Sono-catalytic degradation of orange G and malachite green oxalate dyes using ZnO@SiO₂ nano core shell materials under ultrasonic irradiation

A ZnO@SiO₂ core-shell (ZSCS) catalyst was studied for the ultrasound-driven piezocatalytic degradation of Orange G (OG) and Malachite Green Oxalate (MGO) dyes under aqueous conditions. Characterization showed that the ZSCS catalyst was spherical, nano-sized, and highly crystalline. Ultrasonic irradiation enhanced its surface area and morphology, while EPR studies indicated that reactive hydroxyl (^•OH) radicals contributed to its catalytic activity. We examined factors affecting degradation efficiency, including solution pH, catalyst dosage, dye concentration, electrolyte interference, and ultrasonic energy input. Kinetic studies revealed over 96% degradation of MGO and more than 80% of OG, following pseudo-first-order kinetics. The degradation rate increased with higher catalyst concentrations but decreased with higher initial dye concentrations. Degradation was monitored via UV-visible spectroscopy, COD and TOC measurements, and by-product identification using ESI-MS to propose degradation pathways. Reusability tests showed the ZSCS catalyst to be stable and cost-effective, and it performed well in treating real dye-house effluents, highlighting its practical application in wastewater treatment.