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

Abstract

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