Characteristics of thin-film nanofiltration membranes at various pH-values

Salt rejection and ion selectivity of NF-255 and NF-45 nanofiltration (NF) membranes were investigated. The rejection of two cations (Na⁺, Ca²⁺) and two anions (Cl⁻, SO_4²⁻) which are common in natural and in industrial wastewater, were studied as a function of pH at permanent pressure and temperature. The ion rejection of NF membranes were investigated in single salt solutions like NaCl, CaCl₂, Na₂SO₄, CaSO₄, and in multicomponent systems that contained all the previous ions. We found that, there is a minimum rejection of the Na⁺ and Cl⁻ ions between pH 4-5 in NF-255 and between pH 7-8 in NF-45. The rejection of calcium ions were increased in each case at lower pH in both membranes. However the pH value where the ion rejection behaviour of membranes changed, were different: pH 4 in NF-255 and pH 8 in NF-45. In NF-45 the chloride ion has negative rejection which depends on the quality of ions and the pH. We found that below pH values of 4 the selectivity of mono- and multivalent cations considerable increased in NF-255. This phenomena may be used for separation of calcium ions from sodium ions from weakly acidic (hydrochloric and sulfuric acid) solution, e.g. regeneration solution of sodium form softening ion exchangers.     

Evaluation of a modified spray-applied interfacial polymerization method for preparation of nanofiltration membranes

Nanofiltration (NF) membranes were fabricated by using piperazine (PIP) and trimesoyl chloride (TMC) by conventional and spray-applied interfacial polymerization methods, studying the effect of the application method for both phases, the number of applied layers, and the displacement speed for the spray application. A polysulfone ultrafiltration membrane was used as support. NF membranes were characterized by different spectroscopic, microscopic, and physicochemical techniques. Rejection capacity was evaluated for sodium chloride (NaCl), sodium sulfate (Na₂SO₄), and magnesium sulfate (MgSO₄) salts; the decreasing rejection order was Na₂SO₄ > MgSO₄ > NaCl for each NF membrane. NF membrane prepared with one layer of the sprayed out TMC solution and conventional application of PIP solution exhibited the highest salt rejection (99% for 1000 ppm Na₂SO₄) and a permeated flux of 10.28 L m⁻² h⁻¹ at 0.55 MPa. The modified method is a facile-reproducible preparation methodology that reduces the consumption of time, effort, and reagents leading to a scalable manufacturing process for separation technology. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48129.     

Preparation of microporous polyamide networks for carbon dioxide capture and nanofiltration

For the first time, microporous polyamide networks have been synthesized via the interfacial polymerization of piperazine and acyl chloride monomers containing tetrahedral carbon and silicon cores. These polyamides, with Brunauer–Emmett–Teller surface area between 488 and 584 m² g^?1, show a CO₂ uptake of up to 9.81 wt% and a CO₂/N₂ selectivity of up to 51 at 1 bar and 273 K, suggesting their great potential in the area of carbon capture and storage applications. We have developed the interfacial polymerization on the surface of the porous polyacrylonitrile substrate, resulting in the formation of ultrathin microporous membranes with thicknesses of about 100 nm. These nanofiltration (NF) membranes exhibited an attractive water flux of 82.8 L m^?2 h^?1 at 0.4 MPa and a high CaCl₂ (500 mg/L) rejection of 93.3%. These NF membranes follow the salt rejection sequence of CaCl₂ > NaCl > Na₂SO₄, demonstrating the positively charged character of these membranes.     

