Effect of Ultrasonic Frequency on the Mechanism of Formic Acid Sonolysis

Abstract

The kinetics and mechanism of formic acid sonochemical degradation were studied at ultrasonic frequencies of 20, 200, and 607 kHz under argon atmosphere. Total yield of HCOOH sonochemical degradation increases approximately 6-8-fold when the frequency increased from 20 to 200 or to 607 kHz. At low ultrasonic frequencies, HCOOH degradation has been attributed to oxidation with OH(•) radicals from water sonolysis and to the HCOOH decarboxylation occurring at the cavitation bubble-liquid interface. With high-frequency ultrasound, the sonochemical reaction is also influenced by HCOOH dehydration. Whatever the ultrasonic frequency, the sonolysis of HCOOH yielded H(2) and CO(2) in the gas phase as well as trace amounts of oxalic acid and formaldehyde in the liquid phase. However, CO and CH(4) formations were only detected under high-frequency ultrasound. The most striking difference between low-frequency and high-frequency ultrasound is that the sonolysis of HCOOH at high ultrasonic frequencies initiates Fischer-Tropsch hydrogenation of carbon monoxide.

Influence of inorganic ions and selected emerging contaminants on the degradation of Methylparaben: A sonochemical approach

“…At the lower frequency of 200 kHz, the availability of number of bubbles and acoustic cycles will be relatively less agreeing with the observed lower rate of degradation. The increase in applied frequency to 350 kHz, results in larger number of bubbles and hence an increase in the surface area to volume ratio [24]. But with further increase in the frequency the resonant size starts to decrease.…”

Shock-induced cavitation as a way of accelerating phenol oxidation in aqueous media

“…They are based on the intensive generation of reactive radicals, such as hydroxyls, able to oxidize the organic pollutants contained in wastewaters. Ultrasounds are frequently used in the intensification of chemical processes, among them the oxidation of organic pollutants in wastewaters in which ultrasonic sonochemistry plays an important role for several decades [3][4][5][6][7][8][9][10]. Typically induced by piezoelectric transducers [11], ultrasonic sonochemistry is based in the phenomena of cavitation, i.e.…”

“…In consequence, the influence of the ultrasound frequency on the cavitation phenomena is clearly evidenced in the existing literature, though there is not a general agreement on the frequency ranges and their particular effects (enhancement of cavitation, mass transfer, sonication, formation of radical species, etc.) [5,[16][17][18][19]. The intensity of ultrasonic cavitation is moreover a function of the acoustic pressure in the liquid and of the attenuation of the longitudinal wave within it, as it propagates far away from the excitation source (transducer).…”

Sono-bromination of aromatic compounds based on the ultrasonic advanced oxidation processes

“…In the present study, ultrasonic AOP was applied for the bromination of aromatic compounds. Navarro, et al showed that the sonolysis of HCOOH initiates Fisher-Tropsch hydrogenation of carbon monoxide [39]. In their case, the formation of CH 4 was explained by the secondary CO hydrogenation by hydrogen H 2 produced by sonolysis of water or HCOOH [58].…”

“…Herein, we report a novel ''sono-bromination'' of aromatic compounds with simple alkaline metal bromide associated with the advanced oxidation process [36][37][38][39] by ultrasound. The advantages of the present method are that the manipulation of the reaction is simple and reagents used are readily available, inexpensive, easy-handling, and environmentally friendly apart from carbon tetrachloride.…”