TiO2 based photocatalytic membranes: A review

Enhancing membrane performance for oily wastewater treatment: comparison of PVDF composite membranes prepared by coating, blending, and grafting methods using TiO2, BiVO4, CNT, and PVP

This comparative study investigates the modification of polyvinylidene fluoride (PVDF) membranes with different nanoparticles (TiO2 or TiO2-based composites containing BiVO4 and/or CNT), using three distinct methods (blending, coating, and grafting) and polyvinylpyrrolidone (PVP). The objective was to enhance the photocatalytic and filtration performance for the separation of oil-in-water emulsions. Regarding the UV activity, the PVDF-TiO2/CNT/PVP-coated membrane presented the best performance. Overall, the addition of 2 wt.% CNT to the TiO2 notably enhanced the photocatalytic activity of the membranes for both UV and visible irradiations. Meanwhile, the presence of 2 wt.% BiVO4 was beneficial only for photocatalysis under visible light irradiation. Regarding the filtration of the oil-in-water emulsions, 2 wt.% CNT or BiVO4 addition resulted in the highest fluxes in the series of the PVDF-TiO2-grafted membranes. The presence of pore former PVP led to relatively high fluxes and photocatalytic activities for all series. Regarding the modification methods, coated membranes showed the highest photocatalytic efficiency and lowest fluxes. Grafted membranes showed relatively high photocatalytic efficiencies and the best filtration performances.

Advancements in Inorganic Membrane Filtration Coupled with Advanced Oxidation Processes for Wastewater Treatment

Membrane filtration is an effective water recycling and purification technology to remove various pollutants in water. Inorganic membrane filtration (IMF) technology has received widespread attention because of its unique high temperature and corrosion resistance. Commonly used inorganic membranes include ceramic membranes and carbon-based membranes. As novel catalytic inorganic membrane processes, IMF coupled with advanced oxidation processes (AOPs), can realize the separation and in situ degradation of pollutants, thus mitigating membrane contamination. In this paper, the types and performance of IMF are discussed. The influencing factors of inorganic membranes in practical wastewater treatment are summarized. The applications, advantages, and disadvantages of the coupled process of IMF and AOPs are summarized and outlined. Finally, the challenges and prospects of IMF and IMF coupled with AOPs are presented, respectively. This contributes to the design and development of coupled systems of membrane filtration with inorganic materials and IMF coupled with AOPs for practical wastewater treatment.

Heterostructure g-C3N4/Bi2MoO6 PVDF nanofiber composite membrane for the photodegradation of steroid hormone micropollutants

Photocatalytic membrane reactors (PMRs) are a promising technology for micropollutant removal. Sunlight utilization and catalyst surface sites limit photodegradation. A poly(vinylidene fluoride) (PVDF) nanofiber composite membrane (NCM) with immobilized visible-light-responsive g-C3N4/Bi2MoO6 (BMCN) were developed. Photodegradation of steroid hormones with the PVDF-BMCN NCM was investigated with varying catalyst properties, operating conditions, and relevant solution chemistry under solar irradiation. Increasing CN ratio (0-65 %) enhanced estradiol (E2) degradation from 20 ± 10 to 75 ± 7 % due to improved sunlight utilization and photon lifetime. PVDF nanofibers reduced self-aggregation of catalysts. Hydraulic residence time and light intensity enhanced the photodegradation. With the increasing pH value, the E2 removal decreased from 84 ± 4 to 67 ± 7 % owing to electrical repulsion and thus reduced adsorption between catalysts and E2. A removal of 96 % can be attained at environmentally relevant feed concentration (100 ng.L-1) with a flux of 60 L.m-2.h-1, irradiance of 100 mW.cm-2, and 1 mg.cm-2 BMCN65 loading. This confirmed that heterojunction photocatalysts can enhance micropollutants degradation in PMRs.

Photocatalytic and antifouling performance of titania-coated alumina membranes produced using a facile sol-gel dip-coating approach

Photocatalytic membranes (PM) have been investigated as an antifouling strategy for membrane separation processes. Coating ceramic membranes with photocatalytic layers can provide a highly active surface capable of degrading foulants and smaller molecules improving the membrane's performance when the surface is irradiated by a suitable light. Nevertheless, the coating process often leads to pore blockage due to the formation or deposition of thick layers of photocatalyst on membrane surfaces, which modifies the original membranes' average pore size and reduces membrane permeability. A facile sol-gel dip coating process was used to produce PM without modifying the original surface morphology of alumina microfiltration membranes. A 3.7-fold increase in permeate volume after 90 min of permeation of an acetaminophen solution in continuous filtration mode under UV light (λ = 365 nm LED, 10W) using titania as photocatalyst compared to the bare alumina membrane without irradiation. Furthermore, fouling modelling proved a reduction in the fouling constant, while fouling mechanisms were not modified. Raman analysis showed 100% anatase formed on the membrane surface. Although membranes could remove up to 87% TOC for oily wastewater filtration, antifouling capabilities for this type of effluent were not observed for the photocatalytic membranes mainly due to fouling inside the pores and light attenuation due to the thick fouling layer on the membrane surface.

Recent Advancement in Emerging MXene-Based Photocatalytic Membrane for Revolutionizing Wastewater Treatment

MXene-based photocatalytic membranes provide significant benefits for wastewater treatment by effectively combining membrane separation and photocatalytic degradation processes. MXene represents a pioneering 2D photocatalyst with a variable elemental composition, substantial surface area, abundant surface terminations, and exceptional photoelectric performance, offering significant advantages in producing high-performance photocatalytic membranes. In this review, an in-depth overview of the latest scientific progress in MXene-based photocatalytic membranes is provided. Initially, a brief introduction to the structure and photocatalytic capabilities of MXene is provided, highlighting their pivotal role in promoting the photocatalytic process. Subsequently, in pursuit of the optimal MXene-based photocatalytic membrane, critical factors such as the morphology, hydrophilicity, and stability of MXenes are meticulously taken into account. Various preparation strategies for MXene-based photocatalytic membranes, including blending, vacuum filtration, and dip coating, are also discussed. Furthermore, the application and mechanism of MXene-based photocatalytic membranes in micropollutant removal, oil-water separation, and antibacterial are examined. Lastly, the challenges in the development and practical application of MXene-based photocatalytic membranes, as well as their future research direction are delineated.

