Analysis of the degradation mechanism of methylene blue by atmospheric pressure dielectric barrier discharge plasma

The degradation of a methylene blue solution using the dielectric barrier discharge (DBD) technique is proposed in this paper. The effect of pH on the degradation rate is also investigated. The concentration of oxidants in the liquid phase is tested through iodimetry. The key factors that affect the degradation rate of the methylene blue solution are analyzed. The intermediate and final products are also investigated. The discharge process is studied by analyzing the radical species in both gas and liquid phases. The degradation mechanism of methylene blue is investigated according to the bond energy theory. The results show that the degradation rate in acidic solutions is higher than that in alkaline solutions. The lowest degradation rate is obtained from the neutral solution. The existence of OH− in the liquid phase can promote the generation of hydroxyl radicals during the degradation process. Radical species (e.g., O3 and OH) are the key factors during the degradation process of methylene blue. NO3−, SO42−, and Cl− are discovered in the liquid phase through ionic chromatogram testing. The methylene blue molecules are oxidized into inorganic ions by DBD plasma.