Sustainable approach with enhanced removal performance of organic pollutant for wastewater treatment by ultrasonically regenerated mesoporous nickel oxide nanoparticles

The nickel oxide nanoparticles (NPs) were synthesized using the solvothermal method in the oleic acid to remove congo red via an adsorption process. Furthermore, for the first time, in this study subsequently regeneration of deactivated adsorbent by low-energy ultrasound waves as an inventive technique was investigated. The morphology, porosity, and crystallinity of the as-synthesized NPs were investigated by transmission electron microscopy (TEM), Scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET), and X-ray diffraction (XRD) techniques. Congo red, a water-soluble azo dye, is adsorbed by nickel oxide nanoparticles, reaching about 83.20% adsorption within two hours with a pseudo-first-order rate constant of 0.0099 min⁻¹. In the regeneration process, the nanoparticles regenerated by low-frequency ultrasound waves up to 94.35% within 35 min. The obtained data shows that the amount of regenerated nanoparticles increased with the intensity of ultrasonic irradiation. Most importantly, it can be recycled by ultrasound irradiation, which retains high performance in 3 cycles, proving its promising application for different environmental decontamination.