New insight into the mechanism of enhanced photo-Fenton reaction efficiency for Fe-doped semiconductors: A case study of Fe/g-C₃N₄

Visible light has shown to greatly enhance the activity of iron-doped semiconductor catalyst in a Fenton reaction system, however, the mechanism for this activity enhancement remains unclear. This work attempts to reveal the origin of this visible light driven activity enhancement by studying the iron doped semiconductor catalyst Fe/g-C₃N₄ in both photo-Fenton and dark Fenton reactions. Through analysis of XPS spectra of catalyst, it is found that Fe²⁺/Fe³⁺ ratio for Fe/g-C₃N₄ catalyst remains unchanged and sustained during the photo-Fenton reaction cycles. This is in direct contrast to the progressively decreased Fe²⁺/Fe³⁺ ratio observed in the dark Fenton reaction. It is clear that under visible light, Fe³⁺ is able to capture the photo-generated electrons from the semiconductor and revert back to Fe²⁺, thus sustain the catalytic activity during the photo-Fenton reaction. This new mechanistic insight will guide the future design and optimization of high performance catalysts by immobilizing transition metal ions in semiconductors for advanced oxidation processes.