Photo-Fenton self-cleaning PVDF/NH2-MIL-88B(Fe) membranes towards highly-efficient oil/water emulsion separation

Illuminating for purity: Photocatalytic and photothermal membranes for sustainable oil-water separation

The integration of photocatalytic and photothermal materials with oil-water separation membranes marks a significant advancement in sustainable separation technologies. These hybrid membranes exhibit exceptional functionalities, including resistance to oil fouling, self-cleaning, antibacterial properties, and reduced oil viscosity. Based on their reaction mechanisms, current photocatalytic and photothermal membranes are categorized into four types, i.e., photocatalytic membranes, photo-Fenton membranes, PMS-assisted photocatalytic membranes, and photothermal membranes. Under light irradiation, photocatalytically functionalized membranes generate reactive oxygen species (ROS) that degrade organic pollutants and inactivate bacteria on the membrane surfaces, enabling in-situ cleaning and regeneration. In addition to the above benefits, photothermal membranes achieve reduction of oil viscosity for higher membrane permeation and removal of light oil from membrane surfaces through light-induced heating. This review first explores the mechanisms underlying light-driven advanced oxidation processes (AOPs) and photothermal effects, followed by an in-depth discussion on the fabrication methods of these membranes. Additionally, the applications of photocatalytic and photothermal membranes in oil-water separation are examined, with an emphasis on how the photocatalytic and photothermal materials contribute to membrane functionality. Finally, this review presents the challenges currently faced by photocatalytic and photothermal membranes and outlines future research directions.

Facile Preparation of Sulfonated Polysulfone Composite Membranes with High Hydrophilicity and Visible-Light Driving Self-Cleaning Performance

The photo-Fenton reaction can efficiently degrade organic pollutants and thus is applied intensively for clearing out membrane fouling. However, the pollutant removal efficiency is greatly limited by the redox cycle rate of Fe2+/Fe3+ and the rapid recombination rate of the photogenerated electrons and holes. In order to overcome these drawbacks, a sulfonated polysulfone composite membrane was designed and prepared by incorporating titanium dioxide (TiO2) nanoparticles into a sulfonated polysulfone membrane and sequentially forming β-FeOOHs on the membrane surface. It was found that the synergy of TiO2 and β-FeOOH enhanced the hydrophilicity and improved the pure water flux of the composite membrane. As a result, the composite membrane exhibited superior separation performance for methylene blue and rhodamine B cationic dyes. The rejection rate was larger than 99.5%, and the pure water flux was larger than 125.7 L m-2 h-1, largely surpassing that of nanofiltration membranes. Meanwhile, the composite membrane exhibited an excellent self-cleaning performance, achieving a flux recovery rate over 99.7% after visible-light driving Fenton reaction treatment. The rejection rate still remained above 97.2% after 5 cycles of filtration and recovery, indicating the strong treatment ability of the membrane for dye wastewater.

Effect of degree of polymerization on regenerated cellulose ultrafiltration membrane performance through ZnCl2/AlCl3 aqueous solvent system

The development of a direct method for preparing regenerated cellulose (RC) ultrafiltration membranes from cellulose is urgently needed. In this study, refined cotton was used as the raw material to successfully prepare RC ultrafiltration membranes at room temperature using a ZnCl2/AlCl3 solvent system combined with a nonsolvent-induced phase separation (NIPS) method. This solvent system effectively degrades cellulose, producing RC ultrafiltration membranes with varying degrees of polymerization (DP). The research results indicate that reducing the DP of cellulose significantly decreases the viscosity of the solution, facilitating the formation of an asymmetric, finger-like pore structures in the membrane. Furthermore, a decrease in DP slightly enlarges the surface pore size and significantly thickens the dense layer. At a DP of 250, the water flux of the DP250-ET membrane reached 630 L·m-2·h-1·bar-1, with a molecular weight cut-off (MWCO) of ~300 kDa, enabling efficient separation of viruses (LRV > 3.91) and IgG. The exposure of more hydroxy groups on the RC enhances the membrane's hydrophilicity, indicated by a water contact angle (WCA) of 39.5°. Compared to commercial polyethersulfone (PES) membranes, the DP250-ET membrane exhibited lower protein adsorption and excellent anti-fouling performance in practical applications (FRR > 80 %). Overall, this work confirms the significant potential of the eco-friendly ZnCl2/AlCl3 solvent system in the fabrication of RC ultrafiltration membranes, where the structure and performance of the membrane can be tailored by adjusting the DP of cellulose.

An Assessment of the Catalytic and Adsorptive Performances of Cellulose Acetate-Based Composite Membranes for Oil/Water Emulsion Separation

Cellulose acetate (CA) mixed-matrix membranes incorporating polyvinylpyrrolidone (PVP), bentonite (B or Ben), graphene oxide (GO), and titanium dioxide (TiO2) were prepared by the phase inversion separation technique for oil/water separation. An investigation was performed where the mixed-matrix membrane was tested for the separation performance of hydrophilic and hydrophobic surface properties. An ultrafiltration experiment at the laboratory scale was used to test dead-end ultrafiltration models developed for the treatment performances of oily wastewater under dynamic full-scale operating conditions. Artificial oily wastewater solutions were prepared from hexane, toluene, and engine oil with Tween80 emulsions for oil removal treatment using composite membranes. The impacts of material hydrophilicity, weight loss, permeability, and pore size were investigated, and it was found that the oil retention of membranes with larger pore sizes enabled much more sophisticated water flux. The CA-GO-, CA-B-, and CA-TiO2-incorporated membranes achieved pure water flux (PWF) values of 45.19, 53.41, and 100.25 L/m2h, respectively. The performance of CA-TiO2 in oil/water emulsion rejection was assessed, and the rejection of engine oil/water, toluene/water, and hexane/water mixtures was determined to be 95.21%, 90.33%, and 92.4%, respectively. The CA-based mixed-matrix membrane portrayed better antifouling properties due to enhanced hydrophilicity and water molecules. The CA-TiO2-incorporated membrane possessed the potential to provide high separation efficiency for oily wastewater treatment. This study demonstrates the potential of fine-tuning membrane performances through material hybridization to achieve efficient wastewater treatment.

