Synthesis and characterization of magnetic mesoporous Fe₃O₄@mSiO₂–DODGA nanoparticles for adsorption of 16 rare earth elements

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In this study, novel magnetic mesoporous Fe₃O₄@mSiO₂-DODGA nanoparticles were prepared for efficiently adsorbing and recycling REEs. Fe₃O₄@mSiO₂-DODGA was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA). The adsorption behavior of Fe₃O₄@mSiO₂-DODGA was investigated by ICP-OES. The results showed that the content of DODGA in the adsorbent was 367 μmol g⁻¹. Fe₃O₄@mSiO₂-DODGA exhibited the highest adsorption rates for 15 REEs, except Tm, in a 2 mol L⁻¹ nitric acid solution. Among these elements, the adsorption rates for Nd, Sm, Eu, Dy, Ho, Yb, Lu, Y and Sc ranged from 85.1% to 100.1%. The desorption rates for all 16 REE ions reached their maximum values when 0.01 mol L⁻¹ EDTA was used as the eluent. The desorption rates for Nd, Ce, Sm, Eu, Ho, Yb, Lu, Y, and Sc were 87.7-99.8%. Fe₃O₄@mSiO₂-DODGA had high stability in 2 mol L⁻¹ HNO₃ and could be used five times without significant loss of adsorption capacity. Moreover, these nanoparticles had high selectivity, and their adsorption rate was not affected even in a high-concentration solution of a coexisting ion. Therefore, 8 REE ions (Nd, Sm, Eu, Ho, Yb, Lu, Y, and Sc) were selected for the study of adsorption kinetics and adsorption isotherm experiments. It was demonstrated that the values of Q e (equilibrium adsorption capacity) for Nd, Sm, Eu, Ho, Yb, Lu, Y, and Sc were 14.28-60.80 mg g⁻¹. The adsorption of REEs on Fe₃O₄@mSiO₂-DODGA followed the pseudo-second-order kinetic model, Elovich model and Langmuir isotherm model, which indicated that the adsorption process of Fe₃O₄@mSiO₂-DODGA for REEs comprised single-layer adsorption on a non-uniform surface controlled by chemical adsorption. It was concluded that Fe₃O₄@mSiO₂-DODGA represents a new material for the adsorption of REEs in strongly acidic solutions.