The Reducing Agents in Sonochemical Reactions without Any Additives

Abstract

It has been experimentally reported that not only oxidation reactions but also reduction reactions occur in aqueous solutions under ultrasound without any additives. According to the numerical simulations of chemical reactions inside an air or argon bubble in water without any additives under ultrasound, reducing agents produced from the bubbles are (Formula presented.) (which becomes superoxide anion ((Formula presented.)) in liquid water), (Formula presented.), and (Formula presented.) (which becomes (Formula presented.) in liquid water). In addition, (Formula presented.) sometimes works as a reducing agent. As the reduction potentials of (Formula presented.) and (Formula presented.) (in strongly alkaline solutions for (Formula presented.)) are higher than those of (Formula presented.) radicals, which are usually used to reduce metal ions, (Formula presented.) and (Formula presented.) generated from cavitation bubbles are expected to reduce metal ions to produce metal nanoparticles (in strongly alkaline solutions for (Formula presented.) to work). It is possible that the superoxide anion ((Formula presented.)) also plays some role in the sonochemical reduction of some solutes. In strongly alkaline solutions, hydrated electrons ((Formula presented.)) formed from (Formula presented.) atoms in liquid water may play an important role in the sonochemical reduction of solutes because the reduction potential is extremely high. The influence of ultrasonic frequency on the amount of (Formula presented.) atoms produced from a cavitation bubble is also discussed.