Study On Preparation And Photochromic Properties Of WO₃-TiO₂-ZnO Composite Films

Tungsten oxide(WO3) is one kind of important inorganic photochromic materials. Because of its photochromic reversibility, good thermal stability,strong fatigue resistance and low cost, it has great application potential in many areas such as reusable information storage, data display and smart windows. Recent researches show that its photochromic property can be effectively improved by coupling with other materials. The preparation of WO3 photochromic composite materials has been the research hotspot nowadays.In this thesis, we firstly prepared WO3 colloids, Ti O2 colloids and Zn O colloids by sol-gel method respectively and then mixed them in a certain ratio to obtain WO3-Ti O2 composite colloids and WO3-Ti O2-Zn O composite colloids. TEM and UV-Vis spectroscopy were taken to analyze their morphologies and optical properties. The results showed that when the molecular ratio of WO3:Ti O2:Zn O was 16:2:1, the WO3-Ti O2-Zn O composite colloids hold the best photochromic properties. The average grain size of WO3-Ti O2-Zn O composite colloids was about 10-30 nm. After irradiation by a high pressure mercury lamp of 500 W for 80 s, the WO3-Ti O2-Zn O composite colloids changed from colorless to blue. The composite colloids became photochromic saturated after irradiation for 150 s. And they reverted to colorless after 6 h keeping in the dark in the air at room temperature, which demonstrated a reversibility of the photochromism.Then, we added a certain amount of citric acid into the WO3-Ti O2-Zn O composite colloids for which the molecular ratio of WO3:Ti O2:Zn O is 16:2:1. And WO3-Ti O2-Zn O composite films were successfully prepared on glass substrate by dip coating method. The effect of citric acid concentration on the WO3-Ti O2-Zn O composite film's structure, surface morphology and photochromic property has been studied. The results indicated that citric acid can effectively improve the stability of the WO3-Ti O2-Zn O composite colloids. Citric acid can significantly change the surface morphology of the WO3-Ti O2-Zn O composite film. As citric acid concentration increased, the surface morphology of the WO3-Ti O2-Zn O composite film changed from rectangle nanoplates to cube nanoparticles, and finally became nanorods. When the concentration of citric acid was 0.6 M, the WO3-Ti O2-Zn O composite film had the best photochromic properties. The WO3-Ti O2-Zn O composite film changed from colorless to blue just after irradiation for 10 s by a high pressure mercury lamp of 500 W, and became photochromic saturated after irradiation for 90 s. It changed back to colorless after 12 h keeping in the dark in the air at room temperature.As the third part, we added a certain amount of PEG-400 into the WO3-Ti O2-Zn O composite colloids in which the concentration of citric acid was 0.6 M. The effect of the amount of PEG-400 on the WO3-Ti O2-Zn O composite film's property has been studied. The results showed that the photochromic property of the composite film was firstly increased and then decreased with the increasing amount of PEG-400. When the amount of PEG-400 was 0.5 g, the WO3-Ti O2-Zn O composite had the best photochromic property. The WO3-Ti O2-Zn O composite film became photochromic saturated just after irradiation for 60 s. And it changed back to colorless after 10 h keeping in the dark in the air at room temperature.