Preparation and properties of PVDF/SiO2@GO nanohybrid membranes via thermally induced phase separation method

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Recent Advances on the Fabrication of Antifouling Phase-Inversion Membranes by Physical Blending Modification Method

Membrane technology is an essential tool for water treatment and biomedical applications. Despite their extensive use in these fields, polymeric-based membranes still face several challenges, including instability, low mechanical strength, and propensity to fouling. The latter point has attracted the attention of numerous teams worldwide developing antifouling materials for membranes and interfaces. A convenient method to prepare antifouling membranes is via physical blending (or simply blending), which is a one-step method that consists of mixing the main matrix polymer and the antifouling material prior to casting and film formation by a phase inversion process. This review focuses on the recent development (past 10 years) of antifouling membranes via this method and uses different phase-inversion processes including liquid-induced phase separation, vapor induced phase separation, and thermally induced phase separation. Antifouling materials used in these recent studies including polymers, metals, ceramics, and carbon-based and porous nanomaterials are also surveyed. Furthermore, the assessment of antifouling properties and performances are extensively summarized. Finally, we conclude this review with a list of technical and scientific challenges that still need to be overcome to improve the functional properties and widen the range of applications of antifouling membranes prepared by blending modification.

Recent advances in dual-filler mixed matrix membranes

Mixed matrix membranes (MMMs) have been widely developed as an attractive solution to overcome the drawbacks found in most polymer membranes, such as permeability-selectivity trade-off and low physicochemical stability. Numerous fillers based on inorganic, organic, and hybrid materials with various structures including porous or nonporous, and two-dimensional or three-dimensional, have been used. Demanded to further improve the characteristics and performances of the MMMs, the use of dual-filler instead of a single filler has then been proposed, from which multiple effects could be obtained. This article aims to review the recent development of MMMs with dual filler and discuss their performances in diverse potential applications. Challenges in this emerging field and outlook for future research are finally provided.

A Mini-Review of Enhancing Ultrafiltration Membranes (UF) for Wastewater Treatment: Performance and Stability

The scarcity of freshwater resources in many regions of the world has contributed to the emergence of various technologies for treating and recovering wastewater for reuse in industry, agriculture, and households. Deep wastewater treatment from oils and petroleum products is one of the difficult tasks that must be solved. Among the known technologies, UF membranes have found wide industrial application with high efficiency in removing various pollutants from wastewater. It is shown that the search for and development of highly efficient, durable, and resistant to oil pollution UF membranes for the treatment of oily wastewater is an urgent research task. The key parameters to improve the performance of UF membranes are by enhancing wettability (hydrophilicity) and the antifouling behavior of membranes. In this review, we highlight the using of ultrafiltration (UF) membranes primarily to treat oily wastewater. Various methods of polymer alterations of the UF membrane were studied to improve hydrophilicity, the ability of antifouling the membrane, and oil rejection, including polymer blending, membrane surface modification, and the mixed membrane matrix. The influence of the type and composition of the hydrophilic additives of nanoparticles (e.g., Multiwall carbon nanotubes (MWCNT), graphene oxide (GO), zinc oxide (ZnO), and titanium dioxide (TiO2), etc.) was investigated. The review further provides an insight into the removal efficiency percent.

Completely green and sustainable preparation of PVDF hollow fiber membranes via melt-spinning and stretching method

In this work, the poly(vinylidene fluoride) (PVDF) hollow fiber membranes with switchable pore size were fabricated by melt-spinning and stretching (MS-S) process based on a completely green and sustainable route. The membrane preparation process and pore formation mechanism were discussed and investigated in detail. Meanwhile, the effect of stretching ratio on the membrane structure and property was studied based on scanning electron microscopy (SEM), pore size distribution, N₂ flux, pure water flux, mechanical property and so on. The prepared membranes with different stretching ratios exhibited excellent tensile strength in the range from 23.0 to 62.6 MPa. The mean pore size of the prepared membranes with stretching 100 % (M-100) was about 0.317 μm, which showed a high dye rejection (<93.9 %) for Direct Black 19. Specifically, there were not any organic solvent and low-molecular-weight diluent used during the preparation process. The recycled PEO and water were obtained after treating the wastewater by membrane filtration. In addition, the recycled PEO could be reused as pore forming agent, which could achieve completely green and sustainable membrane preparation process.

