Highly Sensitive and Selective Nonenzymatic Sensing of Glyphosate Using FTO-Modified MOF-Derived CuCo2O4 Nanostructures Intercalated in Protonated-g-C3N4 and 3D-Graphene Oxide Sheets

Owing to the toxicological effects of glyphosate (GLY) in the environment, the development of sensitive and selective sensors has become essential; however, limited studies have been done to detect it. In response to that, a novel MOF-derived copper-cobalt oxide decorated on a protonated-gC3N4 (H-gC3N4) and three-dimensional (3D)-graphene oxide nano -composite (CuCo2O4/H-gC3N4/3D-rGO) has been synthesized by the solvothermal method using a zeolite imidazole framework (ZIF-67) template. The composite was then deposited on fluorine tin oxide (FTO) to fabricate a simple and cheap nonenzymatic electrochemical sensor for the sensing of glyphosate. The morphological evaluation by SEM and TEM techniques demonstrated that distorted dodecahedrons like CuCo2O4 nanostructures are distributed evenly on the surface of H-gC3N4 and intercalated between H-gC3N4 and 3D-rGO sheets. The distinct surface of the H-gC3N4 acts as a bridge between 3D-rGO layers and CuCo2O4 particles. In such structure, H-gC3N4 acts as the nucleation site and N-doped carbon is used to grow CuCo2O4 nanostructures. The CuCo2O4 peak shifting in the XRD profile and appropriate chemical states (Cu2+ in Oh and Co2+ in Td sites) as confirmed from XPS analysis suggested the successful formation of the nanocomposite. In addition, the nanocomposite showcased a high specific surface area of 138 m2 g-1, which help in the increase of electrode reaction sites and thus further improving the sensing performance. In CV analysis, the anodic peak current of the FTO/rGO-H-gC3N4-CuCo2O4 nanocomposite was found to be approximately 2.04, 1.85, 3.17, and 1.04 times higher than those of bare FTO, FTO/3D-rGO, FTO/H-gC3N4, and FTO/CuCo2O4, respectively, due to its highest specific electroactive area (0.17 cm2) calculated using the Randles-Sevcik analysis. After performing different optimization studies, it was found that our sensor showed better sensing performance in pH 5 at 50 mV s-1 after 150 s of accumulation time at room temperature. From the SWV analysis, a lower limit of detection of 0.63 x 10-12 M (sensitivity = 0.016 mu A mM-1) with a wide detection window of 12 mM to 10 pM was achieved. The developed sensor also demonstrated high selectivity toward other pesticides like chlorpyrifos and malathion, as well as high stability for about 35 days. Lastly, the practical suitability of the proposed sensor was analyzed with real fruit samples such as sweet lime and pomegranate with a recovery rate of 98-101%.