Reusable sulfhydryl-modified covalent organic framework for high-performance detection of trace Pb (II)

Increasing the number of active sites in covalent organic framework (COF)-based sensors can indirectly improve their detection performance toward environmental heavy metal pollutants, but a thorough investigation is still crucial for achieving this goal. Herein, a novel electrochemical sensor based on post-synthetic modification of covalent organic framework by sulfhydryl in a carbon paste electrode (COF-SH/CPE) was developed for the determination of trace Pb (II) in coastal water using the square wave stripping voltammetry technique. The electrochemical properties of the as-obtained COF-SH/CPE, characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), confirmed a 4.3-fold increase in performance of COF-based electrodes modified with thiol groups when compared to unmodified COF electrodes, consistent with the electrostatic potential calculations. Under the optimal experimental conditions, COF-SH/CPE exhibited a linear response toward Pb (II) concentrations from 2.41 nM–3.86 μM, suitable for coastal water analysis. The electrode also showed a low limit of detection (LOD) for Pb (II) determination of 0.82 nM, combined with excellent stability at a Relative Standard Deviation (RSD) of 3.6 %. The excellent detection performances of COF-SH/CPE were attributed to its large specific surface area and abundant active sites of COF materials, providing a higher electron density. Overall, the proposed method has potential for improving the performance of future electrochemical sensors for the sensitive determination of heavy metals in environmental samples. • Post-synthetic modification of COFs was successfully synthesized. • Thiol functionalization enhanced the electrode's current intensity by a factor of 4.3. • The sensor realizes the determination of Pb (II) in real samples.