Formation of micro/macroporous hierarchical spheres of titanosilicate umbite

Abstract

Polycrystalline spheres of up to 2 mm diameter of microporous titanosilicate K2TiSi3O9·H2O with umbite structure (Ti-umbite) were prepared without the use of organic structuring agents. The spheres, while preserving the inherent microporosity of the umbite type-material, are organized as hierarchical materials with macropores in the 0.1-1.4-μm size range. Ti-umbite spheres were only produced by hydrothermal synthesis under rotation conditions, at 230°C by using a solution with the following molar composition: 0.284 K2O/0.287 Na2O/SiO2/0.095 TiO2(anatase)/30.8H 2O, and it was observed that the synthesis time and the rotation speed of the autoclave influenced the particle size distribution. When the procedure was carried out at 30 rpm and for 48 h, the size of the Ti-umbite spheres adjusted well to a normal distribution, with a statistical mode of 492 ± 13 μm. Also, under these conditions the amount of unreacted TiO 2 anatase, which has a key role in the formation of the Ti-umbite spheres, was only 14.4 wt.-%. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.