The Gas Sensing Properties Of TiO₂ And Reduced Graphene Oxide Composites

Nowadays,environmental protection is becoming a more and more urgent demand.Coupled with the continuous development of sensor technology itself,which is pushing the environmental monitoring is expected to be born in the field of Internet of things applications in the vertical field.Among the sensors,the gas sensor is "one of the three major cornerstone" of environment monitoring system,widely used in industrial and civil environment monitoring.Especially it takes the lead in popularity in the field of civil life.this year the market is growing rapidly.According to Yole Developpement prediction,gas sensor market will include $920 million in 2021,compound growth rate of 7.3% in the next five years.Environmental monitoring is ranking the third in all application fields.In the field of gas sensors,TiO₂ nanomaterials as gas-sensing materials is developed for a long time.Like TiO₂ nanotubes and nanoball,the TiO₂ hollow ball,TiO₂ single layer or doping Au particles of TiO₂ et al,which has a showing in gas detection.But TiO₂ nanomaterials as traditional gas sensitive material,need to be under the environment of high temperature?200 ?--400 ??or plus a UV lamp for normal work.In order to make the gas sensors which is based the TiO₂ nanomaterials to work at the room temperature,the paper uses the sol-gel method to prepare the TiO₂ microspheres particles,then use one-step reduction method to reduce the oxide graphene in the hydrothermal process to composite TiO₂ and graphene materials.A resistive-type gas sensor based on prepared rGO-TiO₂ composites was fabricated on Al₂O₃ ceramic substrate.The rGO-TiO₂ composites was characterized by XRD,SEM,TEM,PL and XPS.The results indicate that the composites have two special micro structure.One is bridge structure,which means grapheme layers as a bridge to connect the monodisperse TiO₂ microspheres particles.Another is graphene layers is partial wrapped on the TiO₂ microspheres.And the gas sensitive test results indicate the composites is sensitive to NH₃ among HCHO? C₂H₅OH? CH₄O ?CH₃COCH and NH₃.Also the paper has further studied the stability of the gas sensor,the response time,recovery time,the best working temperature and humidity,and the effect on sensor performance with different content of rGO.The end of the paper explores the gas-sensing mechanism of the composite material response to ammonia.The composite materials with the bridge structure increase the surface area,which lead to increase the gas adsorption in the process of gas detection.In the detecting ammonia gas,water molecules are essential elements.Ammonia ionized above the surface of reduction oxide grapheme and the electronic will move along the grapheme layer,finally accumulate in the surface of TiO₂ micropheres.And the macro phenomenon is that the resistance rise until reached the max value.In summary,grapheme materials could improve the performance of the traditional gas sensors.The composites with the bridge structure have a good performance in gas detecting at room temperature.And the materials have showed a good performance in the stability and repeatability.