André Ayral

Potentiality of organic solvents filtration with ceramic membranes. A comparison with polymer membranes

The objective is to identify the main interfacial interactions influencing the flow of organic solvents through ceramic oxide membranes exhibiting a submicronic porous structure, in particular ceramic nanofilters. Three microporous (rp ≤ 1 nm) composite ceramic oxide membranes (3Al2O32ZrO2, SiO2ZrO2, SiO2TiO2) prepared by the sol-gel process were investigated. Permeation experiments were operated with polar (ethanol) and non-polar (hexane, heptane, toluene) organic solvents. Ceramic oxides are considered as high energetic surfaces for non-polar liquids leading to attractive interactions and stable substrate-wetting films when el < es. In the case of a porous substrate, capillary pressure is the parameter generally used to account for liquid penetration in the pores. For submicronic pore sizes, an additional contribution to the surface energy (the disjoining pressure or the fluid density variation resulting from molecular ordering of solvent molecules at solid interfaces) may explain observed deviations to the Darcys law. Results are in good agreement with these interfacial energy concepts. The specific permeation observed for each solvent/membrane pair could be explained by the relation existing between the acid-base surface properties of ceramic oxides and the solid surface energies.

Design of nanosized structures in sol-gel derived porous solids. Applications in catalyst and inorganic membrane preparation

Recent advances in sol-gel processing, with the aim of porous ceramic oxide preparation and applications in catalysis and membrane separation, are reviewed. Recent results from our group in porous solid preparation are presented. Three topics of particular interest are reported which highlight the potential of sol-gel methods to tailor microporous and mesoporous structures in solids, and also the possibility to combine catalyst and ceramic membrane properties. The first one deals with the preparation and the characterisation of supported microporous layers (e.g. with pore diameter of less than 2 nm) and the applications linked to ceramic nanofilters. The second topic illustrates improvements expected in sol-gel processing of oxide catalysts and the possibility of forming supported catalytic layers and membranes. The last one has to do with the role of surface active agents in the control of the sol-to-gel transition and in the formation of tailor-made porous structures in oxide materials.

Synthesis and characterization of inorganic gels in a lyotropic liquid crystal medium. Part 2.—Synthesis of silica gels in lyotropic crystal phases obtained from cationic surfactants

Microporous silica materials with tailored porosity are synthesized by the sol–gel process using lyotropic liquid-crystal phases as templates. The starting isotropic sol is obtained by mixing tetramethoxysilane, water and an alkyltrimethylammonium bromide. The polymerization of the silica network and the formation of the amphiphilic mesophase are simultaneous and cooperative. After thermal elimination of the surfactant molecules, an ordered porous texture is maintained in the silica material. The pore size is related to the size of the templating unit and modulated by the length of the alkyl chain of the used surfactant. In this paper, the various steps of the synthesis are studied and the porous texture of the final material is characterized and discussed in terms of templating effects.

One pot synthesis of hierarchical porous silica membrane material with dispersed Pt nanoparticles using a microwave-assisted sol–gel route

A versatile sol–gel route has been developed for the preparation of hierarchical porous silica membrane material with highly dispersed platinum nanoparticles (Pt-NPs). The outstanding feature of the “one pot” synthesis developed in this work lies in the successful preparation of a stable complex suspension made of silica sol, multi-scale porogens and Pt nanoparticles. The multi-scale porogens were based on non-ionic triblock copolymers and aqueous latex suspension to create mesopores and macropores, respectively, with finely tuned pore size and organization. For further functionalization of the membranes, Pt nanoparticles of about 4 nm in diameter were prepared by irradiating with microwaves (MW) the Pt precursors added in the starting suspension. This original path is suggested to enable a pre-organization of Pt nanoparticles in the ordered mesoporous structure. The suspensions were then deposited as thin films on either dense or macroporous supports, and further thermally treated at 450 °C to remove the porogen units. Hierarchical porous layers composed of micropores (<2 nm), ordered mesopores (∼4 nm) and macropores (∼70 nm) with or without Pt were prepared and characterized. The resulting membranes are foreseen to exhibit great potential as multifunctional membranes for gas separation coupled with catalytic reaction.

Microporous Silica Membrane: Basic Principles and Recent Advances

Publisher Summary This chapter discusses the basic principles and the recent advancement of microporous silica membrane. It discusses several inorganic membranes are available, focusing on the synthesis and applications of microporous amorphous silica membranes. Microporous amorphous silica exhibits a weak stability in aqueous solutions or wet streams, which limits its use as separative membranes to specific applications. The main current developments deal with gas separation applications—in particular hydrogen separation. The thermal stability of silica membranes compared with organic and hybrid layers and their interconnected porosity inside a stiff oxide skeleton enable to reach very good permeability–selectivity balances. The chapter discusses different synthesis methods used to prepare supported amorphous silica membranes. The designing of silica membrane and associated separative properties are also explained.

