Research On Construction Of DMMP Gas Sensors And Their Sensing Mechanism

Organophosphate compounds are a kind of phosphoric acid derivatives containing organic groups,which has a strong inhibitory effect on acetylcholinesterase in organisms and is widely used in agriculture fields as insecticide.At the same time,organophosphate compounds with high toxicity are also used as chemical warfare agents.With the widespread use of organophosphorus pesticides and the frequent occurrence of terrorist incidents,the development of gas detection instruments with high sensitivity,fast response and low cost for the detection of organophosphate compounds has become a research hotspot and difficulty in the field of gas detection.Chemiresistive gas sensors have great application prospects in the detection of organophosphate compounds due to their advantages of small volume,simple structure,low cost and easy integration.At present,many researches mainly focus on the side-heated gas sensor based on oxide semiconductor and the room temperature gas sensor based on carbon materials.However,the working temperature of the oxide semiconductor-based gas sensors is higher,while the room temperature-based gas sensors have low sensitivity and slow response recovery speed.Moreover,the interaction mechanism between sensing materials and organophosphate molecules in the sensing process needs further study and summary.To solve the above problems,this paper takes dimethyl methylphosphonate（DMMP）,a mimic of organic phosphate compounds,as the detection object,and takes tin dioxide（SnO₂）and graphene as two typical sensing materials.By adjusting the surface and interface structure of the sensing materials,the recognition function,conversion function and sensor utilization rate of the sensing materials for DMMP molecules are improved,thus improving the sensing properties of the sensor.In addition,the internal relationship between microstructure and gas sensing performance of sensing materials have been studied in detail,and the sensing mechanism of different DMMP gas sensors is summarized.The main research contents are as follows:（1）The high-performance DMMP gas sensor based on Au nanoparticles（Au NPs）modified oxygen vacancy-enriched SnO₂ was constructed,and the sensitization mechanism based on the synergistic effect of noble metal activation and oxygen vacancy regulation is proposed.Commercial tin dioxide（C-SnO₂）was selected as the matrix materials,oxygen vacancies and Au NPs were introduced on the C-SnO₂ surface（Au-O-SnO₂）through metal organic chemistry-assisted strategy and in-situ reduction method,respectively.The response of Au-O-SnO₂ sensor to 680 ppb DMMP at 320℃ is 1.67,which is obviously better than that of C-SnO₂ and O-SnO₂ sensors.In the sensing mechanism,on the one hand,the introduction of oxygen vacancies increases the concentration of chemically adsorbed oxygen on the sensing materials surface;On the other hand,the chemical and electronic sensitization of Au NPs reduces the activation energy of gas sensing reaction.（2）The high-performance DMMP gas sensor based on self-assembled Au NPs and SnO₂ NPs were constructed,and the sensing mechanism based on the interaction of catalytic reaction and hydrogen bonds was proposed.Au NPs modified SnO₂ sensing materials（Au-SnO₂）were prepared by electrostatic self-assembly of colloidal particles.The response of Au-SnO₂ sensor to 680 ppb DMMP reaches 1.88 at 200℃.The reduced size of the sensing materials not only reduces the working temperature of the sensor,but also improves the sensitivity of the sensor.By studying the DMMP sensing performance of Au-SnO₂ sensor in oxygen（air）and absence of oxygen（N₂）background atmosphere,it is summarized that the enhanced sensing performance of the sensor is attributed to the chemical reaction between DMMP molecules and surface chemisorbed oxygen and the hydrogen bond between DMMP molecules and SnO₂.Finally,the mobile detection device is constructed to realize the leakage warning of low concentration DMMP by designing the external detection circuit.（3）The high-performance room-temperature DMMP gas sensor based on polypyrrole（PPy）decorated reduced graphene oxide（rGO）was fabricated,and the room-temperature sensing mechanism based on hydrogen bonding was proposed.PPy modified rGO sensing materials were prepared by one-step hydrothermal method based onπ-πinteraction between pyrrole monomer and graphene oxide.The response of PPy-rGO sensor to 100 ppm DMMP at room temperature is 12.9%,which is three times higher than that of rGO sensor（3.4%）.PPy-rGO sensor also shows fast response and recovery time（43 s/75 s）,low detection limit（5 ppm）and excellent repeatability.The enhanced DMMP sensing mechanism of PPy-rGO sensor is attributed to the formation of reversible hydrogen bonding between DMMP molecules and PPy in sensing materials.（4）The room temperature flexible DMMP gas sensor based on Cu^x+ion modified PPy-rGO materials was developed,and the novel sensing mechanism based on Cu^x+ions-assisted heightening hydrogen bonds was proposed.Cu^x+ion modified PPy-rGO sensing materials were prepared by impregnation method,and then used to construct flexible DMMP sensors.The influence of Cu^x+ions introduction on the microstructure and gas sensing properties of the sensing materials was systematically investigatied.The response of Cu^x+-PPy-rGO sensor to 100 ppm DMMP at room temperature is four times that of PPy-rGO sensor,and its detection limit is reduced to2 ppm.Through density functional theory（DFT）calculation and quartz crystal microbalance（QCM）test,it is confirmed that the introduction of Cu^x+ions to enhance the hydrogen bonding force between PPy and DMMP,which significantly improves the adsorption capacity of sensing materials to DMMP molecules.（5）The room temperature flexible DMMP gas sensor based on hexafluoroisopropanol benzene（HFIP）group modified PPy-rGO was constructed,and the novel sensing mechanism based on the synergistic effect of two hydrogen bonds was proposed.HFIP functionalized PPy-rGO sensing materials（HFIP-PPy-rGO）were prepared by aryl diazonium functionalization method.Compared with PPy-rGO sensor,HFIP-PPy-rGO sensor shows enhanced response and selectivity to DMMP is attributed to the modification of HFIP group enhances the recognition function and conversion function of PPy-rGO sensing materials to DMMP molecules.In addition,the portable intelligent detection system was developed,which realizes the real-time detection of DMMP concentration in the environment.