Separation performance of a nanofiltration membrane influenced by species and concentration of ions

Nanofiltration (NF), which has been largely developed over the past decade, is a promising technology for the treatment of organic and inorganic pollutants in surface and ground waters. The ESNA 1 membrane from the Nitto Denko Corporation of Japan is made of aromatic polyamide, which provides salt rejection from 50% to 90%. In this paper permeation experiments of aqueous solutions of five chlorides (NH₄Cl, NaCl, KCl, MgCl₂ and CaCl₂), three nitrates (NaNO₃, Mg(NO₃)₂ and Ca(NO₃)₂), and three sulfates (NH₄)₂SO₄, Na₂SO₄ and MgSO₄) were carried out. The effects of species and concentration of salts on the separation performance of the ESNA 1 membrane were investigated. The experimental results showed that the rejection to most salts by the ESNA 1 membrane decreased with the growth of the concentration. Then, the reflection coefficient and solute permeability of ESNA 1 membrane were calculated by the Spiegler-Kedem equation from experimental data. The reflection coefficients of the ESNA 1 membrane to salts are all above 0.95. The salt permeabilities, except for magnesium and calcium salts, increased with the growth of concentration. The sequence of rejection to anions by the ESNA 1 membrane is R(SO²⁻₄) > R(Cl⁻) > R(NO⁻₃) at the same concentration which ranges from 10 mol/m³ to 100 mol/m³. The sequence of rejection to anions by the ESNA 1 membrane can be written as follows: R(Na⁺) > R(K⁺) > R(Mg²⁺) > R(Ca²⁺) at 10 mol/m³ concentration and R(Mg²⁺) > R(Ca²⁺) > R(Na⁺) > R(K⁺) at 100 mol/m³ concentration.     

Synthesis of 4-Aminobenzoylpiperazine for Preparing the Thin Film Composite Nanofiltration Membrane by Interfacial Polymerization with TMC

A new synthesis method of aromatic diamine, 4-aminobenzoylpiperazine (4-ABP), was studied from 4-aminobenzoic acid and 1-formyl piperazine for the preparation of nanofiltration membrane. The structure of 4-ABP was identified by FT-IR spectra and ¹H NMR spectra. The resulting 4-ABP was used as aqueous monomer to fabricate a thin film on porous polyethersulfone (PES) ultra filtration membranes by interfacial polymerization (IP) with trimesoyl chloride (TMC) as organic monomer. The salt rejection order of these thin film composite (TFC) nanofiltration(NF) membranes is Na₂SO₄>MgSO₄>MgCl₂>NaCl. This sequence indicated that the membranes were negatively charged.     

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.     

Selective separation of contaminants from paper mill effluent using nanofiltration

Biologically treated newsprint mill effluent containing 57 mg L⁻¹ DOC and 1430 TDS was used in a screening study of nine commercial NF membranes for use as pretreatment for reverse osmosis in an end of pipe water recycling application. A salt-organic-separation (SOS) efficiency factor was developed to help rank the performance of the membranes. The SOS measures the ratio of the sum of the percentage rejection of organics and divalent cations over the percentage rejection of monvalents. It can be used to discriminate between NF membranes that are not too permeable to divalent cations or organics in which case the NF permeate will have a high chlorine demand due to the carryover of organics, or too retentive in which case all the material in the effluent will be retained and fouling problems are likely to occur. The optimum SOS efficiently for this study appeared to range from 3.5 to 5.6 for six membranes, DK, HPA-150, ESNA1-LF2, DL, TFC-SR2 and NF-270, which were categorised as membranes with an intermediate rejection. Out of these membranes ESNA1-LF2, TFC-SR2 and NF-270 were capable of operating up to 90% recovery with high permeabilities ranging from 17.7 to 22.3 L m⁻² h⁻¹ bar⁻¹.     

Preparation and characterization of a composite nanofiltration membrane from cyclen and trimesoyl chloride prepared by interfacial polymerization

