Symposium SM13—Advances in Membrane and Water Treatment Materials for Sustainable Environmental Remediation

Oily wastewater generated by industries such as crude oil production, oil refining, and metal manufacturing, can cause major environmental issues, and affect human health [1]. In oily wastewater, oils are classified into two types, a mixture of oil/water, and oil-in-water
emulsion. The later has stable microdroplets smaller than 20 µm with complex wetting behavior [2]. The separation of oil-in-water emulsions has become an extremely important for both environmentally and industrial related applications. Various traditional methods have been used to separate oils [3,4,5]. Herein, a graphene-based sponge (rGO@MF) was developed and utilized for separating various heavy oil-in-water emulsions as well as oil/water mixtures [6]. The superhydrophobic sponge was engineered through facile surface-treatment and hydrothermal steps. The commercially available MF sponges were initially surface treated and subsequently coated with rGO sheets. The surface and structural properties of the rGO@MF sponge and the nanoemulsions were thoroughly characterized by advanced techniques. The high-resolution SEM and EDX mapping confirmed the homogeneous distribution of rGO sheets surrounding the fibers. The developed rGO@MF sponge showed excellent chemical stability and durability. Five different oils and organic solvents with high concentration (up to 30 g/l) were tested. We aimed to formulate stable and different sized emulsions to explore and study in detail the correlation between the oil type, droplet size and concentration of oil/water mixtures and emulsions, and the rGO@MF adsorption capacity and removal efficiency. The developed superhydrophobic rGO@MF sponge showed water contact angle of ~164 and exhibited superior adsorption capacity and removal efficiency of up to 5647 mg/g and 95 ± 3% respectively, for crude oil-in-water emulsions of 30 g/l. In addition, the rGO@MF sponge maintained its high separation performance over ten consecutive adsorption cycles. The adsorption capacity of the rGO@MF sponge maintained up to 92% of its initial values after ten cycles. The calculated activated adsorption energy for crude oil-in-water emulsion on rGO@MF sponge was 16.59 kJ mol^{- 1} indicating a physical adsorption process. The adsorption kinetics and interactions were carefully explored and a general mechanism of separation for both oil-in-water nanoemulsions and oil/water mixtures was introduced.

References

[1] B. Dubansky, A. Whitehead, T. Miller, C. D. Rice, F. Galvez, Multitissue Molecular, Genomic, and Developmental Effect of the Deep water Horizon Oil Spill on Resident Gulf Killifish (Fundulus grandis), Environ. Sci. Technol. (2013): 5074-5082.
[2] A. Gupta, H. B. Eral, T. A. Hatton, P. S. Doyle, Nanoemulsions: Formation, properties and applications, Soft Matter. 12 (2016) 2826–2841.
[3] J. Saththasivam, K. Loganathan, S. Sarp, An overview of oil-water separation using gas flotation systems, Chemosphere. 144 (2016) 671–680.
[4] J. Huang, Z. Yan, Adsorption Mechanism of Oil by Resilient Graphene Aerogels from Oil-Water Emulsion, Langmuir. 34 (2018) 1890–1898.
[5] S.V. Thakkar, A. Pinna, C.M. Carbonaro, L. Malfatti, P. Guardia, A. Cabot, M.F. Casula, Performance of oil sorbents based on reduced graphene oxide-silica composite aerogels, J. Environ. Chem. Eng. 8 (2020) 103632.
[6] R. M. G. Ahmed, B. Anis, A. S. G. Khalil. "Facile surface treatment and decoration of graphene-based 3D polymeric sponges for high performance separation of heavy oil-in-water emulsions." Journal of Environmental Chemical Engineering: 9 (2021) 105087.

Recently, oil-contaminated wastewater treatment has become a research hotspot for both the scientific community and the industry due to the potential disastrous impact of oily wastewater on environment and human health. Huge volumes of stable oil/water emulsions are usually produced from a variety of industries such as oil and natural gas exploration and processing, metallurgical, petrochemical, pharmaceutical, and food industries [1]. Several previously reported techniques are widely used for separation of oil/water mixtures, which involve gravity separation, dissolved air flotation, solvent extraction, coagulation, biodegradation and adsorption [2]. However, these conventional methods have their own drawbacks, such as, high cost, using toxic compounds, large space for installation and generation of secondary pollutants [3]. Membrane separation technology, in particularly, ultrafiltration (UF), has attracted attention as an effective approach for removing dispersed oil droplets smaller than ~10 µm in emulsions. However, membrane fouling is regarded as the key challenge for membrane-based separation processes that results from deposition of oil droplets/aggregates on membrane surface or inside membrane pores causing a severe flux decline
Here, we present the separation performance of isotropic PES membrane that has been successfully developed via VIPS, for different high concentration oil-in-water nanoemulsions [4,5]. Detailed comparison with the well-developed anisotropic membrane was carried out. The as-prepared membranes were analyzed with respect to surface morphology, surface roughness, pore size, overall porosity, water uptake, underwater oil contact angle (UOCA) and surface wettability. The membrane separation performances were evaluated in terms of water permeance, oil separation efficiency, antifouling performance, and cyclic reusability. Remarkably improved surface hydrophilicity for isotropic PES membrane (contact angle, CA=39°) compared to anisotropic PES membrane (CA=70°), resulting in superior pure water permeance, attaining 4721 L/h.m².bar at operating pressure of 0.5 bar. The isotropic PES membrane achieved superior crude oil-in-water nanoemulsion separation (permeance of 713 L/h.m².bar and 100 % rejection) at oil concentration of 1 g/L. At extremely high oil concentration of 50 g/L, the PES membrane was not completely fouled and showed permeance of 65 L/h.m².bar and 98.2% rejection. Moreover, the flux recovery of the fouled isotropic PES membrane exceeded 59.5% over three subsequent cycles of filtration and back-washing with water. Overall, this study might provide substantial guidance for large-scale manufacturing and application of isotropic PES membrane in treating oil-in-water nanoemulsion under harsh conditions.

Keywords: Isotropic PES membrane, oil-water emulsion separation, super permeance, fouling mitigation

References
[1] T. Sirivedhin, L. Dallbauman, Organic matrix in produced water from the Osage-Skiatook Petroleum Environmental Research site, Osage county, Oklahoma, Chemosphere 57 (2004) 463–469.
[2] S. Jamaly, A. Giwa, S.W. Hasan, Recent improvements in oily wastewater treatment: Progress, challenges, and future opportunities, Int. J. Environ. Sci. 37 (2015) 15–30.
[3] G. Crini, E. Lichtfouse, Advantages and disadvantages of techniques used for wastewater treatment, Environ. Chem. Lett. 17 (2019) 145–155.
[4] Abdel-Aty, A. A., Aziz, Y. S. A., Ahmed, R. M., ElSherbiny, I. M., Panglisch, S., Ulbricht, M., & Khalil, A. S. G. (2020). High performance isotropic polyethersulfone membranes for heavy oil-in-water emulsion separation. Separation and Purification Technology, 253, 117467.
[5] Elrouby, A. A., Ali, A. S., Abdel-Aty, A. A., Abu-Elnaga, A. M., & Khalil, A. S. (2020, November). Low-Cost Production of 3D Printed Lab-on Chip (LOC) Device for Oil-in-Water Emulsion Separation. In 2020 27th IEEE International Conference on Electronics, Circuits and Systems (ICECS) (pp. 1-4).

