Inorganic nanotubes and fullerene-like nanoparticles
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We have proposed in 1992 that nanoparticles of layered compounds will be unstable against folding and close into fullerene-like structures and nanotubes (IF). Nanotubes and fullerene-like structures were prepared from numerous compounds with layered and recently also non-layered structure by various groups. Much progress has been achieved in the synthesis of inorganic nanotubes and fullerene-like nanoparticles of WS2 and MoS2 and many other metal dichalcogenides over the last few years. Substantial progress has been accomplished in the use of such nanoparticles for tribological applications and lately for impact resilient nanocomposites. These tests indicated that IF-MoS2 and IF-WS2 are heading for large scale applications in the automotive, machining, aerospace, electronics, defense, medical and numerous other kinds of industries. A few products based on these nanoparticles have been recently commercialized by “ApNano Materials, Inc”. Novel applications of inorganic nanotubes and fullerene-like nanoparticles in the fields of catalysis; microelectronics; Li rechargeable batteries; medical and opto-electronics will be discussed.
I. INTRODUCTION
The discovery of C60-the fullerene molecule with the highest symmetry and the most stable one of this series1 in 1985 and the later discovery of carbon nanotubes2 has established a new paradigm in chemistry. A new field of nanomaterials with polyhedral (hollow) nanostructures was thus born. Chemical bonding in general does not favor hollow spaces, which explains the initial reluctance to accept the notion of fullerenes. This reluctance was diffused once large amounts of C60 were purified and its nuclear magnetic resonance (NMR) spectrum proved its structure unequivocally in 1990.3 Graphite is a quasitwo-dimensional (2D) (layered) compound consisting of molecular sheets arranged in a honeycomb lattice, i.e., (3-fold) sp2 bonded carbon atoms. These graphene sheets are stacked together by weak van der Waals forces. Graphite is the most stable polymorph of carbon in ambient conditions, but it transforms under a pressure of about 1.7 GPa to diamond, which is a carbon lattice made
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Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http:// www.mrs.org/jmr_policy This review article is based on the author’s 2005 MRS Medal talk titled “Inorganic Nanotubes and Inorganic Fullerene-Like Materials: From Concept to Applications,” presented at the 2005 MRS Fall Meeting on November 30, 2005. DOI: 10.1557/JMR.2006.0354 2726
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J. Mater. Res., Vol. 21, No. 11, Nov 2006 Downloaded: 21 Aug 2014
of sp3 (4-fold) bonded atoms. In the nano-size regime, however, the flat graphitic sheets (graphenes) become unstable due to the abundance of 2-fold bonded carbon atoms on the rim of the molecular sheet. This instability induces folding of the molecular graphene s
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