Efficient degradation of carbamazepine by electro-Fenton system without any extra oxidant in the presence of molybdate: The role of slow release of iron ions

In this study, the removal efficiency of carbamazepine (CBZ) was significantly improved in an electro-Fenton system without any extra oxidant (e.g., O 2 or H 2 O 2 ) in the presence of sodium molybdate (EF-Na 2 MoO 4 system). The slow release of iron ions of EF-Na 2 MoO 4 system greatly reduced the generation of iron sludge and effectively promoted the utilization of iron ions. The pseudo-first-order rate constants ( k obs ) for CBZ removal by EF-Na 2 MoO 4 process (0.0417 min −1 ) was much higher than those of sole electrolysis (0.0007 min −1 ) and EF-Na 2 SO 4 systems (0.0044 min −1 ). Meanwhile, the total iron concentration in EF-Na 2 MoO 4 process was 4.93 mg/L for 60 min, which was extremely lower than that of EF-Na 2 SO 4 process (271.22 mg/L). Besides, the primary reactive species was proposed to be superoxide radical (O 2 − ), while hydroxyl radical ( OH) and MoO 2 (O 2 ) 2 2− acted as the secondary reactive species. Our work elucidated the possible mechanism that the slow release of iron ions promotes pollutants degradation.