The conversion of CO2 into solar fuels by photocatalysis is a promising way to deal with the energy crisis and the greenhouse effect. The introduction of oxygen vacancy into semiconductor has been proved to be an effective strategy for enhancing CO2 photoreduction performance. Herein, TiO2- x nanostructures have been prepared by a simple solvothermal method and engineered by the reaction time. With the prolonging of reaction time, the oxygen vacancy signal gradually increases while the band gap becomes narrow for the as-synthesized TiO2- x nanostructures. The results show that the TiO2- x-6 h, TiO2- x-24 h, and TiO2- x-48 h samples have the main product of CH4 (more) and CO (less) for CO2 photoreduction. Among the three oxygen vacancy photocatalysts, the TiO2- x-24 h sample shows the highest CH4 generation rate of 41.8 μmol g− 1 h− 1. On the basis of photo/electrochemical measurements, the TiO2- x-24 h sample exhibits efficient electron–hole separation and charge transfer capabilities, thus allows much more electrons to participate in the reaction and finally promotes the photocatalytic CO2 reduction reaction. It further confirms that the optimization of oxygen vacancy concentration could facilitate the photoinduced charge separation and accordingly improve photocatalytic CO2 conversion.

    Abstract
    1 Introduction
    2 Experimental section
        2.1 Materials preparation
        2.2 Materials characterization
        2.3 Photocatalytic CO2 reduction test
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Hexia Deng(Analysis and Testing Center and School of Chemistry and Environmental Engineering, Wuhan Institute of Technology)
• Xueteng Zhu(Analysis and Testing Center and School of Chemistry and Environmental Engineering, Wuhan Institute of Technology)
• Zhangjing Chen(Analysis and Testing Center and School of Chemistry and Environmental Engineering, Wuhan Institute of Technology)
• kai Zhao(School of Materials Science and Energy Engineering, Foshan University)
• Gang Cheng(Analysis and Testing Center and School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Key Laboratory for Palygorskite Science and Applied Technology of Jiangsu Province, National and Local Joint Engineering Research Center for Mineral Salt Deep Utilization, Huaiyin Institute of Technology)