Michel J. Genet

Surface Chemical Composition of Diatoms

Among diatoms, Phaeodactylum tricornutum is a peculiar species that exists in three morphotypes with distinct cell wall structures and low silica content. X‐ray photoelectron spectroscopy (XPS) analysis was performed on P. tricornutum and compared with diatom Thalassiosira pseudonana; the results provide new information on the chemical composition (elements, chemical functions, classes of biochemical compounds) of the cell surface. Two types of silicon were found: condensed silica (SiO2) and weakly polymerised silicate. Cells of T. pseudonana showed the highest concentration of silicon, with a majority in the form of condensed silica. For the fusiform and triradiate morphotypes of P. tricornutum, the majority of the small concentration of silica found was in the form of weakly polymerised silicate. For all morphotypes of P. tricornutum, higher polysaccharide concentrations replaced silica as a structural part of the cell wall. In both diatoms, a high concentration of lipids was measured, in the form of carboxylic esters. Protonated nitrogen and phosphate were found in correlated amounts and attributed not only to phospholipids but also to phosphoproteins. Chloride ions characterised by a high electron density might be associated to these moieties. Sulfate groups were also detected, principally in P. tricornutum, and attributed to monoesters of polysaccharides.

Unsupported Cobalt Molybdenum Sulfide Catalysts .2. Characterization and Evolution of Physicochemical Properties During Catalytic Reaction

Abstract Cobalt molybdenum sulfide catalysts were prepared by two different methods, comaceration (CM) and homogeneous sulfide precipitation (HSP). Both types o catalysts were characterized by several techniques, DTA, XPS, AEM, conductivity measurements and temperature programmed reduction. Physicochemical properties were determined for different states of the catalyst:precursor, fully sulfided and catalytically tested. It is confirmed t

Redox Behavior of Transition-metal Ions in Zeolites .8. Characterization of a Ruthenium Metal Phase in Nay Zeolite

RuNaY zeolite was prepared by ion exchange with Ru3+-hexammine. This complex was decomposed and the ions reduced to the metal state. The influence of water present during the reduction and the sintering of the metal in oxygen was investigated at different temperatures.Temperature programmed oxidation experiments allow an overall characterization and the detection of possible bidisperse systems of metal particle sizes. Ruthenium is held very easily in the zeolite supercages. When water is present during reduction Ru agglomerates are built up in holes of the zeolite crystals. In the presence of oxygen excessive sintering occurs and large crystals are formed outside the zeolite. This picture is obtained using transmission electron microscopy, microprobe analysis and X-ray line broadening techniques. Chemisorption of hydrogen and its desorption during a temperature programmed run indicate that the metal particles absorb subsurface hydrogen. The determination of Ru-particle sizes from the latter measurements is not straight-forward.

Surface lipids and their distribution on willow (Salix) leaves: A combined chemical, morphological and physicochemical study

The surfaces of leaves of three willow (Salix spp.) clones with different frost tolerance and biomass productivity were investigated in order to elucidate further the previously observed relationship between high epicuticular leaf wax load, high biomass productivity and poor overwintering survival of Salix clones. Morphological studies by scanning electron microscopy (SEM) were combined with contact angle measurements, surface overall chemical analysis by X-ray photoelectron spectroscopy (XPS) and gas chromatographic (GC) analyses of extracted waxes and cutin. The GC analyses revealed that epicuticular waxes contained n-alkanes, n-alcohols, n-aldehydes, wax esters and free fatty acids. Mono- and dihydroxy hexadecanoic and monohydroxy octadecanoic acids were major cutin acids in the leaves of the three Salix clones. Overall chemical analysis showed that the Salix leaf surfaces were composed primarily of carbon (about 90%) and oxygen (about 10%). SEM showed that the leaf surfaces of the three Salix clones were partly (15-40% of the area) covered by smooth spherical particles on or in a planar matrix. By combining these chemical and morphological analyses, it was concluded that the particles observed by SEM were composed of epicuticular waxes, and the planar matrix between the particles was cutin. The high epicuticular wax load and the high amounts of n-alkanes, high levels of dihydroxy hexadecanoic acid and total C-16 acids in cutin, and the high leaf-surface coverage by the wax spheres correlated with the poor frost tolerance and high productivity of the three Salix clones in this study. Furthermore, water contact angles on the leaf surface of the frost-susceptible high-producerclone were 93 degrees, about 20 degrees higher than on the leaf surfaces of the two other clones

Catalytic synergy between MoO3 and BiPO4 in N-ethyl formamide dehydration: II. Characterization of mixtures of MoO3 and BiPO4

This paper concerns the physicochemical characterization of mixtures of BiPO4 and MoO3 powders whose catalytic activity in the dehydration of N-ethyl formamide has been reported previously. The aim of the work was to investigate whether the existence of any mixed BiPMo oxide species, due to a contamination of the surface of one phase by elements coming from the other phase, could explain the synergy. Analytical Electron Microscopy (AEM) detects a contamination of BiPO4 by MoO3 only when the mixture is prepared from suspensions of BiPO4 and MoO3 in water. Electron Spectroscopy for Chemical Analysis-X-Ray Photoelectron Spectroscopy (ESCA-XPS) results cannot give any valuable information with respect to contamination, due to the relatively important thickness of the surface layer analyzed. Ion Scattering Spectroscopy shows a contamination in the same case as AEM. The MoO3-contaminated layer is easily removed by ion sputtering. We conclude that, except for the fresh mixture prepared with water, no surface contamination of one phase by elements of the other phase can be detected in fresh catalysts or in catalysts having worked in the reacting mixture of N-ethyl formamide and oxygen at moderate temperatures.

