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De novo synthesis of bifunctional conjugated microporous polymers for synergistic coordination mediated uranium entrapment Boxuan Yu1,2,3,§, Lei Zhang1,4,§, Gang Ye1,5 (), Qingzhi Liu4,6, Jiongli Li2,3, Xudong Wang2,3, Jing Chen1,5, Shengming Xu1,5 (), and Shengqian Ma4,† () 1

Collaborative Innovation Center of Advanced Nuclear Energy Technology, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, China 2 Beijing Institute of Graphene Technology, Beijing 100094, China 3 Beijing Institute of Aeronautical Materials, Beijing 100085, China 4 Department of Chemistry, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL 33620, USA 5 Beijing Key Lab of Radioactive Waste Treatment, Tsinghua University, Beijing 100084, China 6 College of Chemistry and Pharmaceutical Sciences, Qingdao Agricultural University, Qingdao 266109, China † Present address: Department of Chemistry, University of North Texas, 1508 W. Mulberry St, Denton, TX 76201, USA § Boxuan Yu and Lei Zhang contributed equally to this work. © Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 7 September 2020 / Revised: 19 October 2020 / Accepted: 29 October 2020

ABSTRACT This work reports a de novo synthesis of novel bifunctional conjugated microporous polymers (CMPs) exhibiting a synergistic-effect involved coordination behavior to uranium. It is highlighted that the synthetic strategy enables the engineering of the coordination environment within amidoxime functionalized CMP frameworks by specifically introducing ortho-substituted amino functionalities, enhancing the affinity to uranyl ions via forming synergistic complexes. The CMPs exhibit high Brunauer–Emmett–Teller (BET) surface area, well-developed three-dimensional (3D) networks with hierarchical porosity, and favorable chemical and thermal stability because of the covalently cross-linked structure. Compared with the amino-free counterparts, the adsorption capacity of bifunctional CMPs was increased by almost 70%, from 105 to 174 mg/g, indicating evidently enhanced binding ability to uranium. Moreover, new insights into coordination mechanism were obtained by in-depth X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculation, suggesting a dominant role of the oxime ligands forming a 1:1 metal ions/ligands (M/L) coordination model with uranyl ions while demonstrating the synergistic engagement of the amino functionalities via direct binding to uranium center and hydrogen-bonding involved secondary-sphere interaction. This work sheds light on the underlying principles of ortho-substituted functionalities directed synergistic effect to promote the coordination of amidoxime with uranyl ions. And the synthetic strategy established here would enable the task-specific development of more novel CMP-based functional materials for broadened applications.

KEYWORDS conjugated microporous polymers, uranium, adsorption, synergistic coordination, density functional theory

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