New interpretation of the effects of argon-saturating gas toward sonochemical reactions

Abstract

A number of literature reports showed that argon provides a more sonochemical activity than polyatomic gases because of its higher polytropic ratio; whereas several recent studies showed that polyatomic gases, such as O₂, can compensate the lower bubble temperature by the self decomposition in the bubble. In this work, we show for the first time a numerical interpretation of these controversial reported effects. Computer simulations of chemical reactions inside a collapsing acoustic bubble in water saturated by different gases (Ar, O₂, air and N₂) have been performed for different frequencies (213-1100 kHz). In all cases, OH radical is the main powerful oxidant created in the bubble. Unexpectedly, the order of saturating gases toward the production rate of OH radical was strongly frequency dependent. The rate of production decreases in the order of Ar>O₂>air>N₂ for frequencies above 515 kHz, and Ar starts to lose progressively its first order to the following gases with a gradually decreasing of frequency below 515 kHz up to a final order of O₂>air∼N₂>Ar at 213 kHz. The analysis of chemical kinetic results showed a surprising aspect: in some cases, there exists an optimum bubble temperature during collapse at which the chemical yield is much higher than that of the maximum bubble temperature achieved in the bubble. On the basis of this, we have concluded that the lower sonochemical activity induced by Ar for frequencies below 515 kHz is mainly due to the forte consumption of radicals inside a bubble prior the complete collapse being reached.

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

“…It should be noted here that the mechanism of how saturating gases affect the sonochemical reaction is well discussed in our previous paper using a single-bubble sonochemistry model [36,55].…”

“…Initially, the positive effect of high acoustic powers on the sonochemical degradation of organic pollutants in the absence of PS is well known [54][55][56] and was simply confirmed by the higher measured yield of H 2 O 2 (Table 1), which reflects higher concentration of hydroxyl radical in the solution (detailed interpretation of the effect of acoustic power on the free radicals production in collapsing bubbles is available in our previous work [57]). The simulation results also showed higher production rates of free radicals at higher acoustic power.…”

A parametric review of sonochemistry: Control and augmentation of sonochemical activity in aqueous solutions

“…The effective temperatures for this process were suggested to be near to 900 K. Sufficiently high temperatures can destroy chemically active components within the bubble. This is concurrent with temperature dependant determination of an ionisation or disassociation process, which in turn can govern the number of reactive species produced [17,25,82,84,85]. For a multibubble sonoluminescence system the pressure inside the bubbles has been estimated to be in the order of 300 bar in argon saturated silicone oil, consistent with adiabatic compression [86].…”

“…In terms of sonochemical reactions, a frequency dependence for potassium iodide oxidation was found; 20 kHz gave greater efficiency for argon, whilst 60 kHz was found to be more efficient for air [150]. More recently, frequencies above 515 kHz have been calculated to decrease •OH production rate in the order Ar > O 2 > air > N 2 , while decreasing frequency to 213 kHz the order becomes O 2 > air ~ N 2 > Ar [84]. This may be reflective of bubble size and the change in available time for reactions to occur which is dependent upon the applied frequency.…”

Thermosonication processing of quince (Cydonia Oblonga) juice: Effects on total phenolics, ascorbic acid, antioxidant capacity, color and sensory properties

“…In contrast, ascorbic acid increased after ultrasound treatment applied to strawberry juice (Wang;Vanga;Raghavan, 2019b). The amount of amino acid in the juice dissolves in the presence of gases (O 2 ), the ascorbic acid compound reacts with free radicals, and can be reduced by factors such as acoustic power and temperature effects (Merouani et al, 2015;Santhirasegaram;Razali;Somasundram, 2013). Amplitude (X 3 ) (%) 50.9…”