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Highly purified and uniformly distributed carbon nanotube (CNT) network is one of the key issues for developing advanced nanocomposites. However, the challenge for mitigation of the aggregation of CNT bundles during the CNT film fabrication still remained. In this work, debundling and reorganization of CNT bundles have been realized simultaneously by using a high-temperature thermal treatment. The debundling of large CNT bundles into small ones started after they were heat treated under 1400 °C and uniformly distributed CNT networks with small bundles were obtained after heat treated under 1800 °C. The tensile strength of the CNT film significantly increased by about 64% compared to the pristine film. Microstructural observations showed that the iron nanoparticles started to evaporate at 1400 °C and were completely removed at 1800 °C. Hollow amorphous carbon shells wrapped on the nanoparticles were left inside the CNT networks after the removal of the iron nanoparticles. Interestingly, these amorphous carbon shells act as carbon source for the deposition of a carbon layer on the CNT surface when the heat treatment temperature was up to 2000 °C, and they were completely consumed after being treated at 2800 °C. The microstructural evolution process of CNT bundles during heat treatment suggests the simple high-temperature treatment strategy could be applied for fabrication of highly purified CNT networks with well-distributed small bundles, enabling the development of advanced multifunctional nanocomposites in the near future. A high-temperature heat treatment is used to investigate the microstructure evolution and mechanical properties of CNT films. Benefiting from the high-purity and uniformly distributed CNT networks with small bundles after heat treated under 1800 °C, the tensile strength of the CNT film has significantly increased by ∼64% compared to the pristine film. When heat treated under 2800 °C, the hollow amorphous carbon shells are completely consumed and act as carbon source for deposition of carbon layer on the CNT surface. [Display omitted] • Debundling of large CNT bundles was observed after a high temperature treatment. • A regenerative carbon layer was deposited on CNT surface under high temperature. • The microstructural evolution of CNT networks under high temperature was proposed. [ABSTRACT FROM AUTHOR]

Boundary layer chemical vapour synthesis is a fabrication approach which exploits random fluctuations within the viscous boundary layer established between a laminar flow of pyrolyzed ferrocene and a rough substrate, to yield iron filled radial carbon nanotubes (CNTs). The key feature of this method is the significant enhancement of the encapsulated nanowire-length, which has been explained in terms of the diffusion gradient established at the open-tip of growing CNTs. In this work, we carried out a statistical investigation on the possible relationship between the width of the inner-CNT-cavity and the nanowire diameter within radially grown iron filled CNTs. A systematic analysis of nanowire-continuity allowed for the identification of particularly high filling rates, with nanowire-lengths up to 20 μm and an almost complete filling of the CNT-capillary. Two types of contact-modes could be identified between the catalyst particles and the CNTs: the first type, in which the catalyst-diameter is comparable with the width of the inner CNT-cavity (full catalyst encapsulation), and the second type, in which the base particle is found to be not fully encapsulated (i.e. only partially encapsulated within the inner CNT-cavity). The observed CNT/catalyst-base interactions resemble those reported in recent studies for tangential and intermediate-tangential growth-modes occurring after nanotube-cap nucleation. Comparative statistical analyses performed on other types of Fe-filled CNT films (flower-like structures and buckypaper) obtained by pyrolysis of ferrocene or ferrocene/dichlorobenzene mixtures are further discussed. [ABSTRACT FROM AUTHOR]

The growth control of α-Fe inside multiwall carbon nanotubes has challenged researchers for more than a decade owing to the coexistence of this phase with Fe3C and γ-Fe. Previously, long heating treatments of 20 h have been used to decompose the encapsulated Fe-phases in C and Fe; however, these methods were limited by an unusual oxidation process leading to nanotube decomposition. In this letter, we report an alternative chemical vapour deposition approach that through an accurate control of the ferrocene-vapour flow-rate allows to achieve the direct encapsulation of 95% of α-Fe without additional heating treatments. [ABSTRACT FROM AUTHOR]

To drive the Fe-based application for the Oxygen Reduction Reaction (ORR) in alkali media, this work found the Carbon Nanotube supported Fe-Polyaniline (Fe-PANI/CNT) catalyst from controlled Molecular Self-assembly (MS) method is comparable to the commercial Pt/C catalyst in mass current density and ORR stability, but with large gap on specific current density. This can be due to that the controlled MS method help establish the most active site of Fe-N coordination in the PANI pore, whose hydrophilic state inhibits O 2 transfer and whose poor conductivity restricts O 2 utilization jointly. In the meanwhile, we revealed that the enormous impact of OH adsorption (OH ad ) on ORR activity and stability, exhibiting negative results on the Pt/C catalyst but beneficial results for Fe-based catalysts, especially in the “indirect 2e+2e pathway” relating to the inner and outer-sphere electron transfer processes. All these progress facilitate the clarification for the structure-catalysis and encourage preparation towards controlled MS methods. [ABSTRACT FROM AUTHOR]