Jean-Luc Blin

Complete benzene oxidation over gold-vanadia catalysts supported on nanostructured mesoporous titania and zirconia

Abstract The new generation of gold-vanadia catalysts supported on mesoporous titania and zirconia for complete benzene oxidation were explored. The catalysts were characterized by X-ray, TEM, SEM, N2 adsorption analysis, TPR and ESR spectroscopy. The vanadia loading stabilized structure of the both mesoporous supports and this effect is stronger for zirconia comparing to titania. The presence of gold enhanced the V5+→V3+ reduction step and depending on the preparation method, differences in the reduction behavior were established. The catalytic activity of the catalysts also strongly depends on the preparation techniques. For the both series of the studied catalysts when the gold is loaded firstly the activity in complete benzene oxidation is higher than when the vanadia is deposited firstly (VAT>AVT and VAZ>AVZ). A strong synergistic effect between gold and vanadia supported on titania was observed and the catalysts on titania exhibit higher catalytic activity than the catalysts based on zirconia. Comparing the activity of the gold-vanadia/zirconia and gold/zirconia catalysts, it was established for the both catalysts high and equal activity in the reaction studied. The observed differences in the structural and catalytic properties of the both series of the studied catalysts were connected with the nature of the supports used.

Electrochemical evaluation of polysiloxane-immobilized amine ligands for the accumulation of copper(II) species

Accumulation of copper(II) by amine ligands immobilized by covalent binding to silica-based materials was examined by electrochemistry at modified carbon paste electrodes. Three samples were compared: a silica gel grafted with aminopropyle groups, an organic–inorganic hybrid resulting from the condensation of tetra-ethoxysilane and aminopropyle-triethoxysilane and a mesoporous pure silica MCM-41 material grafted with aminopropyle groups. These solids were characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, acid–base titration, N2 adsorption and for their ability to accumulate copper(II) species. Electrochemical detection was achieved after accumulation of copper(II) at open circuit and both preconcentration and detection steps were optimized by varying pH, preconcentration time and the composition of the detection medium. Results are discussed with respect to the nature of the modified silicas.

Synthesis of nanostructured mesoporous zirconia using CTMABr–ZrOCl2·8H2O systems: a kinetic study of synthesis mechanism

Abstract A systematic kinetic study of mesoporous zirconia formation has been performed in order to optimize the synthesis conditions without addition of structure stabilizing agents such as sulfate or phosphate anions. We have investigated in particular the effect of synthesis time and temperature. On the basis of TEM, SEM, XRD and N 2 adsorption–desorption results, a synthesis mechanism has been proposed. It is observed that at low temperature or for short durations at higher temperatures, the obtained materials are first supermicroporous, then if hydrothermal treatment is prolonged, a breakdown of the walls separating adjacent pores allows the transformation to mesopores. The obtained materials have a uniform pore size and their surface can reach 300 m 2 /g. The channel array is, at least part of samples, wormlike. However, if hydrothermal treatment is performed at too high temperature or for too long durations, mesoporous compounds are no longer obtained, but thermodynamically more stable crystalline zirconium oxides with very low specific surface area, namely the tetragonal and monoclinic forms, are the final phases.

One-pot surfactant assisted synthesis of aluminosilicate macrochannels with tunable micro- or mesoporous wall structure

A one-step surfactant assisted synthesis pathway was developed leading to novel hierarchical macro-meso- (or micro-)porous aluminosilicates made of an assembly of macrochannels with openings between 0.5 and 2.0 microm and wormhole-like amorphous walls with tunable pore sizes.

Chemistry of silica at different concentrations of non-ionic surfactant solutions: effect of pH of the synthesis gel on the preparation of mesoporous silicas

Ordered and disordered mesoporous silicas have been synthesized through an assembly of non-ionic decaoxyethylene cetyl ether [C16(EO)10] and a tetramethoxysilane silica source by variation of the pH value of the synthesis gel. The structure, texture and morphology of the mesoporous silicas, synthesized with concentrated and diluted surfactant solutions, have been discussed from the perspective of silicas chemistry upon a variation of pH values of the synthesis gel (micellar solution). With concentrated surfactant solutions (50 wt%), disordered compounds are obtained in a range of pH from 2.0 to 7.0 (micellar solution). As the pH increases, however, the pore size distributions (PSD) become broader and bimodality appears due to the micelle-templated silica (MTS) mesopores and openings arising from silica dissolution-reprecipitation processes. Also, the MTS pores expand due to a change in conformation of the surfactant hydrophilic head upon pH increase. On the other hand, diluted surfactant solutions (10 wt%) lead to ordered materials in a pH range from 2.0 to 7.0 (synthesis gel). The PSD remain very narrow but interparticular porosity appears and the morphologies undergo deep changes from toroids, gyroids and ropes to aggregates of very small particles with increasing pH.

