Development of\nAmino-Functionalized Silica by Co-condensation\nand Alkylation for Direct Air Capture

CO<sub>2</sub> chemisorption using amine-based sorbents\nis one\nof the most effective techniques for carbon capture and storage. Solid\nCO<sub>2</sub> sorbents with amines immobilized on their surface have\nbeen attracting attention due to the easy collection of sorbents and\nreusability. In this study, we developed a solid CO<sub>2</sub> adsorbent\nby co-condensation of a silanizing reagent having a chloroalkyl group\nand tetraethyl ethoxysilane, followed by alkylation of the chloroalkyl\ngroup with diamine. The fabricated amine-immobilized silica with a\nhigh density of amino groups on its surface achieved the chemical\nadsorption of 400 ppm of CO<sub>2</sub> with 4.3 wt<sub>CO<sub>2</sub></sub> % loading, CO<sub>2</sub> release upon heating at 80 °C,\nand reusability for adsorption and desorption cycles with high amine\nutilization efficiency (0.20 mol<sub>CO<sub>2</sub></sub>/mol<sub>–N</sub>). This surface modification method is applicable\nto various amines bearing more than two amino functional groups, enabling\nthe development of solid CO<sub>2</sub> sorbents for the selective\ncapture of low-concentration CO<sub>2</sub> directly from the air.