Insight into radical-nonradical coupling activation pathways of peroxymonosulfate by CuO for antibiotics degradation.

In this work, a heterogeneous catalyst of CuO was rationally designed by using Cu-based metal organic frameworks (marked Cu-BDC) as the template, and was used to degrade tetracycline (TC) via activation of peroxymonosulfate (PMS). The optimal CuO-350 showed excellent catalytic efficiency for TC degradation, and the reaction rate constant (0.104 min) was 8 times higher than that (0.013 min) of raw Cu-BDC. The characterization observations confirmed that CuO-350 possessed multiple valence states (CuO and CuO) and oxygen vacancies (O), both of which were favorable for the activation of PMS, resulting in promoting the generation of active species in the CuO-350 + PMS system. Different from the free radical pathway in Cu-BDC + PMS system, a radical-nonradical coupling process was detected in the CuO-350 + PMS system, which was confirmed by quenching experiments and EPR measurements. Moreover, the toxicity prediction showed that the toxicity of degradation intermediates declined compared with TC. This work not only opened up a new strategy for the rational design and preparation of high-efficient catalysts by employing metal organic frameworks precursors, but also offered an insight into the reaction mechanism of PMS activation through a radical-nonradical coupling process catalyzed by CuO-350 derived from Cu-BDC.