Synthesis of metal–organic framework ZIF-9-Mel and its application as an electrochemical modifier in Pb2+ detection

Abstract

In this study, a selective electrochemical sensor was introduced for determination of lead ions based on a metal–organic framework (MOF)-melamine together with carbon black (CB) on the glassy carbon electrode (GCE). Herein, the zeolitic imidazolate framework-9-Mel (ZIF-9-Mel), which is a type of MOF, was synthesized and used as an electrode modifier. The interaction between Pb2+ and amine groups is conditioned by dative attachment, which causes the complexation of Pb2+-N through soft–soft interactions. To enhance the performance of the modified electrode, several parameters such as the pH of the buffer solution, the deposition potential, and the deposition time that affect response were optimized. Under optimized conditions (pH = 3, deposition time = 270 s, deposition potential = −0.7 V) the ZIF-9-Mel/CB/GCE sensor shows two linear ranges (0.5 nM–50 nM and 50 nM–1000 nM), low detection limit (0.16 nM), long-term stability, good repeatability and desirable reproducibility by differential pulse voltammetry (DPV) technique. To display the sensor ability for actual application, ZIF-9-Mel/CB/GCE was used for Pb2+ detection in lettuce and tomato samples with excellent results. According to the introduced method, MOFs are satisfactory materials for fabricating effective electrochemical sensors to detect Pb2+ ions simply and cost-effectively.