An Anchored Fe-Cu LDH onto a Polyvinylidene Fluoride Membrane with Strong Peroxymonosulfate Activation-Induced Degradation of Methylene Blue and Self-Cleaning Property of Oil/Water Separation

Developing a strong catalytic antifouling membrane to achieve efficient sewage purification has great potential for alleviating water crisis. In this work, we designed and prepared an Fe/Cu-layered double hydroxide (Fe-Cu LDH)-coated polyvinylidene fluoride (PVDF) composite membrane (PVDF/Fe-Cu LDHs) with strong antifouling and activating peroxymonosulfate (PMS) catalytic degradation performance through polydopamine-coordination anchoring and hydrothermal reaction. The results showed that abundant hydroxyl groups of the LDH surface endowed the superhydrophilicity (water contact angle <10°) and underwater superoleophobicity (underwater-oil contact angle >150°) of the membrane surface, which displayed outstanding resistance to crude oil adhesion. With assistance of the LDH surface-bound sulfate radical of the peroxymonosulfate system, the PVDF/Fe-Cu LDH membrane demonstrated robust catalytic degradation performance for the methylene blue (MB) in the dark; the degradation rate constant (k, min-1) reached 0.96. Meanwhile, facing the oily wastewater, the selective wettability and charge effect of LDH of the surface made the PVDF/Fe-Cu LDH membrane realize the separation for the various surfactant-free and surfactant-stabilized emulsions. Importantly, the PMS-activation catalytic produced the ROS (•SO4-,•OH, •O2-, and 1O2), which enhanced the regeneration of the fouled PVDF/Fe-Cu LDH membrane and obtained a high flux recovery ratio in the dark (94.7%) after 10 cycles of separation experiments. Hence, we believed that the PVDF/Fe-Cu LDH membrane can provide inspiration for the development and further practical application of antifouling membranes.

Bioinspired superwetting oil-water separation strategy: toward the era of openness

Bioinspired superwetting oil-water separation strategies have received significant attention for their potential in addressing global water scarcity and aquatic pollution challenges. Over the past two decades, the field has rapidly developed, reaching a pivotal phase of innovation in the oil-water separation process. However, many groundbreaking studies have not received extensive scientific recognition. In this review, we systematically examine the application of bioinspired superwetting materials for complex multiscale oil-water separation. We discuss the development of 2D membrane filtration and 3D sponge adsorption materials in confined spaces, summarizing the core separation mechanisms, key research findings, and the evolutionary logic of these materials. Additionally, we highlight emerging open-space separation strategies, emphasizing several novel dynamic separation devices of significant importance. We evaluate and compare the design concepts, separation principles, materials used, comprehensive performance, and existing challenges of these diverse strategies. Finally, we summarize these advantages, critical bottlenecks, and prospects of this field and propose potential solutions for real oil-water separation processes from a general perspective.

Construction of self-cleaning g-C3N4/Bi2MoO6/PVDF membrane and coupling with photo-Fenton-like reaction for sustainable removal of antibiotics in wastewater

Constructing a photocatalytic membrane and photo-Fenton reaction coupling system is a novel strategy to enhance the photocatalytic activity of the membrane and eliminate the problem of membrane contamination. Herein, a g-C3N4/Bi2MoO6/PVDF photocatalytic membrane was prepared using a tannic acid-assisted in-situ deposition method. The membrane was characterized by three advantages of photocatalytic, self-cleaning, and antibacterial properties. Under the photo-Fenton-like conditions, the membrane had superior photodegradation efficiency of 90.7% for tetracycline, one of the main antibiotic contaminants in the China's aquatic system. Moreover, the membrane had excellent photo-Fenton self-cleaning ability, its flux recovery rate was up to 96%-98% after the self-cleaning process. Photoluminescence spectra, diffuse UV-visible spectrum, transient photocurrent responses, and electrochemical AC impedance spectrum results show that the heterojunction structure formed by g-C3N4 and Bi2MoO6 could improve the separation efficiency of photogenerated electrons-hole pairs. Electron spin resonance spectroscopy confirmed the photo-electrons facilitated the formation of hydroxyl radical (·OH) in the existence of H2O2, which enhanced tetracycline degradation. Moreover, the superior photo-Fenton self-cleaning performance, which mainly relied on the active free radicals produced by the photo-Fenton-like membrane to remove dirt on the membrane surface or in the membrane pore channel. Our results may shed new light on the development of promising photocatalytic membrane systems by coupling with photo-Fenton-like processes, and facilitate their applications for wastewater treatment.

