Ultrasound and ionic liquid: an efficient combination to tune the mechanism of alkenes epoxidation.

In this proof of concept study, the advantageous properties of both H(2)O(2)/NaHCO(3)/imidazole/Mn(TPP)OAc oxidation system and MOPyrroNTf(2) ionic liquid have been combined under ultrasonic irradiation to give an exceptionally favorable environment for Mn(TPP)OAc catalyzed olefin oxidations. The results reveal the crucial role played by the ultrasonic irradiations that influence drastically the oxidation process. In MOPyrroNTf(2) and under ultrasonic irradiation, the mechanism probably involves an oxo-manganyl intermediate at the expense of the classical bicarbonate-activated peroxide route.

Sonochemical efficiency dependence on liquid height and frequency in an improved sonochemical reactor.

The aim of this study was to evaluate the effects of liquid height and frequency on sonochemical efficiency of a cup-horn sonoreactor. The selected frequencies (22, 371, 504 kHz) and liquid height (29-348 mm) were applied while measuring acoustic yield, I(3)(-) formation rate and the resulting sonochemical efficiency. The frequency effect was shown to be coupled to liquid height effect. Indeed, acoustic zones (i.e. Fresnel and Fraunhöfer zones), which limits depends on both transducer diameter and frequency, significantly determine the production of radicalar species quantified by I(3)(-) formation rate. An increase of ultrasonic frequency results in lower acoustic yield and higher sonochemical efficiency. Theoretical physical and chemical effects attributed to collapsing bubbles were considered. Sonochemical efficiencies obtained at 500 kHz were similar or higher than those at 371 kHz, depending on liquid height. The effect of reactor configuration was further investigated as an hypothesis to explain unsignificant effect of standing waves in our study. Therefore, the dependence of sonochemical efficiency with liquid height might be firstly attributed to reactor configuration prior to frequency effects.

Sonochemical and sonocatalytic degradation of monolinuron in water.

The degradation of the phenylurea monolinuron (MLN) by ultrasound irradiation alone and in the presence of TiO(2) was investigated in aqueous solution. The experiments were carried out at low and high frequency (20 and 800 kHz) in complete darkness. The degradation of MLN by ultrasounds occurred mainly by a radical pathway, as shown the inhibitory effect of adding tert-butanol and bicarbonate ions to scavenge hydroxyl radicals. However, CO(3)(-) radicals were formed with bicarbonate and reacted in turn with MLN. In this study, the degradation rate of MLN and the rate constant of H(2)O(2) formation were used to evaluate the oxidative sonochemical efficiency. It was shown that ultrasound efficiency was improved in the presence of nanoparticles of TiO(2) and SiO(2) only at 20 kHz. These particles provide nucleation sites for cavitation bubbles at their surface, leading to an increase in the number of bubbles when the liquid is irradiated by ultrasound, thereby enhancing sonochemical reaction yield. In the case of TiO(2), sonochemical efficiency was found to be greater than with SiO(2) for the same mass introduced. In addition to the increase in the number of cavitation bubbles, activated species may be formed at the TiO(2) surface that promote the formation of H(2)O(2) and the decomposition of MLN.

A new ozone denuder for aerosol sampling based on an ionic liquid coating.

A new ionic liquid 1-octyl-3,5-dimethylpyridinium iodide ([O35LUT](+)[I](-)) was synthesized and utilized as coating for an ozone denuder device based on a high-volume aerosol sampler (30 m(3) h(-1)). Particle transmission of the denuder was studied, and over 99% of particles ranging from 10 to 2,500 nm were transmitted. The device, containing 4.66 g of ionic liquid, was used outdoors, under dry and damp atmospheric conditions. In order to expose the device to an average concentration of 120 ppbv (240 microg m(-3)) of ozone in air, an additional production of ozone was directly injected into the denuder. Under these conditions, over 97% of ozone was removed for approximately 120 h (5 days). Therefore, iodide-based ionic liquids can be used as a new alternative to conventional denuder coatings in order to reduce artifacts occurring during sampling of particulate matter. Future applications are not limited to ozone removal for specific aerosol sampling methods.

A general ultrasound-assisted access to room-temperature ionic liquids.

The replacement of common organic solvents by room-temperature ionic liquids (RTILs) is a topical subject in both academia and industry. In the last decades, the number of applications for RTILs has followed an exponential curve and spilled over the boundaries of chemistry. Still, one of the main drawbacks of these compounds is their difficult access. The present ultrasound-assisted method affords a general and easy access to a large variety of room-temperature ionic liquids.