Mesoporous N-P-codoped anatase-TiO₂ nano-sheets were successfully synthesized by a sol-hydrothermal method which utilized urea and phosphorous acid as dopants, and glacial acetic acid as inhibiting agent. Their photoactivities were evaluated by the photocatalytic degradation of 4-chlorophenol (4-CP) in aqueous solution under simulated sunlight irradiation. In combination with XRD, TEM, BET, XPS, DRS, PL and zeta potential characterization, the effect mechanisms of N and P doping on the photoactivities of TiO₂ were discussed. The results revealed that the N-P-codoped TiO₂ exhibited higher photocatalytic activity for 4-CP degradation than the undoped, N-doped or P-doped TiO₂. The visible light response of the N-P-codoped sample may be attributed to narrowing of the band gap resulted from hybridization by the 2p orbits of N atom, 3p orbits of P atom and the 2p orbits of O atom, respectively. The N-P-codoping can further improve the surface texture properties of TiO₂, and increase the surface hydroxyl, and inhibit the recombination of photogenerated electrons and holes, and enhance the dispersive capacity in water due to the increase of the surface acidity, which imply that the N-P-codoping produces synergetic effects, therefore resulting in the enhanced photoactivity of N-P-codoped TiO₂.

Key words: nano-TiO₂, N-P-codoping, sol-hydrothermal, visible light response, synergetic effect