Synthesis,modification And Dielectrophoretic Manipulation Of ZnO One-dimensional Nanomaterials And Fabrication Of Gas Sensors

With the deterioration of the ecological environment and the urgent need for efficient and real-time monitoring of the environment, gas sensors with higher performance have been expected. How to improve the selectivity, long-term stability and response recovery speed, and how to reduce power consumption and the costs are the main challenges for the new gas sensors. Therefore, the development of noval gas sensitive materials, exploring new gas sensing mechanism and the design of devices with new structures have become an important research direction in this field. First of all, as far as gas sensing materials, metal oxide semiconductor materials are widely used at present. However, the metal oxide semiconductor often has some shorcomings like high working temperature, bad selectivity. Therefore, there are many difficulties to overcome during the development of gas sensors with strong practicability, high performance and low cost. Developmet new technologies in material science have provided us an effective way to solve the problems mentioned above. For example, the disadvantages of high working temperature and bad selectivity can be improved by the method of metal surface modification of sensitive materials. Secondly, in terms of the structures of the device, the new micro-(nano-) manipulation technology can significantly alleviate the technical difficulties and reduce the requirements in the fabrication of noval micro-(nano-) devices. In this paper, dielectrophoresis was used to manipulate one-dimensional nanomaterials in the process of gas sensor fabrication, which made the nanomaterials bridge the gaps between two sides of the electrode.In this research, ZnO nanorods were synthesized by chemical water-bath method, and gas sensing performance was tested. However, due to the drawbacks of pristine ZnO nanorods in gas selectivity, response-recovery speed and sensitivity, it is difficult to meet the needs of practical application, so it is very important to produce modified ZnO or composites. In addition, in order to take advantage of the structural merits of nano materials, it is necessary to fabricate the one-dimensional nanomaterials based devices assembled with ordered arrangement. Considering the reduction of the requirements and technical difficulties, we adopted the dielectrophoresis(DEP) technique(which is relatively simple to handle) to construct gas sensors based on ordered one-dimensional zinc oxide materials.The study can be divided into three sections:The first part: ZnO nanorods were decorated by Ag nanoparticles via photochemical deposition. In the experiment, PVP was used as stabilizer; as a result, Ag nanoparticles were attached on the surface of ZnO nanorods forming Ag/ZnO heterostucture. In addition to this, two different kinds of electrodes were used in the paper, ie La NiO3 film electrodes and Ag-Pd integrated electrodes. The results turned to that the gas sensing performance of two kinds of sensors was similar, it is indicated tha nobole metal electrode can be replaced by cheap La NiO3 oxide electrode.The second part: Cu O/ZnO hetero-structured composites were prepared via photochemical deposition on the surface of ZnO nanorods and the gas sensing performance of them was tested. Cu(NO3)2 aqueous solution with different concentrations(25μM、50μM and 200μM) were used as precursor, and the Cu O/ZnO hetero-structures were obtained by ultra-violet irradiation for some time. Afterwards, gas sensing properties were tested, results indicate that ZnO nanorods and Cu O/ZnO hetero-structured composites showed the best response to H2 S, and the optimal working temperature is at 250℃.The third part: MWCNT/ZnO hetero-structured composites were prepared during the growth of ZnO nanorods in aqueous solution and the gas sensing performance of the composites was tested at room temperature. Results indicate that the MWCNT/ZnO hetero-structured composites showed the best sensing response to NO2 at room temperature. Through adjusting the the different molar ratios of multi-walled carbon nanotubes and ZnO nanorods, the most suitable prescription of gas sensors were discussed in the experiment.