Metal-organic-framework protected multi-enzyme thin-film for the cascade reduction of CO2 in a gas-liquid membrane contactor

Abstract

Abstract Enzymatic reduction of CO2 through cascade reactions into useful chemicals or fuels is a promising option to reduce CO2 emission. However, the temperature of exhaust flue gas from power plants can reach temperatures as high as 150\xa0°C which would denature the enzymes. Recently, the biomineralization of thermally robust metal-organic framework (MOF) as a protective coating around enzymes have shown to improve its stability against harsh temperature conditions. This mimics the self-assembly process found in nature where enzymes can concentrate the framework building blocks and induce crystallization around the enzymes. In this work, we synthesised a UiO-66-NH2 thin film via a novel water-based, room temperature approach as well as a zeolitic imidazolate framework (ZIF-8) thin-film with two encapsulated enzymes, carbonic anhydrase and formate dehydrogenase. Both biocatalytic UiO-66-NH2 and ZIF-8 membranes exhibited excellent thermal stability even after treatment in boiling water for an hour where the bioactivity was essentially retained. The performance of the UiO-66-NH2 and ZIF-8 biocatalytic membranes in a gas-liquid membrane contactor showed formic acid yields of 13% (3.7\xa0μmol) and 22% (5.6\xa0μmol) respectively after 4\xa0h of catalysis, which is quite competitive to that reported in the literature. Furthermore, a synergistic effect for ZIF-8 and CA enzyme in the hydration of CO2 to bicarbonate due to the contribution of imidazole group was found to increase the overall catalytic activity by 1.6 folds compared to the case without ZIF-8. The biocatalytic UiO-66-NH2 membrane showed superior storage stability and reusability compared to biocatalytic ZIF membranes (ZIF-8, ZIF-L, ZIF-90), where 80.6% of the original enzyme activity can be retained after 10 catalysis cycles. This work demonstrates the potential of enzyme-MOF thin-film for enzymatic applications in aqueous solution at high temperatures.