Surface modification of polyamide TFC membranes via redox‐initiated graft polymerization of acrylic acid

In this work, the redox‐initiated graft polymerization of acrylic acid (AA) onto the surface of polyamide thin film composite membranes has been carried out to enhance membrane separation and antifouling properties. The membrane surface characteristics were determined through the attenuated total reflection Fourier transform infrared spectra, scanning electron microscopy, atomic force microscopy, and water contact angles. The membrane separation performance was evaluated through membrane flux and rejection of some organic compounds such as reactive red dye (RR261), humic acid, and bovine serum albumin in aqueous feed solutions. The experimental results indicated that the membrane surfaces became more hydrophilic and smoother after grafting of AA. The modified membranes have a better separation performance with a significant enhancement of flux at a great retention. The fouling resistance of the modified membranes is also clearly improved with the higher maintained flux ratio and the lower irreversible fouling factor compared to the unmodified one. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45110.     

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.     

An improved method for surface modification of porous water purification membranes

The surfaces of polysulfone and polyethersulfone ultrafiltration membranes were coated with polydopamine, yielding hydrophilic membranes that, under constant transmembrane pressure fouling conditions, have previously shown enhanced flux relative to unmodified membranes. When evaluated under constant permeate flux fouling, however, modified membranes exhibited higher transmembrane pressures than their unmodified analogs. This increased transmembrane pressure in the coated membranes was ascribed to the decrease in membrane permeance resulting from applying the polydopamine coating. The membrane permeance could be tuned by varying polydopamine deposition time and, even at the shortest deposition times studied here, a few minutes, a substantial increase in membrane hydrophilicity could be achieved. Therefore, polydopamine was deposited on a membrane of relatively high permeance until the pure water permeance of the modified membrane matched that of a membrane having lower native permeance, permitting a comparison of the fouling performance of a modified and unmodified membrane with the same pure water permeance. This approach was repeated, using a single, high permeance membrane as the base membrane for modification, to produce a family of modified membranes having the same initial pure water permeances as lower permeance, unmodified membranes. When unmodified and modified membranes of the same initial permeance were compared at constant flux fouling conditions, the modified membranes consistently exhibited lower transmembrane pressures and similar organic rejections to the unmodified membranes. Because many porous water purification membranes are operated at constant flux in industrial settings, an interesting methodology for membrane surface modification may be to surface-modify a membrane of high permeance until the desired permeance is achieved, rather than by surface modification of a membrane that natively has the desired water transport characteristics, since the surface modification procedures almost invariably lead to lower pure water permeance.     

Surface modification of polyacrylonitrile based ultrafiltration membrane

Ultrafiltration membrane based on polyacrylonitrile prepared by phase inversion method using zinc chloride as an additive showed more than 90% rejection for BSA and 90–110 lm^?2 h^?1 water flux. The surface modification of this membrane was studied using ethanolamine, triethylamine, sodium hydroxide, and potassium hydroxide solutions. The effect of base treatment time and temperature on water flux and rejection was investigated. The membranes exhibited swelling by NaOH treatment followed by deswelling by HCl post‐treatment, similar to pH responsive membranes. The treatment by organic as well as inorganic bases improved water flux with a slight lowering in BSA rejection by dead‐end mode type treatment. A 230% increase in water flux was achieved by sodium hydroxide treatment in crossflow mode without a noticeable pore swelling by SEM. The contact angle of the modified membranes was decreased as compared to the unmodified one indicating appreciable surface modification. As the treatment time or temperature increased, the ESCA analysis showed increased population of Na‐carboxylate groups. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4378–4385, 2006     

Effect of surface‐modifying macromolecules and membrane morphology on fouling of polyethersulfone ultrafiltration membranes

Polyethersulfone (PES) ultrafiltration (UF) membranes with and without surface‐modifying macromolecules (SMMs) were prepared and characterized in terms of the mean pore size and pore‐size distribution, surface porosity, and pore density. The results demonstrated that both the mean pore size and the molecular weight cutoff (MWCO) of the SMM‐modified membranes are lower than those of the corresponding unmodified ones. Membrane fouling tests with humic acid as the foulant indicated that the permeate flux reduction of the SMM‐modified membranes was much less than that of the unmodified ones. Therefore, fouling was more severe for the unmodified membranes. Moreover, the dry weight of the humic acid deposited on the membrane surface was considerably higher for the unmodified membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3132–3138, 2003     

Membrane fouling and chemical cleaning in water recycling applications

Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18 h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10 mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca²⁺ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface.     

