No abstract

Reductive alkylation of N-MWNTs with Li/NH 3 results in fracturing of the nanotubes, ripping channels that breach the central core and generating significant new pore volume.

Nitrogen-containing multiwalled nanotubes (N-MWCNTs), formed by CVD from a nitrogen-containing feedstock have a 'bamboo' structure in which the axes of the graphene planes are not parallel to the axis of the nanotube and the core is periodically bridged. We find that thermal and chemical treatment of these materials can produce nanotubes that have been cut longitudinally in either a linear or in a spiral manner. In addition, these longitudinally cut nanotubes can be partially or fully unrolled by sonication in an aqueous surfactant, producing graphite platelets as well as narrow structures that could be thin graphite ribbons or very narrow, intact N-MWCNTs. These different morphologies of graphite, available from one source, suggest that there are multiple structures of N-MWCNTs present, few as simple as stacked cups or nested scrolls.

ABSTRACT:The adsorption of water by the graphene surfaces of multi-wall carbon nanotubes (MWCNTs) in either the untreated (4.3 atom% oxygen) or oxidised (22.3 atom% oxygen) surface states has been studied. Different concentrations of surface oxygen groups, which have been directly measured using XPS, give rise to distinctly different shapes of water adsorption isotherms. Those from the untreated materials follow the pressure axis which lends them a Type III character in the BDDT classification. However, since they display a clear point of inflection at the lowest pressure, they are strictly speaking Type II isotherms but indicative of relatively few polar interactions and weak water adsorptivity. In sharp contrast, the isotherms from the oxidised MWCNTs are typically Type II and are characterised by a marked positive curvature in their low pressure region due to the increased numbers of specific interactions occurring between water molecules and the polar surface oxygen groups.The water adsorption data were modelled by the equation of D'Arcy and Watt with a direct correlation being observed between the surface polarity parameters (a mL and a 0 ) and also a s (the limiting water uptake) and the surface oxygen levels of the MWCNTs. The difference in polar surface energy was confirmed by measurements of the calorimetric enthalpies of immersion in water (∆h i ), which were -54 mJ/m 2 for the untreated and -192 mJ/m 2 for the oxidised materials. These values also reflect the difference in the integral net enthalpies of adsorption for the two hydrophilic surfaces: a value of ca. -35 mJ/m 2 being obtained for an oxygenfree (hydrophobic) surface. Water adsorption on these hydrophilic graphene surfaces was shown to occur by specific hydrogen bonding and was therefore strongly dependent on the numbers of oxygen-containing polar surface sites. This behaviour is well known for other types of porous and non-porous carbon materials and is also predicted for carbon nanotubes by molecular simulation studies. The work described herein therefore provides early experimental confirmation of the quantitative role of surface oxygen chemistry in determining the water adsorption character of MWCNT graphene surfaces; it also validates previous simulation studies.

Well‐aligned carbon multiwalled nanotubes (MWNTs) have been synthesized continuously by pyrolysis of xylene–ferrocene mixtures. To study the MWNT growth mechanism, two‐step processes and various chemical vapor deposition (CVD) parameters have been employed. Transmission electron microscopy observations support a tip‐root growth model of MWNTs by floating catalytic CVD. Hydrocarbon analyzer is used to measure the total carbon balance within the CVD reactor, while mass spectra analyses monitor the concentrations of hydrocarbon species, which helps to understand the catalyst deactivation and pyrolysis chemistry of xylene over catalyst Fe(C) nanoparticles. MWNTs can be treated to attach required functional groups on nanotube walls and/or caps for specific applications by various methods including acid oxidation, reduction, addition of radicals, and cycloadditions. Carbon nanotubes (CNTs) have shown promising applications in advanced CNT–polymer composites. To realize CNT potentials to enhance the properties of matrices, several important issues such as dispersion, orientation, interfacial effects, and processing parameters have been addressed. The dependence of the CNT–polymer composite properties on CNT diameter, length, and interfacial effects has been used to develop models to predict and optimize variables for maximum composite performance. CNT–polymer composites have been developed for enhanced mechanical, electrical, and thermal properties, which have wide applications for the next generation of truly multifunctional materials as well as lighter weights and increased manufacturability over current materials.