Dynamic Fouling Experiments Research Articles

Fouling Resistant Liquid-Infused membranes for oil separations

Bioinspired membranes offer an alternative approach to improving the fouling resistance of commercial membranes for oil separations. Here, two perfluoropolyether oils, a lower viscosity Krytox 103 (K103) and a higher viscosity Krytox 107 (K107), were infused into commercial polyvinylidene fluoride (PVDF) ultrafiltration membranes to mimic the Nepenthes pitcher plant. The transmembrane pressure required to perform long-term oil permeance tests was optimized by testing the liquid-infused membranes at different applied pressures. Crystal violet staining and variable pressure scanning electron microscopy qualitatively suggest that the oil layer remained on the membranes after the oil separation experiments were conducted. Over 5 cycles, K103- and K107- liquid-infused membranes exhibited a consistent permeance of ∼ 30000 L m-2h−1 bar−1 at 1.0 bar and ∼ 14500 L m-2h−1 bar−1 at 0.5 bar, respectively. The steady performance further supports a long-lasting oil layer persists on the membrane surface and inside membrane’s pores. Next, experiments were conducted to determine the stability of the Krytox oil post accelerated cleaning tests using bleach. No structural changes to the Krytox oils were detected by thermogravimetric analysis or nuclear magnetic resonance spectroscopy. Dynamic fouling experiments using Escherichia coli K12 revealed that the liquid-infused membranes had higher flux recovery ratios (∼95 %) than the bare PVDF control membranes (∼55 %). Our results demonstrate that liquid-infused membranes exhibit chlorine stability and superior fouling resistance, presenting a promising bioinspired membrane that can be used in pressure-driven oil separation applications.

Crystallization Fouling on Different Surfaces under Static and Dynamic Experiments

Crystallization fouling is a typical problem in heat exchangers, which leads to the deterioration of heat transfer performance and energy loss. Surface modification and fluid shear are important factors to control crystal nucleation, aggregation, growth, and removal. This study performed static fouling experiments of calcium sulfate crystallization on patterned polymethyl methacrylate for different stages and real-time dynamic fouling experiments on metal surfaces. The grooves provide nucleation sites, and the nuclei prefer aggregation, forming blossoming-like crystals. After washing the fouled sample with distilled water, the size of blossoming-like crystals decreases and it is difficult to fully clean blossoming-like crystals compared with dispersed crystals. The fouling performance for the second time after the cleaning demonstrates that the existent crystals create nucleation sites, leading to a higher deposition rate than that of the first fouling. Furthermore, the fouling morphology is flaky gypsum on the metal surfaces under the dynamic experiment and fouling removal caused by the fluid shear is obvious. The deposition mass per unit area on metal materials under dynamic experiment in descending order is 0.0353 mg/mm2 of copper, 0.0154 mg/mm2 of titanium, 0.0146 mg/mm2 of aluminum, and 0.0070 mg/mm2 of stainless steel, respectively, which is significant to the mitigation of crystallization fouling on different materials.

Design of anti-fouling membranes via prebiotic chemistry-inspired aminomalononitrile (AMN) coating strategy: Aldehyde-mediated chemical immobilization of pseudo-zwitterionic compounds

Although zwitterionic polymers were extensively explored for anti-fouling surface modification, the resulting significant loss in membrane permeability is undesirable. Assisted by co-deposition of aminomalononitrile (AMN) and terephthalaldehyde (TA), in this study a high-performance membrane with low fouling propensity was designed via chemical immobilization of a novel pseudo-zwitterionic compound, namely 3-(dimethyl(3-((3-sulfonatopropyl)ammonio)propyl)ammonio)propane-1-sulfonate (DMPDA-QS), onto the polyethersulfone (PES) substrate. The optimal membrane showed high water permeance (∼366 L m−2 h−1 bar−1) and high rejection (>98.0 %) to model proteins. The immobilization of this pseudo-zwitterionic compound led to a nearly neutral surface and enhanced hydrophilicity, and the dynamic fouling experiments proved its excellent antifouling performance against both negatively (i.e., bovine serum albumin, BSA) and positively (i.e., lysozyme, LYZ) charged foulants with flux recovery of >93% and >88% after 3-cycle filtration, respectively. A mathematical model was used to quantify the contribution of mass transfer resistance caused by reversible and irreversible fouling, showing nearly unchanged resistance of the modified membranes in contrast with 260% increase of the pristine PES after 3 filtration cycles. The developed fabrication strategy provided a viable and versatile route for designing high-performance antifouling membranes.

