| Industrial development has brought about a variety of environmental problems,and environmental issues have always been paid more attention by Chinese government,especially the detection of toxic and hazardous gases in the environment.Among many poisonous and inflammable gases,hydrogen sulfide?H2S?gas is a neurotoxic,suffocating and harmful gas commonly found in human habitation,and it may also relate to diseases such as Alzheimer's,Down syndrome,Liver cirrhosis.Therefore,effective detecting and monitoring H2S level are essential since it becomes a potential threat to human health.Metal oxide semiconductor based gas sensors have been widely studied due to their advantages such as low cost,flexible process,simplicity,and compatibility with modern electronic devices.However,metal oxide semiconductor based gas sensors still remain certain shortcomings in practical applications,such as low sensitivity,high operating temperature,long response time,and insufficient selectivity.Morphology control and the usage of noble metal additives are most common methods to increase the sensitivity of metal oxide semiconductor based gas sensors.In this dissertation,p-type semiconductor CuO was selected as a sensitive material,and the composite structure and doping noble metal nanoparticles were used to improve the sensitivity of CuO gas sensors to H2S gas,and the mechanism for enhanced sensing properties of such gas sensors was thoroughly discussed.The main results of this paper are concluded as follows:?1?A facile method was used to prepare Pd-doped CuO nanoflowers with various doping concentrations.The samples were characterized through XRD,SEM,TEM,EDX,ICP-AES,and BET.The responses(Rg/Ra or Ra/Rg,where Rg is the resistance in gas,and Ra is the resistance in air)of such sensors exposed to CH4,NO2,C2H5OH,H2S,NH3,and H2 were measured for comparison.For 1.25 wt%Pd-doped CuO nanoflowers,the response?Rg/Ra=15.7?to 50 ppm H2S was 123.4 at 80oC,which was significantly higher than that of pure CuO?Rg/Ra=15.7?.Furthermore,excellent stability and repeatability of the gas sensor were also demonstrated.By applying a 4.6 V voltage pulse,we solve the common problem that the sensor is difficult to desorb at low operating temperature.?2?The pristine and Pt-doped CuO nanoflowers were fabricated utilizing a simple heating route carried out in a water bath,and the morphology and characteristics of nanomaterials were examined by XRD,SEM,EDX,ICP-AES,BET,and XPS.The H2S gas sensing properties were examined at different operating temperatures,and their dependence on doping ratio of Pt to CuO was also investigated.Results showed that the CuO sensor doped with 1.25 wt%Pt exhibited the highest response of 135.1 to 10 ppm H2S at 40oC,which was 13.1 times higher than pristine CuO sensor.At the same time,Pt doping enhances the selectivity of the sensor to H2S gas.?3?A semiconducting heterostructure composed of CuO micorspheres whose surface was modified with CuFe2O4 nanoparticles.The CuO microspheres were fabricated utilizing a simple heating route carried out in a water bath,while CuFe2O4 modification of CuO was carried out by a facile tow-step method.The morphology and characteristies of the samples were examined by SEM,HRTEM,EDX,XPS,TG-DTA,and XRD.The gas sensitivity tests of CuO microspheres,pure CuFe2O4 and CuO/CuFe2O4 core-shell structures were performed.And the results showed that the response of the optimized CuFe2O4-modified CuO heterostructures to 10 ppm H2S gas was approximately 20 times higher than that of the initial CuO microspheres at the optimal optimal operating temperature?240oC?.We also discussed the gas-sensitive mechanism of the above core-shell structure from the aspects of the formation of p-n heterojunctions. |
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