Membrane Surface Hydrophilicity Research Articles

Reduction of Recombination Processes in PVC Photocatalytic Membranes Modified with Green Prepared Nanoparticles

The enhanced photocatalytic membranes were prepared by green synthesized Tin dioxide (SnO2) and manganese dioxide (MnO2) nanoparticles (NPs) blended with polyvinyl chloride (PVC) polymeric solution to produce a photocatalytic flat sheet membrane that was used in wastewater treatment. The surface and morphological structure of the produced membranes were studied using atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM). The elemental compositions and chemical bonding of the membranes were examined using Raman and Fourier transform infrared spectroscopy (FTIR). A sessile-drop approach was used to look at the membrane surface's hydrophilicity. Images of FESEM, AFM, Raman spectra, and FTIR analysis proved the existence of NPs on membrane surfaces. The modified membrane's hydrophilicity was significantly improved after NPs addition. Furthermore, Humic acid removal under darkness was enhanced for the modified membrane than the blank PVC. At the same time, it enhanced from 81% to 92, 100, and 99% for SnO2, MnO2, and SnO2/MnO2 respectively. The photocatalytic ability of the Photocatalytic membranes was examined in sunlight where it was found to be enhanced when exposed to sunlight as compared to when kept in the dark. The prepared membranes exhibited an enhancement removal performance. Both the water flux and the rejection were enhanced in sunlight. The SnO2/MnO2 photocatalytic membrane exhibited a better removal ability and good water flux. The potential utility of our research lies in its application within the water treatment industry, specifically as an effective technique for modifying PVC membranes.

Unveiling the impact of monomer reactivity on the morphology and functionality of thin-film composite membranes

This study delves into the impact of monomer selection and reaction pH on the morphology and performance of thin-film composite (TFC) membranes. The research provides an understanding of how polyamide (PA), polyester amide (PEA), and polyester (PE) membranes can be tailored for specific applications, employing piperazine (PIP) and glucose as monomers in aqueous solution alongside trimesoyl chloride (TMC) as a monomer in an organic solution. PEA-based membranes containing glucose demonstrated several notable improvements, including a reduced contact angle of 60 degrees, a smoother surface, and a more negative zeta potential. These enhancements underscore their increased hydrophilicity, decreased susceptibility to fouling, and heightened surface charge. Controlling pH during fabrication significantly changed the membrane surface charge, hydrophilicity, water flux, and rejection rate. At pH 11, the PA membrane excelled in rejection performance (99.5% Na2SO4, 32% NaCl, and 97.8% methyl orange) with a trade-off in lower water flux (56 LMH). Conversely, the PE membrane achieved the highest water flux (173 LMH) but lower rejection (58% Na2SO4, 10% NaCl, and 97% methyl orange). The PEA membrane offered notable water flux (82.5 LMH) and high rejection for methyl orange (99.3%) and Na2SO4 (99.2%). Increasing the pH reduced permeation rates but enhanced rejection, especially for NaCl. The PE and PEA membranes exhibited remarkable antifouling properties, boasting a flux recovery ratio compared to the PA membrane. This study highlights the pivotal role of monomer selection and pH control in TFC membrane performance, offering prospects for innovative design and optimization in water treatment membrane technology.

Tracking fouling layer formation in membrane distillation of landfill leachate concentrate: Insights from periodic membrane autopsies

This study tracked the fouling layer formation in the operation of membrane distillation (MD) for the treatment of landfill leachate concentrate. At periodic intervals, the membrane fouling layer was autopsied by spectroscopic and compositional analyses, to provide insight into foulant evolution and interaction mechanisms. Results show that water flux declined rapidly at the beginning of MD operation as protein and sodium chloride (NaCl) preferentially attached and crystalized onto the membrane surface, respectively, to initiate the formation of fouling layer. Such decline became relatively smooth between the water recovery of 20–30% due to the interaction of humic acid with protein which slightly aggravated organic fouling and thus increased membrane surface hydrophilicity. Nevertheless, the enrichment of calcium (Ca2+) and magnesium (Mg2+) ions with further water recovery from leachate concentrate bridged organic foulants, particularly polysaccharide and humic acid, to further thicken the hydrophilic fouling layer to reduce water flux. Indeed, compositional quantification also evidenced a considerable increase in the content of humic acid and divalent cations (Ca2+ and Mg2+) in the fouling layer after a water recovery of 30%.

