Preparation and characterization of polypyrrole-silica colloidal nanocomposites in water-methanol mixtures

The effect of methanol cosolvent on the synthesis of polypyrrole-silica colloidal nanocomposites using ultrafine silica sols in combination with both FeCl3 and APS oxidants has been investigated. Two protocols were evaluated: the addition of methanol to an aqueous silica sol and the addition of water to a methanolic silica sol. The latter protocol proved to be more robust, since it allowed colloidally stable dispersions to be prepared at higher methanol content (up to 50 vol% using the APS oxidant). This allowed greater control over the particle size of the nanocomposite particles. In general, the spectroscopic data, the particle size range, silica contents and electrical conductivities of these nanocomposites were similar to those reported earlier for purely aqueous formulations. Polypyrrole contents ranged from 49 to 71% by mass and particle diameters varied from around 160 to 360 nm. In terms of colloid stability, the APS oxidant was preferred for nanocomposite syntheses in the presence of methanol. However, the FeCl3 oxidant generally gave higher conductivities and narrower size distributions under comparable conditions. HF etching experiments combined with transmission electron microscopy studies indicated that, to a first approximation, these nanocomposite particles had core-shell morphologies, with a hydrophobic polypyrrole core and a hydrophilic silica shell that compose approximately one monolayer of silica sol particles. Finally, aqueous electrophoresis measurements suggested that the polypyrrole-silica nanocomposites were silica-rich and that the methanolic silica sol was more hydrophobic (lower surface charge density) than the aqueous silica sol.     

Dual-function of alcohols in gold-mediated selective coupling of amines and alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic-oxygen-activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co-adsorbed. For effective oxygen-assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β-hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100?% in excess methanol.     

Dual‐Function of Alcohols in Gold‐Mediated Selective Coupling of Amines and Alcohols

Oxidative coupling of alcohols (methanol and ethanol) and dimethylamine on atomic‐oxygen‐activated Au(111) occurs entirely on the surface to form the corresponding amides when the alkoxy of the alcohol and the amide derived from the amine are co‐adsorbed. For effective oxygen‐assisted coupling the formation of the amide requires excess methanol. Mechanistic studies reveal that molecularly adsorbed methanol removes excess adsorbed atomic oxygen efficiently, precluding either secondary oxidation or oxidative dehydrogenation of dimethylamide to the imine. The adsorbed amide then can react with the aldehyde produced by β‐hydride elimination from the alkoxy to form the hemiaminal, the reactive intermediate leading to coupling. The selectivity for formamide production can be increased to nearly 100 % in excess methanol.     

Kinetic studies on light-induced cationic ring-opening reactions on 2,3-epoxypropyl phenyl ether

Light-induced cationic ring-opening reactions of 2,3-epoxypropyl phenyl ether (phenyl glycidyl ether, PGE) in acetone, methanol and bulk were studied. Cations are produced by electron transfer from excited sensitizers (anthracene, An; 9,10-phenanthrenequinone, PQ; benzophenone, BP) or from photolytically cleaved sensitizer (benzoin isoproyl ether, BIPE) to diphenyliodonium hexafluorophosphate. With excess of acetone and methanol, addition reactions take place resulting in 2,2-dimethyl-4-phenoxymethyl-1,3-dioxolane and 1-methoxy-3-phenoxy propan-2-ol as main products. The efficiency of the sensitizers taken from the quantum yields of PGE conversion, follows the order An ? BIPE > PQ > BP in acetone and An ～ BP > BIPE ? PQ in methanol. Unlike bulk polymerization, in these addition reactions no steady-state concentration of cations exists and the reaction accelerates with time. When alcohol is added in only small proportions, the initial addition reactions goes over into a linear oligomerization. The relatively higher basicity of methanol over PGE influences the nature of the active center, and the course of reaction depends on methanol concentration. Kinetic expressions, which account for all possible types of active centers, have been derived to express the rate of PGE reactions in methanol.     

