Gliding Arc Plasma Synthesis of MnO2 Nanorods for the Plasma-Catalytic Bleaching of Azo⟨c Amaranth Red Dye

Manganese (IV) oxide (MnO2) nanoparticles were synthesized, via a plasma-chemical route by using a gliding arc discharge at atmospheric pressure. alpha-MnO2 nanorods were obtained from the chemical reduction of KMnO4. The synthesis yield was 96.8% after 4.5 min of exposure of the solution to the plasma. Further increase of the exposure time induced a decrease of MnO2 yield because of its reductive transformation into Mn2+ ions. Particles were characterized by X-ray powder diffraction, scanning electron microscopy, Fourier Transform Infrared spectroscopy, and nitrogen physisorption. The plasma-catalytic properties of the synthesized material were tested in the bleaching of amaranth red (AR). AR bleaching efficiencies of 17 and 44% were respectively obtained when the plasma and plasma-catalyst processes were applied for 30 min with initial pH 10. The influence of the initial pH, and catalyst concentration were investigated: the AR bleaching efficiency increased linearly with the catalyst concentration and increased markedly when the pH of the solution decreased.