Microporous Materials with an Integrated Skeleton of AgTi2(PO4)3 and Ti(HPO4)2·2H2O Crystals

Abstract

AgTi2(PO4)3 with a three-dimensional network structure and Ti(HPO4)2·2H2O with a two-dimensional layered structure are phosphate crystals with different properties: the former shows excellent bacteriostatic activity and the latter is possible to be modified chemically by intercalation. A new type of microporous material with an integrated skeleton of AgTi2(PO4)3 and Ti(HPO4)2·2H2O crystals has been fabricated by acid treatment of the porous glass ceramic with the surface consisting predominantly of AgTi2(PO4)3 crystals and the interior phase of LiTi2(PO4)3 crystals prepared by exchange of Ag+ ions for Li+ ones. This processing is based on a phenomenon that LiTi2(PO4)3 is converted into Ti(HPO4)2·2H2O in acid solutions at temperatures >50 °C. Bulk materials with continuous pores of various diameter sizes ranging from 10 nm to 1 μm with two main peaks located at ≈40 and ≈200 nm in the distribution can be obtained without serious cracking or deformation after acid treatment at ≈100 °C for 12 h. The specific surface area is ≈30 m2/g. The porous materials have various functions such as bacteriostatic activity, adsorption of ammonia gas, and intercalation of polar molecules which induces water-repellent properties. As the amount of Ag+ ions released from the material into phosphate buffer solution was determined to be very small (<10 μequiv/g), the porous glass ceramics are expected to be novel bacteriostatic materials with multifunctionality and are medically safe.