Dialdehyde cellulose (DAC) and polyethyleneimine (PEI) coated polyvinylidene fluoride (PVDF) membrane for simultaneously removing emulsified oils and anionic dyes

Developing high-efficiency membrane for oil and dye removal is very urgent, because wastewater containing them can cause great damage to human and environment. In this study, a coated membrane was fabricated by applying DAC and PEI onto the commercial PVDF microfiltration membrane for supplying the demand. The coated membrane presents superhydrophlic and superoleophobic properties with a water contact angle of 0o and underwater oil contact angle exceed 150°, as well as excellent low underwater oil adhesion performance. The coated membrane shows high separation efficiency exceeded 99.0% and flux 350.0 L·m-2·h-1 when used for separating for six kinds of oil including pump oil, sunflower oil, n-hexadecane, soybean oil, diesel and kerosene in water emulsions. Additionally, the coated membrane can effectively remove anionic dyes, achieving rejection rates of 94.7%, 93.4%, 92.3%, 90.7% for the CR, MB, RB5, AR66, respectively. More importantly, the membrane was able to simultaneously remove emulsified oil and soluble anionic dyes in wastewater containing both of them. Therefore, this novel coated membrane can be a promising candidate for treating complex wastewater.

Assembling 99% MOFs into Bioinspired Rigid-Flexible Coupled Membrane with Significant Permeability: The Impacts of Defects

Assembling metal-organic frameworks (MOFs) into high-performance macroscopic membranes is crucial but still challenging. MOF-containing hybrid membranes can effectively integrate the advantages of flexible guest materials and MOFs. Nevertheless, the inherent limitations in fully harnessing the distinct characteristics of MOFs persist due to the substantial guest material content necessitated in membrane fabrication. Herein, inspired by the rigid and flexible structures in biological systems, rigid MIP-202(Zr) and defective MIP-202(Zr) (D-MIP-202(Zr)) modified flexible graphene oxide (GO) sheets are synthesized in situ and then assembled into a rigid-flexible coupled MOF-based membrane. The defects in D-MIP-202(Zr) are introduced by using acetic acid as the modulation agent. The obtained GO@MIP-202(Zr) membrane possesses a hierarchical porous structure with a 99 wt% MOF proportion, which is higher than the GO@D-MIP-202(Zr) (75 wt%) membrane with a compact bulge-structured surface. The water permeability of the GO@MIP-202(Zr) membrane attains remarkedly 5762.92 L h-1 m-2 bar-1 , which is 960 and 2.6 times higher than that of the GO membrane and GO@D-MIP-202(Zr) membrane. Additionally, benefiting from the superhydrophilicity and underwater superoleophobicity, the resultant membrane not only demonstrates high rejection for oil-water emulsions but also exhibits exceptional recyclability and anti-fouling ability. These findings provide valuable insights into the assembly of MOFs into high-performance membranes.

Application and prospects of metal–organic frameworks in photocatalytic self-cleaning membranes for wastewater treatment

By loading photocatalytic MOF onto the separation membrane, the self-cleaning function of the membrane can be realized. This paper discusses the structure, synthesis, and properties of photocatalytic MOFs.

Super-wetting and self-cleaning polyvinyl alcohol/sodium alginate nanofiber membrane decorated with MIL-88A(Fe) for efficient oil/water emulsion separation and dye degradation

Membrane separation is considered an effective approach to water purification. Nevertheless, membrane fouling dramatically decreases the separation efficiency and lifetime of membranes, thus limiting its further development and application. Herein, a multifunctional self-cleaning MIL-88A(Fe) decorated polyvinyl alcohol/sodium alginate (MIL-88A(Fe)@PVA-SA) nanofiber membrane was prepared by electrospinning and in-situ growth methods for the separation of oil/water emulsions and photo-Fenton degradation of dyes. The membrane possesses superhydrophilicity with a water contact angle (WCA) of 0° and superoleophobicity with underwater oil contact angle (UCA) of 161.7°, and exhibits superior separation efficiency (>99.5 %) and permeation flux (1140-2455 L/m2/h) for different oil/water emulsions. Moreover, the membrane exhibited an outstanding photo-Fenton performance under visible light, with degradation efficiencies (~99.9 %) towards methylene blue (MB) and reactive red 24 (RR24) within 90 min. Importantly, the membrane can be easily regenerated by simple rinsing and photo-Fenton self-cleaning treatment. In this study, MIL-88A(Fe)@PVA-SA nanofiber membrane has a promising application in dye removal and oil/water separation, providing a new idea to develop novel membrane materials.

Research progress of MOF-based membrane reactor coupled with AOP technology for organic wastewater treatment

MOF-based catalytic membrane reactor (MCMR), which can simultaneously achieve membrane separation and chemical catalytic degradation in an integrated system, is a cutting-edge technology for effective treatment of organic pollutants in water. The coupling of MCMR and advanced oxidation process (AOP) not only significantly improves the pollutant removal efficiency but also inhibits the membrane pollution through self-cleaning effect, thus improving the stability of MCMR. This paper reviews different MCMR systems combined with photocatalysis, Fenton oxidation, and persulfate activation, elucidates the reaction mechanism, discusses key issues to improve system effectiveness, and suggests future challenges and research directions.

Recent Developments in Two-Dimensional Materials-Based Membranes for Oil-Water Separation

The industrialization witnessed in the last century has resulted in an unprecedented increase in water pollution. In particular, the water pollution induced by oil contaminants from oil spill accidents, as well as discharges from pharmaceutical, oil/gas, and metal processing industries, have raised concerns due to their potential to pose irreversible threats to the ecosystems. Therefore, the effective treating of these large volumes of oily wastewater is an inevitable challenge to address. Separating oil-water mixtures by membranes has been an attractive technology due to the high oil removal efficiency and low energy consumption. However, conventional oil-water separation membranes may not meet the complex requirements for the sustainable treatment of wastewater due to their relatively shorter life cycle, lower chemical and thermal stability, and permeability/selectivity trade-off. Recent advancements in two-dimensional (2D) materials have provided opportunities to address these challenges. In this article, we provide a brief review of the most recent advancements in oil-water separation membranes modified with 2D materials, with a focus on MXenes, graphenes, metal-organic frameworks, and covalent organic frameworks. The review briefly covers the backgrounds, concepts, fabrication methods, and the most recent representative studies. Finally, the review concludes by describing the challenges and future research directions.

