Calcination-induced enhancement of Cd2+ and Pb2+ electrochemical detection capabilities of nano-ag-supported CoZn bi-metal ZIFs

Abstract

Electrode materials with a large specific surface area, good conductivity, and efficient electrochemical catalytic activity are necessary for the rapid and accurate electrochemical detection of heavy metal ions. Based on the advantage of the high specific surface area of MOF materials, in this study, an Ag nanoparticle-supported CoZn bi-metal zeolitic imidazolate framework (Ag@ZIF) was decorated on working electrodes for Pb²⁺ and Cd²⁺ detection, and its conductivity and electrochemical catalytic activity were boosted to a high scale via calcination. A systematic study was conducted to discern the impact of the calcination temperature on the composition, structure, and electrochemical performance of Ag@ZIF. The investigation indicated that as the calcination temperature was increased from 600 °C to 1100 °C, the Co²⁺ and Zn²⁺ ions in Ag@ZIF were first combined into Co₃ZnC and then transferred to metallic Co and Zn, accompanied with the complete evaporation of Zn at a high calcination temperature of 1000 °C. While the morphology of the calcinated Ag@ZIF turned from multiporous dodecahedra to multiporous spheres, followed by the collapse of the framework at 1100 °C. The Ag@ZIF calcinated at 1000 °C exhibited optimal performance for heavy metal ion detection, with a low limit of detection (Pb²⁺ 7.28 nM, Cd²⁺ 14.63 nM) and high sensitivity (Pb²⁺ 8.907 μA μM⁻¹, Cd²⁺ 4.757 μA μM⁻¹). Moreover, the fabricated sensor also demonstrated excellent selectivity, repeatability, and stability, making it suitable for detecting Pb²⁺ and Cd²⁺ in real water samples.