MOF-Derived N-Doped Carbon Nanotube-Confined Ni Nanoparticles for the Simultaneous Electrochemical Detection of Cu²⁺ and Hg²⁺ with High Sensitivity and Stability

Heavy metal pollution has posed a serious threat to the ecological environment and human health. Thus, the development of accurate and effective methods for their detection is crucial. In this study, a novel electrochemical sensor was fabricated to detect Cu²⁺ and Hg²⁺, based on N-doped carbon nanotube-wrapped Ni nanoparticle (Ni@N-CNT) sensing material, which was derived from the pyrolysis of Ni²⁺ doped ZIF-8. For electrode material design, the packaging structure not only protected the encapsulated Ni nanoparticles from electrochemical corrosion in the acid electrolyte but also provided excellent electro-catalytic activity and electrical conductivity by controlling their size. Thanks to the overall performance of the Ni@N-CNT composite, the proposed sensor exhibited excellent analytical performance for Cu²⁺ and Hg²⁺ detection, with ultra-low detection limits of 33.3 ng⋅L^-1 and 33.3 ng⋅L^-1, respectively. The sensor also demonstrated good repeatability, reproducibility and selectivity. In addition, the method was successfully applied to the electrochemical analysis of Cu²⁺ and Hg²⁺ in actual Chinese cabbage samples with satisfactory recovery, confirming its practical applicability.