Preparation method of fluorescent probe for monitoring chloride ions in cement base and detection equipment

Abstract

The invention belongs to the field of fluorescence monitoring, and particularly relates to a preparation method of a fluorescent probe for monitoring chloride ions in a cement base and detection equipment, and the preparation method comprises preparation of sodium alginate fluorescent nanoparticles, preparation of a cellulose acetate membrane solution and preparation of the fluorescent probe. The prepared sensor is excellent in performance, the detection range of chloride ions in a cement matrix reaches 0.001-0.3 M, the average measurement error is only 1.4%, the single measurement error is smaller than or equal to 3%, the single measurement time is only 6 seconds, and in-situ, rapid and high-precision monitoring of the chloride ions is achieved. The invention provides an effective new technical means for concrete structure durability monitoring, and has important engineering application value.

Description

Technical Field

[0001] This application belongs to the field of fluorescence monitoring, and specifically relates to a preparation method and detection equipment of a fluorescence probe for monitoring chloride ions in cement-based materials. Background Art

[0002] Reinforced concrete structures are a widely used building form, combining the high strength and ductility of steel bars with the high compressive strength of concrete, and having excellent mechanical properties, construction convenience and economy. However, chloride-induced corrosion of steel bars is one of the main problems causing its damage. Chloride ions penetrate the concrete protective layer, damage the passivation film on the surface of the steel bars, and cause steel bar corrosion. At the same time, the volume of the corrosion products expands, generating internal stress in the concrete and causing cracks. The crack propagation weakens the compressive strength of the concrete, reduces the bearing capacity and durability of the structure, and increases the risk of structural failure. In reinforced concrete structures, chloride ions mainly exist in two forms: free chloride ions and fixed insoluble chloride ions. Among them, free chloride ions are the most likely to cause steel bar corrosion and are the main cause of corrosion of reinforced concrete structures. Therefore, it is necessary to monitor and warn the concentration of free chloride ions in the concrete environment, so as to discover problems and solve them in time at the initial stage of chloride-induced steel bar corrosion, improve the durability of reinforced concrete structures and extend their service life.

[0003] At present, most fluorescence optical fiber sensors directly fix fluorescent dyes on the surface of optical fibers through coating materials and then directly use them for chloride ion concentration detection. Due to the lack of protection for the dyes, problems such as dye leakage, decreased durability of the probe, and inability to reuse the probe are likely to occur during use; at the same time, the reusability of the sensor and its detection ability in actual concrete have not been explored, resulting in doubts about the practicality of the developed sensor. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a preparation method and application of a fluorescence optical fiber sensor capable of continuously monitoring the chloride ion concentration in cement-based materials.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method of a fluorescence probe for monitoring chloride ions in cement-based materials, including the preparation of sodium alginate fluorescent nanospheres, the preparation of cellulose acetate membrane solution, and the preparation of fluorescence probes;

[0007] Preparation of sodium alginate fluorescent nanospheres: Based on the dissolution of calcium carbonate nanoparticles under the action of an acid agent of glucono-δ-lactone to release Ca 2+ and rapid cross-linking with sodium alginate to form a gel-like sphere, and incorporating a chloride ion-sensitive rhodamine 6G fluorescent dye during this process to wrap and prepare sodium alginate fluorescent nanospheres;

[0008] Preparation of cellulose acetate membrane solution: When preparing the cellulose acetate membrane solution, disperse the sodium alginate fluorescent microspheres in the cellulose acetate membrane solution;

[0009] Use the dip coating method to coat the cellulose acetate membrane solution on the surface of the treated quartz optical fiber to prepare a chloride ion-sensitive fluorescent probe.

