Effect of PEG on rheology and stability of nanocrystalline titania hydrosols

Very stable titania hydrosols were prepared by fast hydrolysis of titanium isopropoxide in a large excess of water. XRD patterns show that these sols contain nanocrystals (5–6 nm) of anatase (70%) and brookite (30%). TEM images indicate that these primary particles form aggregates whose mean hydrodynamic diameter, determined by photon correlation spectroscopy, is in the range of 80–90 nm. The flow curves of these colloids, recorded for several volume fractions of nanoparticles, can be perfectly fitted, in the range 0–100 s1, with a power-law model. In this range the behavior is Newtonian but for larger shear rates a shear thinning is observed. The viscosity dependence on particle concentration can be predicted by a Batchelor-type model were the volume fraction of particles is replaced by an effective volume fraction of aggregates, taking into account their fractal dimension. Addition of polyethylene glycol (PEG 2000) induced a marked decrease (more than 50%) of the sol viscosity down to a minimum. This is explained by assuming that PEG adsorbs on the surface of TiO2 particles producing stabilization by steric effects and leading to formation of more compact aggregates. Without PEG the sol viscosity strongly decreases on aging. This effect is not caused by the growth of primary particles. It is rather interpreted as a progressive reorganization of the aggregates toward a more compact packing

Rheological behaviour and spectroscopic investigations of cerium-modified AlO(OH)colloidal suspensions

The rheological behaviour of aqueous suspensions of boehmite (AlO(OH)) modified with different Ce-salts (Ce(NO3)3, CeCl3, Ce(CH3COO)3 and Ce2(SO4)3) was investigated at a fixed Ce/Al molar ratio (0.05). Freshly prepared boehmite suspensions were near-Newtonian and time-independent. A shear-sensitive thixotropic network developed when Ce-salts with monovalent anions were introduced in the nanoparticle sols. The extent of particle aggregation dramatically increased with ageing for Ce(NO3)3 and CeCl3 whereas an equilibrium value was reached with Ce(CH3COO)3. The addition of Ce2(SO4)3 with divalent anions involved no thixotropy but rather a sudden phase separation. The combined data set of IRTF and DRIFT spectra indicated that free View the MathML source anions of peptized boehmite adsorb on the nanoparticle surface by H-bond. The introduction of Ce-salts in the boehmite sol led to the coordination between Ce3+ ions and View the MathML source anions adsorbed on boehmite i.e. to [Ce(NO3)4(H2O)x]− complex. Such coordination led to a thixotropic behaviour which was lower with Ce(NO3)3 compared to CeCl3 and Ce(CH3COO)3. In contrast, Ce2(SO4)3 formed insoluble complexes with dissolved aluminium species. The formation of H-bonded surface nitrate complexes was found to play a decisive role on the particle–particle interactions and consequently on the rheological behaviour of the sols

An efficient route to aqueous phase synthesis of nanocrystalline γ-Al2O3 with high porosity: From stable boehmite colloids to large pore mesoporous alumina

In this paper we emphasise the important role of Pluronic F127 on the porosity of mesoporous alumina prepared from boehmite colloids. By focusing on the F127/boehmite interactions we show how the concepts of interface science may help to predict and improve the textural characteristics of mesoporous alumina. By varying the synthetic parameters, in particular the copolymer content, we show that the porosity of c-Al2O3 can be enhanced by 400% and the average pore diameter can be expanded from 5 to 14 nm. These results are discussed in terms of interactions between the Pluronic F127 and boehmite colloids, and are correlated to the critical micelle concentration (CMC) of the copolymer. The textural characteristics of the mesoporous alumina can be further improved either by introducing hydrocarbons in the preformed boehmite/copolymer sols or by concentrating the sols. In comparison with as-synthesised alumina, those prepared with F127 showed improved thermal stability. Furthermore, boehmite/copolymer sols were stable for all surfactant concentrations investigated and can give high quality coatings suitable for catalytic applications

Systèmes fluorés pour la conception de matériaux poreux : Matrices pour la physisorption de biomolécules

