Green synthesis of ZnO NPs & ZnO-Ag Nanocomposites Using Leaf Extract of B.Polystachya & Evaluation of their Antibacterial Activity

Abstract

In this study, pure eco-friendly plant extract of Buddleja Polystachya (Anfar), zinc acetate (Zn(CH3COO)2) as host, and silver nitrate (AgNO3) as dopant precursors were used to synthesize zinc oxide (ZnO) nanoparticles and zinc oxide–silver (ZnO–Ag) nanocomposites. The synthesis condition of ZnO-Ag nanocomposites was optimized using a central composite design (CCD). Temperature (Temp), pH, and AgNO3 solution concentration (Conc. Ag) were used as independent variables in the model, while absorbance intensity of the nanocomposite was used as the dependent variable.The prepared nanoparticles and nanocomposites were characterized by using various analytical and spectroscopic tools such as UV-visible spectroscopy, Fourier Transform Infrared Spectroscopy, powder X-ray diffraction, and Dynamic Light Scattering. Along with this study, the antibacterial activity of the biosynthesized ZnO-NPs and ZnO–Ag NCs was investigated against Streptococcus aureus and Escherichia coli. The phytochemical analysis revealed that tannins, steroids, phlobatanins, saponins flavonoid, phenols and terpenoids are the major chemical constituents of the extracts obtained from B.polystachya leaf extracts. The predicted optimal synthesis condition ZnO-Ag NCs was found to be Temperature = 53.709 °C, pH = 8.794, and Conc.Ag= 91.454 mM with maximum absorbance intensity of 1.951. The UV-visible spectroscopy result shows that, the maximum absorbance intensity of ZnO NPs and ZnO-Ag NCs were found to be 2.073 and 1.905 respectively. Moreover, the bandgap energy was found as 3.31 eV and 3.28 eV for ZnO NPs and ZnO-Ag NCs, respectively. The XRD analysis revealed that the average crystallite size was discovered to be 24.50 and 23.55 nm for ZnO and ZnO–Ag nanoparticles, respectively. According to dynamic light scattering results, the average size of ZnO NPs and ZnO Ag NCs was 78.69 nm and 35.48 nm, respectively, indicating that the nanomaterials were successfully formed. Finally, the antibacterial activity results showed that ZnO-Ag NCs displayed higher activity against the bacterial strains compared with pure ZnO NPs with the maximum zone of inhibition 15 ± 0.31 and 8 ± 0.37 mm for E. coli and, S.aureus respectively. As a result, this study reports a rapid and environmentally friendly path for the synthesis of ZnO NPs and ZnO-Ag NCs with moderate antibacterial activity