Synthesis Of Novel CdS/TiO₂ Nanocomposites And Their Application For Photocatalytic Degradation Of Fermentation Waste Solution

Photocatalysis can mineralize all contaminants in waste water and exhaust gas completely, having many merits including the low energy consumption, the gentle reaction condition, the small secondary pollution and the repeated use of catalysts. TiO₂ has been used as photocatalyst widely, because it has stable chemical property, oxidation-reducion ability and anticorrosion. Additionally, TiO₂ is nontoxic and cheap. In this dissertation, with the background of solar energy utilization and wastewater treatment and the aim of enhancing the photocatalytic activity of nano-TiO₂ under visible-light irradiation, CdS/TiO₂ nanotubes composites and CdS/TiO₂ macroporous network composites had been prepared. The photocatalytic activities of as-prepared photocatalysts were evaluated by measuring the degradation of methylene blue (MB) under visible irradiation. Meanwhile, CdS/TiO₂ nanotubes composites were used in the photodegradation of fermentation waste solution.First of all, TiO₂ nanotubes were prepared by hydrothermal method and calcined to improve their crystallinity. Then, CdS/TiO₂ nanotubes composites were prepared by liquid phase depositon and chemical reduction method, respectively, and characterized by transmission electron microscopy (TEM) and high resolution TEM (HRTEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse refection spectroscopy and FT-IR spectra etc. It is found that CdS nanoparticles mainly form inside TiO₂ nanotubes and have the fusion trend to be nanorod, which can be assigned to the capillarity and space-confinement effect of TiO₂ nanotubes. The photocatalytic activity of CdS/TiO₂ nanotubes composites was evaluated by the degradation of methylene blue in aerated aqueous suspension under visible illumination. CdS/TiO₂ nanotubes composites exhibit higher photodegradation efficiency. It is inferred that the adsorptive capacity of TiO₂ nanotubes and the unique structure of CdS/TiO₂ nanotubes composites act an important role for the improvement of their photocatalytic activity.Secondly, CdS/TiO₂ macroporous network composites had been prepared by a sol-gel method and dipping-reduction process, using eggshell membrane as template. The experimental results indicate that the photoresponse and photocatalytic activity of the composites in the visible region have been improved. On the one hand, TiO₂ nanomaterials with macroporous network have large specific area and high porosity which lead to have more contact with reactants. On the other hand, the doped carbon form carbonate species on the surface of TiO₂ nanoparticles can be excited with CdS by visible light, and the photo-induced electron can be transferred to the conduction band of TiO₂. Then the photons efficiency and transmission rate of photo-induced electron within CdS/TiO₂ composites have also been enhanced.Thirdly, CdS/TiO₂ nanotubes composites were used to the photodegradation of fermentation waste solution. The amount of catalyst, the initial pH value of the reaction system, the injection of oxygen or not were all considered. The experimental results indicate that the optimal amount of catalyst is 1g/L; the photodegradation efficiency in basic condition is higher than that in acidic condition; the injection of oxygen makes for the degradation of fermentation waste solution.