Tailoring the selectivity of quasi-PIMs nanofiltration membrane via molecular flexibility of acyl chloride monomers for desalination from dye effluents

Nanofiltration is a promising technology to recover dye from textile wastewater with highly saline for sustainable resource recovery. However, it is difficult for the conventional piperazine-based nanofiltration membranes, which usually have a tight polyamide matrix structure, to precisely separate dye and salt in wastewater. In this study, 5,5,6’,6’-tetrahydroxy-3,3,3’,3’-tetramethyl spirobisindane (TTSBI) with rigidly contorted structure has been used instead of piperazine as aqueous-phase monomer to fabricate polyarylate (PAT) nanofiltration membranes with quasi-PIMs structure via interfacial polymerization (IP) with three types of acyl chloride, i.e., rigid trimesoyl chloride (TMC), short-chain glutaryl chloride (GC) and long-chain sebacoyl dichloride (SDC). The contorted structure of TTSBI introduces extra microporosity in nanofiltration membranes, and the differentia of three acyl chlorides in molecular flexibility further endows with tailoring the stacking density of as-formed PAT networks. The PAT NF membranes thereby exhibited high permeability and tunable size-selectivity in desalination from dye effluent. Among these PAT membranes, TTSBI-TMC membranes had the highest water flux of 480.5 LMH, nearly 7-fold increase compared traditional PA NF membranes, whereas TTSBI-SDC membranes had the highest dye rejection of 97.4%, and TTSBI-GC membrane had the relatively balanced dye desalination performance with high rejection 95.4% for Congo Red and 8.3% for NaCl accompanied by high flux of 402.4 LMH. Therefore, this study provides a new prospective for the fabrication of highly permeable nanofiltration membranes for precise separation.