Product study of the reaction of CH3 with OH radicals at low pressures and temperatures of 300 and 612 K

The product distribution for the title reaction was studied using our time-of-flight mass spectrometer (TOFMS) connected to a tubular flow reactor. The methyl and hydroxyl radicals were produced by an excimer laser pulse (lambda = 193 nm) photolyzing acetone and nitrous oxide in the presence of excess water or hydrogen. Helium was used as the bath gas; the total density was held constant at 1.2 x 10(17) cm(-3). At 300 K the observations were consistent with singlet methylene ((1)CH(2)) and water as the main product channel with a small contribution of methanol. In contrast, at about 610 K three channels-formaldehyde isomers and methanol in addition to (1)CH(2) + H(2)O-are formed with similar yields. When acetone-d(6) was used, the production of both CHDO and CD(2)O was observed, indicating that two different formaldehyde-producing channels are operating simultaneously. These experimental results are compared with RRKM and master equation calculations on the basis of the properties of the methanol potential energy surface from a recent ab initio study.     

Hydrolysis and polycondensation of acid-catalyzed Phenyltriethoxysilane (PhTES)

The effects of acid catalyst, water content and reaction temperature on the hydrolysis and polycondensation of phenyltriethoxysilane (PhTES) were studied using ²⁹Si NMR spectroscopy. The sol catalyzed by hydrochloric acid showed the simultaneous progress of hydrolysis and polycondensation. In addition, the reaction rate was almost independent of reaction temperature. On the other hand, the polycondensation in the PhTES-derived sol mixed with an excess amount of water and acetic acid as a catalyst proceeded after completion of the hydrolysis. In the acetic acid-catalyzed system, the degree of the hydrolysis and polycondensation largely depends on the reaction temperature.     

Starved Water Hydrolysis of Different Precursors and its Influence on the Properties of Precipitated Zirconia

The chemical composition of zirconia gels precipitated from methanol solutions with excess, stoichiometric or deficient amounts of water as well, as the phase composition of fine ZrO₂ powders obtained by thermal treatment of gels prepared by this method, were investigated. It was observed that both the stoichiometry and crystalline phase formation during thermal treatment of zirconia gels are strongly influenced by the amount of water added to the initial reaction mixture. Heating the hydrated zirconia gels in an inert oxygen-free atmosphere produced a black nonstoichiometric oxide. The degree of nonstoichiometry of zirconia and its microstructure are influenced by the initial conditions in the reaction mixture. The X-ray patterns of thermally treated samples prepared with a substoichiometric amount of water show power lines of monoclinic and tetragonal zirconia, while after the same thermal treatment to 700°C, those prepared with excess water in the initial methanol solution, show mainly tetragonal diffraction lines.     

酸碱性硅溶胶对浆状Cu/Zn/Al催化剂性能的影响

在完全液相法研究发现的基础上,选用酸、碱性硅溶胶,制备Cu/Zn/Al/Si浆状催化剂,采用X射线衍射(XRD)、氢气程序升温还原(H₂-TPR)、红外光谱分析(FT-IR)、氮气吸附、氨气程序升温脱附(NH₃-TPD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)等对催化剂进行了表征。结果表明,两类硅溶胶引入Cu/Zn/Al催化体系后,与前驱体制备环境一致的酸性硅溶胶能显著提高催化剂的CO的转化率和二甲醚的选择性,最高分别可达65.38%和76.26%。酸性硅溶胶削弱了Cu与其他组分的相互作用力,催化剂表现为易于还原、晶粒度大,暴露出丰富的反应所需的Cu⁰活性晶面。此外,硅溶胶的酸碱性质还改变催化剂酸中心的强度和数量且使强、弱酸中心均向低温方向迁移,酸性硅胶制备的催化剂中弱酸中心数量多,进而提高了催化剂活性和二甲醚的选择性。大比表面积和介孔孔隙丰富的催化剂孔结构亦有利于催化剂活性和二甲醚选择性的提高。     

Viscosity,particle size distribution,and structural investigation of tetramethyloxysilane/2‐hydroxyethyl methacrylate sols during the sol–gel process with acid and base catalysts

The tetramethoxysilane (TMOS)/2‐hydroxylethyl methacrylate (HEMA) hybrid gels were synthesized with acid and base catalysts, via the in situ polymerization of HEMA, with and without the cosolvent methanol. With methanol in the TMOS/HEMA sol, the enhanced esterification and depolymerization reactions of the silanols resulted in a slower growth of silica particles. The silica particles that were synthesized with an acid catalyst were less than 40 nm. The thermal resistance of the poly(2‐hydroxyethyl methacrylate) (PHEMA) chains was enhanced by the addition of colloidal silica. The Fourier transform infrared characterizations and the exothermal peaks on the differential scanning calorimetry traces of these hybrid gels indicated chemical hybridization occurring as a result of condensation of the colloid silica and PHEMA at higher temperatures. Hence, the residual weight content of the hybrid gel after its synthesis with the base catalyst was even higher than the content of TMOS in the hybrid sol. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3476–3486, 2004     

