Selective entrapment of thorium using a three-dimensional covalent organic framework and its interaction mechanism study

Abstract

A novel porous material tailored for Th (IV) entrapment with not only large capacity but also high selectivity is highly desired for the thorium fuel cycle. Here, a three-dimensional COF (covalent organic framework) material, named COF-DL229 was prepared for the efficiently selective entrapment of Th (IV). Batch sorption experiments indicated that the entrapment of Th (IV) was a pH-dependent, rapid (equilibrium was reached within 1 min) process. The maximum saturated entrapment capacity could reach 513 mg g−1, which is higher than that of the reported two-dimensional COF. The single-component batch experiments and muti-components dynamic experiments suggested that COF-DL229 has a strong affinity towards Th (IV), but little affinity with other ions, which makes COF-DL229 a promising material for selective thorium recovery from waste solution. The interaction mechanism was Th-N coordination, which was confirmed by characterizations (Fourier Transform infrared spectroscopy, FT-IR, X-ray photoelectron spectroscopy, XPS, energy dispersive spectrometer, EDS) and density functional theory (DFT) calculations. The density of states indicated that the doping of the Th (IV) can lower the band gap of the COF-DL229, indicating higher electrical conductivity and stronger adsorption energy. The differential charge exhibited an obvious charge transfer between Th (IV) and the N atom in COF-DL229.