Antifouling poly(vinylidene fluoride) hollow fiber membrane with hydrophilic surfaces by ultrasonic wave‐assisted graft polymerization

Acrylic acid (AA)‐grafted poly(vinylidene fluoride) (PVDF) hollow fiber membrane was obtained by ultrasonic wave‐assisted graft polymerization. The grafting density (GD) of AA on the PVDF membrane surface could be controlled by altering the reaction conditions, such as ultrasonic time, ultrasonic power, monomer concentration and initiator concentration. The attenuated total reflectant Fourier transform infrared spectra (FITR‐ATR) and X‐ray photoelectron spectroscopy were used to investigate the chemical composition of modified membranes. The changes of surface morphology and roughness were characterized by field emission scanning electron microscope and atomic force microscopy. Results show that AA was successfully grafted on the membrane surface. With increasing GD, the static water contact angle was decreased from 95.7 to 41.4°, indicating that hydrophilicity of modified membrane was significantly enhanced. Pure water flux before and after bovine serum albumin (BSA) contamination was measured. The modified membrane with the GD of 0.76 mg/cm² has the highest water flux as high as 350 L/m²·h. When compared with the pristine membrane(M0), the flux recovered ratio was improved from 52.75 to 96.29% at the GD 2.76 mg/cm² (M3), which suggested the protein fouling could be effectively prevented for the modified membrane. POLYM. ENG. SCI., 2018. © 2018 Society of Plastics Engineers POLYM. ENG. SCI., 59:E446–E454, 2019. © 2018 Society of Plastics Engineers     

Surface modification of poly(ether sulfone) ultrafiltration membranes by low‐temperature plasma‐induced graft polymerization

Low‐temperature helium plasma treatment followed by grafting of N‐vinyl‐2‐pyrrolidone (NVP) onto poly(ether sulfone) (PES) ultrafiltration (UF) membranes was used to modify commercial PES membranes. Helium plasma treatment alone and post‐NVP grafting substantially increased the surface hydrophilicity compared with the unmodified virgin PES membranes. The degree of modification was adjusted by plasma treatment time and polymerization conditions (temperature, NVP concentration, and graft density). The NVP‐grafted PES surfaces were characterized by Fourier transform infrared attenuated total reflection spectroscopy and electron spectroscopy for chemical analysis. Plasma treatment roughened the membrane as measured by atomic‐force microscopy. Also, using a filtration protocol to simulate protein fouling and cleaning potential, the surface modified membranes were notably less susceptible to BSA fouling than the virgin PES membrane or a commercial low‐protein binding PES membrane. In addition, the modified membranes were easier to clean and required little caustic to recover permeation flux. The absolute and relative permeation flux values were quite similar for the plasma‐treated and NVP‐grafted membranes and notably higher than the virgin membrane. The main difference being the expected long‐term instability of the plasma treated as compared with the NVP‐grafted membranes. These results provide a foundation for using low‐temperature plasma‐induced grafting on PES with a variety of other molecules, including other hydrophilic monomers besides NVP, charged or hydrophobic molecules, binding domains, and biologically active molecules such as enzymes and ribozymes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1699–1711, 1999     

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

For 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 modification of polyamide nanofiltration membrane by grafting zwitterionic polymers to improve the antifouling property

