Antifouling Membranes Research Articles

Mechanisms and Enhancement of Hydrogen Evolution for Membrane Anti-fouling and Methane Upgrading by Sacrificed Anode in a Novel Electro-AnMBR

Severe membrane fouling and low CH4 content in the produced biogas have restricted the applicability and energy recovery profit of the anaerobic membrane bioreactor (AnMBR). Herein, a novel AnMBR was constructed with an electrochemical hydrogen evolution reaction (electro-HER) by double anodes and a titanium membrane-cathode (eHAnMBR). The electro-HER was controlled and enhanced by sacrificed iron anode under low voltage, to mitigate membrane fouling and upgrade biogas simultaneously. The critical factors in electro-HER were investigated to influence the AnMBR system, including hydrogen, applied voltage, and Fe ions. The voltage and hydrogen enhanced the hydrogenotrophic methanogenesis process and enriched hydrophilic Methanobacterium and Methanosarcina, thereby improving biogas purity by up to 28% and increasing total CH₄ production by 46%. Furthermore, the electro-HER on the membrane-cathode decreased the transmembrane pressure by 30%. Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMs) was innovatively applied to visualize the organic foulants in membrane pores. The electro-HER not only produced H2 to optimize cake layer structure but also produced local alkalinity on the membrane surface, to remove extracellular polymeric substances in membrane pores. Additionally, Fe2+/Fe3+ released from the sacrificial iron anode, facilitated phosphate precipitation and removal from 15.7% to 37.9%. This study presents a novel and sustainable wastewater treatment solution by integrating the electro-HER process with AnMBR, enabling both energy recovery and membrane antifouling.

Photo-stimulated self-cleaning oxidized g–C3N4-polypyrrole composite membrane for fractionating EBT dyes from salts and separating oil-in-water emulsions

The widespread discharge of industrial wastewater containing dyes and emulsified oils significantly contributes to water pollution. Photoactive self-cleaning membranes can effectively filter out these contaminants; however, developing a stable and efficient photoactive layer remains challenging. This study addresses this by oxidizing graphitic carbon nitride (g–C3N4) to enhance its interaction with polypyrrole. The oxidized g–C3N4 was then polymerized with pyrrole to form a durable self-cleaning composite membrane capable of separating Eriochrome Black T (EBT) dye from salts and removing surfactant-stabilized oil from water. To prepare the membrane, g–C3N4 was synthesized from melamine using a single-step thermal process, followed by oxidation to produce O–g–C3N4. The resultant α-Al2O3@PPy/O–g–C3N4 membrane exhibited superior structural stability, hydrophilicity (contact angle of 13 ± 0.69°), and underwater oleophobicity (153.2 ± 2.14°), attributed to its polar functional groups. The membrane also showed excellent fractionation performance, effectively separating EBT from various salts, with salt permeabilities of NaCl, Na2SO4, MgSO4, and MgCl2 in the range of 82 to 97 %, and achieving over 96 % rejection of EBT dye. The α-Al2O3@PPy/O–g–C3N4 membranes also demonstrated outstanding separation efficiency (>99 %) for water’s vegetable, diesel, and petroleum ether emulsions. It has been observed that α-Al2O3@PPy/g–C3N4 membranes have less fouling resistance than α-Al2O3@PPy/O–g–C3N4. After EBT fouling, membranes were exposed to solar light for 30 min, restoring 96 % of flux with unchanged separation efficiency. The photo-responsive self-cleaning feature of α-Al2O3@PPy/O–g–C3N4 renders it an advanced anti-fouling membrane suitable for separating various emulsions and dye/salt fractionation.

