Rational design of Ag-ZnO-Fe3O4 nanocomposite with promising antimicrobial activity under LED light illumination

Surface plasmon resonance effect, Fenton's reaction, plant extract, and nanoparticles have all proven to be efficient in killing or reducing the activity of numerous microorganisms. To study the synergetic effects among these key parameters, Ag-ZnO-Fe3O4 nanocomposites have been synthesized via solution combustion approach in the presence of aqueous extract of Thymus vulgaris leaves. The successful construction of Ag-ZnO-Fe3O4 nanocomposite and its purity were confirmed by X-ray diffraction, X-ray photoelectron spectra, and energy dispersive X-Ray spectroscopy analyses. Dynamic light scattering and transmission electron microscopy measurements showed that the size of the obtained particles is in the nanoscale. The synthesized nanocomposite showed broad inhibition against the selected bacteria and yeast under LED light. UV-vis absorption measurement showed that the heterostructure exhibits broad plasmonic peak centered around 434 nm. Hot charge carriers are generated in Ag under LED light illumination and separated through Ag-ZnO heterojunction resulting in the production of a considerable amount of (OH)-O-center dot radicals as confirmed by ESR analysis. Moreover, Ag acts as H2O2 donator and photogenerated electrons provider for the Fenton's reaction, resulting in the generation of much more (OH)-O-center dot radicals. Therefore, Ag-ZnO-Fe3O4 nanocomposite shows improved microbial activity under LED light illumination.