Biosynthesis of Co3O4 and ZnO Nanoparticles Using Ehretia cymosa thonn Plant Leaf Extract: Comparative Study of Their Antibacterial Activity

Abstract

Biosynthesis method using plant extract is a low cost and novel approach that is used to develop a variety of nanoparticles (NPs) that have numerous applications. In this work, cobalt oxide and zinc oxide nanoparticles were synthesized within 1:2, 1:1, and 2:1 volume ratios using their corresponding precursor salt and Ehretia cymosa thonn leaf extract that act as a reducing and capping agent to get stable NPs. Furthermore, the synthesized nanoparticles were characterized using X-Ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and Ultra visible (UV-Vis) spectroscopic techniques, in order to get and gather as well confirm the formation of the NPs. The XRD analysis showed that ZnO NPs were highly crystalline, pure and the average crystalline size for the 1:2, 1:1, and 2:1 volume ratios were 22.96, 17.92, and 21.80 nm, respectively. In the same manner, the average crystal size and purity of the green formed NPs in the ratios of 1:2. 1:1, and 2:1 were found to be , , and , respectively. SEM image analysis indicates surface morphology and all of the three ratios of ZnO NPs were found to be hexagonal in shape. Of the three ratios, (1:1) found to be more homogeneous. Likewise, the SEM analysis of Co3O4 NPs reveals the shape and morphology of the various volume ratios of Co3O4 NPs were found to be cubic. The UV-Vis analysis proves the optical property and so, the calculated band gap energy were found to be found 3.34, 3.27, and 3.25 eV for the 1:1, 2:1, and 1:2 volume ratios, respectively. While the band gap energy of Co3O4 NPs were found as , and for the , , and , respectively. The FTIR analysis shows the interaction between the extract with ZnO and Co3O4 NPs and the analysis proves as it contains several functional groups of bioactive molecules such as flavonoid, ketone, carboxylic acid, and alcohol, saturated and unsaturated hydrocarbons. The antibacterial activity for the (2:1, 1:1, and 1:2) was investigated using S. Aureus and E. coli within three concentrations of 50, 75, and 100 µg/mL. The antibacterial activities increase with increasing the concentration of ZnO NPs. In the same fashion, the antibacterial efficiency of synthesized NPs was tested for S. Aureus and E. coli using , , and concentration. ( ) shows zone of inhibition of , , and , and for E. coli and S. Aureus, respectively. ( ) shows zone of inhibition of 8, 9, 10 and 9, 10 and against E. coli and S. Aureus. Finally, ( ) with the same concentration showed zone of inhibition of 9, 11, 12 and 9, 11, against E. coli and S. Aureus, respectively.