Plasma-induced redox reactions synthesis of nanosized α-, γ- and δ-MnO2 catalysts for dye degradation

Mesoporous alpha- and delta-MnO2 with specific surface areas of 98 and 186 m(2)/g, were obtained via plasmachemical-reduction of KMnO4 solutions induced by flashing them with a gliding arc plasma operated at respectively high and low voltages. Correspondingly, gamma- and delta-Mno(2) with 48 and 289 m(2)/g, were obtained via plasmachemical-oxidation of Mn(CH3COO)(3) solutions. At lower humid airflow, the plasma also led during the reduction of KMnO4 to changes of structure and morphology, and to increased specific surface areas. These changes are hypothesized to be due to a variation of the amount of radicals generated by the plasma along its creation parameters. Performances of the prepared catalysts were evaluated in the oxidation of Tartrazin Yellow (TY) chosen as a model dye polluting wastewaters. TY bleaching was significantly different from one plasma-synthesized material to another. alpha-MnO2, being the best of the plasma synthesized material appears to be recyclable and resistant to dissolution. This contribution confirms the importance of mastering the structure and texture of MnO2 catalysts during their synthesis. Gliding arc plasma is revealed as an easy and efficient method to achieve so.