Enhancement of sonochemical reaction rate by addition of micrometer-sized air bubbles

The sonochemical reaction rate has been enhanced by the introduction of tiny air bubbles. The bubbles including micrometer-sized ones are produced by method of atomization and are introduced into aqueous luminol solution under 141-kHz sonication in order to investigate the enhancement of sonochemical reaction rate by introduction of tiny bubbles through the intensity measurement of sonochemiluminescence (SCL). It is shown that the introduction of tiny bubbles under sonication accomplishes the large SCL intensity compared to the cases of sonication only and liquid flow under sonication. It is also shown that it is important to adjust the configuration of tiny-bubble addition to the sound field. Through the investigations on the intensity and the spatial pattern of luminol-SCL, it has been clarified that tiny bubbles added into the sonicated liquid not only cause the liquid flow but also increase the number of collapsing bubbles active for sonochemical reaction. It is also shown that the tiny-bubble addition enhances the reaction rate of KI oxidation under sonication. Therefore, the present method of introduction of tiny bubbles is effective for enhancement of sonochemical reaction rate.     

Fabrication of zinc ferrite nanocrystals by sonochemical emulsification and evaporation: observation of magnetization and its relaxation at low temperature

A new ultrasound assisted emulsion (consisting of rapeseed oil and aqueous solution of Zn(2+) and Fe(2+) acetates) and evaporation protocol has been developed for the synthesis of zinc ferrite (ZnFe(2)O(4)) nanoparticles with narrow size distribution. The as-synthesized sample consisted of crystalline zinc ferrite particles with an average diameter of approximately 4 nm, whereas the average size of the heat-treated ferrite particles increases to approximately 12 nm. To remove the small amount of oil present on the surface of the as-synthesized ferrite sample, heat treatment was carried out at 350 degrees C for 3 h. The as-synthesized and heat-treated ferrites were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), TGA/DTA, transmission electron microscopy (TEM), and energy dispersion X-ray spectroscopy (EDS) techniques. Magnetic measurements show that the nanocrystalline ZnFe(2)O(4), prepared through this technique, is either at par with those obtained in other cases or even more improved. Both the as-synthesized and heat-treated samples reveal relaxation of magnetization. Our study also shows that one can tailor the magnetization and relaxation pattern by suitably controlling the particle size of the nanocrystalline ZnFe(2)O(4). The key features of this method are avoiding (a) the cumbersome conditions that exist in the conventional methods, (b) the usage of necessary additive components (stabilizers or surfactants, precipitants), and (c) calcination requirements. In addition, rapeseed oil has replaced organic nonpolar solvents used in earlier studies. As a whole, this simple straightforward sonochemical approach results in a better pure phase system of nanoferrite with improved magnetic properties.     

A Direct S0→Tn Transition in the Photoreaction of Heavy‐Atom‐Containing Molecules

According to the Grotthuss–Draper law, light must be absorbed by a substrate to initiate a photoreaction. There have been several reports, however, on the promotion of photoreactions using hypervalent iodine during irradiation with light from a non‐absorbing region. This contradiction gave rise to a mystery regarding photoreactions involving hypervalent iodine. We demonstrated that the photoactivation of hypervalent iodine with light from the apparently non‐absorbing region proceeds via a direct S₀→T_n transition, which has been considered a forbidden process. Spectroscopic, computational, and synthetic experimental results support this conclusion. Moreover, the photoactivation mode could be extended to monovalent iodine and bromine, as well as bismuth(III)‐containing molecules, providing new possibilities for studying photoreactions that involve heavy‐atom‐containing molecules.