Mercury adsorption by sulfur- and amidoxime-containing bifunctional silica gel based hybrid materials

Novel sulfur- and amidoxime-containing bifunctional silica gel based hybrid materials, SG-HE-S-AO and SG-HO-S-AO, were prepared by heterogeneous and homogeneous methods. Their structures were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), porous structure analysis and elemental analysis. The results showed that higher degree of functionalization was obtained by the heterogeneous method than the homogeneous method. The static saturated adsorption for Ag(I), Pb(II), Cu(II), Ni(II) and Hg(II) showed that both adsorbents exhibited better adsorption selectivity for Hg(II) than other metal ions. For Hg(II) adsorption, SG-HE-S-AO exhibited better capability than SG-HO-S-AO due to its higher content of functional groups. The Hg(II) adsorption kinetics of the two adsorbents followed the pseudo second-order process at different concentrations. Langmuir and Freundlich isotherm models were both employed to analyze the experimental data, and the Langmuir model fitted better. We also found that increased temperature was beneficial for adsorption. The dynamic adsorption and desorption were investigated and the results showed that the Hg(II) loaded on the two adsorbents were easily eluted by 5% thiourea in 0.5 mol L−1 HNO3. The adsorption mechanism of these materials for Hg(II) was discussed.

The synthetic schemes of sulfur- and amidoxime-containing bifunctional silica gel-based hybrid materials using heterogeneous and homogeneous methods.Figure optionsDownload as PowerPoint slideHighlights
► Two novel sulfur- and amidoxime-containing bifunctional silica gel based hybrid materials were prepared.
► Higher content of functional groups was found in heterogeneous-prepared absorbent than the homogeneous-prepared one.
► The Hg(II) adsorption kinetics of the two adsorbents followed the pseudo second-order process.
► The adsorption of Hg(II) on the two adsorbents fit well with the Langmuir isotherm model.