Silver zeolites were developed from an invention titled "Methods of producing hard water-softening agents with germicidal action" patented in 1938. The purpose of the invention was to decrease the hardness of drinking water, and to obtain aseptic water. Using natural or synthetic zeolites as carriers, anti-bacterial zeolites are prepared by the ion exchange reaction of metal ions having an anti-bacterial effect such as silver, zinc, and copper ions. Compared with organic anti-bacterial agents which are alcohol, quaternary ammonium salt, thiabendazole, and ortho-phenylphenol, the inorganic anti-bacterial agents have excellent properties such as wide anti-bacterial spectrums, a high safety, long effective duration, and high heat-resistance. Zeolite and silver have been registered as food additives, and among the anti-bacterial zeolites, the zeolite A-silver, zinc, and ammonium compound zeolite was registered as an indirect food additive by the United States FDA in June 2000. Silver is a common metal, which has been used for tableware, spoons, costume accessories, and coins. With regard to the anti-bacterial effect of metals, Nepli discovered in 1893 that 0.1 ppm silver ions killed spirogyra, and it has been reported that silver, mercury, zinc, copper, tin, lead, bismuth, cadmium, and chromium are also anti-bacterial metals. Although the characteristics of the anti-bacterial zeolites significantly depend on the combination of the types of zeolites and those of the anti-bacterial metals, the specific combination has been determined based on experience. In this study, the combination types were investigated by preparing anti-bacterial zeolites using the zeolite A, which is a typical zeolite, and using silver, zinc, and copper, which are comparatively safe metals, and then comparing their anti-bacterial effects. It was found that the anti-bacterial effects of silver ion were quite high, showing that silver is an essential metal for anti-bacterial zeolites. Furthermore, the anti-bacterial effects of the zeolite A increased with the concentration of silver. To investigate the influence of the pore size of the zeolites on the anti-bacterial effects, silver zeolites were prepared using zeolite Y as carriers, and natural zeolite produced in Miyagi prefecture, which is directly used for water purification equipment, and then comparing the anti-bacterial effect of each zeolite with that of zeolite A. No differences in the anti-bacterial effects were observed regarding these types of zeolites.
