Chemical Synthesis And Assembly Of Three-Dimensional Hierarchical Micro/Nanostructures Of Metal Oxide And Selenide

In this dissertation, a series of new chemical routes were developed for the synthesis and assembly of various 3D hierarchical structures. Various hierarchical structures of PbSe and CdSe were synthesized by adjusting the manner of crystal growth in the solution-based reaction systems. Co₃O₄ hierarchical structures were rationally prepared by the pyrogenation of the as-obtained precursor templates. In(OH)₃ and In₂O₃ hollow microspheres constructed by nanocubes were achieved with assistance of the soft template. Hollowα-MnO₂ hierarchical microspheres were obtained, based on the anisotropic growth of the product's crystal and the self-generated template route. The details are summarized briefly as follows:1. The author developed the solution-based chemical synthesis and simultaneous assembly routes to synthesize various submicrostructures of metal selenide semiconductors by controlling the producing rate of Se^2- in the reaction systems, which determined the nucleation and growth of the product's crystal. (1) Well-crystalline PbSe multiple-dendritic hierarchical structures and cuboidal microcrystals were controllably synthesized by choosing different Se source in an alkaline glycerol/water solution system. The possible growth mechanisms for the two kinds of PbSe microstructures were proposed from the point of crystallographic and kinetic views. (2) A series of CdSe submicrostructures, including rods, fringy structures, and fasciculate tubes with high hierarchy, have been selectively prepared by simply changing the feeding quantity of aqueous ammonia (25% NH₃). Ammonia in the reaction system plays a dual role: providing an alkaline medium for the formation of Se^2- and acting as a coordinating agent for Cd²⁺ . This concise and novel one-step route has special advantages, suggesting a new path for convenient synthesis of CdSe materials with novel morphologies.2. The authors developed the precursor-template pyrolysis method to achieve the synthesis and assembly of inorganic nanomaterials. Based on the structural characteristics of the precursor and the target product, the hierarchical structures of the target product were obtained through the pyrolysis of the as-prepared precursor-template. Highly uniform 3D sisal-like, dandelion-like and rose-like architectures of cobalt hydroxide carbonate were synthesized through a facile hydrothermal process at 100℃, 140℃and 180℃, respectively. Subsequently, Co₃O₄ superstructures with the corresponding morphologies were obtained by the pyrolysis of the as-prepared precursors.3. The authors designed a novel vesicle-template-interface route to assemble the three-dimensional hollow microspheres by the inducement of soft template. In(OH)₃ hollow microspheres constructed by numerous nanocubes were successfully prepared in the "formamide-resorcinol-water" system. As desired, InO₃ hollow microspheres were obtained from annealing the designed In(OH)₃ hollow structures, and the as-obtained InO₃ hollow microspheres performed well as a gas-sensing material in response to both ethanol and formaldehyde gases and as a photocatalyst for photocatalytic degradation of rhodamine B.4. Based on the anisotropic growth of the product's crystal and the self-produced template route, we successfully realized the assembly of one dimensional nanostructures into three dimensional hierarchical hollow microspheres. Novelα-MnO₂ hollow urchins were synthesized on a large scale by a facile and efficient mild reduction route, without templates or surfactants in the system. The formation mechanism for the hollow urchins was proved to be the Ostwald ripening process by tracking the crystallization and morphology of the products at different reaction stages. Theα-MnO₂ hollow urchins exhibited good chemical property when used as the cathode material in Li batteries. This synthetic procedure is straightforward and inexpensive and thus facilitates the mass production ofα-MnO₂ hollow hierarchical structures.