Symposium NM04 : Porous Materials and Nanocomposites for Catalysis

We explore the opportunities offered by spatially integrating photoactive molecular building blocks into the crystalline lattice of covalent organic frameworks (COFs), thus creating models for organic bulk heterojunctions and porous electrodes for photoelectrochemical systems. In this presentation, we will address means of controlling the morphology and packing order of COFs in thin films (1) and with spatially locked-in building blocks.(2) Regarding the latter, the design of well-defined periodic docking sites enables us to achieve remarkably high crystallinity with several multidentate building blocks and a series of linear bridging units.

We will discuss different strategies aimed at creating electroactive networks capable of light-induced charge transfer. For example, we have developed a COF containing stacked thienothiophene-based building blocks acting as electron donors with a 3 nm open pore system, which showed light-induced charge transfer to an intercalated fullerene acceptor phase.(3) Contrasting this approach, we have designed a COF integrated heterojunction consisting of alternating columns of stacked donor and acceptor molecules, promoting the photo-induced generation of mobile charge carriers inside the COF network.(4) Moreover, additional synthetic efforts have led to several COFs integrating extended chromophores capable of efficient harvesting of visible light, for example (5). Extending newly developed thin film growth methodology to a solvent-stable oriented 2D COF photoabsorber structure, we have recently established the capability of COF films to serve in photoelectrochemical water splitting systems.(6) The great structural diversity and morphological precision that can be achieved with COFs make these materials excellent model systems for organic optoelectronic and nanostructured catalytic systems.

(1) D. D. Medina, J. M. Rotter, Y. H. Hu, M. Dogru, V. Werner, F. Auras, J. T. Markiewicz,
P. Knochel, T. Bein, J. Am. Chem. Soc. 2015, 137, 1016.
(2) L. Ascherl, T. Sick, J. T. Margraf, S. H. Lapidus, M. Calik, C. Hettstedt, K. Karaghiosoff, M. Döblinger, T. Clark, K. W. Chapman, F. Auras, T. Bein, Nature Chem. 2016, 8, 310.
(3) M. Dogru, M. Handloser, F. Auras, T. Kunz, D. Medina, A. Hartschuh, P. Knochel,
T. Bein, Angew. Chem. Int. Ed. 2013, 52, 2920.
(4) M. Calik, F. Auras, L. M. Salonen, K. Bader, I. Grill, M. Handloser, D. D. Medina,
M. Dogru, F. Lobermann, D. Trauner, A. Hartschuh, T. Bein, J. Am. Chem. Soc. 2014, 136, 17802.
(5) N. Keller, D. Bessinger, S. Reuter, M. Calik, L. Ascherl, F. C. Hanusch, F. Auras, T. Bein, J. Am. Chem. Soc. 2017, 139, 8194.
(6) T. Sick, A. G. Hufnagel, J. Kampmann, I. Kondofersky, M. Calik, J. M. Rotter, A. Evans, M. Döblinger, S. Herbert, K. Peters, D. Böhm, P. Knochel, D. D. Medina, D. Fattakhova-Rohlfing, T. Bein, submitted.

Nanostructured photocatalysts have the potential of combining large potential-driven chemical driving forces with the near-volumetric system scaling achieved by surface reactions on dispersed, nanoscale particles. With increased biodiesel production over the past 20 years having saturated the glycerol market and thereby devaluing biodiesel, glycerol photoreforming presents a useful model photocatalytic reaction. Titania remains the dominant photocatalyst today but, despite nanostructuring and phase engineering efforts, continues to suffer from low photocatalytic efficiencies. Previous work has shown brookite-phase TiO₂ nanorods to have improved photoreforming efficiency in comparison to other TiO₂ phases and morphologies. In this contribution, we present the synthesis of composites of these TiO₂ nanorods with graphitic carbon nitride (g-C₃N₄), a 2D semiconducting polymer, to improve upon this relatively high performance by introducing a heterojunction with favorable band positioning (based on bulk material properties) to suppress electron-hole recombination. These composites, in combination with platinum nanoparticles, demonstrate much larger steady-state hydrogen production rates from glycerol photoreforming than do either of the individual components alone or a physical mixture of the two components, highlighting the synergism between the two phases that is related to band positioning and intimate contact between the two building blocks. Controlled synthesis of the composites, including the ability to tune TiO₂ nanorod length and exfoliate and etch sheets of g-C₃N₄, enables a more controlled study of electron excitation and charge transfer in these materials to then understand what limits their photocatalytic performance. By first studying the electronic structure and optical properties of the TiO₂ nanorods and the g-C₃N₄ individually, a more detailed mechanistic picture can be put together of process energetics and relevant energy barriers. This mechanistic understanding will be useful in designing higher efficiency photocatalytic systems moving forwards.

Platinum nanocrystals (Pt NCs) have been widely used as the ideal electrocatalyst for hydrogen evolution reaction (HER). Although non-noble metal catalysts have been extensively developed to reduce the material expense and replace Pt in recent, their catalytic activities have been still far inferior to Pt in acidic media [1]. However, HER performance with Pt catalyst is swiftly decreased for long-time operation. One of the critical reasons for such a poor stability is the weak-binding interaction with carbon electrode, which leads to coalescence, detachment and dissolution of Pt NCs from carbon [2]. Therefore, the rigid immobilization of Pt NCs to electrode is crucial to suppress the loss of active sites and to retain HER activity. Here we develop Pt nanocrystals that are implanted in molybdenum sulfide selenide (MoSSe) alloy layer, and this Pt NCs/MoSSe layers coaxially coat carbon nanotube (CNT) electrode. The MoSSe/CNT was prepared through hydrothermal reaction, and Pt NCs were subsequently synthesized through photochemical reduction reactions. The MoSSe was grown along to the sidewall of CNT with bilayer or trilayer, which may allow for smooth electron transfer in between Pt NCs and CNT electrode. In addition, the attached Pt NCs are uniformly distributed with an average diameter of ~2 nm on the catalyst support of MoSSe. The Pt/MoSSe/CNT shows higher catalytic activity for HER in comparison with commercial Pt/carbon (C) in 0.5 M H₂SO₄ at 25 ^oC. When Pt loading is controlled to ~20 wt%, the Pt/MoSSe/CNT shows an onset potential of 21 mV vs RHE, a Tafel slope of 29.7 mV dec⁻¹ and negligible HER activity loss up to 3000 cycles of cyclic voltammetry (-0.3 ~0.7 V vs RHE). By comparison, commercial Pt/C exhibits an onset potential of 35 mV and a significant decrease in HER activity within 3000 cycles. This remarkable HER activity for Pt/MoSSe/CNT may be attributed to modulation of electronic structure of Pt NCs from MoSSe in addition to low electrical resistance of bilyaer/trilayer MoSSe. Besides, the strong attachment of Pt NCs to MoSSe layer, which might be achieved from photochemical reduction process, enhances the stability. In this presentation, I will discuss the structural advantage of Pt/MoSSe/CNT we prepared and the correlated catalytic performance in details.



[1] Adv. Mater. 2017, 29, 1605838.
[2] Topics in Catalysis, 2007, 46, 285–305.

Electrocatalysts are essential components in electrochemical energy conversion systems. For example, hydrogen fuel can be generated by electrochemically splitting water through the hydrogen and oxygen evolution reactions (HER and OER). Electricity can be regenerated in fuel cells where the oxygen reduction reaction (ORR) occurs in the air cathode. Developing noble-metal free electrocatalysts is of great importance for the low-cost and large-scale application of these technologies. Two general guidelines have been adopted to fabricate electrocatalysts. One is to improve the intrinsic activity of active sites, and the other is to increase the number of active sites, both of which require the delicate manipulation of the composition and structure in nano-/micrometer scale. We recently demonstrate several works that enable the controllable synthesis of high-performance electrocatalysts with designable composition and nanostructure.
High-surface-area carbon has been widely used as electrocatalyst support to ensure a large electrochemically active surface. However, the weak interaction between porous carbon support and electroactive components would deteriorate the activity and durability of the catalysts. Additionally, active components formed in conventional one-pot synthesis are usually less controllable. To address these issues, we developed a post-decoration method for the synthesis of efficient Fe-N-C type ORR catalysts (Adv. Energy Mater. 2017, 1701154). The active components in such catalysts, including Fe-N_x and Fe-O_x moieties, are in situ formed by reacting pre-synthesized N-doped porous carbon with iron carbonyl. The pore structure and formation of active sites can be independently modulated and optimized, leading to a remarkable ORR activity comparable to that of Pt/C in alkaline electrolyte.
Alternatively, we have been focused on developing functional materials using metal-organic frameworks (MOFs) for electrochemical energy storage and conversion (Adv. Mater. 2017, DOI: 10.1002/adma.201703614). In virtue of the diverse compositional and structural features of MOFs, they are very unique platforms to synthesize functional materials with desirable nanostructures and composition for various applications. We demonstrate a MOFs-assisted strategy to synthesize mesoporous molybdenum carbide for efficient hydrogen production (Nat. Commun. 2015, 6512). The synthesis relies on the confined and in-situ carburization reaction occurring in a unique MOFs-based compound, which enables the formation of metal carbide nanocrystallites embedded in an amorphous carbon matrix. The porous molybdenum carbide exhibits remarkable electrocatalytic activity for HER in both acidic and basic solutions with good stability. Similar strategy has also been extended to synthesize other high-performance electrocatalysts, including metal-nitrogen-carbon and metal selenide-carbon composite electrocatalysts for various energy conversion applications.

Progress over the past decade in the chemistry of covalent organic frameworks (COFs) has generated a diversity of ordered organic structures with various chemical compositions. The ordered skeletons and aligned open channels make 2D COFs an intriguing platform to explore well-defined catalysts in the sense that if catalytic sites can be successfully integrated to the frameworks. We developed three different approaches to catalytic COFs. The first strategy is to integrate building units that possess catalytic sites into the skeletons; by this method we developed photocatalytic systems. The second way is based on pore surface engineering that enables postsynthetic integration of catalytic sites onto the channel walls of COF; using this approach, we explored organocatalytic systems for promoting asymmetric transformation. The third tactic is using templated carbonization of COFs to achieve conducting catalytic carbons; with this method, we demonstrated the construction of electrocatalytic systems. In this lecture, we will report the design strategy of these approaches and show their distinct features in developing heterogeneous catalytic systems.

Abstract not available.

Abstract not available.

For the past years, there have been extensive research reporting porous graphene in the energy storage and conversion applications, attributing to its pronounced electronic properties and large surface areas.¹ Structurally analogous to graphene, hexagonal boron nitride (h-BN) is of wide-spread interest as well. Owing to the chemical inertness and thermal stability, porous BN nanosheets have been proposed for effective water cleaning.² Remarkably, affinity but different from either graphene or h-BN, ternary boron carbon nitride (BCN) nanosheets could exhibit striking performances by integrating the advantages of both graphene and h-BN. Since the band gap (0-5.5 eV) is adjustable for the novel semi-conductive material.^3,4 Moreover, the heteroatoms of B,N co-doping provides the hetero-polarity, thereby stimulating the electrochemical activity.⁵ That makes it reasonable for BCN nanosheets as potential electrochemical catalysts. To further improve the catalytic performance, it is necessary to elaborately tailor the porosity. In the previous work, soft template surfactant-poly (ethylene oxide-co-propylene oxide) (P123) is introduced to create pores and regulating the nanosheets structure.⁵ The as-prepared BCN nanosheets display high surface area of 817 m² g^-1 with both meso and micro pores. Interestingly, as electrochemical catalyst, the hierarchically porous BCN show impressive oxygen reduction reaction (ORR) catalytic performances in both alkaline and acid environment. It is worth noting that, for single N-doped carbon materials, the increased proton concentration in low pH solution would deteriorate the ORR reaction kinetics with protonation of negatively charged N atom. Nevertheless, for BCN nanosheets, the positively charged B atoms likely alleviates the protonation process, which narrows the gap of ORR catalytic performance between alkaline and acid conditions. Furthermore, the micropores and mesopores are able to support a shorter ion-transport pathway, facilitating the exchange of molecules and ions in the electrolytes. However, it should be noted that too large surface areas would conversely decrease the conductivity, thus lessening the catalytic activity. Therefore, there should be a balance between porosity and conductivity when considering rational design of porous BCN nanosheets for ORR.
1 D. Liu, W. Lei, D. Portehault, S. Qin, Y. Chen, J. Mater. Chem. A 2015, 3, 1682.
2 W. Lei, D. Portehault, D. Liu, S. Qin, Y. Chen, Nat. Commun. 2013, 4, 1777.
3 J. Wang, J. Hao, D. Liu, S. Qin, C. Chen, C. Yang, Y. Liu, T. Yang, Y. Fan, Y. Chen, W. Lei
Nanoscale 2017, 9, 9787.
4 J. Wang, C. Chen, C. Yang, Y. Fan, D. Liu, W. Lei, Curr.Graph.Sci. 2017, 1, 1
5 J. Wang, J. Hao, D. Liu, S. Qin, D. Portehault, Y. Lin, Y. Chen, W. Lei, ACS Energy Lett. 2017, 2, 306.

A series of boron-doped graphene-supported Pt (Pt/BG) nanosheets were designed and synthesized using a one-step facile hydrothermal method. ICP, XPS, and TPD results confirmed boron atoms were successfully embedded into graphene matrix. Selective catalytic reduction of nitric oxide with hydrogen (H₂-SCR) was tested over Pt/BG catalysts. The multi-roles of doped-boron were investigated by Raman, BET, CO-Chemisorption, H₂-TPD, XPS, and NO-TPD. Boron doping led to higher dispersion and smaller size of Pt nanoparticles, facilitated hydrogen spillover, promoted more metallic Pt formation, and increased both H₂ and NO chemisorption, which were attributed to enhanced Pt nucleation rate over doped-boron, electron donation from boron to Pt, and extra chemisorption sites. The reaction performance (conversion 94.7%, selectivity 90.3%, and TOF 0.092 s^-1) were greatly promoted attributing to a bifunctional catalytic mechanism. This work paves a way to modify structure and tune chemisorption ability of graphene-based catalysts, and provides novel insights for designing high performance catalyst.

