Antimicrobial and Ion-exchange Properties of Layered KHSi₂O₅ Compounds Prepared Using Amorphous Silicon Dioxide (a-SiO₂) Blocks

Abstract

A layered silicate, KHSi₂O₅, was synthesized via a hydrothermal method using an amorphous silicon dioxide (SiO₂) block, which is industrial waste. This layered silicate was used as a host compound for ion-exchange reactions with Ag⁺ and Cu²⁺ ions, and the antibacterial properties of the ion-exchanged compounds were investigated. The crystal structures of the compounds were retained during the ion-exchange reaction; however, in the case of Cu²⁺, a small amount of Cu(OH)₂ coexisted. The M/Si (where M is Ag or Cu) ratios of the ion-exchanged compounds were 0.03 - 0.50 and 0.01 - 0.32 for M = Ag and Cu, respectively. The antibacterial activity was analyzed by the inhibition zone method using two standard model bacteria: Staphylococcus aureus (S. aureus,gram-positive) and Escherichia coli (E. coli, gram-negative). The Ag-KHSi₂O₅ and Cu-KHSi₂O₅ samples showed good antibacterial activity owing to the release of Ag⁺ and Cu²⁺ ions from their host silicates. Here, the antibacterial activity of each sample were compared by relative antibacterial activity which was calculated based on the bacterial inhibition zone area. The antibacterial activity of Ag-KHSi₂O₅ against S. aureus was higher than that against E. coli, whereas the antibacterial activity of Cu-KHSi₂O₅ against S. aureus was lower than that against E. coli.