5 - Computer simulation of N2O/argon gas mixture effect on the acoustic generation of hydroxyl radicals in water: toward understanding the mechanism of N2O inhibited/improved-sonochemical processes

Abstract

Injecting of soluble gases in water under sonication is an important tool for improving the efficiency of the sonochemical treatment of water. Among several used gases, nitrous oxide (N2O) has shown a special effect. Instead other gases, dissolving pure N2O in solutions suppresses all sonochemical effects. However, when low amount of this gas is injected in argon matrix, the sonochemical activity was improved. The mechanism by which N2O nullifies or enhances the sonochemical activity is until now under debate. In this chapter, thanks to confronting simulation results for single bubble sonochemistry with literature observations, the mechanism of N2O on the sonochemical activity was discussed. The acoustic generation of ●OH radical under N2O–argon gas mixture of different proportions was simulated for different conditions of frequency (213–875kHz), acoustic intensity (0.5–1.25W/cm2), and liquid temperature (10°C–50°C). It was concluded that pure N2O atmosphere acts as suppressor of inertial cavitation responsible for radicals generation, but when it is used at low concentration, N2O can increase both the single bubble yield and the number of active bubbles through increasing nucleation sites for cavitation.