Rational Design of Regenerable Amino-Functionalized Fluorescent Covalent Organic Framework for the Exclusive...

Goal-oriented development of novel covalent organic frameworks (COFs) to construct a sensing platform for highly toxic mercury (II, Hg²⁺) is of tremendous significance. Recently, numerous COFs with sulfur-based ligands were developed for Hg²⁺ monitoring; however, strong binding of Hg²⁺ by sulfur makes their regeneration very tough. Herein, we designed and developed an amino-functionalized fluorescent COF (COF-NH₂) through facile postmodification for Hg²⁺ detection in which the π-conjugation skeleton is the signal reader and the nitrogen-based side is the highly selective Hg²⁺ receptor. More importantly, this nitrogen-based receptor permits the reversible binding of Hg²⁺. As a sensing platform, the outstanding performance of COF-NH₂ for Hg²⁺ detection was reached with respect to high sensitivity with an ultralow detection of 15.3 nM, real-time response with rapid signal change of 10 s, and facile visualization with significant fluorescence color change. Expectedly, COF-NH₂ obtained facile recycling which still shows excellent response performance toward Hg²⁺ after six cycles based on the reversible interaction between amino groups and Hg²⁺. Our work not only shows an attractive foreground of fluorescent COF for Hg²⁺ detection but also emphasizes the easy construction of novel COF materials via the rational introduction of metal ligands for the recognition of other metal ions.