Developing thin‐film‐composite forward osmosis membranes on the PES/SPSf substrate through interfacial polymerization

A new scheme has been developed to fabricate high‐performance forward osmosis (FO) membranes through the interfacial polymerization reaction on porous polymeric supports. p‐Phenylenediamine and 1,3,5‐trimesoylchloride were adopted as the monomers for the in‐situ polycondensation reaction to form a thin aromatic polyamide selective layer of 150 nm in thickness on the substrate surface, a lab‐made polyethersulfone (PES)/sulfonated polysulfone (SPSf)‐alloyed porous membrane with enhanced hydrophilicity. Under FO tests, the FO membrane achieved a higher water flux of 69.8 LMH when against deionized water and 25.2 LMH when against a model 3.5 wt % NaCl solution under 5.0 M NaCl as the draw solution in the pressure‐retarded osmosis mode. The PES/SPSf thin‐film‐composite (TFC)‐FO membrane has a smaller structural parameter S of 238 μm than those reported data. The morphology and topology of substrates and TFC‐FO membranes have been studied by means of atomic force microscopy and scanning electronic microscopy. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Effect of surface properties of polysulfone support on the performance of thin film composite polyamide reverse osmosis membranes

In this work, influence of initial conditions and surface characteristics of porous support layer on structure and performance of a thin film composite (TFC) polyamide reverse osmosis (RO) membrane was investigated. The phase inversion method was used for casting of polysulfone (PSf) supports and interfacial polymerization was used for coating of polyamide layer over the substrates. The effect of PSf concentrations that varied between 16 wt % and 21 wt %, and kind of the solvent (DMF and NMP) used for preparation of initial casting solution were investigated on the properties of the final RO membranes. SEM imaging, surface porosity, mean pore radius, and pure water flux analysis were applied for characterization of the supports. The substrate of the membrane, which synthesized with 18 wt % of PSf showed the most porosity and the synthesized RO membrane had the lowest salt rejection. In case of the solvents, the membranes synthesized with DMF presented better separation performance that can be attributed to their lower thickness and sponge‐like structure. The best composition of support for TFC RO membranes reached 16 wt % PSf in DMF solvent. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44444.     

压力驱动薄层复合膜中微孔基底的研究进展

压力驱动薄层复合膜（TFC）因其高分离效率和低能耗等优点,在水处理领域得到广泛应用。TFC膜的开发及性能提升可针对聚酰胺（PA）分离层和微孔基底两方面进行优化。其中,微孔基底对其上通过界面聚合（IP）形成的PA层的结构和分离性能具有重要影响。本文对NF/RO TFC膜中微孔基底的研究工作进行了评述。首先对两类微孔基底（相转化微孔基底和静电纺丝微孔基底）进行了概述,进而介绍了传统相转化微孔基底对IP过程的影响机理,并对相转化微孔基底的改性方法（聚合物共混、纳米材料掺杂、表面改性等）进行了总结,最后展望了共价有机框架（COFs）中间层表面改性微孔基底在构建高选择性、高渗透通量压力驱动TFC膜中的发展方向及面临的挑战。     

Preparation of sulfonated polysulfone/polysulfone and aminated polysulfone/polysulfone blend membranes

Sulfonation and amination of polysulfone (PSf) were performed in this study to improve the hydrophilicity of PSf membranes. The sulfonated polysulfone (SPSf) and aminated polysulfone (APSf) membranes with a higher degree of reaction exhibited a higher water flux and worse mechanical strength than that of the original PSf membranes. Therefore, SPSf/PSf and APSf/PSf blended membranes were prepared in this study to improve their individual properties. By altering the formulations of casting solutions and forming conditions of the membranes (e.g., blending ratios of both polymers, additives, evaporation time, and gelation temperature), different SPSf/PSf and APSf/PSf blending membranes were prepared; and their performance in water flux and salt rejection were measured and are discussed. A difference in salt rejection was also observed between both SPSf/PSf and APSf/PSf blending membranes that rejected the various salts. Experimental results indicated that water flux increased and salt rejection decreased with an increase of the SPSf/PSf blending ratio from 1: 9 to 2: 1. The order of salt rejection, in which the SPSf/PSf blended membranes rejected four varieties of salts, was Na₂SO₄ > MgSO₄ > NaCl > MgCl₂. Furthermore, the opposite order was obtained by the APSf/PSf blended membranes. © 1996 John Wiley & Sons, Inc.     

