Growth of nanocarbons by catalysis and their applications
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troduction It may seem strange to some readers that the idea of nanocarbons was basically nonexistent when one of us (P.T.) started work on carbon materials at the United Kingdom Atomic Energy Research Establishment, Harwell, in 1960. The materials we worked on then were macroscopic in scale, and the major funding for carbon research worldwide was from atomic-energy agencies who were interested in understanding the behavior of graphite blocks in nuclear reactors, where they were mostly used as a moderator for the highenergy neutrons produced during the fission of uranium atoms. When Thrower left Harwell in 1969 and went to work at The Pennsylvania State University, there was research on the new microcarbon, carbon fibers, conducted in his Harwell group, but it was classified as secret. The identification and systematic production of carbon nanotubes was still more than 20 years away. This does not mean that nanocarbons did not exist in those days. We simply did not have ways to separate, identify, and investigate them. R.T.K. Baker, from Harwell, for instance, was investigating fibrous carbon that sometimes formed in a graphite-moderated gas-cooled nuclear reactor, undoubtedly the result of catalytic processes.1 There is no doubt that these contained carbon nanotubes and metallic particles, but the nanotubes could not be fully identified.
In those days a “high-resolution” transmission electron microscope (TEM) could resolve only ∼1.2 nm on a good day, and it would be a few years before the atomic layers in graphite (graphene layers) were first resolved. In 1968, Heidenreich, Hess, and Ban2 used a customized TEM installation to accomplish this goal. The word “graphene” to describe a single layer of carbon atoms in graphite did not appear in the literature until 1987, although we can argue that the material has been used for centuries. When the ancient Greeks were writing with crude pencils, they had no idea they were sliding graphene sheets from graphite onto paper.
Carbon nanotubes Carbon nanotubes were reported in 1991 by Iijima, whose Nature paper3 remains one of the most cited ones in the scientific literature (>44,000 according to Google Scholar). It soon became obvious that although carbon nanotubes had a very high tensile strength, measuring their other properties was quite complex. Although a single-wall carbon nanotube (SWCNT) could be simply thought of as being formed by “rolling” a graphene sheet into a cylinder, there are many ways of doing this. As shown in Figure 1, the graphene can be rolled such that the tube axis is either parallel to or perpendicular to a carbon–carbon bond and there could also be an offset in the join, producing what is known as chirality.
Peter A. Thrower, Department of Materials Science and Engineering, The Pennsylvania State University, USA (retired); [email protected] Hui-Ming Cheng, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences; and Tsinghua-Berkeley Shenzhen Institute, Tsinghua University, China; cheng@im
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