State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

Bobon, Miroslav; Christy, Alfred A.; Kluvanec, Daniel; Illášová, Ľudmila

doi:10.1007/s00269-011-0453-0

Cited by 44 publications

(55 citation statements)

References 24 publications

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“…All IR spectra appear to be very similar to previous studies (e.g. Langer & Flörke, 1974;Graetsch et al, 1994;Ilieva et al, 2007;Ostrooumov, 2007;Bobon et al, 2011). The characteristic IR bands for water in opal are found in the area between 1500-4000 cm À1 (Fig.…”

Section: Infrared Spectroscopysupporting

confidence: 73%

“…%, Graetsch et al 1994;. Infrared studies at ambient conditions indicate that water is present in various forms: free water between spheres, surface water, and silanol (Si-OH) groups on the surface of the silica spherules (Day & Jones, 2008;Bobon et al, 2011). The presence of silanol groups in silica has been firmly established by nuclear magnetic resonance spectroscopy (Brown et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

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Ordering of water in opals with different microstructures

Eckert¹,

Gourdon²,

Jacob³

et al. 2015

ejm

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Opal has long fascinated scientists. It is one of the few minerals with an amorphous structure, and yet, compared to silica glass, it is highly organized on the mesoscale. By means of inelastic neutron scattering (INS), we could document that in four samples of opal at low temperature an ice-like structure of water is present, with details depending on microstructural characteristics. While FTIR spectra for all samples are nearly identical and thus not very informative, INS shows clear differences, highlighting the significance of microstructures. Neutron diffraction at 100 K on one of the opal samples provides evidence for crystalline cubic ice.

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Section: Infrared Spectroscopysupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Ordering of water in opals with different microstructures

Eckert¹,

Gourdon²,

Jacob³

et al. 2015

ejm

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show abstract

“…The first two bands are due to the OH groups of water molecules hydrogen bonded to free silanol groups, OH groups of water molecules hydrogen bonded to vicinal silanol groups on the surface respectively. The water molecules attached to geminal silanol groups absorb at a frequency slightly red shifted from 5270 cm -1 (5265 cm -1 ) [11]. These absorptions are indicated in Fig.…”

Section: Introductionmentioning

confidence: 86%

“…Christy has recently published a series of articles relating to silica gel and shown that the characteristics of silanol groups can be shown by Near infrared spectroscopy in combination with second derivative techniques [9][10][11][12]. The approach provided a way to distinguish between adsorption of water by hydrogen boned vicinal groups , geminal and free silanol groups on the surface.…”

Section: Introductionmentioning

confidence: 99%

The Nature of Rest Silanol Groups on the Surfaces of Silica Based Solid Phase Extraction Materials

Christy

2013

AMR

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Abstract. Chemically bonded solid phase materials are very important in separation chemistry. The chemically modified silica gel contains rest silanol groups that can affect the retention properties when they are used for separation of compounds. Some commercially available solid phase extraction (SPE) materials based on silica gel were analysed for rest silanol groups by near infrared spectroscopy. The combination frequency of the water molecules in the 5500-5000 cm -1 region was used in identifying the nature of water molecules on the surface and the information was used to identify the types of silanol groups on the surface. Second derivative technique was employed in the detailed analysis.Nine different SPE materials including C18, C8, C 6 H 5 , NH 2 , OH, CN, SiOH, SA (SCX) and SB (SAX) were examined by near infrared spectroscopy for rest silanol groups. The results show that the non-polar and polar stationary phases contain vicinal silanol groups and the ion exchange solid phase materials contain free, vicinal and geminal silanol groups. IntroductionSolid phase extraction (SPE) columns are important tools of an analytical chemist in pre-concentrating analyte from solutions containing the analyte. The separation is carried out by passing the solution containing the component of interest through a column containing a suitable SPE material. When suitable SPE material used, the separation is based on the fact that the solid phase has greater affinity to the solute or components a chemist wants to separate from the solution matrix. This fact helps a chemist to preconcentrate either analyte from a solution matrix (isolation) or get rid of unwanted components (interference retention) in the solution matrix so that the filtrate is free from interfering components in the determination of the analyte. When the retained components on the SPE material are of interest then the components are eluted from the stationary SPE material using a suitable eluent (elution). Solid phase extraction is very widely used in isolating the analyte of interest from a variety of samples such as urine, blood serum, water etc. The mechanism of interaction of the components in the solution matrix and the solid stationary phase includes non polar, polar interactions, van der Waals interactions etc.

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“…These absorptions arise in the region 5200-5500 cm -1 (see Fig. 1) A summary of NIR absorptions of the silica gel samples can be found elsewhere [15].…”

Section: Introductionmentioning

confidence: 94%

Effect of Heat on the Adsorption Properties of Silica Gel

Christy¹

2012

IJET

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Abstract-Adsorption properties of silica gel have been attributed to the surface hydroxyl groups of silica gel. Some hydroxyl groups are free standing and called free silanol groups. Some are hydrogen bonded to neighbouring silanol groups. Christy has shown that a high silanol number and a balanced concentration proportionality between these two different types of hydroxyl groups is necessary for effective adsorption of water molecules.Thermal treatment of silica gel samples alters the proportions of these groups and the above fact was investigated by using thermally treated silica gel samples. Two silica gel samples of varying surface areas and silanol numbers were dried under vacuum at 200 o C and their adsorption characteristics were followed by using NIR spectroscopy. Then the samples were subjected to heating at 350, 450, 600 degrees to cause changes in the concentrations of the surface silanol groups and their surface and adsorption characteristics were followed.The results clearly indicate that the heating process both remove free and hydrogen bonded silanol groups and alter the ratio between the two. Furthermore, the heating causes reduction in silanol umber and upsets the balance in the proportionality of the silanol groups for effective adsorption of water molecules.

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State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

Cited by 44 publications

References 24 publications

Ordering of water in opals with different microstructures

Ordering of water in opals with different microstructures

The Nature of Rest Silanol Groups on the Surfaces of Silica Based Solid Phase Extraction Materials

Effect of Heat on the Adsorption Properties of Silica Gel

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