Efficient removal of Pb(II) from water using chitosan-coated magnetic Fe3O4-SiO2 nanocomposites: adsorption performance, mechanism, and reusability

A chitosan coated Fe3O4-silica magnetic nanocomposite (CS/Fe3O4-SiO2) was successfully synthesized and utilized for removal of Pb(II) ions from the aqueous solution in this study. The Fe3O4 nanoparticles were first synthesized with a chemical co-precipitation technique by mixing FeCl3.6H2O and FeCl2.4H2O in a basic medium. Then, the magnetic nanoparticles were coated by silica by the modified Stöber method using tetraethyl orthosilicate (TEOS) for the purpose of enhancing the structural stability and surface functionality. Finally, the Fe3O4-SiO2 nanoparticles were dispersed in a chitosan solution with pH in the range of 3-5 using ultrasonic agitation and then continuously stirred to obtain a stable magnetic chitosan-based polymer nanocomposite material with a large number of amino and hydroxyl functional groups. The synthesized nanocomposite was analyzed by BET, FT-IR, FESEM, EDX and VSM analysis. The characterization results verified that the nanocomposite has been successfully synthesized with a relatively high specific surface area of 149.84 m2/g and good magnetic properties of saturation magnetization of 46.85 emu/g, facilitating the fast separation of magnetic particles after adsorption. The influence of pH, adsorbent dosage, contact time, initial concentrations of the metal, adsorption kinetics, adsorption isotherms and thermodynamic behavior was studied by carrying out batch adsorption experiments. The adsorption efficiency was found to be higher with the increase in the dosage of the adsorbent and the contact time while the optimal adsorption efficiency was obtained at pH = 6.4, maximum adsorption capacity = 294.12 mg/g, and the removal efficiency was about 98% at maximum. The pseudo-second order model was found to be the best model to describe the adsorption kinetics, which suggested chemisorption as the primary adsorption process. The results from the equilibrium tests were best correlated to the Langmuir isotherm model implying a monolayer adsorption on homogenous active sites. Thermodynamic analysis showed that the adsorption process was spontaneous and exothermic. Besides this, the nanocomposite also had good adsorption performance after multiple regeneration cycles. The results showed that the synthesized CS/Fe3O4-SiO2 magnetic nanocomposite is a promising, reusable and efficient adsorbent for removing the Pb(II) from contaminated water systems.