Synthesis, characterization, and ion exchange behavior of a framework potassium titanium trisilicate K2TiSi3O9 center dot H2O and its protonated phases
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abstract
A framework potassium titanium silicate K2TiSi3O9H2O, compound I, was synthesized by the reaction of a titanium-hydrogen peroxide complex and SiO2 in alkaline media under mild hydrothermal conditions (180 C). This compound was converted to the corresponding sodium phase, Na2TiSi3O9H2O (IV) and two proton-containing phases, K1.26H0.74TiSi3O91.8H2O (II) and K0.3H1.7TiSi3O92.4H2O (III) by ion exchange. These products were characterized by elemental analysis, TGA, FT-IR, MAS 29Si NMR, and X-ray diffraction. The ion exchange behavior of K2TiSi3O9H2O and K0.3H1.7TiSi3O92H2O toward alkali, alkaline earth, and some transition metal ions solutions was studied. A high affinity of the protonic form of titanium trisilicate exchanger for cesium and potassium makes it promising for radionuclide-contaminated groundwater treatment and certain analytical separations. The crystal structure of K2TiSi3O9H2O 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 and selectivity of the Zr and Ti phases rationalized on the basis of the tunnel sizes. The structure of II was solved on the basis of a monoclinic cell, whereas the K2TiSi3O9H2O phase is orthorhombic. The relationship of structure II, monoclinic, to the parent orthorhombic structure is described. Phase III yielded a complex X-ray pattern with evidence of disorder and a highly complex 29Si NMR spectrum. On reexchanging with K+, the original crystal lattice was restored.