Polyetherimide (PEI) is a membrane forming material with excellent chemical and mechanical stability. Nevertheless, further chemical modification might be demanded by the designated application. The hydrophobic nature of PEI could cause adsorption of solutes if the material is used in aqueous environments, whereas application in organic solvents may necessitate further stabilization via cross-linking [1]. In these cases PEI has the additional advantage that a ring-opening at the imide groups in the polymer backbone using suitable nucleophiles allows for chemical modification, a strategy that has been widely explored as a method for post-functionalization of PEI membranes and particles. The reaction with water soluble diamines can result in cross-linking via formation of amide or imine groups. An excess of diamine would drive the reaction towards a non-crosslinked state, while also hydrolysis could occur if the pH exceeds a certain value[2]. Also, the chain-length and stiffness of the diamine is likely to have an effect.
Here, we use ultrathin films (1-2 nm) at the air-water interface to investigate the chemical functionalization of PEI surfaces. In contrast to thicker films or bulk materials, where the majority of molecules is not accessible for chemical reactions, nearly all imide groups can be converted in ultrathin films, making them especially sensitive tools to study the effects of post-functionalization.

By means of interfacial rheology, we determine the optimal conditions for cross-linking of PEI, together with surface potential measurements to detect the formation of a positively or negatively charged groups in consequence of either partial hydrolysis or protonation of free amine groups. We further evaluate the effects of catalytic strategies for amine bonding based on carbodiimides or Lewis acids, and investigate whether tetrafunctional amines result in a better cross-linking than bifunctional ones. The outcome of the chemical modifications is further investigated using IR and/or Raman spectroscopy. In addition, we evaluate the influence of the chemical treatments on the Young’s modulus of the modified PEI and determine the molecular arrangement of the chains by atomic force and electron microscopy.

The ultrathin PEI films presented here are not only of interest as model systems for the surfaces of PEI membranes, but also as present stable thin films with can be functionalized and transferred onto almost any substrate.

References

[1] K. Vanherck, A. Cano-Odena, G. Koeckelberghs, T. Dedroog and I. Vankelecom, J. Membr. Sci. 353 (1), 135-143 (2010).
[2] S. Basu, M. Heuchel, T. Weigel, K. Kratz and A. Lendlein, Polymers for Advanced Technologies 26 (12), 1447-1455 (2015).

The accumulation of micro-pollutants such as pesticides and pharmaceuticals in water supplies is of growing concern to public health, as these compounds can bioaccumulate, causing potential health issues as well as being resistant to the methods of wastewater treatment currently employed. Photocatalysis shows promise as a potential solution to this problem but is currently hindered in two main ways:. Photocatalytic slurries require downstream separation or can pose a risk to health themselves, while supported photocatalysts suffer from low exposed surface areas and efficiencies as well as potential leaching, again potentially posing a health risk.
In this work, we present a novel ZnO photocatalytic foam. Briefly, the synthesis is a modification to abased on sol gel synthesis of ZnO, incorporating direct aeration during gel formation followed by high temperature sintering (900 ^oC, 12 hrs) to form a highly porous yet mechanically stable ZnO structure in as macroscale foam monoliths (20 mm in height and diameter) without the use of foaming agents nor supercritical drying. These “monoliths or “molecular foams”” were then used in the photocatalytic degradation of carbamazepine as a target pollutant in both batch and recirculating systems. This novel work solves both issues traditionally associated with photocatalysts, as the highly porous nature of the monoliths allows for a high surface area of catalyst to be used, similar to a slurry, while the removal of a support and having a structure of ZnO only, means that there are no binding interactions between catalyst and support, removing the risk of leaching entirely.
These foamsmonoliths were characterised as pure wurtzite ZnO and highly crystalline in nature as well as showing high porosity (90 %), measured using an Archimedes method, and a hierarchical structure, which showed promise for the degradation of target pollutants. FE-SEM micrographs of the foams show a structure consisting of both large channels and smaller pores, allowing for both flow through the foamsmonoliths and a reactive surface for degradation to occur at. Initial photocatalytic tests in the batch system showed 55 % degradation after 4 hours and a kinetic constant of 3.3 X 10^-3 min^-1 using 0.5 g L^-1 loading of foam catalyst. The batch kinetics of the foam system shows promise, as it they are is higher than literature values for immobilised catalysts, but still lower than those reported for slurry systems. and the next goal of the project is to demonstrate kinetics that are comparable to slurries. Building upon this, further studies were conducted, applying foams in a recirculating batch system where an increase in photocatalytic activityies, of both removal and kinetic constant, was observed. This is attributed , as when applied in this mannerto a fuller use of the as flow of solution through the foam takes advantage of the highly porous and hierarchical structure of the foams, allowing for greater utilisation of the photocatalyst as well as greater mass transfer of the pollutant to the catalyst surface.
These results show promise for the potential application of photocatalytic foam structures as a tertiary treatment step n addition to traditionalin wastewater treatment, for the removal of currently persistent micropollutants. The proposed 3D structure combines the advantages of slurries and immobilised catalysts while simultaneously addressing drawbacks.

