Thiol modified Fe3O4@SiO2 as a robust, high effective, and recycling magnetic sorbent for mercury removal

The SiO2 shell was coated on Fe3O4 nanoparticle by hydrolyzation of Na2SiO3, and then thiol groups were modified on the Fe3O4@SiO2 through silanization reaction to form Fe3O4@SiO2-SH sorbents. Characterization with transmission electron microscope (TEM), Energy-dispersive spectroscope (EDS), and X-ray photoelectron spectroscopy (XPS) proved that SiO2 and thiol groups were successfully covered on the surface of Fe3O4 nanoparticle. The Fe3O4 core possessed superparamagnetism for magnetic separation, and the SiO2 shell could protect the Fe3O4 core from being oxidized or dissolved under acid solution and provide good modificability. Due to the strong interaction between mercury and thiol groups, the synthesized sorbents exhibited high adsorption capacity and good anti-interference ability during mercury adsorption. The maximum adsorption capacity calculated from Langmuir fitting was 148.8 mg/g at pH 6.5, and the sorbents still maintained good adsorption ability at low solution pH and high concentration of coexisting cations. Mercury loaded on the sorbents could be easily desorbed with 1 mol/L HCl containing 3 wt.% of thiourea, and the sorbents showed good reusability. The adsorption capacities were still kept over 110 mg/g in tested natural water samples, showing practical significance in remediation of mercury contaminated actual water.