The use of ozone gas started about a century ago and it has been used to purify water polluted by microorganisms. The chemistry of ozone in aqueous solutions is complex, and the direct reaction with molecular ozone and the indirect reaction with radicals generated when ozone is dissolved in water are considered for the process of water treatment with ozone. The direct and indirect reaction pathways of ozone generate different oxidation products and they are controlled by different kinetics.
Direct reaction of ozone has been quite well understood by previous researchers. The studies of ozone reactions and decomposition are still active, and most researchers are working on kinetics. The exact analysis of ozone reactions is still difficult due to very complex ozone reactions and insufficient information on reaction kinetic constants.
In theoretical studies of the UV-induced destruction of ozone layers in the earth's atmosphere, some researchers performed calculations of the stability of ozone-water vapor complex. The previous studies dealt with the reaction between molecular ozone and water vapor, but no first-principles studies have been carried out on the case of ozone gas dissolved in water. Therefore, first-principles study of ozone decomposition in water is necessary to improve the efficiency of water treatment by ozone.
Choe Un Hwa, a researcher at the Faculty of Physics, has determined reaction pathways for enhancing the efficiency of ozonation through first-principles considerations of ozone decomposition in water.
She newly defined the transition state that might be found during ozone decomposition in water and carried out a quantitative chemical calculation of ozone decomposition reactions in water by using the density functional method (DFT/6-31G*).
The results showed that the relative probability of the reaction to obtain H2O2 + O2 among the four possible reactions between O3 and H2O in gas and water is high, which indicates that the improved oxidation of ozone can be used to improve ozonation efficiency.