[ 2011.07.14 ] hydrogen storage inside graphene-oxide frameworks (Yue Chan and James M. Hill)

Hydrogen molecules can be stored inside graphene-oxide frameworks, which comprise two parallel graphenes separated by the benzenediboronic acid pillars. We calculate the hydrogen uptake for graphene-oxide frameworks using the continuous approximation and an equation of state for both the bulk and adsorption gas phases. We determine the hydrogen uptake for the four graphene-oxide frameworks, i.e. GOF-120, GOF-66, GOF-28 and GOF-6, and we obtain 1.68, 2, 6.33 and 0 wt% at 77 K and 1 bar, respectively. The high hydrogen uptake value obtained for GOF-28 could be explained by the fact that the ligands between graphene sheets not only provide mechanical support and porous spaces for the molecular structure but also induce the higher binding energy to enhance the hydrogen storage inside graphene-oxide frameworks, and this effect diminishes as the ligand density decreases. In the absence of conflicting data, the present work indicates GOF-28 as a likely contender for practical hydrogen storage.

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[ 2011.03.25 ] Single-file transport of water through carbon nanotube membranes (Yue Chan and James M. Hill)

Carbon nanotubes embedded inside polymer membranes are shown to execute rapid water transport. In particular, for nanotubes with ultra-small radii, most heavy ions are repelled from nanotubes due to the energy barriers existing at the nanotube entremi bies, and allow only water molecules. Such results can be used to facilitate efficient polymer membranes for seawater desalination purposes under the reverse osmosis operating mode. Water flow inside such ultra-small nanotubes reveals a peculiar single-file transport driven entirely by molecular vibrations, which is different from macroscopic fluidic flow for which the Navier-Stokes equations are applicable. In this research article, we carefully adopt both the discrete and continuous approaches to model the molecular interactions between water molecules, and between water molecules and the nanotube. Classical phonon theory is then used to capture the molecular vibrations between molecules resulting in coupled ordinary differential equations, which can be solved analytically using Laplace transforms. Deterministic and stochastic pressures can be easily incorporated into the theoretical framework. However, in this case only numerically solutions can be sought, which might be exploited to open up a precise engineering approach for using such nanotube membranes in practical applications.

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[ 2011.02.18 ] Memory device in nanoscale (Yue Chan, Richard K. F. Lee and James M. Hill)

"I don’t believe that it will be cheaper to build transistors from another material other than silicon, but carbon nanotubes can be used to produce smaller and faster components. This will also result in computers that consume less energy" says Johannes Svensson. To this end, we investigate the idea of using a hybrid carbon nanostructure which comprises three single –open carbon nanotubes and a metallofullerene. An external electric field is used to initiate the metallofullerene to overcome the energy barrier generated by the central nanotube to pass from one nanotube to the other representing a bit information. The key issues in this study are that the radii of nanotubes and metallofullerene are purposely chosen so that the metallofullerene can not enter the central nanotube spontaneously, and the minimal energy is required for the metallofullerene to overcoming the energy barrier. The volatility of the memory device is therefore achieved and controlled to meet different electronic purposes, which is not previously investigated.

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[ 2010.05.14 ] Reveiw of nanotubes geometry (Richard K. F. Lee, Barry J. Cox and James M. Hill)

It is clear from the various structures seen at the nanoscale such as the cylindrical shapes of nanotubes or the spherical and spheroidal shapes of fullerenes, that the complex atomic interactions often lead to symmetric configurations. In satisfying a minimum energy constraint, the system often (although not always) adopts a symmetric structure which shares the energetic costs of bending and stretching of the covalent bonds equally to all components in the structure. By assuming a symmetric structure at the outset, it is possible to reduce fundamentally complex problems of molecular structure to problems with are more mathematically tractable, from which we may derive results which may be confirmed by experiment and molecular dynamics simulation but can also be used to predict ideal systems and novel structures in certain extreme cases.

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