Effect of cation insertion on the stability of gliding arc plasma-precipitated mesoporous MnO2 dye bleaching catalysts

Abstract

α-MnO2 and γ-MnO2 polymorphs were, respectively, obtained from the plasma precipitation of KMnO4 and Mn(CH3COO)3⋅2H2O precursors. The obtained powders were calcined at 150 °C, 210 °C and 400 °C, and characterized by X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), nitrogen physisorption and Scanning electron microscopy (SEM). As a result, the calcination does not significantly affect textural properties and crystalline structure of the α-MnO2, while γ-MnO2 is transformed into β-MnO2 for temperatures above 400 °C. The thermal stability α-MnO2 is due to the K+ ions insertion in its 4.6 Å × 4.6 Å tunnels and corroborated the catalytic performance of 100, 98, 98 and 97% compared to 71, 54, 52 and 48% for γ-MnO2 after four successive reuse cycles on Tartrazine Yellow dye. The insertion of cationic species (K+, Na+, Mg2+) into the structure of MnO2 reinforces its crystalline structure and promotes the formation of powerful oxidizing species through oxygen vacant sites.