Multiscale insights into polyamide membrane fouling during reverse osmosis of rare earth wastewater

The rare earth elements (REEs) industrial wastewater is characterized by high ammonium nitrogen and low-strength organic compounds. Reverse osmosis (RO) process is effective for the REEs wastewater treatment. However, membrane fouling deteriorated the RO process. In this work, the fouling mechanism during RO process of REEs wastewater was elucidated via multiscale methods. A series of bench-scale fouling tests with simulated REEs wastewater containing high NH4+–N and different concentrations of 2-ethylhexyl phosphonic acid mono-(2-ethylhexyl) ester (P507) were performed with a commercial RO membrane to evaluate the fouling extent of the RO process. A critical P507 concentration (0.25 mg L−1) was observed where the fouling pattern changed qualitatively. When the P507 concentration was lower than 0.25 mg L−1, the relative flux increased and the membrane surface became more hydrophilic. When P507 reached this critical point, severe fouling occurred accompanied with a more hydrophobic membrane surface. Multiscale simulations [i.e., molecular dynamics (MD) and dissipative particle dynamics (DPD)] revealed that the fouling layer network varied with P507 concentration. This work provides in-depth insights into membrane fouling mechanism in the REEs wastewater, and has enlightening significance for fouling control strategies and the innovation of anti-fouling membrane materials.

Zwitterionic Nanochannels in Covalent Organic Framework Membranes for Improved Flux and Antifouling Property.

Zwitterionic membranes demonstrate excellent antifouling property in water purification. The covalent organic frameworks (COFs), due to the ordered channels and abundant organic functional groups, have distinct superiority in constructing zwitterionic surfaces.Here, the zwitterionic COF membrane is prepared with precise framework structures and uniform charge distribution. The negatively charged 4,4'-diaminobiphenyl-2,2'-sisulphonic acid sodium (SA) and positively charged ethidium bromide (EB) fragments are used to react with 1,3,5-triformylphloroglucinol (TP) at the gas-liquid interface to prepare zwitterionic COF membrane. The complementary charged fragments in the inter-layer and inner-layer facilitate the formation of continuous and tight hydration layer on the membrane surface and pore walls to resist the adsorption of pollutants. The zwitterionic COF membrane effectively resists both negatively charged bovine serum albumin and positively charged lysozyme pollutants with flux recovery ratio (FRR) of 97% and 85%, respectively. Furthermore, the regular nano-channels and balanced interactions between water and surface/pore walls of the zwitterionic membrane result in outstanding permeability of up to 146 L m-2 h-1 bar-1 and excellent dye/salt separation selectivity. The water permeation and antifouling mechanism of membranes are elucidated by experimental and molecular dynamics calculation. Zwitterionic COF membranes can find promising applications in preparing high-performance antifouling membranes.

In situ microbubble-mediated strategy for highly efficient anti-crude oil-fouling membrane with parallel nanosheet structure

Membrane fouling caused by highly viscous oils severely hampers the long-term application of oil–water separation membranes. In situ aeration, achieved by applying a voltage to the membrane to produce bubbles, can effectively reduce the adhesion of oil contaminants. Herein, the parallel NiFe-layered double hydroxide arrays were successfully constructed on Ni foam using a hydrothermal method. Compared with NF@NFLDH having randomly aligned nanosheet arrays, NF@NFLDH-P can produce more numerous micro-size bubbles. A substantial number of the microbubbles spontaneously coalesced with oil droplets, and the synergy of buoyancy and kinetic energy significantly hindered oil fouling on the NF@NFLDH-P membrane. Specifically, this microbubble–mediated anti-oil-fouling strategy substantially reduced the flux attenuation and maintained a high flux recovery ratio during long-term crude oil–water separation, exhibiting a great operational life. This study suggests an innovative way to design future anti-fouling membranes with bubble-mediated capabilities.

