Development of Amino-Functionalized Silica by Co-condensation and Alkylation for Direct Air Capture

CO₂ chemisorption using amine-based sorbents is one of the most effective techniques for carbon capture and storage. Solid CO₂ sorbents with amines immobilized on their surface have been attracting attention due to the easy collection of sorbents and reusability. In this study, we developed a solid CO₂ adsorbent by co-condensation of a silanizing reagent having a chloroalkyl group and tetraethyl ethoxysilane, followed by alkylation of the chloroalkyl group with diamine. The fabricated amine-immobilized silica with a high density of amino groups on its surface achieved the chemical adsorption of 400 ppm of CO₂ with 4.3 wt_CO2 % loading, CO₂ release upon heating at 80 °C, and reusability for adsorption and desorption cycles with high amine utilization efficiency (0.20 mol_CO2/mol_–N). This surface modification method is applicable to various amines bearing more than two amino functional groups, enabling the development of solid CO₂ sorbents for the selective capture of low-concentration CO₂ directly from the air.