| Photocatalytic materials are a new type of promising environmental protectionmaterials with an important research value and significance. Among them, Zinc Oxide(ZnO) exhibits a wide direct-band-gap of3.37eV and a large exciton binding energy of60meV which is much higher than that of other wide band-gap semiconductor materials, thusgiving rise to the fact that ZnO has a higher photocatalytic property and then has attractedextensive attention in the environmental purification.The nano-ZnO powders were prepared by sol-gel method and the morphologycharacteristics and microstructure were characterized by X-ray diffraction (XRD),Transmission electron microscope (TEM) and Scanning electron microscope (SEM),respectively. Meantime, the luminescent properties and the photocatalytic properties weremeasured by fluorescence spectrophotometer and photocatalytic device. The main resultsare as follows:(1) For the pure ZnO powders prepared by sol-gel method with the calcined time of3hours and the calcination temperature of773~1073k, all of ZnO powders possessed goodcrystallinity. And the crystallinity enhanced as the calcination temperature increased. Whenthe calcination temperature was873K, ZnO powders showed the complete rods and hadgood blue-violet fluorescence intensity. Furthermore, it also exhibited the highestphotocatalytic efficiency. When the calcined time changed from1h to4h at a sametemperature of873K, the ZnO powders showed spherical shape with lots of fluffs and thediameters of them changed with the calcined time. When the calcined time was3h, thediameters of them reached the minimum and were about5μm and65nm respectively, thusresulting in the fact that ZnO powders had the maximum specific surface area and then thehighest photocatalytic efficiency.(2) For the Mg-doped ZnO powders, when the doping concentration of Mg ions reached10%, an energy gap of3.31eV was obtained which was less than the energy gap of pureZnO powder (3.37eV). This could give rise to decrease of the bandgap and theenlargement of the absorption spectra. According to the Raman spectra and the infrared spectrum, there were lots of oxygen vacancies and zinc interstitial defected which coulddecrease electron-hole recombination and then increase the photocatalytic efficiency. Thephotocatalytic efficiency could reach highest photocatalytic efficiency when the dopingconcentration was about10%.(3) For the Ce-doped ZnO, the nano-ZnO powders prepared with the calcined time of3hand the calcined temperature of773K couldn’t show clear CeO2when the doping ratio ofCeO2: ZnO was less than1:99. All the samples exhibited nanometer rod. With theincrease of the doping ratio from0.3:99.7to1:99, the photocatalytic efficiency of thenano-ZnO powder first increased and then decreased, reaching the highest photocatalyticefficiency for the doping ratio of0.5:99.5.(4) When the doping ratio of CeO2: ZnO was higer than1:99, all samples showedobvious CeO2structure. Moreover, CeO2and ZnO could form heterojunction and thenpromote the separatation of light generated-electrons and holes, thus increasing thephotocatalytic efficiency. With the increase of the doping ratio of CeO2, the photocatalyticefficiency of ZnO powders first increased and then decreased, reaching the highestphotocatalytic efficiency for the doping ratio of4:96, which was larger than thephotocatalytic efficiency for the doping ratio of0.5:99.5.(5) In addition, the calcined time and the calcined temperature could change the structureof ZnO powders and then have an important effect on the photocatalytic efficiency. Theresearches showed that for the Ce-doped ZnO powders with the doping ratio of0.5:99.5,the photocatalytic efficiency of the nano-ZnO powder first increased and then decreasedwith the increase of the calcined temperature, reaching the highest value at773K. Whenthe calcined temperature kept773K, the photocatalytic efficiency of the nano-ZnO powderfirst increased and then decreased with the increase of the calcined time, reaching thehighest value at3h. |
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