A hydrazone-linked covalent organic framework with abundant N and O atoms for detecting heavy metal ions

The bioaccumulation of heavy metal ions (HMIs), even at low concentrations, will lead to high toxicity. So, in this work, a hydrazone-linked covalent organic framework (COF) with abundant N and O atoms was prepared for sensitive HMIs detection. Under the room temperature, terephthaloyl dihydrazide (TD) and triformylphloroglucinol (TP) reacted to form the hydrazone bond, and a new hydrazone-linked TP-TD COF was prepared. During the reaction, enole-keto tautomerism occurred, and NH···OC hydrogen bond was formed, which improved the crystallinity and chemical stability of COF. Accordingly, the hydrazone-linked TP-TD COF presented three-dimensional network morphology. The porous channels could promote the migration of HMIs, and the affinity of N and O atoms to HMI was utilized. There were abundant O·N·O sites in each unit, so the hydrazone-linked TP-TD COF was applied to the sensing of HMIs. The electrochemical sensor constructed by TP-TD COF was used to detect Cd2+, Pb2+, Cu2+ and Hg2+ simultaneously. Under optimized conditions, the electrochemical sensor based on TP-TD COF showed fast response speed, sensitive detection ability and the potential for practical sample detection.