| In the recent years, people become more concerned on the harmness of UV radiation acting on human, industrial materials and entironment. Meanwhile, some kinds of sunscreen materials have entered into the life of people. In general, TiO2 and ZnO have the most favorite sunscreen capability among various sunscreen materials. However, these inorganic materials possess some shortcomings such as the high photo-catalytic activity. For the purposes of reliability of materials, the lower catalytic activity is desired for the sunscreen materials to avoid decomposing the environmental medium. Hence, TiO2 and ZnO are greatly restricted on sunscreen application. From the view points of alleviating the UV radiation threat, to develop a new kind of sunscreen materials with effective sunscreen capability and lower photo-catalytic, oxidation catalytic activities as well becomes the topic of this research.The UV absorption photo-catalytic oxidation catalytic capabilities and surface modification of zinc and cerium oxides (ZCO)were researched. ZCO powders in the size of 10nm was used while nano- TiO2, ZnO and CeO2 were also tested for .comparison. The apparatus for photo-catalytic and oxidation catalytic experiments were self-designed. The UV absorption, photo-catalytic and oxidation catalyticcapabilities of ZCO were measured and compared with those of rutile TiO2 and ZnO; And the likely methods depress the oxidation catalytic activities of ceria were presented based the principles of crystal defect chemistry. The polymer surface modification of ZCO was studied experimentally under different conditions.The experiments of UV-visible measurement indicate that ZCO has strong absorption in the wavelength range of 200-400nm with a high peak value, also shows excellent permeation in the visible light spectrum range.In the photo-catalytic experiment, the methyl orange solution mixed with the same quantities of ZCO , ZnO , rutile TiO2 and CeO2 were radiated under three 30w violet lamps in the wavelength of 253. 7nm. The concentrations of all solutions including the blank were measured at the same time intervals. And the results indicate that the tested solution concentration of ZCO is 3mg/L and 7mg/L higher than those of rutile TiO2 and ZnO respectively. This fact reveals that the photo-catalytic activity of ZCO is lower than that of ZnO and TiO2 respectively.In the oxidation catalytic experiment, the same quantities of ZCO and CeO2 powders were mixed with castor oil and the solutions were bubbled by air. The volatile gas was introduced into the deionized water. The electrical conductivities of deionized water including the blank sample were measured. And the results indicate that the electric conductivity's change speed of deionized water corresponding to ZCO is about 3.39uS/h lower than that of CeO2. This shows that the oxidation catalytic activity of ceria is restrained by doped zinc oxide.The mechanism of zinc-doped ceria was analyzed in the terms of the principles of crystal defect chemistry. Three interpretations to depress the oxidation catalytic activity of ceria were presented by the author as follows: (A) the metal ions doped possess positive four values and the radius is between 0.102nm and 0.117nm; (B} the metal ions doped possess lower values and the radius is between 0.102nm and 0.117nm; (3) the metal ions doped possess lower values and the radius is smaller than 0.092nm. The defect equation of emitting and absorbing oxygen of ceria and of MO doping into ceria were presented. The mistakes of defect equation published by some Japanese scholars were discussed and rectified.The polymer surface modification of ZCO was researched experimentally. The different surface modification effects were examined under different solicitation,temperatures in ultrasonic implement and electricity oven. So the optimized process parameters were obtained as follows: The ZCO quantity percentage roughly shares the MMA quantity of 4.6%; The better solicitation is H2O2 and its volume is about 1.5% of MMA; The temperature in ultrasonic... |
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