Research On Preparation Of Layered Double Oxide Gas Sensors And Sensing Properties Towards Reducing VOCs

Volatile organic compounds（VOCs）are those chemicals having a low boiling point at room temperature.Some are common indoor air pollutants（such as formaldehyde）,while others are important industrial products（such as acetone）.Those VOCs have paid much attention because various diseases it induces,such as bronchial asthma,atopic dermatitis and sick building syndrome.In order to protect the human health,it is of great significance to prepare safe and reliable gas-sensitive sensors.Binary metal oxide semiconductor materials are used widely in gas detection by reason of their good synergistic effect and heterojunction effect.According to the distribution of minority carriers,bimetal oxides of different heterojunction types（p-p,n-p,n-n type）have different response characteristics to reducing VOCs gas.In view of the current research and development trend of gas sensors,this paper presents an effective method to develop layered double oxide（LDOs）based gas sensor for VOCs detection by adjusting different heterojunction types and constructing amplification circuit.In this study,rarely explored p-type Cu-Cr layered double hydroxides（Cu Cr-LDHs）was successfully prepared by introducing sodium dodecyl sulfate（SDS）and adjusting p H value.Cu Cr,Zn Cr and Zn Ti-LDOs were prepared by using corresponding LDHs as precursors and self-sacrificing templates in order to investigate the effects of three types of heterojunctions on gas sensitivity.In terms of morphology,the three type of composite oxides exhibit two-dimensional layered structures similar with the employed precursor of LDHs.It is indicated that the heterostructured oxide based on p-Cr₂O₃ and p-Cu O,i.e.,the developed Cu Cr-LDOs,exhibits much larger sensing response towards reducing VOCs at room temperature,which is 3.5 or 13.3 times that of Zn Cr-or Zn Ti-LDOs,respectively.The response differences of the layered bimetal oxides were analyzed in terms of the local charge region modulation associated with heterojunction formation,and it is further demonstrated based on first-principles calculations and valence electron theory.The n-type ZnTi-LDOs composite gas sensor with the lowest gas response was improved by designing a system based on n-type enhanced FET for amplifying,transmitting and displaying response signals to realize effective amplification of weak response signals and display and storage of response signals in computer terminal.The results of gas sensitivity show that the n-type enhanced FET can amplify the response value of the n-type metal oxide gas sensor without affecting the response/recovery time.And the experimental data show that the magnification increases with the increase of gas concentration.At 40 ppm ethanol vapour,the designed amplification system can amplify the gas-sensitive response of the Zn Ti-LDOS sensor by 5 times.The n type oxide gas sensor have good detection and application of low concentration reducing VOCs gas by connecting n-type enhanced FET.