Ion-exchange and antibacterial properties of layered silicate, Na-kenyaite, prepared using amorphous silicon dioxide (a-SiO₂) blocks

Abstract

Na-kenyaite, a layered silicate, was synthesized via the hydrothermal method at 190 °C for 24 h using amorphous SiO₂ blocks as a starting material. Changes in the thermal structure of Na-kenyaite were investigated using the in situ high-temperature synchrotron X-ray diffraction data. Na-kenyaite was dehydrated at 200 °C, and its crystal structure was maintained from 200 to 700 °C despite its low crystallinity. It finally decomposed and crystallized to cristobalite via α-quartz. Na-kenyaite was ion-exchanged with Ag⁺ and Cu²⁺ ions in different ratios (Ag/Si = 0.01–0.077 and Cu/Si = 0.009–0.044), and the antibacterial properties of the ion-exchanged compounds were evaluated using gram-negative [Escherichia coli (E. coli)] and gram-positive [Staphylococcus aureus (S. aureus)] bacteria. Ion-exchanged compounds exhibited an increasing bactericidal effect when the ion-exchange ratios of the compounds increased owing to the release of metal ions with antibacterial properties from the host material. The antibacterial activity of the ion-exchanged compounds was compared based on the relative antibacterial activity, calculated using the inhibition zone obtained after two days of incubation. Cu-kenyaite exhibited better antibacterial activity than Ag-kenyaite against E. coli and S. aureus.