Hydrogen-based sono-hybrid catalytic degradation and mitigation of industrially-originated dye-based pollutants

Hazardous pollutants in water bodies have increased global concern due to their considerable toxicity and threat to the environmental matrices. Conventional remediation approaches are futile for eliminating various toxic dyes and other related pollutants. Regulations compliances for wastewater expulsion have forced scientists to either introduce new methods or upgrade present technologies to attain operative deprivation and mineralization of pollutants. Advanced oxidation processes (AOPs) relying on the generation of highly reactive oxidizing radicals, like ^•O, and ^•OH are considered efficient to attain high mineralization of a large number of dye pollutants and many other organic contaminants. Compared to conventional AOPs, including photocatalysis, Fenton, photo-ferrioxalate, ozone/UV, ozonation, H₂O₂/UV, etc., sonolysis is a comparatively newer AOP that implicates the use of ultrasound irradiation for generating oxidizing radicals, leading to the degradation of recalcitrant dyes. Due to no chemical catalyst requirement and being executed at ambient pressure and temperature, ultrasound-assisted AOPs have become robust hybrid AOPs to degrade environmental contaminants. Ultrasound treatments to mitigate pollutants are important because of the cavitation phenomenon. This review focuses on the degradation of dyes through ultrasound-based advanced oxidation processes. Firstly, we have described the ecotoxicity and health hazards of dye pollutants, then different sono-based methods such as sono-hybrid Fenton (US + Fe⁺²/H₂O₂), Fenton like (Fe⁺³/H₂O₂) process, sono-hybrid photo-Fenton process (US + Fe²⁺/H₂O₂/UV system, sono-hybrid hydrogen peroxide (US + H₂O₂), sono-hybrid catalytic (photo/electro) processes have been examined in details for their efficacy for degradation of dyes in wastewater. Future perspectives of ultrasound-assisted AOPs for dyes removal have also been discussed.