Comparative analysis of amine-functionalized silica for direct air capture (DAC): Material characterization, performance, and thermodynamic efficiency

Direct air capture (DAC) technology faces challenges due to energy-intensive processes and limited CO2 capture capacity under atmospheric concentration. Utilizing adsorption techniques with solid sorbents offers a sustainable solution. This study investigates the performance, efficiency, and regeneration energy of various amines (TEPA, low and high molecular weights PEI and APTES) functionalized mesoporous silica (SBA-15) for DAC. Comprehensive investigations, including characterization and thermodynamic efficiency evaluation, are conducted for CO2 adsorption under dry and humid conditions (50 % RH). Functionalizing SBA-15 with TEPA, PEI-L and PEI-H, and TEPA significantly improves CO2 adsorption, increasing capacities to 2.1, 1.36, and 1.11 mmol/g, respectively, and introduction of humidity further increases CO2 capacities to 3.17, 2.87, and 1.68 mmol/g, respectively. However, there's a trade-off in thermodynamic efficiency due to energy consumed in desorbing water molecules. S-TEP exhibits the highest thermodynamic efficiency in dry conditions, while S-PEI-L achieves the highest efficiency in humid conditions. Stability tests of all material in addition to, the commercial material, lewatit demonstrate robust regenerability over 10 cycles under both dry and humid conditions (50 % RH). This study provides insights into functionalized SBA-15 performance in CO2 adsorption, with implications for efficient and sustainable indoor DAC processes.