Solvothermal preparation of amorphous carbon nanotubes and Fe/C coaxial nanocables from sulfur, ferrocene, and benzene
Introduction
Porous carbonaceous materials are important in many areas of modern science and technology, including water and air purification, catalysis, and energy storage [1]. In recent years, there has been growing interest in new applications of porous carbon materials, such as the storage of natural gas and as electrodes of an electric double-layer capacitor [2]. In the past decade, the study of synthesis of new porous carbon materials has made the greatest process in two areas: synthesis of ordered porous carbon materials with ordered porous silica templates, and synthesis of carbon nanotubes via a variety of methods [3]. Since their initial observation by Iijima in 1991 [4], carbon nanotubes have become the most active area of carbon materials research. Many methods of producing single- or multi-wall carbon nanotubes have been developed, such as laser vaporization [5], [6], arc discharge [7], [8], pyrolysis [9], [10], plasma-enhanced or thermal chemical vapor deposition (CVD) and solvothermal processes. Usually mesoporous carbon materials have amorphous structures, whereas the walls of most carbon nanotubes consist of crystallized graphitic layers.
Recently, amorphous carbon nanotubes have been synthesized via some novel approaches. Shih and co-workers prepared vertically aligned amorphous carbon nanotubes on anodic alumina by using a microwave electron cyclotron resonance chemical vapor deposition (ECR-CVD) method [11]. Ci and co-workers produced amorphous carbon nanotubes by the floating catalyst method [12]. Bao and co-workers and Xie and co-workers synthesized amorphous carbon nanotube bundles by catalytic assembly of carbon rings [3], [13]. Nishino et al. obtained amorphous carbon nanotubes from poly(tetrafluoroethylene) and ferrous chloride via chemical vapor deposition (CVD) technology at high temperatures [14], [15].
Lately, coaxial nanocable structures have become a significant issue for a more diverse range of application. Park [16] and coworkers synthesized SiC–C coaxial nanocables via the direct growth of SiC nanowires from silicon substrates and subsequent carbon deposition using pyrolysis of methane at 1100 °C. Ga2O3–C coaxial nanocables were generated via co-thermal evaporation of gallium oxide and activated carbon powder [17]. Fe3O4–C coaxial cables have been synthesized by pyrolyzing an ethanol/ferrocene mixture [18]. Yu and coworkers reported the synthesis of Ag–C coaxial nanocables by a hydrothermal method [19].
Here we report the synthesis of long amorphous carbon nanotubes and iron/carbon core-shell coaxial nanocables.
Section snippets
Experimental
In a typical experiment for generating long amorphous carbon nanotubes, 1 mmol ferrocene and 2 mmol sulfur powder were put into a 50 mL Teflon-lined autoclave, which was filled with benzene to 90% of total volume. After being sealed, the autoclave was maintained at 200 °C for 70 h and then cooled to room temperature naturally. The black and sponge-like product was filtered and washed with distilled water and ethanol, and then dried in vacuum at 60 °C.
Results and discussion
The products are characterized by XRD on a Philips X’Pert PROSUPER X-ray powder diffractometer using Cu-Kα radiation (λ = 1.541874 Å). Fig. 1A shows the XRD pattern of raw product before washing in acid solution. All the peaks can be indexed as iron sulfide (JCPDS Card File, No. 42-1340). The iron sulfide can be removed by acid solution, and amorphous carbon nanotubes obtain, as confirmed by the XRD pattern shown in Fig. 1B.
The morphologies and structure of the as-prepared product were examined by
Conclusion
In summary, long amorphous carbon nanotubes were synthesized by the solvothermal treatment, in which ferrocene and sulfur powder were the reactants and benzene served as solution. We believe that iron sulfide and cyclopentadienyl groups served as the catalyst and carbon source for the formation of amorphous CNTs. HRTEM and EDX experiments reveal that carbon nanotubes have an amorphous wall structure, which is different from those graphite cylindrical structures of carbon nanotubes reported
Acknowledgements
Financial support from the National Natural Science Funds and the 973 Projects of China [2005CB623601] is gratefully acknowledged.
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