The self-assembly properties of surfactants and those of silica chemistry have led to the preparation of ordered mesoporous materials with hexagonal, cubic or lamellar symmetry and with pore sizes varying from 2 to more than 10 nm. Recently, they have aroused of great deal of interest to academics and industrialists for the development of fundamental and applied research. However, their use in any industrial process needs a careful consideration of the total comprehension of the synthesis mechanism as well as the control of their structural and textural properties. In this work, the relation between the physicochemical properties of a fluorinated surfactant, C7F15C2H4(OC2H4)8OH, and the characteristics of mesoporous silica was investigated. In spite of the existence of a micellar phase, only wormlike mesoporous materials were obtained. On the other hand, the addition of the perfluorodecalin led to the organisation of the channels according to a hexagonal symmetry. The use of various fluorocarbons of different molecular structures evidenced that this phenomenon is associated to the shift of the cloud point curve towards higher temperatures. Hierarchically porous silica were also prepared from oil-in-water emulsions and their characteristics were correlated to the phase inversion temperature of the surfactant/water/oil system. Finally, the mesoporous materials were used as hosts for the physisorption of enzymes and the results showed that the catalytic activity of the immobilised lipases is preserved.Les propriétés d'auto organisation de tensioactifs ainsi que celles de la chimie de la silice ont permis de préparer des matériaux mésoporeux organisés selon une symétrie hexagonale, cubique ou lamellaire dont la taille des pores varie de 2 à plus de 10 nm. Ils sont depuis quelques années le centre d'intérêt d'universitaires et d'industriels qui développent des recherches fondamentales et appliquées. La compréhension globale des mécanismes de synthèse et la maîtrise des propriétés structurales et texturales des matériaux mésoporeux sont nécessaires pour envisager leur utilisation dans un quelconque procédé industriel. Dans ce cadre, nous avons étudié les relations entre les propriétés physico-chimiques d?un tensioactif fluoré C7F15C2H4(OC2H4)8OH et les caractéristiques des silices mésoporeuses. Malgré l?existence d'une phase micellaire, les canaux poreux des matériaux obtenus avec ces solutions micellaires ne sont pas organisés. En revanche, l'addition de la perfluorodécaline provoque une structuration du matériau selon une symétrie hexagonale. L'utilisation de divers fluorocarbures, ayant des structures moléculaires différentes, montre que le phénomène est associé au déplacement de la courbe de point de trouble vers les hautes températures. De plus, il a été montre que la préparation de matériaux à porosité hiérarchisée à partir d'émulsions de type huile dans eau est corrélée à la température d?inversion de phase du système eau/huile/tensioactif. Enfin, les matériaux mésoporeux ont été mis à profit pour immobiliser des enzymes et les résultats montrent que les lipases physisorbées conservent une activité catalytique

Fluorinated systems for the design of porous material : Matrices for the physisorption of biomolecules

Les propriétés d’auto organisation de tensioactifs ainsi que celles de la chimie de la silice ont permis de préparer des matériaux mésoporeux organisés selon une symétrie hexagonale, cubique ou lamellaire dont la taille des pores varie de 2 à plus de 10 nm. Ils sont depuis quelques années le centre d’intérêt d’universitaires et d’industriels qui développent des recherches fondamentales et appliquées. La compréhension globale des mécanismes de synthèse et la maîtrise des propriétés structurales et texturales des matériaux mésoporeux sont nécessaires pour envisager leur utilisation dans un quelconque procédé industriel. Dans ce cadre, nous avons étudié les relations entre les propriétés physico-chimiques d’un tensioactif fluoré C7F15C2H4(OC2H4)8OH et les caractéristiques des silices mésoporeuses. Malgré l’existence d’une phase micellaire, les canaux poreux des matériaux obtenus avec ces solutions micellaires ne sont pas organisés. En revanche, l’addition de la perfluorodécaline provoque une structuration du matériau selon une symétrie hexagonale. L’utilisation de divers fluorocarbures, ayant des structures moléculaires différentes, montre que le phénomène est associé au déplacement de la courbe de point de trouble vers les hautes températures. De plus, il a été montre que la préparation de matériaux à porosité hiérarchisée à partir d'émulsions de type huile dans eau est corrélée à la température d’inversion de phase du système eau/huile/tensioactif. Enfin, les matériaux mésoporeux ont été mis à profit pour immobiliser des enzymes et les résultats montrent que les lipases physisorbées conservent une activité catalytique.The self-assembly properties of surfactants and those of silica chemistry have led to the preparation of ordered mesoporous materials with hexagonal, cubic or lamellar symmetry and with pore sizes varying from 2 to more than 10 nm. Recently, they have aroused of great deal of interest to academics and industrialists for the development of fundamental and applied research. However, their use in any industrial process needs a careful consideration of the total comprehension of the synthesis mechanism as well as the control of their structural and textural properties. In this work, the relation between the physicochemical properties of a fluorinated surfactant, C7F15C2H4(OC2H4)8OH, and the characteristics of mesoporous silica was investigated. In spite of the existence of a micellar phase, only wormlike mesoporous materials were obtained. On the other hand, the addition of the perfluorodecalin led to the organisation of the channels according to a hexagonal symmetry. The use of various fluorocarbons of different molecular structures evidenced that this phenomenon is associated to the shift of the cloud point curve towards higher temperatures. Hierarchically porous silica were also prepared from oil-in-water emulsions and their characteristics were correlated to the phase inversion temperature of the surfactant/water/oil system. Finally, the mesoporous materials were used as hosts for the physisorption of enzymes and the results showed that the catalytic activity of the immobilised lipases is preserved

