Zwitterionic nanofiltration membrane with enhanced perm-selectivity and antifouling property via introducing acyl chloride monomer with rigid pyrrolidinyl group

The enhancement in perm-selectivity and antifouling property of nanofiltration (NF) membranes is quite meaningful for expanding application areas and improving economic benefits. The moderately increased pore size and zwitterions could endow NF membranes with excellent perm-selectivity and antifouling, respectively. In this research, a novel zwitterionic NF membrane was prepared by polymerizing 5-(1-pyrrolidinyl)-1,3-benzenedicarbonyl dichloride (PIPC) and trimesoyl chloride with piperazine by interfacial polymerization (IP) for forming the polyamide (PA) layer, and then the grafting reaction of 3-bromopropionic acid was carried to form the zwitterionic surface. The PIPC monomer with dual-functional group had two acyl chloride groups (−COCl) and a rigid pyrrolidinyl group (−NC4H8), which could loosen the PA layer structure. Consequently, the moderate enlargement in pore size facilitated the passing of water molecules and monovalent ions, improving the permeability and monovalent/divalent salt separation performance. The resulting zwitterionic NF membrane achieved pure water flux of 36.03 L·m−2·h−1, with outstanding Na2SO4 rejection of 98.48 %. Meanwhile, it exhibited low NaCl rejection of 29.31 %, resulting in high NaCl/Na2SO4 selectivity of 46.51 in mixed salts solution. Moreover, the zwitterionic membrane surface significantly enhanced its hydrophilicity, which endowed the membrane with improved antifouling performance to humic acid. This study might offer a useful and facile tactic for constructing NF membrane with enhanced perm-selectivity and antifouling property.