Formation of NO2- and NO3- in the sonolysis of water: Temperature- and pressure-dependent reactions in collapsing air bubbles

The formation of NO2- and NO3- in the sonolysis of water under air was investigated to evaluate the chemical properties of collapsing air bubbles that reached high-temperature and high-pressure conditions. The sum of initial rates of NO2- and NO3- formation and the ratio of these rates showed different dependences on ultrasonic power. By analyzing the adiabatic compression equations, it was confirmed that the increment ratio of the bubble pressure was much larger than that of the bubble temperature, suggesting that the bubble pressure affects the chemical reactions occurring in a bubble. Therefore, we analyzed the effect of temperature and pressure on the formation of NO2 and NO, the main precursors of NO3- and NO2-, respectively, using chemical equilibrium calculations to interpret the difference in power dependence. The results suggest that NO2- was formed more easily at higher temperatures, while NO3- formed more easily at higher pressures. We propose that NO2- and NO3- can be used as probes for temperature-and pressure-dependent reactions to improve the understanding of the physicochemical properties of collapsing air bubbles.

Automated summary

This study investigates the formation of NO2- and NO3- in sonolysis of water, evaluating the relationship between the chemical properties of collapsing air bubbles and ultrasonic power. Results show that the pressure of bubbles has a greater impact on chemical reactions than temperature under different conditions.