Kinetic study of self-assembly of Ni(II)-doped TiO2 nanocatalysts for the photodegradation of azo pollutants

Ni(II)-doped TiO2 nanoparticles were fabricated by a simple and reliable hydrothermal method. Morphology, crystallographic structure and light-absorption properties of the formed photocatalysts were characterized. In addition, both the adsorption phenomena and photodegradation of two types of azo dyes in the presence of Ni(II)-doped TiO2 were investigated. The experimental results showed that the dye adsorption follows the Langmuir adsorption pathway, and the dye degradation was significantly enhanced by doping of Ni ions into TiO2 photocatalysts. The optimal doping of Ni ions for the removal of RB5 and 3R dyes was found to be 1%, giving a degradation efficiency 3 times for RB5 dye and 3.5 times for 3R dye higher than those of un-doped TiO2. Furthermore, the underlying kinetic mechanism was systematically studied, in which the second-order kinetic model was found to be the explicit mechanism for dye degradation on TiO2 with Ni(II) doping.