CO₂ Capture by As-Synthesized Amine-Functionalized MCM-41 Prepared through Direct Synthesis under Basic Condition

The as-synthesized amine-functionalized MCM-41 material was prepared through direct synthesis by co-condensation of tetraethyl orthosilicate (TEOS) with 3-aminopropyl triethoxysilane (APS) at different molar ratios and a pH of approximately 13 for CO2 capture under various CO2 concentrations, temperatures, and moistures. The prepared as-synthesized APS-functionalized MCM-41 (as-APS/MCM) possessed nitrogen content up to 3.46 mmol N/g and CO2 adsorption capacities up to 1.18 mmol/g under 15% CO2 in N2 at 35 °C and 1.74 mmol/g under pure CO2 at 25 °C. The CO2 adsorption capacity was 73% higher than the APS-grafted calcined MCM-41 prepared by postmodification. Because the CO2 adsorption capacity of the as-APS/MCM was found to come mainly from the coated APS rather than the incorporated APS, prehydrolysis of TEOS and post-treatment including template removal and APS neutralization were not required. Dynamic adsorption–desorption cycles revealed that the as-APS/MCM possessed high thermal stability for CO2 capture.