Hydrogen physisorption and selectivity in single-walled silicon carbon nanotubes: a grand canonical Monte-Carlo study

We report grand canonical Monte-Carlo simulations of pure hydrogen physisorption and its binary mixtures with nitrogen and methane H/N2H2/CH4 in single-walled silicon carbon nanotubes (SWSiCNTs). We investigate the effect of temperature, pressure, tube diameter and the influence of the presence of the second molecule on the adsorption of hydrogen. Some obtained results have compared with that of boron nitride and carbon nanotubes and it shows that the SWSiCNT has more hydrogen adsorbable than single-walled boron nitride (SWBNNT) and carbon nanotube (SWCNT) in same chirality of nanotube and same thermodynamic conditions. Furthermore, the influence of tube length on hydrogen adsorption capacity has been illustrated in various SWSiCNT, SWBNNT and SWCNT and the calculations show that the hydrogen adsorption holds the line when the tube length increases. In addition, pure hydrogen adsorption is investigated in rhombic and square SWSiCNT arrays, while the results of this investigation illustrate that rhombic and square SWSiCNT arrays have gravimetric hydrogen capacities between rhombic and square silicon and carbon nanotube arrays, in same thermodynamics conditions and same tube diameters. The simulation data of pure hydrogen fit to Langmuir, Freundlich and Langmuir-Freundlich equations and the Langmuir-Freundlich equation has the best behavior fitting to hydrogen adsorption data; it emphasizes that the multi-layer pure hydrogen adsorptivity occurs more prominently in SWSiCNTs. Also, the excess and delivery isotherms of hydrogen were calculated for various SWSiCNTs, SWBNNTs and SWCNTs. Furthermore, the adsorption selectivity in different mole fractions of hydrogen/methane and hydrogen/nitrogen mixtures in SWSiCNTs has investigated at 77 and 298 K on (8,8) and (15,15) SWSiCNTs, and results show that selectivity-based adsorption decreases at 298 K in both mixtures while increasing pressure and temperature can increase selectivities and the selectivity is not related to the diameter of nanotubes.