Zeolites belong to a most prominent class of nanoporous materials which have been considered as potential sorbents for hydrogen storage. The adsorption of hydrogen molecules on MFI, MOR and LTA zeolites, which encompass a range of different pore structure and chemical composition, has been simulated employing Grand Canonical Monte Carlo (GCMC) method. We compare their capacities of hydrogen storage at different temperatures and pressures. The results show that the adsorbed amounts is in order of LTA>MOR>MFI at the same condition. The effects of pore structure of zeolites, temperature and pressure on the hydrogen adsorption has been examined. The results clearly show that: (1) the temperature effect on the adsorption decreases with decreasing in the number of hydrogen molecules adsorbed. (2) A large volume of micropores and a suitable diameter near to the kinetic diameter of a hydrogen molecule are important for improving the hydrogen-storage capacity of zeolites. Based on this, we can conclude that the LTA zeolite with a large pore volume and a suitable channel diameter exhibits a most efficient hydrogen storage capacity than MOR and MFI zeolites.
Using first-principles density-functional theory investigate (5, 5) capped single-walled carbon nanotubes adsorbed at one end by hydrogen molecule with and without an applied electric field. It is found that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions. The induced dipole moments is the direction of the applied electric field,and the LUMO-HOMO energy gaps decrease. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of hydrogen molecules, and are consistent with the experimental results.
Carbon nanotubes(CNTs) films were fabricated by microwave plasma chemical vapor deposition (MPCVD) on stainless steel substrates. In order to study the reason that its emission current weakens, the CNTs films were treated by hydrogen plasma. The research discovered that the hydrogen plasma treatment to the carbon nanotubes films reduced the surface work function of the film and its filed emission current, this mainly due to the etching of hydrogen plasma to sp2 carbon on the surface, it leads emission area to decrease.
Grand Canonical Monte Carlo (GCMC) method is employed to simulate the adsorption of methane in several nanoporous zeolites. Adsorption isotherms over the temperature 177-398K and the pressure 0-12MPa are simulated. And their adsorption capacities of methane in these zeolites at different temperatures and pressures are also compared. The results show that: (1) the methane uptake is in the order of LTA>MOR>MFI at the same condition. The isosteric heat can support this conclusion: the value of isosteric heat in LTA is the largest, intermediate in MOR and the least in MFI. (2) The effects of the pore volume, channel size and the energetic interactions between zeolite and methane on adsorption amounts are considered. A large pore volume and a suitable channel size near to the kinetic diameter of a methane molecule are very important for improving the storage capacity of zeolites. Based on this, we conclude that LTA zeolite with a large pore volume and a suitable channel diameter exhibit a most efficient methane storage capacity than MOR and MFI zeolites.
The field-emission properties of capped(5, 5) single-walled carbon nanotubes with hydrogen adsorbed on the tip with and without an applied electric field have been investigated using first-principles density-functional theory. It is found that the structure of carbon nanotubes with hydrogen molecules is stable under field-emission conditions. The local density of states at the Fermi level increases with the adsorption of hydrogen molecules. These results elucidate that the field-emission properties of carbon nanotubes can be enhanced by the adsorption of hydrogen molecules, and are consistent with the experimental results.
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