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Study On Photocatalytic Property Of ZnO And Its Composits

Posted on:2013-02-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:W XieFull Text:PDF
GTID:1111330374471173Subject:Building materials and engineering
Abstract/Summary:PDF Full Text Request
Environmental pollution and energy crisis are becoming a serious problem. The photocatalytic technology based on ZnO, TiO2and the other semiconductor oxides has been attracting much attention due to high efficiency, low energy consumption, moderate reaction condition, lower secondary pollution and the other advantages. In this dissertation, a series of explorations have been carried out on the photocatalytic (photothermocatalytic) properties of microscale ZnO, nano ZnO, Ag/ZnO TiO2-modified ZnO photocatalysts. The main results and innovation points can be summarized as follows:Firstly, The photocatalytic performance of microscale ZnO, nano ZnO, and Degussa titania (P25) were compared. It was found that the microscale ZnO exhibits2.6~35.7times higher photocatalytic activity for the photodegradation of typical organics than P25both under UV-visible and visible irradiation, and shows much better photostability than nano ZnO. The photostability of the microscale ZnO can be greatly improved by surface modification with an appropriate amount of TiO2.Secondly, a novel device based on the microscale ZnO and TiO2-modified ZnO coupling photodegradation with light-to-electricity conversion was developed, which is a promising candidate for the photocatalytic removal of dye pollutants and renewable energy source.Thirdly, Ag/ZnO photocatalysts with different Ag loading were prepared by photocatalytic reduction of Ag+on ZnO, in which silver exists in the form of metallic species. It was found that loading an appropriate amount of Ag on ZnO not only enhances its photocatalytic activity, but also improves its photostability. The chemisorption of molecular oxygen and the chemisorption of atomic oxygen on Ag in the surface of Ag/ZnO photocatalysts were observed. It was found that the metallic Ag in the Ag/ZnO photocatalysts does play a new role of O2chemisorption sites except for electron acceptor, by which thus facilitates the trapping of photogenerated electrons and further improves the photocatalytic activity of the Ag/ZnO photocatalysts.Fourthly, nano ZnO photocatalysts were prepared by calcining the formed precipitate. It has been found that the photocatalytic activity for the gas-phase photocatalytic oxidation of acetone on the nano ZnO photocatalysts significantly increases with increasing reaction temperature. Under photothermocatalytic condition, the photocurrent of nano ZnO significantly increases with increasing temperature, resulting in the significant enhancement of photocatalytic activity, which is attributed to a great enhancement in the separation efficiency of photogenerated charge carriers with increasing temperature due to the temperature effect of ionized impurity scattering. The results of PL and PAS indicate the presence of defects such as monovacancies and vacancy clusters as ionized impurities in the nano ZnO samples.
Keywords/Search Tags:Microscale ZnO, photocatalytic, O2chemisorption, nano ZnO, gas-phasephotocatalytic oxidation
PDF Full Text Request
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