Synthesis and Structural Characterization of Microporous Framework Zirconium Silicates

The synthesis and structural characterization of synthetic analogues of the microporous zirconium silicate minerals petarasite (AV-3), gaidonnayite (AV-4), and umbite (AM-2) are reported. AM-2 materials have been synthesized with different levels of titanium substitution (Zr/Ti molar ratios of ∞,1.9, 0.5, and 0) indicating the existence of a continuous solid solution. All materials have been characterized by several techniques, viz., SEM, powder XRD, single- and triple-quantum 23Na and 29Si MAS NMR, water adsorption measurements, and TGA analysis. As a common structural feature, all these solids possess corner-sharing [ZrO6] octahedra and [SiO4] tetrahedra forming a three-dimensional framework. Unlike framework microporous titanosilicates where Ti−O−Ti−O chains are usually present, petarasite, gaidonnayite, umbite, and their synthetic analogues display structures where the [ZrO6] octahedra are isolated from each other by [SiO4] tetrahedra and, hence, Zr−O−Zr−O chains do not occur. All these materials are thermally stable up to, at least, 550 °C. The hydration−dehydration processes seem to be reversible.