Highly Enhanced Photoactivity of Anatase TiO₂ Nanocrystals by Controlled Hydrogenation-Induced Surface Defects

Abstract

Anatase TiO₂ nanocrystals (aTiO₂) of a uniform size have been synthesized and were subject to a successive hydrogenation under a H₂ gas flow at elevated temperatures (500–700 °C). We found that the concentration of Ti³⁺ defects, such as Ti³⁺ interstitials and oxygen vacancies, and their distribution between surface and bulk varied significantly, depending on the hydrogenation temperature and time. Such changes in defects were found to be critical in enhancing the photoactivity of the hydrogenated TiO₂ (H-aTiO₂) by an order of magnitude. In our case, H-aTiO₂ nanocrystals hydrogenated at 600 °C for longer than 10 h showed 10 times higher photoactivity than aTiO₂, which was explained from a high surface-to-bulk defect ratio and a nonuniform distribution of defects between bulk and surface due to a preferential diffusion of bulk defects to the surface. Our study showed that a kinetically controlled hydrogenation condition could be used not only to control the surface/bulk defects but also to enhance the photoactivity of oxide nanocrystals