Different roles of Fe atoms and nanoparticles on g-C3N4 in regulating the reductive activation of ozone under visible light.

[Display omitted] • Dramatic activity enhancement was observed over Fe-doped g-C 3 N 4. • Two-photoelectron reduction pathway was verified in Fe/g-C 3 N 4 Vis-O 3 system. • The different roles of single Fe atoms and nanoparticles was explored. • Fe(II)N x sites promoted the adsorption and reduction of O 2 rather than O 3. The identification of active sites and the establishment of structure-reactivity relationship at atomic scale is important for designing efficient catalysts and understanding the reaction mechanism. Here, single atom catalysts (SACs) of Fe anchored on g-C 3 N 4 were synthesized. The catalysts have larger surface area, more photo-generated electrons with stronger reduction ability and faster charge carrier migration than g-C 3 N 4 , thereby exhibited dramatically enhanced activity and stability in electron reduction of ozone (O 3) under visible light. However, lower catalytic performance was observed when Fe nanoparticles coexisted, which regulated more photoelectrons to reduce O 2 to OH via two or three-electron reduction pathways rather than one-electron reduction of O 3. Mössbauer spectrum and X-ray adsorption spectroscopy indicated that the presence of Fe nanoparticles led to higher proportion of Fe(II)N x , which played more significant role in the adsorption and reduction of O 2. The insight on the contribution of different Fe sites with well-defined local coordination structure is beneficial for rational design of efficient catalysts in photocatalytic ozonation. [ABSTRACT FROM AUTHOR]