Search results for "Gel"

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.

Sol–Gel Synthesis of Tunable Cerium Titanate Materials

2008

Cerium titanate structures present a high technological interest because of their optical and catalytic properties. This work reports the synthesis of these materials by a sol–gel methodology that allows mixed oxides with TiIV/CeIII, TiIV/CeIV or TiIV/CeIII–CeIV species to be obtained. Crystallization of CeO2–TiO2 mixed oxides and Ce2Ti2O7 pyrochlore phase was corroborated by XRD and Raman spectroscopy. Magnetic and EPR measurements were performed in order to clarify the oxidation state of the cerium ions in the system as a result of the easy oxidation of CeIII. The firing atmosphere is crucial for the CeIII/CeIV ratio, which is responsible for the different structure, but it also affects t…

Soluble oligo(phenylenevinylene)s with electron withdrawing substituents for the use in light emitting diodes

2000

Poly(p-phenylenevinylene) (PPV) and its derivatives are one of the most widely used classes of phosphors in light emitting diodes. Central problems are the imbalanced charge carrier injection and transport properties due to the high lying conduction band. A series of good soluble oligo(phenylenevinylene)s (OPV) with five benzene rings and a variety of electron withdrawing and accepting substituents have been prepared and may serve as model compounds for PPV with increased electron affinity. The central ring of the OPVs is substituted with two octyloxy groups to ensure good solubility and the lateral styrene units carry further chromophoric groups of different electronic character. The synth…

Chemical waves and pattern formation in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/water lamellar system

2004

Catalysis in Supramolecular Systems: the Case of Gel Phases

2021

Supramolecular gels are a fascinating class of materials, originated by the self-assembly of low molecular weight molecules. Underpinned by non-covalent interactions, they find application in a diverse range of fields. Among these, supramolecular gels can be considered as organized, non-conventional reaction media, able to influence reactivity in a radically different way, compared with what happens in solution. This short review will focus on this aspect, covering literature from 2010 onwards, addressing the application of supramolecular gels as reaction media. In particular, in the first section we explore organocatalytic reactions in gel phase, with wide synthetic relevance, such as aldo…

Second harmonic generation in SiO2 sol-gel films functionalized with Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) mol…

2010

Abstract High concentrations of Ethyl-[4-(4-nitro-phenylazo)-phenyl]-(2-oxiranylmethoxy-ethyl)-amine (ENPMA) chromophores were linked covalently to two different kinds of SiO 2 matrices prepared by the sol–gel method. The matrices differed in their reticulation level, determined by the organometallic precursor used during the synthesis. The materials were deposited as films by spin-coating. The chromophores in the films were oriented in a non-centrosymmetric way by a modified Corona poling set-up, and the nonresonant second order non-linear optical coefficient d 33 (0) of the films was determined by means of the Maker fringe technique. It was found that there is an optimum concentration of …

Phase analysis and oxygen strorage capacity of ceria-lanthana-based TWC promoters prepared by sol-gel routes

2002

Ceria–lanthana-based promoters of three-way catalysts are synthesized by two different sol–gel routes, involving nitrate precursors. The oxygen uptake ability of these compounds is measured by O2 chemisorption. The specific surface area is determined by N2 adsorption (BET). X-ray diffraction data are analyzed by Rietveld refinement, demonstrating that lanthanum forms solid solution with CeO2; its total amount in ceria depends on the competitive formation of La–Al mixed oxides and on the synthetic method. The O2 uptake ability is essentially determined by the La content in the ceria–lanthana solid solution, while it is independent on the surface area and on the CeO2 particle size. The O2 upt…

A Liquid-Liquid Biphasic Homogeneous Organocatalytic Aldol Protocol Based on the Use of a Silica Gel Bound Multilayered Ionic Liquid Phase

2012

An innovative two stage liquid–liquid biphasic homogeneous protocol for the asymmetric organocatalytic aldol reaction is proposed, based on the use of the cis-ion-tagged proline 8 dissolved in the liquid film of a multilayered ionic liquid covalently bonded to silica gel 4. The resulting catalytically active material 9 is first soaked with cyclohexanone in the presence of water, resulting in a semi-transparent gel, then the aldehyde is added and the mixture stirred at RT. In the first stage, 4 acts as a catalyst reservoir that delivers 8 to the cyclohexanone phase allowing the reaction to take place homogeneously. In the second stage, cyclohexanone is removed under vacuum and the resulting …

Baeyer−Villiger Oxidation with Potassium Peroxomonosulfate Supported on Acidic Silica Gel

2005

[reaction: see text] Potassium peroxomonosulfate deposited onto silica SiO2 x KHSO5 efficiently reacts with ketones in dichloromethane at room temperature to give the corresponding esters or lactones in quantitative yields. This method avoids hydrolysis of the reaction products. The Baeyer-Villiger reaction is catalyzed by potassium hydrogensulfate present in the supported reagent.

Temperature and polymer crosslinking degree influence on drug transfer from alpha,beta-polyasparthydrazide hydrogel to model membranes. A calorimetri…

1998

Abstract A non-steroidal anti-inflammatory drug, diflunisal, has been chosen as drug model to be incorporated in α , β -polyasparthydrazide (PAHy) matrices to study the effect of polymer crosslinking degrees on the release processes from hydrogel ( X =0.4 and X =0.8) to a model membrane represented by unilamellar vesicles of dipalmitoylphosphatidylcholine. The technique employed to monitor these processes was differential scanning calorimetry that appears to be particularly suitable to follow the transfer kinetics of a drug from a controlled release system to void biomembrane model. The drug release from the two PAHy hydrogels differently crosslinked by glutaraldehyde to the lipidic model w…