Preparation And Ammonia Gas Sensing Behavior Of Flexible SiO₂/PANI Composite Nanofibers

Air pollution is one of the four major environmental hazards with noise pollution,water pollution and solid pollution,which has received great attention of the whole society due to its significant harm to human health and circumstances.The monitoring of pollutant is a timely and effectively measure to control air pollution.Gas sensor is a kind of sensing element that convert the target gas information into electrical signal by physical or chemical reaction.Moreover,the research of novel gas sensing material is the core motivation of sensor development.In recent years,inorganic/organic composite sensing material have aroused much attention because of their high response values,ideal selectivity and repeatability,which are developing towards wearable application.In this paper,we prepared two kinds of gas sensing materials by using flexible silica?SiO₂?nanofibers membrane as template,and applied them for detecting ammonia?NH₃?at different concentration.The main research contents are as follow:The flexible SiO₂ nanofibers membranes were prepared by the combination of sol-gel,electrospinning and calcination process with tetraethyl orthosilicate?TEOS?as Si source.The morphology of SiO₂ nanofibers were studied by scanning electron microscope?SEM?and digital photographs,in order to investigate the effect of calcination temperature on nanofibers morphology.Energy dispersive X-ray?EDX?,X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?were utilized to research the chemical composite and crystal form of nanofibers.In addition,the forming process of flexible SiO₂ nanofibers were restored by thermogravimetric analyzer?TG?.Results show that the SiO₂ nanofibers obtained from600�C and 800�C had well flexibility,and the nanofibers were amorphous in structure.Upon increment of calcination temperature to 1000�C,the nanofibers aspect ratio increased sharply.Meanwhile,the amorphous phase transferred into cristobalite phase with a small amount of tridymite phase and nanofibers membranes changed from flexible to brittle.The flexible and free-standing of SiO₂ nanofibers were closely related to the type of precursor polymer,parameter of precursor solution and calcination temperature.The SiO₂/PANI composite nanofibers were fabricated via in-situ polymerization based on SiO₂ nanofibers.The morphology and component of composite nanofibers were characterized by SEM,XRD,EDX and FTIR.The ammonia sensing behavior of SiO₂/PANI composite nanofibers were investigated by gas sensitive test system,and the response mechanism of this material was analyzed from multi-angle.The results show PANI was deposited on the surface of SiO₂ nanofibers,and SiO₂/PANI composite nanofibers presented well core-shell structure.Further tests indicated that the SiO₂/PANI had outstanding selectivity,repeatability and reversibility,even the minimum measurable concentration could reach to ppb level.The high sensing responses was ascribed to the SiO₂ structure and distinct protonation/deprotonation reaction between PANI and ammonia.To further improve the ammonia sensing properties of materials,the SiO₂-CeO₂composite nanofibers were prepared by sol-gel,electrospinning,electrospray and calcination technological means.And SiO₂-CeO₂/PANI composite nanofibers were obtained on this foundation via in-situ polymerization.The morphology and component of composite nanofibers were characterized by SEM,XRD,EDX and FTIR,and the gas sensing properties and response mechanism were studied.The results demonstrated that the CeO₂ particles were loaded on the surface of the nanofibers.The introduction of CeO₂ helped to improve the ammonia sensing performance of composite materials,which may combined effected by protonation/deprotonation reaction and the formation of p-n heterojunction.