned by varying the surfactant and the fraction of the “bricks”, and thicknesses ranging from few nanometers to several micrometers are accessible. These mesostructured and crystalline films were employed as active layers in thin dye-sensitized solar cells exhibiting high conversion efficiency due to short diffusion paths. We will also discuss the integration of additional sensitizing approaches such as extremely thin absorber layers (ETA) and alternative solid hole conductors. When doped with Nb, the mesoporous networks resuling from the assembly of the nanoparticles become electrically conducting. Finally, we will show that the ultrathin crystalline walls of the mesoporous brick & mortar titania feature extremely fast lithium insertion kinetics. [1] J. M. Szeifert, J. M. Feckl, D. Fattakhova-Rohlfing, Y. Liu, V. Kalousek, J. Rathousky, T. Bein, J. Am. Chem. Soc., 2010, 132, 12605–12611.[2] H. Nemec, P. Kuzel, F. Kadlec, D. Fattakhova-Rohlfing, J. Szeifert, T. Bein, V. Kalousek, J. Rathousky, Appl. Phys. Lett., 2010, 96, 062103.[3] Y. Liu, J. M. Szeifert, J. M. Feckl, B. Mandlmeier, J. Rathousky, O. Hayden, D. Fattakhova-Rohlfing, T. Bein, ACS Nano, 2010, 4, 5373–5381.[4] J. M. Szeifert, D. Fattakhova-Rohlfing, D. Georgiadou, V. Kalousek, J. Rathousky, D. Kuang, S. Wenger, S. M. Zakeeruddin, M. Grätzel, T. Bein, Chem. Mater., 2009, 21, 1260-1265.
10:00 AM - GG1.3
Titanium Dioxide Nanobelts and Mesoporous Film for Dye-sensitized Solar Cell and Gas Sensing Applications.
Ghim Wei Ho 1 , Shweta Agarwala 1 , Wei Li Ong 1
1 Electrical & Computer Engineering, National University of Singapore, Singapore Singapore
Show AbstractThere is a great interest in the development of titania-based solids with nanoscale dimensions and specific morphology such as nanobelts, nanowires and mesoporous film depending on the applications. In our work, one-dimensional titania nanostructures are prepared by hydrothermal method from titania nanoparticles precursor via hydrolysis and ion exchange processes. The formation mechanism and the reaction process of the nanobelts are elucidated. The nanobelts are produced in gram quantities and easily made into nanostructure free standing sheet for the bulk study on their electrical and sensing properties. The sensing properties of the nanobelts sheet are tested and exhibited response to H2 gas. Another work involves mesophase ordering and structuring to attain optimized pore morphology, high crystallinity, stable porous framework of titania films. The pore structure (quasi-hexagonal and lamellar) can be controlled via the concentration of copolymer, resulting in two different types of micellar packing. The calcination temperature is also controlled to ensure a well-crystalline and stable porous framework. Finally, the synthesized mesoporous TiO2 film is fabricated into dye-sensitized solar cell. A combination of factors such as increased surface area, introduction of light scattering particles and high crystallinity of the mesoporous films leads to enhanced cell performance.
10:15 AM - GG1.4
Colloidal TiO2-based Nanocrystal Heterostructures.
P. Davide Cozzoli 1
1 National Nanotechnology Laboratory (NNL), CNR - Istituto Nanoscienze, Lecce Italy
Show AbstractTiO2-based nanomaterials represent exclusive encounter platforms on which diverse optoelectronic, thermal, mechanical, electrochemical and catalytic properties coexist with the potential for low-cost and environmentally safe energy technologies [1]. Among the most powerful synthetic approaches to inorganic nanostructures, colloidal routes have opened access to a variety of finely size- and shape-tailored nanocrystals by control of thermodynamically and kinetically driven growth processes in liquid media [2]. Further challenges are now being imposed on nanochemistry research in the pursuit of increasingly elaborate breeds of so-called hybrid nanocrystals (HNCs) that can offer diversified and/or enhanced properties as well as multifunctional capabilities. HNCs are multicomponent nanoheterostructures with a topologically controlled distribution of their composition, which incorporate epitaxially joint domains of distinct materials into individually processable nano-objects [2-5].Here, we describe recent progress made by our research group in wet-chemical development and characterization of several types of elaborate non-core/shell TiO2-based HNCs, which comprise TiO2 epitaxially bound to different metal and magnetic materials. Heterostructures based on size/shape-engineered sections of different TiO2 polymorphs [6], as well as on combinations of TiO2 sections with either iron oxide [7], Co [8], Ag, Pt [9], Cu or CuxO domains [10] will be described and discussed with regard to their structural, optical, magnetic and catalytic properties. Our results will illustrate how facet-dependent nanocrystal reactivity, lattice strain at the relevant junction regions, and surface-interface energy balance interplay at the nanoscale and dictate the final HNC topology. Useful criteria for the rational design of future prototypes of TiO2-based heterostructures with higher structural complexity and increased functionality will be suggested.References[1] X. Chen, S. S. Mao, Chem. Soc. Rev. 2007, 107, 2891[2] Advanced Wet-Chemical Synthetic Approaches to Inorganic Nanostructures; P.D. Cozzoli Ed.; Transworld Research Network 2008, Kerala (India), pp. pp. 407-453 [3] P. D. Cozzoli et al. Chem. Soc. Rev. 2006, 35, 1195[4] M. Casavola et al. Eur. J. Inorg. Chem. 2008, (6), 837[5] L. Carbone, P.D. Cozzoli Nano Today 2010, 5, 449[6] M. R. Belviso et al., in preparation; [7] (a) R. Buonsanti et al. J. Am. Chem. Soc. 2006, 128, 16953. (b) R. Buonsanti et al. Phys. Chem. Chem. Phys. 2009, 11, 3680 (d) R. Buonsanti et al. J. Am. Chem. Soc. 2010, 132, 2437[8] M. Casavola et al. Nano Lett. 2007, 7, 1386.[9] R. Buonsanti et al., in preparation[10] S. Usseglio Nanot et al., in preparation
10:30 AM - GG1.5
Chemical Vapor Synthesis of TiO2 Nanoparticles: The Time-temperature Profile Influence on Particle Characteristics.
Ruzica Djenadic 1 , Markus Winterer 1
1 Nanoparticle Process Technology, Department of Engineering Sciences and CeNIDE, University Duisburg-Essen, Duisburg Germany
Show AbstractThe application of nanoparticles is strongly influenced by particle characteristics, e.g. particle size, crystallinity, degree of agglomeration, etc. The time-temperature (t-T) profile in the gas phase of the reactor has a profound influence on the particle characteristics such as particle microstructure and surface chemistry and, therefore, on the quality of the powder consisting of nanoparticles. The role of the t-T history in chemical vapor synthesis (CVS) is theoretically and experimentally investigated. A coagulation-sintering model is used to describe the particle formation. The model is compared to experimental results obtained from synthesis of TiO2 nanoparticles from titanium isopropoxide (TTIP) in the gas phase using a hot wall reactor. Different t-T profiles were established using a furnace with an inductively generated heat source. Temperatures were set from 873 till 2023 K. The powder characteristics are analyzed in detail using nitrogen adsorption, X-ray diffraction, dynamic light scattering, and transmission electron microscopy with emphasis on degree of agglomeration. The as-synthesized TiO2 nanoparticles consist of pure anatase up to 1273 K. High temperatures and fast quenching rates should be used to limit formation of hard agglomerates.
10:45 AM - GG1.6
Uniform Titanium Dioxide Nanorods Grown by Atomic Layer Crystallization.
Xudong Wang 1
1 Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractDue to the excellent solid-state physical-chemical properties, Titanium dioxide (TiO2) has demonstrated a wide range of applications in hydrogen storage, lithium-ion batteries, fuel cells, gas sensors, detoxification, photovoltaic, photocatalysis, supercapacitors and so on. In order to achieve high performance in these applications, TiO2 nanostructures with well-controlled phase, dimension, and distribution are desired. Among them, one-dimensional (1D) structures, such as nanowires or nanorods (NRs) are considered superior due to the well defined crystal surfaces and 1D confined transport channels. Although TiO2 NWs have been made via vapor- or solution-based approaches, the nature of TiO2 crystal structure, the complexity of the Ti-O phase diagram, and the extremely low vapor pressure of titanium still make it very challenging to synthesize TiO2 NWs with well-controlled structure, morphology and properties. Recently, we demonstrated a novel approach to grow well controlled and highly uniform anatase TiO2 NRs arrays through a layer-by-layer crystallization process. It is so called atomic layer crystallization (ALC). The ALC technique mimics the atomic layer deposition (ALD) process using separated exposures of TiCl4 and H2O gaseous precursors, where the deposition is dictated by self-limited surface absorption. By increasing the deposition temperature and designing the pulsing and purging time to allow surface chemical reaction and/or atomic reconstruction to complete, 1D growth of anatase TiO2 crystal was achieved. 600 cycles of ALC produced TiO2 NRs with a length of ~300 nm and ~30 nm in diameter. We revealed that the formation of TiO2 NRs is due to the existence of the (001) surface, which showed a fast growth rate of ~0.5 nm per cycle; while the side surfaces had a growth rate of <0.1 nm per cycle. The ALC technique for growing TiO2 NRs inherits most of the merits of ALD, which includes: (1) large area deposition; (2) uniform coverage on high aspect ratio surfaces, such as submicron-sized nanochannels; (3) applicable to a variety of substrates. The resulted TiO2 NRs architecture would offer a very high surface area as well as a good carrier transport property, which could provide a novel TiO2 NR-based electrode for improving the performance of photovoltaic and electrochemical devices.
11:00 AM - GG1: Nanopart
BREAK
GG2: Solar Cells
Session Chairs
Tuesday PM, April 26, 2011
Room 3020 (Moscone West)
11:30 AM - **GG2.1
Mesoscopic Junctions for Light Energy Harvesting and Conversion.
Mohammad Nazeeruddin 1
1 Laboratory of Photonics and Interfaces (LPI), Ecole Polytechnique Federale de Lausanne, Lausanne, Vaud, Switzerland
Show AbstractKeywords: Titanium dioxide, Sensitizers, High molar extinction coefficient dyes, Dye-sensitized solar cell, Mesoporous thin films.Dye-sensitized solar cells (DSSC) consists of a working electrode, which is a sensitizer derivatized mesoporous TiO2 film, and a counter electrode, sandwitched with an iodide/triiodide (I-/I3-) redox electrolyte. The immobilized sensitizer absorbs a photon to produce an excited state, which transfers efficiently its electron into the TiO2 conduction band. The oxidized dye is subsequently reduced by electron donation from the iodide/triiodide redox system. The injected electron flows through the semiconductor network to arrive at the back contact and then through the external load to the counter electrode. At the counter electrode, reduction of triiodide in turn regenerates iodide, which completes the circuit. [1,2] In these cells nanocrystalline TiO2 film, the sensitizer and the redox couple are the key components for high power conversion efficiency. [3] This talk presents the state-of-the art of dye-sensitized solar cells, and strategies for enhancing power conversion efficiencies above 12%.Reference[1]. Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Hum-phry-Baker, R.; Muller, E.; Liska, P.; Vlachopoulos, N.; Grätzel, M. J. Am. Chem. Soc. 1993, 115, 6382. [2]. Bessho, Takeru; Yoneda, Eiji; Yum, Jun-Ho; Gug-lielmi, Matteo; Tavernelli, Ivano; Imai, Hachiro; Roth-lisberger, Ursula; Nazeeruddin, Mohammad K.; Gratzel, Michael. J. Am. Chem. Soc. 2009, 131, 5930. [3]. Yasuo Chiba, Ashraful Islam, Yuki Watanabe, Ryoichi Komiya, Naoki Koide and Liyuan Han, Jpn. J. Appl. Phys. 45 (2006) pp. L638-L640.Acknowledgement. We acknowledge financial sup-port of this work by EU-FP7 and World Class Univer-sity program grant number, R31-1003.
12:00 PM - GG2.2
Enhancing the Efficiency of Solid-state Dye-sensitized Solar Cells with Plasmonic Back Reflectors.
I-Kang Ding 1 , Jia Zhu 1 , Wenshan Cai 1 , Soo-Jin Moon 2 , Mark Brongersma 1 , Michael Graetzel 2 , Yi Cui 1 , Michael McGehee 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States, 2 , Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractSolid-state dye-sensitized solar cells (ss-DSCs) are a type of solar cell that replaces the liquid electrolyte in a conventional DSC with a solid-state hole-transport material. SS-DSCs have already achieved power conversion efficiency over 6%, and they do not have problems with potential leakage and corrosion encountered by liquid electrolyte DSCs. However, current ss-DSCs are limited by both pore filling and electron-hole recombination such that the optimal thickness is around 2 μm, which is far too thin to absorb enough light. We show that the efficiency of ss-DSCs can be greatly enhanced by incorporation of plasmonic back reflectors, which consist of two-dimensional (2D) array of silver nanodomes. The plasmonic back reflectors can be fabricated by nanoimprint lithography. They enhance absorption through excitation of plasmonic modes and increased light scattering. SS-DSCs with plasmonic back reflectors show increased external quantum efficiency, particularly in the long wavelength region of the dye’s absorption band. This approach is effective in increasing the efficiencies of ss-DSCs with normal thickness (2 μm) made with both ruthenium-complex sensitizers and strong-absorbing organic sensitizers, and the short-circuit photocurrents increased by 16% and 12%, respectively. They achieve power conversion efficiencies of 3.9% and 5.9%, on par with the world record for the devices with the same dyes. In addition to the device data, results on the theoretical modeling of plasmonic and photonic effects will also be presented.
12:15 PM - GG2.3
Control of Solid-state Dye-sensitized Solar Cell Performance by Block-copolymer-directed TiO2 Synthesis.
Pablo Docampo 1 , Stefan Guldin 2 , Morgan Stefik 3 , Priti Tiwana 1 , Christopher Orilall 3 , Sven Huttner 2 , Hiroaki Sai 3 , Ulrich Wiesner 3 , Ulrich Steiner 2 , Henry Snaith 1
1 Condensed Matter, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2 Physics, University of Cambridge, Cambridge, Cambridgeshire, United Kingdom, 3 Materials science and engineering, Cornell University, Ithaca, New York, United States
Show AbstractHybrid dye-sensitized solar cells are typically composed of mesoporous titania (TiO2), light-harvesting dyes, and organic molecular hole-transporters. Correctly matching the electronic properties of the materials is critical to ensure efficient device operation. In this study, TiO2 is synthesized in a well-defined morphological confinement that arises from the self-assembly of a diblock copolymer-poly(isoprene-b-ethylene oxide) (Pl-b-PEO). The crystallization environment, tuned by the inorganic (TiO2 mass) to organic (polymer) ratio, is shown to be a decisive factor in determining the distribution of sub-bandgap electronic states and the associated electronic function in solid-state dye-sensitized solar cells. Interestingly, the tuning of the sub-bandgap states does not appear to strongly influence the charge transport and recombination in the devices. However, increasing the depth and breadth of the density of sub-bandgap states correlates well with an increase in photocurrent generation, suggesting that a high density of these sub-bandgap states is critical for efficient photo-induced electron transfer and charge separation. We furthermore prove the concept by assembling a continuous network of TiO2 through the triblock terpolymer poly(isoprene-b-styrene-b-ethylene oxide) (ISO), where the polymer accounts for over 70% of the volume, which leads to over 5% power conversion efficiency for "self-assembled" dye-sensitized solar cells employing spiro-OMeTAD as the molecular hole transporter.
12:30 PM - GG2.4
Nanoporous Spherical TiO2 for Dye-sensitized Solar Cells.
Wan In Lee 1 , Yong Joo Kim 1 , Sang Do Sung 1 , Hark Jin Kim 1
1 Department of Chemistry, Inha University, Incheon Korea (the Republic of)
Show AbstractMonodispersed TiO2 spheres with ultra-high surface areas were synthesized by the controlled hydrolysis of titanium tetraisopropoxide (TTIP) and subsequent hydrothermal treatment at 230oC. The diameters of the TiO2 spheres were selectively controlled in the range of 260-980 nm by adjusting the ratio of TTIP to water (r-factor). The sizes of sphere were linearly proportional to the r-factor in the hydrolysis reaction. The prepared TiO2 spheres, in the pure anatase phase with a crystallite size of ~15 nm, were highly porous structures with the surface areas of 105-115 m2g-1. First, the deformed TiO2 microspheres with the size of 260 nm were applied to the main electrode layer of dye-sensitized solar cell (DSC). The achieved conversion efficiency was remarkably higher than that of the cells derived from the commercial TiO2 pastes. The advantages and disadvantages of the nanoporous TiO2 microspheres were fully analyzed and discussed in the work. Second, several spheres in different sizes were applied as the scattering layer of DSC for the efficient utilization of sun light, and the size-dependent scattering effects for those spheres were investigated. It was found that the 450-nm-sized sphere provides the highest scattering efficiency, and its high scattering efficiency seemed to be caused by a significant photonic reflection at 650-700 nm. As a result, the photovoltaic conversion efficiency was increased from 6.8 to 9.03% by introducing the 450-nm-sized spheres as scattering layer. Third, it has been found that spherical TiO2 can be successfully applied for the formation of flexible DSC. Herein, the 260-nm-sized spherical TiO2 structure was mixed with the 25-nm-sized nanoparticle (Degussa P25) to form the TiO2 layer. Blending of the large TiO2 sphere significantly increased the surface area, improved the electron transport properties, and enhanced the quantum efficiency in the long wavelength region. As a result, the photovoltaic conversion efficiency of DSC processed at 140oC was enhanced from 4.4% to 6.3%.
GG5: Poster Session I
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - GG5.1
Patterned VLS Growth of TiO2 Nanowires on Ti Substrate.
Jong-Yoon Ha 1 2 , Brian Sosnowchik 2 , Liwei Lin 2 , Albert Davydov 1
1 Metallurgy Division, NIST, Gaithersburg, Maryland, United States, 2 Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States
Show AbstractThe single crystalline rutile titanium dioxide (TiO2) nanowires (NWs) were synthesized by tin catalyzed Vapor-Liquid-Solid (VLS) method on a Ti foil substrate. The NW growth was conducted in an inductively heated vertical quartz tube reactor at the 850 °C for 10 min with Ar + 2% H2 carrier gas. The growth of the TiO2 NWs of 3 - 8 μm in length and 50 - 300 nm in diameter grew along the [110] axis and had rectangular cross-section with the (001) and (1-10) type side facets. For the growth, titanium foil served as a source of Ti, while O2 was supplied from residual oxygen in the carrier gas. The structure of the TiO2 NWs was analyzed by X-ray diffraction, high resolution transmission electron microscopy, and electron backscattered diffraction. The shape and compositions of TiO2 NWs were characterized by FESEM and X-ray EDS, respectively. This facile approach utilizes fast heating ramp rate, eliminates the need for a separate titanium source and can be extended for fabricating NWs of other metal oxides.
6:00 PM - GG5.10
Fabrication of Mesoporous Titania Opals and Inverse Opals.
