ZIF-9-Derived Cobalt and Nitrogen-Doped Carbon Nanocomposites for Sensitive Electrochemical Nitrite Determination

The accurate monitoring of nitrite levels is critically important for safeguarding public health and ensuring food safety, as excessive intake presents severe risks. In this study, we developed a highly sensitive electrochemical sensor for nitrite detection utilizing a cobalt-embedded porous carbon material derived from zeolitic imidazolate frameworks (ZIFs) of ZIF-9. The precursor was subjected to pyrolysis at various temperatures, revealing that the sample carbonized at 800 °C (ZIF-9-800) exhibited superior electrocatalytic performance. This enhancement is attributed to its optimized graphitization degree, high specific surface area, and the well-dispersed active sites resulting from the in situ generated cobalt nanoparticles. The ZIF-9-800-based sensor demonstrated outstanding electrochemical performance, achieving a broad linear detection range of 0.2–7000 μM, high sensitivity (848.6 μA mM−1 cm−2), and an impressively low detection limit of 50 nM. Furthermore, the sensor exhibited excellent selectivity in the presence of common interfering ions and remarkable long-term stability, maintaining more than 80% of its initial response after extended storage. This work underscores the effectiveness of MOF-derived carbon-based catalysts, tailored through calcination temperature optimization, for constructing advanced electrochemical sensing platforms.