In the current study, CdS/ZnS core–shell nanoparticles were successfully synthesized from CdSO₄·8H₂O and Zn(NO₃)₂·6H₂O starting reagents in the presence of ultrasonic irradiation. The effects of preparation parameters such as ultrasonic power, irradiation time, and precursor concentration on the morphology of the CdS/ZnS core–shell nanoparticles and the removal of heavy metals (Hg⁺², Pb⁺²) were studied by SEM and batch adsorption studies. The as-synthesized products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution field-emission transmission electron microscopy (HRTEM), photoluminescence spectroscopy (PL), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and ultraviolet-visible (UV-Vis) spectroscopy.