Soft Chemical Synthesis And Characterization Of Transition Metal Oxide Nanocrystals

Transition metal oxide nanomaterials have attracted considerable attentions due to their potential applications in many fields such as optics, electricity, magnetics, catalyst and biomedicine. Great efforts have been contributed on the morphology and particle size of transition metal oxide nanocrystals because of their excellent performance. Controlled sythesis and preparation of nanomaterials are the keys to investigate the properties and put the materials into use. Moreover, the mechanism of the nucleation and growth is rather important.Developing a low cost, low energy consumption and environment benign synthetic method for shape and size controlled nanocrystals is a challenge for chemists. Especially the room temperature synthetic route is rare oweing to complicated factors.Hydrothermal/solvothermal synthesis method is a simple, reliable, soft chemical synthetic method. It has been more than a hundred years since the method was introduced into the synthetic chemistry. It has been adopted not only in the growth of giant crystals such as organic/ inorganic hybrid materials, but also in the synthesis of nanoparticles such as transition oxide and complex metal oxides etc.In this study, we focus on room temperature synthetic route and hydrothermal /solvothermal synthesis of the transition metal oxide nanocrystals with different morphologies and size. The behavior of nano-sized materials strongly depends on the size, shape and morphology of their internal structures. We investigate the effect on the size, shape and morphology of nanocrystals by adjusting the extrinsic factors including solvent, heating temperature, mediate etc.Mn₃O₄ nanoplates have been successfully prepared through redox reaction in the presence of short straight chain n-alkylamine at room temperature. N-alkylamine plays an important role in the reaction as a weak basic and reducing medium. The as-prepared Mn₃O₄ nanoplates were proved to be single crystal in nature. The average particle size is about 22×19 nm. A series of experiments were carried out to investigate the effects on the formation of Mn₃O₄ nanoplates by varying the reaction parameters such as the volume of n-alkylamine, manganese source and the different short chain n-alkylamine. The formation of Mn₃O₄ nanoplates may proceed by a dissolution-growth process. Because of its higher yield, this method could potentially offer large-scale synthesis of Mn₃O₄ nanocrystallites in the future. This room temperature route could be considered as an economical and facile approach to prepare Mn₃O₄ nanoparticles.Fe₃O₄ nanoparticles were also prepared successfully by room temperature synthetic route. XRD pattern of Fe₃O₄ samples showed that it belong to cubic phase with space group of Fd-3m(227), lattice constant a = 8.391?. Morphology and the particle size of the as-prepared Fe₃O₄ nanoparticles were investigated by TEM. The products are made of spheral nanoparticles with average particle size of 9.6nm. The result of magnetic test indicated that the as-prepared Fe₃O₄ sample showed strong ferro- magnetic at room temperature.Hausmannite Mn₃O₄ nanocrystals were successfully synthesized via a facile one-step solvothermal route. The data of XRD showed that the nanostructure of Mn₃O₄ can be obtained in a wide temperature range (60°C¹40°C) and in mediate of many different solvent (acetone, ethanol, DMF, DMSO). The morphology and size were investigated by TEM. It was found that the particle size of the Mn₃O₄ samples could be tailed by varying the organic solvent. Control experiments showed that the ability of which the organic solvent and Mn (â…¡) form Manganese complex is a crucial influencing factors on the particle size of the products. The particle size increased with the rising of reaction temperature when the solvent is the same. The magnetic properties of the as-prepared samples were studied using a superconducting quantum interference device (SQUID) magnetometer. A plausible mechanism is also presented. Metal cation substituted bismuth vanadate (BIMEVOX) possesses high oxygen ion conductivity at lower temperatures. The ionic conductivity of this material at 300°C is 50–100 times more than any other solid electrolyte; in the order of 10-3 Scm-1 at 300°C. To our knowledge, there isn't any report on the BIMEVOXes by hydrothermal synthesis.The parent compound Bi₂V₄O₁₁ and Ag substituted bismuth vanadate (BIAGVOX ) high temperature stabilized phaseγ-Bi₄Ag_0.2V_1.8O_11-δ were prepared by mild hydrothermal method. The TG measurement indicated no visible change of the as-prepared powder mass. The DTA scan for the sample exhibited no thermal effects. It showed that no phase transition occurred in the as-prepared sample. The results of electrical conductivity measurements revealed that the as-prepared samples showed relatively high electrical conductivity at 700°C comparing to other reports in the literature.In summary, we developed a novel, facile, room temperature synthetic route to prepare Mn₃O₄ and Fe₃O₄ nanocrystals. The as-prepared samples showed excellent properties. This synthetic route could be considered as an economical approach to prepare transition metal oxide nanocrystals. Moreover, we extend hydrothermal/ solvothermal method to prepare Aurivillius phase Bi₂V₄O₁₁ and Ag substituted BIAGVOX compound. The electrical properties of the as-prepared samples were investigated and the results showed that they are potentially good electrolyte in the solid oxide fuel cell field.