Studies On The Preparation And Photocatalytic Property Of Bi₄Ti₃O₁₂-based Nanomaterials With Layered Structure

With the rapid development of social economy, the shortage of energy and the environmental pollution have become serious problems that we have to face with. Photocatalysis taking use of solar energy can deal with environmental pollution and even convert solar energy into electrical or chemical energies, which are attracting more and more attention. However, most of the commercial semiconductor photocatalysts have wide band gap that make the photocatalysts use mainly ultraviolet light in the solar spectrum, limiting their extensive applications. Therefore, developing new visible-light-driven photocatalysts becomes the aspiring goal of researchers. Aurivillius compound is a bismuth-containing layered perovskite compound. The existing intra-electric field between different layered-structural-units is assumed to advance the separation of photo-generated carriers, consequently improve the photocatalytic activity of catalysts. Bismuth titanate(Bi4Ti3O12) is a kind of Aurivillius compounds which shows good photocatalytic activity. It is found that doping Fe3+ in Bi4Ti3O12 can improve photocatalytic activity in visible light. Fe doped Bi4Ti3O12 may be a potential visible-light-driven photocatalyst.In this dissertation, the nano-materials of Bi5Ti3FeO15 and terminal compounds Bi4Ti3O12 and BiFeO3 are successfully prepared by hydrothermal method. Bi5Ti3FeO15-BiOCl nano-heterojunction is prepared by an ion replacement method. The morphology, structure, composition and photocatalytic activity of the nano-materials are systematically investigated, and the photocatalytic mechanism of nano-heterojunction is preliminarily interpreted based on the bandgap structure measured in this work. The main contents are as follows:Nanostructured Bi5Ti3FeO15 is synthesized by hydrothermal method, The effects of reaction temperature, time and pH value on the micromorphology and crystal structure of as-prepared samples are investigated. Based on these experiments an optimized hydrothermal processis obtained. Hydrothermal products exhibits flower-liked clusters, which consist of nanoplates with a thickness of ?20nm and a length of 1-2 ?m. Bi4Ti3O12 nanowires and BiFeO3 nanoparticles are synthesized by hydrothermal method and sol-gel method. Rhodamine B is used as an indicator of degradation to study the photocatalytic activities of the samples above. The results show that the visible-light catalytic activity of Bi5Ti3FeO15 nanoplates is much better than Bi4Ti3O12 and BiFeO3.Bi5Ti3FeO15-BiOCl nano-heterojunction is synthesized by reaction of Bi5Ti3FeO15 and HCl by ion replacement method. The effects of reaction time and pH value on the structure, composition and micromorphology of heterojunction are investigated.The investigation of photocatalytic activity of theseheterojunction samples reveals that Bi5Ti3FeO15-BiOCl nano- heterojunctions have excellent photocatalytic activity. Rhodamine B in solution is completely degraded by Bi5Ti3FeO15-BiOCl nano-heterojunctions within 30 minutes under visible light(? > 390 nm). Bi5Ti3FeO15-BiOCl shows better visible-light catalytic activity than P25(TiO2) and BiOCl nano-materials.The band gap and the top edge of valence band of the obtained nanomaterialsare measured by ultraviolet-visible diffuse reflectance spectroscopy(UV-Vis DRS) and X-ray photoelectron spectroscopy(XPS), respectively. Thus the bandgap structure of Bi5Ti3FeO15, BiOCl and Bi5Ti3FeO15-BiOCl heterojunction are determined. Bandpass filters are used to study the photocatalytic activity under visible lights with different specific wavelengths. Based on these results, we propose an interpretion on the mechanism of photocatalytic degradation of rhodamine B by Bi5Ti3FeO15-BiOCl heterojunction. The excellent visible-light catalytic activity of the Bi5Ti3FeO15-BiOCl heterojunction is attributed to the good match of the band gap structures of Bi5Ti3FeO15 and BiOCl, which promote the photosensitized reaction of rhodamine B with BiOCl as the acceptor of electrons from the excited rhodamine B, meanwhile improve the photocatalytic activity of Bi5Ti3FeO15.