Catalyst volume to surface area constraints for nucleating carbon nanotubes

In this Article, we describe a carbon nanotube formation model in which sp2 carbon hemispheres form the embryonic caps from which a nanotube can grow. This requirement leads to a single wall carbon nanotube formation window concomitant with our systematic experimental findings, which show upper and lower diameter limits. Further, the successful formation of a nucleation cap (hemisphere) is governed by catalyst particle volume to surface area considerations. Single wall carbon nanotubes are only obtained when both the nanotube formation window and the precipitating catalyst size distribution cross over. The extent to which these two windows overlap establishes the mean diameter and diameter distribution of the obtained single wall carbon nanotubes.     

碳纳米管的宏量制备及产业化

作为纳米材料的代表之一,碳纳米管因其独特的一维结构具备了优异的力学、电学、热学、光学和反应性能,使其在能源存储与转化、复合材料、多相催化、环境保护及生物医药等领域具有大量的应用潜力.本文总结了多种类型碳纳米管宏量制备的化学及工程原理,并对多壁碳纳米管、单壁碳纳米管、双壁碳纳米管、定向碳纳米管、超顺排碳纳米管、水平超长碳纳米管、掺杂碳纳米管、螺旋碳纳米管、碳纳米管结及碳纳米管/石墨烯杂化物的宏量制备方法进行了评述.同时,对碳纳米管产业化中新的工程问题,如工业标准、环境评估以及产业化进展进行了分析.目前,碳纳米管已经具有成千吨的产能,并广泛应用于锂离子电池电极、导电复合材料、汽车配件和体育用品等领域.尽管如此,高性能的碳纳米管的宏量制备及其配套产业化技术仍有待深入开发,产品需要进一步丰富、市场需要进一步拓展,以望形成大规模纳米产业,促进社会的可持续发展.     

The production of carbon nanotubes from carbon dioxide:challenges and opportunities

Recent advances in the production of carbon nanotubes (CNTs) are reviewed with an emphasis on the use of carbon dioxide (CO2) as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be explored further. A theoretical and analytical comparison of the currently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters (i.e., temperature, pressure, catalyst, etc.) that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology: (1) the CNT-CO2 synthesis and formation mechanism, (2) catalytic effects of transitional metals and mechanisms, (3) utilization of metallocenes in the CNT-CO2 reactions, (4) applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and (5) the effects of process parameters such as temperature, etc.     

The production of carbon nanotubes from carbon dioxide: challenges and opportunities

Recent advances in the production of carbon nanotubes (CNTs) are reviewed with an emphasis on the use of carbon dioxide (CO2) as a sole source of carbon. Compared to the most widely used carbon precursors such as graphite, methane, acetylene, ethanol, ethylene, and coal-derived hydrocarbons, CO2 is competitively cheaper with relatively high carbon yield content. However, CNT synthesis from CO2 is a newly emerging technology, and hence it needs to be explored further. A theoretical and analytical comparison of the currently existing CNT-CO2 synthesis techniques is given including a review of some of the process parameters (i.e., temperature, pressure, catalyst, etc.) that affect the CO2 reduction rate. Such analysis indicates that there is still a fundamental need to further explore the following aspects so as to realize the full potential of CO2 based CNT technology: (1) the CNT-CO2 synthesis and formation mechanism, (2) catalytic effects of transitional metals and mechanisms, (3) utilization of metallocenes in the CNT-CO2 reactions, (4) applicability of ferrite-organometallic compounds in the CNT-CO2 synthesis reactions, and (5) the effects of process parameters such as temperature, etc.     

Utilization of compressed natural gas for the production of carbon nanotubes

The present work aims at utilizing compressed natural gas (CNG) as carbon source for the synthesis of carbon nanotubes (CNTs) over CoOMoO/Al2O3 catalyst via catalytic chemical vapor deposition (CCVD) method. The as-produced carbonaceous product was characterized by thermal gravimetric analyzer (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The experimental finding shows that CNTs were successfully produced from CNG while carbon nanofibers (CNFs) were formed as the side products. In addition, the catalytic activity and lifetime were found sustained and prolonged, as compared with using high purity methane as carbon source. The present study suggests an alternative route which can effectively produce CNTs and CNFs using low cost CNG.     

Large scale production of short functionalized carbon nanotubes

A simple mechano-chemical modification of multiwall carbon nanotubes is described. The use of ball-milling in specific atmosphere allows us to introduce functional groups like thiol, amine, amide, carbonyl, chlorine, etc. onto carbon nanotubes. The resulted functional groups are characterized using infrared spectroscopy and X-ray photoelectron spectroscopy.     

