Negatively charged nanofiltration membrane with high performance via the synergetic effect of benzidinedisulfonic acid and trimethylamine during interfacial polymerization

Abstract

Negatively charged surface is preferred for thin film composite (TFC) nanofiltration (NF) membrane with excellent separation performance for divalent anions, and ultra-smooth surface is beneficial for antifouling in practical application. Herein a kind of high-flux sulfonated polyamide TFC NF membrane, termed as TFC-BDSA, was successfully fabricated via interfacial polymerization (IP) between the aqueous monomers, 2,2-benzidinedisulfonic acid (BDSA) mixed with piperazine (PIP), and the organic monomer, trimesoyl chloride (TMC), with triethylamine (TEA) as aqueous catalyst. The results proved that BDSA and TEA have synergetic effect on the performance of the fabricated NF membrane. BDSA enabled the formation of more negatively charged, more hydrophilic and much smoother surfaces, which greatly improved the separation performance and antifouling capability of the prepared TFC-BDSA membrane. TEA not only act as an acid receiver, but could form a complex salt with BDSA and thus help to manipulate the diffusion rate of BDSA and PIP as well as the interfacial polymerization process, which helps to form a more smooth, more hydrophilic, more negatively charged, as well as more antifouling and defect-free membrane skin layer. With 1.0 wt% BDSA in the aqueous monomer solution and at pH 11.2 which is adjusted by TEA, the resultant TFC-BDSA membrane displays an excellent water permeance of 122 L m−2h−1 MPa−1, which is more than twice the pristine baseline TFC membrane. Meanwhile, the resultant TFC-BDSA membrane achieved an extremely higher Na2SO4 rejection of 99.6 %, which is more than 2.0 % higher than that of the latter. Moreover, the flux recovery ratios were 101.1 % and 99.5 % (after two cycles of filtration - cleaning) for the TFC-BDSA membrane fouled with sodium alginate and humic acid, respectively, indicating its excellent antifouling performance. Furthermore, the TFC-BDSA membrane shows an excellent operation stability over a 120 h filtration process. In summary, this study provides a new approach to prepare high performance NF membranes for water treatment.