In situ bridges of nano-titanium dioxide constructed in MXene self-cleaning loose nanofiltration membranes for dye wastewater treatment

It has been a longstanding problem to combat the oxidation process of MXene membranes. Here, we propose a strategy to construct nano bridge defect repair loose nanofiltration membrane with the help of MXene oxidation. The oxidation kinetics of Ti3C2Tx was investigated in both model and experimental aspects. The acid solution leads to aggregation and smaller d-spacing. However, the oxidation of MXene was accelerated in alkaline solution via reaction with hydroxyl anions resulting in a hydrophilic MXene membrane surface. The water permeability of the pH = 12-Ti3C2Tx membrane increased to a maximum value of 26.5 L·m−2·h−1·bar−1 together with a high rejection (98 %) of Janus green B (JGB). Titanium dioxide, which was in situ formed by oxidation of MXene, gives the membrane self-cleaning properties under UV light. The water recovery ratio was as high as 96.6 %. To further study the mechanism of in situ oxidation of MXene to form nano-titanium dioxide, the oxidation stages were analyzed which revealed that the in-situ oxidation process involved three different oxidations stages. This research offers a new perspective on MXene membrane design, paving the way for a new method of in situ nano bridge defect repair loose MXene nanofiltration membrane.

Study on UF PES Membranes Spray-Coated with Polymerizable Bicontinuous Microemulsion Materials for Low-Fouling Behavior.

The low-fouling propensity of commercially available polyethersulfone (PES) membranes was studied after modification of the membrane surface via coating with polymerizable bicontinuous microemulsion (PBM) materials. The PBM coating was polymerized within 1 min using ultraviolet (UV) light exposure. It was detected on the PES membrane surface via attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The PBM coating led to an average 10% increase in the hydrophilicity of the PES membrane surface and an increase in total organic content (TOC) removal by more than 15%. Flux-step tests were conducted with model foulant comprising 100 mg L-1 humic acid (HA) solution to detect the onset of critical fouling, characterized by a rapid and substantial increase in TMP, and to compare the fouling propensity of commercially available PES membranes with PBM-coated membranes. The critical flux was found to be about 40% higher for PBM spray-coated membrane and 20% lower for PBM casting-coated membrane than the commercial PES membrane. This demonstrates the performance advantages of the thin PBM layer spray-coated on PES membrane compared to the thick casting-coated PBM layer. The study showcases the potential of PBM spray-coated membranes over commercial PES membranes for use in membrane bioreactors (MBR) for wastewater treatment systems with reduced maintenance over longer operation periods.

Polyelectrolyte-based antifouling and pH-responsive multilayer coatings for reverse osmosis membrane

Membrane fouling, the accumulation of material on the membrane surface, has been a challenge that limits the application of reverse osmosis technology. Ordinary cleaning processes do not remove contaminants from the membrane surface. To effectively clean a membrane, we fabricated a sacrificial multilayer polyelectrolyte coating based on a layer-by-layer assembly approach using chitosan (CS) and tannic acid (TA) on the membrane surface. The CS/TA coated membranes represent a superior permeance flux of 64 L m−2 h−1 with a clear NaCl rejection of 98.89 %. Meanwhile, the membrane surface hydrophilicity was enhanced due to the abundant amino and hydroxyl groups, which shows superior anti-fouling properties against proteins, polysaccharides, and surfactant. Moreover, the coatings were unstable, which would decompose at pH 8.5. The degradation endows the coated membranes approving long-term anti-fouling performance, which the permeance recovery reaching up to 85 %. Constructing pH-responsive smart coatings provides a promising route to address membrane fouling. It can be upscaled in numerous practical applications like sensors, medical devices, and drug delivery.

