Vacuum-treated titanium dioxide nanocrystals: Optical properties, surface disorder, oxygen vacancy, and photocatalytic activities

• Vacuum-treated TiO2 nanocrystals displayed apparent color changes.
• Ti3+ and oxygen vacancy defects existed in vacuum-treated TiO2 nanocrystals.
• Vacuum temperature had a complicated relationship with the defect contents.
• Oxygen vacancy benefited photocatalytic methylene blue (MB) decomposition.
• Oxygen vacancy and Ti3+ defects harmed the photocatalytic hydrogen generation.

In this study, we investigated vacuum-treated TiO2 nanocrystals. They displayed long-wavelength optical absorption due to the existence of oxygen vacancy and Ti3+ defects, and also possibly the surface structural disorder. Both oxygen vacancy and Ti3+ defects influenced the photocatalytic activities in methylene blue decomposition and hydrogen generation. Oxygen vacancy benefited photocatalytic methylene blue (MB) decomposition, but harmed the photocatalytic hydrogen generation. Ti3+ defects displayed a more complicated effect.

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