Nanostructure TiO₂ Surfaces And Their Properties Of Superhydrophilicity And Self-cleaning Under Visible Light

This dissertation firstly gives a brief introduction and presents the last investigation of the self-cleaning surfaces, emphasizes the importance of studying these surfaces. Combination of the two ways (Super-hydrophilicity and Super-hydrophibicity) of achieving self-cleaning, the specific methods is summarized. Subsequently, the advantages and disadvantages of TiO₂ as self-cleaning materials are presented. Finally, dissertation uses"Nanostructure TiO₂ Surfaces and Their Properties of Superhydrophilicity and Self-cleaning under Visible Light"as thesis, mostly describes the following works and results:(1) Porous TiO₂/SiO₂ bi-layer films were prepared by spin coated SiO₂ sol and TiO₂ sol including polyethylene glycol 2000 (PEG 2000) onto glass and subsequent calcination at 550°C. Meanwhile, factors that affect the TiO₂/SiO₂ bi-layer films transmittance and superhydrophilicity were investigated in details by observing their surface morphologies and measuring their water contact angles (WCAs), spreading time and transmittances. The results indicated that the as-prepared TiO₂/SiO₂ bi-layer film showed superhydrophilicity under visible light when 0.5 wt. % PEG 2000 was added in TiO₂ sol. At the same time, its maximum transmittance was as high as 92.3%. The spreading time was only about 0.16 s. More importantly, the resultant film had an excellent stability of the superhydrophilic property.(2) Structural and wetting properties of TiO₂ films prepared on glass substrates using sol-gel process have been examined at different annealing temperatures. The results show that the as-deposited TiO₂ thin films are amorphous, and they transform into the anatase phase at 450 oC. The crystallite size is increased from 9 to 20 nm with increasing annealing temperature. TiO₂ film'morphology is changed smooth surface to nanogranular surface when annealing temperature exceeded 400 oC. At the same time, with the rise of annealing temperature, the porosity is decreased from 42% to 27%. Surprisingly, the TiO₂ film exhibited superhydrophilicity under visible light, starting from the annealing temperature of 400 oC. More importantly, this superhydrophilicity is so stable that the water contact angle of the as-prepared sample only increased slightly even when it is kept in air for about one month.