(425g) Oxidation-Stable Propylamine-Grafted Mesoporous Silica Materials for CO2 Capture from Ambient Air

There is a broad scientific consensus that greenhouse gases (GHGs) trap heat in the atmosphere. From 1960 to 2024, the atmospheric concentration of CO₂, the most abundant anthropogenic GHG, increased from 320 to 425 parts per million by volume (ppmv). According to NASA, this increase contributed to the 1.2 °C increase in global temperature relative to the late 19^th-century average. To reduce CO₂ emissions, the U.S. Department of Energy (DOE) considers different strategies, namely switching to renewable energy, increasing energy efficiency, and carbon capture and storage/utilization. While most CO₂ capture efforts have been dedicated to large point sources such as fossil fuel power plants, CO₂ capture from the atmosphere, also known as direct air capture (DAC), has been gaining momentum recently. The DOE recognizes the critical role of DAC in addressing the climate crisis and achieving net-zero emissions by 2050. Owing to their superior performance, DAC applications involving cyclic adsorption-desorption of CO₂ by amine-functionalized silica materials (i.e., “aminosilica”) have attracted attention in recent years. To that end, the potential of propylamine-grafted silica materials for DAC applications was studied. A commercially available mesoporous silica was grafted with 3-aminopropyltrimethoxysilane (APTMS) using different amounts of amine and water to achieve varying amine loadings. Using thermogravimetric analysis (TGA), the materials were screened for equilibrium CO₂ uptake, amine efficiency, and adsorption kinetics in the presence of dry CO₂ (400 ppmv, balance nitrogen) at 25 °C. One best-performing material with the highest CO₂ uptake and fastest CO₂ adsorption kinetics was chosen for rigorous 50-cycle testing under the above adsorption conditions, followed by regeneration at 120 °C in the presence of air or N₂. In both cases, the results indicated stable performance as evidenced by maintaining 99% of the initial CO₂ uptake throughout cycling. Using column-breakthrough testing, the performance of the final candidate was also evaluated in the presence of humid CO₂, confirming previous reports that humidity boosts the CO₂ uptake of amine-modified materials. These results suggest the high potential of aminosilicas for DAC applications.