Due to the unprecedented intrinsic structural features such as tunable pore sizes, large surface area, flexibility to accommodate various types of functional groups, and capability of anchoring metallic species at defective sites, nanoporous/mesoporous high-surface-area carbon materials have been effectively utilized for liquid phase catalytic transformations of valuable molecules. We have previously developed a synthesis process, via catalytic deposition of carbonaceous species on ZnO nanowires and the subsequent reduction-evaporation of the ZnO nanowire template, to produce mesoporous hollow carbon nanostructures. Atomic resolution electron microscopy images revealed that the synthesized mesoporous carbon is composed of intertwined short segments of graphene sheets with dimensions in the range of 0.3 to 3.0 nm, resulting in highly disordered and defective nanostructures, which can be used to anchor single metal atoms or small metal clusters. Incorporation of noble metal atoms or small clusters into the nanoporous carbons can be facilely accomplished via wet chemistry methods to fabricate single-atom or cluster catalysts. Such nanoporous carbon supported single Pt₁/Pd₁ atoms and clusters were evaluated for liquid phase selective hydrogenation of 3-nitrostyrene. The turn-over-number (TON) for producing 3-vinylaniline (with selectivity of 80%) on the Pt₁/C catalyst is as high as 31,157 /h at 40°C, more than 20 times higher than that of the best catalyst reported in the open literature [1]. The TON for producing 3-ethyl-nitrobenzene (with selectivity of 97%) on the nanoporous carbon supported Pd clusters is as high as 107,040 /h at 40°C, ~ 1000 times higher than that of the best Pd catalysts reported in the open literature [2]. The anchoring of noble metal single atoms onto the defective sites of the nanoporous carbon nanostructures, the catalytic properties of the anchored single metal atoms, and their stability during liquid phase catalytic reactions will be discussed [3].

References
1 H. Wei, X. Liu, A. Wang, L. Zhang, B. Qiao, X. Yang, Y. Huang, S. Miao, J. Liu and T. Zhang, Nat. Commun, 2014, 5, 5634.
2 T. Ishida, Y. Onuma, K. Kinjo, A. Hamasaki, H. Ohashi, T. Honma, T. Akita, T. Yokoyama, M. Tokunaga and M. Haruta, Tetrahedron, 2014, 70, 6150-6155.
3 This work was supported by the National Science Foundation under CHE-1465057.

A 3 step process (mixing, curing, and annealing) was used to grow graphite encapsulated Fe nanoparticles within a porous carbon matrix. Herein we report on the synthesis and growth mechanism of this material and its relation to the growth mechanism of carbon nanotubes using catalytic metal nanoparticles. This mechanism enabled the synthesis of new variants of the metal carbon sponge replacing the Fe nanoparticles with Co, Ni, Cu, Ag, and Al. These new metal carbon sponges were characterized to elucidate the difference between the metals used in the synthesis and the morphology and properties they exhibit. A crystallographic analysis by XRD revealed the presence of graphite encapsulation in the Co and Ni variants while absent from Cu, Ag, and Al. This is due to the high carbon solubility in Fe, Co, and Ni, and low solubility in Cu, Au, and Al which also predicts the metals suitable for catalysis of carbon nanotubes. XRD and EDS also reveals the crystallinity and purity of the metal nanoparticles as well as the role of hydrogen in the annealing of the gelatinous carbon resin precursor. TEM also provides analysis of the metal particle structure using electron diffraction. BET was used to investigate surface area and porosity differences between the variants. This research promises a method to synthesize light-weight porous carbon structures with customizable properties based on the metal chosen for applications as varied as catalysis, electrochemistry, oil separation and sorption, and porous graphene nanoarchitectures from environmentally benign and sustainable precursors in an easily scalable manufacturing process.

Methodologies to enhance the activity and longevity of enzymes have occupied the significant positions in the enzyme-based biotechnologies. Enzyme immobilization in the solid support has been the most popular methods to fulfil the two key requirements. However, a few reports employed bicontinuous porous structures in nanoscale for mass transport and nanoscale space for efficient enzymatic functions simultaneously. Recently, we reported caging lipase in nanoporous covalent frameworks prepared from the polymer/poly-urea network mixtures via organic sol-gel(OSG) method. A new type of polymeric membrane with bicontinuous nanoporous morphology could be obtained through phase separation of polyethylene glycol(PEG) and poly-urea sol nanoparticles during solvent evaporation, followed by selective PEG extraction. The nanoporous membrane was employed as a trap for enzyme immobilization, with improved lifespan compared to free enzymes. To broaden the scope of the enzymes and examine the effects of confinement on the activity, we studied the enzymatic reactions from other categories of enzyme. The enzyme was immobilized in the nanopores by permeation through the nanoporous membrane applying an appropriate pressure. Enzymatic activity assay was performed using the enzyme-loaded membranes to investigate the optimized conditions in batch mode. The result shows the general applicability of caging in the nanoporous framework to promote the enzymatic activity in addition to a prolonged lifespan.

Exploring efficient earth-abundant electrocatalysts to replace platinum for hydrogen evolution reaction (HER) is of great significance for sustainable energy generation and use.^1-4 MoS₂ is a promising HER electrocatalyst. It has been experimentally and theoretically demonstrated that the catalytic activity correlates with the active edge sites rather than the exposed basal planes area. Thus, one feasible strategy toward enhanced HER performance is to increase the number of active edge sites. Herein, we develop a template-free method to synthesize ultrasmall MoS₂ nanoparticles (~3 nm) decorating porous N-doped carbon network (MoS₂@PNCN) via pyrolysis of the dicyandiamide/ammonium tetrathiomolybdate mixture. The novel 3D architecture of MoS₂@PNCN with rich porosity has a continuous conducting network and provides full contact between the catalyst and the electrolyte. Due to the abundant active edge sites of MoS₂, this catalyst exhibits high HER activity with a low onset potential of -30 mV, a small overpotential of 104 mV at a current density of 10 mA cm^-2, and a Tafel slope of 58.6 mV dec^-1. Meanwhile, the ultrasmall MoS₂ nanoparticles protected by few-layered carbon shells show a superior stability even after 10 h of continuous operations. This study opens up a new path for synthesis of 3D porous nanomaterials for electrocatalysis and beyond.
Reference:
[1] H. Wang, Y. Cao, C. Sun, G. Zou, J. Huang, X. Kuai, J. Zhao, L. Gao. Strongly coupled molybdenum carbide on carbon sheets as a bifunctional electrocatalyst for overall water splitting, ChemSusChem, 2017, 10, 3540-3546.
[2] H. Wang, Y. Cao, G. Zou, Q. Yi, J. Guo, L. Gao. High-performance hydrogen evolution electrocatalysat derived Ni₃C nanoparticles embedded in a porous carbon network, ACS Applied Materials & Interfaces, 2017, 9, 60-64.
[3] H. Wang, Q. Yi, L. Gao, Y. Gao, T. Liu, Y. Jiang, Y. Sui, G. Zou. Hierarchically interconnected nitrogen-doped carbon nanosheets for efficient hydrogen evolution reaction, Nanoscale, 2017, DOI: 10.1039/C7NR06374A.
[4] H. Wang, L. Gao. Recent developments in electrochemical hydrogen evolution reaction, Current Opinions in Electrochemistry, 2017, DOI: 10.1016/j.coelec.2017.09.025.
Acknowledgements:
We thank the funding by National Natural Science Foundation of China (grant U1401248) and the financial support from the program of China Scholarship Council (no. 201706920081).

As demands of hydrogen energy become more increased, the development of electrocatalyst, which has high electrochemical activity, long stability and low-cost is inevitable for hydrogen evolution reaction (HER). In this paper, we report easy method to mass-produce nanosized Ni catalyst using late transition metal oxides, CeO₂ and La₂O₃, on carbon support. The Ni_La_0.67Ce_0.33O_1.67/C catalyst was synthesized by co-precipitation and solvo-thermal that are simple methods and can make higher activity and durability catalyst. Ni_La_0.67Ce_0.33O_1.67 play a key role to reduce size of Ni particles and serve to improve the characteristics of the catalyst in a reducing atmosphere by forming solid solution. Ni_La_0.67Ce_0.33O_1.67/C catalyst was recorded the lower overpotential of 124 mV at current density 10 mA/cm² and higher long-term stability compared to Ni/C catalyst. We suggest that La_0.67Ce_0.33O_1.67 forms a partial alloy with Ni to prevent Ni detaching and acts as a barrier to prohibit Ni migration. We proposed mechanism of Ni catalyst degradation in the HER electrode based on the results of this work.

Activated carbon supported nanocomposites attract attention due to functionality, low-price and simple synthetic method. Such nanocomposites are used as catalysts, adsorbents, electrodes and in other areas. Carbon support provides high surface area, protects metal nanoparticles and adsorbs various chemicals. So far, carbon based nanocomposites are synthesized by impregnation methods.

In this study, we prepare porous carbon nanocomposite materials by carbonizing copper nanoparticle and polymer mixtures in a tubular furnace under inert atmosphere. Resulting material was analyzed in BET instrument to determine surface area, ICP-MS to determine metal content, XRD to analyze metal crystallinity and TEM to analyze surface morphology. Porous carbon and copper nanocomposite was then studied for CO₂ reduction with H₂ gas. The products were identified using GC-MS system and catalytic parameters like temperature, flow rate and regeneration were carefully screened.

MoS₂/carbon hybrid materials have been shown to be promising non-precious metal electrocatalysts for the hydrogen evolution reaction (HER). However, a facile method for synthesizing them is still a big challenge, let alone patterning them through a design. In this work, we present a novel strategy to synthesize and pattern MoS₂/carbon hybrid materials as electrocatalysts for the HER through a one-step direct laser writing (DLW) method under ambient conditions. DLW on citric acid–Mo–S precursors leads to the in situ synthesis of small-sized MoS₂ nanoparticles (NPs) anchored to the carbon matrix. Largely exposed catalytically active sites from the MoS₂ NPs and the synergetic effect from the carbon matrix make the hybrid materials exhibit superior catalytic performance and stability for the HER in acidic solutions. Through computer-controlled laser beams we can design arbitrary patterns made of these catalysts on targeted substrates, which will open a new route for fabricating on-chip microfuel cells or catalytic microreactors.

A triboelectric nanogenerator (TENG) is of great interest as an emerging power harvester owing to its simple device architecture with unprecedented high efficiency. Despite the substantial development of new constituent materials and device architectures, a TENG with a switchable surface on a single device, which allows for facile control of the triboelectric output performance, remains a challenge. Here, we demonstrate a supramolecular assembly route for fabricating a novel TENG based on an alkali metal-bound nanoporous film, where the alkali metal ions are readily switched among one another. Our soft nanoporous TENG contains numerous SO₃^- functional groups on the surface of nanopores prepared from the supramolecular assembly of sulfonic acid-terminated polystyrene (SPS) and poly(2-vinylpyridine) (P2VP), followed by soft etching of P2VP. Selective binding of alkali metal ions, including Cs⁺, K⁺, Na⁺ and Li⁺, with SO₃^- groups enables the development of mechanically robust alkali metal ion-decorated TENGs. The triboelectric output performance of the devices strongly depends on the alkali metal ion species, and the output power ranges from 11.5 to 256.5 μW. This wide-range triboelectric tuning can be achieved simply by a conventional ion exchange process in a reversible manner, thereby allowing reversible control of the output performance in a single device platform.

In this study, a simple and cost effective method is developed for the production of graphene reinforced metal matrix composites and high surface area graphene foams. First graphene is grown on spherical copper powders via CVD. For graphene-metal nanocomposite formation the graphene coated copper powders are pressed. For free standing high surface area graphene foam formation the metal part is etched away. The obtained structures are characterized using SEM, Raman spectroscopy, XRD, EBSD and also their mechanical, thermal and electrical tests are performed. It is shown that this process is a very versatile method to produce both graphene-copper composites on a large scale, with a good dispersion and improved interface with the metal matrix and high surface area graphene foams. The porous structure can be further tailored by controlling the Cu powder size. (This study is supported by TUBITAK 1005 grant no 216M042.)

Although, Manganese is used as a representative low-temperature Selective Catalytic Reduction (SCR) catalyst, main catalyst components of Mn cause some problems such as high activity only with a high contents and it has problems of poisoning by sulfur. Therefore, in this study, we synthesize low-temperature SCR catalysts with high activity by nano-dispersion of Mn and Ce as active materials by applying Reduced graphene oxide (rGO) support. When graphene is applied, it improves the catalytic reaction site and resistance of particle aggregation based on high specific surface area and electron mobility, and it can suppress SCR side reaction by dispersing nanoparticles.
To confirm this, Mn-Ce was nano-dispersed in rGO support using impregnation method, and SCR catalyst with rGO support was synthesized by adding existing TiO₂ support. And for comparison, MnCe and MnCe/TiO₂ catalysts were synthesized under the same conditions and then the characteristics were compared. And in order to investigate characteristics of SCR catalysts, De-NOx efficiency, NH₃-TPD, TEM comparison and XRD, Raman and BET analyzes are evaluated.

Diabetes is a sophisticated and increasingly prevalent condition that affects millions of people worldwide and has become the third main cause of death. Constant monitoring of glucose level is the most effective way of controlling diabetes. Among various methods available for determination of glucose, electrochemical technique obtained significant recognition over the past few years due to its high sensitivity, Low limit of detection, promising response speed, and low cost whereas, traditional enzymatic glucose sensors are suffering from complicated immobilization process of enzymes, sensitivity to the environmental conditions and lack of long-term stability. Consequently, non-enzymatic glucose sensors have emerged as a viable alternative to enzymatic glucose sensors which can effectively overcome their drawbacks. In this presentation we will discuss CoNi₂Se₄-rGO nanocomposite as an efficient non-enzymatic glucose sensor which can electrochemically oxidize glucose at very low applied potential. The CoNi₂Se₄/rGO on Ni Foam (CNSE/rGO-NF) was synthesized via single-step electrodeposition on hydrothermally prepared reduced graphene oxide on Ni Foam substrate (CNSe/rGO-NF) and the electrocatalytic activity for glucose sensing was studied for the first time. The developed sensor exhibits exceptional performance in term of extremely low working potential of +0.35 V vs. Ag|AgCl, the lowest working potential reported to date, with superior sensitivity of 15571 µA mM^-1 cm^-2, wide linear range between 0.01 µM - 2.0 mM, low detection limit of 0.65 µM (S/N = 3), high selectivity in the presence of interfering species (such as dopamine, fructose, ascorbic acid, and NaCl), and excellent operational stability over an extended period of time. In this work, the electrochemical sensing behavior of the CNSe-rGO/NF electrode towards glucose sensing was investigated using amperometric techniques. Also, we have employed SEM, EDX, PXRD, XPS, TEM and Raman techniques to characterize the structure and morphology of the catalyst. In this presentation we will discuss about the details of glucose sensing, and the effectiveness of the sensor based in sensitivity, accuracy, and selectivity.

