Modification of NiTiO3 visible light-driven photocatalysts by Nb doping and NbOx heterojunction: Oxygen vacancy in the Nb-doped NiTiO3 structure

•Nb-doped NiTiO3 and NbOx/NiTiO3 photocatalysts are prepared with various Nb amounts.•Nb-doped NiTiO3 exhibits higher photocatalytic activity than pure NiTiO3.•Incorporation of Nb into the NiTiO3 lattice induces Ti3+ sites and oxygen vacancies.•High Nb doping into NiTiO3 results in formation of a triple metal oxide phase.•Inappropriate band structures of NbOx and NiTiO3 decrease photocatalytic activity. [Display omitted] In this study, two types of niobium-containing NiTiO3 photocatalysts — Nb-doped NiTiO3 and NbOx/NiTiO3 heterojunction — were prepared with different Nb contents to enhance photocatalytic activity for dye photodegradation under sunlight irradiation. Nb-doped NiTiO3 exhibited higher photocatalytic activity than pure NiTiO3, whereas the heterojunction of NbOx with NiTiO3 caused a decrease in photocatalytic activity. The incorporation of Nb into the NiTiO3 lattice structure induced the formation of Ti3+ and Nb3+ sites, which considerably increased the number of oxygen vacancies in those photocatalysts; this conclusion was confirmed by the results of X-ray photoelectron spectroscopy. Eventually, the Nb-doped NiTiO3 photocatalyst at the highest Nb content (NT-Nb-10) was transformed into a triple metal oxide phase with the highest surface area and oxygen vacancy. The abundant oxygen vacancy of NT-Nb-10 resulted in the lowest photoluminescence emission intensity, which resulted in the highest apparent photocatalytic reaction rate constant (kapp) of 14.1 min−1 owing to the suppression of the recombination process. The formation of the triple metal oxide phase in this study may allow a potential way to modify low cost visible light-driven NiTiO3 photocatalysts for sustainable photocatalytic application.