用于反渗透复合膜的海绵状结构支撑膜制备研究

通过调节铸膜液中聚砜浓度和非溶剂含量,浸没沉淀法制备海绵状结构的支撑膜,并在支撑膜上界面聚合制备聚酰胺反渗透复合膜。分别对支撑膜及反渗透复合膜的结构和性能进行表征,考察聚砜浓度对支撑膜结构和性能的影响,以及不同结构支撑膜对反渗透复合膜结构和性能的影响。结果显示,随着聚砜浓度的增加,支撑膜表面孔径和孔隙率下降,断面结构变致密,耐压性增强。在不同支撑膜上制备的反渗透复合膜具有不同的通量和脱盐率。综合考虑支撑膜及反渗透复合膜的性能,以聚砜浓度为15%制备的海绵状结构支撑膜更适于作为制备反渗透复合膜的支撑层。     

Effects of the support‐layer hydrophilicity on the active‐layer formation of composite membranes

To understand the effects of the hydrophilicity of the support layer on the formation of the active layer and the performance of composite membranes, a support layer was prepared from a polysulfone (PSf) blend with a hydrophilic copolymer, and then its top surface was overcoated with an active layer fabricated by an interfacial reaction of m‐phenylenediamine (MPDA) with trimesoyl chloride. The time required for impregnating the support layer with an aqueous solution containing MPDA was gradually decreased by increases in the hydrophilicity of the support layer. The required soaking time was greater than 9 min for the formation of the defect‐free active layer when the support layer prepared from PSf was used, whereas it could be reduced about 1 min by the use of the hydrophilic support layer. Furthermore, composite membranes prepared with the PSf/hydrophilic copolymer blend as the support layer always exhibited higher salt rejection and water permeability than those prepared with PSf as the support layer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Thin-film composite forward osmosis membranes with substrate layer composed of polysulfone blended with PEG or polysulfone grafted PEG methyl ether methacrylate

To advance commercial application of forward osmosis (FO), we investigated the effects of two additives on the performance of polysulfone (PSf) based FO membranes: one is poly(ethylene glycol) (PEG), and another is PSf grafted with PEG methyl ether methacrylate (PSf-g-PEGMA). PSf blended with PEG or PSf-g-PEGMA was used to form a substrate layer, and then polyamide was formed on a support layer by interfacial polymerization. In this study, NaCl (1 mol?L⁻¹) and deionized water were used as the draw solution and the feed solution, respectively. With the increase of PEG content from 0 to 15 wt-%, FO water flux declined by 23.4% to 59.3% compared to a PSf TFC FO membrane. With the increase of PSf-g-PEGMA from 0 to 15 wt-%, the membrane flux showed almost no change at first and then declined by about 52.0% and 50.4%. The PSf with 5 wt-% PSf-g-PEGMA FO membrane showed a higher pure water flux of 8.74 L?m⁻²?h⁻¹ than the commercial HTI membranes (6–8 L?m⁻²?h⁻¹) under the FO mode. Our study suggests that hydrophobic interface is very important for the formation of polyamide, and a small amount of PSf-g-PEGMA can maintain a good condition for the formation of polyamide and reduce internal concentration polarization.     

Engineering design of outer‐selective tribore hollow fiber membranes for forward osmosis and oil‐water separation

Outer‐selective thin‐film composite (TFC) hollow fiber membranes offer advantages like less fiber blockage in the feed stream and high packing density for industrial applications. However, outer‐selective TFC hollow fiber membranes are rarely commercially available due to the lack of effective ways to remove residual reactants from fiber's outer surface during interfacial polymerization and form a defect‐free polyamide film. A new simplified method to fabricate outer‐selective TFC membranes on tribore hollow fiber substrates is reported. Mechanically robust tribore hollow fiber substrates containing three circular‐sector channels were first prepared by spinning a P84/ethylene glycol mixed dope solution with delayed demixing at the fiber lumen. The thin wall tribore hollow fibers have a large pure water permeability up to 300 L m^?2 h^?1 bar^?1. Outer‐selective TFC tribore hollow fiber membranes were then fabricated by interfacial polymerization with the aid of vacuum sucking to ensure the TFC layer well‐attached to the substrate. Under forward osmosis studies, the TFC tribore hollow fiber membrane exhibits a good water flux and a small flux difference between active‐to‐draw (i.e., the active layer facing the draw solution) and active‐to‐feed (i.e., the active layer facing the feed solution) modes due to the small internal concentration polarization. A hyperbranched polyglycerol was further grafted on top of the newly developed TFC tribore hollow fiber membranes for oily wastewater treatment. The membrane displays low fouling propensity and can fully recover its water flux after a simple 20‐min water wash at 0.5 bar from its lumen side, which makes the membrane preferentially suitable for oil‐water separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4491–4501, 2015     

