| Zinc oxide(ZnO)is often widely used as a gas sensing material because of its high carrier mobility and easy modification at room temperature.However,intrinsic ZnO have some disadvantages including the high operating temperature,low response value and poor selectivity etc.Interestingly,the multi-component metal-doped synergistic low-dimensional nanostructure can substantially improve the adsorption and recognition of target gas molecules.In this paper,ZnO nanosheets,ZnO rod-like nanoflowers,ZnO sheet-like nanospheres and ZnO/r GO nanocomposite structures are prepared using the hydrothermal method.They are doped and modified by noble metals Au and Pt,and the effects of microstructure morphology,crystal structure and components of the samples on the selectivity and response sensitivity of various gases are investigated,and the corresponding gas-sensitive mechanisms are discussed and explained.The main contents are as follows:(1)ZnO nanosheets/r GO composite nanostructures are synthesized by hydrothermal methods.When r GO is introduced into the synthesis system,the thickness of ZnO nanosheets is decreased while the number of channels and pores on the surface of the nanosheets is increased,which provides more active sites for gas adsorption.As prepared ZnO/r GO gas sensor show a response value of 277 for 100 ppm ethylene glycol at 220 °C,with a detection limit as low as 1 ppm.After the surface modification of ZnO/r GO by using noble metal Au,it is found that the response value to ethylene glycol gas is as high as 330.226,which is about1.2 times higher compared with ZnO/r GO.The selectivity and response recovery is improved,and the corresponding gas-sensitive mechanism is explored.(2)Au-modified ZnO rod-like nanoflower structures are prepared.Scanning electron microscopy(SEM)morphologies show that the nanoflowers are made of multiple hexagonal ZnO nanorods grown in a staggered manner and radiating from the center to the surrounding space.The gas sensitivity test results indicate that the gas sensor assembled with this nanocomposite structure had good response performance to ethanolamine gas at 100 ppm,with a response value of 138.27 at an operating temperature of 210 ℃.The response and recovery time is 15 s and 34 s,respectively,and a lower detection limit as low as 1 ppm.We propose that the modification of Au nanoparticles enables the construction of rich electron localized transport channels between the scattered ZnO nanorods,which effectively enhances the chance of free electron interaction with the target gas molecules adsorbed on the active sites on the nanorod surface.(3)The structures of noble metal Pt-doped ZnO nanospheres are synthesized in combination with hydrothermal method.The microstructure morphologies show that the nanospheres are composed of nanosheets interspersed layer by layer and stacked self-assembled to form a regular and ordered nanosphere structure with large and spherically intact gaps between the sheets and a large specific surface area.The gas-sensitive performance displays that the Pt-doped ZnO nanosphere assembled gas-sensitive sensor has a high response value of 310.74 for 100 ppm of ethylene glycol gas at an optimal operating temperature of210 °C,and the response and recovery time is 45 s and 14 s,respectively,with a lower detection limit of 1 ppm.The noble metal Pt not only increases the number of oxygen negative ions adsorbed by the sensor,but also rapidly enhances the reaction rate with the target gas,which is conducive to improving the response sensitivity of the sensor. |
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