Portail HAL ENSCP
Not a member yet
9647 research outputs found
Sort by
Evidence for Methylaluminoxane (MAO) Molecular Structure and Reactivity from Ultrahigh Magnetic Field <sup>27</sup>Al MAS NMR Spectroscopy Combined with DFT Calculations
No full textInternational audienceThe structure and reactivity of methylaluminoxane (MAO), a reagent of major interest for olefin polymerization, both industrially and academically, has been probed using ultrahigh magnetic field solid‐state NMR (28.2 T, 1200 MHz for 1H Larmor frequency). High resolution methods combined with density functional calculations allowed for the identification and quantification of five major aluminum sites, providing precise information on the structure of MAO at the molecular level. Based on reactivity studies with THF and [ZrCp2AlMe2], the main reactive centers are identified as bismethyl aluminum species stabilized via a bridging methyl group from a neighboring Al center, featuring both high chemical shift and quadrupolar coupling constants (162 ppm and 27.4 MHz, respectively). This approach demonstrates the ability to monitor the chemistry of MAO with unprecedented precision, enabling a state‐of‐the‐art understanding of its structure and reactivity
Anticancer Iron–Iridium Organometallic Conjugates
No full textInternational audienceThe diiron vinyliminium complexes [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(3-C5H4N)CHCN(R)(Me)}]CF3SO3 (Cp = η5-C5H5; R = 2,6-C6H3Me2 = Xyl, 2a, R = Me, 2b) reacted with [IrCp*(Phpy)Cl] (IrCl; Cp* = η5-C5Me5, Phpy = κN,κC-2-phenylpyridine) and AgCF3SO3 to afford the bis-cationic iron–iridium conjugates [Fe2Cp2(CO)(μ-CO){μ-η1:η3-C(3-C5H4NIrCp*Phpy)CHCN(Me)(R)}][CF3SO3]2 (4a–b), in nearly quantitative yields. Similarly, the reaction of the ferracyclic compound [FeCp(CO){CN(Me)(Xyl)CHC(3-C5H4N)C(═O)}] (3a) with [IrCp*(Phpy)Cl]/AgNO3 led to the monocationic species [FeCp(CO){CN(Me)(Xyl)CHC(3-C5H4NIrCp*Phpy)C((═O)}]NO3 (5a, 70% yield). The new complexes 4a–b and 5a were characterized by mass spectrometry, IR and 1H and 13C NMR spectroscopy. NMR and DFT analyses indicate that they exist as pairs of diastereoisomers due to the chirality centers in the iron and iridium scaffolds, and that the coordination strength of the pyridyl ligand to iridium is comparable to that observed in the iridium-pyridine adduct [IrCp*(py)(Phpy)] (Irpy). The cytotoxicity of 4a–b and 5a was evaluated on cancer (A2780, A549, U87) and noncancerous (MRC-5) cell lines, with 5a exhibiting superior activity compared to cisplatin and Irpy, along with a tendency toward selectivity. The activity of 4a–b and 5a, which is significantly higher compared to their iron precursors, is associated with enhanced iridium uptake in cancer cells (aligning with lipophilicity, determined as Log Pow values), suppression of oxygen consumption rate and elevated ROS production
Digital correlation analysis and optimization of microporous layer through a machine learning workflow for PEMFC applications
No full textInternational audienceThe Microporous Layer (MPL) plays a crucial role in Proton Exchange Membrane Fuel Cells (PEMFCs), as it influences the overall transport properties within these devices. This study introduces a novel Machine Learning (ML) approach to optimize the MPL microstructure and properties. Synthetic datasets were generated by considering key manufacturing parameters, including Carbon Particle (CP) diameter, CP Solid Volume Percentage (SVP), and polytetrafluoroethylene (PTFE) SVP, and used to calculate MPL output properties such as relative diffusivity, thermal conductivity, and electrical conductivity. Our ML framework achieved an R2 score of 0.92, with a decrease in computational time for predicting MPL properties from ∼1 h (using physics-based methods) to ∼7 s (using the ML model). Finally, the optimizer suggested a low solid weight % (carbon and PTFE) for maximum diffusivity, while high carbon SVP and low PTFE SVP for maximum conductivities. Among the three evaluated MPL output properties, the electrical conductivity and relative diffusivity are consistent with experimental literature. In contrast, thermal conductivity is one to two orders of magnitude higher than experimental values. This discrepancy is difficult to assess because of the significant dispersion of experimental data found in the literature, which may arise from different manufacturers, fabrication methods and measurement techniques
Electroactive molecular layers produced by reduction of an aryldiazonium salt scrutinized by Tip Enhanced Raman Spectroscopy
No full textInternational audienceSurface modification methodologies are continuously refined, which in parallel necessitates accurate analytical methods to probe their chemical composition at the nanoscale. We describe here our electrochemical and Tip Enhanced Raman Spectroscopy results on surfaces modifiedthrough reduction of an electroactive aryldiazonium salt. Grafting may be first triggered electrochemically. In this case, thick and disorganized layers are produced, with important changes in spectral responses in comparison to the parent system. Conversely, spontaneous reduction of the salt also occurs during simple immersion in the diazonium solution, which leads to low surface coverages (i.e. thin layers) and preservation of the molecular backbone of the molecule. This study highlights the advantages of TERS to recover chemical information at the nanoscale even for complex surface modification processes
