TiO/TiO heterophase junctions with enhanced charge separation and spatially separated active sites for photocatalytic CO reduction.

It is strongly desired to develop highly active photocatalysts for CO reduction by accelerating charge separation and realizing spatially separated active sites. In this work, TiO/TiO heterophase junctions with enhanced charge separation and spatially separated active sites were facilely prepared via in situ thermal oxidation of commercial TiO in air at an appropriate annealing temperature. The as-prepared TiO/TiO heterophase junctions, especially the temperature-optimized T550 sample, displayed high photocatalytic activity for CO reduction to yield CH (∼0.65 μmol g h), CO (∼2.64 μmol g h) and O (∼5.66 μmol g h), which was 4 times higher than that of bulk TiO and nearly 2 times higher than that of rutile TiO. Based on the surface photovoltage spectra, related produced OH radical measurement and electrochemical reduction, the high photoactivity could be attributed to the metallic TiO, which trapped the photogenerated electrons from TiO through the formed TiO/TiO heterophase junctions to enhance charge separation. Remarkably, it was confirmed from theoretical calculations based on density functional theory, Kelvin probe and CO-TPD measurements that the TiO/TiO heterophase junction possesses spatially separated active sites for CO reduction and water oxidation. Metallic TiO as a reduction site activated and catalyzed CO to produce solar fuels such as CO and CH, while TiO as an oxidation site oxidized HO to produce O and protons. The designed concept of heterophase junctions and simultaneously activating CO and HO at different spatial sites may offer a new strategy to suppress the reverse reactions during photocatalysis for efficient solar energy conversion.