Modulating interfacial polymerization via 1-methylimidazole as reactive additive for nanofiltration membrane with high-performance

Nanofiltration (NF) membrane technology has become the most critical alternative to resolve fresh water resources shortage and water pollution. Preparing polyamide (PA) NF membrane with excellent water permeance and mono/multivalent salts selectivity is highly desired. Herein, we introduced 1-methylimidazole (1-MI) as a reactive additive into interfacial polymerization (IP) to prepare NF membrane and attempted to improve the NF membrane performance. 1-MI modified NF membranes exhibited enlarged pore size and thickness of PA layer, as well as a smooth and hydrophilic membrane surface, the water permeance improved from 7.7 L/(m2·h·bar) of Virgin-NF to 13.1 L/(m2·h·bar) of 1-MI-0.05-NF. The Na2SO4 rejection was maintained at 95.01% while NaCl rejection dramatically reduced from 25.79% to 13.29%, and the Cl−/SO42− selectivity slightly increased from 21.47 to 23 under the mixed salts solution as feed. The enhancement of water permeance was ascribed to the looser PA layer and enhanced hydrophilicity. The retaining Na2SO4 rejection was attributed to electrostatic repulsion caused by more carboxylic acid groups, and the decreased NaCl rejection was ascribed to the looser PA layer. Besides, the modified membrane had an acceptable pH stability. In summary, 1-MI modified NF membrane was suitable for the separation of monovalent/divalent anionic salts.

Thin film composite membrane with self-cleaning properties via a catalytic interlayer for dye wastewater treatment

Fouling control is the most critical concern in the implementation of nanofiltration (NF) for dye wastewater treatment. In this study, integration of NF and Fenton-like advanced oxidation was realized by tailoring a thin film composite NF membrane (TFNi) with in situ synthesized PDA/MnO2 interlayer. TFNi was optimized by controlling the amount of MnO2 nanoparticles incorporated within the interlayer which endowed the membrane with self-cleaning property. Besides it improved the membrane surface hydrophilicity and optimized the water transport path, resulting in alleviated fouling risks and an enhanced water permeance of 24 ± 2 L m−2 h−1 bar−1 compared to the control membrane. Fouling and subsequent chemical cleaning experiments were carried out on TFNi under various water chemistry conditions to elucidate the underlying mechanisms governing the self-cleaning properties. Accordingly, a high flux recovery ratio (FRR) (above 95%) was maintained thanks to the generation of free radicals by MnO2–H2O2 system which was validated by determining the free radical scavenging activities. Moreover, the interlayer confined radicals can facilitate the decomposition of foulants on TFNi. Conclusively, H2O2-initiated self-cleaning of TFNi can be of great prospect for the efficient treatment of dye wastewater via in-situ generated free radicals.

Nanocelluloses fine-tuned polyvinylidene fluoride (PVDF) membrane for enhanced separation and antifouling

To mitigate membrane fouling and address the trade-off between permeability and selectivity, we fabricated nanocellulose (NC) fine-tuned polyvinylidene fluoride (PVDF) porous membranes (NC-PVDFs) using phase inversion method through blending NCs with varied aspect ratios, surface charges and grafted functional groups. NC-PVDF presented rougher surface (increased by at least 18.3 %), higher porosity and crystallinity compared to PVDF membrane. Moreover, cellulose nanocrystals incorporated PVDF (CNC-PVDF) elevated membrane surface charge and hydrophilicity (from 74.3° to 71.7°), while 2,2,6,6-tetramethylpiperidine-1-oxyl-oxidized cellulose nanofibers modified PVDF (TCNF-PVDF) enhanced the porosity (from 25.0 % to 40.3 %) and tensile strength (63.6 % higher than PVDF). For separation performance, NC improved flux, rejection and fouling resistance due to facilitation of phase transition thermokinetics as pore-forming agent and increased hydrophilicity at both interface and pore wall. For water flux, NC-PVDFs (139–228 L·m−2·h−1) resulted in increased permeability compared to bare PVDF. CNC-PVDF membrane exhibited the highest water flux because of improved porosity, roughness and hydrophilicity. For bovine serum albumin (BSA) rejection, the removal rates of all NC-PVDFs were all above 90 %. Notably, TCNF-PVDF exhibited the most remarkable elevation of BSA rejection (95.1 %) owing to size exclusion and charge repulsion in comparison with PVDF.

