The adsorption property and mechanism for Hg(II) and Ag(I) by Schiff base functionalized magnetic Fe3O4 from aqueous solution

Abstract

Schiff-base functionalized magnetic Fe3O4 were prepared by feasible one-pot subsequent homogeneous method (Fe3O4@SiO2–HO–S) and heterogeneous method (Fe3O4@SiO2-HE-S), respectively. The as-prepared adsorbents were used for the adsorption of aqueous Hg(II) and Ag(I). The effects of solution pH, time, temperature, coexisting metal ions, and initial metal ion concentration on the adsorption were investigated. The as-synthesized adsorbents were characterized by transmission electron microscope, scanning electron microscope, and X-ray photoelectron spectroscopy. The effect of solution pH indicates the optimal adsorption pH is 6. The adsorption equilibrium time are 180 and 220 min for both Hg(II) and Ag(I) under the concentration of 0.002 and 0.004 mol L−1, respectively. The adsorption kinetic process is proved to be dominated by film diffusion process and follows pseudo-second-order kinetic model. The adsorption isotherm process is proceeded by chemical mechanism and can be described by Langmuir model. Thermodynamic parameters indicate that the adsorption process is spontaneous, endothermic, and entropy increase. Adsorption selectivity demonstrates Fe3O4@SiO2-HE-S and Fe3O4@SiO2–HO–S exhibit good adsorption selectivity for Hg(II). The adsorption mechanism demonstrates the N atoms of Schiff base functional group mainly dominate the adsorption of Fe3O4@SiO2-HE-S and Fe3O4@SiO2–HO–S for metal ions. The regeneration property indicates the adsorbents can be reused with practical value.