Search results for "Material chemistry"
showing 10 items of 413 documents
11B-MAS NMR approach to the boron adsorption mechanism on a glucose-functionalised mesoporous silica matrix
2018
[EN] Boron chemistry has raised much interest because, despite the difference between necessities and toxicity being very narrow, it is still widely used in industrial processes. In a previous work we reported an adsorbent for boron extraction from water by the functionalisation of a UVM-7 mesoporous silica matrix with gluconamide moieties. The ability of this material to adsorb boron is based on its well-known affinity for coordinating the cis-diols present in attached saccharide. Although much research on the formation of boron esters with sugars and sugar derivatives in solution has been done, very few reports have dealt with the adsorption mechanism of boron onto functionalised material…
Photosensitivity and second harmonic generation in chalcogenide arsenic sulfide poled glasses
2011
International audience; The present work investigates the photoinduced Second Harmonic Generation processes in thermally poled arsenic sulfide glasses. SHG Maker fringes patterns associated to SHG kinetic measurements about illumination and Raman spectroscopy have been conducted in order to bring new information which confirm the combined influence of charge carriers and mid-range glass structural modification on the poling and the photodarkening mechanisms.
Chalcogenide Glasses Based on Germanium Disulfide for Second Harmonic Generation
2007
International audience; High second-order susceptibilities are created by thermal poling in bulk germanium disulfide based chalcogenide glasses. Experimental conditions of the poling treatment (temperature, voltage, time) were optimized for each glass composition. The second-order nonlinear signals were recorded by using the Maker fringes experiment and a second-order coefficient χ(2) up to 8 pm V-1 was measured in the Ge25Sb10S65 glass. This value is obtained using a simulation based on accurate knowledge of the thickness of the nonlinear layer. Two mechanisms are proposed to explain the creation of a nonlinear layer under the anode: the formation and the migration of charged defects towar…
Nitrogen Hydrate Cage Occupancy and Bulk Modulus Inferred from Density Functional Theory-Derived Cell Parameters
2021
International audience; Gas clathrate hydrate solid materials, ubiquitous in nature as found either on the ocean floor, permafrost on the Earth, or in extraterrestrial planets and comets, are also technologically relevant, for example, in energy storage or carbon dioxide sequestration. Nitrogen hydrate, in particular, is of great interest as a promoter of the kinetics of the methane replacement reaction by carbon dioxide in natural gas hydrates. This hydrate may also appear in the chemistry of planets wherever nitrogen constitutes the majority of the atmosphere. A fine understanding of the stability of this hydrate under various thermodynamic conditions is thus of utmost importance to asses…
Self-organization of porphyrin units induced by magnetic field during sol-gel polymerization
2007
The use of a magnetic field as a controlling factor during the hydrolysis-polycondensation of porphyrin precursors substituted by Si(OR)(3) groups, induces a self-organization of porphyrin moieties due to the stacking of these units in the hybrid material and this study also confirms the effect of the magnetic field in the nano- and micrometric organization during the kinetically controlled polycondensation process.
Photo-induced magnetic bistability in a controlled assembly of anisotropic coordination nanoparticles.
2011
International audience; Anisotropic coordination nanoparticles of the photomagnetic network Cs(I)(2)Cu(II)(7)[Mo(IV)(CN)(8)](4) are obtained through a surfactant-free high-yield synthetic procedure in water. These particles are organised as Langmuir-Blodgett films with a preferential orientation of the nano-objects within the film that exhibit a magnetic bistability below 20 K with a very large coercivity due to an efficient photo-transformation.
Porous materials applied to biomarker sensing in exhaled breath for monitoring and detecting non-invasive pathologies
2020
International audience; Overview of the use of porous materials for gas sensing to analyze the exhaled breath of patients for disease identification.The quantification of specific gases among thousand of VOCs (Volatile Organic Compounds) present in the human breath at the ppm/ppb level can be used to evidence the presence of diseases in the human body. The detection of these biomarkers in human exhaled breath through a noninvasive approach is an important field of research which is still attracting important attention to this day. A portable device working at room temperature and usable directly on exhaled breath samples is still a challenge requiring a sensing material with high performanc…
Photocatalytic degradation enhancement in pickering emulsions stabilized by solid particles of bare TiO 2
2019
Pickering emulsions provide a new way to enhance the efficiency of photocatalytic degradation of water-insoluble pollutants. Indeed, the semiconductor solid particles dually act as the photocatalyst and stabilizer of the emulsion droplets whose size dramatically affects the photocatalytic reaction. The present work aims at the validation of this concept by using bare TiO 2 without any surface modification. Nanostructured TiO 2 has been prepared by a simple sol-gel process and characterized by X-ray diffraction, specific surface area analysis, scanning electron microscopy, and diffuse reflectance spectroscopy. The emulsions were prepared by using 1-methylnaphthalene (1-MN) as a model organic…
Nanoscale structural and electrical properties of graphene grown on AlGaN by catalyst-free chemical vapor deposition
2020
The integration of graphene (Gr) with nitride semiconductors is highly interesting for applications in high-power/high-frequency electronics and optoelectronics. In this work, we demonstrated the direct growth of Gr on Al0.5Ga0.5N/sapphire templates by propane (C3H8) chemical vapor deposition (CVD) at temperature of 1350{\deg}C. After optimization of the C3H8 flow rate, a uniform and conformal Gr coverage was achieved, which proved beneficial to prevent degradation of AlGaN morphology. X-ray photoemission spectroscopy (XPS) revealed Ga loss and partial oxidation of Al in the near-surface AlGaN region. Such chemical modification of a 2 nm thick AlGaN surface region was confirmed by cross-sec…
Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids
2011
Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The…