(284f) Thermal Treatments to Improve the CO2 Capacity of Grafted Amine Sorbents

Reducing emissions alone is no longer feasible to meet net-zero greenhouse gas emission goals and CO₂ removal technologies, such as direct air capture (DAC) from the atmosphere, are required. While multiple materials have been investigated for DAC, amine-grafted solid sorbents are of particular interest for their strong, yet reversible binding of CO₂ at atmospheric conditions, mild regeneration conditions, diversity of structure, and ease of fabrication. This study investigates the effect of elevated thermal treatments on the CO₂ capacity of aminosilane-grafted SBA-15 silica sorbents under DAC conditions. Exposing samples to temperatures higher than required for a typical degas (200–250 ºC compared to 80–120 °C) in an inert environment resulted in improved CO₂ capacity (5–21%) that was sustained over multiple adsorption/desorption cycles. The origins and limitations of this phenomenon are explored through elemental analysis, thermogravimetric analysis, mass spectrometry, and diffusive reflectance infrared Fourier transform spectroscopy. The thermal treatments improve the CO₂ adsorption capacity through a combination of desorbing strongly chemisorbed CO₂, freeing additional silanols on the silica surface, and increasing the amine efficiency through favoring carbamic acid binding; however, these enhancements need to be balanced against the higher propensity for thermal degradation at elevated temperatures. The marked increase in CO₂ sorption was consistent across multiple amine types, grafting densities, and oxide supports. These findings offer new insights into the CO₂ adsorption behavior of amine-grafted sorbents and highlight the importance of processing parameters on maximizing material performance.