Controlled Synthesis Of Stannates Nanomaterials By Hydrothermal-ion Exchange Method

Stannate nanomaterial has drawn more and more research attention because of its unique characteristic dielectrical and chemical properties. It has been recently considered to be a new material for semiconductor gas sensors, ceramic material, catalysis and anodic material for lithium ion batteries. It will be a useful tool for the tailoring of properties/applications of stannate material if we can precisely control the sizes, dimensionalities, shape, structure and compositions in nanoscale. In this thesis, salutary explorations have been developed on the synthetic strategy and formation mechanism of stannate nanomaterial. The main points can be summarized as follows:A new novel hydrothermal-ion exchange method has been developed to prepare CdSnO₃·3H₂O nanocubes with well-defined size by designing a reasonable chemical reaction. Our method involves the preparation of precursors Na₂Sn(OH)₆ via a hydrothermal method in an ethanol/water solution, followed by the ion-exchange reaction between solid Na₂Sn(OH)₆ crystals and Cd²⁺ solution, assisted by ultrasonic treatment. In the hydrothermal process, the growth of crystal variation resulting from the introduction amount of ethanol to the solvent plays an important role in determining the morphology of precursor Na₂Sn(OH)₆, and the special microsheet Na₂Sn(OH)₆ supplies a benefit condition to synthesize nanocubes. In ion-exchange process, the formation mechanism of nanocubes is observed by changing the ultrasonic time, which opens a new view about the mechanism of stannate nanomaterial.Based on the structure similarity between MSnO₃(M=Ca,Ba,Sr) and CdSnO₃, the hydrothermal-ion exchange method is extended to fabricate MSnO₃(M=Ca,Ba,Sr) nanomaterials, and a series of MSnO₃ 1D nanostructures, such as BaSnO₃ nanorod, SrSnO₃ nanobelt are obtained. In addition, a special morphology of CaSn(OH)6 is obtained when the order of the reactant introducing is changed. The sample shows morphology similar to that of the micrometer sphere, which is the secondary structure made from a self- assemble of nanorods with diameters of 50 nm and lengths up to 200 nm. The formation mechanism of the microsphere has been investigated based on SEM observation. The application of hydrothermal-ion exchange method provides an efficient way for exploring the physical-chemical properties and the synthesis of this special perovskite-structure.