Preparation of Superhydrophilic/Underwater Superoleophobic and Superhydrophobic Stainless Steel Meshes Used for Oil/Water Separation

Robust membrane materials with high efficiency have attracted extensive attention in oil/water separation. In this work, carbon particles via candle combustion were firstly adsorbed on the surface of stainless steel meshes (SSMs), which formed a thin hydrophobic coating, and a rough structure was then constructed through chemical vapor deposition and high temperature calcination, with the resultant SSM surface wrapped with uniform silica coating possessing the characteristic of superoleophobicity underwater. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray powder diffraction (XRD) were used to characterize the modified SSMs. The prepared SSMs were superhydrophilic in air, and they had superoleophobicity underwater (157.4°). The separation efficiency of five oil/water mixtures was above 98.8%, and the separation flux was 46,300 L·m^-2·h^-1. After it was immersed in 1 mol/L NaOH, 1 mol/L HCl and 3.5 wt% NaCl for 24 h, respectively, the efficiency was still above 97.3%. Further immersion in the solution of dopamine and octadecylamine resulted in the transformation of superhydrophililc/superoleophobicity-underwater SSMs to superhydrophobic SSMs, and the resultant SSMs with reverse surface wettability was also used for the oil/water separation with good separation efficiency and separation flux.

A solar-driven degradation-evaporation strategy for membrane self-cleaning in the efficient separation of viscous crude oil/water emulsions

Membrane separation techniques are promising methods for effectively treating hazardous emulsified oily wastewater, but membrane fouling remains a serious challenge because the high viscosity and complex composition of crude oil make it easy to adhere to membranes and difficult to be removed by conventional physical or chemical cleaning means. Herein, a two-stage solar-driven (photo-Fenton degradation/evaporation) strategy was proposed to realize the self-cleaning of membranes fouled by viscous crude oil (>60,000 mPa s), wherein the photo-Fenton process helped to degrade the heavy components into light components, and all light components removed during the solar-driven evaporation process. A 1D/2D heterostructure membrane with photo-Fenton activity and anti-crude-oil-fouling performance was prepared via a facile self-assembly vacuum-assist method. The addition of rod-like g-C₃N₄ (RCN) increased the interlayer distance of α-FeOOH/porous g-C₃N₄ (FPCN) nanosheets, resulting in a high permeation flux. The FPCN-RCN membrane exhibited both high permeation flux of 779 ± 19 L m^-2h^-1bar^-1 and a separation efficiency of 99.4% for highly viscous crude oil-in-water emulsion. Importantly, the viscous crude oil fouled on the membrane was completely removed by the photo-Fenton degradation/solar-driven evaporation strategy, and the flux recovery rate of the membrane was ∼100%. Therefore, the FPCN-RCN membrane combined with the novel self-cleaning strategy exhibits great potential for practical emulsified oily wastewater treatment.

Ultrathin g-C3N4 composite Bi2WO6 embedded in PVDF UF membrane with enhanced permeability, anti-fouling performance and durability for efficient removal of atrazine

A novel Bi₂WO₆-g-C₃N₄/polyvinylidene fluoride (PVDF) composite ultrafiltration (UF) membrane (BWO-CN/PVDF) was prepared by microwave hydrothermal and immersion precipitation phase transformation method. The BWO-CN/PVDF-0.10 exhibited an outstanding photocatalytic removal rate of atrazine (ATZ) (97.65 %) under the simulated sunlight and enhanced permeate flux (1356.09 L·m^-2·h^-1). The multiple optical and electrochemical detection confirmed that combining ultrathin g-C₃N₄ and Bi₂WO₆ can increase carrier separation rate and prolong its lifetime. The quenching test revealed that h⁺ and ¹O₂ were the prominent reactive species. Additionally, after a 10-cycle photocatalytic process, the BWO-CN/PVDF membrane presented remarkable reusability and durability. And it showed excellent anti-fouling performance by filtering BSA, HA, SA, and Songhua River under simulated solar irradiation. The molecular dynamic (MD) simulation showed that the combination of g-C₃N₄ and Bi₂WO₆ can enhance the interaction between BWO-CN and PVDF. This work opens up a new idea for designing and constructing a highly efficient photocatalytic membrane for water treatment.

A novel design of Cu(I) active site on the metal-organic framework for exploring the structural transformation of Fenton-like catalysts through in situ "capturing" OH. J Colloid Interface Sci 2023;648:778-786. [PMID: 37321097 DOI: 10.1016/j.jcis.2023.05.189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

The mutual transformation of reactive oxygen species may affect the structural transformation of catalysts during the Fenton-like processes. Its in-depth understanding is essential to achieve high catalytic activity and stability. In this study, a novel design of Cu(I) active sites based on the metal-organic framework (MOF) is proposed to "capture" OH^- produced via Fenton-like processes and re-coordinate the oxidized Cu sites. The Cu(I)-MOF presents an excellent removal efficiency for sulfamethoxazole (SMX), with a high removal kinetic constant of 7.146 min^-1. Combing DFT calculations with experimental observations, we have revealed that the Cu of Cu(I)-MOF exhibits a lower d-band center, enabling efficient activation of H₂O₂ and spontaneous "capturing" of OH^- to form Cu-MOF, which can be reorganized into the Cu(I)-MOF through molecular regulation for recycle. This research demonstrates a promising Fenton-like approach for solving the trade-off between catalytic activity and stability and provides new insights into the design and synthesis of efficient MOF-based catalysts for water treatment.

