Rational Design of Regenerable Amino-Functionalized Fluorescent Covalent Organic Framework for the Exclusive Detection of Mercury(II).

Goal-oriented development of novel covalent organic frameworks (COFs) to construct a sensing platform for highly toxic mercury (II, Hg) is of tremendous significance. Recently, numerous COFs with sulfur-based ligands were developed for Hg monitoring; however, strong binding of Hg by sulfur makes their regeneration very tough. Herein, we designed and developed an amino-functionalized fluorescent COF (COF-NH) through facile postmodification for Hg detection in which the π-conjugation skeleton is the signal reader and the nitrogen-based side is the highly selective Hg receptor. More importantly, this nitrogen-based receptor permits the reversible binding of Hg. As a sensing platform, the outstanding performance of COF-NH for Hg 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-NH obtained facile recycling which still shows excellent response performance toward Hg after six cycles based on the reversible interaction between amino groups and Hg. Our work not only shows an attractive foreground of fluorescent COF for Hg 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.