Catalytic activation of peroxymonosulfate with manganese cobaltite nanoparticles for the degradation of organic dyes.

In this work, we report the facile hydrothermal synthesis of manganese cobaltite nanoparticles (MnCo2O4.5 NPs) which can efficiently activate peroxymonosulfate (PMS) for the generation of sulfate free radicals (SO4˙-) and degradation of organic dyes. The synthesized MnCo2O4.5 NPs have a polyhedral morphology with cubic spinel structure, homogeneously distributed Mn, Co, and O elements, and an average size less than 50 nm. As demonstrated, MnCo2O4.5 NPs showed the highest catalytic activity among all tested catalysts (MnO2, CoO) and outperformed other spinel-based catalysts for Methylene Blue (MB) degradation. The MB degradation efficiency reached 100% after 25 min of reaction under initial conditions of 500 mg L-1 Oxone, 20 mg L-1 MnCo2O4.5, 20 mg L-1 MB, unadjusted pH, and T = 25 °C. MnCo2O4.5 NPs showed a great catalytic activity in a wide pH range (3.5-11), catalyst dose (10-60 mg L-1), Oxone concentration (300-1500 mg L-1), MB concentration (5-40 mg L-1), and temperature (25-55 °C). HCO3 -, CO3 2- and particularly Cl- coexisting anions were found to inhibit the catalytic activity of MnCo2O4.5 NPs. Radical quenching experiments revealed that sulfate radicals are primarily responsible for MB degradation. A reaction sequence for the catalytic activation of PMS was proposed. The as-prepared MnCo2O4.5 NPs could be reused for at least three consecutive cycles with small deterioration in their performance due to low metal leaching. This study suggests a facile route for synthesizing MnCo2O4.5 NPs with high catalytic activity for PMS activation and efficient degradation of organic dyes.