Investigation of 1800–1400 cm<sup>–1</sup>region of infra-red spectrum of aerosil silicas

Hambleton, F. H.; Hockey, J. A.; Taylor, John A.

doi:10.1039/tf9666200795

“…Some studies suggest that this peak may be due to strongly hydrogenbonded, surface-adsorbed water (23)(24)(25)44,45). However, the persistence of this peak on silica gels heated above 400 °C (28,32), the absence of a water deformational band at 1620 cm*1 when the 3500-cm'1 band was present (26), and the effects of H2180 exchange on fine structure in the spectrum (46) point to strongly hydrogen-bonded surface silanols as being primarily responsible for this peak. The near-IR studies of Bush et al (47) offer the most convincing evidence that surfaceadsorbed water is not present on silica gels heated above 180 °C.…”

Section: Methodsmentioning

confidence: 98%

“…There is no doubt that the majority, if not all, of physisorbed water is removed under vacuum at room temperature or by treatment at 115 °C. However, there are several reports indicating that bound water is not completely removed until temperatures approach anywhere from 150 to 300 °C (23)(24)(25)(26)(27). Pore structure is apparently important in determining the exact temperature at which a gel is dehydrated.…”

Section: Introductionmentioning

confidence: 99%

Analysis of thermally and chemically modified silica gels by heterogeneous gas-solid chromatography and infrared spectroscopy

Boudreau¹,

Cooper²

1989

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The effects of thermal pretreatments at 180, 400, and 840 °C on the subsequent chemical modification of silica gel have been characterized by heterogeneous gas-solid chromatography (HGSC) and Infrared spectroscopy. Silica gel treated at 400 °C exhibited a surface area, surface polarity, and surface selectivity similar to those of the same material treated at 180 °C, even though the 400 °C gel could be modified to a much greater extent by gas-phase sllanization with hexamethyldlsllazane. The HGSC and IR results taken together Indicate that there are strongly hydrogen-bonded surface hydroxyl species on silica gel (sllanols or bound water), which are Inactive with regard to physical adsorption but which prevent complete stoichiometric modification of the silica surface. These Inactive sllanols can be removed with heating at elevated (>200 °C) temperatures, suggesting that thermal pretreatment of the silica support can be utilized to make more homogeneous and therefore more efficient bonded liquid chromatography stationary phases. Thermal treatment at 840 °C produces a silica gel with free (nonbound) Internal sllanols and external sllanols that can be completely modified with surface ligands, but the sintering that occurs at this temperature reduces the surface area of the silica gel such that It is no longer chromatographically useful.

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“…After such modification, in some originally geometric wells due to roughness (they were suggested also in [8]) the molecule may be almost completely surrounded by halogen atoms bonded to the surface. This is schematically illustrated by the two dimensional picture in Fig.…”

Section: Evaluation Of Desorption Energies From Gas Chromatographic Ementioning

confidence: 96%

“…; X = halogen) have been known to react with both the silanols and siloxans and thus deeply modify the surface [8,9]. As a result, it gets covered by halogen atoms attached to the surface Si atoms and by fragments of the agent molecule attached to the Si as well as O atoms; this prevents the molecules under study from contacting the bare SiO 2 lattice.…”

Section: Evaluation Of Desorption Energies From Gas Chromatographic Ementioning

confidence: 98%

Bulk chemical properties of new elements from one-atom-at-a-time data

Zvára

¹

2006

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For the volatile (oxo)halides of known elements the energies of desorption from the surface of fused silica measured in radiochemical gas-solid chromatographic experiments proved close to the sublimation energies. This could hardly be expected for interaction of isolated molecules with bare surface of ionic SiO 2 . Because such regularity shows great promise for evaluation of bulk properties of transactinoid compounds we need to understand the origin of apparent inconsistency. The clue seems to be the real structure of the surface. It is initially rough (from µm down to nm scale), inherently heterogeneous at the molecular level, and contains atoms and groups with excessive energy. Exposing to ambient air produces numerous surface ≡SiOH groups. The halogenating agents employed in transactinoid studies chemically modify such surface: it gets tightly covered by halogen atoms and fragments of the agent molecule attached to the Si and O atoms. Now the molecules of new compounds cannot touch SiO 2 lattice; moreover, in some initially geometric wells (due to roughness), they get surrounded by halogen atoms bonded to the surface -the situation resembling that in their own bulk condensed phase. Hence, there must be sites with desorption energies up to the sublimation energy.

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“…; X = halogen) have been known to react with both the silanols and siloxans and thus deeply modify the surface [8,9]. ; X = halogen) have been known to react with both the silanols and siloxans and thus deeply modify the surface [8,9].…”

Section: Evaluation Of Desorption Energies From Gas Chromatographic Ementioning

confidence: 99%

Bulk chemical properties of new elements from one-atom-at-a-time data

Zvára

¹

2006

Czech J Phys

0

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For the volatile (oxo)halides of known elements the energies of desorption from the surface of fused silica measured in radiochemical gas-solid chromatographic experiments proved close to the sublimation energies. This could hardly be expected for interaction of isolated molecules with bare surface of ionic SiO 2 . Because such regularity shows great promise for evaluation of bulk properties of transactinoid compounds we need to understand the origin of apparent inconsistency. The clue seems to be the real structure of the surface. It is initially rough (from µm down to nm scale), inherently heterogeneous at the molecular level, and contains atoms and groups with excessive energy. Exposing to ambient air produces numerous surface ≡SiOH groups. The halogenating agents employed in transactinoid studies chemically modify such surface: it gets tightly covered by halogen atoms and fragments of the agent molecule attached to the Si and O atoms. Now the molecules of new compounds cannot touch SiO 2 lattice; moreover, in some initially geometric wells (due to roughness), they get surrounded by halogen atoms bonded to the surface -the situation resembling that in their own bulk condensed phase. Hence, there must be sites with desorption energies up to the sublimation energy.

show abstract

Investigation of 1800–1400 cm^–1region of infra-red spectrum of aerosil silicas

Cited by 16 publications

References 2 publications

Analysis of thermally and chemically modified silica gels by heterogeneous gas-solid chromatography and infrared spectroscopy

Analysis of thermally and chemically modified silica gels by heterogeneous gas-solid chromatography and infrared spectroscopy

Bulk chemical properties of new elements from one-atom-at-a-time data

Bulk chemical properties of new elements from one-atom-at-a-time data

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Investigation of 1800–1400 cm–1region of infra-red spectrum of aerosil silicas

Cited by 16 publications

References 2 publications

Analysis of thermally and chemically modified silica gels by heterogeneous gas-solid chromatography and infrared spectroscopy

Analysis of thermally and chemically modified silica gels by heterogeneous gas-solid chromatography and infrared spectroscopy

Bulk chemical properties of new elements from one-atom-at-a-time data

Bulk chemical properties of new elements from one-atom-at-a-time data

Contact Info

Product

Resources

About

Investigation of 1800–1400 cm^–1region of infra-red spectrum of aerosil silicas