Silanol groups SiOH

The most widely used particulate support is diatomaceous earth, which is composed of the silica skeletons of diatoms. These particles are quite porous, with surface areas of 0.5-7.5 m /g, which provides ample contact between the mobile phase and stationary phase. When hydrolyzed, the surface of a diatomaceous earth contains silanol groups (-SiOH), providing active sites that absorb solute molecules in gas-solid chromatography. 

It is well know that the zeolite materials synthesized in alkaline systems usually have a high number of silanol groups (=SiOH) named defect groups [10] which possess a moderated Bronsted acidity [11]. Oppositely, Silicalite-1 synthesized in fluorine media are relatively defect-free [12] and the fluorine ions remain in the small cages of the MFI structure even after the calcination process [12]. The 29Si-NMR analyses carried out on samples Na-Silicalite-1 and F-Silicalite-1 confirm the presence of silanol groups only on the SI support surface (results not showed). Delaminated zeolites (ITQ-6) are obtained by exfoliation of as-synthesized lamellar precursor zeolites [13]. After this process, the final structure of the delaminated zeolite results in a completely hydroxylated and well-ordered external surface [13]. 

Figure 20 shows the H MAS NMR spectra of zeolite HZSM-5 (ksi/wai — 21.5) before (a) and after (b) adsorption of acetone-tfg at room temperature. The ll MAS NMR signals at 4.0 and 1.8 ppm are attributed to bridging OH groups (SiOHAl) and silanol groups (SiOH), respectively (Fig. 20a). Upon adsorption of 0.33 mmol...

Silanes react with silanol groups ( SiOH) on silicon surfaces according to the reaction shown in Fig. 10.5 [423] (review Ref. [424]). This reaction, which is usually carried out in organic solvents, is called silanization. Trifunctional silanes bind to the surface silanol groups,... 

The adsorption characteristics of MCM-41 for polar molecules greatly depend on the concentrations of surface silanol groups (SiOH) [121], It has been demonstrated that different types of SiOH groups exist over MCM-41 surfaces, which can be qualitatively and quantitatively determined by a number of techniques [121],... 

Silanol groups SiOH condense with OH groups of MOH surfaces, where M is a metal that will form a silicate at the pH and temperature involved. The reaction is represented as follows ... 

Silica particles have surface silanol groups, — SiOH. These are used for chemical bonding of stationary phases by silination reactions with chlorosilanes ... 

The presence of silanol groups, =SiOH, at the surface of silica gels has been demonstrated in many ways [17]. It has been supposed that at the surface of glass (= SiOX) groups exist which may be silanol (X = H) or pseudo silicate groups X = Na, for example. 

From the chemical standpoint a nucleus of an HDS particle is a three-dimensional polymer whose structural units are silicon-oxygen tetrahedra bonded by disiloxane bridges Si—O—Si. On the surface of HDS particles there are groups O—H chemically bonded with silicon atoms (silanol groups SiOH). The hydroxylic cover of HDS gives rise to a high hydrophilicity of its surface and, correspondingly, to its ability to sorb polar molecules. 

The silicon ion on the end-position of the chain, forming the silanol group SiOH, tends to pass to the solution with the ion H SiO formation, which is disturbing the equilibrium in solution, causing the releasing of Ca + ions to the liquid phase. The process is intenupted on the structural element Y (see Fig. 7.7). 

For the electrostatic boundary condition, in this work we use the Basic Stem (BS) model developed by Behrens and Grier [9] in which the silica surfaces acquire charges in contact with water by the dissociation of silanol groups, SiOH SiO + H, so that the zeta potential (0 on the interface can be expressed as a function of the surface charge density (cr) ... 

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