Scalable Zwitterionic Polymer Brushes for Antifouling Membranes via Cu0-Mediated Atom Transfer Radical Polymerization

Polymer brush layers have attracted significant interest for versatile, controlled surface modification enabling fabrication and functionalization of membranes for water treatment and reuse applications. In particular, zwitterionic polymer brushes have been shown to provide strong resistance to organic fouling, oil fouling, biofouling, and inorganic fouling as membrane coatings for a variety of membrane processes. However, despite the demonstrated performance of polymer brush membranes, there are significant challenges associated with commercial scale-up of traditional fabrication methods. In this work, we demonstrate scalable grafting of zwitterionic polymer brushes from microfiltration membrane substrates under ambient conditions, and with low chemical consumption, for the first time, via Cu0-mediated surface-initiated atom transfer radical polymerization (Cu0-SI-ATRP). We demonstrate that Cu0-SI-ATRP is effective for brush grafting from porous membrane substrates, including samples of up to 150 cm2. Furthermore, we systematically investigate the effect of polymerization in confinement on brush growth kinetics and fouling resistance, using colloid probe force microscopy and dynamic fouling experiments. Results demonstrate that Cu0-SI-ATRP results in poly(sulfobetaine methacrylate) brush layers that significantly improve fouling resistance; however, polymerization methods significantly impact fouling resistance, for both Si wafer and membrane substrates. We identify polymerization methods that enhance fouling resistance even for thin brush layers. The results of this study provide pathways to the scalable fabrication and design of robust, antifouling membranes for applications in water treatment, water reuse, and resource recovery from waste streams.

Bio-inspired fabrication of adsorptive ultrafiltration membrane for water purification: Simultaneous removal of natural organic matters, lead ion and organic dyes

Conventional ultrafiltration membrane is difficult to achieve the multi-component removal of water contaminants including macromolecules and small ions. Meanwhile, a large number of petrochemical-based polymers as membrane material is raising concerns about environmental risk. In this study, we present a feasible way for the manufacture of multifunctional cellulose-based nanocomposite membranes via bio-fabrication by Acetobacter xylinus for water purification. The harvested bacterial cellulose (BC) pellicle was coated by polydopamine (PDA) as a functional layer and molecular linker to immobilize carboxylated cellulose nanocrystals (C-CNCs) to prepare BC/PDA14h/CNCs membrane (BCM/PDA14h/CNCs). The composited PDA and C-CNCs on the BC nanofibers endowed the membrane with a maximum adsorption capacity of up to 167.80 mg g−1 for Pb2+, and 251.58 mg g−1 for methylene blue (MB). Multiple contaminants (heavy metals, organic dyes, and natural organic matter (NOM)) can also be treated by BCM/PDA14h/CNCs simultaneously during the dynamic filtration process. The removal efficiency of BCM/PDA14h/CNCs against the mixture of metal ions is inversely proportional to the radius of hydrated ions. The selective separation studies on binary dye mixtures showed that the separation efficiency of the membrane is mainly related to the electronegativity of dyes. The BCM/PDA14h/CNCs exhibited preferential adsorption for cationic dyes, with a separation efficiency was up to 98%. Dynamic fouling experiments confirmed that the BCM/PDA14h/CNCs presented excellent antifouling performance and showed a high flux recovery ratio. The multifunctional characteristic, high removal efficiency, excellent reusability and stability as well as environmentally friendly feature of the prepared membrane in the present study provide a sustainable approach for membrane fabrication and promising application in water purification.

