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Abstract In this study, the novel technique, namely interfacial polymerization (IP) coupled with surface amidation, was proposed to fabricate polyamide thin-film composite (TFC) membranes for improved reverse osmosis performance. TFC membrane with loose polyamide separation layer was firstly prepared through conventional IP process. Surface amidation was then performed through covering the surface of the loose polyamide layer with aqueous 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) solution. Amidation reaction between the free carboxylic and amino groups on membrane surface was confirmed through ATR-FTIR and XPS analyses. Permeation tests revealed that the step of surface amidation could effectively improve the ability of membrane rejection to solute, showing significant increases of NaCl, NaNO 3 and glycerol rejections from about 96.4%, 90.5% and 78.4% to 97.8%, 93.7% and 91.3%, respectively. The water permeability of the membrane obtained via IP followed with surface amidation was at least 22.3% higher than the membrane of the same NaCl rejection obtained via conventional IP process. Thus, the method developed was attractive for the fabrication of TFC reverse osmosis membranes with improved permeability to water and rejection ability to solutes. Additionally, the step of surface amidation of present work can be potentially applied to the in-situ rejuvenation of used polyamide reverse osmosis membranes. Highlights • TFC membrane was fabricated via interfacial polymerization and surface amidation. • Surface amidation was facilely implemented via using acidic EDC aqueous solution. • PA selective layer composed of a top dense skin on loose bulk was obtained. • PA TFC membrane with improved reverse osmosis performance could be obtained. [ABSTRACT FROM AUTHOR]

Divalent metal nitrates were pre-loaded on polysulfone support to modulate the interfacial polymerization between piperazine (PIP) and trimesoyl chloride (TMC). It is found that the nano-porosity and nano-morphology of thus formed thin film composite polyamide (TFC-PA) nano-filtration (NF) membranes as well as their filtration performance could be effectively tuned by the type and concentration of the divalent metal salts, especially the divalent cations used. Main group cations, such as Mg (II) and Ca (II), increased the water flux of the NF membranes by increasing their surface nano-scale nodular arrays without altering the pore sizes and rejections of the membranes, while transitional metal cations such as Zn (II), Cu (II) and Co (II) increased the water flux of the NF membranes not only by the formation of high surface area nano-scale Turing type crisscrossed ridge networks, but also by the increase of their nano-pore sizes due to their coordination with the >NH groups of the PIP. The prepared NF membranes pore sizes adjustable from 0.54 Å to 0.90 Å could be developed to have varied selectivity and rejections among inorganic salts and organic dyes. [Display omitted] • Nano-porosity of NF membranes could be tuned in the IP processes. • Retention selectivity of TFC-PA NF membranes could also be tuned. • Divalent transitional metal cations increased both pore size and surface area. • Divalent main group metal cations increased water flux without changing selectivity. • Anions Cl- may act as a ligand to impeach the action of divalent transitional cations. [ABSTRACT FROM AUTHOR]

Abstract: Monodispersed spherical mesoporous nanosilicas were synthesized by the hydrothermal method using tetraethoxysilane as silica source, cetyltrimethylammonium bromide as template, ethanol as co-solvent, and sodium hydroxide as alkali source. The synthesized silica has an average particle diameter of 164nm with a relative standard deviation of 4.87%, specific surface area of 1141m2·g−1, pore size of 2.47nm, pore volume of 0.77cm3·g−1, and a pore structure radiating from the heart to the outer surface of the sphere. The spherical mesoporous nanosilica–polyamide thin film composite reverse osmosis (TFC RO) membranes were obtained by interfacial polymerization. The silica nanoparticles are visible in the TFC RO membranes based on the surface and cross-sectional SEM images. Correspondingly, energy dispersive X-ray spectroscopy analysis confirms that the silica has been successfully doped into the TFC RO membranes. The hydrophilicity of the TFC RO membranes is improved and water flux is increased from 19L·h−1·m−2 (without nanosilica) to 53L·h−1·m−2 (with 0.1% (w/v) mesoporous nanosilica loading), whereas all solute rejection rates are greater than 96%. [Copyright &y& Elsevier]