Thermodynamics and kinetics control of support layer synthesis for enhanced thin film composite membrane performance

The desalination performance of a thin film composite (TFC) membrane hinges highly on the surface characteristics of support membrane. In this study, good wettability, regular pore size, and moderate roughness were identified as the critical surface properties of support membrane in forming a defect‐free, uniform, and structurally stable polyamide film. These features were tailored by adjusting the thermodynamics and kinetics properties of the polymer solution via polysulfone (PSf)/polyvinylpyrrolidone (PVP) ratio as well as using N,N‐dimethylacetamide (DMAc) and N,N‐dimethylformamide as co‐solvent. It was found that the membrane formation was controlled kinetically by altering the PSf/PVP ratio but thermodynamically by using co‐solvent. The TFC membrane with better desalination performance was achieved with the support membrane prepared at PSf/PVP ratio of 0.941 without any co‐solvent. The resulting TFC membrane attained the highest permeability ratio of 0.691 bar^?1 for water/NaCl filtration in this study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45802.     

In-situ generated ZnO nanoparticles for enhanced performance of thin film nanocomposite membrane in forward osmosis process

This work developed a novel approach to the in-situ synthesis of ZnO nanoparticles to modify the polysulfone (PSf) porous membrane substrate. The zinc acetate was added to the casting solution, and ZnO nanoparticles were synthesized during phase inversion. The non-solvent pH and zinc acetate concentration controlled the ZnO synthesis and loading. Their effect on the substrates properties in terms of morphology, hydrophilicity and porosity was studied thoroughly. The result shows that the ZnO nanoparticles was not formed in acidic pH, while ZnO nanoparticles with size of 20 nm could be easily formed in basic pH. The successful synthesis of ZnO nanoparticles was investigated using FTIR and EDX analysis. The EDX images verify that in-situ synthesis led to a more uniform dispersion than conventional incorporation method. Then the effect of ZnO loading on the interfacial reaction and polyamide (PA) structure was investigated. SEM images verify the successful synthesis of a uniform and defect-free PA thin film on ZnO modified substrates. FO performance results show an enhancement in water flux and salt rejection as a result of ZnO incorporation in thin film nanocomposite (TFN) membranes, where TFN 1 wt.% in-situ membrane showed 40% higher water flux than the control TFC membrane. The porous and hydrophile substrate in TFN 1 wt.% in-situ membrane is responsible for improved separation performance. These modified membranes displayed uniform dispersion of ZnO nanoparticles within substrates, confirming that this method could effectively restrain the aggregation of the nanoparticles.     

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricart)oiiyl trichloride on polysulfone (PSf) support membranes blended with K^+-responsive poly(N-isopropylacryamideco- acryloylamidobenzo-15-crown-5)(P(NIPAM-co- AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that:(1) Under K^+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections;(2) With K^+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K^+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic;(3) After a curing treatment at 95℃, the improved NF membrane achieved an even higher pure water permeability of 10.97 L·m^-2·h^-1 - bar1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.     

Effective incorporation of TiO2 nanoparticles into polyamide thin‐film composite membranes

The effectiveness of TiO₂ nanoparticles in improving the performance of polyamide (PA) thin‐film composite (TFC) membranes has been investigated. PA TFC membranes were prepared by interfacial polymerization with m‐phenylenediamine (MPD) and 1,3,5‐benzene tricarbonyl trichloride (TMC) where TiO₂ particles were added during and after interfacial polymerization. To distribute the TiO₂ nanoparticles uniformly in the PA films, colloidally stable TiO₂ sols were synthesized and added to the aqueous MPD solution rather than to an organic TMC solution. Through the use of different incorporation methods, TiO₂ particles were located on the top surface, in PA film layer, and in both positions. In the case of dense PA layers, the hydrophilicity of the membranes was significantly improved due to the presence of TiO₂ particles, resulting in an increased water flux. On the other hand, the enhancement of water flux was less significant when TiO₂ particles were incorporated into a loose PA film that was prepared with additives. In addition, a BSA fouling test confirmed that TiO₂ nanoparticles effectively improve the antifouling properties of the membranes for both dense and loose PA films. This effect is possibly due to increased hydrophilicity, covering of the fouling space, and a reduction in surface roughness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43383.     

