The Hierarchical Structures Of ZnO And Their Photocatalytic Properties

Zinc oxide is a kind of wide band-gap semiconductor, which has thepotential application as a photocatalyst due to its excellent photoelectricproperty. As we all know, the properties of semiconductor materials arerelated to their morphologies, size, and crystalline. It is significant tosynthesize novel structures of zinc oxide， pursuing for new particularproperties. Hierarchical structure has an inerratic geometric morphology,which is composed by alignment of nano-materials, defined as basic units, ina specific order. So, its size can reach the micro level. Compared with thepreparation of nano-materials, the hierarchical structural materials are easierto prepare, at the same time, maintain the properties of nano-materials.In my research work, we started from the synthesis of zinc oxide.Through a simple and quick solution-phase method, a flower-like zinc oxidewas prepared. It was a hierarchical structure which was consisted of nanoflakes with a thickness of5nm. Then its photocatalytic property wasexplored. We found that the flower-like ZnO could effectively photocatalyzethe methyl orange （MO） solution. After annealing at600℃in the air for2h,the crystalline of flower-like ZnO increased, and the oleic acid moleculesexisted on its surface were decomposed, which benefited the improvement ofits photocatalytic efficiency.Graphene is an ideal two-dimensional material which has good electricalconductivity to store and transform electrons. It can be used to promote thetransferring and separation of photoexcited carriers, and restrict theirrecombination. In this case we synthesized the graphene surface modifiedflower-like ZnO. The photocatalytic efficiency increased58.5%compared to0.852h^-1.A rod-like ZnO mesocrystal, consisted of ZnO nanoparticles, was alsoprepared. Due to its unique structural features, the rod-like ZnO mesocrystalsshare some similar properties with nanoparticulate, mesoporous, andsingle-crystal materials. The experimental results showed that rod-like zincoxide has excellent photocatalytic performance, which can photocatalyze themethyl orange solution, and photoreduce Cr6+. Compared with nanoparticles,the rod-like ZnO mesocrystal showed a better photocatalytic efficiency andstability.