Comproportionation of CO₂ and Cellulose to Formate Using a Floating Semiconductor-Enzyme Photoreforming Catalyst

Formate production via both CO₂ reduction and cellulose oxidation in a solar-driven process is achieved by a semi-artificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO₂ |FDH) producing up to 1.16±0.04 mmol_formate  g $$ ^-1 in 24 hours at 30 °C and 101 kPa under anaerobic conditions. Isotopic labeling experiments with ¹³ C-labeled substrates support the mechanism of stoichiometric formate formation through both redox half-reactions. TiO₂ |FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmol_formate per m² irradiation area after 24 hours. This work demonstrates the synergistic solar-driven valorization of solid and gaseous waste streams using a biohybrid photoreforming catalyst in aqueous solution and will thus provide inspiration for the development of future semi-artificial waste-to-chemical conversion strategies.