Surface Modification Of Membranes Research Articles

Fabrication of LD-slag derived zeolite Y coated polysulfone (PSf) membrane for decontamination of groundwater

Faujesite type zeolite Y was prepared via ultrasonic energy facilitated hydrothermal technique using Linz-Donawitz (LD) process slag as a precursor material. The surface modification of the polysulfone membrane was conducted with the as-synthesized zeolite powder in the presence of N-methyl pyrrolidone (NMP) solvent. The synthetic zeolite nanoparticles (ZNPs) were sonicated by mixing them in NMP solvent before spreading over the membrane surface. The ZNPs layered flat sheet membrane was fabricated via dry-cast technique followed by phase inversion. The optimization of drying temperature and time was studied along with the variation of ZNPs wt.% to obtain defect-free membranes. The developed ZNPs layered membranes were characterized for membrane morphology, surface roughness, mechanical strength, thermal stability, functional group analysis, and surface hydrophilicity. The chemical characterization of all fabricated membranes was examined by X-ray photoelectron spectroscopy (XPS). An increased water flux of 28.83 L/m2h was obtained whereas the fluoride concentration was reduced to 1.47 mg/L (∼50.33 % reduction) for the optimized PSf/Zeolite-1 wt% membrane. Moreover, other contaminants namely chromium (Cr6+) and manganese (Mn2+) were removed very significantly by utilizing the modified PSf/Zeolite-1 wt% membrane. The regeneration experiment was conducted utilizing an HCl solution through dead-end filtration. The flux recovery of membrane PSf/Zeolite-1 wt% was found to be 85.43 % with an antifouling improvement of 42.70 %.

Efficient separation of phosphate ions in water using tris(hydroxymethyl)aminomethane modified polyaniline-p-phenylenediamine composite membrane

In this study, polyaniline-p-phenylenediamine (PAPD) was employed as an amino monomer to fabricate a polyaniline-p-phenylenediamine composite membrane (PAPD/PES) with a nanoparticle-like surface morphology. Additionally, we used interfacial polymerization of Tris(hydroxymethyl)aminomethane (THAM) to hydroxylate the PAPD/PES composite membrane, resulting in the formation of a TPAPD/PES composite membrane. THAM is an economical and environmentally friendly monomer, rarely used for surface modification of composite membranes through interfacial polymerization. Following the introduction of THAM, a significant abundance of hydroxyl groups appeared on the membrane’s surface, enhancing its hydrophilicity and electronegativity. This, in turn, improved both flux and rejection capabilities. Simultaneously, the introduction of THAM led to the formation of a hydration layer growing on the membrane’s surface, further enhancing its antifouling performance. The optimal polymerization concentration (0.5 mol/L) of THAM was used to synthesize the TPAPD/PES composite membrane, resulting in a flux of 84.18 L m−2 h−1 bar−1, which was 1.46 times higher than that of the PAPD/PES composite membrane before polymerization. Additionally, the phosphate rejection rate was determined to be 92.14 % (with an initial phosphate concentration of 10 mg P/L). Long-time running and operating pressure tests results confirmed the remarkable stability of the TPAPD/PES composite membrane. Furthermore, the phosphate separation property of the TPAPD/PES composite membrane was evaluated using real wastewater samples (with an initial phosphate concentration of 1.03 mg P/L) as the research object. After separation, the permeate displayed a phosphate concentration of 0.28 mg P/L, meeting the first-class A standard for urban sewage treatment in China (0.5 mg P/L). This indicates that the prepared TPAPD/PES composite membrane has significant potential for practical application.

