Spontaneously self-assembled dual-layer mixed matrix membranes containing mass-produced mesoporous TiO₂ for CO₂ capture

Herein, a high performance mixed matrix membrane (MMM) is reported, through control of the solvent evaporation rate based on the spontaneous self-assembly of mesoporous TiO₂ (m-TiO₂) fillers in a poly(vinyl chloride)-g-poly(oxyethylene methacrylate) (PVC-g-POEM) graft copolymer matrix. In particular, a facile, non-hydrothermal and mass-producible preparation method for m-TiO₂ is described. Slow solvent evaporation resulted in the formation of dual-layer MMMs consisting of a top PVC-g-POEM rich layer over a bottom m-TiO₂ rich layer, whereas fast evaporation led to the case of single-layer MMMs. Both CO₂ permeability and CO₂/N₂ selectivity increased as the m-TiO₂ content increased up to 20 wt% for single-layer as well as dual-layer MMMs, due to loose packing structures and increased chain flexibility. However, above 20 wt% loading, dual-layer MMMs exhibited much higher CO₂ permeabilities and CO₂/N₂ selectivities than single-layer MMMs, resulting from self-assembled dual-layer architecture as well as better interfacial adhesion properties. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and density measurements revealed that the PVC-g-POEM graft copolymer chains penetrated into the m-TiO₂ rich layer to generate web-like interconnected structures, forming proper pore sizes for selective CO₂ transport. The dual-layer MMMs exhibited excellent improvements in CO₂ permeability of over 3000% from 46.2 to 1430.9 Barrer (1 Barrer = 1×10^-10 cm³ (STP) cm /cm² s cmHg) with a CO₂/N₂ selectivity of 22.4, which was only slightly below the upper bound (2008).