Multinuclear NMR Spectroscopy Studies of Silica Surfaces

Maciel, Gary E.; Bronnimann, Charles E.; Zeigler, Robert C.; Chuang, I-Ssuer; Kinney, David R.; Keiter, Ellen A.

doi:10.1021/ba-1994-0234.ch014

Cited by 31 publications

(35 citation statements)

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“…In the deconvoluted spectra, besides the major signal at -84 ppm, several other peaks at -80, -90, and -95 ppm coexisted. They can be attributed to (AlO) 3 SiOH or (SiO)(AlO)Si(OH) 2 (-84 ppm), (AlO) 2 Si(OH) 2 (-80 ppm), (SiO) 2 Si(OH) 2 (-90 ppm), and (SiO) 2 (AlO)SiOH (-95 ppm) species, respectively [54][55][56]. Together with the 27 Al NMR results, this observation supports the presence of joint 4R units in these samples.…”

Section: Resultsmentioning

confidence: 99%

An investigation into the crystallization of low-silica X zeolite

Zhang

Huang

2015

J Porous Mater

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The crystallization of low-silica X (LSX) zeolite with FAU topology was examined under hydrothermal synthesis conditions. PXRD was employed to follow the evolution of the long-range ordering of the gel. Raman spectra provided information on various ring and cage species existing in the gel. 27 Al and 29 Si solid-state NMR spectroscopy was utilized to monitor the change in local environment of tetrahedral sites. The results indicate that an amorphous aluminosilicate phase was formed immediately upon mixing different reactive species. Hydrothermal treatment led to the formation of sodalite-cage like species and the species with larger cavities, joint four-member rings (4Rs) and branched 4Rs, which are the structural building units of the FAU framework. These units were assembled into the crystalline structure of LSX zeolite. 23 Na and 39 K solid-state NMR results show that the transformation process was accompanied by the changes of the local structure of hydrated Na ? and K ? ions. The two types of cations may work synergistically to template the crystallization of LSX zeolite.

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Section: Resultsmentioning

confidence: 99%

An investigation into the crystallization of low-silica X zeolite

Zhang

Huang

2015

J Porous Mater

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“…The functionalized silica samples have been characterized by quantitative combustion analysis (C,H,N analysis), BET measurements, and DRIFT spectroscopy. 13 C{ 1 H} CP MAS, 29 Si{ 1 H} CP MAS and 1 H MAS, solid-state NMR spectroscopy were employed in selected cases to confirm the structure formation. , The assignments of the 13 C and 29 Si NMR signals to specific surface groups were carried out according to refs and .…”

Section: Methodsmentioning

confidence: 99%

“… a The solid-state CP MAS 29 Si{ 1 H}NMR spectra indicate oligomerized silane reagents on the silica surface (T 3 -signal). , …”

Section: Methodsmentioning

confidence: 99%

Hydrogen-Bond Donating and Dipolarity/Polarizability Properties of Chemically Functionalized Silica Particles

and

Reuter

1998

Langmuir

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Linear solvation energy (LSE) relationships are employed to characterize the surface polarity of organically functionalized silicas. The polarity of the silica surfaces should be quantitatively described by three independent terms: the dipolarity/polarizability (π*), the hydrogen-bond donating ability (α), and the hydrogen-bond accepting ability (β). These terms can be defined by using the Kamlet−Taft solvent parameters α, β, and π* as a reference system. Kamlet−Taft α and π* values and Reichardt's E T(30) values are presented for 30 differently functionalized silica particles and bare silicas. The surface polarity parameters α and π* were determined by means of correlation analyses of the energy of the UV−vis absorption maxima (νmax) of selected solvatochromic probe dyes which are adsorbed to the particle surfaces. The following surface polarity indicators have been used: 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate and its penta-tert-butyl substituted derivative, cis-dicyanobis(1,10-phenanthroline)iron(II), and bis-4,4‘-(N,N-dimethylamino)benzophenone. The α values of organically modified LiChrosphers, which were synthesized with monofunctional silanes, linearly decrease with the amount of surface coverage of the functional group μmol m-2. Using trifunctional silanes as reagents, the α value of modified silicas is influenced in a more complex manner because the functionalization process occurs not uniform. Correlations of the values of surface polarity parameters with each other and with literature data demonstrate that the reported values are relevant empirical constants. The E T(30) parameter of chemically modified silicas can be expressed by the specific LSE equation: E T(30)(measured) = 14.84α + 5.33π* + 36.1; n = 30, r 2 = 0.9334. This E T(30) LSE relationship, derived for functionalized silicas, is compared to the equation derived for pure solvents as reported by Marcus (Marcus, Y. Chem. Soc. Rev. 1993, 409).

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“…In from silicas prepared in a liquid medium by their small order to better understand and control the properties of silica particle size (10-20 nm), their nonmicroporous surface, and much work has therefore been devoted to the study of surface their lower hydroxyl density (5). Moreover, prepared at protons, most noticeably by IR (3)(4)(5)(6), { 1 H- 29 Si} CP MAS-high temperature followed by rapid quenching, they are only NMR (5,(7)(8)(9)(10)(11), and , MAS, partially hydrated and present numerous unstable strained CRAMPS (7,8), and multiple coherence (13)). Surface siloxane bridges susceptible to relaxation by hydroxylation hydroxyl groups have been classified according to their coor-(21).…”

Section: Introductionmentioning

confidence: 99%