Photocatalysis: Utilizes UV light and a catalyst, typically titanium dioxide (TiO2), to produce hydroxyl radicals. Ozone-based AOPs: Involve the use of ozone (O3) either alone or in combination with hydrogen peroxide (H2O2) to generate radicals. Fenton and Photo-Fenton Processes: Use iron salts and hydrogen peroxide to produce hydroxyl radicals, with the photo-Fenton process incorporating light to enhance radical production. Sonolysis and Sonocatalysis: Utilize ultrasonic waves to produce radicals either alone or in combination with catalysts.