Sonochemical treatment for removal of aqueous organic pollutants: principles, overview and prospects

Sonochemistry, as an emerging and rapidly advancing research field, has extensive applications in environmental remediation, chemical synthesis, and microbiology due to its high efficiency. Sonochemistry is an integral part of green chemistry. Based on the unique physicochemical phenomena generated by ultrasound in solutions, it exhibits significant potential for environmental remediation. Firstly, ultrasound alone can effectively degrade organic pollutants by generating free radicals. Furthermore, when combined with other oxidants, ultrasound can enhance pollutant removal capabilities. In both processes, ultrasound acts solely through the energy of sound waves in the solution without introducing new substances, demonstrating its highly efficient and clean advantages. The key aims of this comprehensive review are to (a) explain the traditional mainstream phenomenon of cavitation in solutions and its principles, while also incorporating the latest theory on the formation of nonequilibrium plasma inside the collapsing bubble; (b) describe cavitation bubbles using formulas; (c) discuss the major influencing factors on the removal of organic pollutants by ultrasound systems; (d) focus on exploring the removal mechanisms and applications of different ultrasound-hybrid homogeneous systems for organic pollutant removal; and (e) offer our perspectives on the intermediate products generated in sonochemical reactions, emphasizing the need for further research to improve the efficiency of ultrasound-hybrid system and its industrial applications.