Hydroxyl Content in Silica Gel “Aerosil”

Fripiat, J. J.; Uytterhoeven, Jan B.

doi:10.1021/j100811a007

Cited by 217 publications

(91 citation statements)

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“…Our results [301][302][303][305][306][307][308][309][310][311][313][314][315]317,[334][335][336][337][338] accord well with the data on the dehydroxylation of the amorphous silica surface obtained by Fripiat, Uytterhoeven et al [58,74]. These authors determined the silanol number h OH on the basis of the reaction of OH groups with organometallic reagents CH 3 Li and CH 3 MgI.…”

Section: Dehydroxylation and Rehydroxylation Of The Silica Surface Dsupporting

confidence: 88%

“…Thus, Baverez and Bastick [66] on the basis of IR spectroscopic analysis found that T B $ 240°C. Fripiat and Uytterhoeven, using the same method, came to the conclusion [58] that physically adsorbed water is completely removed only at 300°C. Some Russian and Ukrainian researchers suggested a concept according to a part of Si atoms on the silica surface are coordinately unsaturated (so-called nonhydroxyl centers of the II-type).…”

Section: Boundary Temperature For Remo6ing Physically Adsorbed Water mentioning

confidence: 95%

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The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,057

142

1,967

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A review article is presented of the research results obtained by the author on the properties of amorphous silica surface. It has been shown that in any description of the surface silica the hydroxylation of the surface is of critical importance. An analysis was made of the processes of dehydration (the removal of physically adsorbed water), dehydroxylation (the removal of silanol groups from the silica surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of experimental and theoretical studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chemistry of amorphous silica. The main advantage of this physico-chemical model lies in the possibility to determine the concentration and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the silica surface as a function of the pretreatment temperature of SiO 2 samples. The model makes it possible to determine the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO 2 skeleton. The magnitude of the silanol number, that is, the number of OH groups per unit surface area, h OH , when the surface is hydroxylated to the maximum degree, is considered to be a physico-chemical constant. This constant has a numerical value: h OH,AVER =4.6 (least-squares method) and h OH,AVER = 4.9 OH nm − 2 (arithmetical mean) and is known in literature as the Kiselev-Zhuravlev constant. It has been established that adsorption and other surface properties per unit surface area of silica are identical (except for very fine pores). On the basis of data published in the literature, this model has been found to be useful in solving various applied and theoretical problems in the field of adsorption, catalysis, chromatography, chemical modification, etc. It has been shown that the Brunauer -EmmettTeller (BET) method is the correct method and gives the opportunity to measure the real physical magnitude of the specific surface area, S Kr (by using low temperature adsorption of krypton), for silicas and other oxide dispersed solids.

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Section: Dehydroxylation and Rehydroxylation Of The Silica Surface Dsupporting

confidence: 88%

Section: Boundary Temperature For Remo6ing Physically Adsorbed Water mentioning

confidence: 95%

The surface chemistry of amorphous silica. Zhuravlev model

Zhuravlev

2000

Colloids and Surfaces A: Physicochemical and Engineering Aspect

2,057

142

1,967

View full text Add to dashboard Cite

show abstract

“…The terminal oxygen functions -the silanols -have been shown by infrared studies to be geminal, vicinal, or isolated (15)(16)(17)(18)(19)(20)(21)(22)(23). These functions, in an amorphous framework, serve to render the silica gel surface inhomogeneous.…”

Section: Introductionmentioning

confidence: 99%

“…Heat treatment of silica gel first induces loss of the physically adsorbed water molecules and, subsequently, dehydroxylation of the silanol groups. The number of hydroxyl groups on the silica gel surface depends strongly on the temperature of pretreatment of the samples studied (15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Measurements performed by Fripiat and Uytterhoeven (21), amongst others, indicate that the amount of free water rapidly decreases with increasing temperature and, for temperatures higher than about 250°C, it is ' Publication 315 from the Photochemistry Unit.…”

Section: Introductionmentioning

confidence: 99%

“…Up to 450°C the dehydroxylation process can be reversed by exposing the silica gel to water vapour, for higher temperatures this process is slow. If the heating is taken to -700°C, or higher, only isolated O H groups remain on the surface (21,23). Fripiat and uytterhoevenls (21) findings have been recently supported by nmr studies (24) in which, additionally, the proportion of geminal-hydroxyl sites to single hydroxyl sites, previously the subject of much debate, was determined.…”

Section: Introductionmentioning

confidence: 99%

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Surface photochemistry: the effect of surface modification on the photophysics of naphthalene and pyrene adsorbed on silica gel

Bauer¹,

Mayo²,

Natarajan³

et al. 1984

Can. J. Chem.

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The influence of heat treatment and of added coadsorbates on the surface photophysics of pyrene and naphthalene adsorbed on silica gel is reported. When the silica gel surface is partially dehydroxylated, the distribution of pyrene or naphthalene is inhomogeneous, as indicated by multiexponential fluorescence decay and broad emission spectra. Addition of polar coadsorbates renders the surface more homogeneous with singlet lifetimes approaching solution values. The pretreatment and addition of coadsorbates, in the case of pyrene, also influence the relative importance of dynamic excimer formation vis-a-vis ground state association.

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Silica

Uhrlandt¹

2006

Kirk-Othmer Encyclopedia of Chemical Technology

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In recorded history, there are numerous indications of the omnipresence of silicates in humanity’s natural habitat. Siliceous minerals were either utilized by processing natural silica deposits, eg, clay, porcelain, glass or enamel, or obtained by means of chemical conversion. Silica in the form of amorphous white powders can also be made synthetically, using a thermal process (fumed silica) or a wet process (precipitated silica, silica gels). Forms of amorphous silica are used in various industries, such as food, feed, coatings, plant protection, tires, personal care, and many others, and are an essential part of many products of our everyday life. This article briefly covers crystalline silica. The major focus is amorphous silica, its production processes, physical‐chemical characteristics, and uses in various everyday products. Health and safety aspects are also discussed.

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Hydroxyl Content in Silica Gel “Aerosil”

Cited by 217 publications

References 1 publication

The surface chemistry of amorphous silica. Zhuravlev model

The surface chemistry of amorphous silica. Zhuravlev model

Surface photochemistry: the effect of surface modification on the photophysics of naphthalene and pyrene adsorbed on silica gel

Silica

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