Comparison of Hydroxyl Radical Production Rates in H2O2 Solution under Homogeneous Catalysis of Fe~(3+) or Fe~(2+)
Fe3+或Fe2+均相催化H2O2生成羟基自由基的规律

The production of *OH radicals was investigated by using the electron spin resonance (ESR) method with 5,5-dimethyl-1-lpyrroline-1-oxide (DMPO) as spin trap reagent. ESR signals composed of 4 lines with a 1:2:2:1 intensity ratio indicated the formation of *OH radicals in the Fenton-like reaction. For both systems, the production rates of hydroxyl radicals in the initial stage were considerably high, and increased with increasing concentrations of H2O2 and Fe2+ or Fe3+. However, the radical production rate in Fenton reaction system was markedly higher than that in Fenton-like reaction under similar dosing conditions. The differences of radical production rates between the reaction systems remained even in the slow reaction stage. The optimum pH ranges of the production of *OH radicals in Fenton process and Fenton-like process were 2.5 to approximately 3.5 and 2.8 to approximately 3.0 respectively. The above results demonstrate that the Fenton system and Fenton-like system are possibly based on different reaction mechanisms.