Porous Sol Gel Research Articles

Subwavelength-structured antireflective surfaces on glass

The usability of porous sol–gel coatings and periodic or stochastic subwavelength surface-relief structures for low-cost broadband antireflective (AR) surfaces on glass and on plastics was studied experimentally. Porous sol–gel coatings were produced by dip-coating on glass. Large-area periodic subwavelength surface-relief master structures were manufactured by holographic exposure of photoresist and transferred into nickel by electroforming. Stochastic surface-relief master structures were produced by a PVD process. The surface-relief structures were replicated in organically modified sol–gel materials on glass and in acrylic materials by embossing. With porous sol–gel coatings and periodic subwavelength surface-relief master structures, hemispherical reflectance values of <1% were achieved for non-absorbing planar sheets. In the case of stochastic surface-relief structures, scatter could not be avoided. Therefore, only very low values of the specular reflectance (<0.5%) were achieved with this approach.

Monolithic columns containing sol–gel bonded octadecylsilica for capillary electrochromatography

A new method for preparing monolithic capillary columns is reported. A fused-silica capillary packed with porous octadecylsilica (ODS) particles using a CO 2 slurry was partially filled with a siliceous sol formed by hydrolysis and polycondensation of tetramethoxysilane and ethyltrimethoxysilane. After gelling and aging of the siliceous sol at room temperature, the column was dried with supercritical CO 2. The scanning electron micrograph of a cross-section of the capillary column revealed that the ODS particles were bonded to each other and to the column inner wall by the sol–gel, forming a monolith. The performance of the monolithic column was evaluated for capillary electrochromatography using small aromatic compounds and polycyclic aromatic hydrocarbons with Tris buffer in aqueous acetonitrile mobile phase. The electroosmotic flow velocity increased with a decrease in Tris buffer concentration from 10 to 5 m M. The electroosmotic flow velocity increased significantly with an increase in Tris buffer pH from 5 to 7.5, and then remained nearly constant with Tris buffer pH between 7.5 to 9.0. The electroosmotic flow velocity increased with an increase in acetonitrile content from 20 to 50%, and then remained nearly constant with acetonitrile content between 50 to 90%. No bubble formation was observed during CEC operation, and all of the test compounds eluted as symmetrical peaks. The logarithms of the retention factors of the aromatic compounds and polycyclic aromatic hydrocarbons decreased linearly with an increase in acetonitrile content. For a 21/29 cm×75 μm I.D. monolithic column containing 9% sol–gel bonded 5 μm ODS, approximately 2.7×10 4 theoretical plates (plate height 7.8 μm; 1.3×10 5 theoretical plates per meter) were measured. It was found that the resistance to mass transfer of unretained thiourea was small, which was attributed to partial filling of the small pores in the particulate packing and partial filling of the interstitial space by the porous sol–gel network. The procedure for column fabrication was simple, and three columns were prepared without failure.

Glazing with very high solar transmittance

Different attempts have been made to produce anti-reflection (AR) layers for solar applications. The most promising solutions are based on the principle of mixing bulk material with air on a subwavelength scale in order to obtain the very low effective refractive indices suitable as AR coatings for glazing. Possibilities for achieving this are given by porous media and subwavelength surface-relief gratings. Subwavelength grating structures, which were embossed in organically modified sol-gel materials or acrylic materials, and porous sol-gel coatings were investigated and compared theoretically and experimentally by the Fraunhofer Institutes. It is shown, theoretically and experimentally, that an increase of solar transmittance of ≈3% per glass surface can be achieved with a porous sol-gel coating.

Dehydrogenation of Pure Cyclohexane in the Membrane Reactor and Prediction of Conversion by Pseudo Equilibrium Model.

Three kinds of membrane reactor, porous Vycor glass, ceramic Sol-gel, and Palladium-silver membrane reactors, are used to study the dehydrogenation of pure cyclohexane. The reactors are intended to be applied as chemical heat pumps, therefore they were fed with pure cyclohexane. The experimental results show that the higher conversions exceeding the equilibrium one, αeq = 6.4%, were achieved up to 27% and 11% for Pd-Ag (PT-2), and porous Vycor glass membranes respectively. A pseudo equilibrium (PE) model was proposed to predict the conversion achieved in the reactor. In the Damkohler number (Da) range employed of 1.05–4.48, the model is in good agreement with the experimental results. The prediction becomes less accurate with increasing pressure difference.

