Polysulfone-titanium dioxide ultrafiltration membrane with enhanced fouling resistance for humic acid removal

Abstract

This study is aimed to prepare polysulfone ultrafiltration (PSF UF) membranes with enhanced fouling resistance for humic acid (HA) removal separations. The effect of the addition 2 wt. % of titanium dioxide (TiO2) in the dope formulation on the membrane performance and membrane morphology has been studied. Two types of UF membranes, i.e. PSF membranes with and without addition of TiO2 were prepared via a simple dry/wet phase inversion technique. The membranes were characterized using contact angle goniometer, x-ray diffractometer (XRD), differential scanning calorimeter (DSC), thermal gravitational analysis (TGA), field emission scanning electron microscopy (FESEM), ultrafiltration (UF) membrane system, molecular weight cut off (MWCO) and anti-fouling measurement. The separation performances of these membranes were evaluated using humic acid solution. The presence of TiO2 showed significant improvement in the properties of membranes such as hydrophilicity, thermal stabilities, mechanical properties, permeation and antifouling. Based on these aspects, the PSF membrane with TiO2 was chosen for further investigation by varying the air gap in the range of 0 – 13 cm. Results showed that the membrane prepared from zero air gap during hollow fiber spinning displayed the best performance in terms of water permeation and HA removal. This membrane was further used to investigate the effect of the physicochemical environment (pH and ionic strength) on HA rejection. pH and ionic strength of the feed solution played a significant impact on the HA removal since both of these factors would influence the solute-solute and solute-membrane interactions. A promising result was achieved with the average filtrate flux coupled with higher removal of HA around 10.5 x 10 -6 m3/m2.s and 97 %, respectively at pH 3 with 0.1 M ionic strength. This study indicated that membranes with the presence of TiO2 and fabricated from zero air gap exhibited the highest permeability coefficient, high humic acid removal, moderate high flux and significant enhancement of anti-fouling ability. Thus, this membrane is suitable to be used in surface water treatment with the optimal pH and ionic strength was 3 and 0.1 M NaCl to obtain the higher HA removal. This research is believed to contribute to the advancement in using membrane technology for water treatment.