Preparation, Characterization And Applications Of Some Polyoxometalate Composite Photocatalysts

Photocatalytic technology based on TiO₂ has provided an effective and promising means for the remediation of environmental pollutants in air and water. However, some obvious shortage such as low quantum efficiency (～4%), hampered its widespread practical applications. Modification of the surface properties of TiO₂ particles to enhance the photoconversion efficiency, to maximize the rate of photoinduced charge separation, and to extend the photoresponse of the semiconductor catalyst into the visible range is a major challenge to relevant researchers in this field.This thesis is divided into four chapters.Chapter one systemically reviews the development and the existent problem of the photochemical catalytic materials including TiO₂, polyoxometalate and conducing polymers (CPs). The mechanism of photocatalytic reaction, some factors affecting photocatalytic activity, the relationship between the structure and properties of the catalysts, material modification technology, and so on are described in detail.In chapter two, a novel nanocomposite photocatalyst PMo₁₂/PANI/TiO₂ has successfully been prepared first by using a chemical oxidation method with (NH4)2S2O8 as an oxidant to form polyaniline-wrapped TiO₂ nanoparticles and then by an electrostatic assembly of PMo₁₂3- anions. The resulting materials are characterized by Fourier transformation infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) techniques respectively. This new photocatalyst exhibits very high photocatalytic activities to decompose 7 various organic dyes including azo dye eriochrome blue black R, fluorescent dyes rhodamine B, acridine red 3B and acridine yellow G, heteropolyaromatic dyes methylene blue and thionine chloride, and triphenylmethane dye fuchsine basic in aqueous systems under ultraviolet light irradiation, and in given time over 90% of each dye is degraded. It is also showed that the degradation reaction obeys first-order dynamic equation and Langmuir-Hinshelwood dynamic model. In addition, Degradation of an actual dye wastewater is also carried out and the results are satisfactory. In chapter three, a novel nanocomposite photocatalyst PW₁₂/PANI/TiO₂ is successfully prepared using the same method as above. The resulting materials are characterized by Fourier transformation infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and scanning electron microscopy(SEM) techniques respectively. This new photocatalyst exhibits very high photocatalytic activities to decompose methyl orange(MO) in aqueous system under visible light irradiation, and within 90 min the decolorization rate of the dye exceeds 98%. It is also showed that the degradation reaction obeyed first-order dynamic equation and Langmuir–Hinshelwood dynamic model.In chapter four, composite photocatalysts PMo₁₂/SiO₂ and PW₁₂/SiO₂ have been prepared by a sol-gel method and chacterized Fourier transformation infrared spectra (FT-IR), UV visible diffuse reflections spectrometry(UV-Vis-DRS), differential thermogravimetry (TG) techniques respectively. And resulting catalysts show very high thermal stability and photocatalytic activity to degradation of methyl orange (MO) under solar light. Higher catalytic activity of PW₁₂/SiO₂ than PMo₁₂/SiO₂ resulted from its stronger acidity. The degradation reaction of this dye obeys a first-order dynamic equation.