Preparation And Gas Sensing Properties Of MOF-Based Oxide Composites

In recent decades,due to the increase of volatile and toxic gases emitted by industry,agriculture,and vehicles,the air pollution has become one of the hottest topics of discussion today.Air pollution mainly refers to a mixture of fine dust particles and gases that reach harmful concentrations indoors and outdoors,such as soot,smoke,mold,pollen,methane,carbon dioxide,and hydrogen sulfide.It may cause people to sneeze and cough,and eye discomfort.Problems with headaches and dizziness.In addition,long-term exposure to volatile toxic and harmful gases will also have a serious negative impact on human health.Therefore,it is imminent to research low-cost,high-efficiency,easy-to-operate,simple-structured gas sensors to monitor toxic and harmful gases and detect the lowest concentration.Because the gas-sensitive performance of the sensor is related to the morphology and structure of the material,Therefore,by increasing the specific surface area of nanomaterials,the adsorption capacity of the target gas is improved,and optimizing the sensing performance of the gas sensor.The present study based on gas sensor performances and applications is carried as follows:NiCo₂O₄ with different shapes was prepared by adding three different active agents through hydrothermal process:pin-shaped,stick-shaped and flower-shaped NiCo₂O₄.Among them,the specific surface area of the flower-shaped-shaped NiCo₂O₄ is 121.52 m²g^-1.By comparing the results of four target gases H₂S,NO₂,NH₃,and CO,it is found that all three gas sensors have maximum gas sensing response and high selectivity towards H₂S gas.At an optimal working temperature of 250℃,the fabricated sensors show highest responses to 100 ppm H₂S gas are12.5,followed by pin-shaped 5.03,and finally stick-shaped-shaped 1.98.ZIF-67 was synthesized via hydrothermal method followed by template-assisted method of ZIF-67 to design and synthesize Co₃O₄/NiCo₂O₄ double-shelled nanomaterials.Microscopic analysis shows that ZIF-67 is a smooth solid dodecahedron with a specific surface area of 60m²g^-1,Co₃O₄/NiCo₂O₄ is a dodecahedron with a rough surface and a double-shelled hollow surface and a specific surface area of 103 m²g^-1.Monitoring the response of four target gases of H₂S,NO₂,NH₃,and CO found that both samples have good selectivity for H₂S gas.ZIF-67 has a higher response to H₂S gas,at 225℃and 100 ppm,the response is 9.36.At the same time,the response of Co₃O₄/NiCo₂O₄ at 250℃and 100 ppm is 6 times that of single-layer solid ZIF-67,up to 57.We doped CNTs in materials and successfully prepared bimetallic Zn-Co MOF@CNT,and based on this,we synthesized tri-metallic Zn-Co（-Ni）MOF@CNT with high specific surface area(363 m²g^-1).Through microscopic analysis,it was found that the bimetallic composite material was in the shape of a solid leaf with a smooth surface,while the trimetallic composite material was in the shape of a hollow leaf with a rough surface.The best response of bimetallic composite to reducing gas H₂S at the optimum temperature of 300℃and 100 ppm is 58;Tri-metallic composite has the highest response to 100 ppm H₂S at 325℃,166.