Controlled Synthesis And Characterization Of ?-Fe₂O₃ And CoO Nanomaterials With Hierarchical Structure

Transition metal oxide nanomaterials have attracted a great deal of attention because of their wide range of applications.The aggregates constructed by nanostructure unit show unique physical and chemical properties which different from the block materials.In this work,the controlled synthesis of Fe,Co oxides hierarchical nanomaterials was investigated through a simple solvothermal method.The reaction mechanism and the gas sensing or electrochemical properties of the samples were also studied in detail.This research work mainly includes the following three contents:1.A series of controlled single-crystal ?-Fe2O3 hollow nanostructures have been synthesized via a simple one-pot solvothermal synthesis.With the amount of NaAc increased,the shell thickness of hollow spheres decreases till the hollow structures disappeared and changed to nanoflower aggregates.Reaction temperature and solvent ratio also play important roles in the synthesis of hollow nanospheres.The gas sensing properties indicated that all samples exhibited good sensitivities towards acetone gas,and the gas sensing performance was related to the morphologies and the specific surface area of the samples.Hollow spherical structure has better sensitivity than nanoflower structure(12.0 vs 10.1).2.A series of ?-Fe2O3 aggregates have been prepared via a simple solvothermal method and sequential calcinations using mixtures of inorganic salts and HMTA in solvents.Various hierarchical structures can be controlled synthesized by changing the chain length and the polarity of solvents.The gas sensitivity experiment indicates that all samples show good sensitivity for acetone gas.As to 1000 ppm of acetone gas,the maximum sensitivity is up to 31.73.The gas sensitivity has been greatly influenced by the specific surface area,pore size distribution and morphology of the samples.3.Octahedral CoO nanostructures with average size of ca.500 nm were synthesized by a simple,environmentally friendly method using inorganic salts in mixtures of alcohols.By changing the cobalt source can be obtained the distorted octahedral CoO(average size of ca.100 nm).Hysteresis loop line shows the products,octahedral CoO nanostructure and distorted octahedral CoO nanostructure,are corresponded to antiferromagnetic,and the different magnetization can be related to the different microstructures of the samples.When the magnetic field strength is 80 kOe,the magnetization for those nanostructures is 5.6 and 4.9 emu/g,respectively.The electrochemical properties show that the distorted octahedral CoO materials behave higher activity of oxidoreduction,as a result of the lower charge transfer impedance and faster electronic transmission compared to the octahedral CoO.