Silica gel

About: Silica gel is a research topic. Over the lifetime, 22313 publications have been published within this topic receiving 325516 citations. The topic is also known as: Amorphous silica & Precipitated amorphous silica.

Properties and diversity of C18 bonded phases

Abstract: The effect of the properties of the silica gel matrix, and of the octadecylsilane used, on the chromatographic selectivity of C18 bonded phases is described. Preparation of bonded phases with monochlorodimethyloctadecylsilane is easier because absolute water exclusion is not required in this case. The surface coverage (μmol/m2) is smaller than with dichloromethyl- or trichlorooctadecylsilanes, but in these cases a secondary silanization with HMDS is essential to remove newly formed silanol groups. Bonded phases on Si 60 give the largest amount of hydrocarbon per unit column volume, large k′ values and good selectivity, however, surface coverage and efficiency of these packed columns is less than with Si 100 silica. The chemical properties of the silica surface also influence bonded phase selectivity. Bonded phases should not be compared with only a single eluent, because properties of bonded phases differ with test solutes and test conditions, i.e. eluent composition.

Surface-Mediated Reactions. 8. Oxidation of Sulfides and Sulfoxides with tert-Butyl Hydroperoxide and OXONE1

Abstract: Silica gel and alumina have been found to mediate the oxidation of sulfides and sulfoxides with (CH3)3COOH and OXONE. With all combinations except (CH3)3COOH/alumina, sulfides were oxidized with reasonably good selectivity to sulfoxides. These studies afforded insights into the mechanisms of surface-mediated processes. Adsorption studies, combined with the effect of partial silylation of silica gel, indicate that oxidation of sulfides by (CH3)3COOH/silica gel occurs at least predominantly via nucleophilic attack by the sulfide on (CH3)3COOH, which is activated by being bound to isolated silanol sites on the silica gel surface (Scheme 2), whereas oxidation of sulfoxides involves nucleophilic attack by (CH3)3COOH on the sulfoxide, which is activated by being bound to associated silanol sites (Scheme 3). Oxidation of sulfoxides by (CH3)3COOH/alumina involves attack of (CH3)3COO- on the sulfoxide bound to free Al+ sites on the surface (Scheme 4B). Mediation of oxidation by OXONE involves instead activation by...

One-step immobilization of glucose oxidase in a silica matrix on a Pt electrode by an electrochemically induced sol-gel process.

Abstract: We demonstrate here that the electrochemical generation of hydroxyl ions and hydrogen bubbles can be used to induce the synthesis of enzyme- or protein-encapsulated 3D porous silica structure on the surface of noble metal electrodes. In the present work, the one-step synthesis of a glucose oxidase (GOD)-encapsulated silica matrix on a platinum electrode is presented. In this process, glucose oxidase was mixed with ethanol and TEOS to form a doped precursory sol solution. The electrochemically generated hydrogen bubbles at negative potentials assisted the formation of the porous structure of a GOD-encapsulated silica gel, and then the one-step immobilization of enzyme into the silica matrix was achieved. Scanning electron microscopy (SEM) and scanning electrochemical microscopy (SECM) characterizations showed that the GOD-encapsulated silica matrix adhered to the electrode surface effectively and had an interconnected porous structure. Because the pores started at the electrode surface, their sizes increased gradually along the distance away from the electrode and reached maximum at the solution side, and effective mass transport to the electrode surface could be achieved. The entrapped enzyme in the silica matrix retained its activity. The present glucose biosensor had a short response time of 2 s and showed a linear response to glucose from 0 to 10 mM with a correlation coefficient of 0.9932. The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3. The apparent Michaelis-Menten constant (K m app) and the maximum current density were determined to be 20.3 mM and 112.4 microA cm-2, respectively. The present method offers a facile way to fabricate biosensors and bioelectronic devices in situ.