Graphene oxide-mediated green synthesis of Ag, Co3O4 and ZnO nanocomposites for multifunctional antimicrobial applications

Abstract

This paper presents the antibacterial and antifungal activities of Ag/GO, Co₃O₄/GO, and ZnO/GO nanocomposites prepared using Moringa oleifera. The composite nature of the materials was confirmed due to the presence of principal peaks of GO, Ag, Co₃O₄ and ZnO in the UV–visible absorption spectra at 230, 420, 315, and 380 nm, respectively. The absorption data was further analyzed to estimate the bandgap energy of the nanocomposites. The formation of ZnO and Co₃O₄ in the GO nanocomposites was also verified due to the appearance of Zn–O and Co–O bands in FTIR spectra. However, the absence of Ag–O band in FTIR analysis further verified the formation of only Ag in the Ag/GO nanocomposite. The X-ray diffraction (XRD) analysis also revealed the existence of preferential diffractions due to hexagonal ZnO and cubic Ag and Co₃O₄ in the XRD patterns of GO nanocomposites. Moreover, the average crystallite sizes were found to be 53.10, 84.05, and 86.41 nm for ZnO/GO, Ag/GO, and Co₃O₄/GO nanocomposites, respectively. The crystallite size of GO content was noticed 18.39, 27.58, and 44.14 nm in Co₃O₄/GO, ZnO/GO, and Ag/GO nanocomposites, respectively. This increase in GO crystallite size was also correlated with the decrease in bandgap energy of Co₃O₄/GO (2.77 eV), ZnO/GO (2.62 eV) and Ag/GO (2.42 eV) nanocomposites, respectively. Thermal study revealed the higher stability of ZnO/GO nanocomposite in comparison to Co₃O₄/GO and Ag/GO nanocomposites. The different surface morphologies were noticed in scanning electron micrographs of the nanocomposites. Moreover, the antibacterial and antifungal activity studies demonstrated higher activity posed by ZnO/GO nanocomposite than Ag/GO and Co₃O₄/GO while using five Gram-positive bacteria, eleven strains of Gram-negative and six filamentous fungi.

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