[0010] Preferably, the preparation method of sodium alginate fluorescent nanospheres is as follows:

[0011] Step 1, Prepare 20 mL of 0.01 M sodium alginate solution, add 0.02 - 0.03 g of calcium carbonate nanoparticles and 0.05 - 0.06 g of glucono delta-lactone, and perform ultrasonic treatment to fully disperse the solid particles;

[0012] Step 2, Add 5 - 10 mL of 0.01 M rhodamine 6G aqueous solution and 50 mL of cyclohexane to the solution to form a water-in-oil structure, then add 1 - 2 mL of polyglycerol ricinoleate as an active agent, seal and continuously stir to make the reaction proceed fully;

[0013] Step 3, After stirring is completed, add ethanol or acetone to break the emulsion to precipitate the product;

[0014] Step 4, Use a high-speed centrifuge to centrifuge and wash to remove impurities;

[0015] Step 5, Dry and grind the product at 45 - 55 °C to finally obtain sodium alginate fluorescent nanospheres.

[0016] Preferably, the preparation method of the cellulose acetate membrane solution is as follows:

[0017] Step 1, Dissolve 0.15 - 0.20 g of cellulose acetate in 3 ml of acetone, seal and stir at 20 - 40 °C for 2 hours to fully dissolve it;

[0018] Step 2, Add 0.03 - 0.05 g of the fluorescent nanospheres prepared above to this solution, and also seal and stir in the dark at 20 - 40 °C to obtain the cellulose acetate membrane solution.

[0019] Preferably, for the preparation of the fluorescent probe, the coating parameters are set as follows: pulling speed 2400 - 2600 μm / s, descending speed 2400 - 2600 μm / s, dipping time 10 - 30 s, interval time 10 - 30 s, to prepare a chloride ion-sensitive fluorescent probe.

[0020] A chloride ion detection device for cement-based materials includes a fluorescent probe, as well as an adapter, a connector, a Y-shaped branched optical fiber, a light source, and a fluorescence spectrometer; the branched ends of the Y-shaped optical fiber are respectively connected to the fluorescence spectrometer and the light source, and the combined end is connected to the fluorescent probe through the adapter and the connector; the fluorescent nanospheres at the end of the fluorescent probe emit fluorescence under the irradiation of ultraviolet light emitted by the light source. When the probe contacts chloride ions, fluorescence quenching occurs and the fluorescence intensity decreases. This optical signal is recorded by the spectrometer and processed through the Stern-Volmer equation.

[0021] Preferably, after the fluorescent probe completes the equation calibration in the simulated cement paste pore solution, the chloride ion concentration in the same actual cement paste pore solution is repeatedly detected. After each measurement, wait for the fluorescence intensity of the probe to recover, and then perform the detection again until a large error appears in the probe measurement and stop the detection. Compare the chloride ion concentration obtained from each detection with the chloride ion concentration in the actual cement paste pore solution to obtain the error value, and then explore the upper limit of the number of times the probe can be reused.

[0022] Preferably, during the pouring process of the cement paste, two fluorescent probes that have completed the standard equation calibration in advance are respectively implanted at different depth positions inside the specimen. After the specimen is cured for T days, connect the experimental device to conduct in-situ monitoring of the chloride ion concentration; record the fluorescence intensity of the two probes once every t minutes to obtain the change diagram of the fluorescence intensity of the two probes over time, and finally measure the chloride ion concentration with the two probes.

[0023] Compared with the prior art, the beneficial effects of this application are as follows:

[0024] In the preparation method provided by the present invention, the preparation of sodium alginate fluorescent nanospheres: (1) a simple synthesis route, mild reaction conditions, short time, low raw material cost, and no toxic by-products are generated; (2) high fluorescence intensity, chloride ion sensitivity, and successfully protect and fix the fluorescent dye, effectively preventing the leaching of the dye.

[0025] The fluorescence optical fiber sensor prepared by the preparation method provided by the present invention has the advantages of simple operation, no pollution, high accuracy, high stability, strong chloride ion selectivity, and anti-photobleaching.

[0026] In the fluorescence-based optical fiber sensing provided by the present invention, the fluorescence intensity of the fluorescent probe is linearly related to the chloride ion concentration. The average detection error is 1.4%, the single measurement error is not more than 3%, and the time required to complete one measurement is 6 s. It can realize the in-situ monitoring of chloride ions in the concentration range of 0.001 M - 0.3 M in cement-based materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] For a further detailed introduction of the present invention, the following is the description of the drawings.

