| In recent years, researchers pay more attention to the preparation of large sized LDHs with high crystallinity and well-defined hexagonal shapes, especially in the transition metal LDHs materials. LDHs materials not only have specific physical and chemical properties, which result in their wide applications in magnetism, catalysis, electro-and photoactive materials, and so on, they but also can be delaminated into their elementary nanosheets, and the obtained nanosheets with large size and regular morphology are regarded as a building block to create other new functional nano-materials. Because large sized Fe3+-based LDHs materials with high crystallinity and well-defined hexagonal shapes have more unique features in the optical, electrical and magnetic fields, the research on their preparation and application attracts more attention for researchers.In this work, high crystallized Ni2+-Fe3+ layered double hydroxide material with large size up to 4μm and regular morphology is prepared via a topochemical approach by using urea as hydrolysis agent, a-type Ni2+-Fe2+ hydroxide with micrometer size and hexagonal shape is firstly prepared, and then a-type Ni2+-Fe2+ hydroxide material is oxidized by iodine in chloroform to be transformed to Ni2+-Fe2+ LDHs material. The effects of the reaction time, total metal ion concentration and the amount of urea on the particle size and morphology of the obtained a-type Ni2+-Fe2+ hydroxide are investigated.The main works are as follows:(1) Topochemical synthesis of large sized Ni2+-Fe3+ layered double hydroxide material with high crystallinity and well-defined hexagonal shapesBy using urea as hydrolysis agent, NiCl2·6H2O and FeCl2·4H2O as raw materials and mannitol as a stabilizer, a-type Ni2+-Fe2+ hydroxide with micrometer size and hexagonal shape is firstly prepared, and then a-type Ni2+-Fe2+ hydroxide material is oxidized by iodine in chloroform to be transformed to Ni2+-Fe2+ LDHs material via a topochemical approach. The effects of the reaction time, total metal ion concentration and the amount of urea on the particle size and morphology of the obtained a-type Ni2+-Fe2+ hydroxide are investigated. The optimal formation parameters of a-type Ni2+-Fe2+ hydroxide with large size up to 4μm and regular hexagonal shape are the reaction time of 10 h, the total metal ion concentration of 10 mM, reaction temperature of 90℃, and the molar ratio of 50 for urea amount to the total metal ion concentration. Fe (П) chemical state for the precursorα-type Ni2+-Fe2+ hydroxide can be oxidized into Fe (Ш) one in Ni2+-Fe3+ LDHs material in an I2/CHCl3 solution, which can not cause no obvious change in crystallinity, morphology and size before and after the oxidation process.(2) Large sized Ni2+-Fe3+ layered double hydroxides with high crystallinity and well-defined hexagonal shapes is synthesized by a hydrothermal treatment technologyBy using urea as hydrolysis agent, NiCl2·6H2O and FeCl2-4H2O as raw materials, a-type Ni2+-Fe2+ hydroxide with uniform morphology via a hydrothermal treatment method The effects of the reaction time, total metal ion concentration and the amount of urea on the particle size and morphology of the obtainedα-type Ni2+-Fe2+ hydroxide are investigated. The optimal formation parameters of a-type Ni2+-Fe2+ hydroxide with size up to 2-3μm and regular hexagonal shape are the reaction time of 24 h, the total metal ion concentration of 10 mM, and the molar ratio of 5 for urea amount to the total metal ion concentration, the size of Ni2+-Fe2+ LDHs is 1-2μm. Because the reaction system must be kept under N2 inert atmosphere, thus the method is difficult to synthesize a-type Ni2+-Fe2+ hydroxide with large size and high crystallinity.(3) Research on the physical-chemical properties of large sized Ni2+-Fe3+ LDHs material with high crystallinity and well-defined hexagonal shapeThe thermal stability, surface property, and capacitance of large sized Ni2+-Fe3+ LDHs with high crystallinity and well-defined hexagonal shapes are investigated. The research results show that the layered structure of large sized Ni2+-Fe3+ LDHs with high crystallinity and well-defined hexagonal shape can be remained to 200℃, and the layered structure is collapsed above 300℃.The large sized Ni2+-Fe3+ LDHs with high crystallinity and well-defined hexagonal shape is caicined at 300℃, and the obtained material has the largest BET surface area. The BET surface area and the average pore of the obtained materials are dependent on the calcination temperature. Ni2+-Fe3+ LDHs material shows poor capacitance in alkaline electrolyte, and the capacitance decline in lithium acetate solution as the scan rate increases. |
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