Nowadays various methods and technological process are conventionally employed for water treatment and filtration, attempting to contrast the pollution of chemicals, particles and emerging contaminants (i.e. microplastics, industrial residue, oil, pharmaceutical components..). Generally all the processes proposed for water treatment require multistep protocols and the use of expensive device. Over the last decade, a wide range of functional materials have been investigated to separate multiphase liquids and immiscible mixtures, electrochemical catalysts, photocatalysts, reactive and nanomaterials have been recently successful tested for water treatment. Good results in terms of efficiency in separating oil/water mixtures have been obtained using polymeric functionalized membranes but big restrictions still remain unsolved. Different technological methods of microfabrication (two-photon polimerization, soft interference lithography, replica molding and self-folding polymers) have been used but, chemical-physical pre-treatments are often required to gain the desired final properties. To avoid this problem a number of methods have been developed for the fabrication of polymer films, such as solution casting method, interfacial methods, layer-by layer technique or solvent evaporation method. Unfortunately, all this techniques still require special equipment and have severe limitations with respect to the substrate size as well as film quality, stability and, moreover, until now the self-assembling of thin polymeric film into complex 3D structures remains problem. Actually there is a growing interest in competitive candidates methods for membrane technology with the following properties: large area coverage, high structural flexibility, low temperature processing, especially low cost, formation in situ and three-dimensional shaping. Here we describe a water-based bottom-up approach in which we let a biopolymer self-assemble with unprecedented degree of freedom over the water surface. Being a liquid, water can assume flexible shapes taking on the form of its container and, as a direct consequence, the polymer, dispensed over the water using the method described, could self-assemble into different geometries generating thin polymeric films following the existent water profile in a very direct and simple way.The membranes are formed in-situ, directly in the place of interest without the need of handling thin membranes and the subsequent risk of deforming and damaging them. The polymer film could be the external container of a liquid core or a free standing layer with personalized design. The membranes produced encasing water have been characterized in terms of physical properties and morphology. The quick liquid packaging approach could be used to lay a film over micropillars, organic and inorganic micro-objects and colloidal particles. With the same technology it is possible to create also millimetre membrane accommodating the area of interest. The packaging process is described in details reporting, for the first time, the real time characterization of the membrane formation in static and dynamic condition, while various application are proposed. We believe that the proposed technology could be further improved in the future also for selective adsorption of pollutants, filtering and liquid separation moreover, being the polymer used a biodegradable one we foresee application of biocompatibility.

1. Yulaev, A. Lipatov, A. X. Lu, A. Sinitskii, M. S. Leite, A. Kolmakov, Adv. Mater. Interfaces 4, 1600734 (2016).
2. Wickman, H. H. and Korley, J. N. Nature 393, 445–447 (1998).
3. Coppola S. et al. Science Advances 5, eaat5189 DOI: 10.1126/sciadv.aat5189 (2019)

Thin-film is one of the important components in material world. From semiconductor layer detection to water membrane measurement, quantitative thickness mapping for thin-film has been a widely studied issue in the past decade. However, with the development of imaging technology, single-point measurement of film thickness has been unable to meet the changing scientific requirements. Full-field visualizing and characterizing for thin-film evolution is taking place as a principal tool for related study, which can provide effective data support for membrane science, polymer chemistry, biomaterials, applied Chemistry, etc. In this paper, we show that digital holographic thickness mapping could be a powerful solution to reveal the full-field drainage of thin liquid film. Digital holography (DH) is an interference imaging technology, it has possibility to achieve requisite spatial and temporal resolution for evolution measurement of transparent and translucent materials. In our study, DH has been performed to reveal the thickness mapping of soap films when moving inside a cylindrical metal tube.Herein, customized tubes with different customized radius were used to generate and hold flat thin soap films. The thin-film is formed inside the tube by immersion. The drainage with different air pumping rates is analyzed. In the recording geometry, the tube is placed vertically, then the object beam of DH passes through the film when the film is moved from the middle of the tube to the top. The object beam will carry full-field thickness information and meet the reference beam on the screen of the camera. Finally, the hologram of related thickness distribution will be created by interference. The film will start to drainage and create multiple fingerings due to Marangoni flows around the edges of the film once it moves inside the tube. Thanks to DH, the full-field evolution process of film thickness will be continuously recorded, so we can quantitatively analyze all features of the film surface, by means of a-posteriori holographic numerical reconstruction. In this case, the relationship between film thickness features with motion speed and tube diameter was studied, this will allows revealing the Marangoni flow formation process in the flat film. In order to obtain highly continuous full-field thickness evolution data, we also proposed a 4D phase unwrapping algorithm based on time series in holographic numerical reconstruction. Comparing with the conventional phase unwrapping algorithm, the new approach utilizes the phase change of the same points in the field of view under a long-time sequence to achieve phase tracking, then the accurate phase unwrapping is achieved. Once supported by the large number of continuous experimental records, 4D phase unwrapping allow us to obtain no phase-jump full-field phase distribution, which is the key to perform quantitative holographic thickness mapping with nanometer precision. In this paper, thanks to the customized thin-film generator and 4D holographic thickness extraction algorithm, the drainage process of the flat film during pumping uplift is quantitatively revealed. A series of space-time drainage modes are made to show the thinning process of the soap films, based on holographic thickness mapping. The results show that DH is a reliable and powerful tool that can effectively reveal the full-field thickness variation of thin liquid film under different conditions.

Introduction
Electro-thermal (ET) membranes based on the joule heating concept were developed for evaporation and membrane distillation applications. This approach is novel since voltage is applied to a porous thin-film carbon nanotube (CNT)/polymer composite membrane, creating a localized heating effect within the bulk of the membrane, allowing vapour pressure difference to occur and flux of fresh water to permeate. We investigated the effect of joule heating in ionizable environments such as high-salinity brines through the use of a novel class of freestanding MWCNT/PVDF composites within an ET setup.
Methods
CNT/PVDF membranes were fabricated using a tape casting method, as illustrated in figure 1. This method requires low energy and is scalable.

Figure 1 – Fabrication of freestanding CNT/PVDF membranes using tape casing method, different concentrations percentages of CNT were used to test their joule heating behaviour.
Evaporation experiments were performed to provide supplementary understandings for electrothermal powered MD, as illustrated in figure 2.
Figure 2 – Electrothermal evaporation setup incorporating different membrane compositions.
Results
The results show the high temperatures achievable in response to current passage through the in-lab developed CNT/PVDF composite sheets. Moreover, the thermoelectric effect only resulted in fresh water flux when A.C. voltage was applied.
Figure 3 – The temperature response for the CNT composite sheets under different applied voltages, and the performance of the thermoelectric sheets under different D.C. and A.C. voltages.
Discussion
A big challenge was given by the ionisable nature of the saline water, but was overcome by performing A.C. voltage experiments, which have likely prevented concentration polarization effects and limited both the side reactions and electrode degradation. The ET technology presents a great filtration ability to purify different types of feed streams such as high salinity water, brines and brackish water, and calls for the need for further developments.

