First-principles study of the effect of oxygen vacancy and iridium doping on formaldehyde adsorption on the La2O3(001) surface.

ABSTRACT

Formaldehyde adsorption on intrinsic La2O3 surface, four-fold coordinated oxygen vacancy (VO4c), six-fold coordinated oxygen vacancy (VO6c), and iridium-doped La2O3(001) surface was studied by the first-principles method. The results show that formaldehyde adsorption on the Ir-doped La2O3(001) surface with VO6c is the strongest because of the directional movement of electrons caused by the interaction of the Ir-5d orbitals and internal oxygen vacancy, wherein the adsorption energy is 3.23 eV. This model showed a significant increase in adsorption energy, indicating that Ir doping improves the formaldehyde adsorption capacity of the La2O3(001) surface. The energy band analysis shows that iridium doping introduces impurity energy levels into the intrinsic La2O3 energy band, which enhances the interaction between the La2O3(001) surface and formaldehyde molecules. Density of state analysis indicated that the adsorption of formaldehyde molecules on the La2O3(001) surface is mainly due to the interaction between the O-2p, C-2p orbitals of formaldehyde and the Ir-5d orbital of iridium atoms. Furthermore, the existence of VO4c and VO6c defects has no effect on the position and shape of the valence and conduction bands. The effects of oxygen vacancy and iridium doping on the optical properties mainly appeared in the low-energy infrared and visible regions, making the O-2p, C-2p orbitals of formaldehyde and the Ir-5d, O-2p orbitals of the La2O3(001) surface become hybridized near the Fermi level and the electronic transition from the valence band to conduction band more likely to occur. The La2O3 material can be used as an ideal photocatalytic material for formaldehyde degradation.