COF/MWCNTs/CLS-Based Electrochemical Sensor for Simultaneous and Sensitive Detection of Multiple Heavy Metal Ions

A novel electrochemical sensor based on a covalent organic framework (COF) together with calcium lignosulfonate (CLS)–modified multiwalled carbon nanotubes (MWCNTs) and Nafion was developed for the simultaneous analysis of Cu(II), Pb(II), and Cd(II). COF with a three-dimensional (3D) porous structure containing a large number of amino groups was synthesized by the condensation of cyanuric chloride with p-phenylenediamine through a simple hydrothermal reaction. Therefore, COF can efficiently enrich a large number of heavy metal ions in a short time. MWCNTs significantly improved the conductivity of the sensing interface. Besides, a large number of hydrophilic groups in the structure of CLS can effectively solve the aggregation of MWCNTs. The COF nanocomposite material was characterized by transmission electron microscopy (TEM), scanning electron microscopy techniques (SEM), and Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS). The influence of buffer solution type, deposition time, deposition potential, and pH in the heavy metal ion detection process were studied, and the working parameters were optimized. Under the optimal conditions, the fabricated sensor showed superior wide linear responses in the concentration ranges of 0.6–63.5 μg/L, 2.1–207.2 μg/L, and 1.1–112.4 μg/L for Cu(II), Pb(II), and Cd(II) with a low detection limit (LOD) of 0.2 μg/L, 0.7 μg/L, and 0.4 μg/L (S/N = 3), respectively. Moreover, the mutual interference mechanism of three ions was also investigated. The sensor showed good reproducibility, stability, and anti-interference performance. Besides, the fabricated sensor detected HMIs in edible mushrooms with high recovery between 96 and 109%. This study provides a new method for the detection of HMIs in food.