Preparation of homogeneous nitrogen-doped mesoporous TiO2 spheres with enhanced visible-light photocatalysis

Abstract

A series of mesoporous TiO2 spheres of nanosized crystals with high monodispersity and dimensional homogeneity are synthesized by a simple reflux method. In order to improve the visible light response and to further narrow the band bap of TiO2 sphere, nitrogen is used as the dopant in a hydrothermal method. Different from the traditional nitrogen doping in TiO2 solid sphere, the nitrogen is uniformly distributed from bulk to the surface of mesoporous TiO2 sphere, which is beneficial to the generation of the successive energy bands inside the TiO2 band gap. Interestingly, the XPS results indicate that the nitrogen doping concentration could reach 1.31% (only 0.17% for nitrogen doped solid TiO2 sphere), owing to the homogeneous doping in the mesoporous TiO2 spheres. The nitrogen doped TiO2 spheres exhibit such excellent characteristics as high specific area, relatively small particle size, pure anatase phase and excellent UV–vis absorption capacity in the range of 400–800nm, which are all beneficial to the photo-degradation of Rhodamine B under the visible light irradiation. The high photocatalytic activity could be ascribed to the homogeneous nitrogen doping on the deep adjustment of energy band of TiO2 sphere from the bulk to the surface.