Chemical vapor deposition (CVD) is the most popular method of producing carbon nanotubes (CNTs). However, there are two weak points of the existing CVD-CNT technique. No.1: it is a natural resource-dependent technique. No.2: the CNT yield is not more than 20–30% of the raw material used. That is, 70-80% of the feedstock goes waste and adds to the environmental load. According to the principles of "Green Chemistry", the feedstock of any industrial process must be renewable, rather than depleting a natural resource. Moreover, the waste product must be minimized. We have succeeded in growing gram quantities of CNTs from camphor (C10H16O, a tree product) by a technique greatly complying with these principles.
This well-valued material of biotechnology was successfully brought to nanotechnology with the first report of "CNTs from camphor" [1] in 2001. Since then, we remained involved with this environment-friendly source of CNTs and established the conditions for growing single-wall & multiwall nanotubes (SWNTs, MWNTs) [2] and vertically aligned MWNTs [3] by a simple and inexpensive CVD technique. Recently, using a zeolite powder as the catalyst support, we grew MWNTs at a temperature as low as 550°C, whereas SWNTs could be grown at higher temperature [4]. Using the same materials and method, we have now optimized the relative concentrations of camphor, catalyst and support material in the reactor to achieve a gigantic growth of MWNTs, which we call gigas growth. CVD of 12g camphor at 650°C for 30min yields ~6g MWNTs of diameter ~10nm with an as-grown purity of 88%. That is, camphor-to-CNT production efficiency is 50%. This is the highest efficiency ever achieved from any material by any method. It may be debatable whether the key of this gigas growth lies in the source material: camphor, or in the optimization of the control parameters; nevertheless, there is no doubt that this is a breakthrough in the utmost utilization of a carbon source for CNT growth.
[1] M. Kumar, X. Zhao, Y. Ando, Internat. Symp. Nanocarbons, Japan (Nov. 14-16, 2001) Abstract pp244-245.
[2] M. Kumar, Y. Ando, Diamond Related Materials 12 (2003) 1845.
[3] M. Kumar, Y. Ando, Chem. Phys. Lett. 374 (2003) 521.
[4] M. Kumar, Y. Ando, Carbon 43 (2005) 533.
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