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.