Jian Li,Pei Xiao,Jie Yu,Lei Li,Yiyun Zhang,Yun Ma,Fei Liu,Yi Li
Nanofiltration (NF) technology is attractive in desalting and concentrating dyeing wastewater in the textile industry. A highly efficient NF membrane is critical in reducing the cost of the process. Here, a facile and reliable approach to prepare an NF membrane for the selective separation of dye/salt is proposed by surface grafting of 3-aminopropyltriethoxysilane (APTES) on a fresh polyamide (PA) layer after interfacial polymerization (IP). A thin layer of APTES with a thickness of ∼64 nm was found successfully covalently bonded onto the PA surface via esterification and amidation reactions. The thin-film composite (TFC)-1.0 membrane grafted with 10% APTES achieved a high water permeance of 44.8 L m–2 h–1 bar–1, which was 4.7 times higher than that of the control TFC membrane. Interestingly, the rejection of monovalent salt (NaCl, 11.5%) and divalent salt (Na2SO4, 17.2%) decreased significantly, while the rejection for different dyes (Congo red, reactive blue-19, Coomassie blue G-250, and methyl blue) remained over 99.0%. These noticeable changes in separation performances could be attributed to the large pore size of the active layer, resulting from the interference of APTES on the post-cross-linking of a PA network. The poly(ethylene glycol) (PEG) filtration experiments confirmed that the mean pore size of the membrane was enlarged significantly from 0.51 to 1.17 nm after surface modification. Finally, the modified membrane showed good long-term stability and excellent separation efficiencies in fractionation of a high salinity Congo red/NaCl (0.2/50 g L–1) mixture. Overall, this work provides a practical strategy to prepare a permeable and selective NF membrane for dye and salt separation by surface grafting of the nascent PA layer.
Jingyu Wang,Yuling Ren,Huiru Zhang,Jianquan Luo,John M. Woodley,Yinhua Wan
Separation of monosaccharides and monovalent salts is important in the biorefinery and food industry. Nanofiltration (NF) technology is promising for this purpose but its poor selectivity still needs to be addressed. In this work, the separation of monosaccharides and monovalent salts by NF is improved by regulating the surface charge and pore size distribution of polyamide NF membranes. The carboxyl groups on the polyamide membrane are selectively activated by N-(3-Dimethylaminopropyl)-N′-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS), and subsequently molecules with amino groups are grafted on the membrane to reduce the effective pore size and electronegativity. The conditions and grafted molecules are optimized, and polyethyleneimine (600 Da) is selected as the best for enhancing the separation of glucose/fructose and KCl. Such targeted modification is found to reduce the effective mean pore size while maintaining the porosity of the NF270 membrane, due to pore segmentation. This results in a remarkable improvement in glucose/fructose rejection (from 67.96% to 84.14%) and separation factor (from 2.20 to 6.78), with only a 4.70% permeability loss. The modified membrane also maintains separation performance in crossflow filtration and after alkaline cleaning (pH 12), which outperforms the pristine NF270 and those modified by mussel-inspired coating and simple physical adsorption.
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