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

Abstract

AgTi 2 (PO 4 ) 3 with a three-dimensional network structure and Ti(HPO 4 ) 2 ·2H 2 O 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 AgTi 2 (PO 4 ) 3 and Ti(HPO 4 ) 2 ·2H 2 O crystals has been fabricated by acid treatment of the porous glass ceramic with the surface consisting predominantly of AgTi 2 (PO 4 ) 3 crystals and the interior phase of LiTi 2 (PO 4 ) 3 crystals prepared by exchange of Ag + ions for Li + ones. This processing is based on a phenomenon that LiTi 2 (PO 4 ) 3 is converted into Ti(HPO 4 ) 2 ·2H 2 O 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 m 2 /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.