Abstract
The high antibacterial activity of MoO3 is thought to be due to a decrease in pH caused by the generation of H3O+ upon contact with water. The antibacterial activity of H2MoO4, WO3, H2WO4, H-type Y zeolite, and H-type modonite zeolite, which are poorly water-soluble powders expected to generate H3O+, was examined against Escherichia coli along with MoO3. Antibacterial activity was observed not only for MoO3 but also for H2MoO4, but not for WO3, H2WO4, H-type Y zeolite, or H-type modonite zeolite. MoO3 and H2MoO4, which exhibited antibacterial activity, were left in de-ionized water for one day, and their pH values were measured. The pH values of MoO3 and H2MoO4 were 3.52 and 4.34, respectively. On the other hand, the pH values WO3 and H2WO4, which did not exhibit antibacterial activity, were above 5.0, and those of H-type Y zeolite and H-type modonite zeolite were above 6.2. Futhermore, the resistivity of the compacts, related to ionic conduction, was measured at room temperature under a pressure of 100 MPa. MoO3 and H2MoO4 had resistivities at least one order of magnitude lower than the other samples, suggesting that the concentrations of H+ or H3O+, which are thought to be ionic conduction species, were high. The low pH values of MoO3 and H2MoO4, i.e., the generation of large amounts of H3O+, are thought to affect their antibacterial activity.