Nacre-inspired graphene oxide/polyethyleneimine-based ultra-thin heterogeneous superwetting membrane for highly stable separation of oil-in-water emulsions

Since the massive discharge of oily wastewater seriously affects both humans and natural development, the performance of conventional membrane materials in terms of interfacial stability and antifouling in the treatment of surfactant-containing emulsified oily wastewater is a major challenge. In this work, a novel nacre-inspired graphene oxide/polyethyleneimine-based ultra-thin chemically heterogeneous superwetting membrane was fabricated through vacuum-assisted self-assembly and post-modification methods for oil-in-water emulsion separation. The nacre-inspired heterogeneous membrane exhibited superhydrophilicity, underwater superoleophobicity (underwater oil contact angle was 157.7°), excellent crude oil adhesion resistance, high acid/alkaline stability, outstanding salt resistance, and good mechanical properties (Young’s modulus 1391.7 MPa). The heterogeneous membranes showed separation efficiencies of more than 99.9 % for a range of oil-in-water emulsions. The high-value membranes could achieve the permeances of 917–1256 L m−2h−1 bar−1 for pure water and 339.7–577 L m−2h−1 bar−1 for emulsion through a dead-end filter device, with the optimal long-term stable permeance only decreasing by 30.0 % compared to the initial value. After six test cycles, the membrane’s antifouling and self-cleaning properties were enhanced by constructing heterogeneous superwetting properties, and the flux recovery rate remained at 96.5 %. All of these results indicated that this method provides new ideas for the design and fabrication of highly stable and antifouling membrane materials.

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.

Swelling-assisted surface grafting strategy for multichannel antifouling membranes: Reconstruction of surface pore structure and applications in microalgae harvesting and blood purification

Membrane fouling remains a major challenge in membrane separation. The modification of hydrophilic membrane surfaces can mitigate irreversible fouling deposition, thereby improving antifouling properties. Effective surface modification strategies are essential techniques for developing highly efficient antifouling membranes. In this work, a swelling-assisted surface grafting strategy was proposed for multichannel antifouling membranes, where various lengths of polyvinylpyrrolidone (PVP) brushes were grafted on the surface of polysulfone membrane using reversible addition-fragmentation chain transfer polymerization. The successful grafting of PVP polymer brushes was confirmed using Fourier transform infrared spectrometer and X-ray Photoelectron Spectroscopy. Changes in membrane morphology and pore structure were observed via scanning electron microscope and atomic force microscope. During the grafting process, the amphiphilic macromolecules formed through grafting were selectively swelled by graft solvent, leading to the formation of mesopores in both the surface layer and sublayer of the membrane, which formed additional water transport channels. The introduction of hydrophilic polymer brushes and the change of pore structure significantly boosted the hydrophilicity and permeability of the membranes. As a result, the water contact angle decreased from 85° to 42°, accompanied by an approximate 3.24-fold increase in pure water flux (PWF). Due to superior hydrophilicity, modified membranes demonstrated exemplary performance in microalgae harvesting, boasting a microalgae retention rate nearing 100 % and low fouling resistance (2.12 × 1012 m−1). In algal filtration experiments, a confocal laser scanning microscope was employed to assess the activity of filtered algae on the membrane surface. The prepared membranes effectively maintained the bioactivity of algae while also achieving a high flux recovery rate (90.7 %) following filtration and cleaning. Furthermore, in blood cell compatibility tests, the modified membranes exhibited resistance to blood cell adhesion and sustained a low hemolysis rate (0.06 %). Overall, this strategy offers unique insights into the fabrication of antifouling surfaces and shows considerable promise for large-scale applications in microalgae harvesting and blood purification.

Photo-responsive anti-fouling polyzwitterionic brushes: a mesoscopic simulation.

