Synthesis and uranium adsorption studies of UiO-66 (Ce) based metal organic frameworks from aqueous solutions

Abstract

Ce based Metal Organic Framework (MOF) UiO-66 (Ce) and a MOF-composite CeO2@UiO-66 (Ce) were prepared by conventional heating and hydrothermal method respectively. Both the MOFs were characterized using X-ray Diffraction (XRD) technique, Fourier Transform Infra Red (FT-IR) spectroscopy, Field Emission-Secondary Electron Microscopy (FE–SEM), Small Angle X-ray Scattering (SAXS), Thermogravimetric Analysis (TGA), Differential Thermal Analysis (DTA) and Transmission Electron Microscopy (TEM). N2 adsorption-desorption isotherms of UiO-66 (Ce) showed large specific surface area of ∼981 m2/g and a reasonably large pore volume compared to the composite sample. Their uranium adsorption capacity in aqueous solutions was investigated in the pH range 2–6. Uranium adsorption experiments indicated reasonably higher uranium adsorption capacity of 239 mg/g for CeO2@UiO-66 (Ce) compared to UiO-66 (Ce) (190 mg/g). Kinetic studies revealed rapid uranium adsorption in pure MOF compared to the composite material which was attributed to the blocking of pores by CeO2 nanoparticles in the composite material. These frameworks showed good thermal stability as revealed by the thermogravimetric studies. The synthesized MOFs exhibit moderate recyclability using dilute acid and can be utilized in successive cycles. The selectivity studies showed that these MOFs are highly selective to U (VI) compared to Fe (III), Co (II), Ni (II) and Sr (II). This study could pave a way for more advanced material synthesis involving MOFs which could prove very beneficial for the wastewater remediation thus creating a safer environment to live in.