Microwave sterilization with metal thin film coated catalyst in liquid phase

We developed a novel sterilization method by which Microwave (MW) irradiation sterilizes Escherichia coli and Bacillus subtilis using a unique material of catalyst. These materials contained SiO2- and/or Al2O3-TiO2 that were coated with Pt and/or Ag. The pellets coated with micrometer size metal had a porous structure and a phase structure that maintained anatase in the system of SiO2-TiO2. We showed that MW irradiation completely sterilized the E. coli and B. subtilis that were loaded inside the pellet. The results suggested that other factors, besides temperature, contributed to effective sterilization. This is because there is a limit temperature for the life maintenance of such microorganisms. We showed that a very short time was needed to sterilize these microorganisms in comparison with the conventional methods. The coated metal ion absorbed the energy of the MWs quickly and easily, and the anatase crystal generates hydroxyl radicals. Results indicated that the active hydroxyl radical generated by the irradiation of MWs played an important role in the sterilization of microorganisms.