Synthesis and Characterization of a Hollow Spherical Form of Monolayer Aluminosilicate

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Abstract
Hollow spherical particles of aluminosilicate having diameters of 80 to 100 Å and high electric charge were synthesized by heating solutions containing Si and Al concentrations of about 2 mM (Si/Al molar ratio = 1.0–1.2; pH = 9.0) at 95°–100°C for 7 days. Electron microscopy, X-ray powder diffraction, and infrared spectroscopy suggested that the walls of the spherical particles consisted of monolayer aluminosilicate, most probably having a 1:1 layer structure. Chemical analysis supported this supposition but indicated modifications as shown in the formula (Si1.85Alo0.62)IV(Al1.38)VI(OH)4.10O4.96Na0.62, compared with (Si2)lv(Al2)VI(OH)4O5 for an ideal 1:1 layer silicate. High-resolution 29Si and 27A1 nuclear magnetic resonance spectroscopy indicated the substitution of Al for Si in the tetrahedral sheet, the presence of A1IV and A1VI, and the presence of Si bonded through oxygen to three Al atoms and one H. A natural counterpart of the synthesized aluminosilicate may be a precursor of halloysites formed by weathering of volcanic ash and pumice and have a close structural relation with allophane and imogolite