An antifouling loose nanofiltration membrane prepared by cross-linking HPAN ultrafiltration membrane with zwitterionic polymer PEI-CA for efficient dye desalination

In this study, a novel antifouling loose nanofiltration (LNF) membrane was prepared by the cross-linking and grafting of hydrolyzed polyacrylonitrile ultrafiltration (HPAN UF) substrate with a polyethylenimine (PEI) based zwitterionic polymer PEI-CA through the covalent amide bond. The successful introduction of PEI-CA was verified by various techniques. The tailored membrane HPAN-PEICA exhibited ultra-high water permeance (73.5 L m−2 h−1 bar−1) and meanwhile maintained excellent rejection (~99.9 %) for dye Brilliant Blue R (BBR), Methyl Blue (MB), Congo red (CR) and Chrome Black T (CBT). In addition, it exhibited ultralow rejection (below ~6 %) towards the inorganic salts (NaCl, Na2SO4, MgCl2 and MgSO4), with excellent dye/salt selectivity of ~65. The as-fabricated membrane HPAN-PEICA was proved having good long-term operation stability and pressure resistance properties. Dynamic fouling experiments confirmed that the membrane HPAN-PEICA presented excellent antifouling performance towards four typical model foulants (LYZ, SA, HA and BSA). Over all, we believed that the tailored LNF membrane HPAN-PEICA having great application prospects in textile effluent treatment.

Preparation of antifouling TFC RO membranes by facile grafting zwitterionic polymer PEI-CA

In this work, we synthesized a zwitterionic polymer PEI-CA for the first time and then grafted it onto the surface of polyamide RO membrane via layer-by-layer interfacial polymerization (LbL-IP). XPS and ATR-FTIR techniques were used to verify the successful modification with PEI-CA. The zwitterionic hyperbranched polymer PEI-CA endowed the modified membrane with much improved surface hydrophilicity and decreased surface negative charge. The tailored M-PEICA exhibited a high water permeance up to 3.92 L m−2 h−1 bar−1 (increased by 62 %) while holding a good NaCl rejection (98.93 %). The dynamic fouling experiments proved that grafting of PEI-CA can help to effectively elevate its antifouling performance against most organic foulants except small molecular negatively charged surfactant SDS. Therefore, we further employed the mixed reagents modification strategy with arginine and PEI-CA, the resulting RO membrane M-mixed presented obviously improved antifouling performance towards SDS, the overall antifouling performances are even better than the well-known RO membrane CR100 of DOW FILMTEC™, that well illustrated multiple reagents modification strategy could be an efficient way that can meet all critical standards. Overall, the novel polymer PEI-CA and as-fabricated RO membranes with outstanding antifouling performances in this study have vast application potential in field of water treatment.

Dopamine-triggered one-step codeposition of zwitterionic surfactants for anti-fouling polyethersulfone ultrafiltration membrane modification

We report a facile ultrafiltration (UF) membrane modification strategy to impart anti-fouling properties to a polyethersulfone (PES) membrane via a simple codeposition of polydopamine (PDA) and the zwitterionic surfactant, 3-(N, N-Dimethylmyristylammonio) propane sulfonate (SB3-14). The effect of SB3-14 concentration (from 0.5, 1 to 2 mM) was also studied. The proposed modification notably increased membrane anti-fouling property without compromising membrane transport properties. As demonstrated by dynamic fouling experiments using BSA as a model foulant, the modified membranes presented significantly alleviated flux decline and decreased fouling resistance compared to the pristine membrane. Especially, the membrane modified with low SB3-14 concentration (i.e., 0.5 mM) possessed the optimal antifouling performance compared to those modified with higher concentrations, which may be attributed to reduced efficiency in PDA/SB3-14 aggregates functionalization on membrane surface in the presence of excessive zwitterions. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) results illustrate that Lewis acid-base (AB) played a dominant role during the fouling construction, and the presence of SB3-14 could tremendously decrease AB energy. This codeposition of PDA and non-polymer zwitterionic surfactant could be applied to prepare anti-fouling PES membranes with low reversible and irreversible fouling, which provides a new scope for post modification of UF membranes.

Metal-Coordinated Nanofiltration Membranes Constructed on Metal Ions Blended Support toward Enhanced Dye/Salt Separation and Antifouling Performances.

