Synthesis And Characterization Of Nanotubular Magnesium-based Oxides

Series of Magnesium-based oxide nanomaterials have been synthesized via wet-chemical methods (such as hydrothermal method or template hydrothermal method) in this thesis, including Mg(OH)2,MgO,Mg3Si2O5(OH)4,MgBO2(OH) and Mg2V2O7 nanotubes. The morphologies of the products were controlled by adjusting reaction conditions. Multi-techniques such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), scanning electron microscopy (SEM), and X-ray photoelectron spectra (XPS) were used to characterize the crystal structures, compositions, morphologies and dimensions of the products. And the formation mechanisms of the products are discussed. Catalysis performance of some products were also tested.The main results were summarized as follows:1. Hydrothermal synthesis and characterization of magnesium hydroxide and magnesium oxide nanotubeA large number of Mg(OH)2 nanotubes with inner diameter of ca.6 nm, outer diameter of ca.26 nm have been successfully synthesized by a hydrothermal method. MgO nanotubes can be obtained by calcinating Mg(OH)2 nanotubes under 450℃.The morphologies and structures of the nanotubes were characterized by x-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS),transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) and so on. Based on the morphologies of Mg(OH)2 nanotubes obtained via different hydrothermal time,we proposed a growth mechanism. MgO nanotubes have special surface composition and surface acidity. The isopropanol decomposition showed MgO nanotubes have high catalytic activity and selectivity in acetone. It is expected to have good application system in catalytic reaction.2. Composite-Hydroxide-Assisted Hydrothermal Synthesis of Magnesium Silicate NanotubeA novel, mild, and highly efficient method for the synthesis of uniform magnesium silicate nanotubes with the assistance of potassium hydroxide and sodium hydroxide was successfully developed. The eutectic solution of potassium hydroxide and sodium hydroxide offers high dissolvability for the reactants and benefits the reaction among the reactants to accelerate the conversion process.Compared with traditional hydrothermal method, this composite-hydroxide-assisted approach is a mild and highly efficient procedure. This novel approach will find many applications in the controllable synthesis of nanostructured complex oxides with novel properties and morphologies.3. Magnesium borate nanotube and Magnesium vanadate nanotube obtained via template methodThe Magnesium borate nanotubes and Magnesium vanadate nanotubes were synthesized using Mg(OH)2 nanotubes as self-template by hydrothermal method. The structures, morphologies, sizes and compositions were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and so on. The analysis results show that most of the products have nanotube-like morphology. The Magnesium vanadate nanotubes mainly composed of Mg2 V2O7 and β-Mg2V2O7 crystalline phase.