Preparation, characterization, and adsorption studies of core@shell SiO$_{2}$@CeO$_{2}$ nanoparticles: a new candidate to remove Hg(II) from aqueous solutions

SiO$_{2}$ supported core@shell nanoparticles (CSNs) have recently attracted great attention due to their unique, tunable, optical, photocatalytic, and higher adsorption properties. In this study, SiO$_{2}$@CeO$_{2}$~CSNs were synthesized using a chemical precipitation technique and characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) analysis. XRD analysis showed that SiO$_{2\, }$particles were the core while CeO$_{2}$ particles were the shell. It was seen as a new band at 961 cm$^{-1}$ of the oxygen bridge between Si and Ce atoms from FT-IR results; SiO$_{2}$ and CSNs were spherical (0.5--0.6 $\mu $m) from SEM and TEM analyses. Different parameters such as contact time, initial concentration, pH, and temperature were investigated. The optimum conditions for temperature, pH, and contact time were 25 $^{\circ}$C, 8.0, and 60 min, respectively. In addition, the equilibrium adsorption data were interpreted using Langmuir and Freundlich models to describe the uptake of Hg(II). The Freundlich isotherm model (R$^{2}$: 0.99) fit better than Langmuir and the $q_{max} $value was 153.8 $\mu $g g$^{-1}$ at various concentrations (0.1--1 mg L$^{-1})$. The thermodynamic parameters were also calculated and, from these results, it can be shown that our synthesized particles can be used in water purification systems to remove Hg(II).