Synthesis, characterization, and ion exchange behavior of a framework potassium titanium trisilicate K2TiSi3O9 center dot H2O and its protonated phases

A framework potassium titanium silicate K2TiSi3O9. H2O, compound I, was syn thesized by the reaction of a titanium-hydrogen peroxide complex and SiO2 i n alkaline media under mild hydrothermal conditions (180 degrees C). This c ompound was converted to the corresponding sodium phase, Na2TiSi3O9. H2O (I V) and two proton-containing phases, K1.26H0.74TiSi3O9. 1.8H(2)O (II) and K 0.3H1.7TiSi3O9. 2.4H(2)O (III) by ion exchange. These products were charact erized by elemental analysis, TGA, FT-IR, MAS Si-29 NMR, and X-ray diffract ion. The ion exchange behavior of K2TiSi3O9. H2O and K0.8H1.7TiSi3O9. 2H(2) O toward alkali, alkaline earth, and some transition metal ions solutions w as studied. A high affinity of the protonic form of titanium trisilicate ex changer for cesium and potassium makes it promising for radionuclide-contam inated groundwater treatment and certain analytical separations. The crysta l structure of K2TiSi3O9. H2O was found to be isomorphous with that of the zirconium analogue and contains a framework enclosing two types of tunnels. The exchange properties were interpreted on the basis of this structure an d selectivity of the Zr and Ti phases rationalized on the basis of the tunn el sizes. The structure of II was solved on the basis of a monoclinic cell, whereas the K2TiSi3O9. H2O phase is orthorhombic. The relationship of stru cture II, monoclinic, to the parent orthorhombic structure is described. Ph ase III yielded a complex X-ray pattern with evidence of disorder and a hig hly complex Si-29 NMR spectrum. On reexchanging with K+ the original crysta l lattice was restored.