Constructing Cu defect band within TiO₂ and supporting NiO nanoparticles for efficient CO₂ photoreduction

Effectively harnessing solar energy for the conversion of CO₂ into valuable chemical energy presents a viable solution to address energy scarcity and climate change concerns. Nonetheless, the limited light absorption and sluggish charge kinetics significantly hinder the photoreduction of CO₂. In this study, we employed a facile sol-gel method combined with wetness impregnation to synthesize Cu-doped TiO₂ coated with NiO nanoparticles. Various characterizations verified the successful incorporation of Cu ions into the TiO₂ crystal lattice and the formation of NiO co-catalysts within the composites. The optimal performance attained with CTN-0.5 demonstrates an output of 11.85 μmol h^-1 g^-1 for CO and 9.51 μmol h^-1 g^-1 for CH₄, which represent a 4.4-fold and 15.6-fold increase, respectively, compared to those achieved with pure TiO₂. The induced Cu defect band broadens the light absorption by decreasing the conduction band edge of TiO₂, while NiO upshifts the valence band of TiO₂ because of the interaction of valence orbitals. Light irradiation EPR and FTIR tests suggest that the collaboration of CuO and NiO promotes the formation of oxygen vacancies/defects and a rapid charge transfer pathway, thereby provides numerous active sites and electrons to enhance CO₂ photoreduction performance.