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Abstract In this study, a novel acyl chloride monomer trimellitic anhydride chloride (TAC) with an anhydride group was blended with trimesoyl chloride (TMC) as organic phase monomers to fabricate high-flux nanofiltration membranes. Due to the reaction activity differences of organic phase monomers (TMC and TAC) with piperazine, the chemical compositions and structures of polyamide active layer could be tailored through varying the TAC content. It was found that the participation of TAC could yield a looser polyamide separation layer on the polysulfone support membrane, along with an increased surface roughness, hydrophilicity, pore size and negative charge density. As a result, the resultant membrane exhibited excellent water-salt separation. When the TAC concentration was increased to 0.04 wt%, the optimized membrane exhibited a high pure water permeability (PWP) of 13.2 L m−2 h−1 bar−1, up to 2-fold, in comparison with the pristine membrane, whereas the salt rejections of Na 2 SO 4 , MgSO 4 and NaCl were 97.6%, 92.7%, and 34.0%, respectively. This work provided a novel and facile strategy to develop high-flux NF membrane. Highlights • NF membranes were prepared with mixed organic phase reactants of TMCand TAC with an anhydride group. • Membrane physicochemical properties and permselectivity were tuned by varying the TAC content. • The water flux of optimal NF membrane was 2 times to that of controlled membrane under the almost same salt rejections. [ABSTRACT FROM AUTHOR]

Extraction of lithium from salt lakes is an important route for lithium sources. Due to the unique structure and separation mechanism, i.e., size exclusion and Donnan effect, nanofiltration (NF) is considered as a promising way to separate magnesium (Mg2+) and lithium (Li+) ions. However, the Mg2+/Li+ separation factor of NF membrane fabricated by traditional interfacial polymerization (IP) is usually dissatisfactory. Here, a swelling-embedding-shrinking strategy was proposed to modify polyethyleneimine (PEI)/trimesoyl chloride (TMC) NF membranes using diethylenetriamine (DETA) to improve the performance in Mg2+/Li+ separation. The pristine PEI/TMC NF membrane was swollen with methanol to increase the polyamide chain spacing followed by embedding electropositive DETA as a modifier. The charge properties and pore structure of the active layer could be regulated by optimizing the modification conditions. Within comparison to the pristine membrane (TFC-0), the pure water flux of modified NF membrane (TFC-3) increased by 63.6% because of the rougher surface and the larger pore size. Meanwhile, the embedding of electropositive DETA reduced the electronegative property of membrane surface. In consequence, TFC-3 membrane exhibited higher rejection of MgCl 2 (93.9% against 88.4%) and lower rejection of LiCl (31.0% against 32.1%), thus showing a twofold improvement in Mg2+/Li+ separation factor (S Li, Mg = 11.38 against 5.87). The swelling-embedding-shrinking strategy in this article provided a good reference for the modification of NF membranes in the separation of multivalent and monovalent ions. [Display omitted] • A swelling-embedding-shrinking strategy was proposed to enhance membrane performance. • Surface property and pore size could be regulated by embedding diethylenetriamine (DETA). • Modified PEI/TMC NF membrane had higher rejection of Mg2+ but lower rejection of Li+. • Mg2+/Li+ separation factor reached up to 11.38 compared to 5.87 of pristine membrane. [ABSTRACT FROM AUTHOR]

[Display omitted] • New polyamide layer with rigid-flexible microstructure was constructed. • Both internal pores and positive charge density were remolded at molecular level. • "Useless pores" were widened and "defect pores" were repaired simultaneously. • Modified membrane exhibited much higher Mg2+/Li+ selectivity factor of 15.38. Lithium extraction from salt-lake brine with a high Mg2+/Li+ ratio is crucial for mitigating lithium supply shortage. Positively charged polyamide nanofiltration membranes, which are often prepared by performing interfacial polymerization (IP) using polyethyleneimine and trimesoyl chloride, are considered to be promising candidates for Mg2+/Li+ separation owing to their high energy efficiency and low environmental impact. However, the performance of these membranes is severely hindered by "useless pores" and "defects" present in the flexible polyamide layer. Herein, we provide a facile strategy for modifying flexible semi-aromatic polyamide chains by intercalating a rigid electropositive monomer, histamine, to remold the internal pores and positive charge density at a molecular level. Two routes, namely, "swelling-embedding-reacting-shrinking (SERS)" and "in-situ interposition (SIP)" were used to construct a new polyamide layer with rigid–flexible microstructures. The fabricated SERS-0.50 membrane showed a 5-fold higher water flux and 2-fold increase in the Mg2+/Li+ separation factor compared with the IP membrane. Moreover, the SIP-0.15 membrane with an enhanced positive charge density exhibited a considerably higher Mg2+/Li+ separation factor (15.38, 500 % increase compared with that of the IP membrane) for brine with a Mg2+/Li+ ratio of 20. This study provides a reference for developing nanofiltration membranes used for high-efficiency Mg2+/Li+ separation. [ABSTRACT FROM AUTHOR]

