Probing the formation and optical properties of Ti3+-TiO2 with (001) exposed crystal facet by ethanol-assisted fluorination

In TiO2 based photocatalysis, it is crucial to conceal the catalytically active Ti3+ defect sites inside the crystal, since the Ti3+ defects on the surface can be rapidly lost after capturing O-2 molecules in the air. In this work, we report a novel method to synthesize TiO2 with Ti3+ defects that are exclusively embedded in the bulk lattice near the surface. We show that the binary synthetic system consisting of ethanol and HF is indispensable for the precise location control of the formed Ti3+ defects, and the near-surface bulk Ti3+ defects can only be formed under the coexistence of both these reagents. The underlying mechanism of achieving such remarkable control of the position of the Ti3+ defect sites was clarified by extensive analysis through X-ray diffraction, electron microscopy, electron spin resonance, X-ray photoelectron spectroscopy, as well as theoretical simulation using the DFT+U method. We show that ethanol plays a crucial role in assisting fluorine atoms adsorbing on the exposed (001) crystal facets, penetrating the near-surface bulk lattice and inducing Ti3+ defect formation via substitution of oxygen atoms.

Automated summary

This work presents a novel method for synthesizing TiO2 with Ti3+ defects exclusively embedded in the bulk lattice near the surface. The presence of both ethanol and HF is essential for precise location control of the formed Ti3+ defects. Extensive analysis using various techniques and theoretical simulation clarify the mechanism behind the precise control of the Ti3+ defect sites.