Free radical behaviours during methylene blue degradation in the Fe2+/H2O2 system

Behaviours of the free radicals during the methylene blue (MB) oxidation process in the Fe2+/H2O2 system were studied to reveal the reason for the low utilization efficiency of H2O2. The roles of , and radicals were proven to be different in the MB oxidation process. The results showed that radicals had a strong ability to oxidize MB; however, they were not the main active substances for MB degradation due to the low concentration in the traditional Fe2+/H2O2 system. radicals could not oxidize MB. radicals were the main active substances for MB oxidation. In the short initial stage, the utilization efficiency of H2O2 was high, because the generation rate of was much higher than that of . More radicals were involved in the MB oxidation reaction. In the long deceleration stage (after the short initial stage), a large amount of H2O2 was consumed, but the amount of oxidized MB was very small. Most of the radicals were consumed via the rapid useless reaction between and in this stage, resulting in the serious useless consumption of H2O2. It is a feasible method to improve the utilization efficiency of H2O2 by adding suitable additives into the Fe2+/H2O2 system to weaken the useless reaction between and .