The synergistic effect of calcite and Cu on the degradation of sulfadiazine via PDS activation: A role of Cu(Ⅲ).

A system of Cu/calcite/PDS was constructed to degrade sulfadiazine (SDZ). Different from the traditional Cu-mediated activation, a low concentration of Cu that met drinking water standards (≤ 1 mg/L) transformed into Cu(Ⅱ) solid in the presence of calcite, and then enhanced the degradation of SDZ via PDS activation over a pH range from 3 to 9. According to scavenger and chemical probe experiments, Cu(Ⅲ), rather than radicals (hydroxyl radicals and sulfate radicals) and singlet oxygen, was the predominant reactive species, which was responsible for the degradation of SDZ. Based on the results of XRD, ATR-FTIR, and CV curves et al., CuCO was the main complex with high reactivity for PDS activation to form Cu(Ⅲ). Moreover, detailed degradation pathways of sulfadiazine were proposed according to the UPLC-ESI-MS/MS and their toxicity was predicted by ECOSAR. Besides, the real water matrix would not seriously affect the degradation of SDZ in the Cu/calcite/PDS system. In summary, this study reveals a new insight into the synergistic effect of Cu and calcite on the SDZ degradation, and promotes an understanding of the environmental benefits of natural calcite.