Preparation And Properties Of Metal Oxide NO₂ Sensor

With the development of oil and gas resources and the improvement of people's living standards,a large amount of nitrogen dioxide?NO₂?is discharged into the air.NO₂ is a typical atmospheric pollutant,which not only damages the environment,but also threatens human health.It is extremely urgent for us to develop a high-performance NO₂ sensor.Metal oxide semiconductor?MOS?gas sensor is widely used due to its small size,fast response,high sensitivity,and low cost.Tungsten trioxide?WO₃?and indium oxide?In₂O₃?both have good gas-sensing properties for NO₂,but the disadvantages of high working temperature,high detection limit,poor selectivity and complicated preparation methods still restrict its development.Based on these shortcomings,this paper designs a variety of simple methods to regulate the structure of metal oxides to enhance their gas-sensing properties.The main contents are as follows:?1?Using sodium tungstate as a precursor,WO₃ composed of nanosheets was synthesized by one-step hydrothermal method.The characterization results show that pH is the main reason that affects the morphology and specific surface area of the material.The WO₃ material obtained at different pH values was fabricated into a gas sensor and tested for gas sensing properties.The results show that the sensor based on WO₃ hollow spheres?pH is0.7?shows higher response to ppb level NO₂ gas at lower temperature,and has a lower detection limit and a stronger selectivity.?2?Two kinds of hierarchically In₂O₃ materials were prepared by solvothermal method using indium chloride as precursor:flower-like In₂O₃ and urchin-like In₂O₃.Characterization and gas sensitivity tests were carried out respectively.The results show that the two gas sensors both have higher response to ppm and ppb levels of NO₂ at lower operating temperatures.Sensors based on flower-like In₂O₃ have shorter response/recovery time and good long-term stability at this temperature.Compared with flower-like In₂O₃,urchin-like In₂O₃ has higher response to NO₂ gas under the same conditions,lower detection limit.This paper attributed it to the better dispersibility of flower-like In₂O₃,while urchin-like In₂O₃ has a large specific surface area and a small structural size.