Efficient environmental detection of heavy metal ions using porous Co-N/C rhombic dodecahedra from Zeolitic Imidazolate Frameworks (ZIF-67) via pyrolysis

The diverse functional groups, marvelous surface area, designability, and abundant mesoporous structure of metal organic frameworks (MOFs) have led to their widespread electrochemical applications. This work reports the preparation of carbonized ZIF-67 (Zeolitic Imidazolate Framework-67) named as Co-N/C porous rhombic dodecahedra (RDs) by pyrolysis at two different temperatures, i.e. 350 °C and 500 °C. The surface, morphological, and structural analysis evidenced the formation of Co-N/C porous RDs. Pyrolysis at a higher temperature (500 °C) produced the highly porous ZIF-67 derived Co-N/C. After carbonization, N-doped on carbon matrix and Co particles in Co-N/C synergically enhanced the electrocatalytic performance and electron transport properties. The electrochemical behavior of ZIF-67 derived Co-N/C RDs based glassy carbon electrodes (GCEs) was explored for detecting the heavy metal ions (HMIs), i.e., Hg²⁺ and Cr³⁺, using cyclovoltammetry (CV) and differential pulse voltammetry (DPV) measurements. The Co-N/C@500 °C modified GCE displayed promising detectability and the highest reproducible sensitivity of ∼240 ± 0.04 μA/μM·cm² for Cr³⁺ ions with a reasonable LOD of ∼412 nM. The reliability and repeatability of Co-N/C@500 °C modified GCE were also investigated. Herein, the promising sensing performance by Co-N/C@500 °C based GCE mainly benefited from the high porosity, which provided a large number of active sites for the adsorption and reduction of HMIs.