Positively Charged Polysulfone and Polyether Sulfone Mixed Matrix Membranes Modified with Polyethylenimine: Enhancing Heavy Metal Rejection and Antifouling Properties

In this study, a PSU or PES/Ox-CNT mixed matrix membrane with carboxylic functional groups on the surface underwent modification with polyethylenimine (PEI). The treatment resulted in the introduction of amine functional groups and the conversion of carboxylic acid to amide. The modification was confirmed through FT-IR and XPS, which showed the presence of amine functional groups on the membrane surface and the conversion of carboxylic acid to amide. The zeta potential of the modified membrane was more positive under acidic conditions due to the protonation of the amines on the membrane surface. A positive charge on the membrane surface improves the antifouling properties and enhances heavy metal rejection by electrostatic repulsion. The surface roughness slightly increased after the surface treatment, indicating the formation of amide linkages on the membrane surface. However, the bulk morphology of the membrane remained unchanged. The modified PSU/Ox-CNT membrane with PEI gave slightly improved heavy metal rejection and BSA rejection compared to the modified PES/Ox-CNT membrane with PEI, owing to the structural difference between them. For the same reason, the antifouling properties were enhanced. However, both membranes exhibited similar to 98% heavy metal rejection and similar to 95% BSA rejection, which were higher than those of the unmodified membranes. This has implications for applications such as water treatment, where the goal is to purify water by removing contaminants such as heavy metal ions.