Spheres of Microporous Titanosilicate Umbite with Hierarchical Pore Systems

Abstract

Micrometric polycrystalline spheres of up to 1 mm diameter of microporous titanosilicate K2TiSi3O9·H2O with umbite structure have been prepared without the use of organic structuring agents. These spheres are organized as micro/macroporous hierarchical materials with macropores in the 0.2–1.4 µm range of average size, showing that intraparticular resistance to water transport is not limiting. Also, similar ion exchange performance can be observed in the Ti‐umbite spheres and in the single crystals obtained under the same synthesis conditions.

Formation of Micro/Macroporous Hierarchical Spheres of Titanosilicate Umbite

“…In spite of the interesting results obtained in our previous work, [12] the mechanism of formation of the hierarchically structured spheres remains unclear, and the key role of the operating conditions (presence of rotation, type of Ti precursor) needs to be clarified for this methodology to be extended to the preparation of other micro/macroporous systems. The present work explores these aspects by studying a wider range of conditions (regarding synthesis time and rotation speed) and by using a battery of characterization techniques to understand how the Ti-umbite crystals are assembled to produce solid spheres in which micropores and macropores are combined.…”

“…In a previous work, micrometric spheres of microporous titanosilicate umbite (Ti-umbite) having hierarchical pore systems were prepared by direct liquid-phase hydrothermal synthesis under a range of synthesis conditions in which a successful synthesis always required agitation by rotation and the use of TiO 2 anatase as a Ti source. [12] The micro/ macroporous hierarchical architecture of these spheres was effective in reducing intraparticular transport resistances, as demonstrated for water and Sr 2+ cations. Umbite is a microporous silicate mineral with the stoichiometry K 2 -(Zr 0.8 Ti 0.2 )Si 3 O 9 ·H 2 O.…”

“…[12] In all the experiments carried out here, XRD analysis indicated that Ti-umbite was the only crystalline phase produced, together with some unreacted TiO 2 anatase. A second critical factor for the production of the spheres was the chemical composition of the starting synthesis solution: in particular the TiO 2 /SiO 2 ratio has an important effect, so that below 0.021 (other parameters being constant) the composition gave rise only to crystals and not to spheres.…”

“…A TiO 2 /SiO 2 ratio of 0.095 was selected for this work, which produced good results as established in our precedent report. [12] TiO 2 anatase was used before to synthesize titanosilicate ETS-10, [23,24] and depending on the conditions it was frequently detected by XRD in the final product as an unreacted material. Figure 1 compares the XRD pattern of pure Ti-umbite prepared by using TiCl 3 instead of TiO 2 and without any Na source [25] with those corresponding to spheres produced in 3-96 h, where a strong intensity corresponding to TiO 2 anatase appears.…”

Deeping into the microporosity of porous silicates Ti- and Sn-umbite

“…2.7 Â 5.5 Å) is occupied by K + and reversible water molecules [6]. Additionally, crystallization of different umbite-type materials has been reported to create micro/macroporous hierarchical spheres of millimeter diameters [12,13].…”