| In recent years,with the increasing degree of the air pollution,people pay more and more attention to the air quality of their living and working environment.Some harmful gases such as formaldehyde,benzene,methanol and acetone are the main reasons causing leukemia,the respiratory,nervous and immune system diseases.To detect low concentration of these toxic and harmful gases has become one of the important topics in the scientific community.What is more,the concentration of methanol and acetone gas exceeds a certain quantitative will cause explosion accidents.In order to reduce the damage caused by complex gas pollution,therefore,not only are gas-sensing materialsand the sensor array with high selectivity,high response,low energy consumption,low cost and simultaneous detection of various toxic and harmful gases necessary,but also have important application prospect.Although the detection of toxic and harmful gasesin the field of gas sensors has achieved some results,but the current sensors cannot meet the standard of practical requirements in the aspects of sensitivity,selectivity and operating temperature.Hence,in this dissertation,Ag-LaFeO3(ALFO)was further modified to achieve formaldehyde and benzene sensors with high sensitivity,high selectivity and low operating temperature.In this dissertation,using molecular imprinting technique(MIT),formaldehyde and benzene used as template molecule,respectively,an ideal gas-sensing material ALFO explored by our group used as crosslinker,then materials with specific recognition sites and high selectivity respectively to formaldehyde and benzene were achieved.The materials are formaldehyde molecular imprinted polymer based on ALFO(FMI-ALFO)and benzene molecular imprinted polymer based on ALFO(BMI-ALFO).Then FMI-ALFO and BMI-ALFO were optimized with morphology control and graphene series materials.The structure,component,morphology and special surface area were characterized by XRD,SEM,TEM,FT-IR and BET,etc.The gas-sensing properties(including sensitivity,selectivity,response-recovery characteristic,the optimal operating temperature and stability)were tested through gas-sensing tester.The main results are as follows:(1)FMI-ALFO and BMI-ALFO were prepared by hydrothermal and templating methods into materials with special microscopic appearance,such as one-dimensional fibers,three-dimensional sphere and hollow cage.The special morphology of the material is arranged by the small particles of tens of nanometers.The particles are arranged in a certain order and configuration in order to improve the efficiency of electron transmission to a certain extent,thereby reducing the operating temperature.FMI-ALFO and BMI-ALFO fiber or cage possess high sensitivity,high selectivity and low operating temperature to formaldehyde and benzene.(2)FMI-ALFO and BMI-ALFO were modified by using low resistivity graphene series materials(Graphene(rGO),graphene oxide(GO),graphene quantum dots(CQDs)and B,N,S and Cl doped CQDs).GO and rGO were prepared by Hummers method,and CQDs were prepared by liquid phase exfoliation method,the structure,morphology,optical properties and gas-sensing properties of the graphene series materials were characterized,the results proved that the prepared materials are indeed a series of graphene materials.And it is found that by doping CQDs with the B element with the outermost electron number less than C element obtained p-type CQDs.While doping CQDs with the N,S and Cl element obtained n-type CQDs.The operating temperature of both FMI-ALFO and BMI-ALFO is 125?.When the FMI-ALFO and BMI-ALFO are modified by GO or rGO,the operating temperature can be reduced by 40 ? on the basis of the original 125? under the premise of maintaining high response and high selectivity.The p-type B doped CQDs(B-CQDs)can reduce the operating temperature by 60-70? because of the synergistic effect of the gas sensing mechanism with p-type ALFO.(3)A gas sensor array that can simultaneously detect formaldehyde,benzene,methanol and acetone:FMI-ALFO,BMI-ALFO,and ALFO based methanol-and acetone-sensing materials from our group were adopted.The 4 kinds of materials were fabricated on an array,and the gas-sensing properties of the array were tested.Results show that the array can simultaneously detect formaldehyde,benzene,methanol and acetone or any combination of them even with the disturbance of the interferences.Furthermore,the array exhibits good stability and the relationship between response and gas concentration is near linear,indicating that the array could be applid to the real-time monitor of formaldehyde,benzene,metnanol and acetone in air.(4)The mechanism of improving selectivity by MIT,reducing operating temperature by morphology control and graphene modification were clarified.This research is innovative in modification method,original in simultaneous detection method of various gas and advanced in main performances of the sensors. |
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