Theoretical investigation of pristine and functionalized AlN and SiC single walled nanotubes as an adsorption candidate for methane

Abstract

In order to search for novel nanomaterial to adsorb methane (CH4) molecule, the adsorption of CH4 on the hydrogenated edges of armchair (4,4) aluminum nitride (AlN) and silicon carbide (SiC) nanotubes has been systemically investigated using two different density functional theory (DFT) methods. Two MPW1PW91 and PBEPBE functional are employed in all calculations for the considered structures, adsorption energy, and NBO analysis. The CH4 molecule physisorbed on Tn (n=1 and 2) sites on the surface of pure AlN and SiC nanotubes with an adsorption energy of about −4.42 and −1.43kJ/mol respectively. The properties of CH4 molecule adsorbed on Ni-doped AlN and SiC nanotubes are also investigated. The adsorption energy rises to about −60.36 and −39.26kJ/mol for AlNNiCH4 and SiCNiCH4 respectively, when the CH4 adsorbed to Ni-doped nanotubes. Compared with the weak adsorption on pure AlN and SiC nanotubes, CH4 molecule tends to be strongly physisorbed to the Ni-doped AlN and SiC nanotubes with appreciable adsorption energy. The increase in adsorption energy is due to the charge transfer from Ni-doped AlN and SiC nanotubes to the CH4 molecule. A considerable amount of charge transfer during the adsorption process on Ni-doped AlN and SiC nanotubes may account for the changes of the electronic properties. With the adsorption of CH4 molecule on functionalized nanotubes, the band gap of AlNNiCH4 and SiCNiCH4 systems are increased, thus leading to decreased reactivity of the systems, the stability of the systems increased. These observations show that functionalized AlN and SiC nanotubes are highly sensitive toward CH4 molecule. Moreover, the present results may be useful for the design of AlN and SiC nanotubes based nanomaterials candidates such as adsorbent and storage.