| ZnO nanomaterials are the most promising function material for gas sensor. It is an inevitable development trend to achieve multi-functional device for gas sensor. The electronic nose can achieve multi-gas detector, but it has some disadvantages like complex circuits, the high failure rate etc. Large-area patterned ZnO sensing material preprated in a controlled manner can not only solve the above shortcomings, but also optimize the performance of gas sensor. Various micro-patterning methods, such as nanoimprint, deposition, lithography and conventional ink-jet printing, do not meet the low-cost feature and the universality of gas sensor. These methods are limited by high temperature treatment, high vacuum system, complex process, low-resolution pattern, needing a mask/mold or expensive equipments. Patterned hierarchical ZnO nanorod arrays (ZnO-NAs) are preprated by mechanoelectrospinning-assisted continuous hydrothermal method, and the gas performance of ZnO-NAs has been characterized and optimized in this thesis. The main research work and contributions of the dissertation are as follows:The effects of material and process parameters, including molecular weight, concentration, applied voltage, electrode spacing and diameter of nozzle, are experimentally investigated. Theose parameters would affect the morphology and consistency of electrospun polyoxyethylene fibers. The controllability of electrospinning process is improved. Mechanoelectrospinning (MES) has been proposed based on traditional electrospinning and near field electrospinning. The liquid jet in MES is pulled by the combination of electrical field force and tunable mechanical drawing force. It leads that MES have high positionability and direct-write high-resolution patterns. The electrical field is utilized to generate Talyor cone which the jet is pulled from, also acts as part of drawing force to pull the jet. The mechanical drawing force is derived from the motion stage and tuned by the velocity of the motion stage, so the diameter of the jet can be controlled.Mechanoelectrospinning-assisted continuous hydrothermal method is proposed to direct-write the precursor patterns for growth of ZnO-NAs, in a digital, low-cost, and mask-free manner. It is a facile and repeatable two-step process. Firstly, the ZnO seed precursor solution is direct-written by mechanoelectrospinning. Secondly, the hydrothermal method is adopted to fabricate ZnO nanorod arrays. The diameter, interval, orientation and distribution of ZnO nanorods can be tuned proactively by changing growth time, solution concentration, the nature of precursor layer, and the pattern for MES.ZnO-NAs can be utilized as gas sensors. The morphology and distribution of hierarchical ZnO nanorods, having a tremendous impact on gas response, are determined by the process parameters of MES-CHSM. ZnO-NAs exert excellent Ohmic contact with interdigital electrodes. Gas sensing results show highly sensitive and repeatable response-recovery cycles. The dynamic response of gas sensor shows temperature-dependent response to NO2. The best gas response is located between 200? and 225?. Gas sensors, prepared by different process parameters, show two laws between the corresponding responses and NO2 concentrations:approximately linear and saturation regions. The optimal process parameters are presented to postpone the occurrence of saturation region, to enlarge measuring range.Hierarchical Ag/ZnO nanorod arrays are prepared by MES-CHSM and photoreduced method. Ag+ is successfully photoreduced as Ag nanoparticles on the surfaces of ZnO nanorods. Ag nanoparticles have enhanced gas sensing performance. The gas sensing performance of hierarchical Ag/ZnO nanorod arrays is related with the photoreduction time. Ag/ZnO nanorod arrays with photoreduction time of 30 min achieve the best gas sensing response. The beneficial influence of Ag nanoparticles on the gas sensing performance has been analyzed. |
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