[Mechanisms of Fe-cyclam/H2O2 System Catalyzing the Degradation of Rhodamine B].

Fenton reaction is a traditional method for the treatment of dye-containing wastewater. However, this process should be performed in a narrow pH range and requires large amounts of ferrous salt input, limiting its application. In this work, a robust iron complex bearing a cross-bridge cyclam ligand (Fe-cyclam) was successfully prepared. This complex could effectively activate H2O2 to degrade rhodamine B at a pH range of 2-7. The Fe-cyclam/H2O2 system was more effective in the degradation of rhodamine B than the Fenton reaction, when the input [Fe] was lower than 50 μmol·L-1. Moreover, in addition to rhodamine B, the Fe-cyclam/H2O2 system was also capable of degrading dyes such as acid red 88, acid orange II, reactive red 24, and neutral red. This system was more efficient in the degradation of azo dyes than that of triphenylmethane dyes. The removal of rhodamine B remained higher than 90% in three cycle experiments, indicating the excellent stability of Fe-cyclam. The quenching experiments proved that the degradation of rhodamine B by Fe-cyclam/H2O2 was a free-radical-control process. Meanwhile, the electron paramagnetic resonance captured the signals of high valent FeV-oxo species, indicating that FeV-oxo possibly mediated the degradation of rhodamine B in the Fe-cyclam/H2O2 system. This work proves the potential application of Fe-cyclam/H2O2 in the degradation of dyes in a practical environment.