Zeolites are well known as typical examples of inorganic ion exchangers. Zeolites are capable of supporting various metals through cation exchange of Na+ ions or Ca.sup.2 + ions in the interior of their crystals for metal cations in an aqueous solution. Further zeolites have excellent characteristics with respect to specific surface area, heat resistance, water resistance, mechanical strength, etc. and are therefore widely used as gas adsorbing and separating agents, agents for treating waste water containing heavy metals, ion fixing agents and carriers for metal catalysts.
Zeolites are crystalline substances consisting primarily of SiO.sub.2 and Al.sub.2 O.sub.3, and the crystals thereof have three-dimensional structure and have regular minute pores. The composition is expressed generally by (M.sub.2, M')O. Al.sub.2 O.sub.3. mSiO.sub.2. nH.sub.2 O wherein M and M' are monovalent and bivalent metal ions, respectively, m is the coefficient of silica, and n is the coefficient of crystal water. Zeolites include the faujasite group (sodalite group), chabazite group and mordenite group which are different in the structure of crystals. The cations present in the voids or channels of zeolites can be exchanged for other metal ions, so that zeolites are utilized for softening hard water and separating off metal ions. When the alkali metal of zeolites is exchanged for bivalent or trivalent metal ions or hydrogen ions, the zeolite forms a strong solid acid, which is useful as an excellent catalyst for cracking petroleum and various carbonium ion reactions. Zeolites carrying silver, copper, zinc or the like supported thereon are kneaded with polymers to prepare antibacterial wrapping materials for preventing deterioration for use in the field of foods. Especially, the silver-incorporating zeolite is also excellent in ethylene-adsorbing ability and is therefore valuable for use.
However, the zeolites incorporating silver, copper or zinc fail to fulfill the requirement of being inexpensive which is characteristic of inorganic materials because of material costs and complex manufacturing process, and are very expensive materials.
Accordingly, the object to be achieved by the present invention is to develop a novel inorganic material which is usable in place of the silver-, copper- or zinc-incorporating zeolites and which has ethylene-adsorbing ability and antibacterial activity.
This object is fulfilled by exchanging Ca.sup.2 + ions, of these ions and monovalent cations, such as Na+ ions, which are present between the layers of a tobermorite for silver ions into the tobermorite although this has never been practiced in the past.
A description will be given with reference to Na+ ion which is typical of monovalent cations.
We have directed attention to tobermorites which are fibrous layered compounds heretofore widely used as lightweight heat-insulating materials and noncombustible building materials because of their resistance to a high temperature of 650.degree. C. and excellent heat-insulating properties, and conceived the entirely novel idea that the Ca.sup.2 + ions, or these ions and Na+ ions which are present between the layers of the mineral can presumably be exchanged for silver ions by cation exchange. We have carried out intensive research based on this idea and consequently succeeded for the first time in the cation exchange of Ca.sup.2 + ions, or these ions and Na+ ions, which are present between the layers of a tobermorite, for silver ions. We have further found that this novel substance has ability to adsorb ethylene and antibacterial activity.