Engineering a surface defect-rich Ti₃C₂quantum dots/mesoporous C₃N₄hollow nanosphere Schottky junction for efficient N₂photofixation

Photo-driven fixation of nitrogen (N2) to ammonia (NH3) is a kinetically complex multielectron reaction process. The key to photocatalytic N2 fixation lies in designing photocatalysts with high photoinduced carrier separation efficiency and sufficient active sites for adsorbing and activating N2 molecules. Herein, we constructed a Schottky junction photocatalyst made of mesoporous hollow carbon nitride (C3N4) spheres decorated with partially reduced Ti3C2 quantum dots (r-Ti3C2 QDs) on the surface for efficient N2 photofixation. The Schottky junction is formed at the interface between C3N4 spheres and r-Ti3C2 QDs, which enables the spatial separation of photogenerated electrons and holes, resulting in suppression of charge carrier recombination. Notably, the surface of r-Ti3C2 QDs is rich in Ti3+ sites and oxygen vacancy (OV) defect state sites. Such double defect sites of Ti3+ and OVs facilitate the capture and activation of N2 molecules, leading to efficient reduction of preactivated N2 molecules to NH3 by the trapped electrons transferred from the photoexcited C3N4 hollow spheres. The resultant photocatalysts exhibited a remarkably enhanced N2 photofixation activity with an optimal NH3 production rate of 328.9 μmol h-1 gcat-1. This work not only provides an alternative strategy to engineer defect sites and regulate the charge transfer pathway on photocatalysts, but also sheds new light on developing efficient MXene-based photocatalysts for broadening their photocatalytic applications.