Application of Photo-Fenton-Membrane Technology in Wastewater Treatment: A Review

Photo-Fenton coupled with membrane (photo-Fenton-membrane) technology offers great potential benefits in future wastewater treatment because it can not only degrade refractory organics, but also separate different pollutants from water; additionally, it often has a membrane-self-cleaning ability. In this review, three key factors of photo-Fenton-membrane technology, photo-Fenton catalysts, membrane materials and reactor configuration, are presented. Fe-based photo-Fenton catalysts include zero-valent iron, iron oxides, Fe-metal oxides composites and Fe-based metal-organic frameworks. Non-Fe-based photo-Fenton catalysts are related to other metallic compounds and carbon-based materials. Polymeric and ceramic membranes used in photo-Fenton-membrane technology are discussed. Additionally, two kinds of reactor configurations, immobilized reactor and suspension reactor, are introduced. Moreover, we summarize the applications of photo-Fenton-membrane technology in wastewater, such as separation and degradation of pollutants, removal of Cr(VI) and disinfection. In the last section, the future prospects of photo-Fenton-membrane technology are discussed.

Fabrication of Anatase TiO2/PVDF Composite Membrane for Oil-in-Water Emulsion Separation and Dye Photocatalytic Degradation

At present, the types of pollutants in wastewater are more and more complicated, however, the multifunctional membrane materials are in short supply. To prepare a membrane with both high efficient oil-in-water emulsion separation performance and photocatalytic degradation performance of organic dyes, the bifunctional separation membrane was successfully prepared by electrostatic spinning technology of PVDF/PEMA and in situ deposition of anatase TiO₂ nanoparticles containing Ti³⁺ and oxygen vacancies (O_v). The prepared composite membrane has excellent hydrophilic properties (WCA = 15.65), underwater oleophobic properties (UOCA = 156.69), and photocatalytic performance. These composite membranes have high separation efficiency and outstanding anti-fouling performance, the oil removal efficiency reaches 98.95%, and the flux recovery rate (FRR) reaches 99.19% for soybean oil-in-water emulsion. In addition, the composite membrane has outstanding photocatalytic degradation performance, with 97% and 90.2% degradation of RhB and AG-25 under UV conditions, respectively. Several oil-in-water separation and dye degradation experiments show that the PVDF composite membrane has excellent reuse performance. Based on these results, this study opens new avenues for the preparation of multifunctional reusable membranes for the water treatment field.

Hydrogel/β-FeOOH-Coated Poly(vinylidene fluoride) Membranes with Superhydrophilicity/Underwater Superoleophobicity Facilely Fabricated via an Aqueous Approach for Multifunctional Applications

Hydrogel coatings that can endow various substrates with superior properties (e.g., biocompatibility, hydrophilicity, and lubricity) have wide applications in the fields of oil/water separation, antifouling, anti-bioadhesion, etc. Currently, the engineering of multifunctional hydrogel-coated materials with superwettability and water purification property using a simple and sustainable strategy is still largely uninvestigated but has a beneficial effect on the world. Herein, we successfully prepared poly(2-acrylamido-2-methyl-1-propanesulfonic acid) hydrogel/β-FeOOH-coated poly(vinylidene fluoride) (PVDF/PAMPS/β-FeOOH) membrane through free-radical polymerization and the in situ mineralization process. In this work, owing to the combination of hydrophilic PAMPS hydrogel coating and β-FeOOH nanorods anchored onto PVDF membrane, the resultant PVDF/PAMPS/β-FeOOH membrane achieved outstanding superhydrophilicity/underwater superoleophobicity. Moreover, the membrane not only effectively separated surfactant-stabilized oil/water emulsions, but also possessed a long-term use capacity. In addition, excellent photocatalytic activity against organic pollutants was demonstrated so that the PVDF/PAMPS/β-FeOOH membrane could be utilized to deal with wastewater. It is envisioned that these hydrogel/β-FeOOH-coated PVDF membranes have versatile applications in the fields of oil/water separation and wastewater purification.

Next-generation graphene oxide additives composite membranes for emerging organic micropollutants removal: Separation, adsorption and degradation

In the past two decades, membrane technology has attracted considerable interest as a viable and promising method for water purification. Emerging organic micropollutants (EOMPs) in wastewater have trace, persistent, highly variable quantities and types, develop hazardous intermediates and are diffusible. These primary issues affect EOMPs polluted wastewater on an industrial scale differently than in a lab, challenging membranes-based EOMP removal. Graphene oxide (GO) promises state-of-the-art membrane synthesis technologies and use in EOMPs removal systems due to its superior physicochemical, mechanical, and electrical qualities and high oxygen content. This critical review highlights the recent advancements in the synthesis of next-generation GO membranes with diverse membrane substrates such as ceramic, polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The EOMPs removal efficiencies of GO membranes in filtration, adsorption (incorporated with metal, nanomaterial in biodegradable polymer and biomimetic membranes), and degradation (in catalytic, photo-Fenton, photocatalytic and electrocatalytic membranes) and corresponding removal mechanisms of different EOMPs are also depicted. GO-assisted water treatment strategies were further assessed by various influencing factors, including applied water flow mode and membrane properties (e.g., permeability, hydrophily, mechanical stability, and fouling). GO additive membranes showed better permeability, hydrophilicity, high water flux, and fouling resistance than pristine membranes. Likewise, degradation combined with filtration is two times more effective than alone, while crossflow mode improves the photocatalytic degradation performance of the system. GO integration in polymer membranes enhances their stability, facilitates photocatalytic processes, and gravity-driven GO membranes enable filtration of pollutants at low pressure, making membrane filtration more inexpensive. However, simultaneous removal of multiple contaminants with contrasting characteristics and variable efficiencies in different systems demands further optimization in GO-mediated membranes. This review concludes with identifying future critical research directions to promote research for determining the GO-assisted OMPs removal membrane technology nexus and maximizing this technique for industrial application.