Diastereoselectivity control in photosensitized addition of methanol to (R)-(+)-limonene

Highly diastereodifferentiating bimolecular asymmetric photoreaction was achieved in the photosensitized polar addition of methanol to (R)-(+)-limonene. The diastereomeric excess (de) of the photoadduct could be controlled and fine-tuned by changing the internal/external factors such as solvent polarity, reaction temperature, and structure of the sensitizers. The de increased from 23% obtained upon xylene photosensitization in pure methanol at room temperature to >96% upon singlet sensitization with methyl benzoate at -75 degrees C in 0.5 M methanol/diethyl ether solution.     

Alumina-catalyzed condensation of 2-methylquinoline with methanol

The alumina-catalyzed reaction of 2-methylquinoline with excess methanol at 500° produced a mixture of 2-ethyl-, 2-isopropyl-, and 2-isopropenylquinolines in yields of 10%, 7%, and 2%, respectively. A mechanistic interpretation of this reaction is presented.     

Excess volumes,isentropic compressions,and isobaric heat capacities for methanol mixed with other alkanols at 25°C

Excess volumes, excess isentropic compressions and excess isobaric heat capacities for binary liquid mixtures of methanol with ethanol, 1-propanol and 1-butanol have been determined at 25° C. These thermodynamic functions are smaller than those for alkanol + water mixtures and are correlated with the difference in the alkyl chain length in two of the alkanol molecules. The behavior of the component molecules in solution is found to be similar to that in the pure liquid. The excess isentropic compressions of methanol + 1-butanol show an S-shaped concentration dependence with a positive lobe in the methanol rich range and a negative lobe in the methanol poor range, which resembles that of the excess Gibbs energy reported by Polak et al.     

Ortho‐Alkylation of Phenol with Methanol Using Pb‐Cr Promoted Magnesium Oxide Catalysts

In this study, Pb‐Cr promoted magnesium oxide catalysts were used to catalyze the ortho‐alkylation of phenol in the presence of excess methanol. The Cr/MgO catalyst exhibited a high conversion of phenol and a relatively high selectivity for the ortho‐alkylation of phenol. The catalytic activity and the stability of Cr/MgO were improved by the addition of a fairly small amount of Pb. The Pb‐Cr/MgO catalyst showed specificity for the ortho‐alkylation of phenol, which was proved by a series of phenol derivative reactions with methanol.     

Pseudotemplate synthesis of copper nanoparticles in solutions of poly(acrylic acid)-pluronic blends

It was found that the reduction of copper(II) ions in solutions of poly(acrylic acid)-pluronic blends results in a stable sol of metallic copper with a particle size below 10 nm, whereas a less stable sol with coarse aggregates of particles is formed in the presence of poly(acrylic acid) alone and an insoluble complex of this polymer with copper nanoparticles is produced in the presence of pluronic alone. The addition of poly(acrylic acid) to the complex causes the transfer of a portion of nanoparticles from the precipitate into the sol. In mixed poly(acrylic acid) and pluronic solutions, no formation of a polymeric complex with reasonable stability was detected. It was assumed that such a polycomplex is stabilized in the presence of copper nanoparticles. Owing to its amphiphilic nature, the complex forms stable protective shields on the surface of nanoparticles, and the stability of the sol is determined by free fragments of poly(acrylic acid).     

Thermodynamics of solutions of methanol and solvating components

A model is proposed to correlate the excess Gibbs free energies and excess enthalpies of binary solutions of methanol and a solvating component. Solution nonideality from ideal solutions is given by the sum of the chemical contribution term, which is due to self-association of methanol and solvation between methanol and a nonassociating component, and the physical contribution term with allowance for the NRTL equation. The model uses the following data for methanol: two enthalpies for formation of the hydrogen bonds for the dimer and all larger polymeric species, three equilibrium constants of stepwise association for the dimer, trimer and other polymeric species, and an equilibrium constant for cyclic species of more than tetramer. The association model further includes an additional solvation equilibrium to allow for the interaction between the terminal hydroxyl group of methanol polymeric species and a solvating component. The model is extended to predict vapor—liquid equilibria, liquid—liquid equilibria and excess enthalpies for ternary solutions containing methanol and two nonassociating components from only binary information. Calculated results are in good agreement with experimental data as shown by selected illustrative examples.     

