Effect of hydrophilic-hydrophilic interactions between the foulant and membrane surface on the fouling propensity of different foulants

Polyethersulfone (PES) membrane was grafted with sulfobetaine methacrylate (SBMA) zwitterion to obtain a membrane surface with improved hydrophilicity. Successful grafting was confirmed by FTIR-ATR, and grafting density was controlled by adjusting the 3-aminopropyltrimethoxysilane (APTMS)/ trimethoxy(propyl)silane (TMPS) ratio. The interactions between different foulants with the membrane surface were evaluated. Three different foulants, namely, humic acid (HA), bovine serum albumin (BSA), and sodium alginate (SA) were used to evaluate the anti-fouling properties of the grafted PES membrane. It was expected that increasing the surface hydrophilicity would decrease membrane fouling. However, a completely different trend of fouling propensity was observed for the three different foulants. For the grafted membrane with higher hydrophilicity, a considerable anti-fouling phenomenon property was observed when it was exposed to BSA. In contrast, when SA was used as the foulant, there was a slight increase in the anti-fouling propensity, and surprisingly, when HA was used, the modified hydrophilic membrane showed higher fouling than that of the pristine membrane. These results propose that the different trends of fouling are related to the interactions of the foulant molecules with the membrane material. Considering the hydrophilic nature of the HA and SA, and SBMA grafted on the membrane, it was concluded that the conventional approach of making a membrane surface hydrophilic by grafting to avoid its fouling by protein-type foulants may result in even worse results for some types of foulants such as SA and especially HA.