The NO₂ Sensing Properties Of Monolayer Graphene And Its Composites

Nitrogen dioxide is one of the main air pollutants,which can affect human health and daily life.Therefore,it is very important to monitor the concentration of nitrogen dioxide gas.Most commercial gas sensors are made of metal semiconductor oxide material now.Although the preparation process is mature,the sensor has the disadvantages of low integration,high cost,high operating temperature,large power consumption and short life.Graphene is a new type of gas sensing material with high electron mobility,unique physical and chemical properties and large specific surface area.Graphene has great potential in the field of nitrogen dioxide gas sensing.This article introduces the preparation and modification of graphene materials and the development status of graphene-based sensing materials.The gas sensitive characteristics of graphene and its composite materials are studied.The sensing mechanism of material is analyzed.The main work includes:1.The monolayer graphene sensor based on a silicon material is studied.Monolayer graphene was prepared by chemical vapor deposition（CVD）,and monolayer graphene was transferred to a silicon substrate to prepare a silicon-based monolayer graphene sensor by the wet transfer method.The structure of monolayer graphene was characterized by Raman spectroscopy.And the detection performance of the sensor for nitrogen dioxide gas with a concentration of 0.5 to 10 ppm was studied.When nitrogen dioxide gas with a concentration of5 ppm is introduced,the response time of the monolayer graphene sensor is 180 s,the recovery time is 2400 s,and the responsivity is 0.04.When the gas concentration is 10ppm,the response time is 280 s,the recovery time is 4852 s,and the responsivity is 0.064.2.The SnO₂NPs/monolayer graphene composite sensor was studied.The SnO₂ NPs/monolayer graphene composite sensor was prepared by using nano-tin dioxide particles（SnO₂NPs）on the monolayer graphene by drip coating and wet transfer methods.The material was characterized by Raman spectroscopy and scanning electron microscopy.The detection performance of the sensor for nitrogen dioxide gas with a concentration of 0.5 to 10 ppm was tested.When the gas concentration is 10 ppm,the response time of the SnO₂-Gr-2（0.3 mg/ml SnO₂ nano solution-doped monolayer graphene）material sensor is 182 s,the recovery time is525 s,and the responsivity is 0.25.Compared with intrinsic single-layer graphene sensing,the responsivity is increased by about 4 times,and the recovery time is shortened by about 9 times.The SnO₂ NPs/monolayer graphene composite material sensor has excellent gas sensing performance.3.The effect of ultraviolet laser on the gas sensing performance of monolayer graphene was studied.The monolayer graphene was transferred to a D-type optical fiber manufactured by femtosecond laser micromachining.A monolayer graphene/fiber microstructure sensor was prepared,and an ultraviolet laser with a wavelength of 355 nm was passed into the optical fiber.The gas-sensitivity performance of single-layer graphene/optical fiber microstructure sensors to nitrogen dioxide gas with a concentration of 100 to 5000 ppb under different laser powers was tested.When the nitrogen dioxide gas concentration is 500 ppb and the output power of ultraviolet laser is 30 mw,the response time of sensor is 380 s,the recovery time is 1407 s,and the responsivity is 0.205.Compared with the dark environment,the sensor responsivity is increased by 25 times.It can be concluded that ultraviolet laser illumination can improve the performance of the monolayer graphene/optical fiber microstructure sensor.4.The effect of UV LED light on the performance of SnO₂ NPs/monolayer graphene composite sensor was studied.Short-time ultraviolet light irradiation at room temperature can accelerate the desorption of nitrogen dioxide molecules from the sensing material.And the detection performance of the UV LED light assisted sensor for nitrogen dioxide gas with a concentration of 0.5 to 10 ppm was studied.When the gas concentration is 10ppm,the responsivity of sensor is 0.25,the response time is 140 s,and the recovery time is 9 s.Compared with the SnO₂-Gr-2 material sensor without UV light,the recovery time is accelerated by about59 times.Therefore,SnO₂ NPs/single-layer graphene sensor can accelerate the desorption of nitrogen dioxide gas by ultraviolet LED light irradiation,and realize rapid detection.