Pierre Eloy

Tuning the acid/metal balance of carbon nanofiber-supported nickel catalysts for hydrolytic hydrogenation of cellulose.

Carbon nanofibers (CNFs) are a class of graphitic support materials with considerable potential for catalytic conversion of biomass. Earlier, we demonstrated the hydrolytic hydrogenation of cellulose over reshaped nickel particles attached at the tip of CNFs. The aim of this follow-up study was to find a relationship between the acid/metal balance of the Ni/CNFs and their performance in the catalytic conversion of cellulose. After oxidation and incipient wetness impregnation with Ni, the Ni/CNFs were characterized by various analytical methods. To prepare a selective Ni/CNF catalyst, the influences of the nature of oxidation agent, Ni activation, and Ni loading were investigated. Under the applied reaction conditions, the best result, that is, 76 % yield in hexitols with 69 % sorbitol selectivity at 93 % conversion of cellulose, was obtained on a 7.5 wt % Ni/CNF catalyst prepared by chemical vapor deposition of CH(4) on a Ni/γ-Al(2)O(3) catalyst, followed by oxidation in HNO(3) (twice for 1 h at 383 K), incipient wetness impregnation, and reduction at 773 K under H(2). This preparation method leads to a properly balanced Ni/CNF catalyst in terms of Ni dispersion and hydrogenation capacity on the one hand, and the number of acidic surface-oxygen groups responsible for the acid-catalyzed hydrolysis on the other.

Comparative study of the sulfur loss in the xerogel and aerogel sulfated zirconia calcined at different temperatures: effect on the n-hexane isomerization

Aerogel and xerogel sulfated zirconia exhibit different structure and texture at various calcination temperatures. At 560°C the aerogel develops only the tetragonal phase, whereas the xerogel contains both the monoclinic and the tetragonal phases. Heating at higher temperature causes the transition of the tetragonal phase into the monoclinic one for all the samples by loss of sulfur, but the tetragonal phase remains significantly more stable in the aerogel. Characterization indicates that the loss of sulfur at higher temperature is easier for the xerogel. The ability of the aerogel to retain sulfur at higher temperature explains its better stability and confers it a good catalytic performance in the n-hexane isomerization reaction.

Polythiolactone-Based Redox-Responsive Layers for the Reversible Release of Functional Molecules

The development of thin macromolecular layers with incorporated disulfide bonds that can be disrupted and formed again under redox stimulation is of general interest for drug release applications, because such layers can provide rapid and reversible responses to specific biological systems and signals. However, the preparation of such layers from polythiols remains difficult, because of the fast oxidation of thiol groups in ambient conditions. Here we propose water-soluble thiolactone-containing copolymers as stable precursors containing protected thiol groups, allowing us to produce on demand polythiol layers on gold substrates in the presence of amine derivatives. Electrochemical, water contact angle, X-ray photoelectron spectroscopy, and X-ray reflectometry measurements evidence the formation of uniform copolymer layers containing both anchored and free thiol groups. The number of free thiols increases with the content of thiolactone units in the copolymers. In a second step, a thiolated dye, used as a model drug, was successfully grafted on the free thiol groups through disulfide bonds using mild oxidizing conditions, as proved by fluorescence and quartz crystal microbalance measurements. Finally, the reversible release/regrafting of the dye under redox stimulation is demonstrated.

Porosity control and surface sensitivity of titania/silica mesoporous multilayer coatings: applications to optical Bragg resonance tuning and molecular sensing

Mesoporous dielectric multilayer films exhibit an optical response (Bragg resonance) that is highly sensitive to the chemical environment. Using sol–gel preparation and spin-coating deposition method, titania/silica mesoporous layers were alternatively deposited and consolidated to form a Bragg stack on a glass substrate. Tuning of the effective refractive index of titania layers through the control of their porosity allowed us to tailor the optical response of the multilayer film, and in particular its color, to infiltrate liquids and/or molecules dissolved in a solvent. Selective grafting of hydrophobic molecules on the pore surfaces of titania mesoporous layers was likely to be at the origin of unusual behavior of the Bragg resonance spectral shift and intensity variation. The pore accessibility of the different layers forming the stack was investigated through the infiltration of Rhodamine 6G fluorescent dye. Confocal microscopy revealed a homogeneous distribution of the dye across all the layers of the stack. Capillary attraction induced by adequate pore size distribution between adjacent layers was found to play a key role in liquid infiltration throughout the entire mesoporous dielectric structure.

Minimal amounts of dipalmitoylphosphatidylcholine improve aerosol performance of spray-dried temocillin powders for inhalation

Administration of antibiotics by inhalation can greatly improve drug targeting to the site of respiratory infections. In addition, dry powder inhalers are particularly convenient for the patients. The purposes of this study were to demonstrate the interest of pulmonary temocillin delivery to reach high temocillin concentrations locally in the lungs as well as to prepare a spray-dried temocillin powder for inhalation using a minimal amount of generally recognized as safe excipients. Intratracheal instillation of a temocillin solution allowed to reach higher and more sustained drug concentrations in the lungs than intravenous injection in mice, although a 10-fold lower temocillin dose was delivered intratracheally than systemically. A spray-dried powder of pure temocillin presented a fine particle fraction of 9% of the dose loaded in the inhaler. However, the incorporation of 0.5% to 20% of dipalmitoylphosphatidylcholine (DPPC) in the powder increased the fine particle fraction 4- to 5-fold. X-ray photoelectron spectroscopy and X-ray diffraction revealed that DPPC concentrated at the particle surface with its aliphatic chains laterally packed. The minimal amount of DPPC needed to improve the aerosol performance of temocillin supports the use of this excipient in the formulation of cohesive antibiotic powders for inhalation.