Layer-by-layer assembled graphitic carbon nitride membranes for water treatment

Meeting societal demand for potable water supply remains one of the prioritized challenges faced in the modern era. The anthropogenic intervention has led to a dire situation threatening ecological balance and human health. There is an inevitable need for the development of new technologies and innovations in existing technologies for water treatment. Photocatalytic Membrane technology, encompassing the merits of membrane filtration and photocatalytic degradation has evolved as a potential and reliable technology for sustainable water treatment. Innovations in photocatalytic materials and membrane fabrication techniques can lead to the goal of commercialization of membrane water treatment technology. Herein, we demonstrate the potential of graphitic carbon nitride (g-C3N4) and its functionalized analog as photocatalytic membranes for sustainable water treatment. g-C3N4 and Tetracarboxyphenylporphyrin sensitized g-C3N4 (g-C3N4/TCPP) was introduced onto commercial nylon membrane surface via a layer-by-layer (LBL) assembly method using chitosan and sodium salt of polystyrene sulphonic acid as polyelectrolytes. The fabricated membranes were characterized to ensure the integration of the photocatalysts. The performance of the membranes for water treatment was assessed by selecting some common dyes as model pollutants. The modified membranes exhibited excellent flux recovery and could afford high rejection rates upon irradiation indicating the prospects for sustainable filtration.

Membrane-catalysis integrated system for contaminants degradation and membrane fouling mitigation: A review

The integration of catalytic degradation and membrane separation processes not only enables continuous degradation of contaminants but also effectively alleviates inevitable membrane fouling, demonstrating fascinating practical value for efficient water purification. Such membrane-catalysis integrated system (MCIS) has attracted tremendous research interest from scientists in chemical engineering and environmental science recently. In this review, the advantages of MCIS are discussed, including the membrane structure regulation, stable catalyst loading, nano-confinement effect, and efficient natural organic matter (NOM) exclusion, highlighting the synergistic effect between membrane separation and catalytic process. Subsequently, the design considerations for the fabrication of catalytic membranes, including substrate membrane, catalytic material, and fabrication method, are comprehensively summarized. Afterward, the mechanisms and performance of MCIS based on different catalytic types, including liquid-phase oxidants/reductants involved MCIS, gas involved MCIS, photocatalysis involved MCIS, and electrocatalysis involved MCIS are reviewed in detail. Finally, the research direction and future perspectives of catalytic membranes for water purification are proposed. The current review provides an in-depth understanding of the design of catalytic membranes and facilitates their further development for practical applications in efficient water purification.

Effect of basic and basic/acid modifications on the surface of PVDF membranes for the insertion of TiO2 and its use in environmental applications

Supporting titanium oxide (TiO2) on polymeric membrane surfaces is a strategy to increase the photocatalytic activity of this material as well as to modify membrane surface with antifouling properties or to develop hybrid processes of water treatment. The chemical characteristics of the polymeric membrane surfaces are a determining factor in the correct impregnation of TiO2 particles. In this work, the titanium oxide was immobilized on polyvinylidene fluoride (PVDF) membrane surface by direct impregnation during the synthesis of the inorganic particles by sol-gel route. The PVDF membranes were previously modified by treatments based on an alkaline attack followed by acid treatment. The final TiO2-modified membranes were characterized by infrared and Raman spectroscopy, as well as by scanning electron microscopy. In addition, the changes on the surface characteristics were determined by contact angle measurements. Finally, the membranes were tested on the photocatalytic degradation of methyl orange (MO). The results obtained indicate that the basic/acid pretreatment allows the generation of active sites in the membrane and that when carrying out the synthesis of TiO2 on the membrane, it can be anchored stably on its surface and through the pores. The microscopies indicate that the structure of the membrane is not compromised by the pretreatment. The amount of TiO2 deposited on the membrane was of 0.1580 ± 0.01773 mg TiO2/cm2 membrane. With this amount of TiO2, a degradation percentage of 98.2% is achieved after 450 min; when the membrane is used for a second cycle, a degradation percentage of 82.0% is obtained, which remains constant for 3 subsequent cycles. This method, which uses the PVDF membrane as a support for TiO2 particles, represents a low-cost and easy-to-prepare insertion procedure, with good degradation percentages, which means that the membrane can be used for subsequent studies in filtration systems in the treatment of effluents from the textile industry.

A novel copper oxide/titanium membrane integrated with peroxymonosulfate activation for efficient phenolic pollutants degradation

Herein, a novel CuO catalyst functionalized Ti-based catalytic membrane (FCTM) was prepared via the regulated electro-deposition technique followed with low-temperature calcination. The morphology of CuO catalyst and oxygen vacancy (OV) content can be controlled by adjusting the preparation conditions, under optimal condition (400 °C, electrolyte as sulfuric acid), the fern-shaped CuO catalyst was formed and the OV content was up to its highest level. Under the optimal treatment condition, the 4-chlorophenol (4-CP) removal of the membrane filtration combined with peroxymonosulfate (PMS) activation (MFPA) process was up to 98.2% (TOC removal of 88.2%). Mechanism studying showed that the enhanced performance in this system was mainly due to the increased production of singlet oxygen (1O2) via the co-effect of fern-shaped CuO (increased specific surface area) and its fine-tuned OV (precursor of 1O2), which not only synergistically enhanced adsorption ability but also offered more active sites for PMS activation. Theoretical calculations showed that the OV-rich CuO displayed high adsorption energy for PMS molecule, leading to the change in OO and OH bond (tend to 1O2) of the PMS molecule. Finally, the possible three degradation pathways of 4-CP were formed by the electrophilic attacking of 1O2.

