Site-exposed Ti3C2 MXene anchored in N-defect g-C3N4 heterostructure nanosheets for efficient photocatalytic N2 fixation

Abstract

Exploring highly active centers for NN triple-bond activation and the suppression of the competing H₂ evolution reaction (HER) are key considerations for photocatalytic N₂ fixation. As a novel 2D transition-metal carbide, Ti₃C₂ nanosheets (MXenes) have been recently considered as a promising N₂ reduction reaction (NRR) active center. However, little of the expected progress in the use of Ti₃C₂ for photocatalytic N₂ fixation has been achieved. Herein, we report a novel 2D/2D Ti₃C₂/N-defect g-C₃N₄ heterostructure photocatalyst exhibiting highly enhanced photocatalytic nitrogen fixation activity, with an NH₃ yield of 5.792 mg h⁻¹ g⁻¹. This study demonstrates that the heterostructure was constructed by filling the oxygen-terminals of Ti₃C₂ in the N-defects of g-C₃N₄ to form C–O–Ti interactions. Together, the construction of the hetero-interface and the introduction of N-defects contribute to rapid interfacial charge transfer to the active sites. Importantly, the exposed edge Ti of Ti₃C₂ was confirmed to be the active site for N₂ adsorption and activation, and these active Ti sites exhibit desirable NRR selectivity via suppressing the competing HER. Finally, a mechanism for photocatalytic N₂ fixation was proposed to reveal the evolution of the redox circle that originated from the multi-valence Ti species during the N₂ adsorption, activation, and dissociation process.