Research On Controllable Preparation, Microstructure And Physicochemical Properties Of Metal Oxide Nano-semiconductor Materials

As an important functional material,metallic oxide nanomaterial has good optical,electrical,thermal and mechanical properties,which demonstrates extensive application prospects in many areas such as solar cells,catalysis,sensors,and magnetic storage media.The chemical and physical properties of materials depend greatly on their morphology and microstructure,thus it is necessary to correlate properties with morphology and microstruture of metallic oxide nanomaterials.In this thesis,preparation,microstructure,physical and chemical properties of metallic oxide nanomaterials are systematically investigated.In Chapter 1,the preparation,physical and chemical properties,application fields of metallic oxides nanometerials are reviewed.In addition,the photocatalytic and humidity-sensing properties of nanomaterials are introduced in details.In Chapter 2,we use vacuum annealing to reduce the ?-Fe₂O₃ nanoblades and obtain reduced ?-Fe₂O₃ nanoblades with various defects including oxygen vacancies,dislocations and dense pores.Under the same experimental conditions,reduced ?-Fe₂O₃ nanoblades have higher photocatalytic degradation efficiency compared with ?-Fe₂O₃ powder and nanoblades.We demonstrate that defects can reduce the recombination of electrons and holes and accelerate the decomposition of the rhodamine B.Thus reduced ?-Fe₂O₃ nanoblades can significantly enhance the photocatalytic degradation efficiency.In Chapter 3,we synthesized SnO₂ nanostructures with different morphologies including three-dimensional?3D?hierarchical SnO₂ dodecahedral nanocrystals?DNCs?,3D hierarchical SnO₂ nanorods and SnO₂ nanoparticles through hydrothermal process,and studied the performance of the humidity sensors based on different SnO₂ nanostructures.Interestingly,the 3D hierarchical SnO₂ DNCs show excellent humidity-sensing performance including fast response and recovery times,narrow hysteresis loop,high sensitivity and good stability due to the unique 3D open structure and high chemical activity of the exposed {101} facets.In Chapter 4,two modulated structures were investigated by high-resolution transmission electron microscopy in ?-Fe₂O₃ nanowires.These two superstructures were produced by introduction of oxygen vacancies on every tenth?30???0?plane and every sixth?11???0?plane.The atomic ratios of Fe and O?Fe/O?are 0.7407 and 0.7273 in the nanowires with oxygen-vacancy ordering,respectively,which are very close to that of Fe₃O₄.Electron energy-loss spectroscopy studies show that the Fe/O ratio of nanowires will be close to that of Fe₃O₄ when the oxygen pressure is not sufficient,which makes the nanowires energetically favorable.