Optimization of surface silanol groups in mesoporous SBA-15 and KIT-6 materials: Effects on APTES functionalization and CO2 adsorption

Hybrid mesoporous silicas are potentially reusable promising adsorbents for CO₂ capture. Here SBA-15 and KIT-6 mesoporous silicas were synthetized by the sol-gel technique using a lower calcination temperature than the conventional one: 300 °C vs. 550 °C. This strategy aimed to maximize the surface hydroxyl group density and consequently, to improve functionalizing agent-loading performed by the post-synthesis grafting method. The as-obtained silica-based samples were then characterized and applied to CO₂ capture. A correlation between chemical-textural properties and adsorption capacities of pure and modified materials was discussed. The calcined at 300 °C silica supports, SBA-15-300-1 and KIT-6-300-1, with high silanol group densities showed better adsorption capacities overall pressure range. It is worth highlighting that the KIT-6-300-1: APTES adsorbent had a good stability performance, showing a drop of around 8 % over the aging time of a year. While, the SBA-15-300-1: APTES solid presented an excellent recycled performance after 10 adsorption-desorption cycles, maintaining about 95 % of its initial capacity.