En route to controlled catalytic CVD synthesis of densely packed and vertically aligned nitrogen-doped carbon nanotube arrays

Abstract

SummaryThe catalytic chemical vapour deposition (c-CVD) technique was applied in the synthesis of vertically aligned arrays of nitrogen-doped carbon nanotubes (N-CNTs). A mixture of toluene (main carbon source), pyrazine (1,4-diazine, nitrogen source) and ferrocene (catalyst precursor) was used as the injection feedstock. To optimize conditions for growing the most dense and aligned N-CNT arrays, we investigated the influence of key parameters, i.e., growth temperature (660, 760 and 860 °C), composition of the feedstock and time of growth, on morphology and properties of N-CNTs. The presence of nitrogen species in the hot zone of the quartz reactor decreased the growth rate of N-CNTs down to about one twentieth compared to the growth rate of multi-wall CNTs (MWCNTs). As revealed by electron microscopy studies (SEM, TEM), the individual N-CNTs (half as thick as MWCNTs) grown under the optimal conditions were characterized by a superior straightness of the outer walls, which translated into a high alignment of dense nanotube arrays, i.e., 5 × 108 nanotubes per mm2 (100 times more than for MWCNTs grown in the absence of nitrogen precursor). In turn, the internal crystallographic order of the N-CNTs was found to be of a ‘bamboo’-like or ‘membrane’-like (multi-compartmental structure) morphology. The nitrogen content in the nanotube products, which ranged from 0.0 to 3.0 wt %, was controlled through the concentration of pyrazine in the feedstock. Moreover, as revealed by Raman/FT-IR spectroscopy, the incorporation of nitrogen atoms into the nanotube walls was found to be proportional to the number of deviations from the sp2-hybridisation of graphene C-atoms. As studied by XRD, the temperature and the [pyrazine]/[ferrocene] ratio in the feedstock affected the composition of the catalyst particles, and hence changed the growth mechanism of individual N-CNTs into a ‘mixed base-and-tip’ (primarily of the base-type) type as compared to the purely ‘base’-type for undoped MWCNTs.

Nitrogen-Doped Bagasse-Derived Carbon/ Low Pt Composite as Counter Electrodes for High Efficiency Dye-Sensitized Solar Cell

“…The D band is associated with structural defects and partially disordered structures, which arises from A 1g vibration; whereas the G band attributes to the E 2g vibrational mode present in the sp 2 bonded graphitic carbons, which is beneficial for enhancing the electrical conductivity of carbon materials. 37 The relatively strong intensity of this peak indicates good graphitization of the carbon materials. The intensity of G band in the sample of NBC/Pt is higher than the D band, suggesting the sample of NBC/Pt with good graphitization, which it has better electrical conductivity, as equally observed from the XRD result above.…”

“…The peaks at 2928 cm −1 , 1384 cm −1 and 1216 cm −1 correspond to the symmetric stretching of C-H bond and stretching vibration bond of C-OH in bagassederived carbon materials, respectively. 37,38 The distinct and wide peak between 3000 cm −1 and 3700 cm −1 manifests the presence of C-H stretching vibration of hydroxyl groups in water. 37 For the samples of NBC and NBC/Pt, the peak between 3000 cm −1 and 3700 cm −1 is assigned to not only O-H but also N-H stretching vibrations.…”

“…37,38 The distinct and wide peak between 3000 cm −1 and 3700 cm −1 manifests the presence of C-H stretching vibration of hydroxyl groups in water. 37 For the samples of NBC and NBC/Pt, the peak between 3000 cm −1 and 3700 cm −1 is assigned to not only O-H but also N-H stretching vibrations. 39 The peak at frequency of 1619 cm −1 is assigned to C=N stretching vibration band.…”

“…Herein, the C1s spectrum can be deconvoluted into three well resolved peaks corresponding to the functional groups: C-H (284.2 eV), C-N and C-O (285.1 eV) and O=C-N (287.2 eV), 43 which agrees with the result of FT-IR. The Pt4f lines in Figure 3c were obtained from BC/Pt and NBC/Pt, where can be deconvoluted into three pairs of doublets, which can be attributed to metallic Pt, Pt 2+ and Pt 4+ , 37 respectively. The related data is listed in Table I.…”

Amalgamation of complex iron(III) ions and iron nanoclusters with MWCNTs as a route to potential T2 MRI contrast agents

“…11 As a consequence, iron (and iron-based phases) nanoparticles can be encapsulated in multiwall carbon nanotubes (MWCNTs) produced by catalytic chemical vapor deposition (c-CVD), leading to ferromagnetic and/or superparamagnetic properties. 12 For this reason, one could portray the nanoparticulate iron designating the pristine nanomaterial as Fe@MWCNT. Furthermore, CNTs expand their applicability by functionalization.…”