Lianbin Xu 1 2 , Zhiyan Hu 1 , Shaohua Cai 1 , Zhongjiong Hua 1 , Jianfeng Chen 1 , Yushan Yan 2
1 Key Lab for Nanomaterials, Ministry of Education, Beijing University of Chemical Technology, Beijing China, 2 Department of Chemical and Environmental Engineering, University of California at Riverside, Riverside, California, United States
Show AbstractThree-dimensionally (3D) ordered mesoporous titania (TiO2) opals and inverse opals were fabricated through a combination of colloidal crystal based micromolding (hard-templating) and triblock-copolymer-templating (soft-templating) approaches. Poly(methyl methacrylate) (PMMA) inverse opals and opals were use as the hard templates for the synthesis of mesoporous TiO2 opals and inverse opals, respectively. PMMA inverse opals were prepared by templating silica opals, while PMMA opals were produced by self-assembly of monodisperse PMMA spheres. Titania precursor, consisting of amphiphilic triblock copolymer Pluronic P123 as a mesopore-directing agent and titanium tetraisopropoxide as a titanium source, was infiltrated into the void spaces of the PMMA templates (PMMA inverse opals or opals). Subsequent thermal treatment produced 3D ordered mesoporous TiO2 opals or inverse opals. The obtained mesoporous TiO2 materials exhibit a well-defined mesoporous structure with narrow pore size distribution, and the mesopore walls are composed of nanocrystalline anatase TiO2. Details on the fabrication and characterization of these materials are presented including scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, nitrogen adsorption, and photocatalytic activity studies.
6:00 PM - GG5.11
Highly Active Titania Decorated Titanate Nanotubes for Photocatalytic Organic Substances Degradation.
Soonhyun Kim 1 , Minsun Kim 1 , Sung-Ho Hwang 1 , Sang Kyoo Lim 1
1 , Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of)
Show AbstractAnatase titania decorated titanate nanotubes (TiNT-AT) are prepared by acid treatment at 80 °C from titanate nanotubes (TiNT) which are produced from the alkaline hydrothermal reaction of P25. The obtained TiNTs with 10 ~ 20 nm in diameter and several hundred nanometers in length. They composed low crystalline titanate and their surface area were ca. 152 m2/g. However, they did not show any photocatalytic activities due to a lot of defect sites which could act as recombination center of photogenerated electron and hole pairs. On the other hands, TiNT-ATs show the efficient photocatalytic activities for both gaseous CH3CHO and aqueous DCA degradation. The physicochemical properties and the photocatalytic activities of TiNT-ATs are strongly affected by the hydrothermal temperature and the subsequently treated acid concentration due to the phase transition from titanate to anatase or rutile phase of titania. However, these phase transitions could be inhibited by the surface modification of TiNT, which could be responsible for the highly enhanced photocatalytic activities and the stable TiNT-AT structures. More detailed results will be presented and discussed.
6:00 PM - GG5.12
Nb-substituted TiO2 Nanosheet Exfoliated from Layered Titanate for TCO and Photocatalysis.
Haiyan Song 1 , Anja Sjastad 1 , Poul Norby 2 , Ornulv Vistad 3 , Helmer Fjellvag 1
1 Department of Chemistry and Centre for Materials Science and Nanotechnology, University in Oslo, Oslo Norway, 2 Materials Research Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark, Roskilde Denmark, 3 , SINTEF Materials and Chemistry, Oslo Norway
Show Abstract Layered titanate Cs0.7Ti1.825■0.175O4 (■ = vacancy) with lepidocrocite structure provide opportunities for interlayer chemistry [1]. The structure contains defect host layers of edge-shared TiO6-octahedra. Interlayer cesium ions compensate for negative charge arising from Ti-vacancies. Substituted CsxTi2-x/2Mx/2O4 ,M = Mg, Fe, Co, Ni, Cu, Zn are intensively studied for ion-exchange/ intercalation [2-6]. Nb-substituted anatase films show electric and optic properties quite comparable with those of ITO [7]. We here explore Nb-substituted nanosheets as precursors for Nb-TiO2 thin films with TCO and photocatalytic properties.Phase-pure, layered Nb-substituted Cs0.7Ti1.8-xNbxO4 (x = 0 – 0.03) were synthesized by a novel sol-gel assisted solid state reaction route. XRD data indicates small, yet significant changes in unit cell dimensions caused by Nb(V) replacing Ti(IV) without structural deterioration. Layered Nb- substituted titanates were exfoliated into single layer nanosheets by proton-exchange followed by reaction with tetrabutylammonium hydroxide. The Nb-content of the layers is not affected by the ion exchange. AFM shows exfoliated nanosheets with average thickness and area of ca. 1 nm and 0.54 μm2. The thickness corresponds well to single titania blocks in the layered H0.7Ti1.825■0.175O4 mother phase. Cotton-like restacked materials were obtained by freeze-drying stable suspensions of exfoliated nanosheets. These exhibit lamellar structure with 1.75 nm interlayer distance and convert on heating into anatase and subsequently rutile. Substitution of Nb(V) for Ti(IV) into anatase suppresses the transition to rutile. Slightly expanded unit cells of both the Ti(Nb)O2 polymorphs prove that Nb enters as a solid solution, in agreement with findings for ceramically synthesized rutile type samples.AFM and XRD show that exfoliated nanosheets can be fabricated into tiled mono- and multilayer films by a layer-by-layer procedure. These were investigated for TCO and photocatalytic properties. Information on Ti and Nb oxidation states is deduced on basis of XPS, NMR and magnetic susceptibility data.References:[1] England, W. A. et al. J. Solid State Chem. 1983,49,300.[2] Reid, A. F. et al. A. D. Acta Cryst. 1968,B24,1228.[3] Groult, D.et al. J. Solid State Chem. 1980,32,289.[4] Verbaère, A. et al. Rev. Chim. Minér. 1975,12,156.[5] Hervieu, M. and Raveau, B. Rev. Chim. Minér. 1981,18,642.[6] Birchall, T. et al. J. Chem. Soc. A 1969,16,2382.[7] Furubayashi, Y. et al. Appl. Phys. Lett. 2005,86,252101[8] Song, H. Y. et al. Inorg. Chem. 2009, 48, 6952
6:00 PM - GG5.13
Porous TiO2 Multilayers via Anodization.
Lingxia Zheng 1 , Yangyang Li 1
1 Department of Physics and Materials Science, City Unversity of Hong Kong, Hong Kong China
Show AbstractSelf-organized TiO2 nanotube arrays grown by controlled anodic oxidation of a Ti substrate attracted broad scientific interest due to wide potential applications. Most anodic TiO2 nanostructures studied to date are single-layered or double-layered nanotubular films. Here we report a facile approach to fabricate multilayered porous TiO2 films by anodizing Ti foils in an organic electrolyte using a multi-step pulsed voltage waveform. The fabricated TiO2 multilayers feature mesopores, tens of layers with each layer thickness of a few hundred nanometers, and different film colors. The experimental data reported in this study is also potentially important to understand the forming mechanism of the anodic TiO2 nanostructures.
6:00 PM - GG5.14
Morphology Control of Anodic TiO2 via Mechanical Pretreatment of Ti Foils.
Hui Li 1 2 , Lingxia Zheng 1 , Yangyang Li 1
1 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong China, 2 Department of Physics, University of Science and Technology of China, He Fei China
Show AbstractSelf-organized TiO2 nanotubes conveniently fabricated by anodizing Ti foils have attracted much attention for various applications. Characteristics and performance of the anodic TiO2 nanotubes have proven largely dependent on its morphology. Here we report that mechanical pretreatment (e.g., cold rolling) of the Ti foils has a strong impact on the morphology of the subsequently etched TiO2 nanostructures. By controlling the amount of cold work applied to the Ti foils, different types of TiO2 nanostructures (e.g., self-organized nanotubes, interweaving elliptical nanotubes, or self-organized nanoporous sponge) can be obtained under the identical anodization conditions. In addition, the anodic TiO2 film etched from a cold-worked Ti foil exhibits a much cleaner and smoother top surface than the counterpart generated on an untreated Ti foil, indicating that the cold-work treatment results in a film top surface that is more resistant to the corrosion of the fluoride species in the electrolyte. This feature of smooth top surface is particularly desirable for optical sensors that are based on TiO2 interference films, because it enables well-defined Fabry-Pérot fringes. The effects of cold work treatment of the Ti foil on the morphology of the subsequent etched TiO2 nanostructures are found reversible by the thermal annealing treatment of the Ti foil, suggesting that the growth of the anodic TiO2 nanotubes is possibly affected by the grain size, defect density, and/or residual strain of the Ti foil (because cold work tends to increase the density of imperfections, reduce the grain size, and induce residual strain, whereas thermal annealing promotes recovery and recrystallization reversing the impact of cold work).
6:00 PM - GG5.17
Mesoporous Nanostructured Nb-doped Titanium Dioxide Microspheres as Catalyst Supports for PEM Fuel Cell Electrodes.
Laure Chevallier 1 , Alexander Bauer 2 , Rob Hui 2 , Jacques Roziere 1 , Deborah Jones 1
1 ICGM-Aggregates, Interfaces and Materials for Energy,, CNRS Montpellier, Montpellier France, 2 National Research Council of Canada, Institute for Fuel Cell Innovation, Vancouver, British Columbia, Canada
Show AbstractCrystalline microspheres of 5 at.% Nb-TiO2 (anatase form) with a high specific surface area have been synthesized using a templating method using ionic interactions between the nascent inorganic structure and polyelectrolyte template. A core-shell arrangement is obtained, with a meso-macroporous core structure, and a mesoporous shell. The material has been investigated as catalyst support for polymer electrolyte membrane fuel cells. A uniform dispersion of Pt particles on the Nb-doped TiO2 support was obtained using a microwave method. The electrochemical properties of Pt deposited on TiO2 based microspheres were compared with those of commercial carbon supported Pt. Nb-TiO2 supported Pt shows promising electrochemical properties, comparable to those of Pt/C. Furthermore, Nb-TiO2 supported Pt demonstrated very high stability after 1000 voltammetric cycles, since 85% of the electroactive Pt area remained after the stability testing, while only 47% of the electroactive Pt area remained in the case of Pt supported on carbon. For the oxygen reduction reaction, the highest stability was again obtained for the Nb doped TiO2 based material even though the mass activity calculated at 0.9 V vs. RHE was slightly lower. The microsphere structured and mesoporous Nb-doped TiO2 is an appealing alternative to carbon support for high temperature PEM fuel cells.
6:00 PM - GG5.18
Surface Modification of Titanium Alloy Surfaces to Enhance Osteoblast Cells Growth.
Domenico Regonini 1 , Yu Hsu 2 , Chris Bowen 1 , Irene Turner 2
1 Materials Research Centre, Mechanical Engineering, University of Bath, Bath United Kingdom, 2 Centre for Orthopaedic Biomechanics, Mechanical Engineering, University of Bath, Bath United Kingdom
Show AbstractIn this work we present our study on the surface modification of Ti alloy in order to enhance the proliferation and maturation of osteoblast type cells. In particular, two different techniques, anodisation and Micro-Arc Oxidation (MAO) are explored to generate either a nano-tubular or porous layer of TiO2 on the alloy. The materials are comprehensively characterised by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. This allows us to establish the optimal structure (tubes vs pores) as well as the crystallographic structure (amorphous or crystalline) to be used for the growth of the osteoblasts. In vitro cell culture studies to investigate the attachment of the cells on the modified surfaces are presented. Finally their behaviour when exposed to a simulated body fluid (SBF) at a different pH levels at body temperature is also discussed as localised pH changes are relevant in the postoperative wound healing situation.
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Biosensor Applications of Functionalized Singular TiO2 Nanotube Device.
Mingun Lee 1 , Jie Huang 1 , Antonio Lucero 1 , Moon J. Kim 1 , Hyunjung Shin 2 , Kook-Nyung Lee 3 , Jiyoung Kim 1
1 MSEN, University of Texas at Dallas, Richardson, Texas, United States, 2 , Kookmin University, Seoul Korea (the Republic of), 3 , KETI, Seongnam Korea (the Republic of)
Show AbstractTitanium dioxide nanotubes are an excellent candidate for high sensitivity chemical sensor application because of their large surface-area to volume ratio. Unlike other metal oxides such as ZnO and Al2O3, TiO2 exhibits minimal toxicity and good bio-compatibility, even at high concentrations. Therefore, TiO2 nanotubes are well suited to the biological sensor applications. In addition, electrical conductance of TiO2 nanotubes can be modulated by injecting chemical signals onto the surface.In this study, TiO2 nanotubes are fabricated by nanotemplate-assisted atomic layer deposition (ALD). ALD enables minimization of nanotube sidewall thickness, which improves nanotubes’ performance as a chemical sensor; thinner sidewalls lead to a larger difference between the areas of conductance and depletion regions, and thus higher conductance swing for better sensitivity. Focused ion beam deposition (FIB) was used for creating electrical connections to the nanotubes for characterization. We have evaluated TiO2 nanotube functionalization for material-type specific biochemical detection. To endow selectivity for streptavidin, the surface was treated with biotin or its derivative; selective binding between the chemical pair ensures excellent detection rate. Precise control over the nanotube sidewall thickness is critical in fine-tuning performance parameters of the resulting nanotube biosensors. Single stand-alone nanotube devices were selected rather than nanotube bundles for study, as the former has a brighter prospect in miniaturization and multichannel device applications.This research was supported by a grant (code #:2010K000351) from 'Center for Nanostructured Materials Technology' under '21st Century Frontier R&D Programs' of the MEST and International Semiconductor R&D program of COSAR-MKE, Korea.
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Nanostructured TiO2 Fibers Produced by Electrospinning.
Osnat Landau 1 , Eyal Zussman 2 , Il-Doo Kim 3 , Avner Rothschild 1
1 Materials engineering, Technion - Israel Institute of Technology, Haifa Israel, 2 Mechanical engineering, Technion - Israel Institute of Technology, Haifa Israel, 3 Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractIn recent years, fabrication of novel 1D and quasi-1D nanostructured architectures has gained increased interest. Although a few other methods of fabrication such as phase separation and template synthesis are reported in the literature, electrospinning offers several advantages including ease of fabrication and versatility for producing ceramic nanofibers that can be exceptionally long in length, uniform in diameter, and diversified in composition. These nanostructured fibrillar morphologies produced by electrospinning show a bimodal pore size distribution with large voids (on the scale of sub-micron to micron) and small mesopores. This unique morphology is specially suited for gas sensing applications. The layer’s large voids facilitate fast gas transport in and out of the sensing layer and the small mesopores contribute to the high surface to volume ratio of these layers (surface area on the order of 100’s of m2/g), providing an elegant and effective solution to one of the greatest challenges in metal oxide gas sensors.Our current research in this area focuses on detailed investigation of the correlation between processing parameters and microstructure of electrospun TiO2 fibrillar morphologies to optimize the bimodal pore size distribution. In this paper we shall report on our progress in tailoring the morphology and pore size distribution by controlling the sol-gel chemistry, electrospinning conditions, and post-deposition thermo-compression and calcination processes.
6:00 PM - GG5.23
Growth Mechanism and Wetting Behavior of Polycrystalline TiO2 Thin Films Fabricated by Plasma Enhanced Chemical Vapor Deposition.
Ana Borras 1 , Agustin Gonzalez-Elipe 1
1 Materials Science Institute of Seville, CSIC-University of Seville, Seville Spain
Show AbstractThis work presents a thorough analysis on the growth of polycrystalline TiO2 thin films by plasma enhanced chemical vapor deposition (PECVD) and their wettability. First, the study of the microstructure and texture of the thin films at different stages of deposition by high resolution SEM, XRD, GAXRD and AFM demonstrates that their growth mechanism follows the Kolmogorov Model premises (i.e. a model developed to describe the crystal growth from a homogeneous phase). Moreover, the formation of crystal domains is shown as a characteristic feature of the growth by PECVD. The wettability (water contact angle and control of the contact angle by light irradiation) of polycrystalline anatase TiO2 thin films of different thickness was analyze within the Wenzel, Cassie and Miwa model assumptions to ascertain the effect of roughness and other surface heterogeneities on their characteristic parameters. The roughness factors defined in the different models were calculated from AFM images of the films at two different observation scales in the framework of the Dynamic Scaling Theories. The obtained results show that the wetting angle of an equivalent flat anatase surface with a value of 82° can only be properly estimated for observation scales of 5x5 µm and the Miwa model. Experiments of UV induced hydrophilization and posterior recuperation point out a clear dependence of the light induced wettability on the texture and crystal size of the anatase films.
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Synthesis and Photocatalytic Characteristics of Vertically-aligned Fe-doped TiO2 Nanobelts.
Hun Hoe Heo 1 , Nguyen Thi Quynh Hoa 1 , Lam Van Nang 1 , Zonghoon Lee 2 , Eui-Tae Kim 1
1 Departement of Materials Science & Engineering, Chungnam National University, Daejeon Korea (the Republic of), 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractOne-dimensional (1-D) TiO2 nanostructures such as nanowires, nanotubes, and nanobelts have been extensively studied for promising photocatalysis applications in elimination of pollutants and splitting of water for hydrogen fuel. In particular, the synthesis of well-ordered 1-D TiO2 nanostructures on a supporting substrate is of great interest. Unlike suspended photocatalysts, 1-D TiO2 nanostructures on a substrate can avoid the agglomeration problem and provide an easy recovery process for photocatalyst, including colleting them after use. Another important aspect is the modification of TiO2 by doping to realize photocatalytic reactivity under visible light. The wide bandgap energy (~3 eV) of TiO2 limits its photocatalytic reactivity to ultraviolet light. In order to extend the photocatalytic reactivity to visible light regime, transition metals or nonmetals such as carbon and nitrogen should be doped into TiO2. Most doping studies on 1-D TiO2 nanostructures have been focused on a post-doping process such as ion implantation and annealing with CO gas. In this study, we report the metallorganic chemical vapor deposition (MOCVD) synthesis of vertically-aligned Fe-doped TiO2 (Fe:TiO2) nanobelts on a Si substrate, in which Fe can be successfully in-situ doped. The dopant selection can be numerous because of the chemical flexibility of MOCVD. The Fe:TiO2 nanobelts showed high-efficient visible-light photocatalytic activity, which was evaluated by the decomposition of methylene blue under visible light irradiation. We will further discuss the photocatalytic characteristics and growth mechanism of vertically-aligned Fe:TiO2 nanobelts.
6:00 PM - GG5.25
Role of Nano-links between TiO2 Hollow Hemispheres in the Enhancement of Gas Sensing Properties of Embossed TiO2 Films.
