Efficient adsorption of mercuric ions from an aqueous medium by novel chitosan-coated silica nanoparticles based on Oman’s white sand

Abstract

Two solid adsorbents were synthesized: silica nanoparticles (SNp) and chitosan coated-silica nanoparticles (CSNp) as a novel composite based on Oman’s white sand for the effective adsorption of mercuric ions (Hg^2 +) from water. Solid adsorbents were described via TGA, N₂ adsorption-desorption, X-ray diffraction analysis (XRD), zeta potential, attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis. These techniques revealed that CSNp has a higher thermal stability with 33.6 % mass loss at 900 °C, higher specific surface area (S_BET, 483.2 m²/g), nearly neutral point of zero charge at pH 6.7, rich with surface chemical active groups, and 120 nm as TEM average particle size. The prepared adsorbents were utilized in the batch adsorption process to remove Hg²⁺, with varying application parameters such as adsorbent dose, initial concentration, pH, agitating time, and temperature. The results demonstrated that the CSNp composite had the highest Langmuir adsorption capacity with 497.45 mg/g. The adsorption is well described by nonlinear Langmuir adsorption isotherm (R² >0.9684, χ² 0.1043–4.1389) and PSO kinetic models (R² > 0.9896 and χ² > 0.3347). The adsorption of Hg²⁺ on the synthesized solid adsorbents was found to be endothermic (∆H^o, 3.007–6.295 kJ/ mol), spontaneous (∆G^o, –6.340 to –8.250 kJ/ mol), fav^orable (0 <K_L <1, 0.0106–0.0120), and physical adsorption process (b_T > 43.318 J/mol) in nature. With only a 5 % decline in its adsorption capacity, regeneration depicted that CSNp exhibited a high reusability degree even after ten cycles of adsorption-desorption processes using EDTA as an excellent eluent for Hg²⁺ desorption.