The antifouling effects of a toothbrush-shaped photo-responsive polyzwitterionic membrane were studied via dissipative particle dynamics simulations in this work. The results reveal that the membrane modified by spiropyran methacrylate brushes displays photo-switchable and antifouling capability due to the photo-induced ring-opening reaction. Namely, surface morphology and hydrophilicity change in response to visible or UV light irradiation, which can be observed visually by protein adsorption and desorption. Further study indicates that: (1) brush-modification density can influence the structure and properties of the membrane. With low modification density, systems cannot establish an intact selective layer, which hinders the antifouling ability; as the modification density increases, the intact selective layer can be formed, which is conducive to the expression of photo-responsiveness and antifouling capability. (2) Factors of toothbrush-hair length and grafting ratio can influence the establishment of a light-responsive surface: as the grafting ratio and toothbrush-hair length increase, the light-responsive surface is gradually formed, meanwhile, the antifouling ability can be continuously reinforced under UV light irradiation. (3) As the brushes switch into a zwitterionic merocyanine state under UV exposure, the selective layer swelling becomes stronger than that with a hydrophobic spiropyran state under visible exposure. This is owing to the enhanced interaction between zwitterionic brushes and water, which is the root of the antifouling effect. The present work is expected to provide some guidelines for the design and development of novel antifouling membrane surfaces.

Molecular Dynamics Study on Adsorption and Desorption of the Model Oligosaccharide above Polymer Antifouling Membranes.

Polysaccharide foulants play a key role in the adhesion of many fouling organisms, which may cause severe marine biofouling. However, the detailed interaction mechanism between polysaccharides and antifouling membranes is still indistinct compared with that between the fouling protein and antifouling surfaces. In this paper, a model oligosaccharide built based on the monosaccharide composition found in diatom extracellular polymeric substances (EPS) was used as a model foulant to investigate its adsorption and desorption above three T4 antifouling membranes. It was found that the anionic poly(3-(methacryloyloxy)propane-1-sulfonate) (T4-SP) antifouling membrane had excellent antifouling ability with respect to the model oligosaccharide, while the oligosaccharide can be easily adsorbed on the poly(2-(dimethylamino)ethyl methacrylate) (T4-DM) membrane with vdW attraction and on the zwitterionic poly(sulfobetaine methacrylate) (T4-SB) membrane with electrostatic attraction. As little is known about the details of polysaccharides' adsorption above antifouling membranes at the molecular level, we hope this work will serve as a theoretical basis for finding more effective materials to prevent or control marine biofouling.

Tourmaline triggered biofilm transformation: Boosting ultrafiltration efficiency and fouling resistance

Ultralow pressure filtration system, which integrates the dual functionalities of biofilm degradation and membrane filtration, has gained significant attention in water treatment due to its superior contaminant removal efficiency. However, it is a challenge to mitigate membrane biofouling while maintaining the high activity of biofilm. This study presents a novel ceramic-based ultrafiltration membrane functionalized with tourmaline nanoparticles to address this challenge. The incorporation of tourmaline nanoparticles enables the release of nutrient elements and the generation of an electric field, which enhances the biofilm activity on the membrane surface and simultaneously alleviates intrapore biofouling. The tourmaline-modified ceramic membrane (TCM) demonstrated a significant antifouling effect, with a substantial increase in water flux by 60 %. Additionally, the TCM achieved high removal efficiencies for contaminants (48.78 % in TOC, 22.28 % in UV254, and 24.42 % in TN) after 30 days of continuous operation. The fouling resistance by various constituents in natural water was individually analyzed using model compounds. The TCM with improved electronegativity and hydrophilicity exhibited superior resistance to irreversible fouling through increased electrostatic repulsion and reduced adhesion to foulants. Comprehensive characterizations and analyses, including interfacial interaction energies, redox reaction processes, and biofilm evolutions, demonstrated that the TCM can release nutrient elements to facilitate the development of functional microbial community within the biofilm, and generate reactive oxygen species (ROS) on the membrane surface to the degrade contaminants and mitigate membrane biofouling. The electric field generated by tourmaline nanoparticles can promote electron transfer in the Fe(III)/Fe(II) cycle, ensuring a stable and sustainable generation of ROS and bactericidal negative ions. These synergistic functions enhance contaminant removal and reduce irreversible fouling of the TCM. This study provides fundamental insights into the role of tourmaline-modified surfaces in enhancing membrane filtration performance and fouling resistance, inspiring the development of high-performance, anti-fouling membranes.