Fabrication of a novel composite nanofiltration membrane with effective treating dye wastewater via integration of phase inversion and interfacial polymerization

In this work, we proposed using the combination of nonsolvent induced phase separation (NIPS) technology and interfacial polymerization (IP) process upon polyvinylidene fluoride (PVDF) substrate as a novel and simple method for preparing high-flux composite nanofiltration membranes. The surface chemical properties, physical structure, hydrophilicity, zeta potential, and permeation experiments of the composite membranes that were prepared with graphene oxide (GO), cyclodextrin (CD), or GO@CD as aqueous monomers were studied. The results indicated that the selective polyester active layer successfully covered the PVDF substrate, and the optimal GO@CD50/PVDF membrane was fabricated using the modification conditions of 1.0 wt% of GO@CD50, 5 min of phase transition time, 0.2 wt% of TMC, and 60 min of IP reaction time, which achieved a high pure water flux (84.8 L m−2 h−1 bar−1) and dye permeation flux (48.7 L m−2 h−1 bar−1 for Rose Bengal); in addition, the dye rejection rate was also high (e.g., 99.6 % for Rose Bengal). Besides, CD nanomaterials can be effectively inserted into the GO lamella to increase the layer spacing of GO sheets and expose more oxygen-containing functional groups; this, in turn, enhances the long-term stability and permeability of the membrane. This study provides practical ways to treat dyes wastewater.

Synthesis and performance of ultrafiltration membranes incorporated with different oxide nanomaterials: experiments and modeling

Abstract In membrane filtration technology, membrane fouling is the primary obstacle to optimizing efficiency and results in a short membrane lifetime and high operating costs. By incorporating nanomaterials into the membrane synthesis process, a mixed-matrix membrane with significantly enhanced characteristics and performance may be obtained. Graphene oxide (GO), aluminum oxide (Al2O3), tin oxide (SnO2), and titanium oxide (TiO2) were incorporated into a polyethersulfone (PESU) membrane. The water permeability of the modified membranes showed improvements when compared with the pure membrane. It increased from 65 L/m2 h bar for the pristine membrane (PES-1) to 143.6, 83.68, 92.12, 75.43 L/m2 h bar for Al2O3 (PES-2), TiO2 (PES-3), SnO2 (PES-4), and GO (PES-5) membranes, respectively. It was discovered that the membrane's surface hydrophilicity was significantly and directly affected by the incorporation of nanoparticles. Fouling parameters include Rr (Reversible fouling ratio), Rir (irreversible fouling ratio), Rt (total fouling ratio), and Frr (flux recovery ratio) and were measured to determine the membrane's fouling tendency. The results showed that the membrane's propensity for fouling could be reduced when nanoparticles were incorporated into it. The experimental results are best explained by the cake layer and both standard and intermediate blocking mechanism models, as determined by the traditional single fouling models.

The structure and hydrophilicity of MWCNT-COOH /TiO2 modified PVDF membrane

MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane was created using a blended modification process with carboxyl carbon nanotubes (MWCNT-COOH) and TiO2 nanoparticles as modification additives in order to further enhance the hydrophilicity of the PVDF membrane surface. Using the techniques of scanning electron microscopy, Fourier transform infrared spectrum, and a water angle of engagement analyzer, the membrane’s structure and hydrophilicity were identified. Investigations were conducted into the effects of various MWCNT-COOH dosages on membrane structure and hydrophilicity. The results of the investigation indicated that 0.03 g of MWCNT-COOH in the casting solution was the ideal dose. The manufactured MWCNT-COOH/TiO2 modified PVDF ultrafiltration membrane had the best hydrophilicity.