Membrane based water purification processes are of enormous importance in water and wastewater treatment due to their scalability, reliability, energy efficiency, and high effluent quality. Fouling, defined by performance loss due to the adsorption and accumulation of feed components on the membrane surface, is likely the most important obstacle to broader use of membranes in these applications. Zwitterions, moieties with equal numbers of positive & negative electrostatic charges, strongly resist the adsorption of biomacromolecules due to their high degree of hydration. This unique characteristic of zwitterions makes them a promising candidate to be incorporated into membranes to restrict fouling. Linear random copolymers of zwitterionic segments and non-zwitterionic (hydrophobic) segments have recently been shown to be extremely promising materials for membrane selective layers that combine exceptional fouling resistance, narrow pore size distribution, and high water permeability. These copolymers self-assemble to form a bicontinuous zwitterionic network with an approximate ∼1.5 nm interconnected domains, held together by a hydrophobic phase. While this pore size is intriguing for a variety of wastewater treatment applications, there is a need for a novel, fast, scalable, and versatile approach to tune the effective pore size of these zwitterionic membranes while retaining their fouling resistance and water permeability. This approach needs to be fast and efficient enough to be integrated into roll-to-roll manufacturing techniques. In this current work, we introduce the first use of thiol-ene click chemistry to tune the effective pore size of self-assembled membranes, leading to the formation of robust membranes with high flux, divalent ion rejection, and fouling resistance. The use of click chemistry allows significant changes in effective pore size, measured through the rejection of both organic solutes and salts, in a matter of seconds, with 40 seconds of cross-linking leading to the doubling of riboflavin rejection. These highly cross-linked membranes also combine high divalent salt rejection (e.g. 80% Na₂SO₄ rejection) whereas the monovalent salt rejection was fairly low (e.g. 28% NaCl rejection). The pore size can be easily tuned by simply changing the crosslinking time, hence the selectivity of these membranes are easily tunable for various membrane selectivity. This unique crosslinking technique can be beneficial for tunable separation properties to address specific processes in bio-separations as well as water and wastewater treatment.

The self-assembly of block polymers into microphase-separated domains provides exciting opportunities for the design of high-performance membranes. In this talk, two block-polymer-based membrane systems will be discussed. In the first, we used a co-casting strategy to rapidly and scalably synthesize membranes that exploit the disordered morphology of block polymers. The polymer in our demonstration contained an etchable poly(lactide) block and a copolymer block comprising poly(methyl methyacrylate-stat-styrene), with the polymer chemistry tuned to enable an accessible order-disorder transition temperature (T_ODT). Rapid thermal quenching from the disordered state kinetically trapped this bicontinuous morphology, with subsequent etching enabling continuous, tortuous pores without need for channel alignment. We employed a co-casting approach wherein a thin block polymer/solvent layer was coated atop a polysulfone/solvent layer. Rapid drying followed by immersion in non-solvent (water) created composite membranes with discrete layers. Competitive water permeances along with sharp molecular-weight cut-offs were achieved. In the second system, we explore the synthesis of polymeric microcapsules as a proof of concept for dispersible facilitated transport membranes, particularly serving as robust analogs of emulsion liquid membranes. The microcapsules were fabricated using a double-emulsion technique and comprised a commercial poly(styrene)-block-poly(butadiene)-block-poly(styrene) as a diffusive matrix for facilitated transport, in which a copper-selective small-molecule ligand was dissolved. The ligand allowed for selective uptake of copper ions, which were transported into inner acid-containing, aqueous compartments in exchange for protons. Furthermore, the microcapsule approach allows for simple packing into columns to enable simple cycling of extraction and stripping steps. The two systems are both promising demonstrations of block polymer membranes for practical aqueous separations.

Oil and water separation and treatment are significant for the oil and gas industry, including clean-up. The preparation of filter formats or coatings has been used to improve the efficiency of the process. We will focus on using new high-performance thermoset and nanocomposite materials for both coatings and 3D printing format in this talk. Polybenzoxazine chemistry and polymerization have enjoyed tremendous growth due to its versatility in chemistry. Several advantages in properties for high-temperature applications compared to epoxy, PU, PF, resins. We report on the preparation of nanostructured polybenzoxazine (PBZ) nanocomposites prepared with nano clay, nano-silica, and graphene to obtain very robust and superhydrophobic coatings that have resulted in efficient anti-corrosion properties and oil-water separators, including anti-icing properties. The monomers are prepared by simpler chemistry enabling additives and other preparation protocols that lead to robust coatings. The addition of telechelic polybutadiene and polyaniline as part of the interpenetrating network (IPN) and semi-interpenetrating network (SIPN) composition results in robust and very conformal coating compositions. Excellent adhesion properties to substrates even at higher temperature (HT) operations may enable these materials to be applied in more demanding conditions. Nanostructured and nanocellulose materials have also been used to produce highly efficient oil-water separators based on the superhydrophobic and super oleophilic properties of coated filters. In another aspect of high-performance materials, we have demonstrated the use of 3D printing to create membranes and oil soaking objects that can be used for clean-up based on elastomeric silicone materials. Lastly, we demonstrate the use of 3D printing of superhydrophobic structures to demonstrate controlled wetting behavior.

Contamination of groundwater by organic compounds, heavy metals, and chlorinated compounds is a current environmental issue. In-situ remediation techniques that use adsorptive materials have recently been developed for more sustainable treatment of contaminated aquifers. Biochars (BCs) are a biomass-derived black carbon with a highly ordered, interconnected networks of micropores, mesopores, and macropores, which is an economical substitute for conventional adsorbents. In this work, we studied the physical and chemical modification processes of the BCs on their surface area, adsorptive capacity, and surface functional groups. We focused on investigating BCs made from three different shell-type biomasses: walnut shells, pecan shells, and peanut shells. The BCs were produced through pyrolysis process at varied temperatures in the range between 500 °C and 900 °C in an inert gas environment. To tailor the physical and chemical properties of the BCs, the pre-pyrolysis processes and post-pyrolysis techniques (e.g., base treatment and acid activation) were employed. The different BCs were used and assessed for effective remediation of toxic pollutants (i.e., trichloroethylene (TCE), and perchloroethylene (PCE)) from water. The unmodified and modified BCs were compared in terms of microstructures and surface states as well as TCE and PCE adsorptive capacity in this study.
The materials were physically and chemically characterized using various tools. Scanning electron microscopy (SEM) characterization showed different porous surface morphologies of various BCs. The surface hydrophilicity of the different types of BCs were characterized by a sessile test, which was correlated with surface functional groups analyzed by Fourier transform infrared spectroscopy (FT-IR). The pyrolysis process of BCs has been fully understood with thermogravimetric analysis (TGA). The results of this work can advance the understanding of different modification effects on BCs’ properties, aiming at the wide adoption of cost-effective and eco-friendly adsorbents.

