Tea ( <i>Camellia sinensis</i> ) Extract-Mediated Green Synthesis of Co ₃ O ₄ and Co ₃ O ₄ @Graphene Nanocomposites for Multifunctional Applications in Pollutant Degradation, Sensing, and Energy Storage

A novel solution-mixing method was proposed to synthesize Co₃O₄/graphene nanocomposites (Co₃O₄@Gr) using a green tea leaf (<i>Camellia sinensis</i>) extract as the reducing agent. XRD analysis shows that the as-prepared Co₃O₄@Gr exhibits a cubic spinel crystal structure. From morphological analysis, the obtained Co₃O₄ NS forms spherical clusters that are uniformly distributed on the graphene surface. FT-IR and Raman analyses confirmed the strong molecular and vibrational interactions between the Co₃O₄ NS and Gr. The suppressed PL intensity peak of the Co₃O₄@Gr NCs indicated significant inhibition in the recombination of charge carriers between the hybrid orbitals within the composites. As a result, the catalytic efficiency of Co₃O₄@Gr NCs increased to 80% compared to pristine Co₃O₄, which exhibited only 45% efficiency against methylene blue (MB) dye. Moreover, the as-prepared NCs exhibited a detection limit of 0.01-224 μM, demonstrating a superior low-DPA detection with high sensitivity. The Co₃O₄@Gr/GCE exhibits admirable selectivity for various pesticides, fungicides, and metal ions, with outstanding reproducibility and stability. From electrochemical investigations, the highest specific capacitance values of the as-synthesized Co₃O₄@Gr were 349 F/g at a scan rate of 5 mV/s and 158 F/g at a current density of 1 A/g.