Grand canonical Monte Carlo molecular simulations have been carried out for adsorption of nitrogen at 77 K on square arrays of open and closed single-wall carbon nanotubes with diameters of 6-30 Å and nanotube separations of 4-30 Å. Exohedral spaces for arrays of closed nanotubes with small tube separations are microporous. For large separations, two-stage adsorption occurs, corresponding to monolayer formation followed by a condensation step. Filling of the exohedral space is dominated by geometrical factors that allow the calculation of adsorbate molecular packing factors, which are close to that for liquid nitrogen. The amounts adsorbed in arrays of open nanotubes are higher than for closed tube arrays, as expected. The highest increase is for arrays with small tube separations and large tube diameters, where endohedral adsorption dominates; for wider tube separations the increase in amount adsorbed is less because exohedral adsorption becomes important. Arrays of single-wall carbon nanotubes have the potential to develop very high adsorptive capacities, to which the interstitial spaces between the nanotubes make significant contributions. The adsorptive capacity can be optimized when exohedral adsorption dominates, that is, with arrays of narrow single-wall nanotubes with wide spacings between them.

CT angiography is an accurate, cost-effective tool in the diagnosis of acute GI bleeding and can show the precise location of bleeding, thereby directing further management.

Grand canonical ensemble Monte Carlo (GCEMC) molecular simulations of hydrogen storage at 298 and 77 K in triangular arrays of single wall carbon nanotubes (SWCNT) and in slit pores (modeling activated carbons) were performed. At 298 K the US DOE target gravimetric hydrogen storage capacity (6.5 wt %) is reached at 160 bar for optimally configured arrays of open SWCNT of wide diameter, but the equivalent volumetric capacity is ∼40% of the DOE target [695 (STP) v/v]. For slit pores at 298 K the optimal volumetric capacity is ∼20% of the target. Simulations for 77 K and 70 bar indicate that triangular arrays of open and closed SWCNT of various diameters in a wide range of configurations exceed the DOE gravimetric target. A capacity of 33 wt % is found for arrays of narrow, open, or closed SWCNT that are widely spaced.Here, adsorption occurs entirely in the interstitial space between the nanotubes. Volumetric capacities close to the DOE target are found for arrays of narrow, open or closed SWCNT with a range of interstitial spacings. The maximum volumetric capacities for simulations with slit pores at 77 K and 70 bar are ∼73% of the DOE target for a range of pore widths. Capacities from simulations for nanotubes and slit pores at 298 and 77 K are in reasonable agreement with experimentally measured capacities. It is concluded that the potential of carbon nanotubes for storage of hydrogen is superior to that of activated carbons.

No abstract