MXene-based membranes in water treatment: Current status and future prospects

Emerging highly selective MXene-based membranes have drawn a greater scientific interest in the field of water treatment due to their ion-selective and controlled molecular transport characteristics. However, MXene-based membranes have limitations in water treatment due to the difficulties including permeability-selectivity trade-off, swelling, fouling, oxidation, etc. Thus, a better understanding of the rational structural design principles of the membranes and their separation mechanisms are essential to further their development in water treatment. This review provides a concise overview of the key timeline in the fabrication of MXene-based membranes, the membrane characterization approaches used to understand their structure-property correlations, and the present difficulties in synthesizing high-performance MXene-based membranes. To overcome these challenges, new designing approaches are comprehensively reviewed to enhance the permeability, selectivity, stability, and antifouling properties of MXene-based membranes. These approaches include physical intercalation, chemical cross-linking, membrane surface modification, etc. Then, the separation mechanisms involved in the membranes in water treatment are presented, followed by the related applications. Looking forward, the perspective is provided on the future research directions for further advancing the membranes. This timely review may help to bridge the gap between academic research and industrial needs of MXene-based membranes for water treatment.

Nanoengineering membrane surfaces: A new paradigm for efficient CO2 capture

Thin-film composite (TFC) membranes with superior separation properties for H2/CO2, CO2/N2, and CO2/CH4 are of great interest for CO2 capture. As the selective layer of the membranes becomes thinner (∼100 nm or less) to enhance gas permeance, it can be surface-engineered to significantly improve gas separation properties. This paper aims to critically review scalable nanotechnologies adopted to modify membrane surfaces to improve CO2 capture performance, including atomic layer deposition, chemical vapor deposition, plasma treatment, direct fluorination, ion/electron beam treatment, ozone treatment, and surface-initiated polymerization. We first describe the mechanisms of these nanotechnologies to achieve desired surface chemistries and nanostructures. Second, examples of surface-modified membranes with enhanced CO2 capture performance are highlighted, and they are compared with state-of-the-art membranes to showcase their potential for gas separations. Finally, we summarize the pros and cons of these technologies to transform membrane technology for practical applications.

Poloxamer 407 Combined with Polyvinylpyrrolidone To Prepare a High-Performance Poly(ether sulfone) Ultrafiltration Membrane.

At present, the design and fabrication of polymer membranes with high permeability and good retention ability are still huge challenges. In this study, the commercial Poloxamer 407 (Pluronic F127) is selected as a multifunctional additive, and polyvinylpyrrolidone is used as a pore-forming agent to modify the poly(ether sulfone) membrane by liquid-liquid phase conversion technology to prepare an ultrafiltration membrane with excellent performance. The hydrophobic poly(propylene oxide) segment in Poloxamer 407 guarantees that this copolymer can be firmly anchored to the poly(ether sulfone) matrix, and the hydrophilic poly(ethylene oxide) segments in Poloxamer 407 impart a stronger hydrophilic nature to the modified membrane surface. Therefore, the permeability and hydrophilicity of the modified membrane are significantly improved and the modified membrane also has good stability. When the amount of Poloxamer 407 added to the casting solution reached 0.6 g, the water flux of the modified membrane was as high as 368 L m-2 h-1, and the rejection rate of bovine serum albumin was close to 98%. In the test to isolate organic small molecule dyes, the retention rate of the modified membrane to Congo red is 94.27%. In addition, the modified membrane shows an excellent water flux recovery rate and antifouling ability. It performs well in subsequent cycle tests and long-term membrane life tests and can be used repeatedly. Our work has resulted in poly(ether sulfone) membranes with good performance, which show great potential in the treatment of biomedical wastewater and the removal of industrial organic dye wastewater, it provides ideas for the development and application of amphiphilic polymer materials.

Distribution patterns of reactive species in the interaction between atmospheric pressure plasma jet and fiber membrane

Surface modification of polymer fiber membranes using atmospheric pressure low-temperature plasma has gained significant attention in recent years. The effectiveness of surface modification determined by the uniform distribution of reactive species when plasma touching the fibers. In this study, we investigated the distribution patterns of plasma reactive species on the fibers surface with different fiber spacings by both experiment and modeling. The results revealed that reduced fiber spacing produced an obstructive effect on the propagation of reactive species. This obstruction was primarily caused by the accumulation of a significant charge on the windward side of the fiber. Consequently, there was a substantial difference in the fluxes of reactive species between the windward and leeward sides of the fiber membrane, resulting in poor uniformity of the reactive species distribution. It was worth noting that the fluxes of reactive species exhibited a double-peak distribution on the circumferential surface of the fiber filaments. This phenomenon was attributed to the coupling effect between the fiber filaments, wherein the electric field strength was higher within the gap. High electric field strength facilitated the generation and propagation of reactive species. However, as the fiber spacing decreased, the propagation of high field strength became limited until it merged into the fiber gap.