High performance polyvinylidene fluoride (PVDF) mixed matrix membrane (MMM) doped by various zeolite imidazolate frameworks

Zeolitic imidazolate framework (ZIF-8) in three particle sizes (40, 70 and 100 nm) was prepared through both solvothermal and hydrothermal methods and employed to decorate polyvinylidene fluoride (PVDF). The finger-like macro-voids, sponge-like poly-porous morphology and surface roughness of prepared membranes were characterized by SEM and AFM microscopy. The FTIR spectrum and XPS analysis bear out the chemical component. ZIF-8 has the characteristics of higher porosity and appropriate pore size, which is a condition for improving the permeability and pollution resistance of the modified membrane. Results indicated that different ZIF-8s have different enhancement effects on PVDF MMM. 100 nm ZIF-8 membrane possessed pure water flux (PWF) of 350 L m−2h−1, which was 10 times more than the bare membrane (30 L m−2h−1), and OVA flux recovery ration (FRR%) is 98%. 40 nm ZIF-8 membrane owned BSA FRR% of 98.4%. The 70 nm ZIF-8 showed the best mechanical properties. The dynamic contact angles of UP-Z70 ranged from 104.5° to 62.5° within 180 s. Furthermore, pore size distribution, molecular weight cut-off (MWCO) and porosity were also researched to evaluate the MMM. The dislodge of Reactive Black KN-B, Reactive Red 3BS and Reactive Brilliant Blue KN-R dyes by MMM were studied under different dye concentrations and transmembrane pressures. The membrane can provide selective separation methods for dyes and Reactive Brilliant Blue KN-R up to 99%. Overall, the permeability, hydrophilicy, anti-fouling performance and wastewater treatment of modified membranes were regulated by the ZIF-8 in a steerable blending reaction modification process.

Noncovalently Functionalized Sulfated Castor Oil-Graphene Oxide-Strengthened Polyetherimide Composite Membranes for Superior Separation of Organic Pollutants and Their Fouling Mitigation

A novel sulfated castor oil (SCO)-graphene oxide (GO)-strengthened polyetherimide (PEI) membrane was prepared for the first time via phase inversion process for the efficient separation of multiple organic pollutants with superior long-term antifouling stability. X-ray diffraction, attenuated total reflectance-Fourier transfer infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and mechanical strength studies revealed that the SCO and GO were successfully incorporated into the PEI membrane with enhanced mechanical strength. The water flux of the PEI/SCO@GO membrane (410.6 L m^-2 h^-1) was about 50 times that of bare PEI (7.8 L m^-2 h^-1) and about 6 times that of PEI/SCO (64.5 L m^-2 h^-1) membranes. The surface hydrophilicity of the PEI/SCO@GO membrane was significantly increased in terms of the decrease of the water contact angle from 98.5° (bare PEI) to 40.4°. The PEI/SCO@GO membrane separation efficiency was found to be greater than 99.0%, particularly for both the oil-in-water emulsion and the humic acid solution, respectively. Because of the higher flux recovery ratio and the lower total fouling rate of the PEI/SCO@GO membrane, a comprehensive antifouling performance was observed during the long-term foulant filtration cycle analyses. Hence, the incorporation of both SCO and GO into the PEI matrix would render the highly hydrophobic PEI material as the suitable and desirable antifouling membrane toward the treatment of various organic foulants in wastewater.

Synthesis of polyethersulfone (PES)/GO-SiO2 mixed matrix membranes for oily wastewater treatment

The treatment of oily wastewater continues to pose a challenge in industries worldwide. Membranes have been investigated recently for their use in oily wastewater treatment due to their efficiency and relatively facile operational process. Graphene oxide (GO) and silica (SiO₂) nanoparticles have been found to improve membrane properties. In this study, a polyethersulfone (PES) based GO-SiO₂ mixed matrix membrane (MMM) was fabricated, using the phase inversion technique, for the treatment of oil refinery wastewater. The PES/GO-SiO₂ membrane exhibited the highest water flux (2,561 LMH) and a 38% increase in oil removal efficiency by comparison to a PES membrane. Compared to PES/GO and PES/SiO₂ membranes, the PES/GO-SiO₂ MMM also displayed the best overall properties in terms of tensile strength, water permeability, and hydrophilicity.

