Plasma Spray Fabrication And Antibacterial Properties Of Titania Hollow Microspheres And Their Coatings

The increasing shortage of fresh water resource provides a greater awareness of the importance of cherishing and saving water, which also improves the sewage treatment technology and water purification technology rapidly. Among them, photocatalytic oxidation is of increasing interest due to its complete degradation of organics and disinfection of most microbes in the water, using the clean and sustainable sunlight as power. As a representative of semiconductor photocatalysts, titania has a broad application prospect in environmental protection, sanitation, energy and so forth attributing to its chemical stability, long durability, nontoxicity, low cost, and other significant advantages. However, particle-type photocatalysts, especially nanoscale catalysts, are prone to agglomerate which lowers the photocatalytic performance and difficult to recycle and reuse. Immobilized photocatalysts and films or coatings can overcome these difficulties effectively, but their preparation technics and performance impose restrictions on scale-up and industrialization process.On the aim of solving the problem of recycle and reuse, this thesis used titania nanoparticles and magnetic ferriferrous oxide nanoparticles as raw materials to prepare TiO2 hollow microspheres and Fe3O4-TiO2 hollow microspheres by suspension plasma spray technology. Particle sizes are range from 10 to 60 microns and the thickness of shell is 1/30~1/5 of particle diameter. The large interior cavity decreases powder density but increases the specific surface area. Residual organics in the powder can keep particle shape and play a key role in preparation process of hollow microspheres. In addition, spraying power has a prominent influence on powder morphology, structure, phase component and so on. Hollow microspheres have excellent performance in visible light. They will not agglomerate and are easy to recycle by filtration in applied process. Magnetic property makes powder easier to recycle by external magnetic field, and the presence of Fe element improves the photocatalytic disinfection performance of the as-prepared powder.Then TiO2 photocatalytic coatings were elaborated by suspension plasma spray at three low-powers of 12 kW, 16 kW and 20 kW using hollow microspheres which have unique structure as raw material and using traditional agglomerated TiO2 powder as the control sample. The coatings made of hollow spheres have a lower degree of phase transformation, larger specific surface area, and higher porosity, leading to better photocatalytic degradation of organics and photocatalytic disinfection performance.During plasma spraying process, the gases generated from the rapid evaporation of solvent and decomposition of organics do not have enough time for escaping from the particle and would expand the particle to form hollow structure due to the high internal pressure. This method just use simple equipment and easy to operate. It could fast and efficiently prepare those hollow microspheres and it is easy to scale-up and industrialize. Moreover, the as-prepared hollow products save material and have excellent visible light photocatalytic activity, which improves the utilization of solar energy and provides broad application prospects in energy, environment and other fields.When hollow spheres are chosen as novel spray powder to elaborate coating, the unique structure will have an influence on the heat and mass transfer and the microstructure and performance of the as-prepared coatings more or less, which provides a great guidance for preparation of functional coatings.