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Corrosion inhibition mechanism of 2,6-pyridinedicarboxylate depending on magnesium surface treatment
No full textInternational audienceA B S T R A C T 2,6-pyridinedicarboxylate (2,6-PDC) was studied as corrosion inhibitor for pure magnesium. The surface was prepared either by polishing or polishing followed by treatment with 1 M NaOH solution. The results show that 2,6-PDC promotes the formation of a denser protective oxide/hydroxide layer poor in PDC. The mechanism proposed includes forming weak PDC-Mg complexes that lower the free Mg 2+ concentration available for the formation of Mg(OH) 2 . This leads to growth of smaller Mg(OH) 2 platelets that are more densely packed and hence form a more protective layer. The highest inhibition efficiency of 2,6-PDC was achieved for samples with surface hydroxylated by NaOH treatment.</div
Influence of Silsesquioxane-Containing Ultra-Thin Polymer Films on Metal Oxide Gas Sensor Performance for the Tunable Detection of Biomarkers
No full textInternational audienceCertain biomarkers in exhaled breath are indicators of diseases in the human body. The non-invasive detection of such biomarkers in human breath increases the demand for simple and cost-effective gas sensors to replace state-of-the-art gas chromatography (GC) machines. The use of metal oxide (MOX) gas sensors based on thin-film structures solves the current limitations of breath detectors. However, the response at high humidity levels, i.e., in the case of exhaled human breath, significantly decreases the sensitivity of MOX sensors, making it difficult to detect small traces of biomarkers. We have introduced, in previous work, the concept of a hybrid gas sensor, in which thin-film-based MOX gas sensors are combined with an ultra-thin (20-30 nm) polymer top layer deposited by solvent-free initiated chemical vapor deposition (iCVD). The hydrophobic top layer enables sensor measurement in high-humidity conditions as well as the precise tuning of selectivity and sensitivity. In this paper, we present a way to increase the hydrogen (H 2 ) sensitivity of hybrid sensors through chemical modification of the polymer top layer. A poly(1,3,5,7-tetramethyltetravinylcyclotetrasiloxane) (PV4D4) thin film, already applied in one of our previous studies, is transformed into a silsesquioxane-containing top layer by a simple heating step. The transformation results in a significant increase in the gas response for H 2 ~709% at an operating temperature of 350 • C, which we investigate based on the underlying sensing mechanism. These results reveal new pathways in the biomedical application field for the analysis of exhaled breath, where H 2 indicates gastrointestinal diseases
A Novel Family of Luminescent Pyrenyl‐(N‐Heterocyclic Carbene)‐ Halogenated Coinage Metal Complexes: Synthesis, Crystal Structures, and Optical Properties
No full textInternational audienceA family of luminescent pyrenyl‐(NHC)‐M‐Cl coinage metal complexes has been prepared and fully characterized (NHC = N‐heterocyclic carbene). Two classes of complexes are described: (M = Cu (1a), Ag (2a), Au (3a) where pyrenyl‐(NHC) = 1‐pyrenyl‐3‐methyl‐Imidazolin‐2‐ylidene and M = Cu (1b), Ag (2b), Au (3b) with pyrenyl‐(NHC) = 1‐pyrenyl‐3‐naphthyl‐Imidazolin‐2‐ylidene. The molecular structures of the six complexes were confirmed by single crystal X‐ray diffraction studies. All complexes were found to be emissive in solution and solid state. The use of the chromophoric‐(NHC) ligand endows to these complexes emissive properties in solution in the blue region (376‐397nm). The presence of the naphthyl‐substituent in the 1b‐3b series enhances the quantum yields relative to the methyl‐series 1a‐3a. In particular, the carbene gold complexes were the most emissive and displayed the highest quantum yields</p
Investigation of Iron Dissolution Mechanism in Acidic Solutions with and without Dissolved CO2—Part I: Electrochemical Impedance Spectroscopy Measurements
No full textInternational audienceAqueous CO2 corrosion of mild steel is one of the major problems in the oil and gas industry. While current understanding primarily focuses on cathodic reaction mechanisms, less attention has been given to the impact of aqueous CO2 on the anodic iron dissolution reaction. In contrast, the mechanism of iron dissolution in strongly acidic environments has been thoroughly investigated. Among the reaction mechanisms found in the open literature, a multipath mechanism was identified that could explain the iron dissolution in strong acidic sulfate solution; both in terms of steady-state polarization sweeps and impedance data at various pH values and current densities. However, the role of aqueous CO2 in solutions containing chlorides on the mechanism of iron dissolution remained an open question. The present study used electrochemical impedance spectroscopy (EIS) as the main technique, to study the mechanism of iron dissolution in strong acid chloride solution with and without the presence of CO2. Results showed that the presence of chloride ions (0.5 M) decreased the rate of iron dissolution by competing with hydroxide ions to adsorb on the metal surface, forming chloride-containing intermediate species that participate in the iron dissolution reaction. The resulting decrease in the availability of hydroxide intermediates, which are more effective at enhancing the reaction rate compared to chloride-containing intermediates, leads to an overall decrease in the rate of iron dissolution. While the presence of CO2 increases anodic current density, EIS investigation revealed that neither aqueous CO2 nor other carbonic species directly react on the bare metal surface to form adsorbed intermediates involved in the anodic reaction. EIS investigation suggested that aqueous CO2 may induce changes in the chemical composition of adsorbed species, rate constants, and surface coverage, thereby altering the kinetics of the underlying reactions
