Regenerable Carbohydrazide-Linked Fluorescent Covalent Organic Frameworks for Ultrasensitive Detection and Removal of Mercury

Mercury is one of the most toxic elements in the environment. Recently, a number of covalent organic frameworks (COFs) were developed for simultaneous detection and removal of mercury. They rely on post-synthetically modified sulfur-based ligands for irreversible mercury binding. In addition, their rigid structures resulted in low fluorescence yields. Herein, a novel highly luminescent COF named TFPPy-CHYD with a quantum yield of 13.6% was designed by integrating a pyrene-based building block with a flexible carbohydrazide linker. The nitrogen-based ligand allows reversible and highly selective binding of Hg2+. As a sensing platform, it has an ultralow detection limit of 17 nM mercury. More importantly, TFPPy-CHYD exhibits excellent performance in removing mercury from both air and water, providing very high Hg0 and Hg2+ adsorption capacities of 232 and 758 mg g–1, respectively. This work demonstrates enormous potential of luminescent COF for metal detection and remediation. By rational introducing metal ligands, a suite of new COF materials might be synthesized for the detection and removal of other metal ions.