Studies On The Synthesis, Characterization, Growth Mechanism And Properties Of One-dimensional Metal Borates Nanostructures

Nanomaterials have attracted extensive attentions because of their significance in both fundamental science and potential applications. There are many conventional methods to produce nanostructures. However, the products fabricated using traditional methods usually have a size distribution and disordering in structures, which might smear the quantum effects in the samples. It is desirable and a challenge to produce well mono-sized one-dimensional nanostructures. In this thesis, we will report unique methods to produce such one-dimensional nanostructures. The major part of this thesis deals with the synthesis and characterization of three types of metal borates nanostructures; these are Al₁₈B₄O₃₃ nanowires, Al₄B₂O₉ nanowires and Mg₂B₂O₅ nanowires and nanorods respectively by using different unique methods. Also in this thesis the photoluminescence properties (Pl) of these metal borates have been investigated as an adjunct aim.1) Nanowires made of aluminum borate Al₁₈B₄O₃₃ have been synthesized in high yield by improving the traditional chemical flux method for the growth of aluminum borate with the fibrous structure. In this study, aluminum powder was added into the aluminum oxide and boron oxide reactants as an additive in order to control the morphology of the final products. The chemical method reported here is utilized to decrease the diameters of traditional aluminum borate fiber into nanoscale and to increase their lengths. The optimum experimental parameters and possible growth mechanism for the compound nanowires have been presented.2) Single-crystalline aluminum borate Al₄B₂O₉ nanowires in large scale have been synthesized by a direct calcination of a precursor powder made of Na₂B₄O₇-10H₂O and Al (NO₃)₃·9H₂O at low temperatures of 850 and 900℃. The nanowires, with the diameter of 20-40 nm and the length up to several micrometers, possess smooth surfaces and uniform sizes along the entire wire. The growth mechanism of the nanowires is attributed to a solid-liquid-solid process. The as-obtained Al₄B₂O₉ nanowires have been converted to Al₁₈B₄O₃₃: Eu nanowires to examine the photoluminescence properties. The result shows that, Al₁₈B₄O₃₃ nanowires exhibited three emission bands peaking at 591.0, 613.4 and 628.8 nm for Al₁₈B₄O₃₃: Eu³⁺ and broad band emission with maximum peak situated at 450 nm for Al₁₈B₄O₃₃: Eu²⁺ nanowires.3) A facile route of a large-scale of Mg₂B₂O₅ nanowire bundles has been achieved via a sole-gel method and later subsequent heating. SEM and TEM images showed that the nanowires stuck together at one end and then fanning out to form a typical nanowire bundles. Based on the SEM images, we found that the amount of citric acid (CA) which acts as ferment agent and the reaction temperature played important roles in the morphology control of the final Mg₂B₂O₅ products. The growth mechanism of these nanowire bundles follows the self-catalyst growth mechanism.4) Another single-crystalline of magnesium borate Mg₂B₂O₅ nanorods of monoclinic structure have been successfully synthesized via a simple route based on the calcination of mixed powder containing Mg (OH)₂ and H₃BO₃. The as-received nanorods have typical diameters in the range of 70-120 nm and lengths up to a few micrometers. An optimal synthesis temperature for Mg₂B₂O₅ nanorods was obtained, and the possible growth mechanism was also presented. Furthermore, Mg₂B₂O₅: Eu nanorods of triclinic structure have been prepared by re-calcined a mixture powder of the as-obtained Mg₂B₂O₅ nanorods of monoclinic structure and Eu₂O₃ in order to investigate the photoluminescence properties in which Mg₂B₂O₅: Eu²⁺ exhibited a broad band emission situated at 412 nm and also a very weak emission band at 615 nm, corresponding to ⁵D₀→⁷F₂ transitions centered on Eu³⁺ ion could be observed.