Photodegradation of CV over nanocrystalline bismuth tungstate prepared by hydrothermal synthesis

A nanocrystalline bismuth tungstate (Bi2WO6) with sheets morphology was successfully prepared by hydrothermal method and characterized by the field emission scanning electron microscopy with the energy dispersive X-ray spectrometer (FE-SEM-EDS), the X-ray diffractometer (XRD), and the high resolution X-ray photoelectron spectroscopy (HR-XPS). At alkaline condition, having pH 9, Bi(NO3)3·5H2O and H2WO4 as the starting materials, the reaction mixture was kept at 160 °C for 24 h, 48 h and 72 h to produce a high yield of Bi2WO6 with flower-like architecture. Moreover, the binding energy shift of Bi element was clearly observed, proposing that Bi(+3−x) formal oxidation state could most probably be attributed to the substoichiometric forms of Bi at outer site of the particles, and the formation of the low oxidation state resulted in oxygen vacancy in the crystal surface. The photocatalytic activities of the as-synthesized catalysts were evaluated by the photodegradation of crystal violet (CV) dye, while the nineteen intermediates were separated and characterized by the HPLC-PDA–ESI-MS techniques. The results demonstrated that the N-de-methylation degradation and the oxidative degradation of the CV dye took place during the degradation process. Based on these products, the probable degradation mechanisms were further proposed and discussed.

Graphical abstractSchematic illustration of the growth process of Bi2WO6 shows a plausible process of the sheet-like flower formation from fine amorphous particles. FE-SEM observation suggested that sheet-like flowers were produced through crystal plane-selective growth starting through aggregation of platelets produced dependently. Such anisotropic crystal growth was generally achieved by a selective adsorption of additives on specific sites suppressing isotropic crystal growth.Figure optionsDownload full-size imageDownload high-quality image (185 K)Download as PowerPoint slideHighlights► The binding energy of Bi(+3−x) formal oxidation state was clearly observed. ► The flower-like architecture Bi2WO6 was produced by hydrothermal reaction. ► The photocatalytic degradation of crystal violet was evaluated by HPLC-PDA–ESI/MS.