Constructing a composite microfiltration carbon membrane by TiO2 and Fe2O3 for efficient separation of oil-water emulsions

Membrane-based separation technology has attracted enormous attention for oil/water emulsion treatment. Here, composite microfiltration carbon membranes (MCMs) were prepared from the precursor of phenolic resin doping with TiO2 and Fe2O3 via the processes of stereotype and pyrolysis. The functional groups, thermal stability, porous structure, microstructure, morphology, and hydrophilicity of the membrane samples were analyzed by Fourier-transform infrared spectroscopy, thermogravimetric analysis, bubble pressure method, X-ray diffraction, scanning electron microscope, and water contact angle, respectively. The effect of dopant amount on the separation performance of MCMs was investigated. The results show that a mixed matrix system is constructed by TiO2 and Fe2O3 in MCMs, which is beneficial for further optimizing the pore size, porosity, and hydrophilicity of MCMs for oily wastewater treatment by varying the dopant amount. The maximum oil rejections are achieved at 98.9% and 99.6% for MCMs with a dopant content of TiO2 and Fe2O3 at 25%, respectively. In brief, this study offers an attractive strategy for improving the separation performance of MCMs for oily wastewater.

Going beyond Cellulose and Chitosan: Synthetic Biodegradable Membranes for Drinking Water, Wastewater, and Oil-Water Remediation

Membrane technology is an efficient way to purify water, but it generates non-biodegradable biohazardous waste. This waste ends up in landfills, incinerators, or microplastics, threatening the environment. To address this, research is being conducted to develop compostable alternatives that are sustainable and ecofriendly. Bioplastics, which are expected to capture 40% of the market share by 2030, represent one such alternative. This review examines the feasibility of using synthetic biodegradable materials beyond cellulose and chitosan for water treatment, considering cost, carbon footprint, and stability in mechanical, thermal, and chemical environments. Although biodegradable membranes have the potential to close the recycling loop, challenges such as brittleness and water stability limit their use in membrane applications. The review suggests approaches to tackle these issues and highlights recent advances in the field of biodegradable membranes for water purification. The end-of-life perspective of these materials is also discussed, as their recyclability and compostability are critical factors in reducing the environmental impact of membrane technology. This review underscores the need to develop sustainable alternatives to conventional membrane materials and suggests that biodegradable membranes have great potential to address this challenge.

Investigation of Photocatalytic PVDF Membranes Containing Inorganic Nanoparticles for Model Dairy Wastewater Treatment

Membrane separation processes are promising methods for wastewater treatment. Membrane fouling limits their wider use; however, this may be mitigated using photocatalytic composite materials for membrane preparation. This study aimed to investigate photocatalytic polyvinylidene fluoride (PVDF)-based nanocomposite membranes for treating model dairy wastewater containing bovine serum albumin (BSA). Membranes were fabricated via physical coating (with TiO₂, and/or carbon nanotubes, and/or BiVO₄) and blending (with TiO₂). Another objective of this study was to compare membranes of identical compositions fabricated using different techniques, and to examine how various TiO₂ concentrations affect the antifouling and cleaning performances of the blended membranes. Filtration experiments were performed using a dead-end cell. Filtration resistances, BSA rejection, and photocatalytic cleanability (characterized by flux recovery ratio (FRR)) were measured. The surface characteristics (SEM, EDX), roughness (measured by atomic force microscopy, AFM), wettability (contact angle measurements), and zeta potential of the membranes were also examined. Coated PVDF membranes showed higher hydrophilicity than the pristine PVDF membrane, as evidenced by a decreased contact angle, but the higher hydrophilicity did not result in higher fluxes, unlike the case of blended membranes. The increased surface roughness resulted in increased reversible fouling, but decreased BSA retention. Furthermore, the TiO₂-coated membranes had a better flux recovery ratio (FRR, 97%) than the TiO₂-blended membranes (35%). However, the TiO₂-coated membrane had larger total filtration resistances and a lower water flux than the commercial pristine PVDF membrane and TiO₂-blended membrane, which may be due to pore blockage or an additional coating layer formed by the nanoparticles. The BSA rejection of the TiO₂-coated membrane was lower than that of the commercial pristine PVDF membrane. In contrast, the TiO₂-blended membranes showed lower resistance than the pristine PVDF membrane, and exhibited better antifouling performance, superior flux, and comparable BSA rejection. Increasing the TiO₂ content of the TiO₂-blended membranes (from 1 to 2.5%) resulted in increased antifouling and comparable BSA rejection (more than 95%). However, the effect of TiO₂ concentration on flux recovery was negligible.

UV-LED silicon carbide composite photocatalytic membrane reactor for the degradation of organic contaminants

The utilization of membranes in the water industry has been growing rapidly; however, the technology still experiences problems with fouling. A potential solution is to immobilize photocatalyst particles on the surface of the membranes to encourage in situ degradation of the organic contaminants contributing to the fouling. In this study, we developed a photocatalytic membrane (PM) by coating a silicon carbide membrane with Zr/TiO₂ sol. The performance of the PM in degrading different concentrations of humic acid was evaluated comparatively under UV irradiation of two wavelengths, 275 and 365 nm. The results indicated that (i) the PM achieved high levels of humic acid degradation, (ii) the photocatalytic activity of the PM reduced the formation of fouling and hence the loss of permeability, (iii) the formation of fouling was reversible; no trace of fouling was observed after cleaning, and (iv) the PM showed high durability during multiple rounds of operation.

