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 (Fe1/C) toward N2 photofixation. PPh3 molecules mainly adsorbed on the active carbon to form Fe1/C–PPh3/NaI. During N2 photofixation, Fe1/C–PPh3/NaI exhibited an NH3 production rate of 98 μmol/(gcat.·h) without any sacrificial agents, even 1.5 times as high as that for Fe1/C using tris(2,2′-bipyridyl)dichlororuthenium(II) ([Ru(bpy)3]Cl2) as the photosensitizer. Further mechanistic studies revealed that Fe1/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• radicals. The hot electrons reduced N2 to NH3 over Fe single atoms, while PPh3-I• radicals were regarded to oxidize H2O to O2.