Photoinduced enzymatic conversion of CO2 gas to solar fuel on functional cellulose nanofiber films
Functional cellulose nanofiber films for the production of solar fuel from CO2 gas were prepared by immobilizing dendrimer and porphyrin derivative and loading an electron donor and enzymes (formate, aldehyde, and alcohol dehydrogenases) on the films. Porphyrin derivative is a photosensitizer, and the dendrimer plays the role of a reservoir of guest gases and carrier of electron/proton in addition to acting as an intermediate for the binding of porphyrin derivative on the nanofiber. However, after laser irradiation, whereas the remaining amount of gas on the film without an electron donor and enzymes was almost half of that without laser irradiation, it on the films loaded with an electron donor and enzymes was almost equal to or slightly higher than that without laser irradiation, whereas it was almost equal to or slightly higher than that on the films loaded with an electron donor and enzymes without laser irradiation. These results suggest the conversion of CO2 gas under laser irradiation. The conversion efficiency from CO2 to formic acid was only half because of the fact that only the adsorbed CO2 in the vicinity of the reaction system reacted; however, the conversion efficiencies from formic acid to formaldehyde and from formaldehyde to methanol were ∼80 and ∼90 wt%, indicating the successful stepwise conversion by the photoinduced enzymatic reaction.