From H₂O₂ to OH: A First-Principles Investigation of the Heterogeneous Fenton-Like Reaction

Heterogeneous Fenton and Fenton-like reactions have superior advantages over homogeneous Fenton or Fenton-like reactions for various advanced oxidation processes (AOPs). An in-depth analysis of the heterogeneous Fenton and Fenton-like reactions is necessary to address the challenges facing their widespread application. First-principles DFT calculations are employed to study the heterogeneous Fenton-like reaction using the pristine Fe(110) surface in an aqueous medium. Spin-polarized DFT calculations are used in place of traditional DFT calculations to address realistic electronic properties. The adsorption energies of *OH• formed on the surface after spontaneous H₂O₂ dissociation are calculated at various surface coverages. The electronic structural calculations reveal that the difference in *OH adsorption at higher coverage arises due to the destabilization of Fe-O bonding. Partial oxidation of Fe surface layers is observed at higher *OH coverage due to the charge transfer from the surface Fe atoms to the oxygens. Even though the surface deprotonation of *OH is highly exergonic, at larger *OH concentrations, the surface contains both *OH and *O^- on the surface. These results reveal that the Fe atoms are not fully oxidized in heterogeneous Fenton-like reactions using ZVI, unlike in homogeneous Fenton reactions. The *OH formed in the heterogeneous Fenton-like reaction is less reactive than OH-(aq), its reduction potential is only 0.15 V vs SHE (at pH 14), and its ability to degrade organic pollutants is decreased. Further studies on surface corrosion mechanisms and reactions on oxide/hydroxide layers are necessary for analyzing heterogeneous Fenton and Fenton-like reactions.