Novel, Organically Doped, Sol-Gel-Derived Materials for Photonics: Multiphasic Nanostructured Composite Monoliths and Optical Fibers

Three-Dimensional pH Mapping within Model Hybrid Xerogel Thin Films

When xerogel films derived from carboxyethylsilanetriol (COE) and tetraethoxysilane (TEOS) or 3-aminopropyltriethoxysilane (APTES), n-octyltriethoxysilane (C8), and TEOS are formed on Al₂O₃ they exhibit chemically segregated domains with unique chemistries and topographies. These characteristics are important for marine antifouling. By using the ratiometric fluorescent probe 5 (and 6)-carboxy SNARF-1 (C.SNARF-1) in concert with confocal fluorescence microscopy, we determine the pH in three dimensions within these hybrid films. For the COE/TEOS film, 4-5 μm diameter dendritically shaped features form, and they extend ∼100 nm above the film base. These dendritic features are acidic (pH < 7) in comparison to the film base. Their average diameter decreases as we progress from the solution-film interface toward the film-Al₂O₃ interface. Planes located at the solution-film interface, film center, and film-Al₂O₃ interface exhibit acidic surface areas that are 20% below, 50% above, and 70% below the average COE mole fraction used to create the film. In the APTES/C8/TEOS films, 1-3 μm diameter mesa-shaped features form, and they extend up to 450 nm above the film base. These mesa features are basic (pH > 7) in comparison to the film base and are columnar in shape, extending without change in diameter throughout the entire film. From the solution-film interface the planes located within the first 3/4 of the film exhibit basic surface areas that are equivalent to the average APTES mole fraction used to create the film. However, as one approaches the film-Al₂O₃ interface, many new 100-200 nm basic subsurface regions appear. The basic surface area in those film planes within 400-500 nm of the film-Al₂O₃ interface are enriched in APTES by up to 500% above the average APTES mole fraction used to create the film.

A Novel Dye-Doped Sol–Gel Silica Sorbent for the Removal of Cobalt

A TAR [4-(2-thiazolylazo)resorcinol] doped sol–gel silica sorbent (red colour, porous, stable, hard, non-swelling) was prepared, characterized and investigated for the removal of Co(II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and effect of pH on such removal were studied to optimize the conditions necessary for large-scale application. Rapid equilibration was observed with adsorption equilibria being attained within 10 min. The adsorption of cobalt ions onto the plain (undoped) sol–gel silica was negligible. The maximum adsorption of Co(II) ions onto the TAR-doped sol–gel silica from single solutions was 12.6 mmol/g. The TAR-doped sol–gel silica could be regenerated by washing with a 0.1 M HCl solution to give a maximum regeneration value as high as 98.5%. The TAR-doped sol–gel silica could be used for more than three consecutive adsorption/desorption cycles without experiencing any considerable loss of adsorption capacity. The adsorption process and the nature of the Co–TAR complex were discussed.

Polymer Monoliths Containing Two-Photon Absorbing Phenylenevinylene Platinum(II) Acetylide Chromophores for Optical Power Limiting

A series of platinum(II) acetylide complexes containing p-phenylenevinylene and moieties end-capped with triphenylamine groups have been incorporated into poly(methyl methacrylate) (PMMA) monoliths for optical power limiting applications. The one- and two-photon photophysical properties were investigated and compared to the photophysical properties in THF. The absolute two-photon absorption cross-section values for the monolith samples were measured and are comparable to the values obtained in solution. In the PMMA monoliths, the complexes retained the important two-photon absorption and reverse saturable absorption properties necessary for optical power limiting via dual mode mechanism, and their strong nonlinear absorption property was demonstrated by the open-aperture Z-scan method. Photostability studies of the p-phenylenevinylene platinum(II) acetylide complexes showed two photodegradation processes: a trans-to-cis isomerization and a singlet-oxygen sensitized self-oxidative cleavage. The photostability of the least photostable complex TPV0 was increased upon incorporation into a PMMA matrix.

Sol-gel Approaches for Elaboration of Polyol Dehydrogenase-Based Bioelectrodes

This review describes the input of sol-gel chemistry to the immobilization of polyol dehydrogenases on electrodes, for applications in bioelectrocatalysis. The polyol dehydrogenases are described and their application for biosensing, biofuel cell and electrosynthesis are briefly discussed. The immobilization of proteins via sol-gel approaches is described, including a discussion on the difficulty to maintain the activity of proteins in a silica matrix and the strategies developed to offer a proper environment to the proteins by developing optimal organic-inorganic hybrid materials. Finally, the co-immobilization of the NAD + co-factor and of mediators for the elaboration of reagentless devices is presented, based on published and original data. All-in-all, sol-gel approaches appear to be a very promising for development of original electrochemical applications involving dehydrogenases in near future.

One-step patterning of hybrid xerogel materials for the fabrication of disposable solid-state light emitters

The one-step room-temperature micropatterning of a fluorophore-doped xerogel material on silicon oxide substrates is reported. The organo-alkoxysilane precursors and organic fluorescent dyes, as well as the polymerization experimental conditions, were tailored in order to obtain a highly homogeneous transparent material suitable for photonic applications. A thorough structural characterization was carried out by Fourier transform infrared (FT-IR) spectroscopy, (29)Si nuclear magnetic resonance ((29)Si NMR), thermogravimetric analysis (TGA), N(2) adsorption Brunauer-Emmett-Teller (BET) porosimetry, and confocal microscopy. These studies revealed a stable nonporous highly cross-linked polymer network containing evenly dispersed fluorescent molecules. Xerogel microstructures having thicknesses between 4 and 80 μm and height-to-width ratios between 0.04 and 4, as well as showing different geometries, from well arrays to waveguides, were patterned in a single step by micromolding in capillaries (MIMIC) soft lithographic technique. The reliability of the replication process was tested by bright-field optical microscopy and scanning electron microscopy (SEM) that show the close fidelity of the microstructures to the applied mold. The optical performance of the developed material was demonstrated by fabricating waveguides and evaluating their corresponding spectral response, obtaining absorption bands, at the expected excitation wavelengths of the corresponding fluorescent dyes and gain due to photonic re-emission (fluorescence) at their corresponding dye emission wavelengths. The hybrid xerogel material and the application of the simple fabrication technology presented herein can be directly applied to the development of cost-effective photonic components, as could be light emitters, to be readily integrated in single-use lab-on-chip devices and other polymeric microsystems.

