Interaction between a single Pt atom and a carbon nanotube studied by density functional theory

Using density functional theory with the generalized gradient approximation, we have studied the interaction between a single Pt atom and a carbon nanotube. The bridge adsorption site on the outer wall of nanotube is favorable. The curvature affects the binding strength. Compared to the larger nanotube, Pt could bind stronger to the outer wall of a small radius nanotube. For zigzag nanotube, the most stable site on the outer wall is the bridge site with the underlying $\mathrm{C}\text{−}\mathrm{C}$ bond being parallel to the axis of the nanotube, while for the armchair nanotube it is the bridge site with the underlying $\mathrm{C}\text{−}\mathrm{C}$ bond being tilted to the axis of the nanotube. The energy in average differs by $\sim 1.5\mathrm{eV}$ for adsorbing on both sidewalls of small radius nanotube, while it decreases much for the larger nanotube. Either by penetrating the wall or by substituting one C atom on the wall, the Pt atom is found to be hard to diffuse from the outside to the inside. The studied charge density suggests the weak covalentlike bonding between Pt and C atoms.

Figure 1

(Color online) The optimized geometrical structures of the Pt adsorbed on carbon nanotubes. The small balls are for C atoms and the big balls are for Pt atoms. (a) Pt adsorbed on the inner wall of the (5,5) tube; (b) Pt adsorbed on the outer wall of the (5,5) tube; (c) Pt adsorbed on the inner wall of the (8,0) tube; and (d) Pt adsorbed on the outer wall of the (8,0) tube. For each figure, the left gives the lowest energy structure, and the right one shows its low-lying energy state.

Figure 2

(Color online) The initial and final states for Pt approaching the (10,10) tube along the paths which are perpendicular to the wall of the tube. (a) Path B, approaching toward the center of the corresponding $\mathrm{C}\text{−}\mathrm{C}$ bond; and (b) Path H, approaching toward the center of the corresponding hexagon. The big balls are for Pt atoms, and the small balls are for C atoms.

Figure 3

(Color online) The geometrical structures of saddle points which were found by the dimer method. (a) Saddle point P, Pt passing through the center of the hexagon; and (b) Saddle point S, Pt entering by substituting one C atom. The big balls are for Pt atoms, and the small balls are for C atoms.

Figure 4

(Color online) The isosurface of the charge density of $0.5\mathrm{e}∕{\mathrm{\AA }}^3$. The left one is for the Pt adsorbed on the (5,5) tube, and the right one is for the Pt adsorbed on graphene. The small balls stand for C atoms.

Figure 5

The band structures of the bare and Pt-deposited carbon nanotubes, and the projected density of states of the adhered Pt atoms. (a) For the (5,5) nanotube; and (b) for the (8,0) nanotube. For each figure, the left two panels are for the band structures, and the right one is for the projected density of states (the unit is the states per atom). The Fermi energies were shifted to zero.