Free radical behaviours during methylene blue degradation in the Fe/HO system.

Behaviours of the free radicals during the methylene blue (MB) oxidation process in the Fe/HO system were studied to reveal the reason for the low utilization efficiency of HO. 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 Fe/HO system. radicals could not oxidize MB. radicals were the main active substances for MB oxidation. In the short initial stage, the utilization efficiency of HO 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 HO 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 HO. It is a feasible method to improve the utilization efficiency of HO by adding suitable additives into the Fe/HO system to weaken the useless reaction between and .