Study On Controllable Preparation And Properties Of Calcium Molybdate And Manganese Dioxide Micro - Nano Materials

Micro/nano materials usually possess larger specific surface areas than their bulk counterparts and show the interface effect, quantum size effect, small size effect and macroscopic quantum tunneling effect, etc.. Thus they can exhibit many excellent properties and have broad application in catalysis, medicine, light absorption, magnetic media and new materials. Recently, the design of simple, cheap, environmental friendly and efficient synthetic methods and the development of novel micro/nano materials in structure have become the focus in the material world. This paper mainly concentrates on the control of structure and composition of semiconducting metal oxides and salts (MnO2 and CaMoO4) micro/nano materials, the preparation of novel CaMoO4 and MnO2 nanomaterials, the possible formation mechanisms, and the photoluminescence or catalytic degradation performance.Specific work includes the following aspects:1. Coupled twin-shaped hollow hemispherical calcium molybdate (CTHH-CaMoO4) was fabricated through the control of ethanol and ethylenediamine tetraacetic acid (EDTA) via an ultrasound-assisted approach. The solvent effect of ethanol and the structure-directing role of EDTA were found playing important roles for the formation of this unique structure through the control of the experimental conditions. Based on the time-dependent experiments and observations, the oriented attachment and the Ostwald Ripening mechanism of crystal growth were proposed for the formation of this novel structure.2. Three dimensional (3D) hierarchical flower-like CaMoO4 balls were synthesized through a facile ultrasonic-assisted method at room temperature in the case of pure water as the solvent. Based on a series of time-dependent experiments and characterizations, the self-assembly mechanism related to nucleation-dissolving-recrystallization was proposed for the 3D flower-like balls. This kind of 3D layered structure possesses larger specific surface, mesoporous structure, higher crystallinity and better photoluminescence properties.3. Hollow sea urchin-like manganese dioxide (MnO2) was fabricated by adding the Ag+ and sodium dodecyl sulfate (SDS) to the hydrothermal system using potassium permanganate as the raw material. Based on the time-dependent experiments and morphologies, the Ostwald Ripening mechanism was proposed for the formation of the hollow sea urchin-like MnO2. The Brunauer-Emmett-Teller (BET) surface areas for hollow sea urchin-like MnO2 and commodity MnO2 are 47.8 m2·g-1 and 25.4 m2·g-1, respectively. The larger BET surface area of the former one may come from the hollow interior. In addition, hollow sea urchin-like MnO2 showed excellent catalytic performance in the presence of oxidant H2O2 for the degradation of methylene blue, which may be due to the larger surface area and more active sites.