Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases

et al. 2017

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133

This work explores the effect of persulfate (PS) on the sonochemical degradation of organic pollutants taking naphthol blue black (NBB), an anionic diazo dye, as a substrate model. The sonolytic experiments were conducted in the absence and presence of PS under various experimental conditions including acoustic power (10-80W), frequency (20 and 585kHz) and saturating gas (argon, air and nitrogen). Experimental results showed that PS decomposition into sulfate radical (SO) takes place by sonolysis and increasing PS concentration up to 1g/L would result in an increase in the NBB degradation rate. It was found that the PS-enhanced effect was strongly operating parameters dependent. The positive effect of PS decreased with increasing power and the best enhancing effect was obtained for the lowest acoustic power. Correspondingly, the PS-enhanced effect was more remarkable at low frequency (20kHz) than that observed at high frequency ultrasound (585kHz). Nitrogen saturating gas gave the best enhanced effect of PS than argon and air atmospheres. Theoretical (computer simulation of bubble collapse) and experimental measurements of the yields of free radical generation under the different experimental conditions have been made for interpreting the obtained effects of PS on the sonochemical degradation of the dye pollutant. The experimental findings were attributed to the fact that radical-radical recombination reactions occur at faster rate than the radical-organic reaction when the concentration of free radicals is too high (at higher sonochemical conditions).

Section: •−mentioning

confidence: 70%

Section: Theoretical Packagementioning

confidence: 99%

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Persulfate-enhanced sonochemical degradation of naphthol blue black in water: Evidence of sulfate radical formation

Ferkous

et al. 2017

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133

“…Between air and N 2 , because the difference in the solubility of gases is not considerable, the [53] that the production rate of • OH radical from the collapsing bubble is strongly dependent on the trapped amount of the N 2 gas at the collapse, and the higher the concentration of N 2 , the lower will be the production rate of • OH radical from the collapsing bubble. The reason for this trend was associated to the consumption of • OH radical through the reaction NO+ • OH+M ↔ HNO 2 +M.…”

Section: Effect Of Dissolved Gasmentioning

confidence: 99%

Sonochemical degradation of naphthol blue black in water: Effect of operating parameters

Ferkous

2015

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In this work, the sonochemical degradation of naphthol blue black (NBB), an acidic diazo dye, in water was investigated. The effects of several operating parameters such as initial NBB concentration, acoustic intensity, ultrasonic frequency, nature of the dissolved gas and solution pH on the degradation of the dye were carried out. The obtained results showed that ultrasound completely destroyed NBB (5 mg L(-1)) after 45 min of sonication and most of the chemical oxygen demand was eliminated after 90 min of treatment. It was found that the initial rate of sonolytic degradation increased with increasing the initial NBB concentration. The fitting of the experimental data by a heterogeneous Langmuir-kinetics model showed that NBB degraded mainly at the interfacial region of the bubble by hydroxyl radical (OH) attack. The degradation rate of the dye increased substantially with increasing acoustic intensity in the range of 0.44-3.58 W cm(-2) and decreased with increasing frequency in the range of 585-1140 kHz. The rate of NBB degradation decreased in the order of Ar>air>N2. The significant degradation was achieved in acidic conditions (pH 2) where the initial degradation rate was 1.37 and 1.66 higher than those observed at pH 6 and pH 10, respectively.

“…The chemistry inside a bubble was also affected by the liquid temperature as a result of lowering bubble temperature. In fact, the number of the chemical reactions in the bubble decreased as the bubble temperature Tables 1 and 2 are refined from 73 possible reactions [42] according to the importance of each reaction toward the production/consumption of the main oxidizing species ( Å OH, O, HO 2 Å , H 2 O 2 and O 3 ). The criterion of refining is that each Table 1 The important chemical reactions inside a collapsing air/water vapor bubble when the maximum bubble temperature is 4430 K, which is the maximum bubble temperature at 300 kHz when the bulk liquid temperature is 25°C.…”

Section: Single Bubble Yield Dependence Of Liquid Temperaturementioning

confidence: 99%

Experimental and numerical investigation of the effect of liquid temperature on the sonolytic degradation of some organic dyes in water

Boutamine

et al. 2016

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This paper presents a comprehensive experimental and numerical investigation of the effects of liquid temperature on the sonochemical degradation of three organic dyes, Rhodamine B (RhB), Acid orange 7 (AO7) and Malachite green (MG), largely used in the textile industry. The experiments have been carried out for an ultrasonic frequency of 300 kHz. The obtained experimental results were discussed using a new approach combining the results of single-bubble event and the number of active bubbles. The single-bubble event was predicted using a model that combines the bubble dynamics with chemical kinetics occurring inside a bubble during the strong collapse. The number of active bubbles was predicted using a method developed in our previous work. The experiments showed that the degradation rate of the three dyes increased significantly with increasing liquid temperature in the range 25-55°C. It was predicted that the main pathway of pollutants degradation is the attack by OH radicals. The simulations showed that there exists an optimum liquid temperature of about 35°C for the production of OH inside a bubble whereas the number of active bubbles increased sharply with the rise of the liquid temperature. It was predicted that the overall production rate of OH increased with increasing liquid temperature in the range 25-55°C. Finally, it was concluded that the effect of liquid temperature on the sonochemical degradation of the three dyes in aqueous phase was controlled by the number of active bubbles in the range 35-55°C and by both the number of bubbles and the single bubble yield in the range 25-35°C.