Silver Nanoparticles@Zeolite Composites: Preparation, Characterization and Antibacterial Properties

The presence of various Ag species (Ag⁺ ions, Ag clusters, and Ag nanoparticles (NPs)) in Ag-zeolite nanocomposites strongly influences their catalytic, photocatalytic, and antibacterial properties. To tailor materials for specific applications, it is essential to employ strategies that control the redox processes between Ag⁺ and Ag⁰ and facilitate the formation of active Ag-containing composites. In this study, we present a comparative analysis of Ag-zeolite nanocomposites, focusing on their synthesis methods, structural characteristics, and antibacterial activity against Escherichia coli. Ag NPs were synthesized using three approaches: solid-state thermal reduction, chemical reduction in aqueous solutions with a mild reducing agent (sodium citrate, Na₃Cit), and chemical reduction with a strong reducing agent (sodium borohydride, NaBH₄). The resulting materials were characterized by X-ray diffraction (XRD), diffuse reflectance UV-Vis spectroscopy (DR UV-Vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM), while antibacterial activity was assessed using biological assays. Microscopic and spectroscopic analyses confirmed the formation of Ag NPs and the co-existence of immobilized Ag⁺ ions within the zeolite framework. The specific influence of the treatment method of Ag⁺-zeolite on the presence of silver species in the nanocomposites and their role in antibacterial properties were evaluated. The highest antibacterial efficiency was observed in the nanocomposite produced by thermal treatment of Ag-exchanged zeolite. Thus, the crucial function of Ag⁺ ions in the mechanism of bacteria cell death was suggested.