Black TiO2 samples with different concentrations of Ti3+ on the surface were fabricated by heat treatment in air. After heat treatment, the concentrations of Ti3+ on the surface of black TiO2 samples decreased and a layered structure was not observed. Oxygen vacancies were demonstrated to be the origin of visible light absorption. Ti3+ oxidation on the surface of black TiO2 samples caused the decrease of oxygen vacancies. In addition, black TiO2 samples with different Ti3+ concentrations showed differences in visible light absorbance, band gap, fate of photogenerated electrons, and photocatalytic activity. The optimum concentration of Ti3+ for achieving is shown to be the highest photocatalytic activity under the irradiation of visible light. (C) 2018 Elsevier Inc. All rights reserved.