Research On Room Temperature Ammonia Sensor Based On Polyaniline/Oxide Nanostructure Sensing Material

Gas sensors are key devices for obtaining information on gas concentration or types,and have important applications in many fields such as environmental monitoring,security monitoring,smart home and smart medical.Among them,gas sensors based on conductive polymer sensing materials have the advantages of low cost,simple fabrication process,low operating temperature and good selectivity,which are powerful alternatives for low-power and high-performance gas sensors,and have received wide attention.In this thesis,PANI/oxide nanostructure was used as the matrix sensing materials,and the room temperature ammonia sensors based on PANI/Au/SnO₂hollow nanospheres,PANI/Rh/SnO₂hollow nanotubes,PANI/Mo S₂nanosheets/SnO₂nanotubes and PANI/SnO₂/Zn₂SnO₄porous nanospheres were constructed by hydrothermal synthesis,electrospinning and in situ chemical oxidation polymerization,respectively.And the sensitivity,limit of detection and response/recovery characteristics of PANI sensors were effectively improved by oxide nanostructure modulation,two-dimensional nanostructure assembly,noble metal modification and heterogeneous composite strategies.The prepared sensing materials were characterized structurally and morphologically,and the sensitization mechanism was systematically investigated as follows.（1）The room temperature NH₃ sensor with low lower detection limit based on PANI/Au/SnO₂hollow nanosphere sensing material and the highly sensitive room temperature NH₃sensor based on PANI/Rh/SnO₂hollow nanotube sensing material were fabricated using the strategies of oxide nanostructure modulation and noble metal modification,respectively.First,PANI/Au/SnO₂hollow nanosphere sensing materials were prepared by hydrothermal synthesis,impregnation and in situ chemical oxidation polymerization,and planar room temperature NH₃sensors based on PI substrates were fabricated.The results showed that the sensor based on PANI/2%Au/SnO₂sensing material showed a 2-fold increase in response value to NH₃with an extremely low limit of detection（10 ppb）compared with the sensor based on PANI sensing material.Next,a room temperature NH₃sensor based on PANI/Rh/SnO₂hollow nanotube sensing material was constructed using electrospinning and in situ chemical polymerization.The results showed that the fabricated sensor exhibited the best NH₃sensitivity performance at room temperature when Rh was added at 0.5mol%,with a response value of 13.6 for 100 ppm NH₃.Notably,the response value for 50 ppm NH₃was only decayed by 13%after 500 times of continuous bending,demonstrating good bending resistance properties.The initial exploration for the development of a flexible wearable gas sensor was carried out.The improved gas sensing performance is mainly attributed to the high catalytic activity of noble metals on NH₃molecules and the synergistic sensitization effect of PANI-SnO₂heterojunction.（2）The room temperature NH₃ sensor based on PANI/Mo S₂nanosheet/SnO₂nanotube sensing materials was constructed through oxide nanostructure design and two-dimensional nanomaterial assembly strategy by taking advantage of the good carrier transport ability of two-dimensional nanomaterials,which effectively enhanced the sensitivity and response speed of the sensor.The PANI/Mo S₂nanosheet/SnO₂nanotube composite sensing materials were prepared by electrospinning,hydrothermal and in situ chemical oxidation polymerization methods.The structure,morphology,thermal stability and specific surface area of the sensing materials were characterized by XRD,XPS,TGA-DSC,BET and SEM/TEM.SnO₂was a hollow tubular structure with a diameter of about 400 nm,and Mo S₂nanosheets and PANI nanofibers were uniformly wrapped on the surface of SnO₂hollow nanotubes.The results showed that the response value of PANI/Mo S₂/SnO₂-based sensor was 3.1times higher than that of the PANI-based sensor for 100 ppm NH₃.The sensor showed a response time of only 21 s for 20 ppm NH₃,and also exhibited good repeatability and selectivity.The improved sensor sensitivity performance was attributed to the special nanofiber/nanosheet/hollow nanotube assembly structure and the p-n heterojunction formed between PANI-Mo S₂.（3）To further enhance the sensitivity of the sensor,a highly sensitive room temperature NH₃sensor based on PANI/SnO₂/Zn₂SnO₄porous nanospheres was constructed by oxide composite nanostructure material design and heterostructure building strategy.The core-shell structured sensing materials with PANI nanofibers as the shell and SnO₂/Zn₂SnO₄porous nanospheres as the core were prepared by hydrothermal method and in situ chemical oxidation polymerization with a large specific surface area（64.8 m²/g）.The sensor with PANI/10 mol%SnO₂/Zn₂SnO₄porous nanospheres as the sensing material exhibited the highest response value（20.4）for 100 ppm NH₃,which was 6.6 times higher than that of the pure PANI-based sensor.The sensor exhibited a lower detection limit of 500 ppb for NH₃and response and recovery times of 46 s and 54 s for 100 ppm NH₃,respectively,along with good repeatability,selectivity and stability.The significant improvement of the sensor sensitivity performance related to the deprotonation of PANI and the p-n heterojunction formed by PANI/SnO₂/Zn₂SnO₄composite was further verified using electrochemical impedance tests.