[0028] Figure 1 It is a fluorescence intensity comparison diagram between rhodamine 6G fluorescent dye and sodium alginate fluorescent nanospheres encapsulating rhodamine 6G;

[0029] Figure 2 FTIR comparison diagram between rhodamine 6G fluorescent dye and sodium alginate fluorescent nanospheres encapsulating rhodamine 6G;

[0030] Figure 3 It is a TEM diagram of sodium alginate fluorescent nanospheres;

[0031] Figure 4 It is a dye leaching comparison diagram between rhodamine 6G fluorescent dye and sodium alginate fluorescent nanospheres encapsulating rhodamine 6G;

[0032] Figure 5 It is a structural schematic diagram of the prepared fluorescent probe;

[0033] Figure 6 It is a structural schematic diagram of the constructed fluorescence optical fiber sensor;

[0034] Figure 7a It is the fluorescence spectrum diagram calibrated during the error measurement and analysis of the fluorescence optical fiber sensor;

[0035] Figure 7b It is the linear fitting diagram calibrated during the error measurement and analysis of the fluorescence optical fiber sensor;

[0036] Figure 8a It is the fluorescence spectrum diagram calibrated during the repeatability detection of the fluorescence optical fiber sensor;

[0037] Figure 8b It is the linear fitting diagram calibrated during the repeatability detection of the fluorescence optical fiber sensor;

[0038] Figure 9 It is the response time recording diagram of the fluorescence optical fiber sensor;

[0039] Figure 10 It is the structural schematic diagram of the device for electrochemically accelerating the penetration of chloride ion concentration in cement paste specimens;

[0040] Figure 11a It is the diagram of the change of fluorescence intensity of the shallowly buried fluorescent probe with time;

[0041] Figure 11b It is the diagram of the change of fluorescence intensity of the deeply buried fluorescent probe with time;

[0042] In the figure, 1 is an adapter, 2 is a connector, 3 is a Y-shaped optical fiber splitter, 4 is a light source, 5 is a fluorescence spectrometer, 6 is a computer, 7 is a fluorescent probe, 8 is a DC power supply, 9 is a water tank made of acrylic plate, 10 is a cement paste specimen, 11 is a wet sponge, 12 is deionized water, 13 is a stainless steel plate, and 14 is a 0.6M sodium chloride aqueous solution. Detailed implementation mode

[0043] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0044] On the contrary, the present invention covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention as defined by the claims. Further, in order to enable the public to better understand the present invention, some specific details are described in detail in the following detailed description of the present invention. Those skilled in the art can fully understand the present invention without the description of these details.

[0045] Example 1: Synthesis of sodium alginate fluorescent nanospheres

[0046] Calcium carbonate nanoparticles: glucono-delta-lactone were added to 20 mL of 0.01 M sodium alginate solution at a mass ratio of 0.02-0.03:0.05-0.06, and ultrasonic treatment was performed for 5 min to fully disperse the solid particles. Then, 5-10 mL of 0.01 M rhodamine 6G aqueous solution and 50 mL of cyclohexane were added to the solution to form a water-in-oil structure, and 1-2 mL of polyglycerol ricinoleate was added as an active agent. After sealing with plastic wrap, continuous stirring was carried out for 24 h to allow the reaction to proceed fully; after the stirring was completed, ethanol or acetone was added for demulsification to precipitate the product, and then the product was centrifuged and washed twice at a speed of 9000 rpm to remove impurities. Finally, the product was dried and ground at 45-55 °C to prepare sodium alginate fluorescent nanospheres. Figure 1 It is a fluorescence intensity comparison diagram of the prepared fluorescent nanospheres and fluorescent dyes. It can be seen that due to the scattering effect of the nanomaterials, the fluorescence intensity of the fluorescent dyes has been greatly improved after being prepared into fluorescent nanospheres.

