Design\nof Silica-Cobalt\nComposite Microporous Structures\nwith Dispersed Carbon Particles for Highly Permselective Gas Separation\nMembranes

Metal-doped silica membranes, fabricated\nvia the sol–gel\ntechnique using metal nitrates, hold promise for high-temperature\nseparation processes, such as H<sub>2</sub> separation in steam reforming\nreactions. However, controlling the status of the doped metal is challenging\nand often leads to defect formation owing to the aggregation of metal\noxides. In this study, we designed a uniform carbon–Co–SiO<sub>2</sub> ceramic membrane using a one-pot sol–gel method with\ncopolymerization, employing tetraethoxysilane and cobalt acetylacetone(III)\n(Co-(acac)<sub>3</sub>) as precursors. Organic chelate ligands within\nthe amorphous silica network formed by the polymerization reaction\nwere carbonized by calcination at 250–750 °C in an inert\natmosphere. This approach suppressed defect formation and tailored\nthe microporous structures to a wide range of separation systems.\nFor example, the SiO<sub>2</sub>–Co-(acac)<sub>3</sub> membrane\ncalcined at 550 °C demonstrated a notable C<sub>3</sub>H<sub>6</sub> permeance of 4.0 × 10<sup>–8</sup> mol m<sup>–2</sup> s<sup>–1</sup> Pa<sup>–1</sup> (GPU:\n120), with a high C<sub>3</sub>H<sub>6</sub>/C<sub>3</sub>H<sub>8</sub> selectivity of 46, attributed to the molecular sieving effect, whereas\nthe membrane calcined at 650 °C exhibited a remarkable He permeance\nof 4.6 × 10<sup>–7</sup> mol m<sup>–2</sup> s<sup>–1</sup> Pa<sup>–1</sup> (GPU: 1400), with a high He/CH<sub>4</sub> selectivity of 830. This study provides valuable insights\ninto the development of defect-free carbon–cation–SiO<sub>2</sub> ceramic membranes for a broad range of gas separation processes.