Surface mercapto engineered magnetic Fe3O4 nanoadsorbent for the removal of mercury from aqueous solutions

In this study, mercapto-functionalized nano-Fe3O4 magnetic polymers (SH-Fe3O4-NMPs) have been prepared and characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), thermogravimetry and differential thermogravimetry analyses (TG–DTA), as well as Fourier-transformed infrared spectroscopy (FTIR). The adsorptive characteristics of the SH-Fe3O4-NMPs intended for removal of mercury (II) were deeply studied. The results showed that the adsorption efficiency increased with pH increasing and reached a plateau at pH above 3.0. The adsorption data obtained at the optimized condition, i.e., 308 K and pH of 3.0, were well fitted with the Freundlich isotherm. The adsorption of Hg(II) reached equilibrium within 60 min. Thermodynamic parameters such as ΔHθ, ΔSθ and ΔGθ suggested that the adsorption processes of Hg(II) onto the SH-Fe3O4-NMPs were endothermic and entropy favored in nature, with ΔHθ at 30.31 kJ mol−1, ΔSθ at 111.41 J mol−1 K−1. The effects of mercury salts, i.e., Hg(NO3)2, HgSO4, and different acids, were also deeply investigated and showed that the adsorption capacity of Hg(II) onto the SH-Fe3O4-NMPs decreased when Cl− existed.

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► SH-Fe3O4-NMPs have been synthesized in an environmentally friendly method.
► The uptake of Hg(II) by SH-Fe3O4-NMPs was much higher than those of other adsorbents.
► Effects of pH value and conjugate anions were intensively studied.
► Role of surface SH on adsorption mechanism of Hg(II) ions was investigated.
► SH-Fe3O4-NMPs can be separated easily after adsorption by an external magnet.