Preparation Of Silica Fluorescent Nanoparticles And Its Application In Fiber Optic Chloride Sensors

The problem of reduced service life of reinforced concrete structures due to insufficient durability in high-alkaline environments is widespread around the world,and the corrosion of chloride ions is one of the main factors that affect the concrete durability.When the concentration of invading chloride ions exceeds the critical level in the reinforced concrete structure,which will destroy the passive film of rebar and continue to corrode,thereby reducing the strength,rigidity,ductility and aesthetic quality of the structure.Therefore,it is urgent to study and development a method for real-time,continuous and stable monitoring of chloride ions in the reinforced concrete environment.Fluorescence-based optical fiber sensor has become one of the best choice for chloride ion detection because of its many advantages such as anti-electromagnetic interference,portability,high selectivity,and continuous monitoring.The key of the fluorescent optical fiber sensor is a sensitive material that has a specific response function to chloride ions,and the sensitive material must have good optical performance and good compatibility.Therefore,the silica fluorescent nanoparticles with good light stability and specific response to chloride ions have been developed in this thesis.Based on this sensitive material,a fluorescent optical fiber sensor was developed for detection of chloride ions in the concrete environment with continuous,real-time and high sensitivity.This can not only give early warning of chloride ion corrosion in concrete to improve its durability,but also reduce the serious casualties and economic losses caused by concrete engineering accidents,which have important economic value and social significance.This thesis were supported by the fund of National Natural Science Foundation of China“Research on Chloride Penetration Characteristics in Concrete Based on Real-time Monitoring of Microstructure Optical Fiber Sensors”（No.51878524）.The main research contents and results are as follows:（1）Silica fluorescent nanoparticles doped with lucigenin were synthesized by the reverse microemulsion method.The structure,composition,optical characteristics of SiO₂ fluorescent nanoparticles were characterized by SEM,automatic specific surface area and porosity analyzer,FT-IR,fluorescence lifetime tester,ultraviolet-visible absorption spectrometer and fluorescence spectrometer,respectively.The chemical properties,optical properties and response to chloride ions of the lucigenin in silica fluorescent nanoparticles were studied.The performance of silica fluorescent nanoparticles in the detection of chloride ion in aqueous solution was studied,and the detection concentration range and standard curve were obtained.（2）Cellulose acetate（CA）and sol-gel chloride ion sensitive membranes were prepared by the embedding method.The morphology and composition of the sensitive film were characterized by SEM and FT-IR.The sensitivity of two kinds of sensitive membranes to chloride ion were studied.The results show that both sensitive membranes can respond quickly to chloride ion,but the sensitivity of Sol-gel sensitive membrane to chloride ion is relatively high.（3）Optical fiber sensor probes based on CA and Sol-gel sensitive film were prepared by pulling coating method.SEM were used for characterizing morphology of fiber optic probes,and the influence of fiber optic probe film thickness and chloride ion sensitivity were studied.The calibration experiment and anti-interference ion experiment of the chloride ion concentration detection by the optical fiber sensor were studied.The linear relationship between the fluorescence change ratio I₀/I of the fiber optic sensor based on the CA sensitive film and the chloride ion concentration C was analyzed by the Stern-Volmer equation,and the standard curve for the detection of chloride ion by the fiber optic sensor was obtained in the range of 0.02M-0.06M.The linear relationship between the fluorescence change ratio I₀/I of the fiber optic sensor based on the Sol-gel sensitive membrane and the chloride ion concentration C was analyzed by the Stern-Volmer equation,and the standard curve for the detection of chloride ion by the fiber optic sensor was obtained in the range of 0.01M-0.08M.At the same time,the detection of chloride ion in the simulated concrete pore solutions with different p H by the fiber optic sensor based on Sol-gel sensitive membrane was studied.