Design And Performance Research Of CO Sensor Based On MOFs Composite Sensitive Film Integrated Special Optical Fiber

Carbon monoxide is a flammable,explosive,colorless and odorless poisonous gas.In order to protect people's life and property safety,it is very necessary to effectively monitor the concentration of carbon monoxide.Sensitive materials with excellent performance are an important prerequisite for making carbon monoxide sensors with excellent sensing performance.Metal-organic frameworks(MOFs),which are constructed from organic ligands and metal ions,have been widely used in sensing in recent years.Optical fiber sensors have the advantages of simple manufacture,compact device,high sensitivity,etc.,and are widely used in the field of sensing.The sensitive material has a specific adsorption effect on CO molecules.The refractive index of the sensitive film will change after adsorbing CO molecules,resulting in wavelength shift or intensity change of the output interference spectrum.By analyzing and constructing the relationship between this change and the concentration of carbon monoxide,The monitoring of carbon monoxide can be realized.The main research work of this paper is as follows:(1)Insert the fiber sensing probe with the structure of Single-mode fiber(SMF)-Waist-enlarged Taper(WET)-Thin-core fiber(TCF)into A certain concentration of silver nitrate,cobalt nitrate hexahydrate,2-Methylimidazole and N,N-dimethylformamide mixed solution.At low temperature and normal pressure,by in-situ growth,a layer of bimetallic ligand MOFs material Ag/Co-MOF is coated on the surface of the optical fiber to form an intensity-modulated carbon monoxide optical fiber sensor based on Kelson interference.The resulting composites were characterized by X-ray diffraction,X-ray photoelectron spectroscopy and N₂ adsorption-desorption.In the CO concentration of 0-60ppm,the average sensitivity of the sensor is 0.4515 d B/ppm,the response time is about 110s,the sensor time stability and anti-temperature interference characteristics is excellent.(2)A Michelson interferometric fiber optic sensor with a sensing structure of SMF-WET-NCF was fabricated by using No-core fiber(NCF).The bimetallic coordination ion MOFs material Co/Ni-MOF-74 was prepared by solvothermal method.Characterization analysis such as XRD and XPS showed that Co/Ni-MOF-74 with the same crystal structure as Ni-MOF-74 was successfully prepared.The surface of the optical fiber is coated with a Co/Ni-MOF-74 sensitive film,and the carbon monoxide sensitivity test is carried out on the sensor.In the CO concentration range of 0-35 ppm,the sensitivity is 0.02235 d B/ppm,and the linear fit between the concentration and the light intensity is as high as 0.999358.The calculated limit of detection(LOD)is about 1.99046 ppm,and the response time and recovery time are about 90 s and 110 s,respectively.Compared with other gases,it is found that the sensor has excellent selectivity.In addition,the sensor also has excellent anti-temperature interference characteristics and good time stability.(3)Under normal temperature and pressure,Ni-MOF-74 was immersed in cobalt acetate tetrahydrate solution,so that part of the nickel ions in Ni-MOF-74 was replaced by cobalt ions to generate bimetallic Co/Ni-MOF-74(referred to as Co/Ni-MOF-74-II in the text),and then calcined to generate Co/Ni O,which was integrated into the Mach-Zehnder fiber sensing system for carbon monoxide sensing.In the CO concentration range of 0-60ppm,the sensitivity reaches 67.785 pm/ppm and the calculated LOD value is 0.17976 ppm.In addition,the sensor also has a high concentration-wavelength linear fit(R²=0.97176),excellent selectivity and good time stability.