| Increasing attention had been paid to the new styles of nanoscale structures with various application in the field of material, physics and chemistry, due to the unique properties and considerable potencial of the microporous nanostructures and quantum dots. Transition metal oxides had attracted a lot of attention because of their potential applications as magnetic storage device, catalyst, battery cathodes, gas sensor materials, and so on. The design and preparation various new-style nanostructures of transition metal oxides with magnetic and optical properties would make it possible to beat the superparamagnetic limit and find the new catalyst. In this thesis, the synthesis, characterization, magnetic and optical properties of the transition metal oxides (CoO and NiO) with new-style nanostructures were investigated.CoO microporous nanoparticles with tunable particle sizes were obtained by one-pot synthetic technique using a single cobalt precursor without extra surfactant-templates in a mild temperature organic solution. It was found that the CoO microporous nanoparticles were formed through the early CoO nanocrystal nucleus growth on byproduct gas as template. All samples had micropores with the average size about 1 run. Varied molar ratio of Co(acetylacetonate)3 to oleylamine were used to prepare nanoparticles with particle sizes tunable from about 13 to 50 nm in diameter, which makes it possible to further study the variety of physical and chemical properties of CoO microporous nanostructure.The optical, photocatalysis and magnetic properties of CoO microporous nanoparticles were deeply investigated. It was found that the spectral absorption characteristics of CoO microporous nanoparticles produced fundamental change in nanometer size. First of all, in the visible region, the absorption wavelength of samples were less than the bulk CoO, and with the decrease of particle size, sample absorption wavelength became shorter, i.e. blue shift phenomenon. Secondly, in the ultraviolet region, a new spectral absorption was found; The self-assembled nanoparticle film with hierarchical pore structure were used to study the photocatalytic activity. It was found that samples with smallest particle size had the best photocatalytic performance; CoO microporous nanoparticles exhibited ferromagnetism and exchange bias effect at low temperatures. And this observed exchange bias effect was explained in terms of the exchange interaction between the antiferromagnetic core and the ferromagnetic shell.Organic solution-phase reaction under oxygen atmosphere for synthsis of single crystalline and uniform sub-3 nm NiO quantum dots had been developed. Larger NiO nanoparticles with diameter about 26 nm could be also prepared by seed-mediated growth method. Optical property of the NiO nanoparticles was conducted by means of UV-vis spectrum, exhibiting obviously blue shift compared with the bulk counterpart due to the quantum confinement effect. The photocatalytic activity in degradation of rhodamine B was also investigated. The results showed that the sub-3 nm NiO quantum dots exhibited much higher activity for UV-photodegradation than the as-synthesized larger NiO particles and commercial 30 nm nanopowder.The low temperature magnetic properties, exchange bias effect and training effect of sub-3 nm NiO quantum dots were systematically investigated. It was found that the uncompensated spins in the surface part of the quantum dots exhibited ferromagnetism or spin-glass like behavior at low temperatures. The observed exchange bias effect could be attributed to the exchange coupling between the ferromagnetic spins and spin-glass like phase. Moreover, consecutive hysteresis loops at 10 K exhibited that the HEB and He decrease with magnetic field cycling, which was defined as the training effect and showed that there were two different reversing mechanism in the ferromagnetic phase. |
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