Catalytic property of ferryl (IV) species in the heterogeneous thermal Fenton-like oxidation system

During the oxidative degradation of nonbiodegradable Orange IV by means of H2O2/FeIIIF2+/R oxidation method (FeIIIF2+ complex supported on cationic exchange resin as a catalyst), the binding energy of the Fe(2p3/2) region for X-ray photoelectron spectroscopy (XPS) spectra increased with the reaction time during the initial 2.5 h and then decreased continuously. The electron paramagnetic resonance (EPR) signal for hydroxyl radical (OH) spin trap adduct of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) also increased with the reaction time within a certain period of time. These results confirmed that ferryl (IV) (FeIVF=O+/R) species was generated along with the formation of OH radicals at the beginning of the reaction. The formed ferryl (IV) species enhanced the DMPO-OH signal compared with the catalyst of FeIIIF2+/R. The addition of t-butanol did not significantly reduce the reaction rate, which increased with reaction time in the process of ferryl (IV) catalytic decomposition of H2O2. This indicated that there was a more reactive species than ferryl (IV), which cannot be scavenged by t-butanol, and it was likely to be Fe (V). A possible mechanism for a resin-supported thermal Fenton-like oxidation reaction is proposed to better understand the process in the presence of iron complex catalysts.