Single-Atom Pt–N₃ Sites on the Stable Covalent Triazine Framework Nanosheets for Photocatalytic N₂ Fixation

The commercial Haber-Bosch process for NH₃ production not only requires large amounts of energy and hydrogen supply but also generates tremendous greenhouse CO₂ emission. To mitigate energy and environmental challenges, renewable ammonia production technologies based on electrochemical and photochemical methods, in particular, photocatalytic nitrogen fixation in aqueous phase for ammonia production is highly desired. In the present work, single-atom Pt anchored at the −N₃ sites of stable and ultrathin covalent triazine framework (CTF) nanosheets have been successfully synthesized (Pt-SACs/CTF). The well-defined coordination structure of Pt–N₃ sites in the Pt-SACs/CTF catalyst have been characterized using HAADF-STEM and EXAFS, as well as ab initio molecular dynamics simulations. The ammonia production rate over the as-synthesized Pt-SACs/CTF catalyst is 171.40 μmol g^–1 h^–1 in the absence of sacrificial agent. On the basis of density functional theory calculations, it has been found that the alternating mechanism is energetically more favorable than the distal mechanism over the well-defined Pt–N₃ sites. The significance of the present work is to demonstrate that the single-atom metal catalysts are anchored at the two-dimensional stable CTF nanosheets for photocatalytic nitrogen fixation to ammonia.