Graphical abstract

Photocatalytic nitrate (NO₃^-) reduction to NH₃ (PcNRA) is a sustainable alternative that is considered advantageous over N₂ fixation, which suffers from the high dissociation energy and sluggish activation of inactive N₂. Although PcNRA has recently been shown to achieve excellent selectivity, its sluggish kinetics restrict the NH₃ production efficiency. Herein, we present a single-atom Cu-incorporated TiO₂ nanosheet (Cu-TNS) photocatalyst for efficient and selective PcNRA. Single Cu atoms displacing Ti sites accumulate photogenerated electrons, ensuring efficient charge separation and surface NO₃^- reduction. Moreover, introducing Cu atoms into the TiO₂ matrix induces spontaneous defect formation, resulting in oxygen vacancies and lattice strain that promote NO₃^- adsorption and activation. The simultaneous presence of single Cu atoms and structural defects in Cu-TNS synergistically stimulates PcNRA, leading to a 62-fold enhancement over pristine TiO₂ in NH₃ production with 97.6% selectivity and an unprecedently high apparent quantum yield of 11.7% at 330 nm under optimized conditions.