Adsorption sensitivity of Pd-doped SWCNTs to small gas molecules

The adsorption of three types of gas molecules (SO₂, CH ₃OH, and CH₄) on to Pd-doped (5,5) single-walled carbon nanotubes (Pd-SWCNTs) has been investigated within density functional theory. The Pd-SWCNTs can be utilized as good sensors for the three types of small molecules due to strong binding energy and large electron charge transfer between the Pd-SWCNTs and these small molecules. The adsorption features of the three types of molecules are all different from one another. The adsorption of SO₂ and CH₃OH on to the Pd-SWCNTs is attributed to chemical adsorption and physical adsorption, respectively, while the interaction between CH₄ and the Pd-SWCNT is electrostatic interaction and a bound complex of (Pd-SWCNT)-(CH₄)⁺ forms due to charge transfer between them. Density of states and molecular orbital of the Pd-SWCNT and M-Pd-SWCNT (M = SO₂, CH₃OH, and CH₄) were analyzed to interpret the changes in electronic structure, conductivity, and binding energy upon adsorption.