Abstract: Bi₂WO₆ nanosheets with highly efficient photocatalytic activity under visible light irradiation were prepared by a hydrothermal method using Bi(NO₃)₃·5H₂O and Na₂WO₃·2H₂O as starting materials and citric acid as the chelating agent. The properties of the as-prepared samples were investigated by X-ray diffraction, field emission high resolution transmission electron microscopy, Raman spectroscopy, and UV-Vis diffusion reflectance spectroscopy. The photocatalytic properties of the Bi₂WO₆ catalyst were also investigated. The results show that Bi₂WO₆ nanosheets with orthorhombic structure can be obtained by adjusting the pH value of the reaction system. Compared with the Bi₂WO₆ catalyst prepared without citric acid, the Raman bands of the nanosheets assisted with citric acid present blue shift and show a significant red shift in the absorption band and its band gap was narrowed to 2.55 eV. The pH value of the reaction system is the main factor affecting the visible light-driven photocatalytic activity. The Bi₂WO₆ sample prepared at pH = 7.0 shows a higher photocatalytic activity. Over this catalyst, the 100% degradation of methyl orange solution (10 mg/L) is obtained after visible light irradiation for 15 min. In addition, after 5 recycles, there is no significant decrease in its photocatalytic activity, indicating that Bi₂WO₆ is a stable photocatalyst for degradation of methyl orange under visible light irradiation.

Key words: tungsten acid bismuth, hydrothermal synthesis, citric acid, nanosheet, photocatalysis, methyl orange