Solvothermal synthesis of hair-like carbon nanotubes onto sub-micron-sized spherical metal oxide catalyst cores

Kazuya Kobiro; Hinako Kimura; Saki Hirose; Makoto Kinjo; Hiroshi Furuta

doi:10.1039/d3ra00770g

Solvothermal synthesis of hair-like carbon nanotubes onto sub-micron-sized spherical metal oxide catalyst cores

RSC Adv. 2023 May 5;13(20):13809-13818. doi: 10.1039/d3ra00770g. eCollection 2023 May 2.

Authors

Kazuya Kobiro^{1

2}, Hinako Kimura¹, Saki Hirose¹, Makoto Kinjo¹, Hiroshi Furuta^{1

3}

Affiliations

¹ Graduate School of Engineering, Kochi University of Technology 185 Miyanokuchi, Tosayamada Kochi 782-8502 Japan kobiro.kazuya@kochi-tech.ac.jp furuta.hiroshi@kochi-tech.ac.jp.
² Center for Structural Nanochemistry, Research Institute, Kochi University of Technology 185 Miyanokuchi, Tosayamada Kochi 782-8502 Japan.
³ Center for Nanotechnology, Research Institute, Kochi University of Technology 185 Miyanokuchi, Tosayamada Kochi 782-8502 Japan.

Abstract

Long- and uniform-length, and high-density hair-like carbon nanotubes (CNTs) were produced by CNT growth on sub-micron-sized spherical catalyst supports. The nanosized catalysts (FeO _x , CoO _x , and NiO _x ) that were supported in/on the sub-micron-sized spherical metal oxides (TiO₂, ZrO₂, SnO₂, and CeO₂) were prepared via one-step solvothermal and/or two-step impregnation methods. The nanosized catalysts supported in/on the spherical metal oxide supports were converted into CNT conjugates with the CNT-hair morphology via a chemical thermal vapor deposition technique using ethyne gas as a carbon source; the CNTs grew on the central spherical metal oxide core under the base growth process conditions. Among the many types of candidate spherical catalyst materials, the combination of FeO _x as a catalyst for CNT growth and ZrO₂ as a support led to the best growth of CNT-hair under the reaction conditions, which included a temperature of 730 °C, pressure of 65 Pa, a 10 sccm ethyne gas flow, and a reaction time of 10 s. The CNTs consisted of five-to-eight-layered multi-wall structures with lengths of approximately 3 μm. The CNT-hair that was obtained using the solvothermally embedded catalyst showed higher crystallinity and was dense, thick, and straight, while the corresponding CNT-hair obtained using the impregnated catalyst was slightly sparse, thin, and curly. A unique layer structure constructed using large quantities of uniform CNT-hair, including multiple CNT yarns similar to fuzzy balls or cotton candies, was assembled. The CNT-hair conjugate, specifically constructed in a layer structure with core FeO _x /ZrO₂ catalysts and tangled CNT yarns, had an appearance similar to frog eggs. Therefore, we successfully prepared suitable catalysts for CNT-hair production and fabricated a layer structure consisting of large numbers of CNT-hair conjugates. The unique structures are expected as a new metamaterial with intriguing physical properties, including isotropic absorption of polarized light and electromagnetic waves.