Synthesis of coal fly ash supported MnO₂ for the enhanced degradation of Acid Red 73 in the presence of peroxymonosulfate

Abstract

In this study, coal fly ash supported MnO₂ (CFA@MnO₂) was synthesized as heterocatalyst for the activation of peroxymonosulfate to degrade Acid Red 73 (AR73). The synthesized catalyst was characterized by X-Ray Fluorescence Spectrometer (XRF), X-ray powder diffraction (XRD), Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET). The composite of CFA@MnO₂ possesses a large surface area of 74.59 m²/g. In the catalytic experiment, CFA@MnO₂ exhibits excellent catalytic performance with 99.13% AR73 removed within 40 min with a high kinetic rate constant of 0.124 min^-1, 5.49 times higher than that of pure MnO₂. The operating parameters of CFA@MnO₂-based fenton catalytic system were discussed, including MnO₂ loading, solution pH, PMS dosage and temperature. The catalyst maintained a relatively high removal rate (>85%) over 5 cycles and degradation intermediates are detected on the catalyst surface after cycled via XPS analysis. The degradation mechanism was investigated by quenching experiments and Electron Paramagnetic Resonance technology. The surface-bound ^·OH and SO₄ ^·- are considered as the main active radicals in the degradation process. The composite of CFA@MnO₂ provides a low-cost and efficient alternative for the catalytic oxidation of organic pollutants.