Activating Molecules, Ions, and Solid Particles with Acoustic Cavitation

Abstract

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO 2 powder in pure water yields stable colloids of plutonium due to both effects. Video LinkThe video component of this article can be found at

Insight into ultrasound-mediated reactive oxygen species generation by various metal-porphyrin complexes

“…Acoustic cavitation is a highly complex phenomenon that is not yet completely understood despite being well known in a variety of scientific fields, from physics to chemistry and medicine. For some researchers, acoustic cavitation is an extreme phenomenon that is responsible for generating excessive vibration, erosion, reduced hydraulic performance and structural damage [22], while, for others, it is seen as an enormous concentration of energy with a wide range of unexplored chemical and physical consequences [23,24]. In particular, the emission of SL [25][26][27] has been proposed as the pivotal trigger for the sonosensitiser-mediated generation of reactive oxygen species (ROS) in SDT [28,29].…”