Highly permeable and antifouling TFC FO membrane prepared with CD-EDA monomer for protein enrichment

Adsorption-enhanced Fenton catalytic membrane for high-efficiency, high-quality drinking water treatment

To efficiently remove micropollutants from drinking water, this study developed an adsorption-enhanced Fenton catalytic membrane with a two-dimensional structure composed of graphene oxide loaded with iron-cyclodextrin metal-organic frameworks (FeCD-MOF). As water passes through the interlayer channels, micropollutants and hydrogen peroxide (H2O2) are adsorbed into the voids of the FeCD-MOF and the cavities of the CD. This process increases the concentration of micropollutants and H2O2 in the confined space, thereby significantly enhancing the efficiency of the Fenton catalytic reaction. Under a constant flux of 90 L/m2h and influent concentrations of 10 mg/L bisphenol A (BPA) and 3 mM H2O2, the membrane consistently maintained over 97.4 % BPA removal for 72 h. FeCD-MOF's excellent adsorption properties also enhance the stability of the treated water quality. Even with sudden increases in micropollutant concentration or interruptions in oxidant supply, the membrane maintained over 89.7 % BPA removal for an extended period solely through its adsorption capacity. Experimental results demonstrate that the membrane effectively removes various micropollutants, performs stably across a wide pH range, and resists interference from natural organic matter and ions, making it highly promising for drinking water treatment. Furthermore, compared to other MOF materials, FeCD-MOF has a significantly lower cost, enhancing its practicality.

Recent advances in surface tailoring of thin film forward osmosis membranes: A review

The recent advancements in fabricating forward osmosis (FO) membranes have shown promising results in desalination and water treatment. Different methods have been applied to improve FO performance, such as using mixed or new draw solutions, enhancing the recovery of draw solutions, membrane modification, and developing FO-hybrid systems. However, reliable methods to address the current issues, including reverse salt flux, fouling, and antibacterial activities, are still in progress. In recent decades, surface modification has been applied to different membrane processes, including FO membranes. Introducing nanochannels, bioparticles, new monomers, and hydrophilic-based materials to the surface layer of FO membranes has significantly impacted their performance and efficiency and resulted in better control over fouling and concentration polarization (CP) in these membranes. This review critically investigates the recent developments in FO membrane processes and fabrication techniques for FO surface-layer modification. In addition, this study focuses on the latest materials and structures used for the surface modification of FO membranes. Finally, the current challenges, gaps, and suggestions for future studies in this field have been discussed in detail.

The recent advance of precisely designed membranes for sieving

Developing new membranes with both high selectivity and permeability is critical in membrane science since conventional membranes are often limited by the trade-off between selectivity and permeability. In recent years, the emergence of advanced materials with accurate structures at atomic or molecular scale, such as metal organic framework, covalent organic framework, graphene, has accelerated the development of membranes, which benefits the precision of membrane structures. In this review, current state-of-the-art membranes are first reviewed and classified into three different types according to the structures of their building blocks, including laminar structured membranes, framework structured membranes and channel structured membranes, followed by the performance and applications for representative separations (liquid separation and gas separation) of these precisely designed membranes. Last, the challenges and opportunities of these advanced membranes are also discussed.

Electroless deposition of copper nanoparticles integrates polydopamine coating on reverse osmosis membranes for efficient biofouling mitigation

In this study, highly antimicrobial CuNPs were integrated into a hydrophilic polydopamine (PDA) coating and immobilized on a RO TFC membrane via a mild and facile reduction approach to form a stable and durable dual-functional layer. Based on the XDLVO analysis, the introduction of PDA increased the membrane-foulant total interaction energy (ΔG_mwf) to 14.13 mJ/m², resulting in improved anti-adhesive properties as demonstrated by a 37% decrease in BSA adsorption for the modified membranes. The well dispersed and high loadings of CuNPs induced by PDA conferred strong bacterial toxicity to the modified membranes, reducing the viability of E. coli by 76%. Furthermore, the presence of catechol groups on PDA favors the formation of covalent bond with CuNPs, thus prolonging the durability of the copper-based anti-biofouling membranes. The combination of PDA coating and CuNPs functionalization imparts the membrane with simultaneous anti-adhesive and anti-microbial properties, leading to a substantial reduction in biofouling propensity in dynamic biofouling experiments. Specifically, the flux decline due to biofouling observed for the modified membranes significantly decreased from 65% to 39%, and biofilm thickness and TOC biomass were 58%, and 55% lower, respectively. This study provides a facile and versatile strategy to construct high performance RO membranes with excellent anti-biofouling functionality.