According to several recent reports from the United Nations, WHO, and UNICEF, water contamination is a prevalent issue around the world that needs to be addressed. The current water treatment methods, specifically the primary and secondary treatments, are very good at removing large scale waste but fail at removing some microcontaminants and emerging pharmaceutical water contaminants. Developing novel materials for adsorption to complement the filtration of granular materials in the tertiary treatment step of water processing is a promising way to resolve this issue. Nanocellulose is a strong candidate for a filtration material due to its high surface area, zeta potential, and capability for functionalization. It is an excellent adsorbent for dyes, metals, and other organic molecules. Here, we will demonstrate the high potential of cellulose-based materials as an adsorbent for conventional contaminants, as well as emerging microcontaminants, such as opioids. In the case of amine compounds, through adsorption testing we have recently shown that sulfonated cellulose membranes have high adsorption capacity (i.e. 68.56 mg/g). These membranes are fabricated via a two-step process, first sulfonated the cellulose and then crosslinked with chitosan for mechanical stability. We will also discuss the opportunities for using agricultural cellulose waste streams like rice husks and sugarcane bagasse for producing these filters. Scanning electron microscopy demonstrated degradation of the cellulose surfaces after sulfonation, and a reorganization of the cellulose layers when crosslinked with chitosan. Through Fourier transform infrared spectroscopy it was determined that there were chemical changes through the oxidation and sulfonation steps. The maximum concentration of sulfonate groups was determined to be 194.4 mmol/g using a conductometric titration method. The thermal stability of the cellulose membranes was demonstrated through TGA, showing an extrapolated onset temperature of 281°C. The adsorptive capabilities of these membranes, tested through kinetic and isothermal models, will be presented. Finally, a performance comparison between activated carbon and these cellulose membranes will be performed.

Water scarcity is a growing concern across the globe.^1,2 It is imperative that communities develop and implement energy efficient technologies to treat water contaminated by industrial activity, human waste, or harmful microorganisms. Current best methods, such as advanced oxidative processes (AOPs), can be highly effective against targeted contaminants, but often require chemical additives (e.g. chlorine, peroxide, ozone) which increase costs and may lead to the formation of undesirable disinfection byproducts.^3,4 The use of immobilized photocatalysts with strong light absorption, chemical stability, and high surface area could greatly reduce the need for oxidant feedstocks and improve the affordability of UV-AOPs.

Here, we report on the fabrication and characterization titania-based photocatalysts immobilized on quartz-fiber felt for UV-driven water treatment. Our supported titania is mesoporous which, combined with the macroporous (Φ >0.95) fiber, yields a high surface area beneficial for mass transport. By using quartz fibers, we maximize the optical path length of UV (250 – 400 nm) light through our system. Our titania may also be loaded with Au nanoparticles to increase the generation of reactive oxygen species (ROS) and provide alternative reaction pathways for degrading contaminants. We propose a cost/benefit breakdown for the addition of Au in our photocatalytic system.

We test the long-term (>24 hours) stability and efficacy of our fiber-supported photocatalysts to degrade model contaminants under illumination from both UV-A LEDs and germicidal UV-C lamps. Our immobilized photocatalysts produce >100 μM *OH in 20 seconds in a flow reactor and achieve an Electrical Energy per Order (EE_O) of <0.6 for the degradation of Rhodamine B. We also examine the impact of water quality (pH, TOC, scavengers) and propose mechanisms for pollutant breakdown. Lastly, we will discuss the reactor design and relevant transport conditions for our supported photocatalysts, and the improvements necessary to scale our material for practical applications.

1. Liu, et al. Environ. Sci. Technol. 2016, 50, 17, 9736–9745.
2. Stefan, Mihaela I. (Ed.) Advanced Oxidation Processes for Water Treatment: Fundamentals and Applications. London: IWA Publishing, 2019.
3. Richardson, et al. Environ. Sci. Technol. 1996, 30, 3327-3334.
4. Mian, et al. Water Research. 2018, 147, 112-131.

Sustainable water treatment materials can be derived from carbon-rich agro-industrial wastes through thermal treatment and physical activation, thus shifting away from traditional disposal – landfilling or composting. Cherry pits are an abundant carbon-rich waste biomass in the Great Lakes region and represent a viable feedstock for conversion to biochars and activated biochars for soil amendments and heavy metal adsorbents. These sustainable materials have the potential to remediate local water quality issues including the hazardous eutrophication of the Great Lakes and heavy metal contamination of the region’s drinking water. In this work, slow pyrolysis was used to convert waste cherry pits to biochars (1 hour at peak temperatures of 450 and 600°C) and activated biochars (1 hour at peak temperatures of 800 and 900°C). Biochars produced have surface areas between 206 and 274 m²/g and increased bioavailability of Fe, K, Mg, Mn, and P. The biochars can be implemented as soil amendments to reduce nutrient run-off and serve as a valuable carbon sink (biochars contain 74-79% carbon), potentially mitigating harmful algal blooms in the Great Lakes. The CO₂-activated biochars exhibited selective metal adsorption of As, Cu, Pb, and Zn from simulated contaminated drinking water. Physical activation increased the metal adsorption capacity by 2.8 and 4.2 times for the biochars activated at 800 and 900°C, respectively. The increased capacity is attributed to high surface areas (up to 629 m²/g) and a hydrophilic surface (confirmed via FTIR functional group analysis). Through sustainable waste-to-byproduct valorization we convert this waste food biomass into biochar for use as a soil amendment and into activated biochars to remove metals from drinking water, thus alleviating economic issues associated with cherry pit waste handling and reducing the environmental impact of the cherry processing industry.

Atomically thin graphene with a high-density of precise subnanometer pores represents the idealmembrane for ionic and molecular separations. However, a single large-nanopore can severely compromisemembrane performance and differential etching between pre-existing defects/grain boundaries in grapheneand pristine regions presents fundamental limitations. Here, we show for the first time that size-selectiveinterfacial polymerization after high-density nanopore formation in graphene not only seals larger defects (>0.5nm) and macroscopic tears but also successfully preserves the smaller subnanometer pores. Low-temperaturegrowth followed by mild UV/ozone oxidation allows for facile and scalable formation of high-density (4–5.5 ×10^12 / cm^2) useful subnanometer pores in the graphene lattice. We demonstrate scalable synthesis of fullyfunctional centimeter-scale nanoporous atomically thin membranes (NATMs) with water (∼0.28 nm)permeance ∼23× higher than commercially available membranes and excellent rejection to salt ions (∼0.66nm, >97% rejection) as well as small organic molecules (∼0.7–1.5 nm, ∼100% rejection) under forward osmosis.

