Adsorption And Diffusion Of NO Molecule And N Atom On TiO₂ Surface

The nitrogen oxides(NOx)have caused a lot of environmental problems,and their degradation is of great interest to engineers and researchers.One of the most impor-tant methods to degradate NOx is the photocatalytic method,using the TiO2 as the photocatalyst.There are several important steps in the photocatalytic process,which may affect the rate of the catalytic reaction,such as the absorption of the photon,the adsorption of the reactant molecules,and the diffusion of the intermediates.Study of these steps could help us to understand the mechanism of the reactions,and provide some advises to improve the properties of the photocatalyst.Adsorption and global diffusion properties of N atom on rutile(110),anatase(001)and(101)surface are studied by first principle calculations.Four types of adsorption configurations are found on rutile(110)surface and also four on anatase(001)and(101)surface.On all above surfaces,the N atom tends to adsorb on sites around surface Ti-O bonds.The golbal diffusion paths of N atom combining fractional diffusions paths aquired with NEB method are calculated to study the global barrier of diffusion on both surfaces,indicating that diffusion of N atom on anatase(001)surface is isotropic globally while that on anatase(101)and rutile(110)surface are anisotropic,and the height of energy barrier of all surfaces are quite high,which explains the experimental result the the N atom can be observed on Ti02 surfaces,but seldom take part in the reaction to form the N2 molecule.NO adsorption on n-type and p-type modified anatase(101)surfaces is studied with first principle calculations.Both types of modifications can facilitate the adsorption of a NO molecule on an anatase(101)surface.The adsorption mechanisms for these two types of adsorption are different.On n-type modified surfaces,the N atom of the NO molecule is bonded to a surface Ti5C ion,that is,the unpaired electron on the ?*orbital of the NO molecule forms a bond with an extra 3d electron of the surface Ti ion.On p-type modified surfaces,the N atom of the NO molecule is bonded to a surface O2C.The unpaired electron of the NO molecule fills the empty 2p orbital of the modified surface,and the ?*orbital of the NO molecule hybridizes with the surface valence band.