Investigation On Adjusting Carbon Nano-capsule Composite For High-performance Gas Sensor

The gas sensor plays an important role in the research area of environmental safety,due to its the unique advantages of gas-sensing function,fast response,and wide application range.In addition,the design,construction and optimization of new materials directly determine the level of miniaturization and refinement for sensors.The rapid development of sensors put forward higher requirements for preparation technology and innovation of related sensing materials.The core materials of gas sensors can be roughly summarized as carbon materials,metal oxides,polymer materials and so on.Among them,the carbon materials were diffusely studied composite substrates,according to different bonding methods(sp,sp²,sp³,etc.),which are divided into carbon nanotubes(twisted sp²),graphene(sp²),diamond(sp³)and their homologs.However,due to the good chemical stability of carbon-based materials,the as-designed corresponding sensors possess poor selectivity and unsteadiness.Essentially,carbon materials are difficult to chemically combine with other gas molecules,resulting into a limited application field.Therefore,it is necessary to design novel carbon-based composite to enhance the surface durability,Chemical binding force and adjust interface and band structure.In particular,carbon nano-capsule(CNC)materials with unique hollow structures accordingly come to arise.CNC are self-tunable,hollow,and open-ended with the feature of thin-wall,defect-rich edges and good conductivity and stability.The advantageous CNC structure owns larger surface area with abundant active sites,but the performances of separately designed CNC are inadequate and limited by many factors.To utilize the advantages of unique structural and obtain better gas-sensitivity for CNC,reasonable technical means are employed to design novel materials.Above all,the design of the novel CNC composite structure relies on the development of novel composite materials with three-dimensional conductive network and CNC encapsulating the traditional semiconductor metal oxides to form novel composite material with unique ring structure,giving rise to excellent performances of gas sensors.Firstly,conductive polymer materials are the key research focus,of which polyaniline is of particular interest owing to its diversified molecular structure.Moreover,it possesses high sensitivity,fast response speed and good reversibility to ammonia.Because of those advantages,it becomes one of the hot conductive materials currently studied.In the meanwhile,the CNC structure owns rich oxygen-containing groups as template of composite material to achieve in-situ polymerization of polyaniline.Therefore,the designed CNC/polyaniline composite material with a unique three-dimensional hollow hybrid structure has excellent structural stability.The composite material possesses fine interface structure with large surface area,delivering a large quantity of ammonia adsorption sites which are extremely sensitive to low-concentration ammonia,laying a solid foundation for good response characteristics.Furthermore,the CNC in the middle layer serves as a three-dimensional conductive network,which also enables the composite material to respond and recover quickly for ammonia sensing.Moreover,the synergistic effect between polyaniline and CNC makes the composite material own superior ammonia response characteristics.The improvement of its response characteristics is reflected in the high response value of 1.30 and the short response/recovery time of 34s/42s for NH₃ at a concentration of 10 ppm.In addition,the carbon nano-capsule/polyaniline composite material has excellent repeatability,high selectivity and robust stability at ambient temperature.Further,the sensor also exhibits high sensitivity to NH₃concentration as low as 5 ppm(response value is 1.10)and has a linear response in the wide range of NH₃ concentrations.Furthermore,this paper utilizes traditional semiconductor metal oxide nanomaterials to seek new breakthroughs.Therein,ferrite has been widely researched as a classic semiconductor material,which is highly and promptly sensitive to ethanol.The?-Fe₂O₃nanomaterials with unique ring structure are picked out as compound raw materials.Carbon nano-layer is precisely coated on?-Fe₂O₃ nanoring with a catalytic chemical vapor deposition(CCVD)method.The prepared CNC/?-Fe₂O₃ composite material with three-dimensional hollow ring novel microstructure,whose inner diameter is?60.1 nm and wall thickness is?46.8 nm.The double surficial strain effects of?-Fe₂O₃@C nano-cylinders make atomic carbon layers effectively adsorb ethanol,which results in the improvement in material response characteristics.At the same time,the composite effect of carbon nano-capsules and?-Fe₂O₃ enhances the electronegativity of O 2p electrons in?-Fe₂O₃ with improved response/recovery time and enhanced stability.At the same time,the characterizations demonstrate that the composite effect between carbon nano-capsules and?-Fe₂O₃ enhances the electronegativity of O 2p electrons in?-Fe₂O₃,which also allows for significant enhancements in sensing properties.When applied as gas sensing material,the?-Fe₂O₃@C NCs showed?twice faster response/recovery time.Moreover,it showed much more remarkable gas selectivity for ethanol as compared with other gaseous species,with outstanding stability reaching 384 hours.In summary,this work develops a novel type of carbon nano-capsule composite structures for gas sensitive materials,providing promising opportunities to achieve high-performance next-generation gas sensors for better real-life applications.