Microwave-sonochemical synergistically assisted synthesis of hybrid Ni-Fe3O4/ZnO nanocomposite for enhanced antibacterial performance

Abstract The synergistic effect of microwave irradiation and ultra sonication on the bactericidal performance of Fe3O4/ZnO and the hybrid Ni doped Fe3O4/ZnO nanocomposites was demonstrated. The synthesized nanocomposite materials were characterized by ultra-violet visible spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. The diffraction patterns revealed clearly the integration of Ni ions into the Fe3O4/ZnO crystal lattice without changing the crystal structure. The crystallite size of Fe3O4/ZnO decreased with Ni dopant concentration, which supports antibacterial activity. The infrared spectra revealed significant transferences in the peaks with Ni addition, representing the successful incorporation of Ni ions into Fe3O4/ZnO. The energy band gap of Fe3O4/ZnO decreased from 2.4 to 2.2 eV, which established the existence of Fe3O4/ZnO stimulus interaction with different dopant level of Ni catalyst. Fe3O4/ZnO exhibited strong blue emission at 470 nm, which shifted to the green at 560 nm, when Ni2+ ions binded together with Fe3O4/ZnO nanoparticles, which is favorable for better antibacterial activity. Subsequently, with the addition of Fe3+ and Ni2+ ions, the spherical shaped morphology of Fe3O4/ZnO transformed to nano foil like structure. A novel approach for modifying the reactive oxygen species mechanism of the hybrid nanocomposite was made using ultra sonication. The potential toxicity of nanosized Fe3O4/ZnO and the hybrid Ni doped Fe3O4/ZnO nanocomposites were investigated with both Gram-positive and Gram-negative bacteria as test organisms. Compared to 3% Ni, 5% Ni doped Fe3O4/ZnO nanocomposite was found to show better antibacterial performance for both Gram-positive and Gram-negative bacteria due to large H2O adsorption, condensed particle size and improved particle surface reaction after sonication. Also S. aureus bacteria was found to show larger bactericidal efficiency with high zone of inhibition of 13-14 mm when tested with Ni-Fe3O4/ZnO nanocomposite than K. pneumoniae bacteria which was attributed to the thicker layers of peptidoglycan structure.