Distinctive Microstructures Of Bismuth (â…¢) Oxide: Solution Synthesis, Growth Mechanism And Optical Properties

Bismuth oxide (Bi2O3) is an important functional material with wide band-gap,high refractive index, dielectric permittivity, high oxygen conductivity, remarkablephotoconductivity and photoluminescence. These unique characteristics make Bi2O3suitable for applications in solid oxide fuel cells, sensors, photoelectric materials, hightemperature superconductor materials, functional ceramics and catalysts. Thedevelopment on its simple and mild preparation and morphology-controlled strategyare important topics, which are worthy of study for theoretical research andapplication. In this paper, various Bi2O3microstructures, including oblique prism-like,hierarchical flowerlike and tetrahedral, were synthesized via a one-step solutionprecipitation method. And on the basis of experiment and characterization, we alsodid an in-depth study on the growth and formation mechanisms of each microstructure.The main research results and innovations of the thesis are given in the followingparts.First,1D oblique prism-like Bi2O3have been synthesized in aqueous-phase atlow temperature and ambient pressure in the presence of sodiumdodecylbenzenesulfonate (SDBS). The oblique prism-like Bi2O3have betterdistribution with an average diameter of2μm and length of up to tens of micrometers.A combined growth mechanism of oriented attachment followed by Ostwald ripeningis proposed for the formation of oblique prism-like Bi2O3. The optical absorption andphotoluminescence (PL) characteristics of the prepared sample were investigated.Secondly,3D hierarchical siamesed-flowerlike microstructures of α-Bi2O3havebeen synthesized by a glycerin-assisted hydrothermal method. The microflowers of30μm were built up of oblique prism-like nanorobs, with mean width of300nm andthickness of100nm. In the hydrothermal process, hierarchical microstructures constructed by nanoribbons, ultrathin nanoflakes and oblique prism-like nanorobs canbe found at different step of crystal growth. Morphology evolution of α-Bi2O3wasanalyzed and the probable formation mechanism was described as combination of twosteps of self-assembly: layer-by-layer self-assembly of nanoribbons to the obliqueprism-like nanorobs and self-assembly of nanorobs to hierarchicalsiamesed-flowerlike microstructures. Glycerin plays crucial role in the formation ofthe hierarchical structure (the formation of junction). The vibrational properties,optical absorption and photoluminescence (PL) characteristics of the sample wereinvestigated.Thirdly, we reported a facile solution precipitation method to fabricate the3Dhierarchical flowerlike microstructures of α-Bi2O3composed of decahedrons and rods.How do temperature and pressure affect morphologies of “petals” and flowerlikemicrostructures in the glycerin system?①At90℃and ambient pressure, the OH(hydroxyl radical) of glycerol molecules are more favorably coupled on the polarfaces, which decreases the growth in the [001] direction of α-Bi2O3to formdecahedral shape.②a) At high temperature and pressure, the coupling effect of OHon polar faces is greatly weakened, which leads to an elongation of crystal shape(rod-like shape), and glycerol molecules are more favorably adsorbed on the tip of thepetals to form hierarchical flowerlike structures. b) In addition, steric hindrance ofdecahedron is much higher than robs, which lead to formation of flower clustercomposed of more rods and incomplete flowerlike microstructures composed of a fewdecahedrons. The small difference of optical absorption and photoluminescence (PL)characteristics arises from diversity of morphology.Finally, we studied the synthesis and property of γ-Bi2O3.Metastable γ-Bi2O3siamesed-tetrahedra have been synthesized at70℃with the assistance of PEG (Mw=400). The obtained tetrahedra are built up of ultrathin triangular nanosheets vialayer-by-layer self-assembly. Oxygen atoms in γ-Bi2O3play critical role inunderpinning tetrahedral structures. The concentration of NaOH solution tunes themorphology and PEG influences not only in the morphology but also in phase transferof sample. Compared with the PL spectrum of α-Bi2O3, the emission peak located around567nm disappears, which are caused by the reduction in crystal defects(oxygen vacancies) of γ-Bi2O3.In conclusion，distinctive microstructures Bi2O3composed of different buildingblocks are obtained by solution precipitation method. Our findings will help for betterunderstanding of the formation of hierarchical microstructures and will also contributesome valuable information to novel microstructures of Bi2O3.