The Investigation Of Design,Fabrication And Gas-sensing Properties Of Graphene Based Nanocomposite Films

Air pollution recently has been regarded seriously for its damage to human health and public security.Therefore,the development of high-sensitivity gas sensors for real-time rapid detection of toxic and flammable gases is significant and valuable.Graphene,with all carbon atoms exposure to ambient,possesses fancy electrical properties and performs excellently in the field of room-temperature gas sensing.However,pristine graphene shows inherent difficulty in the aspects of saturation,restoration and gas selectivity during the sensing process,due to its intrinsic wrinkles and cumulative electrons effect.In this paper,different technical routes and processes,including the optimization of the preparation process of rGO and conducting polymer based composite film,fabrication of rGO-metal oxide-conducting polymer based ternary composite gas-sensing materials,establishment of the internal mechanism of heated GO film and improvement of morphology modification of rGO film were employed to improve the sensing performance of interdigital electrodes-based sensors through compositing with metal oxides or conducting polymers.The homologous gas-sensing mechanisms were also investigated and analyzed.The main content includes the following points:1.A co-sprayed method was developed to fabricate rGO-P3HT composite film for NH₃ sensing application.This new technique could mix mutually exclusive materials completely by using associated quasi-gaseous dispersed sensitive solution.The results showed theπelectrons could delocalize between the soft composite films.The sensing results revealed that the co-sprayed rGO-P3HT composite sensor exhibited better room-temperature sensing properties,including responsivity,sensitivity,repeatability,restoration speed and selectivity,in comparison to single rGO,P3HT and rGO/P3HT layered-film sensors,due to its improved contact interfaces,the formation ofπelectrons delocalization-transiting system and p-n heterojunction between rGO and P3HT.2.rGO@SnO₂-PANI composite film was fabricated for the NH₃ detection by using in-situ chemical oxidation polymerization and spin coating method.The spectral analysis results showed the interaction between rGOS and PANI was improved and band gap was broadened in composite film.The XRD results showed that rGOS plates anchored with PANI nanofibers,establishing a stable physical structure.The morphologies of porous sensitive films showed the composite could obtain thinner nanofibers with higher specific surface area due to the introduction of rGOS.The composite sensor possessed advantages in the fields of restoration speed,repeatability and sensitivity compared with that of bare rGOS and PANI based sensors.Besides,the composite sensor reached a detection limit of 69 ppb and bare PANI-based sensor showed that of 803 ppb through the analysis of noise theory,further indicating the advantage of composite sensor.3.rGO/TiO₂ layered composite sensor was developed for formaldehyde sensing application through spray and thermal reduction method.The spectral analysis results showed Ti-O-C bond was formed between rGO and TiO₂ after the thermal treatment.An interesting abruption behavior of rGO sheets during the heating process was observed using SEM,which would be induced by the pristine negative thermal expansion characteristics of graphene.The sheets would be ruptured along with the hollows and defects left on carbon network when the accumulated tension reaches a certain value.While the dissociation of rGO honeycomb network was prevented in rGO/TiO₂ layered film upon elevated temperature due to the supporting function of subjacent TiO₂ nanoparticles.Restoration of conductivity was verified by measuring the resistance of rGO-based sensor（19.78 kΩ）and composite sensor（1.27 kΩ）.The composite sensor showed excellent sensing properties to 0.1 ppm-0.5 ppm formaldehyde.In addition,a verification test was proposed and executed to analyze the role of TiO₂ nanoparticles in composite sensor during the sensing process.The results indicated the combination of catalytic activity and supporting function of TiO₂nanoparticles contribute to the improved sensing performance of rGO/TiO₂ layered composite sensor.4.rGO-TiO₂ composite sensor was fabricated for the NH₃ sensing application by hydrothermal method,and the influence of TiO₂ on the rGO physical appearance was also investigated.The spectral analysis results showed Ti-O-C bond could be established between rGO and TiO₂ during the hydrothermal process.The SEM results showed porous rGO film could be induced by the introduction of TiO₂.Moreover,the quantity of TiO₂ compositing with rGO played an important role for the sensing properties of rGO-TiO₂ composite sensor.The rGO-96TiO₂ composite sensor（the weight ratio between GO and TTIP is 1:96）showed a best sensing performance under10 ppm NH₃ with high responsivity（-1.7）,good restoration ratio（100%）,fast responding/restoring speed（114 s/304 s）.In comparison to bare rGO based sensor,the composite sensor revealed a significantly enhanced sensing performance due to its improved porous morphology and consequently increased active adsorption sites.