Biosynthesis of Ag/bentonite, ZnO/bentonite, and Ag/ZnO/bentonite nanocomposites by aqueous leaf extract of Hagenia abyssinica for antibacterial activities

Abstract

Abstract We report the synthesis of Ag/bentonite, ZnO/bentonite and Ag/ZnO/bentonite nanocomposites (NCs) using Hagenia abyssinica plant extract and their antibacterial study. The synthesized NCs were characterized by using many advanced techniques. The X-ray diffraction and high resolution transmission electron microscopy analysis confirmed the formation of composites with different phases. The average crystallite size (D) values of pure Ag nanoparticles (NPs), ZnO NPs, and activated bentonite (Na-AB) were found to be 8.14, 18.1, and 37.6 nm, respectively. The Ag/bentonite NCs, ZnO/bentonite NCs, and Ag/ZnO/bentonite NCs exhibited the D values of 7.4, 9.4, and 9.4 nm, respectively. The Fourier transform infrared spectral analysis revealed the presence of hydroxyl, carbonyl, and other functional groups on the surface of the synthesized NCs. The transmission electron microscopic analysis revealed the formation of Ag and ZnO NPs with hexagonal, rod-shaped, and spherical structures. HRTEM also revealed the presence of (102) plane of ZnO and (220) plane of Ag in Ag/ZnO/bentonite NCs. The antibacterial activities of the composites suspension were evaluated against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 by the disc diffusion and broth dilution methods. The ternary NC and Ag/ZnO/bentonite exhibited better zone of inhibition of 14.3 ± 0.3 and 17.3 ± 0.2 mm at 10 mg·mL−1 toward E. coli and S. aureus bacterial strains. The minimum inhibitory concentration and minimum bactericidal concentration values of Ag/ZnO/bentonite NCs were found to be 156.25 and 312.5 µg·mL−1 for E. coli. The investigation results revealed that the low temperature bio-synthesized Ag/ZnO/bentonite is a promising bactericide over the binary composites.