Couplage C(sp<sup>2</sup>)–H/C(sp<sup>2</sup>)–H du limonène pallado-catalysé
No full textInternational audienceLimonene undergoes a regioselective Pd(II)-catalyzed C-(sp 2 )-H/C(sp 2 )-H coupling with acrylic acid esters and amides, α,βunsaturated ketones, styrenes, and allyl acetate, affording novel 1,3-dienes. DFT computations gave results in accord with the experimental results and allowed for the formulation of a plausible mechanism. The postfunctionalization of one of the coupled products was achieved via a large-scale Sonogashira reaction conducted under micellar catalysis.Le limonène est engagé dans un couplage C-(sp2 )-H/C(sp2 )-H régiolélectif pallado-catalysé avec des acrylates, des acrylamides, des cétones α,β-insaturées, des styrènes et l'acétate d'allyle. Ce couplage génère des nouveaux diènes-1,3. Des calculs DFT ont donné des résultats en accord avec les résultats expérimentaux et ont permis la proposition d'un mécanisme plausible. La post-fonctionnalisation d'un des produits de couplage a été possible par une réaction de Sonogashira sur grande échelle par catalyse en milieu micellaire
Theoretical insights into homogeneous catalysis impact on ion transfer-electron transfer coupled processes at thick-film modified electrodes
No full textInternational audienceThe ion transfer-electron transfer coupled reactions that occur in thick-film modified electrodes is analysed in this work, including a homogeneous catalytic reaction in one of the phases. The model of two polarized interfaces composed in series presented investigates the similarities and differences that arise when compared with the classical electrochemical chemical catalytic mechanism (EC') in a single electrode|solution interface. Special attention is paid to the charge balance of the diffusive flux at each of these two interfaces and to the distribution of the total applied potential at each one. The aim is to find how the applied potential is distributed between the S|L interface and the L|L interface and its dependence on simple external parameters. This will allow us to fully understand the system for its future application in the interfacial electrosynthesis of new materials
Incorporation of CF 3 -pseudoprolines into polyproline type II foldamers confers promising biophysical features
No full textInternational audienceThe development and the use of fluorinated polyproline-type II (PPII) foldamers are still underexplored. Herein, trifluoromethyl pseudoprolines have been incorporated into polyproline backbones without affecting their PPII helicity. The ability of the trifluoromethyl groups to increase hydrophobicity and to act as 19F NMR probes is demonstrated. Moreover, the enzymatic stability and the non-cytotoxicity of these fluorinated foldamers make them valuable templates for use in medicinal chemistr
Structural disorder determines capacitance in nanoporous carbons
No full textInternational audienceThe difficulty in characterizing the complex structures of nanoporous carbon electrodes has led to a lack of clear design principles with which to improve supercapacitors. Pore size has long been considered the main lever to improve capacitance. However, our evaluation of a large series of commercial nanoporous carbons finds a lack of correlation between pore size and capacitance. Instead, nuclear magnetic resonance spectroscopy measurements and simulations reveal a strong correlation between structural disorder in the electrodes and capacitance. More disordered carbons with smaller graphene-like domains show higher capacitances owing to the more efficient storage of ions in their nanopores. Our findings suggest ways to understand and exploit disorder to achieve highly energy-dense supercapacitors
Olivine NaMn0.66Fe0.34PO4 as a Cathode Material for Advanced Sodium Ion Batteries
No full textInternational audienceSodium‐ion batteries continue to rise in the energy storage landscape, their increasing adoption being driven by factors such as cost‐effectiveness and sustainability. As a consequence, there is a growing emphasis on the development of new electrode materials. Among these, olivine phosphates emerge as a promising family of cathode materials. However, viable synthesis routes are still lacking. In this study, cathode materials of olivine NaMn 1‐x Fe x PO 4 (x=0.34 and 1) were prepared by directly sodiating Mn 1‐x Fe x PO 4 through a solid‐state process at 300 °C. X‐ray diffraction, Mössbauer spectroscopy and electrochemical measurements were employed to study their structural and electrochemical features. NaMn 0.66 Fe 0.34 PO 4 exhibits two pseudo‐plateaus profile with an average potential of ~3.2 V vs. Na + /Na 0 with a reversible capacity reaching 75 mAh/g at C/20 via a monophasic (de)intercalation mechanism. In parallel, the intermediate composition Na 0.5 Mn 0.66 Fe 0.34 PO 4 could be prepared via the solid‐state reaction of NaMn 0.66 Fe 0.34 PO 4 and Mn 0.66 Fe 0.34 PO 4 . Such a solvent‐free sodiation process not only provides a simplified preparation of NMFP, but also offers easy scalability compared to the more laborious electrochemical sodiation route, making it an interesting prospect for future industrialization. Finally, this research confirms that the olivine NMFP is indeed an attractive candidate as a cathode material for SIBs