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 (Mw) alternating copolymer of maleic anhydride (MA) and styrene (St) was synthesized and directly grafted to the γ-alumina membrane, while commercially available low Mw 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 Mw of the copolymer applied is potentially the key for improving the membrane performance. When a high Mw 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 Mw 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 Mw 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. [Display omitted] •Optimal selective layer structure of hybrid ceramic-polymeric membrane has been explored.•Grafted membranes exhibited excellent performance compared to state-of-the-art membranes.•Membrane grafted with high molecular weight copolymer showed higher permeability and rejection.