Density Functional Theory Calculation of Hydroxyl Radical Formation by Fenton and Fenton-Like Reactions

Reaction free energies of hydrogen peroxide (H₂O₂) and hydrated transition metal ions to form hydroxyl radical, which is known as Fenton or Fenton-like reactions, are calculated by DFT methods. Standard electrode potentials of M²⁺/M³⁺ (M = Ti, V, Cr, Mn, Fe, Co) in aqueous solutions are calculated as benchmarks for the selected hybrid functionals and the basis sets. Mean absolute errors of the calculated redox potentials are comparable to those of the previous DLPNO-CCSD(T) calculation in most of the combinations. In contrast, calculated Gibbs free energies of hydroxyl radical formation are dependent on the choice of the functionals, and PBE0 gives the best results. The effect of anion substitution in the first hydration shell and Fenton-like reactions of other metal ions (Ti³⁺, V²⁺, Cr²⁺, Mn²⁺) are also examined.