Synthesis, photocatalytic activities and degradation mechanism of Bi2WO6 toward crystal violet dye

Nanocrystalline Bi2WO6 (BWO) with square-plates morphology was prepared by the hydrothermal synthesis in autoclave. Bi(NO3)3·5H2O with (NH4)10W12O41·5H2O was reacted in pH 9 solution at 160 °C for 24 h, 48 h and 72 h to yield the resulting Bi2WO6 as a white precipitate. Bi2WO6 was characterized by the field emission scanning electron microscopy with the energy dispersive X-ray spectrometer (FE-SEM–EDS), the X-ray diffractrommeter (XRD), and the high resolution X-ray photoelectron spectroscopy (HR-XPS). The XPS spectra showed a binding energy shift of Bi element, suggesting that the Bi(+3−x) formal oxidation state could be the substoichiometric forms of Bi within the Bi2O2 layer. The photocatalytic activities of the prepared BWO samples were evaluated by the photodegradation of crystal violet (CV) dye under UV-light irradiation (365 nm). The intermediates were separated and characterized by HPLC-PDA-ESI/MS techniques and the results indicate that the N-de-methylation with oxidative degradation of the crystal violet dye took place. Based on these intermediates, we propose and discuss the degradation pathways.