PREPARATION AND CHARACTERIZATION OF FLY ASH ADDITIVE MODIFIED POLIESTER BASED MEMBRANE

Recently, Polyethersulfone (PES) polymer material based on flat sheet membranes reached much attention in membrane technology. However, PES polymer has low hydrophilicity. This study describes PES-based membranes incorporating fly ash as an additive. The first analysis was conducted by Fourier Transform Infrared, Scanning Electron Microscope, tensile strength, and porosity tests. Four membranes, including pure PES membranes, were prepared via the phase inversion process, namely MA–0, MA–0.1, MA–1, and MS–1. The characteristics of the membrane samples were analyzed in terms of chemical group, morphology, mechanical and membrane surface hydrophilicity. The characterization results show that additive incorporation increased pure water flux performance, and the highest pure water permeability increased up to 70% by the MA–1 membrane. Moreover, it increased by 19% compared to pure silica-modified PES membrane (MS–1). In addition, the MA-1 membrane at a pressure of 3 bar reached significant performance in the trend of pure water flux values because of these improvements in membrane characteristics. The membrane also shows a higher tensile strength with adding additives to the membrane prepared.

Poly(ionic liquid) blended polyphenylene sulfone ultrafiltration membranes with enhanced surface hydrophilicity and antifouling performance

Membrane fouling is a key challenge in the process of utilizing polyphenylene sulfone(PPSU) ultrafiltration (UF) membranes. To address this issue, an amino-functionalized poly(ionic liquid), poly(1-vinyl-3-propylamine imidazolium bis(trifluoromethane sulfonyl) imide) (PIL[TFSI]), was synthesized via free radical polymerization and incorporated into the prepared UF membranes-based PPSU with nanochannels through nonsolvent induced phase separation method. 1H NMR, ATR-FTIR, XPS and EDS spectra verified the introduction of PIL[TFSI]. The AFM and SEM images showed the membrane possessed a classical asymmetrical structure, featuring a higher surface roughness and dense cortex with pits. The decreased water contact angle by the incorporation of PIL[TFSI] indicates the formation of an improved hydrophilic membrane surface. The hydrophilicity of the blended membranes was enhanced by the increasing incorporation of PIL[TFSI]. Meanwhile, the flux decreased slightly, but the selectivity improved significantly. The PIL[TFSI]/PPSU UF membrane with 5% PIL[TFSI] maintained a flux (275 L/m2 h) and a high rejection for bovine serum albumin (BSA) (>99.9%). Additionally, the blended membrane has a superior removal performance for Congo red (>99.9%) and Evans blue (>99.9%). More importantly, the PIL[TFSI]/PPSU UF membranes present excellent antifouling with an increased flux recovery rate from 60.2% to 91.1%. Furthermore, the existence of hydrogen bonds and π-π interactions between PIL[TFSI] and PPSU is conducive to the good stability and sustained hydrophilicity of blended membrane even after continuous immersion for a month.

Loose Nanofiltration Membrane Incorporating CeZnFe Layered Double Hydroxide with Enhanced Dye/Salt Separation Performance and Self-Cleaning Ability.

The high-salinity wastewater from the textile industry faces a significant challenge in effectively separating dyes and salts. In this study, a CeZnFe-layered double hydroxide (LDH)-incorporated nanofiltration (LNF) membrane was fabricated using the conventional interfacial polymerization (IP) technique to fractionate dyes and salts within the wastewater. The impact of CeZnFe LDH on various aspects of membrane performance was examined, including water flux, dye removal efficiency, dye/salt separation capability, self-cleaning ability, and membrane integrity. The addition of LDHs resulted in improved membrane surface hydrophilicity, thereby enhancing water flux. The optimized TFN membrane (0.050 wt% LDH in PIP solution) significantly improved pure water flux, exceeding 150%. All TFN membranes exhibited excellent performance in dye and salt fractionation (93% for Congo red, 2.6% for NaCl, and 40.7% for Na2SO4). Also, excellent self-cleaning ability was observed for the optimized membrane, exhibiting a remarkable water flux recovery rate after three operation cycles. Moreover, including CeZnFe LDH in the optimized TFN membrane played a significant role in enhancing membrane integrity. This study provides new inspiration for fabricating self-cleaning loose NF membranes using CeZnFe LDH for effective dye/salt separation.

