Preparation And Gas-sensing Properties Of ZnSnO₃-based Composites Materials

With the development of industrialization and urbanization, air pollution is worsening. Meanwhile, citizens’ environmental awareness is increased gradually. The detection and control of the polluting gases such as toxic and hazardous, flammable and explosive gases has drawn much social concern, so gas sensor has been widely used in atmospheric pollutants, industrial exhaust gases monitor and ambient air quality assessment. Sensitive material, as a core component of the gas sensor, is the measure standard of gas-sensing properties. It is the development trend in gas-sensing field to prepare new sensitive materials, simultaneously, achieve low-dimensional and self-assemble into more complicated structures（hollow structure, porous structure, hierarchical structure, etc.）. How to achieve controlling the size and structure, and developing a new method to improve gas-sensing property of the sensitive materials will become one of the most leading subjects.ZnSnO₃, as an important composite metal oxide, has been used widely in gas-sensing fields due to its better gas-sensing properties than single metal oxide; Graphene-like materials, as new carbon material, have broad application in gas-sensing field due to its unique structure and electrical properties. This research decided to take ZnSnO₃ and graphene oxide（GO） as the research object. From the point of view of the relationship of composition, structure and property, through changing the experimental method and reaction condition to achieve controlling the structure, size and phase composition, ZnSnO₃ solid microspheres, hollow microspheres and ZnSn O₃/GO composites were prepared successfully. Meanwhile, the gas-sensing properties of the as-prepared materials were researched.The main research contents are as follows:（1） ZnSnO₃ microspheres were prepared successfully using in-situ precipitation method combined with subsequent calcination. The as-prepared ZnSnO₃ microspheres with diameters of about 1.8 μm have good crystallinity and uniform morphology, and microsphere with rough surface is composed of small nanoparticles. Meanwhile, ZnSnO₃ with different particle-size and morphology was prepared by adjusting reaction conditions. In the application point of view, the sensor based on ZnSnO₃ microspheres also showed high sensitivity, fast response, and short recovery time. The response and recovery time of ZnSnO₃ microspheres were 6 and 18 s to 20 ppm formaldehyde at 260 oC, which indicated ZnSn O₃ microspheres have superior gas sensing properties to formaldehyde.（2） ZnSnO₃ hollow microspheres were prepared successfully by a simple one-pot template-free and general in-situ precipitation method. The as-prepared ZnSnO₃ hollow microspheres with diameters of about 1.3-1.6 μm have good crystallinity and uniform morphology, and the shell with thickness of 200 nm is composed of small nanoparticles. The orientation and morphology of ZnSnO₃ can be carefully controlled by adjusting reaction conditions. The morphological evolution of ZnSnO₃ hollow microspheres is completed, and a possible formation mechanism for hollow structures is discussed. In the application point of view, the as-prepared ZnSnO₃ hollow microspheres exhibited good response and recovery to ethanol compared to ZnSnO₃ solid microspheres. The sensor based on ZnSn O₃ hollow microspheres can detect ethanol down to 5 ppm and the corresponding response is about 4.5, which much higher than the response of ZnSnO₃ solid microspheres（1.5）.（3） ZnSnO₃/graphene oxide（GO） composites were successfully synthesized by a facile method through hydrothermal treatment. The prepared composites were characterized using many instruments. The results showed that ZnSnO₃/GO composites were successfully synthesized, and ZnSnO₃ nanoparticles with diameters of ⁸0 nm coted GO surface have uniform morphology and good dispersion. Furthermore, the gas sensing properties were further investigated. Compared with the sensors based on pure ZnSnO₃ nanoparticles, the sensors based on ZnSnO₃/GO composites exhibit better gas sensing properties in selectivity and sensitivity. To 10 ppm formaldehyde, the gas response（S） of the composites was 11.5 at the optimum operating temperature of 230 oC, which is much higher than that of pure ZnSnO₃ nanoparticles（5.3）. These results showed that the as-prepared ZnSnO₃/GO composites could have a potential application in formaldehyde sensing field.