Enhancing the hemocompatibility of polyethersulfone (PES) hemodialysis membranes using synthesized pseudo zwittronic polymers with various orientations

The incompatibility of membrane materials with blood in the dialysis process has resulted in extensive number of side effects as well as undesired mortality rates for end-stage renal disease (ESRD) patients. Recent attention has been directed at enhancing the hemocompatibility of dialysis membranes. This study synthesized polyether sulfone (PES) mixed matrix membranes (MMMs) containing modified silica nanoparticles (SiO2 NPs) using the phase inversion technique. SiO2 NPs were modified with pseudo-zwitterionic (pZW) coatings of different structures. The modification of SiO2 NPs and their presence in casted MMMs were confirmed using Fourier-transform infrared (FTIR) spectroscopy. Molecular dynamics (MD) simulations were used to compute the quantity and energy of hydrogen bonds, which serve as a metric of hemocompatibility. Surface charge measurements were used to confirm the neutralization of the modified membrane surface charge. Atomic force microscopy (AFM) analysis revealed the influence of the structure of the SiO2 NPs on casted MMM surface roughness. The influence of the pZW coating structure on MMM hemocompatibility was examined in vitro using patient serum to investigate the inflammatory biomarkers released (C5a, IL-1α, IL-1β, IL-6, properdin, C5b-9). The clinicalex-vivo studies showed improvement of hemocompatibility in terms of IL-1α, IL-1β, Properdin, and C59-9. 5 % lower secretion of complement factor and interleukins reflected an improvement of hemocompatibility. Comparing MMM-1 to the other samples, the hemocompatibility profile was better. MD results were in agreement with the clinical outcomes as MMM-1 had the highest number of hydrogen bonds (8) and hydrogen bonding energy value (0.72 kcal/mol), indicating greater water interaction.

Surface modification of PVDF membrane by radiation-induced admicellar polymerization of acrylamide in the presence of cationic surfactant

This article discusses the admicellar polymerization induced by radiation on the poly(vinylidene fluoride) (PVDF) membrane. There are four major stages of admicellar polymerization, which are admicelle formation, adsolubilization, polymerization, and purification. The polymerization stage was realized by using cobalt-60 (Co-60) gamma ray and PVDF as a membrane in water treatment processes, but the use of the latter is restricted due to its inherent hydrophobicity, high fouling tendency, and lack of functional groups. Therefore, this study aims to improve the water flux and permeation efficiency of the PVDF membrane by incorporating complex coordination functional groups, such as amino and carboxyl groups. Acrylamide (AAm) was radiation-grafted onto PVDF membrane in the presence of cationic surfactant, inducing admicellar polymerization. The PAAm-grafted PVDF membrane was obtained by varying the monomer concentration and irradiation dose, while the degree of grafting was found to be proportional to the concentration of monomer and irradiation dose. The changes in properties of PVDF-g-PAAm were investigated by Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry, atomic force microscopy (AFM), scanning electron microscopy (SEM), and contact angle measurement. As the amount of polyacrylamide grafted increased, the hydrophilicity introduced by AAm grafting improved in water flux.

