Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes

Abstract

The paper reports the synthesis of carbon nanotubes from ethanol over group VIII (Fe, Co, Ni) catalysts derived from corresponding metallocenes. Several unexpected cooperative effects are reported, which are never observed in the case of individual metallocenes such as the commonly used ferrocene catalyst Fe(C5H5)2. The formation of very long (up to several µm) straight monocrystal metal kernels inside the carbon nanotubes was the most interesting effect. The use of trimetal catalysts (Fe1-x-yCoxNiy)(C5H5)2 resulted in the sharp increase in the yield of carbon nanotubes. The electrical conductivity of the produced nanotubes is determined by the nature of the catalyst. The variation of individual metals in the Ni-Co-Fe leads to a drop of the electrical resistivity of nanotube samples by the order of magnitude, i.e., from 1.0 × 10−3 to 1.1 × 10−5 Ω∙m. A controlled change in the electrophysical properties of the nanotubes can make it possible to expand their use as fillers in composites, photothermal and tunable magnetic nanomaterials with pre-designed electrical conductivity and other electromagnetic properties.

Metal Cluster Size-Dependent Activation Energies of Growth of Single-Chirality Single-Walled Carbon Nanotubes inside Metallocene-Filled Single-Walled Carbon Nanotubes

“…The third group of authors showed that Ni and Co catalysts had a similar effectiveness in the PECVD synthesis of nanotubes, which was higher than for Fe catalyst [ 88 ]. The observed differences were explained by different solubility and diffusion constants of carbon in metals and rates of integration of carbon into growing tubes [ 127 , 128 , 129 , 130 , 131 , 132 , 133 ].…”

Solutions to the Challenges of Lithium–Sulfur Batteries by Carbon Nanotubes

“…[4,5] nanomaterials (constructed by sp 2 bonded carbon atoms) with a high aspect ratio (≈10 3 ), [6] and the hollow voids of the graphitic layers arranged in the cylinder shape endow them with a low density (≈2 g cm −3 ). [7] It has been shown that the electrical conductivity of an individual CNT is dependent on both intrinsic factors (including the length, [8] diameter, [9] and chirality (for single-wall carbon nanotubes, SWCNTs) [10] ) and external stimuli (such as the temperature change [11] and the applied pressure [12] ), with the measured resistivity of pristine CNTs measured to be ≈10 −5 Ω m. [13] Furthermore, CNTs are mechanically strong with the reported Young's modulus and tensile stress of an individual CNT in the range of TPa [14] and GPa, [15] respectively. In addition to their outstanding chemical stability, CNTs are thermally stable at high temperatures (double-wall carbon nanotubes with an inner diameter above >0.9 nm are structurally stable at ≈2000 °C [16] while SWCNTs with a diameter smaller than 0.4 nm are mechanically stable at ≈1100 °C [17] ).…”

Effect of a Metallocene Catalyst Mixture on CNT Yield Using the FC-CVD Process

“…Mixing two metal catalysts has shown an increase in CNT yield for the substrateassisted CVD method [47][48][49][50]. However, there are limited publications available in the literature where cobaltocene [51,52] or nickelocene or their combination [51][52][53][54][55] are used for the synthesis of CNT aerogel from the FC-CVD method.…”

“…Syntheses of CNT aerogel at 1150 • C using different ratios of ferrocene, nickelocene, and cobaltocene were studied [52]. Carbon nanotube production increased significantly using a mixture of metallocene (Fe 1−x−y Co x Ni y )(C 5 H 5 ) 2 .…”

“…Analysis of the literature [47][48][49][50][51][52][53][54][55] shows that depending on the condition of the synthesis, the CNT product changes. Most of the summarized work used vertical tube FC-CVD reactors operating at a temperature range of 800-1200 • C. The published work reports an increase in CNT production with the use of a multi-metallic catalyst system.…”