Christian Pétrier

Ultrasonic treatment of water contaminated with ibuprofen

The application of ultrasound (US) waves for remediation of wastewater is an area of increasing interest and promising results. The aim of this paper is to evaluate the influence of several parameters of the US process on the degradation of ibuprofen (IBP), a widely used non-steroidal anti-inflammatory recalcitrant drug found in water. Applied US power, dissolved gas, pH and initial concentration of IBP were the parameters investigated under sonication (300 kHz). Ultrasound increased the degradation of IBP from 30 to 98% in 30 min. Initial rate of IBP degradation was evaluated in the range of 1.35 and 6.1 micromolL(-1)min(-1) for initial concentrations of 2 to 21 mgL(-1) or 9.7 micromolL(-1) to 101 micromolL(-1), respectively. Under air and oxygen the degradation rate of IBP was 4 micromolL(-1)min(-1) being higher than that when argon was used. The most favorable degradation pH was acidic media. Complete removal of IBP was achieved but some dissolved organic carbon (DOC) remained in solution showing that long-lived intermediates were recalcitrant to the US irradiation. However, chemical and biological oxygen demands (COD and BOD(5)) indicated that the process oxidize the ibuprofen compound to biodegradable substances removable in a subsequent biological step.

Ultrasonic waste-water treatment : incidence of ultrasonic frequency on the rate of phenol and carbon tetrachloride degradation

Organic compounds in aqueous solution submitted to an ultrasonic irradiation behave differently according to their physical and chemical properties. In this work, hydrogen peroxide formation and the degradation rate of phenol and carbon tetrachloride have been studied at different frequencies: 20, 200, 500 and 800 kHz. Whatever the frequency, it is easier to decompose CCl4 than phenol by means of ultrasonic wave. It is shown that the rates of reactions involving hydroxyl radicals (hydrogen peroxide formation and phenol degradation) have a maximum value at 200 kHz. The best yield observed at 200 kHz for the phenol degradation may be the result of better HO radicals availability outside of the bubble of cavitation. The degradation rate for carbon tetrachloride which decomposes into the bubble of cavitation increases with frequency. Calculating the reaction rate for one ultrasonic period shows that the efficiency of one ultrasonic cycle decreases as frequency increases.

Selective tin and zinc mediated allylations of carbonyl compounds in aqueous media

Abstract Aldehydes undergo preferential allylation in the presence of ketones by the tin or zinc mediated method, easily effected in aqueous media.

Sonochemical degradation of carbon tetrachloride in aqueous solution at two frequencies: 20 kHz and 500 kHz

Abstract Sonochemical degradation of carbon tetrachloride in an aqueous solution with ultrasound has been compared at two frequencies: 20 and 500 kHz. The halocarbon seems to be decomposed inside the cavitation bubble, leading mostly to carbon dioxide and chloride. Determination of the mass balance showed that the initial pollutant is mineralized within five hours irradiation. Based on the determination of products by GC/MS, a reaction scheme is proposed. Activated species, such as a chlorine radical, trichloromethyl radical and dichlorocarbene, seem to be formed during the process.

Effect of pH on the ultrasonic degradation of ionic aromatic compounds in aqueous solution

The sonolysis of 4-nitrophenol (4-NP) and aniline in O2-saturated aqueous solutions was performed at 610 kHz with ultrasonic power of 25 W and aqueous temperature of 15 +/- 1 degrees C. The initial rate of degradation of both 4-NP and aniline in sonolysis of aqueous media follows pseudo-first-order reaction kinetics. Investigation of the H2O2 generation rate in phosphate buffer media (0.01 M) over the range of pH 2-9 revealed a maximum yield at pH approximately 3.2. The pH, which results in modification of the physical properties (including charge) of molecules with ionisable functional groups, plays an important role in the sonochemical degradation of chemical contaminants. For hydrophilic substrates, the neutral species more easily diffuse to and accumulate at the hydrophobic interface of liquid-gas bubbles in comparison with their corresponding ionic forms. As a consequence, the degradation rate of 4-NP under ultrasonic irradiation decreases with increasing pH. In contrast, the disappearance rate of aniline exhibits a maximum under alkaline conditions due to the high solubility of the ionic anilinium ion and the (potentially) preferential movement of the uncharged form to the interface. Additionally, the rate of reaction of the uncharged aniline molecule (which dominates at pH > 4.6) with hydroxyl radicals is reported to be about three times as fast as the rate of reaction of the cationic anilinium species.

Effects of ultrasound on adsorption–desorption of p-chlorophenol on granular activated carbon

The aim of this work is the evaluation of the effects of ultrasound on p-chlorophenol adsorption-desorption on granular activated carbon. Adsorption equilibrium experiments and batch kinetics studies were carried out in the presence and the absence of ultrasound at 21 kHz. Results indicate that the adsorption of p-chlorophenol determined in the presence of ultrasound is lower than the adsorption observed in the absence of ultrasound. Desorption of p-chlorophenol from activated carbon with and without the application of ultrasound was studied. The desorption rates were favoured by increased ultrasound intensity. This rise is more noticeable as temperature increases. The addition of ethanol or NaOH to the system causes an enhancement of the amount of p-chlorophenol desorbed, especially in the presence of ultrasound. A synergetic enhancement of the desorption rate was observed when ultrasonic irradiation was coupled with ethanol chemical regeneration.