Hi Gyu Moon 1 2 , Dong Su 3 , Hyung-Ho Park 2 , Seok-Jin Yoon 1 , Ho Won Jang 1
1 Electronic Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Materials Science and Engineering, Yonsei University, Seoul Korea (the Republic of), 3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York, United States
Show AbstractTiO2 is a promising material for gas sensors. To achieve high sensitivities, the material should exhibit a large surface-to-volume ratio and possess the high accessibility of the gas molecules to the surface. Accordingly, a wide variety of porous TiO2 nanomaterials synthesized by wet-chemical methods have been reported for gas sensor applications. Nonetheless, achieving the large-area uniformity and comparability with well-established semiconductor production processes of the methods is still challenging. An alternative method is soft-templating which utilizes nanostructured inorganic or organic materials as sacrificial templates for the preparation of porous materials. Fabrication of macroporous TiO2 films and hollow TiO2 tubes by soft–templating and their gas sensing applications have been reported recently. In these porous materials composed of assemblies of individual micro/nanostructures, the form of links or necks between individual micro/nanostructures is a critical factor to determine gas sensing properties of the material. However, a systematic study to clarify the role of links between individual micro/nanostructures in gas sensing properties of a porous metal oxide matrix is thoroughly lacking. In this work, we have demonstrated a fabrication method to prepare highly-ordered, embossed TiO2 films composed of anatase TiO2 hollow hemispheres via soft-templating using polystyrene beads. The form of links between hollow hemispheres could be controlled by O2 plasma etching on the bead templates. This approach reveals the strong correlation of gas sensitivity with the form of the links. Our experimental results highlight that not only the surface-to-volume ratio of an ensemble material composed of individual micro/nanostructures but also the links between individual micro/nanostructures play a critical role in evaluating the sensing properties of the material. In addition to this general finding, the facileness, large-scale productivity, and compatability with semiconductor production process of the proposed fabrication method promise applications of the embossed TiO2 films to high-quality sensors.
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Supersonic Plasma Jet Deposition of Titanium Dioxide Nanomaterials.
Fabio Di Fonzo 1 , Francesco Fumagalli 2 , Moreno Piselli 2 , Dario Tassetti 2 , Carlo Bottani 1 3 , Claudia Riccardi 2
1 , Center for Nano Science and Technology-IIT@POLIMI, Milano Italy, 2 Department of Physics, Università degli Studi di Milano Bicocca, Milano Italy, 3 Department of Energy, NEMAS, Politecnico di Milano, Milano Italy
Show AbstractWe present a novel plasma based deposition technique for the large scale, large area deposition of titanium dioxide nanomaterials with controlled chemistry, morphology and porosity from metallorganic precursors. The novelty of the proposed approach is the segmentation of the gas phase material synthesis in two separate steps: chemistry control in a reactive non-thermal plasma environment; nucleation and self-assembling control by means of a supersonic inseminated jet over a substrate. Flow-dynamic isolation, by means of a supersonic expansion, allows separate optimization of the dissociation and reaction phase towards the formation of the radicals needed for precursor dissociation. Successively, cluster nucleation and aggregation occurs in the supersonic plasma jet expanding from the plasma into a high vacuum chamber. Furthermore, the use of a supersonic jet maintains beam focalization and reduces time of flight, allowing a better control in the cluster sizes and then in the structure of the thin film. More in detail, since the supersonic plasma jet plume is limited by a shock wave zone (the Mach disk, beyond which the speed decreases abruptly) it is possible to intercept species with different sizes and energies by changing nozzle to substrate distance: clusters of few atoms with high kinetic energy are collected at small distances, while more massive nanoparticles with low kinetic energy appears increasing the distance. This reflects on the material growth mechanism: compact films with minimal roughness appears minimizing the nozzle-substrate distance; porous and nanostructured materials form at larger distances. Furthermore, a supersonic beam allows to obtain clusters of nanoparticles, with a small dispersion of sizes. By a proper choice of deposition conditions it is possible to tune grain size and morphology to a large extent and even to obtain hierarchical nanostructures and graded films. In order to achieve a complete understanding of the as produced nanostructured TiO2 films, a thorough material and process characterization has been performed by means of Electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), UV-vis, X-ray Photoelectron spectroscopy (XPS) analysis and atomic force microscopy (AFM), Optical Emission Spectroscopy (OES), mass spectroscopy (MS) in the plasma state and in particular in the plasma plume expanding in vacuum. We point out that such a plasma-source configuration is readily extensible to a linear or even to a two dimensional lay-out compatible with large scale, large area deposition of Titanium Dioxide Nanomaterials for applications, for example, in photocatalysis and Dye Sensitized Solar Cells.
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Low Temperature Synthesis of Oriented {001} Anatase Films.
Andrew Ichimura 1 , Shirin Usmani 1 , Diana Marx 1
1 Chemistry & Biochemistry, San Francisco State University, San Francisco, California, United States
Show AbstractTitanium dioxide finds extensive use in applications that range from coatings and pigments to oxidative photocatalysis and dye-sensitized solar cells (DSSC). In these and other applications, the properties depend on the material phase (anatase or rutile), particle size and morphology, and surface chemistry. For example, because of the high surface area, nanoparticle anatase is commonly used for photocatalysis and DSSC. Both computational and experimental work suggest that the {001} surface of anatase is the most reactive.1,2 A synthetic route to powders with dominant {001} surface area up to 47% was reported.2 The key synthetic ingredient is fluoride, which binds to anatase lowering the overall surface energy, but selectively stabilizes the {001} relative to {101} facets. In this work, we report a route to polycrystalline anatase films with a dominant {001} texture.Our initial efforts tested ITO, glass, and gold films as potential substrates. A gold film (200 nm) that was evaporated and annealed on freshly cleaved 1” mica wafers yielded the largest uniform areas. Anatase was prepared by hydrothermal synthesis from TiF4 and NH4F homogeneous solutions and film growth was studied as a function of temperature, time, and reagent concentration. At all temperatures from 90-180oC, continuous single phase anatase films grew from the gold surface to a thickness between 200 nm (30 min.) and 600 nm (18 hrs). Over the range of conditions studied, the crystals that cover the surface of the polycrystalline film are approximately square in shape and arrayed ~parallel to the substrate. On the basis of the crystal morphology, grazing angle x-ray diffraction (GA-XRD), and electron backscatter diffraction (EBSD) experiments, the exposed surfaces are {001} facets. Thicker films show trapezoidal {101} facets at edges. GA-XRD measurements confirm the dominant c-axis orientation of the films in that peaks without a c-axis component, e.g., (200), (220), etc., are weak or absent. The advantage of our hydrothermal synthesis method is that resultant films are highly ordered polycrystalline arrays in which monolithic crystals span the film from substrate to external surface. Such films may facilitate charge transport across the layer. Thin films of oriented reactive crystals could serve as models for surface studies and may find applications as photocatalysts and as components of solar cells. Our synthetic strategy for preparing anatase films with tunable thickness and crystal morphology, and the results of various physical measurements (GA-XRD, EBSD, EM, EPR) will be described.1. Gong, X.Q.; Selloni, A. J. Phys. Chem. B, 2005, 109, 19560-19562.2. Yang, Y.G.; Sun, C.H.; Qiao, S.Z.; Zou, J.; Liu, G.; Smith, S.C.; Cheng, H.M.; Lu, G.Q. Nature 2008, 453, 638-642.
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Effect on Nucleation and Growth Kinetics of TiO2 Films Radio-frequency Sputtered in Ar/oxygen Atmosphere.
Monika Rathi 1 , Pavel Dutta 2 , Phil Ahrenkiel 1 , Venkateswara Bommisetty 2
1 , South Dakota School of Mines and Technology, Rapid City, South Dakota, United States, 2 , South Dakota State University, Brookings, South Dakota, United States
Show AbstractAmorphous TiO2 thin films were prepared by radio-frequency sputtering from a TiO2 target in only Ar and mixed Ar/oxygen atmosphere at room temperature on molybdenum transmission electron microscope (TEM) grids. TiO2 deposited grids were observed under TEM during in situ annealing in a TEM heating stage. Electron diffraction reveals that the TiO2 thin films are of anatase crystallographic phase. TiO2 deposited only in Ar atmosphere crystallized at 300 oC whereas TiO2 deposited in 5 % oxygen: 95 % Ar atmosphere crystallized at a much higher temperature 450 oC. This enhancement of crystallization temperature might be attributed to oxygen vacancy filling leading to a reduction of defect states in mixed Ar/O2 plasma deposited TiO2. Further, the effect of oxygen vacancy filling on the nucleation and growth kinetics was studied by monitoring the evolution of grain size and grain boundaries of TiO2 thin films. Measurement of crystalline volume fraction and grain number density was done using two dimensional TEM images obtained during the annealing process. Local work function and charge transport measurement of the as deposited and annealed films will be conducted using Kelvin Probe Force Microscopy (KFM) and Conducting Atomic Force Microscopy (C-AFM) to gain further understanding of the effect of oxygen incorporation in TiO2.
6:00 PM - GG5.3
Influence of Post-annealing Temperature on the Properties of Ti-Doped In2O3 Transparent Conductive Anti-fogging Films by DC Ratio-frequency Sputtering.
Lei Li 1
1 , Jilin university, Changchun, Jilin, China
Show AbstractIn this paper, titanium doped indium oxide (TIO) thin films deposited on quartz glass substrates by DC sputtering were presented. Deal with different temperature of post-annealing to make samples to display different optical and electric properties. The effects of sputtering on the structural, morphologic, optical and electrical characteristics of TIO thin films were investigated by XRD, Hall measurements and optical transmission spectroscopy. The deposited films exhibited polycrystalline in the preferred (222) orientation, with higher mean grain size and lower resistivity 1.26 ×10-4Ωcm at the post-annealing temperature at 520 centigrade. The average optical transmittance of the films is over 90%, and the transmittance has only around 1.8% change with different post-annealing temperatures.
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Controlled Synthesis of Nanoparticles of TiO2 byPrecipitation in Aqueous Solution for the Control of the Properties.
Sophie Cassaignon 1 , Olivier Durupthy 1 , Jean-Pierre Jolivet 1
1 LCMCP, UPMC, Paris France
Show AbstractTitanium dioxide is largely used in technological applications as a white pigment for paints or cosmetics, as a support in catalysis and as a photocatalyst. It is also a common material for photovoltaic cells. As for many other solids, nanosized TiO2 particles are of a particular interest because of their specifically size-related properties. Hence, many works have focussed on the synthesis of titanium dioxide nanoparticles. The uses and performances of a material for a given application are however strongly influenced by the crystalline structure, the morphology and the size of the particles. In addition, particles with varying mean size and narrow size distribution can be needed to study the surface effects over an extended range of surface/volume ratio. For metal oxide particles, the precipitation or coprecipitation of cations in aqueous solutions is an easy and cheap synthesis route. Various techniques consist in limiting the space available for the particle growth by precipitating ions in microemulsions, vesicles, polymer solutions or gels. Complexing agents are also often used but they mostly act on the morphology of the particles. Such methods raise difficulties in getting out particles free from polymer, surfactant or ligands, the adsorption of such species mostly inducing surface effects strongly influencing the behavior of particles. Actually, a careful control of the conditions of precipitation in aqueous medium, especially nature of the precursors, acidity and temperature, allow to control the crystal structure, the size and the morphology of particles. This presentation is focused on the synthesis of TiO2 polymorphs (anatase, brookite and rutile) by hydrolysis of TiCl4 and/or TiCl3 in water and on the influence of the synthesis parameters on the nature of the particles obtained. In addition we will discuss on the effect of the structure and the morphology on the properties, in particular in the photovoltaic devices and in lithium batteries.
6:00 PM - GG5.4
Lithium Ion Intercalation Performance of Polymorphs Chrysanthemum-like C/TiO2.
Po-Chin Chen 1 , Min-Chiao Tsai 1 , Chi-Young Lee 1 2 , Hsin-Tien Chiu 3
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Center for Nanotechnology, Materials Science, and Microsystems, National Tsing Hua University, Hsinchu Taiwan, 3 Department of Applied Chemistry, National Chiao Tung University, Hsinchu Taiwan
Show AbstractThe flake chrysanthemum-like TiO2 with TiO2-B and anatase phases can be obtained through hydrothermal method using acetic acid and tetrakis(isopropoxy) titanium (IV) (TTIP). Different TiO2-B/anatase ratio was controlled by different annealing conditions. In order to be used as an anode of lithium ion battery, the conductivity of TiO2 was improved via carbon coating. The anode of lithium ion battery made by carbon coated chrysanthemum-like TiO2 which was annealed under 500 °C for 4 hours shows high capacity, good cycle performance and high rate charge/discharge ability. The capacity of lithium intercalation into chrysanthemum-like TiO2 with carbon coating at 0.1C charging rate reach 320 mAh/g and the reversible capacity (lithium extraction) is 252 mAh/g in the first cycle. After 100 cycles, the capacity to extract lithium still remains 141 mAh/g. For high charging rate (1C), the capacity of lithium insertion reach 250 mAh/g and the reversible capacity is 209 mAh/g in the first cycle. After 100 cycles, the capacity of extract lithium maintain at 122 mAh/g. These results indicate that although the as-prepared product was annealed under 500 °C for 4 hours, the TiO2-B phase didn’t convert to anatase entirely. This phenomenon may be a reason to explain the good cyclability of the chrysanthemum-like TiO2 with carbon coating at high charge/discharge rate. In conclusions, the chrysanthemum-like TiO2 with carbon coating is promising as a negative electrode material in lithium ion battery with high capacity, good cyclability and high rate capability.
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The Visible Light Photocatalytic Performance of Rutile TiO2 Nanorods Assisted by H2O2.
Min-Han Yang 1 , Tsung-Ying Ke 1 , Chi-Young Lee 1 2 , Hsin-Tien Chiu 3
1 Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Center for Nanotechnology, Materials Science, and Microsystems, National Tsing Hua University, Hsinchu Taiwan, 3 Department of Applied Chemistry, National Chiao Tung University, Hsinchu Taiwan
Show AbstractOne dimensional single crystalline rutile TiO2 was synthesized by hydrothermo method using titanate as precursors in acid solution. The morphology of rutile TiO2 nanorods could be adjusted through the concentration of hydrochloric acid. As concentrated HCl was used, thin TiO2 nanorods with large surface area were obtained, whereas thick rutile rods were obtained in dilute HCl solution. The degradation of methyl orange in hydrogen peroxide solution by rutile TiO2 and commercial P25 was examined under AM 1.5 solar simulator. The results showed that the performance was intensely enhanced by the H2O2 addition and reaction rate increased with surface area. The reaction kinetic tended to be a zero-order reaction. Compared with commercial P25, the reaction rate coefficient of rutile TiO2/H2O2 system is 2.6 times larger than that of P25/H2O2. According the results, the photocatalytic performance of rutile TiO2 with the assistance of H2O2 was dramatically promoted in visible light illumination. It makes the degradation of organic pollutants by solar energy more possible.
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First-principles Study of Oxygen Deficiency in Rutile Titanium Dioxide.
Hsin-Yi Lee 1 , Stewart Clark 2 , John Robertson 1
1 Engineering, University of Cambridge, Cambridge United Kingdom, 2 Physics, University of Durham, Durham United Kingdom
Show AbstractThe energy levels of the different charge states of oxygen vacancy and the titanium interstitial in rutile TiO2 were calculated using the screened exchange (sX) hybrid functional. The screened exchange method [1] mixes a Thomas-Fermi screened Hartree-Fock exchange into the local-density approximation (LDA) to correct the band gap error of LDA or GGA. Using the screened exchange method, we got 3.1 eV for the band gap of rutile TiO2, which is close to the experimental value (3.1 eV). The oxygen vacancy and titanium interstitial both create defect states inside the energy gap. We have studied the defect formation energy about the oxygen deficient structure. It is found that the defect formation energies, for the neutral charge state, of oxygen vacancy and titanium interstitial are quite similar, 2.40 eV and 2.45 eV respectively, for an oxygen chemical potential of the O-poor condition. The similar size of these two calculated energies indicates that both are a cause of oxygen deficiency, as observed experimentally [2]. The transition energy of oxygen vacancy lies within the band gap, corresponds to the electrons trapped at adjacent titanium sites. The screened exchange method gives a correct description of the localization of defect charge densities, which is not the case for GGA [3-5]. The singly positive oxygen vacancy has an unpaired electron which is localized around the two titanium atoms close to the oxygen vacancy site, not all three titaniums.1. S J Clark, J Robertson, Phys Rev B 82 085208 (2010)2 S Wendt et al, Science 320 1755 (2008)3 B J Morgan, G W Watson, Surface Sci 601 5034 (2007); Phys Rev B 80 233102 (2009)4 C DiValentin, G Pacchioni, A Selloni, J Phys Chem C 113 20543 (2009)5 S Lany, A Zunger, Phys Rev B 80 085202 (2009)
6:00 PM - GG5.8
Growth of (101) Oriented TiO2 Thin Films on F Doped SnO2 by RF Magnetron Sputtering.
Naresh Bhende 1 , Mamidanna Sri Ramachandra Rao 1
1 Department of Physics, Nano Functional Materials Technology Centre and Materials Science Research Centre, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
Show AbstractTiO2 exists in three different polymorphs such as anatase, rutile and brookite [1]. Anatase and rutile crystallize in tetragonal structure whereas brookite is orthorhombic [1]. Anatase phase is stable at low temperatures (up to 600 OC) and rutile structure is stable at high temperatures (700 - 800 OC). TiO2 has its applications in photo-catalysis, sensors and dye sensitized solar cells [1, 2]. Anatase TiO2 is preferred in dye sensitized solar cells due to higher (0.2 eV) Fermi energy level compared to rutile TiO2 [3]. The oriented TiO2 thin films have potential applications in dye-sensitized solar cells (DSSCs) and photocatalysis [4]. The adsorption of dye molecules on (101) oriented TiO2 is 4 times compared to P-25 [4].TiO2 thin films were deposited on fluorine doped SnO2 conducting glass substrate at 200 OC and 340 OC for 3 h using rf magnetron sputtering. The deposition of TiO2 thin films were carried out at 0.03 mbar of Ar atmospheric pressure and at a radio frequency power of 200 W. As grown thin films were amorphous in nature while the deposited thin films were then post annealed in air and oxygen atmosphere at 500 OC for 2 h which resulted in crystalline anatase phase with (101) orientation. The structural characterization of TiO2 thin films was carried out by X-ray diffraction (XRD) and Raman spectroscopy. Morphology and optical properties of thin films were studied using Atomic Force Microscopy (AFM) and UV-Visible spectroscopy. The thin films exhibited all the characteristic vibration modes (Ag +2Bg+3Eg) of TiO2 in Raman spectra. The transmittance of the 200 OC substrate temperature deposited TiO2 thin films are higher compared to those deposited at 340 OC. The thin films annealed in oxygen atmosphere showed lower transmittance when the substrate temperature is 200 OC compared to that of annealed thin films at 340 OC. From the transmission spectra of the thin films, band gap of TiO2 thin films was estimated. These results will be discussed in detail.References:[1]. Gratzel, M.; Curr. Opin. Colloid Interface Sci., 314, (1999)[2]. Matthews R.W., Journal of Catalysis, 111, 264 (1988)[3]. Huang S. Y., Kavan L., Exnar I., and Gratzel M., J. Electrochem. Soc. 142, L142 (1995)[4]. Motonari Adachi, Yusuke Murata, Jun Takao, Jinting Jiu, Masaru Sakamoto, and Fumin Wang, J. Am. Chem. Soc., 126 (45), 14943 (2004)
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Anion Effects on Conduction Band Edge and Charge Transfer Kinetics in Dye-Sensitized Ionic Liquid Solar Cells.