Interfacially polymerized thin film nanofiltration membranes on TiO2 coated polysulfone substrate

In this study, a new approach was developed to prepare the novel thin film composite nanofiltration membranes. In this new approach, nanoparticles were coated completely under the polymeric thin film layer. Thin film composite (TFC) membranes were fabricated by interfacial polymerization on polysulfone (PSf) sublayer using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) respectively as amine monomer and acid chloride monomer. Scanning electron microscopy and atomic force microscopy were used to study surface morphology and roughness properties of NF membranes. Energy dispersive X-ray microanalysis (EDX) was used to analyze the elemental change before and after filtration experiment. Chemical structure and thickness of polyamide formed on TFC membranes were observed by Fourier transmission infrared attenuated total reflectance (FTIR-ATR) spectroscopy. Permeability, salt rejection and pepsin macromolecule rejection of prepared membranes were tested using dead end filtration cell. Antifouling behavior of the membranes was studied by filtering pure water before and after pepsin solution filtration. A smoother and thicker surface without any defect appeared as the concentration of nanoparticle was increased. NaCl rejection was increased from 70% for neat nanofiltration membrane to 84% for 0.5 wt% TiO₂ modified nanofiltration membrane. Antifouling and permeability behavior of the prepared membranes were improved in the new approach. Antibacterial property of prepared membranes was improved as a result of photocatalytic characteristic of TiO₂ nanoparticles.     

A study on the characteristics and pervaporation performance of polyamide thin‐film composite membranes with modified polyacrylonitrile as substrate for bioethanol dehydration

To improve the pervaporation performance in separating an aqueous ethanol solution, polyamide thin‐film composite (TFC) membranes (m‐tolidine‐H‐TMC/mPAN) were prepared through the interfacial polymerization reaction between trimesoyl chloride (TMC) and 2,2'‐dimethylbenzidine hydrochloride (m‐tolidine‐H) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the feed ethanol concentration on the pervaporation performance and the durability of m‐tolidine‐H‐TMC/mPAN TFC membranes were investigated. To choose the optimal mPAN membrane as the TFC substrate, the effect of hydrolysis time on the chemical properties and separation performance of an mPAN substrate was also studied. An appropriate hydrolysis time of 15 min was chosen to obtain the mPAN substrate due to the corresponding high permeation flux. The m‐tolidine‐H‐TMC/mPAN TFC membrane exhibited a high pervaporation performance for ethanol dehydration. A positron annihilation lifetime spectroscopy experiment was used to estimate the mean free‐volume radius of the m‐tolidine‐H‐TMC polyamide selective layer, which lay between the radii of the water and ethanol molecules. © 2013 Society of Chemical Industry     

Alkyl amine functional dextran macromonomer‐based thin film composite loose nanofiltration membranes for separation of charged and neutral solutes

Thin film composite (TFC) nanofiltration membranes with defined porous structure of the separation layer are desirable for the concentration of neutral solute and separation of salts from a mixture. Herein, we report the formation of TFC membranes composed of polyamide (PA) separation layer by the interfacial polymerization between new dextran‐butyl amine (Dex‐NH₂) macromonomer and trimesoyl chloride on polysulfone support membrane. The membranes prepared with 1%–1.5% (wt/vol) of Dex‐NH₂ exhibited water permeance of 110–116 L m^?2 h^?1 MPa^?1 with 62%–71% rejection of Na₂SO₄ and 12%–14% rejection of MgCl₂. The membranes also showed about 91% rejection of poly(ethylene glycol) of molecular weight 2000 g/mol and about 11% rejection of NaCl. A decrease in permeance and ions selectivity was observed with increasing concentration of Dex‐NH₂. The dextran chains attached to the PA network restrict the diffusion of Dex‐NH₂ toward the interfacial zone and thereby assist the formation of porous and thin PA layer compared to that when free amine (alkyl diamine) was used. These membranes are applicable for the separation of small molecular weight neutral solutes from mixture containing monovalent salts. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45301.     

Preparation and characterization of low-pressure nanofiltration membranes and the application in the separation process of dye molecules

Low-pressure nanofiltratioin (NF) membranes were prepared with hydroxyl groups ended hyperbranched polyester (HPE) using polysulfone (PSf) ultrafiltration membrane as the porous support. The prepared membranes are characterized using Fourier transforms infrared spectrometry, scanning electro microscopy, atom force microscopy, X-ray photoelectron spectroscopy and water contact angle. The results indicated that the crosslinked HPE formed a uniform, ultra-thin and active layer on PSf support. Water permeability and salt rejection of the membranes were measured at the trans-membrane pressures as low as 0.3?MPa. NF membranes exhibited high enhancement in water permeability while maintaining high rejection of salts. The rejections of the nanofiltration membrane to Rhodamine B and Xylenol orange were 100 and 98.4%, respectively. The study indicated that these NF membranes could be applied to separate small organic molecules.     

