Activation of peroxymonosulfate by a waste red mud-supported Co3O4 quantum dots under visible light for the degradation of levofloxacin

In this work, iron-rich red mud (RM), a industrial waste generated from alumina production by Bayer process, was used as a potential carrier for supporting Co3O4 quantum dots (QDs). A novel heterogeneous catalyst of RM-based Co3O4 QDs (Co3O4/RM) composite was prepared via a simple method and used for the activation of peroxymonosulfate (PMS) under visible light (Vis) to degrade levofloxacin (LVF). The characterization results demonstrated that in-situ growth of Co3O4 QDs on the surface of RM could increase the surface area, reduce the aggregation, enhance the visible light response and accelerate the separation of photogenerated electron-hole pairs, all of which effectively improved the catalytic activity of Co3O4/RM composite. Approximately 95.3 % of LVF was decomposed at 20 min in the PMS/Vis system catalyzed by the optimal Co3O4/RM-1200 composite. Both SO4·- and h+ generated in Co3O4/RM-1200/PMS/Vis system were responsible for the rapid LVF degradation; especially the SO4·- was the dominant active specie. Based on LC-MS technology and DFT calculation, the reasonable degradation pathways of LVF in Co3O4/RM-1200/PMS/Vis system were proposed. The ecotoxicity of degradation intermediates was evaluated according to the Toxicity Estimation Software Tool (T.E.S.T.) software. In addition, critical influencing factors on the degradation of LVF in Co3O4/RM-1200/PMS/Vis system were investigated. Exhilaratingly, it was found that the Co3O4 QDs were deposited homogeneously on the surface of RM with the Fe-O-Co bond between Co3O4 component and Fe2O3 component, which not only prevented the leaching of metal ions but also contributed to the superior stability and reusability. This work has designed a new perspective for the development of a cost-efficiency and stable RM-based Co3O4 QDs catalyst to activate PMS under visible light for the degradation of LVF.