Preparation of pH-responsive asymmetric polysulfone ultrafiltration membranes with enhanced anti-fouling properties and performance by incorporating poly(2-ethyl-2-oxazoline) additive

Abstract

Inspired by the special pH value-responsive and strong hydrophilic ability of poly(2-ethyl-2-oxazoline) (PEOX), in this study, asymmetric polysulfone (PSf) and PSf/PEOX ultrafiltration membranes were prepared by a phase separation method, wherein different dosages of PEOX (0–3 wt%) were incorporated into the PSf casting solution as polymeric additives. The effects of PEOX dosages on the phase separation kinetics, chemical properties, morphology, hydrophilicity, porosity and performances such as pure water flux (PWF), Bull Serum Albumin (BSA) rejection, pH value responsiveness and anti-fouling property were investigated in detail. The hydrophilicity, pure water flux, BSA rejection and anti-fouling property were improved significantly after the incorporation of PEOX. The PWF increased from 213.5 L m⁻² h⁻¹ to 419.8 L m⁻² h⁻¹ as the PEOX dosage increased from 0 to 1 wt%, meanwhile, the BSA rejection increased to more than 98.4%. Viscosity and effective diffusion coefficient of PSf/PEOX solution were studied to elucidate the role of PEOX in phase separation and morphology of the membrane. Results showed that the incorporation of PEOX leads to the phase separation of casting solution by making it more prone to instantaneous demixing, further determining the morphology and performances of the membrane. Interestingly, the resulting membranes showed pH value-responsive properties, whereby the water flux increased along with an increase in the pH value. This interesting feature of the membranes broadens their application potential in many specific cases. The related filtration mechanism has also been proposed.