Studies On Fluorescence Sensing Of Sulfur Dioxide Gas Based On Metal-organic Framework Composite Optical Fibers

Sulfur dioxide is one of the most common,simplest and highly dangerous atmospheric pollutants and scientists have been working on various detection methods for gaseous sulfur dioxide.Fluorescence analysis methods are widely used because of its high selectivity,high detection speed,relatively high sensitivity and low detection limit.Nonetheless,there is a lack of highly selective fluorescence sensing materials,and while in applications,limited fluorescence sensing materials are usually present in unstable forms such as powders,dispersions or films.Besides,the optical paths of traditional fluorescence detection have extremely strict requirements on the environment condition,which currently makes it unable for fluorescence sensing to realize high sensitive,long-term stable,in-situ real-time and remote online detection.Therefore,it is of great significance to explore the preparation and integration of fluorescence sensing materials to maximize the probe function and practical utilizations.Aiming at these problems,this thesis has investigated highly selective fluorescence sensing materials,composite fluorescence sensing optical fibers and highly sensitive fluorescence sensing technology.The specific research contents and results are as follows:?1?In the aspect of highly selective fluorescence sensing materials,the controllable preparation and performance regulation methods of rare earth metal-organic frameworks were studied.Using rare earth salt and a linear organic ligand 2-aminoterephthalic acid which has specific recognition function for SO₂,Eu-BDC-NH₂ was synthesized through nuclear-cluster strategy where 2-fluorobenzoic acid served as a cluster structure directing agent.The material is of high crystallinity and thermally stable,and when exposed to ultraviolet light,it will emit narrow and sharp Eu³⁺characteristic fluorescence.Highly selective sensing of gaseous sulfur dioxide can be realized based on the principle of fluorescence resonance energy transfer.?2?Design,fabrication and sensing applications of silica based fluorescence sensing material composite optical fiber.Based on the self-developed fluorescence sensing material and fluorescence enhancement effect of composite optical fiber structure,a gas environment-adapted silica based Eu-BDC-NH₂ composite sensing optical fiber was designed and developed.The fluorescence effect was extended from a single point to several centimeters through evanescent wave coupling,which improved the sensitivity of detection.Highly selective and sensitive detection of SO₂ was experimentally demonstrated with this silica based composite optical optic,which showed the merit of repeated measurement.The selectivity for SO₂ is more than ten times over other common gases,the fluorescence signal-to-noise ratio is 17.26 d B,the sensitivity is 39.8 ppm^-1 and the detection limit is 0.37ppm.It has the potential to form an all-fiber distributed multi-parameter optical fiber fluorescence sensing network.?3?Design,fabrication and sensing applications of integrated fluorescence sensing material composite flexible optical fiber.In order to further improve the sensitivity of SO₂sensing and gas environmental adaptability of sensing optical fiber,we designed integrated composite method and optimized optical fiber construction to stabilize and increase the overlap between light field and fluorescence sensing material.PDMS based Eu-BDC-NH₂composite flexible optical fiber with core-cladding structure was developed to further realize the enhancement of fluorescence excitation and collection efficiency.Highly selective and sensitive sensing of SO₂ was realized with this PDMS based flexible optical fiber,which showed the merit of repeated measurement.The selectivity for SO₂ is more than ten times over other common gases,the fluorescence signal-to-noise ratio is 21.41 d B,the sensitivity is99.2 ppm^-1 and the detection limit is 0.24 ppm.It greatly improves the stability and environmental adaptability of composite optical fiber sensor devices,and is expected to serve as a multi-functional intelligent sensing platform integrating additional functions like wearability,visualization and biocompatibility.