Interconnected nanopores as a continuous phase throughout the matrix have been interested in various field using molecular separation and storage, catalyst, or catalyst support materials. In particular, we have been interested in the possibility as catalyst support materials. Following previous researches, immobilizing catalysts to the solid support is not only facilitating catalyst recovery and simplifying of the reaction work-up, but even affects improvement of the catalytic efficiency or reaction rate. Thus, in this study, we report the immobilization of Ru(‖) based catalysts on polyurea network based nanoporous frameworks.
Previously, we discussed the polymerization of multifunctional amine-isocyanate pair induces the dispersion (sol) of nano-particulate polyurea networks in organic solvent below a concentration of gelation. The method enables facile solution-processing of insoluble covalent molecular network. We fabricate biconinuous nanoporous membrane via interplay of phase separation between urea network and polymer or inorganic precursor and sol-gel transition. The Ru(‖) based catalysts are immobilized physically or chemically by using the interaction between the catalyst and the support; covalent binding, adsorption. The immobilized catalyst is confirmed by electron microscopy (SEM, TEM) and XPS. We investigate how the composition ratio and formation temperature of nanoporous networks affect its nanoporous channel and explored experimental conditions optimized for catalyst immobilization. Then, we also explore the catalytic efficiency and stability of the catalyst on the membrane.

In this talk, I will summarize the recent research on the crystal phase-engineering of novel nanomaterials in my group. It includes the preparation of novel crystal phase of noble metal nanomaterials, such as hexagonal-close packed (hcp) Au nanosheets (AuSSs), 4H hexagonal phase Au nanoribbons (NRBs) and other 4H metal nanostructures, and the phase transformation of two-dimensional transition metal dichalcogenide (TMD) nanomaterials. In addition, we start to investigate the crystal phase-based properties and catalysis applications. Importantly, the concept of crystal-phase heterostructure is proposed.

Owing to their high surface areas, tunable pore dimensions, and adjustable surface functionality, metal-organic frameworks (MOFs) can offer advantages for a variety of gas storage and gas separation applications. In an effort to reduce the major energy requirements for the separation of mixtures of light hydrocarbons via cryogenic distillation, we are developing new MOFs with a high capacity for the selective adsorption of unsaturated hydrocarbons at higher temperatures. In particular, the compounds M₂(dobdc) (M = Mg, Mn, Fe, Co, Ni; dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and M₂(m-dobdc) (m-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate), featuring open M²⁺ cation sites, have been evaluated for their performance in the separation of mixtures of C1-C3 hydrocarbons at 45 °C. The results indicate that these materials have significant potential for applications in adsorption-based processes for natural gas purification and olefin/paraffin separations. In addition, it will be shown that certain structural features within MOFs can enable the fractionation of hexane isomers according to the degree of branching and the separation of xylene isomers.

Demand for functional materials targeted for specific applications is ever increasing as societal needs and demands mount with advancing technology. The building-block approach, whereby at the design stage the desired properties and functionality can be introduced in preselected molecular building blocks (MBBs) prior to the assembly process, has emerged as a prominent pathway for the rational construction of functional solid- state materials. One class of inorganic-organic hybrid materials, metal-organic frameworks (MOFs), has burgeoned in recent partly years due to effective design strategies (i.e. reticular chemistry) for their synthesis and their inherent [and readily interchangeable] hybrid, functional character. MOFs have emerged as a unique class of materials amenable to design and manipulation for desired function and application. Several design strategies have been utilized and developed to target viable MOF platforms, from the single-metal-ion molecular building block (MBB) approach to the hierarchical supermolecular building block and supermolecular building layer approaches (SBB and SBL, respectively). This inherent built-in information allows access to highly stabile and made-to-order porous materials toward applications pertaining to energy and environmental sustainability. Specifically, made-to-order MOFs addressing the energy-intensive separations, gas storage, and catalysis will be discussed

To address increasing environmental and energy concerns, generating clean-energy fuel via a sustainable route is highly desirable. Hydrogen production from water splitting is one of the most promising technologies for meeting this target. The key to industrial application of water splitting is the design of efficient, robust, and cost-efficient catalysts as the electrodes.

As electrocatalysis reactions are surface processes, the activity of an electrocatalyst is usually dependent on the amount of accessible surface-active sites, the facileness of mass transport to/from the surface, and the electrical conductivity of the catalyst.¹ Metal-organic frameworks (MOFs) provide an ideal platform for designing promising catalysts because of their high porosity and diverse nanostructures and compositions.² However, one of the challenges of using MOFs for electrocatalysis is the very small pore size (usually within few nanometers) of bulk MOF materials, which inhibits the effective mass transport of electrolyte to the active sites and the diffusion of products, leading to impeded electrode performance. Despite the great promise of MOF electrocatalyst, significant research effort is still needed to overcome the inherit disadvantages of MOF.

Herein, we synthesized self-supported Co-based MOF nanosheets on carbon cloth and converted it to sponge-like Co-Ni hydroxide (Co-Ni-OH) by Ni salt etching method and then phosphorized the obtained product at low-temperature. Finally, the obtained sponge-like Co-Ni phosphide was converted into corresponding hydroxide (Co-Ni-OH-D) by linear scanning voltammetry scans in alkaline. The as-synthesized Co-Ni-OH-D is structurally different from the precursor Co-Ni-OH and cannot be directly synthesized with the method for growing Co-Ni-OH. The sponge-like Co-Ni-OH-D provided abundant meso-/micro-porosity for prompting the reaction rate. Co-Ni-OH-D electrode exhibits excellent electrocatalysis activities toward water splitting. This work provides a general method for deriving efficient catalyst from MOF.

References: (1) J. Duan, et al. Nat. Commun. 8 (2017). (2) G. Cai, et al. Chem 2.6 (2017) 791-802.

Hierarchical porous structures with different levels of porosity allow for efficient diffusion of guests through the network of pores and channels, making them promising materials for a wide range of applications including gas adsorption, separation, and catalysis. Although many approaches have been attempted to increase the pore size of metal–organic framework (MOF) materials, it is still a challenge to construct MOFs with customized hierarchical porous architectures. In this talk, we present a new method, linker labilization, to increase the porosity and pore size of microporous MOFs, giving rise to hierarchical-pore MOFs. Microporous MOFs with robust metal nodes and pro-labile linkers were initially synthesized. The mesopores were subsequently created as crystal defects through the splitting of a pro-labile-linker and the removal of the linker fragments by acid treatment. We demonstrate that linker labilization method can create controllable hierarchical porous structures in stable MOFs, which facilitates the diffusion and adsorption process of guest molecules to improve the performances of MOFs in adsorption and catalysis.

Global problems including energy conversion and storage or clean water require increasingly complex, multi-component hybrid materials with unprecedented control over composition, structure, and order down to the nanoscale. This talk will give examples for the rational design of block copolymer-nanoparticle self-assembly derived synthetic porous materials with amorphous, polycrystalline, and epitaxially grown single-crystal structures as well as asymmetric membranes structures. Experiments will be compared to theoretical predictions to provide physical insights into formation principles and specific function. The aim of the described work is to understand the underlying fundamental chemical, thermodynamic and kinetic formation principles as well as nanostructure-property correlations enabling generalization of results over a wide class of materials systems. Examples will cover the formation of hierarchical structures at equilibrium as well as via processes far away from equilibrium. Targeted functions of the prepared systems will include nanostructured porous composites for energy conversion and storage devices, metamaterials with specific optical and phononic properties, as well as the formation of first self-assembled superconductors.

References
1.)K. E. Fritz, P. A. Beaucage, F. Matsuoka, U. B. Wiesner, J. Suntivich, Mesoporous titanium and niobium nitrides as conductive and stable electrocatalyst supports in acid environments, Chem. Comm. 53 (2017), 7250-7253.
2.)Ordered gyroidal tantalum oxide photocatalysts: eliminating diffusion limitations and tuning surface barriers, Nanoscale 8 (2016), 16694 - 16701.
3.)K. W. Tan, B. Jung, J. G. Werner, E. R. Rhoades, M. O. Thompson, U. Wiesner, Transient Laser Heating Induced Hierarchical Porous Structures from Block Copolymer Directed Self-Assembly, Science 349 (2015), 54-58.
4.)C. Cowman, E. Padgett, K. W. Tan, R. Hovden, Y. Gu, N. Andrejevic, D. Muller, G. Coates, U. Wiesner, Multicomponent Nanomaterials with Complex Networked Architectures from Orthogonal Degradation and Binary Metal Backfilling in ABC Triblock Terpolymers, J. Am. Chem. Soc. 137 (2015), 6026-6033.
5.)Z. Li, K. Hur, H. Sai, T. Higuchi, A. Takahara, H. Jinnai, S. M. Gruner, U. Wiesner, Linking experiment and theory for three-dimensional networked binary metal nanoparticle -triblock terpolymer superstructures, Nat. Commun. 5 (2014), 3247.

We present a one-pot solution method to fabricate bicontinuous nanoporous organic framework membranes and their bio-catalytic applications. Temporary spinodal microstructures of phase-separating sol mixtures transform directly to covalent frameworks upon evaporation of solvent. The sol mixture consists of a linear polymer and a reactive network nanoparticle in an organic solvent, in which the nanoparticle is a cross-linked molecular level network and grown to a few tens of nanometers via solution-polymerization of di-isocyanate and tetra-amine monomers below the critical gelation point of concentration or temperature. Phase-separation-induced cross-over of sol-gel boundary is most likely a mechanism for capturing spinodal decomposition. Bicontinuous nanoporous membranes are obtained by extraction of the soluble polymer from the gelled network/polymer blend. The resultant nanoporous frameworks are built upon molecular networks, and thus exhibit superior chemical, thermal, and dimensional stabilities. A wide variety of new covalent framework materials can be derived by varying the chemical structures and compositions of the constituents. Their properties may be customized for different applications. We demonstrate that the bicontinuous nanoporous framework membrane can be utilized as an efficient nano-cage into which enzymes can be loaded quantitatively by simply applying pressurized solutions. The resultant enzyme-caged membranes show long-term stability and reusability in biocatalytic reactions operated in batch or continuous flow mode.

Carbon materials have been widely used as one of the candidates to address global energy and environmental issues due to their extraordinary, tuneable physicochemical properties, rich abundance and low cost. Freestanding porous carbon membranes particularly hold great promise in the fields of catalysis, water treatment, biofiltration, gas separation and optoelectronics, just to name a few, due to their structural integrity, continuity and purity. Typical synthetic methods involve mechanical rolling of thermally expanded graphite flakes, chemical vapour deposition and vacuum filtration of dispersions of graphene sheets or carbon nanotubes. In addition pyrolysis of thermosetting polymer precursors could lead to carbon membrane sieves with micropores, which exhibited high-performance for gas separation. Precise control over the atomic order, local chemical composition, nanoscale morphology and complex pore architecture, as well as easy access to porous membranes of large size and large surface area, is highly relevant but can hardly be fully met by the state-of-the-art synthetic protocols. Particularly, a high degree of graphitization and hierarchical pore architecture with interconnected pores over a broad length scale are eagerly being pursued because they could offer fast electron conduction, and rapid mass transport through large pores along with a simultaneously high-reaction capacity via the large accessible surface area provided by the micro/mesopores.

Through a bottom–up approach, we are able to fabricate hierarchically structured, nitrogen-doped, graphitic nanoporous carbon membranes from their porous polymer counterpart. In particular, the pores along the membrane cross-section assume a gradient distribution in their sizes, which is seldom observed in such membranes. The pristine nanoporous carbon membranes exhibit unusual single-crystal-like characteristics across their entire body. As a prototypical application, when loaded with cobalt nanoparticles, these highly conductive porous carbon membranes due to the binder-free nature serve as an active carbon-based bifunctional electrocatalyst for overall water splitting. In addition, by loading Co/CoP Janus-type nanocrystals, such hybrid membranes serves as excellent hydrogen evolution electrode in both acid and alkaline environment.

References
[1] Wang, H.; Yuan, J.; Wu, T., et al., Nat. Commun. 2017, 8, 13592.
[2] Wang, H.; Yuan, J.; Wu, T., et al., ACS Nano, 2017, 11 (4), 4358–4364.

Despite drawing on a limited pool of available elements, nature has developed sophisticated mechanisms to fabricate nanostructured minerals under environmental conditions. Biominerals characteristically represent organic/inorganic composite materials with hierarchical organization spanning multiple length scales, where these complex architectures often lead to astounding (mechanical) properties adapted to suit a specific function. Unsurprisingly, the study of biominerals has therefore inspired a substantial body of research activities, which are aiming to transfer key concepts of biological mineralization, e.g. the use of structure-directing organic matrices and confined reaction environments, into artificial systems. This approach is particularly exciting in view of low-temperature synthetic routes for the preparation of technologically relevant materials showing inherent functional properties (e.g. optical, electronic or catalytic).

In our here presented work we specifically focus on spinel cobalt(II,III) oxide (Co₃O₄) and related mixed metal spinels, where these represent a highly promising class of materials for a wide range of applications, particularly in the field of heterogeneous catalysis. In this context, the catalytic activity of the functional oxide largely depends on its morphology (exposed lattice planes), nanostructure and specific surface area (porosity). Therefore, eco-efficient routes towards nanostructured cobalt oxide are in great demand.

We here explore a bio-inspired approach, in which a thermally unstable cobalt hydroxide carbonate precursor is precipitated under biomimetic conditions in the presence of water-soluble synthetic polymers with flexible chains. Calcination at relatively moderate temperatures converts the mineral precursors into the functional spinel oxide phase, while retaining the gross morphology induced by the structure-directing additives. We demonstrate that highly unusual Co₃O₄ structures such as thin films or microspheres with a nanoparticular substructure can be generated based on bio-inspired concepts.¹

The products of the polymer-mediated mineralization reactions are analyzed before and after calcination by means of electron microscopy (SEM and TEM) and small-angle x-ray scattering (SAXS). With the aim to ultimately establish structure-property relationships, the electrocatalytic activity of the resulting materials is investigated with respect to selected model reactions such as electrocatalytic water splitting.

[1] Anna S. Schenk, Sabine Eiben, Miriam Goll, Lukas Reith, Alexander N. Kulak, Fiona C. Meldrum, Christina Wege, Holger Jeske, Sabine Ludwigs, Virus-directed formation of electrocatalytically active nanoparticle-based Co₃O₄ tubes, Nanoscale 2017, DOI: 10.1039/C7NR00508C.