Min Zhang 1 , Peng Wang 1
1 , Changchun Institute of Applied Chemistry (CIAC),Chinese Academy of Sciences (CAS), Changchun, Jilin, China
Show AbstractThe restricted storage of fossil fuels on the earth and environmental problems concomitant with their usage are presently putting forward the search of alternative clean renewable energy as an imperative issue for the boom of future global economy. Over the past years, more and more but still a minority of solar power has been exploited to supply a sustainable and clean electricity based upon the well-established silicon technology, despite that the price/performance ratio remains a big challenge. In the pursuit of more affordable fashions for the conversion of solar to electric power, the dye-sensitized solar cell technology has received an ever-increasing amount of scientific and industrial attention in the foregone two decades, owing to its feasibility to serve as a low-cost candidate in appeasing the future planetary energy demand. At the moment, one big challenge toward its large-scale application relies on how to realize a sensible efficiency for cells without the use of volatile solvents, which brings a serious encapsulation issue. Herein we report evident effects of the dicyanamide anion versus tetracyanoborate on the energetics of titania conduction band edge and the kinetics of multi-channel charge-transfer reactions in ionic liquid solar cells employing a high-absorption coefficient ruthenium sensitizer C106. The tetracyanoborate electrolyte confers a relatively shorter photoluminescence lifetime on the dye C106 anchored on titania nanocrystals. However, a higher charge separation yield at the titania/dye/electrolyte interface is counterintuitively determined for the tetracyanoborate case, mainly benefited from an almost 3-fold faster electron injection as revealed by transient emission measurements, which is in good agreement with an almost indistinguishable ratio of external quantum efficiency enhancement in the whole spectral response region. Compared to tetracyanoborate, the presence of dicyanamide at the titania/electrolyte interface evokes a 27-fold slower charge recombination with triiodide, accounting for the open-circuit photovoltage variation observed in current-voltage measurements.
Symposium Organizers
Xiaobo Chen Lawrence Berkeley National Laboratory
Michael Graetzel Ecole Polytechnique Federale de Lausanne
Can Li Chinese Academy of Sciences
P.Davide Cozzoli Universita del Salento - Facolta di Ingneria Industriale
and Nanoscience Institute of CNR -
National Nanotechnology Laboratory
GG10: Poster Session II
Session Chairs
Wednesday PM, April 27, 2011
Salons 7-9 (Marriott)
1:00 AM - GG10: Poster
GG10.34 Transferred to GG11.5
Show AbstractGG6: Synthesis Nanotube
Session Chairs
Thomas Bein
P. Davide Cozzoli
Wednesday PM, April 27, 2011
Room 3020 (Moscone West)
9:30 AM - GG6.1
Synthesis of Highly-ordered, Debris-free TiO2 Nanotube Arrays in Ionic Liquid Electrolytes.
Huaqing Li 1 2 , Jun Qu 1 , Hanbing Xu 1 , Huimin Luo 3 , Sheng Dai 4 , Ilia Ivanov 5 , Harry Meyer 1 , Miaofang Chi 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics, University of Tennessee, Knoxville, Tennessee, United States, 3 Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 5 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractSelf-aligned TiO2 nanotube arrays have great potential in energy harvesting and storage applications due to their larger surface area, chemical stability, and the ability to provide an excellent electron percolation pathway. The most common synthesis method is anodization of titanium metal in aqueous or organic polarized electrolytes containing fluoride species. However, anodization-produced TiO2 nanotubes (NTs) are usually covered by a nanoporous debris layer. This debris layer causes a longer charge transport time, reduced transmittance, and limited NT accessibility, which deteriorates the performance of the tubes. In this study, we have successfully synthesized debris-free TiO2 NT arrays using a new group of ionic liquids (ILs) based electrolytes. This lack of debris layer formation is attributed to the high ionic conductivity leading to a high chemical dissolution rate that prevents the accumulation of etched oxides and electrolyte decomposition products on the top of the NTs. The NTs’ size, morphology, and growth rate were found to be directly related to the dissolution rate of the electrolyte, which can be tailored by adjusting the ratio of ILs, water, and inactive organic compounds. Another potential advantage of using IL electrolytes is the possibility of inherent doping. X-ray photoelectron spectroscopy (XPS) examination has revealed evidence of boron and fluorine doping in TiO2 NTs grown in an IL with tetrafluoroborate (BF4−) anions. Initial diffuse reflectance measurements suggested enhanced absorptance for visible and infrared light. Notice: This abstract has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes." Research sponsored by the U.S. Department of Energy, EERE Industrial Materials Program, under the American Recovery and Reinvestment Act. The characterization work was partially supported by the ORNL SHaRE User Program and Center for Nanophase Materials Sciences of Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.
9:45 AM - GG6.2
Preparation of TiO2 Nanotubular and Nanoporous Arrays by Electrochemical Anodization on Metallic, Transparent, Ceramic and Flexible Substrates.
Guido Faglia 1 2 , Vardan Galstyan 1 2 , Alberto Vomiero 2 1 , Elisabetta Comini 1 2 , Giorgio Sberveglieri 1 2
1 Chemistry and Physics for Materials, University of Brescia, Brescia Italy, 2 , CNR IDASC, Brescia Italy
Show AbstractAnodization of titanium in hydrofluoric acid (HF) containing electrolytes produces nanotube arrays whose length is currently limited up to 500 nm, due to the high chemical dissolution rate of the anodized TiO2 layer. Moreover, when nanoporous or nanotubular structures are prepared starting from a thin layer of titanium, the presence of highly aggressive HF in the electrolyte prevents the use of plastic substrates.We demonstrated that discrete and well-aligned TiO2 nanotubular and nanoporous structures can be obtained over indium tin oxide (ITO)-coated polyethylene terephthalate (PET) (from Sigma-Aldrich) flexible substrates, by electrochemical anodization of thin films of Ti in neutral glycerol based electrolytes. Nanoporous arrays were produced by galvanostatic mod and nanotubular arrays by potentiostatic mod. TiO2 nanotubes prepared at room temperature on ITO-PET in 0.5 wt.% NH4F, 2 mol L-1 H2O in glycerol by anodization voltages 25, 35, 50 and 70 V present a very homogeneous size distribution of tubes, which average inner diameter is approximately 30, 55, 70 and 80 nm, respectively. Beside in glycerol based electrolytes fluorine ions mobility is quenched and the chemical dissolution of the oxidized TiO2 is essentially suppressed in comparison with acidic aqueous solution, enhancing formation of longer -up to a few microns- nanotubes at the expense of lengthy anodization times (up to 140min). The tubes are closed at the bottom, as it is typical for anodization process, and exhibit a closely packed hexagonal geometry on a short range scale. The nanotubes surface is very clean, and is obtained without the need of any post-growth treatment other than mild bath in ethanol, while composition is consistent with Ti:O=1:2 atomic ratio within the uncertainty of SEM-related EDX measurement. Full oxidation of Ti film cannot be achieved, a residual metal layer (100 – 200 nm thick) still remains even for prolonged treatments.Furthermore the same structures were obtained on other substrates like alumina, glass covered SnO2:F and titanium sheets. By tailoring the anodization parameters identical nanotubular arrays were obtained irrespective of the substrate. As an additional feature, on rough surfaces (alumina) the tubes develop as clusters on each grain, producing structures tailored for applications where high specific areas are required, like catalysis and gas sensing, The functional properties of the obtained TiO2 nanotubular and nanoporous structures were benchmarked both as highly ordered photoanode architectures, offering longer electron diffusion lengths, for next generation excitonic solar cells and as high surface area chemical gas sensors. We acknowledge for funding ORAMA project FP-NMP-2009-LARGE-3 NMP-2009-2.2-1, Grant Agreement 246334: Oxide materials for electronics applications.
10:00 AM - GG6.4
Elaborate TiO2 Nanostructures Anodized from Mechanically Processed Ti Foils: Nanopores, Elliptical Nanotubes, Interweaving Nanotubes and Multilayers.
Lingxia Zheng 1 , Hui Li 1 2 , Yang Yang Li 1
1 Dept. of Physics and Materials Science, City Univ. of Hong Kong, Kowloon Hong Kong, 2 Dept. of Physics, University of Science and Technology of China, Hefei, Anhui, China
Show AbstractSelf-organized TiO2 nanotube arrays grown by anodic oxidation of a Ti substrate attracted broad scientific interest due to wide potential applications. Here we report that cold working of the Ti substrate before anodization can greatly affect the morphology of the formed anodic TiO2 nanostructures – e.g., one can specifically achieve nanotubes or nanopores simply by adjusting the amount of cold work. Moreover, various exotic TiO2 nanostructures, such as elliptical nanotubes, interweaving nanotubes and multilayers, have been enabled using the cold-worked Ti substrates.
10:15 AM - **GG6.5
Charge Separation and Collection in Dye-sensitized Mesoscopic TiO2 Solar Cells.
Qing Wang 1 , James Jennings 1 , Feng Li 1
1 Department of Materials Science and Engineering, Nanocore, National University of Singapore, Singapore Singapore
Show AbstractDye-sensitized solar cells (DSCs) using mesoscopic TiO2 as photoanode currently present a credible alternative to conventional solar cells. The validated overall solar to electric power conversion efficiency has now reached a value close to 12% under standard AM 1.5 illumination conditions. This talk will focus on our recent advances in the fundamental understanding of charge separation and charge collection — the two crucial, efficiency-determining processes, as relevant to DSCs. The predicted effect of sensitizer regeneration on the j-V characteristics of DSCs will be discussed and recent experimental results will be highlighted. Problems surrounding the experimental determination of electron diffusion length in dye-sensitized solar cells will be addressed, together with the physical interpretation of this quantity and its usefulness in predicting charge collection losses in working dye-sensitized solar cells. In addition, evolution of charge separation and charge collection upon prolonged aging test and their effects on the stability of DSCs will be discussed in a case study. It is anticipated that these results will help us to have a better understanding on the factors dictating the operation of DSCs for more efficient and more stable solar energy conversion.
GG7: Solar Cell/Photovoltaic
Session Chairs
Md. K. Nazeeruddin
Qing Wang
Wednesday PM, April 27, 2011
Room 3020 (Moscone West)
11:15 AM - GG7.1
Titanium Dioxide as Solution-processed Electron Transport Layer for Single and Tandem Organic Solar Cells.
Afshin Hadipour 1 , Barry Rand 1 , Paul Heremans 2
1 IMEC-PV-PMEPV-OPV, IMEC, Leuven Belgium, 2 IMEC-TU-SSET-LAE, IMEC, Leuven Belgium
Show AbstractThis work presents a solution-processed electron transport layer (ETL) processed from a TiOx sol-gel. The TiOx layer can be deposited inside the glove-box at room temperature without any further treatment such as thermal annealing in air or photo doping with UV light. As such, this is the first metal-oxide-based ETL which is able to produce an optimum performance directly after processing. This is an important issue since many organic materials that make up the active layers in organic solar cells are not compatible with exposure to oxygen and water vapor during annealing, or to UV light. Based on this TiOx layer, single cells with conventional and inverted structures and also three-electrode parallel and series tandem cells are produced with high performances. Specifically, we are able to produce inverted solar cells with fill factor (FF) = 63.6%, short-circuit current density (JSC) = 9.8 mA/cm2, open-circuit voltage (VOC) = 0.6 Volt, and efficiency = 3.8%. This compares well with the conventional structure, which has FF =64%, JSC = 10.8 mA/cm2, VOC = 0.6 Volt, and efficiency =4.1 %. For the tandem cells, the series-connected cell has a VOC which is the sum of the subcells, whereas the parallel-connected device has a JSC which is equal to the sum of the subcell currents, indicating a properly-functioning middle electrode incorporating metal oxides.
11:30 AM - GG7.2
In Search of the Most Advantageous Processing Route of TiO2 Hole Blocking Layer for Hybrid Solar Cell Devices.
Diana Iza 1 , David Munoz-Rojas 1 , Jonas Weickert 2 , Holger Hesse 2 , Andreas Wisnet 3 , Markus Thomann 3 , Lukas Schmidt-Mende 2 , Judith MacManus-Driscoll 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Physics & Center for NanoScience, Ludwig-Maximilians University (LMU) Munich, Munich Germany, 3 Department of Chemistry & Center for NanoScience, Ludwig-Maximilians University (LMU) Munich, Munich Germany
Show AbstractIn the last few decades solar energy has started being harvested to help meet global demand, and stands as one of the most promising green energy sources to meet energy needs by the middle of this century. Hybrid solar cells provide a balance between cost and efficiency of these devices, which is needed to compete with current energy sources and thus achieve mass implementation. For such cells, the polymer is processed below 150 °C and it is important to grow the oxide in highly crystalline form at as low temperature as possible. However, high quality oxides are traditionally grown at high temperatures. In our group, we are developing technologies to grow high quality oxides at lower temperatures. In this work, hybrid devices were produced using titanium dioxide (TiO2) as a hole blocking layer in poly(3-hexylthiophene):phenyl-C61- butyric acid methyl ester (P3HT:PCBM) devices. The titanium dioxide hole blocking layers were produced via four different methods to determine the effect processing conditions have on over-all photovoltaic performance. Electrochemical deposition (ED), sputtering (SPU), spray pyrolysis (SPR) and atmospheric atomic layer deposition (AALD) were used to produce the TiO2 films. Cell devices were then made in the same batch using the different films in order to reduce any differences arising from other manufacturing stages. Sputtered, spray pyrolysed and AALD layers resulted in the higher performing devices achieving efficiencies of up to 3%. Electrodeposited films, on the other hand, presented cracks and more defects associated with them, resulting in shunt paths in the films and lower performing devices. Despite SPU, SPR and AALD films showing similar performances, the advantages of AALD are highlighted as it is a reliable, no vacuum, low temperature, and easily scalable process offering conformal coating and high crystallinity at low temperatures.
11:45 AM - **GG7.3
Sensitized Titanium Dioxide Photovoltaic Cells: New Nanostructures for Enhanced Performance.
Kevin Sivula 1 , Nicolas Tetreault 1 , Michael Graetzel 1
1 , Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Show AbstractNanostructured titanium dioxide electrodes offer the ability to decouple light absorption and carrier transport in both dye and inorganic semiconductor sensitized solar cells. This allows the relaxation of individual material constraints and permits the separate optimization of the processes occurring in these promising photovoltaic devices. Here we describe our latest advances in nanostructuring titanium dioxide for the sensitized solar cell including using mesoporous beads to control light scattering, nanowires to facilitate electron transport, and inverse opal structures to create photonic crystals. In addition we discuss the dependence of the orientation of anatase single crystals on charge transfer processes in the dye sensitized solar cell and our recent progress employing high-absorption-coefficient inorganic semiconductors as extremely thin absorber (ETA) photovolatics.
12:15 PM - GG7.4
Investigation of Surface State Contributions to Electron Transfer from Nanoparticle TiO2 Films to Outer-sphere Redox Shuttles with Highly Positive Formal Potentials.
Jesse Ondersma 1 , Thomas Hamann 1
1 Chemistry, Michigan State University, East Lansing, Michigan, United States
Show AbstractThe electron transfer properties of nanoparticle TiO2 films, identical to those used in dye-sensitized solar cells, were investigated with a series of one-electron outer-sphere redox couples whose formal potentials are more than 1 V positive of the TiO2 conduction band. Cyclic voltammetry and electrochemical impedance spectroscopy were employed to probe the electron transfer dynamics of nanoparticle-based TiO2 in contact with the redox shuttle series. Analysis of the impedance spectra allowed determination of relative electron transfer rates as well as redox couple diffusion. Compact blocking layers of TiO2 (either from atomic layer deposition or spray pyrolysis) deposited between the fluorine-doped tin oxide and the nanoparticle film, were found to be highly active with the redox couples in this study. Insulating polymer blocking layers were utilized in order to isolate the nanoparticles’ contribution to electron transfer. The highly positive redox shuttles were compared to more commonly investigated cobalt bipyridyl complexes. The mechanism of electron transfer and degree of surface state activity was found to differ greatly between redox shuttles.
12:30 PM - GG7.5
3D Electron Microscopy of a TiO2-based Solar Cell Prototype.
Giorgio Divitini 1 , Andrea Li Bassi 2 3 , Fabio Di Fonzo 3 , Carlo Casari 2 3 , Valeria Russo 2 , Xiaoyu Peng 1 , Caterina Ducati 1
1 Materials Science & Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Dipartimento di Energia and NEMAS - Center for NanoEngineered Materials and Surfaces, Politecnico di Milano, Milan Italy, 3 , Center for Nano Science and Technology - IIT@PoliMI, Milan Italy
Show AbstractThe global need for sustainable energy production is pushing scientific research towards the development of inexpensive solar cells which can compete with established commercial silicon-based technologies. Titanium dioxide based devices are promising for both dye-sensitized and heterojunction systems, in which the nanoscale structure of the semiconducting phase and the interfacial properties between different components play a vital role in determining the overall efficiency of the cell. In order to optimize the performance of final devices, a thorough understanding of the phenomena occurring at the nanoscale is thus needed.Here we present our study of a polymer heterojunction solar cell, where a hierarchically structured TiO2, produced by pulsed laser deposition, has been employed as a photoanode. Such a structure is composed by small (10-20 nm) crystalline particles assembled in columnar aggregates, which constitute a forest-like film with high porosity. This system is a good candidate for solar energy harvesting since it combines a large surface area with good electrical transport properties and promising performance, as we recently showed for dye sensitized solar cells [1]. Moving beyond the morphological characterization achieved in the scanning electron microscope, we have applied advanced transmission electron microscopy (TEM) techniques to the study of hybrid solar cells. In particular we have combined high resolution TEM crystallographic studies with three-dimensional structural data acquired through dark field electron tomography, thus obtaining information on surfaces and interfaces of the nanocrystalline titania, as well as a view of the fine scale cell architecture. We have employed a dual beam FIB (FEI Helios Nanolab) to prepare a cross-section of a polymer heterojunction solar cell (TiO2 back electrode, polythiophene hole transporter), thinned to about 200 nm to ensure electron transparency. We acquired a tilt series from the cross-sectional device using scanning transmission electron microscopy (performed in a Tecnai F20, 200 kV acceleration voltage), from which a 3D reconstruction was built. This investigation provides in-depth quantitative information on the nanostructured photoanode, on the interface between the semiconducting particles and the hole-transporting polymer and on the final structure of the assembled solar cell. In particular, it confirms that three-dimensional structure of the photoanode is preserved through the fabrication process, and the polymer effectively infiltrates the nanocrystalline film.[1] Hierarchical TiO2 Photoanode for Dye-Sensitized Solar Cells – F. Sauvage, F. Di Fonzo, A. Li Bassi, C. S. Casari, V. Russo, G. Divitini, C. Ducati, C.E. Bottani, P. Comte and M. Graetzel - Nano Lett., 2010, 10 (7)
GG9: Photocatalysis
Session Chairs
Huiming Cheng
Hugo Destaillats
Wednesday PM, April 27, 2011
Room 3020 (Moscone West)
4:30 PM - GG9.1
Self-assembled Mesoporous TiO2 Nanocrystal Cluster and Its Photocatalytic Applications.