Recent advances in mitigating membrane biofouling using carbon-based materials

Biofouling is the Achilles Heel of membrane processes. The accumulation of organic foulants and growth of microorganisms on the membrane surface reduce the permeability, shorten the membrane life, and increase the energy consumption. Advancements in novel carbon-based materials (CBMs) present significant opportunities in mitigating biofouling of membrane processes. This article provides a comprehensive review of the recent progress in the application of CBMs in antibiofouling membrane. It starts with a detailed summary of the different antibiofouling mechanisms of CBM-containing membrane systems. Next, developments in membrane modification using CBMs, especially carbon nanotubes and graphene family materials, are critically reviewed. Further, the antibiofouling potential of next-generation carbon-based membranes is surveyed. Finally, the current problems and future opportunities of applying CBMs for antibiofouling membranes are discussed.

Highly Stable and Antibacterial Two-Dimensional Tungsten Disulfide Lamellar Membrane for Water Filtration

Two-dimensional (2D) lamellar membranes consisting of restacked WS₂ nanosheets have shown excellent separation properties for water filtration. The stability, antifouling properties, and antibacterial activities of the WS₂ laminar membranes were investigated for practical application. We discovered that the separation properties of the WS₂ laminar membranes changed slightly after soaking in water for 28 days as well as that of a 45 h-cross-flow filtration, demonstrating an extraordinary operational stability of the WS₂ laminar membranes. The remarkable stability is related to the dominant van der Waals interactions between WS₂ nanosheets. In addition, the WS₂ laminar membranes exhibited excellent antibacterial properties against S. aureus and E. coli with antibacterial rates of 91.3 % and 89.7 %, respectively. These properties of the WS₂ laminar membranes make them promising candidates for application in water filtration.

Fabrication of a PPS Microporous Membrane for Efficient Water-in-Oil Emulsion Separation

Separation of emulsified water/oil mixtures is a worldwide concern. However, poor chemical and solvent resistance of general polymeric membranes limit these membranes for application in the separation process. In this study, a poly(phenylene sulfide) (PPS) porous membrane with a rough concave topographic feature was fabricated, which exhibited excellent superoleophilicity and under-oil superhydrophobicity. The membrane is capable of separating both surfactant-free and surfactant-stabilized emulsions with a high flux. All of the water contents of the treated oils were below 300 ppm. The excellent water resistance property and cycling performance support the PPS membrane displaying an excellent reusability. Additionally, this PPS membrane was also certified to be used in strong solvents for a long time. In conclusion, the successful application of the thermally induced phase separation (TIPS) method may provide a new approach to fabricate the PPS membrane and improve its properties, and the application of the PPS membrane to separate water-in-oil emulsions is promising in practical applications.

Inorganic Membranes: Preparation and Application for Water Treatment and Desalination

Inorganic membrane science and technology is an attractive field of membrane separation technology, which has been dominated by polymer membranes. Recently, the inorganic membrane has been undergoing rapid development and innovation. Inorganic membranes have the advantage of resisting harsh chemical cleaning, high temperature and wear resistance, high chemical stability, long lifetime, and autoclavable. All of these outstanding properties made inorganic membranes good candidates to be used for water treatment and desalination applications. This paper is a state of the art review on the synthesis, development, and application of different inorganic membranes for water and wastewater treatment. The inorganic membranes reviewed in this paper include liquid membranes, dynamic membranes, various ceramic membranes, carbon based membranes, silica membranes, and zeolite membranes. A brief description of the different synthesis routes for the development of inorganic membranes for application in water industry is given and each synthesis rout is critically reviewed and compared. Thereafter, the recent studies on different application of inorganic membrane and their properties for water treatment and desalination in literature are critically summarized. It was reported that inorganic membranes despite their high synthesis cost, showed very promising results with high flux, full salt rejection, and very low or no fouling.

Preparation of a polyphenylene sulfide membrane from a ternary polymer/solvent/non-solvent system by thermally induced phase separation

Polyphenylene sulfide (PPS) membranes were prepared via a thermally induced phase separation (TIPS) method.

A PVDF/PVB composite UF membrane improved by F-127-wrapped fullerene for protein waste-water separation

F-127-wrapped fullerene was prepared successfully in a solvent before casting solution preparation, the composite membrane shows excellent hydrophilicity and capacity for protein waste-water separation.

Novel synthesis of pure VO2@SiO2 core@shell nanoparticles to improve the optical and anti-oxidant properties of a VO2 film

A novel moderately surfactant-free strategy for the synthesis of pure VO₂@SiO₂ core@shell nanoparticles to improve the optical and anti-oxidant properties of VO₂ particles, which involves potential interface chemistry.