Doping Mechanism of N-TiO_2/ZnO Composite Nanotube Arrays and Their Photocatalytic Activity

TiO2/ZnO and N-doped TiO2/ZnO composite nanotube arrays were synthesized by the sol-gel method using ZnO nanorod arrays as a template.Scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS),and diffuse reflectance UV-Vis spectroscopy (UV-Vis) were used to characterize the samples.The nanotubes had a uniform hexagonal shape.The diameter and wall thickness of the nanotubes were about 100 nm and 20 nm,respectively.Some N dopants were substitutionally doped into the TiO2 lattice,while the N-Ox,N-C,and N-N were chemically absorbed onto the surface of the TiO2/ZnO composite nanotubes.Dopant-induced narrowing of the bandgap resulted from the doping of N ions into the TiO2 lattices.The surface N species enhanced the visible-light response and promoted the separation of photogenerated carriers.Compared with the TiO2/ZnO composite nanotube arrays,the NTiO2/ZnO composite nanotube arrays exhibited higher photocatalytic activity.