Qiao Zhang 1 , Yadong Yin 1
1 Chemistry, University of California, Riverside, Riverside, California, United States
Show AbstractMesoporous anatase TiO2 nanocrystal clusters with large surface area and enhanced photocatalytic activity have been successfully synthesized. The synthesis involves the self-assembly of hydrophobic TiO2 nanocrystals into submicron clusters, coating of these clusters with a silica layer, thermal treatment at high temperature to remove organic ligands and improve the crystallinity of clusters, and finally etching of the silica to expose the mesoporous catalysts. With the help of silica coating, the clusters not only maintain their small grain size but also keep their mesoporous structure after calcination at high temperature (with BET surface area as high as 270 m2/g). The etching of SiO2 renders the clusters high dispersity in water. Careful optimization of the synthesis condition, i.e., calcination temperature and nitrogen-doping, leads to photocatalysts with enhanced catalytic efficiency in the decomposition of organic molecules under illumination of UV light, visible light and natural sunlight. The organizing nanocrystals into mesoporous clusters represents a versatile and useful strategy for designing photocatalysts with enhanced activity and stability.
4:45 PM - **GG9.2
TiO2 Nanomaterials Used as Photocatalysts for Selective Heterogeneous Syntheses of Alcohols to Aldehydes in Water.
Leonardo Palmisano 1 , Vincenzo Augugliaro 1 , Marianna Bellardita 1 , Di Paola Agatino 1 , Elisa Garcia Lopez 1 , Vittorio Loddo 1 , Giuseppe Marci 1 , Giovanni Palmisano 1 , Francesco Parrino 1
1 ”Schiavello-Grillone" Photocatalysis Group, Dipartimento di Ingegneria Elettrica, Elettronica e delle Telecomunicazioni, University of Palermo, Palermo Italy
Show AbstractHeterogeneous Photocatalysis (HP) in the presence of irradiated semiconductor oxides is an unconventional technology that has been applied mainly to degrade a lot of organic and inorganic pollutants both in vapour and in liquid phase in mild conditions of temperature and pressure. Various semiconductor materials have been tested as oxidation photocatalysts, but it is generally accepted that TiO2 the most reliable material due to its low cost, high(photo)stability under irradiation and its ability to be activated by near UV-light and also by the solar radiation. Applications of HP for synthetic purposes are rare especially by using water as the solvent. The reason can be found (i) in the fact that the photocatalytic reactions are unselective processes and the presence of water, both as vapour and liquid phases, induces the production of OH radicals, highly oxidant species, under irradiation of the photocatalyst; (ii) many organic molecules (reagents and/or products) are not very soluble in water or are virtually insoluble. Traditional methods for performing such partial oxidations involve the use of environmentally harmful organic solvents at high temperature and pressure by employing stoichiometric oxygen donors (such as chromate and permanganate) that not only are expensive and toxic compounds but also produce high amounts of dangerous wastes. This presentation will report the photo-oxidation of some aromatic alcohols (benzyl, 4-methylbenzyl, 4-methoxybenzyl, 4-nitrobenzyl alcohols) to the corresponding aldehyde by using homemade and commercial TiO2 photocatalysts in the anatase, rutile and brookite phases. The results indicate that the presence of electron donor groups (-OCH3 and -CH3) positively affects the selectivity for both commercial and home prepared photocatalysts, and the commercial samples showed also the worst performance. The electron withdrawing group (-NO2) was detrimental and a very scarce selectivity was observed. It favours the reaction pathway leading to the breakage of the arornatic ring with formation of over oxidized species and eventually CO2.References[1] G. Palmisano, S. Yurdakal, V. Augugliaro, V. Loddo, and L. Palmisano, Adv. Synth. Catal., 349 (2007) 964.[2] S. Yurdakal, G. Palmisano, V. Loddo, V. Augugliaro, and L. Palmisano, J. Am. Chem. Soc., 130 (2008) 1568. [3] M. Addamo, V. Augugliaro, M. Bellardita, A. Di Paola, V. Loddo, G. Palmisano, L. Palmisano and S. Yurdakal, Catal. Lett. 126 (2008) 56.[4] V. Augugliaro, T. Caronna, V. Loddo, G. Marcì, G. Palmisano, L. Palmisano and S. Yurdakal, Chem. Eur. J. 14 (2008) 4640.
5:15 PM - GG9.3
Processing of Porous TiO2 Films with Plasma-enhanced Rapid Expansion of Supercritical Solutions.
Eunyoung You 1 , Nicholas Hendricks 2 , YuYing Tang 2 , Christos Karanikas 1 , James Watkins 2
1 Department of Chemical Engineering, University of Massachusetts, Amherst, Massachusetts, United States, 2 Department of Polymer Science and Engineering, University of Massachusetts, Amherst, Massachusetts, United States
Show AbstractCrystalline, nanostructured titania films are of interest for numerous applications including next-generation energy conversion and environmental photocatalysis. We have developed a direct, spray-on technique to rapidly deposit crystalline nanoscale dendritic titania onto inorganic substrates. We call this technique PRESS, for Plasma-enhanced Rapid Expansion of Supercritical Solutions. This process is a combination of a solution precursor plasma spray (SPPS) process with a rapid expansion of supercritical solutions (RESS), which produces an ultrafine precursor aerosol. In summary, a solution of metal oxide precursor in supercritical carbon dioxide was expanded across a nozzle into the plasma jet where it is converted to metal oxide. We have investigated TiO2 as our model system using titanium tetra isopropoxide (Ttip) as a precursor. The structure of the films depends on several process variables including precursor concentration, precursor solution flow rate and plasma gun to substrate distance. For example, a deposition using 25 volume % solutions of Ttip in CO2 at 10.3 MPa and 60 °C expanded across a 125 micron capillary nozzle yields denritic TiO2 films. X-ray diffraction indicated that the TiO2 films have mixed crystalline phases of rutile and anatase. SEM analysis revealed a highly branched dendritic morphology. TiO2 films deposited onto FTO substrates (transparent conductive glass) via PRESS were used to fabricate dye-sensitized solar cells. The high surface area of the PRESS-deposited films is also attractive for applications in photocatalysis. As an exemple, samples produced with PRESS technique were used for photodegradation of organics in water upon UV exposure.
5:30 PM - GG9.4
The Application of Electrospun TiO2 Nanofibers in Heterogeneous Catalysis.
Wayne Jones 1 , Dickson Andala 1 , Emilly Obuya 1 , Eliud Mushibe 1
1 Chemistry Department, Binghamton University, Binghamton, New York, United States
Show AbstractThe synthesis and application of environmentally benign, efficient, low cost heterogeneous catalysts is increasingly important for affordable and clean chemical technologies. Nanomaterials have been proposed to have new, exciting properties relative to bulk materials due to the quantum level interactions that exist. These materials also offer enormous surface to volume ratios that would be invaluable in heterogeneous catalysis applications. Recent studies point at titanium dioxide nanomaterials as having strong potential to be applied in heterogeneous photocatalysis for environmental remediation and pollution control. In addition to their potential to act as support material for metal nanoparticles in heterogeneous catalysts in the C-C bond formation. This work reports the use of surface modified anatase TiO2 nanofibers with gold (Au) nanoparticles in the photodegradation of methyl orange and methyl red as organic pollutants.Similarly, TiO2 nanofibers were applied as catalyst supports for palladium (Pd) nanoparticles were applied as heterogeneous catalysts in the Heck C-C reaction showed an enhanced catalytic activity and selectivity compared to amorphous C supports.
5:45 PM - GG9.5
Photocatalytic Degradation of Organic Molecules on Visible Light Responsive Sn(II) Doped Titania.
Bharat Boppana 1 , Douglas Doren 2 , Raul Lobo 1
1 Department of Chemical Engineering, University of Delaware, Newark, Delaware, United States, 2 Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware, United States
Show AbstractWe report the first proof of visible light photocatalytic activities of Sn2+ doped TiO2. The catalysts are synthesized from a simple reaction between titanium butoxide and tin precursors at 80oC. Those synthesized with SnCl2 have band gaps red-shifted to the visible region from the introduction of Sn 5s orbitals in the valence band. These catalysts possess the anatase polymorph of titania which is unchanged even at higher loadings of Sn2+. When the precursor is changed to SnCl4, a predominantly rutile phase is obtained but with no reduction in the band gap. The structure and electronic properties are investigated utilizing XRD, XPS, XAS, photoluminescence, UV-Vis, Raman & IR spectroscopy and other techniques. It is found that the majority of surface cation sites are composed of tin as Sn2+ with a fraction of tin also being incorporated in the crystal as Sn4+. The experiments also indicate the presence of chlorine which influences the optical and catalytic properties as evidenced by analyzing similar catalysts synthesized with bromide precursors. These catalysts are photocatalytically active for the degradation of organic molecules in visible light with rates higher than the standards due to the generation of highly oxidizing hydroxyl radicals. We believe this protocol could be extended to incorporate Sn2+ into other oxide semiconductors to synthesize visible light active photocatalysts with interesting electronic properties. The applicability to analyze dye de-ethylation mechanism using multivariate chemometric methods will also be described in this presentation.
GG10: Poster Session II
Session Chairs
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
9:00 PM - GG10.1
Photocatalytic Activity, Hydrophilic and Optical Properties of Nanocrystalline Titania Thin Films Prepared by Sol-gel Dip Coating.
Cristina Ferrara 1 , Luciano Pilloni 2 , Anna Mevoli 1 , Saverio Mazzarelli 1 , Leander Tapfer 1
1 UTTMATB, ENEA, Brindisi Italy, 2 UTTMAT-CHI, ENEA, Roma Italy
Show AbstractNanocrystalline anatase titania thin films were prepared by using two different precursor solutions, a highly acid solution (Sol-1) and a polymer-like solution (Sol-2), via the dip-coating technique on different substrates (<100>-Si wafer, fused silica and glass). The influence of the two sol-gel titania precursor solutions and of the substrate type on the film morphology, coating porosity, surface roughness, crystalline phases and grain size of the titania films were investigated in detail. The relationship between microstructural/morphological properties and the optical properties (energy gap, refractive index and extinction coefficient) and the hydrophilic performance of the coatings were evaluated. Our experimental results clearly indicate that the sol - composition and substrate type remarkably influence the microstructural/morphological properties of the titanium dioxide. They consequently modify the optical response and hydrophilic performances of the samples. The results show that the samples are characterised by low values of the crystalline domain dimension: from 11 to 14 nm for the samples obtained by Sol-1 and less than 5 nm for the samples obtained by the polymer type sol (Sol-2). Moreover, the films prepared from the highly acid solution have a much higher mass density (about 90-96% of the theoretical value) and a refractive index; conversely, the layers grown by the polymer sol have the lowest mass density (about 70% of the theoretical bulk value of anatase), and exhibit high hydrophilic properties. The optical results reveal a band structure mutation from indirect to direct transition and clearly show a blue shift of the band gap energy (Eg values between 3.78 and 4.13 eV instead of 3.2 eV of the anatase bulk) caused by the quantum size effect that is induced by the small TiO2 crystallites size. The hydrophilic properties and the change of the band gap transition can be attributed to oxygen vacancy on the surface of the titania nanocrystallites that gives rise to Ti3+ sites and, consequently, to structural changes/defects of the anatase nanoarchitecture. Finally, the photocatalytic oxidations of the methylene blue in water and of an aqueous phenol solution were monitored to investigate on the photocatalytic activity of the titania coatings and the results were put in relation with the hydrophilic and optical properties of the films. The results demonstrate that the optical and hydrophilic properties of nanocrystalline titania can be tailored opportunely tuning the size dimension of the crystalline domain according to the specific coating applications.
9:00 PM - GG10.10
Wastewater Remediation Using Titanium Dioxide-graphene Composite Material.
Basheer Chanbasha 1
1 Department of Chemsitry, King Fahd University of Petroleum and Minerals, Dhahran Saudi Arabia
Show AbstractAbstractSince conventional wastewater treatment plants (WWTPs) effects only partial removal of alkylphenols, advanced oxidation process (AOP) involving titanium dioxide is a promising remediation technique. However, the low photodegradation efficiency of titanium dioxide limits its practical application. In this paper, it is proposed that the presence of graphene can enhance the photocatalytic efficiency of titanium dioxide. The titanium dioxide-graphene (TiO2-G) composites were prepared via sonochemical and calcinations methods. The synthesized composite was characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), tunneling electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and fluorescence spectroscopy. The photocatalytic efficiency was evaluated by studying the degradation profiles of 3 alkylphenols using gas chromatography-flame ionization detector (GC-FID). It was found that the synthesized TiO2-G composites exhibit enhanced photocatalytic efficiencies as compared to pristine TiO2. The presence of graphene not only provides a large surface area support for the TiO2 photocatalyst, but also stabilizes charge separation by trapping electrons transferred from TiO2, thereby hindering charge transfer and enhancing its photocatalytic efficiency.
9:00 PM - GG10.11
Effects of the Size of Ag Nanoparticles on the Plasmonic Photocatalytic Properties of TiO2 Thin Films.
Joon-Ho Oh 1 , Hyunju Lee 1 , Donghwan Kim 1 , Tae-Yeon Seong 1
1 Materials Science and Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractTiO2 thin films are of considerable technological importance for various applications including anti-reflection coating in thin-film solar cells, transparent electrodes. Recently, intense research interests were also focused on the TiO2 thin films having anatase phase, which exhibited photocatalytic properties when illuminated with UV light. For example, the exposure of anatase TiO2 films (having a bandgap of 3.26 eV) to UV light (photon energy (hν) > Eg(TiO2) ) generates electron-hole pairs. The holes and subsequently formed OH radicals are very efficient for the oxidation of most of organic contaminants. This effect will be especially useful for high-efficiency solar cells, considering the fact that an output reduction of up to 50% may be observed when spot dirt or contaminant occupies as little as 3% of a photovoltaic module area as reported by Kobayashi et al. In this regard, many research efforts were devoted to further improvement of the performance of TiO2 photocatalytic self-cleaning films. Recently, Awazu et al. reported that the photocatalytic behavior of TiO2 deposited by a spin-coating and subsequent heating was greatly boosted by introducing plasmonic silver (Ag) nanoparticles (NPs). They reported that the measured photocatalytic activity under near UV illumination of such a plasmonic photocatalyst was enhanced by a factor of 7. However, little work has been performed on the size effects of the Ag NPs on the photocatalytic properties of TiO2 thin films. In this presentation, we investigated the effect of Ag NP size on the photocatalytic properties of TiO2 thin films. We succeeded to form TiO2 thin films (~100 nm in thickness) having only anatase phase by a RF magnetron sputtering deposition and subsequent rapid thermal annealing (RTA). We also formed Ag NPs by the combined process of the deposition of Ag thin films (with thicknesses of 2, 7 and 12 nm) by an e-beam evaporator and subsequent RTA treatment. It is shown that as the Ag NPs size increases, plasmonic peaks shift towards the longer-wavelength region and become widened. It is also shown that the TiO2 films with Ag NPs having thicknesses of 2 and 7 nm exhibit higher transmittance in the 600/700 – 1100 nm wavelength region than the TiO2 films without the Ag NPs. It is further shown that under UV-illumination (354 nm), all the TiO2 films with the Ag NPs at the glass/TiO2 interfaces show higher methylene blue (MB) decomposition rates compared to the TiO2 films without the Ag NPs, and the TiO2 films with Ag NPs (7 nm) show the best decomposition rate. This behavior will be explained in terms of optimized forward plasmonic scattering and near-field enhancement by the Ag NPs.
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Mesoporous TiO2 photoelectrodes: A Comparison of Sol-gel and Nanoparticle Based Thin Films.
Pascal Hartmann 1 , Doh-Kwon Lee 2 , Bernd Smarsly 1 , Juergen Janek 1
1 Physikalisch-Chemisches Insitut, Justus-Liebig-Universitaet Giessen, Giessen Germany, 2 , Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractIn the reported work we prepared nanocrystalline mesoporous (mp-TiO2) thin films either using TiCl4 as classical precursor for sol-gel TiO2 or using crystalline TiO2 nanoparticles as precursor. Well defined porosity was introduced via an evaporation induced self assembly (EISA) process of block-copolymers.[1],[2] Both types of mp-TiO2 thin films were characterized with respect to their efficiency in photoelectrochemical hydrogen generation. Besides PEC, wide and small angle scattering, scanning electron microscopy, optical absorption and secondary ion mass spectrometry experiments were carried out to characterize the films. As a major result we can show that only small differences in the micro- and mesostructure lead to large differences in PEC water splitting efficiencies: SEM investigations have shown that both films feature a regular mesoporosity with a pore diameter of about 15 nm and a high film quality with large crack free areas. The nanoparticle films show a higher density of accessible pores at the surface than the sol-gel samples. Films prepared by the sol-gel process have a significantly thicker TiO2 framework with about 15 nm thick pore walls compared to 7-8 nm of the nanoparticles.The external quantum efficiency ηQE or photon-to-current efficiency (IPCE) gives the ratio between the number of incident photons and generated electronic charge carriers, and therefore, the amount of produced H2 and O2. In our experiments the sol-gel samples have shown a maximum IPCE of about 40% which is about 10 times higher than for the nanoparticle based films.[1] Smarsly, B. M., and Antonietti, M., Block Copolymer Assemblies as Templates for the Generation of Mesoporous Inorganic Materials and Crystalline Films Eur. J. Inorg. Chem. (2006) 1111-1119[2] Brezesinski, T., et al., Templated nanocrystal-based porous TiO2 films for next-generation electrochemical capacitors, J. Amer. Chem. Soc. 131 (2009) 1802-1809
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Coupled Titanium Dioxide Carbon Nanotubes Composites.
Dunlin Tan 1 , Beng Kang Tay 1 , Yaron Paz 2
1 School of Electrical & Electronic Engineering, Nanyang Technological University, Singapore Singapore, 2 Chemical Engineering Department, Technion, Haifa Israel
Show AbstractTitanium dioxide is considered by many as the photocatalyst of choice for water and air purification as well as for self–cleaning and anti-bacterial surfaces. Despite the progress that was made by Fujishima and Honda, several obstacles still remained in route for successful widespread applications. The main challenges are related to the wide bandgap of the photocatalyst, which limits its use to UV photons of less than 360 nm in wavelength that amount to no more than 2.5% of the solar flux impinging on earth, and are negligible under indoor conditions. Other problems include insufficient adsorption and mass-transport of contaminants, as well as high recombination rate of the photoinduced charge carriers. Recent years have witnessed the introduction of dopants such as carbon and nitrogen into titanium dioxide matrices, thus narrowing the effective bandgap of the photocatalyst, however the progress that was made so far is still modest.The use of composite films, made of titanium dioxide and carbon nanotubes may assist in overcoming these problems. In this context the carbon nanotubes may act as ideal places for physisorption of contaminants and in parallel, may act as photosensitizers that absorb visible light and transfer photoinduced charge carriers to the titanium dioxide. Indeed, charge transport from fullerenes to titanium dioxide as well as from titanium dioxide to fullerenes was observed, its direction being dependent on the wavelength of the impinging photons. The combination between carbon nanotubes and titanium dioxide has another, no less important, benefit- the high surface area associated with such structures, which may assist in obtaining high efficiency, not to mention the high strength of carbon nanotubes that can be used to reinforce the titanium dioxide nanostructures for better durability. In this work, we develop composite structures made of carbon nanotubes and titanium dioxide nanoparticles to understand the photoconductivity of the coupled system. Carbon nanotubes were functionalized to form carboxyl groups for the attachment of titanium dioxide nanoparticles. The results from photoconductivity measurements carried out on a conductive atomic force microscope would be discussed.
