Enhanced generation of active oxygen species induced by O3 fine bubble formation and its application to organic compound degradation.

By using O3 fine bubbles that promote the mass transfer of O3 to the liquid phase and the conversion of the dissolved O3 into active oxygen species with a high oxidation potential, an improved liquid-phase oxidation technique was developed to accelerate the degradation of an organic compound at a constant O3 flow rate. By the use of a dielectric-barrier-discharge reactor, O2 was converted into O3 at an O2 flow rate of 0.56 mmol/(L·min), with 5 mol% O2-to-O3 conversion. Using a self-supporting bubble generator, O3 bubbles with an average diameter (dbbl) of 50 µm were continuously supplied into a solution in TBA (OH• scavenger) at 303 K, and the TBA being degraded. For comparison, O3 bubbles with dbbl values of 200-5000 µm were obtained using a dispersing-type generator. It was found that the minimization of bubble diameter accelerated both O3 dissolution, as a consequence of the increase in the gas-liquid interfacial area and the residence time of the bubbles, and enhanced OH• generation, because of the increase in contact probability between dissolved O3 and OH- at the minute gas-liquid interfaces, caused by the accumulation of OH- around the fine bubble surfaces. To ascertain the influence on organic compound degradation of the improved oxidation potential, bisphenol A, as a model compound, was degraded by O3 bubble injection at different dbbl values. Sequentially, the high OH• selectivity obtained by minimizing the bubble diameter can effectively achieve the rapid degradation of organic compounds and intermediates under a constant O3 flow rate.