Single-Atom Fe-N4 sites promote the triplet-energy transfer process of g-C3N4 for the photooxidation

Abstract

Polymeric carbon nitride materials show intriguing prospects in numerous light-to-energy conversion applications, but seldom studies focus on their triplet energy transfer, leading to the insufficient lifetime for the photochemical process. Inspired by the porphyrin molecular photocatalyst, single-atom sites (Fe-N4) as triplet sensitizing sites were fabricated in g-C3N4 for the preparation of Fe-g-C3N4, which processes a long-lived triplet emissive state (τPH = 4.93 μs). But under realistic condition for the large-scale production of catalyst, single atoms are inevitable to sinter, resulting in the formation of other metal species. Therefore, the photooxidation of 1,5-dihydroxynaphthalene (1,5-DHN) and the photocatalytic E-Z Isomerization of stilbene were selected as the model reactions to evaluate the influence of various Fe species on the triplet energy transfer. It was found that Fe-N4 sites promote the triplet energy transfer process, while Fe nanoclusters (Fe0) promote the electron transfer and inhibit triplet energy transfer. This finding provides guidance for the rational design of photocatalysts to efficiently improve triplet energy transfer process and its application.