Growth Of Double-walled Carbon Nanotubes Research Articles

Fabrication of a Co-Mo-Based Metal-Organic Framework for Growth of Double-Walled Carbon Nanotubes.

Double-walled carbon nanotubes (DWCNTs) make up a unique class of carbon nanotubes (CNTs) that are particularly intriguing for scientific research and are promising candidates for technological applications. A more precise level of control and greater yields can be achieved via catalytic chemical vapor deposition (CCVD), which involves the breakdown of a carbonaceous gas over nanoparticles. The addition of molybdenum to the system can increase the selectivity with regard to the number of walls that exist in the obtained CNTs. As reported herein, we have designed and synthesized a novel Co-Mo-MOF, [Co(3-bpta)1.5(MoO4)]·H2O (where 3-bpta = N,N'-bis(3-pyridyl)terephthalamide), and employed the Co-Mo-MOF as a bimetallic catalyst precursor for the CCVD approach to prepare high-quality DWCNTs. The Co-Mo-MOF was employed after being calcined in N2 and H2 at 1100 °C and decomposing into CoO, CoMoO4, and MoO3. Existing CoMoO4 is unaltered after reduction in H2 at 1100 °C, while CoO and MoO3 are converted into Co0 and MoO2, and more CoMoO4 is created at the expense of Co0 and MoO2 without clearly defining agglomeration. Finally, the interaction between metallic Co particles and C2H4 is what initiates the formation of DWCNTs. In-depth discussion is provided in this paper regarding the mechanism underlying the high selectivity and activity of Co-Mo catalysts in regulating the development and structure of DWCNTs. The DWCNTs also offer excellence performance when they are used as water purification agents and as selective sorbents. This work opens a feasible way to use MOFs as a way to produce MWCNTs, thus blazing a new trail in the field of MOF-derived carbon-based materials.

Growth of double-walled carbon nanotubes from silicon oxide nanoparticles

Double-walled carbon nanotubes (DWCNTs) were synthesized by a metal-catalyst-free chemical vapor deposition method using silicon oxide nanoparticles as a catalyst. The diameters and lengths of the DWCNTs are in the ranges of 3–5nm and 1–5μm, respectively. The amount of DWCNTs produced is about 70%, while the remainder is single-walled carbon nanotubes. A heat treatment of the SiO2/Si substrate used was found to be crucial for controlling the size of the catalyst nanoparticles, and hence for the growth of the DWCNTs. Flat or cone-shaped caps were observed for the DWCNTs, indicating that the growth of the DWCNTs from the non-metal catalyst follows a vapor–solid–solid mechanism. Energy dispersive spectroscopy and X-ray photoelectron spectroscopy characterizations confirmed that no metal impurity exists in the obtained DWCNT samples.

Selective growth of double-walled carbon nanotubes on gold films

Growth of high-quality vertical aligned carbon nanotube (CNT) structures on silicon supported gold (Au) films by thermal chemical vapor deposition (TCVD) is presented. Transmission electron microscopy (TEM) images show that the growth is highly selective. Statistical study reveals that 79.4% of the as-grown CNTs are double-walled. The CNTs synthesized on Au films are more porous than that synthesized on silicon substrates under the same conditions. Raman spectroscopy and electrical characterization performed on the as-grown double-walled CNTs (DWNTs) indicate that they are competitive with those CNTs grown on silicon substrates. Field emission tests show that closed-ended DWNTs have lower threshold field than those open-ended.

Growth of carbon nanotubes by the catalytic decomposition of methane over Fe-Mo/Al 2O 3 catalyst: effect of temperature on tube structure

The effects of temperature, reaction time, and flow rate on the structure of carbon nanotubes (CNTs) were studied using catalytic chemical vapor deposition of methane over an Fe-Mo/Al 2O 3 catalyst. Results show that the temperature is a key parameter to control the wall thickness of the CNTs. Low temperature leads to the formation of multiwalled carbon nanotubes (MWCNTs) with wall thickness of 2–7 nm. Relatively high temperature is in favor of the growth of double-walled carbon nanotubes (DWCNTs), whereas high temperature promotes the generation of single-walled carbon nanotubes (SWCNTs). A further increase of temperature results in the generation of MWCNTs with a wall thickness of 3–15 nm and large carbon particles.

The confined growth of double-walled carbon nanotubes in porous catalysts by chemical vapor deposition

Double-walled carbon nanotubes (DWCNTs) were prepared from methane using a Fe/MgO porous catalyst. A series of catalyst powders with different pore size distributions were obtained by compression at pressures of 0–233 MPa. These were used to decompose methane and synthesize DWCNTs which differed in activity, purity, yield and degree of perfection. Characterization by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, thermo-gravimetric analysis, N 2 adsorption measurement (Brunauer–Emmett–Teller (BET)) and Hg penetration provided direct evidence that a compact catalyst structure is not good for the nucleation and growth of DWCNTs, e.g., a catalyst with a compact structure that did not have pores larger than 30–50 nm mostly produced multi-walled carbon nanotubes. The confined growth and buckling model of DWCNTs inside the porous catalysts are proposed to explain the growth behavior. These results suggest that a porous catalyst for DWCNT synthesis should have a large pore size distribution or loose stacked structure, which provides new guidelines for catalyst design.

