Covalent Organic Framework Nanosheet-Based Ultrasensitive and Selective Colorimetric Sensor for Trace Hg2+ Detection

Covalent organic frameworks (COFs) have shown extensive applications in energy storage, catalysis, and gas adsorption because of their regular pore structure, flexible topological connectivity, and excellent adjustable functionality. However, their potential applications in colorimetric sensing have not yet been explored. In this study, we synthesized bipyridine-containing covalent organic framework nanosheets (Tp-Bpy NSs) with a regular pore structure and abundant nitrogen-containing functional groups that function as active sites for the in situ generation of AuNPs to form AuNPs@Tp-Bpy. The anchoring of AuNPs onto Tp-Bpy NSs through coordination bonds can significantly enhance the dispersibility, stability, and catalytic activity of the AuNPs. We find that the synergistic effect of increased mimetic activity of gold amalgam and the higher access probability of Hg2+ provided by Tp-Bpy nanosheets makes the AuNPs@Tp-Bpy nanocomposite exhibit a high performance for the detection of Hg2+ with an ultralow detection limit of 0.33 nM. This sensing platform has been successfully used for the sensitive and stable detection of Hg2+ in various environmental samples. The present study extends the application of COFs and opens a new frontier for the design of novel nanocomposites for a variety of potential applications.