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 2.5h 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.