The origin of enhanced photocatalytic activities of hydrogenated TiO nanoparticles.

The photocatalytic activity of semiconductors is largely governed by their light absorption, separation of photoinduced charge carriers and surface catalytically active sites, which are primarily controlled by the morphology, crystalline size, structure, and especially the electronic structure of photocatalysts. Black TiO is recognized as one of the most promising visible-light photocatalysts, due to its significantly enhanced visible-light photocatalytic performance in comparison to intrinsic TiO. In this work, black TiO is synthesized through the hydrogenation process. The sample shows a TiO@TiO core/shell structure which is attributed to hydrogenation. By using X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and nuclear magnetic resonance (NMR) spectroscopy, we identified the featured midgap electronic states in black TiO, which gave rise to the TiO shell layer. These states lead to the improvement of visible-light absorption and the separation of photoinduced charge carriers, which consequently result in remarkable enhanced photocatalytic activities in black TiO.