Europium-doped silica nanoparticles for efficient and sustainable lead removal from aqueous solutions

This study reports the synthesis and characterization of Europium-doped silica nanoparticles (adsorbent) ( S 1 ), prepared via an eco-friendly sol-gel method, aimed at the efficient removal of lead (Pb 2+ ) ions from aqueous solutions. Comprehensive structural and surface analyses were performed using Scanning Electron Microscopy (SEM), Dynamic Light Scattering (DLS), Fourier-transform Infrared Spectroscopy (FTIR), and Thermogravimetric Analysis (TGA) to confirm the formation and stability of the nanoparticles. The maximum adsorption capacity of S 1 for Pb 2+ ions was achieved at a solid-to-solution ratio of 4 g/L. Equilibrium was reached within 60 min. The adsorption kinetics followed a pseudo-second-order model, indicating that chemisorption played a significant role in the extraction process. Furthermore, the adsorption isotherm data fitted well with the Langmuir model, yielding a maximum adsorption capacity of 25.73 mg/g at 298.15 K. This suggests that adsorption predominantly occurs at specific active sites on the nanoparticle surface, involving interactions between Pb (II) ions and oxygen atoms present on the surface. Thermodynamic studies revealed that the adsorption process is spontaneous. The enthalpy data indicated that the interaction involves both electrostatic and chemical contributions. A 90 % recovery of the used S 1 material was achieved using 20 mM HCl under the following conditions: 2-h contact time, temperature of 298 K, shaking rate of 180 rpm, and an adsorbent dose of 10 mg/L. The material maintained its efficiency over five adsorption-desorption cycles. These results demonstrate the potential of europium-doped silica nanoparticles as effective and reusable adsorbents for sustainable heavy metal remediation, contributing to advancements in colloid and interface science for environmental applications.