Transmission near-infrared technique for evaluation and relative quantitation of surface groups on silica

Bush, S. G.; Jorgenson, James W.; Miller, Mark L.; Linton, Richard W.

doi:10.1016/0021-9673(83)80001-6

Cited by 32 publications

(5 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The general behavior of the dehydration (removal of physisorbed water) and dehydroxylation (removal, as water, of hydroxyl groups that were covalently bonded at the silica gel surface) under vacuum at various temperatures can be summarized as follows: (1) Physisorbed water can be completely removed by evacuation, even at 25 °C (dehydration). ,,,,,,,,,,, (2) Both hydrogen-bonded and isolated (non-hydrogen-bonded) silanols are major components on a fully hydroxylated, dry silica surface. ,− ,,,,,− (3) For a wide variety of amorphous silicas, the average OH coverage on a fully hydroxylated surface is 4.9 OH/100 Å 2 , independent of the origin and structural characteristics ,,,− (5) Upon heating under vacuum, hydrogen-bonded silanol groups on the surface start to experience the elimination of water via condensation (dehydroxylation) and form siloxane linkages at about 190 °C; the stronger the hydrogen bonding, the easier the hydroxyl group is removed. …”

Section: Discussionmentioning

confidence: 99%

“…Many applications of silicas and modified silicas rely on their unique surface properties, which in turn are largely determined by the concentration, distribution, and nature of hydroxyl groups (silanols) on the surface. − Various spectroscopic techniques, including NMR, − infrared, − ,,− and Raman 16,17,27,32,57-59 spectroscopies, as well as chemical probes ,,,,− ,,− ,,…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Detailed Model of Local Structure and Silanol Hydrogen Bonding of Silica Gel Surfaces

1997

View full text Add to dashboard Cite

A refined and generalized version of a previously suggested model of the silica surface, in which geminal silanols are situated on surface segments similar to (100)-type faces of the β-cristobalite structure and single silanols are situated on surface segments similar to corresponding (111)-type faces, is supported by extensive spectroscopic data. In this model single silanols on the same (111)-type surface segment cannot form hydrogen bonds with each other. Whether or not adjacent geminal silanols on the same (100)-type surface segment can form hydrogen bonds with each other depends on the relative orientation of their hydroxyl groups. When two surface segments of either (100)- or (111)-type intersect convexly, hydroxyl groups cannot participate in hydrogen bonding across the intersection; but when two surface segments intersect concavely, those silanols situated at the intersection can form hydrogen bonds with their counterparts across the intersection. All the hydrogen-bonding silanols in this generalized β-cristobalite model have a common feature: when any two silanols are hydrogen bonded to each other, the two silicon atoms containing them are also situated on the same (100)-type surface segment. This idealized structure of the surface of silica gel, which is clearly known from X-ray diffraction to be an amorphous material, may be distorted for various thermodynamic or kinetic reasons during its formation; therefore, a wide range of hydrogen-bonding strengths between two hydroxyls is likely on a real silica gel surface. The generalized β-cristobalite surface model can also explain the reversible dehydroxylation and rehydroxylation processes on silica surfaces. Both single and geminal silanols participating in hydrogen bonding are most easily dehydroxylated under evacuation at temperatures between 170 and 450 °C and form low-strain bicyclo[3.3.0]octasiloxane rings. The mode of dehydroxylation on a silica surface undergoes a transformation between 450 and 650 °C, yielding highly strained trisiloxane rings for dehydroxylation at T ≥ 650 °C.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Detailed Model of Local Structure and Silanol Hydrogen Bonding of Silica Gel Surfaces

1997

View full text Add to dashboard Cite

show abstract

“…Since the natures of the hydroxyl groups on the silica gel surface are different, the environments of the adsorbed water molecules on the surface are also different. The state of the water molecules on silica gel particles and related substances have been studied by using several different techniques including TGA [2], NMR [3,4], IR and NIR [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], AB initio calculations [20] and dielectric measurements [21]. Most of these studies were trying to give a picture of the water structure on silica surface based on the results from the respective analytical techniques.…”

