Preparation And Properties Of Polyaniline Heterostructure Nanofibers As Gas Sensors Materials

Gas sensor is a kind of equipment that some physical or chemical properties would be changed when it is exposed to aim gas and then transfer that into composition and content information.As one of the sources that human live on,atmosphere and its quality have attracted lots of attentions.So gas sensing materials have been applied in many fields.By now most sensing materials are inorganic semiconductor which has high work temperature,energy consuming and rigid.This work focus on the preparation and study on flexible heterostructured ammonia sensor with high response values,high sensitivity,ideal selectivity and repeatability.Flexible electrospun nanofiber membranes as templates,polyaniline（PANI）composite nanofibers with heterojunctions were prepared,and the effect of heterojunction on the gas sensing properties was also studied,aiming to provide some theory for the development of wearable gas sensors.Main research topics and conclusions are below:Polyamide 6/titanium dioxide/polyaniline（PA6/TiO₂/PANI）composite nanofibers were prepared by electrospinning,electrospray and in situ polymerization process.Scanning electron microscope（SEM）and transmission electron microscopy（TEM）were utilized to research morphology of the prepared composite nanofibers and the distribution of TiO₂nanoparticles in the composite nanofibers and electrospraied particles.Fourier transform infrared spectroscopy（FT-IR）and X-ray diffraction（XRD）were used to study the chemical construction and crystallization behavior.At last,the gas sensing properties were tested by gas sensor test system,and the mechanism was studied.Results show that the Ti O₂/PVP particles were core-shell structure,and the improvement in gas sensing behaviors was attributed to the P-N heterojunctions formed between p-type PANI and n-type TiO₂.Electrospun cellulose acetate（CA）nanofibers were deacetylated to prepare regenerated cellulose nanofibers,and static water contact angles were used to investigate the hydrophily.The obtained cellulose nanofibers were immersed into TiO₂ sol to adsorb TiO₂ nanoparticles and then in situ polymerization was used to prepare cellulose/TiO₂/PANI nanofiber gas sensing materials.SEM was used to investigate the effect of adsorption time and the deposition of PANI on the morphology of the prepared fibers.XRD was used to detect the crystal form of TiO₂ particles and FTIR was utilized to study the content and structure of the materials prepared in every steps.In addition,the relationship between gas sensing properties and adsorption time and fiber morphology was studied.Results show that,hydrophobic CA was modified into hydrophilic cellulose nanofibers,and plentiful hydroxyl on the surface is beneficial to the adsorption of TiO₂ nanoparticles.The deposited TiO₂ nanoparticles were both anatase and rutile.When adsorption time was between one to three weeks,the gas sensing behaviors of cellulose/TiO₂/PANI improved with the increase of adsorption time,and when it was four weeks,the gas sensing behaviors got worse which may the results of bad morphology.Sol-gel,electrospinning and calcination methods were used to prepare flexible titanium oxide/silicon oxide（TS）nanofiber membrane to avoid the dependence on polymeric nanofibers as templates.In situ polymerization was used to deposite PANI on the TS nanofibers surface to obtain TS/PANI composite nanofibers as well.Morphology was investigated by SME,TEM and digital photos,and the effect of quality of tetrabutyl titanate（TBT）in the electrospinning solution on the fiber morphology was studied.Crystallinity of the TS nanofibers was investigated by XRD.Results show that when TBT was 8.5 g,there were slubs and beads.The prepared TS nanofibers membrane had ideal flexibility,and the most of the TiO₂ nanoparticles were rutile and a small amount was anatase.When TBT was8.5 g in the solution,the inorganic nanofibers became fragile,and gas sensing tests results show that,with the increase in TiO₂ quality,TS/PANI composite nanofibers got better sensing behaviors.However,when TBT was 8.5 g,their gas sensing properties became worse which maybe the results of the slubs and beads in the nanofibers.Acted as the source of copper oxide（CuO）,cupric acetate was added into the TS precursor electrospinning solution.Elelctrospinning and calcination methods were used to prepare CuO-TS nanofibers.PANI was deposited onto the surface of CuO-TS/PANI with heterojunciton by in situ polymerization.The effect of cupric acetate content in the solution on the morphology and gas sensing behaviors was investigated.Results show that when cupric acetate was more than 0.30 g,beads came out.Heterostructured CuO-TS/PANI composite nanofibers show high response values,ideal sensitivity and selectivity and repeatability.CuO helped to improve the ammonia sensing of the composite naofibers which may result from the dedoping of PANI,interaction of different heterojunctions,and the structure similar to field-effect tube（FET）formed by PANI,CuO,TiO₂,SiO₂,which can amplify signal during the gas sensing process.Finally,the study about ammonia sensing process of PANI in molecular scale was operated with molecular dynamics（MD）.MAPS and VMD were the main software as tools to do radial distribution function（RDF）,mean square displacement（MSD）and interaction energy analysis for the simulation systems to help us understand better about athe mechanism of PANI ammonia sensing process in molecular scale.