Simultaneous detection of Cd(II) and Pb(II) by differential pulse anodic stripping voltammetry at a nitrogen-doped microporous carbon/Nafion/bismuth-film electrode

Recently, metal-organic frameworks (MOFs) and their carbon derivates have been demonstrated as new electrode modifying materials for electrochemical sensing. In this work, the first example of the detection of heavy metal ions with a MOF-derived sensing platform was presented. The platform was based on a glassy carbon electrode (GCE) modified by Nafion-bismuth/nitrogen doped microporous carbon (NMC) composite, in which the NMC was derived from a zeolitic imidazolate framework-8 (ZIF-8). The good dispersibility, large specific surface area (941 m2 g−1), high nitrogen content (25.0 at.%) and good electrical conductivity of the NMC materials, as well as the synergistic effects of Nafion and bismuth-film contributed to the enhanced signals of the electrode during the differential pulse anodic stripping voltammetry (DPASV) measurements for simultaneous detection of trace Cd(II) and Pb(II) in aqueous solution. The calibration curves for Cd(II) covered two linear ranges varying from 2 to 10 μg L−1 and 10 to 100 μg L−1. As for Pb(II), the linear calibration curves ranged from 0.5 to 10 μg L−1 and 10 to 100 μg L−1. The detection limits were estimated to be 1.5 μg L−1 (S/N = 3) for Cd(II) and 0.05 μg L−1 (S/N = 3) for Pb(II), which were 2 times and 200 times lower than the guideline values of drinking water given by the World Health Organization (WHO), for Cd(II) and Pb(II), respectively. In addition, the good reproducibility and stability of the modified electrode offered a promising perspective for the detection of trace metal ions in practice. Compared with other porous carbon modified electrodes that obtained by either drop-casting or screen-printing method, the proposed Nafion/Bi/NMC/GCE showed a much lower detection limit for Pb(II) and a lower or comparable detection limit for Cd(II). Moreover, the obtaining of uniformly ordered N-doped carbon polyhedron could shed light on the preparation of other heteroatom-doped electrode modifying materials for the detection of heavy metal ions.