A comparative study of the sonocatalytic degradation of methylene blue by using silicon carbide and titanium dioxide

The acoustic catalytic degradation of methylene blue (MB) was studied using silicon carbide (SiC) nanowires and commercial TiO2 (P-25). SEM images show that the average diameter of SiC nanowires is less than 500 nm and the length is up to tens of microns. XRD patterns and FTIR spectra confirmed the high purity of SiC in the catalyst. The catalytic performance of the two catalysts is better under alkaline conditions. The Kapp values (pseudo-first-order kinetics) of the synergistic effects of ultrasonic treatment and adsorption processes using SiC and TiO2 are 1.36 and 1.31 times the sum of the Kapp values of the two separate processes, respectively. This finding indicates that acoustic catalysis can improve the photocatalytic performance of SiC and TiO2 on MB. Compared with TiO2, SiC nanowires exhibit better acoustic catalytic performance, and hydroxyl radicals are more significant in the acoustic catalytic degradation of SiC to MB. Meanwhile, hydroxyl radicals play a leading role in the degradation process of MB. Under ultrasonic irradiation, the bubbles periodically expand and collapse rapidly. SiC is stimulated by UV irradiation through sonoluminescence to produce photoinduced e--h+ pairs and (OH)-O-center dot, then methylene blue is completely mineralized.