Gas-Phase Photocatalytic Coprocessing of CO₂ - H₂O_(v) to Energy Products Promoted by the n,n-Junction In₂O₃@g-C₃N₄...

Carbon dioxide capture and utilization is a strategic technology for moving away from fossil-C. The conversion of CO₂ into fuels demands energy and hydrogen that cannot be sourced from fossil-C. Co-processing of CO₂ and water under solar irradiation will have a key role in the long-term for carbon-recycling and energy products production. This article discusses the synthesis, characterization and application of the two-phase composite photocatalyst, In₂O₃@g-C₃N₄, formed by thermal condensation of melamine in the presence of indium(III)nitrate. The composite exhibits a n,n-heterojunction between two n-type semiconductors, g-C₃N₄ and In₂O₃, leading to a more efficient charge separation. The composite has a flat band potential enabling it to effectively catalyze the reduction of CO₂ in the gas phase to produce CO, CH₄ and CH₃OH. While the composite's overall photocatalytic efficiency is comparable to that of neat g-C₃N₄, its ability to promote multielectron-transfer and Proton Coupled to Electron Transfer (PCET) suggests that there is a potential for further optimization of its properties. The use of labelled ¹³CO₂ has allowed us to clearly exclude that the reduced species are derived from the photocatalyst decomposition or the degradation of contaminants.