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

[Display omitted] •A type of EF-Na2MoO4 system without addition of oxidant was developed.•CBZ is effectively degraded and the production of iron sludge is greatly reduced.•The utilization rate of iron was greatly improved by the slow release of iron ions.•EF-Na2MoO4 system is mainly a radical pathway dominated by O2−. In this study, the removal efficiency of carbamazepine (CBZ) was significantly improved in an electro-Fenton system without any extra oxidant (e.g., O2 or H2O2) in the presence of sodium molybdate (EF-Na2MoO4 system). The slow release of iron ions of EF-Na2MoO4 system greatly reduced the generation of iron sludge and effectively promoted the utilization of iron ions. The pseudo-first-order rate constants (kobs) for CBZ removal by EF-Na2MoO4 process (0.0417 min−1) was much higher than those of sole electrolysis (0.0007 min−1) and EF-Na2SO4 systems (0.0044 min−1). Meanwhile, the total iron concentration in EF-Na2MoO4 process was 4.93 mg/L for 60 min, which was extremely lower than that of EF-Na2SO4 process (271.22 mg/L). Besides, the primary reactive species was proposed to be superoxide radical (O2−), while hydroxyl radical (OH) and MoO2(O2)22− acted as the secondary reactive species. Our work elucidated the possible mechanism that the slow release of iron ions promotes pollutants degradation.