Molecular separation using poly (styrene-co-maleic anhydride) grafted to Γ-alumina: Surface versus pore modification

Here, we report the covalent coupling of poly (styrene-co-maleic anhydride) onto γ-alumina to develop high-performance organic solvent nanofiltration (OSN) membranes. A high molecular weight (M_w) alternating copolymer of maleic anhydride (MA) and styrene (St) was synthesized and directly grafted to the γ-alumina membrane, while commercially available low M_w random copolymers of St and MA were also investigated. We show that solute rejection and membrane permeability strongly depend on the nature of the applied copolymer. In particular, the M_w of the copolymer applied is potentially the key for improving the membrane performance. When a high M_w copolymer was applied, the grafted layer covered the surface of the membrane. This results in membranes with significantly improved rejection, while maintaining a high permeability. In contrast, we observed pore grafting by applying low M_w copolymers, which resulted in membranes with slightly higher rejection and dramatically lower permeability compared to unmodified membrane. The best results were obtained by grafting γ-alumina with a high M_w alternating copolymer. These membranes showed a solute rejection of 98% for Sudan Black B (457 g mol⁻¹) in toluene, while the permeability remained high at 2.9 L m⁻² h⁻¹ bar⁻¹.