An enzyme-free electrochemical sensor based on reduced graphene oxide/Co₃O₄ nanospindle composite for sensitive detection of nitrite

Cobalt oxide (Co₃O₄) nanospindles-decorated reduced graphene oxide (RGO) composite is prepared via thermal decomposition of a three-dimensional coordination complex precursor, cobalt benzoate dihydrazinate, at 200 °C. Transmission electron microscopy reveals that Co₃O₄ nanospindles with an average particle size of <25 nm are decorated on the RGO surface. The low decomposition temperature and lack of residual impurities are significant aspects of this simple and facile method. The electrochemical performance of the proposed sensor is investigated using cyclic voltammetry and chronoamperometry. Under optimum conditions, anodic peak currents are linearly proportional to their concentrations, in the range of 1-380 μM for nitrite with a regression equation of I (μA) = 2.0660 C + 6.7869 (R² = 0.9992). The sensor exhibits a high sensitivity of 29.5 μA μM^-1 cm^-2, a rapid response time of 5 s, and a low detection of limit of 0.14 μM. The proposed electrode shows good reproducibility and long-term stability. The sensor is used to determine the nitrite level in tap water with acceptable recovery, implying its feasibility for practical application.