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Zusammenfassung:
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 O2 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.