A passive-active combined strategy for ultrafiltration membrane fouling control in continuous oily wastewater purification

Membrane-based technology has been confirmed as an effective way to treat emulsified oily wastewater, however, membrane fouling is still one of practical challenges in long-term operation. Herein, a novel passive-active combined strategy was proposed to control membrane fouling in continuous oily wastewater purification, where the δ-MnO₂ decoration layer helped to reduce the total fouling ratio (passive strategy for fouling mitigation) and the catalytic cleaning effectively removed the irreversible oil fouling (active strategy for fouling removal). The functional membrane was prepared via in-situ modification, referred to as δ-MnO₂@TA-PES. The morphology, crystalline phase, chemical structure and surface properties of the membranes were systematically characterized. Compared with PES, the δ-MnO₂@TA-PES possessed superhydrophilicity, enhanced electronegativity and narrowed pore size. The δ-MnO₂@TA-PES achieved high water permeation flux of 723.9 L·m ^- 2·h ^- 1·bar^-1, excellent oil rejection with separation efficiency above 98.5% for various emulsions, and durable anti-oil-fouling performance with FRR_b of 98.0%. Notably, the oil cake layer fouling on δ-MnO₂@TA-PES was greatly alleviated owing to its enhanced surface properties. In addition, δ-MnO₂@TA-PES showed high cleaning efficiency in the peroxymonosulfate (PMS) cleaning process, where the radical and nonradical pathways occurred simultaneously. And the active substances generated in the nonradical process (especially ¹O₂) were considered as the main contributor to the reduction of irreversible fouling. Overall, the novel strategy of fouling control ensured the efficient operation of ultrafiltration membranes for the continuous oily wastewater purification.

Membranes for Oil/Water Separation: A Review

Recent advancements in separation and membrane technologies have shown a great potential in removing oil from wastewaters effectively. In addition, the capabilities have improved to fabricate membranes with tunable properties in terms of their wettability, permeability, antifouling, and mechanical properties that govern the treatment of oily wastewaters. Herein, authors have critically reviewed the literature on membrane technology for oil/water separation with a specific focus on: 1) membrane properties and characterization, 2) development of various materials (e.g., organic, inorganic, and hybrid membranes, and innovative materials), 3) membranes design (e.g., mixed matrix nanocomposite and multilayers), and 4) membrane fabrication techniques and surface modification techniques. The current challenges and future research directions in materials and fabrication techniques for membrane technology applications in oil/water separation are also highlighted. Thus, this review provides helpful guidance toward finding more effective, practical, and scalable solutions to tackle environmental pollution by oils.

Metal-organic framework-based materials for the abatement of air pollution and decontamination of wastewater

Developing new and efficient technologies for environmental remediation is becoming significant due to the increase in global concerns such as climate change, severe epidemics, and energy crises. Air pollution, primarily due to increased levels of H₂S, SO_x, NH₃, NO_x, CO, volatile organic compounds (VOC), and particulate matter (PM) in the atmosphere, has a significant impact on public health, and exhaust gases harm the natural sulfur, nitrogen, and carbon cycles. Similarly, wastewater discharged to the environment with metal ions, herbicides, pharmaceuticals, personal care products, dyes, and aromatics/organic compounds is a risk for health since it may lead to an outbreak of waterborne pathogens and increase the exposure to endocrine-disrupting agents. Therefore, developing new and efficient air and water quality management systems is critical. Metal-organic frameworks (MOFs) are novel materials for which the main application areas include gas storage and separation, water harvesting from the atmosphere, chemical sensing, power storage, drug delivery, and food preservation. Due to their versatile structural motifs that can be modified during synthesis, MOFs also have a great promise for green applications including air and water pollution remediation. The motivation to use MOFs for environmental applications prompted the modification of their structures via the addition of metal and functional groups, as well as the creation of heterostructures by mixing MOFs with other nanomaterials, to effectively remove hazardous contaminants from wastewater and the atmosphere. In this review, we focus on the state-of-the-art environmental applications of MOFs, particularly for water treatment and air pollution, by highlighting the groundbreaking studies in which MOFs have been used as adsorbents, membranes, and photocatalysts for the abatement of air and water pollution. We finally address the opportunities and challenges for the environmental applications of MOFs.

