Research Of Ethanol Gas Sensor Based On ZnO And Graphic Carbon Nitride Nanocomposite

With the improvement of living standards,people are paying more and more attention to the threat to human health caused by various harmful gases from industrial production.Therefore,efficient detection of toxic gases is essential to improve the quality of people’s work and life quality.Gas sensors based on metal oxide semiconductor nanomaterials attract many researchers because of their high sensitivity,low price and fast response.It is one of the research hotspots to combine gas-sensitive metal oxide nanomaterials with two-dimensional carbon materials with other excellent properties to form gas-sensitive materials with more excellent properties.In this thesis,a composite of ZnO and the emerging two-dimensional carbon material graphic carbon nitride(g-C3N4)was used as the research object.According to different material design ideas,gas sensing materials with specific microstructure were synthesized and thoroughly tested using various characterization methods.Finally,gas-sensitive materials with different morphologies and properties were successfully prepared by hydrothermal method,and gas sensors based on them were constructed.Gas sensing test results showed that the constructed sensors had excellent gas sensitivity.The specific research content is as follows:(1)A gas sensing test system was designed and fabricated.A comprehensive analysis of the laboratory’s requirements for gas sensing system was made at first.According to the analysis results,test gas box was completed,measuring device and sensor heating power source were selected,test circuit was designed and manufactured,the software of gas sensing test system was implemented.The finished test system is able to provide excitation to the sensor through a constant current source.The problem of impedance matching was avoid by directly measuring the resistance of the sensor under constant excitation.Through PID control algorithm,fast,accurate and no overshooting sensor temperature control was accomplished.The system also provides real-time observation of the sensor resistance curve and the function of saving all the test data of the entire test process,which greatly facilitates the subsequent data processing.(2)According to the material design idea of sensitizing ZnO/reduced graphene oxide(rGO)composite by g-C3N4 rather than noble metal nanoparticles,ZnO/rGO/g-C3N4 ternary nanocomposite based on 0D-2D nanostructure was synthesized by hydrothermal method.The nanostructures of 2D graphene oxide(GO)-hybridized by g-C3N4 were synthesized in advance by combining ultrasonic dispersion and electrostatic self-assembly strategy.ZnO nanoparticles were coated on GO/g-C3N4 through a hydrothermal process,in which GO was totally reduced to rGO.The material characterization results show that the new materials formed meet the design ideas.The ternary nanocomposite showed the highest response of 178 to 100 ppm ethanol at 300℃ with a detect limitation lower than 500 ppb,which was about 9-folds higher than ZnO,Its response and recovery time for 100 ppm ethanol are 76 s and 6 s,respectively.At the same time,the material also exhibits excellent selectivity and stability.Sensitive mechanism analysis believes that the gas sensing properties of the reinforcing materials may be due to the small size effect of ZnO nanoparticles,the enhanced electron conduction properties of rGO and the catalytic activity of g-C3N4 nanosheets.(3)According to the material design idea of modifying the two dimensional g-C3N4 surface with ZnO nanorods,a ZnO nanorod/g-C3N4 composite based on 1D-2D structure was synthesized by a two-step seed method.At first,ZnO nanoparticles are distributed as seeds on the surface of g-C3N4 by ultrasonication and calcination.Then,the ZnO nanorods were grown in situ at the position of seeds by aqueous chemical growth.The material characterization results show that the new materials formed meet the design ideas.The gas sensitivity test results show that the response of ZnＯ/g-C3N4 sensor can achieve 110 to 100 ppm ethanol at an optimum operating temperature of 350℃,which is almost 8 times than that of pure ZnO synthesized by the same method.The minimum detection limit is less than 500 ppb.Its response and recovery time for 30 ppm ethanol are 21 s and 20 s,respectively.At the same time,the material also exhibits excellent selectivity and stability.Sensitive mechanism analysis believes that the gas sensing properties of the reinforcing materials may be due to the small size effect of ZnO nanorods and electron sensitization of g-C3N4 nanosheets.