| In recent years,along with the continuous demand of high-performance gas sensors in the fields of environment,medical care and safety,it has provided an opportunity for the development of gas sensors.However,how to design and fabricate one kind of gas sensor with high sensitivity,fast response and recovery characterization and good stability is still one major challenge for the research workers.It is well known that excellent sensor materials are the basis for building high-performance gas sensors.Researches show that semiconductor oxides exhibit unique advantages in the detection of toxic,harmful and flammable and explosive gases,making semiconductor gas sensors to be a focus and hot spot in the field of gas sensors.The surface morphology and structure of the semiconductor oxides have large effects on the receptor function,transducer function and utility factor of the sensing materials,further influence the gas sensing properties.Today,the rapid development of nanotechnology provides a new opportunity for constructing high-performance gas sensor.Nanostructured semiconductor oxides can effectively enhance the performance of gas sensors due to their high surface activity and high surface utilization efficiency.Among those nanostructures,the hollow nanostructures have been demonstrated to have good sensing properties owing to their high specific surface area,low density,good surface permeability and high interfacial charge-transfer efficiency.Tin oxide(SnO2)as an important n-type semiconductor material,has been recognized as the most potential sensing material because it has response to the target gases and easily for synthesizing.Although some important progresses have been made toward the study of SnO2 based gas sensors,the sensitivity to target gases must be further enhanced in order to meet practical application requirements.In fact,along with the deepen of the research about how to improve the sensitivity of SnO2,current modification method mainly focuses on the formation of heterogeneous cationic doping,catalyst(noble metal)surface loading and composite oxide heterostructures.Among them,the heterogeneous structure of the composite oxide formed by the combination of two or more kinds of semiconductor oxides can effectively control the acidity on the surface,activity point density,specific surface area and the width of space charge layer,significantly enhanced the sensitivity.In this paper,the hollow SnO2 nanospheres were prepared by one-step hydrothermal method without template,and the "structural enhanced sensitivities" were realized by using the structural advantages.According to the interaction mechanism between the target gases and the sensing material,SnO2 hollow structure modified with second component which has different work function and good catalytic activity,constructed the micro-nano-scale heterogeneous contact,could further enhanced the sensitive characteristics,achieve the "modified enhanced sensitization".The main study contents are as following:CeO2 nanoparticles were decorated on the surfaces of SnO2 hollow spheres by hydrothermal process to form CeO2/SnO2 composites material.According to the formation of n-n heterojunction between the two kinds of materials as well as the redox of Ce3+ and Ce4+ states,successfully enhanced the sensitivity of SnO2.CeO2/SnO2 hollow spheres composites showed 2.7 times higher gas sensing response to 100 ppm ethanol(response value is 37.0)at 225? than pure SnO2 hollow spheres(response value is 13.7),which demonstrates the CeO2/SnO2 heterojunction could obviously improve the response of SnO2.ZnO/SnO2 heterostructure composites material with a hollow structure was successfully synthesized based on SnO2 hollow spheres by two steps.Firstly,fabrication the ZnO seed layer on as-synthesized SnO2 hollow spheres.Secondly,ZnO was grown onto the surface of SnO2.The application of as-synthesized composite as sensing material was investigated and the result revealing that such composite has excellent sensing performance that the response to 30 ppm ethanol(response value is 34.8)was nearly 6.8 times higher than pristine SnO2(response value is 5.1)at its optimism temperature(225?).Moreover,such gas sensor showed a good response-recovery characterization,low detection limits(even to ppb-level)and excellent long-term stability.The enhanced sensing properties may be attributed to the heterojunction between SnO2 and ZnO changed greatly in different gas atmospheres.Besides,the increasing of adsorbed oxygen on the surface of the composites is also beneficial to the enhanced sensing properties. |
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