Comparative study of the surface hydroxyl groups of fumed and precipitated silicas. 2. Characterization by infrared spectroscopy of the interactions with water

Burneau, A.; Barrès, Odile; Gallas, J.P.; Lavalley, J.C.

doi:10.1021/la00098a008

Cited by 194 publications

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“…The absorptions at 1628 cm -1 , 1639 cm -1 and 1631 cm -1 , ν 2 , were assigned to silica-1, silica-2 and silica-3, respectively suggesting that in the three samples the water molecules are proton donors 31 . Thus, the basicity of the silica surface can be characterized by an analysis of the shapes and positions of the bands associated with the surface adsorbed water vibrational modes 31,32 . The greater the wavenumber of the ν 2 absorption, the higher the basicity of the silica surface 31,32 and therefore the increasing order of basicity is silica-1 < silica-3 < silica-2.…”

Section: Characterization Of the Modified Silicamentioning

confidence: 91%

“…Detailed interpretation of the IR of various forms of silica has been published in the literature [26][27][28][29][30][31] .…”

Section: Characterization Of the Modified Silicamentioning

confidence: 99%

“…Thus, the basicity of the silica surface can be characterized by an analysis of the shapes and positions of the bands associated with the surface adsorbed water vibrational modes 31,32 . The greater the wavenumber of the ν 2 absorption, the higher the basicity of the silica surface 31,32 and therefore the increasing order of basicity is silica-1 < silica-3 < silica-2. As expected, a decrease in the wavenumber of the band due to the combination ν 2 + ν 3 of the hydrogen-bonded H 2 O molecules is observed and follows the trend silica-1 > silica-3 > silica-2.…”

Section: Characterization Of the Modified Silicamentioning

confidence: 99%

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Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

Pinto¹,

Braga²,

Rezende³

et al. 2000

J. Braz. Chem. Soc.

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O uso de cromatografia sob pressão ("flash chromatography") utilizando-se coluna de gel de sílica impregnada com hidróxido de potássio levou ao fracionamento dos constituintes químicos de Copaifera cearensis Huber ex Ducke. A fração ácida, após esterificação com diazometano, foi analisada por cromatografia gasosa de alta resolução acoplada à espectrometria de massas ou à espectrometria no infravermelho, possibilitando a identificação de onze diterpenos ácidos. Fracionamentos adicionais da fração ácida por cromatografia líquida de alta eficiência em fase reversa levaram ao isolamento de diversos ácidos diterpênicos e de um sesquiterpênico que foram identificados através de seus dados espectroscópicos. A análise da sílica impregnada com hidróxido de potássio mostrou que, além da deposição do hidróxido na superfície da sílica, ocorreu troca iônica com formação de resíduos Si-OK.Various acid diterpenes of Copaifera cearensis Huber ex Ducke were isolated from the crude extract by flash Silica Gel/Potassium Hydroxide Chromatography. The main components were identified by GC-MS analyses. Further fractionation by reversed phase (RP) semi-preparative HPLC allowed isolation and identification of minor components and provided additional spectral data of those compounds. It was possible to detect the presence of eleven acid diterpenes in addition to a sesquiterpene acid. In addition to potassium hydroxide deposition on the silica surface, the presence of Si-OK residues, resulting from a cation exchange process, was established.

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Section: Characterization Of the Modified Silicamentioning

confidence: 91%

“…Detailed interpretation of the IR of various forms of silica has been published in the literature [26][27][28][29][30][31] .…”

Section: Characterization Of the Modified Silicamentioning

confidence: 99%

Section: Characterization Of the Modified Silicamentioning

confidence: 99%

See 1 more Smart Citation

Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

Pinto¹,

Braga²,

Rezende³

et al. 2000

J. Braz. Chem. Soc.

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“…The classical sol-gel science reported by Iler [52] describes that silanol groups form less rigid structure within the silica matrix which are less stable and interact with water molecules. Likewise silica rehydration occurs, where siloxane bridges break down forming silanol groups [53]. Many of these silanol groups become unconstrained and mobile when exposed to water, thus broadening the pore sizes of silica structures [54].…”