[0047] Example 2: Preparation of cellulose acetate membrane solution

[0048] 0.15-0.20 g of cellulose acetate was dissolved in 3 ml of acetone, and after sealing with plastic wrap, it was stirred at 20-40 °C for 2 hours to fully dissolve it; then, 0.03-0.05 g of the above-prepared fluorescent nanospheres was added to the solution, and it was also sealed and stirred in the dark at 20-40 °C for 6 hours to obtain a cellulose acetate membrane solution.

[0049] Example 3: FTIR, TEM, and dye leakage analysis of sodium alginate fluorescent nanospheres

[0050] Figure 2 Figure is the FTIR comparison chart of sodium alginate fluorescent nanospheres and rhodamine 6G. In the spectrum of the fluorescent microspheres, the strong absorption peak at 1420 cm -1 represents the shift of the COO- peak to lower wavenumbers. The reason is that after the dissolution of calcium carbonate nanoparticles, Ca 2 + coordinates with the carboxyl group, resulting in a decrease in electron cloud density, which proves the occurrence of the cross-linking reaction (Ca 2+ binds to sodium alginate). At the same time, both samples show obvious C=O stretching vibration peaks at 1716 cm -1 and 1721 cm -1 , benzene ring skeletal vibration peaks at 1607 cm -1 and 1605 cm -1 , and C-N stretching vibration peaks at 1029 cm -1 and 1025 cm -1 . These peaks all come from rhodamine 6G, indicating that the structure of rhodamine 6G is not damaged during the process of being encapsulated into the fluorescent nanospheres. The perfect matching of these key functional group characteristic peaks fully proves that the preparation process of the fluorescent microspheres effectively retains the molecular structure integrity of the rhodamine 6G dye, and there is no obvious chemical interaction between the dye and calcium carbonate nanoparticles.

[0051] To explore the microscopic morphology of sodium alginate fluorescent nanospheres, transmission electron microscopy was used for microscopic characterization. Sodium alginate fluorescent nanospheres were added to absolute ethanol and ultrasonically oscillated for 5 min to disperse them fully. A small amount was aspirated with a pipette and dropped onto a copper grid. After natural drying at room temperature, it was scanned with a transmission electron microscope to observe its morphology.

[0052] Figure 3 Figure is the TEM image of sodium alginate fluorescent nanospheres. The alginate fluorescent nanospheres are prepared based on water-in-oil emulsification, internal gelation, and combined with calcium carbonate nanoparticles as the calcium source. During this process, calcium carbonate nanoparticles dissolve under the action of the acidic agent glucono-delta-lactone, and the released Ca 2+ rapidly cross-links with sodium alginate to form a gel-like sphere. At the same time, the discharge of CO2 gas during the dissolution process can cause pores to appear on the surface of the sphere, which is beneficial for chloride ions to enter and quench the dye encapsulated inside. Secondly, the surfactant polyglyceryl ricinoleate added in this process can effectively reduce the oil-water interfacial tension, promote droplet splitting, and then reduce the droplet size, resulting in smaller-sized alginate gel microspheres. The particle size of the microspheres is distributed in the range of 60 nm - 140 nm.

[0053] Figure 4 The same mass of fluorescent nanospheres and fluorescent dyes were respectively immersed in the same volume of deionized water. After 72 hours of immersion, they were irradiated with an ultraviolet light source, and a comparative graph of dye leaching was recorded. After 72 hours of immersion, the fluorescent dye completely dissolved in the centrifuge tube, and the entire centrifuge tube was filled with fluorescence ( Figure 4 left). In Figure 4 the right, it can be seen that the fluorescent nanospheres containing the fluorescent dye aggregated at the bottom of the centrifuge tube, and no dye was precipitated in the upper layer. The fluorescent nanospheres effectively prevented the leakage of the dye.