Abstract: A novel thin-film composite polyamide nanofiltration membrane was prepared through interfacial polymerization of polymeric polyamine polyvinylamine (PVAm) with isophthaloyl chloride (IPC) on a polysulfone supporting film. The composite membranes were prepared under different conditions and characterized in terms of chemical and morphological structures, surface zeta potential, pure water permeability, and rejection to different solutes including electrolytes and sucrose. The results showed that the membrane performance was significantly affected by the content of amine units of PVAm and the concentrations of PVAm and IPC. The increase of the content of amine units of PVAm and the concentration of IPC resulted in an augment in salt rejection and a decrease in permeability, while the increase of PVAm concentration led to enhancement in both the salt rejection and water flux. The obtained membranes were positively charged at pHs lower than 6.5 and negatively charged at pHs higher than 7.0. The rejection order of the membrane changed from MgCl2 >MgSO4 >NaCl>Na2SO4 at pH 3.0 to MgSO4 >Na2SO4 >MgCl2 >NaCl at pH 7.5. The decrease of feed pH from 7.5 to 3.0 resulted in an over 35.0% augment in permeability. Furthermore, the novel nanofiltration membrane is of good performance stability and particularly suitable for treating acidic feed. [Copyright &y& Elsevier]

Abstract: This study focus on the surface modification and the improved acid stability and chlorine resistance of the commercial thin-film composite polyamide reverse osmosis membranes coated with hydrophilic copolymers poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-co-Am)) surface layer. The virgin flat-sheet polyamide membranes were modified in situ with dilute P(NIPAM-co-Am) aqueous solution, and the modified membranes were then tested for their acid stability and chlorine resistance through long-term cross-flow permeation tests with aqueous solution containing 0.5mol/l HCl and 2000ppm NaCl and chlorine exposure experiments with hypochlorite aqueous solutions of different concentrations, respectively. The membrane properties were characterized in terms of reverse osmosis performance and surface chemical structure. The membrane modification was found to improve the chlorine tolerance and acid stability significantly. The P(NIPAM-co-Am) surface coating layer would impede the hydrolysis and the replacement of hydrogen with chlorine on the amide groups of the aromatic polyamide thin-film through enhancing intermolecular hydrogen bonding, and prevent the attack of acid and chlorine on the underlying polyamide film as a protective and sacrificial layer. The P(NIPAM-co-Am)-coated membrane would offer a potential use as a new type of thin-film composite polyamide membrane with improved acid stability and chlorine resistance. [Copyright &y& Elsevier]

Abstract: Commercial thin-film composite aromatic polyamide reverse osmosis membranes were modified by depositing N-isopropylacrylamide-co-acrylic acid copolymers (P(NIPAm-co-AAc)) on the membrane surface, and the modified membranes showed improved membrane properties. P(NIPAm-co-AAc) copolymers were synthesized by free radical copolymerization and their aqueous solutions of different concentrations were used to modify the polyamide membranes through in situ surface coating technique. The deposition of P(NIPAm-co-AAc) layer was shown to increase membrane surface hydrophilicity and surface charge at neutral pH, but offer additional resistance to water permeation. The effect of surface modification on membrane salt permeability was investigated through permeation tests with different salts under different pHs. The membrane modification was found to decrease the salt permeability of NaCl and Na2SO4 under neutral and alkaline conditions, and the decrease was significant for Na2SO4 that has divalent anions than for NaCl that has monovalent anions. The results of the fouling experiments with bovine serum albumin (BSA) aqueous solution and washing experiments with de-ionized water of different temperatures also revealed that the P(NIPAm-co-AAc) coating layer improved the fouling resistance to BSA and the cleaning efficiency. The phase transition of the coating layer under temperatures above its LCST would facilitate the removal of foulants located on the membrane surface. [Copyright &y& Elsevier]

Abstract: A novel thin-film composite (TFC) seawater reverse osmosis membrane was developed by the interfacial polymerization of 5-chloroformyloxyisophthaloyl chloride (CFIC) and metaphenylenediamine (MPD) on the polysulphone supporting membrane. The performance of the TFC membrane was optimized by studying the preparation parameters, which included the reaction time, pH of the aqueous-MPD solution, monomer CFIC concentration, additive isopropyl alcohol content in aqueous solution, curing temperature and time. The reverse osmosis performance of the resulting membrane was evaluated through permeation experiment with synthetic seawater, and the structure of the novel membrane was characterized by using SEM, AFM and XPS. Furthermore, the separation properties of the TFC membrane were tested by examining the reverse osmosis performances of various conditions, the boron rejection performance and the long-term stability. The results show that the desired TFC seawater reverse osmosis membrane has a typical salt rejection of 99.4% and a flux of about 35L/m2 h for a feed aqueous solution containing 3.5wt.% NaCl at 5.5MPa, and an attractive boron rejection of more than 92% at natural pH of 7–8; that the novel seawater reverse osmosis membrane appears to comprise a thicker, smoother and less cross-linking film structure. Additionally, the TFC membrane exhibits good long-term stability. [Copyright &y& Elsevier]