Hydrothermal synthesis and characterization of alkali metal titanium silicates

Abstract

Preparation of granulated alkali metal titanium silicates is described in which the desired silicon to titanium ratio is controlled via a sol-gel route, using hexamethylenetetramine as an inner gelation reagent. The amorphous precursors are treated hydrothermally in the presence of NaOH or KOH solution under mild conditions (150-250 °C). By varying the Si:Ti molar ratio in the precursor, concentration of alkali, temperature and duration of treatment, six granular sodium titanium silicates (Na₂Ti₂O₃SiO₄·2H₂O, Na₂TiSi₂O₇·2H₂O, Na₂TiOSiO₄ and three novel phases characterized by the first reflection in the XRD at 10.8, 7.2 and 5.4 Å, respectively) and two potassium titanium silicates [K₃H(TiO)₄(SiO₄)₃·8H₂O, K₂TiSi₃O₉·H₂O] were synthesized. All compounds were characterized by elemental analysis, TGA, powder XRD, SEM and ²⁹Si MAS NMR spectroscopy. Some of the titanium silicates are thermally stable, possessing unique ion exchange properties for alkali, alkaline earth, and some toxic heavy metal cations.

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