Peroxydisulfate activation process on copper oxide: Cu(III) as the predominant selective intermediate oxidant for phenol and waterborne antibiotics removal

In this study, activated peroxydisulfate (PDS) by micrometer copper oxide (CuO) particles effectively degraded phenol and several antibiotics in water. Cupryl ion (Cu(III)) was proposed for the first time to be the predominant reactive species accounting for contaminants degradation in the CuO/PDS oxidation system. Singlet oxygen was also heavily produced from the superoxide radical anion (•O2−) decomposition was found to be but slightly involved in the degradation since it was rapidly quenched by water. Transformation pathways of phenol and several antibiotics were elucidated. The proposed mechanism mainly involved the generation of •O2− resulting from an outer-sphere surface PDS complexation which prompted the reduction of Cu(II) to Cu(I). Cu(I) was oxidized in Cu(III) by PDS or H2O2 and was reduced to Cu(II) by a one-electron oxidation of contaminants so that the catalytic effect involved alternate oxidation and reduction of copper. As the degradation process did not rely on sulfate or hydroxyl radical, chloride and bicarbonate ions showed no effect on phenol degradation, while sulfate ions and humic acid slightly hindered phenol degradation probably due to their sorption on CuO. Interestingly, the copper leaching from CuO was significantly limited to < 500 µg/L in wastewater. These findings indicated the potential applicability of CuO/PDS system for electron-rich compounds degradation including antibiotics due to good catalyst stability against time.