Poly(ionic liquid) blended polyphenylene sulfone ultrafiltration membranes with enhanced surface hydrophilicity and antifouling performance

Membrane fouling is a key challenge in the process of utilizing polyphenylene sulfone(PPSU) ultrafiltration (UF) membranes. To address this issue, an amino-functionalized poly(ionic liquid), poly(1-vinyl-3-propylamine imidazolium bis(trifluoromethane sulfonyl) imide) (PIL[TFSI]), was synthesized via free radical polymerization and incorporated into the prepared UF membranes-based PPSU with nanochannels through nonsolvent induced phase separation method. 1H NMR, ATR-FTIR, XPS and EDS spectra verified the introduction of PIL[TFSI]. The AFM and SEM images showed the membrane possessed a classical asymmetrical structure, featuring a higher surface roughness and dense cortex with pits. The decreased water contact angle by the incorporation of PIL[TFSI] indicates the formation of an improved hydrophilic membrane surface. The hydrophilicity of the blended membranes was enhanced by the increasing incorporation of PIL[TFSI]. Meanwhile, the flux decreased slightly, but the selectivity improved significantly. The PIL[TFSI]/PPSU UF membrane with 5% PIL[TFSI] maintained a flux (275 L/m2 h) and a high rejection for bovine serum albumin (BSA) (>99.9%). Additionally, the blended membrane has a superior removal performance for Congo red (>99.9%) and Evans blue (>99.9%). More importantly, the PIL[TFSI]/PPSU UF membranes present excellent antifouling with an increased flux recovery rate from 60.2% to 91.1%. Furthermore, the existence of hydrogen bonds and π-π interactions between PIL[TFSI] and PPSU is conducive to the good stability and sustained hydrophilicity of blended membrane even after continuous immersion for a month.