Spray coating of 2D materials in the production of antifouling membranes for membrane distillation

Membrane surface coatings with 2D materials have been shown to exhibit antifouling properties for water-treatment applications; however, synthesis methods currently based on vacuum filtration are not easily scalable. This study describes a scalable method for coating membranes with a range of 2D materials including graphene oxide (GO), hexagonal boron nitride (hBN), molybdenum disulphide (MoS2) and tungsten disulphide (WS2). Isopropyl alcohol solutions containing each class of the 2D flakes were spray-coated onto commercial polyvinylidene fluoride (PVDF) using a pyrolyser. The nanomaterials were secured with polydopamine (PDA) as a crosslinker in a method that could easily be integrated into a scalable roll-to-roll process. Changes in morphology, surface roughness, hydrophobicity, mechanical durability and chemical composition were evaluated using scanning electron microscopy, atomic force microscopy, contact angle, tensile strength measurements and Fourier-transform infrared spectroscopy. The 2D nanomaterials-coated membranes were tested in membrane distillation (MD) experiments over 72 h and compared to pristine PVDF and PDA/PVDF membranes. Salt rejection and MD performance stability were evaluated using feedwaters with high concentrations of humic acid (150 ppm) and paraffin oil (200 ppm) simulating simple organic wastewater from oil and gas extraction. The flux decline ratio was measured in terms of percentage permeate loss per hour (%/h), to allow for future comparisons with studies with different experimental times. The pristine PVDF membrane failed after 10 h by pore-wetting due to fouling while the PDA/PVDF membrane had the largest flux decline ratio (0.3 %/h). The membranes coated with GO and hBN had flux decline ratios orders of magnitude lower (0.0021 ± 0.005 and 0.028 ± 0.01 %/h, respectively). All membranes had a high salt rejection (>99.9 %). The GO-coated membrane was the only membrane type that was able to treat both surfactant-containing and foulant-containing feedwaters. The improved performance is attributed to the decrease in both surface roughness and hydrophobicity, which reduces the adsorption of foulants onto the membrane surface. This work shows a facile, scalable method to overcome fouling limitations in MD.

A green zwitterionic bi-continuous membranes prepared by dual-bath procedure for mitigating biofouling during bacterial removal from water

This work explores the possibility of forming green microfiltration antifouling membranes based on polyvinylidene fluoride (PVDF) and a zwitterionic copolymer derivative of sulfobetaine methacrylate (SBMA), utilizing gamma-valerolactone (GVL) as the solvent and a mixture of ethanol and water as non-solvents. Efforts were initially focused on adjusting the immersion time of the matrix polymer in alcohol alone to obtain a porous structure, and 15 s were sufficient to achieve a symmetric, open porous morphology. Next, the polymer/copolymer/solvent blend was characterized. While it did not show the characteristics of a fully miscible system, DLS and visual observations revealed the obtaining of a homogeneous (relatively narrow particle size) and transparent to translucent system. Thus, membranes could be cast, and were shown to be stable. The addition of the copolymer maintained the physical characteristics of microfiltration membranes, but an FT-IR analysis revealed its effect on the dominant crystalline polymorph (switching from β to α). The membrane wettability was enhanced in an important extent with a dynamic water contact angle (WCA) gradually falling to < 40° (while the virgin membrane's WCA remained about 138° all test long), and a hydration capacity reaching about 530 mg/cm3 against <10 mg/cm3 for the virgin membrane. It reflected on the antifouling abilities of the membranes as tested using bovine serum albumin, fibrinogen, Escherichia coli, and Stenotrophomonas maltophilia, with relative decreases in adsorption during static tests measured to be 95 %, 70 %, 91 % and 98 %, respectively. Finally, compared to the virgin membrane, the modified membrane featured improved flux recovery (32 % vs. 11 %), significantly higher rejection (98.9 % vs. 89.1 %) and lower irreversible fouling tendency (68 % vs. 89 %) during cyclic water/bacterial solution filtration in dead-end mode, making it potentially suitable for addressing bacterial pollution in wastewater.