Noble metal aerogels that possess high surface area and tunable porosity offer a wide range of catalytic applications. Control over monolith shape, pore size, and ligament diameter is desired in order to tune device integration, electrolyte mass transport properties, electronic conductivity, and mechanical robustness. Aerogel synthesis techniques such as solvent mediated aggregation, linker molecules, sol–gel, hydrothermal, and carbothermal reduction do not offer synthesis control over all desired material properties. Here we present the synthesis of palladium and platinum aerogels using gelatin and carboxymethyl cellulose nanofiber biotemplates for catalysis that provides control over aerogel shape, pore size, conductivity, and elastic modulus. Biotemplate hydrogels were formed via covalent cross linking using glutaraldehyde for gelatin, and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) with a diamine linker molecule for carboxymethylated cellulose nanofibers. Biotemplate hydrogels were incubated in precursor palladium and platinum salts, reduced with sodium borohydride, and rinsed. Final aerogel structures were achieved using super critical point drying. Scanning electron microscopy indicated contiguous three dimensional nanowire structures for both gelatin and carboxymethyl cellulose biotemplated nanowires, and X-ray diffractometry confirmed metal content with no oxide peaks. Gas adsorption, impedance spectroscopy, and cyclic voltammetry were correlated to determine aerogel surface area. A four point probe was used to determine electronic conductivity, and atomic force microscope nanoindentation was used to determine material elastic moduli. Platinum and palladium aerogel catalysis was evaluated for hydrogen adsorption and desorption in 0.5M H₂SO₄. These self-supporting biotemplated palladium and platinum aerogels are envisioned to offer a flexible synthesis scheme to control shape, porosity, electrical conductivity, and mechanical robustness catalytic, sensing, and energy applications.

Nanostructured porous (inorganic) materials are receiving much attention in recent years owing to their potential for next-generation device applications. Despite the progress made in the preparation, stable non-binary metal oxides are often ill-defined from a structural/morphological point of view. The major reason is that the crystallization (nucleation, crystal growth, etc.) is difficult to control.
In the first part of this talk, I will describe the block-copolymer-templating synthesis of a series of high-quality sol-gel derived spinel ferrite thin films with a unique mesoporous morphology, including LFO (lithium ferrite), CFO (cobalt ferrite), and NFO (nickel ferrite). In the second part, I will show that the general idea of combining nanomagnetism and lithium-ion battery storage concepts can be applied to transition metal ferrites. When using the above-mentioned thin film materials as insertion anodes in lithium cells, they allow for the intriguing possibility of tuning of magnetization at room temperature without compromising the lattice or pore structure.

Nanostructured materials have been utilized in various technologies due to their unique physical and chemical properties derived from their large active surface area and nanoscale size. In the synthesis of the nanomaterials, however, the addition of ligands, stabilizers, and reducing agents is required to disperse the nanomaterials without aggregation and obtain desirable properties and structures, though those chemicals on the surface of nanostructures can substantially affect the surface-related activity. Here, we report the virus-directed formation of a porous matrix of palladium nanostructures without any surface stabilizers or chemical reagents to investigate the impact of ligand-free clean surface and porous network structure of virus-templated palladium nanowires on their catalytic activity and stability. A filamentous M13 virus displaying a glutamate trimer on the major coat protein (p8), denoted as an ‘E3-M13 virus’, was employed as a negatively charged template to assemble positively charged palladium precursors via the electrostatic complexation, forming virus-metal complex hybrids. The E3-M13 virus templates induce self-crystallization of palladium colloidal nanostructures through the spontaneous biomineralization process without any additional chemicals or stabilizers, maintaining ligand-free clean surface and highly entangled porous nanostructures. The advantage of the virus-templated palladium nanostructures is demonstrated in the Suzuki-coupling reactions. The virus-templated palladium nanocatalysts exhibit high catalytic activity due to the ligand-free clean catalytic surface. The well-entangled porous matrix of the nanostructures also prevents the aggregation of catalysts, maintaining the active surface area and catalytic activity during repeated catalysis. On the contrary, conventional colloidal palladium catalysts undergo the fast degradation of catalytic activity originated from surface contamination by the stabilizer and aggregations during repeated uses. This work emphasizes the importance of the ligand-free surface and porous matrix structure of the bio-templated nanostructures in maintaining functionalities without surface contamination and aggregation. This research was supported by Nano Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (NRF-2017M3A7B4052798)

Cu-Zn loaded onto core-shell Al-MCM-41 with various copper and zinc species, prepared by a combination of three methods—substitution, ion exchange, and incipient wetness impregnation, was studied as a catalyst for NO_x reduction via selective catalytic reduction with NH₃ (NH₃-SCR). The effects of Zn promoter on the acidity and the NO_x adsorption properties of the catalysts were investigated by in situ Fourier transform infrared spectroscopy (FTIR) of NH₃ and NO_x adsorption, and temperature-programmed desorption (TPD) of NH₃ and NO_x. Meanwhile, the roles of Zn in the nature of Cu were studied by in situ FTIR of CO adsorption and H₂ temperature-programmed reduction (H₂-TPR). The catalytic results demonstrated that Cu-Zn/core-shell Al-MCM-41 exhibited higher catalytic activity compared to that of Cu/core-shell Al-MCM-41 for whole reaction time, as it could achieve a maximum NO conversion of 100% with an average NO conversion of 73%. It was found that the Zn introduction could promote a number of acid sites, enhance the NO_x adsorption capacity by providing the additional sites for nitrates formation, and also hinder the reduction of Cu⁺ to Cu⁰, resulting in higher number of Cu⁺ sites in the reduced catalysts. All of which are beneficial for NH₃-SCR reaction. However, the catalytic activity was clearly improved for Cu-ZnO/core-shell Al-MCM-41, in which Zn was loaded as ZnO instead of various Zn species. Cu-ZnO/core-shell Al-MCM-41 showed better catalytic performance with longer working reaction time, and achieved the average NO conversion of 77%.

The rate of oxide formation during growth of pores structures on silicon was investigated by an advanced in-situ I-V measurements. The measurements were designed to get two I-V curves in a short time (300 sec.) taking into account the gap (in mA/cm²) for each corresponding voltages. [i]^,[ii] The in-situ I-V measurements were made at different pore depth/time, while etching takes place based on p-type Si. This was related to the expected diffusion limitation of oxide forming (H₂O) molecules reaching at the electrolyte-pore tip and the anodizing current while etching takes place. The study showed that the rate of oxidation (I-V gap) during the formation of macropores, with straight walls and relatively deep structures, decreases as the pores grow down with time. This oxidation rate increases by increasing the anodizing current. However, pores with spongy like structure (irregular structures) with multi-channelled tends to show an increasing of the current gap in time. On the other hand, the rate of oxidation (or I-V gap) for nanopores and electropolishing tends to show a decreasing and constant I-V gap in time was shown, respectively. The method can be developed further and has the potential to be applied in other electrochemically etched porous semiconductor materials.


[i]. A. Benor, J. Nanomaterials, 2017, 1-7 (2017).

[ii]. A. Benor, Materials Science and Engineering B., In Press (2017).

Mesoporous ceramic nanofibers provide advantageous chemical and physical properties beneficial for heterogeneous catalysis. Electrospun nanofibers usually have a solid interior and smooth surface. The interest in complex structured fibers with multifunctional, specific properties has been growing over in recent years. In particular, porous core-shell structures are attractive since they integrate different functional components into a single element, thus providing advantageous properties and synergetic effects for different applications such as catalysis, energy storage and conversion. The structure can also provide new strategies for modern material design with higher surface area. Electrospinning (ES) is an effective route to polymer, ceramic and composite fibers of controlled diameters and morphologies.

Core-shell electrospun nanofibers were previously fabricated using coaxial nozzles or emulsion methods. Recently, we synthesized ceramic nanofibers with unique lamellar-like mesoporous structure using a single nozzle ES process, followed by thermal treatment. The fibers morphology consist of inner Fe-Al-O core with elongated mesopores and an outer thin accordion-like Fe-rich shell. A general mechanism for the formation of this morphology is suggested, where the final structure depends greatly on the heating rate stage and chemical composition of the metal oxide precursors and polymer matrix. The proposed mechanism suggests that this structure is possible in the presence of a metal-organic component with low melting point and high volatility below the polymer main decomposition temperature.

Titanium-based materials have been investigated intensively as a stable oxide semiconductor. Nevertheless, new designs with improved properties are necessary to meet the demands and requirements in the energy market. Development of nanostructured titanium-based materials with engineered compositions and morphologies have the potential to provide a breakthrough in this area. Overall, the presented nanofibers are highly promising in material research, especially in applications requiring an accessible high surface area porous media.

Nano-sized Au and Pt bimetallic nanoparticles loaded metal-organic frameworks (Au-Pt@UiO-66) have been synthesized at ambient conditions, and they were being utilized in an electrochemiluminescence (ECL) biosensor for protein kinase A (PKA) activity analysis and relevant inhibitor screening based on their catalytic properties. After being phosphorylated by PKA in the presence of ATP, Au-Pt@UiO-66 probes were specifically chelated to the modified electrode by the Zr-O-P bonds formed between the surface defects of UiO-66 and the phosphorylate groups of phosphorylated kemptide. The bimetallic Au and Pt nanoparticles catalyzed the luminol-H₂O₂ ECL reaction by accelerating the decomposition of H₂O₂ to produce OH^● and O₂^{● -}, which could activate the luminol ions. Light was emitted when the activated luminol ions returned to their ground state, and then utilized for PKA activity detection. Due to the high synergistic catalysis activities of bimetal Pt and Au nanoparticles to the luminol-H₂O₂ reaction, the Au-Pt@UiO-66 probes greatly enhanced the ECL signal of luminol and offered a high sensitive ECL strategy for PKA activity analysis. In addition, the ECL intensity of the ECL system was significantly amplified, for the UiO-66 with large surface area and high porosities accommodated bimetallic Pt and Au nanoparticles which not only can provide multiple catalytic centers toward the luminol-H₂O₂ reaction but also promoted the electron transfer on the electrode interface. Moreover, UiO-66 could also prevent the nanoparticles from aggregating during the catalytic reactions, thus the catalytic efficiency and stability of the biosensor was further improved. Under the optimized conditions, the detection limit for PKA activity was 0.009 UmL^-1 (S/N=3). Finally, the ECL biosensor was successfully applied in inhibitor screening and cell lysates PKA activity analysis, showing great promise in kinase related research. More importantly, this strategy provides a new opportunity to promote the application of Au-Pt@UiO-66 in electrochemical related sensors.

In this work, we report an innovative mechanism, the Kirkendall effect, in creating three-dimensional (3D) microporous catalysts with tunable pore sizes for the growth of hierarchic ultrathin graphite foams (HP-UGFs) with unique properties. Employing the Kirkendall effect is one of the first demonstrated for fabricating 3D porous catalysts, where tunable pores of 1.9–8.3 μm are created on 3D interconnected struts (∼100 μm). With the catalysts, we readily synthesized freestanding HP-UGFs that offer higher crystallinity and electric conductivity, larger surface area, as well as enhanced electric invariance to strains compared to those of conventional ultrathin graphite foams. A gauge factor as low as ∼10 at a strain as high as 80% is achieved owing to the unique porous corrugations created on the microstruts of the HP-UGFs. This work may inspire a new paradigm in designing and synthesizing a new type of 3D porous architecture made of 2D materials with controlled local corrugations, which could greatly benefit flexible electronics.

Identifying the key reaction sites in supported-metal nanoparticles (NPs) is critical in designing high-performance catalysts for industrial chemical reactions, such as catalytic conversion of methane (CH₄). However, the high-temperatures (> 400^oC) required for CH₄ conversion cause the metal NPs to aggregate into larger crystallites, and thus make the direct relationship between structure and function in these catalysts difficult to identify. Here we overcome this issue by designing a post-encapsulated composite structure in which individual Pt NPs are surrounded by gas-permeable and catalytically active CeO₂ shell. In particular, we analyze the catalytic activities for CH₄ combustion of the encapsulated catalysts by varying the size of the Pt cores precisely and thus changing the metallic surface and metal-oxide interface site densities. The specific surface area of the Pt exposed to gas in each particle is obtained through chemisorption analysis, and the Pt/ceria interface density is reliably deduced using the CO oxidation as a reference reaction. Based on these observations, we succeed in unambiguously identifying the CH₄ combustion occurs actively at the Pt/ceria interface. Our results suggest a reliable approach to explore the active sites for various high-temperature catalysis.

Due to climate change and depletion of fossil fuels, the advanced technologies for clean and renewable energy storage and conversion system, such as fuel cells, water splitting, and metal-air batteries, have become a crucial role in next-generation energy system. Among the next-generation energy systems, the oxygen-related electrochemistry is considered a key reaction. However, the oxygen-related electrochemical reaction, especially oxygen evolution reaction (OER) has sluggish kinetics, due to the complex proton-coupled electron transfer, which hinder the practical implementation for energy conversion systems. Highly active catalyst use is essential to achieve high efficiency for the energy system. Typically, precious metal-based electrocatalysts including iridium and ruthenium oxide are well-known to be efficient for the OER. Though they has highly electrocatalytic activity, their high cost and low durability are pointed out as a limitation. Among the innovative attempts for addressing challenge, transition metal-based electrocatalysts have been proposed to replace the precious metal catalysts, particularly cobalt-based electrocatalysts has high electrocatalytic activity and high stability at high potential for electrocatalysis. In Co-based materials, cobalt nitride (Co_xN) has metallic electronic structure with high electrical conductivity, and its high electrocatalytic activity is already reported. Additionally, foreign metal atoms into the original crystal lattice of transitiom metal based materials can increase the electrocatalytic activities of bimetallic materials. Metal organic framework (MOF) is the porous material with remarkably high surface area that allows extensive electrolyte contact and numerous active sites. Due to these advantages, MOF-derived materials are undergoing much research in the electrocatalysis field. In addition, it is possible to develop MOF structure of various composition through the change of metal ion during the synthesis process. Therefore, the electronic structures of MOF-derived materials can be easily tuned through the foreign metal-doped MOF structure. In this work, Co-based MOF (ZIF67) was fabricated using solution synthesis and transformed into a nanosheet structure. The composition of foreign metal atom was controlled by the content of metal precursor in ZIF67 synthesis process. Through ammonia heat treatment, the Co-based bimetallic nitride nanosheets were prepared. The synthesized Co-based bimetallic nitride nanosheet achieved low overptential for the OER in alkaline media (520 mV in 0.1 M KOH), and has a higher current density than the particles at the same potential. Through this work, the bimetallic nitride materials with 2D nanosheet structure can promote their practical use with their remarkable structural and electronic characteristics.

