Observation of strong Kondo like features and co-tunnelling in superparamagnetic GdCl3 filled 1D nanomagnets

Filling of carbon nanotubes has been tailored over years to modify the exceptional properties of the 1-dimensional conductor for magnetic property based applications. Hence, such a system exploits the spin and charge property of the electron, analogous to a quantum conductor coupled to magnetic impurities, which poses an interesting scenario for the study of Kondo physics and related phenomena. We report on the electronic transport properties of MWNTs filled with GdCl3 nanomagnets, which clearly show the co-existence of Kondo correlation and cotunelling within the superparamagnetic limit. The Fermi liquid description of the Kondo effect and the interpolation scheme are fitted to the resistance-temperature dependence yielding the onset of the Kondo scattering temperature and a Kondo temperature for this nanocomposite, respectively. Cotunneling of conduction electrons interfering with a Kondo type interaction has been verified from the exponential decay of the intensity of the fano shaped nonzero bias anomalous conductance peaks, which also show strong resonant features observed only in GdCl3 filled MWNT devices. Hence, these features are explained in terms of magnetic coherence and spin-flip effects along with the competition between the Kondo effect and co-tunneling. This study raises a new possibility of tailoring magnetic interactions for spintronic applications in carbon nanotube systems

Few Layer Graphene sticking by biofilm of freshwater diatom Nitzschia palea as a mitigation to its ecotoxicity

Carbon-based nanoparticles such as graphene have many applications leading to their industrial production. Few-Layer Graphene (FLG) is thus likely to be found in the environment, and especially in rivers. In this study, the effect of FLG on the photosynthetic benthic diatom Nitzschia palea was assessed making distinction between the impact of a direct contact with FLG and a shading effect of FLG on diatoms. Growth inhibition of diatoms exposed to FLG at 50 mg L-1 was observed at 48 h of exposure associated with an increase in diatoms mortality. At 144 h, the growth rate was recovered. However, in shading condition, at 48 h of FLG exposure, a persistent growth inhibitionwas observed at 50 mg L-1. Microscopic observations and a monitoring of FLG concentration in the medium allowed to conclude that exopolymeric substances (EPS), naturally secreted by N. palea, strongly interact with FLG, sticking nanoparticles at the bottom of wells. Our results highlight the potential mechanisms of clarification of the water column by diatoms biofilms, by sticking FLG even at high concentration. Overall, these results suggest that one potential toxicity process of graphene could be a combination of direct and shading effect leading to a strong interaction between biofilm and nanoparticles

Surface area of carbon-based nanoparticles prevails on dispersion for growth inhibition in amphibians

The attractive properties of carbon-based nanoparticles such as graphene and its derivatives or carbon nanotubes lead to their use in many application fields, whether they are raw or functionalized, such as oxidized. These particles may finally contaminate the aquatic compartment, which is a major receptacle of pollutants. The study of their impact on aquatic organisms is thus essential. At the nano scale, recent studies have highlighted that specific surface area should be used as the most relevant descriptor of toxicity instead of the conventional mass concentration. By using a dose-response model, this work compares the chronic toxicity observed on Xenopus laevis larvae after 12-day in vivo exposure to raw, oxidized carbon allotropes, or in the presence of chemical dispersant. We show that chemical dispersion does not influence the observed chronic toxicity, whether it is through surface chemistry (oxidation state) or through the addition of a dispersant. The biological hypothesis leading to growth inhibition are discussed. Finally, these results confirm that surface area is the more suited metric unit describing growth inhibition

Investigating a transcriptomic approach on marine mussel hemocytes exposed to carbon nanofibers: An in vitro/in vivo comparison

