Study on the immobilization of carbonic anhydrases on geopolymer microspheres for CO2 capture

Abstract

The present study entails the immobilization of carbonic anhydrases on geopolymer microspheres and the CO2 capture and sequestration performance of immobilized enzyme. The optimum immobilization conditions were found out to be (a) pH value, 8.0; (b) temperature, 30 °C; (c) incubation duration, 2 h; (d) geopolymer microspheres dose, 100 mg; (e) glutaraldehyde concentration, 0.2 wt%; (f) cross-linking duration, 1 h. Compared with free enzyme, the optimum pH of the immobilized carbonic anhydrases increased from 7.5 to 8.0 and the optimum temperature increase from 25 °C to 30 °C. The thermal stability of immobilized enzyme was better than its free counterpart. The storage stability of the immobilized enzyme at different temperatures was improved, and the relative activity of the enzyme remained 46.1% after five cycles of continuous operation. The Michaelis constant (Km) and Vmax of free carbonic anhydrases were determined to be 7.6283 mM and 1.6011 mM min−1, while that of the immobilized enzyme were 21.549 mM and 5.0525 mM min−1, respectively. The overall activity (Kcat/Km) of them were 61.5015 and 12.3593 M−1 s−1, respectively. The catalytic performance of immobilized carbonic anhydrases was investigated by carrying out the CO2 adsorption assay. Detailed parameters like temperature, gas flow and enzyme dose were explored. The carbonation study was also performed to demonstrate the feasibility of converting CO2 into bicarbonate. The carrier, the immobilized enzyme and the precipitate were characterized by various techniques like XRD, SEM, EDS, etc. It appeared to us that the immobilization of carbonic anhydrases on geopolymer microspheres represented a potential strategy for tackling the intrinsic fragile nature of enzyme and was potential in promoting the capture and sequestration of CO2 in a biological route.