Large-Scale Synthesis of High-Quality Single-Walled Carbon Nanotubes by Catalytic Decomposition of Ethylene

Converting Carbon Dioxide into Carbon Nanotubes by Reacting with Ethane

The urgency to mitigate environmental impacts from anthropogenic CO2 emissions has propelled extensive research efforts on CO2 reduction. The current work reports a novel approach involving transforming CO2 and ethane into carbon nanotubes (CNTs) using earth-abundant metals (Fe, Co, Ni) at 750 °C. This route facilitates long-term carbon storage via generating high-value CNTs and produces valuable syngas with adjustable H2/CO ratios as byproducts. Without CO2, direct pyrolysis of ethane undergoes rapid deactivation. The participation of CO2 not only enhances the durability of the catalyst, but also contributes about 30 % of the CNTs production, presenting a viable solution to CO2 challenges. The CNT morphology depends on the catalyst used. Co- and Ni-based catalysts produce CNT with a 20 nm diameter and micrometer length, whereas Fe-based catalysts yield bamboo-like structures. This work represents a pioneering effort in utilizing CO2 and ethane for CNT production with potential environmental and economic benefits.

The Reduction Temperature Effect of Fe–Co/MgO Catalyst on Characteristics of Multi-Walled Carbon Nanotubes

Diameters and crystallinity of multi-walled carbon nanotubes (MWCNTs) dependent on reduction temperature of the Fe–Co/MgO catalyst were investigated. MWCNTs were synthesized by catalytic chemical vapor depositing and the Fe–Co/MgO catalyst was fabricated by using a sol-gel method. According to Raman analysis, transmission electron microscopy and thermogravimetric analysis, the diameter distribution of MWCNTs was broadened with increasing reduction temperature of the Fe–Co/MgO catalyst and crystallinity was improved. The above results are attributed to an increased size and enhanced crystallinity of metal catalyst particles by increasing reduction temperature.

Floating catalyst CVD synthesis of single walled carbon nanotubes from ethylene for high performance transparent electrodes

We have developed the floating catalyst chemical vapor deposition (FCCVD) synthesis of single walled carbon nanotubes (SWCNTs) using C2H4 hydrocarbon as a carbon source and iron nanoparticles as the catalyst in an environmentally friendly and economical process. For the first time, ethylene was used as the only carbon source in FCCVD with N2 as the main carrier gas. No sulphur and less than 15% H2 in a N2 carrier gas were used. By varying the ferrocene concentration, the diameter of the SWCNTs was tuned in the range of 1.3-1.5 nm with the optimized control of ferrocene concentration. The process produced SWCNTs with an average length of 13 μm and with a low level of bundling, that is a high proportion (28%) of individual tubes. The electron diffraction (ED) pattern indicated a random chirality distribution of the tubes between armchair and zigzag structures. The ED analysis also revealed that 35-38% of tubes are metallic. As a result of having long SWCNTs with a low level of bundling and a high fraction of metallic tubes, we produced a highly conductive transparent film with a sheet resistance of 51 Ohm per sq. for 90% transmission at 550 nm after HNO3 treatment, this being one of the lowest sheet resistance values reported for SWCNT thin films.

Large-scale synthesis and characterization of super-bundle single-walled carbon nanotubes by water-assisted chemical vapor deposition

A large-scale synthesis of water-assisted super-bundle single-walled carbon nanotubes was investigated by catalytic chemical vapor deposition. The product yield dramatically improved from 40 to 206 wt%.

Carbon nanotube mass production: principles and processes

Our society requires new materials for a sustainable future, and carbon nanotubes (CNTs) are among the most important advanced materials. This Review describes the state-of-the-art of CNT synthesis, with a focus on their mass-production in industry. At the nanoscale, the production of CNTs involves the self-assembly of carbon atoms into a one-dimensional tubular structure. We describe how this synthesis can be achieved on the macroscopic scale in processes akin to the continuous tonne-scale mass production of chemical products in the modern chemical industry. Our overview includes discussions on processing methods for high-purity CNTs, and the handling of heat and mass transfer problems. Manufacturing strategies for agglomerated and aligned single-/multiwalled CNTs are used as examples of the engineering science of CNT production, which includes an understanding of their growth mechanism, agglomeration mechanism, reactor design, and process intensification. We aim to provide guidelines for the production and commercialization of CNTs. Although CNTs can now be produced on the tonne scale, knowledge of the growth mechanism at the atomic scale, the relationship between CNT structure and application, and scale-up of the production of CNTs with specific chirality are still inadequate. A multidisciplinary approach is a prerequisite for the sustainable development of the CNT industry.

