In recent years, ultrasonic radiation (20 kHz–10MHz) [5,7] has been
used to prepare nanoparticles [5,7]. The chemical effects of the
ultrasound arise from acoustic cavitation—formation, growth, and
implosive collapse of bubbles in liquids. There are two regions of
sonochemical reactivity, the inside zone of the collapsing bubble and the
interface between bubbles and the liquid. The cavitation may generate
very high temperature over 5000 K and pressure over 20MPa, which
enable many chemical reactions to occur. In short, during the process,
the implosive collapse of bubbles generates localized hot spots through
adiabatic compression or shockwave formation within the gas phase of
the collapsing bubbles. These extreme conditions attained during
bubble collapse have been exploited to prepare various materials with
different morphologies [7,8].