Effect of Bi2WO6 nanosheets on the ultrasonic degradation of organic dyes: Roles of adsorption and piezocatalysis

The piezoelectric Bi 2 WO 6 nanosheets with in-plane spontaneous polarization were synthesized by hydrothermal method . The adsorption and piezocatalytic properties of the synthesized Bi 2 WO 6 nanosheets were investigated upon different variants including synthesis conditions, model dye species, and pH of the dye solution. The materials exhibited positive surface charge and selective adsorption ability for the anionic dye methyl orange (MO) in acidic and neutral conditions. The ultrafast removal of MO ( k obs  = 0.718 ppm s −1 ) under ultrasonic vibration was mainly controlled by monolayer adsorption, which followed the pseudo-second-order adsorption kinetics and the Langmuir adsorption isotherm . To eliminate the interference of adsorption, the cationic Rhodamine B (RhB) was adopted as the target pollutant for piezocatalytic experiments. The maximum rate constant of RhB removal (3.9 × 10 −2  min −1 ) was obtained in Bi 2 WO 6 sample with the largest specific surface area of 32.8 cm 2 g −1 . The catalytic nature of the dye degradation phenomenon was confirmed by detection of free radicals and the quenching effect of radical scavengers. The present work demonstrates the potential of Bi 2 WO 6 nanosheets in piezocatalytic applications. Moreover, the synergistic effect of adsorption and piezocatalysis is valuable for in-situ regeneration of the piezoelectric adsorbents.