Effects of ultrasonic frequency and initial concentration on degradation of methylene blue

Abstract

The ultrasonic degradation of hazardous organic compounds in an aqueous solution is an attractive technology for wastewater treatment. The kinetics of ultrasonic degradation has been investigated. However, there have been only a few quantitative studies of the effect of ultrasonic frequency on degradation rate. In this study, the ultrasonic degradation of methylene blue was performed at various frequencies, especially in the high frequency region, and various initial concentrations. From the results of the time dependence of the methylene blue concentration in this study, ultrasonic degradation was considered to be a pseudo-first-order reaction. The apparent degradation rate constant and sonochemical efficiency have a linear relationship, and the apparent rate constant and initial concentration have an inversely proportional relationship. These phenomena well agree with our proposed formula for estimating the apparent degradation rate constant. In addition, our proposed model is also applicable to the ultrasonic degradation of nonvolatile and hydrophilic compounds.

Critical factors in sonochemical degradation of fumaric acid

“…2 is similar as the sonochemical degradation of methylene blue, i.e., the degradation rate decreases with increasing initial concentration [30].…”

“…This result is consistent with the sonochemical degradation of hydrocarbons, chlorinated hydrocarbons, phenol, methylene blue, etc. [25][26][27][28][29][30].…”

“…In addition, the oxidative degradation of fumaric acid with OH radicals is much slower than that of phenol as fumaric acid has a much lower atmospheric OH rate constant (K OH : 7.949 Â 10 À12 -cm 3 /mol sec at 25°C) [37] than phenol (K OH : 2.63 Â 10 À11 cm 3 /mol sec at 25°C) [38]. The previous study has denoted that the degradation of volatile, hydrophobic compound such as carbon tetrachloride is considered to occur in the bubble of cavitation, while the degradation of non-volatile, hydrophilic compounds such as phenol and methylene blue takes place through oxidation process in aqueous solution [30]. This is the reason why fumaric acid and other short-chain carboxylic acids exist as intermediates during the sonication of phenol-containing solutions.…”

Improvement of the rate of sono-oxidation in the presence of CO2

“…In particular, in the case of an ultrasonic frequency of 200 kHz and an output power of 100 W, the rate of sono-oxidation with CO 2 was seven times as high as that without CO 2 . The ultrasonic frequency dependence of sonication was reported previously, 13,[19][20][21] and almost all studies recommended 200-300 kHz as an effective frequency. Our results for an Ar atmosphere and even a CO 2 -Ar atmosphere also support their conclusions.…”

Effect of Particle Addition on Ultrasonic Degradation Reaction Rate

“…Especially, degradation of phenol and some of its derivatives such as chlorophenol and nitrophenol using ultrasound has been investigated by many researchers [7]- [11]. The ultrasonic degradation of dyes has also been investigated [12]- [18]. In these studies, the effects of ultrasonic frequency, power, dissolved gas and solution pH on degradation have been investigated.…”