Membrane Antifouling Properties Research Articles

Study of synergetic effect and comparison of novel sulfonated and carboxylated bulky diamine-diol and piperazine in preparation of negative charge NF membrane

Two new sulfonated (SDA) and carboxylated (CDA) aromatic diamine-diol monomers were synthesized and applied to prepare thin-film composite (TFC) nanofiltration (NF) membranes with improved antifouling and performance properties. The interfacial polymerization method was used to make sulfonated and carboxylated TFC-NF membranes with reaction of trimesoyl chloride (TMC) in the organic phase with amine and hydroxyl agents in the aqueous phase. Herein, for the first time, a comparison between carboxylated and sulfonated TFC was carried out. Moreover, the probability of synergetic effect between these two synthetic monomers (CDA and SDA) and piperazine monomer was studied (the sulfonated monomer and piperazine showed a synergetic effect). The outcomes of flux recovery ratio (FRR), flux and contact angle showed that in the presence of newly synthesized monomers, membrane hydrophilicity considerably improved. The salt retention sequence for all membranes was Na2SO4 ≫ NaCl > CaCl2, which means all membranes had a negative charge. Among the five prepared TFC membranes (SDA, CDA, PIP, SDA/PIP, and CDA/PIP), the SDA/PIP showed the best salt rejection (97% Na2SO4) with flux (50 Lm−2 h−1) and 91% FRR, at operating pressure of 10 bars. Although the SDA showed the highest permeability (62 Lm−2 h−1) and FRR of 92%, it presented the lowest Na2SO4 rejection. The results indicated that mixing carboxylated monomers with PIP caused deterioration in properties, while mixing sulfonated monomer with PIP enhanced the performances of the related TFC. Better permeability of the membrane made by newly synthesized monomers is ascribed to the existence of strong hydrophilic sulfonic acid, carboxylic acid and terminal hydroxyls, and amine groups at polyamide top layer producing enhanced membrane antifouling properties.

Investigations on the Properties and Performance of Mixed-Matrix Polyethersulfone Membranes Modified with Halloysite Nanotubes.

Ultrafiltration (UF) polyethersulfone (PES) membranes were prepared by wet phase inversion method. Commercial halloysite nanotubes (HNTs) in the amount of 0.5–4 wt % vs PES (15 wt %) were introduced into the casting solution containing the polymer and N,N-dimethylformamide as a solvent. The morphology, physicochemical properties and performance of the membranes were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), zeta potential, porosity and contact angle analyses, as well as permeability measurements. Moreover, the antifouling properties of the membranes were evaluated during UF of a model solution of bovine serum albumin (BSA). The research revealed a positive influence of modification with HNTs on hydrophilicity, water permeability and antifouling properties of the PES membranes. The most significant improvement of permeability was obtained in case of the membrane containing 2 wt % of HNTs, whereas the highest fouling resistance was observed for 0.5 wt % HNTs content. It was found that a good dispersion of HNTs can be obtained only at loadings below 2 wt %. Based on the results a relation between severity of membrane fouling and surface roughness was proved. Moreover, an increase of the roughness of the modified membranes was found to be accompanied by an increase of isoelectric point values.

One-bath two step method combined surface micro/nanostructures treatment to enhance antifouling and antibacterial property of PTFE flat membrane

Abstract To improve antifouling and antibacterial property of Polytetrafluoroethylene (PTFE) flat microfiltration (MF) membrane, a novel and facile method was developed to modify the membrane via the polymer of Laccase-catalyzed self-polymerization of Gallic acid (GAL) and cross-linked to Chitosan (CS) using Citric acid (CA) as a cross-linker, and then surface micro/nanostructures treated by 3-Triethoxysilylpropylamine (KH550). The surface chemical composition, surface morphology, hydrophilicity, antifouling and antibacterial property of the PTFE flat membrane were investigated by ATR-FTIR, XPS, FESEM, water contact angle (WCA), bovine serum albumin (BSA) filtration and antibacterial measurements, respectively. After using this low-cost and simple modification method, the PTFE flat membranes were endowed with excellent hydrophilicity, antifouling and antibacterial properties. Finally, the surface stability of the modified membranes were studied and the modified membrane showed excellent stability under pH = 3–12.

Exploiting Synergetic Effects of Graphene Oxide and a Silver-Based Metal-Organic Framework To Enhance Antifouling and Anti-Biofouling Properties of Thin-Film Nanocomposite Membranes.