A novel nanofiltration (NF) membrane was prepared with cyclen and trimesoyl chloride by interfacial polymerization on a poly(ether sulfone) ultrafiltration membrane with a molecular weight cutoff of 50,000 Da. The effects of the reaction time, monomer concentration, and heat‐treatment temperature are discussed. The physicochemical properties and morphology of the prepared NF membrane were characterized by Fourier transform infrared spectroscopy–attenuated total reflectance, scanning electron microscopy, energy‐dispersive spectrometry, and atomic force microscopy. The NF performances were evaluated with solutions of Na₂SO₄, MgSO₄, Mg(NO₃)₂, and NaCl. The salt‐rejection order of the prepared NF membrane was as follows: Na₂SO₄ > MgSO₄ > Mg(NO₃)₂ > NaCl. The resulting rejection of Na₂SO₄ and PEG600 (polyethylene glycol with the average molecular weight of 600) were more than 90%, whereas that of NaCl was approximately 10%. After the addition of silica sol in the aqueous phase (silica sol concentration = 0.1% w/v), the salt rejection of the membrane changed slightly. However, the water flux was from 24.2 L·m^?2·h^?1 (25°C, 0.6 MPa) up to 38.9 L·m^?2·h^?1 (25°C, 0.6 MPa), and the resulting membrane exhibited excellent hydrophilicity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42345.     

Flux,antifouling and separation characteristics enhancement of nanocomposite polyethersulfone mixed-matrix membrane by embedding synthesized hydrophilic adipate ferroxane nanoparticles

Polyethersulfone (PES) nanofiltration (NF) membranes were prepared by blending of synthesized hydrophilic adipate ferroxane nanoparticles (AFNPs) as a novel multifunctional nanofiller via the phase inversion method. The water contact angle measurement indicated the higher hydrophilicity of the NF membranes. The water flux of the membranes improved significantly after the addition of AFNPs, from 10.4 to 32.2 kg/m²h. Antifouling characteristics of AFNPs/PES membranes were improved by increased hydrophilicity and decreased membrane surface roughness. The 0.6 wt% AFNPs/PES membrane exhibited the highest FRR (96%) and the lowest irreversible fouling resistance (6%). The nanofiltration performance of the prepared membranes was evaluated by dye removal and salt retention. The results proved the high dye removal capability of modified membranes (98% rejection) compared with the unfilled PES membrane (89% rejection). The salt retention sequence for membrane with 0.2 wt% of nanoparticles was Na₂SO₄ (70%)>MgSO₄ (60%)>NaCl (18%).     

Preparation of graphene oxide/polyamide composite nanofiltration membranes for enhancing stability and separation efficiency

Polyamide (PA) NF membranes are synthesized on a hollow fiber support by the interfacial polymerization (IP) of piperazine (PIP) and trimesoyl chloride (TMC). Then, GO is coated on the PA layer to decorate the NF membrane surface (denoted GO/PA-NF). This strategy aims to improve the hydrophilicity, chlorine resistance and separation stability of the membrane. The optimization, chemical composition, morphology, and hydrophilicity of the synthesized GO/PA-NF membrane are characterized. Results indicate that the optimized GO/PA-NF in terms of rejection rate and flux are with 0.05 wt% GO. The rejection of GO/PA-NF for Na2SO₄ and MgSO₄ is 99.4% and 96.9%, respectively. Even if the GO/PA-NF is immersed in 1000 ppm NaClO solution for 48 h, the NF membrane still maintains stable salt rejection. The developed NF membranes exhibit excellent treatment performance on dying wastewater. The permeate flux and rejection of GO/PA-NF toward Congo red solution are determined to be 44.2 L/m²h and 100%, respectively. Compared with the PA membrane, GO/PA-NF presents a higher rejection for Na₂SO₄ (99.4%) and a lower rejection for NaCl (less than 20%), which shows that the NF membranes have a better divalent/monovalent salt separation performance. This study highlights the superior performance of GO/PA-NF and shows its high potential for application in wastewater treatment.     

