Insights on the sonochemical synthesis, characterization, and effective lead (Pb2+) adsorption ability of nano lanthanum oxide (La2O3).

Lead contamination in water sources due to industrial pollution, informal recycling, the use of leaded products, and mining is a severe public health crisis affecting millions, resulting in significant economic losses and health impacts that require urgent treatment strategies to address lead-contaminated water. The key innovation of this research is the surfactant-free sonochemical synthesis of non-agglomerated, highly active nano La2O3, designed for the rapid, sustainable, and highly recyclable removal of lead (Pb2+) from water. This synthesis method utilized acoustic cavitation, which results in the formation of dense surface oxygen vacancies and native hydroxyl (-OH) functional groups. The morphology, composition, and surface properties were studied using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX), and Fourier transform infrared (FTIR) spectroscopy. The average size of nano La2O3 was 15 nm, as obtained from XRD and TEM analyses. A surface charge of +22 mV was obtained using the zeta potential technique. Batch sorption experiments were conducted by varying the parameters such as the solution pH (2.0-7.0), agitation time (2-30 min), temperature (15-45 °C), and adsorbent dosage (0.1-0.5 g L-1). Almost 98% of Pb2+ ions were removed from a 100 mL solution containing 50 mg Pb2+ per L within 30 min. The experimental data of Pb2+ adsorption were fitted to the pseudo-first-order and pseudo-second-order kinetic models, and the pseudo-second-order kinetic model was the best-fitted model, indicating the chemisorption of Pb2+ ions onto nano La2O3. The rate of equilibrium adsorption capacity (q e, mg g-1) of lead uptake was obtained to be 19.12 mg g-1. Desorption studies were successfully performed for five cycles to regenerate the spent nano La2O3 using HNO3 (0.05 M) as the desorbing agent, thereby enabling stability and reuse.