Sonochemical Disproportionation of Carbon Monoxide in Water: Evidence for Treanor Effect during Multibubble Cavitation

Abstract

Eighty years after the discovery of ultrasound-induced chemical processes, [1] known as sonochemistry, it remains a subject of extensive research. [2] It is generally accepted that sonochemistry arises from acoustic cavitation, which is the nucleation, growth, and implosive collapse of microbubbles in liquids subjected to ultrasonic waves. Nevertheless, debate still continues over the origin of extreme conditions created by the bubble collapse. Usually the sonochemical reactions are interpreted according to Flynns "thermal" hypothesis presuming adiabatic or quasi-adiabatic transient heating of gases and vapours inside the cavitating bubble. [3] However, the recent observation of light emission from positively charged O 2 + species during single-bubble collapse in H 2 SO 4 provided evidence for nonthermal plasma formation inside the bubble. [4] The relationship between the mechanisms of single-bubble and multibubble cavitations is still not clear. Recent studies of multibubble sonoluminescence in H 2 SO 4 and water revealed some similarities in the origin of both kinds of processes. [5,6] In this view thermal equilibration during the cavitation event remains an important question that is not yet resolved. Herein, we report the first "chemical" evidence for nonequilibrium molecule vibrational excitation occurring during multibubble cavitation.We studied the ultrasonically driven disproportionation of carbon monoxide (DCO) in water saturated with a CO/Ar gas mixture. To our knowledge, this reaction had never been studied under ultrasonic irradiation. By contrast, the plasmachemical DCO reaction in the gas phase has been a very active topic of research as working media for CO lasers and as a promising method for carbon isotope separation. [7] According to published results, the strongly endothermic DCO reaction (DH = 5.5 eV mol À1 , E a = 6 eV mol À1 ) can be significantly accelerated by the vibrational excitation of CO molecules. The population of highly vibrational states CO*(n n ), n 40, occurs through an anharmonic vibrationto-vibration pumping mechanism (V-V), known as the

Sonoluminescence from OH(C2Σ+) and OH(A2Σ+) Radicals in Water: Evidence for Plasma Formation during Multibubble Cavitation

“…This is in line with the recently reported Treanor effect during carbon monoxide sonochemical disproportionation in water. [21] Therefore, the present data clearly point to non-thermal plasma formation during multibubble cavitation in water in the presence of Kr and Xe. This indication of more extreme conditions is consistent with higher SL yields observed when these gases are used.…”

The Origin of Isotope Effects in Sonoluminescence Spectra of Heavy and Light Water

“…[10] experiments because of the absorption by water and the lack of sensitivity of the grating in this spectral range. At 230-260 nm the OH(C 2 S + ÀA 2 S + ) system exhibits numerous overlapping emission bands such as 0-n''(6-9), 1-n'' (7)(8)(9), and (3,7) while the OD(C 2 S + ÀA 2 S + ) system shows only few 0-n'' (11;12) bands in this spectral range. [18,19] Consequently, the intensity of OD(C-A) emission bands in water is much lower than that of OH(C-A).…”

“…[2] This finding correlates with the Treanor kinetic isotope effect reported for carbon monoxide disproportionation in aqueous solutions driven by power ultrasound. [3] To date, there is only limited information about the isotope effects in SL spectra. Hiller and Putterman reported a dramatic effect of heavy water on single bubble sonoluminescence (SBSL) in the presence of H 2 and D 2 .…”

Turning single bubble sonoluminescence from blue in pure water to green by adding trace amount of carbon nanodots

“…As we know, during bubble collapsing, the volume of the bubble is rapidly reduced and the energy maintaining inside the bubble becomes highly condensed. The violent collapse of the bubble can lead to the generation of the shock wave with a velocity of about 4000 m/s from the bubble wall [7] , [53] . In the presence of CNDs in water, the high energy release and the strong inward shock-wave during can accelerate the carboxylate radicals to gain high kinetic energy.…”