Novel bio-mediated Ag/Co3O4 nanocomposites of different weight ratios using aqueous neem leaf extract: Catalytic and microbial behaviour

An environmentally safe, economically, fast, and green synthetic approach was presented in this work for the fabrication of Ag-NP, Co₃O₄-NP and different weight ratio of Ag/Co₃O₄-NC. The synthesized samples were characterized by Fourier-transform infrared spectroscopy (FT-IR) and UV–visible spectrophotometry, Transmission Electron Microscopy (TEM), Scanning electron microscopy (SEM) along with X-ray energy dispersive spectroscopy (EDAX), and X-ray diffraction (XRD). The catalytic behaviour of the synthesized samples toward the reduction reaction of 4-nitrophenol in the presence of NaBH₄ was studied. It is indicated that the synthesized nanocomposites show a satisfactory catalytic activity. The catalytic reduction of p-NP to p-AP obeys first-order kinetics with rate constant in the following order (Ag-NP> (Ag/Co₃O₄-NC) ?1:1 > 1:3 > 3:1> Co₃O₄). This may be attributed to the high dispersion of Ag-NP compared to cobalt oxide nanoparticles. The microbial activity of the samples was analyzed using seven species of pathogenic microorganisms; 1) two species belongs to Gram negative bacteria; Escherichia coli (E.coli), and Salmonella, 2)four species belongs to Gram positive bacteria Marsa, Listeria, Staphylococcus aureus (S. aureus), bacillus subtilis (B.subtilis), and 3) one pathogenic fungal species Candidia. The data show that all samples exhibited an excellent range of inhibition toward all tested pathogenic microorganisms.