Capture and Sequestration of CO2 by Human Carbonic Anhydrase Covalently Immobilized onto Amine-Functionalized SBA-15

Human carbonic anhydrase (HCA) was immobilized onto mesoporous SBA-15 surfaces that had been covalently functionalized using one of three amine compounds, namely, tris(2-aminoethyl)amine (TAEA), tetraethylenepentamine (TEPA), and octa(aminophenyl)-silsesquioxane (OAPS). Amine functionalization over SBA-15 was characterized by XRD, FE-SEM, BET analysis, and Si-29 and C-13 CP MAS NMR spectroscopy. HCA immobilization was verified by FT-IR spectroscopy. The catalytic activity toward hydrolysis of p-nitrophenylacetate (p-NPA) was calculated for free and immobilized HCA. The k(cat) values for HCA/TEPA/SBA-15, HCA/TAEA/SBA-15, and HCA/OAPS/SBA-15 were found to be 7182, 7368, and 7569 M-1 s(-1) respectively. The activities of immobilized HCA were retained even after long-term storage, exposure to high temperatures, and reuse for 40 cycles. For comparison, CO2 hydration and sequestration were measured in the presence of both free and immobilized HCA. Importantly, the CO2 conversion efficiency was calculated using the ion chromatography method. The CO2 capture efficiency of immobilized HCA was 36 times higher than that of free HCA, and 75% of the initial enzymatic activity was retained through 40 cycles.