P25/PVC-g-POEM mixed matrix membranes with simultaneously improved permeability and selectivity for CO₂/N₂ separation

Conventional gas separation membranes have a trade-off relation between permeability and selectivity. Here, we report simultaneously improved permeability and selectivity through a mixed matrix membrane (MMM) consisting of P25 and amphiphilic graft copolymer. A graft copolymer composed of poly(vinyl chloride) (PVC) and poly(oxyeth-ylene methacrylate) (POEM) as the backbone and side chains, respectively, was synthesized. The glass transition temperature (T_g) of PVC-g-POEM decreased upon addition of P25, indicating a decrease in chain rigidity. The crystalline structure, d-spacing, morphology and thermal properties of membranes were characterized by X-ray diffraction (XRD), small angle X-ray scattering (SAXS), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Compared to pristine PVC-g-POEM, the CO₂ permeability through P25/PVC-g-POEM MMM increased by 122% from 46.2 to 102.8 Barrer, while the CO₂/N₂ selectivity increased by 32% from 29.6 to 39.1. The increased CO₂ permeability mostly resulted from increased diffusivity, while the increased selectivity was attributed to decreased solubility of N₂.