Surface functionalization of MIL-101(Cr) by aminated mesoporous silica and improved adsorption selectivity toward special metal ions

Abstract

Developing novel solid adsorbents with high efficiency and excellent selectivity is always an important target in the removal of toxic metal ions from waste water. In this study, a composite nano-adsorbent NH₂-mSiO₂@MIL-101(Cr) has been fabricated and applied in the efficient removal of Pb(II) and Cr(VI) for the first time. The nanocomposites were characterized by using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), fourier-transform infrared (FT-IR) spectroscopy and thermal gravimetry analysis (TG). The results indicate that a typical core@shell structure has been fabricated by fully coating a mesoporous SiO₂ shell over the micro/mesoporous MIL-101(Cr). As a result, the surface charge and the zeta potentials change significantly. Two toxic metal ions, namely, Pb(II) and Cr(VI) were chosen as the main adsorption targets to evaluate the surface adsorption activities. The adsorption conditions were optimized, the influences of other coexisting ions were explored, and the adsorption selectivity was investigated. Interestingly, the NH₂-mSiO₂@MIL-101(Cr) nanocomposites display a prominent adsorption activity compared with the original MIL-101(Cr) and non-aminated mSiO₂@MIL-101(Cr) and excellent selectivity toward Pb(II) in the presence of other divalent metal ions. The adsorption kinetics and adsorption thermodynamics were simulated accordingly, and the enhanced adsorption mechanism was also suggested. The good reusability and adsorption selectivity of the NH₂-mSiO₂@MIL-101(Cr) suggest their potential applications in the selective removal of special metal ions such as Pb(II) from the waste water.