Influence of Carbon Curvature on Molecular Adsorptions in Carbon-Based Materials: A Force Field Approach

Abstract

A general force field methodology is developed for description of molecular interactions in carbon-based materials. The method makes use of existing parameters of potential functions developed for sp(2) and sp(3) carbons and allows accurate representation of molecular forces in curved carbon environment. The potential parameters are explicitly curvature and site dependent. The proposed force field approach was used in molecular dynamics (MD) simulations for hydrogen adsorption in single-walled carbon nanotubes (SWNTs). The results reveal significant nanotube deformations and the calculated energies of adsorption are comparable to the reported experimental heat of adsorption for H2 in SWNTs.

Adsorption and separation of linear and branched alkanes on carbon nanotube bundles from configurational-bias Monte Carlo simulation

“…In fact, the curvature-induced charge redistribution and polarization in curved carbon nanotubes have been recognized, 107 and the force field parameters of the gascarbon interaction potential in carbon nanotubes have been found to be curvature dependent. 108 To account for the influence of surface curvature, an accurate interaction potential obtained, for example, from quantum chemical calculations should be used. However, the interaction governing adsorption behavior here is mainly dispersive van der Waals forces, which are difficult to calculate accurately from quantum chemistry unless with sufficiently high level theory, very large basis set, and a great deal of CPU time is used.…”

Description of Adsorbed Phases on Carbon Surfaces: A Comparative Study of Several Graphene Models

“…To reach this it is necessary to have with a well description of the molecular bonds, because the approximations would neglect the effect of the hybridization differences of the carbon atomic orbitals, induced by the curvature of the surface. To solve this problem force fields were derived (Kostov et al, 2002) where the curvature effect was taking into account, however, the parameters calculated for these fields overestimate the interaction of the nanotubes of smaller radius, because they are considered as a model molecule with free radicals. In order to describe the potential energy that suffer a molecule near the surface of different nanotubes, theoretical calculations at DFT level were performed (Albesa et al, 2009) for hydrogen, nitrogen and methane, were the surface was mimicked by deforming a coronene molecule (see Fig 6).…”

Comment on “Theoretical evaluation of hydrogen storage capacity in pure carbon nanostructures” [J. Chem. Phys. 119, 2376 (2003)]

“…4 The adsorption is reported to occur exclusively at the interstitial sites, which is also consistent with what we have predicted. We have recently made systematic improvements to our computational method 9 and have performed extensive simulations of hydrogen adsorption in many discrete types of SWNT that we plan to publish shortly. 5 It is interesting to note that regardless of what force fields one uses, the extent of nanotube deformation in the classical MD simulations is much less than what is observed in quantum-mechanical MD studies.…”

“…We have recently suggested a simple computational procedure that combines force field parameters developed for sp 2 and sp 3 carbons to describe the nonbonding interactions, including H 2 -C and C-C, in curved carbon materials. 9 In doing so, we obtained all the force field parameters that are strongly curvature dependent. For example, the well depths for H 2 in ͑5,5͒, ͑9,9͒, and ͑5,0͒ nanotubes at the exohedral site are 4.62 kcal/mol, 3.50 kcal/mol, and 6.78 kcal/mol, respectively.…”

“…For example, the well depths for H 2 in ͑5,5͒, ͑9,9͒, and ͑5,0͒ nanotubes at the exohedral site are 4.62 kcal/mol, 3.50 kcal/mol, and 6.78 kcal/mol, respectively. 9 We subsequently performed constant-NVT molecular dynamics simulation using the derived force field for a ͑9,9͒ nanotube lattice at 0.4 wt. % H 2 loading at room temperature, giving a calculated adsorption energy of 4.50 kcal/mol.…”