X-ray reflectometry characterization of SON 68 glass alteration films

Abstract This paper presents the first direct and simultaneous density and thickness measurements by X-ray reflectometry (XRR) of films that develop during aqueous alteration of the French SON 68 (R7T7-type) nuclear glass which is a multi-component silicate. The feasibility of XRR for this type of glasses is investigated by comparing the results with those obtained using other techniques. The influence of drying and the presence of crystalline phases on the XRR signal is studied. It is shown that XRR still yields useful data when a traditional method such as solution sampling cannot be used anymore. The evolution of the layers with alteration time was followed during 134 days. Three different steps are observed: an interdiffusion step, the formation of a homogeneous gel and finally an electronic density gradient (porosity and/or composition) within the gels at long reaction times. This density gradient could explain the protective properties of the gel.

Sol–gel systems with controlled structure formed in surfactant media

The structure and mechanisms of formation of silica and zirconia gels produced by alkoxide hydrolysis [tetramethylorthosilicate (TMOS) and Zr (OPri)4)] in different surfactant media have been investigated using small-angle neutron scattering and other techniques. Inverse micelle and lamellar phase systems have been formed with non-ionic octylphenyl polyether alcohol surfactants, C8ΦEx, where x, is 5 and 10, respectively. In these three-phase systems (water–surfactant–organic solvent) a large proportion of water is bound to the hydrophilic polyoxyethylene chains of the surfactant molecules. This has an important role in controlling the formation of the gel and its structure. Inverse micelles act as nucleation sites for the formation of very small oxide particles (⩽3 nm), which subsequently aggregate to give a fractal structure (D≈ 2.3). The lamellar phases exist as microdomains (0.1–1 µm), and alkoxide hydrolysis occurs predominantly in the surrounding zones, to give fractal aggregates (D≈ 1.9) corresponding to diffusion-limited cluster aggregation (DLCA). Under shear, such lamellar phases are aligned and then produce oriented silica gels with an anisotropic structure. Cylindrical micelles can be formed with the cationic n-alkyl trimethyl ammonium surfactant. With these systems hydrolysis of TMOS occurs in the aqueous phase surrounding the micelles. Such relations can induce the organisation of the micelles to a hexagonal phase. Subsequent elimination of surfactant results in silica xerogels containing cylindrical pores of controlled size.

Synthesis of alumina gels in amphiphilic media

This work deals with the synthesis of alumina gels from aqueous solutions of aluminum chloride in the presence of cationic surfactant molecules. The effect on the sol-gel transition of the reagent concentrations and of the synthesis temperature are first studied. The structure of the resulting wet and dried gels and the formation of liquid crystal mesophases are studied by X-ray diffraction. The thermal and structural evolutions of the gels are then characterized by thermogravimetric and X-ray diffraction measurements. Finally, nitrogen adsorption isotherms are used to investigate the porous texture of the thermally treated materials up to the transformation into α-Al2O3.

Sonochemical deposition of platinum nanoparticles on polymer beads and their transfer on the pore surface of a silica matrix.

This study reported the sonochemical deposition of platinum on the surface of polystyrene beads (PSBs) and the transfer of obtained Pt nanoparticles into a porous silica matrix using the PSB as a sacrificial template. Platinum nanoparticle deposition was ensured by the sonochemical reduction of Pt(IV) at room temperature in latex solutions containing polystyrene beads in the presence of formic acid under Ar or under Ar/CO atmosphere without any additives. After ultrasonic treatments for few hours, well dispersed Pt nanoparticles within the range of 3-5 nm deposited on PSB were obtained in both studied conditions. Samples were then mixed with TEOS, dried, and heated at 450°C to ensure the PSB removal from the silica matrix. TEM and SEM results clearly show that final silica pore size is within the same order of magnitude than initial PSB. Finally, platinum decorated silica matrix with chosen pore sizes was successfully prepared.

Surface modification of titania powder P25 with phosphate and phosphonic acids--effect on thermal stability and photocatalytic activity.

Phosphorus is frequently reported as a doping element for TiO(2) as photocatalyst; however, the previously reported methods used to prepare P-doped TiO(2) do not allow control over the location of the phosphorus either in the bulk or at the surface or both. In this study, we report on the surface modification of Evonik P25 with phosphonic (H(3)PO(3)) and octylphosphonic acid [C(8)H(17)-PO(OH)(2)], done to limit the introduction of phosphorus only to the photocatalyst surface. The effect of this element on the thermal behavior and photocatalytic properties is reported through characterization using elemental analyses, solid state (31)P NMR, X-ray powder diffraction, N(2) porosimetry, dilatometry, etc. Thus, the objective of the work reported here is to focus on the role(s) that phosphorus plays only at TiO(2) crystallite surfaces. For comparison, other samples were treated with phosphoric acid.