A highly hydrophilic hydrazone-linked covalent organic framework as a fluorescent multianalyte sensor for detection of Cu2+ and Hg2+ in aqueous solution

Heavy metal pollution is of great threat to public health and the environment, and an effective method to detect and remove toxic heavy ions from water is highly desirable. The emerging covalent organic frameworks (COFs) with well-defined pore structures and specific functional units provide an excellent platform for fluorescent sensing. The hydrazone-linked framework material SH-COF with excellent hydrophilicity and abundant chelating sites was synthesized by bottom-up strategy under solvothermal conditions. The resultant SH-COF with specific binding sites was proposed to detect and remove Cu2+ and Hg2+. The SH-COF also exhibited the characteristics of high selectivity, high sensitivity, a lower limit of detection (0.244 μM for Cu2+ and 0.239 μM for Hg2+), and real-time response. Furthermore, the highly selective interaction of Cu2+ or Hg2+ with SH-COF was confirmed by X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectra. A proposed sensing mechanism of COF for Cu2+ and Hg2+ was presented. This research also demonstrates the great potential of COFs in practical sensing applications.