<sup>19</sup>F MAS-NMR Study of Structural Fluorine in Some Natural and Synthetic 2:1 Layer Silicates

Huve, Laurent; Delmotte, Luc; Martin, Pascal; Dred, Ronan Le; Baron, J.; Saehr, Daniel

doi:10.1346/ccmn.1992.0400208

Cited by 50 publications

(25 citation statements)

References 19 publications

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“…In analogy to the talc sample, we associate the shift at -176.2 ppm with trioctahedral sites containing only magnesium and the line at -182.8 ppm, is attributed to {Mg-Mg-Li} octahedral sites. Again this is in agreement with results reported by Huve et al (1992a).…”

Section: :1 Layer Silicatessupporting

confidence: 94%

“…We expected the majority of the fluorine to have a resonance at about -134 ppm in analogy to pyrophyllite and a minor peak at some other resonance position for the {A1-Mg-[~} sites. We attribute the single resonance at about -152 ppm to {A1-Mg-D} sites, in agreement with the assignment made by Huve et al (1992a). This observation and assignment has strong implications and implies that fluoride is not statistically distributed in the structure of montmorillonites but is ordered into (A1-Mg-n} sites preferentially over {AI-AI-[~} sites.…”

Section: :1 Layer Silicatessupporting

confidence: 87%

“…Sanz and Stone (1979) and Santaren et al (1990) used relatively low-resolution solid-state NMR techniques, primarily second-moment measurements, to obtain information about the location of F-in the structure of micas and sepiolite. Recently Huve et al (1992aHuve et al ( , 1992b demonstrated the utility of 19F NMR in structural determinations in a variety of natural and synthetic 2:1 layer silicates.…”

Section: Introductionmentioning

confidence: 99%

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A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

Labouriau

1995

Clays and clay miner.

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Abstract--A series of natural clays, including 1:1 layer silicates (serpentines, kaolin minerals), smectites, vermiculite, micas, talc, pyrophyllite, sepiolite, and palygorskite, were studied by tgF magic-angie spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. The 19F chemical shift in these layer silicates is characteristic of the structure, in particular, to the local octahedral cation occupancy. Fluoride ions bonded to three Mg octahedral cations have a chemical shift of about -177 ppm and those bonded to two A1 cations and a vacancy have a chemical shift of about -134 parts per million (ppm). The shift at -182.8 ppm in hectorite is apparently associated with fluoride bonded to two A1 cations and a Li cation. Surprisingly, the difference in chemical shift of the interlayer and inner fluoride in 1:1 layer silicates is insufficient to distinguish these sites. Based on trends in chemical shift, it appears that fluoride substitution for inner hydroxyls in clays with octahedral substitution is not random. Fluoride is apparently preferentially associated with Mg rather than A1 in the octahedral sheet as no resonance due to a fluoride bonded to two A1 cations and a vacancy is observed in clays such as SAz-1.

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Section: :1 Layer Silicatessupporting

confidence: 94%

Section: :1 Layer Silicatessupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

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A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

Labouriau

1995

Clays and clay miner.

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“…Spectra for representative reaction products are shown in Figure 6. The presence of two resonances agrees with earlier studies of fluorinated 2:1 structures (Butruille et al 1993;Huve et al 1992). The upfield line at -16 ppm arises from fluorine atoms triply bridging a positively charged triad of edgeshared octahedra occupied by two Mg 2+ ions and one Li + ion.…”

Section: Fluorohectorite Hydrolysissupporting

confidence: 89%

Acid Hydrolysis of Octahedral Mg²⁺ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms

Kaviratna

Pinnavaia

1994

Clays and clay miner.