Recently, it was demonstrated in a number of studies that transition metal chalcogenide obtained an increasing attention as a promising alternative electrocatalysts for hydrogen evolution reaction [1]. Although transition metal chalcogenide have an appropriate hydrogen adsorption free energy, there still exist some obstacles that they have low electroconductivity and poor active sites[2]. Herein, to make a breakthrough, we develop a template-directed method to synthesize Co-Mo-S hierarchical core shell nanorod array at Nickel foam. At first, the Co(CO₃)_0.5OH●0.11H₂O nanowire array at nickel foam is fabicated by hydrothermal synthesis, which is considered as the template of the nanorod growing. Afterward, the precursor is treated by solvothermal synthesis in mixture of DMF and water. As we predicted, due to the ion exchange mechanism, the small-size Co-Mo-S nanosheets grow from the nanowire spontaneously, which construct a hierarchical core-shell nanorod structure. Through this simple strategy, we can achieve an electrocatalyst which has rich active sites exposed and structure stability to resist restacking without any complicate operations and expensive reagents. Remarkably, the current density of the optimum sample reached as high as 60 mA/cm² at an overpotential of 166.4 mV vs RHE (in 1 M KOH), with Tafel slope of ~60.75 mV/dec, electrical double-layer capacity of 148.06 mF/cm² and excellent long-term stability. Furthermore, in the comparison with CoS@NF and MoS₂@NF, the Co-Mo-S hierarchical core-shell nanorod array has an obvious promotion of the electrocatalytic performance. Overall, we prepared Co-Mo-S hierarchical core-shell nanorod array at nickel foam with a simple template-directed method, which could be a prospective way to extend the future of transition metal chalcogenide in hydrogen evolution reaction.

Reference:
1. Seh, Z. W., Kibsgaard, J., Dickens, C. F., Chorkendorff, I., Norskov, J. K., & Jaramillo, T. F. (2017). Combining theory and experiment in electrocatalysis: Insights into materials design. Science, 355(6321). doi:10.1126/science.aad4998
2. Jiang, J., Gao, M., Sheng, W., & Yan, Y. (2016). Hollow Chevrel-Phase NiMo3 S4 for Hydrogen Evolution in Alkaline Electrolytes. Angew Chem Int Ed Engl, 55(49), 15240-15245. doi:10.1002/anie.201607651

Free-standing and ultrathin, hierarchical porous two-dimensional polycrystalline Co₃O₄ flowers were synthesized by a topotactic transformation of CoO_x precursor systems. The synthesis processes and the structure of the final Co₃O₄ flowers were fully characterized by electron microscopy (SEM and aberration-corrected STEM) and spectroscopy (FTIR, XPS) techniques. The electron microscopy results showed that the CoOx flowers possess sizes ranging from ~ 1 mm to 5 µm and the average grain size is about 1.8 nm. The Co₃O₄ flowers possess abundant grain boundaries and surface steps, and the 2D-sheets range from about 1 nm to 5 nm in thickness. By detailed analyses of numerous aberration-corrected STEM images, we concluded that the 2D-sheets mainly exposed {211} and {100} surfaces. The XPS results revealed that compared with those of the bulk Co₃O₄ the core level energy of the Co 2p of the Co₃O₄ flowers showed a 0.8 eV redshift, caused by the enhanced electron density around the surface cobalt ions, resulting in the reduction of Co-O coordination [1]. Low-temperature CO oxidation over the synthesized 2D-Co₃O₄ flowers showed high activity due to high surface area and abundant surface defects. Dispersion of single metal atoms (e.g., Pt, Pd, and Ir) onto the 2D-Co₃O₄ flowers significantly modifies their catalytic performances for CO oxidation and other selected catalytic reactions [2].
References
[1] Y. Sun, S. Gao, Y. Xie, Chem. Soc. Rev. 43 (2014) 530–546.
[2] This work was supported by the National Science Foundation under CHE-1465057. The authors acknowledge the use of facilities within the John M. Cowley Center for High Resolution Electron Microscopy at Arizona State University. Yafeng Cai gratefully acknowledges financial support from the China Scholarship Council.

Electrochemical water splitting is a promising technology for mass hydrogen production. Efficient, stable, and cheap electrocatalysts are keys to realizing this strategy. However, high price and preciousness of commonly used noble metal based catalysts severely hinder this realization. Herein, we report nickel iron phosphide (Ni-Fe_xP) bifunctional electrocatalyst via the in-situ growth of Ni-Fe(OH)_x on nickel foam (Ni-Fe(OH)_x/NF) followed by low-temperature phosphidation. As a hydrogen evolution reaction (HER) catalyst, the Ni-Fe_xP/NF only needs an overpotential of 119 mV to drive a current density of -10 m A/cm² in a base media. It also shows excellent activity toward oxygen evolution reaction (OER) with low overpotentials of 254 mV, 267 mV, and 282 mV at 50, 100 and 200 mA/cm², respectively. Moreover, when this bifunctional catalyst is used for overall water splitting, a low cell voltage of 1.62 V is needed to deliver a current density of 10 mA/cm², which is superior to commercial electrolyzer and it also shows remarkable stability.

Silver nanowires (AgNWs) and gold nanowires (AuNWs) have high surface area, high electrical conductivity and excellent chemical stability, and hence are attractive building blocks to fabricate low-density metal foams for a wide range of applications. Here we demonstrated using solution synthesis to produce high-purity AgNWs and AuNWs in large quantities, which are subsequently used to fabricate (ultra)low-density forms via freeze-casting approach. As-made metal foams have tunable densities down to single-digit mg/cc. Key factors that affect the pore geometries, including solvent, freezing rate and nanowire concentrations, were systematically investigated. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

Among the various approaches to produce sustainable and clean fuels alternative to fossil fuels, splitting of water into hydrogen and oxygen using sunlight is one of the more promising. The development of industrial electrode materials focuses on low cost, high efficiency and long lifetime.
Stainless steel or Nickel based electrodes are usually employed for practical applications. However, although these show a high initial electrocatalytic activity, under long time operation they experience extensive deactivation. On the other hand, Platinum is the best know catalyst for Hydrogen production since it requires very small overpotentials and it is very stable. Since it is quite expensive, a good approach may consist in using a very thin Pt layer deposited on less noble metal electrodes. In this paper we use Ni foam electrodes functionalized with a thin Pt layer, deposited by spontaneous galvanic displacement. We show that the proposed method has several advantages compared to other deposition techniques. First, it is a simple, low cost deposition method that does not require expensive equipments. It is also scalable and, as it will be shown, it allows to obtain uniform coverage of the 3D structured Ni foam electrode.
We compare different deposition techniques and show that spontaneous galvanic displacement can be properly optimized in order to obtain very uniform Ni coverage. We show that, thanks to the high uniformity, Pt covered Ni foam electrodes exhibit superior stability upon long term stress. An experimental method is also proposed to evaluate the amount of Pt. Optimal results in terms of stability and current are obtained with 0.015 mg/cm² of noble metal per electrode. Such a value is about one order of magnitude lower than the typical values employed in Proton Membrane Exchange electrolyzers, therefore making the proposed approach very promising for efficient hydrogen production.

Ultra-low density (<20 mg/cm³) nanoporous materials are desirable for a number of applications in materials for energy storage, generation, and utilization. Yet such materials are frustratingly difficult to fabricate as well-defined macroscopic structures. The few materials that have historically been fabricated to these specifications (e.g., SiO₂, Fe₂O₃, C) often require complex, multistep syntheses and/or highly specialized equipment. Herein will be discussed recent developments at Lawrence Livermore National Laboratory to produce high-quality metal foams approaching 1 mg/cm³ from nanowire suspensions via a facile freeze-casting approach. Focus will be placed on successes in expanding our compositional repertoire and insights gained as to the evolution of pore structures during non-aqueous and mixed-solvent freeze-casting via ultra-small-angle X-ray scattering and computed tomography. This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.

The effect of promoter addition on iron supported on silica nanosprings (Fe/NS) catalyst for Fischer-Tropsch synthesis (FTS) is investigated. The Fe/NS catalysts with the different metal loading were synthesized by the incipient wetness impregnation technique. The catalyst promoters examined were cobalt (Co), molybdenum (Mo), copper (Cu) and ruthenium (Ru). The physico-chemical properties of the prepared catalysts were characterized before the FT reaction by: BET surface area anlaysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), hydrogen temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The FTS performance of the Fe/NS and promoted catalysts were examined in a quartz fixed-bed microreactor (H₂/CO of 2:1, 250 ^oC and atmospheric pressure) and the products trapped and analyzed by GC-TCD and GC-MS to determine CO conversion and reaction selectivity. The characterization results obtained indicated that the promoted of Fe/NS catalyst with Co, Mo, Cu and Ru oxides enhanced the catalytic activity of Fe/NS catalyst and the selectivity towards hydrocarbons liquid fuels in the C₆ to C₁₆ range compared to the control Fe/NS catalyst. The Ru and Mo promoted Fe/NS catalysts were shown to be best performing FTS catalysts.

Zeolites with low aluminum content (high Si/Al ratio) are more favorable for catalytic applications. Zeolite-Y is the prominent member of zeolite family cannot be directly synthesized with Si/Al ratios over ~2.5. Hence, post-synthetic modification such as hydrothermal dealumination is found to be most feasible way to increase the Si/Al ratio in the framework.^1-4 In general, dealumination refers to the removal of aluminum from zeolitic framework by chemical reactions. Most often, the ‘Al’ removed from zeolitic framework will fall into non-framework (extra framework). Due to EFAL species the degree of crystallinity to be reduced in zeolites, which leads to complicated issues on catalytic applications. To avoid this, selective removal of extra framework aluminum (EFAL) is important for various catalytic applications. In this study, a novel approaches has been developed to remove only EFAL species from commercial Zeolite-USY. Various concentration of water glass was added to commercial zeolites and treated at various temperatures (Room Temp to 100 °C) and duration (0-24hrs) to obtain to remove EFAL from the zeolite materials. All the samples were well characterized by XRD, N₂ adsorption-desorption measurements, ICP-AES, SEM, TEM, FTIR and NMR. A model catalytic cracking reaction was carried out to evaluate the catalytic properties of the EFAL removed samples.

Black titania is a class of materials that are of interest due to their increased absorption in the visible spectrum, as well as their catalytic properties. They have potential applications as materials for photovoltaic (PV) cells, water splitting and waste treatment. Black titania has been synthesized via numerous reduction methods and with various dopants. While the resulting structure and performance of the material is dependant on synthesis, black titania is often described as a core-shell structure of anatase TiO₂ nanoparticles surrounded by a layer of amorphized TiO₂. This amorphized layer usually has an increased concentration of oxygen vacancies and Ti³⁺ ions relative to white TiO₂. The possibility of ion irradiation-synthesized black titania is interesting because the passage of medium energy (< 1MeV) ions through a TiO₂ particle has the potential to amorphize the entire volume rather than just a surface layer. Heavily Si-doped materials are also of interest to PV applications as Si quantum dots (QD) are strong absorbers in the infrared. The porosity of the TiO₂ may decrease the Si-QD formation temperature to that which the porous TiO₂ can survive.
In the present study, a porous layer of TiO₂ nanoparticle film was spin coated on pieces of Pyrex and fused silica. These samples were implanted with 90 keV Si⁺ ions at the following fluences: 5.00x10¹⁴ cm^-2, 1.88x10¹⁵ cm^-2, 7.07x10¹⁵ cm^-2, 2.66x10¹⁶ cm^-2 and 1.00x10¹⁷ cm^-2. The films were observed to be various shades of grey in colour and became increasingly darker at higher fluence. UV-vis absorption measurements confirmed near-uniform increased absorption across the visible spectrum. X-ray diffraction results showed the peaks of anatase-TiO₂ superimposed on the broad amorphous background of the substrate. The peak intensity decreased with increasing fluence and almost disappeared completely at the highest fluence – suggesting complete destruction of TiO₂ crystalline order. Depth-resolved positron annihilation spectroscopy (PAS) is a technique sensitive to point defects and open volume in thin films and layered structures. PAS results on these samples indicate increasing defect concentration with increasing fluence in a way that is uniform throughout the TiO₂ layer.
These results indicate that the Si-ion synthesized black titania is more thoroughly amorphized than previously reported black titania materials – at the highest fluence the entire volume of the nanoparticles through the entire width of the film. Further studies will investigate the role of the implanted Si-ion and the impact of annealing.

Nowadays, accessibility to catalytic sites is one of the main objectives involving the development of heterogeneous catalysts. In this context, several studies seek to reduce crystal diameters or create mesoporosity in zeolites. The present work presents a new way to improve the accessibility of the sites through the synthesis of embryonic zeolites. This method consists of obtaining structures that have a short-range order that improves mass transfer and lead to better catalytic results, especially in the processing of larger molecules. For this, the formation study of NaX, NaA and SOD structures was carried out as a tool to improve the catalytic activity in Knoevenagel condensation between benzaldehyde and ethyl cyanoacetate (T = 30o C e t = 30min). The synthesis of the microporous sieves was carried out under various times at 60° C and all materials obtained, even without crystallinity, were evaluated as catalysts. The highest conversions of benzaldehyde were always reached by the zeolite embryos, regardless of the structure that originated. This higher activity is related to the secondary units of construction of the zeolite structure, which are formed during the induction period, as verified by the FTIR technique. While the zeolite structure is in formation all catalytic sites are accessible to the reactants, as the crystallization process is initiated, some of the sites become inaccessible and consequently a reduction in catalytic activity occurs. By means of the CO2 TPD technique, it was verified that the zeolites with high crystallinity have a greater number of sites in relation to the embryonic zeolites, however, the catalytic activity does not reflect this tendency. That is, as verified by the N2 physisorption, the embryonic zeolites do not have porosity, so the voluminous molecules of the reagents have access to all sites. However, the samples with the highest number of sites have microporosity, that is, not all sites are accessible to catalysis. The embryonic zeolite that gave the NaA zeolite proved to be the most active catalyst of its NaX and SOD homologues. This higher activity is related to the fact that increase in the density of TO4- tetrahedral anions in the structure also promote an increase in the number of basic sites and, therefore, the basicity is also increased. However, when calculating the activity by site (TOF0), it was verified that all the sites have the same activity, that is, the greater catalytic activity is related to the accessibility and the number of sites present in the embryonic zeolites.

A new mesoporous Mn and Ta mixed oxides (Mn-Ta oxide) with 2D-hexagonal ordering were successfully synthesized by soft template method, and their characterization was performed using small-angle powder X-ray diffraction (XRD) measurement, N₂ adsorption-desorption isotherm measurement and transmission electron microscopy (TEM) observation.
Tantalum chloride and manganese chloride were dissolved in ethanol containing poly (alkylene oxide) block copolymer HO(CH₂CH₂O)₂₀(CH₂CH(CH₃)O)₇₀(CH₂CH₂O)₂₀H (Pluronic P-123). After vigorous stirring, the resulting sol solution was aged so that template could be formed by self-assembling the poly block copolymer during drying. Then the dry solid obtained was calcined in air to remove the organic template, obtaining the Mn-Ta oxide. The N₂ adsorption-desorption isotherm of the product was typical type-IV pattern characteristic of many mesoporous materials. The estimated BET surface area was 106 m²g^-1, and the pore size distribution was centered around ca. 4.8 nm. Small-angle powder XRD pattern measured using Cu Kα radiation showed a sharp diffraction peak corresponding to d spacing 7.5 nm together with low-intensity peaks assigned to mesoporous materials. The wall thickness was estimated to be 3.9 nm from the d spacing and the pore size. The mesoporous structure of the prepared Mn-Ta oxide was observed directly by TEM measurement. The 2D-hexagonal arrangement of mesopores could be clearly seen.
Since there are few previous reports concerning the ordered 2D-hexagonal mesoporous oxide composed with two different transition metals, the application of the Mn-Ta oxide would be expected.

