Modulating Skeletons of Covalent Organic Framework for High‐Efficiency Gold Recovery

• Published in: Angewandte Chemie International Edition Vol. 63; no. 1; pp. e202317015 - n/a
• Main Authors: Liu, Minghao, Jiang, Di, Fu, Yubin, Zheng Chen, George, Bi, Shuai, Ding, Xuesong, He, Jun, Han, Bao‐Hang, Xu, Qing, Zeng, Gaofeng
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 02.01.2024
• Edition: International ed. in English
• Subjects: Binding sites; Binding Sites Conversion; Covalent Organic Frameworks; Electronic waste; Gold; Gold Ions Recovery; Ionic Modification; Ionization; Skeleton Engineering; Gold Ions Recovery; Ionic Modification; Covalent Organic Frameworks; Skeleton Engineering; Binding Sites Conversion
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202317015

Covalent organic frameworks (COFs) have attracted considerable attention as adsorbents for capturing and separating gold from electronic wastes. To enhance the binding capture efficiency, constructing hydrogen‐bond nanotraps along the pore walls was one of the most widely adopted approaches. However, the development of absorbing skeletons was ignored due to the weak binding ability of the gold salts (Au). Herein, we demonstrated skeleton engineering to construct highly efficiently absorbs for Au capture. The strong electronic donating feature of diarylamine units enhanced the electronic density of binding sites (imine‐linkage) and thus resulted in high capacities over 1750 mg g−1 for all three COFs. Moreover, the absorbing performance was further improved via the ionization of diarylamine units. The ionic COF achieved 90 % of the maximal adsorption capacity, 1.63 times of that from the charge‐neutral COF within ten minutes, and showed remarkable uptakes of 1834 mg g−1, exceptional selectivity (97.45 %) and cycling stability. The theoretical calculation revealed the binding sites altering from imine bonds to ionic amine sites after ionization of the frameworks, which enabled to bind the AuCl4− via coulomb force and contributed to enhanced absorbing kinetics. This work inspires us to design molecular/ionic capture based on COFs. Skeleton engineering was used to form covalent organic frameworks (COFs) with diarylamine derivatives and ionized skeletons, thus overcoming the weak binding ability of Au ions, giving gold adsorbents with high selectivity and uptakes. Experiments and theoretical calculations show that the transition of binding sites from C=N bonds to ionic amine sites, thereby avoiding the protonation process, contributed to enhanced absorbing kinetics.