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In this work, thin film composite polyamide (PA) membranes are modified by polyethyleneimine (PEI) and 2,6‐diaminopyridine (DAP) through sequential interfacial polymerization to fabricate contact active antibacterial membranes. The modified membranes show improved hydrophilicity and enhancement of zeta potential. Upon tethering with PEI and DAP onto the PA membranes, the membrane flux increases from 35.7 to 46.7 and 50.0 L m−2 h−1, respectively. Further the salt rejection rate improves from 96.6% to 98.0% and 98.8%, respectively. The PA‐PEI membranes have a better antibacterial performance than PA‐DAP, with a bacteria killing ratio for both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) over 96.7%, while a commercial LC LE‐4040 membrane presents bacteria killing ratio of 13.3% for E. coli and 8.4% for S. aureus, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A novel salt-responsive thin-film composite (TFC) reverse osmosis (RO) membrane was prepared by tethering a zwitterionic polymer poly (4-(2-sulfoethyl)-1-(4-vinylbenzyl) pyridinium betaine) (PSVBP) onto a commercial RO membrane. The graft polymerization was conducted by surface-initiated free radical polymerization of SVBP initiated by a K2S2O8–NaHSO3 redox system. The membrane surface before and after graft polymerization was investigated in detail using ATR-FTIR, XPS, zeta potential, water contact angle and SEM. The change on surface chemical composition demonstrated successful grafting of PSVBP onto the RO membrane surface. The PSVBP grafting added negative charge onto the membrane surface and significantly improved membrane surface hydrophilicity. The RO test indicates that PSVBP grafting can increase the rejection from 98.0% to 99.7% with the trade-off 20% of the permeation flux. A cross-flow protein fouling test as long as 100h indicates that the resulted PA-g-PSVBP membrane had superior antifouling property in the short term but lost the advantage for long-term operation. In spite of the long-term fouling, the PA-g-PSVBP membrane can restore 90% of the initial flux by rinsing with brine. The salt-responsive property of the PSVBP brush is believed to provide a driving force for the release of protein foulants. [Copyright &y& Elsevier]

Abstract: A novel random terpolymer poly(methylacryloxyethyldimethyl benzyl ammonium chloride-r-acrylamide-r-2-hydroxyethyl methacrylate) (P(MDBAC-r-Am-r-HEMA)) was synthesized via free radical polymerization and used as the coating material on the polyamide thin film composite (TFC) reverse osmosis (RO) membrane to improve its chlorine resistance and antifouling performance. The chlorine resistance of the membranes was evaluated by cross-flow filtration of the NaClO solution. Antifouling performance was evaluated by cross-flow filtration of the protein solution and cell-culture experiments. The membrane surface was analyzed via ATR-FTIR, XPS, SEM and streaming potential measurements. The coated membrane can tolerate chlorine exposure over 16,000ppmh, which is 7–10 times the pristine membrane. The bacteria growth can be significantly depressed on the coated membrane surface. The coated membrane can retain its flux very well under protein filtration. It is believed that the surface coating layer works as a protective and sacrificial layer, preventing the attack of chlorine on the underlying polyamide film. The PMDBAC and PAm components are essential to the antimicrobial property and the improved surface hydrophilicity is beneficial to the antifouling performance of the membrane. The coated membrane offers potential use as a novel RO membrane with improved antifouling performance and chlorine resistance. [Copyright &y& Elsevier]

The polyamide layer of reverse osmosis (RO) membrane is susceptible to chlorination degradation. Guidelines for validation and integrity monitoring of the low pressure RO (LERO) membrane morphology and performance upon chlorination is still rarely reported. In this study, we selected three commercial LERO membranes (i.e., LP, ULP and LCLE) to study their structure and separation performance change for exposing to chlorine under both pressurized and static chlorination conditions, with different active chlorine concentrations and pH. At the pressurized testing, the membrane water flux increased at the initial stage due to the decrease of water passage restriction by the destroy of the hydrogen bond in the polyamide, and then the water flux sharply decreased and gradually leveled off, which should be resulted from the destroy of chemical structure of polyamide and membrane compaction under high pressure. The salt rejection slightly changed, presumably due to the combination of tightening effect, compactness and defect plugging by foulants. As for the static chlorination test, active chlorine concentration and chlorination time were not unequivocalness at the same chlorination intensity. Higher active chlorine concentration could cause more serious chlorination degradation. Based on the water flux change at neutral pH and under static chlorination conditions, a flux reduction equation with active chlorine concentration was fitted by y = axb (1＜x＜1000), which could help us to predict the water flux under a specific chlorine concentration and time. [Display omitted] • The chlorination of PA membrane was studied in pressurized and static conditions. • The chlorination at pressurized condition was much severer than static condition. • Membranes were severely destroyed under high chlorine content and acid medium. • The role of chlorine concentration in chlorination was greater than exposure time. • The water flux reduction with chlorine concentration can be fitted by an equation. [ABSTRACT FROM AUTHOR]

