Confirmation and application of transmission near infrared absorption technique for absolute quantitation of functional groups on silica gel

Egeberg

2005

Analyst

Concentration of silanol groups on silica gel surface has been quantitatively determined using the deuterium exchange method. Simple and effective procedures have been used in pre-sample drying, deuterium exchange and extraction of resulting isotopic mixture from the exchange reaction. Each of four silica gel samples with varying surface area has been subjected to pre-drying to remove adsorbed water and then quantitatively mixed with deuterium oxide in a steel bomb for isotopic exchange. The resulting D(2)O/water mixture was then extracted by applying high pressure using infrared pellet press. The infrared spectrum of the isotopic mixture was measured and the composition was then determined by a multivariate calibration model established between infrared profiles of water in D(2)O standard mixtures and their composition. The results show that the silanol group concentration determined agrees with the values reported in the literature.

Section: Msi-oh(s)mentioning

confidence: 99%

Quantitative determination of surface silanol groups in silicagel by deuterium exchange combined with infrared spectroscopy and chemometrics

Egeberg

2005

Analyst

“…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%

“…Hence, thick samples can be used in the transmission measurements. However, measurements of dry samples of silica gel needed special setups [12].…”

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

Vibrational Spectroscopy

2010

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

“…Heating can reduce the concentration of hydrogen bonded OH groups of the hydrothermally treated silica gel samples and increase the concentration of free silanol groups by eliminating water from these goups. 18 The above experiments and findings clearly demonstrate that there is a strong relationship between adsorption and the concentrations of hydrogen bonded and free silanol groups on the silica gel surface. Furthermore, these findings pave the way for exploring ways to alter the OH concentrations on the surface so that new silica gel materials can be produced with enhanced adsorption properties.…”

Section: Discussionmentioning

confidence: 61%

“…They cannot be reformed by chemical reaction. Heating can reduce the concentration of hydrogen bonded OH groups of the hydrothermally treated silica gel samples and increase the concentration of free silanol groups by eliminating water from these goups …”

Section: Discussionmentioning

confidence: 99%

Effect of Hydrothermal Treatment on Adsorption Properties of Silica Gel

2011

Ind. Eng. Chem. Res.

It has been proven by coupling near infared spectroscopy to second derivative processing of the spectra that the free and hydrogen bonded silanol groups attached to water molecules absorb at 5314 and 5270 cm−1, respectively. The same method was employed to probe the surface of the hydrothermally treated silica gel samples after pretreatment and evacuation at three different temperatures. The chemical and physical properties of silica gel depend on the nature of the surface silanol groups. Free silanol groups and hydrogen bonded silanol groups play an important role in adsorption of water molecules. Any change or variation in the silanol groups is expected to change the adsorption properties of any silica gel. Two silica gel samples with varying surface characteristics were used in this study. After heating and evacuating at 200, 750, and 1100 °C, the samples were hydrothermally treated in steel bombs and their surface functionalities were probed using near-infrared spectroscopy. The same samples were also dehydroxylated at 450 and 650 °C and analyzed by near-infrared spectroscopy. Furthermore, effectiveness of the treated samples in adsorbing water molecules was followed by monitoring the mass of water adsorbed by silica gel. These investigations form the basis for understanding the relationship between adsorption effeciveness and types of silanol groups on silica gel surface. The results clearly indicate that the hydrothermal treatment of silica gel pretreated at temperatures up to 750 °C increases the concentration of hydrogen bonded silanol groups on the silica gel surface. The sample treated at 1100 °C did not undergo any change under hydrothermal treatment. The concentration of free silanol groups increases in the dehydroxylated samples. The results also show that the adsorption rates of water molecules on the surface decrease significantly after pretreatment of these samples at a particular humidity.