Fabrication And Gas Sensing Properties Of Zinc Stannate Based Semiconductor Materials

Gas sensors are a kind of device that detect the type and concentration of gas.It has been widely used in civil,industry,environmental monitoring and so on.The semiconductor based gas sensors have become a hot spot in the area of gas sensors due to their simple structure,low cost,good sensing properties and high reliability.To deal with increasingly complex requirements of gas monitoring,people realize a need to fabricate high-performance gas sensors,and the core issue of which has a lot to do with the design and preparation of new sensitive materials.In recent years,multiple metal oxides(compounds)have been synthesized with the development of nanotechnology and chemical synthesis technology,which possess the advantages of special crystal structure,abundant defects states and controllable chemical composition,becoming very potential sensitive materials.Thus this thesis selects zinc hydroxystannate[ZnSn(OH)₆]and zinc stannate(ZnSnO₃)material as the research objects,and prepares them into the gas sensors to monitor a variety of Volatile Organic Compounds(VOCs).By regulating the microstructure,constructing heterogeneous structure and modifying precious metals,the gas sensing properties of ZnSn(OH)₆and ZnSnO₃based sensors including response value,operating temperature,response/recovery speed have been enhanced.In addition,the mechanism of the improvement on gas sensing properties has been systematically analyzed.The specific research contents are as follows:1.The shell numbers of ZnSn(OH)₆ hollow cubes were accurately controlled by adjusting the steps of“co-precipitation and alkali etching”,and single-,double-and multi-shelled structures were synthesized.The tests of gas sensitive characteristics showed that the sensing performance improved with the increase of shell numbers.The response value of multi-shelled ZnSn(OH)₆based sensor was 56.6 to 100 ppm of formaldehyde at 60^oC,which was 5.3 times and 2.5 times that of single-and double-shelled ZnSn(OH)₆based sensor,respectively.Meanwhile,its response and recovery time were 1 s/89 s,which were better than that of single-(11 s/131 s)and double-shelled(5 s/125 s)ZnSn(OH)₆based sensors.Furthermore,multi-shelled ZnSn(OH)₆based sensor had good selectivity and repeatability to formaldehyde.The enhanced sensing performance was due to the formation of multi-shelled hollow structure.In addition,the oxygen defect in the material was also the reason why the sensor had a low operating temperature.2.Three ZnSnO₃ hierarchically porous structures were synthesized by using the biotemplates.The tests of gas sensitive characteristics showed that the response/recovery time of ZnSnO₃-1,ZnSnO₃-2 and ZnSnO₃-3 based sensors was 2s/8 s,1 s/10 s and 2 s/20 s to 100 ppm of formaldehyde at 240^oC,respectively.Such a fast response and recovery speed are conducive to realize the real-time monitoring of formaldehyde by the sensor.In addition,three ZnSnO₃based sensors also showed good repeatability,long-term stability and anti-humidity properties.The formation of hierarchically porous structure was the key to the excellent performance of the sensor.3.A flower-like ZnSnO₃/Zn₂SnO₄ heterostructure was designed and synthesized,which was assembled by the ZnSnO₃nanosheets and Zn₂SnO₄nanowires.By studying the effect of reaction time on its microstructure,the growth mechanism of flower-like heterostructures was obtained.The tests of gas-sensitive characteristics showed that the response value of ZnSnO₃based sensor was 3.3 to 20 ppm of phenylamine at 300^oC,while the response value of ZnSnO₃/Zn₂SnO₄based sensor was 12.1 to 20 ppm of phenylamine at 260^oC,which was 3.7 times than that of the pure ZnSnO₃based sensor.The ZnSnO₃/Zn₂SnO₄-based sensor showed fast response/recovery time(1 s/20 s)and low detection limit(50 ppb).At the same time,the sensor had good anti-humidity properties,repeatability and long-term stability.The improved sensing performance was due to the formation of flower-like hierarchical structure and ZnSnO₃/Zn₂SnO₄n-n heterostructure.4.The ZnSnO₃ hollow cubes were designed and prepared,and different amounts of NiO nanosheets were modified on their surface to form ZnSnO₃/NiO heterostructures.The tests of gas-sensitive characteristics showed that the sensing performance of three ZnSnO₃/NiO based sensors was significantly better than that of the pure ZnSnO₃based sensor,and the sensing performance was the best when the molar ratio of Zn to Ni was 2:1.Specifically,the responses of the ZnSnO₃/NiO-2based sensor was 70.6 to 100 ppm of triethylamine gas at 220^oC,which was 6.1 times than that of the pure ZnSnO₃based sensor.At the same time,it exhibited fast response and recovery speed(1 s/18 s),good repeatability and long-term stability.The excellent gas sensing properties was mostly ascribed to the formation of hollow structure and ZnSnO₃/NiO p-n heterostructures.5.The double-shell ZnSnO₃ hollow microspheres were designed and synthesized,and then different amounts of PdO nanoparticles were loaded on their surface.The tests of gas-sensitive characteristics showed that the gas sensing performance of PdO-loaded ZnSnO₃-based sensors was much better than that of pure ZnSnO₃based sensor.Moreover,the sensor showed the best sensing properties when supported PdO content was 4 wt%.Specifically,the response value of 4 wt%PdO-ZnSnO₃based sensor was 30.9 to 100 ppm of n-propanol at 140^oC,and the response/recovery time was 1 s and 25 s,respectively.Moreover,the sensor showed good repeatability and long-term stability.The excellent sensing performance was due to the formation of double-shelled hollow structure as well as the electronic and chemical sensitization of PdO.Based on the research of multiple metal oxides(compounds)of ZnSn(OH)₆and ZnSnO₃,the correlation between gas sensing properties and morphology,crystal structure,electronic structure and chemical components was analyzed comprehensively,and further studied the enhanced gas sensing mechanism.This work not only enriches the sensitive material systems,but also provides a research idea for the preparation of high-performance semiconductor based gas sensors.