Salt-tuned fabrication of novel polyamide composite nanofiltration membranes with three-dimensional turing structures for effective desalination

Abstract

High performance thin-film nanofibrous composite (TFNC) membranes with Turing structures were constructed by interfacial polymerization (IP) of trimesoyl chloride (TMC) and piperazine (PIP) tuned with high content salt (NaCl) in aqueous phase onto a polyacrylonitrile (PAN) nanofibrous mat for nanofiltration (NF). The concentration of salt in aqueous phase played a key role in the structural transition of polyamide (PA) membrane surfaces with two type Turing structures from the crossed ridge networks to crowed nodular arrays. The introduction of NaCl induced the uneven distribution of the IP reaction and could fine-tune the hydrophilicity and compactness of the formed ultrathin PA layer. The skillful manipulation of IP by regulating the NaCl content in aqueous phase enabled a great improvement in NF performance. Under 0.5 MPa, the flux of the optimized TFNC membrane (20.0 wt% NaCl in aqueous phase) reached 129.0 L m-2 h-1 (Na2SO4 rejection was 99.1%) which was approximately 2.5 times greater than that of the original membrane fabricated without salt addition. Moreover, the resultant membrane exhibited excellent stability and anti-fouling properties for long-term use. This approach is easy to be connected with commercialized IP technology to prepare high-performance NF membranes.