Fabrication and Properties of Doped Porous Polysiloxane Sol-Gel Layers on Optical Fibers

Polysiloxane porous layers doped with TiO- and phenyl-groups were fabricated by the sol-gel method. Starting sols were prepared from alkoxides using catalysis by HCl or HF. Stable SiO-TiO-sols were obtained by using HF. Porous gel layers with thicknesses of 0.3–1.1 μm were coated on fiber surfaces or silicon wafers. Layers with the refractive index of 1.38–1.48 were prepared. The fractional porosity of the layers was estimated to be 0.1–0.35. The interactions of the layers with vapor or liquid chlorinated hydrocarbons, alcohols or aromatic hydrocarbons have been studied in immersing experiments by measuring the output light intensity from the fibers. The observed changes of the output intensity could be correlated to changes of the refractive index of the layer caused by the penetration of the tested chemicals into the layer pores.

Selective-area doping of porous solgel films for integrated optics

A technique for doping of porous films by surface adsorption of ions from aqueous solution is demonstrated. Fabrication of the films by use of the solgel technique gives a nanometer-scale porosity, which provides high doping levels and homogeneity. Doping through a masking layer patterned by photolithography is thus possible. With Pb as a dopant, lead silicate films with refractive indices of 1.46 to 1.55 were obtained, with submicrometer patterning resolution. Linear control of the refractive index is achieved through variation of the solution pH. Applications of this technique in integrated optics and optical elements are proposed.

Porous Sol-Gel Silicates Containing Gold Particles as Matrices for Surface-EnhancedRaman Spectroscopy

Porous Sol-Gel Silicates Containing Gold Particles as Matrices for Surface-EnhancedRaman Spectroscopy

Chemical sensors based on hydrophobic porous sol-gel films and ATR-FTIR spectroscopy

A new chemical sensor based on attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy has been fabricated by coating an ATR crystal with a hydrophobic mesoporous silica film. The highly porous coating can extract hydrophobic analytes, such as benzene, from aqueous solutions and concentrate them inside the film. The enrichment of the analytes inside the film provides the sensor with enhanced sensitivity. The hydrophobic porous film can efficiently exclude water from the region probed by the evanescent wave, thus eliminating the spectral interference due to water absorption bands. Measurement of nitrogen adsorption and desorption isotherms of the films using surface acoustic wave techniques has been used to characterize the pore structure of the films. Relationships between the structure of the porous film and sensor performance are discussed.

Proteins Encapsulated in Porous Sol-Gels: Biomolecules as Pore Structure Templates

AbstractPorous inorganic SiO2 glasses obtained by the sol-gel route represent a unique matrix for encapsulation of biomolecules wherein the pores act as enclosures for high molecular weight proteins. These hybrid materials are characterized by a pore-biomolecule interface between the pore walls and the protein surface. As a specific model protein, cytochrome c (cyt c) is used to elucidate the nature of physical and chemical interactions between the pores of the matrix and the protein. Evidence from optical absorption, and resonance Raman (RR) spectroscopy methods indicates that the dopant protein alters the structural features of the pore walls. The optical and vibrational measurements strongly suggest that the pores that contain the trapped protein undergo little or no structural change during aging and drying as compared to protein-free pores. Vibrational RR analysis of the trapped cyt c also suggests that the protein resides in a pore where the pore dimensions conform to the shape of the protein. The results indicate that noncovalent interactions between the surface of the protein and the pore walls govern the dynamics of pore formation during gelation and individual biomolecules act as structural templates to design local pore structure.

Dissolved oxygen sensor based on fluorescence quenching of oxygen-sensitive ruthenium complexes immobilized in sol–gel-derived porous silica coatings

A dissolved oxygen sensor based on the quenching of fluorescence from a ruthenium dye complex entrapped in a porous sol–gel film is reported. Sol–gel-derived silica films were fabricated by dip-coating on to planar and optical fibre substrates. The films were pre-doped with the oxygen-sensitive ruthenium complex [RII–tris(4,7-diphenyl-1,10-phenanthroline)], the fluorescence of which is quenched in the presence of oxygen. The structure and behaviour of sol–gel films are dependent on the fabrication parameters. In particular, enhancement of the surface hydrophobicity increases the quenching response in water. This is achieved by using suitable proportions of modified precursors of silica of the form R(OEt)3Si, where R is an alkyl group, in the standard fabrication procedure. It is shown that by increasing the ratio of modified precursor, the quenching response in the aqueous phase increases. A very low limit of detection, 6 ppb, was determined for the modified films. Using a high-brightness blue LED, combined with a miniature photodiode detection system, these results indicate the potential for a low-cost, high-performance, portable dissolved oxygen sensor for use in many varied situations from aeration control to on-line river pollution monitoring.