Buoyancy-Assisted Fabrication of Liquid Diode: Janus Nanofibrous Membrane for Efficient Wastewater Treatment.

The pressing need for effective methods to separate oil and water in oily wastewater has spurred the development of innovative solutions. This work presents the creation and evaluation of a Janus nanofibrous membrane, also known as the Liquid Diode, developed using electrospinning (e-spinning) and buoyancy-assisted hydrothermal techniques. The membrane features a unique structure: one side is composed of PVDF nanofibers embedded with a GO/TiO2 composite, exhibiting in-air superhydrophobic and superoleophilic properties, while the reverse side consists of PVDF nanofibers with a ZnO nanorod array, demonstrating in-air superhydrophilic and underwater (UW) superoleophobic properties. This distinct asymmetric wettability enables the membrane to effectively separate both water-in-oil (w-in-o) and oil-in-water (o-in-w) emulsions, achieving an impressive liquid flux and separation efficiency (SEff). The in-air superhydrophobic side of the Janus nanofibrous membrane achieves a maximum oil flux (Fo) of 3506 ± 250 L m-2 h-1, while the in-air superhydrophilic side achieves a maximum water flux (Fw) of 1837 ± 150 L m-2 h-1, with SEff exceeding 98% for both sides. Furthermore, the Janus nanofibrous membrane maintained reliable mechanical stability after 10 cycles of sandpaper abrasion test and demonstrated excellent chemical stability when subjected to acidic, alkaline, cold water and hot water conditions for 24 h. These properties, combined with its ability in breaking down of organic contaminants (98% ± 2% in 210 min) and pharmaceutical contaminants (97% ± 2% in 210 min) under visible light, highlight its photocatalytic potential. Additionally, the membrane's antifouling and antibacterial properties suggest long-term and sustainable use in wastewater treatment applications. The synergistic combination of these superior properties positions the Janus nanofibrous membrane as a promising solution for addressing complex challenges in wastewater treatment and environmental remediation.

Zwitterionic nanospheres engineered co-polymer composite membrane for precise protein-protein separation via dynamic self-assembly micelle deposition

The accurate protein-protein separation is important but technically challenging. Achieving such a precise separation using membrane requires the selective channels with appropriate pore geometry structure and high anti-fouling property. In this study, polyethersulfone-b-poly(sulfobetaine methyl methacrylate) (PES-b-PSBMA) was synthesized and engineered onto polysulfone (PSF) ultrafiltration (UF) membrane to fabricate zwitterionic nanospheres engineered co-polymer (ZN-e-CoP) composite membrane via dynamic self-assembly micelle deposition. On the one hand, self-assembly zwitterionic nanospheres were used as blocks to construct hydrophilic layers with size-dependent sieving channels, endowing ZN-e-CoP composite membranes with enhanced permselectivity and protein-protein separation abilities, meanwhile zwitterionic groups from nanospheres reinforced the structure stability of nanospheres/nanospheres and nanospheres/membrane via multiple intermolecular interactions. On the other hand, zwitterionic nanospheres can induce to produce the hydration layer enveloping themselves by binding water molecules, where hydration layer acts as a protective barrier on the membrane surface, impeding the protein adhesion. Hence, ZN-e-CoP_1a composite membrane exhibited superior separation properties with Lysozyme/Bovine Serum Albumin (BSA) separation factor of 18.1 and 95.4 % rejection against BSA, 10.1 and 2.3 times, respectively, higher these of pristine PSF membrane (1.8 and 42.1 %), without obviously sacrificing water flux. Simultaneously, hydration layer enables the ZN-e-CoP_1a membrane with enhanced anti-fouling performance and durability during the long-term operations. The proposed approach opens new pathways to fabricate excellent anti-fouling membranes for precise protein-protein separation.

