Synthesis, Modification And Photocatalysis Application Of TiO₂and ZnO Based Nanostructrured Thin Films

The photocatalysis technique of semiconductors is the expectation under the shadow of energy shortage and environmental crisis, which is attractive in applications of environmental remediation, photovoltaic cells and clean fuel production. TiO2, a wide band-gap semiconductor, attracts extensive attention and has been regarded as one of the most promising photocatalyst due to its good environmental friendliness, high photochemical stability, low cost and impressive photocatalytic activity under UV-light. Besides, ZnO, as a direct band-gap semiconductor with similar band-gap energy to TiO2, has also received more and more attention for photocatalysis. However, those two semiconductors are only UV-light responsive, which greatly restricts their practical application range. In recent30years, although people have carried out lots of work for modification of semiconductor photocatalysts, they mostly focus on the modification of band structure and surface state of nano-powder photocatalysts based on chemical modification. However, in last several years, people realized that the structure engineering modification based on physical concept for photocatalysts also has great significance. At present, the development of semiconductor photocatalysis technique is still faced with the challenges of cost control, efficiency improvement, broadening of responsive-light range and recycle of products. This dissertation is focused on the synthesis, modification and photocatalysis application of novel TiO2or ZnO based nanostructured thin films photocatalysts, which is modified based on both physical and chemical concepts.The dissertation mainly concerns with the following three aspects:Firstly, a simple and novel preparation process based on direct liquid phase deposition of TiO2in silica opal template has been developed. The obtained samples are novel N-F-codoped TiO2inverse opal films with a hierarchical meso-/macroporous structure, which is a derivative of common inverse opal. It’s demonstrated that this film photocatalyst with special photochemical enhancement effect is responsive to visible-light and easy to recycle. Detailed discussion and analysis for mechanism of sample’s photocatalytic performance is carried out. In all samples, the most improved visible-light photocatalytic degradation rate is about7.4times to that of ordinary N-F-codoped thin film. In addition, the multiple scattering effect and slow photon effect are also comparatively studied in detail, which prove that the multiple scattering effect is more pronounced than the slow photon effect for facilitating the photocatalytic performance in system with a continuous set of incident light wavelength.Secondly, a novel method to fabricate composition-and topology-controlled ZnO/TiO2inverse opals films via selective etching of ZnO inverse opal and liquid phase deposition of TiO2has been developed. The non-close-packed inverse opal structure with special air cylinders is obtained. Besides, it is observed that the wall thickness and the composition of inverse opal are also controllable by changing the reaction time. Furthermore, the influence of compositional and topological variation of inverse opal on its photocatalytic performance is also explored.Thirdly, by a simple ion exchange method, the Ag2S is successfully introduced into CdS nanoparticle-loaded ZnO1D nanorods array film. This obtained three-component semiconductors-photocatalyst is detailedly characterized and analyzed. The Ag2S/CdS-ZnO nanorods array exhibits improved UV-light photocatalytic performance relative to that of CdS/ZnO and ZnO. Furthermore, the mechanisms of charge-carrier transfer in system and improved photocatalytic performance are concluded.Based on the above mentioned studies for TiO2and ZnO based nano-structured thin film photocatalysts, this work realize the strategy of both physical and chemical modification for photocatalysts. The visible-light or UV-light photocatalytic performance for samples are improved. This achievement provides a new viewpoint for designing highly efficient semiconductor photocatalysts.