Novel thin-film composite nanofiltration membranes fabricated via the incorporation of ssDNA for highly efficient desalination

In this work, the biomacromolecule, single-stranded deoxyribonucleic acid (ssDNA) was innovatively incorporated into the polyamide layer to tailor the permeate flux and antifouling performance of the nanofiltration (NF) membranes. With active amines groups, the ssDNA was as the aqueous phase monomers along with piperazine (PIP), and reacted with trimesoyl chloride on polyethersulfone substrate to fabricate thin-film composite (TFC) NF membranes. The NF membrane prepared under optimal ratio of ssDNA/PIP had a pure water permeability of 75.8 L m⁻² h⁻¹ (improved 58% compared to PIP NF membrane) and Na₂SO₄ rejection of 98.0% at 6.0 bar. The rejections for different inorganic salts were the order: Na₂SO₄ (98.0%) > MgSO₄ (89.2%) > MgCl₂ (72.8%) > NaCl (23.0%). Furthermore, the TFC NF membranes showed good antifouling performance in long-term running with 300 ppm bovine serum albumin and humic acid solution. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 47102.     

Study of synthesis parameters and active layer morphology of interfacially polymerized polyamide–polysulfone membranes

Thin film composite (TFC) polyamide membranes were prepared on a polysulfone support membrane and the effect of various synthesis conditions on the active layer morphology, the physicochemical properties and the membrane performance was investigated. The support membrane porosity factor had a significant effect on the TFC membrane performance. A polyamide top layer was formed within 15 s of reaction. Prolonging the reaction time, although resulting in a thicker active layer, only had a minor influence on the membrane performance. This highlights the importance of the incipient layer of the polyamide structure on its performance. The addition of both a surfactant and a base to the amine solution resulted in a change of the active layer morphology and an improved performance. The effect of additives was attributed to changes in the polymerization mechanism. In addition, it was demonstrated that curing at 50 °C resulted in an improved membrane performance, due to more cross-linking of the active layer. Curing at higher temperatures deteriorated the structure of the support membrane. This research shows that the TFC membrane performance is well correlated with the changes in the active layer morphology, measured using SEM, AFM and TEM; whereas only minor changes in the physicochemical characteristics of the membranes were detected by zeta potential and ATR-FTIR spectroscopy when the same synthesis parameters were varied.     

Photo‐induced grafting of poly(ethylene glycol) onto polyamide thin film composite membranes

In this study, the surface grafting of poly(ethylene glycol) (PEG) onto commercial polyamide thin film composite (TFC‐PA) membranes was carried out, using ultraviolet photo‐induced graft polymerization method. The attenuated total reflection Fourier transform infrared spectra verify a successful grafting of PEG onto the TFC‐PA membrane surface. The scanning electron microscope and atomic force microscope analyses demonstrate the changes of the membrane surface morphology due to the formation of the PEG‐grafted layer on the top. The contact angle measurements illustrate the increased hydrophilicity of the TFC‐PA‐g‐PEG membrane surfaces, with a significantly reduced water contact angles compared to the unmodified one. Consequently, the separation performance of the PEG‐grafted membranes is highly improved, with a significant enhancement of flux at a great retention for removal of the different objects in aqueous feed solutions. In addition, the antifouling property of the modified membranes is also clearly improved, with the higher maintained flux ratios and the lower irreversible fouling factors compared to the unmodified membrane. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45454.     

Improvement of performance of polyamide reverse osmosis membranes using dielectric barrier discharge plasma treatment as a novel surface modification method

In this research, surface modification of aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes was carried out using dielectric barrier discharge (DBD) plasma treatment to improve the performance and fouling resistance of prepared RO membranes. First, polyamide TFC RO membranes were synthesized via interfacial polymerization of m‐phenylenediamine and trimesoyl chloride monomers over microporous polysulfone support membrane. Next, the DBD plasma treatment with 15 s, 30 s, 60 s, and 90 s duration was used for surface modification. The surface properties of RO membranes were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR), SEM, AFM, and contact angle measurements. The ATR‐FTIR results indicated that DBD plasma treatment caused hydrogen bonding on the surface of RO membranes. Also, the contact angle measurement showed that the hydrophilicity of the membranes was increased due to DBD plasma treatment. The changes in the membranes surface morphology indicated that the surface roughness of the membranes was increased after surface modification. In addition, it was found that the DBD plasma treatment increased the water permeation flux significantly and enhanced sodium chloride (NaCl) salt rejection slightly. Moreover, the filtration of bovine serum albumin revealed that the antifouling properties of the modified membranes had been improved. POLYM. ENG. SCI., 59:E468–E475, 2019. © 2018 Society of Plastics Engineers