Abstract
The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. The anatase TiO2(001) and its (1 × 4) reconstructed surfaces were theoretically considered to be the most reactive and have been heavily pursued by synthetic chemists. However, the lack of direct experimental verification or determination of the active sites on these surfaces has caused controversy and debate. Here we report a systematic study on an anatase TiO2(001)-(1 × 4) surface by means of microscopic and spectroscopic techniques in combination with first-principles calculations. Two types of intrinsic point defects are identified, among which only the Ti3+ defect site on the reduced surface demonstrates considerable chemical activity. The perfect surface itself can be fully oxidized, but shows no obvious activity. Our findings suggest that the reactivity of the anatase TiO2(001) surface should depend on its reduction status, similar to that of rutile TiO2 surfaces.
Highlights
The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades
We systematically investigate the structures and the reactivity of the oxidized and reduced (1 Â 4) reconstructed surfaces of anatase TiO2(001) thin films epitaxially grown on SrTiO3 using scanning tunnelling microscopy (STM) or scanning tunneling spectroscopy, X-ray/ultraviolet photoemission spectroscopy (XPS/UPS) and first-principles calculations
TiO2 films with a typical thickness of 30–60 nm were grown on Nbdoped SrTiO3(001) substrates at various temperatures under an O2 pressure of 1.5 Â 10 À 3 Pa
Summary
The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. We systematically investigate the structures and the reactivity of the oxidized and reduced (1 Â 4) reconstructed surfaces of anatase TiO2(001) thin films epitaxially grown on SrTiO3 using scanning tunnelling microscopy (STM) or scanning tunneling spectroscopy, X-ray/ultraviolet photoemission spectroscopy (XPS/UPS) and first-principles calculations. At a temperature of 80 K, the Ti-rich point defects at the ridge in the reduced surface can act as chemically active sites for H2O and O2 molecules. The Ti-rich point defects on the reduced surface are fourfold-coordinated, that is, Ti3 þ sites. This model provides consistent explanations for our experimental findings from microscopic and spectroscopic measurements
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