Structure in Nascent Carbon Nanotubes Revealed by Spatially Resolved Raman Spectroscopy

The understanding of carbon nanotubes (CNT) growth is crucial for the control of their production. In particular, the identification of structural changes of carbon possibly occurring near the catalyst particle in the very early stages of their formation is of high interest. In this study, samples of nascent CNT obtained during nucleation step and samples of vertically aligned CNT obtained during growth step are analysed by combined spatially resolved Raman spectroscopy and X-Ray diffraction measurements. Spatially resolved Raman spectroscopy reveals that iron-based phases and carbon phases are co-localised at the same position, and indicates that sp2 carbon nucleates preferentially on iron-based particles during this nucleation step. Depth scan Raman spectroscopy analysis, performed on nascent CNT, highlights that carbon structural organisation is significantly changing from defective graphene layers surrounding the iron-based particles at their base up to multi-walled nanotube structures in the upper part of iron-based particles

Instabilités structurales de cristaux moléculaires apériodiques

La thèse porte sur l étude de la famille des urée alcane qui sont des modèles de composites dont la caractéristique principale est l incommensurabilité qui existe entre les paramètres de maille des deux sous-réseaux hôte et invité selon une direction. Depuis les années 1980, il est maintenant admis que les cristaux apériodiques retrouvent une périodicité dans des superespaces cristallographiques, espaces de dimensions supérieures à 3. Dans ce mémoire, nous nous focalisons tout particulièrement sur les transitions de phase à l'intérieur de ces superespaces mettant en évidence une multiplication des solutions structurales. En jouant sur la versatilité de la famille de molécules invitées (alcane) dans la matrice hôte, nous illustrons la compétition entre les différentes interactions antagonistes favorisant l'incommensurabilité ou ancrage dans cette famille prototype. La très haute résolution spatiale nécessaire pour de telles études a été obtenue combinant diffraction de neutrons froids, diffraction haute résolution X, rayonnement synchrotron et diffraction cohérente sur source synchrotron.This thesis concerns the study of the urea alkane family which are prototypes composites. Their main characteristic is the incommensurability which exists between the cell parameters of the two host guest sublattices. Since the 1980's, it's known that aperiodic crystals get back periodicity in crystallography superspaces of dimensions larger than 3. In this work, we focus on the phase transitions within these superspaces showing the multiplication of structural solutions. With the help of the versatility of the guest family (alkane molecules) within the host matrix, we illustrate the competition between the antagonistic interactions which favour incommensurability or lock-in. The very high spatial resolution needed for such studies was obtained combining cold neutron diffraction, high resolution X ray and synchrotron diffraction and coherent diffraction on synchrotron source.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Intracellular fate of carbon nanotubes inside murine macrophages: PH-dependent detachment of iron catalyst nanoparticles

BACKGROUND: Carbon nanotubes (CNT) are a family of materials featuring a large range of length, diameter, numbers of walls and, quite often metallic impurities coming from the catalyst used for their synthesis. They exhibit unique physical properties, which have already led to an extensive development of CNT for numerous applications. Because of this development and the resulting potential increase of human exposure, an important body of literature has been published with the aim to evaluate the health impact of CNT. However, despite evidences of uptake and long-term persistence of CNT within macrophages and the central role of those cells in the CNT-induced pulmonary inflammatory response, a limited amount of data is available so far on the CNT fate inside macrophages. Therefore, the overall aim of our study was to investigate the fate of pristine single walled CNT (SWCNT) after their internalization by macrophages. METHODS: To achieve our aim, we used a broad range of techniques that aimed at getting a comprehensive characterization of the SWCNT and their catalyst residues before and after exposure of murine macrophages: X-ray diffraction (XRD), High Resolution (HR) Transmission Electron Microscopy (TEM), High Angle Annular Dark Field-Scanning TEM (HAADF-STEM) coupled to Electron Energy Loss Spectroscopy (EELS), as well as micro-X-ray fluorescence mapping (μXRF), using synchrotron radiation. RESULTS: We showed 1) the rapid detachment of part of the iron nanoparticles initially attached to SWCNT which appeared as free iron nanoparticles in the cytoplasm and nucleus of CNT-exposed murine macrophages, and 2) that blockade of intracellular lysosomal acidification prevented iron nanoparticles detachment from CNT bundles and protected cells from CNT downstream toxicity. CONCLUSIONS: The present results, while obtained with pristine SWCNT, could likely be extended to other catalyst-containing nanomaterials and surely open new ways in the interpretation and understanding of CNT toxicity