[0054] Example 4: Preparation of the Fluorescent Probe

[0055] The cellulose acetate membrane solution was coated on the surface of the treated quartz optical fiber by the dip-coating method. The parameter settings for the coating operation were: dip speed 2400 - 2600 μm / s, withdrawal speed 2400 - 2600 μm / s, immersion time 10 - 30 s, and interval time 10 - 30 s. A chloride ion-sensitive fluorescent probe was prepared. The structural schematic diagram of the fluorescent probe is as Figure 5 shown.

[0056] Example 5: Construction of the Fluorescent Fiber Optic Sensor

[0057] The structural schematic diagram of the fluorescent fiber optic sensor is as Figure 6 shown, and the specific components are a fluorescent probe 7, an adapter 1, a connector 2, a Y-shaped optical fiber splitter 3, a light source 4, a fluorescence spectrometer 5, and a computer 6. The fluorescence spectrometer and the light source are respectively connected to the splitting ends of the Y-shaped optical fiber, and the fluorescent probe is connected through the adapter and the connector at the combining end. The fluorescent nanospheres at the end of the fluorescent probe emit fluorescence under the ultraviolet light emitted by the light source. When the probe contacts chloride ions, fluorescence quenching occurs and the fluorescence intensity decreases. This optical signal is recorded by the spectrometer and processed by the Stern-Volmer equation. This equation is a quantitative relationship equation between chloride ions and fluorescence intensity, and its basic form is as follows:

[0058]

[0059] where I0 and I respectively represent the original fluorescence intensity of the fluorescent indicator and the fluorescence intensity after quenching, Q represents the concentration of the quencher (chloride ion solution), and K SV is the quenching constant, and the magnitude of its value indicates the sensitivity of the fluorescent indicator to the quencher.

[0060] Example 6: Performance Evaluation of the Fluorescent Fiber Optic Sensor

[0061] The prepared fluorescence optical fiber sensor is subjected to error measurement analysis, repeatability detection, and response time recording to evaluate the performance of the sensor. Before each performance evaluation of the sensor, the probe needs to be calibrated. The calibration process is carried out in a self-prepared simulated cement paste pore solution. The simulated cement paste pore solution is based on a saturated calcium hydroxide solution (pH = 12.5), and different masses of sodium chloride are added to it to obtain 5 kinds of simulated concrete pore solutions with chloride ion concentrations of 0.001M, 0.002M, 0.003M, 0.004M, and 0.005M as standard solutions. The purpose of calibration is to set the unique Stern-Volmer equation for the probe, so as to calculate the chloride ion concentration through the change in fluorescence intensity.

[0062] Error measurement analysis: Three actual cement paste pore solutions with different chloride ion concentrations are selected for detection. Then, the chloride ion concentration in the actual cement paste pore solution is compared with the chloride ion concentration measured by the probe to obtain the measurement error. The actual cement paste pore solution is an aqueous solution obtained by sampling and grinding the cement paste specimen and then soaking it. Take actual cement paste pore solutions with chloride ion concentrations of 0.002260M, 0.003277M, and 0.006717M. When the sensor calibration is completed, the fluorescence spectrum diagram and linear fitting diagram are shown in Figures 7(a) and (b), and the recorded data is shown in Table 1:

[0063] Table 1 Calculation results of the measured errors

[0064]

[0065]

[0066] It can be seen from Table 1 that the average detection error of the sensor in the actual cement paste pore solution is 1.44%, and the single detection error does not exceed 3%.

[0067] Repeatability detection: After the fluorescence optical fiber sensor completes the equation calibration in the simulated cement paste pore solution, the chloride ion concentration in the same actual cement paste pore solution (concentration of 0.006648M) is repeatedly detected. After each measurement, wait for the fluorescence intensity of the probe to recover, and then perform the detection again until a large error appears in the probe measurement and stop the detection. Compare the chloride ion concentration obtained from each detection with the chloride ion concentration (0.006648M) in the actual cement paste pore solution to obtain the error value, and then explore the upper limit of the number of times the probe can be reused. When the sensor calibration is completed, the fluorescence spectrum diagram and linear fitting diagram are shown in Figures 8(a) and (b), and the recorded data is shown in Table 2:

[0068] Table 2 Calculation table of the error results of each measurement of the sensor

[0069]

[0070] As can be seen from Table 2, the same sensor can complete 10 times of chloride ion concentration detection, and the average error is 5.30%.

