Decolorization of an aqueous solution of methylene blue using a combination of ultrasound and peroxate process

Abstract

For oxidative decolorization of an aqueous solution of methylene blue (MB), the “Sonoperoxate” process, a combination of ultrasonic (US) irradiation and “Peroxate” process, – US/H2O2/KIO4 was used in the current work. In order to minimize the costs of oxidants, energy consumption, and reduce the duration of decolorization, the studies were performed to understand the influence of the molar ratio MB:H2O2:KIO4, the MB initial concentration, the ultrasonic power, and the pH value of the initial solution on the decolorization of MB. The best conditions for decolorization of an MB aqueous solution using the “Sonoperoxate” process have been established as initial MB concentration of 62.6 μM, the molar ratio MB:H2O2:KIO4 of 1:100:25, pH of 4.00, US power of 60 W and the decolorization duration of 300 s. Under these conditions, the decolorization extent was quite high (95.6%). An increase in the processing duration to 3600 s led to a marginal increase in the decolorization extent of MB to 98.2%. The rate constants of the processes US/H2O2, US/KIO4, H2O2/KIO4, and US/H2O2/KIO4 were used to calculate the value of the synergetic coefficient for the hybrid process, US/H2O2/KIO4. The obtained synergetic coefficient was 3.25 at the molar ratio MB:H2O2:KIO4 as 1:100:25, and 1.62 at the molar ratio of 1:200:50 indicating the dominant contribution of KIO4. The effect of ultrasound as an activator of oxidants (periodate, hydrogen peroxide) has been conclusively established in the current work.