Fe Single-Atom Catalyst for Visible-Light-Driven Photofixation of Nitrogen Sensitized by Triphenylphosphine and Sodium Iodide

Photosensitizers with charge-separated excited states are commonly introduced into photocatalytic systems to accomplish photon-to-electron transformation. Unfortunately, the photosensitizers in current use are mostly precious metal complexes and synthetically elaborate organic dyes. Herein, we successfully applied a low-cost triphenylphosphine (PPh3)/sodium iodide (NaI)-based photosensitizer to heterogeneous catalysis using Fe single-atom catalysts (Fe-1/C) toward N-2 photofixation. PPh3 molecules mainly adsorbed on the active carbon to form Fe-1/C-PPh3/NaI. During N-2 photofixation, Fe-1/C-PPh3/NaI exhibited an NH3 production rate of 98 mu mol/(g(cat.).h) without any sacrificial agents, even 1.5 times as high as that for Fe-1/C using tris(2,2'-bipyridyl)dichlororuthenium(II) ([Ru(bpy)(3)]Cl-2) as the photosensitizer. Further mechanistic studies revealed that Fe-1/C-PPh3/NaI effectively harvested photons by delivering hot electrons from adsorbed PPh3/NaI to Fe single atoms under light irradiation, together with the generation of PPh3-I-center dot radicals. The hot electrons reduced N-2 to NH3 over Fe single atoms, while PPh3-I-center dot radicals were regarded to oxidize H2O to O-2 .