Study On Gas Sensing Properties And Mechanism Of Multi Dimension Assembly SnO₂

In type metal oxide semiconductor gas sensor played a huge role in the field of prevent the fire explosion accident, atmospheric environmental testing as well as the industrial production of poisonous and harmful gas detection. However, at present the development of semiconductor gas sensitive material is still obvious deficiencies in selectivity, stability and other aspects, therefore, the research and development of new high performance gas sensors will have very important realistic meaning and practical value. In the study of gas sensors, many research focus on development of new gas sensitive material, in order to improve the sensor performance. Because of the different aspects of gas-sensing mechanism is not clear, the lack of a universally applicable air sensitive sensitive mechanism, therefore poor selective, weak stability problems are difficult to solve.This work selects the multidimensional assembly of nanometer gas sensitive SnO₂ nano materials asthe research system. As the most important oxide gas sensitive material, SnO₂ has been accepted widely attention all over the world.In this paper, Weprepared zero-dimensional, one-dimensional and two-dimensional assembly of nano SnO₂ powder materialsrespectively, andinvestigatedtheir gas-sensing properties under different working conditions.Based on the First-principlestheory, we calculated the SnO₂ surface atomic structure and gas adsorption performance. And then we put forward the gas-sensing mechanism inculdingoxygen adsorption and non-oxygen adsorption model to reveal the essence sensing effectof SnO₂. Phenomenon of experiment are analyzed from the the electronic structure viewpoint, verify the feasibility of two kinds of gas adsorption model.The main results obtained in current work are as follows:?1?We successfully obtained three different morphology of zero dimensional SnO₂ nanomaterials, and the growth mechanism of different morphology and gas properties were analyzed.Under the hydrothermal process, we select SnCl4?5H2O, NaOH, citric acid, SDS, Zn?Ac?2, Na2SnO3, ethanol and deionized water as raw materials. Different zero dimensional morphology of SnO₂ nanomaterials can be obtained throughcontrolling of reaction conditions. Solid spheres and the hollow sphericalcan by prepared under different ratio of SnCl4?5H2O, anhydrous ethanol, deionized water, and NaOH. Topography SnO₂ nano materials can be obtained by adding the amount of active agent; Change the surfactant SDS, square block SnO₂ nano materials can be produced; Growth mechanism of SnO₂ morphology were proposal in detail under different conditions of experiment; The samples of topographySnO₂ show excellent gas-sensing properties, which may be widely applicated in the future.?2?We mainly discussed three kinds of one-dimensional SnO₂ nanomaterials by self-assembly to form a different spatial structure and its gas sensing performance. We found that the one-dimensional SnO₂ nano material show gas sensing performance. In addition, one-dimensional SnO₂ self-assembly structurecan be obtained through the different hydrothermal temperature, hydrothermal time and different surface active agent.This method is economic, simple and effective, which are benifited for the wide application of gas sensing materials. Different structure of SnO₂ material will show different gas sensing performances. More open porous structure, fewer connecting points, lower barrier can greatly improve the gas-sensing properties of one-dimensional assembly SnO₂ materials. Change in microstructure to improve the gas sensing performance,which are also has guiding significance.?3?We prepared flake nano flowersbyone step hydrothermal methodand its petal thickness can be controlled accurately by controlling the amount of NaOH. With nanometer thickness thinning, the specific surface area of nano piece and defects will increase, which will significantly improve the gas-sensing performance of SnO₂. In addition, we found that gas sensing performance of the sensors prepared bythree kinds of two-dimensionalaccemble to three-dimensional SnO₂ materials are follow order as: blooming < half blooming<mesoporous half blooming flowers. This can be attributed to a sufficient number of gas diffusion, rather than the speed of spread, and puts forward the effective for oxygen vacancy density in terms of the number of donor states gas-sensing mechanism. Comprehensive the above two groups, SnO₂ can form the structure of the nano flake flowers, mainly because of orientation adsorption and corrosion. Nano trailers have superior performance, but we still hope to be able to further enhance its gas sensing performance.?4?We measure the gas sensing property of different SnO₂ materials under atmospheric environment and vacuum conditions respectively. The gas sensor show similar performance under two condiction. This means the gas sensing precess of SnO₂ may not be depended on oxygen adsorption only. Calculation results also proved this conclusion. Hydrogen molecules can directly react with SnO₂ surfaceandthis reaction can produced electron exchange between the H atom and surface bridge oxygen. At the same timea electron transfer path will be formed between H and O. Electron transfer process so as to realize the gas sensitive response. So, for the gas-sensing mechanism of SnO₂, there should be two ways, namely the surface oxygen adsorption gas molecules and after adsorption oxygen to produce electronic exchange; Another kind is a gas molecule with SnO₂ surface atoms produced electronic exchange directly.In the current work, we study the gas sensing properties and growth mechanism of zero dimensional, one dimensional and two dimensional assembly of nano SnO₂. We proposal oxygen adsorption and non oxygen adsorption modelduring gas sensing process.