Oxygen vacancy self-doped black TiO2 nanotube arrays by aluminothermic reduction for photocatalytic CO2 reduction under visible light illumination

In this work, black titania nanotube arrays (B-TiO2 NTAs) were prepared by aluminothermic reduction of anodized TiO2-NTAs. It was found that the oxygen partial pressure atmicro-region of TiO2-NTAs surfacewas critical for the creation of black TiO2 NTAs. The oxygen vacancies in the prepared B-TiO2 NTAs induced new defect energy levels in the band gap of TiO2, which reduced the band gap and broadened their visible light absorption. Furthermore, the oxygen vacancies could also act as the catalytic sites and accelerate surface reactions for the photocatalytic reduction of CO2 to CO, which also was proved by isotope experiment. Especially, B-TiO2 NTAs annealed at 600 degrees C showed an excellent photocatalytic CO2 reduction to CO performance with the yield of 185.39 mu mol g(-1)h(-1) under visible light illumination because the oxygen vacancy self-doping largely enhanced three key factors in this process, including photoinduced charge generation, charge separation and transportation and interfacial reaction. This facile and versatile method could be potentially used for large scale production of colored TiO2 with a high photocatalytic CO2 reduction capability in the visible light illumination.