Smoothed boundary method for phase field modeling of biphasic lithiation dynamics in Li Fe PO 4 cathode
No full textInternational audienceAn appropriate description of the lithiation dynamics in biphasic primary cathode particles of Li-ion batteries requires an accurate treatment of the conditions holding at the interface between the particle and the surrounding liquid electrolyte. We propose a phase field model based on the Allen-Cahn approach within which the particle-electrolyte interface is smooth [smoothed boundary method (SBM)], to simulate arbitrarily shaped particles. Surface terms are added to the evolution equations, and SBM calculations are compared with benchmark simulations for which the boundary conditions are explicitly imposed at the borders of the calculation domain. Our findings highlight the necessity of introducing strengthening factors for the surface terms to achieve the desired conditions for the phase and elastic fields, and to enable an accurate reproduction of stress distributions within the particle. This refinement of the SBM is critical for reliable predictions of Li insertion/extraction rates and lithium diffusion behavior in the context of Li-ion batteries. We perform also a simulation under potentiostatic conditions with a full coupling of the different physical processes at play. It illustrates the applicability of our approach and demonstrates the capabilities of the SBM for a simulation of lithiation dynamics with coupled electrochemistry and mechanics
Transient Supramolecular Polymers by pH‐Gated Conformational Control of a Self‐Assembling Cyclodextrin
No full textInternational audienceLinking a cyclodextrin (CD) host to a hydrophobic guest can result in two distinct conformations: an introverted form (in), in which the guest is self‐included within the CD cavity, and an extraverted form (out), which enables intermolecular interactions and thus the formation of a supramolecular polymer. In this study, we demonstrate that a subtle variation of the linker enables interconversion between these two conformations, the in conformer being thermodynamically the most stable in water. At basic pH (>8) the out conformer is instantly converted into the in. In contrast, at acidic pH (<2), the out monomer can be kinetically trapped and can self‐assemble into a supramolecular polymer. DFT calculations reveal that the interconversion mechanism is governed by a key hydrogen bond that locks the conformational states. Furthermore, we show that pH provides fine kinetic control over the interconversion rate and, consequently, the polymerization process. The system can then be reset toward the out conformation by using DMSO. This system stands in contrast to known transient supramolecular polymerization processes, which rely on metastable (non‐assembled) monomers. Here, it is the kinetic trapping of the assembling monomer that allows control over the lifetime of the transient supramolecular polymer via a pH‐responsive mechanism
CoRE MOF DB: A curated experimental metal-organic framework database with machine-learned properties for integrated material-process screening
No full textInternational audienceWe present an updated version of the Computation-Ready, Experimental (CoRE) Metal-Organic Framework (MOF) database, which includes a curated set of computation-ready MOF crystal structures designed for high-throughput computational materials discovery. Data collection and curation procedures were improved from the previous version to enable more frequent updates in the future. Machine-learning-predicted properties, such as stability metrics and heat capacities, are included in the dataset to streamline screening activities. An updated version of MOFid was developed to provide detailed information on metal nodes, organic linkers, and topologies of an MOF structure. DDEC6 partial atomic charges of MOFs were assigned based on a machine-learning model. Gibbs ensemble Monte Carlo simulations were used to classify the hydrophobicity of MOFs. The finalized dataset was subsequently used to perform integrated material-process screening for various carbon-capture conditions using high-fidelity temperature-swing adsorption (TSA) simulations. Our workflow identified multiple MOF candidates that are predicted to outperform CALF-20 for these applications
Développement et caractérisation de glaçures au bismuth sans plomb pour céramiques ornementales