Thermal decomposition of ferrocene as a method for production of single-walled carbon nanotubes without additional carbon sources

A new method to grow bulk quantities of single-walled carbon nanotubes (SWCNTs) by a catalytic chemical vapor deposition (CVD) process with the possibility of varying the pressure has been developed and is reported in this paper. Thermal decomposition of ferrocene provides both catalytic particles and carbon sources for SWCNT growth using Ar as a carrier gas. Upon an increase in the pressure, the mean diameter of the SWCNTs decreases. In fact, high abundances of SWCNT with diameters as small as 0.7 nm, which is the limit for stable caps with isolated pentagons, can be obtained. An additional advantage of this method is that as no external carbon sources are required, SWCNT synthesis can be achieved at temperatures as low as 650 degrees C.     

Thermokinetics simulation for multi-walled carbon nanotubes with sodium alginate by advanced kinetics and technology solutions

To accomplish an effective analysis of adsorption, the strong acid dye from aqueous solution of sodium alginate (SA) and multi-walled carbon nanotubes (MWCNTs) composite gel beads were used as important parameters. Differential scanning calorimetry (DSC) was used to measure the heat of breakdown reaction. The experimental conditions were set at 0.5, 1, 2, 4, and 8 °C min^?1, and the temperature range was 30–300 °C. The heating rates and the temperature range were set as follows: Four kinds of proportion in this experiment contained 2 SA % w/v (SA), 0.03, 0.09, 0.18, 0.36 % w/v (MWCNTs), and 10 % w/v calcium chloride, respectively. Four samples, 5, 6, 7, 8, and 9 mg, were used to detect the experimental data. It contributed to understanding the reaction for the distinctive MWCNTs. With the thermokinetic data by isoconversional approach obtained from advanced kinetics and technology solutions (AKTS), the related thermal safety information can be obtained from the thermal reaction of MWCNTs. Valuable parameters, such as activation energy (E _a) and heat of decomposition, can be applied in operation, including adsorption and desorption processes. After DSC tests, and under the four compositions of SA/MWCNTs, at different heating rates of 0.5, 1, 2, 4, and 8 °C min^?1, primarily we found that when the heating rate was increased, exothermic onset temperature would increase gradually. After analyzing E _a value by isoconversional kinetics, we learned that in four different adsorption compositions, SA/MWCNTs_0.03 (161.20 kJ mol^?1) was the minimum. Among them, the highest value was SA/MWCNTs_0.18 (220.48 kJ mol^?1). However, in this study, for SA/MWCNTs compositions we found that E _a value will drop in the final material SA/MWCNTs_0.36. Accordingly, if the ratio of SA and calcium chloride was fixed, then different compositions of the MWCNTs would affect adsorption efficiency of SA/MWCNTs and E _a variation.     

Fe—Co双金属催化剂对纳米碳管规模化生产的影响

在C2H2和N2的氛围下,以Fe－Co双金属氧化物为催化剂,利用催化裂解法大量制备了多壁纳米碳管,实验结果表明,以Fe－Co双金属氧化物为催化剂制备纳米碳管的产量明显高于Fe或Co单独存在时所得的纳米碳管的产量,且Fe摩尔分数为0.2时效果最佳;同时发现,在制备的产品中存在很多螺旋形的纳米碳管,此方法工艺简单,有利于纳米碳管的规模化、大批量生产,为纳米碳管的深入研究及广泛应用打下了基础。     

Development of technology to introduce carbon nanotubes into a polyester-binder composition

Technological regimes of introducing carbon nanotubes (CNTs) into a polyester matrix composite are considered, and the properties of the obtained composition are studied. It is established that agglomerates that cannot be broken up by a mechanical stirring are formed at the moment of CNT wetting with the polyester binder. The use of an ultrasound disperser makes it possible to get rid of agglomerates but leads to enhanced porosity, with additional technological operations being necessary for reducing the latter.     

A multi-stage growth model leading to high-yield production of carbon nanotubes

A novel growth model leading to high-yield production of carbon nanotubes with crystallized Ni(x)Mg(1-x)MoO(4) as the catalyst is revealed.     

