Preparation Of Tin Zinc Based Oxides And Gas Sensing Properties

Metal oxide semiconductors can be used as gas-sensing materials with low power consumption,low cost,high sensitivity and real-time operation.With the development of gas sensors,researchers are more interested in exploring emerging materials and their gas sensing properties,expecting them to have higher sensitivity,lower operating temperature and faster response-recovery time.Compared with traditional metal oxides,ternary oxide semiconductors have more stable chemical properties,and they are easy to achieve more diverse functions and properties by adjusting the element content,which arouse researchers'attention.Tin zinc oxides(ZnSnO₃ and Zn₂SnO₄),multi-functional materials with good conductivity and high electron mobility,offer various applied prospects in the fields of photoelectrochemistry,photocatalysts,and gas sensors.Studies have shown that there is a strong correlation between the gas sensing properties of tin zinc oxides and their structure,morphology,and crystal size.In this paper,based on the design of gas-sensitive materials,zinc tin oxide composites with various morphologies and structures were prepared by hydrothermal method.The gas-sensing performance of the materials were improved by constructing the metal oxide semiconductor heterostructure,forming a hollow structure,and surface modification.The micro-morphology and structure of as-prepared composites were characterized by XRD,SEM,TEM,XPS and EDS.The possible growth mechanism was discussed.Meanwhile,the sensor prototypes were built for gas-sensing test.The main research contents of this thesis include:SnCl₄·5H₂O,Zn(CH₃COO)₂·2H₂O and Cu(NO₃)₂·3H₂O were used as raw materials.The ZnSnO₃/Cu O composite was synthesized by hydrothermal method under alkaline conditions.The hollow cubic ZnSnO₃ was formed by adjusting the hydrothermal conditions and Cu O nanorods adhere to the surface of the hollow cubic ZnSnO₃ to form p-n heterostructure.The effect of Cu²⁺concentration on the formation of ZnSnO₃/Cu O heterostructure was studied.The results showed that the ZnSnO₃/Cu O heterojunction greatly improves the sensitivity of the sensing material to low-concentration H₂S with a low detection limit of 1 ppb.In addition,ZnSnO₃/Cu O sensor exhibited rapid response-recovery times(27 s and 45 s)and appreciated response value was 1.7 to 100 ppb H₂S at 40°C.The p-n junction formed between n-type ZnSnO₃ and p-type Cu O can effectively achieve the separation of electrons and holes,which played a key role in the process of gas sensing.The molar ratio of Zn/Sn in the chemical reagents was adjusted under alkaline conditions.ZnSnO₃/Zn O composite was synthesized by one-step hydrothermal method,which took cubic ZnSnO₃ as the core,and Zn O nanoparticles were grown on the cube surface.The hollow ZnSnO₃/Zn O composite was prepared through the alkali etching while maintaining its morphology and composition.The possible growth mechanisms have been studied.Compared with the ZnSnO₃ sensor,the sensitivity of ZnSnO₃/Zn O and hollow ZnSnO₃/Zn O sensor to triethylamine(TEA)gas was significantly increased by 2.7 times and 4.9 times respectively.The response of hollow ZnSnO₃/Zn O sensor was 101 in 50 ppm TEA at 160°C,and its response-recovery time was 32 s and 41 s.The results showed that the n-n heterojunction and hollow structure of ZnSnO₃/Zn O composite enhanced the electron transport capability,which promoted the redox reaction.And they effectively improved the gas sensing performance of the sensor.According to the transition process of ZnSnO₃ phase to Zn₂SnO₄ phase at high temperature,hollow octahedral Zn₂SnO₄ was successfully prepared by gradient hydrothermal method,and Zn₂SnO₄ nanosheets were grown orderly on the surface of octahedron.The formation mechanism of the hollow octahedral Zn₂SnO₄ with unique morphology was studied by characterizing the structure and morphology of the product under different hydrothermal time,and combining the"dissolution-recrystallization"phenomenon.The results showed that the hollow octahedral Zn₂SnO₄ could effectively shorten the gas diffusion distance,provide more active surface for the target gas,and significantly improve the gas sensitivity.The response of hollow octahedral Zn₂SnO₄ sensor was 65.4 in 50 ppm TEA at 200°C.The lower limit of detection was 1 ppm.There was a linear relationship between sensing responses and TEA gas concentration in the range of 1 to 100 ppm.The hexagonal nanoflakes-textured hollow octahedron Zn₂SnO₄ was synthesized by gradient hydrothermal method.Ag nanoparticles(NPs)were deposited on the surface of hollow octahedral Zn₂SnO₄ based on the redox reaction of Ag NO₃ and N₂H₄·H₂O.The gas-sensing properties of the materials were studied with different doping amounts of Ag.The results showed that the modification of Ag NPs significantly improved the gas sensitivity of the materials and reduced the operating temperature.When the doping amount of Ag was 3%,the sensing response to 50ppm TEA had been improved to 83.6 at 220°C,which was twice that of the pristine Zn₂SnO₄ sensor.Moreover,it also had very short response time(?1 s)and recovery time(20 s).The surface modification of Ag NPs promoted the generation of more active oxygen ions,which played a catalytic role in the sensing process.The Schottky junction had been formed between Ag NPs and Zn₂SnO₄,which increased the change of the sensor resistance and enhanced gas-sensitive performance.