Green synthesis of silver and cobalt oxide nanoparticles using Croton macrostaychus plant extract and evaluation of their antibacterial activity

Cognizant of the harsh chemical method of nanoparticles synthesis, researchers are shifting towards the green phyto-mediated synthetic approaches. We herein report the green synthesis of Ag NPs and Co3O4 NPs using silver nitrate solution and cobalt nitrate solution as precursors added to aqueous extract of Croton Macrostachyus leaf extract to evaluate their antibacterial activity. 

The Characterization of the biosynthesized NPs were carried out by using spectroscopic techniques as X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FTIR), and scanning electron microscopy (SEM).

The average crystallite size of Ag NPs was found to be 12.62 nm from the XRD data, indicating a cubic crystal structure whereas that of Co3O4 NPs was found to be 12.75 nm, indicating a cubic spinel crystal structure.  The energy band gap for Ag NPs and Co3O4 NPs were 3.38 eV, and 3.34 eV respectively. The SEM images showed non-homogeneity of particles distribution with irregular geometries attributable to their shape and size for Ag NPs whereas spherical as well as irregular geometries attributed to non-homogeneity of the particles for Co3O4 NPs. The FTIR identifies the functional groups of the bioactive molecules that were actively involved as stabilizing and capping agents to prevent agglomeration of Ag NPs and Co3O4 NPs. The agar-well diffusion method was employed to evaluate the antibacterial activities of the produced nanoparticles against gram-positive (S. aureus and E. faecalis) and gram-negative (E. coli, S. typhimrium) bacterial strains. 

The biosynthesized nanoparticles showed promising antibacterial activities with Ag NPs exhibiting the best inhibition activities towards all bacteria species.