Metal-phenol coordination is a widely used method to prepare nanofiltration membrane. However, the facile, controllable and scaled fabrication remains a great challenge. Herein, a novel strategy was developed to fabricate a loose nanofiltration membrane via integrating blending and interfacial coordination strategy. Specifically, iron acetylacetonate was firstly blended in Polyether sulfone (PES) substrate via non-solvent induced phase separation (NIPS), and then the loose selective layer was formed on the membrane surface with tannic acid (TA) crosslinking reaction with Fe3+. The surface properties, morphologies, permeability and selectivity of the membranes were carefully investigated. The introduction of TA improved the surface hydrophilicity and negative charge. Moreover, the thickness of top layer increased about from ~30 nm to 119 nm with the increase of TA assembly time. Under the optimum preparation condition, the membrane with assembly 3 h (PES/Fe-TA3h) showed pure water flux of 175.8 L·m−2·h−1, dye rejections of 97.7%, 97.1% and 95.0% for Congo red (CR), Methyl blue (MB) and Eriochrome Black T (EBT), along with a salt penetration rate of 93.8%, 95.1%, 97.4% and 98.1% for Na2SO4, MgSO4, NaCl and MgCl2 at 0.2 MPa, respectively. Both static adhesion tests and dynamic fouling experiments implied that the TA modified membranes showed significantly reduced adsorption and high FRR for the dye solutions separation. The PES/Fe-TA3h membrane exhibited high FRR of 90.3%, 87.5% and 81.6% for CR, EBT and MB in the fouling test, stable CR rejection (>97.2%) and NaCl permeation (>94.6%) in 24 h continuous filtration test. The combination of blending and interfacial coordination assembly method could be expected to be a universal way to fabricate the loose nanofiltration membrane for effective fractionation of dyes and salts in the saline textile wastewater.

Enhanced flux and fouling resistance forward osmosis membrane based on a hydrogel/MOF hybrid selective layer

Although forward osmosis (FO) technology has been widely adopted for water treatment, it still faces great challenges, including low permeability and fouling problem. Herein, a novel forward osmosis membrane was developed with a stable, uniform and defect-free polyvinyl alcohol/polydopamine coated zeolitic imidazolate framework (PVA/PDA@ZIF-8) hybrid selective layer to simultaneously enhance its transport property and fouling resistance. The prepared FO membrane exhibits improved water flux without losing the selectivity, since the PDA@ZIF-8 provide additional preferential passageway for water transporting while hinder the diffusion of salt. The optimized membrane shows a higher water flux than pristine PVA membrane (14.2 vs. 8.7 L m−2 h−1 in FO mode, 24.3 vs. 14.8 L m−2 h−1 in PRO mode) with a reasonable selectivity considering as Js/Jw value (0.44 vs. 0.4 g L−1 in FO mode, 0.38 vs. 0.33 g L−1). Moreover, the dynamic fouling experiments with organic foulants (protein and polysaccharide) indicate that the prepared membrane exhibits strong antifouling property and excellent permeation recovery ability (>95.0%) due to the optimized surface property. This study opens a new avenue for treatment wastewater by developing a forward osmosis membrane based on a hydrogel/MOF hybrid selective layer.

Fabrication of antifouling thin-film composite nanofiltration membrane via surface grafting of polyethyleneimine followed by zwitterionic modification

In this work, antifouling thin-film composite (TFC) nanofiltration (NF) membrane having zwitterionic PEI moieties was fabricated through the layer-by-layer interfacial polymerization (LbL-IP) via grafting hyperbranched polyethyleneimine (PEI) onto the polyamide surface, followed by in-situ N-methylation of PEI and then quaternization using 3-bromopropionic acid to form zwitterionic PEI. The successful surface modifications of TFC NF membrane with PEI and zwitterionic PEI were confirmed by XPS and ATR-FTIR results. Benefitting from the strong hydrophilicity and hyperbranched steric structure, the zwitterionic PEI-grafted TFC membrane (NF-ZPEI) exhibited a stronger hydration capacity and a thicker hydration layer than the PEI-grafted TFC membrane (NF-PEI) and the control sample (NF-PA). Meantime, the water permeability of NF-ZPEI membrane was enhanced by 11.6% higher than the control sample. The NF-ZPEI membrane also exhibited the improved ion selectivity of having a decreased rejection towards NaCl and maintaining a high rejection towards divalent ions. Dynamic fouling experiments were performed to demonstrate the impact of surface hydrophilicity and surface charge on the membrane fouling performances. Results illustrate that the zwitterionic PEI grafted on the TFC NF membrane mitigated the electrostatic attraction between the membrane surface and protein foulants, and exhibited the improved antifouling properties of having a low flux decline and a high flux recovery. Our work provides some insights on the zwitterionic surface modification of the TFC NF membrane with both the enhanced water permeability and the antifouling properties towards charged foulants.

