Facile Synthesis of Ternary Boron Carbonitride Nanotubes
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In this study, a novel and facile approach for the synthesis of ternary boron carbonitride (B–C–N) nanotubes was reported. Growth occurred by heating simple starting materials of boron powder, zinc oxide powder, and ethanol absolute at 1150 °C under a mixture gas flow of nitrogen and hydrogen. As substrate, commercial stainless steel foil with a typical thickness of 0.05 mm played an additional role of catalyst during the growth of nanotubes. The nanotubes were characterized by SEM, TEM, EDX, and EELS. The results indicate that the synthesized B–C–N nanotubes exhibit a bamboo-like morphology and B, C, and N elements are homogeneously distributed in the nanotubes. A catalyzed vapor–liquid–solid (VLS) mechanism was proposed for the growth of the nanotubes.
KeywordsB–C–N nanotubes Synthesis Stainless steel foil Characterization VLS model
Ternary boron carbonitride (B–C–N) nanotubes have recently attracted much attention because of their excellent mechanical properties, electrical properties, and anti-oxidant capacities [1, 2]. In addition, theoretical studies have revealed that the band gaps of B–C–N nanotubes can be tailored over a wide range by simply varying the chemical composition rather than by geometrical structure [3–7], which is superior to their carbon and boron nitride (BN) counterparts. This gives B–C–N nanotubes potential for use in electronics, electrical conductors, high temperature lubricants, and novel composites . Compared with the very extensive study about carbon and BN nanotubes, however, very little work was reported about B–C–N nanotubes. Since the discovery of B–C–N nanotubes in 1994 , several methods have been devoted to the synthesis of B–C–N nanotubes, such as arc-discharge , laser ablation , chemical vapor deposition (CVD) [12, 13], template route, and pyrolysis techniques [14, 15]. Particularly, single-walled B–C–N nanotubes have been recently synthesized by Wang et al.  via a bias-assisted hot-filament method. However, most of them usually used risky reagents such as diborane (B2H2)/ammonia (NH3), or produced nanotubes with low purity and high-cost and encountered the phase separation problem of BN and C. Thus, it is of great significance to explore novel and simple routes to prepare B–C–N nanotubes with uniform distribution of component B, C, and N elements. The current work reports a relatively safe and effective approach for growing high-purity B–C–N nanotubes directly on commercial stainless steel foil, by using simple raw materials of boron, zinc oxide (ZnO), and ethanol absolute. The reaction of boron and ZnO at high temperature produces boron oxide vapor that is the source of B, while ethanol absolute and nitrogen provide the source of C and N, respectively. It is interesting that the stainless steel foil is not only the support substrate but also the catalyst for the growth of the nanotubes. The obtained nanotubes have an average diameter of about 90 nm and the B, C, and N elements are found to be homogeneously distributed in the nanotubes. The growth mechanism of the nanotubes is also investigated in this study. To the best of our knowledge, it is the first time to report the synthesis of ternary B–C–N nanotubes via such a relatively simple route.
The growth of nanotubes was carried out in a conventional tube furnace. An alumina boat loaded with about 1.0 g mixture of hexagonal ZnO and amorphous B powder (with a ZnO:B molar ratio of 1.5:1) was inserted into a quartz tube and placed at the center of the furnace. Commercial stainless steel-304 foil with a thickness of 0.05 mm was inserted into the quartz tube as the substrate. Prior to heating, the chamber was flushed with high-purity N2flow to eliminate the residual air. Then the furnace was heated to 1150 °C under a mixture gas flow of N2(60 mL min−1) and H2(40 mL min−1). Ethanol absolute (AR grade) was introduced into the chamber when the furnace temperature reached at 1150 °C, which was carried by another N2flow with a rate of 20 mL min−1. The furnace was maintained at 1150 °C for 90 min. Finally, the furnace was cooled naturally to ambient temperature under the protection of N2flow. After taken from the furnace, the stainless steel substrate was found to be covered with white–gray deposit in the temperature range of 1000–1100 °C. The product was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S5500), high-resolution transmission microscopy (HRTEM, JEM-2010F), X-ray energy dispersive spectrometer (EDS), and electron energy loss spectroscopy (EELS), respectively.
Results and Discussion
In summary, a simple but efficient route to synthesize B–C–N nanotubes directly onto commercial stainless steel foil is demonstrated by using raw materials of boron powder, zinc oxide powder, and ethanol absolute. The nanotubes are pure with bamboo-like morphology and an average diameter of about 90 nm. During the formation process, the stainless steel foil plays a catalyst role additionally besides the substrate role for the B–C–N nanotube growth. A VLS process is proposed to be responsible for the growth of the B–C–N nanotubes.
The authors acknowledge financial support from the National Natural Science Foundation of China (NSFC, Grant No. 50862001), Ministry of Education of China (MOE, Grant No. 208106), Tsinghua University State Key Laboratory of New Ceramics & Fine Processing and Guangxi University (Grant No. DD040042).