Section: Membrane Performancementioning

confidence: 99%

High performance ES40-derived silica membranes for desalination

Wang¹

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Access to potable water has become one of the top 10 global problems facing our contemporary society. Desalination of vast amounts of seawater is a promising measure to ameliorate this stress.Numerous thermal and membrane processes have been employed to desalt seawater, of which reverse osmosis (RO) using polymeric membranes is the most mature technology and has been regarded as the benchmark in current desalination technologies. However, due to the high pressure requirement for RO operation, other membrane processes, such as membrane distillation and pervaporation have been developed as the alternatives to further reduce the energy cost.Furthermore, due to the lack of chemical/thermal stability and high tendency to scaling and fouling of polymeric membranes, novel inorganic membranes, in particular silica derived membranes, are emerging as potential candidates for desalination. The majority of published works on silica membranes utilizes tetraethyl orthosilicate (TEOS) as the silica precursor and interlayers are generally required to reduce the roughness of the porous substrates, followed by 4 to 6 thin-film coatings and calcinations with heating rates of 1-2 º C min -1 to form defect free silica membranes, which consume 10-14 days with extra cost. Therefore, the major target of this research is to produce interlayer-free silica membranes fabricated by rapid thermal processing (RTP) for desalination application.Ethyl silicate 40 (ES40) is used as precursor to prepare silica membranes in this work owing to their superior thermal stability as compared to the TEOS analogous product. Firstly, the sol-gel processing of ES40 was investigated in this thesis. At different temperatures and H 2 O/Si ratios, ES40 underwent various degrees of phase separation behaviour and sol-gel reactions. It was found that the hydrolysis and condensation reactions decreased with decreasing reaction temperature.Dense silica structures were obtained using low H 2 O/Si ratios, whereas higher porosity was produced from a phase-separated sol-gel system with high H 2 O/Si ratios. This tailoring process facilitated further condensation reactions and crosslinking of silica chains, leading to stronger silica matrices which were more resistant to densification.The second part of this work is focused on improvement of the hydrostability of ES40-derived silica membrane materials by adjusting the reactant ratios of sol-gel synthesis process, as the low resistance of silica membranes to water vapor attack, which induce enlargement of the pore size followed by failure in salt rejection, can be detrimental to desalination performance. Investigations were carried out on the effects of reactant ratios on the microstructure of the silica matrices and their hydrothermal stability under harsh conditions (550 °C, 75 mol% vapour). The most hydrothermally stable matrix was obtained by decreasing the ethanol ratio whilst increasing water II and acid ratios. The improved hydrothermal stability was attributed to the further transition of silanol to siloxa...

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“…In the OH region, only a broad band around 3530 cm -1 decreased on addition of 40 mTorr of BF3 (spectrum 1), which means that hydrogen-bonded OH groups were used for the formation of the species A, B, and C. No decrease was observed in intensity of the 3746 cm -1 band due to the isolated OH groups, as also pointed out by Morrow et al 6 The remaining broad band centered around 3660 cm -1 is due to inaccessible OH groups which do not take part in any reaction with molecules. 4,[9][10][11][12][13] The degree of the increase was larger than that of the decrease in the region of 1600 -1300 cm -1 after the addition of BF3. This is because the species A that formed first was transformed to the species B and C at a larger rate than that of the transformation of gaseous BF3 to the species A.…”

Section: Cases Of Bf3 With Low Pressure and 473-k-preheated Silicamentioning

confidence: 99%

Infrared Spectroscopic Analyses of Transformations of Chemical Species on the Silica Highly-Reacted with Gaseous BF 3

2003

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Transformations of chemical species formed by the reaction of gaseous BF3 with high pressure and silica preheated at 473 and 1093 K were studied with the use of infrared absorption spectrometry. The species containing -BF2 and the species containing >BF were transformed to each other on the highly-reacted silica depending on the pressure of BF3 in cell, and some of the species containing -BF2 were also desorbed without their transformations to the species containing >BF. H2O played important roles in these transformations.

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Comparative study of the surface hydroxyl groups of fumed and precipitated silicas. 2. Characterization by infrared spectroscopy of the interactions with water

Cited by 194 publications

References 0 publications

Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

Separation of acid diterpenes of Copaifera cearensis huber ex ducke by flash chromatography using potassium hydroxide impregnated silica gel

High performance ES40-derived silica membranes for desalination

Infrared Spectroscopic Analyses of Transformations of Chemical Species on the Silica Highly-Reacted with Gaseous BF 3

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