Deeping into the microporosity of porous silicates Ti- and Sn-umbite

The present study analyzes the microporosity of two isostructural microporous materials, Ti- and Sn-umbite, which possess a framework structure built of MO6 (M = Ti or Sn) octahedra and SiO4 tetrahedra. With this study, we try to cover the existing lack of information about their microporosity which cannot be evidenced with the most usual adsorption technique (i.e. N2 adsorption at −196 °C) because their small micropore opening. With such purpose, the present work addresses different data: water temperature programmed desorption (TPWD), CO2 adsorption at 0 and 25 °C, H2 adsorption at −196 °C, water adsorption, picnometry measurements (e.g. He and water density), thermogravimetry and X-ray diffraction analyses. The results obtained confirm that both Ti- and Sn-umbite materials have a narrow framework microporosity being for Sn-umbite higher than Ti-umbite. In summary, the water, H2 and CO2 adsorption characterization carried out reveals exceptional small (functional) pore size of umbite-type materials, approximately between water and H2 kinetic diameters for Ti-umbite (2.7–2.9 Å) and between CO2 and N2 kinetic diameters for Sn-umbite (3.3–3.6 Å).

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► Ti- and Sn-umbite have framework structures of MO6 octahedra and SiO4 tetrahedra.
► Ti- and Sn-umbite have a narrow microporosity, for Sn-umbite higher than for Ti-umbite.
► The pore size is between H2O and H2 kinetic diameters for Ti-umbite (2.7–2.9 Å).
► The pore size is between CO2 and N2 kinetic diameters for Sn-umbite (3.3–3.6 Å).