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Comparison between the Optical and Surface Properties of TiO2 and Ag/TiO2 Thin Films Prepared by Sol-gel Process.
Nelcy Mohallem 1 , Marcelo Viana 1
1 Chemistry, Federal University of Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
Show AbstractTransparent and homogeneous TiO2 and Ag/TiO2 thin films were prepared by sol-gel process using the dip-coating method from titanium alkoxides and silver nitrate. After coating on borosilicate substrates, the samples were dried at room temperature and heated between 100 and 700 °C. The thin films were structurally and morphologically characterized using low angle X-ray diffractometry, and high-resolution electron microscopy. The textural and optical characteristics were investigated by atomic force microscopy (AFM) and UV-vis spectroscopy. Both the films are evaluated and compared according their optical and surface properties such as transmittance, photocatalysis, hydrophobic/hydrophilic capacity and bactericidal ability.
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Novel Hole Transport Layer infiltrated to TiO2 Nanowire Array Anode by Physical Vapor Deposition for Solid State Dye-sensitized Solar Cell.
Akshay Kumar 1 , Cody Schlenker 2 , Francisco Navarro 2 , Kuan-Teh Li 1 , Chao Wu 2 , Philipp Isken 2 , Mark Thompson 2 , Chongwu Zhou 3
1 Mork Family Department of Chemical Engineering and Material Science, University of Southern California, Los Angeles, California, United States, 2 Chemistry, University of Southern California, Los Angeles, California, United States, 3 Ming Heish Department of Electric Engineering, University of Southern California, Los Angeles, California, United States
Show AbstractThe widespread applicability of dye-sensitized solar cells (DSCs) is hindered by the volatile solution phase electrolyte system. Hence, solid state hole transport materials(HTMs) are required to overcome the potential problems of packing and module constructions in the future. HTMs depositions are usually carried out via solution-based techniques, where materials such as poly(3-hexylthiophene) P3HT and spiro-OMeTAD(2,20,7,70-tetrakis-(N,N-di-p-methoxyphenylamine)9,90-spirobifluo -ene, are dissolved in a solvent and drop cast or spin cast onto the substrate, whereas capillarity forces might hinder the interface of the HTMs and dye when the solvent evaporates. In this work, we report a solid state dye sensitized solar cell (sDSC) constituting a novel HTM deposited by a conformal physical vapor deposition method to obtain TiO2-infiltrating domains of a new, highly conductive hole transport medium comprising 1,4-bis(2-naphthylphenylamino)benzene (NNP) doped with tetrafluorotetracyano-p-quinodimethane (F4TCNQ). Single crystalline TiO2 NWs arrays are favorable not only for charge transports but also allow a complete infiltration of the HTM from deep within an array of isolated nanowires facilitates regeneration of the dye following photoinduced electron transfer from the dye to the nanowire array. The technique is low-cost, facile and scalable which provide a new path to commercialize dye sensitized solar cells.
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Improved-performance Solar Cells by Using Anatase TiO2 Chain-networked Photoanodes.
Wen-Yin Ko 1 , Yin-Cheng Yen 1 , Jing-Zhi Chen 1 , Kuan-Jiuh Lin 1
1 Chemistry, National Chung-Hsing University, Taichung Taiwan
Show AbstractEnergy supply has become one of the most significant problems for mankind due to the exponential shortage of the fossil fuel supplies. Solar light, the only inexhaustible energy source, could continuously deliver ~1.2×1017 W of solar power which is dramatically exceeds the rate of worldwide energy consumption of ~ 1.3×1013 W. Therefore, how to efficiently convert the solar energy into electricity to satisfy our life is the most important challenge. Solid state heterojunction hybrid solar cells based on the incorporation of the inorganic nanomaterials with conjugated polymer were considered as the ideal alternative for future solar cell industry because they use inexpensive materials, have long lift time, and could be produced in large-scale size and easier for mass production. However, interface problems of organic/inorganic materials and infiltration of the inorganic nanomaterials lead to high recombination that would decrease the photon to current efficiency. TiO2 is a popular inorganic candidate for the use in solid state solar cell due to its non-toxicity and low-cost. Recently, we proposed a novel sandwich-layered architecture, Ti/chain-TiO2/Ti/FTO, by a low cost, low temperature, and ease in scale-up hydrothermal process, where the Ti-layers play a critical role in the formation of lengthened pear-necklace chains made up of interconnected anatase TiO2 nanoparticles (chain-TiO2). The novel one-dimension structures are capable of enhancing the electron transport characteristics and the interfacial area which may open up numerous possibilities in the development of advanced applications in solid state heterojunction hybrid solar cells and highly efficient photocatalysis.
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Well Ordered Nanotube Arrays of Pure Anatase by Anodization with Significantly Enhanced Thermal Stability up to 800oC.
Qing Ma 1 , Shaojun Liu 1 2 , Lvqian Weng 1 , Shang Gao 1
1 Materials Science and Engineering, Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen, Guangdong, China, 2 State Key Laboratory for Powder Metallurgy, Central South University, Changsha, Hunan, China
Show AbstractAmong of three common titania polymorphs, anatase, rutile and brookite, anatase is preferred to be used in dye-sensitized solar cells and photocatalysts due to its smaller electron effective mass that results in a higher mobility. It is of significant importance to growing well ordered nanotube arrays of pure anatase with good thermal stability. In the present work, a simple and efficient method, which it is different from the one that stabilizes nanostructured anatase phase at a relative high temperature by doping ions, is proposed to grow well ordered nanotube arrays of pure anatase with significantly enhanced thermal stability. The well ordered titania nanotube arrays are >10μm long. XRD and Raman results evidence that pure anatase phase is retained while FESEM results show a quite well maintained nanotubular architecture of nanotube arrays annealed at 800oC in pure oxygen. The significantly enhanced thermal stability is realized by isolating the influence of Ti support that subsequently inhibits the anatase-rutile transition initiating from the nanotube-support interface. A better thermal stability can be further achieved in titinia nanotubes with larger length. These findings can be used to guide the fabrication of titania nanotubes for applications in dye-sensitized solar cells and photocatalysts where well ordered nanotube arrays of pure anatase with good thermal stability is required.
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Ellipsometric Characterization of Thin Nanocomposite Films with Tunable Refractive Index for Biochemical Sensors.
Peter Petrik 1 , Holger Egger 2 , Stephanie Eiden 2 , Robert Horvath 1 , Miklos Fried 1 , Timo Aalto 3 , Kolari Kai 3 , Domenico Giannone 4
1 , MTA-MFA, Budapest Hungary, 2 , Bayer Technology Services GmbH, Leverkusen Germany, 3 , VTT, Espoo Finland, 4 , Multitel, Mons Belgium
Show AbstractTo design biosensor chips based on polymer Photonic Crystal (PhC) micro-cavities, two polymeric materials with a maximum refractive index difference are necessary. Since polymers itself usually do not have very high or low refractive indices, their refractive values shall be manipulated by preparing nanocomposite materials. Incorporation of high index materials into polymers is intensively studied and it has been shown that the refractive index can be increased significantly. One way is to incorporate nanoparticles with a very high refractive index (like a couple of inorganic oxides) without losing the other desired properties of the polymers. This is also the most promising way thinking of processability of the composite materials. Therefore, the optimum particles concerning material, size etc. shall be identified to adjust the desired refractive index and to obtain the best processable materials. In this study we present optical models to measure the layer thickness, vertical and lateral homogeneity, the refractive index and the extinction coefficients of the polymer films with nanocrystal inclusions using spectroscopic ellipsometry. The optical properties can be determined in a broad wavelength range from 190 to 1700 nm. The sensitivity of spectroscopic ellipsometry allows a detailed characterization of the nanostructure of the layer, i.e. the surface nanoroughness, the interface properties, the optical density profile within the layer, and any other properties that can be modeled in a proper and consistent way. In case of larger particles even the particle size can be determined from the onset of depolarization due to light scattering. Besides the refractive index the extinction coefficient, that is a critical parameter for waveguiding layers, was also determined in a broad wavelength range. Using the above information from the ellipsometric models the preparation conditions resulting in best layer formation can be identified. A range of samples were investigated including spin coated and doctor bladed films using different nanoparticle materials (TiO2, SnO2). We have used complementary measurement techniques to verify the optical models.
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Preparation and Evaluation of Titanium Dioxide Nanoparticles for As(V) Removal from Water.
Burcu Aciksoz 1 , Zuleyha Kocabas 1 , Yuda Yurum 1
1 Material Science and Engineering, Sabanci University, istanbul Turkey
Show AbstractTitanium dioxide has been extensively tested in environmental applications due to its physical and chemical stability, lower cost and nontoxicity. In the present study the effectiveness of titanium dioxide (TiO2) nanoparticles synthesized by sol-gel method was evaluated in removing As(V) ions from water. The different crystalline structure, morphology and particle size of TiO2 nanoparticles were obtained by varying the water/alcohol molar ratios and pH values of solution. The sol-gel derived samples were converted fully to crystalline anatase and rutile nanoparticles at different calcination temperatures for 2 hours and synthesized powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By considering main peaks of anatase and rutile, the average crystallite sizes have been determined by Debby–Scherrer formula and the minimum particle size was 13.6 nm for anatase and 53 nm for rutile nanoparticles. In order to analyze As(V) removal capacity of anatase and rutile nanoparticles from water, batch adsorption experiments were carried out. Under various experimental conditions including adsorbent to As(V) ratio, pH and contact time, the optimum sorption process conditions were determined. Over 94.7% As(V) have been removed within 2 hours reaction time by anatase nanoparticles, in contrast maximum 73.6% As(V) have been taken up within 10 hours for rutile nanoparticles. The results of the sorption experiments, which take into consideration the effects of equilibrium concentration on adsorption capacity, were analyzed with two popular adsorption models, Langmuir and Freundlich models. From the comparison of R2 values, the adsorption isotherms of As(V) for anatase and rutile nanoparticles were fitted satisfactorily well to Langmuir equation with a correlation coefficient to be greater than 99.92 for anatase and 99.65 for rutile. This study proposes the potential environmental application of titanium dioxide nanoparticles as an adsorbent material for removing As(V) ions from water.
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Low Cost, Environmentally Benign Patterning Nanostructured TiO2 Thin Films.
John Bass 1 , Charles Schaper 2 , Charles Rettner 1 , Noel Arellano 1 , Xin Ai 1 , Qing Song 1 , Campbell Scott 1 , Fahhad Alharbi 3 , Robert Miller 1 , Ho-Cheol Kim 1
1 , IBM Almaden Research Center, San Jose, California, United States, 2 , Transfer Devices, Inc., Santa Clara, California, United States, 3 , King Abdulaziz City for Science and Technology, Riyadh Saudi Arabia
Show AbstractPractical exploitation of nanostructured titania thin films in domains such as photovoltaics, environmental photocatalysis and coatings, requires efficient low-cost fabrication techniques. We describe how an environmentally friendly, water based PVA microtransfer molding approach can be adapted to create nanoscale TiO2 structures on substrates, using dissolution for soft release. Feature sizes below 50 nm and aspect ratios reaching nearly 5 to 1 are achieved using sol-gel and nanoparticle-based precursors, while multilayer stacking can create unique closed-cell and open-cell 3D nanostructures from mixed templates. From an applications perspective, templated 1D high-aspect ratio TiO2 posts are shown to greatly increase the short-circuit current in PbS nanopartical solar cells, achieving power conversion efficiency of > 5%. Applications in other areas, such as antireflection coatings, are also discussed.
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Anodic Growth of TiO2 Nanotube Arrays and Their Crystallization Behavior.
Ik Jae Park 1 , Sangwook Lee 1 2 , Dong Hoe Kim 1 , Hyun Suk Jung 3 , Kug Sun Hong 1 2
1 Department of Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Research Institute of Advanced Materials, Seoul National University, Seoul Korea (the Republic of), 3 School of Advanced Materials Engineering, Kookmin University, Seoul Korea (the Republic of)
Show AbstractTiO2 Nanotube arrays preferred oriented to (004) plane of anatase crystal were grown by electrochemical anodization of Ti-foil, and followed annealing process. Ethylene glycol/NH4F–based organic electrolyte was used for electrolyte solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), and Scanning electron microscopy (SEM) were used to investigation crystallinity and morphology of TiO2 nanotube arrays. According to various electrolyte conditions, XRD peak intensity ratio, (004) to (200), varied obviously. We can obtain (004)-preferred-oriented TiO2 nanotubes under a certain composition of electrolyte. The crystallographic orientation behavior of nanotubes was attributed to the hydroxyl groups injected in the nanotube body during anodizing. In deficiency of H2O conditions, Ti is oxidized to TiOx, and etched out finally. On the other hand, in sufficient H2O conditions, lots of OH- ion insertion occurs during anodizing process, which may randomize the crystallographic direction of grains of TiO2 nanotube array. In optimum amount of injected hydroxyl groups, the grains of TiO2 nanotube arrays are oriented to [001]-direction.
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On the Sol-gel Synthesis and Characterization of Titanium Oxide Nanoparticles.
Varun Chaudhary 1 , Amit Srivastava 1 , Jitendra Kumar 1
1 Materials Science Programme, Indian Institute Of Technology Kanpur, Kanpur, Uttar Pradesh, India
Show AbstractTitanium dioxide (TiO2) exhibits unusual structural, optical, electronic, magnetic and chemical properties. As a consequence it has found wide applications in pigments, UV protection creams, photo-catalysis, solar cells, water and air purification, synthesis of inorganic membranes, etc [1]. Its most important phases include anatase, rutile (both tetragonal, described by sharing of (TiO6)2- octahedra) and the more recently discovered oxygen deficient λ-Ti3O5, having monoclinic crystal structure [2]. In this work, TiO2 nanoparticles have been prepared by sol-gel process using titanium isopropoxide Ti(OC3H7)4 as a precursor with ethanol and water as solvents. The synthesis involves gel formation, digestion for 24h, drying at 100oC for 10h, and calcination in air at 500-800oC for 2h. The resulting powder has been studied with respect to phase(s), morphology, optical absorption and photoluminescence (PL) behaviour. The calcination of dried sol-gel product, presumably Ti(OC3H7)3OH, at 500oC for 2h leads to formation of anatase phase that possesses a tetragonal structure ( a ~ 3.786 Å, c ~ 9.514 Å, z =4), average crystallite size ~ 11 nm and band gap 3.34 eV. Further, increasing the time of calcination causes growth to average crystallite size ~ 17.7 nm for the case of 24 h. However, calcination of sol-gel product at 800oC for 2h gives rise to tetragonal rutile phase ( a ~ 4.596 Å, c ~ 2.957 Å, z =2), average crystallite size ~ 25 nm and bandgap of 3.02 eV. Also, rutile phase shows a red shift and PL intensity weaker than the anatase sample. This observation has been attributed size effect, i.e., decrease in the crystallite size and increase of defect centres. The anatase powder is shown to emit strong and wide luminous radiation in the wavelength range of 625- 660 nm with the excitation wavelength of 420nm.References1) U. Diebold, Surface Science Reports 48 (2003) 53-229.2) S. Ohkoshi et al., Nature Chemistry 2 (2010) 539-545.
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Direct Synthesis of Highly Ordered TiO2 Nanotubes onto Patterned Si or Glass Substrates and Their Applications to Chemical Sensors.
Do Hong Kim 1 2 , Hi Gyu Moon 1 , Young-Seok Shim 1 , Byeong-Kwon Ju 2 , Seok-Jin Yoon 1 , Ho Won Jang 1
1 Electronic Materials Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 School of Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractTiO2 is of great interest owing to its various applications such as dye-sensitized solar cells, photoelectrochemical water splitting, antireflection coatings, Li-ion batteries, and chemical sensors. For these applications, since the device performance largely depends on the surface-to-volume ratio of the TiO2 electrodes or catalysts, tremendous efforts have been devoted to synthesize TiO2 nanomaterials with large specific surface areas. Among them, TiO2 nanotubes have attracted great interest due to the facile synthesis of them using anodic oxidation processes. Most of studies on TiO2 nanotubes were based on anodization of Ti or Ti-alloy foils, which results in TiO2 nanotubes on thick metal substrates. For high-quality gas sensors or solar cells, the separation and transfer of TiO2 nanotube arrays from the metal substrates onto Si or glass substrates are needed. However, using the synthesis-and-transfer method, obtaining highly ordered TiO2 nanotubes on the Si or glass substrates is challenging because TiO2 nanotubes are very fragile and thus the separation of large-area TiO2 nanotubes is difficult. Alternatively, direct synthesis of TiO2 nanotubes on Si or glass substrates have been reported, but the quality of the TiO2 nanotubes fell far behind those from anodization of Ti foils. In this work, we report direct synthesis of highly ordered TiO2 nanotubes onto patterned Si or glass substrates. By anodizing Ti films on patterned Si or glass substrates, we could obtain highly ordered TiO2 nantubes on the substrates. The orderness of the TiO2 nanotubes is unparalleled with those of the previously reports. Furthermore, the directly synthesized TiO2 nanotubes on the Si or glass substrates could be used as chemical sensors without additional processes. The experimental results reveal that the chemical sensors based on the high-quality TiO2 nanotubes exhibits superior gas, UV, and biomedical sensing performance to flat TiO2 thin films.
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Growth of TiO2 Thin Films by High Power Impulse Magnetron Sputtering.
Fridrik Magnus 1 , Arni Ingason 1 2 , Kristjan Leosson 1 , Sveinn Olafsson 1 , Jon Gudmundsson 1 3
1 Science Institute, University of Iceland, Reykjavik Iceland, 2 IFM-Materials Physics, Linkoping University, Linkoping Sweden, 3 UM-SJTU Joint Institute, Shanghai Jiao Tong University, Shanghai China
Show AbstractHigh power impulse magnetron sputtering (HiPIMS) has been shown to have several advantages over conventional dc or rf magnetron sputtering. These include increased film density, lower surface roughness, enhanced step coverage, increased reactivity at low growth temperatures and the possibility of phase tailoring [1]. Here we study these factors for TiO2 thin films grown by reactive and non-reactive HiPIMS from a Ti and TiO2 target, respectively. The growth temperature is varied from 30 to 700 °C. We examine how the phase can be tailored from anatase to rutile by varying the substrate temperature, working pressure and substrate bias [2]. Crystal phases, density and roughness are studied by x-ray diffraction and reflection measurements. Rutherford back scattering measurements are also employed as an alternative means of finding the film density. In addition, the refractive index of the films is determined by spectroscopic ellipsometry. The properties of HiPIMS-grown films are compared to those of films grown by reactive dc magnetron sputtering.1.Helmersson, U., M. Lattemann, J. Bohlmark, A.P. Ehiasarian, and J.T. Gudmundsson, Thin Solid Films, 2006. 513(1-2): p. 1-24.2.Alami, J., K. Sarakinos, F. Uslu, C. Klever, J. Dukwen, and M. Wuttig, Journal of Physics D-Applied Physics, 2009. 42(11): p. 115204.