Surface modification of NF membrane via an environmentally friendly and rapid approach for desalination Process: Performance and stability evaluation

In this study, an environmentally friendly and rapid surface modification method known as surface mineralization was adopted to alter the polyamide (PA) layer of commercial NF270 thin film composite (TFC) membrane, aiming to improve its characteristics for enhanced desalination process. An alternate soaking process was applied on the membrane surface by using barium chloride solution and sodium sulfate solution at varying concentrations (0.01 M, 0.05 M and 0.1 M). The reaction of these two salts can form a layer of barium sulfate (BaSO4) minerals atop the PA layer via an ionic interaction. Our result revealed that the best-performing membrane could be developed using salt solutions at 0.05 M with its water contact angle descended to 33.5° compared to the pristine membrane of 46.4°. Furthermore, the surface roughness of the BaSO4-mineralized membrane was reported to be higher than the pristine membrane. The increase in surface roughness together with improved surface hydrophilicity yielded the BaSO4-mineralized membrane to exhibit 12% higher water flux than the pristine membrane. Nonetheless, the difference in Na2SO4 rejection before and after surface mineralization was not found to be statistically significant owing to the high Na2SO4 rejection of the control membrane. The BaSO4-mineralized membrane also achieved excellent performance in filtering solutions containing sodium alginate and showed very stable salt rejection for multiple cycle of combined chemical cleaning and water filtration process. These results highlighted the potential of the surface mineralization process in overcoming the trade-off effect between water flux and selectivity of TFC membrane.

Use of electrochemical impedance spectroscopy to assess the stability of the anion exchange membrane MA-41, modified by poly-N,N-diallylmorpholine bromide in overlimiting current modes

The paper presents the results of studying the electrochemical characteristics and long-term stability of MA-41 membranes on the surface of which poly-N,N-diallylmorpholinium bromide was applied. The deposition of a polyelectrolyte on the membrane surface leads to an increase in the limiting current from 0.8 to 1.1 mA/cm2. The comparison of the experimental and theoretically calculated values of the limiting current density allows us to conclude that the modification of the membrane surface by poly-N,N-diallylmorpholinium bromide does not lead to the formation of a continuous polyelectrolyte film on the surface, but its fixation occurs due to the sorption of macromolecules on the surface of the ion-exchanger particles. To quantify the rate of the water dissociation reaction at the membrane/solution interface, the method of electrochemical impedance was used, which makes it possible to compare the rate constants of the water dissociation reaction for different membranes, assuming that the reaction is described by the Gericher impedance. It is shown that modification of the MA-41 membrane surface leads to a decrease in the rate of the water dissociation reaction in the current range i = 1.5–4ilim by a factor of 2–6. The reduction in water dissociation reaction rate is attributed to the substitution of catalytically active secondary and tertiary amino groups in the surface layer of the pristine membrane by stable heterocyclic ammonium bases of poly-N,N-diallylmorpholinium. The study of the long-term stability of the resulting membrane showed that when the membrane is polarized with a current equal to twice the limiting current, the desorption of the modifier occurs within 25 h, and the properties of the membrane become close to those of the unmodified MA-41 membrane. It was shown that the electrochemical impedance method can be used as a very sensitive method for studying the long-term stability of ion-exchange membranes.

Toward fabrication of fouling resistant pervaporation membrane for desalination: Surface modification of TFC membrane via grafting of mPEG-NH2

A highly hydrophilic and fouling resistant membrane was developed via surface modification of a thin film composite membrane (TFC), prepared from polyacrylonitrile/polyvinyl alcohol (PAN/PVA), by polydopamine (PDA) coating and methoxy polyethylene glycol amine (mPEG-NH2) grafting (TFC/PDA-g-PEG). Various analyses were done on the membranes to investigate the quality and effectiveness of the modification. Based on the results, the pristine TFC membrane was positively charged (+7.71 mV), while the PDA coated TFC membrane (TFC/PDA) showed negative zeta potential (−1.65 mV), and TFC/PDA-g-PEG membrane had almost neutral surface charge (+0.15 mV). The water contact angle of the TFC membrane reduced from 74.1° to 46.2° after PDA coating. By grafting of mPEG-NH2 on TFC/PDA membrane, a further decrease in the water contact angle of the membrane was obtained (27.6°). The permeation flux of 75.7 kg/(m2.h) and salt rejection of 99.91 % were attained by TFC/PDA-g-PEG membrane in the treatment of 35 g/L salt solution at 65 °C. The antifouling behavior of virgin and modified TFC membranes against the foulant solution revealed that TFC/PDA-g-PEG membrane had an excellent resistance against fouling agents compared to TFC/PDA and unmodified membranes.