Sonochemical degradation of phenol in water: a comparison of classical equipment with a new cylindrical reactor.

Cavitation due to ultrasonic waves produces highly reactive oxidising species in water. As a result, it can be used to oxidise organic pollutants such as aromatic compounds in dilute aqueous solutions. Recent studies have demonstrated that reactors operating in the high frequency range (e.g. 500 kHz) are more efficient than reactors working at lower frequency (20 kHz) for the destruction of these kinds of contaminants. Our study describes the degradation of phenol with the help of a cylindrical ultrasonic apparatus that operates at 35 kHz (Sonitube-SODEVA). To date, the use of this type of reactor has not been reported. The reaction rates thus obtained were compared to those obtained at the same ultrasonic power (50 W) with more classical devices operating at 20 and 500 kHz. The general result is that in aqueous solution, the rate of phenol destruction is higher at 500 kHz than at 35 or 20 kHz. Addition of hydrogen peroxide and copper sulphate to the medium provides a different oxidative system that proceeds more efficiently at 35 kHz; the time of destruction was about one-third of the time needed at 500 kHz. It was also observed that the intermediate organic compounds are eliminated much faster at 35 kHz in comparison with the two frequencies. The observation of such different behaviour is not necessarily a pure frequency effect, but can be due to a response to other parameters such as the acoustic field and intensity.

Influence of bicarbonate and carbonate ions on sonochemical degradation of Rhodamine B in aqueous phase

The influence of bicarbonate and carbonate ions on sonolytic degradation of cationic dye, Rhodamine B (RhB), in water was investigated. As a consequence of ultrasonic cavitation that generates .OH radicals, carbonate radicals were secondary products of water sonochemistry when it contains dissolved bicarbonate or carbonate ions. The results clearly demonstrated the significant intensification of sonolytic destruction of RhB in the presence of bicarbonate and carbonate, especially at lower dye concentrations. Degradation intensification occurs because carbonate radicals sonochemically formed undergo radical-radical recombination at a lesser extent than hydroxyl radicals. The generated carbonate radicals are likely able to migrate far from the cavitation bubbles towards the solution bulk and are suitable for degradation of an organic dye such as RhB. Therefore, at low dye concentrations, carbonate radical presents a more selective reactivity towards RhB molecules than hydroxyl radical. In the presence of bicarbonate, degradation rate reached a maximum at 3 g L(-1) bicarbonate, but subsequent addition retards the destruction process. In RhB solutions containing carbonate, the oxidation rate gradually increased with increasing carbonate concentration up to 10 g L(-1) and slightly decreased afterward. Carbonate radicals sonochemically generated are suitable for total removal of COD of sonicated RhB solutions.

Conjugate additions to α,β-unsaturated carbonyl compounds in aqueous media

Abstract Alkyl halides in the presence of zinc copper couple add smoothly to α-enones and α-enals in aqueous solvents. Sonication enhances the efficiency of the process, which leads to the conjugate adducts in high yields. The reaction follows most probably a radical pathway, and can be used for the addition of functionalized groups.

Kinetics and mechanisms of ultrasonic degradation of volatile chlorinated aromatics in aqueous solutions

Ultrasonic decompositions of chlorobenzene (ClBz), 1,4-dichlorobenzene and 1-chloronaphthalene were investigated at 500 kHz in order to gain insight into the kinetics and mechanisms of the decomposition process. The disappearance of ClBz on sonication is almost simultaneously accompanied by the release of chloride ions as a result of the rapid cleavage of carbon-chlorine bonds with a concomitant release of CO, C2H2, CH4 and CO2. The intermediates resulting from attack of HO. radicals were detected but in a quite low yield (less than 2 microM). The generation of H2O2 on sonolysis is not significantly affected by the presence of aqueous ClBz while the generation of NO2- and NO3- is inhibited initially due to the presence of ClBz which diffuses into the gas-bubble interfaces and inhibits the interactions between free radicals and nitrogen. Moreover, brown carbonaceous particles are present throughout the ultrasonic irradiation process, which are consistent with soot formation under pyrolytic conditions. These important features suggest that, at the relatively high initial substrate concentrations used in this study, ultrasonic degradation of ClBz takes place predominantly both within the bubbles and within the liquid-gas interfaces of bubbles where it undergoes high-temperature combustion. Under these conditions, the oxidation of ClBz by free radical HO. outside of bubbles is a minor factor (though results of recent studies suggest that attack by HO. is more important at lower initial substrate concentrations). The sonochemical decomposition of volatiles follows pseudo-first-order reaction kinetics but the degradation rates are affected by operating conditions, particularly initial substrate concentration and ultrasonic intensity.