Carbonic anhydrase, a biocatalyst that accelerates the hydration of carbon dioxide (CO2) to bicarbonate (HCO3-), is immobilized in the form of nanoscale enzyme reactors (NER) with the introduction of ammonium sulfate precipitation (P-NER). Magnetically-separable mesoporous silica (Mag-S-MCF) is used as carrier for enzyme immobilization, which allows magnet separation.
P-NER is prepared via a three-step process, enzyme adsorption, precipitation and crosslinking. The addition of precipitation step results in higher recovery of enzyme activity by integrating enzyme molecules during crosslinking step and forming stable enzyme aggregates on the surface of Mag-S-MCF. P-NER stabilizes enzyme activity under harsh shaking (200 rpm, 45° tilted), by achieving the half-life of 761.7 days, while the half-lives of its controls, enzyme adsorption in Mag-S-MCF (ADS) and NER, are 6.1 and 373.3 days, respectively.
Highly loaded and stabilized carbonic anhydrase is used for the conversion of CO2 to HCO3-, which is further transformed into calcium carbonate. After each cycle of reaction, P-NER is reused via magnetic separation. The reusability of P-NER after 10 cycles of uses is estimated as 89%, while ADS and NER show 35 and 79%, respectively. The present work suggests effective immobilization and stabilization approach of CA for the successful demonstration of biocatalytic CO2 conversion.
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