Nonradical activation of peroxymonosulfate by hematite for oxidation of organic compounds: A novel mechanism involving high-valent iron species

Peroxymonosulfate (PMS) activated by Hematite (alpha-Fe2O3) was capable of degrading different organic compounds. Several lines of experimental evidence are presented which argue against the generation of radical species as well as singlet oxygen (O-1(2)). Tests using radical scavengers and probes, and electron paramagnetic resonance (EPR) spectroscopy suggested that the PMS-activation by alpha-Fe2O3 does not involve the generation of SO4 center dot-, (OH)-O-center dot, and O-2(center dot-). The possibility of O-1(2) generation was also excluded by EPR spectroscopy and kinetic experiments performed in deuterium oxide. The ternary reactive complex that mediates the electron-transfer between target organic compounds and PMS (frequently proposed as a nonradical mechanism in previous studies) was not likely formed in this system. Based on the electrochemical analyses as well as other experiments, a high-valent iron species (most likely ferryl species, Fe(IV)) is believed to be responsible for the oxidation of organic compounds by the alpha-Fe2O3/PMS system.