scholarly journals The Nature of Silanol Groups on the Surfaces of Silica, Modified Silica and Some Silica Based Materials

2014 ◽  
Vol 998-999 ◽  
pp. 3-10 ◽  
Author(s):  
Alfred A. Christy
Keyword(s):  
Silica Gel ◽  
Near Infrared ◽  
Water Molecules ◽  
Modified Silica ◽  
Near Infrared Reflectance ◽  
Modified Silica Gel ◽  
Silanol Groups ◽  
Near Infrared Spectra ◽  
Chemically Modified Silica ◽  
Adsorption Of Water

Silica gel, a material that is produced from the condensation polymerisation of silicic acid, contains surface silanol groups formed during the condensation. The silanol groups on the surface are mostly of free and vicinal silanol groups. These silanol groups can be modified in several different ways. Thermal treatment and hydrothermal treatment can be carried out to alter the concentration proportions between free and hydrogen bonded silanol groups on the surface. They can also be chemically treated with suitable chlorosilanes to modify the silanol groups into polar or non polar materials that can be used in separation science.This article explores the chemical nature of silanol groups on the surfaces of different materials. Near infrared reflectance spectroscopy was used as the instrumental technique in this study. The silanol groups classifications were made by analyzing the near infrared spectra obtained during the adsorption of water molecules. Absorption of the combination frequencies of water molecules in the region 5500- 5000 cm-1were used in characterizing the silanol groups on the surfaces. Second derivative technique was employed in the resolution and detailed analysis of these absorptions.The study reveals that the materials contain free, vicinal and gem silanol groups. Silica gel contains free and vicinal silanol groups, thermally treated silica gel contains fewer vicinal silanol groups compared to the base silica gel, and hydrothermally treated silica gel contains higher concentrations of vicinal silanol groups compared to the base silica gel. Furthermore, the chemically modified silica gel contains vicinal or geminal silanol groups depending on the type of functionality introduced.

scholarly journals Comparison of adsorption properties of commercial silica and rice husk ash (RHA) silica: A study by NIR spectroscopy

2021 ◽  
Vol 19 (1) ◽  
pp. 426-431
Author(s):  
Alfred A. Chirsty ◽  
Pathmanathan Sivarukshy
Keyword(s):  
Silica Gel ◽  
Rice Husk ◽  
Infrared Spectra ◽  
Near Infrared ◽  
Rice Husk Ash ◽  
Adsorption Properties ◽  
Water Molecules ◽  
Silanol Groups ◽  
Near Infrared Spectra ◽  
Adsorption Of Water

Abstract Adsorption properties of Silica gel (commercial silica), rice husk ash (RHA) silica, and their hydrothermally treated products towards water molecules were studied in this work. RHA silica was prepared by heating rice husk to 650°C for 4 h after pretreatment with hydrochloric acid. Portions of the samples of silica were evacuated at 200℃ and then allowed to adsorb water molecules from the surrounding air at either 42 or 50% humidity. The near infrared spectra of these samples were measured at different time intervals during their adsorption of water molecules. The evolved near infrared spectra were analyzed using second derivative techniques. Adsorption properties of these samples were further studied by gravimetric analysis. Surface functionalities and adsorption evolution of water molecules on silica samples studied showed that the adsorption of water molecules on commercial silica gel sample and RHA silica Samples takes place readily with hydrogen-bonded silanol groups on the surfaces of the samples. This adsorption arising from the OH stretching and bending vibrations of these water molecules gives rise to a band at 5,270 cm−1 in the near infrared region. The adsorbed water molecules then continue at the free silanol groups which is indicated by the absorption around 5,314 cm−1. The results clearly show that the silica made from rice husk adsorb water in the same manner as the commercial silica, but the quantity of water molecules adsorbed is less compared to commercial silica used in this experiment. However, the study clearly shows that the rice husk silica can replace the commercial silica as a substitute for desiccant purposes in industry.

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

2013 ◽  
Vol 650 ◽  
pp. 66-71 ◽  
Author(s):  
Alfred A. Christy
Keyword(s):  
Infrared Spectroscopy ◽  
Solid Phase Extraction ◽  
Silica Gel ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Solid Phase ◽  
Water Molecules ◽  
Phase Extraction ◽  
Modified Silica Gel ◽  
Silanol Groups

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, C6H5, NH2, 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.

scholarly journals Water Adsorption Properties of Free and Dehydrated β-Cyclodextrin Studied by near Infrared Spectroscopy and Gravimetry

2016 ◽  
Vol 689 ◽  
pp. 143-147 ◽  
Author(s):  
Alfred A. Christy
Keyword(s):  
Hydrogen Bonds ◽  
Infrared Spectra ◽  
Water Adsorption ◽  
Near Infrared ◽  
Adsorption Properties ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Oh Groups ◽  
Near Infrared Spectra ◽  
Adsorption Of Water

β-cyclodextrin, like other carbohydrates has a tendency to adsorb water molecules and the properties are attributed to the hydroxyl groups in the molecules. β-cyclodextrin, the cyclic oligomer of glucose has a hydrophobic interior and hydrophilic exterior. The cyclic structure favours the formation of hydrogen bonds between the OH groups on the adjacent glucose units and affects the formation of hydrogen bonds with water molecules. The hydoxyl groups engaged in hydrogen bondings can be eliminated at high temperatures and the adsorption properties of the dehydrated β-cyclodextrin will depend on the new functional groups formed. The aim of the report is to discuss the issue of the water adsorption properties of free and dehydrated β-cyclodextrin. Dry β-cyclodextrin and dehydrated β-cyclodextrin at temperatures 250, 300 and 350 °C were allowed to adsorb water from a humidity controlled air environmennt and the evolving near infrared spectra were measured using a near infrared spectrometer equipped with a transflectance accessory. The near infrared spectra in the region 10,000-4000 cm-1 and their second and fourth derivative profiles were used in studying the variation in the adsorption characteristics of dehydrated β-cyclodextrin. The results of the analyses show that the adsorption of water by β-cyclodextrin decreses at 300 °C compared to 200 and 250 °C. Dehydration forms more of the ethereal type-O-bonds in the molecule and explains the decrease in the water molecular adsorption at higher dehydration temperatures.

Potentiometric study using chemically modified silica gel with pyridinium as membrane for ClO 4 − ions

1995 ◽  
Vol 117 (3-4) ◽  
pp. 239-244 ◽  
Author(s):  
Lilian L. Lorencetti ◽  
Yoshitaka Gushikem ◽  
Lauro T. Kubota ◽  
Graciliano de Oliveira Neto ◽  
João R. Fernandes
Keyword(s):  
Silica Gel ◽  
Modified Silica ◽  
Modified Silica Gel ◽  
Potentiometric Study ◽  
Chemically Modified ◽  
Chemically Modified Silica ◽  
Chemically Modified Silica Gel
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