Comparative Study on Gas Adsorption in Defected Carbon and Boron Nitride Nanotube

Investigations on gas adsorption in nanostructures are important for potential applications such as fuel cell, gas sensor, hydrogen storage etc. Of all nanomaterials, carbon (CNTs) and boron nitride nanotubes (BNNTs) are analyzed widely, since they are porous, having large surface area and high thermal stability. It is interesting to note that while CNTs exhibit both semiconducting and metallic behaviour, BNNTs show only semiconducting nature. Factors like topological defects, doping and functionalization are observed to enhance the effect of adsorption in these nanotubes. We have considered physisorption of H-2, N-2 and O-2 in armchair (5,5) nanotubes of both carbon and boron nitride and estimated the binding energies through simulation. To study the role of defects, we have introduced a combination of an octagon and a pair of pentagon (5-8-5) called divacancy defect in the hexagonal structure and calculated adsorption binding energy (E-ads) of gas molecules at the defected site. We could observe 59.72% increment in E-ads in defected CNTs and 122.7% enhancement in defected BNNTs compared to defect-free tubes for hydrogen. With nitrogen molecule as adsorbate, we found 58.49% and 84.13% increase in E-ads in defected CNTs and BNNTs respectively. The results lead to the conclusion that defects plays a vital role on physisorption in both carbon and boron nitride nanotubes.