Carbonic anhydrase conjugated to nanosilver immobilized onto mesoporous SBA-15 for sequestration of CO2

Human carbonic anhydrase (HCA) was conjugated via electrostatic interactions onto silver nanoparticles confined to amine-functionalized mesoporous SBA-15. Three amine compounds were tested for their effectiveness in immobilizing silver nanoparticles: tris(2-aminoethyl)amine (TAEA), tetraethylenepentamine (TEPA), and octa(aminophenyl)silsesquioxane (OAPS). The enzymatic activities of the free and nanosilver conjugated HCA were assessed by measuring the hydrolysis of p-nitrophenylacetate (p-NPA) and the hydration of CO2, which was sequestered as CaCO3. The CO2 conversion efficiency was calculated using ion chromatography methods, and CaCO3 formation was observed by polarized light microscopy. Precipitated CaCO3 was characterized by XRD and FE-SEM. After 30 cycles, the silver conjugated HCA showed the highest operational stability, and the CO2 capture efficiency was ∼25 fold higher than that of free HCA. Storage stability studies suggested that conjugated HCA retained nearly 87% of its activity after 30 days. The results demonstrated that immobilized HCA was reusable and stable under storage conditions. Thus, this nanobiocatalyst is a suitable candidate for the capture and sequestration of CO2.