Sonochemical versus hydrothermal synthesis of bismuth tungstate nanostructures: Photocatalytic, sonocatalytic and sonophotocatalytic activities

In the present work, an ultrasound-assisted hydrothermal method was applied as a new approach for the synthesis of Bi2WO6 nanostructures. In sonication, a cup horn system as an indirect high intensity sonicator was used. To determine the influence of ultrasonic waves on the morphology, Bi2WO6 was also synthesized using the hydrothermal method. The conventional and sonochemical products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier transform infrared (FTIR), Raman, photoluminescence (PL), and UV-Vis (UV-Vis) spectroscopies. The XRD patterns confirmed that the sonosynthesized sample has higher crystallinity than the conventional one. The results also showed that ultrasound decreased the particle size and improved the size distribution. In comparison with the hydrothermal sample, the flower like structures formed under sonication have many hollow sites, resulting in higher harvesting and scattering of visible light. The efficiency of resulting nanoparticles in degradation of a binary mixture (RhB/MB) as pollutant was evaluated by photocatalytic, sonocatalytic, and sonophotocatalytic processes. The sonosynthesized sample removed the pollutants four times faster than the hydrothermal sample in sonophocatalytic process. Besides, determining factors including pH, pollutant concentration, temperature, and ultrasound amplitude were optimized in the sonophotocatalytic process.