Proteins dominate in the surface layers formed on materials exposed to extracellular polymeric substances from bacterial cultures

Abstract The chemical compositions of the surface conditioning layers formed by different types of solutions (from isolated EPS to whole culture media), involving different bacterial strains relevant for biocorrosion were compared, as they may influence the initial step in biofilm formation. Different substrata (polystyrene, glass, steel) were conditioned and analyzed by X-ray photoelectron spectroscopy. Peak decomposition and assignment were validated by correlations between independent spectral data and the ubiquitous presence of organic contaminants on inorganic substrata was taken into account. Proteins or peptides were found to be a major constituent of all conditioning layers and polysaccharides were not present in appreciable concentrations; the proportion of nitrogen which may be due to DNA was lower than 15%. There was no significant difference between the compositions of the adlayers formed from different conditioning solutions, except for the adlayers produced with tightly bound EPS extracted from D. alaskensis.

Supported Pd nanoparticles prepared by a modified water-in-oil microemulsion method

Supported Pd nanoparticles (1.6 wt. %) with different diameters were synthesized by the modified water-in-oil microemulsion method using hydrazine as reducing agent. The size of palladium nanoparticles was investigated by varying the nature of the organic surfactant and solvent. The catalysts were characterized by XRD, XPS, ICP, and TEM. Supported palladium nanoparticles (1–8 nm) were obtained. The results confirmed the dependence of the particle size on the nature of organic surfactants. Smaller particles were obtained with organic solvents and anionic surfactants.

Supported vanadium oxide nanoparticles: effect of preparation method, support and type of precursor on the catalytic performances in the ODH of methanol to formaldehyde

Abstract The deposition of vanadia on silica and titania/silica supports was achieved by chemisorption of a reactive vanadium precursor (VO(O-Pr i ) 3 ) onto surface hydroxyl groups of the mentioned supports. This method was also used for the preparation of the (TiO 2 /SiO 2 ) support by grafting tetra-isopropoxide on the silica. A detailed study of the chemical adsorption of vanadyl alkoxide on the surface of the TiO 2 /SiO 2 support was carried out. The influence of this preparation method on the surface structure, acidic properties and catalytic activity was demonstrated by examining also the corresponding conventionally impregnated catalysts. The catalysts were characterized by chemical analysis, BET, TPD, RAMAN and XPS spectroscopies and tested in the ODH of methanol to formaldehyde. The main findings of this work showed that the surface dispersion of vanadia species is an important parameter to obtain good performances both in terms of activity and selectivity.

Reversible Protein Adsorption on Mixed PEO/PAA Polymer Brushes: Role of Ionic Strength and PEO Content

Proteins at interfaces are a key for many applications in the biomedical field, in biotechnologies, in biocatalysis, in food industry, etc. The development of surface layers that allow to control and manipulate proteins is thus highly desired. In previous works, we have shown that mixed polymer brushes combining the protein-repellent properties of poly(ethylene oxide) (PEO) and the stimuli-responsive adsorption behavior of poly(acrylic acid) (PAA) could be synthesized and used to achieve switchable protein adsorption. With the present work, we bring more insight into the rational design of such smart thin films by unravelling the role of PEO on the adsorption/desorption of proteins. The PEO content of the mixed PEO/PAA brushes was regulated, on the one hand, by using PEO with different molar masses and, on the other hand, by varying the ratio of PEO and PAA in the solutions used to synthesize the brushes. The influence of ionic strength on the protein adsorption behavior was also further examined. The behavior of three proteins-human serum albumin, lysozyme, and human fibrinogen, which have very different size, shape, and isoelectric point-was investigated. X-ray photoelectron spectroscopy, quartz crystal microbalance, atomic force microscopy, and streaming potential measurements were used to characterize the mixed polymer brushes and, in particular, to estimate the fraction of each polymer within the brushes. Protein adsorption and desorption conditions were selected based on previous studies. While brushes with a lower PEO content allowed the higher protein adsorption to occur, fully reversible adsorption could only be achieved when the PEO surface density was at least 25 PEO units per nm2. Taken together, the results increase the ability to finely tune protein adsorption, especially with temporal control. This opens up possibilities of applications in biosensor design, separation technologies, nanotransport, etc.

Self-assembled hybrid precursors towards more efficient propane ODH NiMoO4 catalysts

This work shows a novel method to synthesize bulk NiMoO4 from hybrid materials made of guest ions (Ni and Mo precursors) and a polyampholytic comb-like copolymer displaying a supramolecular organization. This supramolecular organization is crucial because the copolymer serves as a nanostructuring template. While non-porous α-NiMoO4 is obtained with classical methods, mesoporous β-NiMoO4 is prepared here. The β-phase is more efficient in the oxidative dehydrogenation of propane (ODHP). Our strategy assumed that the properties of a catalyst strongly depend on the features of the precursor from which it comes. This is why the precursors were meticulously characterized. Homogeneous hybrids were successfully synthesized where MoO42− anions establish electrostatic interactions with the copolymers positive charges. The nickel cations are stabilized inside the matrix thanks to their coordination by the copolymer COO− functions. By bridging two copolymers, such coordination bonds reinforce the copolymer organization and enable to generate the organized hybrids. Some hybrids were then calcined, characterized and tested in the ODHP reaction. Preparing the β-phase generally requires temperatures beyond 600 °C which favours sintering and makes NiMoO4 poorly active. The use of supramolecularly organized precursors and the possibility it offers to form oxides under “soft conditions” lead to mesoporous β-NiMoO4. The most propene selective β-NiMoO4 is generated here without sacrificing its specific surface area, maintaining its remarkably high activity level. This enables reaching higher propene yields than usual.