Nanocomposites with Graft Copolymer-Templated Mesoporous MgTiO₃ Perovskite for CO₂ Capture Applications

Mesoporous MgTiO₃ perovskite with a high porosity and interfacial properties were synthesized via a solvothermal reaction at 150 °C for 10 h using a graft copolymer, i.e., poly­(vinyl chloride)-g-poly­(oxyethylene methacrylate) (PVC-g-POEM) with a well-ordered micellar morphology as a structure-directing agent. A PVC-g-POEM graft copolymer with a wormlike morphology was utilized as a soft matrix to prepare a mixed matrix membrane (MMM) with mesoporous MgTiO₃ perovskite through a solution-casting method. The structure and morphology of PVC-g-POEM graft copolymer was carefully tuned by controlling polymer-solvent interactions, as characterized by transmission electron microscopy (TEM). The average pore diameter of the MgTiO₃ perovskite was 10.4 nm, which is effective in facilitating gas transport via Knudsen diffusion through mesopores as well as improving interfacial contact with the organic polymer matrix. Because of a high porosity (0.56), the density of mesoporous MgTiO₃ (1.75 g/cm³) was much lower than that of dense nonporous MgTiO₃ (4 g/cm³) and not significantly higher than that of PVC-g-POEM (1.25 g/cm³), leading to a uniform distribution of MgTiO₃ in MMM. The permeability of MMM with MgTiO₃ was greater than those of MMM with only MgO or TiO₂, indicating the simultaneous improvement of solubility and diffusivity in the former, as supported by CO₂ temperature-programmed desorption (TPD) measurements. The MMM with MgTiO₃ 25 wt % exhibited a CO₂ permeability improvement of 140% up to 138.7 Barrer (1 Barrer = 1 × 10^–10 cm³(STP) cm cm^–2 s^–1 cmHg^–1) without a large loss of CO₂/N₂ selectivity.