Synthesis of ordered Ca- and Li-doped mesoporous silicas for H2 and CO2 adsorption at ambient temperature and pressure

Abstract

Ca- and Li-doped mesoporous silicas have been prepared successfully using cetyltrimethylammonium bromide (CTAB) surfactant in basic media. Sol–gel synthesis and hydrothermal treatment produced highly ordered mesoporous Ca and Li loaded silica particles. The MCM-41 type mesostructures, the porosity, the pore sizes as well as the surface area of Ca- and Li-silicas have been thoroughly investigated using small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N₂ sorption analysis. Samples prepared with varying amounts of Li and Ca loading have been further analyzed using inductive coupled plasma-atomic emission spectroscopy (ICP-AES) and field-emission scanning electron microscopy (FESEM) with an energy dispersive spectral attachment (EDS), which confirmed quite a large amount of Ca while the amount of Li was not enough. Additionally, H₂ and CO₂ gas uptake studies of these metal-loaded silicas have been carried out using a thermogravimetric analyzer (TGA) at normal temperature (25 °C) and pressure (1 atm). H₂ uptake of up to 10 mmol g⁻¹ by Ca-doped silica was recorded. CO₂ and H₂ selectivity were tested with both pure metal-MCM-41 and amine loaded silica using pure N₂ gas and a mixed flow of CO₂/N₂ and H₂/N₂. The effect of temperature on CO₂ uptake was also studied using Ca-MCM-41 materials.