Silica gel

About: Silica gel is a(n) research topic. Over the lifetime, 22313 publication(s) have been published within this topic receiving 325516 citation(s). The topic is also known as: Amorphous silica & Precipitated amorphous silica.

The nature of the silica cage as reflected by spectral changes and enhanced photostability of trapped Rhodamine 6G

Abstract: Rhodamine 6G was embedded in a matrix of silica gel glass by the sol to gel technique. The special features of an inorganic oxide glass as a carrier of an organic dye are discussed in comparison with other solid environments, such as adsorption on powders and within porous glasses, thin films, and doping of plastic matrices. Among the advantages mentioned are photostability of the glass matrix, trapping of the dye molecule, and its total isolation from undesired interactions with its neighboring dye molecules, impurities, and photodecomposition products; nonleachability of the dye; the ability to reach stable very high dye concentrations; reduction of translational, rotational, and vibrational degrees of freedom of the trapped dye; good transparency down to the UV. Embedding R6G in the silica glass enables one to reach high concentrations without undesirable dye aggregation. Stokes shift is larger in the glass than in water. Photostability of the dye is higher in the glass than in water. A remarkable front-face fluorescence stability is observed. These observations, and a critical review of the literature, are used to elucidate the nature of the silica glass cage: it is suggested that it is a hydroxylic polar environment, though somewhat less polar than water. The rigidity of the cage is discussed in terms of required reorientation of the environment around an excited state.

A Recyclable Ru-Based Metathesis Catalyst

Abstract: A Ru carbene (8, Scheme 2) that contains an internal metal−oxygen chelate is an active metathesis catalyst and is readily obtained by the sequential treatment of Cl2Ru(PPh3)3 with (2-isopropoxyphenyl)diazomethane and PCy3 This Ru-carbene complex offers excellent stability to air and moisture and can be recycled in high yield by silica gel column chromatography The structures of this and related complexes have been unambiguously established by NMR and single-crystal X-ray diffraction studies

Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions.

Abstract: Increased utilization of mechanically stable synthetic matrices particularly silica gel as a solid support and its surface modification either by impregnation of organic ligands directly or covalent grafting through spacer unit for extractive concentration of trace elements are highlighted in the present article. Experimental evidences for existence of surface silanol and its chemical nature have explored the idea of silica surface modification. Recent methods of development in functionalized silica synthesis by attachment of various ligands or organic reagents to the silica surface and techniques of characterization of the modified surface have been reported. Analytical applications of various modified silica surfaces, in particular, adsorption of trace elements taking separation and preconcentration into account from complex synthetic mixture as well as natural water is presented.

Nuclear Magnetic Resonance Studies in Multiple Phase Systems: Lifetime of a Water Molecule in an Adsorbing Phase on Silica Gel

Abstract: Further evaluation studies of nuclear resonance relaxation phenomena of the hydrogen nuclei of HzO adsorbed on silica gel observed by means of radio frequency pulse techniques are described. A stochastic theory for multiphase systems sometimes encountered in relaxation phenomena is presented. Special emphasis is directed toward a theoretical understanding of two phase systems observed in the study of water vapor adsorbed on silica gel, Adsorption experiments are discussed which directly demonstrate, for a s ecific x / m value the simultaneous existence of (a) two phase behavior for transverse (T t ) relaxation measurements and (i) single hase behavior for longitudinal relaxation ( T I ) data. Finally, a close estimate is obtained of the life-time of a water molecuk in an adsorbing phase at low coverage on silica gel.