| Excessive concentration of toxic and harmful gases affects economic benefits and safety of human life and property.For example,excessive concentration of ammonia in aquaculture farms leads to animal death or production reduction;ammonia leakage in cold storage causes fires and explosions;and gas explosions occur from time to time in the process of coal mining.These accidents often occur because the sensor detection lags behind,so it is very important to study the gas sensor with high sensitivity and low detection limit in order to prevent them from happening.In this thesis,graphene oxide with different contents of hydroxyl,epoxy and carboxyl groups was prepared from flake graphite by modified Hummers method,low temperature water addition and chloroacetic acid modification,and its structure and functional groups were analyzed.Then,uniform thickness graphene oxide gas sensitive films were prepared by spin coating method.The gas sensitivity of NH3,H2O and CH4 was studied and the sensitive mechanism was revealed.On this basis,the sensor array is composed of NH3,H2O and CH4gas sensors with strong selectivity.The qualitative and quantitative detection of NH3 and humidity,CH4 and humidity in mixed atmosphere is carried out,and the response model of sensor array is established,and the final test results are evaluated.The results show that GO prepared by modified Hummers method can control the relative content of hydroxyl by changing the amount of oxidant(KMnO4).When the mass ratio of potassium permanganate to graphite is 3:1,the content of hydroxyl is the highest,reaching43.75%.The sensitivity of GO gas sensor to NH3 is positively correlated with the relative content of hydroxyl group(C-OH).When the relative content of hydroxyl group is the highest(GO-3),the maximum sensitivity to 20 ppm NH3 is 36.5%,and the response time is 43 s.Its response mechanism is the ionic conductivity mechanism of NH4~+formed by the hydrolysis of NH3 molecules into the interlayer water molecule layer of GO and the charge transfer mechanism of the oxygen-containing functional groups adsorbed on the GO structure layer.The relative content of functional groups in GO,especially epoxy group,can be effectively changed by adding water at low temperature.When 40 mL concentrated sulfuric acid and 5mL concentrated sulfuric acid are added,the content of epoxy group can reach 21.56%.This GO has better selectivity to humidity than GO with high hydroxyl and carboxyl groups.At low humidity(<50%RH),the hydrogen peroxide molecule only adsorbed on the GO surface,with good recovery and repeatability;at high humidity(>50%RH),the hydrogen peroxide molecule will enter the GO layer,and it is not easy to recover.The adsorption mechanism is mainly hydrophilic functional group adsorbing hydrogen peroxide molecule,polar functional group ionizing hydrogen peroxide molecule,forming ion channels between layers,enhancing conductivity;the combination of epoxy group and hydrogen peroxide molecule will form hydrogen bond network,which is conducive to electronic transmission.Modification with chloroacetic acid can effectively increase the relative content of carboxyl group in GO.When the addition of chloroacetic acid is 1.5 g,the content of carboxyl group increases significantly,from the initial 5.28%to 16.83%.The carboxylated GO has a good sensitivity to CH4 gas,and the sensitivity to CH4 gas of 800 ppm is about 80%.The sensitive mechanism is that H in CH4 gas molecule can be connected with O in GO functional group by hydrogen bond to form hydrogen bond.After obtaining the response characteristics of three kinds of gas sensors to three kinds of gases,high performance gas sensor arrays are screened and constructed,and the steady-state response of sensor arrays in single atmosphere and mixed atmosphere is obtained.The response models of single atmosphere and mixed atmosphere are fitted and analyzed by least square principle,and the results of single atmosphere in unknown concentration mixing atmosphere are predicted and tested.The results show that the fitting method of this mathematical model can effectively detect the concentration of single gas in mixed atmosphere,The error is less than10%,which can meet the detection requirements of NH3 and CH4 in special occasions. |