A simple two‐step surface modification method of polyamide nanofiltration membrane, involving the activation of amide groups by formaldehyde and the subsequent cerium [Ce (IV)]‐induced graft polymerization of zwitterionic 3‐(methacryloylamino) propyl‐dimethyl‐(3‐sulfopropyl) ammonium hydroxide) (MPDSAH) monomers, was employed to improve membrane antifouling property. The membranes before and after modification were characterized by attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR), scanning electron microscopy, and atomic force microscopy. The changes in both surface chemical composition and morphology of membranes confirmed the successful graft polymerizations of MPDSAH onto polyamide nanofiltration membrane. The static water contact angle measurements showed that surface hydrophilicity of the modified membranes was significantly enhanced. As the MPDSAH concentration increased, the water flux of grafted membrane decreased gradually, while salt rejection increased slightly. The fouling experiments with bovine serum albumin solution demonstrated that modified membranes exhibited better resistance to protein fouling. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41144.     

Development of antifouling polyamide thin‐film composite membranes modified with amino‐cyclodextrins and diethylamino‐cyclodextrins for water treatment

The fouling behavior of polyamide thin‐film composite (TFC) membranes modified with amino‐ and diethylamino‐cyclodextrins (CDs) through an in situ interfacial polymerization process is reported. Modified polyamide TFC membranes exhibited improved hydrophilicity, water permeability, and fouling resistance as compared to the unmodified TFC membranes, while restricting the passage of NaCl salt (98.46 ± 0.5%). The increase in hydrophilicity was attributed to the secondary and tertiary hydroxyl groups of the CDs, which were not aminated. The membranes modified with amino‐CDs had increased surface roughness while the membranes modified with diethylamino‐CDs had smoother surfaces. However, despite the surface roughness of the membranes modified with amino‐CDs, low fouling was observed due to the highly hydrophilic surfaces, which superseded the roughness. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40109.     

Polypropylene membranes with the double sensitivity effect

This article describes the modification of polypropylene membranes leading to the preparation of thermo‐ and pH‐sensitive structures. Poly(N‐isopropylacrylamide), poly(acrylic acid), or copolymer poly(N‐isopropylacrylamide‐co‐acrylic acid) was grafted on to the membranes' surface activated by dielectric barrier discharge plasma. The properties of the modified membranes were evaluated by means of infrared spectroscopy and contact angle measurements. The effect of modification was monitored by the determination of water flux at two temperatures (20 and 45°C) and at various pH values (2.8–8.0). The membrane separation properties were investigated for the solutions of o‐bromocresol purple. It was found that membranes grafted with copolymer were responsive to both stimuli and they could be used for separation purpose. The separation performance was tailored by alteration of pH and temperature of feed solution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41763.     

Preparation of chlorinated poly(vinyl chloride)‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membranes and their water permeation properties

Chlorinated poly(vinyl chloride) (CPVC) membranes for microfiltration processes were prepared with the combined process of a solvent evaporation technique and the water‐vapor induced‐phase‐inversion method. CPVC membranes with a mean pore size of 0.7 μm were very hydrophobic. These membranes were subjected to surface modification by ultraviolet (UV)‐assisted graft polymerization with N‐vinyl‐2‐pyrrolidinone (NVP) to increase their surface wettability and decrease their adsorptive fouling. The grafting yields of the modified membranes were controlled by alteration of UV irradiation time and NVP monomer concentration. The changes in chemical structure between the CPVC membrane and the CPVC‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membrane and the variation of the topologies of the modified PVC membranes were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, and field emission scanning electron microscopy. According to the results, the graft yield of the modified CPVC membrane reached a maximum at 5 min of UV exposure time and 20 vol % NVP concentration. The filtration behavior of these membranes was investigated with deionized water by a crossflow filtration measurement. The surface hydrophilicity and roughness were easily changed by the grafting of NVP on the surface of the CPVC membrane through a simultaneous irradiation grafting method by UV irradiation. To confirm the effect of grafting for filtration, we compared the unmodified and modified CPVC membranes with respect to their deionized water permeation by using crossflow filtration methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3188–3195, 2003     

Depositing lignin on membrane surfaces for simultaneously upgraded reverse osmosis performances: An upscalable route