Towards enhanced antifouling and flux performances of thin-film composite forward osmosis membrane via constructing a sandwich-like carbon nanotubes-coated support

In this work, we fabricated a sandwich-like single-walled carbon nanotubes (SWCNTs)-coated support for the preparation of high-performance antifouling thin-film composite (TFC) forward osmosis (FO) membrane. This sandwich-like support was prepared through the deposition of polydopamine modified SWCNTs (PDA-SWCNTs) on both sides of the polyethersulfone (PES) microfiltration (MF) membrane. The CNTs top layer was found to facilitate the formation of polyamide layer. The CNTs back layer provided an antifouling surface for the prevention of foulants adsorption and intrusion into the PES support. Results demonstrate that the CNTs back layer imparted superior rejection towards bovine serum albumin (BSA) (~98.1%) and enhanced hydrophilicity. The TFC FO membrane (TFC-modified) having the sandwich-like SWCNTs-coated support exhibited excellent perm-selectivity with the water flux Jw of 35.7 Lm−2 h−1 and the reverse salt flux Js of 1.42 gm−2 h−1 when tested in the mode of active layer facing to draw solution (AL-DS) using 1 M NaCl as a draw solution. Dynamic fouling experiments confirm that the TFC-modified membrane possessed effective antifouling performances with a low relative fouling degree (RFD) of 19.0% during the cross-flow run and 8.4% during the BSA adsorption test, which were much lower than the corresponding values of 36.1% and 15.4% for the TFC-control membrane.

Fabrication of high performance polyamide reverse osmosis membrane from monomer 4-morpholino-m-phenylenediamine and tailoring with zwitterions

It is well known that the water flux and antifouling performance of polyamide (PA) membrane are strongly associated with their surface characters, especially for surface hydrophilicity, roughness, and charge. In this study, a zwitterionic surface TFC reverse osmosis (RO) membrane was fabricated by small molecule 3-bromopropionic (3-BPA) modification on the pristine membrane that fabricated through interfacial polymerization (IP) technique using a new aqueous monomer 4-morpholinobenzene-1,3-diamine (MpMPD) and trimesoyl chloride (TMC). The as-fabricated RO membranes were well analyzed by various techniques, that the zwitterionic MpMPD-PA membrane surface exhibited greatly enhanced hydrophilicity with water contact angle of 28.1° and surface roughness as low as 26.0 nm. The water permeability of membrane MpMPD-PA reached 1.65 L m−2 h−1 bar−1, which exhibited ~24% increase compared to our lab-made MPD membrane, meanwhile kept a high NaCl rejection of 97.8%. In addition, the dynamic fouling experiments illustrated that the zwitterionic surface RO membrane possess excellent fouling resistance to protein BSA, polysaccharides SA, and surfactant SDS. Therefore, this work provide a simple and convenient way to fabricate novel zwitterionic surface RO membrane with high performance from the molecular level design.

Constructing zwitterionic polymer brush layer to enhance gravity-driven membrane performance by governing biofilm formation

In this study, zwitterionic polymer brushes with controlled architecture were grafted on the surface of gravity-driven membrane (GDM) via surface-initiated reaction to impart antifouling property. A variety of membrane characterization techniques were conducted to demonstrate the successful functionalization of zwitterionic polymers on PVDF hollow fiber membrane. The membrane underwent 90 min of reaction time possessing strong hydrophilicity and high permeability was determined as the optimal modified membrane. Long-term GDM dynamic fouling experiments operated for 30 days using sewage wastewater as feed solution indicated zwitterionic polymer modified membrane exhibit excellent membrane fouling resistance thus enhanced stable flux. Confocal laser scanning microscopy (CLSM) imaging implied that zwitterionic polymer modification significantly inhibit the adsorption of extracellular polymeric substances (EPS) which dominates fouling propensity, resulting in the formation of a thin biofilm with high porosity under synthetic functions of foulants deposition and microbial activities. Interfacial free energy prediction affirmed the presence of zwitterionic functional layer on membrane surface could substantially decrease the interactions (e.g., electrostatic attractions and hydrophobic effects) between membrane and foulants, thereby reduced flux decline and high stable flux. Our study suggests surface hydrophilic functionalization shows promising potential for improving the performance of ultra-low pressure filtration.