Cheng et al. Nano Lett. 2020
Cheng et al. Nanoscale. 2021
Kidambi et al. Adv. Mat. 2018
Kidambi et al. Adv. Mat. 2018
Kidambi et al. ACS App. Mat. Int. 2018
Kidambi et al. Adv. Mat. 2017
Kidambi et al. Adv. Mat. 2017
Kidambi et al. Nanoscale 2017

Over the recent years, zinc oxide (ZnO) nanostructures have gained remarkable attention in the field of semiconductor photocatalysis for water treatment applications. In our previous work, we demonstrated that ZnO nanostructures can be produced in a simple, cost-effective, and environmentally-friendly manner by the method of hot water treatment (HWT) and the nanostructures produced by this method can be used to degrade organic pollutants via photocatalysis. In this work, we investigate how the photocatalytic degradation is affected by changing the amount of the HWT ZnO nanostructure photocatalyst and the concentration of the organic pollutant. The ZnO nanostructure suspension was made by the HWT of zinc plates in DI water at 75°C for 5 hours. Since the ZnO nanostructures are released into the water as a result of the HWT of the Zn plates, our ZnO nanostructures are in the form of a suspension in water. In order to change the amount of photocatalyst, we changed the volume of the ZnO nanostructure suspension being added. We used 10 ml, 25 ml, and 50 ml of the ZnO nanostructure suspension, added it to methylene blue (MB) at an initial concentration of 2.5 ppm and exposed the mixture to UV light for 4 hours. We observed that 25 ml of the ZnO nanostructure suspension gave the maximum degradation of MB (~65%). When we used 50 ml, the degradation percentage decreased to about 45%. This might be due to increase in turbidity of the mixture, which can lead to a decrease in the penetration of UV light. We then used 25 ml of the ZnO nanostructure suspension and conducted MB degradation tests at 4 different initial concentrations of MB. Maximum MB degradation was at 1 ppm (~84%) and minimum at 10 ppm (~18%). This decrease in MB degradation can be due to the decrease in UV light being absorbed by the photocatalyst as more and more MB molecules get adsorbed to the photocatalyst surface. As a preliminary study, we also did HWT of Zn plates in tap water instead of DI water. We were able to form ZnO suspension in tap water too, and we observed ~47% degradation of MB during photocatalytic degradation experiment. This is an encouraging result as the use of tap water instead of DI water can further bring down the cost and increase the scalability of nanostructure fabrication by HWT.

Graphene oxide (GO) is considered to have great potential for chemical separation applications due to its unique properties of enhanced 2-D nanofluidic and the ability to control interlayers spacing for size-based chemical selectivity. A GO membrane with highly aligned GO grains was fabricated through a slip casting process and studied for alcohol-water separation application. We found the pressure-driven permeance of water, MeOH and IPA through 5 µm thick GO membranes to be 0.4, 0.12 and 0.8 LMH/Bar (L/m²-hr-Bar) respectively consistent with literature examples without defects that had given erroneously high flows. Interestingly, the permeance of alcohol-water mixture was found to be dramatically lower (~ 0.01 LMH/Bar) than any of its individual components. Such a mixture of solvents does not permanently affect the GO membrane, as the permeance of pure solvent was recovered to its original level upon removal of alcohol-water solvent mixture. The drop in transmembrane flux was also observed in osmotic tests when alcohol-water solvent mixture was in the feed solution side of the membrane. The osmotic tests showed the selectivity of water over alcohol through GO membrane and rejection of salt. The interlayer space of a dried GO membrane was found to be 8.52 Å which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. When water saturated GO membranes were exposed to MeOH, a 2 Å decrease in interlayer spacing of GO membrane was seen suggesting the removal of OH groups from GO. Such phenomenon was accompanied by a color change of the membrane at the same time. Permeation was recovered with exposure to oxidants (H2O2). These observations support a newly proposed mechanism of a partial reduction of GO through a catalytic reaction with alcohol-water mixtures.

Titanium dioxide (TiO₂) is one of the well-studied materials for applications in photocatalysis. Various forms of TiO₂, such as commercially available Aeroxide® P25, nanowires, phase-pure Anatase crystals, and phase-pure Rutile crystals have been explored for photocatalysis. The capability of TiO₂ in generating reactive oxygen species (ROS) when exposed to ultraviolet (UV) light has been extensively utilized for both removing contaminants (e.g. dyes) from water and disinfecting water. Here, the high specific surface area obtained when TiO₂ is made in nanocrystalline form (nanoparticles and nanowires) aids in engineering both the efficiencies and the kinetics of the water remediation processes. However, one of the major hurdles in the widespread use of photocatalysis for water remediation is the need to extensively pre-process and post-process the source water and the treated water, respectively for making the source water transparent to light and for the recovery of the TiO₂ photocatalyst. This makes it tedious to employ photocatalysis, unlike processes such as chlorination. In this work, we present a few strategies useful for overcoming the above-mentioned bottlenecks. Flow pattern changes, photocatalyst morphology alterations, and surface chemical compositional changes in a TiO₂ nanowire-based photocatalyst have been employed to make the photocatalysis process useful for treating any kind of water with minimal post-processing. These strategies will be discussed in detail in this talk. The steps involved in implementing these strategies in a bench-scale setup capable of continuously disinfecting 3 gallons of water per minute will also be discussed. The central ideal here is that making photocatalysis easy to implement and effective makes it employable at any stage in the train of technologies used for treating water.

Biochar is a carbonaceous solid commonly referred to as charcoal which results from the pyrolysis of organic matter. These materials are important domestic and industrial adsorbents due to their rich surface chemistry, large micropore volume, and high specific surface area. Recent research indicates that biochar can remove both organic and inorganic contaminants from gas and liquid streams. Careful biomass pyrolysis can lead to structures with the right combination of surface morphology and chemistry to adsorb specific adsorbates. However, biochar morphology and function are both inextricably linked to the pyrolysis conditions and the biomass source. Adsorption methodology has a large effect on the adsorption behavior of high surface area materials which hinders reproducibility. Therefore, a design of experiments was created to attempt to determine ideal conditions for maximum contaminant uptake. Experimental designs for three biochar-contaminant mixing methods, the orbital shaker, rotational mixer, and resonant acoustic mixer (RAM), were formed, with three variable factors being taken into consideration for each: biochar mass, length of mixing time, and intensity of mixing. High, middle range, and low values for each factor were combined to create the matrix for each mixing method. Similar adsorption behavior is noted for the three methods with the time required for maximum adsorption being considerably different between the three methods.

Solar-powered water evaporation provides a means for sustainable seawater desalination and water purification technologies. Advanced material and structural designs of the evaporative materials are essential for efficient freshwater production. Here we will present our representative works on rational design and molecular engineering of hydrogels and their applications in solar-powered water purification. We designed hybrid hydrogels composed of a hydrophilic polymer framework and solar absorption materials to harvest solar energy and remove contaminants. By tuning the micro/nanostructures and chemical/physical interactions between components, the hybrid gels exhibit attractive synergistic characteristics including high solar absorption, reduced energy consumption for water evaporation, fast water transport, effective thermal management and antifouling property. The highly hydratable polymer networks can be architected to tune the water state, activating water molecules and facilitating water evaporation. The hydrogel evaporator with topology-controlled hydration behavior is also designed to achieve water and heat management simultaneously. These works provide fundamental design principles regarding material selection, molecular engineering and structural modification of these emerging hydrogels for the development of next-generation solar evaporators for seawater desalination and water purification.

