Synthesis of DtBuCH18C6-coated magnetic metal–organic framework Fe3O4@UiO-66-NH2 for strontium adsorption

Abstract

The selective adsorption of radioactive strontium is of great importance for environmental protection and human health. In this work, a novel adsorbent for removing strontium ions from aqueous solution was prepared by coating the crown ether 4ʹ,4ʹʹ(5ʹʹ)-di-tert-butyldicyclohexano-18-crown-6 (DtBuCH18C6) onto the porous magnetic metal–organic framework Fe3O4@UiO-66-NH2, which permitted convenient removal of the adsorbent using an external magnetic field. The structure of the synthesized DtBuCH18C6@Fe3O4@UiO-66-NH2 was characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, vibrating-sample magnetometry, and nitrogen adsorption/desorption analysis. The adsorption behavior was evaluated as a function of the HNO3 concentration and contact time and using two adsorption isotherm models. The maximum distribution coefficient values for strontium ions obtained in 7.0 mol L−1 HNO3 solution were 143 mL g−1 and 284 mL g−1 for strontium ion concentrations of 0.005 mg L−1 and 0.05 mg L−1, respectively. The adsorption of strontium ions by the adsorbent obeyed the Freundlich model. Our results indicate that functionalized magnetic metal–organic frameworks may have potential applications in strontium removal.