Research On Preparation And Self-assembly Of One-dimensional Transition Metal Oxide And Chalcogenide Nanostructures And Their Properties

One dimensional and hierarchical nanostructures have been paid much attention owing to their peculiar and intriguing chemical and physical properties, and have been used in many fields such as catalysis, optoelectronic devices, biochemical sensors and electrode materials for lithium batteries. Thus, it is of great importance to explore and design some simple and economical routes for one dimensional and hierarchical nanostructure fabrication.In this thesis, one dimensional and hierarchical transition metal oxide and selenide nanostructures with high crystalline quality and uniform size have been synthesized through solution-based synthetic strategy (evaporation-induced growth method and hydrothermal growth method). The relevant properties of the prepared samples including gas sensing properties, PL properties and photocatalytic properties have been studied in detail. Additionally, The relationship between the properties and morphologies and structures has been studied carefully. The main points of the thesis are summarized as follows:(1) Ultra-long Ag2Se nanowires with lengths up to several hundred micrometers and diameters of100-300nm have been successfully fabricated by water evaporation-induced growth method at120℃for6h. Experiments have revealed that the growth of Ag2Se nanowires is dominated by oriented attachment mechanism. The continuous water evaporation plays an important role for the formation of long nanowires, since it can cause high overall supersaturation and crystal/solution interfacial supersaturation in the system, which can induce secondary nucleation, and thus promote the oriented attachment growth of long nanowires.(2) a-MnO2hierarchical hollow nanospheres with diameters of1-2.5μm, which are composed of densely aligned nanowires with diameters of10-15nm and length of about1μm on the shell, have been prepared via a simple water-evaporation-induced self-assembly (WEISA) route. MnSO4-H2O and (NH4)2S2O8have been used as raw materials with the presence of Ag+ions in the reaction system. Experiments reveal that a-MnO2hierarchical hollow nanospheres derive from solid nanospheres composed of nanowire clusters shortly after evaporation (0.5h) and finally split into randomly dispersed nanowires with longer evaporation time (8h). The process can be explained by Ostwald ripening mechanism. In addition to the evaporation time, the existence of Ag+ions plays an important role in controlling the phase and morphology of the evaporation product. Furthermore, the ammonia gas sensing properties of the as-prepared samples have been investigated at room temperature with a simply adapted resistance-type gas sensor. The sensors exhibit good sensing performances with quick response and recovery, good repeatability and no need for heat regeneration. The results indicate that the sensor based on α-MnO2hierarchical hollow nanospheres exhibits higher response to ammonia gas than the one based on α-MnO2 nanowires.(3) Wide band gap BexZn1-xO nanorod arrays and rose-like structures have been successfully prepared on Zn foil substrates by a hydrothermal method at80℃for24hours. The structure, morphology and optical properties of the arrays were studied by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Photoluminescence (PL). Additionally, the influence of Be2+concentration in solution and solution pH on the morphology of the BexZn1-xO product has been studied in detail. The experimental results show that BexZn1-xO nanorod arrays can be obtained in alkaline and neutral solution, while BexZn1-xO rose-like structures are prepared in acidic solutions. The PL emission peak energy of the BexZn1-xO products increased with increasing x, as expected, and these materials should be suitable for developing UV-based optoelectronic devices.(4) Hierarchical Cd/ZnO heterostructures have been successfully prepared on Zn foil substrates through hydrothermal route for the first time. The different morphologies of the products are tuned by varying Cd2+concentration in solution. The photocatalytic properties of the products with different morphologies to RhB solutions are studied in detail, and the catalytic mechanism has been proposed. Experimental results indicate that the Cd/ZnO leaf-like structures exhibit better photocatalytic properties than Cd/ZnO comb-like structures.