Biomimetic Sequestration of CO2 and Reformation to CaCO3 Using Bovine Carbonic Anhydrase Immobilized on SBA-15

The biocatalytic capture of CO2, and its precipitation as CaCO3, over bovine carbonic anhydrase (BCA) immobilized on a pore-expanded SBA-15 support was investigated. SBA-15 was synthesized using TMB as a pore expander, and the resulting porous silica was characterized by XRD, BET, IR, and FE-SEM analysis. BCA was immobilized on SBA-15 through various approaches, including covalent attachment (BCA-CA), adsorption (BCA-ADS), and cross-linked enzyme aggregation (BCA-CLEA). The effects of pH, temperature, storage stability, and reusability on the biocatalytic performance of BCA were characterized by examining para-nitrophenyl acetate (p-NPA) hydrolysis. The Kcat/Km values for p-NPA hydrolysis were 740.05, 660.62, and 680.11 M−1 s−1, respectively, whereas the Kcat/Km value for free BCA was 873.76 M−1 s−1. The amount of CaCO3 precipitate was measured quantitatively using an ion-selective electrode and was found to be 12.41, 11.82, or 11.28 mg CaCO3/mg for BCA-CLEA, BCA-ADS, or BCA-CA, respectively. The present results indicate that the immobilized BCA-CLEA, BCA-ADS, and BCA-CA are green materials, and are tunable, reusable, and promising biocatalysts for CO2 sequestration.