Diffusion of Simple Liquids in Porous Sol-Gel Glass

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDiffusion of Simple Liquids in Porous Sol-Gel GlassN. Koone, Y. Shao, and T. W. ZerdaCite this: J. Phys. Chem. 1995, 99, 46, 16976–16981Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100046a025RIGHTS & PERMISSIONSArticle Views425Altmetric-Citations53LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Chemical Sensor Based on an Artificial Receptor Element Trapped in a Porous Sol-Gel Glass Matrix

A synthetic organic receptor, dansyl-tethered β-cyclodextrin, is doped into an inorganic sol-gel matrix and spin cast as a film on fused-silica plates. The entrapped receptor exhibits changes in its fluorescence in the presence of borneol. Thus, this new material can be used as a reversible sensor. Various aspects of a sol-gel matrix as a host for recognition molecules were explored. This system demonstrates the possibility of using artificial receptors and sol-gel porous glass films for chemical sensing purposes.

Reorientational relaxation of cyclohexane in porous silica

Rotational correlation function and rotational relaxation times of cyclohexane in porous sol—gel glass were obtained by Raman spectroscopy at temperature ranging from 173 to 323 K. Three sets of sol—gel glass of diameters 29, 54 and 220 Å were studied. The effects of physical confinement on the rotational motion were observed and related to pore diameters. The experimental results were compared with computer simulation data.

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.

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.

SOL-GEL DERIVED SENSOR MATERIALS FOR USE IN AQUEOUS TRANSITION METAL ION DETECTION

ABSTRACTOpto-chemical transducers, which exhibit changes in luminescence and/or absorption characteristics as a function of local conditions, are currently of great interest for use in performing quantitative chemical analyses. Present research is focused on the preparation and characterization of novel optrode materials which may be remotely interrogated via optical fiber carriers. The approach under investigation involves preparation of sol-gel derived films which are sensitized by the entrapment of analyte-complexing organic probe molecules. Zn(II)aq induced perturbations to the luminescence behavior of a porphyrin derivative entrapped within a porous sol-gel derived host matrix are detailed.

Photolithographic Imaging of Planar Optical Waveguides and Integrated Optic Devices onto Porous Silicate Glasses and Silica Sol-Gels

ABSTRACTThe success of photonic switching depends on the development of materials capable of processing light signals without the interweaving conversion to electronic signals. The photodeposition of metal oxides onto porous Vycor glass and silica glass sol-gels produce changes in the index of refraction of the glass of the order of 0.1 to 0.001. Nonlinearities in transmission and refractive index allow the deposition of 1.0-10.0 μm width planar waveguides with attenuations of 0.6 dB/cm. This technique is being evaluated for the optical performance of couplers, dividers, and interferometers. Also 3-dimmensional interactive planar waveguide structures are being fabricated in silica sol-gel thin-films.

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.

Inorganic ultrafiltration membranes prepared by a combination of anodic film and sol-gel technologies

Composite ultrafiltration membranes have been prepared by depositing ultrathin porous solgel layers onto stripped anodic film microporous membrane substrates. Two ultrafiltration variants, 5.5 nanometers and 10 nanometers pore size, were selected for flux and filtration performance characterization. Molecular weight cut-off (MWCO) for the 5.5 nanometer pore size variant was about 10,000 Da, and the cut-off transition was quite sharp. Both inorganic ultrafiltration membranes exhibited satisfactory pure water and protein solution fluxes, in addition to good retention of proteins of molecular weight greater than their MWCO. Inorganic membranes of this type also exhibit good solvent and chemical resistance.

TEM visualization of surface replicated acid and base catalyzed sol-gel glasses

Traditionally ceramics have been shaped from powders and densified at temperatures close to their liquid point. New processing methods using various types of sols, gels, and organometallic precursors at low temperature which enable densificatlon at elevated temperatures well below their liquidus, hold the promise of producing ceramics and glasses of controlled and reproducible properties that are highly reliable for electronic, structural, space or medical applications. Ultrastructure processing of silicon alkoxides in acid medium and mixtures of Ludox HS-40 (120Å spheres from DuPont) and Kasil (38% K2O &amp;62% SiO2) in basic medium have been aimed at producing materials with a range of well defined pore sizes (∼20-400Å) to study physical phenomena and materials behavior in well characterized confined geometries. We have studied Pt/C surface replicas of some of these porous sol-gels prepared at temperatures below their glass transition point.