Graphene oxide (GO) has emerged as an efficient adsorbent for environmental remediation, playing an important role in water treatment. GO-based materials have been developed for the sorption and removal of contaminants from water, including dyes,¹ metallic ions,² radionuclides,³ aromatic organic compounds,⁴ and so on. In particular, dyes can cause damages to humans and aquatic biota for being toxic and carcinogenic.⁵ The chemical composition, degree of oxidation, and size strongly affect the adsorption properties of GO. Herein, we report the repeated oxidation of GO using milder conditions of a modified Hummers’ method to obtain the modified graphene oxide (Ox-GO). The impact of the repeated oxidation was evaluated by studying the adsorption performance of the materials towards methylene blue (MB), one of the most used cationic dyes. The materials were characterized by X-ray powder diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, total X-ray scattering, and pair distribution function analysis. Our results show that the additional oxidation step does not lead to an increased content of oxygenated groups but instead, it causes a small change in the amounts of each functionality, reduces the size and introduces holes in the sheets, facilitates the exfoliation. The adsorption experiments reveal that when using an initial MB concentration of 200 mg L^-1 at pH 6, Ox-GO shows a dye adsorption capacity of 695.36 mg g^-1, nearly 1.32-fold higher than that of GO (527.07 mg g^-1). Thus, more than 90% of MB can be removed by Ox-GO, while GO removes only 72.2%. When the pH is decreased to 2 at the same dye concentration, the difference in removal for both materials is more pronounced, where Ox-GO adsorbs 1.45 times more MB than GO, reaching an efficiency of around 79.5%. On the other hand, under alkaline conditions (pH 10), GO can adsorb almost 100% of the dye, but Ox-GO presents a catalytic behavior to converting MB into a different species, violet-colored. Therefore, the additional oxidation step of GO is an efficient method to enhance the MB adsorption performance, enabling the application in water treatment. Moreover, the material also shows catalytic properties that allow more potential applications.
Acknowledgments
This research was funded by São Paulo Research Foundation (FAPESP; grants 2018/08271-7, 2016/25267-8, 2018/00033-0, 2017/01267-1).
References
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Escalating global water scarcity necessitates high-performance desalination membranes, for which fundamental understanding of structure–property–performance relationships is required. In this study, we comprehensively assess the ionization behavior of nanoporous polyamide selective layers in state-of-the-art nanofiltration (NF) membranes. In these films, residual carboxylic acids and amines influence permeability and selectivity by imparting hydrophilicity and ionizable moieties that can exclude coions. We utilize layered interfacial polymerization to prepare physically and chemically similar selective layers of controlled thickness. We then demonstrate location-dependent ionization of carboxyl groups in NF polyamide films. Specifically, only surface carboxyl groups ionize under neutral pH, whereas interior carboxyl ionization requires pH >9. Conversely, amine ionization behaves invariably across the film. First-principles simulations reveal that the low permittivity of nanoconfined water drives the anomalous carboxyl ionization behavior. Furthermore, we report that interior carboxyl ionization could improve the water–salt permselectivity of NF membranes over fourfold, suggesting that interior charge density could be an important tool to enhance the selectivity of polyamide membranes. Our findings highlight the influence of nanoconfinement on membrane transport properties and provide enhanced fundamental understanding of ionization that could enable novel membrane design.

There has been a high discharge of non-biodegradable dyes into natural streams and water bodies, thus contaminating them. Many of these dyes are synthesized by carcinogens and can be water-soluble, therefore being more problematic to remove. One of the largest categories of colorants are the azo dyes, over 50% of all the dyes used are azoic dyes. The problem with azo dyes is that they can be reduced into aromatic amines, which are potentially hazardous. One effective way to remove these dyes from our water sources is by using semiconductor nanoparticles in a photocatalytic degradation process. Titanium dioxide is a semiconductor material with intrinsic optical and electronic properties that promote its use in several applications including catalytic processes and organic synthesis. The photocatalytic capacity of TiO2 nanostructures is based on the generation of electron-hole pairs due to the UV excitation of TiO2. The generated pairs diffuse to the surface of the material and participate in the surface reaction leading to the decomposition of absorbed matter. The generation of reactive oxygen species by the electron-hole pairs is responsible for the degradation of organic contaminants like dyes. Based on the considerations above, the objective of this research was to study and evaluate the photocatalytic capacity of the Titanium Dioxide NPs on organic dyes. The results evidenced that the photocatalytic properties of TiO2 degraded the dyes in its majority. The effect of catalysts concentration on the reaction rate constants will be discussed.

Cerium Oxide Nanoparticles (CeO₂ NPs) are recognized as important functional materials because of their exciting applications. These nanoparticles are used as catalytic converters for; internal combustion engines, polishing lenses, optical instruments, pigments, solar cells, and photocatalytic processes. Preliminary studies have reported that CeO₂ has the potential capacity to destroy organic dyes because of their capacity to generate reactive oxygen species (ROS) in aquatic environments as hydroxide radicals (OH). However, there is a concern about the potential adsorption of CeO₂ in aquatic organisms and later toxicity in these living systems. In this way, scarce studies about the nanotoxicity of CeO₂ in the aquatic organism have been reported. Based on the mentioned before, the objectives of this work were: 1) Characterize Cerium Oxide Nanoparticles, 2) Study the photocatalytic degradation of organic dyes with two different sizes of CeO₂ NPs, 3) Evaluate the CeO₂ nanoparticles ROS production capacity (as toxicity in marine organisms), and 4) Determine the effect of the pH in the photocatalytic capacity of CeO₂ NPs. Nanoparticles of CeO₂ evidenced a high absorption peak in the ultraviolet range, which suggests the charge-transfer transition from O₂- (2p) to Ce⁴⁺ (4f) orbitals in CeO₂. It is known that Azo dyes are disposed of in aquatic environments without treatment. These dyes are used in printing, pharmaceuticals, laboratory research, and in the textile industry. These toxins can enter the body through the skin and cause; fast heart rate, lung tissue death, and vomiting. In this research, we focused on the azo dye, Tropaeolin O. The catalytic activity of two different Cerium Oxide size nanoparticles were evaluated in aqueous solutions of Tropaeolin O at 70µM of concentration. These solutions were put in a UV light at 302 nm for intervals until it reached 160 minutes. The smallest Cerium Oxide NPs (<5.0 nm) degraded about 40%. The biggest Cerium Oxide NPs (<25.0 nm) degraded about 20%. This result shows that (<5.0 nm) CeO₂ NPs degraded more due to its greater surface area and its capacity to generate more reactive oxygen species (ROS). The capacity of CeO₂ NPs to generate ROS was examined and investigated with the intoxication experiment of shrimps. The toxicity was evaluated in marine crustaceans at different CeO₂ concentrations in the 0ppm to 1000ppm range. The results indicated that Cerium Oxide had a negative interaction in marine organisms with increased concentration and exposure time. At 24 hours of exposure, the smallest NPs had a high mortality rate at CeO₂ concentrations higher than 100ppm. However, when the exposure time was increased by 48 hours, nanoparticles were toxic at concentrations higher than 10ppm. In contrast, the biggest NP showed no high mortality rate after 48 hours of exposure and higher concentrations. This experiment explains that (<5.0 nm) Cerium Oxide nanoparticles are more toxic because of the greater surface area and the generation of ROS radicals. We are currently working with the optimization of both sizes of the CeO₂ NPs by changing their acidic pH to a basic pH. In theory, this would optimize and give a better photocatalytic effect and a more significant degradation percent of different azo dyes like Tropaeolin O.