PVDF/MOFs mixed matrix ultrafiltration membrane for efficient water treatment

Polyvinylidene fluoride (PVDF), with excellent mechanical strength, thermal stability and chemical corrosion resistance, has become an excellent material for separation membranes fabrication. However, the high hydrophobicity of PVDF membrane surface normally leads a decreased water permeability and serious membrane pollution, which ultimately result in low operational efficiency, short lifespan of membrane, high operation cost and other problems. Metal-organic frameworks (MOFs), have been widely applied for membrane modification due to its large specific surface area, large porosity and adjustable pore size. Currently, numerous MOFs have been synthesized and used to adjust the membrane separation properties. In this study, MIL-53(Al) were blended with PVDF casting solution to prepare ultrafiltration (UF) membrane through a phase separation technique. The optimal separation performance was achieved by varying the concentration of MIL-53(Al). The surface properties and microstructures of the as-prepared membranes with different MIL-53(Al) loading revealed that the incorporation of MIL-53(Al) enhanced the membrane hydrophilicity and increased the porosity and average pore size of the membrane. The optimal membrane decorated with 5 wt% MIL-53(Al) possessed a pure water permeability up to 43.60 L m-2 h-1 bar-1, while maintaining higher rejections towards BSA (82.09%). Meanwhile, the prepared MIL-53(Al)/LiCl@PVDF membranes exhibited an excellent antifouling performance.

Corrosion inhibition of a novel antihistamine-based compound for mild steel in hydrochloric acid solution: experimental and computational studies

Focused on the assessment of the diphenhydramine hydrochloride (DPH) capabilities as an alternative to conventional and harmful industrial corrosion inhibitors, electrochemical techniques were employed. The optimum concentration of 1000 ppm was determined by molecular simulation and validated through electrochemical experiments. The results acquired from the electrochemical impedance spectroscopy (EIS) study showed that DPH at a concentration of 1000 ppm has a corrosion efficiency of 91.43% after 6 h immersion. The DPH molecules' orientation on the surface was assessed based on EIS predicting horizontal adsorption on the surface. Molecular simulations were done to explore the adsorption mechanism of DPH. The DPH molecules' orientation on the surface was also assessed based on computational studies confirming the horizontal adsorption predicted by EIS.

Collagen fiber membrane as multi-functional support enabled rational design of ultrahigh-flux separation membrane for the remediation of oil contamination in water

Membrane separation is a promising approach for the remediation of oil contamination in water. High-flux separation of membrane relies on the rational design of ultrathin active layer to significantly reduce mass transfer distance for achieving high separation flux, while the ultrathin active layer is usually fragile with poor mechanical strength, which has to be supported on a support. Herein, we employed collagen fiber membrane (CFM) as multi-functional support for the in-situ growth of polyacrylonitrile (PAN) layer by electrospinning to prepare the high-performance PAN/CFM composite membrane. Due to the amphiphilic nature and strong capillary effect, CFM played the role as multi-functional support to provide separation effectiveness and boosted separation flux. The PAN/CFM composite membrane enabled ultrahigh separation flux (e.g., 51751.59 L m^-2 h^-1 bar^-1) to a variety of oil-in-water emulsion, which was one order of magnitude higher than that of commercial polyethersulfone membrane and 1.86-fold to that of cellulose acetate membrane. Furthermore, the PAN/CFM composite membrane retained high separation flux (e.g., 11046.97 L m^-2 h^-1 bar^-1) during the 5th separation cycle, providing appreciable anti-fouling capability. Therefore, our findings provided a promising way to effectively resolve the problem of oil contamination in water.

Simultaneous Nitrite Resourcing and Mercury Ion Removal Using MXene-Anchored Goethite Heterogeneous Fenton Composite

The integrated system of gas-phase advanced oxidation process combined with sulfite-based wet absorption process is a desirable method for simultaneous removal of SO₂, NO, and Hg⁰, but due to the enrichment of nitrite and Hg²⁺, resourcing harmless wastewater is still a challenge. To tackle this problem, this study fabricated a bifunctional β-FeOOH@MXene heterogeneous Fenton material, of which the crystalline phase, morphology, structure, and composition were revealed by using X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive x-ray spectroscopy, and transmission electron microscopy. It exhibits excellent performance on nitrite oxidation (99.5%) and Hg²⁺ removal (99.7%) and can maintain stable outstanding ability after 13 cycles, with superior Hg²⁺ adsorption capacity (395 mg/g) and ultralow Fe leaching loss (<0.018 wt %). The synergism between MXene and β-FeOOH appears as follows: (i) MXene, as an inductive agent, directionally converted Fe₂O₃ into β-FeOOH in the hydrothermal method and greatly reduced its monomer size; (ii) the introduced ≡Ti(III)/≡Ti(II) accelerated the regeneration of ≡Fe(II) via rapid electron transfer, thereby improving the heterogeneous Fenton reaction; and (iii) MXene strongly immobilized β-FeOOH to greatly inhibit Fe-leaching. HO^•, ^•O₂^--, and ¹O₂ were the main radicals identified by electron spin resonance. Radical quenching tests showed their contributions to NO₂^- oxidation in the descending order HO^• > ¹O₂ > ^•O₂^-. Quantum chemical calculations revealed that ^•OH-induced oxidation of NO₂^- or HNO₂ was the primary reaction path. Density functional theory calculations combined with X-ray photoelectron spectroscopy and Raman characterizations displayed the Hg²⁺ removal mechanism, with Hg₂Cl₂, HgCl₂, and HgO as the main byproducts. This novel material provides a new strategy for resourcing harmless wastewater containing nitrite and Hg²⁺.