A novel procedure to fabricate quaternized cellulose triacetate reverse osmosis (QCTA-RO) membranes via the etherification procedure between partially hydrolyzed CTA-RO membrane and 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (CHPTAC) in alkaline solutions (pH = 9–11) for different reaction time (1, 2, 3 and 4 h) was proposed. The structure and performances of the obtained QCTA-RO membranes were characterized and their antibacterial performances against E. coli and S. aureus were evaluated through colony counting method. The results showed that quaternary amine group was successfully grafted on the surface of membrane via covalently bond without significant damage to morphology, mechanical performance and thermal stability. The permeation flux values increased with prolonging modification time to 3 h, while the salt rejection decreased slightly but remained above 92%. QCTA-RO membranes displayed good antibacterial activity against Gram-negative E. coli and Gram-positive S. aureus and their bactericidal rates were 78.7–89.0% and 64.7–76.6% respectively at the optimized modification time of 2–3 h. [ABSTRACT FROM AUTHOR]

• Both aqueous and organic additives improve water flux without loss of rejection. • Both additives promote MPD diffusion and improve crosslinking. • Aqueous additives result in thinner and smoother PA layer with less mass. • Organic additives sustain the solubility of PA leading to thicker film. • The greater PA mass from organic additives correlates with higher water flux. Additive approach provides a simple, yet very effective way of improving the performance of polyamide (PA) thin film composite (TFC) membranes. However, the correlation between physical and chemical properties of a wide range of additives and the final membrane properties is still barely understood. In this work, a variety of additives were systematically used to prepare RO membranes to provide fundamental mechanistic understanding of membrane performance improvement by additives. The membranes were characterized in detail by FTIR, XPS, SEM, AFM, water contact angle, zeta potential, QCM etc. The separation performance of the TFC membrane was measured with 2000 ppm NaCl solution at 1.5 MPa and 25 °C. The results show that by adding DMSO, formamide, acetamide into the aqueous solution, or cyclohexanone into the organic phase, approximately 2 times higher water flux was achieved without significantly decreasing salt rejection. Both aqueous and organic phase additives bring out better MPD diffusion and higher crosslinking density. However, their effect on the kinetic of interfacial polymerization are different. The aqueous phase additives promotes the formation of a thinner and smoother PA selective layer with less film mass, while the organic phase additives sustain the solubility of PA oligomers so that the film mass increases and greater film mass correlates with improved membrane flux. [ABSTRACT FROM AUTHOR]

• Cellulose acetate RO membrane was bi-antibacterial modified under mild condition. • Bromoacetyl bromide and tertiary amine were introduced in turn. • Modifying affected membranes hydrophilic, electronegative and mechanical property. • N,N- dimethyloctylamine modifying led to the best comprehensive membrane performance. • Bactericidal rates of broad-spectrum antibacterial RO membrane were higher than 99.9%. In order to improve the antibacterial efficiency and spectrum of cellulose acetate reverse osmosis membrane (CA–RO), both quaternary ammonium and bromoacetyl groups were introduced into cellulose diacetate under mild conditions forming CA–RO with bi-antibacterial groups for seawater desalination. Bromoacetyl bromide and a series of tertiary amine were chosen as the modification agents respectively. The characterization results showed that both two antibacterial groups were successfully introduced with a certain density. The obtaining membrane had a less hydrophilic but more electronegative surface as well as improved mechanical property. The flux values increased firstly and decreased subsequently after twice modifications while the salt rejection rose. The membrane modified with N,N- dimethyloctylamine (DMOA) had the optimal comprehensive performance of flux and salt rejection. The antibacterial testing results indicated that the resulting RO membranes showed high antibacterial efficiency and broad-spectrum. Their bactericidal rates against gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) were more than 99.9%. [ABSTRACT FROM AUTHOR]

The synergized optimization of water flux and salt rejection by blending with inorganic fillers has been achieved for the polyamide (PA) thin film nanocomposite (TFN) membrane. However, it is difficult to characterize its mass transport properties due to the very thin and heterogeneous PA film. In this work, we select cellulose triacetate (CTA) as the base to prepare hybrid films and their transport properties were studied according to solution-diffusion theory. A series of inorganic fillers, such as reduced graphene oxide (RGO), zeolites, ZIF-8, SiO 2 and graphene oxide (GO) were incorporated. The SEM and EDX results indicate a less than 1 wt% filler content for a uniform dispersion. The blending of inorganic fillers leads to enhanced glass transition temperature (T g ) and density, little effect on the water transport property but dramatically decreased salt permeability values, which are nearly ten-fold of that of the CTA film. The blending of GO can densify and hydrophilize CTA simultaneously, which is most promising for a desalination application. The increased water uptake should contribute to its increased water permeability, while the decreased free volume size and FFV value and various interactions between the ions (Na + , Cl - ) and GO sheets account for salt permeability decrease. [ABSTRACT FROM AUTHOR]

