Dual-frequency (20/40 kHz) ultrasonic assisted photocatalysis for degradation of methylene blue effluent: Synergistic effect and kinetic study

Dual-frequency ultrasonic assisted photocatalysis (DUAP) was proposed to enhance the degradation efficiency of methylene blue (MB) solution. The influence of operational parameters, i.e., irradiation time, ultrasonic arrangement, TiO2 concentration and power density, was studied. The results implied that the rapid degradation of MB solution was achieved in 18 min under DUAP with the dual frequencies of 20/40 kHz. Kinetic investigation of MB degradation for the DUAP process was conducted on the basis of first-order kinetic equation and the synergistic effect was assessed by examination of the apparent rate constant. The effect of ultrasonic arrangement was analyzed by comparison of the pressure amplitude of ultrasonic superposition field. The evolvement of intermediate products and the role of active species during DUAP were distinguished by UV–Vis spectra and the free radical scavenging experiment.

► Dual-ultrasonic assisted photocatalysis (DUAP) was employed to degrade methylene blue (MB) solution.
► The synergistic effect of DUAP was intensified to exist obviously.
► MB degradation under DUAP process obeys first-order kinetics.
► Increasing ultrasonic power density facilitates the increase of the apparent rate constant.