Preparation And Gas Sensing Properties Of Conductive Metal Organic Frameworks(MOFs)

As the transportation industry continues to develop in recent years,both the massive emissions of automobile exhaust and the possible gas leaks in industrial transportation may cause serious pollution of the atmosphere.In the actual complex environment,it is of great relevance to identify the toxic and harmful gases quickly and efficiently at room temperature.However,most current gas sensors operate at temperatures above 200℃.They are difficult to work at room temperature.Metal organic frameworks（MOFs）materials have become one of the candidates for detecting hazardous gases at room temperature due to their high specific surface area,structural tunability and high density of active sites.This paper aims to prepare conductive MOFs gas-sensitive materials which have high response value,high selectivity and high response speed at room temperature.Two series of conductive MOFs materials were synthesized by hydrothermal method,the samples were structurally characterized and tested for gas-sensitive performance,and the application of conductive MOFs materials in flexible sensors was explored.The main studies are as follows.（1）Three conductive MOFs materials Cu₃（HHTP）₂,Ni₃（HHTP）₂,and Zn₃（HHTP）₂ were successfully prepared using coordination reactions between transition metal ions(Cu²⁺,Ni²⁺,Zn²⁺)and hexahydroxytriphenylene（HHTP）under hydrothermal conditions.The results of the gas-sensitive performance tests show that Zn₃（HHTP）₂ has good selectivity and high response（74.7%）to NO₂ gas at 100 ppm at room temperature,and it also provides excellent response（55.9%）to low concentration of NO₂ gas（5 ppm）in a short time（10 min）.Comparing with the literature reports of existing NO₂ gas sensors,Zn₃（HHTP）₂ is an ideal sensing material for NO₂gas detection and identification at room temperature.（2）Three conductive MOFs materials LaHHTP,NdHHTP,and HoHHTP with rare earth metals ions(La³⁺,Nd³⁺and Ho³⁺)as metal centers were successfully prepared by hydrothermal method.Among them,the NdHHTP material has excellent response（51.0%）with good selectivity to 100 ppm H₂S gas at room temperature within a short response time（3.3 min）.In the dynamic response resistance curves,the NdHHTP material exhibits a fast response and stable response resistance values that are rare among MOFs materials,and the response value has a good linear relationship with the gas concentration（R²=0.993）,and these response characteristics are favorable for detecting the concentration of H₂S gas in practical applications.Comparing with the literature reports of existing H₂S gas sensors,NdHHTP is an ideal sensing material for H₂S gas detection and identification at room temperature.（3）Methyl vinyl silicone rubber/carbon black（VMQ/CB）composites were prepared by mechanical compounding method.The Cu₃（HHTP）₂/VMQ/CB flexible gas sensor was successfully prepared by uniformly loading Cu₃（HHTP）₂ on the material surface by spraying method.The gas-sensitive performance test revealed that the flexible sensor has a more sensitive and stable response value（9.4%）for 500 ppm NH₃ gas in a short time（5 min）,and it can better resist the effect of repeated bending deformation from-15°to 15°on the response value.The results revealed that the flexible sensors prepared by the conductive MOFs materials synthesized in this project have good application prospects in the field of room temperature gas sensing.