Preparation and characterization of chloromethylated/quaternized poly(phthalazinone ether sulfone ketone) for positively charged nanofiltration membranes

Chloromethylated poly(phthalazinone ether sulfone ketone) (CMPPESK) as a novel membrane material was successfully prepared from poly(phthalazinone ether sulfone ketone), with concentrated sulfuric acid as the solvent and catalyst, and chloromethyl octyl ether with lower toxicity as the chloromethylated regent. The effects of the reaction conditions on the preparation of CMPPESKs with different degrees of chloromethylation were examined. The quantity of chloromethyl groups per repeated unit (DCM) of CMPPESK was determined by the method of analysis of the chlorine element, and structures were characterized by ¹H‐NMR spectroscopy. The introduction of chloromethyl groups into the polymer chains led to a decrease in the decomposition temperature. With increasing DCM, the initial degradation temperature declined. CMPPESK had good solubility and was soluble in N‐methyl‐2‐pyrrolidone (NMP), N,N‐dimethylacetamide (DMAc), and chloroform. However, quaternized poly(phthalazinone ether sulfone ketone) (QAPPESK) had excellent solvent resistance, was only partly soluble in sulfuric acid (98%), and was swollen in N,N‐dimethylformamide. QAPPESK nanofiltration (NF) membranes had about 90% rejection for MgCl₂, and the performance of the NF membrane prepared with DMAc as the solvent was superior to that of the NF membrane prepared with NMP as the solvent. In addition, the rejection to the different salt solutions followed the following sequence: MgCl₂ > MgSO₄ > NaCl > Na₂SO₄. Furthermore, the thermotolerance of the QAPPESK NF membrane was examined, and the results show that when the solution temperature rose from 11 to 90°C, the water flux increased more than threefold with stable salt rejection. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Positively charged loose nanofiltration membrane grafted by diallyl dimethyl ammonium chloride (DADMAC) via UV for salt and dye removal

A novel positively charged loose nanofiltration (NF) membrane was fabricated feasibly by UV-induced photografting polymerization of diallyl dimethyl ammonium chloride (DADMAC) on Polysulfone ultrafiltration membrane. A possible reaction mechanism was proposed that a linear chain structure and/or pyrrole like five-membered nitrogen heterocycles structure on the side chain were grafted to form the active barrier layer. NF membrane demonstrated a looser average pore size of 8.6 nm and positive charges surface. Owing to the nanoscale ultrathin nanoscale barrier layer and the combination of Donnan exclusion and steric hindrance, NF membrane exhibited good hydrophilicity, a high pure flux of 60 L/m² h (0.5 MPa), a good salt rejection to Mg²⁺ (90.8%), Al³⁺ (94.0%), Ca²⁺ (91.5%), and a high dye rejection to methylene blue (99.4%) and congo red (100.0%) respectively. The salts rejection of NF membrane to different salts followed the order of AlCl₃ > CaCl₂ > MgCl₂ > NaCl > LiCl > MgSO₄ > Na₂SO_4. NF membrane showed certain fouling resistance to seawater and BSA solution. The grafting polymerization kinetics were comprehensively investigated including irradiation time, monomer concentration and irradiation intensity. X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurement were employed to investigate membrane chemistry, morphologies, and hydrophilicity.     

Preparation and characterization of a composite nanofiltration membrane interfacially polymerized from cis,cis‐1,3,5‐triaminocyclohexane and trimesoyl chloride

cis,cis‐1,3,5‐Triaminocyclohexane (TAC) was synthesized and used to prepare composite nanofiltration (NF) membranes by interfacial polymerization with trimesoyl chloride (TMC). The surface elemental composition, morphology, and hydrophilicity of the prepared NF membranes were characterized. The separation performances were examined with various salts and polyethylene glycol (PEG400, PEG600) solutions. The effects of preparation conditions were also systematically studied. The NF membrane was negatively charged and exhibited a salt rejection in the order Na₂SO₄ (98.2%) > MgSO₄ (90.8%) > MgCl₂ (84.5%) > NaCl (54.6%). The water permeability was 1.56 L m^?2 h^?1 bar^?1, and the molecular weight cutoff was 600 Da. The TAC/TMC membrane exhibited some characteristics that were different from the ones made from common diamines such as m‐phenylenediamine: (1) the surface was smoother, without a ridge‐and‐valley structure; (2) there were two kinds of crosslinking points in the polyamide chains; (3) the active layer was formed faster (only 5 seconds was required to reach a Na₂SO₄ rejection of 98%). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43511.     