Reverse osmosis (RO) have been widely used to produce clean water and there is a strong need to enhance their permeability at no sacrifice of their other performances, e.g., selectivity. We deposit low‐cost biopolymer, lignin, onto the surface of RO membranes by a simple filtration method. Lignin is deposited to the membrane surface via both hydrogen bonding and π‐π interaction. Lignin deposition reduces the surface roughness of the membrane and enhances its negatively charging, while the surface hydrophilicity is maintained. Surprisingly, water permeation, salt rejection, and fouling resistance of the lignin‐deposited membranes are simultaneously improved. More importantly, we demonstrate that this deposition method can be easily extended to modify commercial RO membrane modules, indicating the excellent upscalability of this method. We use the lignin‐deposited membranes to treat real effluents of dyeing and papermaking and they perform much better than the virgin, unmodified membranes. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2221–2231, 2017     

Membrane functionalization using bisamide-based organic frameworks for molecular weight cutoff reduction

Functional polymers or copolymers have been added to separations membranes by incorporating them in the membrane dope prior to casting, by in situ polymerization, and by postsynthesis surface modification of existing membranes. Here, a postsynthesis membrane functionalization that targeted decreasing the molecular weight cutoff (MWCO) and increasing the hydrophilicity without significantly decreasing the operating flux was studied. Hybrid bisamide molecules with added amine and carboxylic acid functionalities as end groups were synthesized to form a selective layer on membrane surface via covalent attachment to the membrane. Fourier transform infrared spectroscopy analysis showed the functional groups corresponding to bisamide molecules were present on modified membranes. Furthermore, modified membranes displayed MWCO of 400 Da as compared to 1000 Da MWCO of unmodified membranes, along with an increase in the hydrophilicity of modified membranes. Modified membranes showed an improvement in divalent salt rejection and percent flux recovered after reverse-flow filtration as compared to unmodified membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48327.     

Synergistic effect of silica nanoparticles in the matrix of a poly(ethylene glycol) diacrylate coating layer for the surface modification of polyamide nanofiltration membranes

In this study, a commercial polyamide nanofiltration membrane was modified by a combination of poly(ethylene glycol) diacrylate (PEGDA) in situ polymerization and silica (SiO₂) nanoparticles. The PEGDA layer was polymerized on the surface of the membranes alone or mixed with SiO₂ nanoparticle. The surface modification influence on the water flux, salt rejection, and antifouling behavior was investigated. The effects of the nanoparticles and PEGDAylation on the membrane properties were characterized by Fourier transform infrared spectroscopy, contact angle measurement, and scanning electron microscopy analyses. The membranes that were in contact with 30 wt % PEGDA and then treated with ultraviolet light for 5 min had a better water flux than the unmodified membrane. The fouling resistance of the membranes to a foulant solution containing bovine serum albumin, humic acid, and sodium sulfate were studied, and the results show that the membrane with 30 wt % PEGDA had better antifouling properties. After the weight percentage of PEGDA for the prepolymerization solution was optimized (30 wt % was the best), the SiO₂ nanoparticle concentration in the prepolymerization matrix was optimized. The presence of SiO₂ nanoparticles in the PEGDA layer increased the membrane flux. The maximum water flux and good antifouling properties were obtained for 0.5 wt % SiO₂ nanoparticles in a 30 wt % PEGDA layer. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43793.     

Influences of extractant on the hydrophilicity and performances of HDPE/PE‐b‐PEG blend membranes prepared via thermally induced phase separation (TIPS) process

Blending the block copolymer into the membrane matrix is a convenient and efficient way for membrane modification. In this study, HDPE/PE‐b‐PEG membranes were prepared via TIPS process, and the extractant effect was investigated. An interesting finding was that a non‐polar extractant (n‐hexane) was more conducive to the surface enrichment of PEG chains than a polar solvent (ethanol). The reason was deemed to be the combined effect of entropy drive, interfacial energy, and the swelling behavior. Besides, membrane performances related to the surface chemical properties were studied. Results suggested that the prepared blend membranes extracted by n‐hexane showed enhanced hydrophilicity, anti‐fouling property and water flux. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2680–2687, 2013     