Thin-film composite (TFC) membranes still suffer from fouling and biofouling. In this work, by incorporating a graphene oxide (GO)-silver-based metal-organic framework (Ag-MOF) into the TFC selective layer, we synthesized a thin-film nanocomposite (TFN) membrane that has notably improved anti-biofouling and antifouling properties. The TFN membrane has a more negative surface charge, higher hydrophilicity, and higher water permeability compared with the TFC membrane. Fluorescence imaging revealed that the GO-Ag-MOF TFN membrane kills Escherichia (E.) coli more than the Ag-MOF TFN, GO TFN, and pristine TFC membranes by 16, 30, and 92%, respectively. Forward osmosis experiments with E. coli and sodium alginate suspensions showed that the GO-Ag-MOF TFN membrane by far has the lowest water flux reduction among the four membranes, proving the exceptional anti-biofouling and antifouling properties of the GO-Ag-MOF TFN membrane.

Quorum quenching bacteria encapsulated in PAC-PVA beads for enhanced membrane antifouling properties

In order to improve the antifouling properties of quorum quenching (QQ) bacteria immobilized beads, the mechanical strength and permeability of QQ beads were modified by adding powdered activated carbon (PAC) based on traditional polyvinyl alcohol (PVA)-boric acid method. Optimal PAC concentration was investigated through measuring the mechanical strength, permeability and N-octanoyl-DLhomoserine lactone (C8-HSL) removal ratio of the PAC-PVA beads. Particularly, the enhanced antifouling effects of the optimal PAC-PVA beads were compared with those of original QQ beads through a membrane filtration experiment under constant pressure. The optimal concentration of PAC was 1% (w/v), under that PAC concentration, the mechanical strength, permeability and removal ratio of C8-HSL increased by 11.3%, 29.3% and 12.4% respectively. Synergistic effect between adsorption and biodegradation of 1% PAC-PVA beads was also observed. In membrane filtration experiment, membrane permeability with the 1% PAC-QQ beads decreased to 55.4% after 14 days, while the membrane permeability with 0% PAC-QQ beads decreased to 39.9%. The addition of PAC (1%) increased the antifouling efficiency of the QQ beads 15.5%. This paper demonstrated PAC-PVA bead as a QQ bacteria immobilized method had a great potential for biofouling control in membrane bioreactors (MBRs).

Simultaneous Improvement of Antimicrobial, Antifouling, and Transport Properties of Forward Osmosis Membranes with Immobilized Highly-Compatible Polyrhodanine Nanoparticles.

This work shows that incorporating highly compatible polyrhodanine nanoparticles (PRh-NPs) into a polyamide (PA) active layer allows for fabricating forward osmosis (FO) thin-film composite (TFC)-PRh membranes that have simultaneously improved antimicrobial, antifouling, and transport properties. To the best of our knowledge, this is the first reported study of its kind to this date. The presence of the PRh-NPs on the surface of the TFC-PRh membranes active layers is evaluated using FT-IR spectroscopy, SEM, and XPS. The microscopic interactions and their impact on the compatibility of the PRh-NPs with the PA chains were studied using molecular dynamics simulations. When tested in forward osmosis, the TFC-PRh-0.01 membrane (with 0.01 wt % PRh) shows significantly improved permeability and selectivity because of the small size and the high compatibility of the PRh-NPs with PA chains. For example, the TFC-PRh-0.01 membrane exhibits a FO water flux of 41 l/(m2·h), higher than a water flux of 34 l/(m2·h) for the pristine TFC membrane, when 1.5 molar NaCl was used as draw solution in the active-layer feed-solution mode. Moreover, the reverse solute flux of the TFC-PRh-0.01 membrane decreases to about 115 mmol/(m2·h) representing a 52% improvement in the reverse solute flux of this membrane in comparison to the pristine TFC membrane. The surfaces of the TFC-PRh membranes were found to be smoother and more hydrophilic than those of the pristine TFC membrane, providing improved antifouling properties confirmed by a flux decline of about 38% for the TFC-PRh-0.01 membranes against a flux decline of about 50% for the pristine TFC membrane when evaluated with a sodium alginate solution. The antimicrobial traits of the TFC-PRh-0.01 membrane evaluated using colony-forming units and fluorescence imaging indicate that the PRh-NPs hinder cell deposition on the TFC-PRh-0.01 membrane surface effectively, limiting biofilm formation.