Rapid Probing of Self-Cleaning Activity on Polyester Coated by Titania-Natural Silica Nanocomposite Using Digital Image-Based Colorimetry

Titania-silica nanocomposites (TiO₂-SiO₂) show outstanding performance and is very well applied in photocatalysis. In this research, SiO₂ extracted from Bengkulu beach sand will be used as a supporting material of the TiO₂ photocatalyst for application to polyester fabrics. TiO₂-SiO₂ nanocomposite photocatalysts were synthesized using the sonochemical method. The coating of the TiO₂-SiO₂ material on polyester was carried out using the sol-gel-assisted sonochemistry method. The method of determining self-cleaning activity uses a digital image-based colorimetric (DIC) method, which is much simpler than using an analytical instrument. The scanning electron microscopy-energy dispersive X-ray spectroscopy results showed that the sample particles adhered to the fabric surface and the best particle distribution was shown in pure SiO₂ and 1:0.5 TiO₂-SiO₂ nanocomposites. Analysis of Fourier-transform infrared (FTIR) spectroscopy proved the presence of Ti-O and Si-O bonds as well as the typical spectrum of polyester, which indicated that the fabric had been successfully coated with nanocomposite particles. The analysis of the contact angle of the liquid on the polyester surface showed a significant change in the properties of the TiO₂ and SiO₂ pure coated fabrics, but changes occur only slightly in the other samples. Self-cleaning activity against the degradation of methylene blue dye has been successfully carried out using DIC measurement. The test results showed that the best self-cleaning activity was shown by TiO₂-SiO₂ nanocomposite with a ratio of 1:0.5 with the degradation ratio reaching 96.8%. Furthermore, the self-cleaning property remains after the washing process, which shows excellent washing resistance.

Water-alcohol-TiO2 dispersions as sustainable ink

Nanocrystalline titanium dioxide (TiO₂) is a widespread multifunctional and environmentally friendly material that has numerous applications requiring micro-/nanofabrication or thin film deposition. In most cases, the fabrication of titania films can be achieved using cost-efficient solution chemistry combined with various coating or printing techniques. The practical implementation of these methods requires the preparation of a suitable ink with properly adjusted rheological properties. Conventionally, such adjustments are achieved based on TiO₂ hydrosols containing various organic surfactants and stabilizing agents. However, the use of such additives may affect the properties of the deposited functional layer, which can be crucial for electronic and optical applications. In this work, we address a comprehensive study of simple surfactant-free TiO₂ dispersion systems based on various water-alcohol solvents and demonstrate the possibility of controlling the rheological properties of the titania ink in a wide range that is suitable for several printing applications. As a particular example, we demonstrate the application of a water-i-propanol-TiO₂ dispersion as a functional ink for the offset printing of interference images.

Antifouling and Antimicrobial Study of Nanostructured Mixed-Matrix Membranes for Arsenic Filtration

Membrane fouling is a major drawback in the membrane filtration industry for water treatment. Mixed-matrix membranes (MMMs) are well known for their enhanced antifouling and antibacterial properties, which could offer potential benefits for membrane filtration processes in the water treatment field. In this work, three electrospun nanofibrous MMMs (P, CP, and MCP, which were, respectively, the pristine polysulfone membrane and mixed-matrix membranes (MMMs) consisting of GO-ZnO and GO-ZnO-iron oxides) were studied for antifouling and antibacterial properties with respect to the arsenic nanofiltration process. The effects of these composites on the antifouling behaviour of the membranes were studied by characterising the bovine serum albumin (BSA) protein adsorption on the membranes and subsequent analysis using microscopic (morphology via scanning electron microscopy) and Brunauer-Emmett-Teller (BET) analyses. The antibacterial properties of these membranes were also studied against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli). The composite nanoparticle-incorporated membranes showed improved antifouling properties in comparison with the pristine polysulfone (PSF) membrane. The excellent antimicrobial properties of these membranes make them appropriate candidates to contribute to or overcome biofouling issues in water or wastewater treatment applications.

Porous nanocomposites for sorptive elimination of ibuprofen from synthetic wastewater and its molecular docking studies

Pharmaceuticals are a new developing pollutant that is threatening aquatic ecosystems and impacting numerous species in the ecosystem. The aim of this study is the green synthesis of TiO₂-Fe₂O₃-Chitosan nanocomposites in conjunction with Moringa olifera leaves extract and its applicability for ibuprofen removal. Various characterization studies were performed for the synthesized nanocomposites. Box-Behnken design (BBD) is employed to optimize pH, agitation speed, and composite dosage. Equilibrium results show that adsorption process matches with Langmuir isotherm, demonstrating adsorption on the nanocomposite's homogenous surface and follows pseudo-first-order kinetics. Using the BBD, pH, adsorbent dose, and agitation speed were examined as adsorption parameters. Ibuprofen elimination was demonstrated to be most successful at a pH of 7.3, using 0.05 g of nanocomposites at a rotational speed of 200 rpm. Thermodynamic parameters for ibuprofen sorption were carried out and the ΔH and ΔS was found to be 76.23 & 0.233. Molecular Docking was performed to find the interaction between the pollutant and the nanocomposite. UV-vis spectra confirm the 243 nm absorption band corresponding to the nanocomposite's surface plasmon resonances. Fourier transform infrared spectroscopy spectra relate this band to a group of nanocomposites. The findings of this work emphasize the importance of TiO₂-Fe₂O₃-Chitosan nanocomposites for removing ibuprofen from wastewater.

