In2S3/TiO2 heterostructures for enhanced photocatalytic nitrogen fixation under ambient conditions

The development of sustainable routes for ammonia production under ambient conditions is a critical challenge, driven by the high energy demand and carbon footprint of the Haber-Bosch process. Photocatalytic N2 fixation has emerged as a promising alternative; however, conventional TiO2-based systems suffer from rapid charge-carrier recombination, resulting in poor efficiency. Herein, we report the design of a noble-metal-free In2S3/TiO2 heterostructure photocatalyst for photocatalytic N2 fixation to NH4+ under mild conditions. The coupling of TiO2 nanoparticles with In2S3 aims to promote charge carrier separation and suppress electron-hole recombination, thereby overcoming the intrinsic limitations of bare TiO2. Structural, morphological, optical, and electronic characterizations confirmed the successful formation of the heterojunction and the strong interfacial interaction between the two semiconductors. UVVis diffuse reflectance spectroscopy revealed an extended light absorption toward the visible region, while photoluminescence and XPS analyses evidenced enhanced charge separation and interfacial charge redistribution. Among the investigated compositions, the In2S3(10%)/TiO2 sample exhibited the best photocatalytic performance, achieving an NH3 production of 214.0 μmol·gcat−1 after 3 h of irradiation, significantly higher than pristine TiO2. Experimental and DFT investigations demonstrated the formation of a type-II heterojunction, promoting electron migration from In2S3 to TiO2 and suppressing electron-hole recombination. The combined experimental and theoretical results highlight the potential of noble-metal-free In2S3/TiO2 heterostructures as efficient photocatalysts for sustainable N2 fixation under ambient conditions.