Application of Zwitterions in Forward Osmosis: A Short Review

Forward osmosis (FO) is an important desalination method to produce potable water. It was also used to treat different wastewater streams, including industrial as well as municipal wastewater. Though FO is environmentally benign, energy intensive, and highly efficient; it still suffers from four types of fouling namely: organic fouling, inorganic scaling, biofouling and colloidal fouling or a combination of these types of fouling. Membrane fouling may require simple shear force and physical cleaning for sufficient recovery of membrane performance. Severe fouling may need chemical cleaning, especially when a slimy biofilm or severe microbial colony is formed. Modification of FO membrane through introducing zwitterionic moieties on the membrane surface has been proven to enhance antifouling property. In addition, it could also significantly improve the separation efficiency and longevity of the membrane. Zwitterion moieties can also incorporate in draw solution as electrolytes in FO process. It could be in a form of a monomer or a polymer. Hence, this review comprehensively discussed several methods of inclusion of zwitterionic moieties in FO membrane. These methods include atom transfer radical polymerization (ATRP); second interfacial polymerization (SIP); coating and in situ formation. Furthermore, an attempt was made to understand the mechanism of improvement in FO performance by zwitterionic moieties. Finally, the future prospective of the application of zwitterions in FO has been discussed.

Robust and Large-Area Calix[4]pyrrole-Based Nanofilms Enabled by Air/DMSO Interfacial Self-Assembly-Confined Synthesis

The modular construction of defect-free nanofilms with a large area remains a challenge. Herein, we present a scalable strategy for the preparation of calix[4]pyrrole (C[4]P)-based nanofilms through acryl hydrazone reaction conducted in a tetrahydrazide calix[4]pyrrole (CPTH)-based self-assembled layer at the air/DMSO interface. With this strategy, robust, regenerable, and defect-free nanofilms with an exceptionally large area (∼750 cm²) were constructed. The thickness and permeability of the film systems can be fine-tuned by varying the precursor concentration or by changing another building block. A typical nanofilm (C[4]P-TFB, ∼67 nm) depicted high water flux (39.9 L m^-2 h^-1 under 1 M Na₂SO₄), narrow molecular weight cut-off value (∼200 Da), and promising antifouling properties in the forward osmosis (FO) process. In addition, the nanofilms are stable over a wide pH range and tolerable to different organic solvents. Interestingly, the introduction of C[4]P endowed the nanofilms with both outstanding mechanical properties and unique group-selective separation capability, laying the foundation for wastewater treatment and pharmaceutical concentration.

Novel strategy for membrane biofouling control in MBR with CdS/MIL-101 modified PVDF membrane by in situ visible light irradiation

Novel control strategies for membrane biofouling with eco-friendly photocatalytic technology are critically needed in practical operation of membrane bioreactors (MBRs). In this study, a metal-organic frameworks (MOF) based photocatalytic membrane was firstly applied in an anammox MBR for a long-term biofouling control, where bacteria were inactivated and foulants were degraded simultaneously, with environmentally friendly and renewable visible light energy. By physicochemical characterization, the synthesized photocatalyst of CdS/MIL-101 showed superior visible-light photocatalytic ability, and the 1 wt% CdS/MIL-101 modified membrane C2 showed enhanced hydrophilicity and water permeability compared with the pristine membrane C0. In the long-term operation of anammox MBRs under waterproof lights irradiation, the filtration cycles of C2 (25-26 d) were obviously extended compared with C0 (10-14 d), while their average total nitrogen removal efficiencies were comparable up to 84%, indicating an excellent biofouling alleviation effect by using C2 with a satisfactory nitrogen removal performance maintained. By analysis of the biofilm on the fouled membranes, the organic foulants (especially extracellular polymeric substances) were degraded, and the live bacteria were inactivated effectively by the photocatalytic reactions of CdS/MIL-101 on C2. In the antimicrobial tests against model bacteria, C2 exhibited remarkable antimicrobial effect against both Gram-negative and Gram-positive bacteria with visible light irradiation by destruction of cell integrity with the inhibition rate of 92% for Escherichia coli and 95% for Staphylococcus aureus, respectively. In the model foulants (bovine serum albumin, sodium alginate, and humic acid) filtration tests, C2 showed higher antifouling capabilities, lower flux declining rates, and higher foulants rejection rates under visible light irradiation compared with C0. The reactive species of ·OH, e^- and h⁺ generated on C2 were verified to play the predominant role in the anti-biofouling processes by simultaneous bacteria inactivation and foulants degradation. The findings offer a novel insight into the biofouling controlling in MBRs by simultaneous bacteria inactivation and foulants degradation with an eco-friendly method.

