Study On The Preparation Of TiO₂ Photocatalyst And Device Design Used For Wastewater Treatment And Air Purification

With the rapid development of global industrialization and the demand for high quality of life, water pollution and indoor air pollution are more attention. Water and indoor air pollution become the key problems needed to resolve. Photocatalytic degradation of organic matter in water and organic volatile in the air has gradually become the important way to solve the problem of the pollution. Developing highly photocatalytic active, high stability, low cost and non-toxic photocatalyst, designing efficient, cheap, and sewage disposal and gas processing device is the key of the research field.In numerous photocatalysts, the excellent chemical stability and nontoxicity of titanium dioxide ?TiO₂? has attracted much attention for its potential use as a solid photocatalyst for environmental purification. However, a major drawback that impedes the practical applications of pristine TiO₂-based photocatalytic oxidation is the fact that the large band gap of TiO₂. As a consequence, only UV light can be utilized to generate electron-hole pairs and to initiate the photocatalytic oxidation process. Recently, Ti³⁺self-doped TiO₂ has emerged as an effective approach to introduce visible photoactivity and efficient electronic conductivity. If the Ti³⁺ self-doped TiO₂ compose with carbons that have high electrical conductivity, the photocatalytic activity will further be improved. In addition, if the powder of Ti³⁺ self-doped TiO₂ make to thin film and plus a certain bias, the separation of electrons and holes will be promote. For this reason,this dissertation adopts the Ti³⁺ self-doping modification of TiO₂ and composes with quantum dot content carbon. In addition, the prepared powder catalyst was made into film, study their photocatalytic perf-ormance. Specific work focused on the following aspects:1. Ti³⁺ self-doped TiO₂/N-doped carbon nanostructure composites were prepared via a facile one step hydrothermal method to optimize the use of visible light and reduce recombination of photogenerated electrons and holes. The composites were characterized by X-ray diffraction, transmission electron microscopy ?TEM?,high-resolution TEM, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The amounts of carbon and nitrogen sources affect the morphology and photocatalytic performance. At low amounts of the sources, the N-doped carbon nanostructure is an amorphous film and is well-combined with TiO₂-x nanoparticles through surface carbon-oxygen groups. At high amounts of the sources,N-doped carbon quantum dots ?NCQDs? were obtained, and carbon atoms could substitute for oxygen atoms in the TiO₂ lattice to form Ti-C structures, which are responsible for the high photocatalytic activity under visible light illumination.Transient photocurrent response and electrochemical impedance spectroscopy results indicate that the amorphous hybrid film becomes a trap for electrons and that NCQDs can accelerate electron transfer. The improved visible light photocatalytic property for the Ti³⁺ self-doped TiO₂/NCQDs composite can be attributed to the enhancement of light absorption and inhibition of the photogenerated electron-hole recombination of anchored NCQDs.2. To improve the harvesting of visible light and reduce the recombination of photogenerated electrons and holes, Ti³⁺ self-doped TiO₂ nanoparticles were synthesized and assembled into photoanodes with high visible light photoelectrochemical properties. X-ray diffraction, transmission electron microscopy,X-ray photoelectron spectra,electron resonance spectroscopy and energy dispersive x-ray spectra were used to characterize the structure, crystallinity, morphology and other properties of the obtained nanoparticles. UV-visible diffuse reflectance spectra showed that the Ti³⁺ self-doped TiO₂ nanoparticles had a strong absorption between 400 and 800 nm. Moreover, when hydrothermal treatment time was prolonged to 22 h, the heterogeneous junction was formed between the anatase and rutile TiO₂, and where the anatase particles exposed highly active {001} facets. Under visible light irradiation, the Ti³⁺ self-doped TiO₂ electrode exhibited an excellent photoelectrocatalytic degradation of rhodamine B ?RhB? and water splitting performance. Intriguingly, by selecting an appropriate hydrothermal time, the high photoconversion efficiency of 1.16% was achieved.3. In order to achieve the practical application of photocatalytic technology, a device model for wastewater treatment and air purification was designed. By using the coupling process of photocatalysis and membrane separation, a kind of solid supported swirl type photocatalytic reactor was designed. In this reactor, the catalyst load on the surface of function membrane, to overcome the shortcomings of suspended photocatalyst clogging; primary filter and activated carbon layer is used to remove larger particles of pollutants, reduce the concentration of pollutants; remove dust particles and even inhalable particles, smoke, bacteria for efficient membrane. Finally,the catalyst can efficiently filter the catalytic process by interception of water or air shock down, to prevent the loss of catalyst. In the cyclone reactor, water flow and air flow in the cyclone, increasing the contact area of catalyst and pollution, prolong water and air flow in the reactor, which increased the photocatalytic reaction time. The coupling of photocatalytic technology and membrane separation technology at the same time can produce synergies.