In-situ graft-polymerization modification of commercial ultrafiltration membranes for long-term fouling resistance in a pilot-scale membrane bioreactor

Despite significant advances in the design of submerged membrane bioreactors for wastewater treatment, membrane organic- and biofouling remain major obstacles to effective operation, decreasing process performance and membrane lifetime. In this work, we report an improved methodology to minimize fouling in commercial polyvinylidene fluoride (PVDF) ultrafiltration (UF) membranes using redox-initiated copolymer grafting. To effectively bind a copolymer that possesses oppositely charged groups to the surface, we modified the membranes during filtration using positively charged [2-(methacryloyloxy)ethyl]-tri-methylammonium (MOETMA) and negatively charged 3-sulphopropyl methacrylate (SPM) monomers, which provide the polyampholyte coating. The binding of the grafted copolymer was verified using Fourier-transform infrared spectroscopy and contact angle measurements. Bench-scale dynamic fouling experiments were employed to optimize the modification time and verify the effectiveness of the modification in mitigating fouling from soluble microbial products and extracellular polymeric substances extracted from municipal wastewater. After demonstrating fouling resistance at the bench scale, membrane fibers were tested in a custom-made membrane bioreactor treating municipal wastewater. During 22 days of testing, fouling was consistently reduced in the case of modified membranes due to the presence of the polyampholyte copolymer barrier that hinders foulant adsorption. At the end of the testing period, the flux of modified fibers was 123% higher than that of the PVDF control. Overall, this work demonstrates a facile and effective modification technique to reduce fouling in ultrafiltration with proven performance during long-term treatment of municipal wastewater.

Dual-functionalization of polymeric membranes via cyclodextrin-based host-guest assembly for biofouling control

We demonstrated a dual-functionalization strategy of polymeric membrane with both “defensive” (adhesion resistance) and “offensive”(bacterial inactivation) efficacies via combining external-hydrophilic β-cyclodextrins (β-CDs) and bactericidal enrofloxacin (ENR) for combating biofouling. β-CDs were immobilized onto polydopamine (PDA) pre-modified membrane surface, followed by host-guest assembly of ENR. Both static adhesion tests and dynamic fouling experiments implied that the CD-modified membranes showed significantly reduced adsorption and lower water flux decline against organic foulant. The enhanced “defensive” (fouling resistance) capacity of CD-modified membrane was mainly attributed to hydrophilicity improvement. Next, antimicrobial tests demonstrated that the integration of ENR in the functional layer could improve the “offensive” (biocidal) activity of modified membrane. Conspicuous reduction in biomass and ATP content further illustrated that the PVDF/CD-ENR membranes could effectively suppress biofilm formation during dynamic cross-flow biofouling tests. Finally, flow cytometry (FCM) assessment was first combined with heterotrophic plate counts (HPC) method in the present study, implying that the antimicrobial mechanism of the dual-functional membrane lies in inhibition of bacterial breed without disrupting the cell membrane.

Surface modification of polyamide reverses osmosis membrane by phosphonic acid group with improved performance

ABSTRACTA facial method for preparing reverse osmosis polyamide (PA) membranes of excellent antifouling and separation performance was developed via covalently grafting phosphonic acid on membrane surface. First, a pristine PA layer was synthesized by interfacial polymerization between m‐phenylenediamine and trimesoyl chloride. Then, a second interfacial reaction was implemented between ethylenediamine and the residual acryl chloride on the pristine PA layer, generating an active layer enriched by primary amine. Finally, the amine‐rich surface treated by formaldehyde and phosphorous acid to produce a membrane surface modified by phosphonic acid groups. Surface characterization by attenuated total reflectance infrared, X‐ray photoelectron spectroscopy and zeta‐potential measurements illustrated the presence of phosphonic acid group. The lowest contact angle of modified membrane was 26°, demonstrating the membrane possessed an outstandingly wettable surface. The optimal separation performance was 88 L m−2 h−1 of water flux and 99.4% of salt rejection under 1.55 MPa. In addition, bovine serum albumin was used as organic foulant to measure the antifouling property of membranes. The result of dynamic fouling experiments indicated that the modified membrane exhibited better antifouling (of which the irreversible fouling degree was 7.1%) compared with commercial membrane BW30 (of which the irreversible fouling degree was 13.5%). © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 46931.

