CO₂ Adsorption Studies of Hydrophobic Silica Sorbent Functionalized with Silicone Oil-Amine Blends under Low-Temperature Conditions

CO2 uptake using multifunctional, porous solid sorbents has gained significant attention due to their high thermochemical stability and selectivity. In this study, hydrophilic nanosilica was functionalized with blends of silicone oil and amines to develop hydrophobic silica sorbents capable of adsorbing CO2 at low temperatures in the presence of moisture. The adsorption performance of these sorbents was evaluated at 35 and 40 °C using silicone oil blends containing monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA). Among these, the sorbent prepared with MEA, a primary amine, demonstrated the highest CO2 adsorption capacity. Further enhancement was achieved by functionalizing silicone oil with aminopropyltrimethoxysilane (APTMS). The optimized silica sorbent, with a 1:1 APTMS-to-silicone oil ratio, exhibited a maximum adsorption capacity of 0.75 and 0.86 mmol/g at 35 and 40 °C, respectively, and a water contact angle of 134°, achieving an optimal balance between hydrophobicity and amine reactivity. Their enhanced adsorption capacity and structural resilience suggest applications where intermittent moisture exposure may occur, such as indoor air purification systems, industrial enclosures, and controlled environments like greenhouses or cabin spaces. The hydrophobic surface is expected to improve durability and minimize water interference in such applications.