Room Temperature Flexible NH₃ Gas Sensors Using Polyaniline-based Nanocomposites Sensitive Materials

Gas sensor is an important means to obtain the information of gas composition and concentration,and has important applications in military/anti-terrorism/industrial/household security,environmental monitoring,medical diagnosis,and artificial intelligence.This research focuses on the construction of room temperature flexible NH₃ sensor with polyaniline?PANI?nanocomposite sensitive materials,combines with the current research status and development trend of flexible room temperature sensor.Systematical research works have been carried out in terms of the design/preparation/optimization of new sensitive materials,the study of material structure and device performance,and the discussion of sensitive mechanism.Porous structure of SnO₂@PANI,flower-like WO₃@PANI,hollow spherical WO₃@PANI and Au-loaded mesoporous In₂O₃ nanosphere@PANI composite sensitive materials were prepared by hydrothermal and in-situ chemical oxidation polymerization methods.The flat room temperature NH₃ sensors were fabricated on flexible polyethylene terephthalate?PET?substrates,and NH₃ sensing properties were investigated.The rambutan-like polyaniline hollow nanosphere?PANIHs?and graphene oxide?GO?-PANIHs hybrid were prepared by in-situ chemical oxidative polymerization method and assembled to the high performance gas sensor based on flexible PET substrate for NH₃ detection at room temperature.Compared with the PANI sensor,the NH₃ sensitivity was significantly improved.The details research contents are as follows:?1?The NH₃ sensor based on SnO₂@PANI nanohybrids were successfully synthesized via a combined approach of hydrothermal and in-situ polymerization and the gas sensing properties were studied at room temperature.From SEM and TEM images of the obtained SnO₂,we could see the SnO₂ with loose porous structure was made up of pretty small particles.The SnO₂@PANI nanocomposites were prepared by in-situ polymerization and assembled on PET substrates to prepare room temperature NH₃ sensors.The results of gas sensing performance indicated that:compared with PANI sensor,the device utilizing 20 mol%SnO₂@PANI?PASn20?hybrid exhibited 10.3 times higher response(R_gas/R_air=31.8)to 100 ppm NH₃ at room temperature.Furthermore,the PASn20 sensor possessed ultra-low detection limit of 10 ppb NH₃ and outstanding selectivity.The enhanced sensing performance was attributed to the micro-structure with large specific surface area and the formation of p-n heterojunctions at the surface between PANI and SnO₂.?2?In order to study the effect of morphology on the gas sensing properties of sensitive materials,gas sensors based on flower-like WO₃@PANI nanohybrid and WO₃ hollow sphere@PANI nanohybrid were prepared.The hierarchical flower-like WO₃ and hierarchical WO₃ hollow spheres were synthesized by hydrothermal method.SEM and TEM images showed that the flower-like WO₃ were assembled by many smooth nanosheets with a thickness of approximate 50 nm,and the WO₃hollow spheres were composed of organized WO₃ nanocrystals,both the prepared hierarchical WO₃ nanomaterials had great dispersity.The NH₃ sensor based on the flower-like WO₃@PANI hybrids and the WO₃ hollow sphere@PANI hybrids were prepared by in-situ polymerization.Gas-sensing performances of fabricated flower-like WO₃@PANI sensors were tested and results indicated that the sensor with 10 mol.%flower-like WO₃@PANI exhibited the highest response value at approximately 20.1 to 100 ppm NH₃ at room temperature.Notably,the lowest detection limit of 500 ppb to NH₃ was obtained at room temperature.For WO₃hollow spheres@PANI hybrid sensors,the NH₃ sensing properties demonstrated that the device utilizing 10 mol%WO₃ hollow spheres@PANI?PAWHs 10?hybrid exhibited the best sensing performance to 100 ppm NH₃?response value at 25?at room temperature.Moreover,the PAWHs10 hybrid sensor also achieved ppb-level detection limit?1.67-500 ppb NH₃?.Compared with the PANI sensor,the gas sensing properties of both WO₃@PANI hybrids sensors were greatly improved,due to the morphology structure of WO₃ and p-n heterojuction between PANI and WO₃.?3?Room temperature gas sensor based on Au-loaded mesoporous In₂O₃nanospheres@PANI core-shell nanohybrid assembled on flexible PET substrate for NH₃ detection were developed.The mesoporous In₂O₃ nanospheres were synthesized by hydrothermal method,and Au nanoparticles were introduced for modifying the mesoporous In₂O₃ nanospheres by wet impregnation method.The impacts on the sensing performance of Au-loaded mesoporous In₂O₃ nanospheres@PANI core-shell nanohybrid sensors were well studied.The results showed that the sensor utilizing 1 at%Au-loaded 20 mol%mesoporous In₂O₃ nanospheres@PANI core-shell nanohybrid?PAIn20A1?exhibited the highest response value?⁴6?to 100ppm NH₃ at room temperature,which were about 14 times and 4 times higher than those of pure PANI and PAIn10.The improved sensing performance was attributed to synergistic effect of p-n junction of PANI and mesoporous In₂O₃ nanospheres and the catalytic effect of Au.?4?Room temperature high performance NH₃ sensor based on GO-rambutan-like polyaniline hollow nanosphere hybrid assembled to flexible PET substrate were designed.SEM and TEM images displayed that the diameter of the uniform rambutan-like PANI hollow nanosphere with a large number of nanorods was about 400-500 nm,the diameter of hollow sphere and the length of nanorods array were about 250 nm and 100 nm,the hollow rambutan-like structure was favorable to increase the specific surface area and adsorption sites.The gas sensing performance of the assembled sensors indicated that the sensor based on GPA0.5exhibits the best sensitivity of response value of approximately 31.8 to 100 ppm NH₃,excellent selectivity and ultra-low detection limit of 50 ppb.This enhanced sensing performance is related to the rambutan-like polyaniline hollow nanosphere nanostructure and synergetic effects of GO and PANIHs.