LAUSR

Abstract It is significant to quantitative test ·OH for understanding the reaction mechanisms of Fenton. OH concentration was directly measured in Fenton system via the spectrophotometric method based on Russell mechanism, and the drawbacks were analyzed. The influences of H2O2 and dimethyl sulfoxide (DMSO, the trapping agent of OH) on the spectrophotometric measurement were studied. The Fe2+/Fe3+ concentrations were tested during the Fenton reaction. The results show that it was difficult to detect ·OH directly in Fenton system. The effect of DMSO on the detection of diazosulfones was related to its concentration. Under most conditions (DMSO concentration was lower than 2000 mmol L−1), DMSO did not affect the detection of diazosulfones. The interference of DMSO on the colour reaction was weak. H2O2 had a significant influence on the test result by reacting with methyl radicals, diazosulfones, and disturbing the colour reaction. High concentration of H2O2 was the main reason why OH concentration was hard to be detected in Fenton system. A low concentration of H2O2 was beneficial for decreasing the influence of H2O2 on the measurement. The concentration ratio of Fe3+ to Fe2+ remained approximately constant in the Fenton system except during the short initial stage. Based on the analysis, a modified spectrophotometric method for OH concentration test in Fenton system was proposed. In this method, the H2O2 solution was slowly added into the Fe2+/Fe3+ system obtained from the Fenton solution. The test results showed that the ·OH concentration increased linearly with the consumption amount of H2O2.