Comparative Study of Larvicidal Activity of Spinel Co(3)O(4) Nanorods and Entomopathogenic Metarhizium brunneum Conidia against Culex pipiens

Herein, we report the synthesis of spinel cobalt oxide nanorods (Co(3)O(4) NRs) by a modified co-precipitation approach and examine their larvicidal activity against Culex pipiens. The structure and morphology of the as-prepared Co(3)O(4) NRs were emphasized using X-ray diffraction (XRD), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDAX), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that Co(3)O(4) nanostructures have a face-centered spinel cubic crystal structure with a mean crystallite size of 38 nm. These nanostructures have a rod like shape with a mean diameter of 30 nm and an average length of 60 nm. The TGA measurements revealed the high stability of the formed spinel cubic structure at 400 °C. The optical behavior indicates the direct transition of electrons through an optical band gap in the range of 2.92–3.08 eV. These unique chemical and physical properties of Co(3)O(4) NRs enabled them to be employed as a strong agent for killing the C. pipiens. A comparison study was employed between the as-prepared Co(3)O(4) and the entomopathogenic fungus Metarhizium brunneum as a control agent of C. pipiens larvae. The results revealed that the as-prepared nanorods have higher mortality against C. pipiens larvae compared with the well-known M. brunneum.