Section: Introductionmentioning

confidence: 99%

New insights into the surface functionalities and adsorption evolution of water molecules on silica gel surface: A study by second derivative near infrared spectroscopy

Christy

2010

Vibrational Spectroscopy

View full text Add to dashboard Cite

Surface functionalities and adsorption evolution of water molecules on silica gel samples were studied by second derivative Near Infrared Spectroscopy. Four different silica gel samples with varying surface area were used in this experiment. Each of the dry samples was allowed to equilibrate with surrounding air and the near infrared spectra were accumulated at different time intervals using reflectance technique. The evolved spectra were analysed by using second derivative technique to study the adsorption evolution of water molecules on the surface.The second derivative spectral profiles have revealed some interesting features about the surface functionalities and some events of adsorption on silica gel surface that have never been reported in the literature. The near infrared spectroscopic evidence is provided for the first time to show the presence of hydrogen bonded silanol groups on silica gel surface. The results and the events show that the adsorption of water molecules readily takes take place on the hydrogen bonded vicinal silanol groups and spread over the space and ends with the hydrogen bonding at free silanol groups. Water molecules then build over these molecules to form a network of hydrogen bonded water molecules.There is clear evidence that the presence of hydrogen bonded silanol groups is a necessary condition for the effective adsorption activities on silica gel surface.Furthermore, the study reveals that while mono and multi-layer water molecular adsorption takes place at certain active sites of the surface, a large portion of the surface is free from any adsorption activities.* E-mail address: alfred.christy@uia.no 2

show abstract

“…Since binding to the silica gel (16,17) reduces the concentration and absorbance of the lipophilic acid in solution, the amount of the acid loaded is calculated from the change of UV absorbance from the initial concentration. A report converting the silanol hydrogen (Si-OH) on the surface of silica gel to dimethylsilyl (Si-O-SiH(CH 3 ) 2 ) showed the concentration of silanol groups on silica gel (60 Å) to be 2.54 ± 0.08 mmol/g or 3.3 per 100 Å 2 (18,19). Table 2 shows that the mmol amount of the carboxylic acids binding to silica gel is 20-180-fold lower than the calculated amount of free silanol groups.…”

Section: Resultsmentioning

confidence: 99%

Modified silica gels as recyclable adsorbents of aqueous polycyclic aromatic hydrocarbons

Regan

Dolores

Lepore

et al. 2019

Green Chemistry Letters and Reviews

View full text Add to dashboard Cite

Polycyclic aromatic hydrocarbons (PAHs), a class of toxic organic molecules containing multiple fused aromatic rings, are found in air, soil and water as a by-product from the incomplete combustion of organic matter. We report on the modification of silica gel using lipophilic molecules containing carboxylic acids, for anchoring to the surface via hydrogen bonds. The lipophilic component captures aqueous PAH, specifically phenanthrene, through the agency of π-π and π-sp 3 interactions. The structure-sorption-relationships suggest optimum phenanthrene adsorption is achieved with unsaturated bonds in linear chains or two phenyl rings. Examples include linoleic acid or 2,3-diphenylpropionic acid with removal values of 281 and 283 ng PAH per gram of silica gel, respectively. Saturation adsorption is achieved within four hours. Proposed modes of binding of the new reverse phase silica gels with phenanthrene are described. Recycling of the silica gel is accomplished by washing with organic solvents to remove PAH. ARTICLE HISTORY

show abstract

Transmission near-infrared technique for evaluation and relative quantitation of surface groups on silica

Cited by 32 publications

References 18 publications

A Detailed Model of Local Structure and Silanol Hydrogen Bonding of Silica Gel Surfaces

A Detailed Model of Local Structure and Silanol Hydrogen Bonding of Silica Gel Surfaces

New insights into the surface functionalities and adsorption evolution of water molecules on silica gel surface: A study by second derivative near infrared spectroscopy

Modified silica gels as recyclable adsorbents of aqueous polycyclic aromatic hydrocarbons

Contact Info

Product

Resources

About