Photocatalytic membrane coated with α-Fe2O3/Fe3O4 for enhanced filtration performance and antifouling property in surface water treatment

A photocatalytic membrane coated with α-Fe2O3/Fe3O4 nanoparticles has been developed to address the challenges of membrane fouling and organic removal in the treatment of natural surface water. The photocatalytic and filtration properties of the membranes were investigated through a variety of methods. The successful preparation of iron oxide was confirmed by UV–vis diffuse reflectance spectra and X-ray diffractometry, with α-Fe2O3 identified as the primary photocatalytic agent. A commercial ultrafiltration (UF) membrane was employed as a comparison to evaluate the photocatalytic performance and filtration properties of the modified membrane. Results showed that the photocatalytic membrane achieved better removal rates for UV254 (22.0%) and specific fluorescent organic compounds, such as component 2 (19.38%) and component 3 (16.89%), compared to the control group. Furthermore, both irreversible and reversible fouling resistances of the prepared membranes were significantly lower than that of the control group, with reductions of 39.4% and 50.2%, respectively. The membrane coated with α-Fe2O3/Fe3O4 nanoparticles exhibited moderate removal of protein-like and terrestrially derived humic-like fluorescent organics while controlling membrane fouling. Although the α-Fe2O3/Fe3O4 nanoparticles-coated photocatalytic membrane demonstrated good anti-fouling properties, the removals of organic matters were not as effective as anticipated due to the shorter hydraulic retention time. This study provides valuable insights for enhancing pollutant degradation and anti-fouling properties of membranes through the utilization of solar photocatalytic α-Fe2O3/Fe3O4 surface-modified membranes in the treatment of natural surface water.

Surface Segregation Methods toward Molecular Separation Membranes.

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

Investigation of Low-Temperature Hydrogen Permeability of Surface Modified Pd–Cu Membranes

The Pd60%Cu40% membranes were modified with nanostructured coatings to intensify low-temperature (25–100°C) hydrogen transport. Classical palladium black and filamentous particles were applied as surface modifiers by electrodeposition. The experiment results confirmed significant reducing of surface limitations by modifying layer application on both surfaces of the developed membranes of the Pd60%Cu40% alloy. The study of the developed membranes in the low-temperature hydrogen transport processes demonstrated high and stable flux up to 0.36 mmol s–1 m–2, as well as high hydrogen permeability up to 1.33 × 10–9 mol s–1 m–2 Pa–0.5. In numerical terms, the values of the membranes of the Pd60%Cu40% alloy modified with nanofilaments were up to 1.3 and 3.9 times higher compared to membranes modified with classical black and uncoated ones, respectively. The developed Pd60%Cu40% membranes also demonstrated a high level of H2/N2 selectivity – up to 3552. The strategy of surface modification of palladium-based membranes can shed new light on the development and manufacturing of high-performance and selective membranes for ultrapure hydrogen evolution devices.

Enhancing the antifouling and chlorine resistance capabilities of thin-film composite reverse osmosis via surface grafting of dipeptide

