Enzyme-based CO2/N-2 separation nano-membrane via optimization of carbonic anhydrase-functionalized graphene oxide

Protein-based biomass materials are resource-saving and environment-friendly. Especially, carbonic anhydrase (CA) is an enzyme that catalyzes the conversion of carbon dioxide (CO2) into bicarbonate (HCO3-). Recent studies focused on utilizing CA for a CO2 capture application; however, its application is limited due to its low stability and requirement of water molecules for hydration of CA. In this study, CA was immobilized onto a graphene oxide (GO) sheet by two kinds of adsorption mechanism-physisorption and chemisorption to investigate what interaction is more effective for separation. Depending on the adsorption mechanism, CA position on GO and enzymatic activity of CA can be regulated. Physically interacted or chemically reacted GO-CA was used to prepare a nanoscale multilayer structure with layer-by-layer (LbL) assembly. The physically interacted GO-CA (Ph-GO-CA) nano-membrane has CO2 capture properties (N-2/CO2 selectivity 4.19) that can be attributed to the enlarged interlayer spacing and catalytic conversion of CA molecules. However, Ch-GO-CA nano-membranes rarely capture CO2 gas and have a low N-2/CO2 selectivity. Therefore, Ph-GO-CA is more effective than Ch-GO-CA for capturing CO2 gas.