Oxygen defect modulating the charge behavior in titanium dioxide for boosting photocatalytic nitrogen fixation performance

Extremely high-temperature and high-pressure requirement of Haber-Bosch process motivates the search for a sustainable ammonia synthesis approach under mild conditions. Photocatalytic technology is a potential solution to convert N2 to ammonia. However, the poor light absorption and low charge carrier separation efficiency in conventional semiconductors are bottlenecks for the application of this technology. Herein, a facile synthesis of anatase TiO2 nanosheets with an abundance of surface oxygen vacancies (TiO2-OV) via the calcination treatment was reported. Photocatalytic experiments of the prepared anatase TiO2 samples showed that TiO2-OV nanosheets exhibited remarkably increased ammonia yield for solar-driven N2 fixation in pure water, without adding any sacrificial agents. EPR, XPS, XRD, UV-Vis DRS, TEM, Raman, and PL techniques were employed to systematically explore the possible enhanced mechanism. Studies revealed that the introduced surface oxygen vacancies significantly extended the light absorption capability in the visible region, decreased the adsorption and activation barriers of inert N2, and improved the separation and transfer efficiency of the photogenerated electron-hole pairs. Thus, a high rate of ammonia evolution in TiO2-OV was realized. This work offers a promising and sustainable approach for the efficient artificial photosynthesis of ammonia. [Display omitted] •Anatase TiO2 nanosheets with the abundant surface OVs was successfully synthesized.•Efficient solar-driven N2 fixation to ammonia was achieved over TiO2-OV in the pure water.•Extended light absorption capability, decreased N2 adsorption and activation barriers, and improved charge separation efficiency was realized in TiO2-OV.•TiO2-OV nanosheets displayed 13 times higher ammonia yield than that of the commercial Degussa P25.