| As the nucleus of gas sensors,the gas-sensing material is changing from thesimplex material to the composite material.Conducting polymer/inorganic materialnanocomposites combine the advantages of conducting polymers and inorganicnano-materials,which endows the nanocomposite with excellent gas-sensingcharacteristics.In this dissertation,a series of conducting polymer/inorganic materialnanocomposite ammonia (NH3) gas-sensing thin films were fabricated by an in-situself-assembly approach,which were characterized and analyzed with different methods.The planar micro-interdigital electrodes were designed and prepared,and the deep anddetailed investigation on their NH3 gas-sensing properties was carried out.Furthermore,the discrimination of gas species was achieved by the gas recognition system composedof the gas sensor array with different nanocomposite thin films and the patternrecognition technique of the artificial neuron network (ANN).The main results are asfollows:1.Polypyrrole (PPy) and polypyrrole/titanium dioxide (PPy/TiO2) gas sensitivethin films were developed by an in-situ self-assembly method at room temperature.NH3gas sensitive properties of the PPy/TiO2 nanocomposite thin film was firstlyinvestigated.Spectrum analyses indicated that some kind of interaction did take placebetween PPy and TiO2 nanoparticles.Thermogravimetric analysis (TG) showed that thePPy/TiO2 nanocomposite material exhibited an enhancement of thermal stabilitycompared with pure PPy.The morphology analyses revealed that,a typical core-shellstructure could be found in the PPy/TiO2 nanocomposite material,and the PPy/TiO2nanocomposite thin film with the smaller size of nanoparticles was more uniform andcompact,which resulted in larger surface area and more active sites,decreasingstructural defects and greater selective adsorption.This explained why the gas-sensingcharacteristics of the PPy/TiO2 nanocomposite thin film were superior to a pure PPythin film.The optimum gas-sensing properties of PPy/TiO2 nanocomposite thin filmsensors were obtained with 0.1 wt% colloidal TiO2 under 20 min deposition.Themicroscopic gas-sensing model for the PPy gas sensor was developed,and based on this model,the equilibrium constants of PPy and PPy/TiO2 sensitive thin films for NH3 were1.18×10-2 and 1.32×10-2,respectively.2.Polyaniline (PANI) and polyaniline/titanium dioxide (PANI/TiO2) thin filmswere fabricated,and NH3 gas sensitivity was examined.It was found that smooth andtransparent thin films could be produced when the substrate was dipped into the reactionsolution at the initial stage of polymerization.The PANI/TiO2 nanocomposite thin filmsensor exhibited good detecting ability to lower NH3 gas concentration (1 ppm) andsuperior gas-sensing properties than a pure PANI thin film,which was attributed to theporous structure with an interconnected network of nanofibers that enhanced theadsorption and diffusion of gas molecules,and it was also supposed that a positivelycharged depletion layer on the surface of TiO2 nanoparticles may cause a decrease of theactivation energy and enthalpy of physisorption for NH3 gas.The doping acid and thepolymerization temperature had effects on the morphology and gas sensitivities ofPANI/TiO2 nanocomposite thin film.The experimental results showed that,the responsetime of the sensor prepared using HCl as the doping acid at 10℃was 2 s,and therecovery time was less than 60 s when it was exposed to NH3 (23-141 ppm).Thesensitivity was linear to the concentrations of NH3.The sensor also had goodreproducibility,selectivity and long-term stability.The sensitivity of PANI/TiO2nanocomposite thin film sensor decreased reciprocally with the increase of thetemperature,and the influence of humidity on the response was much less than that oftemperature.3.Polyaniline/indium oxide (PANI/In2O3),polyaniline/tin oxide (PANI/SnO2) andpolyaniline/multi-walled carbon nanotube (PANI/MWNT) nanocomposite thin filmswere prepared by a soft-template technique,and their NH3 gas-sensing performanceswere studied.The effects of a cationic surfactant,tetradecyltrimethylammoniumbromide (TTAB) and a non-ionic surfactant,poly (ethylene oxide) (20) sorbitanmonolaurate (Tween-20) on the morphology and gas-sensing properties of PANI/In2O3nanocomposite thin film were studied.X-ray diffraction spectrometry (XRD) andmorphology analyses showed that TTAB and Tween-20 prevented In2O3 nanoparticlesfrom aggregating to some extent,and hence the nanocomposite thin films by thesoft-template method had more compacted network structure with smaller diameter ofnanofibers.However,different concentrations of TTAB might induce different morphologies and sensitive characteristics of PANI/In2O3 thin films,which might berelated with the super-molecule structure of TTAB in the water-dispersed medium.Thegas-sensing characteristics showed that the nanocomposite thin film was the mostsensitive when TTAB/nanoparticles molar ratio was 0.5,but the response/recovery timeof sensors increased,which was postulated that the compact surface of the film affectedthe adsorption and desorption of gas molecules to a certain extent.The NH3adsorption/desorption kinetics equation of PANI and its nanocomposite thin filmsensors based on the Langmuir adsorption model was established,which revealedeffective by comparing its predictions to experimental curves.4.The quantitative and qualitative analyses of CO and H2 gases in the range of40-1000 ppm were accomplished by the combination of a gas-sensing array with fourseparate commercial semiconductor gas sensors and back-propagation neural network(BPNN) and self-organized competitive network.The original gas sensor array wasdeveloped with PANI and PANI/inorganic nanocomposite thin film micro-gas sensorsfor the first time,which was optimized by the step-clustering analysis.The optimizedarray was composed of PANI,PANI/TiO2,PANI/In2O3 and PANI/MWNTnanocomposite thin film sensors.A gas recognition system composed of the optimizedarray and probabilistic neuron network (PNN) was developed,which distinguished NH3,CO and H2 within a certain concentration range.
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