Cu2O/TiO2 heterostructures for CO2 reduction through a direct Z-scheme: Protecting Cu2O from photocorrosion

The development of artificial photosynthesis aims to solve the increasing energy demand and associated environmental problems. A model photosynthetic system employing a composite of semiconductors with a Z-scheme can potentially mimic the combined power of photosystems 1 and 2 to transfer electrons. In this work, octahedral cuprous oxide covered with titanium dioxide nanoparticles (Cu2O/TiO2) are synthesized by a solvothermal strategy that provides high morphological and crystallographic control. The formation of a p-n heterojunction and characterization of the Type II band alignment of the composite are performed by diffuse reflectance UV-visible (DRUV) spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). Upon UV-visible irradiation (λ ≥ 305 nm) of the composite in the presence of water vapor as the hole scavenger, the photoreduction of CO2(g) proceeds selectively to generate CO(g). The production rate of CO by the composite, RCO = 2.11 μmol gcat−1 h−1, is 4-times larger than for pure Cu2O under identical conditions. Contrasting XPS analyses of Cu2O and Cu2O/TiO2, during photocatalysts operation and the detection of photogenerated hydroxyl radicals (HO) in the heterostructure at variance with the results obtained for pure Cu2O are taken as evidences that TiO2 protects Cu2O from undergoing photocorrosion. These results provide direct evidence of an efficient Z-scheme as the main mechanism for harvesting energy during CO2 reduction in the synthesized materials.