Green Synthesis of Mono and Bimetallic Nanoparticles of Silver and Cobalt Oxide Using Croton Macrostaychus Plant Extract and Evaluation of their Antibacterial Activity

Abstract

In this study, Ag NPs, Co3O4 NPs and Ag/Co3O4 BMNPs were synthesized via the green synthesis method by using Croton macrostachyus leaf extract. The synthesized NPs were characterized by using spectroscopic techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FT-IR) and UV-Vis spectroscopy. The XRD results confirmed cubic crystal structure for the Ag NPs with an average crystallite size of 12.62 nm and cubic spinel crystal structure for Co3O4 NPs having an average crystallite size of 12.746 nm and also the average crystal size of Ag/ Co3O4 BMNPs was found to be 18.07 nm. From the UV-Vis (DRS) data result, the energy band gap of Ag NPs, Co3O4 NPs and Ag/Co3O4 BMNPs were found to be 3.38 eV, 3.34 eV and 3.54 eV respectively. The SEM images showed clusters or large nanoparticles for Ag NPs and spherical as well as irregular geometries which was associated with non-homogeneity of the particles in terms of their shape and size for Co3O4 NPs and Ag/Co3O4 BMNPs. The FT-IR to identify the bioactive molecules which were actively involved during the synthesis process as stabilizing and capping agents to prevent the overall growth of Ag NPs, Co3O4NPs and Ag/Co3O4 BMNPs. The antibacterial activities of the synthesized nanoparticles were tested against gram-negative bacterial strains (Escherichia-coli, Salmonella typhimrium), and gram-positive strains (Staphylococcus aureus and Enterococcus faecalis) using the agar-well diffusion method. Ag/Co3O4 BMNPs exhibited best inhibition activities toward the selected bacterial species (Escherichia-coli and Staphylococcus aureus) than that of Ag NPs and Co3O4NPs inhibition activities. However, Ag NPs exhibited best inhibition activities toward Salmonella typhimrium and Enterococcus faecalis bacteria species. Co3O4 NPs showed least inhibition activities against selected bacterial species compared to Ag NPs and Ag/Co3O4 BMNPs.