Nanofiltration is considered a promising technology for separation of multivalent/monovalent ions such as extracting lithium from Salt Lake brine with high Mg2+/Li+ ratio. However, the nanofiltration membranes fabricated via conventional interfacial polymerization process generally possess negatively charged surface and have low Mg2+/Li+ selectivity. Herein, we proposed a new and facile method, i.e., reversed interfacial polymerization (RIP), to prepare nanofiltration membranes with positively charged surface and uniform charge distribution. The sequence of amine (polyethyleneimine, PEI) and acyl chloride (trimesoyl chloride, TMC) monomers on polysulfone support was reversed compared to the conventional interfacial polymerization (IP) process. Moreover, the solvent of amine monomer was acetone instead of water. The nanofiltration membranes fabricated by this method exhibited higher water flux (from 4.88 to 22.25 Lm−2h−1) and MgCl 2 rejection (from 84.36% to 97.71%). Meanwhile, LiCl/MgCl 2 separation factor in single salt solution reached up to 13.93, which was almost quadruple compared to the conventional control membrane. In addition, the developed nanofiltration membrane also exhibited an excellent separation selectivity (S Li, Mg = 9.22) in mixture system (Mg2+/Li+ mass ratio of 20), which had good application potential in extracting lithium resources from Salt Lake brine. [Display omitted] • A facile reversed interfacial polymerization (RIP) method was proposed. • Positively charged nanofiltration membranes with uniform charge distribution. • Acetone was selected as solvent of polyethyleneimine monomer instead of water. • Mg2+/Li+ selectivity reached 13.93 and 9.22 in single and mixed salt system, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A novel nanofiltration membrane prepared by interfacial polymerization of purposefully synthesized polyhexamethylene guanidine hydrochloride (PHGH) with antibacterial property and trimesoyl chloride (TMC) on polysulfone (PSf) ultrafiltration membrane was investigated. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscope (SEM) and atomic force microscopy (AFM) were employed to characterize the chemical structures and morphologies of the active layers of obtained membranes. The effects of monomer concentrations, reaction time, curing temperature and time on filtration performance of the composite nanofiltration membranes were discussed. It was found that the membrane rejections to different salts followed the order of MgCl2>MgSO4>Na2SO4>NaCl. Dyes rejection results further showed the feasibility for the membranes to separate small organic molecules with a molecular weight cut-off (MWCO) of around 700Da. Antibacterial experiments indicated that the newly prepared composite nanofiltration membrane had effective inhibition against Escherichia coli. Furthermore, a 50h fouling test using high concentration of bacteria solution also demonstrated an enhanced anti-biofouling performance of the composite nanofiltration membrane. [Copyright &y& Elsevier]

The enhancement in selectivity of nanofiltration (NF) membranes is of great significance for extending the application areas and improving the process economy, especially for the separation of monovalent/divalent ions. The characteristics of moderately increased pore size, fewer nonselective defects and a more uniform structure are conducive to NF membrane exhibiting higher rejection of divalent ions but lower rejection of monovalent ions. Nonylphenol polyoxyethylene ether (NP-10) was introduced in interfacial polymerization process in this study to optimize the microstructure and surface properties of polyamide (PA) layer to manufacture highly selective NF membranes. The hydrophobic benzene ring and aliphatic chain in NP-10 could form a local space that restricted the interfacial polymerization reaction on the side of the oil phase, thereby appropriately increasing the pore size of the PA layer. It was advantageous to the permeation of water molecules and monovalent ions with a smaller radius. The long hydrophilic oxyethylene group as a guide could facilitate the uniform diffusion of the monomer to the water/hexane interface. NP-10 as an amphiphilic substance would form a self-assembled network at the water/hexane interface, which was expected to optimize the distribution of aqueous amine monomers at the phase interface. Meanwhile, introducing NP-10 can form a stable interface and reduce the interface disturbance, thus inhibiting the formation of non-selective macropores (or "defects") in PA layer, which could improve the separation selectivity of monovalent/divalent ions. In addition, the hydrophilicity and electronegativity were also enhanced. The results showed that the MWCO of NF membrane increased from 210.1 Da (TFC-0) to 269.6 Da (TFC-0.25), and the average pore radius increased from 0.248 nm to 0.276 nm. The water flux of optimized membrane was doubled compared to the control membrane. Most important, the optimized exhibited higher rejection of divalent Na 2 SO 4 (from 98.07% to 99.43%), and meanwhile lower rejection of monovalent NaCl (from 54.07% to 27.52%). NaCl/Na 2 SO 4 separation factor reached up to 130.53, which was about four times of TFC-0 membrane. [Display omitted] • Separation factor (NaCl/Na 2 SO 4) reached up to 130.53. • Higher rejection of divalent ions but lower rejection of monovalent ions. • Moderately increased pore size, fewer defects, and uniform structure. • Restricted IP reaction to appropriately increase the pore size of PA layer. • A stable interface and reduce the interface disturbance. [ABSTRACT FROM AUTHOR]