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Active bubbles hold potential in fields ranging from water purification to medicine. Researchers can generate microbubbles by exposing liquids to high-intensity ultrasonic waves, a process known as sonication, and these energy waves heat up and pressurize the bubbles. For example, when bubbles in water are adiabatically collapsed by ultrasonic waves, the temperature inside the bubbles reaches more than several thousand degrees and the pressure several hundred atmospheres.

These bubbles are called active bubbles or acoustic bubbles. Osaka Metropolitan University researchers have now found key indicators to assess the chemical activity and temperature of these microbubbles. The findings were in Ultrasonics Sonochemistry.

The group led by Professor Kenji Okitsu of the Graduate School of Sustainable System Sciences showed that, when water is undergoing sonication, the amount of hydrogen is a more important indicator of the chemical activity of acoustic bubbles than hydrogen peroxide during thermal decomposition of the water.

The team also conducted experiments using an aqueous t-butanol (tertiary alcohol) solution to investigate the temperature and number of active bubbles generated when exposed to ultrasonic waves. As the temperature of the solution and the concentration of inorganic salts increased, the temperature of the active bubbles became lower and the number of active bubbles produced decreased.

"Our research provides new insights into the relationship between bubble temperature and chemical activity," Professor Okitsu exclaimed.

"As the characteristics of active bubbles become clearer, more precise control of chemical reactions will become possible. We expect further applications and progress in water purification technology and nanotechnology, such as the decomposition of persistent organic pollutants and the synthesis of highly functional, high value-added nanomaterials."