First-principles study of the effect of oxygen vacancy and iridium doping on formaldehyde adsorption on the...

Formaldehyde adsorption on intrinsic La₂O₃ surface, four-fold coordinated oxygen vacancy (VO_4c), six-fold coordinated oxygen vacancy (VO_6c), 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 VO_6c 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 VO_4c and VO_6c 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.