A series of stimuli-responsive reverse (RO) membranes were prepared by tethering three stimuli-responsive polymers, poly (sulfobetaine methacrylate) (PSBMA), poly (4-(2-Sulfoethyl)-1-(4-vinyl-benzyl) pyridinium betain) (PSVBP) and poly (N-isopropylacrylamide) (PNIPAM) onto the surface of a commercial thin-film (TFC) RO membrane via surface-initiated graft polymerization. The membrane surface was characterized by ATR-FTIR, XPS, zeta potential, water contact angle (WCA), FESEM and AFM. Membrane characterization indicates successful grafting of these polymers, with more negatively-charged, smoother and more hydrophilic surfaces as a result. Long-term fouling-rinsing cycled experiments were conducted to evaluate fouling resistance and cleaning efficiency. With CaCO 3 as the foulant, the modified membranes showed better fouling resistance in the whole testing as long as 320 h; with BSA as the foulant, they only showed better antifouling performance in short term. However, the modified membranes showed much higher cleaning efficiency in both cases, with the PA-g-PSVBP membrane as the best one. [ABSTRACT FROM AUTHOR]

Current reverse osmosis membrane still suffers from permeability/selectivity trade-off, chlorine attack and fouling. To address these problems, a new interlayer-assisted interfacial polymerization (i.e., polyethyleneimine (PEI) interlayer) in the presence of graphene oxide (GO) at various loading was adopted in this work. Their effects on membrane properties and performances were systematically investigated. Results showed that the PEI-interlayered thin film composite (iTFC) membrane exhibited higher pure water permeance (PWP) (1.76 L/m2·h·bar) and NaCl rejection (97.69%) compared to the conventional TFC (cTFC) membrane (1.34 L/m2·h·bar; 96.91%), assigning to the thin and compact PA formed. Performance of iTFC membrane was further enhanced upon inclusion of 0.01 wt/ v % GO, producing PEI-interlayered thin film nanocomposite (iTFN-10) membrane with greater PWP (2.66 L/m2·h·bar) without compensating rejection. This was ascribed to the enhanced surface roughness, hydrophilicity and nanochannels created by GO within the PA. The antifouling property of iTFN-10 membrane was comparable with commercial TFC but better than iTFC membrane. Unlike iTFC membrane, the NaCl rejection of iTFN-10 membrane was least deteriorated after chlorination. This membrane also demonstrated better antibacterial properties (E. coli : 44.26% and S. aureus : 77.55%) than commercial membrane (E. coli : 24.68% and S. aureus : 48.98%) due to the presence of amine groups on membrane surface. [Display omitted] • Interlayer-assisted IP yielded TFC membrane with thin, uniform and compact PA. • Embedding GO in PA layer further enhanced the properties of interlayered membrane. • PEI-interlayered membrane showed improved desalination and antibacterial properties. • The optimized interlayered membrane could also reduce the degree of chlorine attack. [ABSTRACT FROM AUTHOR]

Biofouling severely limits the application of reverse osmosis (RO) for water treatment. In this work, a green surface in-situ reduction method based on the tannic acid-inspired chemistry was used to introduce silver nanoparticles (AgNPs) into the intermediate layer of a thin film nanocomposite (TFN) membrane, as effectively improved the anti-biofouling performance of the membrane without sacrificing its desalination performance. SEM, EDX, AFM, XPS, DSA, ATR-FTIR and zeta potential were used to characterize the membranes. The plate counting method and confocal laser scanning microscopy (CLSM) were used to evaluate the anti-biofouling performance. And the long-term Ag+ release rate was measured using ICP-MS. Compared with unmodified thin film composite (TFC) membranes, the permeation flux of TFN membrane is improved while retaining the salt rejection. By optimizing the soaking time of FeCl 3 and AgNO 3 on the PSF membrane surface during the preparation of the intermediate layer and the M -phenylenediamine (MPD) and trimesoyl chloride (TMC) concentration for the interfacial polymerization. A water flux of 34.5 ± 1.2 L/m2 h and a salt retention of 98.0 ± 0.3% were achieved under the operating pressure of 1.55 MPa and 25 °C, for a 2000 ppm NaCl solution. The killing rates of the membrane to E. coli and S. aureus are almost 100% for a 24 h and 48 h contacting time. The number of bacteria attached to the membrane surface is far less than that of the unmodified membrane. More importantly, the Ag+ release rate was stable and controllable, allowing for long-term antibacterial properties. [Display omitted] • Introducing TA/Fe–Ag intermediate layer to prepare TFN RO membrane. • The Ag+ were reduced by phenol in TA to fix AgNPs into the TFC membrane. • Introduction of the TA/Fe–Ag layer improve flux without jeopardizing rejection. • AgNPs were released in a controlled way to kill bacteria near the surface. • The ultra-smooth surface of RO TFN membrane prevents bacterial adhesion. [ABSTRACT FROM AUTHOR]