[0071] Response time recording: The fluorescent probe in a stable state in the air was quickly immersed in the pore solution of the concrete to be measured, and at the same time, a fluorescence spectrometer was used for real-time monitoring, and the entire time course from the moment the probe contacted the solution, through the dynamic process of fluorescence quenching, until the signal reached stability was completely recorded. The response time recording diagram is as Figure 9 shown. From Figure 9 it can be seen that the time required for the sensor to complete one chloride ion concentration detection is about 6 s.

[0072] Example 7: In-situ monitoring of chloride ion concentration of a fluorescent optical fiber sensor in an actual neat cement specimen.

[0073] An experimental device was designed to verify the in-situ monitoring performance of the fluorescent optical fiber sensor in the neat cement specimen, and its structure is as Figure 10 shown. During the pouring process of the neat cement, two fluorescent probes that had been pre-calibrated with the standard equation were implanted at different depth positions (depth difference ≥ 2 cm) inside the specimen. After the specimen was cured for 28 days, a water tank 9 made of epoxy resin-fixed acrylic plate was fixed on the top of the neat cement specimen 10, and 0.6 M NaCl solution 14 was injected. At the same time, a deionized water-saturated sponge layer, that is, a wet sponge 11, was laid at the bottom of the specimen to construct a chloride ion concentration gradient environment. To accelerate the penetration process, an electrochemical acceleration system was designed: wires were welded to two stainless steel plates, and they were respectively placed in the lower wet sponge and the upper water tank. The two stainless steel plates 13 were connected by a DC power supply 8, where the positive electrode was connected to the lower stainless steel plate (simulating the anode), and the negative electrode was connected to the upper stainless steel plate (simulating the cathode). This design is based on the principle that chloride ions will migrate from the cathode to the anode under the action of an electric field, thereby accelerating the penetration of chloride ions inside the neat cement specimen.

[0074] After connecting the experimental device, turn on the DC power switch. When a stable current appears in the circuit, start data recording and conduct in-situ monitoring of chloride ion concentration. The fluorescence intensities of the two fluorescent probes 7 were recorded once every 10 minutes, and the graphs of the fluorescence intensity of the two probes changing with time are shown in Figures 11(a) and (b). Finally, the chloride ion concentrations measured by the two probes are shown in Tables 3 and 4.

[0075] Table 3 Chloride ion concentration measured by the shallowly buried probe

[0076]

[0077] Table 4 Chloride ion concentration measured by the deeply buried probe

[0078]

[0079] It can be seen from the figure that the deeply buried and shallow buried probes can realize the real-time monitoring of the chloride ion concentration at different depths in the neat cement paste at the same time. The final chloride ion concentration detection range of the fluorescence optical fiber sensor is (0.001M - 0.3M), which completely covers the chloride ion concentration threshold (0.1M - 0.2M) when the steel bars in the cement concrete structure are corroded, providing a reliable technical means for the monitoring and early warning of the chloride ion concentration in the cement-based materials.

[0080] The above description is only one of the embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A preparation method of a fluorescent probe for chloride ion monitoring in cement-based materials, characterized in that, It includes the preparation of sodium alginate fluorescent nanospheres, the preparation of cellulose acetate membrane solution, and the preparation of fluorescent probes. Preparation of sodium alginate fluorescent nanospheres: Calcium carbonate nanoparticles dissolve under the action of an acidifying agent of glucono-δ-lactone to release Ca 2+ and rapidly crosslink with sodium alginate to form a gel-like sphere. Based on this, a rhodamine 6G fluorescent dye sensitive to chloride ions is incorporated during this process for encapsulation to prepare sodium alginate fluorescent nanospheres; Preparation of cellulose acetate membrane solution: When preparing the cellulose acetate membrane solution, disperse the sodium alginate fluorescent microspheres in the cellulose acetate membrane solution. Preparation of fluorescent probes: Use the dip-coating method to coat the cellulose acetate membrane solution on the surface of the treated quartz optical fiber to prepare a chloride ion-sensitive fluorescent probe.

