Effect Of Silver Deposition On Photoelectric And Photocatalytic Performances Of Nitrogen-doped TiO₂ Thin Film

As one of the most important photocatalysts, titanium dioxide（Ti O₂）is widely employed in photocatalytic degradation, photoelectric conversion,solar cells, and so on. However, pure Ti O₂ as photocatalyst has some disadvantages. Firstly, the relatively large band gap of Ti O₂（3.2 e V） means it can only be exited by ultraviolet（UV） light, which only accounts for about 4%of the solar spectrum. Secondly, the fast recombination rate of photogenerated electron-hole pairs reduces the photoelectric properties and photocatalytic activities of Ti O₂. In addition, Ti O₂ as a high surface area powder is easy to agglomerate and difficult to recover from solution. Based on the above problems,titanium nitride（Ti N） thin film was prepared by electrophoretic deposition on Ti substrate in an aqueous suspension of nanosized Ti N powder firstly, and then nitrogen-doped titanium dioxide（N-Ti O₂） thin film was fabricated by thermal oxidation treatment. Ag nanoparticles were deposited on the surface of N-Ti O₂ thin film in different concentration of Ag NO3 solution by photo-reduction deposition. The samples were characterized by X-ray diffraction（XRD）,scanning electron microscope（SEM） and ultraviolet visible light spectroscopy（UV-Vis）. Photoelectric properties and photocatalytic activities were investigated via the measurement of transient photocurrent density and the photocatalytic degradation of Rhodamine B, respectively. Effect of silver deposition on photoelectric and photocatalytic performances of N-Ti O₂ thin film was emphatically studied. Main results are as follows:（1） Titanium nitride thin films were prepared by electrophoretic deposition on Ti substrates, and then N-Ti O₂ thin films were fabricated by heating the Ti N films at 450 ℃ for 15-120 min in air. It turned out that the N-Ti O₂ films have mixed phase structure of anatase and rutile Ti O₂. The N-Ti O₂ thin film formed at 450 ℃ for 60 min shows the most obvious red shift of the UV-Visible absorption edge, which corresponding to the band gap of 2.82 e V,and it has the optimal photoelectric and photocatalytic performances. Under visible light irradiation, the transient photocurrent density of the N-Ti O₂ film is about 0.7 μA/cm2. The photocatalytic activity of the film was evaluated by the degradation of 10 mg/L Rhodamine B solution under visible light irradiation for240 min and the degradation rate is 98%.（2） Ag nanoparticles was deposited on N-Ti O₂ thin film formed at450 ℃ for 60 min heating by photo-reduction deposition in different concentration of Ag NO3 solution. In the process, silver ions in the solution werereduced into neutral Ag atoms. Appropriate amount of Ag’s deposition can significantly improve the photoelectric and photocatalytic performances of N-Ti O₂ thin film, and the optimal concentration of Ag NO3 solution for Ag deposition is 0.05 mol/L in this work. Ag deposited N-Ti O₂ thin film is about 5.4and 5.1 times the transient photocurrent density of N-Ti O₂ thin film under visible and ultraviolet light irradiation, respectively. For Ag deposited N-Ti O₂ thin film, the degradation rate of Rhodamine B is 98% under visible light irradiation for 180 min and 99% under ultraviolet light irradiation for 120 min.