In the past decades mesoporous materials, which have uniform pore size distribution, high surface area and large pore volume, have attracted much attention for their potential applications including catalysis, sensor, medicine and adsorption. Among various mesoporous materials, mesoporous alumina showed advantageous acidic property and great stability in harsh condition, resulting in excellent performance in the catalytic reforming, toxic chemical adsorption. In this study, we prepared spherical mesoporous alumina through sol-gel chemistry derived synthesis followed by heat treatment. We controlled physical properties of spherical mesoporous alumina particle including pore diameter and particle size. The prepared mesoporous alumina particles are characterized by N2 adsorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and Temperature programed desorption analysis. When used as an adsorbent for removal of toxic gas molecules, the spherical mesoporous alumina showed considerable performance under ambient condition. In this presentation, we will discuss further our synthesis, characterization, adsorption performance of Spherical Mesoporous Alumina.

Preferential oxidation of CO (CO-PROX) in H₂-rich stream has been recognized critical to efficiently eliminating the CO molecules to purify hydrogen [1-2]. However, the major challenge for CO-PROX is the low activity at low temperatures and dramatic drop of activity at high temperatures. Although the introduction of Fe species to Pt-based catalysts is able to simultaneously enhance the oxygen activation and weaken the CO adsorption strength these catalysts cannot completely convert CO to CO₂ with excellent O₂ selectivity (O₂ selectivity ≥ 50%) under a wide temperature window ranging from room temperature to 200 ^oC (the operation temperature of a low-temperature shift reactor). In this work, we report a new strategy to synthesize a single molecule catalyst by dispersing single-atom Fe species onto the surfaces of Pt nanoparticles and clusters that are supported on high-surface-area alumina. Such a catalyst is used for oxidation of CO in the excess of H₂ (CO-PROX). The synthesized Fe₁/Pt/Al₂O₃ can achieve 100% CO conversion and 50% O₂ selectivity with a reaction temperature window ranging from 25 ^oC to 200 ^oC (O₂/CO molecular ratio of 1) and 100% CO conversion and 100% O₂ selectivity from 25 ^oC to 140 ^oC (stoichiometric O₂/CO ratio). Moreover, the Pt specific rate of the Fe₁/Pt/Al₂O₃ catalyst is more than 3 times higher than that of the previous best Pt-based catalysts. The structural and electronic stability of single-atom Fe species under reaction conditions and the possible structural model of the Fe₁/Pt systems will be discussed [3].

References
[1] Qiao, B., Liu, J., Wang, Y.-G., Lin, Q., Liu, X., Wang, A., Li, J., Zhang, T. Liu, J. ACS Catal. 2015, 5, 6249-6254.
[2] Liu, K., Wang, A. Q., Zhang, T. ACS Catal. 2012, 2, 1165-1178.
[3] This work was supported by National Science Foundation under CHE-1465057.

Polymer nanocomposite foams bear a technological potential by exclusively embodying multifunctional material properties within low-density structures. Yet, contemporary configurations could only attain limited performance caused either by modest properties of host polymers or nanofiller-averse processing techniques. Delibrately controlled interfacial interactions between nanoparticles and backbone chains constitute another critical element for the nanocomposites to optimize physical properties beyond the state-of-the-art. Aromatic thermosetting copolyester (ATSP), introduced in the late 1990s, utilizes low cost, easily processable and highly crosslinkable oligomers to develop a high-performance polymer system. Here, we present carbon nanoparticle incorporated high-performance ATSP nanocomposite foams. These foams are fabricated through a facile solid-state mixing method wherein carboxylic acid and acetoxy-functional group oligomers are initially combined with chemically pristine carbon nanofillers, all in powder form. The mixtures are then subjected to a thermal condensation polymerization reaction in which the constituent oligomers form the ester backbone of the ATSP matrix and advanced the molecular weight while acetic acid is emitted as the by-product, and generates a porous nanocomposite morphology. In situ hydrodynamic forces induced during the polycondensation reaction enables homogeneous and intact dispersion of the nanoparticles in molten oligomer domain, and correspondingly yields significant improvements in the thermophysical properties. As compared to a neat ATSP foam, the nanocomposite foams exhibit a reduced coefficient of thermal expansion by 25% to 75 x 10^-6 °C^-1. Thermal stability temperature at 5% mass loss is increased by 30 °C exceeding 500 °C. Compressive mechanical strength is enhanced two-fold, reaching 16 MPa along with a nearly doubled fracture strain, which ultimately produces improved material toughness. In addition, the controlled nanoparticle size promotes different electrical percolation thresholds and ultimate electrical conductivities in the nanocomposite foam structures. Microstructural analysis further illustrates nanoparticle distributions in the matrix as well as morphological modifications induced by the conductive percolating networks of the nanofiller particles. Cure characteristics reveal the thermochemical changes formed in the polymerization processes for the GNP content. Besides, chemical spectroscopy of the ATSP nanocomposite morphology exhibits the formation of a robust interfacial coupling mechanism between the carbon nanofillers and ATSP backbone. The aromatic thermosetting copolyester nanocomposite foams are lightweight, mechanically strong, electrically conductive and thermally durable multifunctional structures utilizing strong interactions with the carbon nanofillers which can potentially be used for variety of technological applications.

MXenes are a class of 2D materials first developed by Michael Naguib, Yury Gogotsi and Michel Barsoum at Drexel University in 2011.^[1] They are created by etching out the A layer of layered M_n+1AX_n phases (M=transition metal, A=group 13 or 14 element, X=C,N) with n=1, 2, or 3, resulting in loose stacks of MX slabs. These slabs can then be exfoliated into 2D sheets, dubbed MXenes. The MXenes have a range of interesting properties depending on composition, surface termination, and synthesis conditions.^[2] More recently a similar class of compounds have attracted attention: M_nAB_n (B=boron) phases have a similar layering structure, and also show anisotropic properties.^[3] The bulk boride phases possess a couple properties unique from the MAX phases, including high temperature stability and outstanding hardness. To date, 2D MBene sheets have not been created, and very little attention has been given to them in the literature. However, theoretical work suggests that these materials show great promise as battery electrodes, catalysts, and capacitors.^[4],[5] In view of this, we have discovered a novel synthesis toward 2D MBene layers from the M₂AlB₂ (M=Cr, Mn, Fe) structure. The partial etching of the bulk phase can be finely controlled by tuning the starting composition, creating different porous scaffolds. The exposed surface contains the same active sites as in MoB₂ and FeB₂,^[5],[6] which have recently been reported for their excellent catalytic activity. The HER activity of these new 2D Mbenes will be presented.

References
1. Naguib, M. et al. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 23, 4248–4253 (2011).
2. Hong Ng, V. M. et al. Recent progress in layered transition metal carbides and/or nitrides (MXenes) and their composites: synthesis and applications. J. Mater. Chem. A 5, 3039–3068 (2017).
3. Ade, M. & Hillebrecht, H. Ternary Borides Cr 2 AlB 2 , Cr 3 AlB 4 , and Cr 4 AlB 6 : The First Members of the Series (CrB 2 ) n CrAl with n = 1, 2, 3 and a Unifying Concept for Ternary Borides as MAB-Phases. Inorg. Chem. 54, 6122–6135 (2015).
4. Guo, Z., Zhou, J. & Sun, Z. New Two-dimensional Transition Metal Borides for Li Ion Battery and Electrocatalysis. J. Mater. Chem. A (2017). doi:10.1039/C7TA08665B
5. Park, H., Encinas, A., Scheifers, J. P., Zhang, Y. & Fokwa, B. P. T. Boron-Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction. Angew. Chemie - Int. Ed. 56, 5575–5578 (2017).
6. Li, H. et al. Earth-Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting. Adv. Energy Mater. 7, 1700513 (2017).

Metallic nanoparticles, free standing or supported in nanoporous frameworks, have important applications in catalysis. A comprehensive understanding of the nanoparticle formation is key to controlling the structure and reactivity. Accordingly, the interfacial chemistries strongly dictate this formation. Silver nanoparticle formation within zeolites is strongly dependent on the functionality of the interfaces. Both thermal dehydration of water adsorbed within the zeolite pores and chemical reduction can contribute to Ag-particle formation in Ag-exchanged zeolites. Absorbed water and pore surface functionality (e.g. hydroxyl groups), affects silver cation mobility and, thus, has potential to impact cluster and particle growth kinetics. Thermal dehydration during the high temperature reduction reaction and/or changes to the pore surface, may affect cation mobility in the partially reduced material. Understanding the evolving structure of the clusters and nanoparticles, how this is coupled to desorption of molecular species and changes to surface functionality, and how these can impact reduction and particle growth, is of prime importance in controlling these processes. By probing a single sample within a single in-situ sample environment, inconsistencies that may arise from separate experiments (e.g., environments, procedures, etc.) can be avoided. Herein, we combine simultaneous PDF and DRIFTS measurements with XANES data to study the role of water and surface hydroxyl groups in Ag particle formation in various zeolites: A, X and Mordenite. Experiments were undertaken at elevated temperature in reducing atmosphere, as typical of a solid-gas reaction for industrial catalyst preparation.

Acknowledgements: Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.Work done at Argonne and use of the Advanced Photon Source, an Office of Science User Facility operated for the US DOE/Office of Science by Argonne National Laboratory, was supported by the US DOE, Contract No. DE-AC02-06CH11357.

Metal–organic frameworks (MOFs) are an emerging class of solid-state materials built up from metal-based nodes and organic linkers. They exhibit permanent porosity and unprecedented surface areas which can be readily tuned through coordination chemistry at the inorganic node and/or organic chemistry at the linkers. The high porosities, tunability, and stability are highly attractive in the context of catalysis. As exemplified by many catalytic enzyme assemblies in nature, site-isolation is a powerful strategy for performing catalytic reactions. MOFs provide an exciting platform for deploying catalysts in a site-isolated fashion and the cavities surrounding them can be engineered to conceptually mimic enzymes. This talk will address new advances in the synthesis and catalytic activity of MOF materials developed at Northwestern University.

In its classical definition, a catalyst is a substance that increases the rate of a reaction without being consumed considerably. The active site in the catalyst and its interaction with reactant(s), transition state(s), and product(s) define whether the desired reaction will proceed with a higher rate and selectivity at relatively mild conditions compared to the noncatalysed reaction. It is not surprising that the design of such active sites is one of the main targets of catalyst engineering. However, the nature of the active site is not always clear. In the case of homogeneous catalysts and enzymes, they can be easily identified, however, the description of active sites in the case of heterogeneous catalysts may become more controversial. A typical example is a metal nanoparticle, where the active sites – the metal atoms – may be located at the steps, kinks, terraces, etc., each one of these sites bearing different properties. In this sense, one could easily argue that homogeneous catalysis is a much more powerful approach towards the design of better catalysts given the rather high level of predictability, design, and engineering of these systems, especially when compared to heterogeneous catalysts. Yet, issues related not only to the obvious challenge of recyclability but also to deactivation and the use of low concentrations of homogenous catalysts have placed heterogeneous catalysts at the forefront of chemical industry.
The problems presented by both homogeneous and heterogeneous catalysts have triggered intense research over the last few decades in the quest for alternative systems that, ideally, would bridge the gap between these two subdisciplines of catalysis by implementing truly single catalytic sites at the surface of a solid catalyst. The challenge at hand is certainly not trivial: progress in this direction requires the discovery of new materials able to offer sufficient design possibilities as to allow for an exquisite control in the implementation of catalytic functions. This colloquium will focus on, and stress the advantages of, two classes of materials that have the potential to become the ideal homo-hetero bridge: metal-organic frameworks (MOFs) and porous organic frameworks (POFs).

The past five years have witnessed an increased interest in using metal organic frameworks (MOFs) as scaffolds to nucleate and stabilize metal nanoparticles (NPs) with a narrow size dispersion. Gold is particularly interesting because it exhibits a number of interesting properties in the form of nanoparticles for plasmonic, catalysis, optics, and even biology.[1]

We pesent a new photoreduction approach (UV-vis irradiation of HAuCl₄) that produces Au NPs inside MOFs without additional stabilizing or reducing agents, thus limiting the contaminations sources. Among several MOF structures with different pore sizes, we find that a relatively new MOF (MOF-808) – yields the smallest and most uniform Au NPs when functionalized with SH, compared to the well-studied UiO-66, or HKUST-1, MIL-101 (Cr), or even MOF-808 and MOF-808-NH₂. Combining spectroscopy (IR absorption, Raman, XPS, UV-visible and LEIS) with imaging using high resolution transmission electron microscopy, we find that the diameter of Au-NPs synthesized in MOF-808-SH material (1.0 ± 0.5 nm with narrow distribution) is consistent with the pores size (1.07 ± 0.05 nm) principally due to a combination of a confinement effect relative to the pores sizes and a strong stabilization of the Au NPs surface by the -SH groups.

Care is taken to prove that the Au NPs are located inside the MOF structure because this is difficult to establish with TEM unless time consuming tomographic studies are performed, which can only be done in small selected parts of the sample.[1] In contrast, spectroscopies such as LEIS, IR and Raman probe the whole volumes of MOF samples, thus providing information on the majority species in the sample. The most detailed information is obtained from LEIS and clearly shows that Au is located below the surface of the MOF microcrystals. IR and Raman provide additional information about the interactions within the pores, pointing to the chemical groups directly affected by the presence of the Au (through modification of molecular vibrations and formation of new bonds). These studies thus provide 1) a general view on the inclusion of Au NPs that is more representative of the whole material, and 2) a precise localization of the nanoparticles inside the channels of the porous materials.

Noting that the photocatalytic activities of Au NPs is strongly dependent on the size of the NPs within the 1-5 nm range, we doped MOF-808-SH with titanium by transmetalation prior to the synthesis of Au NPs and tested its photocatalytic activity, specifically the photoreduction of water. An activation period is observed in hydrogen production, which can be related to the growth of Au NPs from 1.0 ± 0.5 nm to 2.0 ± 0.9 nm, as localized surface plasmons are generated, necessary for photocatalytic activity.

Acknowledgement: This work was fully supported by the Department of Energy, Basic Energy Sciences, Grant No. DE-FG02-08ER46491.

References:
[1] A. Dhakshinamoorthy et al., ACS Catalysis (2017), 7, 2896-2919.

