Adsorption of Cr and Pd transition metal atoms on the pristine Zinc oxide nanotube: a DFT Study

The adsorption properties of a single transition metal atom; Cr and Pd on the top of the ZnONT is studied with hybrid density functional B3LYP as implemented in the GAUSSIAN 09 program. It is known that doping is an important and effective method for improving the sensing properties of metal oxide semiconductors [1]. The split-valence basis set 6-31G* is applied to O and H atoms while the effective-core-potential LANL2DZ basis set is used for transition metal atoms. The intermolecular distances between oxygen atom of the ZnONT and the transition metal atoms are 1.835 and 2.105 Å with the binding energies of -7.413 eV and -5.730 eV for Cr and Pd atoms, respectively. Based on the obtained results, it is found that the binding energy of Cr adsorption is higher than that for Pd atom; furthermore, Cr atom could be stably adsorbed on the similar site with respect to Pd atom. Moreover, the natural bond orbital (NBO) analysis has been employed to evaluate the direction of donor–acceptor interactions. The difference between the highest occupied molecular orbital (EHOMO) and the lowest unoccupied molecular orbital (ELUMO) for transition metal atoms and ZnONT are calculated and the value of |EHOMO (ZnONT)-ELUMO (Cr)|, |EHOMO (ZnONT)-ELUMO (Pd)|, |EHOMO (Cr)-ELUMO (ZnONT)| and |EHOMO (Pd)-ELUMO (ZnONT)| energies are obtained 0.895, 1.937, 1.599 and 0.669 eV, respectively. The obtained results reveal that the electron density transfer can be performed between the HOMO orbital of Zinc oxide nanotube and the LUMO orbital of Cr transition metal for the adsorption Cr atom on the pristine nanotube and there is a reverse result for the adsorption of Pd atom on the nanotube surface.