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Anodic Growth of Self-organized TiO2-Nanotubes and Catalytic Properties.
Himendra Jha 1 , Doohun Kim 1 , Indhumati Paramasivam 1 , Robert Hahn 1 , Patrik Schmuki 1
1 Department of Materials Science, Friedrich-Alexander University Erlangen-Nuremberg, Erlangen Germany
Show AbstractSelf organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium [1], have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, solar energy conversion and biotechnology) in a nanotubular morphology. In the first part of the work we report on the growth of anodic TiO2 nanotubes by a simple one-step electrochemical treatment of Ti in a fluoride containing electrolyte (for an overview see [2,3]) and the optimization of the nanotube morphology for catalytic applications.The second part of the presentation will demonstrate that the catalytic properties of these TiO2 nanotubes can be significantly modified by loading with suitable nanoparticles (Ag, Au, Fe3O4) [4], filling with Zeolite [5] or electroless deposition [6]. This allows to fabricate e.g. p-n junction nanomaterial with enhanced charge separation and thus providing enhanced photo-catalytic properties even under visible light irradiation.References:[1] V. Zwilling, M. Aucouturier, E. Darque-Ceretti, Electrochim. Acta, 45, 921 (1999).[2] J.M Macak et al., Curr Opin Solid State Mater Sci 11 (2007).[3] A. Ghicov, P. Schmuki, Chem. Commun. Andrei Ghicov and Patrik Schmuki, Chem. Commun., 2791,(2009)[4] I. Paramasivam, J.M. Macak, P. Schmuki Electrochemistry Communications 10 (2008) 71–75[5] I. Paramasivam, A. Avhale, A. Inayat, A. Boesmann, P Schmuki and W Schwieger Nanotechnology 20 (2009) 225607 (5pp)[6] H. Jha, C. Das, P.Schmuki in preperation
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A Comparison of Anodic TiO2 Nanotubes and Mesosponges in Applications.
Doohun Kim 1 , Kiyoung Lee 1 , Poulomi Roy 1 , Himendra Jha 1 , Robert Hahn 1 , Patrik Schmuki 1
1 Dept. of Material Science and Engineering, University of Erlangen-Nuremberg, Institute for Surface Science and Corrosion (LKO), Erlangen Germany
Show AbstractTiO2 nanotube arrays prepared by electrochemical anodization of Ti in a fluoride electrolyte show impressive functional properties [1,2]. However, in the presentation, we introduce an entirely new generation of an anodic mesoporous structure – a robust TiO2 mesosponge (TMS) structure [3-6] that shows very promising results in view of DSSC or photocatalytic applications. The performance as well as critical factors for the formation and properties of the two structures will be discussed.References[1]J.M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, P. Schmuki, Curr. Opin. Solid State Mater. Sci. 11 (2007) 3.[2]A. Ghicov, P. Schmuki, Chem. Commun. (2009) 2791.[3]D. Kim, K. Lee, P. Roy, B.I. Birajdar, E. Spiecker, P. Schmuki, Angew. Chem. Int. Ed. 48 (2009) 9326.[4]K. Lee, D. Kim, P. Roy, I. Paramasivam, B.I. Birajdar, E. Spiecker, P. Schmuki, J. Am. Chem. Soc. 132 (2010) 1478. [5]D. Kim, P. Roy, K. Lee, P. Schmuki, Electrochem. commun. 12 (2010) 574.[6]P. Roy, T. Dey, K. Lee, D. Kim, B. Fabry, P. Schmuki, J. Am. Chem. Soc. 132 (2010) 7893
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Magneli Phases: Comprehensive Characterisation of the Electrical Properties Over a Broad Range of Temperatures.
Domenico Regonini 1 , Andrew Dent 1 , Chris Bowen 1 , John Taylor 2 , Stephen Pennock 2
1 Materials Research Centre, Mechanical Engineering, University of Bath, Bath United Kingdom, 2 Electronic & Electrical Engineering, University of Bath, Bath United Kingdom
Show AbstractMagnéli phases (TinO2n-1) are a class of sub-stoichiometric titanium dioxide of interest in electrochemical and biomedical applications. They exhibit an electrical conductivity several orders of magnitude higher than stoichiometric titanium dioxide, but little is known of their behaviour and conductivity at relatively high temperatures (above 100°C) before they undergo re-oxidation. We have prepared a mixture of Ti4O7, Ti5O9 and Ti6O11 via carbo-thermal reduction of TiO2 and investigated their ac conductivity by Impedance Spectroscopy (IS) to examine how the electrical properties change over a broad range of temperature. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) help to establish a correlation between the electrical properties and the microstructure. It is also worth noting that for applications where a specific electrical conductivity would be required, the electrical properties of these phases can be tuned by realising TiO2-TinO2n-1 composites. Preliminary results on the conversion of anodised TiO2 nanotubes into TinO2n-1 nanotubes are also presented.
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Titanium Dioxide Gas Sensors Fabricated by Oblique Angle Deposition Technique.
Sun Yong Hwang 1 , Ho Won Jang 2 , Seok-Jin Yoon 2 , Jong Kyu Kim 1
1 Materials Science and Engineering, Pohang University of Science and Technology, Pohang, Gyeongbuk, Korea (the Republic of), 2 Electronic Materials Center, Korea Institute of Science and Technology (KIST), Seoul Korea (the Republic of)
Show AbstractMetal-oxide semiconductor sensors based on TiO2 thin films have been widely investigated due to their structural and thermal stability which enables the gas sensors to be operated at high temperature, and low cost. Since the performances of TiO2 gas sensors are based on surface interactions with reducing or oxidizing species which change the conductivity of the film, nano-structured thin films with large surface-to-volume ratio are expected to enhance gas sensing performances, as they have more surface sites to react with the sensing species. Many methods have been suggested to fabricate TiO2 nano-structures including laser irradiation, etching with anodized aluminum oxide mask, nano-sphere, electron-beam lithography, and nano-imprint techniques, which may be costly and difficult to implement. In addition, such nano-structures can be fabricated only on the surface of thin film, of which the electron depletion effect at surface may not result in a substantial change in the total conductivity. In this study, we fabricated TiO2 gas sensors with an array of TiO2 nano helixes sensing layer to enhance the gas sensing performances such as sensitivity and response time through a large surface-to-volume ratio as well as a new gas sensor design with top- and bottom- electrodes. The array of TiO2 nano helix TiO2 gas sensing layer was fabricated by electron-beam oblique-angle deposition (OAD) technique with which 3-dimensitional nano-structures of thin films can be precisely controlled by changing incident vapor flux angle and substrate rotation speed. Also, a new gas sensor design was designed in order to fully utilize the electron depletion effect of each nano helix so that one can maximize sensitivity and reduce response time. Since anatase phase is required for gas sensing layer, as-deposited TiO2 nano helixes were annealed for 3 hours in air so that the amorphous phase TiO2 could be transformed to anatase phase. Crystallinity of the TiO2 film and the effect was quantitatively investigated. Increase in porosity and surface-to-volume ratio of helix-structured film, and resultant enhancement in gas sensitivity and response time will be discussed theoretically and experimentally in detail.
9:00 PM - GG10.31
X-ray Diffraction Investigations of TiO2 Thin Films, Powders and Nanotubes and Their Thermal Stability.
Radomir Kuzel 1 , Zdenek Matej 1 , Lea Nichtova 1 , Tereza Brunatova 1
1 Department of Condensed Mater Physics, Charles University in Prague, Faculty of Mathematics and Physics, Prague Czech Republic
Show AbstractTitania is well-known material of great interest because of many remarkable properties. In particular, it is a unique material that connects two distinct photo-induced phenomena: photocatalytic activity and photo-induced superhydrophilicity, after UV illumination. However, desired properties are strongly influenced by phase composition (anatase, rutile, brookite, other phases), the crystallinity (amorphous, crystalline, nanocrystalline), and/or their particular microstructure, presence of residual stresses in the films etc. Usually, the entirely amorphous films do not have required properties and crystalline or nanocrystalline form is preferred. In principle, this can be obtained either by finding of suitable deposition parameters or by annealing of amorphous films. At the same time, because of a need of deposition onto substrates like polymers, lower temperatures are required for the preparation. Therefore, temperature evolution of the film structure and microstructure is of high interest and it was studied for both nanocrystalline and amorphous films of different thickness by X-ray diffraction at room temperature and in-situ in high-temperature chamber. Room temperature studies included X-ray reflectivity measurements (film thickness, density, surface roughness), stress and texture measurements and parallel beam glancing angle diffraction evaluated by our own software for total diffraction pattern fitting (lattice parameters, microstrain, crystalite size, residual stress).Isothermal in-situ annealing experiment showed that the time dependence of diffraction peak intensity can be well described by the Avrami equation. Stress and texture evolution with the annealing time was detected as well.A strong influence of film thickness on composition and crystallization of TiO2 thin films was found. In very thin amorphous films the crystallization is significantly slower than for thicker layers. The effect is most probably related to the rapid increase of residual tensile stresses with the decreasing film thickness. The tensile stresses are generated continuously from the beginning of crystallization and then they inhibit the process of crystallization. Relatively large anatase crystallites grow quickly from the very beginning of crystallization and therefore it is difficult to use annealing of amorphous films for preparation of nanocrystalline films unlike amorphous titania powders for which the annealing for specific time at specific temperature can result in predetermined mean crystallite size. Nanocrystalline powders and thin films are relatively stable with the temperature and small crystallites (< 10 nm) remain up to 400–500 °C. Titania nanotubes used for improvement of elastic properties of polymers are studied as well. The first attention is devoted to modelling of specific X-ray diffraction patterns by using the Debye formula. The best results were obtained with the model of folded monoclinic β TiO2 phase.
9:00 PM - GG10.4
Effect of Solvent Acidity on Size and Stability of Anatase Titania Nanoparticles.
Deniz Alpay 1 , Ece Alpaslan 1 , Ozge Malay 1 , Yusuf Menceloglu 1
1 Materials Science and Engineering, Sabanci University, Istanbul Turkey
Show AbstractTitanium dioxide nanoparticles (TNP) have been widely studied for the past 2 decades due to their unique properties. High photocatalytic efficacy and photovoltaic activity are some of the particular properties that attract great attention on nano-sized anatase phase titanium dioxide. Aim of this study was to analyze the effect of synthesis conditions on properties of TNPs. In order to do so, nanoparticles were synthesized using a sol-gel method, with titanium isopropoxide (TIPP) as a precursor in 1-propanol solution. A common challenge with sol-gel route is to eliminate the progress of agglomeration of the particles caused by the high coordination number of TIPP precursor. The initial syntheses were repeated from previously reported studies, and after optimizing the reaction time and concentration, effect of pH on nanoparticle size, morphology, and crystalline structure was further analysed. The optimum pH range for synthesis of stable titanium dioxide nanoparticles with <5nm particle size was obtained through investigation of characterization data of TNPs synthesized in different pH levels. Particle size and stability of sub 10nm TNPs were confirmed with kinetic size distribution analyses via dynamic light scattering. Our findings suggest that equilibrium conditions for sub 10nm sized TNP occur only at a very narrow pH range, at which formation of network structures is inhibited. Obtained data indicates that the pH – particle size correlation is not linear, and that gelation occurs at solutions with acidity ratio [H+]/[Ti] lower than 0.7 for the system under investigation. In normal conditions, TNP form amorphous structures, and the transformation from amorphous to anatase phase can be induced in particles synthesized in low pH conditions via calcination. The optimum (i.e. minimum energy consuming) calcination conditions were determined and phase transformation was confirmed via X-Ray Diffractometry. It was observed that the post-calcination crystals of TNP that have been synthesized outside the narrow pH range were not in anatase phase. The calcination conditions to synthesize particles comprising >90% anatase and <10% rutile, a composition that is mostly preferred for photovoltaic and photocatalytic applications, have also been determined. Images of particles taken via scanning electromicroscopy and atomic force microscopy were also congruent with our findings. Having focused on the effect of pH, concentration, and equilibrium time, we believe that this ongoing study provides a wide range of information on sol-gel synthesis of TNPs.
9:00 PM - GG10.5
Employing Resonating Platforms for Characterization of TiO2-carbon Composite Coatings.
Jessica Torrey 1 , Stephanie Hooker 1
1 Materials Reliability Division, NIST, Boulder, Colorado, United States
Show AbstractThe contamination of fresh water supplies by persistent organic compounds is an increasing problem worldwide. Various treatment techniques have been proposed to remove these compounds from water, including particularly promising adsorbent-photocatalyst composites. Individually, these materials have proven economical and effective, and recent results claim enhanced degradation for the composite. In this research, we have modified an existing quartz crystal microbalance technique and combined it with spectroscopy to form a comprehensive analysis method for detection of adsorption and degradation processes during ultraviolet light induced photocatalysis of organic compounds. Results will be presented on the adsorption and decomposition of methylene blue dye in the individual titanium dioxide and powdered activated carbon (PAC) systems and in the TiO2-PAC composite coating. By varying experimental conditions such as temperature, radiation intensity, dye concentration, and water flow rate, conclusions can be drawn as to the interplay between adsorption and photocatalytic degradation.
9:00 PM - GG10.6
Syntheses and Characterization of Titania Decorated Titanate Nanotubes.
Sung-Ho Hwang 1 , Soonhyun Kim 1 , Sang Kyoo Lim 1 , Hyun Jung Choi 1 , Minsun Kim 1
1 Division of Nano & Bio Technology, Daegu Gyeongbuk Institute of Science and Technology, Daegu Korea (the Republic of)
Show AbstractRecently, as the environmental pollution and safety facilities such as fire protection comes to important issue in world wide, the development of environment-friendly materials capable of replacing the established ones have received a great attention. In the field of construction, much attention have also been paid for the fbrication of various inorganic filler materials as eco-friendly and non-flammable ones due to their heat resistant and flame retardant properties inorder to replace glass fibers. In this work, we have synthesized various titanate nanotubes and studied about their applicable properties as inorganic filler due to their high porous structure along with photocatalytic one.Anatase titania decorated titanate nanotubes (TiNT-AT) are prepared by acid treatment at 80 °C from titanate nanotubes (TiNT) which are produced from the alkaline hydrothermal reaction of P25. The obtained TiNTs with 10 ~ 20 nm in diameter and several hundred nanometers in length. They composed low crystalline titanate and their surface area were ca. 152 m2/g. However, they did not show any photocatalytic activities due to a lot of defect sites which could act as recombination center of photogenerated electron and hole pairs. On the other hands, TiNT-AT shows the efficient photocatalytic activities for both gaseous CH3CHO and aqueous DCA degradation. The photocatalytic superiority of TiNT-AT is attributed to the decorated titania with anatase phase, which could be responsible for the efficient charge separation. Because conduction band and valence band of the titanate nanotube is ca. 0.1 V higher and 0.5 V lower than those of anatase titania, the charge transfer from the conduction band and valence band of titanate nanotube to the surface electron acceptor and electron donor could efficiently occurred through conduction band and valence band of anatase titania, respectively.
9:00 PM - GG10.7
First Principles Study of the Self-doped Effect on the Photocatalytic Activity of Anatase Titanium Dioxide.
Chin-Lung Kuo 1
1 Materials Science and Engineering, National Taiwan University, Taipei Taiwan
Show AbstractIn this study, we use first principles density functional theory (DFT) calculations within the generalized gradient approximation of Perdew and Wang to investigate the electronic and optical properties, as well as the associated photocatalytic activity of the nonstoichiometric oxygen deficient anatase titanium dioxide. Oxygen deficiency was introduced via the removal of oxygen atoms in various sizes and shapes of TiO2 supercells. The effect of oxygen deficiency on the electronic density of states, band structures, and the resulting optical absorbance of titanium dioxide will be highlighted in this presentation. Our calculations show that the concentration of oxygen vacancy and the interaction between different oxygen vacancy pairs may result in considerable changes in the electronic density of states and band structures, leading to different light absorption behaviors of titanium dioxide. These results are in good agreement with the recent experiments and can also help to explain the controversy regarding the self-doped effect on the photocatalytic effect of anatase TiO2.
9:00 PM - GG10.8
Photoactivity of Anatase–rutile TiO2 Nanocrystalline Mixtures Obtained by Heat Treatment of Titanium Peroxide Gel.
Snejana Bakardjieva 1 , Jan Subrt 2
1 , Institute of Inorganic Chemistry ASCR vvi, Rez Czech Republic, 2 CIT, Inst Inorg Chem ASCR vvi, Rez Czech Republic
Show AbstractNanosized titanium dioxide photocatalysts with varying amount of anatase and rutile phases have been synthesized. Homogeneous precipitation of aqueous solutions containing TiOSO4 and ammonia and following treatment with H2O2 of the as-precipitated product was used to prepare porous yellowish (Ti-Per) gel. The gel was lyophilized for 48h and (Ti-Per)LYO-powder was obtained. Photoactive titania powders with variable amount of anatase and rutile phases were prepared by heating of the (Ti-Per)LYO powder in the temperatutre range 500–1000C and series of new samples were prodused. The structure evolution during heating of the starting (Ti-Per)LYO powder was studied by XRD analysis in overall temperature range of phase transformation. The morphology and microstucture characteristics were also obtained by HRTEM, BETand BJH. The lamella-like particle morphology of TiO2 mixtures determined by SEM was stable in air up to 950C. The photocatalytic activity of the sample titania TI-LYO/950 heated to 950C in air, contained 78.4% anatase and 21.6% rutile was higher than that standard Degussa P25. Titania sample TI-LYO/950 reveals the highest catalytic activity during the photocatalyzed degradation of 4-chlorophenol in aqueous suspension under UV-irradiation.
9:00 PM - GG10.9
Silicon Based Water Splitting: ALD-TiO2 Protection on Semiconductor (photo)Anodes for Water Oxidation.
