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991.
Nicolas Dupré Julie Oliveri Jeremy Degryse Jean-Frédéric Martin Dominique Guyomard 《Ionics》2008,14(3):203-207
The growth and evolution of the interphase, due to contact with the ambient atmosphere or electrolyte, are followed using 7Li magic-angle spinning nuclear magnetic resonance (MAS NMR) in the case of two materials amongst the most promising candidates for positive electrodes for lithium batteries: LiFePO4 and LiMn0.5Ni0.5O2. The use of appropriate experimental conditions to acquire the NMR signal allows observing only the «diamagnetic» lithium species at the surface of the grains of active material. The reaction of LiMn0.5Ni0.5O2 with the ambient atmosphere or LiPF6 (1 M in Ethylene Carbonated/DiMéthyl Carbonate (EC/DMC)) electrolyte is extremely fast and leads to an important amount of lithium-containing diamagnetic species compared to what can be observed in the case of LiFePO4. The two studied materials display a completely different surface chemistry in terms of reactivity and/or kinetics of the surface towards electrolyte. Moreover, these results show that MAS NMR is a very promising tool to monitor phenomena taking place at the interface between electrode and electrolyte. 相似文献
992.
Patrick Jollivet Frédéric Angeli Céline Cailleteau François Devreux P. Frugier S. Gin 《Journal of Non》2008,354(45-46):4952-4958
A 5-oxide glass (62.5SiO2, 16.6B2O3, 13.1Na2O, 6.0CaO, 1.8ZrO2) was leached at 90 °C at a high glass-surface-area-to-solution-volume ratio (SA/V = 80 cm?1). Its dissolution rate diminished over time until it became unmeasurable. The alteration layer was characterized by 29Si isotopic tracing in the leaching solution. ToF-SIMS elemental profiles showed that glass dissolution ceased due to clogging of the gel porosity at the gel/solution interface. One of the hypotheses proposed to account for the rate drop observed during borosilicate glass alteration is based on morphological changes in the alteration gel over time. Monte Carlo modeling of glass alteration, especially with simple glasses, indicates a clogging of the porosity on the external portion of the gel (near the solution/gel interface) after densification of the layer by silicon precipitation, but this phenomenon had never previously been directly observed experimentally. The initial results obtained by isotopic tracing provide new data that appears to confirm this hypothesis. 相似文献
993.
Francesco d’Acapito Ana C. Marques Luís F. Santos Rui M. Almeida 《Journal of Non》2008,354(45-46):4940-4943
The local order around ion-implanted Er3+ ions in SiO2–TiO2–HfO2 thin films prepared by sol–gel, was studied by extended X-ray absorption fine structure at the Er-LIII edge. Both the first and second coordination shells of Er3+ were analyzed for different heat-treatments. While the first coordination shell always consisted of ~6–7 oxygen atoms at distances varying between 2.23 and 2.27 Å, the structure of the second shell was found to vary with the film composition and heat-treatment. Namely, whereas Si was found to be the only second neighbor of erbium in binary SiO2–TiO2 films, the addition of HfO2 caused a preferential replacement of Si by Hf. The post-implantation thermal treatments also played a fundamental role in determining the final environment of the erbium ions. 相似文献
994.
Rational Topological Design for Fluorescence Enhancement upon Aggregation of Distyrylfuran Derivatives
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Dr. Charlotte Mallet Dr. Chady Moussallem Alexandre Faurie Magali Allain Dr. Frédéric Gohier Prof. William G. Skene Prof. Pierre Frère 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7944-7953
A series of 2,5‐distyrylfuran derivatives bearing pentafluorophenyl‐ and cyanovinyl units have been synthesized for aggregation‐induced emission (AIE). The effect of the type and extent of the supramolecular connections on the AIE of the furan derivatives were examined and correlated with their X‐ray crystal structures. It was found that the simultaneous presence of cyano and perfluorophenyl units strongly enhances the fluorescence upon aggregation. Single‐crystal X‐ray diffraction analysis confirmed that C?H???F, F???F, C?H???nitrile, Ar???ArF (Ar=aryl, ArF=fluoroaryl), and nitrile???ArF intra‐ and intermolecular interactions drive the topology of the molecule and that solid‐state supramolecular contacts favor AIE of the furan derivatives. 相似文献
995.
“(Diphosphine)Nickel”‐Catalyzed Negishi Cross‐Coupling: An Experimental and Theoretical Study
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Dr. Emmanuel Nicolas Alexia Ohleier Florian D'Accriscio Dr. Anne‐Frédérique Pécharman Dr. Matthieu Demange Dr. Philippe Ribagnac Dr. Jorge Ballester Dr. Corinne Gosmini Dr. Nicolas Mézailles 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7690-7694
The use of a strongly donating “(bis‐dialkylphosphine)Ni” fragment promotes the catalytic coupling of a large range of ArCl and ArZnCl derivatives under mild conditions. Stoichiometric mechanistic investigations and DFT calculations prove that a Ni0/NiII cycle is operative in this system. 相似文献
996.
Dr. Jean-Noël Rebilly Wenli Zhang Dr. Christian Herrero Dr. Hachem Dridi Dr. Katell Sénéchal-David Dr. Régis Guillot Prof. Frédéric Banse 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(3):659-668
Rieske dioxygenases are metalloenzymes capable of achieving cis-dihydroxylation of aromatics under mild conditions using O2 and a source of electrons. The intermediate responsible for this reactivity is proposed to be a cis-FeV(O)(OH) moiety. Molecular models allow the generation of a FeIII(OOH) species with H2O2, to yield a FeV(O)(OH) species with tetradentate ligands, or {FeIV(O); OH.} pairs with pentadentate ones. We have designed a new pentadentate ligand, mtL42, bearing a labile triazole, to generate an “in-between” situation. Two iron complexes, [(mtL42)FeCl](PF6) and [(mtL42)Fe(OTf)2]), were obtained and their reactivity towards aromatic substrates was studied in the presence of H2O2. Spectroscopic and kinetic studies reflect that triazole is bound at the FeII state, but decoordinates in the FeIII(OOH). The resulting [(mtL42)FeIII(OOH)(MeCN)]2+ then lies on a bifurcated decay pathway (end-on homolytic vs. side-on heterolytic) depending on the addition of aromatic substrate: in the absence of substrate, it is proposed to follow a side-on pathway leading to a putative (N4)FeV(O)(OH), while in the presence of aromatics it switches to an end-on homolytic pathway yielding a {(N5)FeIV(O); OH.} reactive species, through recoordination of triazole. This switch significantly impacts the reaction regioselectivity. 相似文献
997.
Over the last years, several variants of multi-constrained Vehicle Routing Problems (VRPs) have been studied, forming a class of problems known as Rich Vehicle Routing Problems (RVRPs). The purpose of the paper is twofold: (i) to provide a comprehensive and relevant taxonomy for the RVRP literature and (ii) to propose an elaborate definition of RVRPs. To this end, selected papers addressing various cases are classified using the proposed taxonomy. Once the articles have been classified, a cluster analysis based on two discriminating criteria is performed and leads to the definition of RVRPs. 相似文献
998.
999.