There has been constant progress in the development of innovative polyamide (PA) thin-film composite (TFC) reverse osmosis (RO) membranes to address limitations in fouling potential, chlorine resistance, salt rejection and water flux trade-offs. In this work, dipeptide of zwitterionic amino acid L-arginine, i.e., arginyl-arginine (Arg-Arg), was grafted on the surface of PA TFC RO membrane in order to simultaneously improve the antifouling properties, chlorine resistance, and separation performance. The interactions between the Arg-Arg dipeptide and PA layer were evidenced by Fourier transforms infrared spectroscopy and nuclear magnetic resonance spectroscopy, which have indicated the distinguished chemical grafting of Arg-Arg dipeptide on the RO membrane surface. The grafting of Arg-Arg dipeptide led to a thinner, smoother, more hydrophilic, and less negatively charged PA surface. The surface-modified membranes simultaneously exhibited enhanced desalination performances, antifouling and chlorine resistance properties. Compared to the neat TFC membrane, the water flux of Arg-Arg dipeptide-modified membrane was improved by 26.19%. The salt rejection also slightly increased from 96.25% to 98%. The roles of Arg-Arg dipeptide in altering the surface chemistry and the structure of the membranes are discussed to highlight the potential of surface-modified membranes in heightening the desalination performances of RO TFC membranes.

Surface modification of thin film composite nanofiltration membrane with graphene oxide by varying amine linkers: Synthesis, characterization, and applications

We report surface modifications of thin film composite nanofiltration (TFC NF) membrane with amine and the characterization of the resulting membrane for anti-biofouling properties. Graphene oxide (GO) was grafted on the surface of the TFC NF membrane using three linkers, ethylene diamine, diethylene triamine and triethylene tetraamine. Grafting of GO on the surface was successfully validated through Raman Spectroscopy and XPS. Ring-like structures were observed on the surface of the dense polyamide layer of TFC NF membranes under SEM after modification with GO. A slight increase in the roughness, and hydrophilicity was noticed in the membranes modified with GO. GO-grafted membranes demonstrated enhanced chlorine stability, lower biofouling tendency, lower flux decline during filtration of seawater and improved hexavalent chromium rejection in the basic pH. The improved chlorine stability is attributed to intermolecular hydrogen bonding between GO and polyamide structure, while the enhanced biofouling resistance and lower flux decline is ascribed to hydrophilic GO. The membranes were further evaluated for rejection of heavy metal ions, in particular hexavalent chromium, which showed about 97% rejection in basic pH attributed to the rise in negative character of the membrane surface due to the grafting of GO. Na2SO4 rejection for control TFC was reduced by 9.6%, while a reduction between 1 and 5.5% was found in fGO grafted membranes after 1 h exposure to 1000 ppm NaOCl.

Fabrication of bamboo cellulose-based nanofiltration membrane for water purification by cross-linking sodium alginate and carboxymethyl cellulose and its dynamics simulation

The cross-linking coating modification strategy was adopted to construct an environmentally sustainable bamboo cellulose-based composite nanofiltration membrane (CL-NF-BCM), with bamboo cellulose providing as the support material. Solid-state Nuclear Magnetic Resonance (13C NMR) results show that alginate (ALG) and carboxymethyl cellulose (CMC) were successfully cross-linked onto the cellulose membrane. Furthermore, the transfer of chemical elements was confirmed by X-ray Photoelectron Spectroscopy (XPS) measurements. The microscopic morphology illustrates that after cross-linking coating modification, the surface of the bamboo cellulose membrane turns from a uniform porous structure to a polymerized layer with interwoven network structure. In addition, the result of Brunauer-Emmett-Teller (BET) shows that the average pore size of the as-prepared CL-NF-BCM of about 1.1 nm. The performance testing results show that the CL-NF-BCM cellulose membrane had a rejection of 48% against 500 ppm NaCl solution and membrane flux of 17 L·m−2·h−1 under a nanofiltration condition of 0.5 MPa operating pressure. This work enriches a high value-added application of bamboo products, as well as provides a novel perspective for membrane surface modification.

Surface Modification of PP and PBT Nonwoven Membranes for Enhanced Efficiency in Photocatalytic MB Dye Removal and Antibacterial Activity.

