Porous Sol-gel Silica Research Articles

Tailoring of Sol−Gel Films for Optical Sensing of Oxygen in Gas and Aqueous Phase

Sol-gel-based optical sensors for both gas-phase and dissolved oxygen have been developed. Both sensors operate on the principle of fluorescence quenching of a ruthenium complex which has been entrapped in a porous sol-gel silica film. A comprehensive investigation was carried out in order to establish optimal film-processing parameters for the two sensing environments. Both tetraethoxysilane and organically modified sol-gel precursors such as methyltriethoxysilane and ethyltriethoxysilane were used. Film hydrophobicity increases as a function of modified precursor content, and this was correlated with enhanced dissolved oxygen (DO) sensor performance. Extending the aliphatic group of the modified precursor further improved DO sensitivity. The influence of water/precursor molar ratio, R, on the sol-gel film microstructure was investigated. R value tailoring of the microstructure and film surface hydrophobicity tailoring were correlated with oxygen diffusion behavior in the films via the Stern-Volmer constants for both gas phase and DO sensing. Excellent performance characteristics were measured for both gas-phase and DO oxygen sensors. The long-term quenching stability of DO sensing films was established over a period of 6 months.

The increase in pH during aging of porous sol-gel silica spheres

The increase in pH in the hydrothermal fluid is studied after hydrothermal aging of porous silica gel spheres of 1–3 mm diameter. The porous silica spheres are formed by the sol-gel process from a supersaturated silica solution. The increase of the pH of the hydrothermal solution affects the silica solubility. A model to explain the increase in pH assumes condensation of sodium complexed silanol groups and the release of ionized monosilicic acid in the fluid. The existence of sodium complexed silanol groups is demonstrated by surface titration experiments.

Organically-doped sol—gel based tube detectors: Determination of iron(II) in aqueous solutions

A novel type of disposable sensor for the determination of iron(II) in aqueous solution is described. The iron sensor serves to exemplify a new class of disposable field tests for field analysis of water pollutants. The sensors are comprised of capillary glass tubes filled with porous sol—gel silica powder doped with o-phenanthroline. When a sample solution is passed through a tube detector the iron ions are complexed by the immobilized o-phenanthroline and a stained section of the capillary develops. Metrological characteristics of these detectors including precision and accuracy and chemical interferences by heavy metals and humic acids are discussed.

A Tunable Visible Solid State Laser

Abstract Laser operation and radiative properties of organically doped porous sol-gel silica have been studied using a range of cavities. Measurements of diffusion, distribution and long term photostability of dopant dye molecules are described. Laser oscillation at wavelengths of between 360 and 630 nm are reported. This represents a substantial increase over the range previously reported for organic dye doped silica lasers. In a Littrow configuration a tuning range of 60 nm and a conversion efficiency of 16% have been observed. A linewidth of <0·05 nm has been obtained using a grazing incidence cavity.

Long-lived photoinduced charge separation in a redox system trapped in a sol–gel glass

A KEY feature in the mechanism of photosynthesis is the initial storage of a substantial fraction of the light energy in the form of a long-lived radical pair1. In attempts to mimic this process in artificial systems2–4, impressive progress has been made in increasing the efficiency of the charge-separation reaction between an excited photosensitizer and an appropriate electron acceptor, but prevention of the energy-wasting back-reaction to neutral species still constitutes a major challenge. The back-reaction limits the length of time during which charge separation (and thus energy storage) can be maintained. Here we report exceedingly long-lived (up to a few hours) photoinduced charge separation in an artificial photosynthetic system that does not require a secondary substrate to react with the charged species. Our system uses pyrene (Py*) as the photosensitized electron donor and N,N'-dimethy 1-4,4'-bipyridinium (methyl viologen, MV2+) as the electron acceptor, both immobilized in a porous sol–gel silica glass5. The redox reaction is carried out by the mediation of a third mobile charge carrier in the intrapore space6. The spatial separation between the donor and acceptor inhibits the back-reaction to produce the long lifetimes of the charge-separated pair.

Rotational diffusion of liquid toluene in confined geometry

The effects of geometrical confinement on the molecular dynamics of liquid toluene in porous sol–gel silica glasses have been studied by the NMR method. The NMR deuteron spin–lattice relaxation times for toluene-d8, ortho-toluene-d1, and para-toluene-d1 were measured as a function of temperature for bulk and confined liquids. The rotational diffusion tensors for overall, internal, and anisotropic rotational diffusion have been determined. The effect of geometrical confinement results in a considerable decrease of the rotational diffusion constants and leads to a lowering of the symmetry of the anisotropic rotational diffusion tensor.

Fluid transport in partially filled porous sol-gel silica glass.

Comparaison des mesures de conductivite electrique-ac a basse frequence, d'un verre poreux rempli avec differentes quantites d'une solution saline, avec le coefficient d'autodiffusion de l'eau mesure dans ce meme echantillon rapporte anterieurement [F. d'Orazio et al., Phys. Rev. Lett.63,43(1989)]. Les deux parametres du transport sont de facon compatible (coherente) lies a travers la relation de Einstein sous des conditions de saturations. Une image beaucoup plus complexe est revelee pour l'echantillon non sature, vu que la presence d'une phase vapeur renforce (augmente) le coefficient d'autodiffusion. Les experiences des mesures de conductivite permettent une evaluation (repartition) independante de la contribution de la phase liquide a l'autodiffusion. Neanmoins, une comparaison entre les deux experiences indique que le role de la phase vapeur n'est pas bien cerne (compris)