Determination of the space between closed multiwalled carbon nanotubes by GCMC simulation of nitrogen adsorption

The first atomistic modelling-aided reproduction of morphologically defective single walled carbon nanohorns

A new modelling-aided approach for the atomistic model of single walled carbon nanohorn (SWNH) creation is presented, based on experimental evidence, on realistic potential of carbon-carbon interactions and on molecular simulations. A new model of SWNHs is next used to predict Ar adsorption properties and to check the molecular fundamentals of the adsorption mechanism. The influence of the apex angle value, nanohorn diameter and nanohorn length on the shapes of isotherms, enthalpy, high resolution α(s)-plots and adsorption potential distribution curves is checked. Finally the comparison with new experimental Ar adsorption results is shown and the conclusions on the porosity of real SWNH aggregates are given.

Adsorption equilibrium of sulfur hexafluoride on multi-walled carbon nanotubes

The adsorption of sulfur hexafluoride (SF(6)) on multi-walled carbon nanotubes (MWNTs) was investigated. The properties of MWNTs were characterized and the adsorption capacities of SF(6) on MWNTs at different concentrations and temperatures were collected. H(2)SO(4)/H(2)O(2) oxidation or KOH activation of MWNTs has effectively introduced the surface oxides and modified the microstructure without destruction of their graphitic crystalline structure. The MWNTs, especially the modified samples, are expected to be promising adsorbents for SF(6) removals from air. The saturated capacities of SF(6) with a concentration of 518 ppmv on the MWNTs ranged from 278 to 497 mg/g at 25 degrees C. The Toth equation has been reported to fit the adsorption data better than the Freundlich or Langmuir equation. The pi-pi dispersion interaction followed by the multi-layer adsorption and the electron donor-acceptor interaction were proposed to be the major adsorption mechanisms, depending on the adsorption temperature. The isosteric heat of adsorption, ranging from 51 to 124 kJ/mol with a loading of 30-300 mg/g, decreased with increasing SF(6) loading, reflecting the energetic heterogeneity of the MWNTs. These results suggest that the adsorption of SF(6) on MWNTs could be associated with binding to defect sites.

Canonical Monte Carlo simulation of adsorption of O2 and N2 mixture on single walled carbon nanotube at different temperatures and pressures

Adsorption of pure and mixtures of O(2) and N(2) on isolated single-walled carbon nanotube (SWCNT) have been investigated at the subcritical (77 K) and different supercritical (273, 293, and 313 K) temperatures for the pressure range between 1 and 31 MPa using (N,V,T) Monte Carlo simulation. Both O(2) and N(2) gravimetric storage capacity exhibit similar behaviors, gas adsorption is higher on outer surface of tube, compared to the inner surface. Results are consistent with the experimental adsorption measurements. All adsorption isotherms for pure and mixture of O(2) and N(2) are characterized by type I (Langmuir shape), indicating enhanced solid-fluid interactions. Comparative studies reveal that, under identical conditions, O(2) adsorption is higher than N(2) adsorption, due to the adsorbate structure. Excess amount of O(2) and N(2) adsorption reach to a maximum at each temperature and specified pressure which can be suggested an optimum pressure for O(2) and N(2) storage. In addition, adsorptions of O(2) and N(2) mixtures have been investigated in two different compositions: (i) an equimolar gas mixture and (ii) air composition. Also, selectivity of nanotube to adsorption of O(2) and N(2) gases has been calculated for air composition at ambient condition.

Can carbon surface oxidation shift the pore size distribution curve calculated from Ar, N(2) and CO(2) adsorption isotherms? Simulation results for a realistic carbon model

Using the virtual porous carbon model proposed by Harris et al, we study the effect of carbon surface oxidation on the pore size distribution (PSD) curve determined from simulated Ar, N(2) and CO(2) isotherms. It is assumed that surface oxidation is not destructive for the carbon skeleton, and that all pores are accessible for studied molecules (i.e., only the effect of the change of surface chemical composition is studied). The results obtained show two important things, i.e., oxidation of the carbon surface very slightly changes the absolute porosity (calculated from the geometric method of Bhattacharya and Gubbins (BG)); however, PSD curves calculated from simulated isotherms are to a greater or lesser extent affected by the presence of surface oxides. The most reliable results are obtained from Ar adsorption data. Not only is adsorption of this adsorbate practically independent from the presence of surface oxides, but, more importantly, for this molecule one can apply the slit-like model of pores as the first approach to recover the average pore diameter of a real carbon structure. For nitrogen, the effect of carbon surface chemical composition is observed due to the quadrupole moment of this molecule, and this effect shifts the PSD curves compared to Ar. The largest differences are seen for CO(2), and it is clearly demonstrated that the PSD curves obtained from adsorption isotherms of this molecule contain artificial peaks and the average pore diameter is strongly influenced by the presence of electrostatic adsorbate-adsorbate as well as adsorbate-adsorbent interactions.

Ar, CCl(4) and C(6)H(6) adsorption outside and inside of the bundles of multi-walled carbon nanotubes-simulation study

This is the first paper reporting the results of systematic study of the adsorption of Ar, C(6)H(6) and CCl(4) on the bundles of closed and opened multi-walled carbon nanotubes. Using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, we also study the effect of the introducing defects in the external and internal walls of osculating and separated nanotubes on Ar diffusion and on adsorption of all three adsorbates. The Ar diffusion coefficients obtained are very sensitive to the presence of defects. Simulated isotherms are discussed to show the relation between the shapes of the high resolution alpha(s)-plots and the mechanisms of adsorption. From obtained data, as well as from geometric considerations, from the VEGA ZZ package, and from simulations (ASA), the values of surface areas of all nanotubes are calculated and compared with those obtained using the most popular adsorption methods (BET, alpha(s) and the A,B,C-points). We show that the adsorption value for the C-point of the isotherm should be taken for the calculation of the specific surface area of carbon nanotubes to obtain a value which approaches the absolute geometric surface area. A fully packed monolayer is not created at the A-, B- or C-points of the isotherm; however, the number of molecules adsorbed at the latter point is closest to the number of molecules in the monolayer as calculated via the ASA method, the VEGA ZZ package or from geometric considerations.