Surface modification of UHMWPE/fabric composite membrane via self‐polymerized polydopamine followed by mPEG‐NH2 immobilization

ABSTRACTIn this work, a novel approach to improve the antifouling properties of membrane surfaces was developed. First, a polydopamine layer was attached onto the surface of an ultrahigh molecular weight polyethylene/fabric composite microporous membrane based on dopamine self‐polymerization and adhesive behavior. Then, methoxy polyethylene glycol amine was covalently bonded with the polydopamine layer via a Schiff base reaction. The physicochemical properties of the modified composite membrane surface were investigated, and the results indicated this modification could effectively enhance the membrane surface hydrophilicity. Furthermore, the protein fouling resistance of both dopamine‐coated and methoxy polyethylene glycol amine immobilized composite membranes was evaluated. It was found that a dopamine coating cannot obviously enhance the membrane antifouling properties due to its strong bioadhesion behavior. However, the antifouling properties of the composite membranes were significantly improved after being immobilized with a methoxy polyethylene glycol amine layer. Consequently, a layer‐by‐layer modified composite membrane with excellent antifouling property was obtained. The pure water flux and flux recovery ratio of the resultant membrane were 764 L m−2 h−1 and 83%, respectively. The aim of this paper was to provide an effective approach to optimizing the separation efficiency and antifouling performance of the ultrahigh molecular weight polyethylene/fabric composite membrane. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46428.

Improving the antifouling property of polypropylene hollow fiber membranes by in situ ultrasonic wave‐assisted polymerization of styrene and maleic anhydride

For the purpose of enhancing the hydrophilicity and antifouling property, styrene‐maleic anhydride copolymer (SMA) was successfully introduced on the surface of polypropylene hollow fiber membranes via in situ ultrasonic wave‐assisted polymerization. It was shown that how to avoid the hydrolysis and esterification of anhydride groups was the key for improving the hydrophilicity and antifouling property of membranes. Some factors were studied in detail, such as solvent, concentration of solution as well as time and temperature of ultrasonic treatment. Results showed that acetone and ethanol as solvents performed different functions during the process of the polymerization, and ethanol, a polar solvent, reacted with anhydride groups to hinder the formation of SMA and improvement of antifouling property. The modified membranes (PPM1 and PPM5) exhibit both high water flux and strong antifouling capability. Besides, antifouling property of modified membranes was very stable, which proved that they can work in reality. This study supplied a new approach to fabricate highly efficient polymeric membranes applicable to wastewater purification. POLYM. ENG. SCI., 59:E51–E58, 2019. © 2018 Society of Plastics Engineers

Fouling-resistant membranes for water reuse

Producing drinkable water is a major issue due to pollution and limited availability of fresh water. Membrane-based desalination is an efficient method to produce drinkable water from saline water and wastewater. Nonetheless, this method is limited by membrane fouling. Deposited foulants cause lower production flux and increase the cost. Hence, recent research has aimed to improve membrane antifouling properties. Here we review fouling-resistant membranes with focus on the membrane fouling phenomena; enhancement of interfacial polymerization procedures and assortment of new initiating monomers; modifying the membrane surface using physical and chemical methods; fabrication of composite membranes using inorganic materials; and modification with zwitterionic materials.

Improvement of antifouling performances for modified PVDF ultrafiltration membrane with hydrophilic cellulose nanocrystal

Hydrophilic cellulose nanocrystal (CNC) was incorporated into hydrophobic poly(vinylidene fluoride) (PVDF) membrane via phase inversion process to improve membrane antifouling property. The effects of CNC on membrane morphology, hydrophilicity, permeability and antifouling property were investigated in-detail. Results indicated that the introduction of CNC into PVDF membrane enhanced the permeability by optimizing membrane microstructure and improving membrane hydrophilicity. A higher pure water flux of 206.9 L m−2 h−1 was achieved for CNC/PVDF membrane at 100 kPa, which was 20 times that of PVDF membrane (9.8 L m−2 h−1). In bovine serum albumin filtration measurements, the permeation flux and flux recovery ratio of CNC/PVDF membrane were increased remarkably, while the irreversible fouling-resistance of CNC/PVDF membrane decreased by 48.8%. These results indicated that the CNC/PVDF membrane possessed superior antifouling property due to the hydrophilicity of CNC that formed a hydration layer on the membrane surface to effectively reduce contaminants adsorption/deposition.