Preparation and characterization of a novel positively charged nanofiltration membrane based on polysulfone

The goal of this study was to prepare positively charged nanofiltration (NF) membranes to remove cations from aqueous solutions. A composite NF membrane was fabricated by the modification of a polysulfone ultrafiltration support. The active top layer was formed by the interfacial crosslinking polymerization of poly(ethylene imine) (PEI) with p‐xylene dichloride (XDC). Then, it was quaternized by methyl iodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, crosslinking time, and MI concentration were optimized. Consequently, high water flux (5.4 L m^?2 h^?1 bar^?1) and CaCl₂ rejection (94%) values were obtained for the composite membranes at 4 bars and 30°C. The rejections of the NF membrane for different salt solutions, obtained from pH testing, followed the order Na₂SO₄ < MgSO₄ < NaCl < CaCl₂. The molecular weight cutoff was calculated by the retention of poly(ethylene glycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41988.     

Catalytic template assisted interfacial polymerization for high-performance acid-resistant membrane preparation

Highly permeable acid-resistant nanofiltration (NF) membranes are of critical significance for the efficient treatment of acidic streams. Enhancing permeability while maintaining the high solute rejection of acid-resistant NF membranes remains a great challenge due to the low reactivity of monomers. In this work, a novel catalytic template assisted interfacial polymerization (IP) strategy of 3-aminobenzenesulfonamide (ABSA) and trimesoyl chloride (TMC) was provided to prepare a poly(amide-sulfonamide) membrane. Aminopyridine doped graphene quantum dots rich in acylation catalytic sites and ZIF-8 nanoparticles are co-loaded on a substrate as template. Benefiting from the enhanced phase integrity and self-inhibition effect of the template assisted IP process, the resulting ultra-thin acid-resistant membrane exhibits an excellent water permeance (20.4 Lm⁻²h⁻¹bar⁻¹) with a high Na₂SO₄ rejection of 90.5%, which outperforms almost all the reported acid-resistant NF membranes. Our work paves a versatile way for synthesis of special separation membranes.     

Dynamic polyacrylamide membranes in the reverse osmosis

Dynamic formation of Polyacrylamide membranes on a Millipore filter in the reverse osmosis was optimised concerning rejection of a standard NaCl water solution.Optimised membranes were tested under 70 bars with selected salts in single-solute water solutions.Exclusion of salts with alcali cations depend on the kind of anion and is in the order SO^2-₄ > F^- > HCO^-₃ > Cl^- > NO^-₃ > J^-.Rejection of salts with alkaline earth cations is generally lower than corresponding salts with alcali cations.Especially concentration dependence of rejection of SO^2-₄ and NO^-₃ through these membranes was tested using different cations.Remarkable is the relatively high rejection of Na₂SO₄, which is 93,6% for a 5 g/l water solution under a flux of 820 l/m²· d.Dynamic PAA membranes are not useful for sea water desalination but they could be used for treatment of water with higher SO^2-₄ content.     

Dye removal from colored textile wastewater using acrylic grafted nanomembrane

In this paper, the dye removal ability of the acrylic grafted polysulfone nanomembrane using ultraviolet radiation was studied to remove dyes from colored textile wastewater. Acrylic acid was used to modify polysulfone ultrafiltration membrane. The effect of different operating parameters such as pressure, salt concentration and chemical structure of dyes was evaluated. Data indicated that the photografted membrane has acceptable performance both in terms of flux and rejection. The dye rejection and hydraulic permeability were 86–99.9% and 7.6 L m^{− 2} h^{− 1} bar^{− 1}, respectively. It was found that the rejection of dyes decreased with salt concentration due to a decrease of the Donnan effect. Also, the low molecular weight dyes and highly charged dyes were more sensitive in the presence of salts. Addition of 80 mM Na₂SO₄ in dye solution decreased the dye rejection more than 15%. The rejection enhancement for all cases was negligible by increasing driving pressure from 1 to 4 bar. Dyes with low charger were more sensitive to operating pressure than that of dyes with higher charges. All findings supported that acrylic grafted nanomembrane is potentially capable to separate dyes from colored textile effluent.     

