Morphology-dependent defect structures and photocatalytic performance of hydrogenated anatase TiO2 nanocrystals

• Defect structures and distributions of hydrogenated TiO2 depend on the morphology.
• Defects of hydrogenated TiO2-{0 0 1} are mainly located in the subsurface/bulk region.
• Defects of hydrogenated TiO2-{1 0 0} and TiO2-{1 0 1} are located on the surface and in the subsurface/bulk region.
• An electric field form between the stoichiometric surface and the reduced subsurface for hydrogenated TiO2-{0 0 1}.
• Hydrogenated TiO2-{0 0 1} with an electric field exhibits enhanced charge separation processes and photocatalytic activity.

Effects of hydrogenation treatments on the structure and the photocatalytic performance in water reduction of anatase TiO2 nanocrystals with various morphologies were studied and strong morphology/facet-dependent effects were demonstrated. F1+ color centers and Ti3+ species are created by hydrogenation treatments of TiO2 nanocrystals predominantly enclosed with the {0 0 1} facets (TiO2-{0 0 1}) and are mainly located in the subsurface/bulk region; O2− species, F1+ color centers, Ti3+ species, and Ti4+–O radical species are created in TiO2 nanocrystals predominantly enclosed by the {1 0 0} facets (TiO2-{1 0 0}) and located from the surface to the subsurface/bulk region; and O2− species, F1+ color centers, and Ti3+ species are created in TiO2 nanocrystals predominantly enclosed by the {1 0 1} facets (TiO2-{1 0 1}) and located from the surface to the subsurface/bulk region. The created defects enhance the light absorption/charge creation of TiO2 nanocrystals but also the charge recombination probabilities, and hydrogenated TiO2-{1 0 0} and TiO2-{1 0 1} nanocrystals exhibit photocatalytic activity similar to that of the corresponding TiO2 nanocrystals. However, an electric field was found to form between the stoichiometric surface and the defective subsurface for hydrogenated TiO2-{0 0 1} nanocrystals. This facilitates charge separation and leads to much higher photocatalytic activity of hydrogenated TiO2-{0 0 1} nanocrystals than of TiO2-{0 0 1} nanocrystals. These results not only shed light on the fundamental understanding of hydrogenated TiO2 photocatalysts but also demonstrate hydrogenated TiO2-{0 0 1} nanocrystals as highly active photocatalysts, nicely exemplifying the concept of morphology engineering as an effective approach to both fundamental studies of oxide catalysis and optimizations of oxide catalysts.

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