Dynamics of Carbon Nanotube Growth from Fullerenes

The growth of double-walled carbon nanotubes from peapods was studied. The transformation was monitored by the decrease of fullerene Raman lines, the growth of inner tube Raman lines, and the development of X-ray diffraction patterns. A visual check of the growth process by HRTEM provided additional information. From the difference in time constants for the bleaching of fullerene Raman lines and for the growth of nanotube Raman lines, the existence of an intermediate phase was concluded that was eventually observed in X-ray diffraction and HRTEM. Time constants for the growth of large diameter inner tubes were up to a factor two larger than for small diameter inner tubes. The results fully support the fullerene coalescence growth model triggered by Stone-Wales transformations.

High-efficient synthesis of double-walled carbon nanotubes by arc discharge method using chloride as a promoter

With trace halide as a promoter in an iron sulfide catalyst, relatively perfect structural integrity double-walled carbon nanotubes (DWNTs) have been synthesized in large quantity and high yield by arc discharge method. Scanning electron microscope (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Raman spectroscopy were used for structural characterization and yield determination. The results revealed that halide was a crucial factor for selectively synthesizing high yield DWNTs. The detailed experimental parameters were systematically investigated. The possible role of halide in growth of DWNTs was discussed as well.

Growth of Double-Walled Carbon Nanotubes Using a Conditioning Catalyst

Here we describe the effect of different synthetic conditions on the quality and purity of double-walled carbon nanotubes (DWNTs) with the aid of a conditioning catalyst. By lowering the reaction temperature down to 875 degrees C and utilizing a conditioning catalyst, increased purity and a decreased inner diameter of the DWNTs was achieved, while adverse results were observed with increasing reaction temperature. Based on detailed high-resolution transmission electron microscopy studies on the diameter distribution of the tubes, preferential growth conditions for DWNTs over single-wall carbon nanotubes are identified solely from increased carbon solubility considerations (caused by an increased portion of active carbon species by use of Mo) for the same distribution of metal particles.

Synthesis and characterization of double-walled carbon nanotubes from multi-walled carbon nanotubes by hydrogen-arc discharge

Double-walled carbon nanotubes (DWNTs) were synthesized in a large scale by a hydrogen arc discharge method using graphite powders or multi-walled carbon nanotubes/carbon nanofibers (MWNTs/CNFs) as carbon feedstock. The yield of DWNTs reached about 4 g/h. We found that the DWNT product synthesized from MWNTs/CNFs has higher purity than that from graphite powders. The results from high-resolution transmission electron microscopy observations revealed that more than 80% of the carbon nanotubes were DWNTs and the rest were single-walled carbon nanotubes (SWNTs), and their outer and inner diameters ranged from 1.75 to 4.87 nm and 1.06 to 3.93 nm, respectively. It was observed that the ends of the isolated DWNTs were uncapped and it was also found that cobalt as the dominant composition of the catalyst played a vital role in the growth of DWNTs by this method. In addition, the pore structures of the DWNTs obtained were investigated by cryogenic nitrogen adsorption measurements.

Growth of double-wall carbon nanotubes with diameter-controlled iron oxide nanoparticles supported on MgO

We have studied the growth of carbon nanotubes by chemical vapor deposition (CVD) on the nanoparticles of iron oxide with two different diameters, 4 and 10 nm, supported on MgO powder. Both nanoparticles catalyzed the growth of double-wall carbon nanotubes (DWNTs) together with a small amount of single-wall carbon nanotubes (SWNTs). We found that the inner- and outer-diameters of the DWNTs were modified by the initial nanoparticle size; smaller nanoparticles catalyzed the growth of the DWNTs with smaller diameters. These results suggest that the MgO support strongly influence the catalytic activity of nanoparticles by reduction of the catalytically-active size.

Raman Characterization and Tunable Growth of Double-Wall Carbon Nanotubes

Double-wall carbon nanotubes (DWCNTs) were synthesized by pyrolyzing C2H2 on the sulfur-promoted floating iron catalyst. Similar to that of SWCNTs, Raman spectra of DWCNTs display two “fingerprint” features of the radial breathing mode (RBM) at the lower frequency range and the splitting tangential mode (TM). However, RBM frequencies of DWCNTs take a wider range and display much richer peaks than those of SWCNTs. The possible match of the inner tubes and the outer tubes according to the RBM bands was assigned, and different chirality types were discussed according to the diameter and chirality dependence of resonant Raman vibration. By changing experimental conditions, we can tunably grow different DWCNTs with various diameter distributions.

27aWB-4 アーク放電による二層カーボンナノチューブ (DWCNT) の成長

27aWB-4 アーク放電による二層カーボンナノチューブ (DWCNT) の成長