Triple antifouling strategies for reverse osmosis membrane biofouling control

Triple antifouling strategies with fouling release, fouling resistance and contact killing attributes have been utilized for the control of reverse osmosis membrane biofouling. The membrane surface modification procedure is simple and time-efficient. After the interfacial polymerization process, the membrane was rinsed by n-hexane with addition of 2,2,3,4,4,4-hexauorobutyl methacrylate (HFBM), then exposed to UV irradiation for 20s, and finally immersed into a tobramycin (TOB) aqueous solution for 30s. The resultant membrane maintains the high permselectivity of the virgin membrane. Because of the synergistic effects of low-surface-energy brushes (fouling release) and hydrophilic TOB segments (fouling resistance) on the modified membrane surface, the membrane demonstrates superior antifouling property. Further, owing to the bactericidal attribute of TOB, the membrane exhibits strong antimicrobial activity. The membrane shows high antibiofouling property due to the triple antifouling strategies. The fouling results of combined foulants also highlight the membrane antifouling and antibiofouling properties. Moreover, the membrane shows excellent performance stability during the long-term cross-flow test and chemical cleaning process.

Separation and antifouling properties of hydrolyzed PAN hybrid membranes prepared via in-situ sol-gel SiO2 nanoparticles growth

In this work, a novel approach of hydrolysis followed by in-situ sol-gel of tetraethyl orthosilicate (TEOS) was developed to modify the polyacrylonitrile (PAN) porous membrane prepared via non-solvent induced phase separation technique for improved separation and antifouling properties. PAN/SiO2 hybrid membranes prepared using different contents of TEOS were characterized through ATR-FTIR, XPS, SEM, EDS, water contact angle measurement, cross-flow permeation test, static protein adsorption test and dynamic cross-flow protein fouling experiment. It was found that the sol-gel of TEOS took placed both on membrane surface and within membrane pore and the generated SiO2 particles affected both membrane surface and permeation properties through the roles of surface deposition and pore-filling, respectively. The in-situ sol-gel of TEOS could efficiently improve membrane separation property through tuning pore size and narrowing pore size distribution. Compared with the base and hydrolyzed PAN membranes of same water permeability, the PAN/SiO2 hybrid membrane exhibited a much lower molecular weight cut-off and thus enhanced rejection performance. Furthermore, both static protein adsorption and dynamic cross-flow fouling experiments with bovine serum albumin aqueous solution demonstrated that the surface deposition of SiO2 could appreciably improve membrane antifouling property through making membrane surface more hydrophilic, negatively charged and enriched with hydroxyl groups.

Preparation and characterization of a novel MMMs by comprising of PSF–HNT/TiO2 nanotubes to reduce organic sediments

Antifouling properties of ultrafiltration-mixed matrix nanocomposite membranes which are combined of polysulfone (PSF) and nanotubes composed of titanium dioxide and clay (HNT/TiO2) were studied. The membrane was prepared by phase separation process using different concentrations of HNT/TiO2 and polysulfone. Morphology (combination) of membrane was determined using a scanning electron microscope and atomic force microscopy. The most important observation was the significant improvement in water flow, which was attributed to improved hydrophilic property. Improved hydrophilic property was approved by water contact angle and porosity measurements. This improvement in hydrophilic property due to the presence of hydroxyl groups on HNT/TiO2 which was determined by (FTIR) spectrum. Fouling resistance of investigated membranes by solution filtration BSA showed that the membranes with 1 and 2% by weight HNT/TiO2 have the best antifouling property, which resulted in flow recovery. The effects of different directions of washing in sediment tests were reported. Vertical washing and parallel washing in period of sediment tests were performed and the effects were evaluated. Nanocomposite membrane HNT/TiO2 with parallel washing showed a significant reusable during filtration. PSF and PSF–HNT/TiO2 (0.5 wt%) showed severe rejection nearly 100%, while this high ability was not observed for membranes with higher percent of HNT/TiO2. In addition, the experimental results confirm that the antifouling on the membranes of pure PSF and PSF–HNT/TiO2 (0.5 wt%), molecules after infection with BSA, is not able to recover their ability to the initial permeability, while the membranes with higher percent HNT/TiO2 show good current recover after washing with pure water.