A review of photocatalysts prepared by sol-gel method for VOCs removal

The sol-gel process is a wet-chemical technique (chemical solution deposition), which has been widely used in the fields of materials science, ceramic engineering, and especially in the preparation of photocatalysts. Volatile organic compounds (VOCs) are prevalent components of indoor air pollution. Among the approaches to remove VOCs from indoor air, photocatalytic oxidation (PCO) is regarded as a promising method. This paper is a review of the status of research on the sol-gel method for photocatalyst preparation and for the PCO purification of VOCs. The review and discussion will focus on the preparation and coating of various photocatalysts, operational parameters, and will provide an overview of general PCO models described in the literature.

Efficacy of a new tan doped sol-gel sorbent for uptake of zinc

A TAN (1-(2-Thiazolylazo)-2-naphthol)) doped sol gel silica sorbent (reddish colour, porous, stable, hard, non- swelling) were prepared and investigated for the removal of Zn (II) from aqueous solutions. The kinetics, adsorption isotherm, equilibration time and pH effect on the removal were studied from non competitive aqueous solution to optimize the conditions to be utilized on a large scale. Fast equilibration was observed and adsorption equilibria were reached within 30minutes. Adsorption of zinc ions on the blank (un-doped) sol gel was found negligible. The maximum adsorption of Zn (II) ions onto the TAN doped sol-gel from single solutions were 2.33mg/g (0.035mmol/g). TAN doped sol gel can be regenerated through washing with a solution of 0.1M HCl solution. The maximum regeneration value was as high as 99.0. The TAN-doped sol gel silica is suitable at least for four adsorption-desorption cycles without experiencing considerable loss of adsorption capacity. The uptake route and the nature of the Zn-TAN complex have been discussed.

Disrupting aggregation of tethered rhodamine B dyads through inclusion in cucurbit[7]uril

Hexano- and dodecano-tethered diesters of rhodamine B were prepared. The absorption and fluorescence spectra of these flexibly tethered dyads were compared with those of the rhodamine 3B ethyl ester. Increased J- and H-type dimer formation and decreased fluorescence emission were observed for the tethered dyads. Complexation of the cationic chromophoric units in cucurbit[7]uril (CB7) hosts decreased H-dimer aggregation, especially for the dodecano-tethered dyad. The monomeric dye and both dye dyads exhibited enhanced fluorescence upon addition of CB7.

Spectroscopic Characterization of Hydroxylated Nanoballs in Methanol

In this report, the photophysical properties of self-assembled [Cu(2)(5-OH-bdc)(2)L(2)](12) [where (5-OH-bdc)(2-) = 5-hydroxybenzene-1,3-dicarboxylate and L is a dimethyl sulfoxide, methanol, or water ligand] hydroxylated nanoballs (OH-nanoball) were examined in methanol using optical absorption and steady-state and time-resolved fluorescence methods. The optical spectrum of the OH-nanoball is dominated by ligand absorbance at 305 nm and a weaker Cu(2+)-to-ligand charge-transfer transition at approximately 695 nm, which are distinct from the absorption of either the free ligand (approximately 312 nm) or Cu(2+)(NO(3))(2) (>750 nm) in methanol. The corresponding emission spectrum of the OH-nanoball originates from the emission of the ligand and is centered at approximately 360 nm with a shoulder at approximately 390 nm. The emission from the OH-nanoball is significantly quenched relative to the free ligand [Phi(5-OH-H(2)bdc) = 0.014 and Phi(OH-nanoball) = (5.6 +/- 0.5) x 10-5]. The addition of bases such as imidazole results in an increase in the emission intensity of the OH-nanoball solution, indicating dissociation of the [Cu(2)(5-OH-bdc)(2)L(2)](12) units. Although the mechanism of (5-OH-bdc)(2-) quenching within the OH-nanoball is not clear, it is likely due to interactions between the ligand pi system and the Cu d orbitals. Fluorescence polarization studies further suggest that the OH-nanoball retains a spherical shape in solution. This is evident by the fact that the fluorescence anisotropy of the nanoball is nearly identical with that of the free ligand, suggesting rapid energy transfer (homogeneous fluorescence resonance energy transfer) between ligands within the OH-nanoball.

Effect of Laponite and a nonionic polymer on the absorption character of cationic dye solutions

The effect of Laponite and an amphiphilic triblock copolymer of poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-poly(ethylene oxide) (PEO) (PEO(99)-PPO(65)-PEO(99), and labeled F127) on the absorption character of two cationic dyes, methylene blue and toluidine blue O, was studied and interpreted in terms of the changing state of aggregation of the dye molecules. The combined effect of the polymer and Laponite on dye absorption was significantly different from their individual influences. Specifically, the presence of Laponite resulted in an increase in monomer population by dispersing the dye on the silicate surface. The presence of F127 also resulted in an increase in the dye monomer population, although to a smaller extent. The combined effect of the polymer and Laponite was an increase in the dimer or aggregate populations attributed to the competition of F127 with the dye molecules for the silicate surface.