Anti-fouling poly(lactic)acid membrane incorporating titanium dioxide‐coated biochar composites for the separation of lipopeptides from Bacillus subtilis fermentation broth

This study focuses on developing anti-fouling membranes composed of poly(lactic)acid (PLA) incorporating titanium dioxide-coated biochar composites, aiming to separate the lipopeptide biosurfactants from clarified Bacillus subtilis fermentation broth efficiently. The surface area of the Ti-biochar composites, incorporated into the PLA membrane, was measured as 191.69 m2/g and the water contact angle of the optimal PLA/Ti-biochar membrane was determined to be 62.3°, indicating its hydrophilic nature. The PLA membrane's pure water flux, containing 1 wt % Ti-biochar was 174.61±0.5 L m–2h–1 with the water content of 86.73±0.8 %, and porosity of 44.72±0.3 %. Then, Bacillus subtilis lipopeptides were separated by the optimal PLA/Ti-biochar membrane, and their characteristics were compared to the crude sample. Additionally, the purified lipopeptides demonstrated enhanced antimicrobial properties, with a significantly lower minimum inhibitory concentration (MIC) of 1.7±0.52 µg/ml against Staphylococcus aureus and 1.5±0.24 µg/ml against Fusarium oxysporum, compared to the crude lipopeptides, which had MIC values of 5.5±0.26 µg/ml and 4.2 ±0.45 µg/ml, respectively. The purified lipopeptides were confirmed by high-performance liquid chromatography and mass spectrometry. These results underscore the antifouling characteristics of the fabricated PLA/Ti-biochar membrane, positioning it as a promising candidate for the separation of biological molecules.

Antifouling Polyvinylidene Fluoride Membrane through Dopamine Self‐Polymerization Enhanced Surface Segregation toward Oil‐In‐Water Emulsions Separation

AbstractSurface segregation method, as an in situ method for simultaneous modification of membrane external surfaces and inner pore surfaces, has been more commonly employed to fabricate antifouling membranes. In this study, dopamine (DA) with self‐polymerization and bio‐adhesion ability is chosen as a surface segregation agent to fabricate antifouling polyvinylidene fluoride (PVDF) membrane for oil‐in‐water emulsions separation through synergistically regulating phase inversion, self‐polymerization of DA, and surface segregation of poly‐dopamine (PDA). During the phase inversion process, DA contacts with an alkaline coagulation bath to trigger self‐polymerization of DA, then the surface segregation of PDA proceeds spontaneously. The addition and self‐polymerization of DA can regulate the phase inversion process to acquire membranes with high porosity, as a result, the water permeance is increased from 134 to 538 L m−2 h−1 bar−1 with the oil rejection higher than 99.8%. Because the hydrophilic PDA layer on membrane and pore surfaces leads to a robust hydration layer, the membrane exhibits super‐oleophobicity underwater and excellent antifouling properties with water recovery ratio of more than 99.4%. This study may open a new route to preparing antifouling membranes by using small molecules as surface segregation agents.

Optimization of Chitosan Synthesis Process Parameters to Enhance PES/Chitosan Membrane Performance for the Treatment of Acid Mine Drainage (AMD).

Acid mine drainage (AMD) is an environmental issue linked with mining activities, causing the release of toxic water from mining areas. Polyethersulphone (PES) membranes are explored for AMD treatment, but their limited hydrophilicity hinders their performance. Chitosan enhances hydrophilicity, addressing this issue. However, the effectiveness depends on chitosan's degree of deacetylation (DD), determined during the deacetylation process for chitosan production. This study optimized the chitin deacetylation temperature, alkaline (NaOH) concentration, and reaction time, yielding the highest chitosan degree of deacetylation (DD) for PES/chitosan membrane applications. Prior research has shown that high DD chitosan enhances membrane antifouling and hydrophilicity, increasing contaminant rejection and permeate flux. Evaluation of the best deacetylation conditions in terms of temperature (80, 100, 120 °C), NaOH concentration (20, 40, 60 wt.%), and time (2, 4, 6 h) was performed. The highest chitosan DD obtained was 87.11% at 80 °C, 40 wt. %NaOH at 4 h of chitin deacetylation. The PES/0.75 chitosan membrane (87.11%DD) showed an increase in surface hydrophilicity (63.62° contact angle) as compared to the pristine PES membrane (72.83° contact angle). This was an indicated improvement in membrane performance. Thus, presumably leading to high contaminant rejection and permeate flux in the AMD treatment context, postulate to literature.

