Intensification of sonochemical degradation of methylene blue by adding carbon tetrachloride

With the emphasis of governments on environmental protection, the treatment of dye wastewater has received extensive attention. Methylene blue (MB) is a typical dye in industrial wastewater. Sonochemical degradation of methylene blue (MB) was investigated by the addition of CCl4 in the present work. The effects of operation parameters were examined including the concentration of CCl4, temperature, initial pH of the solution, and ultrasonic power on the degradation of MB. The concentration of CCl4 and the initial pH of the solution exhibited a more significant effect on MB degradation than the effect on that exhibited by ultrasonic power and temperature. Under the optimum experimental conditions, MB was degraded completely after 30 min of ultrasound irradiation. Considering the costs in practical applications, the ultrasonic power intensity and CCl4 concentration can be further optimized to 60 W/L and 0.05% (35 min degrade 98.6%), respectively. The total organic carbon (TOC) and Cl− concentrations from CCl4 in the degraded solution were 0.23 and 0.13 mmol/L respectively. The red-shift of MB absorption peak (from 665 to 679 nm) was observed during the process of degradation. The identification of the intermediates and degradation pathways by liquid chromatography coupled with mass spectrometry (LC–MS) shows that the n-electron-containing group –Cl is connected with the chromophore groups causing the absorption peak to shift towards the long-wave.