Synthesis And Property Of Hierarchical Micro-/Nanostructures Of Transitional Metal Compounds

The synthesis and self-organization of micro- and nanoscale inorganic materials with special morphology, size, and hierarchy have attracted considerable attention in the past few decades because of their importance in basic scientific research and potential technological applications. Hierarchical micro-/nanostructures, constructed by using various low dimensional nanomaterials as building blocks, may provide an effective strategy for the systematic study of structure-property relationships and improve the physical and chemical properties of the nanoscale materials with simple configurations. Recently, rational control over the morphology, crystalline structure, and size of hierarchical inorganic materials has commanded the attention of many research groups worldwide and efforts have focused on mastering the synthetic routes to afford a host of novel and diverse nano- and microstructured materials. Various synthetic methods have been devoted to the controlled synthesis of hierarchical inorganic materials with specific sizes and morphologies. On the other hand, solution-phase synthetic methods have many advantages, including relatively low reaction temperatures, convenience in handling, inexpensive reaction instruments, and ease in procedural control, making them very promising for the large-scale synthesis of materials. Furthermore, the aggregation-based solution approach is proved to be one of the most effective methods to obtain hierarchical or complex nano-/microstructures. In this thesis, we have successfully synthesized that ultra-long and flexible necklace-like nanostructures of Cd(OH)2 and CuO hierarchical hollow nanostructures through novel double-soft-template mechanism based on the synergistic effect of bubble-template and interface-template in the n-octanol/aqueous liquid system, hierarchically assembled ZnQ2·2H2O microstructures in CTAB microemulsion system, and hierarchical In(OH)3 and CdS architectures with various morphologies through tunable ligand-assisted synthesis.Detailed research contents are summarized as following:1. Ultra-long and flexible necklace-like nanostructures of Cd(OH)2 and CuO hierarchical hollow nanostructures were successfully prepared in the n-octanol/aqueous liquid system through the microwave heating approach, and a novel mechanism based on the synergistic effect of bubble-template and interface-assistance (SEBI) was proposed. Controlled experiments revealed that both bubble and interface play key roles in determining the self-assembly process of Cd(OH)2 and CuO hierarchical nanostructures, and the morphology/size of building blocks and final products could be readily tuned by adjusting reaction parameters. Further experiments evidenced that the hierarchical Cd(OH)2 and CuO nanostructures possessed superior separation performance on negatively charged dye and photocatalytic efficiency on RhB, respectively.2. Assembled ZnQ2·2H2O microstructures, such as microsheet, sandwich-like structure and hexangular microflake, have been successfully prepared in CTAB microemulsion system through the stacking of ZnQ2·2H2O molecules and oriented aggregation of ZnQ2·2H2O original building blocks. Controlled experiments demonstrated that the morphologies of building block and final product could be readily tuned by reaction parameters, and a formation mechanism, involving re-precipitation, growth and oriented aggregation process, has been proposed. The surface photovoltage revealed that the photogenerated charges of ZnQ2·2H2O could be separated distinctly and ZnQ2·2H2O possessed p-type semiconductor characteristics, respectively. Furthermore, UV-vis and PL spectra evidenced the optical properties of ZnQ2·2H2O were sensitive to its microstructure or morphology.3. In(OH)3 nanomaterials with different morphologies or hierarchical structures, such as nanoparticles, monodispersed hierarchical nanocubes and nanospheres, have been successfully synthesized via a ligand-assisted aqueous process. The shape and size of these as-prepared architectures can be tuned effectively by controlling the reaction conditions, such as the molar ratio of ligand/In3+ and different ligands. Furthermore, In2O3 nanoparticles and monodispersed hierarchical nanocubes and nanospheres with well-defined morphologies of the precursors can be also obtained by annealing the corresponding In(OH)3 samples. Gas sensing properties of the as-prepared In2O3 samples demonstrate that hierarchical In2O3 architectures exhibit a superior response to In2O3 nanoparticles, and the hierarchical In2O3 nanocubes have excellent selectivity and sensitivity to ethanol gas. Further more, XPS spectra and N2 adsorption-desorption isotherms achieve a deeper understanding for the effects of final product morphologies on their gas sensing properties.4. Various architectures of CdS were prepared by a ligand-assisted hydrothermal route, and a series of complexing agents were chosen as organic ligands to controlled synthesize CdS architectures, and some CdS nanostructures with hierarchical morphologies, such as hierarchical jointed microspheres assembled by one-dimensional nanoribbons, hierarchical nanoplates assembled by nanoparticles and hierarchical hollow nanospheres assembled by nanoparticles, were obtained. Furthermore, the crystal phase of the products, including hexagonal wurtzite phase and cubic zinc-blende phase, also can be tuned conveniently by adjusting the reaction conditions, including the sort of ligand, the concentration of ligand and reaction temperature. Finally, the photocatalytic activities of as-prepared CdS architectures with different phases and morphologies demonstrate that biodegradation based on one-dimensional building blocks have a better decolorization than those based on building blocks of nanoparticles, and biodegradation based on based on hierarchical nanoplates with cubic zinc-blende phase have a better response than those based on hierarchical nanoplates with hexagonal wurtzite phase.