Preparation And Sensing Performence Of ZnO@C-N Core-shell Materials

Hydrogen sulfide is a toxic gas with acidic property.It is of great significance to detect this gas with low concentration in environment.As excellent gas sensitive materials,metal oxides have been widely used to detect toxic and harmful gases.Metal oxides easily react with hydrogen sulfide gas during the detection process,and result in sensing poisoning.In this case,their response curve to hydrogen sulfide cannot recover to original baseline,which seriously impact the the stability of gas sensors.In this thesis,we propose to modify ZnO nanomaterials matrix with a thin C-N layer to realize the stable detection of hydrogen sulfide gas.On the one hand,the thin C-N layer is capable of preventing the irreversible reaction between ZnO and H₂S.On the other hand,the thin layer does not significantly degrade the H₂S sensing property,and simultaneously endow the sensing materials with corrosion resistance.The liquid impregnation and high-temperature decompose methods were combined to modify the oriented ZnO nanorods with thin C-N layer.The effects of calcination temperatures and soaking times on the sensing performence were studied.The component,structure and sensing mechanism of ZnO@C-N composites were characterized by XRD,SEM,EDS,XPS and other methods.Results showed that the optimum H₂S sensing properties were achieved on the ZnO@Melem composite materials.At room temperature,the ZnO@Melem sensors can repeatedly detect 1ppm H₂S with sensitivity as high as?36.This kind of sensor could also be used to repeatedly detect different H₂S concentration,ranged from 50 ppb to 10 ppm.The sensitivity is about 2.2 for 50 ppb H₂S.The stability of ZnO@Melem sensors used in different environmental condition was also studied.The effects of HCl,SO₂,NH₃ gases on the sensing property of ZnO@Melem sensors were investigated.Experimental results showed that the presence of 10 ppm the three gases does not corrode the ZnO@Melem composite materials,and does not affect the H₂S sensitivity.The ZnO@Melem composite materials can specifically response to H₂S in a reducing mixed atmosphere.The ZnO@Melem sensor was also capable of maintaining its sensing stability after immersion in HCl or NaOH solution.In addition,acidic water-droplet can be bounced off when it was dripped on the ZnO@Melem sensor.Furthermore,temperature tolerance test showed that the ZnO@Melem sensor displayed stable H₂S sensing property after heat treatment at 100?,200? and 300?.