Study on degradation of acid orange II in aqueous solution using one-dimensional MnO₂ nanorods

MnO₂ nanorods were prepared by the reaction of KMnO₄ and MnSO₄ in aqueous media and subsequently followed by hydrothermal methods. The structure and surface morphology of as-prepared powder were characterised by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results indicated that the prepared MnO₂ possessed α- and γ structure. SEM observations showed that the obtained MnO₂ powder possessed a well-defined one-dimensional nanorod-like shape 100 nm wide and 700 nm long. The surface area of the MnO₂ nanorods was 92 m² g⁻¹. The degradation efficiency of MnO₂ nanorods towards the organic pollutants in aqueous solution was evaluated using acid orange II as a model dye. It was found that the degradation efficiency of MnO₂ nanorods was a function of initial acid orange II concentration, MnO₂ nanorods concentration, and the proton concentration. The apparent reaction orders for the initial acid orange II concentration, MnO₂ nanorods concentration and the proton concentration were determined to be −0.76, 0.37 and 0.12, respectively. It was found that the degradation efficiency for 60 ppm acid orange II reached 99% with 0.5 g L⁻¹ MnO₂ nanorods concentration at pH 2.0 after 60 min, demonstrating its higher degradation efficiency in aqueous solution. The apparent activation energy of the degradation reaction of acid orange II was calculated to be 17.3 kJ mol⁻¹. Furthermore, MnO₂ nanorods were demonstrated to have superior durability during regeneration tests.