Composite ultrafiltration membranes from polymer and its quaternary phosphonium-functionalized derivative with enhanced water flux

Abstract

Novel ultrafiltration (UF) membranes were prepared by blending brominated poly(phenylene oxide) (BPPO) and its quaternary phosphonium derivative (TPPOQP-Br) as additive using a phase inversion method. The chemical structure and microstructure of the membranes were characterized by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The XPS results indicated that the BPPO/TPPOQP-Br composite membranes exhibited an increase in the concentration of TPPOQP-Br from the top surface to the bottom surface. In contrast, the composite membranes prepared from BPPO and its quaternary ammonium derivative (TPPOQA-Br) showed an opposite concentration gradient of TPPOQA-Br. This was attributed to the difference in wettability and hydration rate between TPPOQP-Br and TPPOQA-Br, leading to different membrane microstructure and chemical composition distributions. BPPO membrane showed a water flux of 215Lm−2h−1 at 100kPa and its molecular weight cut-off of PEG is 93.8kDa; the corresponding values of the optimal BPPO/TPPOQP-Br membrane are 873Lm−2h−1 and 111.3kDa, both of which are better than those of BPPO/TPPOQA-Br with the similar additive loading (381Lm−2h−1 and 150.2kDa). Therefore, the addition of TPPOQP-Br significantly enhances the water permeability while maintaining the excellent rejection properties in the resultant UF membranes. This work extends the choice of the additives in the UF membrane fabrication, and further proves that the addition of hydrophobic and charged polymer with slow hydration property is an effective strategy for improving flux and anti-biofouling properties of UF membranes.