Two bonding configurations of acetylene on Si(001)-(2x1): A combined HREELS and DFT study

International audienc

Geometrical and vibrartional features of adsorbed acetylene on Si(100)-(2x1)

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Adsorption of ethylene on Si(100)-(2x1) reconstructed surface: molecular modeling and HREELS study

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Surface chemical states of cellulose, chitin and chitosan studied by density functional theory and high-resolution photoelectron spectroscopy

International audienceA combined theoretical and experimental approach has been applied to study the 1s electron-energy surface properties of cellulose, chitin, synthesized chitin nanorods and chitosan using density functional theory and high-resolution photoelectron spectroscopy. This allows to reliably distinguish the contributions of surface hydrocarbon impurities in the photoelectron spectra and to examine in detail the chemical states of the polysaccharide surfaces. Although a stoichiometric structure is suggested for the cellulose surface as more likely, a mechanism for possible degradation of the surface including removal of the OH group bonded to glucose ring is also contemplated. The good agreement between theoretical and experimental results allows suggesting a chitosan-like structure for the surfaces of as-prepared chitin and of chitin nanorods. In addition to the dominant concentration of amino NH2 groups on these surfaces, a small amount of acetyl amine NH2COCH3 groups is also observed on the as-prepared chitin. It is possible that protonated amino NH3+ functional groups instead of acetyl amine are present on the crystalline surface of chitin nanorods. The possible destructive role of X-ray radiation on the studied surfaces is also discussed

Improved silica–titania catalysts by chitin biotemplating

International audienceSilica–titania materials with improved catalytic performance were elaborated as mesoporous microparticlesby combining sol–gel and spray-drying processes with the self-assembly properties of α-chitin nanorodsacting as biotemplates. Three different synthesis approaches are discussed, leading to materials with variedtextural and chemical characteristics studied by SEM, N2 volumetry, TEM, XPS and DR-UV techniques. Theuse of water or ethanol as initial solvent for chitin nanorod suspensions, as well as the mixing conditions ofthe precursors, has been shown to have a significant impact on the final properties. Materials of specificsurface areas of up to 590 m2 g−1 and porous volumes of up to 0.84 mL g−1, with low surface Si/Ti ratio,could be disclosed. Properties were further investigated by employing the silica–titania materials as heterogeneouscatalysts for the sulfoxidation of bulky model compounds. The location of Ti active sites at thepore surface has been maximized and allows for improved productivity

A Facile Strategy for the Preparation of Highly Mesoporous γ-Alumina

International audienceA new, rapid, and very facile strategy for the large-scale preparation of highly porous γ-Al2O3 was developed. Defined γ-alumina microparticles with a narrow mesopore-size distribution, specific surface area of 400 m2 g–1, and a pore volume of 0.65 mL g–1 were obtained by merely employing an aqueous aluminum chloride solution

Mesoporous alumina from colloidal bio-templating of Al clusters

International audienceA simple and green synthesis route was disclosed for the achievement of mesoporous alumina microparticles employing polysaccharide nanoparticles (a-chitin nanorods) as templates. Pore textures can be tuned by the cationic alumina precursor. Compared to small cations,the use of Al13 and Al30 oxo-hydroxo clusters leads to better defined and elongated mesopores. Electron microscopy and spectroscopic (13C, 27Al NMR, XPS) measurements demonstrated that this is related to the effective coating of a-chitin nanorods by these pre-condensed colloids

Theoretical and Experimental Local Reactivity Parameters of3‑Substituted Coumarin Derivatives

International audienceLocal reactivity descriptors, such as atomic charges, atomic electrostatic potential andatomic Fukui indices were computed for a series of 3-substituted coumarin (2-oxo-2H-1-benzopyran)derivatives, using density functional theory (DFT) and Möller−Plesset methods (MP2). The variationof those properties as a function of the substituents was compared with the variation of the measuredXPS binding energies. The atomic electrostatic potentials and XPS binding energies serves as indicatorsof the electrophilicity of a given center within a molecule, while the atomic Fukui indices describe itsdegree of electronic localization, known as atomic softness. The correlation between those theoreticaland experimental properties allowed us to follow the effect of electron withdrawing substituents on theelectrophilicity of a given atomic center. The Fukui indices provided additional information about thesoftening/hardening of the center of interest due to presence of different substituents to the coumarin system. On the basis ofthese analysis, the 1,2-addition would be favored for 3-acetyl, 3-phosphono, and 7-diethylamino substituents, while 3-carboxyl, 3-ethoxycarbonyl, and 3-nitro substituent would favor 1,4-addition. The substituted coumarins would preferably react with softnucleophiles at position 2 and with hard nucleophiles at position 4

New Insights on the Nickel State Deposited by Hydrazine Wet-Chemical Synthesis Route in the Ni/BCY15 Proton-Conducting SOFC Anode

Yttrium-doped barium cerate (BCY15) was used as an anode ceramic matrix for synthesis of the Ni-based cermet anode with application in proton-conducting solid oxide fuel cells (pSOFC). The hydrazine wet-chemical synthesis was developed as an alternative low-cost energy-efficient route that promotes ‘in situ’ introduction of metallic Ni particles in the BCY15 matrix. The focus of this study is a detailed comparative characterization of the nickel state in the Ni/BCY15 cermets obtained in two types of medium, aqueous and anhydrous ethylene glycol environment, performed by a combination of XRD, N2 physisorption, SEM, EPR, XPS, and electrochemical impedance spectroscopy. Obtained results on the effect of the working medium show that ethylene glycol ensures active Ni cermet preparation with well-dispersed nanoscale metal Ni particles and provides a strong interaction between hydrazine-originating metallic Ni and cerium from the BCY15 matrix. The metallic Ni phase in the pSOFC anode is more stable during reoxidation compared to the Ni cermet prepared by the commercial mechanical mixing procedure. These factors contribute toward improvement of the anode’s electrochemical performance in pSOFC, enhanced stability, and a lower degradation rate during operation