Abstract
This work aimed at the characterization and application of a cavitation field induced in water by an ultrasonic reactor operating at 1700 kHz and 15 W. It was found that the size of active bubbles varied from 0.23 to 3 µm. The number of active bubbles increased from 6.1142 × 108 s−1 L−1 at 25 °C to 4.4684 × 109 s−1 L−1 at 55 °C. The most active bubbles were those achieving temperature of 4000 K and pressure of 1000 atm at the collapse. The characterized cavitation field removed efficiently toluidine blue (TB), an emerging organic contaminant, through reaction with hydroxyl radical. The best TB-removal rate was obtained under argon saturation, but CO2 completely suppressed the process. TB degradation rate sensitively enhanced with increasing initial substrate concentration and solution pH, whereas the liquid temperature did not affect the degradation rate. Formic acid, as an organic competitor, reduced considerably the degradation of the pollutant.
Highlights
H2O2 decreased rapidly from 0.95 μM/min in fresh water to 0.78 μM/min in 5 mg/L toluidine blue (TB) solution and does not decrease much beyond this concentration (Fig. 7). These results demonstrated the involvement of hydroxyl radical in the degradation of the dye and reflected a saturation of the bubble surface with TB molecules for C0 > 5 mg/L
Ultrasound via acoustic cavitation event induced in aqueous solution may produce several physical and chemical effects
The degradation of nonvolatile compounds through reaction with the cavitationally generated ·OH radical is one of the most applications of ultrasound in environmental remediation
Summary
High-power ultrasound (frequency ≥ 100 kHz) has become the focus of a new field, known as sonochemistry, which involves the study of the effects of acoustic waves on chemical systems (e.g., synthesis reactions (Serpone and Colarusso 1994), free radical polymerization (Teo et al 2009), enzymatic reactions (Malani et al 2014), photocatalytic reactions (Peller et al 2003; Kaur and Singh 2007; Bekkouche et al 2017), Fenton and photo-Fenton reactions (Basturk and Karatas 2014; Verma et al 2015), electrochemical reactions (Pollet 2010; Sáez et al 2010)). Laboratory of Environmental Engineering, Department of Process Engineering, Faculty of Engineering, Badji Mokhtar – Annaba University, 23000 Annaba, Algeria collapsed by the action of the sound wave This phenomenon is known as acoustic cavitation (Neppiras 1980). If water is the medium, H· and ·OH radicals are generated by the homolysis of water vapor inside the bubble These radicals initiate a gas-phase reactions chain, in which several other reactive species (i.e., HO2· and O,...) may be formed (Yasui et al 2005). A parallel reaction pathway exists where volatile solutes may evaporate into the bubble and be pyrolyzed by the high core temperatures The diffusion of these reactive species in the liquid surrounding the bubble has been used to achieve chemical reactions that include the synthesis of nanomaterials, polymers, degradation of organic pollutants, etc. Bubble collapse can result in light emission, sonoluminescence, originating from the core of the bubble during the final stages of collapse
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