Construction of quaternary ammonium nitroxy-hybrid magnetic mesoporous silica adsorbent system and its selective adsorption research of Re(Ⅶ)/Cu(Ⅱ)

This study focussed on the development of a quaternary ammonium nitroxy-hybrid magnetic mesoporous silica adsorption system (Fe3O4@MS-SiO2@3-CPTES@Tetra-N-ACE, Fe3O4@MS-SiO2@3-CPTES@Tetra-2N-ACE and Fe3O4@MS-SiO2@3-CPTES@Tetra-DE) was established with adsorption structures consisting of 1,4,7,10,13-pentaoxa-16-azacyclooctadecane (N-ACE), 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (2N-ACE) and a similar linear structure, 3,6-dioxy-1,8-octylenediamine (DE) for the selective separation of Re/Cu. The composites were characterized by Fourier transform Infrared spectroscopy(FT-IR), Energy dispersive spectrometer(EDS), X-ray Diffraction(XRD), Transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) measurements. The characterization of composites exhibits mesoporous and rich functional groups. The experimental results demonstrated that the Fe3O4@MS-SiO2@3-CPTES@Tetra-2N-ACE and Fe3O4@MS-SiO2@3-CPTES@Tetra-DE possessed superior adsorption capacities of Re(VII) in a wide acidic environment (pH=3–6). The maximum adsorption capacity of Fe3O4@MS-SiO2@3-CPTES@Tetra-2N-ACE and Fe3O4@MS-SiO2@3-CPTES@Tetra-DE were respectively up to 331.77 mg·g−1, 395.54 mg·g−1 at pH 5.0. Furthermore, the adsorption rate of these adsorbents was fast for only 2 h to absorb more than 80 % of Re(VII). Notably, when Fe3O4@MS-SiO2@3-CPTES@Tetra-2N-ACE and Fe3O4@MS-SiO2@3-CPTES@Tetra-DE were added into the rhenium copper binary solution with the concentration ratio from 1:1 and 1:50, the Re (Ⅶ) / Cu (Ⅱ) selectivity was constantly excellent (SelRe/Cu value > 1.46, SelRe/Cu max = 4.96). After 5 desorption processes for Re (Ⅶ) with 3 mol·L−1 NaCl and 1 mol·L−1 NaCl, respectively, the adsorption efficiency decreased by less than 10 % at Fe3O4@MS-SiO2@3-CPTES@Tetra-2N-ACE and Fe3O4@MS-SiO2@3-CPTES@Tetra-DE. The adsorption mechanism between the adsorbents and Re(VII) was mainly electrostatic interaction and ion exchange through TEM-EDS, FT-IR, and XPS. This novel adsorption system had a promising application in the selective separation of Re(VII)/Cu(Ⅱ).