Controlled Synthesis Of Zinc Oxide With Different Morphology And Their Gas Sensing Properties

Among various metal oxide semiconductor materials, ZnO has been considered as a key technological semiconductor material due to its extensive applications in various fields, such as luminescent materials, electronics, gas sensors, water treatments, catalysts and solar cells.In gas sensing field, ZnO is one of the earliest and studied most gas sensing materials. ZnO materials have attracted considerable attention because of its non-toxicity, high thermal and chemical stability,and high electron mobility. In this paper,ZnO materials with different sizes and well-defined morphologies have been successfully synthesized by solvothermal method,SDS assisted hydrothermal route and oleylamine assisted hydrothermal approach, and the plausible formation mechanisms have also been proposed, respectively. Meanwhile, the gas sensing performance of the ZnO materials with various morphologies has also been explored in detail, respectively. The main contents are as follows:Well-defined ZnO hollow microspheres self-assembled by a mass of nanoparticles were successfully synthesized through a facile solvothermal process employing polyethylene glycol 400 (PEG 400) as solvent, zinc acetate dehydrate as zinc source, urea as alkali source. ZnO hollow sphere has a mean diameter distribution of about 5?m. The thickness of ZnO hollow spheres shell is about 1.0 ?m. The size of ZnO nanoparticles is about 80 nm. The architecture of ZnO hollow microsphere is quite dense. Furthermore,the plausible formation mechanism of ZnO hollow microspheres has also been analyzed. It was described as formation of ZnO nanocrystal, self-assembly, Ostwald ripening, and crystal growth process. PEG 400 played a crucial role as a nonionic surfactant in the formation of the ZnO hollow spheres. Meanwhile,the bubble of carbon dioxide and excess ammonia, generated through the thermal decomposition of urea during the solvothermal process, was also very important.Flower-like ZnO architectures self-assembled by numerous ZnO nanosheets have been successfully prepared via a facile sodium dodecyl sulfate (SDS) assisted hydrothermal route.The flower-like structure is relatively loose. Flower-like ZnO architecture has a mean diameter distribution of about 7 ?m, and the thickness of nanosheet is about 50 nm. In addition, the effects of experimental conditions on the morphology of products have been studied, such as surfactant dosage, reaction temperature, and reaction time. Furthermore, the plausible formation mechanism of the flower-like ZnO architectures has also been proposed.It was described as nucleation, growth, self-assembly and calcination. Based on analysis of morphology and structure, we learned that SDS played an important role as the surfactant in the formation of the flower-like ZnO architectures.Spindle-like ZnO products with a width of about 230 nm and length of about 460 nm have been successfully synthesized by a facile oleylamine assisted hydrothermal approach,using zinc acetate dehydrate as zinc source, hexamethylene tetramine (HMT) as alkali source,oleylamine as surfactant, ethanol-water (volume ratio was 1) mixture as solvent. The possible formation mechanism of the spindle-like ZnO architectures was described as nucleation and crystal growth process. Oleylamine and solvent played vital roles in the formation of the spindle-like ZnO architectures.The gas sensing performance of ZnO hollow microspheres, flower-like ZnO structures and spindle-like ZnO architectures has been investigated carefully. The results indicated that the ZnO products with different morphologies exhibited a good selectivity,high stability and repeatability, fast response and recovery characteristics to ethanol vapor, respectively.However, the spindle-like ZnO architectures with the smallest dimension exhibited the best gas-sensing properties, such as the highest sensitivity, the shortest response and recovery time,the lowest working temperature. The gas sensing performance of flower-like ZnO products with loose architectures was relatively low. The gas sensing performance of ZnO hollow microspheres with dense structures was least. Therefore,the morphology,size and structure of materials have a vital influence on the gas-sensing properties of the ZnO products. The more loose structure, the smaller dimension, the gas-sensing properties of the products are better.