Study On Electrospinning Synthesis And Structural Characterizations Of One-dimensional Nanostructure Of Borate

One-dimensional nanostructures, such as nanowires, nanorods, nanobelts, nanotubes and nanofibers, are defined as two-dimensional directions at nanometers scale. They not only demonstrate quantum confined effect and small size effect which are not seen in the corresponding bulk materials, but also have a high ratio of length to diameter and strong anisotropy properties. Nowadays, they have been attracted much attention due to their potential applications. Fabrications and applications of one-dimensional nanomaterial are the research frontiers in the nanoscience field.Borates have been an attractive subject due to their abundant structure types, excellent physical and chemical characteristics as well as the wide range of applications. Until now, there have been some reports on alkyl metal borates, transition metal borates and rare earth metal borates. Most of them are bulk borates while reports on one-dimensional nonastructure borates are very few. This dissertation studies the preparation of one-dimensional nanostructure of some typical borates by electrospinning method, a simple, efficient and economical preparation method. The main contents and conclusions as follows:(1)Necklace-like Mn₂OBO₃ nanofibers have been synthesized by electrospinning method for the first time. First the PVP/[Mn(CH₃COO)₂+H₃BO₃] composite fibers with an average diameter of 320nm were obtained through the electrospinning process. Then Mn₂OBO₃ nanofibers with the average diameter of 200nm were obtained after high temperature sintering. The results show that sintering temperature has a great influence on the morphology of the fibers. The formation mechanism of necklace-like fiber could be interpreted as the rapid growth of grains which leads to the"phagocytosis"effect significant between the adjacent grains. By analyzing the Mn₂OBO₃ vibration characteristics, the room temperature Raman spectrum of Mn₂OBO₃ nanocrystals were identified and assigned. Necklace-like fibers have greater specific surface area than solid-core fibers, so this new nanostructure of Mn₂OBO₃ provides an experimental basis for further characteristic study.(2)Lanthanum borate nanofibers have been preparaed by electrospinning method for the first time. The PVP/[La(NO₃)₃+H₃BO₃] composite fibers with average diameter about 330nm were first obtained through electrospinning process, and then H-LaBO3(slow heating) and La₃BO₃(fast heating) fibers were obtained by different heat treatment process, respectivly. Research shows that the heating rate is the critical factor for controlling phase structure in the La₂O₃-B₂O₃ system.The reason is that the heating rate influents the degree of decomposition of La(NO₃)₃, so that involving in chemical reactions with different proportion of La₂O₃ and B₂O₃ lead to the final product has different phase structures.(3)Magnesium borate nanofibers have been prepared for the first time by electrospinning method. First, the PVP/[Mg(CH₃COO)₂+H₃BO₃] composite fibers with an average diameter of 500-550nm were obtained by electrospinning process. Then inorganic magnesium borate nanofibers were obtained through heat treatment process. Study found that the initial molar ratio of raw materials directly affect the products phase structure. When the molar ratio of Mg to B is 1:1, the final product is Mg3B2O6 fiber with diameter of 100-300nm after sintering at 850℃. While Mg₂B₂O₅ fibers with average diameter of 280nm were obtained by the same sintering temperature when the molar ratio of that is 1:2. According to the phase diagram of the MgO-B₂O₃ system, the growth mechanism of magnesium borate fiber was analyzed. The phase structure of the final product depends on the mass percentage of MgO and B₂O₃. When the MgO excess, it is easy to generation Mg3B2O6but it is Mg₂B₂O₅.when B₂O₃ excess.(4)Single crystalline Mg₂B₂O₅ nanorods with the diameter of about 200nm and the length of 4-5μm have been synthesized by mechano-chemical technique and sintering process. The growth mechanism for nanocrystal rods as follows:solid state exchange reaction has been taken place in the room temperature during the milling process, and NaCl crystal and amorphous Mg(BH₄)₂ formed. In the sintering process, the amorphous Mg(BH₄)₂ in the precursor powders slowly crystallized into monoclinic Mg₂B₂O₅ crystal nanorods. Research shows that the by-product NaCl is necessary for the formation of the single phase Mg₂B₂O₅.(5)The preparation of polymer/inorganic boron composite nanofibers has been studied. The electrospinning precursor solution was obtained by mechanical mixing PVP polymer with the boron powder in the ethanol solution. Through electrospinning process, the PVP/B composite nanofibers were obtained. The structure and morphology analysis showed that the introduction of the polymer PVP molecules do not destroy the crystalline structure of boron. Composite mechanism can be explained as the intercalation compounding mechanism. Inorganicα-boron with layered structure can be used as the host material, PVP polymers with long chain molecular structure as a gest material, PVP molecular chain intercalate the layer ofα- boron during the long time stirring in ethanol solution. In the electrospinning process, with the rapid evaporation of solvent, quickly solidified into PVP/B composite fiber.In this paper, the feasibility and applicability of the preparation of borates one-dimensional fibers and organic/inorganic nanocomposite fibers using electrospinning technology were studied. The results not only widen the application field of electrospinning technology but also provide an experimental basis for further the preparation and properties studying of borates one-dimensional nanostructural materials and organic/inorganic composite fibers. It is great significance for realization widely used of one-dimensional borates.