Co₃O₄ Nanocubes for Degradation of Oxytetracycline in Wastewater <i>via</i> Peroxymonosulfate Activation

Abstract

Despite significant progress being made in the development of cobaltosic oxide or modified cobaltosic oxide nanomaterials in the degradation of organic pollutants, to our knowledge, there are only very few available reports on the crystal facet effect of Co3O4 with different morphologies on peroxymonosulfate activation for oxytetracycline degradation. Herein, we first reported the synthesis of three kinds of Co3O4 nanocomposites with various morphologies, including nanocubes (Co3O4-c), octahedron (Co3O4-o), and truncated octahedron (Co3O4-t), for activating peroxymonosulfate (PMS) in the degradation of oxytetracycline at 30 °C. The detailed physical characterizations illustrated that Co3O4-c, Co3O4-o, and Co3O4-t possessed a uniform morphology of nanocubes, octahedron, and truncated octahedron, with six {100} exposing facets, six {111} exposing facets, and a mixture of eight {111} and six {100} exposing facets, respectively. In particular, the optimal Co3O4 nanocubes (Co3O4-c) presented the highest catalytic reactivity in the activation of PMS for OTC degradation, with 82.8% degradation efficiency and 46.4% mineralization rate at 30 °C. The DFT results exhibited that the ΔEtotal of PMS on Co3O4 {100} exposing facets (−23.7 eV) was much lower than that of PMS on Co3O4 exposing {111} facets (−17.2 eV), indicating that PMS activation was more likely to occur at the Co3O4 {100} exposing facets, which was in good accordance with the above experimental conclusion. Overall, the explanation of the crystal facet effects on PMS activation proposes a research orientation for the synthesis of crystal engineering of heterogeneous catalysts on wastewater treatment.