Management on the location and concentration of Ti3+ in anatase TiO2 for defects-induced visible-light photocatalysis

Abstract

The defect-induced “black-and-white” issue of TiO2 keeps this material under spotlight in the past decade. This work exhibits an oxidation-based synthesis of anatase TiO2 nanocrystals with various Ti3+ concentrations via a solvothermal process in combination with post-annealing at different temperatures. Strikingly, we found that by simply controlling the annealing temperature, both concentration and location of the Ti3+ defects can be well managed to reside predominately in the subsurface/bulk regions of the post-annealed anatase TiO2 nanocrystals, a highly desired feature for stable visible light-active photocatalysis. The location and quantity of the Ti3+ in anatase nanocrystals pinpointed by X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) suggest that this temperature-mediated management of the location and concentration of Ti3+ defects is achieved through a Ti3+ reversible-diffusion mechanism. As an applicable verification, the sample attained by post-annealing treatment at 500°C, which has the highest Ti3+ concentration predominately in the bulk region, exhibits a 30-fold enhancement in visible-light decomposition of methylene blue and 4 times improvement in the maximal transient photocurrent density compared with P25. This work reveals that managing the location and concentration of Ti3+ defects in TiO2 is a decisive process toward defects-induced visible-light photocatalysis.