In this study, we developed highly efficient nonwoven membranes by modifying the surface of polypropylene (PP) and poly(butylene terephthalate) (PBT) through photo-grafting polymerization. The nonwoven membrane surfaces of PP and PBT were grafted with poly(ethylene glycol) diacrylate (PEGDA) in the presence of benzophenone (BP) and metal salt. We immobilized tertiary amine groups as BP synergists on commercial nonwoven membranes to improve PP and PBT surfaces. In situ Ag, Au, and Au/Ag nanoparticle formation enhances the nonwoven membrane surface. SEM, FTIR, and EDX were used to analyze the surface. We evaluated modified nonwoven membranes for photocatalytic activity by degrading methylene blue (MB) under LED and sunlight. Additionally, we also tested modified membranes for antibacterial activity against E. coli. The results indicated that the modified membranes exhibited superior efficiency in removing MB from water. The PBT showed the highest efficiency in dye removal, and bimetallic nanoparticles were more effective than monometallic. Modified membranes exposed to sunlight had higher efficiency than those exposed to LED light, with the PBT/Au/Ag membrane showing the highest dye removal at 97% within 90 min. The modified membranes showed reuse potential, with dye removal efficiency decreasing from 97% in the first cycle to 85% in the fifth cycle.

Nacre-like graphene oxide–calcium carbonate coated membrane with underwater superoleophobic property for highly efficient oil/water separation

Recently, oily wastewater is causing serious environmental pollution, and an effective disposal method is highly urgent. Membranes with superhydrophilic and underwater-superoleophobic (SUS) properties have shown prospective advantages. The development of a new nacre-like Li-Bentonite/graphene oxide-calcium carbonate coating membranes (Li-Bent/GO-CaCO3@PVDF CMs) was motivated by the unique mastoid structure of the lotus leaf and the robust layer of the nacre. This CMs were synthesized using a facile, cost-effective, and eco-friendly layer-by-layer (LBL) self-assembly approach. The commercially available polyvinylidene fluoride (PVDF) was utilized as a stable base for the fabrication of the CMs. Among these, GO nanosheets were introduced to imitate the “brick and mortar” structure of mother-of-pearl, and “hard bricks” with interspersed Li-Bent and GO were obtained by the LBL self-assembly method. The phenomenon of “biomineralization” confers an intricate surface structure to the membrane, thereby imparting it with a hydrophilic property of 8.3° and an exceptional non-adhesive behavior in submerged conditions. In addition, the membrane has SUS performance and superior permeability (WF ∼ 5476.3 ± 76 L·m−2·h−1), separation (OF∼3123.78 ± 56 L·m−2·h−1, OR ∼ 99.3 %) and anti-fouling properties (FRR decreased only 14.9 %). Significantly, the membrane has good stability, such as alkali, salt-resistance and aging-resistance. Moreover, this method is easy to operate, and is suitable for surface modification of diversified substrate membranes, with high research and application value.

Surface modification of PVDF hollow fiber ultrafiltration membranes for biopharmaceutical products, virus, and bacterial phage removal technology

In this study, radicals were chemically formed at the hydroxyl (-OH) sites on the surface of polyvinylidene fluoride (PVDF) hollow fiber membranes, and anionic-hydrophilic and hydrophobic materials were grafted onto the surface through -OH radical reaction to generate anions (−28, −41 mV). These membranes were then used as biomembranes (BMs) and showed excellent properties. We also studied the effects of chemical surface modification and reduction in pore size (60–130 nm) according to molecular weight. After anionic modification, the electrostatic repulsion between the pore surface and the bacteria prevents adsorption when anionic bacteria pass through the pores. Particles do not pass through the asymmetric pores due to agglomeration, resulting in separation. The hydrophilic membrane had a high initial water flux, but the flux gradually decreased due to fouling. In contrast, the hydrophobic modified membrane had a low initial water flux that eventually stabilized due to excellent fouling resistance. The protein recovery ratio (PRR) was 98.8 % for hydrophilic particles and 99.2 % for hydrophobic molecules, showing a higher PRR than the pristine membrane (96.4 %). An evaluation of removal of the gram-negative bacteria Brevundimonas diminuta (Bd) showed that no bacteria in membrane-purified solutions, confirming 100 % removal efficiencies. The developed membrane can be used in biopharmaceutical production and removal of proteins, retro viruses, and bacteria.