Physical, mechanical, and biological properties of collagen membranes for guided bone regeneration: a comparative in vitro study

BackgroundTo provide a reference for clinical selection of collagen membranes by analyzing the properties of three kinds of collagen membranes widely used in clinics: Bio-Gide membrane from porcine dermis (PD), Heal-All membrane from bovine dermis (BD), and Lyoplant membrane from bovine pericardium (BP).MethodsThe barrier function of three kinds of collagen membranes were evaluated by testing the surface morphology, mechanical properties, hydrophilicity, and degradation rate of collagen membranes in collagenase and artificial saliva. In addition, the bioactivity of each collagen membrane as well as the proliferation and osteogenesis of MC3T3-E1 cells were evaluated. Mass spectrometry was also used to analyze the degradation products.ResultsThe BP membrane had the highest tensile strength and Young’s modulus as well as the largest water contact angle. The PD membrane exhibited the highest elongation at break, the smallest water contact angle, and the lowest degradation weight loss. The BD membrane had the highest degradation weight loss, the highest number of proteins in its degradation product, the strongest effect on the proliferation of MC3T3-E1 cells, and the highest expression level of osteogenic genes.ConclusionsThe PD membrane is the best choice for shaping and maintenance time, while the BD membrane is good for osteogenesis, and the BP membrane is suitable for spatial maintenance. To meet the clinical requirements of guided bone regeneration, using two different kinds of collagen membranes concurrently to exert their respective advantages is an option worth considering.

Fabrication of PES Modified by TiO2/Na2Ti3O7 Nanocomposite Mixed-Matrix Woven Membrane for Enhanced Performance of Forward Osmosis: Influence of Membrane Orientation and Feed Solutions.

Water treatment is regarded as one of the essential elements of sustainability. To lower the cost of treatment, the wastewater volume is reduced via the osmotic process. Here, mixed-matrix woven forward osmosis (MMWFO) PES membranes modified by a TiO2/Na2Ti3O7 (TNT) nanocomposite were fabricated for treating water from different sources. Various techniques were used to characterize the TNT nanocomposite. The crystal structure of TNT is a mix of monoclinic Na2Ti3O7 and anorthic TiO2 with a preferred orientation of (2-11). The SEM image shows that the surface morphology of the TNT nanocomposite is a forked nano-fur with varying sizes regularly distributed throughout the sample. The impact of TNT wt.% on membrane surface morphologies, functional groups, hydrophilicity, and performance was investigated. Additionally, using distilled water (DW) as the feed solution (FS), the effects of various NaCl concentrations, draw solutions, and membrane orientations on the performance of the mixed-matrix membranes were tested. Different water samples obtained from various sources were treated as the FS using the optimized PES/TNT (0.01 wt.%) MMWFO membrane. Using textile effluent as the FS, the impact of various NaCl DS concentrations on the permeated water volume was investigated. The results show that the MMWFO membrane generated with the TNT nanocomposite at a 0.01 wt.% ratio performed better in FO mode. After 30 min of use with 1 M NaCl and various sources of water as the FS, the optimized MMWFO membrane provided a steady water flow and exhibited antifouling behavior. DW performed better than other water types whenever it was used owing to its greater flow (136 LMH) and volume reduction (52%). Tap water (TW), textile industrial wastewater (TIWW), gray water (GW), and municipal wastewater (MW) showed volume reductions of 41%, 34%, 33%, and 31.9%, respectively. Additionally, when utilizing NaCl as the DS and TIWW as the FS, 1 M NaCl resulted in more permeated water than 0.25 M and 0.5 M, yet a higher volume reduction of 41% was obtained.

