(201d) Carbonic Anhydrase-Based Nanocomposites for CO2 Conversion and Utilization

For the reduction of carbon dioxide (CO₂) in atmosphere, biocatalytic CO2 conversion has been considered as one of promising CO₂ reduction technologies. Carbonic anhydrase (CA) is an enzyme that can catalyze the hydration of CO₂ to bicarbonate (HCO₃^-) in a super-fast speed. However, the short lifetime of CA limits its practical application in CO₂ reduction. Here, we prepared CA-based nanocomposites for the stabilization of CA activity. Carboxylated polyaniline nanofibers (cPANFs) were synthesized by the copolymerization of aniline and 3-aminobenzoic acid. CA molecules were immobilized on cPANFs via the approach of enzyme precipitate coating (EPC) that consists of enzyme covalent attachment, precipitation and crosslinking. Amine-functionalized magnetic nanoparticles were also introduced to prepare magnetically-separable EPC (Mag-EPC) for the facile magnetic separation. Mag-EPC stabilized the CA activity, and its half-life was 236 days under rigorous shaking (200 rpm). Mag-EPC maintained more than 90% of its initial activity even after the ethanol sterilization for 300 minutes. The bicarbonate (HCO₃^-) solution from the CA-catalyzed atmospheric CO₂ conversion was utilized as a carbon feed for expedited microalgae growth. Mag-EPC enhanced the microalgae growth by 1.8-folds, which was maintained during the recycled uses of Mag-EPC for three times. Highly-stable and magnetically-separable Mag-EPC has successfully demonstrated its potential application for enzymatic CO₂ conversion and utilization, and its uses can be expanded to various other enzyme applications that are being hampered by poor enzyme stability.