Preparation Of Nano-ZnO And Al₂O₃ And The Investigation Of Their Gas Sensing Properties

Zinc Oxide (ZnO) is a multi-functional material, which has been widely applied in gas sensors, varistors, catalysts and anti-bacterial materials. ZnO nanostructured materials have many novel properties and potential applications in ceramics, electronics, optics, chemical technology and biomaterials. The gas sensing material is one of the important functional materials. Because of the large specific surface area, nanometer materials show better gas sensing properties than common materials.In this paper, ZnO nano particles have been synthesized by wet chemical processes such as gel-net processes, homogeneous precipitation method. These methods reduced the cost of the experiment and pollution of organic solvent. The properties of ZnO nanostuctured materials have been studied by XRD, SEM, TG-DTA, micro-electrophoresis apparatus etc. The XRD testing result reveals that the structure of ZnO is hexagonal wurtzite. The diameter of ZnO nanoparticles prepared by homogeneous precipitation method is about 28nm, but it is only about 14nm by gel-net method. So more minuteness particles can be synthesized by the latter method, which is a simple preparation technique for ZnO nanoparticles.The gas sensing properties were investigated at different concentration of ammonia and trimethylamine (TMA). ZnO nanoparticles have very strong ability for adsorption due to their minuteness diameter and large specific surface area. ZnO belongs to N-type semiconductor, of which resistance minishes encountering reducing gas, and largens meeting oxidation gas. The sensitivity can be calculated by different resistance value. At a certain working temperature, when the concentration of the TMA increases, the resistance of ZnO minishes, and the sensitivity augments. Al₂O₃ or SnO₂ were doped into ZnO at different weight content to form a series of side-heating electrodes, which were studied on the response to TMA. The sensor developed by 5% Al₂O₃ doped into ZnO is sensitive to higher concentration of TMA, but it is sensitive to lower concentration of TMA which developed by SnO₂ doped into ZnO.Physical adsorption theory, chemical adsorption theory and the mechanism of gas-sensing were discussed.