For
the understanding of the activity of TiO2 photocatalysts,
knowledge of the activities of different crystal facets is necessary.
This information can be achieved by the investigation of well-defined
single-crystalline TiO2 surfaces. In this study, the photocatalytic
activity of different anatase, brookite, and rutile single-crystal
wafers with only one exposed surface has been investigated via the
oxidation of methanol and the hydroxylation of terephthalic acid,
respectively. X-ray diffraction, atomic force microscopy, and scanning
electron microscopy measurements have shown that all surfaces are
clearly defined and possess a smooth surface, which allows a reliable
comparison of the photocatalytic activities. The investigated anatase
surfaces show higher activity than the rutile surfaces, while the
brookite surface is interestingly the least active one. To the best
of our knowledge, there are no other reports based on the investigation
and comparison of well-defined TiO2 anatase (100), anatase
(001), and brookite (100) single-crystalline surfaces concerning their
photocatalytic activity. Furthermore, the influence of the coordination
of the superficial titanium and the oxygen ions on the photocatalytic
activity is discussed.
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