Solar desalination system shows great potential as a solution to the issues of global water scarcity because of its eco-friendliness and sustainability. However, the heat loss of evaporation surface to water reservoir, fouling due to the formation of salt crystals on evaporation surfaces, and the difficulty of continuous brine supply without external power are the major obstacles to the practical use of the solar desalination. Herein, using thermosensitive hydrogel composites, a solar evaporator was which could work by diurnal temperature variation with antifouling properties and no heat loss during evaporation. An irreversible water flow was achieved by using composites of thermosensitive poly(N-isopropylacrylamide) (PNIPAm) hydrogel and hydrophobic polydimethylsiloxane (PDMS), which have fast deswelling kinetics. The composites were made by directional melt crystallization (DMC) of solvent. By the DMC method, a porous PNIPAm having aligned and continuous three-dimensional pores was prepared. The structure enables a combination of two different materials. It can be achieved by the infiltration of PDMS to the aligned pores of PNIPAm. Anisotropic composites have PNIPAm/PDMS phase at the bottom of the composites, which has a faster deswelling rate than pure PNIPAm phase. As temperature rises above the LCST of PNIPAm, water can be released from the top surface of the PNIPAm, and this water pumping could be repeated by the diurnal temperature variance. Between the pumping composite and the water reservoir, another porous PNIPAm was placed. During diurnal temperature variance, this bottom PNIPAm can vary its length. At a temperature above LCST, the length of the PNIPAm is shortened, a thermal isolation from the water reservoir results. At a temperature below LCST, PNIPAm is lengthened, and it can absorb brine from the water reservoir and diffuse brine into the entire phases of PNIPAm/PDMS composites. Water from the pumped brine evaporates on the surface of nickel/cellulose composite, which could float on water. Nickel nanoparticles were prepared on the surfaces of cellulose papers. When brine is released, the nickel/cellulose composites float, and salt accumulation is formed at the bottom of the composites. This can solve the decrease in the efficiency of the evaporation due to the fouling by salt crystallization. Our three-dimensional solar desalination system could be operated without artificial power without the fouling problems. Diurnal operating strategy makes the solar evaporator eco-friendly, and the antifouling properties increase the sustainability of solar desalination.

Researches on water treatment technology has been steadily studied for innovative improvement of the performances, i.e., high yield and speed of purification process. Conventionally, water treatment membrane was fabricated from synthetic polymers, such as polysulfone and polyethersulfone, with the controlled pore structure. Non-solvent induced phase separation (NIPs) is the most common method to control the pore structure. In the process, polymer solution should be immersed in a coagulation bath containing non-solvent. The overuse of hazard solvents is inevitable during the fabrication. In order to protect the earth from those kinds of pollutions, a substantial candidate for the membrane is crucial. TEMPO-oxidized cellulose nanofiber (CNF) has high potential for the membrane application due to its high aspect ratio and high mechanical strength. Owing to its carboxylate groups, CNF can be easily dispersed in water which enables the membrane fabrication without the help of toxic solvents. Up to now, a number of studies have been reported for high performance membrane based on CNF. However, it is still challenging to increase pollutant removal performance without sacrificing its water flux.
In the study, high-performance water treatment membrane was fabricated using in-situ synthesized carbon dot (CD) at CNF. Via simple hydrothermal treatment, CD was homogeneously attached to the CNF surface by amide bonding. CD@CNF had a fibrous structure with rough and bumpy morphology, while the chemical structure of cellulose was not changed. The CD attached on the surface decreased the repulsive force between the CNFs and remarkably increased the thermal and dimensional stabilities of the CNF film. With the structural robustness, CD@CNF showed excellent performance as a dye-rejection membrane of high-water flux and high rejection rate. As well the CD@CNF showed superior selective removal results toward cationic dyes. This study suggests the novel synthesizing method of durable CNF membrane by envelopment of CD for effective water treatment.

In recent years, the presence of pharmaceuticals such as diclofenac and sulfamethoxazole in the aquatic environment has been of growing interest as it poses a threat to aquatic organisms and human health. Graphitic carbon nitride (g-C₃N₄) is a promising green photocatalyst with the visible-light-responsive property. However, the high e^--h⁺ recombination rate decreases the photo-activity of g-C₃N₄. Therefore, the doping with other ions as well as the combination with other photocatalysts can not only extends the absorption to the visible light region but also reduces the recombination rate of electron-hole pairs. Herein, the doped C₃N₄ with various morphologies and dimensional was successfully synthesized by a facile hydrothermal–assisted thermal approach as an effective photocatalyst for photocatalytic degradation of pharmaceuticals under visible-light irradiation. The 1-D B, P-codoped g-C₃N₄ various P loadings was fabricated for highly recyclable photodegradation of diclofenac (DFC) under visible light irradiation. The as-prepared 1-D B, P-C₃N₄ exhibits high surface area, visible-light response and photoinduced charge separation to effectively photodegrade > 99% of 10 mg/L diclofenac within 90 min of irradiation. The 1D-BPCN-3 shows good reusability in the photodegradation of DFC for at least 5 consecutive cycles without considerable loss in photocatalytic activity. Moreover, the 3-D flower-like g-C₃N₄@TiO₂ was prepared by the thermal exfoliation of urea and hydrothermal method. The g-C₃N₄@TiO₂ exhibits an excellent photocatalytic performance toward diclofenac degradation under solar light irradiation. The impedimetric and photoluminescence spectra show that 5 wt% g-C₃N₄ can increase the conductivity as well as reduce the recombination rate of g-C₃N₄@TiO₂ nanocomposites, resulting in the enhancement of photodegradation efficiency and rate of diclofenac. The rate constant for diclofenac degradation by 3-D g-C₃N₄@TiO₂ is 0.075 min^-1, which is 3–10 times higher than the other g-C₃N₄@TiO₂. These results clearly demonstrate that the various dimensions of doped g-C₃N₄ are reliable visible-light-responsive photocatalysts for the decomposition of antibiotics and other emerging pollutants in aqueous solutions.