Enhancement of polysulfone membrane with integrated ZnO nanoparticles for the clarification of sweetwater

Clarification is one of the main steps in producing glycerin from glycerin–rich solution (namely sweetwater) in oleo-chemical industry. In this study, ZnO nanoparticles (9–12 nm in diameter) were incorporated into polysulfone (PSf) membranes to improve the membrane antifouling properties toward the fatty acids in sweetwater. The hybrid membranes were fabricated through wet phase inversion method. The modified membranes exhibited better water permeability, membrane surface hydrophilicity (improvement from 82° to 62.1°) and resistance toward fouling by fatty acids. In this study, the best membrane was obtained in the presence of 3% of ZnO nanoparticles, which showed good fouling resistance, high solution flux and a very high rejection of fatty acids (≥80%) in comparison with the pure PSf membranes, at the same experimental conditions. The enhanced membrane performances during the clarification of sweetwater were attributed to the unique properties of ZnO nanoparticles that were uniformly dispersed in the PSf structures.

Bioinspired Polyethersulfone Membrane Design via Blending with Functional Polyurethane

Polyurethanes (PUs) are currently considered to be biocompatible materials but limited by a low resistance to thrombus. We therefore design a heparin-like PU (HLPU) to modify polyethersulfone (PES) membranes approaching integrated antifouling and antithrombotic properties by bioinspiration of heparin structure. Poly(vinyl pyrrolidone)-HLPU (PVP-HLPU) was synthesized via reversible addition-fragmentation chain transfer polymerization of VP using PU as a macroinitiator and then sulfonated by concentrated H2SO4. FTIR and NMR results demonstrated the successful synthesis of PVP-HLPU. By incorporation of PVP-HLPU, the cross-sectional structure of PES composite membranes altered from finger-like structure to sponge-like structure resulting in tunable permeability. The increased hydrophilicity verified by water contact angles benefited both the permeability and antifouling property. As a consequence, the composite membranes showed good blood compatibility, including decreased protein adsorption, suppressed platelet adhesion, lowered thrombin-antithrombin III generation, reduced complement activation, and prolonged clotting times. Interestingly, the PVP-capped HLPU showed better blood compatibility compared to polyethyleneglycol-capped and citric acid-capped HLPUs. The results demonstrated the enhanced antifouling and antithrombotic properties of PES hemodialysis membranes by the introduction of functional HLPUs. Also, the proposed method may forward the fabrication of hemocompatible membranes via bioinspired surface design.

Preparation of hydrophilic and antifouling polysulfone ultrafiltration membrane derived from phenolphthalin by copolymerization method

In this task, carboxylated polysulfone (PSF-COOH) was achieved by introducing the monomer of phenolphthalin (PPL) containing carboxyl to the molecule backbone of polysulfone (PSF). And a series of PSF-COOH copolymers with different carboxylation degree was synthesized by adjusting the molar (%) of bisphenol A (BPA) and PPL in direct copolymerization method and was prepared as PSF-COOH ultrafiltration membranes via phase separation method. The effect of PPL molar (%) in copolymers on the morphology, hydrophilicity, permeation flux, antifouling and mechanical properties of membranes was investigated by scanning electron microscope (SEM), atomic force microscope (AFM), water contact angle, ultrafiltration experiments and universal testing machine, respectively. The results showed that with the increased carboxyl content in membranes, the hydrophilicity, permeation fluxes and antifouling properties of membranes gradually increased. When the molar (%) of PPL to BPA was 100:0, the membrane exhibited the highest pure water flux (329.6L/m2h) and the maximum flux recovery rate (92.5%). When the content of carboxyl in the membrane was 80% or more, after three cycles of BSA solution (1g/L) filtration, the flux recovery rate was basically constant or showed a slightly increase. Thus, it can achieve the goal of long term usage without compromising flux.

Design of poly(vinylidene fluoride)-g-p(hydroxyethyl methacrylate-co-N-isopropylacrylamide) membrane via surface modification for enhanced fouling resistance and release property

Thermo-sensitive polymer poly(N-isopropylacrylamide) (PNIPAAm), hydrophilic polymer poly(hydroxyethyl methacrylate) (PHEMA) and copolymer p(hydroxyethyl methacrylate-co-N-isopropylacrylamide) [P(HEMA-co-NIPAAm)] were synthesized onto poly(vinylidene fluoride) (PVDF) membrane via atom transfer radical polymerization (ATRP) in order to improve not only fouling resistance but also fouling release property. The physicochemical properties of membranes including hydrophilicity, morphology and roughness were examined by contact angle analyzer, scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. The antifouling property of membranes was improved remarkably after surface modification according to protein and bacterial adhesion testing, and filtration experiment. Minimum protein adsorption and bacterial adhesion were both obtained on PVDF-g-P(HEMA-co-NIPAAm) membrane, with reduction by 44% and 71% respectively compared to the pristine membrane. The minimum bacterial cells after detachment at 25°C were observed on the PVDF-g-P(HEMA-co-NIPAAm) membrane with the detachment rate of 77%, indicating high fouling release property. The filtration testing indicated that the copolymer modified membrane exhibited high resistance to protein fouling and the foulant on the surface was released and removed easily by washing, suggesting high fouling release and easy-cleaning capacity. This study provides useful insight in the combined “fouling resistance” and “fouling release” property of P(HEMA-co-NIPAAm) for PVDF membrane modification, even for other types of the membrane in wide application.