From asymmetry to symmetry: Biomimetic multi-channel structures for enhanced desalination using co-dissolving porogens

The asymmetric structures constructed via traditional methods fundamentally determine the “trade-off” bottleneck of cellulose triacetate reverse osmosis (RO) membrane in desalination. So, based on the structure-determined performance, inspired by the pore mechanism of frozen tofu through “water-ice-water” phase transition, the biomimetic RO membrane with high symmetry and homogeneity was successfully utilized in desalination. The co-solubilized N-methyl-2-pyrrolidone (NMP) narrowed the structural differentiation between Top and Bottom, increasing the number of through-water channels, surface hydrophilicity, and flatness of RO membrane. Typically, the prepared membrane with 0.125% NMP concentration has a salt rejection rate of 98.9% for NaCl, and excellent retention rate for other inorganic salts (MgCl2, LiCl). Notably, the NMP-modified membrane has a water flux of up to 17.2 L m−2 h−1, which is nearly 660% higher than that of No porogen-RO membrane (2.6 L m−2 h−1). Further, the membrane retained its separation capacity even after continued operation for 700 min, owing to the enhanced compression of the ductile pores by NMP. Overall, this novel cellulose-based RO membrane represents a structural mechanism for the design of innovative biomimetic multi-channel structures for long-term and efficient desalination.

Preparation and antifouling performance of low-pressure carbon nanotube membranes based on polydopamine biomimetic modification

In order to investigate the antifouling performance of low-pressure carbon nanotube membranes based on polydopamine (PDA) biomimetic modification, layered multi-walled carbon nanotubes PDA membrane (layered MWCNTs-PDA) and PDA blended MWCNTs membrane (blended PDA/MWCNTs) were prepared. The MWCNTs membranes’ antifouling performance and recoverability was significantly improved in filtrating BSA, HA and SA after PDA biomimetic modification, and the total fouling and irreversible fouling were all decreased. Compared with the blended PDA/MWCNTs membrane, the layered MWCNTs-PDA membrane had higher antifouling property as it further improved the electronegativity and hydrophilicity of membrane surface. In addition, denser surface pore size of the layered MWCNTs-PDA membrane can effectively reduce the fouling by trapping foulants on its surface. The combination of PDA biomimetic modification with MWCNTs membrane had a superior antifouling performance and rejection performance in processing NOM and artificial wastewater, and the majority of humic-like foulants could be excluded by the layered MWCNTs-PDA membrane. PDA biomimetic modification alleviated the adhesion of FITC-BSA on the MWCNTs membrane. The layered MWCNTs-PDA membrane especially alleviated the attachment of bacteria and processed excellent antimicrobial ability for bacteria.

A serendipity of nanofiltration membrane modification using a simple approach: Limited sulfonamidation, remarkable improvements

Surface modification via secondary interfacial polymerization (IP) is a promising technology for the enhancement of nanofiltration (NF) membrane performance such as rejection selectivity. In this study, sulfuryl chloride (SC), containing sulfur element, was employed to introduce sulfonic groups into the active layer of membranes, with a main purpose of investigating the secondary IP mechanisms as well as the variation of membrane structural and physicochemical properties. Moreover, the SC-modified membranes would be endowed with favorable performance. Results showed that SC in a hexane environment behaved similarly with small and reactive diacyl dichloride in enhancing membrane surface negative charge density and contracting membrane pores. Membrane surface characterization showed that the sulfur element had a low concentration with an S/N ratio less than 0.04. This indicated that, on the one hand, the residual amine groups in the nascent active layer for secondary IP were quite limited, and on the other hand, the improvement of membrane performance was remarkably affected by the introduced sulfonyl groups. Consequently, SC in the hexane environment could further enhance the crosslinking degree of the active layer. In addition, SC modification could increase the membrane surface hydrophilicity and narrow the pore size distribution. The SC-modified membranes would be suitable for advanced treatment of drinking water. An optimized membrane with SC modification had a molecular weight cutoff of ∼350 Da and a surface zeta potential of ∼−55.8 mV, and could effectively reject five negatively charged per- and polyfluoroalkyl substances (with molecular weight ranging from 214 to 414 Da) by over 80% while with a low rejection of MgCl2 below 30%..