Polydopamine-based multilevel molecularly imprinted nanocomposite membranes comprising metal organic frameworks for selective recognition and separation

Molecularly imprinted nanocomposite membranes with three-dimensional metal-organic frameworks (MOFs)-based structure (MINMs-TM) were successfully prepared by using propranolol as template molecule. Importantly, for the first time, polycarbonate track etch membranes had been used as the supporting surfaces to construct the polydopamine (PDA)-induced MOFs composite structure, in which the as-prepared PDA-modified surface would promote the crystallization and nucleation of ZIF-8-based composite layer. Based on the entire preparation processes of our design, the as-prepared PDA-induced ZIF-8-modified surfaces could be regarded as the imprinted-initiated units of sol-gel imprinting polymerization. Abundant recognition sits of propranolol were achieved in MINMs-TM, which showed characteristic properties of permeability and selectivity. Therefore, high adsorption capacity (41.31 mg/g) and fast adsorption equilibrium rate (within 30 min) had been successfully achieved. Meanwhile, excellent permselectivity rates (β) of MINMs-TM toward propranolol were also obtained as 5.04, 4.79 and 5.14, which MINMs-TM the successful synthesis of high-affinity and high-density propranolol-imprinted sites. Overall, for the practical selective separation and scalability, we had successfully MINMs-TM the preparation of MINMs-TM-based to selective rebinding and separation of propranolol from complex solution system and mimetic water sample, which had further confirmed the desired and potential applications of many environmental pollutants.

Fabrication of photo-Fenton self-cleaning PVDF composite membrane for highly efficient oil-in-water emulsion separation

The anti-fouling performance of membranes is an important performance in the separation of oil/water.

One-step modification of electrospun PVDF nanofiber membranes for effective separation of oil–water emulsion

TA-APTES-SP coating is used to optimize the wettability and stability of PVDF nanofiber membranes for oil–water separation.

Dual-imprinted organic/inorganic nanocomposite membranes with highly selective polydopamine-intimated nanostructures for pharmaceutically active compound separation

Here, the graphene oxide (GO)/SiO₂-loaded dual-imprinted membranes (GS-DIMs) were constructed based on the self-polymerization imprinting technique of dopamine, in which a twice polydopamine (PDA)-based imprinting strategy had been successfully developed to obtain the three-dimensional nanocomposite membrane-based separation system. Meanwhile, the pollution-intensive antibiotics of tetracycline (TC) was used as template molecule throughout the GS-DIMs synthesis, and the dopamine molecules were simultaneously used as functional monomer and cross-linking agent during the twice polydopamine (PDA)-based imprinting processes. Therefore, dual-TC-imprinted sites had been prepared based on the as-designed dual imprinting processes, the as-prepared GS-DIMs-based separation system with dual-TC-imprinted structures could not only allow for the largely enhanced rebinding result of 65.61 mg/g and faster adsorption equilibrium rate within 20 min, but also facilitate the permselectivity performance from TC-based complex separation system and mimetic water sample. Importantly, we demonstrated the applications and effects of the dual-imprinted membrane-based separation materials to selective rebinding and separation of TC from complex solution systems and mimetic water samples. The as-obtained permselectivity factors (β) around 4.0 strongly illustrated the efficiently selective separation ability and high-intensitive recognizability of TC than any other non-template molecules based on our GS-DIMs-based separation system. Overall, the as-designed GS-DIMs had great potential for selective separation applications and provided critical comparisons based on the as-achieved excellent rebinding and permselectivity performance, which encompassed innovative GO/SiO₂-loaded nanocomposite and PDA-based dual-TC-imprinted system.

A Robust PVDF-Assisted Composite Membrane for Tetracycline Degradation in Emulsion and Oil-Water Separation

Tetracycline (TC) contamination in water has progressively exacerbated the environmental crisis. It is urgent to develop a feasible method to solve this pollution in water. However, polluted water often contains oil. This paper reported a glass fiber (FG)-assisted polyvinylidene fluoride (PVDF) hybrid membrane with dual functions: high TC degradation efficiency in emulsion and oil-water separation. It can meet the catalytic degradation of tetracycline in complex water. This membrane was decorated by coating the glass fiber with PVDF solution containing hydrophilic graphene oxide hybridized NH2-MIL-101(Fe) particles. Moreover, due to its strong mechanical strength enhanced by the glass fiber, it can be reused as TC degradation catalysts for dozens of times without cracking. Thanks to the hydrophobicity of PVDF and the surface pore size of MOFs, the prepared membrane showed a good oil-water separation performance. Besides, the hydrophilic graphene oxide (GO) and NH2-MIL-101(Fe) improved the membrane's anti-fouling performance, allowing it to be reused as the separation membrane. Therefore, the outstanding stability and recoverability of the membrane make it as a fantastic candidate material for large-scale removal of TC as well as oil-water separation application.

Hydrophilic and underwater superoleophobic porous graphitic carbon nitride (g-C3N4) membranes with photo-Fenton self-cleaning ability for efficient oil/water separation

Due to the great fouling resistance property, (super)hydrophilic/underwater superoleophobic membranes are prevalent candidates for oil-polluted wastewater treatment. Even so, membrane fouling inevitably occurs during long-term operation. Therefore, it is of great significance to construct anti-fouling membranes with robust flux recovery. Herein, a polyvinyl pyrrolidone (PVP) coated porous potassium-doped g-C₃N₄ (PKCN) membrane was fabricated for the first time by vacuum filtration. The as-prepared membrane displays enhanced hydrophilicity and underwater superoleophobicity. The permeability of the membrane increased significantly after sonication treatment, which is attributed to the increased pore volume and small nanosheets size that shorten the transport pathway of water molecules. Importantly, owing to the high photo-Fenton activity, the PKCN membrane exhibits fast (within 15 min) and excellent flux recovery (96.5%) after the photo-Fenton cleaning process. Furthermore, after 10 repeated usages, the PKCN membrane still keeps stable permeability and excellent purification efficiency. This work opens a door for developing self-cleaning membranes with the superior anti-fouling ability for effective oil/water separation.