Hydrothermal preparation of nanostructured manganese oxides (MnOx) and their electrochemical and photocatalytic properties

Manganese oxides nanomaterial (MnOx) with crystalline phases of MnOOH nanorod and Mn3O4 octahedron-like were synthesized by hydrothermal method based on the redox reaction between MnO4− and CH2O at 120 °C and 200 °C for 10 h, respectively. The β-MnO2 nanowires were prepared by calcining MnOOH nanorods at 300 °C for 3 h in air. Particles were characterized by XRD, FE-SEM, TEM, SA-ED, HR-TEM, Brunauer–Emmett–Teller (BET) and UV–vis diffuse reflectance spectroscopy. Their capability of catalytic degradation of alizarin yellow R with air oxygen in aqueous under visible light irradiation and electrochemical properties of as-prepared nanocrystal modified with carbon paste electrode were comparatively studied. The degradation products were determined by GC–MS. In addition, some influences factors, such as pH and temperature on the photocatalytic degradation were also investigated. Among the as-prepared MnOx nanostructures, β-MnO2 nanowire exhibit higher specific capacitance and better catalytic activity than Mn3O4 octahedron-like and MnO(OH) nanorod. The hydroxyl radical mechanism of the photocatalytic degradation of alizarin yellow R was detected and discussed.

► β-MnO2 nanowires and Mn3O4 octahedrons-like were prepared by calcining of MnO(OH) nanorods and hydrothermal process, respectively. ► The electrochemical characteristics and catalytic degradation efficiency of alizarin yellow R with air oxygen in aqueous solution under the light irradiation. ► The effects of pH and temperature on the photocatalytic degradation were investigated. ► The degradation products were estimated by GC–MS. ► Hydroxyl radical reaction of the photocatalytic degradation was detected by the TA-PL method.