Synthesis and applications of graphitic carbon nitride (g-C3N4) based membranes for wastewater treatment: A critical review

Semiconducting membrane combined with nanomaterials is an auspicious combination that may successfully eliminate diverse waste products from water while consuming little energy and reducing pollution. Creating an inexpensive, steady, flexible, and diversified business material for membrane production is a critical challenge in membrane technology development. Because of its unusual structure and high catalytic activity, graphitic carbon nitride (g-C3N4) has come out as a viable material for membranes. Furthermore, their great durability, high permanency under challenging environments, and long-term use without decrease in flux are significant advantages. The advanced material techniques used to manage the molecular assembly of g-C3N4 for separation membrane were detailed in this review work. The progress in using g-C3N4-based membranes for water treatment has been detailed in this presentation. The review delivers an updated description of g-C3N4 based membranes and their separation functions and new ideas for future enhancements/adjustments to address their weaknesses in real-world situations. Finally, the ongoing problems and promising future research directions for g-C3N4-based membranes are discussed.

Biotechnological advancements towards water, food and medical healthcare: A review

The global health status is highly affected by the growing pace of urbanization, new lifestyles, climate changes, and resource exploitation. Modern technologies pave a promising way to deal with severe concerns toward sustainable development. Herein, we provided a comprehensive review of some popular biotechnological advancements regarding the progress achieved in water, food, and medicine, as the most substantial fields related to public health. The emergence of novel organic/inorganic materials has brought about significant improvement in conventional water treatment techniques, anti-fouling approaches, anti-microbial agents, food processing, biosensors, drug delivery systems, and implants. Particularly, a growing interest has been devoted to nanomaterials and their application for developing novel structures or improving the characteristics of standard components. Also, bioinspired materials have been widely used to improve the performance, efficiency, accuracy, stability, safety, and cost-effectiveness of traditional systems. On the other side, the fabrication of innovative devices for precisely monitoring and managing various ecosystem and human health issues is of great importance. Above all, exceptional advancements in designing ion-selective electrodes (ISEs), microelectromechanical systems (MEMs), and implantable medical devices have altered the future landscape of environmental and biomedical research. This review paper aimed to shed light on the wide-ranging materials and devices that have been developed for health applications and mainly focused on the impact of nanotechnology in this field.

Analytical Review on Membrane Water Filter using Different Materials to Prevent Microbial Activities

Drinking water quality monitoring technologies have made significant progress in monitoring water resources and water treatment plants. This paper discusses the adverse effect of microbial contamination and also gives a brief description of the important parameters for drinking water and the technologies currently available used in this field. This paper is focused on studying the requirement for the development of low-cost filter materials that can be suitable as well as economical to be produced on a large-scale for real applications. There are several parameters such as porosity, contact angle, water flux, thickness, microbial activity needed to be focused on in the future to study the transformation of the hydrophilic property on the surface of the water.

Integrated full-scale solar CPC/UV-LED–filtration system as a tertiary treatment in a conventional WWTP for agricultural reuse purposes

Today, the emergence of increasingly restrictive treatment and reuse policies make the implementation of full-scale tertiary treatment, capable of improving the quality of water, a priority. Full-scale TiO2 photocatalysis systems are resulting in a promising option, since TiO2 is commercially available. However, questions such as how to work continuously during day/night irradiation cycle, or the removing of TiO2 in outlet flow are still unresolved. In this work, a full-scale system integrating a solar CPC/UV-LED step combined with commercial microfiltration membranes was installed in a conventional WWTP for agricultural reuse purposes. After optimization, 0.5 g/L of catalyst and combined SOLAR + UV-LED showing the highest pharmaceutical removal percentages, while a self-designed UV-LED included in the own reaction tank resulting in higher efficiencies compared with commercial lamps. Longer membrane surface area decreased fouling problems in the system. However, 60 min of irradiation time was necessary to reach the most restrictive water quality values according with (EU 2020/741). After optimization step, total costs were reduced by 45%. However, it was shown that a reduction in operating and maintenance costs, along with the development of more effective and economical commercial filtration membranes is a key factor; therefore, working on these aspects is essential in the treated water cost reduction.

Graphical abstract

TiO2 based Photocatalysis membranes: An efficient strategy for pharmaceutical mineralization

Among the various emerging contaminants, pharmaceuticals (PhACs) seem to have adverse effects on the quality of water. Even the smallest concentration of PhACs in ground water and drinking water is harmful to humans and aquatic species. Among all the deaths reported due to COVID-19, the mortality rate was higher for those patients who consumed antibiotics. Consequently, PhAC in water is a serious concern and their removal needs immediate attention. This study has focused on the PhACs' degradation by collaborating photocatalysis with membrane filtration. TiO₂-based photocatalytic membrane is an innovative strategy which demonstrates mineralization of PhACs as a safer option. To highlight the same, an emphasis on the preparation and reinforcing properties of TiO₂-based nanomembranes has been elaborated in this review. Further, mineralization of antibiotics or cytostatic compounds and their degradation mechanisms is also highlighted using TiO₂ assisted membrane photocatalysis. Experimental reactor configurations have been discussed for commercial implementation of photoreactors for PhAC degradation anchored photocatalytic nanomembranes. Challenges and future perspectives are emphasized in order to design a nanomembrane based prototype in future for wastewater management.

