The potential toxicity of heavy metals arising from the discharge of industrial wastewater has become a serious public concern. Fabrication of a thin film composite (TFC) NF membrane with desirable rejection of heavy metal ions is an attracting route to solve this problem. Hereon, we proposed a facile strategy for fabricating a TFC NF membrane with excellent heavy metal removal. The ratio of PIP and TMC was greatly enlarged by decreasing the concentration of TMC to an exceptional low extent. Thus a polyamide film with weak electronegativity and small pore size was successfully constructed on an ultrafiltration substrate membrane. Comprehensive characterizations were adopted to reveal the micro-variation of the resulted NF membranes when regulating TMC concentration . The optimized membrane prepared only with PIP and TMC can exhibit a high pure water permeability of 14.6 L m −2 h −1 bar −1 , desirable rejection of over 98% against Ni 2+ , Zn 2+ , Cu 2+ , and >92.7% against Cd 2+ . This performance could go beyond most of the reported candidates which were prepared with other complicated methods. The simplicity, low cost and scaling up feasibility of the current strategy is expected to well meet the requirements of industrial production of TFC NF membrane for heavy metal removal.
Yang Qin,Hailiang Liu,Yumin Sun,Qinglin Huang,Wei Li,Kaikai Chen,Wei Shu,Changfa Xiao
In this research, a novel interfacial enhanced thin film composite nanofiltration (TFC NF) membrane with nail-fixed like surface structure and wave line like cross-section structure, good permeability and superior interfacial stability was prepared by interfacial polymerization (IP) on one-step in-situ aminated polyvinyl chloride (APVC) support layer. The effects of amination agent (triethylenetetramine, TETA) content on the support layers and the effects of the support layers with different degrees of amination on the performance of the TFC NF membranes were studied comprehensively. Furthermore, the interfacial bonding strength of the TFC NF membrane was explored by the inverse permeation test. It was concluded from the results that higher TETA content in casting solution led to the APVC membrane to form macroporous surface structure, thinner top skin layer and larger mean pore size. Meanwhile, more TETA molecules were grafted onto the PVC chains through nucleophilic substitution to participate in IP in a synergistic manner. Accordingly, the corresponding TFC NF membrane formed a nail-fixed like surface structure similar to semi-free-standing polyamide (PA) layer and wave line like cross-section structure with thinner and denser active layer. The water flux of the TFC NF membrane prepared with the optimized APVC membrane as the substrate membrane was increased by 395% at 0.6 MPa compared with the TFC NF membrane prepared with PVC membrane as the substrate membrane, while Na 2 SO 4 rejection did not sacrifice and increased by 3.48%, which manifested that unique structure was favorable to speed up the water transmission and effectively conquered the trade-off effect. Moreover, the representative TFC NF membrane prepared with optimized APVC membrane as the substrate membrane with strong covalent bond between support layer and active layer demonstrated superior interfacial stability in the short-term circulating inverse permeation test.
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.
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