Electroactive Covalent Organic Frameworks/Carbon Nanotubes Composites for Electrochemical Sensing

An electroactive covalent organic framework (COFThi-TFPB) was prepared by a dehydration condensation reaction between 1,3,5-tris(p-formylphenyl)benzene (TFPB) and thionine (Thi) and wound with carbon nanotubes (CNTs) to design COFThi-TFPB-CNT composites for electrochemical sensing of ascorbic acid (AA) and pH. COFThi-TFPB was a highly ordered two-dimensional (2D) crystalline nanosheet, and its thickness was 0.75 nm. The loading of CNTs onto COFThi-TFPB nanosheets could significantly improve the dispersibility, stability, and catalytic activity of the CNTs. Here CNTs could well catalyze the oxidation of AA, while COFThi-TFPB had a pair of redox peaks that were inert for AA. Accordingly, a ratiometric electrochemical AA sensor was constructed by using the peak of COFThi-TFPB as the reference signal. The ratiometric AA sensor showed a detection limit of 17.68 mu M and linear ranges of 53.04 mu M to 4.00 mM and 4.00-8.00 mM, revealing a good performance, together with satisfactory selectivity, reproducibility, and stability. The redox peak potential of COFThi-TFPB was linearly shifted with the pH, so a pH sensor was constructed. The linear range and sensitivity of the pH sensor were 1-12 and 54 mV pH(-1), respectively. The electroactive COFThi-TFPB-CNT might also be applied to construct other electrochemical sensors.