Synthesis And Gas Sensing Properties Of Metal-oxide Semiconductor Composite Nanostructure

With improvement of technology, people have more and more understanding ofthe microworld. Nanomaterial and nanocomposite have attracted great attention dueto their unique physicochemical property and potential application in some fields.Recent years, the development of nanotechnology injected new elements for theresearch of sensing material and designing of the microstructure in the gas sensingfield. Nanocomposite has a wide application prospects in gas sensing field, because itcan make the advantages of different physical and chemical properties of pure phasematerial rolled into one. Meanwhile, different materials have different catalyticactivities for different gases. The response and selective properties of the sensingmaterial can be improved by changing the component of the composite. In our paper,with the target of improving the gas sensing properties of the metal oxidesemiconductor sensing material, based on regulatory of interface, research therelationship between the structure and composition of nanomaterials and the gassensor performance by preparing the composite materials, heterostructure materialand one-dimensional heterostructure materials. Study the sensing mechanism ofimproving the gas sensing properties by heterostructure materials in deep. Providenew research direction for improving the sensing properties of the semiconductoroxide gas sensor. The main contents are as follows:(1) Using the hydrothermal method for preparing SnO2, ZnO and Bi2WO6hierarchical materials. Changing the microstructure of the materials by tuning thereaction condition. Study different nanostructures for the influence of gas sensingproperties. For SnO2nanomaterials, SnO2nanosheets exhibit better sensing propertiescompared with the other two nanostructures. The better properties were attributed totwo aspects. One is that SnO2with low dimension has a higher surface area compared with the body material or aggregate material. The other is well-aligned structures forthe effective gas diffusion which make SnO2nanosheetd have fasterresponse-recovery speed. The same conclusion also applies to hierarchical ZnOnanostructure and curling-like Bi2WO6nanostructure. These two materials haveexcellent sensing properties for acetone and ethanol gases, respectively;(2) In order to improve the response and selective properties for the purematerials, we study the impact of composite materials on the gas sensing properties.In the light of the composition of sensitive materials and structures, we prepare theNiO/SnO2polyhedron and hollow spheres. And then test the gas-sensing properties ofethanol and ammonia gas, respectively. Comparing with the pure materials, NiO/SnO2has better sensing properties. At the same time we further analysis the sensingmechanism of composite materials. The mechanism of the improvement sensingproperties for NiO/SnO2is that Ni2+has an empty3d orbital, so oxygen has thepreferred adsorption orientation, and it also has activation function to reduction gas.So the introduction of NiO will not only increase the amount of absorbed oxygen, butalso decrease the activation energy of catalytic oxidation, which would decrease theresponse time of the gas sensor. Furthermore, the BET value of NiO/SnO2hollownanosphere was40.3m2g1, which makes it has a higher response and faster responseand recovery speed compared with the solid sphere.(3) We introduce the noble metal oxide PdO to the sensing material surfaceformed heterostructure (PdO/ZnO、PdO/NiO). Continue to develop the impact ofcomposite materials on the gas sensing properties. Compared with the pure ZnO andNiO, PdO/ZnO, PdO/NiO have a better sensing properties. This is because by theassistance of PdO, oxygen moleculescan be more easily adsorbed on the surface. Thisprocess increases both the quantity of adsorbed oxygen and the molecule-ionconversion rate resulting in the greater and faster degree of electron depletion. Thus,the response of the PdO-decorated is distinctly higher than that of the pristine one.(4) Using the electrospinning technology combined with hydrothermal method toprepare one-dimensional heterostructure materials ZnO/TiO2and one-dimensionalhierarchical branched herostructure materials α-Fe2O3/TiO2. And study their gas sensing properties. Then research the gas sensing mechanism of one dimensionheterostructure used in gas sensing field. For one-dimensional hierarchical branchedherostructure materials α-Fe2O3/TiO2, there are two aspects for the enhanced sensingproperties. First, it can be explained that α-Fe2O3/TiO2heterostructure generates anenhanced charge separation at the interface between the α-Fe2O3nanorods and TiO2nanofibers, resulting in the enhanced conductance modulation. For the secondpossible sensing mechanisms, the potential barriers are formed at junctions betweennanofibers, making it modulating for the electrons to travel between adjacentelectrodesIn this paper, we systemically studied the relationship between the structure,combination, size of the nanomaterial and the sensing characteristic through the abovefour parts. Further study of the nanocomposites sensing mechanism. Provide a newtrain of thought for the development of gas sensing materials.