101

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Abstract--The acid hydrolysis products of trioctahedral fluorohectorite and phlogopite have been investigated by XRD, MAS NMR spectroscopy and nitrogen BET surface area analysis in an effort to assess the relative importance of edge attack and gallery access mechanisms. A dramatic loss of X-ray crystallinity and the formation of Q3 and Q" SiO4 sites accompanied the depletion of Mg 2+ from the octahedral sheet of both 2:1 layered structures. Depending on the extent of hydrolysis, the products derived from fluorohectorite exhibited surface areas up to 208 mVg, whereas phlogopite hydrolysis products gave values <20 mY/g. The dramatic differences in surface areas were not related to differences in hydrolysis mechanisms. 19F MAS NMR studies indicated that the hydrolysis of fluorohectorite occurred primarily by an edge attack mechanism equivalent to the hydrolysis pathway for phlogopite. A gallery access mechanism contributed to the hydrolysis of fluorohectorite only at the later stages of octahedral Mg 2+ depletion. Solvation effects appeared to be important in determining the surface areas of the reaction products derived from the swelling (fluorohectorite) and non-swelling (phlogopite) precursors.

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“…The smaller peaks on each side of the strong line are spinning side-bands (indicated by). These peaks are not the true signals since they arise from the MAS process and their positions vary with the spinning speed [21,22]. In contrast, the 19 …”

Section: Mechanism Of Fluoride Removal 331 Hydrotalcite and Its Camentioning

confidence: 99%

Water defluoridation by hydrotalcite and takovite and subsequent formation of new fluoride-bearing phases

Guo

2013

Environmental Technology

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Hydrotalcite, takovite and their calcination products were used to remove fluoride from water at various molar ratios of initial fluoride to solid (F(initial):hydrotalcite or F(initial):takovite) ranging from 0.1 to 2.0, and their theoretical fluoride uptake limit. X-Ray powder diffraction and 19F magic-angle spinning nuclear magnetic resonance spectra were used to characterize the solid samples and to investigate the fluoride removal mechanisms. Water defluoridation by uncalcined and calcined hydrotalcite attributes mainly to the intercalation of F- into their interlayers and adsorption of F- onto their external surfaces. The fluoride removal percent of calcined hydrotalcite are higher than those of uncalcined hydrotalcite at F(initial):hydrotalcite ratios varying between 0.1 and 1.5, whereas the situation is the reverse at a ratio of 2.0 in the 30 d sorption runs. It was induced by the precipitation of fluoride-bearing nordstrandite and sellaite during a long contact of high concentration fluoride solution with uncalcined hydrotalcite. In contrast, the sorption of fluoride by uncalcined and calcined takovite occurs predominantly on their external surfaces. Fluoride-bearing gibbsite or nordstrandite and NiF2 were formed as the fluoride solutions were treated by uncalcined takovite in the 30 d runs, which enhanced its defluoridation effect. The fluoride removal efficiency of calcined takovite is much lower than uncalcined takovite and calcined hydrotalcite, because the expected restoration of original layered structure of takovite did not happen during the reaction of calcined takovite with the fluoride solution.

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¹⁹F MAS-NMR Study of Structural Fluorine in Some Natural and Synthetic 2:1 Layer Silicates

Cited by 50 publications

References 19 publications

A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

Acid Hydrolysis of Octahedral Mg²⁺ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms

Water defluoridation by hydrotalcite and takovite and subsequent formation of new fluoride-bearing phases

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19F MAS-NMR Study of Structural Fluorine in Some Natural and Synthetic 2:1 Layer Silicates

Cited by 50 publications

References 19 publications

A 19F Nuclear Magnetic Resonance Study of Natural Clays

A 19F Nuclear Magnetic Resonance Study of Natural Clays

Acid Hydrolysis of Octahedral Mg2+ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms

Water defluoridation by hydrotalcite and takovite and subsequent formation of new fluoride-bearing phases

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¹⁹F MAS-NMR Study of Structural Fluorine in Some Natural and Synthetic 2:1 Layer Silicates

A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

A ¹⁹F Nuclear Magnetic Resonance Study of Natural Clays

Acid Hydrolysis of Octahedral Mg²⁺ Sites in 2:1 Layered Silicates: An Assessment of Edge Attack and Gallery Access Mechanisms