Highly selective adsorption of rare earth elements by honeycomb-shaped covalent organic frameworks synthesized in deep eutectic solvents

Jing Xiao; Bo Li; Ruibin Qiang; Hongdeng Qiu; Jia Chen

doi:10.1016/j.envres.2022.113977

Highly selective adsorption of rare earth elements by honeycomb-shaped covalent organic frameworks synthesized in deep eutectic solvents

Environ Res. 2022 Nov;214(Pt 4):113977. doi: 10.1016/j.envres.2022.113977. Epub 2022 Aug 24.

Authors

Jing Xiao¹, Bo Li¹, Ruibin Qiang², Hongdeng Qiu³, Jia Chen⁴

Affiliations

¹ CAS Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
² CAS Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China.
³ CAS Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China; University of Chinese Academy of Sciences, Beijing, 100049, China; College of Chemistry, Zhengzhou University, Zhengzhou, 450001, China. Electronic address: hdqiu@licp.cas.cn.
⁴ CAS Key Laboratory of Chemistry of Northwestern Plant Resources and Key Laboratory for Natural Medicine of Gansu Province, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou, 730000, China; University of Chinese Academy of Sciences, Beijing, 100049, China. Electronic address: jiachen@licp.cas.cn.

PMID: 36027963
DOI: 10.1016/j.envres.2022.113977

Abstract

One of the key factors to obtain a highly pure individual rare earth element (REE) is to prepare adsorbents with high selectivity and adsorption capacity. Covalent organic frameworks (COFs), which encompass a variety of properties, including regular/tunable pore size, high specific surface area and easy functionalization, could be effective as adsorbents for separating rare earth elements (REEs). In this paper, TpPa COFs were successfully synthesized using an eco-friendly deep eutectic solvent (DES) as the reaction medium instead of toxic organic solvents at room temperature. TpPa COFs have a good separation effect on the nine REEs investigated in this work. Among them, the separation factors (β) of Eu/Yb, Eu/Tm and Eu/La are 15.34, 14.70 and 10.78, respectively, indicating that the TpPa COFs have good separation performance. Further discoveries showed that the adsorption and separation mechanism of the TpPa COFs for REEs in this experiment may be due to the coordination of REE ions with O to form a stable structure. This study blazed a trial for a green and facile synthesis strategy of TpPa COFs and expanded its implementation as a solid adsorbent in the separation of REEs.

Keywords: Adsorption separation; Covalent organic frameworks; Deep eutectic solvents; Green synthesis; Rare earth elements.