Research On Flexible NO₂ Gas Sensor Based On Polypyrrole Composite Film

NO₂ is a toxic and harmful gas,which has caused serious damage to the natural environment and the human living environment.Over the past few years,with the continuous development of social economy and the enhancement of application demand in the information age,researchers are committed not only in improving the sensitivity of NO₂ sensors,reducing the detection limits,but also in focusing on the research of flexible NO₂ sensors.On the basis of previous research,this work prepared the PPy-CeO₂ or PPy/N-MWCNTs composite films on flexible substrate polyimide?PI?by in-situ self-assembly and chemical oxidation polymerization to detect low concentration?0.5-10 ppm?NO₂ gas at room temperature.Combined with the morphology of the composite film and spectral analysis,the corresponding gas sensing mechanism was established.The specific research contents are as follows:1.Polypyrrole-cerium dioxide?PPy-CeO₂?composite thin film was prepared on polyimide?PI?flexible substrate using pyrrole?Py?as precursor and FeCl₃·6H₂O as oxidizing agent.The obtained PPy and PPy-CeO₂ were characterized and analyzed by UV-Vis,FTIR,SEM,TEM and XRD and XPS.The results showed that PPy and CeO₂is successfully compound with a certain interaction,and PPy-CeO₂ exhibited a typical core-shell structure.The NO₂-sensing properties of pure PPy and PPy-Ce O₂ composite thin film with different proportions were investigated at room temperature.The results indicated that the composite thin film sensor showed the superior response characteristics,and when the molar ratio of Py and CeO₂ is 2,the sensitivity is 12.6times larger than that of pure PPy film Furthermore,the PPy-CeO₂ film sensor possessed good repeatability and selectivity,and when the flexible sensor is bent and stretched for 500 cycles,the response of the film to 10 ppm NO₂ was decreased by 3.4%.Finally,the NO₂-sensing mechanism of PPy-CeO₂ film sensor was analyzed and discussed.2.The PPy/N-MWCNTs composite film was prepared on the flexible substrate in the same way.The morphology of PPy and N-MWCNTs showed a typical core-shell structure by TEM,and the composite film was porous and rod-like structure by SEM.The effect of annealing treatment on the composite film was analyzed.The result showed that the annealed composite films had a higher responsivity to NO₂ gas and10.24 times than that of the unannealed composite films,and the gas-sensing response of the composite films first increased and then decreased at 200?to 400?,reaching the highest at 350?.The gas-sensing effects of different N-MWCNTs doping amounts in the PPy/N-MWCNTs composite films were discussed.When the N-MWCNTs doping amount is 10mg,the sensitivity of composite films to NO₂ is the highest,and the responsivity was-23.84%to 5ppm NO₂.After bending and stretching for 500 times,the responsibity didn't change while there was little difference after 1500 times.Finally,the gas response mechanism of PPy/N-MWCNTs composite films was briefly analyzed.