Hydrophilic polyethyleneimine-TiO2 hybrid layer on polyethersulfone/sulfonated polysulfone blend membrane with antifouling characteristics for the effective separation of oil-in-water emulsions

Abstract

Polyethersulphone/sulfonated polysulfone/TiO2 (PES/SPSf/TiO2) ultrafiltration (UF) mixed matrix membranes (MMMs) were coated with a hybrid layer composed of branched polyethyleneimine (PEI) and TiO2 nanoparticles (NPs) crosslinked by glutaraldehyde (GA) to enhance its stability. The effect of TiO2 NPs loadings on the thickness, surface wettability, surface charge and molecular weight cut-off (MWCO) was explored. The corresponding MWCO decreased from 96 kDa for the pristine PES/SPSf/TiO2 MMM (M0) to 8.5 kDa for PEI-GA@MMMs (M1), and then gradually increased to the range of 15 kDa–40 kDa for PEI-TiO2/GA@MMMs. TiO2 NPs having abundant –OH groups also increased electronegativity and hydrophilicity of the composite membranes. At neutral pH, the zeta potential changed from negative charge of MMMs (−33 mV) into positive charge of M1 (1.3 mV), then into negative charge (−7.4 mV) in the optimum hybrid coated membrane PEI-TiO2 (0.025 wt%)/GA@MMMs (M3). The underwater oil contact angle (UWOCA) of with hexane, gasoline, dichloromethane and petroleum ether was 165°, 167°, 164° and 135°, respectively. The air/water contact angle (WCA) of M3 was 42°, which is lower than that of M1 (63°). It is important to note that M3 demonstrated a high rejection of different oil-in-water emulsions with <300 nm oil droplets (>90 %) and an improved pure water permeance of 62 LMH bar−1 compared to 44 LMH bar−1of M1. M3 also exhibited double the antifouling rates of M1 hence corroborating wettability and surface charge results. In summary, our current study provides an available tuning approach to engineering membranes for the treatment of oil-in-water emulsions containing nano-sized oil droplets.