Sulfur-doped copper-cobalt bimetallic oxides with abundant Cu(I): A novel peroxymonosulfate activator for chloramphenicol degradation

Sulfur-doped copper-cobalt bimetallic oxides (S-CuYO) with abundant Cu(I) were successfully synthesized by a co-precipitation method and were for the first time utilized to activate peroxymonosulfate (PMS) for the degradation of chloramphenicol (CAP). For comparison purposes, sulfur-doped monometallic oxides (S-CuO and S-CoO) and non-doped copper-cobalt bimetallic oxide (CuCoO-1) were also prepared via the same processes. The results demonstrated that S-CuCoO had the highest catalytic activity among the catalysts. The sulfur-doped catalyst significantly improved the catalytic performance and stability. More than 98% of CAP (20 mg/L) was removed within 15 min at the initial pH = 5. The superior catalytic activity of S-CuCoO mainly resulted from the synergy of Cu(I) and Co(II). The presence of Cu(I) improved the conversion of Co(III) to Co(II), which maintained the high catalytic performance of S-CuCoO. In addition, the produced Cu(II) was further converted to Cu(I) by lattice oxygen (O2−), ensuring an adequate supply of Cu(I) in the catalyst. Radical quenching experiments revealed that both the SO4− and OH radicals were generated by the interaction of S-CuCoO with PMS, thereby contributing to the efficient degradation of CAP and the OH radicals played a larger role. The main intermediates of the CAP degradation were identified by high-performance liquid chromatography–mass spectrometry (HPLC-MS/MS). Theoretical calculations of the frontier electron densities (FEDs) were performed to determine the possible degradation pathways of CAP.