Sol-gels, doped

Figure 6. Tip of the 20-pm tip of a fiber optic oxygen microsensor. The tip is coated with a ormosil-type of sol-gel doped with a ruthenium indicator for oxygen that display red luminescence. The sensor measures its decay time as a function of oxygen partial pressure.

The fabrication and characterization of a fiber optic pH sensor based on evanescent wave absorption was presented by Lee63. The unclad portion of a multi-mode optical fibre was coated with the sol-gel doped with pH sensitive dye. The sensitivity of the device increased when the multiple sol-gel coatings were used in the sensing region. The dynamic range and the temporal response of the sensor were investigated for two different dyes -bromocresol purple and bromocresol green. 

The two water-soluble porphyrins, 5,10,15,20-tetra(4-N-methyl-pyridiniumyl) porphyrin (H2TMPyP4+) and 5,10,15,20-tetra(4-sulfonato) porphyrin (H2TPPS4 ), were immobilized in the silica sol-gel matrix and served as the pH sensors as well65. The sol-gels doped with porphyrin were... 

A thin film dissolved oxygen sensor was fabricated by entrapping erythrosin B in a sol-gel matrix95. The silica sol-gel doped with the dye was deposited onto the cleaned glass slides by the spin-coating method. The sensor was linear in the most useful range of dissolved oxygen concentrations, up to 9.1 mg l 1 concentration obtained in air saturated water at 20 °C. 

FIGURE 16.4 Scanning electron micrographs of glassy carbon electrodes coated with (a) titania sol-gel and (b) titania sol-gel doped with HRP (adapted from [35]). 

Starting in late 1996, the University of Jerusalem s Professor David Avnir, the pioneer of sol gel doped materials, has been much more than a mentor. I thank him also for all he has done for me in all these years. The wonderful work of Sharon Marx with chiral sol-gels is impressive, and also, Sharon, the celebration of Hanukkah at your parents home in Jerusalem in late 2001 will not be forgotten. 

In 1995, commenting on the physical nature of the sol-gel entrapment of molecules in porous oxides, the inventor of sol-gel doped materials (first reported in the Journal of Physical Chemistry ten years before)6 emphasized how it was really remarkable to see how many applications... 

Catalysis by sol gel doped silica-based materials has become in the last 20 years a prominent tool to synthesize a vast number of useful molecules both in the laboratory and in industrial plants.12 The underlying basic concept of all sol-gel applications is unique one or more host molecules are entrapped by a sol-gel process within the cages of an amorphous metal oxide where they are accessible to diffusible reactants through the inner pore network, which leads to chemical interactions and reactions (Figure 5.3). 

Another important highly selective and stable hydroformylation sol gel catalyst is made of silica-supported rhodium covalently bound to supported Xantphos family of ligands.36 By incorporating monoliths of the sol-gel doped material into the paddles of an autoclave stirrer, the catalyst (Rotacat) can be used in a continuous liquid flow process. A single sample of this catalyst was used for a variety of different hydroformylation reactions under widely varying conditions over a period of more than a year, still retaining its selective activity. 

Other properties which have contributed to the attractiveness and versatility of the sol-gel doping approach are the chemical, photochemical and electrochemical inertness as well as the thermal stability of the matrix the ability to induce electrical conductivity16 the richness of ways to modify chemically the matrix and its surface as well as the above-mentioned controllability of matrix structural properties the enhanced stability of the entrapped molecule1,17 the ability of employing the chromatographic properties of the matrix for enhanced selectivity and sensitivity of reactions with the dopant4 the simplicity of the entrapment procedure the ability to obtain the doped sol-gel material in any desired shape (powders, monoliths, films, fibers) and the ability to miniaturize it18,19. 

These Si02 microcapsules doped with organic sunscreen molecules were the first large-scale commercial application of sol-gel-doped microparticles labeled UV-Pearls. In cosmetics and medicine, water-based products or emulsions with external water phase are preferred over oil-based products (ointments) or W/0 emulsions. 

Hasani M, Coto Garcia AM, Costa-Fernandez JM, Sanz-Medel A (2010) Sol-gels doped with polymer-coated ZnS/CdSe quantum dots for the detection of organic vapors. Sens Actuators B 144 198-202 Hines MA, Guyot-Sionnest P (1996) Synthesis and characterization of strongly luminescing ZnS-capped CdSe nanocrystals. J Phys Chem 100 468-471... 

Sol-gel-doped SrTiOs with Y and/or Co compounds of formula Y (Sri (Coj,Tii j,03 g were able to photodegrade 2-propanol under solar irradiation giving rise to propanone and acetaldehyde as intermediate products along with CO2 as the final oxidation species (Figure 17.13) [63]. Pure SrTiOs allowed the disappearance of isopropanol after about 90 min of irradiation. During the same run, propanone concentration increased and its degradation began when isopropanol concentration was almost zero. However, propanone, the most stable intermediate, was almost completely oxidized to CO2 and H2O after 360 min of irradiation. 

Redox functionality, surface attributes, permselectivity, and specific interactions are routinely tailored on the molecular scale by sol-gel doping, covalent bonding or impregnation. Comprehensive reviews are available in references (Avnir, 1994, 1995 Dave, 1994), and therefore these methods are only briefly addressed here. 

Nonlinear optical and electrooptic properties of hybrid sol-gels doped with organic chromophores. Opt, Mater., 28, 992-999. 

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