Ultrasonic Spray Pyrolysis Synthesis of Porous Bi2WO6 Microspheres and Their Visible-Light-Induced Photocatalytic Removal of NO

Abstract

In this study, porous Bi2WO6 microsphere photocatalysts were obtained via the ultrasonic spray pyrolysis method using bismuth citrate and tungstic acid as precursors in basic aqueous solution. The characteristics of the resulting samples were investigated in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. The resulting porous Bi2WO6 microsphere was of high crystallinity, which means fewer traps and stronger photocatalytic activity. The band-gap energy of Bi2WO6 microspheres estimated from the (αhν)2 versus photon energy (hν) plots was 2.92 eV. The formation of the porous structure in the as-prepared microspheres can be ascribed to the existence of citrate anions and in situ generated carbon residues that can serve as capping agents and templates, respectively, during the synthesis processes. It was found that the synthesis temperature was an important parameter controlling the morphology of the Bi2WO6 microspheres. As compared with the bulk Bi2WO6 sample, the resulting porous Bi2WO6 microspheres demonstrated superior photocatalytic activities on the removal of NO under either visible light or simulated solar light irradiation. The highest NO removal rates were 110 and 27 ppb/min for the porous Bi2WO6 sample under solar light and visible light (λ > 400 nm) irradiation, respectively. On the basis of the analysis of the characterization and experimental observations, a possible mechanism on the formation of porous Bi2WO6 microspheres was also proposed.