Converting recycled membranes into photocatalytic membranes using greener TiO2-GRAPHENE oxide nanomaterials

Despite the widespread use of membrane separation processes for water treatment, operation costs and fouling still restrict their application. Costs can be overcome by recycled membranes whereas fouling can be mitigated by membrane modification. In this work, the performance of recycled reverse osmosis membranes modified by greener titanium dioxide (TiO₂) and graphene oxide (GO) in different modification routes were investigated and compared. The use of recycled membranes as a support acted more than a strategy for costs reduction, but also as an alternative for solid waste reduction. Low adhesion of nanoparticulate materials to the membrane surfaces were verified in depositions by self-assembly, whereas filtration and modification with dopamine generated membranes with well adhered and homogeneous layers. Considering the stability, permeability, and rejection efficiency of dyes as model substrates, the membranes modified with the aid of dopamine-TiO₂-GO were the most promising. The nanomaterials increased the membrane hydrophilicity and formed a hydrated layer that repels the organic contaminants and reduces fouling. Besides membrane rejection, adsorption (contribution: ∼10%) and photocatalysis (contribution: ∼20%) were additional mechanisms for pollutants removal by the modified membranes. The photocatalytic membrane modified with dopamine-TiO₂-GO was furthermore evaluated for the removal of six different pharmaceutical active compounds (PhACs), noticing gains in terms of removal efficiency (up to 95.7%) and fouling mitigation for the modified membrane compared to the original membranes. The photocatalytic activity still contributed to a simultaneous degradation of PhACs avoiding the generation of a concentrated stream for further disposal.

Bio-Inspired C/N/TiO2 Hybrid Composite Heterostructure: Enhanced Photocatalytic Activity under Visible Light

The hydrothermal treatment was used to create a natural hierarchical bio-inspired carbon and nitrogen-doped C/N/TiO2 hybrid composite. It is the goal of this work to investigate the photocatalytic activity of bio-inspired C/N/TiO2 hybrid composite. Techniques such as X-ray powder diffraction, scanning electron microscopy, UV-Vis absorption spectroscopy, FTIR, Raman, and photoluminescence spectroscopy were used to explore the structural, morphological, and photocatalysis characteristics of the bio-inspired C/N/TiO2 hybrid composite. By doping carbon and nitrogen, TiO2 nanotubes were able to improve the photocatalyst properties of the C/N/TiO2 hybrid composite, decrease the energy band gap (∼2.55 eV), and result in increased electron transfer efficiency when compared to pure TiO2. The photocatalytic degradation of pollutants (rhodamine B (RhB)) is made possible by the use of a bio-inspired C/N/TiO2 hybrid composite that has high interconnectivity and an easily accessible surface.

Development and Investigation of Photoactive WO3 Nanowire-Based Hybrid Membranes

Novel hybrid structures have attracted attention in several instances of scientific research and different technological applications in this decade due to their novel characteristics and wide range of applicability. Hybrid membranes with multiple components (three or more) are also increasingly used in water purification applications, and their ease of handling and reusability make them a promising candidate for the degradation of organic pollutants by photocatalysis. In this study, the preparation and characterization of tungsten trioxide nanowire (WO3 NW)-based hybrid membrane structures are reported. Furthermore, the adsorption properties and photocatalytic efficiency of the as-prepared membranes against methylene blue (MB) organic dye under UV irradiation is also presented. Characterization techniques, such as scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray powder diffraction (XRD) are performed to study the morphology and surface of the as-prepared hybrid membranes. The removal efficiency of the hybrid membranes against MB is 77% in a 120 min decomposition reaction. The enhanced value can be attributed to the hybrid structure of the membrane that enhances not only the adsorption capability, but also the photocatalytic performance. Based on the results obtained, it is hoped that hybrid membrane technology could be a promising candidate for future photocatalysis-based water treatment applications.

Design and Preparation of Polyimide/TiO2@MoS2 Nanofibers by Hydrothermal Synthesis and Their Photocatalytic Performance

Organic–inorganic nanocomposite fibers can avoid the agglomeration of single nanoparticles and reduce the cost (nanoparticles assembled on the surface of nanofibers), but also can produce new chemical, electrical, optical, and other properties, with a composite synergistic effect. Aromatic polyimide (PI) is a high-performance polymer with a rigid heterocyclic imide ring and an aromatic benzene ring in its macromolecular framework. Due to its excellent mechanical properties, thermal stability, and easy-to-adjust molecular structure, PI has been widely used in electronics, aerospace, automotive, and other industries related to many applications. Here, we report that TiO₂ nanorods were grown on polyimide nanofibers by hydrothermal reaction, and MoS₂ nanosheets were grown on TiO₂ nanorods the same way. Based on theoretical analysis and experimental findings, the possible growth mechanism was determined in detail. Further experiments showed that MoS₂ nanosheets were uniformly coated on the surface of TiO₂ nanorods. The TiO₂ nanorods have photocatalytic activity in the ultraviolet region, but the bandgap of organic/inorganic layered nanocomposites can redshift to visible light and improve their photocatalytic performance.

Effect of Polymer Concentration on the Photocatalytic Membrane Performance of PAN/TiO2/CNT Nanofiber for Methylene Blue Removal through Cross-Flow Membrane Reactor

A photocatalytic membrane combining photocatalyst and membrane technology based on polyacrylonitrile (PAN) and TiO2/CNT has been developed. Such combination is to overcome fouling formation on the membrane, thus prolonging the membrane lifetime and enhancing the efficiency on the waste treatment. PAN nanofiber was prepared by electrospinning method. The precursor solution was dissolved PAN and dispersed TiO2/CNT in N,N-Dimethylformamide (DMF). PAN concentration in the precursor solution was varied at 4.5, 5.5, 6.5, 7.5, and 8.5%. The effect of PAN concentration on the fiber morphology and pore size was discussed. The performance of the resulted membrane on methylene blue (MB) removal was also investigated on a cross-flow system. SEM images of the resulted membrane identified that PAN nanofiber was successfully fabricated with random orientation. The PAN 6.5% showed the highest diffraction intensity of the anatase crystalline phase of TiO2. The additions of CNT and TiO2 lead to the formation of a cluster of beads as confirmed by TEM. Increasing the concentration of PAN increased the fiber diameter from 206 to 506 nm, slightly decreased the surface area and pore size, respectively, from 32.739 to 21.077 m2.g−1 and from 6.38 to 4.75 nm. The PAN/TiO2/CNT nanofibers show type IV of the adsorption-desorption N2 isotherms with the H1 hysteresis loops. Membrane PAN/TiO2/CNT at PAN concentration of 6.5% shows the optimum performance on the MB color removal by maintaining the percentage of rejection (%R) at 90% for 240 min and permeability of 750 LMH. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Photocatalytic Reactor as a Bridge to Link the Commercialization of Photocatalyst in Water and Air Purification

