The Preparation And Photocatalytic Performance Of N,S Doped And CdS Composite TiO₂ Photocatalysts On Hydrogen Evolution

Nitrogen-doped, sulfur-doped titanium dioxide nanoparticles(denoted XNTiO₂NP, YSTiO₂NP, where X is the atomic ratio of N and Ti, where Y is atomic ratio of Ti and S) were prepared by sol-gel method with tetra-n-butyl titanate as raw materials and urea, thiourea, as nitrogen and sulfur source respectively. Doped titania nanotubes were synthesized by microwave irradiation method (denoted XNTiO₂NT, YSTiO₂NT). After studying on the photocatalytic performance of above photocatalysts loaded same amount of platinum with different doping, the best doping ratios were found. Then, CdS composite nitrogen, sulfur doped titania nanotubes were prepared by microwave irradiation method (denoted ZCdSXNTiO₂NT, ZCdSYSTiO₂NT, where Z is composite amount of CdS). The effects of the composite amount of CdS on catalytic activities were studied. The catalysts were characterized by the modern techniques (DRS, TEM, XRD, XPS, ICP and EAI, etc.). The relationship between catalysts structure and their photocatalytic activity was also investigated. By changing the amount of urea and thiourea, a series of catalysts were prepared. The results showed that among different ratios of nitrogen-doped catalysts, 3NTiO₂NT had the best catalytic activities, and its absorption edge is about 543nm. Under the conditions of pure water and containing sacrificial agent, its hydrogen production rates were 17.11μmol/(g·h) and 415.4μmol/(g·h) respectively. Among different sulfur-doped catalysts, 15STiO₂NT had the best catalytic activities, and its absorption edge is about 448nm. Under the conditions of pure water and containing sacrificial agent, its hydrogen production rates were 98.06μmol/(g·h) and 2665μmol/(g·h) respectively. Comprehensive characterization illuminated that some nitrogen and sulfur atoms doped into TiO₂ lattice, formed impurity energy level and changed the structure of the catalyst, finally affected the catalytic performance.CdS composite nitrogen, sulfur doped titania nanotubes were prepared with nitrogen, sulfur doped titanium dioxide nanoparticles as raw material. The effects of the composite amount of CdS on catalytic activity were studied. The results indicated that in pure water system, the catalyst which CdS composite amount of 4wt% showed a higher activity. The results from water splitting under visible light showed that the hydrogen production rate of 4CdS3NTiO₂NT was 13.3μmol/(g·h), and the hydrogen production rate of 4CdS15STiO₂NT was 13.9μmol/(g·h). In the system with sodium sulfide and sodium sulfite as sacrificial agent, the catalyst which CdS composite amount of 8wt% showed a higher activity. The results under visible light showed that the hydrogen production rate of 8CdS3NTiO₂NT was 165.3μmol/(g·h), and the hydrogen production rate of 8CdS15STiO₂NT was 656.4μmol/(g·h) respectively. The results of combined characterization analysis indicated that in the system of pure water, the large composite amount of CdS, might cover the surface of titania nanotubes, which prevent titanium dioxide from the light absorption, and resulted in the decreasing of catalytic activity. In the system with sodium sulfide and sodium sulfite as sacrificial agent, cadmium sulfide played a major role in the catalytic activity. The results of XPS showed that the Ti and O atoms of titanium dioxide lost some electron, which made their peaks shift to high-energy direction. And the Cd and S atoms abtained some electron, which made their peaks shift to low-energy direction. The composite cadmium sulfide might change band structure of titanium dioxide, then improved catalytic activity.