Linear and spiral forms of longitudinal cuts in graphitized N-doped multiwalled carbon nanotubes (g-N-MWCNTs)

Abstract

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.

Oxidation of N-doped multiwalled carbon nanotubes and formation of discontinuous spiraled carbon nanoribbons

“…Shortening of tubes lengthwise was not observed from the SEM and TEM (Figure S8) images, unlike what is observed after oxidation with H2SO4/HNO3. Also, the morphology of these spiraled ribbons was quite different from the ones we had seen before with reducing 35 as well as oxidizing (H2SO4/HNO3) conditions. Here, the ribbon texture is more distinct, with the distance between the turns of the helix being 100-150 nm.…”

“…We refer to the resulting tubes as G-N-MWCNTs (Figure 1). 35 The material was subjected to five different sets of oxidizing conditions: 1) refluxing HNO3; 2) H2SO4/H2O2; 3) FeSO4/H2O2; 4) H2SO4/HNO3; and 5) KMnO4/ H2SO4.…”

“…Carbon ribbon structures have been observed by others after oxidation of stackedcup nanotubes. 40 We have previously reported the phenomenon of longitudinal cutting in N-MWCNTs 34,35 under dissolving metal reduction conditions (Li metal in liquid ammonia or ethylenediamine). The most common morphology of fractures observed after oxidation in this mixture was spiraled ribbons.…”

“…In nitrogen-containing multiwalled carbon nanotubes (N-MWCNTs) (Figure 1) the central core is periodically bridged, giving a texture similar to a set of stacked cups. 34,35 In this arrangement, the axes of graphene planes are not parallel to the tube axis, so each graphene sheet must terminate at the surface. We anticipated that the large number of exposed edges would make these materials more reactive than classical cylindrical MWCNTs in which the outer surface is a gently curved graphene plane rather than a set of exposed edges.…”

Nitrogen‐Doped Graphitic Nanoribbons: Synthesis, Characterization, and Transport

“…However, experimental research related to doped graphene and graphitic nanoribbons remains under intense investigation. From the experimental standpoint, various groups have reported the synthesis of undoped graphene and graphene‐NRs using: 1) chemical coupling,12 2) CVD,13, 14 3) graphene nanocutting,15, 16 4) CNTs exfoliation,17 and 5) unzipping 18–20. Other groups have recently developed successful approaches to dope flat and extended sheets of graphene 21.…”