Sulfonated polyphenylsulfone asymmetric membranes: Effect of coagulation bath (acetic acid‐NaHCO3/isopropanol) on morphology and antifouling properties

ABSTRACTSulfonated polyphenylsulfone porous asymmetric membranes, S‐PPSU with different sulfonation degrees, 21, 33, 50 wt %, were prepared by phase inversion. Two different coagulation baths were explored for asymmetric membrane preparation: acetone/isopropanol and acetic acid (AA)‐NaHCO3/isopropanol. The latter bath allows better morphology control for the nucleation and pore formation of the membrane. Scanning electron microscopy of membranes shows that pore interconnectivity is improved, when the mixture of AA‐NaHCO3/isopropanol was used for asymmetric S‐PPSU ultrafiltration membranes preparation. S‐PPSU asymmetric membranes show an increasing hydrophilicity with increasing sulfonation degree. Asymmetric membrane antifouling properties improve as the concentration of sulfonic groups increases in the membrane showing twice the flux recovery ratio and lower BSA protein absorption in static and dynamic flux tests. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44502.

Cellulose acetate ultrafiltration membranes reinforced by cellulose nanocrystals: Preparation and characterization

ABSTRACTCellulose nanocrystals (CNCs) were used as a sustainable additive to improve the hydrophilicity, permeability, antifouling, and mechanical properties of blend membranes. Different CNC loadings (0–1.2 wt %) in cellulose acetate (CA) membranes were studied. The blend membranes were prepared by a phase‐inversion process, and their chemical structure and morphological properties were characterized by attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy, porosity, and mean pore size and contact angle measurement. The blend membranes became more porous and more interconnected after the addition of CNCs. The thickness of the top layer decreased and a few large holes in the porous substrate appeared with increasing CNC loading. In comparison with the pure CA membranes, the pure water flux of the blend membranes increased with increasing CNC loading. It reaches a maximum value of 76 L m−2 h−1 when the CNC loading was 0.5 wt %. The antifouling properties of the CA membrane were significantly improved after the addition of CNCs, and the flux recovery ratio value increased to 68% with the addition of 0.5 wt % CNCs. In comparison with that of the pure CA membranes, the tensile strength of the composite membranes increased by 47%. This study demonstrated the importance of using sustainable CNCs to achieve great improvements in the physical and chemical performance of CA ultrafiltration membranes and provided an efficient method for preparing high‐performance membranes. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43946.

Shielding membrane surface carboxyl groups by covalent-binding graphene oxide to improve anti-fouling property and the simultaneous promotion of flux

Graphene oxide (GO) is an excellent material for membrane surface modification. However, little is known about how and to what extent surface functional groups change after GO modification influence membrane anti-fouling properties. Carboxyl is an inherent functional group on polyamide or other similar membranes. Multivalent cations in wastewater secondary effluent can bridge with carboxyls on membrane surfaces and organic foulants, resulting in serious membrane fouling. In this study, carboxyls of a polydopamine (pDA)/1,3,5-benzenetricarbonyl trichloride (TMC) active layer are shielded by covalently-bound GO. The process is mediated by N-(3-dimethylaminopropyl)-N’-ethylcarbodiimide (EDC)/N-hydroxysuccinimide (NHS). For GO containing low quantities of carboxyls, X-ray photoelectron spectroscopy (XPS) and zeta potential analyzer test results reveal that the carboxyl density decreased by 52.3% compare to the pDA/TMC membrane after GO modification. Fouling experiments shows that the flux only slightly declines in the GO functionalized membrane (19.0%), compared with the pDA/TMC membrane (36.0%) after fouling. In addition, during GO modification process the pDA/TMC active layer also become harder and thinner with the aid of EDC/NHS. So the pure water permeability increases from 56.3 ± 18.2 to 103.7 ± 12.0 LMH/MPa. Our results provide new insights for membrane modification work in water treatment and other related fields.