A Review on Reverse Osmosis and Nanofiltration Membranes for Water Purification

Sustainable and affordable supply of clean, safe, and adequate water is one of the most challenging issues facing the world. Membrane separation technology is one of the most cost-effective and widely applied technologies for water purification. Polymeric membranes such as cellulose-based (CA) membranes and thin-film composite (TFC) membranes have dominated the industry since 1980. Although further development of polymeric membranes for better performance is laborious, the research findings and sustained progress in inorganic membrane development have grown fast and solve some remaining problems. In addition to conventional ceramic metal oxide membranes, membranes prepared by graphene oxide (GO), carbon nanotubes (CNTs), and mixed matrix materials (MMMs) have attracted enormous attention due to their desirable properties such as tunable pore structure, excellent chemical, mechanical, and thermal tolerance, good salt rejection and/or high water permeability. This review provides insight into synthesis approaches and structural properties of recent reverse osmosis (RO) and nanofiltration (NF) membranes which are used to retain dissolved species such as heavy metals, electrolytes, and inorganic salts in various aqueous solutions. A specific focus has been placed on introducing and comparing water purification performance of different classes of polymeric and ceramic membranes in related water treatment industries. Furthermore, the development challenges and research opportunities of organic and inorganic membranes are discussed and the further perspectives are analyzed.

Zwitterion-Ag Complexes That Simultaneously Enhance Biofouling Resistance and Silver Binding Capability of Thin Film Composite Membranes

Biofouling can be overcome with zwitterion grafts and antimicrobial, metallic nanoparticles. However, the mechanism underpinning this effective approach remains unclear. To elucidate the role of each component in this system while maximizing membrane antifouling and antimicrobial properties, here we performed a comparative study to investigate the impact of zwitterion type and their interactions with Ag of various states. Two different zwitterions (SO₃^--based and COO^--based) were employed to modify polyamide (PA) thin film composite (TFC) membranes, and the metallized and mineralized membranes were developed via in situ formation of silver (Ag) nanoparticles and deposition of silver chloride (AgCl) particles on the zwitterion-modified TFC membranes. The presence of zwitterions was key to enhance Ag content, resulting in significantly improved antimicrobial and antifouling properties without compromising the nanofiltration separation performance. COO^--based zwitterions were found more favorable toward Ag metallization and mineralization compared to SO₃^--based zwitterions. The underlying mechanisms underpinning this discovery were further revealed using density functional theory (DFT) to reveal Gibbs free energy of the binding between zwitterions and Ag⁺ ions. This fundamental knowledge is crucial for designing next-generation antibiofouling strategies.

Versatile Surface Modification of TFC Membrane by Layer-by-Layer Assembly of Phytic Acid-Metal Complexes for Comprehensively Enhanced FO Performance

Polyamide TFC membranes are widely applied in membrane-based water treatment but generally suffer various fouling problems. In this work, the layer-by-layer assembly of phytic acid (PA) and metal ions (M) is constructed on the surface TFC membrane for the first time, to improve the bio/organic fouling resistances and separation performance of TFC membranes simultaneously. The PA molecule with six phosphonic acid groups of strong chelation ability acts as the organic ligand, and the metal ion acts as the inorganic cross-linker, inducing the assembly of hydrophilic and antibacterial PA-M (Ag or Cu) complexes on the TFC membrane surface. Various characterizations including FTIR, XPS, SEM, AFM, and EDX are employed to confirm the successful and uniform modification of PA-M. FO performance of the PA-M modified TFC membranes, i.e., TFC_PA-Ag and TFC_PA-Cu, is optimized by varying PA concentration and assembly cycles, where the water flux can be improved by 57% and 68%, respectively, without compromising the membrane selectivity. Additionally, the PA-M modification improves the biofouling and organic fouling resistances of the TFC membrane remarkably, owing to the enhanced antibacterial ability and hydrophilicity. The modified TFC membranes are also proven to show the excellent stability by the quantitative release test.