Chemical Characterization, Structural Features, and Thermal Behavior of Sodium and Hydrogen Octosilicate

Abstract

Abstract--The chemical composition and the thermal behavior of sodium and hydrogen octosilicate was studied by chemical and thermal analysis, infrared (IR), magic-angle-spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray diffractometry. Both compounds are layer silicates with basal spacings of 11.10 and 7.38 ~, respectively. In both forms the ratio of Q4 silicon (connected via oxygen bridges with four silicon atoms) to Q3 silicon (connected with only three other Si atoms) is I. At least a small part of the Q4 silicon can be substituted by aluminum. Elimination of water coordinated to the cations in sodium octosilicate results in a concomitant structural collapse. Replacement of the sodium ions by protons affects the atomic arrangement in the sheets only to a minor degree, but results in a decrease of the periodicity along the crystallographic c axis. Upon heat treatment an endothermal structural rearrangement occurs at about 360 K as revealed by significant changes of the IR and 29Si MAS-NMR spectra. Reexchange with Na ions largely, but not completely, restores the structure of the parent octosilicate.The X-ray diffraction pattern of sodium octosilicate was indexed in the monoclinic system with a = 7.345/~, b = 12.74/~, c = 11.25/~ and t3 = 99.3*. Based on conclusions drawn from the results of the present study, the X-ray pattern of hydrogen oclosilicate was tentatively indexed in the monoclinic system with a = 7.345/k, b = 12.74 A, c = 8.51 /~ and/3 = 119.8 ~

Isomorphic silicon/aluminum substitution on layered ilerite – Structural study and calorimetry of copper interaction

“…This behavior increased the interaction strength between the lamella and hydrated sodium cations and decreased the interlayer spacing. The peaks at higher angles are related to lamellar structure features and also confirm that the ilerite structure was synthesized [4].…”

“…Pure silica samples start their crystallization after 3 days of hydrothermal treatment, as given by very low signals (curve a). After 6 days the ilerite structure is already obtained (curve b), presenting all characteristic diffraction signals [4], however, part of it remains in amorphous phase. Finally, the pure octosilicate structure is obtained after 9 days of reaction (curve c).…”

“…After 6 days the ilerite peaks started to be noticed (curve f), indicating an ilerite co-crystallization process and all previous silicic acid magadiite was converted into ilerite after 9 days (curve g), as observed verified by the absence of the characteristic diffraction signals of the magadiite layered compound. The peaks at 2h 13.2°, 13.6°and 14.7°are due to scattering related to the interatomic vectors amorphous materials for curve g [4,[21][22][23]. These reflections are also present with very low intensity for Na-il-216 (curve c), which indicate that ilerite aluminosilicate presents amorphous regions at higher concentration than pure layered silicate.…”

“…The synthesized ilerite in sodium form, (Na-ilerite), has precise and normal structure and a determined chemical composition [4]. Thus, its unit cell has the formula Na 8 Si 32 O 64 (OH) 8 Á32H 2 O, with an interlayer distance and a layer thickness of 1.10 and 0.73 nm, respectively, indexed as (0 0 1) diffraction planes, with the crystal structure details elucidated also by X-ray diffraction patterns and solid-state NMR spectroscopy [1,5].…”

Preparation of a microporous layered organic–inorganic hybrid nanocomposite using p-aminotrimethoxysilane and a crystalline layered silicate, ilerite

“…To develop the interlayer microporosity of the chemically modified interlayer, we have reported on alkoxysilylation of ilerite [5] (known as layered octosilicate [6] or RUB-18 [7]) with 4,4'-bis(triethoxysilyl)biphenyl [8,9]. More recently, Mochizuki et al have reported on the silylation of ilerite with 4,4'-bis(trichloro-and dichloromethylsilyl)benzene [10].…”