Research On High Sensitivity Ammonia Gas Sensor Based On Light Excitation And Their Sensing Characteristics

As a toxic chemical raw material,ammonia has been widely used in various aspects such as agriculture,food processing,medical diagnosis and environmental restoration.However,it is also one of the most harmful environmental pollutants produced in the manufacturing process and industrial production.The deterioration of high-protein foods will cause most toxic gases（such as ammonia）to be released to the outside.The freshness of such foods can be judged by monitoring the ammonia concentration.Therefore,the development of high-performance gas sensors that can quickly and accurately detect ammonia is of great significance to human safety and health.Light-excited gas sensors have great application prospects in gas detection.In this thesis,the effect of doping different sensitive materials（noble metals,new two-dimensional materials,polymers）on the gas-sensing properties of modified metal oxides under light excitation conditions was investigated.A seed-mediated growth of dumbbell-like Au-Fe₃O₄heteronanostructures gas sensor was first proposed to achieve the purpose of detecting ammonia at room temperature.The ammonia sensing performance of Au-Fe₃O₄heterogeneous nanostructures has been greatly improved by adjusting the size of Au nanoparticles under green light irradiation,which can be attributed to the LSPR effect of the Schottky junction formed at the interface between Au and Fe₃O₄.In addition,the density functional theory（DFT）calculations proved that the doping of Au is beneficial to enhance the adsorption capacity of Fe₃O₄for ammonia.The groups on the surface of polymer will provide a large number of adsorption sites for gas molecules,and the existence of hydrogen bond groups is conducive to the adsorption of amino groups.Based on this,a way is proposed to form heterostructures through two-dimensional polyimide（2DPI）that is rich in hydrogen bond groups combines with metal oxide to improve the sensor’s sensing performance.The DFT results show that 2DPI monolayer with 2D structure and hydrogen bonds is a good candidate for detecting ammonia.Afterwards,the 2DPI modified In₂O₃composite material was synthesized by hydrothermal method.After characterization and sensing performance testing,the corresponding results show that the synergistic effect between 2DPI and In₂O₃leads to a three-fold increase of response under UV irradiation compared with in the absence of UV irradiation.The enhancement of sensing performance can be attributed to 2DPI/In₂O₃helps to enhance utilization of UV light,reduces the recombination rate of active electron-hole pairs,and the hydrogen bond in 2DPI can act as chemisorption promoter in the composite structure.To meet the needs of gas sensors in terms of stability,sensitivity and practicability,this thesis also proposes an ultra-sensitive ammonia gas sensor based on the in-situ growth of（001）Ti O₂on Ti₃C₂T_x,and it can be applied to actual monitoring.The（001）Ti O₂/Ti₃C₂T_xbased sensor has excellent gas sensing performance under UV irradiation.More importantly,a circuit alarm system was designed based on（001）Ti O₂/Ti₃C₂T_xsensor including near field communication（NFC）and microcontroller,which can detect the rotting process of fresh pork,fish and shrimp by monitoring the concentration of ammonia.In this thesis,the light excitation sensitization technology is employed to reveal the scientific issues related to light excitation gas sensing technology at room temperature in detail from the perspective of experiment and theoretical calculation,and a high performance room temperature light excitation resistive ammonia sensor is developed based on the proposed theory,and it can be applied to actual monitoring,which has important reference value for the research and development of a new type of high-performance ammonia gas detection device.