Surface Disorder Engineering of Flake-Like Bi2WO6 Crystals for Enhanced Photocatalytic Activity

Abstract

The NaBH4 reduction method has been used to engineer the surface of flake-like Bi2WO6 (BWO) crystals with the aim of creating disordered surface structure and enhancing the photocatalytic activity. The disorder-engineered BWO samples were investigated by means of x-ray powder diffraction, field-emission scanning electron microscopy, field-emission transmission electron microscopy, x-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, photoluminescence, electrochemical impedance spectroscopy and photocurrent response. Simulated sunlight, UV light and visible light were separately used as the light source to evaluate the photocatalytic activity of the samples toward the degradation of rhodamine B in aqueous solution. It is demonstrated that 0.03 M-BWO treated at 0.03 M NaBH4 solution exhibits the highest photocatalytic activity, ca. 2.4 times higher than pristine BWO under simulated sunlight irradiation. The significant increase in the photocatalytic activity is observed at UV irradiation, which can be explained by the fact that the disordered surface states (formed in the forbidden gap of BWO) can act as electron acceptors to facilitate the separation of photogenerated electron/hole pairs. A slightly enhanced photocatalytic activity is observed under visible light irradiation, which is attributed to the enhanced visible light absorption induced by the disordered surface states. In addition, it is found that the treatment with high NaBH4 concentrations is detrimental to the photocatalytic activity due to the creation of bulk defects in BWO crystals.