Application de la résonance magnétique nucléaire à l’étude de l’eau de constitution des gels de silice

Fraissard, J.; Solomon, I.; Caillat, Roger; Elston, J.; Imelik, Boris

doi:10.1051/jcp/1963600676

Cited by 20 publications

(3 citation statements)

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“…For sample G, the mean available surface area per silanol being 0.17 nm 2 (Table ), the silanols do not fill the surface; they are either clustered or randomly distributed over this surface . The Lorentzian derivative shape of the diluted silanol broad-line spectrum does not exclude the possibility that there are parts of the surface without silanols.…”

Section: Discussionmentioning

confidence: 97%

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K

et al. 1996

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Two silicas obtained by precipitation have been compared using two 1H NMR techniques: broad-line at 4 K with simulation of the spectra and MAS at room temperature. Previous 29Si high resolution NMR results have been used to interpret the spectra. Geminal silanols, single silanols, water molecules relatively strongly hydrogen-bonded to silanols, and water not interacting with OH groups have been characterized and quantified. Differences are found between the two precipitated silicas. Silanols, 70% of which can hydrogen-bond a water molecule, occupy all the surface of one of them. The other sample surface is not so crowded with silanols, and only 37% of them hydrogen-bond water molecules. Both geminal and single silanols hydrogen-bond water. Physisorbed water molecules not interacting with silanols can be equilibrated on both sample surfaces. Room temperature dehydration of the samples in vacuum is studied.

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Section: Discussionmentioning

confidence: 97%

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K

et al. 1996

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“…The preparation and the deuteration of the gel surface have been described previously. 24 The deuteration of the gel surface as well as the transformation of CD3OD into CDsOH were checked by infrared spectroscopy and found almost complete.…”

Section: Methodsmentioning

confidence: 99%

Methanol-silica gel system. II. Molecular diffusion and proton exchange from pulse proton magnetic resonance data

Cruz¹,

Stone²,

Fripiat³

1972

J. Phys. Chem.

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six polar hydroxy sites. Sorbitol, in contrast, appearsAcknowledgmerti. The financial assistance of the to be a struchre breaker, as is indicated by the mono-National Science Foundation is gratefully aeknowlronic negatiw erilhalpies over the entire concentration edged. J. K. S. wishes to thank Professor Y, Marcus range investigated, This behavior of ART, is similar at> the Hebrew University for his hospitality. for XaCE in acjil~aoixs hydrogen peroxideJ5 ureaJ6 and %,hi& differ d r o~i d e s .~ in position of one of their six hy-bility of Inorganic and Organic Compounds,'' Supplement to 3rd Publication costs assisted by the Muage Royal de E'Afrigue CentraleThe proton motions in the methanol-silica gel (Xerogel) systems have been deduced from the measurement of the spin-lattice (TI) and spin-spin (T,) proton relaxation times in the systems C€LOD-XOD, CDIOH-XOK, and CH,OH-XOH, where XOH and XOD stand for the Xerogel-OH or Xerogel-OD surfaces, respectively. In CH30D-XOD, only one TI or T2 is observed. The experimental data may be accounted for by a laandational motion of CH,OD, the methyl. group rotating very rapidly around the triad axis. In CD30H-XOH, one TI aiid two Tt are measured. TI is the superimposition of two functions. The rate of exchange of nuclei between the two populations is fast with respect to T1-l but slow with respect to T2-I. The long TZ represents the diffusion motion observed in the first system, while the short T2 is assumed to be due to a proton exchange process between the hydroxylic protons of C&OH and XOH or between CDIOI~ molecules. Moreover, it has been possible to compute the observed Ti for the CHIOH-XOH system from the data obtained for the two simpler cases. At 25", the surface diffusion coefficient of adsorbed methanol is reduced by two orders of magnitude with respect to that in the liquid for a degree of coverage e ^I 0.6. For 1 < e < 2, the lowering is by a factor of 10. For e 2 0.7, the surface diffusion coefficient at 25' is the same as that in the liquid state at -85". More than three layers should be probably required to find a diffusion coefficient in the adsorbed state close to that in the liquid state. In the assumed exchange process a proton is transferred from the surface into a cluster of adsorbed species where it jumps from a molecule to another before coming back on the surface: [-OH + CB301-I 3 1 0-+ CH10H2+; CH30H2+ + CH80J1 -+ CH30H + C€InOIh+; CH3OH2" + -0-[ -+ ] -OH + CHaOH. The ratio of the exchange to the molecular diffusion jump frequency ( v e / u d ) is 6 x 10-3 for e = 1.7 and 2.5 x 10-2 for e = 0.8. This means that the number of times a methanol molecule is protonated during its stay on an adsorption site increases at decreasing degree of coverage. For 0 = 0.8, u./ud is very close to the value observed in the liquid protonated methanol al, 25" The activation energies of both the diffusion and the proton exchange processes are dose to each other (-6 kcal at 8 = l), and there are approximately equal to half the isosteric heat of adsorption. Both these motio...

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“…The assignment of the other losses is not trivial. The second weight loss could be due to the evolution of chemically bonded water that starts at about 200°C [36] and in some cases could end near 600°C [37]. However, we cannot rule out the evolution of some molecules of ethanol strongly H-bonded to the silica-PEG matrix.…”

Section: Materials Of Class IImentioning

confidence: 99%

Synthesis and characterization of SiO2–PEG hybrid materials

Grandi¹,

Magistris²,

Mustarelli³

et al. 2006

Journal of Non-Crystalline Solids

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Application de la résonance magnétique nucléaire à l’étude de l’eau de constitution des gels de silice

Cited by 20 publications

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Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K

Methanol-silica gel system. II. Molecular diffusion and proton exchange from pulse proton magnetic resonance data

Synthesis and characterization of SiO2–PEG hybrid materials

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Application de la résonance magnétique nucléaire à l’étude de l’eau de constitution des gels de silice

Cited by 20 publications

References 0 publications

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using 1H NMR: Broad-Line at 4 K and HR MAS at 300 K

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using 1H NMR: Broad-Line at 4 K and HR MAS at 300 K

Methanol-silica gel system. II. Molecular diffusion and proton exchange from pulse proton magnetic resonance data

Synthesis and characterization of SiO2–PEG hybrid materials

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Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K

Study of the Constitutive Superficial Water of Precipitated Amorphous Silicas using ¹H NMR: Broad-Line at 4 K and HR MAS at 300 K