Amine grafting of acid-activated bentonite for carbon dioxide capture

Abstract

A low-cost bentonite (ZBent) and acid-activated derived samples have been employed as clay adsorbents to assess their performance for pure CO2 adsorption in a thermogravemetric system. The raw bentonite reached a CO2 uptake of only 6.2 mg/g ads due to its low specific surface area and pore volume. After acid modification, an increase in its specific surface area and pore volume was observed, due to the leaching of octahedral cations and the generation of an amorphous silica phase. However, the degradation of the clay structure only improved slightly the adsorption of CO2. In a next step, raw and acid-treated clay minerals were functionalized with two different amine species (aminopropyl-trimethoxysilane; AP, and diethylene-triamine-trimethoxysilane; DT) by grafting. Unlike the case of DT species, the incorporation of AP moieties favored the chemical interaction between the amines species and the CO2 molecules in all cases. Functionalization with AP molecules increased the adsorption capacity of CO2 up to 29.2 mg/g ads at 30 °C for ZBent-24 h-AP, the material obtained after longer acid treatment time and functionalized with AP. AP-functionalized samples also had good stability and reusability during eight cyclic adsorption/desorption tests.