Biofouling alleviation and flux enhancement of electrospun PAN microfiltration membranes by embedding of para‐aminobenzoate alumoxane nanoparticles

Membrane bioreactor (MBR) as a hybrid technology for wastewater treatment is becoming more popular for wastewater treatment. However, membrane fouling has hindered the widespread application of MBRs. Many efforts have been done for fouling mitigation. In this study, high flux and antifouling microfiltration membranes with unique surface structure, high surface porosity, and permeability were prepared by electrospinning technique. Initially, the optimum thickness of electrospun polyacrylonitrile (PAN) membranes was determined and then, electrospun PAN membrane at optimum thickness were prepared by embedding para‐aminobenzoate alumoxane (PABA) nanoparticles at different concentrations. The effect of PABA nanoparticles on membrane performance was investigated. To investigate the characterization of the prepared membranes Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive X‐ray spectroscopy, and water contact angle measurement were employed. The flux recovery ratio results revealed that the antifouling properties of the electrospun PAN membrane were enhanced by modification. The 3 wt % electrospun PABA embedded PAN had the best permeability, hydrophilicity, and antifouling properties among the fabricated membranes and showed remarkable reusability during filtration. The results obtained suggested that the high flux and antifouling electrospun PAN membranes embedded PABA nanoparticles could be used as MBR membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45738.     

Fouling control in a submerged membrane‐bioreactor by the membrane surface modification

To improve the antifouling characteristics, polypropylene microporous membranes (PPHFMMs) were surface‐modified by the sequential photoinduced graft polymerization of acrylic acid and acrylamide. The grafting density and the grafting chain length, which played important roles in the antifouling characteristics, were controlled in the first and the second step, respectively. The ATR/FTIR results clearly indicated the successful modification on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of the grafting chain length. The contact angle of the acrylic acid modified membranes was lower than that of the acrylamide modified membrane with similar grafting chain length. The grafting chain length increased with the increase of UV irradiation time and monomer concentration. The grafting chain length of poly(acrylic acid) (PAAc) was lower than that of the polyacrylamide (PAAm) under the same polymerization conditions. Pure water flux for the modified membranes increased with the increase of grafting chain length, and had maximums. The antifouling characteristics of the modified membranes in a submerged membrane‐bioreactor (SMBR) were evaluated. The modified membranes showed better filtration performances in the SMBR than the unmodified membrane, and the acrylic acid grafted membrane presented better antifouling characteristics than acrylamide modified membranes. The results demonstrated that the surface carboxyl‐containing membranes were better than the surface amido‐containing membranes. The results of Pearson correlations demonstrated that the PAAc modified membranes with longer grafting chain length had higher flux recoveries, while the PAAm modified membranes with longer grafting chain length had lower flux recoveries. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of organic acids on the performance of cellulose triacetate forward osmosis membrane

Forward osmosis (FO) membrane performance was improved using different organic acids (formic acid, acetic acid, lactic acid) for the addition of the casting solution. Scanning electron microscope (SEM) images of all the FO CTA membranes exhibited essentially the membranes have a structure of looking like two dense skin layers and a sponge‐like supporting layer. Additionally, based on the surface roughness values analysis of Atomic Force Microscope (AFM), the membranes with lactic acid, with similar roughness to the membranes without any acid, have bigger roughness than the membranes with formic acid or acetic acid. Furthermore, the water flux of membranes with acids has been improved and the reverse salt flux decreased. The membranes with lactic acid, with an outstanding penetration performance, were utilized to test the performance when 1 mol/L sodium chloride (NaCl), magnesium chloride (MgCl₂)_, magnesium sulfate (MgSO₄), and sodium sulfate (Na₂SO₄) were, respectively, as the draw solutions. The results revealed that the membranes have a higher rejection ratio for MgSO₄. Besides, in the process of separating oil–water mixture, the membranes with the organic acids have a better separation efficiency than the membrane without any acid during FO process and the water flux recovery rate could achieve above 90% insuring the membrane anti‐fouling. POLYM. ENG. SCI., 59:E138–E145, 2019. © 2018 Society of Plastics Engineers