Impact of repeated temperature cycling on the low-concentration CO2 adsorption capacity of grafted silica-amine

The use of short-chain ethyleneimines (SCEI) and polyethyleneimines (PEI) as CO 2 sorbents has been extensively studied as a potential means of capturing carbon dioxide directly from the atmosphere. Previous work on such sorbents has focused on concentrated sources of CO 2 , such as found in combustion exhaust streams, as well as 400 µLL − 1 CO 2 concentrations more typical of the atmosphere. In this study, we examine changes in the adsorption properties and physical, chemical, and morphological changes induced in grafted SCEI, specifically diethyleneimine and triethyleneimine chains grafted onto two high surface- area silica supports, MCM-41 and SBA-15, when subjected to large numbers of thermal cycles in dry, CO 2 -free air. Emphasis is placed on the adsorption at 400 µLL − 1 CO 2 at 25 ◦C to study the potential suitability of similar grafted imine-containing systems for use as direct air capture (DAC) sorbents. For comparison, we also examine changes in the adsorption capacity at CO 2 concentrations of 5%, which are more typical of combustion exhaust. Notably, the low-concentration capacity is found to generally decrease faster than the capacity at the higher concentration with increased thermal cycling. All sorbents were found to decrease in adsorption capacity after a large number of cycles; however, DAS-derived sorbents were in general more robust. Moreover, the decrease in the CO 2 adsorption capacity at 25 ◦C before and after thermal cycling was found to vary significantly with the adsorptive concentration.