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 (PPh 3 )/sodium iodide (NaI)-based photosensitizer to heterogeneous catalysis using Fe single-atom catalysts (Fe 1 /C) toward N 2 photofixation. PPh 3 molecules mainly adsorbed on the active carbon to form Fe 1 /C–PPh 3 /NaI. During N 2 photofixation, Fe 1 /C–PPh 3 /NaI exhibited an NH 3 production rate of 98 μmol/(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–PPh 3 /NaI effectively harvested photons by delivering hot electrons from adsorbed PPh 3 /NaI to Fe single atoms under light irradiation, together with the generation of PPh 3 -I • radicals. The hot electrons reduced N 2 to NH 3 over Fe single atoms, while PPh 3 -I • radicals were regarded to oxidize H 2 O to O 2 .