Photodegradation of methyl orange aqueous on MnWO4 powder under different light resources and initial pH

The effects of light resource, initial pH and H2O2 on the photodegradation of methyl orange aqueous were studied in this work. Single-phase MnWO4 powder was synthesized by an aqueous reaction method. The TEM micrographs of the powders revealed that the powders were of rodlike morphology with length of 50 nm and width of 15 nm. The photocatalysis experiments reveal that the decolorization efficiency of the methyl orange aqueous (6 × 10− 6 M) on the MnWO4 powder was very fast in sunlight, but relatively slow under irradiation of 40 W-fluorescent lamp. The rate of the decolorization increased as the initial pH of the solution increases, appearing more intense in sunlight. The efficiency at pH = 5 after irradiation of 8 h were 27.19% in sunlight and 37.24% in the lamp, but respectively increased to 91.05% and 49.06% as the pH increases to 9. H2O2 (2% value) can remarkably accelerate the decolorization at low initial pH, but can offset against the photocatalysis of MnWO4 at high initial pH to certain extent. After the sunlight and lamp irradiations of 6 h, the efficiencies respectively reached 93.44% and 73.72% for pH = 5 but were only 60.82% and 44.23% for pH = 9.