Novel PVA-based polymers showing an anti-Hofmeister Series property

A series of poly(vinyl alcohol)-trimellitate (PVA-T) polymers with different esterification degrees (ED: 82, 61, and 32 mol%) were prepared through the esterification of PVA and trimellitic anhydride (TA). Solubilities of these polymers and the swelling properties of PVA-T hydrogels, which were prepared by crosslinking with ethylene glycol diglycidyl ether (EGDGE), were investigated in various salt solutions comprising of SO₄²⁻, Cl⁻, SCN⁻ and Li⁺, Na⁺, K⁺, Cs⁺. The PVA-T polymers proved to have larger solubilities in salt solutions (1 M) than in pure water, and the ionic “salting-in” effect was significant in order of SO₄²⁻ > SCN⁻ > Cl⁻ for anions, and Li⁺ > Na⁺ > K⁺ > Cs⁺ for cations, regardless of their ED values. The PVA-T hydrogels also showed corresponding swelling properties; they significantly swelled in sulfate solutions of medium concentration (0.1-1 M), while in other salt solutions no appreciable swelling occurred. The marked salting-in effects exerted by sulfate anion, which is otherwise a typical “salting-out” agent, means that PVA-T polymers have an “anti-Hofmeister Series” (anti-HS) property. This is naturally ascribed to the trimellitic acid group because the degree of swelling in sulfate solutions was more significant for PVA-T with higher ED values; the combination of π-electron system and acidic protons seems to be essential to endow polymers with the anti-HS property.     

Nanofiltration of Magnesium Chloride,Sodium Carbonate,and Calcium Sulphate in Salt Solutions

Abstract

Nanofiltration (NF) membranes have been employed in pre‐treatment unit operations in both thermal and membrane seawater desalination processes. This has resulted in reduction of chemicals used in pretreatment processes as well as lowering the energy consumption and water production cost and, therefore, has led to a more environmentally friendly processes. In order to predict NF membrane performance, a systematic study on the filtration performance of selected commercial NF membranes against brackish water and seawater is required. In this study, three commercial nanofiltration membranes (NF90, NF270, N30F) have been used to treat highly concentrated different salts solutions (MgCl₂, Na₂CO₃, and CaSO₄) at salinity level similar to that of brackish water and seawater. The main parameters studied in this paper are salt concentration and feed pressure. The experimental data were correlated and analysed using the Spiegler‐Kedem model. In particular, the reflection coefficient (σ) of all studied membranes and the solute permeability (P_s) have been determined for all membranes and at different salinity levels of studied salts. All the studied membranes fitted the model well for all investigated salts except the experimental data of MgCl₂ using N30F membrane, which did not fit well at low rejection. The results showed that NF90 produced a high rejection around 97% for all salts with medium permeate flux while NF270 gave a high flux with medium rejection and N30F gave low rejection and flux.     

Separation performance of thin-film composite nanofiltration membrane through interfacial polymerization using different amine monomers

Four kinds of thin-film composite (TFC) membranes were prepared via interfacial polymerization using diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA) and piperazidine (PIP) as water-soluble monomer, and trimesoyl chloride (TMC) as organic-soluble monomer. The surface chemical features of the resultant membranes were confirmed by contact angle measurement and Fourier transform infrared spectroscopy (FTIR). The membrane morphology and surface charges were investigated through Scanning electronic microscopy (SEM) and Zeta potential, respectively. Salt rejection was used to evaluate the separation performance of the four kinds of TFC membranes. The results showed that all the four kinds of TFC membranes exhibited typical negatively charged nanofiltration membrane characteristics. The salt rejections followed the sequence: Na₂SO₄ > MgSO₄ > MgCl₂ and the rejection of Na₂SO₄ was all over 80%. It was also found that the solubility of water-soluble monomer in organic solvent played an important role in manipulating the membrane structure, charge properties and thus the separation performance.