First-principles study on anatase TiO2 (101) surface adsorption of NO

In this paper, the stable structure and the electronic and optical properties of nitric oxide (NO) adsorption on the anatase TiO2 (101) surface are studied using the plane-wave ultrasoft pseudopotential method, which is based on the density functional theory. NO adsorption on the surface is weak when the outermost layer terminates on twofold coordinated oxygen atoms, but it is remarkably enhanced on the surface containing O vacancy defects. The higher the concentration of oxygen vacancy defects, the stronger the adsorption is. The adsorption energies are 3.4528 eV (N end adsorption), 2.6770 eV (O end adsorption), and 4.1437 eV (horizontal adsorption). The adsorption process is exothermic, resulting in a more stable adsorption structure. Furthermore, O vacancy defects on the TiO2 (101) surface significantly contribute to the absorption of visible light in a relatively low-energy region. A new absorption peak in the low-energy region, corresponding to an energy of 0.9 eV, is observed. However, the TiO2 (101) surface structure exhibits weak absorption in the low-energy region of visible light after NO adsorption.