Tuning Oxygen Vacancies in Ultrathin TiO₂ Nanosheets to Boost Photocatalytic Nitrogen Fixation up to 700 nm

Abstract Dinitrogen reduction to ammonia using transition metal catalysts is central to both the chemical industry and the Earth's nitrogen cycle. In the Haber–Bosch process, a metallic iron catalyst and high temperatures (400 °C) and pressures (200 atm) are necessary to activate and cleave NN bonds, motivating the search for alternative catalysts that can transform N 2 to NH 3 under far milder reaction conditions. Here, the successful hydrothermal synthesis of ultrathin TiO 2 nanosheets with an abundance of oxygen vacancies and intrinsic compressive strain, achieved through a facile copper‐doping strategy, is reported. These defect‐rich ultrathin anatase nanosheets exhibit remarkable and stable performance for photocatalytic reduction of N 2 to NH 3 in water, exhibiting photoactivity up to 700 nm. The oxygen vacancies and strain effect allow strong chemisorption and activation of molecular N 2 and water, resulting in unusually high rates of NH 3 evolution under visible‐light irradiation. Therefore, this study offers a promising and sustainable route for the fixation of atmospheric N 2 using solar energy.