Mechanistic study of Fe(III) chelate reduction in a neutral electro-Fenton process

Fe(III) chelate reduction is of great importance in the homogeneous neutral electro-Fenton (EF) process, but its reduction mechanisms with different reductive species remain unclear. In this study, the reduction mechanisms of several typical Fe(III) chelates through electron and atomic H* were investigated using experiments and density functional theory calculations. The results indicated that the electron reduction efficiencies for [Fe(III)-EDTA] − and [Fe(III)-EDDS] − chelates were 16.23 and 8.31 times higher compared to [Fe(H 2 O) 6 ] 3+ , which was featured by low E LUMO - HOMO and concentrated LUMO distribution around Fe atom. In contrast, the atomic H* reduction efficiency for [Fe(III)-HA] 3+ chelate was 10 times higher than that of electron, attributed to high chelation ability of HA and negative energy barrier of [Fe(III)-HA] 3+ reduction in the atomic H*-dominated system. Additionally, phthalocyanine (Pc) had insignificant effect on pollutant degradation efficiency in the neutral EF systems due to the lower chelate ability of Pc with Fe(III) compared to H 2 O.