Synthesis And Properties Of Noble Metal And Transition Metal Oxide Nanomaterials

Noble metal and transition metal oxide nanomaterials have gained intensiveattention for their potential applications in catalysis, sensors, lithium ion batteries andsolar cells. Nanomaterials with tunable size, morphology and composition often possessunique physical and chemical properties. To fabricate high-quality nanocrystals withwell-defined shape and composition, the rational design of facile and environmental-friendly synthetic strategies is vital of significance. This dissertation focuses on thesolution-based synthetic routes for noble metal and transition metal oxidenanostructures, as well as the relationship between structures and properties of theas-prepared nanomaterials.Based on the solution-based synthetic strategy, a facile method has beenestablished to synthesize monodisperse Ag nanocrystals. The size of the Agnanocrystals can be tuned by varying the synthetic parameters such as metal precursor,reaction time and temperature. Notably, the as-prepared highly uniform nanocrystalscan easily self-assemble into two-dimensional (2D) superlattices without any additionalsteps. The surface-enhanced Raman scattering (SERS) properties of the individual Agnanoparticles and their assemblies have also been investigated. It is noteworthy that theassemblies of the Ag nanoparticles show stronger SERS signals in the presence ofRhodamine B dye. Moreover, the silver sulfide nanocrystals are synthesized usingdodecanethiol and sulfur as sulfur source. Near-infrared photoluminescence of theas-prepared nanocrystals has also been discussed.A rational synthetic strategy has been developed to prepare Au-ZnO hybridnanoparticles. The hybrid nanomaterials were synthesized through a seed-mediatedgrowth process, in which gold nanocrystals were used as the seeds. The as-obtainedhybrid nanoparticles with hexagonal pyramid-like structure present uniform size andshape. It is notable that the Au-ZnO hybrid nanostructures exhibit enhancedphotocatalytic efficiency than the pure ZnO NCs. In addition, the individual zinc oxideswith various sizes and morphologies have also been synthesized under similar condition.Based on the above experiment results, a possible formation mechanism is discussed. Inthis system, the common inorganic salts such as zinc acetate dihydrate were used as the starting reactants and the reaction was carried out under mild condition. Due to thesimplicity of the process, this method is suitable for scalable fabrication of thenanomaterials.A facile hydrothermal approach has been introduced to preparehigh-quality Mn₃O₄nanocrystals. In the presence of oleylamine and dodecanol,the Mn₃O₄nanocrystals with tunable sizes and shapes can be achieved byvarying the reaction parameters such as solvent composition and reactiontemperature. In particular, the as-obtained uniform nanocrystals used as buildingblocks can be assembled into three-dimensional (3D) hydrophilic Mn₃O₄colloidal spheres by the bottom-up assembly strategy. Moreover, theas-prepared3D colloidal spheres can be further converted to Li-ion batterycathode materials (LiMn2O4). Because of their different size and crystallinity,the as-prepared nanomaterials show distinct electrochemical performance. Inaddition, the assembly strategy can also be used to fabricate dual-modeluminescent colloidal spheres using rare-earth fluoride nanocrystals as 'artificialatoms'. The unique binary nanostructures may have potential application inmultifunctional fluorescence imaging.The synthetic strategy for the Mn₃O₄nanocrystals can also be extended tofabricate transition metal (Mn, Co, Ni) hydroxide nanoplates. Notably, theas-obtained transition metal hydroxide nanostructures can be converted to theanode and cathode nanomaterials for lithium ion battery by calcination andsolid-state reactions. Furthermore, the electrochemical performance of thematerials has been investigated in detail.