Kinetic study of MCM-41 synthesis

Abstract A kinetic study of MCM-41-type materials formation has been made to optimize the synthesis conditions in particular the synthesis time and temperature. The changes in morphology and textural properties of materials as a function of hydrothermal synthesis time at four different temperatures have been followed. From the characterization results, the synthesis mechanism is postulated. The present work shows clearly that the thickness of the wall separating two adjacent pores increases with hydrothermal synthesis time and temperature while pore size remains constant. The increase in the wall thickness, indicating the enhancement of polycondensation of silica around the micelles of surfactant, should be very important for strengthening the thermal stability of MCM-41 materials.

pH-controlled delivery of curcumin from a compartmentalized solid lipid nanoparticle@mesostructured silica matrix

Silicalization of curcumin-loaded solid lipid nanoparticle (SLN)/micelle dispersions afforded a compartmentalized nanovector, with both macro- and mesostructured domains. SLNs act as reservoirs of curcumin (CU), while mesopores act as pathways to control drug release. Moreover, the release sustainability depends on the nature of the solid lipid (cetyl palmitate vs. stearic acid) and on the pH of the receiving phase. The meso-macrostructured silica matrix templated by SLNs appears thus as a promising drug delivery system for pH-responsive controlled release.

Tuning the morphology and the structure of hierarchical meso–macroporous silica by dual templating with micelles and solid lipid nanoparticles (SLN)

Solid lipid nanoparticles (SLN) stabilized by nonionic polysorbate or block copolymer surfactants were used for the preparation of hierarchical meso–macroporous silica through a co-templated approach combining a cooperative templating mechanism (CTM) with micelles and spherical soft matter particles imprinting. Depending on the reaction conditions, the morphology of the final material can be tuned to capsules or to block matter. The size of the mesopores is strongly dependent on the nature of the surfactant in excess: 3 nm (Tween 20), 5 nm (Tween 40) or 9 nm (Pluronic® P123), whereas the size of the macropores depends only on the size of SLN (250 ± 150 nm). The macroporous texture was clearly evidenced by TEM. The organization degree of the silica wall depends on the surfactant: only wormlike mesoporous capsules were obtained with Tween 20, and hexagonally ordered microdomains embedded in wormlike mesoporous silica capsules were obtained with Tween 40. Hexagonally ordered silica with circularly ordered mesoporosity could be achieved with Pluronic block copolymer P123. Combining mesoporous silica with solid lipid nanoparticles is a straightforward approach for the design of advanced formulations in drug delivery or food chemistry.

Highly ordered mesoporous titania with semi crystalline framework templated by large or small nonionic surfactants

A relatively simple and effective route has been developed for the synthesis of mesoporous titania with a high mesopore ordering and thermal stability in short synthetic period (3 days). Mesoporous TiO2 has been synthesized by a surfactant templating process that combined the evaporation-induced self-assembly method, the liquid crystal templating pathway and basic atmosphere treatment. The developed method can be applied with either large or small surfactants, and in particular with fluorinated ones. The transformation of the amorphous titania walls into nanosized anatase walls occurs without the mesostructure collapse. Moreover, the pore size can be easily tailored by changing the surfactant.

Non-ionic surfactant (C13EOm, m = 6, 12 and 18) for large pore mesoporous molecular sieves preparation

Abstract Polyoxyethylene tridecylethers (C13EOm, m=6, 12 and 18) have been used as templating agents for synthesis of large pore mesoporous materials. The effect of surfactant/silicium molar ratio, heating time, and temperature, and the number of oxyethylene units on the mesoporous material syntheses has been studied in detail. Final compounds were characterized by different techniques such as SEM, TEM and nitrogen adsorption–desorption analysis. The present work shows that the surfactant/tetramethoxysilane molar ratio has a strong effect on the pore diameter for a given surfactant. It is evidenced that both tetramethoxysilane (TMOS) and surfactant can play a role of swelling agent depending on the surfactant/TMOS molar ratio. It is also shown that the pore diameter depends strongly on the heating time and temperature, oxyethylene unit number and surfactant/TMOS molar ratio. All these factors can affect jointly or separately the pore diameter of obtained materials. It is revealed that the surfactant conformation can be changed with the heating temperature. At higher temperature, a more extended molecular conformation can be obtained, which leads to materials with larger pore size.