High temperature and pressure inside a dissolving oxygen nanobubble.

Numerical simulations of dissolution of an oxygen (O2) nanobubble into water without dynamic stimuli have been performed in order to study the possibility of OH radical formation from oxygen nanobubbles experimentally reported by Liu et al. (2016). The dissolution of an oxygen nanobubble is much faster than that of an air nanobubble due to higher solubility of oxygen in water. However, the temperature and pressure inside an oxygen nanobubble at the final moment of the bubble dissolution are about 2800 K and 4.5 GPa, respectively, which are slightly lower than those inside an air nanobubble due to higher thermal conductivity of oxygen. A few molecules of OH radicals may be formed per 107 bubbles according to the numerical simulation. The estimated production rate of OH radicals is 13 orders of magnitude smaller than the experimentally reported one.