Boosting the activation of Peroxymonosulfate and the degradation of metronidazole over FeCo2O4 quantum dots anchored on β-FeOOH Nanosheets: Inspired from octahedral Co(II) with missing angle

Peroxymonosulfate (PMS) activation by bimetallic Co/Fe oxides, especially spinel FeCo2O4, is a promising way in decontaminating organic pollutants in wastewaters. However, it suffers from low efficiency and the intrinsic catalytic mechanisms are still poorly understood. Therefore, we applied lattice VOs (oxygen vacancies) adjustment strategy to construct a octahedral Co(II)–enriched FeCo2O4 quantum dots anchored on β-FeOOH nanosheets composite (Co(II)-FCQDs/FNS) for boosting PMS activation during the degradation of Metronidazole (MNZ), and pure FeCo2O4 quantum dots (FCQDs) was studied as a comparison. As a result, in PMS/Co(II)-FCQDs/FNS system, 5–30 mg·L−1 MNZ could be completely degraded within 5 min with the usage of 0.05 g·L−1 catalyst, and the degradation efficiency of 100 mg·L−1 MNZ reached 99.92% within 40 min with the PMS utilization of 62.90% at the same condition, whose degradation rate constant was 6.45 times than that of the FCQDs/PMS system. The electron paramagnetic resonance (EPR) and quenching experiments indicated that PMS /Co(II)-FCQDs/FNS system was a pure radical-based (sulfate radicals (SO4•−), hydroxyl radicals (•OH) and superoxide radical (O2•−) oxidation process. Density functional theory (DFT) calculation revealed that the generation of octahedral Co(II) derived from oxygen vacancies, improved the charge transfer in the spinel lattice while providing a new electron transfer channel from lattice Co(II)/Fe(II) to the surface of FeCo2O4. Simultaneously, strengthened the surface adsorption of HSO5− and increased the number of unpaired electrons, thus boosting the PMS activation performance. In addition, the influence of reaction parameters and water matrix were investigated. Finally, the degradation pathway of MNZ was proposed and the toxicity of intermediates was also assessed. This work is expected to facilitate the design and application of PMS/Co(II)-FCQDs/FNS system for decontaminating organic pollutants from wastewater.