Abstract:

TiO2-yNx nanoparticles were prepared by in situ doping sol-gel method using urea as the nitrogen source. Their visible-light photocatalytic activity was evaluated by the photocatalytic degradation of methylene blue(MB) in an aqueous solution under visible-light irradiation. The effects of original pH value, nitrogendoping content and calcination temperature on the as-prepared samples were investigated. The visible-light responsive mechanism of the N-doped sample was studied by means of XRD, XPS, ESR and DRS. The results show that the optimal conditions for the preparation of TiO2-yNx nano-particles are as follows: original pH value 0.52, doping proportion of n(N) to n(Ti) 1∶6, and calcination temperature 440 ℃. The as-prepared sample of single anatase phase with 0.77% N atoms and with average crystal size 19.0 nm exhibits a good visible-light photocatalytic activity. N-doping leads to increasing the surface hydroxyl groups and forming abundant surface oxygen vacancies bounding single-electrons. The O atoms in the TiO2 lattice are substituted by the doped N atoms so that form the N—Ti—O and O—N—Ti bonding structures. N-doping results in a remarkable red-shift of the TiO2 absorption band-edge and significantly increases the absorption of visible-light. The results indicate that N-doping changes the electronic structure of TiO2 and decreases the band-gap. The visible-light response of the N-doped sample is ascribed to a synergetic effect of impurity and defect energy levels that are originated from the substitutional N-doping and the formation of oxygen vacancies accordingly.

Key words: nano titania, N-doping, sol-gel, visible-light response, photocatalysis