The development of clean and sustainable teleology is vital to treat the critical environmental pollutants. In the last decade, the use of photocatalytic reactors has been widely reported for organic pollutants degradation. From photocatalysis’s application in environmental remediation, the primary technical issue to scientists is always the efficiency. The enhanced photocatalytic efficiency is mainly depended on the materials improvement. However, the design of photoreactors lags behind the development of photocatalysts, which strongly limit the widespread use of photocatalysis technology in environmental remediation. The nanoparticles separation, mass transfer limitation, and photonic efficiency have always been problematic and restrict the high photocatalytic efficiency of photoreactors. To overcome these bottleneck problems, the most popular or newfangled designs of photoreactors employed in air and water treatment has been reviewed. The purpose of this review is to systematize designs and synthesis of innovative TiO2-based photoreactors and provides detailed survey and discussion on the enhanced mechanism of photocatalytic performance in different TiO2-based photoreactors. The most studied photoreactors are the following: packed bed reactor, film reactor and membrane reactor, which have some limitations and advantages. A comprehensive comparison between the different photocatalytic performance of TiO2-based photoreactors is presented. This work aims to summarize the progress of TiO2-based photoreactors and provides useful information for the further research and development of photocatalysis for water and air purification.

Emerging Trends in the Remediation of Persistent Organic Pollutants Using Nanomaterials and Related Processes: A Review

Persistent organic pollutants (POPs) have become a major global concern due to their large amount of utilization every year and their calcitrant nature. Due to their continuous utilization and calcitrant nature, it has led to several environmental hazards. The conventional approaches are expensive, less efficient, laborious, time-consuming, and expensive. Therefore, here in this review the authors suggest the shortcomings of conventional techniques by using nanoparticles and nanotechnology. Nanotechnology has shown immense potential for the remediation of such POPs within a short period of time with high efficiency. The present review highlights the use of nanoremediation technologies for the removal of POPs with a special focus on nanocatalysis, nanofiltration, and nanoadsorption processes. Nanoparticles such as clays, zinc oxide, iron oxide, aluminum oxide, and their composites have been used widely for the efficient remediation of POPs. Moreover, filtrations such as nanofiltration and ultrafiltration have also shown interest in the remediation of POPs from wastewater. From several pieces of literature, it has been found that nano-based techniques have shown complete removal of POPs from wastewater in comparison to conventional methods, but the cost is one of the major issues when it comes to nano- and ultrafiltration. Future research in nano-based techniques for POP remediation will solve the cost issue and will make it one of the most widely accepted and available techniques. Nano-based processes provide a sustainable solution to the problem of POPs.

Comprehensive review on advanced reusability of g-C3N4 based photocatalysts for the removal of organic pollutants

Graphitic carbon nitride (g-C₃N₄) has attained significant research attention in energy and environmental remediation due to its excellent electronic structure, greater physical and chemical properties, and abundance. However, graphitic carbon nitride faces severe problems because of its high recombination rate and higher mass loss of the catalyst during recovery operations. This review emphasizes the methods to overcome the difficulties associated with recovery and reusability of the g-C₃N₄ based photocatalyst towards the redemption of pollutants present in wastewater. Different strategies like magnetic g-C₃N₄ based photocatalysts, immobilized photocatalytic systems, and photocatalytic membranes and their usage in photocatalytic applications are well described. Different preparation strategies of the graphic carbon nitride-based composites are elucidated. The key challenges and future perspectives of adopting these methods for photocatalytic applications are also mentioned.

Reusability in visible light of titanate nanotubes for the removal of organic pollutants: role of calcination temperature

Titanate nanotubes (NTs) were synthesised by the hydrothermal method and later calcined at temperatures between 100-500°C. The calcined NTs were characterised and evaluated in the physicochemical adsorption of the safranin dye and photocatalytic degradation of caffeine. The materials calcined at low temperatures displayed a tubular structure and the H₂Ti₃O₇ crystalline phase, which was transformed into anatase nanoparticles at 400°C. The NTs treated at 100°C showed the highest adsorption capacity (94%). Safranin was adsorbed through an ion-exchange mechanism, following the Langmuir isotherm and a pseudo-second-order kinetic model. While NTs calcined at lower temperatures were better for adsorption, the photocatalytic degradation of caffeine increased in samples calcined at higher temperatures with a maximum removal of 72%. The photocatalytic behaviour of the NT samples confirmed that the crystalline anatase structure in conjunction with structural OH groups enhanced the photocatalytic activity. The addition of isopropanol as a scavenger confirmed the important role played by the •OH radicals in the photocatalytic process. NTs calcined at 300°C were efficient for both adsorption and photocatalytic processes. Due to its efficiency, this sample was reused after dye adsorption for the photocatalytic degradation of caffeine under visible light due to its enhanced absorbance in the visible region. This research work shows the potential of NTs for wastewater purification.

