(371b) Amine-Modified Silica Materials for Direct Carbon Dioxide Capture from the Atmosphere

The objective of this research is to develop adsorbent 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 2021, the atmospheric concentration of CO₂, the most abundant anthropogenic GHG, increased from 320 to 417 parts per million by volume (ppmv). According to NASA, this increase contributed to the 1.1°C increase in global temperature relative to the late 19^th century average. In 2018, the Intergovernmental Panel on Climate Change (IPCC) urged a 45% reduction in CO₂ emissions by 2030, relative to 2010 levels, to limit global warming to 1.5°C. To curb CO₂ emissions, the Blue Map Scenario of the International Energy Agency (IEA) recommends different strategies, including switching to renewable energy sources and implementing CO₂ capture technologies. 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 U.S. Department of Energy 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., “aminosilicas”) has attracted tremendous attention from the scientific community and industry alike. However, many relevant studies focus on near-equilibrium CO₂ uptake by aminosilicas, while treating adsorbent stability and adsorption kinetics as secondary factors, or totally disregarding them. While aminosilica stability determines its operational lifetime, fast adsorption kinetics is necessary to increase the amount of CO₂ captured per unit time. This research aims at taking an innovative approach by prioritizing adsorbent stability and fast adsorption kinetics over adsorption uptake, to develop highly efficient and durable aminosilicas for DAC applications. Aminosilicas were synthesized using (i) a commercially available mesoporous silica (G-10, Fuji Silycia), (ii) four polyamines, namely Tetraethylenepentamine (TEPA) and three branched Polyethylenimines (PEI) with different molecular weights (600, 1200, and 1800), and (iii) five levels of amine loadings (10-50 wt.%). The manipulation of synthesis conditions allowed for achieving a delicate balance between maximizing CO₂ uptake, facilitating adsorption kinetics, and maintaining material stability. All materials were evaluated using Thermogravimetric Analysis (TGA) to quantify amine loading, equilibrium CO₂ uptake, and CO₂ adsorption kinetics in the presence of dry CO₂ (400 ppmv, balance nitrogen) over a range of temperatures representing typical Florida conditions (e.g., 25-35°C). The performance of selected performant aminosilicas was assessed in the presence of humid CO₂. Finally, the long-term performance stability of the best-performing material was investigated over successive adsorption-desorption cycles.