Thin-film composite hollow-fiber nanofiltration membranes prepared from benzonitrile containing disulfonated poly(arylene ether sulfone) random copolymers coated onto polyphenylene oxide support membranes

Abstract

A new method for the preparation of chemically robust thin-film composite hollow-fiber (TFC-HF) nanofiltration membranes through a dip-coating process is reported. A negatively charged disulfonated poly(arylene ether sulfone) random copolymer (SPN-20) containing highly polar benzonitrile groups was utilized as a separation layer in a TFC-HF membrane. Only four polar aprotic solvents, N-methyl-2-pyrrolidone (NMP), dimethyl acetamide (DMAc), dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO), proved to be good solvents for SPN-20 possibly due to its rigid chemical backbone and strong intermolecular interactions. In order to avoid dissolution or irreversible swelling of the polymeric supports in the dip-coating process, a polyphenylene oxide (PPO) hollow-fiber membrane was introduced as a novel substrate for TFC-HF fabrications. Solubility investigation using a framework of Hansen solubility parameters (HSPs) revealed that the PPO membrane is a suitable substrate for coating the SPN-20 copolymer due to its tolerance of polar aprotic solvents. By using DMSO as a coating solvent for the SPN-20 copolymer, TFC-HF membranes were successfully prepared with neither dissolution nor any damage to PPO supports. The dip-coating and drying processes were analyzed in detail to optimize the thickness and separation performance of TFC-HF membranes. The resultant membranes showed excellent rejection of Na2SO4 (>98%) and an almost 100% rejection of negatively charged dyes along with a reasonable level of pure water flux (1.0–10.3 [L∙m−2∙h−1∙bar−1]).