Synthesis Of Au Functionalized ZnO Nano Composite Materials For Improved Gas Sensing Performance

As the gas sensors based on semiconductor metal oxides have the advantages of simple structure, low cost, high speed of reaction and broad scope of detection, it has been the best researched type of gas sensor and applied in various areas. Today Zinc Oxide is one of the most important semiconductor gas sensing materials. However, it still has defects like high working temperature, low response and selectivity which significantly limit its further application. The majority of traditional traditional ZnO sensors are is mainly the film or thick-film sensors that are made of powders. With the progress of synthesis of nano-technology, various morphologies and structures of ZnO nano-materials have been synthesized. The research of ZnO sensors are gradually focused turned on the nanostructures. The enhancement of gas-sensitive properties are fundamentally depending depends on the catalytic properties of materials and surface chemical characters. As result, surface modification, the reducing of the particle size and, the synthesis of multi-level structure can substantially improve the gas sensitive properties.Because of rare metals'unique catalytic activity, the performance of synergistic composite materials formed by ZnO and rare metals are supposed to own better performance than pure ZnO. This paper is aimed to improve the sensitivity and selectivity of this material and accelerate the process of response and recovery. We systematically investigate the impacts of different micro/nanostructures on the gas sensing properties of ZnO and deeply researched ZnO modified with nano Au. And in-depth study the sensing properties of ZnO modified by noble metal nano-Au. Also, this paper explains the mechanism of interaction of the various components, which provides the theoretical basis for the development of novel high efficiency and stability of sensitive semiconductor materials. The specific details of our work are demonstrated below.Firstly, we used Chemical Bath Deposition Method in near-room temperature and Hydrothermal Method to prepare forked ZnO clusters of nanorods with uniform size and regular morphology by controlling reaction condition. We systematically detect its synthesis condition, phase and optical property and use XPS, EDS technology to study its surface structure.Secondly, we modified ZnO clusters of nano-needles which were prepared by hydrothermal method with different quantities of Au nanoparticles and characterized these hybrid structures in details. We successfully obtained Au/ZnO composite materials that still maintain ZnO's structure and morphology. Detailed analyses were done on the synthase materials whose content of nano-Au are different. The close contact of Au nanoparticles and ZnO casued chemical surface modification and created a unique active sites that plays a crucial role in the whole reaction. The systematical study gas-sensing properties study of ZnO micro structures modified by Au nanoparticles composite's showed different effects related to Au nano-particles. Moreover, we systematically demonstrated the influence of Au nanoparticles on the gas sensing performance of ZnO. The results showed that Au nanoparticles have different influence on different ZnO nanostructures. When the structure is nanorads,6wt%Au nanoparticles'characterization makes Au/ZnO hybrid structure's perform highest gas sensing property. When the structure is ZnO nano-needles, the best amount of Au nanoparticles'characterization is10wt%. Characterized by Au nanoparticles, the Au/ZnO hybrid structure showed obvious improved gas sensing property in comparison of pure ZnO. Compared with commercial ZnO and, commercial ZnO modified by the same amount of commercial ZnO modified by Au, the multilevel ZnO and Au/ZnO own significantly better performance.Thirdly, we use dip-coating method in room temperature to character ZnO nanorods which were prepared by hydrothermal reaction modified with nano Au. Impregnation method at room temperature can easily formed the Au/ZnO composite materials, and the nanoparticles'size could be unique and controllableed at the same process The Au's amount is identified by EDS. Our research results indicated that when Au's size is about10-30nm, the response of materials would be significantly improved. While when Au's size is2-5nm, the gas sensing property is low, even if the Au's quantity is large. The reason is that Au has not enough contact area with ZnO and limit capacity to contain electrons, due to its small size.