Kinetics of sonophotocatalytic degradation of an anionic dye nigrosine with doped and undoped zinc oxide

The current research focuses on the photocatalytic, sonocatalytic and sonophotocatalytic degradation of nigrosine dye with nitrogen-doped and undoped zinc oxide powders. The sonophotocatalytic degradation of dye was found to occur at a higher rate than during photo- or sonocatalytic processes. Nitrogen-doped and undoped zinc oxide powders were synthesized by a wet chemical method. Further, scanning electron microscopy (FESEM), electron dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), UV-VIS spectroscopy (UV-VIS) and transmission electron microscopy (TEM) were used for the characterization of N-doped ZnO. The kinetics of nigrosine degradation were also studied and the results indicated that the degradation kinetics of nigrosine followed the first-order kinetics. The rate constant and the percentage of degradation were found to be highest, 7.33 × 10−4 (s−1) and 92% respectively, for sonophotocatalytic process after 90 min of reaction. Due to an increase in the available surface area or active sites of the catalyst, a higher rate constant and degradation efficiency was observed in the sonophotocatalytic system than in the photocatalysis system.