Manufactured nanomaterials are an ideal test case of the precautionary principle due to their novelty and potential environmental release. In the context of regulation, it is difficult to implement for manufactured nanomaterials as current testing paradigms identify risk late into the production process, slowing down innovation and increasing costs. One proposed concept, namely safe(r)-by-design , is to incorporate risk and hazard assessment into the design process of novel manufactured nanomaterials by identifying risks early. When investigating the manufacturing process for nanomaterials, differences between products will be very similar along key physicochemical properties and biological endpoints at the individual level may not be sensitive enough to detect differences whereas lower levels of biological organization may be able to detect these variations. In this sense, the present study used a transcriptomic approach on Mytilus edulis hemocytes following an in vitro and in vivo exposure to three carbon nanofibers created using different production methods. Integrative modeling was used to identify if gene expression could be in linked to physicochemical features. The results suggested that gene expression was more strongly associated with the carbon structure of the nanofibers than chemical purity. With respect to the in vitro/in vivo relationship, results suggested an inverse relationship in how the physicochemical impact gene expression

Double-walled carbon nanotubes: Quantitative purification assessment, balance between purification and degradation and solution filling as an evidence of opening

We compared the effect of different oxidizing agents on purification, functionalization and opening of double-walled carbon nanotubes. The oxidative treatments were realized in nitric acid solutions at different concentrations (3 M or 15 M), in a mixture of two oxoacids (conc. HNO3/conc. H2SO4) or in sulphuric acid solutions of KMnO4 or K2Cr2O7. Most of these treatments were very efficient for purification (removal of residual catalytic metal nanoparticles and/or of disorganized carbon) but also caused secondary reactions such as shortening of the nanotubes, creation of functionalized amorphous carbon deposits and covalent functionalization of the outer wall. Secondary treatments were undertaken in order to remove functionalized carbon deposit by washing with sodium hydroxide solutions or by heat treatment in air. A partial filling in solution was obtained with uranyl nitrate, in order to evidence the opening of carbon nanotubes. Effects of purification and filling treatments were characterized both qualitatively by TEM and HRTEM, AFM and Raman spectroscopy, and quantitatively by elemental chemical analysis and chemical titrations

A comparative study on the enzymatic biodegradability of covalently functionalized double- and multi-walled carbon nanotubes

The assessment of the biodegradability potential of carbon nanotubes (CNTs) is a fundamental point towards their applications in materials science and biomedicine. Due to the continuous concerns about the fate of such type of nanomaterials, it is very important to understand if they can undergo degradation under certain conditions and if the morphology and structure of the nanotubes play a role in this process. For this purpose we have decided to undertake a comparative study on the enzymatic degradation of CNTs with concentric multilayers. Double-walled (DW) and multi-walled (MW) CNTs of various lengths, degrees of oxidation and functionalizations using different methods were treated with horseradish peroxidase (HRP). While all tested DWCNTs resulted resistant to the biodegradation, some of the MWCNTs were partially degraded by the enzyme. We have found that short oxidized multi-walled CNTs functionalized by amidation were reduced in length and presented a high amount of defects at the end of the period of treatment with HRP. This comparative study holds its importance in the understanding of the structural changes of different types of nanotubes towards the catalytic enzymatic degradation and will help to design safer CNTs for future applications