Productivity and energy consumption as performance criteria to overcome bias caused by membrane resistance

Membrane scientists and engineers routinely compare the performance of membranes for different applications. Such comparisons are required to optimize surface chemistries and to evaluate and select the best membrane to scale-up industrial applications. In most cases, the potential of the feed to foul membrane surfaces is also critical. When different membranes under consideration have different resistances Rm, such comparisons must be done with care. Here we elucidate the impact of Rm on fouling kinetics for a range of fouling mechanisms and experimental protocols. We show that traditional plots of flux versus time for constant pressure operation, or pressure versus volume in constant flux operation, obscure two important performance criteria: accumulated volume over a defined time period (i.e., productivity) and energy consumption; practical implications include the risk that higher performance may be attributed to membranes that actually have lower productivity and/or that consume more energy, and that lower performing membranes may be inadvertently chosen from screening studies as offering superior performance. To facilitate membrane comparison with different Rm, we have developed a graphical approach using normalized coordinates. This approach yields linear plots having slopes that are a function of fouling parameters only, and are independent of membrane resistance Rm. Therefore, such normalization coordinates, presented for each fouling mechanism and each operation mode, can be employed to isolate fouling potential. In addition, we developed a new graphical approach employing contour plots of iso-volume or iso-energy lines to visualize the potential trade-offs between antifouling performance, membrane permeability, and either productivity in the case of constant pressure operation, or specific energy in the case of constant flux operation. This study provides a framework for judging the performance of different membranes under fouling conditions, considering fouling, energy consumption and productivity as metrics, independent of membrane resistance. This framework will help guide process design and the design and preparation of antifouling membranes.

Rapid attainment of full wettability through surface PEGylation of hydrophobic polyvinylidene fluoride membranes via spray-coating for enhanced anti-biofouling performances

This manuscript explores the development of antifouling membranes fabricated by vapor-induced phase separation (VIPS) process and their spray-coating modification with an aqueous solution of a copolymer comprising butyl methacrylate and poly(ethylene glycol) methyl ether methacrylate, designated as poly(BMA-r-PEGMA). An initial optimization phase focused on improving the modification quality, with the aim of enhancing the wettability on both the top and bottom surfaces of the membranes, despite spraying on the top surface only. Our findings reveal that a sprayed solution concentration of 10 mg/mL, a pressure of 0.25 MPa, and a scan rate of 3000 mm/min achieved a decrease in water contact angle to 0 in less than 12 s for both membrane surfaces (the top surface directly exposed to the spray, and the bottom surface facing the instrument stage), suggesting that the spray-coating modifies the entire membrane’s bulk. The presence of the copolymer on both surfaces was also evidenced by FTIR and XPS tests. Further biofouling assessments demonstrated the performances of the optimized membrane (OM). In static attachment tests, the OM exhibited a high reduction in Escherichia coli adhesion, with less than 10 % adhering bacteria, compared to unmodified membranes. During the filtration of bacteria-containing wastewater, the OM boasted a flux recovery ratio approaching 60 % (against less than 40 % for a commercial hydrophilic membrane), a rejection rate of 99.3 %, and a water permeability of 2500 LMH/bar. Moreover, the OM was stable over a 4-week period, with a resistance to E. coli attachment remaining similar to prior immersion. These findings underscore the significant potential of spray-coating to develop stable and effective antifouling microfiltration membranes for the removal of microorganisms from wastewater.