Engineering a surface defect-rich Ti3C2 quantum dots/mesoporous C3N4 hollow nanosphere Schottky junction for efficient N-2 photofixation

Photo-driven fixation of nitrogen (N-2) to ammonia (NH3) is a kinetically complex multielectron reaction process. The key to photocatalytic N-2 fixation lies in designing photocatalysts with high photoinduced carrier separation efficiency and sufficient active sites for adsorbing and activating N-2 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 N-2 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 N-2 molecules, leading to efficient reduction of preactivated N-2 molecules to NH3 by the trapped electrons transferred from the photoexcited C3N4 hollow spheres. The resultant photocatalysts exhibited a remarkably enhanced N-2 photofixation activity with an optimal NH3 production rate of 328.9 mu mol h(-1) g(cat)(-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.