Ultrasonic treatment effects on hydroxyl radical generation in various solution systems: an iodometric analysis

Area of Science:

• * Environmental Chemistry
• * Physical Chemistry
• * Chemical Engineering

Background:

• * Hydroxyl radicals (•OH) are crucial reactive species in sonochemical processes.
• * Their generation efficiency is highly sensitive to operating parameters and solution composition.
• * Understanding and controlling •OH yield is vital for optimizing sonochemical applications.

Purpose of the Study:

• * To systematically evaluate the apparent •OH yield induced by probe ultrasonication.
• * To investigate the influence of key operating parameters (time, power, duty cycle, probe position) on •OH generation.
• * To assess the impact of various solution compositions (scavengers, salts, catalysts) on the oxidative response.

Main Methods:

• * An iodometric method using a 0.4 mol L^-1 KI background was employed to measure accumulated titratable iodine (I₃^-) as an apparent •OH yield.
• * Probe ultrasonication parameters including sonication time, ultrasonic power, duty cycle, and probe position were varied.
• * The effects of adding ethanol, acetic acid, NaOH, NaHCO₃, NaCl, phosphotungstic acid, hydrogen peroxide, and t-BuOH were examined.

Main Results:

• * Apparent •OH yield increased with sonication time and power, peaking at 60% duty cycle and central probe position.
• * Solution composition significantly affected •OH yield: ethanol and NaOH decreased it, acetic acid showed a biphasic effect, NaHCO₃ decreased it concentration-dependently, and NaCl exhibited non-monotonic behavior.
• * Hydrogen peroxide showed a complex effect, enhancing yield at moderate concentrations but reducing it at higher levels, while t-BuOH confirmed the dominant role of •OH.

Conclusions:

• * Operating parameters like sonication time, power, duty cycle, and probe position significantly influence •OH generation in probe ultrasonication.
• * Solution composition, including scavengers and additives, plays a critical role in modulating the apparent •OH yield.
• * The findings offer practical insights for optimizing sonochemical processes by controlling •OH generation for desired oxidative outcomes.