Study On Photogenerated Charge Behavior And Photocatalytic Property Of Optimized ZnO Materials

There are various reasons for environment pollution, the essence one is the needsfor human survival and the instinct for development. The question about solvingenvironment contamination is the goal strategy of sustainable development.Semiconductor-based photocatalysts can both solve the environmental pollutionproblems and reduce the use of non-renewable energy resources. ZnO with goodphotoelectric properties is an important metal oxide semiconductor, which is widelyused in photoelectric gas sensors, solar cells and photocatalysis in the filed of solarenergy research. However, it has the following disadvantages:(1) it absorbs only inthe UV region and limits the use of sunlight sufficient;(2) high recombinationprobability of photogenerated charge carriers, reducing its photocatalytic activity.Therefore, in order to make it responsive to visible light and improve itsphotocatalytic activity to a certain extent, the work on the modified by transitionmetals incorporating and constructing heterojunctions based on the ZnO materials arecarried out and a further study on between photogenerated charge behavior(generation, separation, transportion and recombination etc.) and photocatalyticproperty is also discussed.In this work, we prepared Fe-doped ZnO (Fe/ZnO), p-Bi2O3/n-ZnOheterojunction and BiOBr-ZnO heterojunction via the simple hydrothermal/solvothermal method, respectively. The photogenerated charge behaviors on surfaceor interface of the materials were studied, and the relationship between photocatalyticactivity and photogenerated charge behavior was explored. These results providedtheoretical basis for explaining of the photodegradation mechanism. Specific work includes the following aspects:1. Fe/ZnO nanoflower photocatalysts were prepared by a simple hydrothermalmethod. The samples were characterized by XRD, XPS and Raman scattering, and theresults indicated that the Fe is present in multivalent forms (Fe3+/Fe2+). Photocatalyticactivities of the catalysts were tested under both UV and visible light irradiation,respectively. The results of SPV and PL demonstrated that under the irradiation of UVlight, Fe acted as the recombination center of the photogenerated electrons and holes,the Fe/ZnO photoactivity was reduced. In the presence of visible light, the existenceof Fe3+/Fe2+can promote the production of much more unstable RhB.+, resulting inthe increase in the photoactivity of Fe/ZnO. It is a process of self-degradation of RhB.2. The Bi2O3/ZnO heterojunction were prepared by a facile one-step approach.Both the results of XRD and XPS indicated that only two phases of ZnO and Bi2O3were existed in the composite. The SPV and SPV phase results demonstrated that theinternal electric field existed between ZnO and Bi2O3restrained the recombination ofphotogenerated charge carriers and changed their transfer direction. Under theirradiation of visible light (λ>420nm), the Bi2O3/ZnO heterojunction exhibitedoutstanding photocatalytic activity.3. The BiOBr-ZnO heterojunction were prepared by a two-step approach. Firstly,the precursor of ZnO was obtained by hydrothermal method. Secondly, we usesolvothermal method to coat a layer of BiOBr nanoflakes onto the surface of ZnO.Under the simulated solar light irradiation, the optimum photocatalytic activity ofBiOBr-ZnO heterojunctions was about3.7and4.7times as high as those of individualBiOBr and ZnO, respectively. The SPV results indicated that the internal electric fieldaccelerated the separation of photogenerated of electron-hole pairs.