Yi Wei Chen 1 , Jonathan Prange 2 , Marika Gunji 1 , Christopher Chidsey 2 , Paul McIntyre 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States, 2 Chemistry, Stanford University, Stanford, California, United States
Show AbstractThe need for technologies to store electricity derived from intermittent sources, such as solar or wind energy, prompts interest in efficient and scalable methods for fuel synthesis with minimal global warming gas emissions. Electrochemical synthesis of hydrogen from water is a leading approach for large-scale energy storage. This involves electrochemically splitting water, reducing protons to hydrogen at the cathode, and oxidizing water or hydroxide ions to oxygen at the anode. The oxidation reaction requires a catalytic anode surface that must sustain water splitting without suffering oxidative corrosion. By absorbing solar energy while performing water oxidation, a photoanode can reduce or eliminate the applied bias that is otherwise required to drive the water splitting reaction. TiO2 (bandgap ~ 3 eV) has long been studied as potential photoanode because of its stability over a range of pH and potentials. However, the relatively large bandgap of TiO2 limits absorption to a small fraction of the solar spectrum in the ultraviolet, resulting in low efficiency. Other photoanodes such as Fe2O3 (bandgap 2.3 eV) are also limited in saturation current densities because of their relatively high bandgaps and modest electronic conductivities. Smaller bandgap semiconductor photoanodes, such as Si (bandgap 1.1 eV), are capable of absorbing most of the incident photons from solar illumination and exhibit efficient electronic carrier transport, but are easily oxidized at the potentials required for water oxidation. In this work, doped Si substrates were coated with a thin, but protective, pinhole-free layer of TiO2 by atomic layer deposition. An ultrathin, optically transparent, Ir layer was then deposited on the top to serve as a water oxidation catalyst and electron transfer mediator. This nanocomposite anode is stable during continuous water oxidation for periods greater than 24 hours in 1M NaOH, an alkaline solution that would instantly oxidize an unprotected Si electrode. With AM1.5G illumination, the onset of water oxidation occurred at ~200 mV below the thermodynamic equilibrium potential, and 550 mV less than the potential required for facile oxidation in the dark. The current density at higher applied biases saturated near 30 mA/cm2, close to the 36 mA/cm2 theoretical limit for AM1.5G illumination of a Si photoanode. The measured overpotentials are similar to the best values reported in literature for dark electrolysis, while the saturation current density is four or five times better than the current state-of-the-art Fe2O3 electrodes. In addition, the inferred photovoltage under illumination of 550 mV approaches the open circuit voltages of state-of-the-art Si solar cells.This ALD tunnel oxide passivation approach is quite general and may be applied to other semiconductor anodes used in water splitting or in other electrochemical reactions.
Symposium Organizers
Xiaobo Chen Lawrence Berkeley National Laboratory
Michael Graetzel Ecole Polytechnique Federale de Lausanne
Can Li Chinese Academy of Sciences
P.Davide Cozzoli Universita del Salento - Facolta di Ingneria Industriale
and Nanoscience Institute of CNR -
National Nanotechnology Laboratory
GG15: Titanium Dioxide Nanomaterials & Energy
Session Chairs
Ulrike Diebold
Annabella Selloni
Friday AM, April 29, 2011
Room 3020 (Moscone West)
9:15 AM - **GG15.1
Nanostructured TiO2 for Lithium Batteries.
Peter Bruce 1 , Valentina Gentili 1 , Yu Ren 1 , Laurence Hardwick 1 , Sergio Brutti 1 2 , Yuri Andreev 1 , Anthony Armstrong 1
1 School of Chemistry, Univeristy of St Andrews, St Andrews, Fife, United Kingdom, 2 , University of Rome “La Sapienza”, Rome Italy
Show AbstractTitanates are attractive as anodes for rechargeable lithium batteries: although their potential is higher than graphite (the dominant anode to date), titanates offer superior safety and higher charge/discharge rates, while preserving low cost and low toxicity. Sustaining higher rates than current Li-ion batteries is important for new applications such as electric vehicles (regenerative breaking). Accessing high rates necessitates the use of nanomaterials. While the titanate spinel, Li4Ti5O12, has been extensively investigated as an anode, TiO2 offers almost twice the capacity to store charge (~ 300mAhg-1). The higher density of TiO2 compared with graphite also leads to higher volumetric capacities, important where space as well as weight is an issue. Although nanoparticles offer enhanced properties compared with their corresponding bulk (micron) materials, nanostructured materials can offer still greater advantages. We have investigated the influence of nanostructure on TiO2 anodes for Li-ion batteries. Such studies have included nanotubes and nanowires based on anatase and TiO2(B) and mesoporous anatase. Capacities of ~300 mAhg-1 (~ 1 Li per Ti) have been obtained at low rates and 130 mAhg-1 at 35C (discharge in 2 mins.) The synthesis, characterization and properties of the nanostructured TiO2 materials will be discussed with emphasis on the unique behaviour that the nanostructuring endows.
9:45 AM - GG15.2
TiO2 Nanoflakes as an Anode Electrode for Lithium Ion Batteries
Ming-Che Yang 1 , Yang-Yao Lee 1 , Kevin Powers 2 , Ying Meng 3 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Particle Engineering Research Center, University of Florida, Gainesville, Florida, United States, 3 Department of NanoEngineering, University of California San Diego, La Jolla, Florida, United States
Show Abstract Anatase Titanium oxide is a promising electrode material for Li-ion batteries due to its good Li-storage capacity, safety against overcharging and stable voltage plateau at 1.78V, which made it possible to be used against high voltage (5V) cathode materials. However, the low electrical conductivity and poor cycling performance because of the structural change during charge/discharge process have limited its application. Titanium oxide nanoflakes are of great interests in electrochemical lithium insertion due to their small grain size (5-8nm), larger surface area and pore volume. Anatase Titanium oxide nanoflakes exhibit larger reversible discharge capacity, better rate capability and excellent cycling stability compared to Anatase Titanium oxide nanoparticles. The Titanium oxide nanoflakes have been synthesized through spreading method. For spreading to be possible, the pentane and titanium tetrabutoxide were used as the precursors and continuously added into the solution on the surface of flowing water. Supercritical drying process was performed to remove the residual water. The size of the synthesized nanoflake is about 40nm in lateral dimension and was composed of 5nm nanograins. After 400°C calcined process, the nanoflakes became pure Anatase phase free of any impurity and were composed of on average 8nm grains and the 7nm pores. Electrochemical performances were investigated by galvanostatic technique combined with Impedance Spectroscopy. The nanosized grains of TiO2 nanoflakes and the pore volume play key factors in determining the electrochemical properties. We will focus on the relationships between crystal structure, surface area, pore volume and electrochemical properties of Anatase TiO2 nanoflakes.
10:00 AM - GG15.3
Designing Transition Metal Oxide Semiconductors for Efficient Photoelectrochemical Energy Conversion.
Lianzhou Wang 1
1 School of Chemical Engineering, University of Queensland, Brisbane, Queensland, Australia
Show AbstractA. Mukherji, G. Liu, M. Lim, GQ Lu, and Lianzhou Wang*ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering, the University of Queensland, St Lucia, 4072, QLD, Australia. Email:
[email protected] The increasing concerns over the climate change and exhausting fossil fuels have seen great efforts being directed toward the development of new energy generation /conversion systems. Innovative materials for energy conversion hold the key for renewable energy production. The ability to design these nanomaterials with tailored structures and functionalised properties is an important challenge that researchers strive to meet. Aimed at developing new nanostructures for efficient photocatalytic and electrochemical energy conversion, we have recently developed the synthesis, band-gap modification, and self-assembly of several types of transition metal oxides including layered titanate, clays, tantalates and niobate-based pervoskites.1-3 The exfoliation of these layered structures led to the formation of colloidal suspensions containing exfoliated nanosheets. These unique nanosheets can be structural modified into ideal two-dimensional building blocks for new nano-architecture fabrication. The self-assembly and flocculation of nanosheets led to multilayer ultrathin films and restacked nanoporous structures, which exhibited excellent visible light photocatalytic and electrochemical performances.References:1.Reviews in a) G. Liu, LZ Wang, HG Yang, HM Cheng, GQ Lu, J. Mater. Chem., 2010, 20,831. b) W. Zhang, L. Zou, L.Z Wang, Applied Catalysis A: General, 371 (2009) 1–9. 2. a) G. Liu, LZ Wang and GQ. Lu et al., Chem. Commun., 1383 (2009); b) G. Liu, LZ. Wang and GQ. Lu et al, Chem. Mater., 21, 1266-1274 (2009). c), A. Mukherji, R. Marschall, S. Smith, GQ Lu, LZ Wang, Adv. Funct. Mater., 2010, in press. 3.(a). M. Lim, LZ. Wang, and GQ. Lu et al., J. Phys. Chem. C, 112, 19655(2008); (b), M. Lim, LZ. Wang and GQ. Lu, et al., Electrochem. Commun. 11 509(2009); (c) M. Lim, LZ. Wang and GQ. Lu, et al., Environ. Sci. Techno., 43, 473(2009).
10:15 AM - GG15.4
Titanium Dioxide Nanomaterials with Long-wavelength Optical Absorption.
Xiaobo Chen 1 , Samuel Mao 1
1 , Lawrence Berkeley National Lab, Berkeley, California, United States
Show AbstractThe optical absorption properties of titanium dioxide nanomaterials are very important to their photocatalytic properties. The possible realizing approaches are investigated and discussed.
10:30 AM - GG15.5
Electrospun TiO2 Nanofibres for Fuel Cells Applications.
Sara Cavaliere 1 , Surya Subianto 1 , Laure Chevallier 1 , Deborah Jones 1 , Jacques Roziere 1
1 Laboratoire des Agrégats Interfaces et Matériaux pour l’Energie, Institut Charles Gerhardt Montpellier, Montpellier cedex 5 France
Show AbstractThe proton exchange membrane fuel cells (PEMFC) have received significant research attention due to their potential as a sustainable source of energy. However, many challenges remain in improving their efficiency and lowering their costs, which concern both the used materials and their micro and nanostructure. The support material for electrocatalysts is a very crucial point in PEM fuel cells performances and development. It must stabilize the catalyst nanoparticles to obtain their maximum exploitation and reduce metal amount, and then electrode costs. Carbon is the most used catalyst support. However, it can be corroded chemically and electrochemically, leading to the detachment of catalyst particles and consequently to the loss of performances. Conductive or semi-conductive oxides (indium tin oxide, TiOx, SnO2, etc…) represent a very attractive alternative to conventional supports for electrocatalysts. Because of their (electro)chemical stability and promoting effects, these materials have shown promising results on the catalytic activity and durability of PEMFC catalysts.Novel nanostructured 1D materials such as conductive nanotubes and nanofibres have attracted significant research attention as catalyst supports for PEMFC due to the influence of their nanostructure and morphology on performance and durability. In this regard, the electrospinning technique is a versatile tool in the synthesis of nanofibres with controlled and uniform diameters and structures1. It is especially attractive for electrode materials, as the high porosity and uniformity of electrospun fibres would allow good diffusion of the reactant gases while maintaining a conducting path through the interconnectivity of the fibres. By combining these trends, we developed novel titania conductive nanofibres (Nb doped) by electrospinning. Furthermore, instead of using a conventional catalyst impregnation method, we integrated Pt nanoparticles by means of a one pot route, which resulted in well dispersed catalytic nanoparticles on the fibres. The morphology of such materials was characterized by SEM and TEM microscopies. The obtained fibers presented a diameter of 80 nm and showed an intrinsic nanostructure and porosity. The in situ grown platinum nanoparticles were dispersed quite homogenously onto the oxide fibers. XRD confirmed the size and the crystallinity of the Pt nanoparticles and showed that the doped TiO2 was present in its anatase form. Further physico-chemical (XPS, N2 adsorption/desorption…) and electrochemical characterisation of the nanofibre/nanoparticle composite will also be discussed with more details. Such nanomaterials elaborated in a novel one-pot, simple and rapid way, are promising electrodes for PEMFC.
10:45 AM - GG15: energy
BREAK
GG18: Titanium Dioxide Nanomaterials - Nanostructures
Session Chairs
Friday PM, April 29, 2011
Room 3020 (Moscone West)
4:30 PM - GG18.1
TiO2 Nanotubes via Electrochemical Anodization: Electronic Structures and Optical Properties Studies of Phase Transformation and Calcium Phosphate Coating.
Lijia Liu 1 , Jeffrey Chan 1 , Sun Kim 1 , Tsun-Kong Sham 1
1 Chemistry, University of Western Ontario, London, Ontario, Canada
Show AbstractElectrochemical anodization is a low-cost and efficient method for synthesizing TiO2 nanotubes (TiO2-NT) vertically grown on a Ti substrate. Among various crystal structures of TiO2, anatase and rutile are most commonly found and used in many applications. The phase transformation from as-made TiO2 (amorphous) to anatase and further to rutile can be controlled by adjusting the calcination temperature. We have studied the electronic structures of TiO2-NT after calcination at a series of temperatures (400°C-800°C) using X-ray absorption near-edge structures (XANES). The phase transformation of TiO2-NT is distinguished by the different crystal field splitting of t2g and eg in anatase and rutile. We have also examined the optical luminescence from TiO2-NT using X-ray excited optical luminescence (XEOL) and have found that anatase TiO2-NT emits visible green light but rutile TiO2 emits near infrared light. The luminescence mechanism is revealed by a combination analysis of XANES and XEOL. In addition, Ti has been recognized as an orthopedic implant material and the TiO2-NT-on-Ti structure can provide a large porous surface area for bone cell growth, and coating of calcium phosphate compounds (Ca-P) can further enhance bone bonding and fixation of the implant. We will demonstrate the deposition of Ca-P on TiO2-NT and the corresponding electronic structures of Ca-P deposited on TiO2-NT of different morphologies and crystal phases using X-ray absorption fine structures (XAFS). Research at UWO is supported by NSERC, CFI, OIT and CRC. Synchrotron experiments were conducted at the Canadian Light Source, which is supported by NSERC, NRC, CIHR and the University of Saskatchewan.
4:45 PM - GG18.2
Vertically Aligned High Surface Area Photoanodes: Fabrication and Characterization.
Rudresh Ghosh 1 , Matthew Brennaman 1 , Rene Lopez 1
1 , University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Show AbstractThe enhancement of performance of metal oxides as photoanodes in dye sensitized solar cells(DSSC) is a constant challenge in the field of renewable energy sources. Obtaining a film-like structure which simultaneously increases the surface area as well improves the charge transfer properties being the main goal. In this work we report the fabrication of such a structure. Controlling of the deposition environment during pulsed laser deposition (PLD) allows us to tailor the structures of the metal oxide films, varying from a compact 2d structure to an extremely porous nanoparticle film. At certain deposition pressure ranges, vertically aligned highsurface area films are obtained which simultaneously increase dye loading and improve charge transfer processes.Photoelectrochemical properties of these structures are measured in terms of light absorption and incident photon to current efficiency (IPCE) of photoanodes. Other characterizations include x-ray photon spectroscopy(XPS), x-ray diffraction(XRD), scanning electron microscopy(SEM), photoluminiscence(PL), Raman, resistivity and ellipsometric measurements.For TiO2 films an enhanced dye loading (~2.5 times) and increased absorbed photon to current efficiencies (APCE), of about 92%, over conventional nanoparticle based films are observed.
5:00 PM - GG18.3
Anodic TiO2-nanotubes and Mesosponge: Growth, Properties and Application.
Robert Hahn 1 , Doohun Kim 1 , Himendra Jha 1 , Patrik Schmuki 1
1 Material Science and Engineering, University Erlangen, Erlangen Germany
Show AbstractSelf organized nanotubular structures of transition metal oxides grown on their metallic substrates, especially titanium [1], have attracted great scientific and technological interest due to the possibility to exploit their functional properties (such in photo-catalysis, solar energy conversion and as host for Li storage). A conventional way to grow anodic TiO2 nanostructures is an optimized electrochemical treatment of metallic Ti in an optimized electrolyte (for a recent overview see [2]).The first part of the presentation will introduce all relevant TiO2 nano-morphologies obtained by this straightforward method e.g. nanotubes, nanobamboo, nanolace [3], nanocolumns [4], nanotubular powders [5], TiO2 mesosponge (TMS) [6] and superlattice nanotube arrays [7] the most promising application of such advanced self-organized structures.Literature:[1] Zwilling, V.; Darque-Ceretti, E.; Boutry-Forveille, A.; David, D.; Perrin, M.Y.; Aucouturier, A., Alloy Surf. Interface Anal. 1999, 27, 629-637.[2] Berger, S.; Hahn, R.; Roy, P.; Schmuki, P., Phys. Status Solidi B, 2010, 247, 10, 2424–2435.[3] S. Albu, D.Kim, P. Schmuki, Angew. Chem. Int. Ed. 2008, 47, 1916 –1919[4] T. Ruff, R. Hahn, P.Schmuki submitted (2010)[5] H. Jha, R. Hahn, P. Schmuki Electrochimica Acta 55, 8883 (2010).[6] D. Kim, K. Lee, P. Roy, B.I. Birajdar, E. Spiecker, P. Schmuki, Angew. Chem. Int. Ed. 48 (2009) 9326.[7] W. Wei, H. Jha, G. Yang, R. Hahn, I.Paramasivam, S. Berger, E. Spiecker, P.Schmuki, Advanced Materials (2010) DOI: 10.1002/adma.201002091
5:15 PM - GG18.4
Monolithic Nanotubular Titania Fabricated by an Atomic Layer Deposition based Templating Approach.
Monika Biener 1 , Juergen Biener 1 , Ted Baumann 1 , Alex Hamza 1
1 , LLNL, Livermore, California, United States
Show AbstractTitania-based nanomaterials have wide spread technological applications due to their interesting catalytic and electronic properties. Here we report on a new general method to fabricate monolithic, low-density, high-surface-area nanoporous bulk samples of titania and alumina with well-controlled and tunable density and feature size by using an atomic layer deposition (ALD) based templating approach. As templates we use nanoporous metals that can easily be formed as monolithic bulk samples by a simple self-organization process, and those feature size can be adjusted using a simple thermal annealing procedure. These templates are coated with conformal, sub-nanometer to several nm-thick oxide films using the ALD technique. Monolithic nanoporous oxide samples are then obtained by removing the metal template using a suitable etch process. The resulting material has a unique nanotubular structure with a unimodal feature size that can be adjusted over a wide range from a few nanometers to the micron length scale.This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
5:30 PM - GG18.5
Novel Titanium Dioxide Nanostructures through the Combination of Supercritical Fluid Deposition and Nanoimprint Lithography.
Nicholas Hendricks 1 , Eunyoung You 2 , Kenneth Carter 1 , James Watkins 1
1 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 Chemical Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractTitanium dioxide nanostructures have long been studied for applications ranging from photovoltaics to photocatalytic oxidation. For such applications the creation of large surface areas within a compact device structure, to either harvest energy or degrade harmful pollutants, is highly desirable. Here we show that the combination of supercritical fluid deposition (SFD) with patterned sacrificial substrates produced by nanoimprint lithography (NIL) yields a new fabrication technique for the nanostructuring of titanium dioxide. The process begins by performing ultraviolet-assisted nanoimprint lithography (UV-NIL) into an acrylate based photopolymer to generate a copy of the features present on the mold. An anisotropic oxygen plasma reactive ion etch (RIE) is then performed to generate free standing polymeric structures that will be used as a sacrificial template to create embedded nanochannels within the titanium dioxide film. A conformal titania film is deposited onto the template using supercritical fluid deposition with carbon dioxide (CO2) as the reaction medium and bis(2,2,6,6-tetramethyl-3,5-heptanedionato) diisopropoxide titanium as the precursor. A hydrothermal treatment is performed to ensure structural integrity of the nanochannels. This is followed by thermal degradation of the polymer template to yield embedded nanochannels within the titanium dioxide film. The resulting films were characterized using electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and other techniques.