Trimodal nanoporous silica as a support for amine-based CO2 adsorbents: Improvement in adsorption capacity and kinetics

A trimodal nanoporous silica (TS) having unique trimodal pore structure viz., internal mesopores, textural mesopores and interconnected macropores, has been functionalized with amine using two different methods covalent grafting and wet impregnation. Both were studied as nanocomposite sorbents for CO 2 capture. The effects of the amine loading, immobilization processes and the type of support were investigated. Commercially available silica gel (SG) with a purely mesoporous structure was studied as the support for the amine in order to compare differences in pore structure and amine loading with differences in CO 2 adsorption capacity and kinetics. Amine-grafted TS exhibited much faster CO 2 adsorption kinetics at 35   °C than amine-grafted SG. At the same amine loading, amine-impregnated TS showed higher CO 2 adsorption capacity and faster CO 2 adsorption kinetics than amine-impregnated SG. The CO 2 adsorption capacity of amine-impregnated TS increased as the amine loading increased until 70%, with the highest value of 172   mg/g, while the amine-impregnated SG reached the highest CO 2 adsorption capacity of only 78   mg/g at 40% amine loading. More importantly, amine-impregnated as-prepared TS exhibited even higher CO 2 capture capacity than amine-impregnated TS when the amine loading was below 60%. Results suggest that amine-modified trimodal nanoporous silica sorbents meet the challenges of current CO 2 capture technology.