Zwitterion-like, Charge-Balanced Ultrathin Layers on Polymeric Membranes for Antifouling Property.

Zwitterions of charge-balanced units have super-low fouling properties induced by ionic solvation, but their extensive applications in polymeric substrates are strictly constrained by current constructing strategies. A zwitterion-like, charge-balanced ultrathin layer with high antifouling capacity was covalently constructed on delicate aromatic polyamide (PA) reverse osmosis (RO) membranes via a mild and solvent-free grafting-to strategy. Two oppositely charged commercial short-chain carbonyl alkenes, 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and methacryloxyethyltrimethylammonium chloride (DMC), were directly mixed-grafted with amino groups on PA RO membrane surface via Michael addition. Under ambient temperature and pressure, these oppositely charged compounds were assembled into a zwitterion-like, charge-balanced ultrathin layer. The dynamic fouling experiments indicated that the modified membrane exhibited strong antifouling properties and excellent permeation recovery abilities. Surface characterization revealed that the selective layer thickness and surface roughness were not measurably changed. More meaningful is that the typical ridge-and-valley surface structure and the excellent separation performance were both well preserved after modification. This opens a universal avenue to construct a zwitterion-like, ultrathin antifouling layer on the delicate polymer substrate without compromising its original matrix structure and performance, which has promising application in areas of biosensors, tissue engineering, and biomaterials.

Tris(hydroxymethyl)aminomethane polyamide thin‐film‐composite antifouling reverse osmosis membrane

ABSTRACTFor the applications of reverse osmosis (RO) process, membrane fouling caused by organic molecule adsorption is still a serious problem which significantly decreases membrane lifespan and increases operation costs. In this present article, we report the thin film composite (TFC) RO membrane functionalized with tris(hydroxymethyl)aminomethane (THAM) using one‐step method for improved antifouling property. The results of surface characterization indicated that THAM was successfully grafted onto the active layer of membrane by covalent linkage. Mult‐hydroxyl‐layer was generated and remained steadily on TFC membrane surface after modification. The contact angle decreased from 75.9 ± 3.0° to 46.9 ± 2.3°, which showed a distinct improvement of membrane surface hydrophilicity after modification. The grafted THAM improved water flux by 28.3%, while salt rejection was almost unchanged in membrane property tests. The modified membranes presented preferable antifouling property to foulants of bovine serum albumin, sodium alginate, and dodecyl trimethyl ammonium bromide than that of pristine membranes during dynamic fouling experiments. The method in this study provided an effective way to improve antifouling property of the polyamide thin‐film‐composite RO membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45891.

Surface functionalization of TFC FO membranes with zwitterionic polymers: Improvement of antifouling and salt-responsive cleaning properties

In this work, a salt-responsive thin film composite (TFC) forward osmosis (FO) membrane has been prepared by grafting poly(sulfobetaine methacrylate) (PSBMA) brushes on a commercial FO membrane surface via an ATRP reaction for advanced treatment of oil/water emulsions. By varying polymerization time, the optimum modified membrane (i.e. TFC-PSBMA) was obtained, which exhibited superhydrophilic and ultralow oil-adhesion properties. Dynamic fouling experiments using a feed solution of 10,000ppm oil/water emulsion demonstrated the superior anti-fouling ability of the TFC-PSBMA membrane, as displayed by the lower water flux decline compared to the TFC-control membrane. Furthermore, multi-cycle FO fouling tests showed that the irreversible membrane fouling of the TFC-PSBMA membrane can be significantly alleviated by using salt cleaning in long-term use. The salt-responsive properties of the PSBMA brushes were considered to provide a driving force for the release of oil foulants from the membrane surface.