Fluorine Route Synthesis of Montmorillonites Containing Mg or Zn and Characterization by XRD, Thermal Analysis, MAS NMR, and EXAFS Spectroscopy

Abstract

EXAFS spectroscopy, combined with X‐ray powder diffraction, chemical and thermal analysis, scanning electronic microscopy, 29Si, 27Al, and 19F MAS NMR spectroscopy, are used in the structural analysis of montmorillonites, synthesised in an acidic fluoride medium. Hydrothermal synthesis performed under mild conditions (493 K, autogenous pressure) enables the formation of montmorillonite clays, containing Al and Zn or Mg in the octahedral sheet. It is shown that montmorillonites can only be synthesized in a narrow range of compositions. An accurate value of the Al for Si substitution rate in the tetrahedral sheet is determined by using 27Al MAS NMR spectroscopy performed under definite conditions. Some interatomic distances are determined by EXAFS spectroscopy (RMg−O = 2.11 Å, RZn−O = 2.08 Å, RZn−Al = 2.98 Å, RZn−Zn = 3.11 Å) which reveals strong local distortions in the octahedral sheet with respect to the ideal montmorillonite structure. Lengthening of the out‐of‐plane Zn−Si(Al) distances also shows the swelling of the whole layer in the neighbourhood of Zn. Moreover, the combination of EXAFS and 19F MAS NMR spectroscopic data reveals a clustering of the divalent elements of the octahedral sheet, which is related to a possible local trioctahedral character of these materials.

Preparation of hectorite-like swelling silicate with controlled layer charge density

“…11) The thermal reaction of talc and sodium fluorosilicate or lithium fluoride has been reported to obtain expandable 2:1 type silicate. 12) In addition to those commercialized products, there are several reports on the preparation of smectite-like silicates 13), 14) and intercalation compounds. 15)-18) One of the advantages of smetites as host material for the nanocomposite and hybrid materials is the variation of cation exchange capacity (CEC).…”

Modified Reverse Osmosis System for Treatment of Produced Waters

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14] During the thermal consolidation of the membranes, the degree of dehydration increases with temperature and treating time.…”

“…The refined clay powders were calcined in air, and then tested by ex-situ XRD to examine the thermal stability of the crystallographic structure. around 10Å indicate closure of the interlayer space after being dried at 45°C for 48 hours, because the thickness of the octahedral clay plates is about 9.6Å [1][2][3][4][5][6][7][8][9][10][1][2][3][4][5][6][7][8][9][10][11][12][13] .…”

“…[1][2][3][4][5][6][7][8][9][10][11] The XRD patterns of the dip-coated membranes had identical relative intensities compared to those of the freeze-dried powders ( Fig. 1-7), indicating the membrane was composed of randomly packed clay particles.…”

Na-Montmorillonite Edge Structure and Surface Complexes: An Atomistic Perspective

“…The random assignment of substitutions and the first constraint that prohibits the presence of Mg-(OH) 2 -Mg pairs in the octahedral sheet are based on 1 H magic angle spinning nuclear magnetic resonance (MAS NMR) and FT-IR spectra from MMTs that show no contributions from Mg-(OH) 2 -Mg moieties and QM simulations that demonstrated that Mg 2+ substitutions are randomly distributed within the octahedral layer [35][36][37]. The second constraint, informed by the properties of synthetic MMTs [38][39][40][41], limits the substitution ratio of the edge PBC (i.e., Mg edge substitutions: total number of octahedral edge sites in the PBC) to less than 0.20, which is the maximum substitution ratio for a synthetic MMT with only octahedral substitutions. The structural characterization of synthetic MMTs with divalent cation substitution ratios greater than 0.20 revealed octahedral sheet occupancies greater than 2.00, which is indicative of an MMT structure with some trioctahedral character, and isomorphic substitutions in the tetrahedral sheet.…”