Spectroscopic study of silver halides in montmorillonite and their antibacterial activity

•The AgX (X = Cl, Br, I)-MMT nanocomposites were synthesized by dispersion method.•There are low data about comparing the antibacterial activity of silver halides in matrices.•The produced Ag NPs and Ksp had an important role in antibacterial activity of AgX-MMT.•AgI-MMT did not produce Ag nanoparticles due to small band gap.•The stability of AgI in MMT was more than AgCl and AgBr.

In this study silver halides (AgX, X = Cl, Br, I) in montmorillonite (MMT) were prepared by dispersion method in dark. AgNO3 was used as a silver precursor. The nanocomposites (NCs) (AgX-MMT) were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectroscopy (DRS). The powder X-ray diffraction showed intercalation of AgCl and AgBr nanoparticles (NPs) into the clay interlayer space. The diffuse reflectance spectra indicated a broad surface plasmon resonance (SPR) absorption band in the visible region for AgCl-MMT and AgBr-MMT NCs, resulting of metallic Ag nanoparticles (Ag NPs). But the results were opposite in case of AgI-MMT NC. The antibacterial activity of NCs was investigated against Gram-positive bacteria, i.e., Staphylococcus aureus and Micrococcus luteus and Gram-negative bacteria, i.e., Escherichia coli, Pseudomonas aeruginosa, by the well diffusion method. The antibacterial effects on Staphylococcus aureus, Micrococcus luteus and Escherichia coli decrease in the order: AgCl-MMT > AgBr-MMT > AgI-MMT. No antibacterial activity was detected for Pseudomonas aeruginosa.

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