Conjugated Polymer Based Toxic And Harmful Gas Sensors

Recently,precise detections of toxic and harmful gases have been widely used to monitor the air quality in real-time.At present,the requirements of common polluting gases proposed by the environmental protection department have reached ppb level,which improved the requirements of sensing performance.Large instruments could achieve high detection accuracy,but they have problem including complex operation and large volume,which are not suitable for great deal application.The grid atmospheric monitoring system mainly relies on low-cost and small gas sensors,such as inorganic semiconductor,electrochemical,catalytic combustion and so on.However,these sensors are difficult to detect gas molecules without obvious redox properties(e.g.,benzenes).The reason is that sensitive materials lack specific recognition ability for these gases.With the development of organic semiconductors,gas sensitive materials represented by conjugated polymers show unique structural tunability and special advantage on sensing mechanism,and have great potential in the detection of toxic and harmful gases.But there is still a lack of specific research on the detection of different types of gases by conjugated polymers based gas sensors.According to the requirement of rapid,sensitive and selective detection toward toxic and harmful gases,we studied the organic thin film gas sensors based on conjugated polymers,the mechanism of gas molecular adsorption and sensing signal generating process were also demonstrated.Toluene,chlorobenzene,1,2-dichlorobenzene and o-xylene with similar chemical structure were discriminatively detected by conjugated polymer based sensor array.In addition,poly(bisdodecylthioquaterthiophene)(PQTS12)-FeCl₃ based flexible gas sensor was prepared to detect the low concentration dimethyl methylphosphonate(DMMP).The specific researches are listed as follow:1.In order to solve the problems including high resistance and low signal-to-noise ratio(SNR)of conjugated polymer based thin films,the p-type polythiophene conjugated polymer poly(bisdodecylquaterthiophene)(PQT12)doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane(F4TCNQ)was demonstrated.The dopant enhanced the carrier transport along the?-?stacking direction,which could help achieve higher conductivity and sensor signal conversion ability through the carrier injection.Inducing by the dopant,the detection of ppm level of 1,2-dichlorobenzene is realized.2.Since benzene gas molecules have similar chemical structures and are difficult to be distinguished,the competitive interaction between swelling effect and molecular rearrangement effect is analyzed by studying the dynamic process of conjugated polymer molecules,and the adsorption mechanism of benzene gas molecules and signal generation mechanism are revealed.Then,by analyzing the sensor signal curve,the recovery factor K of various benzene gas molecules was defined,and the identification methods of toluene,chlorobenzene,1,2-dichlorobenzene and 1,2-xylene with similar chemical structures were demonstrated.3.Nerve agents are much more harmful than benzenes and need to be monitored in real time via wearable devices.In order to realize flexible and wearable function of gas sensor,the nerve agent simulator(DMMP)gas sensor based on conjugated polymer was studied.By using dopant to improve the electrical conductivity of polymer film,we further verified the structure-activity relationship between the chemical structure of the backbone and side chain of conjugated polymers and the bending resistance of the films.Our experiments indicated that PQTS12-FeCl₃ has both high conductivity and good bending resistance.The flexible gas sensor based on this material could achieve sensitive DMMP detection with a 5ppb limit of detection,and still showed good repeatability and stability after multiple bending.In conclusion,the conjugated polymers based gas sensors proposed in our researches can achieve high sensitivity and selectivity detection of benzene gases and DMMP,which has the advantages of simple preparation process,low cost and low power-consumption.We anticipate this general approach could inspire the design and manufacture of toxic and harmful gas sensor.