Search results for "sol-gel"
showing 10 items of 118 documents
Generalised syntheses of ordered mesoporous oxides: the atrane route
2000
Abstract A new simple and versatile technique to obtain mesoporous oxides is presented. While implying surfactant-assisted formation of mesostructured intermediates, the original chemical contribution of this approach lies in the use of atrane complexes as precursors. Without prejudice to their inherent unstability in aqueous solution, the atranes show a marked inertness towards hydrolysis. Bringing kinetic factors into play, it becomes possible to control the processes involved in the formation of the surfactant–inorganic phase composite micelles, which constitute the elemental building blocks of the mesostructures. Independent of the starting compositional complexity, both the mesostructu…
ZnO nanorods covered with a TiO2 layer: simple sol–gel preparation, and optical, photocatalytic and photoelectrochemical properties
2015
In this work, composite core–shell ZnO/TiO2 materials were fabricated by deposition of TiO2 layers via a sol–gel method onto ZnO nanorods hydrothermally grown on an ITO electrode. Two approaches to the sol–gel procedure resulted in strongly different morphologies and thicknesses of the deposited TiO2 layer, as shown in electron microscopy studies. The decrease of the optical band gap energies of the ZnO/TiO2 composites by about 0.2–0.3 eV with respect to the TiO2 nanoparticles and ZnO nanorods was determined from UV-Vis diffuse reflectance spectra. The photocatalytic activities of the systems were determined by investigation of the decolorization of Methylene Blue (MB) in aqueous solution, …
ZrO2SiO2 mixed oxides: surface aspects, photophysical properties and photoreactivity for 4-nitrophenol oxidation in aqueous phase
1996
Abstract Mixed oxides of ZrO2 and SiO2 were synthesized by a sol-gel technique by using zirconyl chloride and commercial silica gel as starting materials. The paper reports some surface features of the powders and the photoreactivity results obtained in the oxidation of 4-nitrophenol in aqueous suspensions of powdered photocatalyst. The optical characterization of the suspension was also performed by measuring the photon flows reflected and absorbed by the reacting system. The photoactivity exhibited by the ZrO2SiO2 samples is very scarce especially if compared with that shown by a TiO2 sample tested at equal experimental conditions. The low photoreactivity can be justified on the basis of…
Exceptional affinity of nanostructured organic-inorganic hybrid materials towards dioxygen: confinement effect of copper complexes
2007
We report the exceptional reactivity towards dioxygen of a nanostructured organic-inorganic hybrid material due to the confinement of copper cyclam within a silica matrix. The key step is the metalation reaction of the ligand, which can occur before or after xerogel formation through the sol-gel process. The incorporation of a Cu(II) center into the material after xerogel formation leads to a bridged Cu(I)/Cu(II) mixed-valence dinuclear species. This complex exhibits a very high affinity towards dioxygen, attributable to auto-organization of the active species in the solid. The remarkable properties of these copper complexes in the silica matrix demonstrate a high cooperative effect for O(2…
Nanoscale Chemical Interaction Enhances the Physical Properties of Bioglass Composites
2013
Bioglasses are favorable biomaterials for bone tissue engineering; however, their applications are limited due to their brittleness. In addition, the early failure in the interface is a common problem of composites of bioglass and a polymer with high mechanical strength. This effect is due to the phase separation, nonhomogeneous mixture, nonuniform mechanical strength, and different degradation properties of two compounds. To address these issues, in this study a nanoscale interaction between poly(methyl methacrylate) (PMMA) and bioactive glass was formed via silane coupling agent (3-trimethoxysilyl)propyl methacrylate (MPMA). A monolith was produced at optimum composition from this hybrid …
The chemical effects of molecular sol–gel entrapment
2007
Chemical conversions within the cages of doped sol-gel porous oxides take place with unique advantages over reactions in solution as the glassy matrix has tremendous effects on the reactivity of the entrapped molecules. The chemical properties of sol-gel materials can be tailored in an immense range of values and chemists are increasingly achieving control on reactions taking place within these matrices, including crucially important photovoltaics. Highlighting recent major advancements, we show in this tutorial review how this is actually taking place.
From Molecules to Systems: Sol-Gel Microencapsulation in Silica-Based Materials
2010
From Spherical Mesopores to Worm-Shaped Mesopores : Morphology Transition in Titania–Polystyrene-b-poly(ethylene oxide) Composite Films with Increasi…
2013
A morphology transition from spherical mesopores to worm-shaped mesopores within titania block copolymer composite thin films has been observed by varying the sol–gel reaction time from 40 min to 48 h in the four-component templating system of polystyrene-$\mathit{b}$-poly(ethylene oxide) (PS-$\mathit{b}$-PEO), 1,4-dioxane, concentrated HCl, and titanium tetraisopropoxide (TTIP) with a PS-$\mathit{b}$-PEO mass concentration of 0.25 wt.-%. The impact of the sol–gel reaction time on the local structure, long-range lateral structure, and vertical structure of the as-prepared, calcined, and UV-degraded thin films as well as the structural changes in solution have been systematically investigate…
Synthesis of Uvarovite Garnet
1989
A garnet with interesting optical properties is synthesized by means of the ceramic method and the formation of gels. Colloidal silica or tetraethoxysilane (TEOS) is used as a starting reagent in the latter method of synthesis, together with nitrate and chloride salts of the remaining components. Use is made of ultraviolet-visible and infrared spectroscopy techniques and X-ray diffraction in studying the evolution of the system. Formation of the garnet phase at lower temperatures is observed when using the gel methods, as well as the absence of chromates during the process in the samples which contained chlorides.
Catalysis with Doped Sol-Gel Silicates
2011
Silicates doped with catalytic species have only been slowly adopted by the fine chemicals and pharmaceutical industries, in spite of their remarkable and unique properties such as pronounced physical and chemical stability; high (enantio)selective activity and ease of materials production and application. This is now changing thanks to stricter safety regulations and to concomitant success of the first commercial catalysts. In this account we tell the story of these materials and identify some deficiencies in the innovation process that may serve as lesson in guiding the future management of innovation in these relevant industries.