2. The preparation method of the fluorescent probe for chloride ion monitoring in cement-based materials according to claim 1, wherein The preparation method of sodium alginate fluorescent nanospheres is as follows: Step 1: Prepare 20 mL of 0.01 M sodium alginate solution, add 0.02 - 0.03 g of calcium carbonate nanoparticles and 0.05 - 0.06 g of glucono delta-lactone, and perform ultrasonic treatment to fully disperse the solid particles. Step 2: Add 5 - 10 mL of 0.01 M rhodamine 6G aqueous solution and 50 mL of cyclohexane to the solution to form a water-in-oil structure, then add 1 - 2 mL of polyglycerol ricinoleate as an active agent, seal it, and continuously stir to make the reaction proceed fully. Step 3: After stirring is completed, add ethanol or acetone to demulsify and precipitate the product. Step 4: Use a high-speed centrifuge to centrifuge and wash to remove impurities. Step 5: Dry and grind the product at 45 - 55 °C to finally obtain sodium alginate fluorescent nanospheres.

3. The preparation method of the fluorescent probe for chloride ion monitoring in cement-based materials according to claim 1, characterized in that, The preparation method of cellulose acetate membrane solution is as follows: Step 1: Dissolve 0.15 - 0.20 g of cellulose acetate in 3 ml of acetone, seal it, and stir at 20 - 40 °C for 2 hours to fully dissolve it. Step 2: Add 0.03 - 0.05 g of the fluorescent nanospheres prepared above to this solution, seal it at 20 - 40 °C, and continue to stir in the dark to obtain a cellulose acetate membrane solution.

4. The preparation method of the fluorescent probe for chloride ion monitoring in cement-based materials according to claim 1, wherein, For the preparation of fluorescent probes, the coating parameters are set as follows: dip-coating speed 2400 - 2600 μm / s, lowering speed 2400 - 2600 μm / s, dipping time 10 - 30 s, interval time 10 - 30 s, to prepare a chloride ion-sensitive fluorescent probe.

5. A chloride ion detection device for cement-based materials, characterized in that, It includes the fluorescent probe obtained by any one of the methods described in claims 1 - 4, as well as a Y-shaped branched optical fiber, a light source, and a fluorescence spectrometer; the branched ends of the Y-shaped optical fiber are respectively connected to the fluorescence spectrometer and the light source, and the combined end is connected to the fluorescent probe through an adapter and a connector; the fluorescent nanospheres at the end of the fluorescent probe emit fluorescence under the ultraviolet light emitted by the light source, and when the probe contacts chloride ions, fluorescence quenching occurs and the fluorescence intensity decreases, and this optical signal is recorded by the fluorescence spectrometer and processed through the Stern-Volmer equation.

6. The chloride ion detection device for cement-based materials according to claim 5, characterized in that, After the fluorescent probe completes the equation calibration in the simulated cement paste pore solution, repeatedly detect the chloride ion concentration in the same actual cement paste pore solution. After each measurement, wait for the fluorescence intensity of the probe to recover, and then perform the detection again until a large error appears in the probe measurement and stop the detection. Compare the chloride ion concentration obtained from each detection with the chloride ion concentration in the actual cement paste pore solution to obtain an error value, and then explore the upper limit of the number of times the probe can be reused.

7. The chloride ion monitoring device for cement-based materials according to claim 5, characterized in that, During the process of cement paste casting, two fluorescence probes that have been pre-calibrated with standard equations are respectively implanted at different depths inside the specimen. After the specimen has been cured for T days, the experimental device is connected to conduct in-situ monitoring of chloride ion concentration. The fluorescence intensities of the two probes are recorded every t minutes to obtain the graphs of the fluorescence intensity of the two probes changing with time. Finally, the chloride ion concentrations are measured by the two probes.

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