Chitosan-coated electrospun nanofibers with antibacterial activity

Charged nanofibers were prepared by electrospinning (ESP) poly(ε-caprolactone) with a copolymer bearing carboxylic acid functions. The presence of these functions allowed exposing some negative charges on the fiber surface, by dipping the fibers in a phosphate buffer. A layer of chitosan, a polycation in acidic medium, was then deposited on the nanofiber surface, thanks to electrostatic attraction. Fibers were characterized at each step of the process and the influence of the copolymer architecture on chitosan deposition was discussed. The antibacterial activity of the resulting fibers was finally assessed.

Analysis of Poly(Ethylene Terephthalate) (PET) by XPS

Poly(ethylene terephthalate) is used in numerous industrial applications. Successful medical applications are in the area of cardiovascular surgery. Its chemical functionality makes it propitious to grafting biochemical compounds; surface modification by plasma treatment may also be used to improve biocompatibility and modify wetting properties. The analyzed specimen was a commercial film (Mylar A). The main C 1s region was decomposed into three main components which were clearly identified on the recorded spectrum: 284.8, 286.4, and 288.8 eV attributed, respectively, to carbon only bound to carbon and hydrogen [C¯–(C,H)], carbon making a single bond with oxygen [C¯–O] and carbon of ester [C¯OO]. Satellite peaks were found at 291.3, 293.5, and 295.8 eV. The molar ratios C¯–(C,H):C¯–O:C¯OO were 3:0.92:0.91 excluding the satellite peaks, to be compared with the expected values of 3:1:1. The O 1s peak showed two partially resolved components at 531.6 [O¯=C–O] and 533.3 eV [O=C–O¯] with a satellite at 538.2 e...

Silanization with APTES for Controlling the Interactions Between Stainless Steel and Biocomponents: Reality vs Expectation

Jessem Landoulsi1, Michel J. Genet2, Karim El Kirat3, Caroline Richard4, Sylviane Pulvin5 and Paul G. Rouxhet2 1Laboratoire de Reactivite de Surface, Universite Pierre & Marie Curie -Paris VI, 2Institute of Condensed Matter and Nanosciences – Bio & Soft Matter, Universite Catholique de Louvain, 3Laboratoire de Biomecanique et Bioingenierie, 4Laboratoire Roberval, 5Genie Enzymatique et Cellulaire, Universite de Technologie de Compiegne, 1,3,4,5France 2Belgium

Calibration of the X-ray photoelectron spectroscopy binding energy scale for the characterization of heterogeneous catalysts: is everything really under control?

Investigations of X-ray photoelectron spectra from solid samples need corrections for the surface charging effect. For powder samples such as heterogeneous catalysts and their supports, the C-(C,H) component of the C 1s peak is often used as an internal standard for the calibration of the binding energy scale. Although this method is widely recognized as suitable for the study of heterogeneous catalysts, we show that a significant calibration bias can be encountered upon comparing samples with different bulk composition. In this paper, a series of SiO2-Al2O3 supports and Pd/SiO2-Al2O3 catalysts with various Si/Al ratios were studied. The spectra issued from these samples were processed with the classical calibration method on the basis of the carbon peak. Important discrepancies in the relative position of the photoelectron peaks were noticed. After systematically discarding instrument-related issues, a true chemical influence of the bulk matrix on the analyzed surface species was evidenced. The extent of this chemical effect was dependent on the composition of the sample and more precisely on its ionicity. Two possible mechanisms for this chemical effect were proposed and discussed. Finally, an alternative calibration method was offered.

Principal component analysis: a versatile method for processing and investigation of XPS spectra.

Given the relevance of principal component analysis (PCA) to the treatment of spectrometric data, we have evaluated potentialities and limitations of such useful statistical approach for the harvesting of information in large sets of X-ray photoelectron spectroscopy (XPS) spectra. Examples allowed highlighting the contribution of PCA to data treatment by comparing the results of this data analysis with those obtained by the usual XPS quantification methods. PCA was shown to improve the identification of chemical shifts of interest and to reveal correlations between peak components. First attempts to use the method led to poor results, which showed mainly the distance between series of samples analyzed at different moments. To weaken the effect of variations of minor interest, a data normalization strategy was developed and tested. A second issue was encountered with spectra suffering of an even slightly inaccurate binding energy scale correction. Indeed, minor shifts of energy channels lead to the PCA being performed on incorrect variables and consequently to misleading information. In order to improve the energy scale correction and to speed up this step of data pretreatment, a data processing method based on PCA was used. Finally, the overlap of different sources of variation was studied. Since the intensity of a given energy channel consists of electrons from several origins, having suffered inelastic collisions (background) or not (peaks), the PCA approach cannot compare them separately, which may lead to confusion or loss of information. By extracting the peaks from the background and considering them as new variables, the effect of the elemental composition could be taken into account in the case of spectra with very different backgrounds. In conclusion, PCA is a very useful diagnostic tool for the interpretation of XPS spectra, but it requires a careful and appropriate data pretreatment.