Synthesis of high-value chemicals through fine tuning of catalytic properties has been considered to be the most fascinating field in catalysis. One of the most intriguing reactions is reduction of nitroarene, in that nitroarenes mostly undergo two reaction pathways to yield aromatic amines. Here, we show unexpected selectivity of affordable nickel nanocomposite catalyst toward coupling of nitroarene to azoarene, which has so far been achieved only by noble metals with base as reagents. Nanocomposite of nickel in highly porous sulfur-doped carbon is able to selectively synthesize value-added azoarene from nitroarene without any by-products. ¹H NMR confirms pure azobenzene when nitrobenzene is heated at 60^oC for 8 hours under ambient air with nickel nanocomposite catalyst and hydrazine. Raney^® nickel, as a control experiment, shows mixture of intermediates such as azoxybenzene, hydrazobenzene, and aniline. The origin of unexpected selectivity is attributed to fine tuning of electronic properties of nickel by sulfur, which is confirmed by XPS. The nickel nanocomposite catalyst also shows high surface area (S_BET= 1300 m²/g) with micro and mesoporosity. The catalyst has an enormous potential to be used in reductive catalytic reactions where noble metal catalysts are studied as a mainstream.

Metal Organic Framework (MOF) structures represent an enormous potential for applications ranging from separation processes to catalysts in energy production and storage. Specifically, encapsulation of functional nanoparticles (NPs) within MOF structures can expand their implementation scope and enhance their functionalities. The versatility of such nanocomposite structures can be attributed to their porous networks, large available surface areas and single crystalline nature in addition to their facilitation of well-dispersed NPs with unobstructed surfaces under the confinement of porous MOFs that can promote catalytic activities. Although a large volume of work in recent years have focused on the synthesis of MOF and MOF/NP composites, a fast, reliable and facile methodology for the fabrication of MOF-confined functional NPs with controlled morphology and uniform spatial distributions is still elusive. Here we report a rapid, facile strategy utilizing our recently developed laser ablation synthesis in solution-galvanic replacement reaction (LASiS-GRR) technique for the first time for the synthesis of Platinum (Pt) NPs confined within two different structures: Zeolitic Imidazolate Framework-67 (ZIF-67) and Zeolitic Imidazolate Framework-8 (ZIF-8). Our results indicate that this technique allows us to achieve superior control on the tailored size, morphology and spatial distributions of NP/MOF porous composites tuning the high-energy physiochemical conditions emerging from liquid-confined, laser-induced plasma as well as the solution-phase reaction pathways driven by the GRR mechanisms. We show that the advantage of such confined nanocomposite structures is in its ability to achieve well-dispersed and spatially confined NPs after calcination treatments on suitable substrates that hinders NP aggregations during catalytic activities. To this end, preliminary results for post-calcined Pt/MOF composites have also shown promising catalytic activities towards Oxygen Reduction (ORR) and Oxygen Evolution Reactions (OER).

The oxygen reduction reaction (ORR) is the most important processes in a wide range of renewable energy technologies, such as in fuel cells and metal–air batteries.¹ Fe-N-C has emerged as a promising noble-metal-free catalyst for the ORR, however, to achieve a catalytic activity comparable to that of Pt in acidic medium remains a great challenge.² Here we develop a simple and scalable atomic isolation technique to synthesize a porous Fe-N-C catalyst with a high concentration of N-coordinated single Fe atoms by pyrrole polymerization on carbon nanotubes (CNTs), followed by Fe³⁺ and Zn²⁺ ion adsorption, and finally one-step pyrolysis.³ Additional acid leaching and a second treatment are not required. During the pyrolysis, Fe atoms are uniformly dispersed with and spatially isolated by Zn atoms and directly convert to N-coordinated single Fe atoms, instead of large inactive Fe particles. Furthermore, pores are formed along with the volatilization of the isolation Zn atoms, and these are greatly beneficial to ORR activity. As a result, the obtained porous carbon composite catalyst exhibits excellent ORR performance with a half-wave potential value of 0.82 V in an acidic medium, 20 mV more positive than that of Pt/C with a “standard” loading of 0.1 mg cm^-2 and only 20 mV more negative than that of Pt/C with the same loading of 0.3 mg cm^-2. The technique can be generalized to other carbon supports, including carbon black, graphene oxide, and flexible films of single-wall CNTs or carbon cloth. The obtained flexible composite films show even better ORR performance with 40-60 mV more positive onset potentials than Pt/C loaded on carbon cloth. Considering the low-cost and simplicity of this fabrication process, these high-efficiency, robust catalysts with a high concentration of single Fe atom sites are promising candidates to substitute for noble Pt-based catalysts in fuel cells.
References
1. J.C. Li, P.X. Hou, S.Y. Zhao, C. Liu, D.M. Tang, M. Cheng, F. Zhang, H.M. Cheng. A 3D Bi-Functional Porous N-Doped Carbon Microtube Sponge Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions, Energy Environ. Sci., 9, 3079 (2016).
2. J.C. Li, P.X. Hou, C. Shi, S.Y. Zhao, D.M. Tang, M. Cheng, C. Liu, H.M. Cheng. Hierarchically Porous Fe-N-Doped Carbon Nanotubes as Efficient Electrocatalyst for Oxygen Reduction, Carbon, 109, 632 (2016).
3. J.C. Li, Z.Q. Yang, D.M. Tang, L.L. Zhang, P.X. Hou, S.Y. Zhao, C. Liu, M. Cheng, G.X. Li, F. Zhang, H.M. Cheng. N-doped carbon nanotubes containing a high concentration of single iron atoms for efficient oxygen reduction, NPG Asia Mater., under publication.

Two-Dimensional (2D) nanomaterials have garnered remarkable interest recently due to their promising potential in versatile applications,
such as energy storage devices of lithium ion batteries (LIB) and capacitors. However, catalytic properties of 2D nanomaterials,
especially for thermo-catalytic reactions, are rarely studied. The 2D structures may facilitate the characterizations of the supported
nanoparticles and help determine the chemistry of active sites.

Water gas shift reaction (WGS) is widely used in industry to produce clean hydrogen for plenty of processes such as ammonia synthesis,
methanol synthesis and hydrocarbon processing. Moreover, WGS is a useful probe reaction that can shed light on fundamental catalytic
processes over considerable catalyst systems. In this presentation, we studied the effect of 2D nanomaterials as support of noble metal for
WGS. Kinetics such as orders of reactants cast light on the absorption and coverage of the reactants. Scanning transmission electron
microscopy (STEM) as well as X-ray absorption fine structure (XAFS) were employed to identify the nature of active sites.

Porous organocatalysts offer confined spaces with tunable functionalities and a green alternative to precious metal catalysts. Imine formation is a key step in the synthesis of amino acids through amino nitriles. A simple and direct route is the oxidative self-coupling of amines. We recently showed that a novel and plausible mechanism that is based on catalytic, quantitative self-coupling of amines by air oxygen can produce substituted amino acid derivatives in excellent yields. The benzoxazole catalysts developed here provide quantitative catalytic activity over 50 cycles with favorable kinetics with no degradation. A time resolved spectroscopic monitoring rules out an aldehyde intermediate route in the imine formation. This work also marks the first use of benzoxazoles for oxidative catalytic reactions and provide new means and understanding for producing range of organic building blocks.

There has been a rapid development in metal-organic frameworks (MOFs), especially porous MOFs, due to their high potential for diverse applications in the past decade, especially for clean energy. Recently, we have successfully synthesized a number of new porous MOFs and found their new applications as catalysts, as supports for metal nanoparticles and as templates/precursors for nanoporous carbon synthesis.^1-2 Novel porous metal-organic frameworks have been synthesized, which present stable catalytic activities for the oxidation of CO to CO₂. Metal nanoparticles (NPs) have been immobilized to MOFs by the solid-grinding method, impregnation method and double-solvents approach in combination with the H₂ reduction, liquid-phase concentration-controlled reduction and the CO-directed reduction at the solid-gas interface, which exhibit excellent catalytic performances for various reactions, including hydrogen generation from chemical hydrides. Porous carbons have been synthesized by using MOFs as templates/precursors and the resultant carbons display high specific surface areas and excellent electrochemical properties as electrode materials for electric double-layered capacitor (EDLC) and as catalysts for oxygen reduction reaction (ORR). This talk will discuss the energy applications of MOFs.

References:
For recent reviews, see: (a) S.-L. Li, Q. Xu, Energy Environ. Sci., 2013, 6, 1656. (b) Q. L. Zhu, Q. Xu, Chem. Soc. Rev., 2014, 43, 5468. (c) J.-K. Sun, Q. Xu, Energy Environ. Sci., 2014, 7, 2071. (d) W. Xia, A. Mahmood, R.-Q. Zou, Q. Xu, Energy Environ. Sci., 2015, 8, 1837. (e) Q.-L. Zhu, Q. Xu, Chem. 2016, 1, 220. (f) H. Wang, Q.-L. Zhu, R. Zou, Q. Xu, Chem. 2017, 2, 52. (g) S. Dang, Q.-L. Zhu, Q. Xu, Nat. Rev. Mater., 2017, 3, 17075.
(a) P. Pachfule, D. Shinde, M. Majumder, Q. Xu, Nat. Chem. 2016, 8, 718. (b) Q.-L. Zhu, W. Xia, T. Akita, R. Zou, Q. Xu, Adv. Mater. 2016, 28, 6391. (c) L.-F. Chen, Q. Xu, Science, 2017, 358, 304. (d) X. Yang, J.-K. Sun, M. Kitta, Q. Xu, Nat. Catal., 2018, 1, 214.

We have synthesized stable homotopic, single-site catalysts supported on MCM-41 by a combination of sol-gel and surface organometallic chemistry (SOMC). We have demonstrated that a variety of metal atoms (Cu, Ru and Rh) can be anchored on these ligands. In addition to incorporation of single metal sites we have been able to incorporate multi-nuclear clusters of metals. We have devised and synthesized monomeric, dimeric, trimeric and tetrameric clusters that have been incorporated in high surface area mesoporous silica with high degree of control. Structural characterization of these catalytic materials has shown desirable properties such as high surface area, high degree of porosity and high thermal stability. We synthesized several versions of MCM-41-supported ligands and characterized them by multinuclear NMR, FTIR, and MS.
Here we present our progress in the area of synthesis of organo-functional hybrid catalysts that are promising towards the direct conversion of alkanes to alcohols. Synthetic analogues have provided some insight into the process of converting alkanes to alcohols with varying degree of control and success. Such hybrid solids are well defined at the molecular level and may allow a greater understanding and a more rational analysis of the structural relationship between reactants and products. We have synthesized Schiff-base functionalized organo-functional hybrid catalysts and then evaluated their activity towards oxidation of alkanes.

Ethylene is an abundant alkene in the US natural gas and petroleum industries. It can be converted to a wide variety of longer C_2n chemicals (such as lubricants, additives, and fuels) via oligomerization reactions. In this work, ethylene oligomerization reaction was performed on a nickel (Ni²⁺)-exchanged titanosilicate zeolite, ETS-10 (Ni²⁺-ETS-10), in an isothermal packed-bed reaction unit at 180^oC and 5 atm. ETS-10 is a thermally stable titanosilicate zeolite (Si/Ti=5) containing tetrahedral [SiO₄] and octahedral [TiO₆] units and can be synthesized using a template-free conventional hydrothermal method. Ni²⁺-ETS-10 has not been studied for ethylene oligomerization before. Our results showed that it is a promising catalyst for alkene oligomerization: Ni²⁺-ETS-10 provides a high loading of isolated Ni²⁺ cationic sites (Ti/Ni≈1) by ion exchange, and the maximum observed activity for Ni²⁺-ETS-10 was 6.45 g_oligomers / (g_catalyst h). C₄ (selectivity>88%) and C₆ (selectivity>10%) oligomers were the main reaction products. Brønsted acid (H⁺) sites were also introduced in Ni²⁺-ETS-10 by selectively replacing the framework Si in [SiO₄] units with trivalent elements (Al, Ga and B) to fine tune product selectivity. We further plan to introduce mesoporosity in the ETS-10 framework to improve catalyst performance.

The rise of more strict environmental regulations have set new challenges for the development of automotive catalysts around the world. It was reported that 50–80% of the CO and total hydrocarbons (HCs) were produced from automobiles during the cold-start period. MnO₂-based oxides would be promising materials, owing to its considerable oxidative catalytic activity and lower price. However, their easily-sintering property or low specific surface area are the main bottleneck for catalytic applications. In this work, MnO₂ and its related mixed oxides with various morphologies and phases were synthetized by controlling the process parameters including precursor types and concentration, hydrothermal temperature and time, acid/basic etching, etc.
The results showed that the catalytic activities were significantly affected by the MnO₂ phase structures, especially by the different linking modes of [MnO₆] octahedral units. The urchin-like γ-MnO₂ had a disordered structure, resulting in larger numbers of active oxygen species, leading to a better catalytic performance. It showed the satisfying NO catalytic oxidation activity and stability, even compared with those of noble-metal-based catalysts. Furtherly, Fe precursor was used for modifying the γ-MnO₂ by different paths. The FeO_x-MnO_x synthesized by hydrothermal method showed the better NO catalytic oxidation activity than single phase MnO₂. in situ IR of NO adsorption indicated that a proper content of Fe could promote the adsorption of NO and decomposition of nitrate at low temperature, leading the improvement of the catalytic activity at low temperature. Those FeO_x-MnO_x synthesized by self-template and etching route displayed hollow structures with ultra-large surface area over 428 m² g⁻¹. They exhibited extremely better oxidative activity, which even could convert 79.1% CO at room temperature.
Considering to improving the stability of MnO_x-based catalysts, some defect-induced Mn contained perovskite oxides were prepared by citrate method and selective etching. After etching, the perovskite structures of the catalysts remained, the surface area apparently enlarged up to > 110 m² g^-1. Mn ions tended to exist in higher valence state and abundant activated oxygen species and vacancies were created, owing to the loss of La³⁺. Similarly, the high-surface-area (> 110 m² g^-1) La-Ce-Mn mixed oxide was successfully synthesized by the same process. The etched catalyst exhibited superior catalytic activities to oxidize CO and C₃H₈, with 90% conversion of CO and C₃H₈ at only 73 and 196 °C, respectively, which would meet the requirements for the emission control during cold-start period. All the catalysts show acceptable stability during the long-term reactions.

