The Fabrication and Investigation of Polyaniline Based Nanocomposite Ammonia-sensing Thin Film

Author:Liu Chun Hua

Supervisor:jiang ya dong


Degree Year:2019





Nowadays,with the rapid development of industry and agriculture and the fast growth of vehicle population,our country has become the biggest emitter of ammonia(NH3).The increasing NH3 pollution not only seriously threatens the health and safety of human,but also as an important cause of haze influences the sustainable development of ecological environment.At the same time,NH3 is a kind of metabolite existed in the exhaled breath of human,which has been proposed as one of the typical markers for particular diseases and could be used in noninvasive clinical diagnostics.Therefore,it has important practical significance to develop low-cost,portable,high-performance NH3sensors.Polyaniline(PANI)is a kind of organic polymer with adjustable electrical conductivity,which has been regarded as a promising NH3-sensing material due to its low-cost raw materials,facile synthesis process,unique proton acids doping behavior,and reversible doping-dedoping property.However,pure PANI materials still suffer from some drawbacks,such as low sensitivity,poor reversibility and long-term stability.In this case,combining PANI with the other NH3-sensing materials maybe an effective method to improve the performances of NH3 sensors by synergy effect.In this work,the resistive-type NH3 sensors based on binary or ternary PANI nanocomposite thin films were designed and prepared,various characterization methods were employed for the material analysis,and the NH3-sensing preformances and sensing-mechanisms of the sensors were evaluated and investigated systematically.The main contents of this dissertation are summarized as follows:1.A NH3 sensor was prepared by depositing polyaniline-titanium dioxide-gold(PANI-TiO2-Au)ternary nanocomposite thin film on silicon substrate with interdigital electrodes through electrostatic self assembly-in situ polymerization method at room temperature.The thin film analysis showed that TiO2 nanoparticles and Au nanorods were packaged by PANI to form a typical"core-shell"structure,and the film possessed a hierarchical-structure including a nanoparticles layer and some dendritic nanofibers,which were not only beneficial to the carrier transfer and the formation of interaction at the interface,but also could enhanced the specific surface area for NH3 molecules adsorption.The NH3-sensing performances evaluation exhibited that the PANI-TiO2-Au sensor possessed superior response characteristics compared with the PANI-TiO2 one,including the higher response values,shorter response/recovery times and better reversibility,which should be ascribed to the catalytic dehydrogenation of Au nanorods and the synergistic enhancement effect of the p-n heterojunction and Schottly junction.Besides,the PANI-TiO2-Au sensor also exhibited excellent repeatability,selectivity,stability and low detectable concentration(≤1 ppm),and it still presented high NH3response in humid air.What’s more,the PANI-TiO2-Au film was also deposited on polyimide(PI)substrate by the same method to prepare a flexible NH3 sensor.The results showed that the preparation method of the film was appropriate for the PI substrate,and the response-recovery property and flexibility of the sensor were remarkable.2.The polyaniline-cerium dioxide(PANI-CeO2)nanocomposite thin film was deposited on flexible PI substrate with interdigital electrodes by electrostatic self assembly-in situ polymerization method for NH3 detection.The analysis of the film showed that the CeO2 nanoparticles were wrapped in PANI randomly,and the addition of CeO2 nanoparticles not only improved the protonation and oxidation degrees of PANI significantly,but also made the PANI presented nanosheet structure which was different from the dendritic nanofibrous structure of pure PANI.The NH3-sensing performances detection showed that the PANI-CeO2 sensor possessed shorter response/recovery times and higher response and sensitivity than the pure PANI one,which probably benefited from the gas-sensing enhancement effect of p-n heterojunction and the improved protonation degree of PANI.Meanwhile,the PANI-CeO2 sensor presented good reproducibility,linearity,selectivity,long-term stability,and ultra-low detectable concentration(≤16 ppb),and it still showed favourable NH3 response behavior in humid air.What’s more,the PANI-CeO2 sensor also possessed outstanding flexibility,which might originate from the electrostatic interaction between PI substrate and nanocomposite thin film,and the good mechanical performance of the PANI-CeO2 nanocomposite.3.The flexible PANI-CeO2-Au ternary nanocomposite thin film sensor was prepared by depositing discrete Au nanoparticles on PANI-CeO2 film through vacuum thermal evaporation method.The Au nanoparticles not only increased the surface area of the film,but also possessed the catalysis for NH3-sensing response.In order to evaluate the detectability of exhaled NH3,the NH3-sensing properties of the sensor were detected in simulated exhaled breath(80%N2,16%O2,and 4%CO2)under35℃and90%relative humidity.The results showed that the PANI-CeO2-Au sensor exhibited better response-rescovery properties for 200-1000 ppb and 2-10 ppm NH3 than those of the PANI-CeO2one,and it also possessed good repeatability,selectivity,flexibility,and linearity.Besides,the NH3-sensing performances of the sensor were also detected in different carrier gases,and the influence mechanisms of the H2O and CO2 molecules were analyzed.4.The polyaniline-gold nanoparticles loaded reduced graphene oxide nanocomposite(PANI-Au@rGO)was synthesized by adding Au@rGO nanosheets into the in-situ polymerization reaction of aniline.And the spin coating method was employed to deposite PANI-Au@rGO dispersion on PI substrate with interdigital electrodes for NH3detection.The analysis showed rough nanosheets were formed by the polymerization of aniline at Au@rGO nanosheet surface,and the PANI showed hybrid structure integrating nanoparticles and nanorods.And,it was found that the continuity of PANI in nanocomposite was enhanced,and its protonation degree was also improved obviously.The sensing propertie detection showed that the PANI-Au@rGO sensor exhibited better response-recovery behavior for 200-1000 ppb and 2-10 ppm NH3 in simulated exhaled breath than that of the pure PANI one,which should attribute to the synergistic effect of PANI and Au@rGO,the catalysis of Au nanoparticles,and the improved protonation degree of PANI.And,the PANI-Au@rGO sensor also exhibited good selectivity,repeatability,and flexibility.Besides,the influences of the test environments on the NH3-sensing properties of the sensor were detected,and mechanisms were analyzed and discussed.5.A flexible NH3 sensor was prepared by depositing tungsten disulfide(WS2)and PANI films successively on microfiltration membrane by spraying and in-situ polymerization methods.The analysis showed that the PANI-WS2 nanocomposite thin film adhered to the nanofibers of microfiltration membrane uniformly and presented a villus surface,which didn’t damage the network structure of the substrate and made the sensor breathable and comfortable as a wearable device.The NH3-sensing testing showed that the PANI-WS2 sensor possessed shorter response/recovery times and better respone-recovery property and repeatability than those of the pure PANI one in simulated exhaled breath for 2-10 ppm NH3,which should benefit from the gas-sensing enhancement effect of the heterojunction between PANI and WS2.Besides,the sensor also exhibited good selectivity,flexibility,linearity,and obvious response for 200-1000 ppb NH3.