No full textInternational audienceBi2O3-based glazes were developed to replace toxic PbO-based glazes from a ternary PbO-B2O3-SiO2 reference industrial composition bearing about 70 wt % PbO for ceramic applications, with the aim of keeping very similar properties and retaining the same glazes deposition process at 840 °C. Compositions in the SiO2-B2O3-Bi2O3 system melted at 1100 °C showed a higher tendency to phase separation and crystallization than the PbO-based reference, probably due to the higher field strength of Bi3+ ion, but the addition of 5–10 mol% Al2O3 led to homogeneous glasses, even after slow cooling. The physical properties of these quaternary glasses (thermal expansion, glass transition temperature, viscosity, density, hardness, elastic modulus) were evaluated, proving comparable to those of the reference PbO-based glass. Coloring pigments (ZnAl2-xCrxO4, 0 ≤ x ≤ 2) incorporated at 840 °C in a Bi2O3-based glaze also showed similar interactions as with the PbO-based glass according to XRD-Rietveld and SEM-EDX analyses. This work leads to conclude that a quaternary SiO2-B2O3-Bi2O3-Al2O3 glass bearing about 78 wt% Bi2O3 can advantageously replace the more toxic PbO-based formulation for glazing purposes without modifying the firing process
Understanding the role of pressurized CO<sub>2</sub> in the direct recycling process of Li-ion battery positive electrode
No full textInternational audienceThe ternary mixture of carbon dioxide (CO2), triethyl phosphate (TEP), and acetone enabled an efficient delamination of Li-ion battery (LIB) positive electrode inciting an interest to study the ternary mixture behavior. Pressurized fluids, such as CO2, are known to be beneficial in various chemical processes. However, the behavior of CO2, when mixed with TEP and acetone is not well understood, particularly under pressure and temperature conditions. This study investigates the behavior of CO2 or nitrogen (N2) in mixtures with TEP and acetone at various compositions, using experimental investigations of the ternary system. Experimental data covers four temperatures at 35° C, 70°C, 100°C and 120°C at a constant pressure of 100 bar. The phase behaviors of the binary and ternary mixtures were observed using a transparent reactor, while the compositions were analyzed in situ with Raman spectroscopy. Under isobaric conditions, a single phase was observed with CO2 at 35°C, both in the binary systems with either TEP or acetone, as well as in the ternary mixture. In contrast, a biphasic system was observed at higher temperatures (70°C, 100°C, and 120°C) in all mixtures containing CO2. Specifically, the biphasic condition at 55°C at 100 bar, of the mixtures were semi-quantitatively investigated using Raman spectroscopy to probe the compositions in the vapor and liquid phases. These observations elucidate the crucial role of CO2 in the delamination of the positive electrode in LIB using the TEP-acetone-CO2 system enabling high efficiency, low solvent consumption, and a faster processing time
Engineering of diamond growth for quantum applications
No full textInternational audienceThe development of applications in quantum sensing requires dedicated solid-state material platforms with unprecedented control over quality, purity and doping. Indeed, Quantum Technologies explore our ability to coherently control the peculiar properties of nanoscale quantum systems and harness their potential in a wide range of fields including health, communications, security and environment.Atomic-scale defects in solid-state materials are among the most promising candidates and several platforms are being considered such as donors in silicon, color centers in semiconductors, rare-earth ions in oxides, quantum dots etc. One of the inherent drawbacks of the extreme sensitivity of such spin systems to the field they are supposed to measure, is the necessity to carefully control their close crystalline environment in order to maximize coherence properties which pushes the fabrication technologies to their limits. In this presentation, we will review the main challenges in the synthesis of suitable “quantum-grade” diamond materials using color centers and more specifically NV centers. Issues related to the control of their density and the maximization of their coherence properties through precise engineering of the growth process will be discussed. (i) Atomic scale defects need to be introduced on demand within diamond. High amounts are usually preferred in most sensing schemes but limits exist in the ability to control growth at high doping levels as well as to avoid interaction between nearby spins. (ii) Nuclear spins within the matrix itself might cause decoherence and growth of isotopically enriched materials allows considerably extending T2 times. (iii) In a similar way, magnetic sensitivity of a sensor based on NV ensembles can be considerably increased by producing diamond with NV centers having preferential orientation which can be obtained by using diamond substrates with specific crystallographic orientation (iv) Controlling the spatial localization of color centers is crucial to the sensing device since their interaction strongly depends on the distance to the field that is to be sensed. (v) Controlling the shape and the size of the diamond platform remains also a very challenging point