Investigation of silicon model nanotubes as potential candidate nanomaterials for efficient hydrogen storage: A combined ab initio/Grand canonical Monte Carlo simulation study

Grand canonical Monte Carlo (GCMC) simulations combined with ab initio QM calculations were employed to study the adsorption capacity of H2 in single-walled silicon nanotubes (SWSiNTs) of a hypothetical armchair structural model. The interaction energy of H2 with a graphite-like sheet from the surface of a single SiNT obtained from the QM calculations was fitted to an accurate potential function used to simulate the system. This theoretical approach is also used in SWCNTs of similar characteristics and at the same thermodynamic states. The GCMC simulation of NT bundles with H2 showed enhancement of H2 adsorptivity of SiNTs, as compared with CNTs. Concretely, the (14, 14) SWSiNTs present remarkable percentage improvement of 100, 70, 44, and 25% in the gravimetric (weight percent) adsorption of H2 at 293 K and 0.1, 1.0, 5.0, and 10.0 MPa, respectively, as compared with isodiameter (22, 22) CNTs. This is attributed to the stronger attractive interaction of H2 with SiNTs as compared to CNTs, found from the first principle calculations. © 2008 American Chemical Society

SiC nnotubes: A novel material for hydrogen storage

A multiscale theoretical approach is used for the investigation of hydrogen storage in silicon-carbon nanotubes (SiCNTs). First, ab initio calculations at the density functional level of theory (DFT) showed an Increase of 20% in the binding energy of H2 in SiCNTs compared with pure carbon nanotubes (CNTs). This is explained by the alternative charges that exist in the SiCNT walls. Second, classical Monte Carlo simulation of nanotube bundles showed an even larger increase of the storage capacity in SiCNTs, especially in low temperature and high-pressure conditions. Our results verify in both theoretical levels that SiCNTs seem to be more suitable materials for hydrogen storage than pure CNTs. © 2006 American Chemical Society

Effect of curvature and chirality for hydrogen storage in single-walled carbon nanotubes: A Combined ab initio and Monte Carlo investigation

Combined ab initio and grand canonical Monte Carlo simulations have been performed to investigate the dependence of hydrogen storage in single-walled carbon nanotubes (SWCNTs) on both tube curvature and chirality. The ab initio calculations at the density functional level of theory can provide useful information about the nature of hydrogen adsorption in SWCNT selected sites and the binding under different curvatures and chiralities of the tube walls. Further to this, the grand canonical Monte Carlo atomistic simulation technique can model large-scale nanotube systems with different curvature and chiralities and reproduce their storage capacity by calculating the weight percentage of the adsorbed material (gravimetric density) under thermodynamic conditions of interest. The author's results have shown that with both computational techniques, the nanotube's curvature plays an important role in the storage process while the chirality of the tube plays none. © 2007 American Institute of Physics

Adsorption of N2, CH4, CO and CO2 gases in single walled carbon nanotubes: A combined experimental and Monte Carlo molecular simulation study

In this study, the adsorption capacity of single-wall carbon nanotubes (SWCNTs) bundles with regard to the pure CH4, N2, CO and CO2 gases at 298 K and pressure range from 0.01 up to 2.0 MPa has been investigated experimentally and computationally. Experimental work refers to gravimetric surface excess adsorption measurements of each gas studied in this nanomaterial. Commercial samples of pristine SWCNTs, systematically prepared and characterized at first, were used for the evaluation of their adsorption capacity. A Langmuir type equation was adopted to estimate the total adsorption isotherm based on the experimental surface excess adsorption data for each system studied. Computational work refers to Monte Carlo (MC) simulation of each adsorbed gas on a SWCNTs model of the type (9, 9) in the grand canonical (GC) ensemble at the same conditions with experiment using Scienomics' MAPS platform software simulation packages such as Towhee. The GCMC simulation technique was employed to obtain the uptake wt% of each adsorbed gas by considering a SWCNTs model of arrays with parallel tubes exhibiting open-ended cylindrical structures as in experiment. Both experimental and simulation adsorption data concerning these gases within the examined carbon material are presented and discussed in terms of the adsorbate fluid molecular characteristics and corresponding interactions among adsorbate species and adsorbent material. The adsorption isotherms obtained exhibited type I (Langmuir) behavior, providing enhanced gas-substrate interactions. We found that both the experimental as well as the simulated adsorption uptake of the examined SWCNTs at these conditions with regard to the aforementioned fluids and in comparison with adsorbate H2 on the same material increase similarly and in the following order: H2 ≪ N2 ≈ CH4 < CO ≪ CO2. Furthermore, for each adsorbate fluid the calculations exhibit somewhat greater gas uptake with pressure compared to the corresponding experiment. The difference in the absolute uptake values between experiment and simulation has been discussed and ascribed to the following implicit factors: (i) to the employed model calculations, (ii) to the remained carbonaceous impurities in the sample, and (iii) to a proportion of close ended tubes, contained in the experimental sample even after preparation. © 2010 Elsevier B.V. All rights reserved