Synthesis and structural characterization of microporous umbite, penkvilksite, and other titanosilicates

Abstract

Synthetic analogues of the microporous minerals umbite (AM-2) and penkvilksite, polytype 2O (AM-3), have been prepared. The facile syntheses of two other titanosilicates, AM-1 and AM-4, have also been reported. AM-1 and the previously reported, layered titanosilicate known as JDF-L1 have been shown to have the same structure. AM-4 is a new microporous titanosilicate with a unique and unknown structure, containing eight different Na sites. All AM-n 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/DSC. AM-n materials are thermally stable up to ca. 600 °C. The dehydration-hydration processes seem to be reversible (or quasi reversible) for AM-1, -2, and -3 but not so for AM-4.