Highly dense and perfectly aligned single-walled carbon nanotubes fabricated by diamond wire drawing dies

We have developed a low-cost and effective method to align single-walled carbon nanotubes (SWNTs) using a series of diamond wire drawing dies. The obtained SWNTs are highly dense and perfectly aligned. X-ray diffraction (XRD) indicates that the highly dense and perfectly aligned SWNTs (HDPA-SWNTs) form a two-dimensional triangular lattice with a lattice constant of 19.62 A. We observe a sharp (002) reflection in the XRD pattern, which should be ascribed to an intertube spacing 3.39 A of adjacent SWNTs. Raman spectra reveal that the radical breath mode (RBM) of SWNTs with larger diameter in the HDPA-SWNTs is suppressed compared with that of as-grown SWNTs. The HDPA-SWNTs have a large density, approximately 1.09 g/cm 3, and a low resistivity, approximately 2 m Omega cm, at room temperature, as well as a large response to light illumination.

RBM band shift-evidenced dispersion mechanism of single-wall carbon nanotube bundles with NaDDBS

The dispersion process of single-wall carbon nanotube (SWNT) by using sodium dodecylbenzene sulfonate (NaDDBS) was studied by means of surface tension measurements, ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), and transmission electron spectroscopy (TEM). The critical micelle concentration (CMC) and the concentration where the surface tension begins to drop increase by the presence of SWNT. The isotherm of NaDDBS amount adsorbed on SWNT shows the plateau region at 0.2-6 mM and the saturated region above 40 mM. The external surface of SWNT bundle is fully covered with adsorbed NaDDBS at the plateau region, showing that SWNTs can be dispersed with the bundle form. On the other hand, SWNTs are dispersed in individual tubes at the saturated region, where the adsorption amount corresponds to coating of individual tube surfaces with NaDDBS. This dispersion state was confirmed by SEM and TEM observations. The effect of the dispersion state of SWNTs on radial breathing mode in Raman spectrum gave inherent peak shifts, being the in situ evidences on the step-wise dispersion mechanism of the SWNT bundle to the individual tubes.

Investigation of Field Emission and Photoemission Properties of High-Purity Single-Walled Carbon Nanotubes Synthesized by Hydrogen Arc Discharge

Single-walled carbon nanotubes (SWCNTs) were directly synthesized by a hydrogen arc-discharge method by using only Fe catalyst. The synthesized carbon materials indicated high-purity SWCNTs without amorphous carbon materials from SEM observation. The SWCNTs had diameters of 1.5-2.0 nm from TEM and Raman observation. After a simple purification, TGA indicated that SWCNTs had a purity of ca. 90.1 wt %. Field emission from the SWCNT emitters which were fabricated by using a spray method was measured by a diode structure. The vertically aligned SWCNT emitters showed the low turn-on voltage of 0.86 V/microm and a high emission-current density of 3 mA/cm2 at an applied field of about 3 V/microm. From a Fowler-Nordheim plot, the vertically aligned SWCNT revealed a high field enhancement factor of 2.35 x 10(4). The photoemission measurements, excited by a photon energy of 360 eV, showed significantly delocalized graphite-pi states at the purified SWCNTs. Here, we investigated that the field-emission properties of SWCNTs would be attributed to the high electronic density of states near Fermi energy, including the delocalized graphite-pi states.

A study of the formation, purification and application as a SWNT growth catalyst of the nanocluster [HxPMo12O40⊂H4Mo72Fe30(O2CMe)15O254(H2O)98]

The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results.

High-Yield Synthesis of Single-Wall Carbon Nanotubes on MCM41 Using Catalytic Chemical Vapor Deposition of Acetylene

High-quality single-wall carbon nanotubes (SWNTs) with narrow diameter distribution have been grown on Fe/Co-loaded MCM41 by using acetylene as the carbon source within a short reaction period, typically 10 min or less. The optimum temperature for SWNTs synthesis is 850 degrees C. Longer reaction time (i.e., 30 min) favors the formation of multiwall carbon nanotubes (MWNTs) and graphitic carbon. When the reaction time is reduced to less than 10 min, formation of MWNTs and graphitic carbon is greatly suppressed, and high-quality SWNTs dominates the yield. The surface of the as-grown SWNTs is found to be free from amorphous carbon, as observed from high-resolution transmission electron microscope (HRTEM) analysis. Raman spectral data show a G/D ratio above 10, indicating that the as-grown SWNTs have very few defects. Furthermore, radial breathing mode (RBM) analysis reveals that the diameter distribution of the current SWNTs is narrow and ranges from 0.64 to 1.36 nm.