The conversion of polyaniline nanotubes to nitrogen-containing carbon nanotubes and their comparison with multi-walled carbon nanotubes

Polyaniline (PANI) nanotubes were prepared by the oxidation of aniline in solutions of acetic or succinic acid, and subsequently carbonized in a nitrogen atmosphere during thermogravimetric analysis running up to 830 °C. The nanotubular morphology of PANI was preserved after carbonization. The molecular structure of the original PANI and of the carbonized products has been analyzed by FTIR and Raman spectroscopies. Carbonized PANI nanotubes contained about 8 wt.% of nitrogen. The molecular structure, thermal stability, and morphology of carbonized PANI nanotubes were compared with the properties of commercial multi-walled carbon nanotubes.     

Synthesis, characterization, and stability of Fe-MCM-41 for production of carbon nanotubes by acetylene pyrolysis

Fe-substituted MCM-41 molecular sieves with ca. 1, 2, and 3 wt % Fe were synthesized hydrothermally using different sources of colloidal silica (HiSil and Cab-O-Sil) and characterized by ICP, XRD, N2 physisorption, UV-vis, EPR, TPR, and X-ray absorption. Catalysts synthesized from Cab-O-Sil showed higher structural order and stability than those from HiSil. The local environment of Fe in the mesoporous material as studied by UV-vis reveals the dominance of framework Fe in all the as-synthesized Fe-MCM-41 samples. Dislodgement of some Fe species to extraframework location occurs upon calcination, and this effect is more severe for Fe-MCM-41 (2 wt %) and Fe-MCM-41 (3 wt %), as confirmed by EPR and X-ray absorption. These materials have been used as catalytic templates for the production of carbon nanotubes (CNTs) by acetylene pyrolysis at atmospheric pressure. A relationship between the Fe loading in MCM-41 and the carbon species produced during this reaction has been established. Using our optimized conditions for this system, Fe-MCM-41 with ca. 2 wt % Fe showed the best results with particularly high selectivity for single-wall carbon nanotube (SWNT) production. This catalyst was selective for carbon nanotubes with a low amount of amorphous carbon for a narrow range of temperatures from 1073 to 1123 K. To account for the different selectivity of these catalysts for CNTs production, the local environment and chemical state of Fe in the used catalyst was further probed by X-band EPR.     

Control of carbon capping for regrowth of aligned carbon nanotubes

The regrowth of carbon nanotubes (CNTs) in a second growth stage after a first growth stage has been completely stopped has been found to be strongly related to the carbon capping present on their catalyst particles. It is shown that the undesirable carbon capping can be prevented from forming or removed and the nanotube growth can be rejuvenated by either control of plasma processing conditions during chemical vapor deposition or by inserting a room-temperature sputter etching process. The ability to cause sequential growth stages to take place in different directions makes it possible for us to clearly compare the occurrence and extent of CNT regrowth. Such a CNT regrowth process and understanding of controlling parameters can enable the creation of new nanowire configurations that could potentially be used for applications such as sharply bending nanointerconnections, nanosprings, bent AFM nanoprobes, or nanobarcodes.     

Fullerenes inside carbon nanotubes and multi-walled carbon nanotubes: optimum and maximum sizes

The potential energies of interaction between carbon nanotubes and internal fullerenes of spherical and ellipsoidal shape, as well as between nanotubes in multi-walled nanotubes were calculated using the Lennard–Jones (LJ) potential for carbon–carbon interactions. The optimum and maximum size of internal fullerenes and multi-walled nanotubes are determined as a function of the external nanotube radius. It was found that at the potential energy minimum, the van der Waals distance is close to that in graphite for all studied cases. The calculated results agree with available experimental observations and could be used as a guide for future experiments.     

Soluble carbon nanotubes

Carbon nanotubes have attracted great interdisciplinary interest because of their unique structure and properties. However, carbon-nanotube research is challenged by several problems, such as: i) mass production of material, ii) control of length, diameter, and chirality, and iii) manipulation for use in diverse technological fields. Issues regarding the synthesis and purification as well as the functionalization and solubilization of carbon nanotubes are relevant topics in this rapidly growing field. In this paper, covalent and noncovalent approaches to functionalized and solubilized nanotubes are examined in detail, with particular emphasis on the change of properties that accompany the chemical modification.     

Polymer-masking for controlled functionalization of carbon nanotubes

An effective and versatile method for tube-length-specific functionalization of carbon nanotubes through a controllable embedment of vertically-aligned carbon nanotubes into polymer matrices is reported, which allows not only asymmetric functionalization of nanotube sidewalls, but also facile introduction of new properties (e.g. magnetic) onto the region-selectively functionalized carbon nanotubes.