A Novel BiOCl Based Nanocomposite Membrane for Water Desalination

In this study, BiOCl based nanocomposites were used as photocatalytic membranes for a simulated study on water desalination in reverse osmosis membrane systems. Through molecular dynamic simulation, the molecular structure of BiOCl, BiOCl/Ag2S and BiOCl/Bi2O3 heterojunctions were designed and their electronic properties, mechanical properties, and membrane performance for water desalination were evaluated for the first time. The molecular structure was created, and a geometry optimization task was used to optimize it. Material Studio 2019 CASTEP was used for simulation of the electronic and mechanical properties and water desalination was performed by ReaxFF software under pressures between 0 and 250 MPa. The novel BiOCl based nanocomposites showed improved electronic and mechanical properties and, most importantly, improvements in salt rejection and water permeability as compared to well-known materials such as graphene and MoS2. BiOCl and BiOCl/Ag2S had a bandgap around two, which is the ideal bandgap for semiconductor photocatalysts. A salt rejection of 98% was achieved under an applied pressure of 10 MPa. Salt rejection was higher for BiOCl/Bi2O3, while water permeability was higher for BiOCl/Ag2S. The monolayer BiOCl was unstable under pressures higher than 50 MPa, but the mechanical stability of BiOCl/Ag2S increased twofold and increased fourfold for BiOCl/Bi2O3, which is even higher than MoS2. However, between the three nanocomposites, BiOCl/Ag2S was found to be the most ideal photocatalytic nanocomposite membrane.

Preparation and Photocatalytic Performance of TiO2 Nanowire-Based Self-Supported Hybrid Membranes

Nowadays, the use of hybrid structures and multi-component materials is gaining ground in the fields of environmental protection, water treatment and removal of organic pollutants. This study describes promising, cheap and photoactive self-supported hybrid membranes as a possible solution for wastewater treatment applications. In the course of this research work, the photocatalytic performance of titania nanowire (TiO₂ NW)-based hybrid membranes in the adsorption and degradation of methylene blue (MB) under UV irradiation was investigated. Characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffractometry (XRD) were used to study the morphology and surface of the as-prepared hybrid membranes. We tested the photocatalytic efficiency of the as-prepared membranes in decomposing methylene blue (MB) under UV light irradiation. The hybrid membranes achieved the removal of MB with a degradation efficiency of 90% in 60 min. The high efficiency can be attributed to the presence of binary components in the membrane that enhanced both the adsorption capability and the photocatalytic ability of the membranes. The results obtained suggest that multicomponent hybrid membranes could be promising candidates for future photocatalysis-based water treatment technologies that also take into account the principles of circular economy.

Photocatalytic Fuel Cells for Simultaneous Wastewater Treatment and Power Generation: Mechanisms, Challenges, and Future Prospects

Technological advancement is accompanied by excessive consumption of fossil fuels and affluent uses of chemical substances in many sectors, including transportation and manufacturing companies, and so on. Being an exhaustible resource, the excessive use of fossil fuels and of chemical substances may lead to a serious energy crisis in the long run, and it may additionally impose environmental pollution. Attempts have been made in the solution of such serious issues from every nook and corner. Nonetheless, no method has been found to be a panacea in waste water treatment and subsequent beneficiaries. One of the attempts in the solution to such issues is the application of photocatalytic technology, which could serve as a dual function in environmental remediation and clean energy production. A photocatalytic fuel cell is a tool developed for the recovery of energy from organic wastes. A rational cell construction needs the fabrication of photoelectrodes, the design of a photoanode and a photocathode chamber, in addition to an ion-transport membrane for pollution treatment and electricity generation. In this review, comprehensive fundamental assessments and recent developments in the design of photocatalytic fuel cells, their applications, future prospects, and challenges are covered.

High-performance photocatalytic membranes for water purification in relation to environmental and operational parameters

Growing technologies, increasing population and environmental pollution lead to severe contamination of water and require advanced water treatment technologies. These aspects lead to the need to purify water with advanced smart materials. This paper reviews the recent advances (during the last 5 years) in photocatalytic composite membranes used for water treatment. For this purpose, the authors have reviewed the main materials used in the development of (photocatalytic membranes) PMs, environmental and operational factors affecting the performance of photocatalytic membranes, and the latest developments and applications of PMs in water purifications. The composite photocatalytic membranes show good performance in the removal and degradation of pollutants from water.

Practical scale evaluation of a photocatalytic air purifier equipped with a Titania-zeolite composite bead filter for VOC removal and viral inactivation

A practical scale photocatalytic air purifier equipped with a TiO₂/H-ZSM-5 composite bead filter was demonstrated to be able to effectively remove indoor volatile organic compounds (VOCs) and viruses with sustainable performances under UVA-LED illumination. TiO₂ hybridized with 5 wt% H-ZSM-5 zeolite significantly enhanced its photocatalytic activity for degrading VOCs including formaldehyde, acetaldehyde, and toluene, than bare TiO₂. H-ZSM-5 provided strong adsorption sites for these compounds, thus accelerating their photocatalytic conversion into CO₂ by adjacent TiO₂ photocatalyst. Moreover, owing to its superior adsorption capacity, the composite bead filter completely prevented the emission of formaldehyde produced by photocatalytic oxidation of toluene. The sustainability of this composite bead filter for VOC removal was confirmed by regeneration and accelerated durability tests. In addition, the photocatalytic air purifier was effective in removing aerosolized viral particles of bacteriophage Phi-X 174. It was confirmed that the viruses on filter surfaces were completely inactivated by photocatalytic oxidation. TiO₂/H-ZSM-5 composite beads also exhibited excellent efficacies for inactivation of pathogenic coronaviruses including SARS-CoV-2. The photocatalytic process degraded viral RNAs of SARS-CoV-2 by more than 99.999% in 1 h, eliminating the viral infectivity. Results of this study suggest that the air purifier equipped with the composite bead filter is ready for practical applications for home and hospital uses.