Batellerie gallo-romaine

Les récentes découvertes d’épaves de barges fluviales gallo-romaines à Lyon (place Tolozan et Parc Saint-Georges) et à Arles, auxquels s’ajoutent les épaves de Chalon-sur-Saône, ont non seulement attiré l’attention sur la batellerie fluviale et lacustre gallo-romaine mais aussi porté au premier plan des recherches le bassin rhodanien et le midi de la Gaule jusque-là peu présent ou même totalement absent du débat. Or les particularités de ces épaves renouvellent fondamentalement le sujet en montrant l’existence d’une tradition régionale « Rhône-Saône » mettant en lumière des influences maritimes méditerranéennes. Dès lors, il devenait intéressant de confronter ces recherches, intéressant le bassin fluvial Rhône-Saône et le midi de la Gaule, à celles menées sur l’Europe du Nord qui avaient monopolisé le débat sur la construction navale gallo-romaine. À partir de données provenant de l’arc rhénan (Allemagne, Pays- Bas) et du lac de Neuchâtel (Suisse), ces recherches avaient jusqu’alors mis en évidence l’existence des seules groupes régionaux « Rhénan » et « Alpin ». Il est aussi apparu enrichissant d’élargir le sujet de cet ouvrage à d’autres épaves, comme l’épave lagunaire de la Conque des Salins (étang de Thau, Hérault), encore peu connue, et l’épave du chaland de la Ljubljanica (Slovénie), de découverte plus ancienne, dont les caractéristiques s’inscrivent dans le cadre de la nouvelle problématique définie autour des notions de pratiques régionales et d’influences maritimes méditerranéennes. C’est, au total, à un renouvellement complet du panorama de la construction navale et de la batellerie gallo-romaine que nous invite cet ouvrage. Ce dernier, richement illustré, comporte de nombreuses contributions de spécialistes français et étrangers qui remettent au premier plan les études sur la batellerie antique et montrent l’intérêt de ces recherches en un domaine trop souvent considéré comme mineur

Fabrication of photocatalysts by laser pyrolysis for alkenes production

International audienceAlkenes, and more particularly ethylene, are essential organic molecules for chemical and petrochemical industries and are needed in ton quantities. New ways are developed to produce ethylene without hydrocarbons. They mainly focus on dehydrogenation reactions from ethanol. However, these processes often require a significant energy consumption despite the use of heterogeneous acid catalysts, with high temperature and/or pressure. In this context, we aim to synthesize environmental-friendly and low-cost photocatalysts, which could degrade organic compounds such as alcohols and acids into alkanes and alkenes. In order to achieve this aim, TiO2-based photocatalysts were synthesized from TTIP (Titanium Tetra Isopropoxide) precursor by an original gas-phase method, the CO2 laser pyrolysis technique. It offers a great flexibility in obtaining small and homogeneous nanoparticles (5-60 nm size ranging), with controlled crystallinity and carbon contain. Addition of graphene in TTIP allowed to obtain graphenemodified TiO2 composites (from 0.04 to 2.00 wt% regarding TTIP). First results show an evolution of the specific surface related to the graphene content. These photocatalysts were first used for photo-oxidation of formic acid and shew an improvement for formic acid degradation at low graphene content by comparison to pure TiO2. Theses composites were also tested for alkene production from propionic acid photo-reduction

Fabrication of photocatalysts by laser pyrolysis for alkenes production

International audienceAlkenes, and more particularly ethylene, are essential organic molecules for chemical and petrochemical industries and are needed in ton quantities. New ways are developed to produce ethylene without hydrocarbons. They mainly focus on dehydrogenation reactions from ethanol. However, these processes often require a significant energy consumption despite the use of heterogeneous acid catalysts, with high temperature and/or pressure. In this context, we aim to synthesize environmental-friendly and low-cost photocatalysts, which could degrade organic compounds such as alcohols and acids into alkanes and alkenes. In order to achieve this aim, TiO2-based photocatalysts were synthesized from TTIP (Titanium Tetra Isopropoxide) precursor by an original gas-phase method, the CO2 laser pyrolysis technique. It offers a great flexibility in obtaining small and homogeneous nanoparticles (5-60 nm size ranging), with controlled crystallinity and carbon contain. Addition of graphene in TTIP allowed to obtain graphenemodified TiO2 composites (from 0.04 to 2.00 wt% regarding TTIP). First results show an evolution of the specific surface related to the graphene content. These photocatalysts were first used for photo-oxidation of formic acid and shew an improvement for formic acid degradation at low graphene content by comparison to pure TiO2. Theses composites were also tested for alkene production from propionic acid photo-reduction

Graphene/TiO2 photocatalysts synthesis by laser pyrolysis for ethylene production

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