Thermodynamics of aqueous solutions of nonelectrolytes. I. Enthalpies of transfer of 1-methyl-2-pyrrolidinone from water to aqueous methanol

Molar excess enthalpies were measured for 1-methyl-2-pyrrolidinone mixed with water and with methanol over the whole concentration range and with aqueous methanol at the low mole fraction of 1-methyl-2-pyrrolidinone at 298.15°K, using a LKB flow microcalorimeter. Enthalpies of transfer of 1-methyl-2-pyrrolidinone from water to aqueous methanol were estimated from the molar excess enthalpies. The result was qualitatively in agreement with the conclusion described by Arnett et al.     

Absorption and surface-enhanced Raman spectra of silver organosols in ethanol

Colloidal silver, dispersed in ethanol and stabilized by adsorbed polymer, shows enhanced Raman scattering of the chromophore dabsyl (N-4-dimethylaminoazobenzene-4′-sulfonyl)aspartate, DABS ASP, in the presence of excess base. The requirement of the base appears linked to the adsorption of the dabsyl aspartate by interaction with the polymer and/or promotion of growth and aggregation of the silver particles. The latter conditions are indicated by changes in the absorption spectrum of the sol upon addition of base. The enhancement is comparable to that observed earlier for DABS ASP on colloidal silver in aqueous medium.     

完全液相法Cu-Zn-Si-Al催化剂一步合成二甲醚

采用完全液相法,以廉价的硅溶胶作为硅原料,制备了一系列的Cu-Zn-Si-Al双功能浆状催化剂,考察不同硅铝比对浆态床CO加氢合成二甲醚的影响。 两周的活性评价表明,硅的引入显著提高了催化剂的活性和稳定性。 当n(Si)/n(Al)=2时,CO转化率最高,为58.1%,且二甲醚的选择性为80.2%。 通过FTIR、XRD、TPR、TPD、BET、XPS和TEM等技术手段对催化剂进行了表征,结果表明,硅组分的添加可以促进活性组分Cu物种的分散,并能够改善完全液相法热处理而导致的积碳现象。 且Si组分的引入与催化剂中的Al相互作用,显著提高了催化剂的甲醇脱水性能,从而使催化剂具有较高的二甲醚选择性。     

Large-Scale Production of 3D Bioactive Glass Macroporous Scaffolds for Tissue Engineering

For tissue engineering applications, a scaffold is required that can act as a template and guide for cell proliferation, cell differentiation and tissue growth. Interconnected pores with diameters greater than 100 m are required for tissue ingrowth, vascularisation and nutrient delivery to the centre of the scaffold. 3D bioactive glass scaffolds have been produced, by foaming sol-gel derived bioactive glasses. The method to produce foams with a modal macropore diameter of 100 m, and a handling strength suitable for cell culture, was to foam 50 ml batches of sol with the aid of a surfactant and gelling agent. In vitro and in vivo tests show that the scaffolds have high potential to be used in bone tissue engineering applications. Larger batches are required to produce scaffolds commercially. The aim of this work was to investigate how the process could be up-scaled for commercial use. This study shows that foaming larger aliquots of sol decreased the scaffold porosity and interconnectivity and investigates methods of modifying the process to obtain large quantities of foam scaffolds with pores in excess of 100 m. The optimum method to produce foams of similar pore structure from 200 ml sol to those produced from 50 ml sol comprised of adding 3 ml surfactant and 12 ml dionised water to the sol to start foaming and injecting a gas mixture (70% helium, 30% nitrogen) at 0.2 bar while applying vigorous agitation.     

Thermogravimetric study of the surfactant–diethanolamine–titanium isopropoxide system behavior

Mesoporous anatase TiO₂ materials with specific surface areas between 70 and 110 m² g^?1 were prepared via sol–gel technique using surfactants oleic acid and Triton-X (TX), in the presence or absence of diethanolamine, in methanol. Surfactants like TX or oleic acid (OA), as well as a gelating and chelate agent like diethanolamine (DEA) are commonly used in TiO₂ formation from a titanium isopropoxide solution. Thermogravimetric methods were applied in order to evaluate the effect of the addition of such molecules in a precursor suspension before TiO₂ materials preparation. The in situ investigation of such systems showed that numerous interactions occur between large molecules such as TX and OA that attributed on both steric effects and hydrogen bond formation. Materials prepared through modified sol–gel technique seem to be stabilized through DEA addition in the precursor suspension.