Reference
Rui Ran, et al, Catalysis Communication, 2017, accepted.
Rui Ran, et al, Applied Catalysis A: General, 2017, 545 (2017) 64–71.
Rui Ran, et al, RSC Advances, 2016, 6, 69855-69860
Rui Ran, et al, Applied Catalysis A: General, 514 (2016) 24–34

The production of renewable fuels and valuable chemicals from CO₂ reduction reaction by highly efficient, selective, Earth-abundant, robust electrocatalytic materials is of vital interest not only to attenuate the climate change but also to find alternative ways to maintain carbon resources. Here we report the hierarchical CuO inverse opal material which is composed of uniform 2D-3D porous network with voids about 200 nm in diameter for promoting electrochemical CO₂ reduction (EC-CO₂RR) activity. The 3D highly ordered, interconnected mesopores in a hexagonal close packed structure arrange in unique 2D sheet-like architecture. The cycle voltammetry reveals the reduction of monoclinic CuO to Cu₂O and metallic Cu in the presence of CO₂. The current densities at different constant potentials are very stable, reaching -10 and -27 mA cm^-2 at -0.8 and -1.1 V vs. RHE. Such a unique mesostructure exhibits a Faradaic efficiency (FE) for CO production of 63% at -0.8 V vs. RHE with mass-normalized production rate of 28.2 mmol g^-1h^-1. It is surprising that hierarchical CuO porous structure significantly suppresses the hydrogen evolution reaction, producing H₂ with 11-13% of FE only at -1.0 V and -1.1 V vs. RHE. While methane is always found together with CO, ethylene is detected in a higher overpotential region (-0.9 to -1.1 V vs. RHE). The formate is also detected by ion chromatography. The results demonstrate that such a 2D-3D hierarchical mesostructure is beneficial to simultaneous production of CO and other C1-C2 products as well as inhibition of undesirable H₂ evolution. The in situ Raman, XRD and X-ray absorption spectroscopy will be further employed to gain deep understanding of the interaction between hierarchical CuO inverse opal and CO₂ during the EC-CO₂RR as well as the chemical and structural changes of CuO under cycling.

Mesoporous thin films have attracted growing interest for developing advanced functional materials considering their high surface area, ordered porosity, and versatile functionalisation of the pore surface^[1].
The evaporation induced self-assembly (EISA) process^[2] is the most versatile method to produce mesoporous silica films but often leads to 2D mesophases oriented parallel to the surface. Cylindrical mesochannels oriented perpendicularly to the substrate are required for technological devices such as separation membranes, sensors or optoelectronic devices.
The preparation of such aligned mesoporous silica films can be achieved by different strategies; using anisotropic external fields (electric or magnetic) or chemically modified substrates. Another way is to use confined space^[3] to guide the mesochannels in a direction. In this way, the structure of the deposited mesoporous materials is greatly influenced by the synthesis conditions, but the surface chemistry, dimensions and structure of the confined regions need to be considered as well.
Under the Advanced Devices by Electroplating project (EPSRC EP/ N035437/1) we are focused on creating hierarchically ordered porous structures by combining top-down lithographical technologies and bottom-up self-assembly chemistry. The aim of this research is to make a reliable template for the electrodeposition of metal and semiconductor nanowires.
Mesoporous silica pores with a vertical alignment and hexagonal packing were deposited into the pores of anodic alumina membranes and patterned silica substrates using the EISA process. This approach employs homogeneous coating solution combining volatile solvent, surfactant concentrations below the critical micelle concentration (CMC) and silica precursor obtained by acid-catalysed hydrolysis of TEOS. The solvent evaporation drives the self-assembly process towards the CMC and induce the silica condensation around the surfactant micelle template leading to formation of 2D mesophases.
The effect of deposition method, composition of the sol coating solution, aging conditions after deposition and pore surface modification on the filling, structure and morphology of the silica mesopores was studied. Two different surfactants were used in this study (CTAB: ionic surfactant and P123: neutral surfactant) to attempt the formation of columnar hexagonal mesochannels of different size. Interestingly, the design of lithographic patterned substrates has made possible to study the influence of pore shape and pore size ratio on the structuration of silica pores as well.

[1] P. Innocenzi, L. Malfatti, Chem. Soc. Rev. 2013, 42, 4198.
[2] Y. Lu, R. Ganguli, C. A. Drewien, M. T. Anderson, C. J. Brinker, W. Gong, Y. Guo, H. Soyez, B. Dunn, M. H. Huang, J. I. Zink, Nature 1997, 389, 364.
[3] A. Yamaguchi, F. Uejo, T. Yoda, T. Uchida, Y. Tanamura, T. Yamashita, N. Teramae, Nat. Mater. 2004, 3, 337.

Using a recently developed solid state foaming technique, loose powder can be created which contains highly interconnected nanoscale to microscale porosity. This simple method uses mechanical alloying to distribute oxide particles and has been applied to create porous nickel-copper alloys. These alloys can be rapidly produced and are suitable for the deposition of nanostructured carbon using chemical vapor deposition. These oxide-dispersed alloys show enhanced carbon deposition rates, especially at lower temperatures. The mechanism is attributed to the in-situ reduction of oxides leading to pore formation and enhanced surface area. This method for creating porous metals and alloys has also been demonstrated in copper, nickel and silver, and it is capable of creating porosity in excess of 40%. It is also compatible with other techniques for creating metal foams to achieve even higher porosities. The process, properties and catalytic applications are described in context with other methods for creating porous metals, and the potential benefits are highlighted.

We develop chemical bath deposition processes for conformal Pt and IrO₂ depositions on titania nanotube array of 800 nm in length. In addition, we develop an anodization process which can control tube diameters and densities of titania nanotube arrays. These Pt and IrO₂ nanotube arrays undergo electrochemical analysis in charge storage capacity (CSC) and electrochemical impedance to evaluate its potential as stimulation electrodes for implantable devices. Images from electron microscopes confirm the formation of uniform Pt and IrO₂ on both internal and external surface of nanotubes. In addition, the cycling lifetime of Pt and IrO₂ nanotube arrays is evaluated by performing CV scans for 1,000 cycles with a scan rate of 0.1 V/s. The Pt and IrO₂ nanotube arrays reveal large CSC values and low electrochemical impedances which are attributed to hollow tubular nanostructure with Pt and IrO₂ deposition.

Despite the excellent properties observed in individual nanoparticle or (sub-nano) cluster, the current possibilities to assemble them into a complex system for practical applications are not sufficient. An important objective of this project is to develop a fabrication technology allowing for simultaneous control of nanoparticle surface chemistry, atomic component distribution, microscale geometry, and large scale assembly. With the cellulose matrix derived from wood as a scaffold, we are going to fabricate hierarchical porous cellulose and cerium doped TiO₂ hybrid materials. The hybrid materials will serve as high surface area support of sub-nano Pt clusters generated by photochemical synthesizing. The as-synthesized materials will be used to promote the low temperature decomposition of trace ethylene which is the main ripening agent that causes a faster deterioration of fresh food. Advances in this field will have an impact on the optimization conflict between large active interfaces required and the difficulties in nanopowder handling in environmental catalysis, including food preservation and indoor air cleaning. Our research can open new avenues for the manufacturing of multifunctional materials with complex architectures by combining the controllable chemical synthesis with the nature-determined scaffold.
Key words: wood science, food preservation, heterogeneous catalysis, porous matrix

A solid acid catalyst has been synthesized from lignin-derived carbon fiber via a straightforward sulfonation reaction. The carbon fiber (CF) and sulfonated carbon fiber (CF-SO₃H) catalysts were characterized by different techniques like PXRD, TGA, TPD-MS, SEM, and XPS to understand the surface chemistry and the nature of sulfonation. It was confirmed that sulfonated sample bearing a high concentration of acid sites (1.86 mmol/g) possess sulfur in its surface in the form of sulfonic acid (-SO₃H) groups. Its catalytic activity was studied using the esterification of oleic acid as an example of biodiesel production, where a quantitative yield of 92% ester was achieved at 80 ^oC for 4 hours with 10 % of catalyst (based on oleic acid mass used) and at a 10:1 molar ratio of methanol/oleic acid. More importantly, CF-SO₃H showed excellent regenerability and stability during catalysis, demonstrating their potential use in the production of biodiesel. In addition, this material is obtained from low-cost lignin which could be a good alternative solid acid catalyst to produce biodiesel such that this fuel can compete with current fossil fuels.

Catastrophic environmental consequences due to oil spills have been of huge concern over the past couple of decades. Even though numerous oil-absorbing materials have been made to decontaminate waterways, they are limited by the cost of production and scalability of the product. Herein we propose an economical, environmentally benign, and highly sorbent material capable of absorbing several varieties of hydrocarbons, organic solvents and toxic contaminants. The material created was fabricated via sol-gel polymerization of polysaccharides with poly-vinyl alcohol (PVA) via oxidation by metal-nitrate precursors under acidic conditions in aqueous solution, followed by a curing and annealing process under a reducing environment. In this study, we measured the oil adsorption performance of different substituted saccharides within the original synthesis model to determine how pore size and surface area varies depending on different carbon structures. Sugars such as Sucrose, Lactose, Dextrose and others, along with a number of organic acids such as adipic and tartaric acid were used to determine which moieties were responsible for the polymerization process. The materials were compositionally and structurally characterized with SEM and analyzed with BET. Such porous and sorbent material shows promising applicability for environmental remediation.

After billions of years of evolution, creatures in nature have formed complicated, elaborate and reasonable structures, which enable lighter materials to have great properties of high strength and tenacity, resistance to bend, reverse and buckling etc. And these structures have properties which beyond the synthetic counterparts a lot. While traditional bionics structure design simulates them in the macro perspective, the newly emerging micro-3D-imaging technology enables researchers explore inside of materials. The new method offers a novel way to break the bottleneck of traditional bionics design. For example, traditionally methods like FEM are used to analyze and optimize the simple ordered porous structure, but for complicated disordered porous structures, they do not have too much more application. Here we use bamboo and aspen samples as examples, try to obtain the correlation between the porous structure and their mechanical properties of them, and intend to direct the structural optimization. Firstly, we got the X-Ray CT images of bamboo and aspen samples and reconstructed their 3D porous models; secondly, based on the porous media theory we extracted pore parameters, such as pore-size distributions, connectivity function curves, tortuosity and so on; Then with the help of 3D models, we simulated their mechanical properties and obtained the correlation of each pore structure parameter and mechanical properties, which were used to find the optimum porous parameters combination; Finally, we used these parameters to reconstruct a new 3D porous structure with machine learning method, and validated its mechanical properties by experiments and the FEM method. Results showed that the specifically designed porous structure has extraordinary resistant bend, reverse and buckle etc.

Pt, Ni and bimetallic Ni-Pt were impregnate on CeO₂ nanorods and tested in the autothermal steam reforming of methanol (ASRM) reaction in the range of 150–400 °C. Samples were characterized by XRD, TPR, H₂-chemisorption, and CO-adsorption techniques. XRD showed the presence of crystalline structure with sharp diffraction peaks revealing a characteristic cubic phase of the cerianite and metallic Ni. No diffraction peaks of the Pt or bimetallic PtNi species were observed by this technique. Pt/CeO₂-NR showed higher metal dispersion than PtNi/CeO₂-NR and Ni/CeO₂-NR catalysts respectively. The catalytic performance of the Pt-base nanocatalysts exhibit better methanol conversion than monometallic Ni/CeO₂-NR sample. At higher temperature, the H₂ selectivity decrease in the bimetallic catalysts, this finding could be attributed at the formation of the bimetallic Pt-Ni alloy nanoparticles.

Introduction: Nonlinear C8 hydrocarbons, like iso-octane, can raise the octane rating of gasoline due to its better anti-knock characteristics, allowing the use of higher compress ion ratios and higher thermal efficiencies. The benefits of nonlinear C8 addition to gasoline have always been recognized for practical reasons. Fischer-Tropsch process and isomerization reaction have been explored to produce nonlinear C8 hydrocarbons by using different types of catalysts such as classical zeolites, metal oxides for commercially applied process. Olefin oligomerization on these catalysts has also been reported to harvest nonlinear C8 hydrocarbons. However, the reaction temperature above 100 ^oC is relatively high, demanding high energy-consumption. Metal-organic Frameworks (MOFs) with coordinated unsaturated sites (CUSs) on late-transition metals have often been researched as desiccant and adsorbent, and are reported being tested in gas-phase olefin dimerization, indicating the MOF materials take the potential value in the application of oligomerization. Herein, highly selective ethylene tetramerization is observed on a Metal-Organic Framework, MIL-100(Fe) under mild conditions to obtain nonlinear C8 hydrocarbons. Methodology: MIL-100(Fe) was synthesized and vacuum treated at different temperatures to obtain MIL-100(Fe) catalysts with CUSs. Then the treated MIL-100(Fe) catalysts were utilized in ethylene slurry oligomerization. Results: All the MIL-100(Fe) catalysts show high selective tetramerization activities. Specifically, the catalytic activity of the catalyst treated under 250 ^oC reaches over 1.27×10⁵ g/(molFe^.h) and the selectivity for C8 is more than 70% under 10 atm at ambient temperature. There is almost 90% nonlinear C8 tetramers components in the obtained tetramers. Conclusion: The operation of ethylene tetramerization on MIL-100(Fe) is more easily realized at mild conditions, which is an energy-efficient procedure. And the tetramers products containing nonlinear C8 components are suitable as the addition to gasoline to increase the octane number.

We report novel porous structures of hematite and Ti-doped FeOOH (Ti-FeOOH) oxygen evolution catalysts (OECs) for efficient PEC water splitting. By selectively decorating Ti-FeOOH OECs on the inner surface of porous hematite, the overall PEC performance was dramatically increased without interrupting light absorption of hematite by outer surface OCEs. The photocurrent density of Ti-FeOOH/hematite PEC systems was 4.06 mA cm^-2 at 1.23V_RHE with excellent long-term stability for 36 h, representing the state-of-the-art performance among hematite-based systems. Importantly, the proposed hematite photoanode and Ti-FeooH OCEs can be fabricated by a simple and cost-efficient solution-based method, suggesting a novel approach to commercialization of hematite based PEC water splitting systems.

Hierarchically structured platinum-palladium alloy macrotubes with square cross-section and porous sidewalls composed of fibril textured nanoparticles were synthesized from high aspect ratio insoluble Mangus’ salt needles in a single reduction step. Salt needle templates formed from the precipitation of oppositely charged square planar ion complexes were reduced in solution and resulted in macrotubes ranging from 10’s to 100’s µm long and 100 to 200 nm wide conforming to template dimensions. Porous sidewall structures varied from spheres to fibrils with the ratio of platinum to palladium in the salt template. X-ray diffractometry indicated alloy metal content with no oxide peaks. Specific capacitance and solvent accessible surface area of macrotubes pressed into free-standing films was determined from electrochemical impedance spectroscopy. Potential for catalysis was assessed from hydrogen adsorption and desorption in 0.5 M H₂SO₄ using cyclic voltammetry. Salt templates offer a synthesis route to achieve a range of porous metal and metal alloy structures for catalytic, sensing, and energy applications.