Effective CO2 photoreduction to methane over Bi2MoO6/ Ni, N co-doped TiO2 nano-photocatalyst

Bi2MoO6/Ni–N co-doped TiO2 (BM/Ni–N-T) composite was prepared by a hydrothermal, and subsequently a solvothermal method and used for CO2 photocatalytic conversion under visible light irradiation. The effect of nickel concentration in TiO2 on the photocatalytic properties and the effect of nitrogen-nickel co-doping in TiO2 structure on methane production were investigated. Furthermore, the effect of constructing a heterojunction structure between modified TiO2 and Bi2MoO6 semiconductors on the photocatalytic performance was investigated. The morphological and structural properties of the samples were characterized by X-ray diffraction, nitrogen adsorption, field emission scanning electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. Doping nickel with different concentrations in TiO2 structure could result in a narrowing of the bandgap and increase the light absorption capacity in comparison to an undoped TiO2 sample. The results reveal that modification of TiO2 with both of nickel and nitrogen elements leads to higher surface area and narrower bandgap than pure TiO2. Incorporation of nickel and, or nitrogen into TiO2 structure suppresses the CO2 absorption on the catalyst surface and results in enhanced electron-hole separation efficiency compared to pure TiO2. The 3Ni-T sample with 3 wt% nickel shows the optimum methane production among single-doped TiO2 samples. The Ni–N co-doped TiO2 sample exhibits a good response in CO2 conversion, which was nine times higher than that of undoped TiO2. The BM/Ni–N-T photocatalyst exhibits excellent photocatalytic performance for CO2 conversion (67.9 μmol/g), which is several times higher than that of pure TiO2 (3.2 μmol/g). The enhanced composite photocatalytic performance is mainly attributed to nitrogen and nickel co-doping in TiO2 and heterojunction structure, which improves light absorption capacity and charge carrier separation efficiency.