Andrei
N. Khlobystov
ab and
Andreas
Hirsch
c
aSchool of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
bNottingham Nanotechnology & Nanoscience Centre, University of Nottingham, NG7 2RD, UK
cDepartment of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich-Alexander-Universität Erlangen-Nürnberg Henkestraße 42, D-91054 Erlangen, Germany
Transition metals in form of nanoparticles are the catalysts of the nanotube formation process, while transition metal surfaces are essential for the formation of graphene. In both cases metal–carbon interactions are controlling the structures and thus the electronic properties of the carbon nanostructures being formed. Similarly, in order to harness their functional properties the inorganic nanocarbons must be connected or interfaced with the macro world. For instance, field effect transistors exploiting the charge mobility and electronic band gap of carbon nanotubes rely on the interface between the carbon atoms of the nanotube and the metal nanoelectrodes connecting the device. The type and quality of the carbon nanotube–metal bonding crucially determine the functional properties of such transistors, sometimes dominating over the intrinsic properties of the nanotube itself.
Individual metal atoms, cations, clusters or even nanoparticles coupled to carbon nanostructures introduce new properties either through covalent metal–carbon bonds or coordination bonds via a ligand group, charge transfer, electrostatic or van der Waals interactions. Many of these properties are not present in all-carbon materials. For example, fullerenes and nanotubes are able to bind metals either directly through M–C bonds or via functional groups containing nitrogen or oxygen donor atoms, or can entrap metal atoms in the internal cavities of the fullerene cages, as elegantly exemplified with the endohedral metallofullerenes. Metals can bring magnetic, optical and redox activities into the carbon nanostructures, thus broadening the spectrum of their practical applications. Endohedral metallofullerenes, for example, can offer fascinating magnetic and photoluminescent properties, not available in metal-free fullerenes, which can be exploited in magnetic resonance imaging and quantum information processing respectively. Considering that many transition metals exhibit excellent catalytic properties, metal nanoparticles anchored on carbon nanotube surfaces are utilised as new heterogeneous catalysts, whereas metal clusters embedded within nanotube cavities give rise to nano-reactors where chemical processes can be controlled with exquisite precision yielding new molecular products, inaccessible by other means.
All the exciting aspects of carbon nanostructures mentioned above ultimately rely on the fundamental principles of inorganic chemistry which describe the mechanisms of bonding with metals. While the chemistry of carbon nanostructures is still hindered by many practical challenges, including their structural complexity, polydispersity and lack of purity, understanding of interactions and bonding with metals is already making big steps forward and opening up new horizons for these fascinating materials.
This journal is © The Royal Society of Chemistry 2014 |