Nanoparticle route for the preparation in aqueous medium of mesoporous TiO2 with controlled porosity and crystalline framework

Mesoporous TiO2 with tunable pore size and mono-, bi-, and tricrystalline frameworks was prepared from titania nanoparticles synthesized by a sol-gel method. The synthesis was performed by using an amphiphilic triblock copolymer, Pluronic F127, as a structure-directing agent and titanium isopropoxide as a precursor. The structure-directing agent was added in a presynthesized colloidal suspension composed of bicrystalline titania nanoparticles dispersed in an aqueous medium. By varying the ratio between the number of ethoxy units and the number of titanium atoms (EO/Ti), mesoporous TiO2 materials with controlled pore size were synthesized. Materials were characterized by TG/DTA, XRD, SEM, TEM, and N2 adsorption-desorption analysis. In the absence of copolymer, the porosity was low, indicating efficiently packed TiO2 nanoparticles. As the EO/Ti ratio was increased, the average pore size and the specific surface area became larger, whereas the crystallite size of anatase and brookite became smaller. The addition of copolymer induced the enrichment of the brookite polymorph, prevented particle growth, and delayed the formation of rutile. Bimodal (mesoporous-macroporous) N-doped titania with a pure anatase framework was obtained by using diethanolamine (DEA) as the source of nitrogen

Cyclodextrin-based supramolecular assemblies: a versatile toolbox for the preparation of functional porous materials

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Systèmes fluorés pour la conception de matériaux poreux (Matrices pour la physisorption de biomolécules)

Les propriétés d auto organisation de tensioactifs ainsi que celles de la chimie de la silice ont permis de préparer des matériaux mésoporeux organisés selon une symétrie hexagonale, cubique ou lamellaire dont la taille des pores varie de 2 à plus de 10 nm. Ils sont depuis quelques années le centre d intérêt d universitaires et d industriels qui développent des recherches fondamentales et appliquées. La compréhension globale des mécanismes de synthèse et la maîtrise des propriétés structurales et texturales des matériaux mésoporeux sont nécessaires pour envisager leur utilisation dans un quelconque procédé industriel. Dans ce cadre, nous avons étudié les relations entre les propriétés physico-chimiques d un tensioactif fluoré C7F15C2H4(OC2H4)8OH et les caractéristiques des silices mésoporeuses. Malgré l existence d une phase micellaire, les canaux poreux des matériaux obtenus avec ces solutions micellaires ne sont pas organisés. En revanche, l addition de la perfluorodécaline provoque une structuration du matériau selon une symétrie hexagonale. L utilisation de divers fluorocarbures, ayant des structures moléculaires différentes, montre que le phénomène est associé au déplacement de la courbe de point de trouble vers les hautes températures. De plus, il a été montre que la préparation de matériaux à porosité hiérarchisée à partir d'émulsions de type huile dans eau est corrélée à la température d inversion de phase du système eau/huile/tensioactif. Enfin, les matériaux mésoporeux ont été mis à profit pour immobiliser des enzymes et les résultats montrent que les lipases physisorbées conservent une activité catalytique.The self-assembly properties of surfactants and those of silica chemistry have led to the preparation of ordered mesoporous materials with hexagonal, cubic or lamellar symmetry and with pore sizes varying from 2 to more than 10 nm. Recently, they have aroused of great deal of interest to academics and industrialists for the development of fundamental and applied research. However, their use in any industrial process needs a careful consideration of the total comprehension of the synthesis mechanism as well as the control of their structural and textural properties. In this work, the relation between the physicochemical properties of a fluorinated surfactant, C7F15C2H4(OC2H4)8OH, and the characteristics of mesoporous silica was investigated. In spite of the existence of a micellar phase, only wormlike mesoporous materials were obtained. On the other hand, the addition of the perfluorodecalin led to the organisation of the channels according to a hexagonal symmetry. The use of various fluorocarbons of different molecular structures evidenced that this phenomenon is associated to the shift of the cloud point curve towards higher temperatures. Hierarchically porous silica were also prepared from oil-in-water emulsions and their characteristics were correlated to the phase inversion temperature of the surfactant/water/oil system. Finally, the mesoporous materials were used as hosts for the physisorption of enzymes and the results showed that the catalytic activity of the immobilised lipases is preserved.NANCY1-Bib. numérique (543959902) / SudocSudocFranceF

Confinement of Candida Antarctica Lipase B in a Multifunctional Cyclodextrin-Derived Silicified Hydrogel and Its Application as Enzymatic Nanoreactor

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