Efficient adsorption and advanced purification of metal ions induced by synergistic effect of amine and thione on covalent organic frameworks

Covalent organic frameworks (COFs) have been widely employed for metal ion adsorption owing to its inherent advantages, encompassing low crystal density, well-organized organic unit structures, adjustable pore size, and remarkable structural stability. However, it is still a great challenge to design excellent COFs with high adsorption and advanced purification capabilities for Pb2+ and Cd2+ ions. Herein, hydrazine-linked COFs (COF-TCH) were prepared for effective adsorption and advanced purification of metal ions. The adsorption capacity of COF-TCH for Pb2+ and Cd2+ ions are 395.3 and 153.5 mg/g, moreover, the Pb2+ and Cd2+ ions in water can be treated from 75 and 30 mg L−1 to less than 0.01 and 0.003 mg L−1, respectively, indicating the excellent adsorption and advanced purification capability of COF-TCH. This is a rare example of COFs adsorbent that deeply purify water to meet the guideline values in drinking water for the World Health Organization. FT-IR, XPS and quantum mechanics calculation were performed to understand the adsorption mechanism. The remarkable adsorption and advanced purification capability of COF-TCH for Pb2+ and Cd2+ ions can be attributed to the synergistic interaction between the amine and thione groups, which can easily complex with Pb2+ and Cd2+ions to form stable five-membered ring structure in COF-TCH. In addition, COF-TCH still remains an adsorption capacity of over 90% after ten adsorption-desorption cycles, indicating its excellent reusability and stability. COF-TCH with high adsorption and advanced purification capability, high stability, low cost and reusability has enormous practical application potential in high-performance remediation of Pb2+ and Cd2+ contaminated water.