Functional Modulation Of Composite Transition Metal Oxide Nanoparticles

Transition metal oxides possess abundant physical and chemical properties,which can be attributed to their variety of valence states and electronic configurations.Moreover these materials with nanostructures have more unique properties.Therefore,transition metal oxide nanomaterials have extremely wide application prospects in many fields such as electronic devices,catalysis,sensors,magnetic storage,energy storage,etc.Meanwhile,it have provoked considerable attention from many experts and scholars around the world.However,nanoparticles are easily affected by chemical bond forces,hydrogen bond forces,capillary forces,and intermolecular forces to agglomerate.As a result,to obtain monodisperse and uniform transition metal oxide nanoparticles in the matrix are still a very difficult challenge that we have to face.Recently,the author found that the transition metal oxide nanoparticles embedded in the solid matrix can avoid the agglomeration of nanoparticles.What is more,the embedded nanoparticles were subjected to the strain imposed by the surrounding matrix materials during their growth.This strain will not only affect the microstructure and physicochemical properties of the transition metal oxide nanoparticles in the matrix,but also greatly change the magnetic properties of the materials.Although transition metal oxide nanomaterials have been studied extensively for many years,the magnetic performances of the composite nanomaterials are related to the elements composition,morphology structure of the material itself as well as the size and so on,and the effect of strain on it is particularly important.So the controllable modulation of the magnetic properties of the material is still of great importance.Transition metal oxides,on the other hand,as a type of predominant gas sensing material,have attracted huge interest because of their low cost,excellent electrical properties and controllable preparation.Nowadays,many studies have reported that the gas-sensing properties of transition metal oxides can be improved by the creation of heterojunctions,which can provide tunable morphologies and compositions.However,the gas-sensing processes of composites that contain gas diffusion,gas reaction,and signal transformation still need to be further improved.In this thesis,composite nanomaterials made of two transition metal oxide nanomaterials（ZnO and Co₃O₄ nanorods）that were prepared into hedgehog-like composite nanomaterials with excellent gas-sensitive properties,showed excellent gas sensitivity,high responsiveness and high selectivity to ethanol.The authors prepared Fe₃O₄ nanoparticles,Fe₂O₃ nanoparticles and BiFeO₃ nanoparticles embedded in Al₂O₃ matrix by pulsed laser deposition and rapid thermal annealing.ZnO nanorods immobilized on the surface of Co₃O₄ nanospheres,namely ZnO/Co₃O₄ composite nanomaterials,were prepared by epitaxial growth method.These samples were characterized by means of transmission electron microscopy,scanning electron microscopy,X-ray photoelectron spectroscopy,X-ray diffraction,Raman spectroscopy,photoluminescence,and comprehensive physical property measurement systems.The strain field distribution of these transition metal oxide nanoparticles embedded in the Al₂O₃ matrix was simulated by the finite element method.The gas sensing properties of ZnO/Co₃O₄ composite nanomaterials were comprehensively tested by gas sensing instruments.And all experimental data are summarized and analyzed in the end.By analyzing the effects of experimental conditions on strain action,the author reveals the scientific mechanism of strain action.At the same time,we further studied the mechanism of strain-modulated magnetism and light-modulated magnetism by exploring the effect of strain on the size,lattice structure,surface effect and energy band of composite transition metal oxide nanoparticles.Meanwhile,through the study of gas sensing properties of composite transition metal oxide nanomaterials,the influence of the nanomaterials morphology on gas sensing properties was explored.These research works above provide a new idea for the functional modulation of materials,and also provide a very significant guiding role for us to explore the physical and chemical properties of composite transition metal oxide nanomaterials.