Search results for "Silanol"
showing 10 items of 58 documents
Improved hydrophobicity of inorganic–organic hybrid mesoporous silica with cage-like pores
2013
International audience; Hydrophobic ordered mesoporous silica particles with cage-like pores (SBA-1 type) were prepared through co-condensation of phenyltriethoxysilane (PhTES) and tetraethylorthosilicate (TEOS) at different TEOS/PhTES molar ratios. It is shown that the hydrophobic character of the particles is enhanced by increasing the phenyl loading (decreasing the TEOS/PhTES molar ratio) and that it could be further enhanced by subsequent trimethylsilyl (TMS) grafting on remaining silanol groups (TMS-PhSBA-1 sample). This increase of hydrophobicity has been evidenced on the internal surface (mesoporosity) of the particles using water adsorption and, on the external surface of the partic…
Structural organization of silanol and silicon hydride groups in the amorphous silicon dioxide network
2011
We present a study on the effects of an isothermal annealing treatment on a-SiO 2 having a significant content of silanol hydride groups (Si-H). We examined the properties of the IR absorption bands of silanol (Si-OH) and silicon hydride groups as a function of the duration of the thermal treatment. We showed that the Si-OH and Si-H groups contents decrease in a linearly correlated way. The annealing dynamics suggest that the two species are close to each other in the amorphous network. We showed that the profile of the silanol groups absorption band is the same as that observed in other commercial a-SiO 2 materials, irrespectively of the concomitant presence of nearby Si-H groups, and, mor…
Secondary chemical equilibria in reversed-phase liquid chromatography
2017
Abstract The addition of reagents to a reversed-phase liquid chromatography (RPLC) mobile phase enables the separation of ionizable compounds, inorganic anions, and metal ions, using conventional instrumentation, silica-based materials, and hydro-organic mixtures, thanks to a variety of secondary equilibria. This gives rise to several chromatographic modes, the main features of which are outlined in this chapter. The effect of the mobile phase pH on the retention of ionizable compounds is described, together with the recommended experimental practice. The mechanism of adsorption of amphiphilic anions or cations on the stationary phase to attract analytes with opposite charge, or suppress th…
The amorphous silica-liquid water interface studied by ab initio molecular dynamics (AIMD): local organization in global disorder
2014
International audience; The structural organization of water at a model of amorphous silica-liquid water interface is investigated by ab initio molecular dynamics (AIMD) simulations at room temperature. The amorphous surface is constructed with isolated, H-bonded vicinal and geminal silanols. In the absence of water, the silanols have orientations that depend on the local surface topology (i.e. presence of concave and convex zones). However, in the presence of liquid water, only the strong inter-silanol H-bonds are maintained, whereas the weaker ones are replaced by H-bonds formed with interfacial water molecules. All silanols are found to act as H- bond donors to water. The vicinal silanol…
Mn 12 single-molecule magnets incorporated into mesoporous MCM-41 silica
2003
Abstract The incorporation of four Mn12 derivatives, namely [Mn12O12(O2CR)16(H2O)4] (R=CH3 (1), CH3CH2 (2), C6H5 (3), C6F5 (4)), into the hexagonal channels of the MCM-41 mesoporous silica have been studied. Only the smallest clusters 1 and 2 that are those with compatible size with the pores of MCM-41 could be incorporated into the mesoporous silica. Powder X-ray diffraction (XRD) analysis and N2 adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn12 clusters are inside the pores. The magnetic properties of the MCM-41/1 nanocomposite material indicate that the structure of the cluster is maintained after incorporat…
Computational study of water adsorption on halloysite nanotube in different pH environments
2020
Abstract The comprehension of structural and energetic features of halloysite nanotube (HNT) in different chemical environments plays a crucial role in developing new HNT based materials. So far these aspects were investigated by means of laboratory techniques that hardly are able to provide hints at atomistic level of detail. Our investigation aims to obtain such accurate informations through density functional theory calculations on HNT models, in order to figure out the most stable forms of HNT under different pH conditions. It turns out that, at low pH, the preferred protonation sites are located in the inner aluminic surface while in alkaline medium the silicic layer can show delocaliz…
Modification of vacuum-ultraviolet absorption of SiOH groups in SiO2 glass with temperature, F2 laser irradiation, and H–D isotope exchange
2006
Abstract Variations of vacuum-ultraviolet (VUV) absorption of silanol (SiOH) groups in synthetic wet SiO 2 glass with temperature, exposure to F 2 laser light, and with H–D isotope exchange were examined at photon energies below 8 eV. The intensity of the VUV absorption band decreases with cooling or with exposure to F 2 laser light. The spectral changes in both cases are qualitatively similar and are attributed to an alternation of the bonding configuration of SiOH groups from isolated into hydrogen-bonded states. However, the resultant states are distinctly different: the hydrogen-bonded state formed on cooling is restored reversibly to the isolated state on heating, while that induced by…
Understanding the Acidic Properties of the Amorphous Hydroxylated Silica Surface
2019
Amorphous silica is an intrinsic challenging system to study. In the last decades, some particular chemical properties have been discovered and described, but their description and understanding at the molecular level are experimentally difficult. Therefore, theoretical quantum chemical methods and descriptors, combined with experimental input, are a very appropriate set up to tackle this topic. In this study, the acidity of silanol groups of amorphous silica in hydrated conditions is investigated. Special attention has been drawn to the chemical shift, but also Bader charges, and vibrational frequencies with their intensities. The known bimodal acidity behavior was recovered and rationaliz…
Temperature dependence of the absorption properties of silanol groups in amorphous : Are silanol groups organized in clusters?
2011
Abstract We present a study on the vacuum-ultraviolet (VUV) and infrared (IR) absorption of silanol groups in amorphous silicon dioxide ( a - SiO 2 ) in the range of temperature from 4 to 300 K. The observed temperature induced modifications of IR and VUV absorption spectra are interpreted as due to a process of conversion of free into H-bonded silanol groups. The changes of the amplitude of the VUV absorption spectra are shown to be linearly correlated to the changes of the IR absorption of free Si–OH groups. This point together with the evidence that the shape of the Si–OH VUV absorption does not depend on temperature demonstrates that the different silanol group sub-species have differen…
The Nature of Rest Silanol Groups on the Surfaces of Silica Based Solid Phase Extraction Materials
2013
Author's version of an article in the journal: Advanced Materials Research. Also available from the publisher at: http://dx.doi.org/10.4028/www.scientific.net/AMR.650.66 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…