Research On Design And Performance Of Fluoride Ion Sensor Based On Michelson Interferometer

Fluoride ion(F^-),a ubiquitously present anion in aqueous environments,is of great biological significance in the maintenance of healthy bones and teeth.However,an excessive intake of F^-can cause several diseases.Therefore,it is urgent to detect the concentration of fluoride ion in water.The technique of optical fiber sensor has been widely researched because of the unique advantages such as the possibility of applications in extreme environments,real-time monitoring,and compact size,etc.Thus,it is of great significance to apply this to the detection of fluoride ion.Besides,compared with other fiber-optic sensor like Fabry-Perot interferometer(FPI),Sagnac interferometer(SI),and Mach Zehnder interferometer(MZI),Michelson interferometer(MI)has a rather simple fabrication and measurement processes.Thus,three kind of Michelson interferometers for fluoride-ion detection are proposed.The main research of this paper is as follows:(1)The single-mode fiber(SMF)is spliced with the three-core fiber,a waist-enlarged taper is spliced between them.This fiber-optic sensor has the sensitivity of 58.500nm/RIU to the refractive index(RI).CeO₂/SiO₂ sensing material is coated on the three-core fiber by the dip-coating method.The functionalized sensor with CeO₂/SiO₂ is examined with different concentrations of fluoride-ion.When the fluoride-ion concentration is in the range of 0.1-1.0 ppm,the sensitivity is 2.465 nm/ppm,the response time of the sensor is about 10 s.Besides,the sensor has excellent fluoride-ion selectivity and p H stability.(2)To improve the sensitivity of the sensor,the SMF,no-core fiber(NCF)and thin-core fiber(TCF)are used to fabricate a fiber-optic sensor based on the structure of SMF-TCF-NCF.Besides,a waist-enlarged taper is spliced between TCF and NCF.Next,to choose the optimistic sensing film,the fluoride-ion fiber-optic sensors based on?-Fe₂O₃,ZrO₂,and?-Fe₂O₃/ZrO₂ sensing films are fabricated respectively.Then,a series of experiments are proposed to choose the best sensing units and the thickness of the sensing film.The experimental results show that the?-Fe₂O₃/ZrO₂ fluoride-ion sensor with the sensing film of 570 nm presents the highest sensitivity.Besides,both TCF and NCF are seen as the sensing unit.When the fluoride-ion concentration is in the range of 0.1-1.0 ppm,the sensitivity is 8.790 nm/ppm,the response time of the sensor is about 15 s.The sensor also has excellent fluoride-ion selectivity,p H and temperature stabilities.(3)A fiber-optic fluoride-ion sensor based on metal-organic framework(MOFs)UiO-66(Zr)is proposed.This sensor is based on the structure of SMF-TCF,a core-offset fusion is spliced between them,which can detect the fluoride-ion concentration ranging from 0-10 ppb.Characterization and analysis of X-ray diffraction(XRD)proved that the material is successfully made.Scanning electron microscope(SEM)shows that the thickness of the sensing film is about 600 nm.When the fluoride-ion concentration is in the range of 0.01-1.00 ppb,the sensitivity is 612 pm/ppm,the response time of the sensor is about 10 s.Besides,this sensor has good repeatability.Finally,the sensing mechanism is uncovered according to the results of the X-ray photoelectron spectroscopy(XPS)and Fourier transform infrared spectrometer of the UiO-66(Zr)before and after the adsorption of fluoride ion.