Tailored metal-organic frameworks facilitate the simultaneously high-efficient sorption of UO22+ and ReO4− in water

Abstract

The simultaneously efficient extraction of radioactive metal cations and anions from radioactive waste is of great interest for the proper disposal of spent fuel and environmental protection. Modifying metal-organic frameworks (MOFs) into multifunctional materials with controllable and desired properties is an efficient strategy for broadening their practical applications. Herein, poly(ethyleneimine) (PEI) tailored MIL-101(Cr) (MILP) was obtained through an easy operation and low-cost strategy and was utilized to simultaneously extract uranium (UO22+) and rhenium (ReO4−) from water. The effects of PEI coating amounts, system pH, contact time, initial UO22+/ReO4− concentrations, ionic strength, as well as interfering ions were studied to evaluate the sorption performance of MILP composites. The maximum sorption capacity was 416.67 mg/g for UO22+ at pH 5.5 and 434.78 mg/g for ReO4− at pH 3.5, levels that are superior to those of most adsorbents. The sorption of UO22+/ReO4− occurred in a pH-dependent, spontaneous and endothermic manner, which showed preferable modeling by the pseudo-second-order (PSO) kinetic equation and Freundlich isotherm equation. The adsorption of ReO4− was inhibited by the coexistence of UO22+ and high ion strength. Batch experiments and X-ray photoelectron spectroscopy (XPS) results indicate that UO22+/ReO4− sorption was driven by the abundant amino groups and unsaturated metal sites in the MILP-3 composites. MILP-3 also showed excellent recycling performance and maintained high sorption capacities for UO22+/ReO4− in different simulated water samples. This study shows that MILP composites can effectively extract radioactive metal cations and anions from water, and lays a foundation for designing an excellent new category of candidates with versatile functions for wastewater management.