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Colored TiO2 has attracted enormous attention due to its visible light absorption and excellent photocatalytic activity. In this report, we develop a simple and facile solid-state chemical reduction approach for a large-scale production of colored TiO2 at mild temperature (300–350 °C). The obtained sample possesses a crystalline core/amorphous shell structure (TiO2@TiO2−x). The oxygen vacancy results in the formation of a disordered TiO2−x shell on the surface of TiO2 nanocrystals. XPS and theoretical calculation results indicate that valence band tail and vacancy band below the conduction band minimum appear for the TiO2−x, which implies that the TiO2@TiO2−x nanocrystal has a narrow band gap and therefore leads to a broad visible light absorption. Oxygen vacancy in a proper concentration promotes the charge separation of photogenerated carriers, which improves the photocatalytic activity of TiO2@TiO2 …