Review of TiO₂-Based Nanocatalysts for Photocatalytic Nitrogen Reduction to Ammonia

The traditional ammonia synthesis process of the Haber–Bosch method must be carried out at high temperatures and high pressure with energy-intensive consumption and carbon emission. As a green and low-energy alternative technology, photocatalytic ammonia synthesis technology has received increasing attention. Recent advances in the fabrication of TiO2-based nanocatalysts for the photocatalytic N2 reduction reaction (NRR) under mild conditions are reviewed and summarized. In this paper, we compare and analyze various methods for detecting low ammonia concentrations with advanced detection techniques in the field. In order to enhance the activity of TiO2-based nanocatalysts for photocatalytic NRR, various methods are summarized such as molecular structure engineering, interfacial modulation engineering, crystallographic engineering, surface modulation engineering, and morphology engineering. Besides, the mechanism of the photocatalytic ammonia synthesis was analytically proven. A comparison for the advantages of the TiO2-based nanocatalyst synthesis process is presented and discussed, as well as its future potential applications in NRR.