Regulating the dominant reactive oxygen species from Fe(IV)-oxo to 1O2 by deprotonation of Fe(IV)-oxo in electro-Fe(II)/periodate system

[Display omitted] •Electro-Fe(II) can significantly promote PI to degrade SMX.•Fe(IV)-oxo and 1O2 as the main reactive species are generated under the E(Fe/C)/PI system in pH=3 and 6.5, respectively.•Density functional theory (DFT) calculations are employed to reveal the differences of catalytic mechanisms in both pH conditions.•SMX degradation intermediates and toxicities are presented through experimental results and DFT calculations. The ferrous species (Fe(II))-periodate (PI) system employs efficient decontamination by generating ferryl species (Fe(IV)-oxo) under acidic pH conditions. However, the mechanisms by which the Fe(II)/PI system operates across a broad pH range remain elusive. In light of the rapid oxidation and consumption of Fe(II) at neutral pH, we developed an electro-Fe(II) system utilizing an iron plate anode to activate PI (E(Fe/C)/PI). Efficient sulfamethoxazole (SMX) degradation was achieved under the E(Fe/C)/PI system across a range of pH values. Quenching and chemical probe experiments revealed a transition from Fe(IV)-oxo to singlet oxygen (1O2) as the predominant reactive species from acidic to near-neutral pH, respectively. Density functional theory (DFT) calculations indicated that the differences in one-electron transfer capacity and hydrolysis pathways for various protonated Fe(IV)-oxo species underlie the variations in catalytic mechanisms. This study not only enhances the efficiency of the Fe(II)/PI system but also provides a comprehensive understanding of the activation mechanisms at different pH levels.