Engineering a surface defect-rich Ti3C2 quantum dots/mesoporous C3N4 hollow nanosphere Schottky junction for efficient N2 photofixation

Abstract

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 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.