Nano tracer agent for detecting and quantifying residual organic pollutants in underground aquifer

Abstract

The invention relates to a nano tracer for detecting and quantifying residual organic pollutants in an underground aquifer, which is characterized in that firstly, a nano carrier is prepared, the nano carrier and signal molecules are assembled to obtain the nano tracer, and the nano tracer can detect and quantitatively analyze the residual organic pollutants; the nano tracer agent can be used for detecting residual organic pollutants in the underground aquifer. The nano tracer prepared by the method is high in colloidal stability, the penetration rate of the nano tracer in the underground aquifer is nearly 100%, the saturation detection limit of organic pollutants is as low as 0.6%, and the nano tracer can be used for detecting and quantifying residual organic pollutants in the underground aquifer.

Description

Technical Field

[0001] The invention belongs to the field of environmental technology, and in particular relates to a nano-tracer for detecting and quantifying residual organic pollutants in underground aquifers. Background Art

[0002] Heavy non-aqueous liquids (DNPLs), such as trichloroethylene (TCE), are important organic pollutants that cause groundwater contamination. Due to their environmental persistence, resistance to biodegradation, sustained release, and toxicity to humans, animals, and plants, research into their impact on groundwater pollution and other environmental issues has become a hot topic in environmental science. Once contamination occurs, organic pollutants infiltrate downward from the surface, passing through shallow surface soil, the vadose zone, and aquifers, ultimately accumulating on the impermeable floor. Significant amounts of these pollutants remain in the pores of the media along their vertical migration paths. Under the action of groundwater flushing, these organic pollutants migrate laterally with the flow, remaining in the pores of the media along these lateral migration paths. Due to their low solubility, these pollutants continue to dissolve and release into the groundwater, resulting in persistent groundwater contamination. The migration and distribution of organic pollutants are influenced by multiple factors, including hydrogeological conditions and groundwater flow rates, ultimately forming a highly variable contamination plume within the aquifer. The remediation technology for residual organic pollutants in underground aquifers needs to consider the remediation effect, economy, practicality, etc. Before effectively remediating residual organic pollutants, it is crucial to accurately detect and quantify organic pollutants.

[0003] Currently, most research and application on the detection of organic pollutants in underground aquifers uses drilling sampling. This method requires the deployment of several sampling wells within the contaminated site to obtain single-point sampling data. Detection accuracy is directly related to the number and density of wells drilled. For some contaminated sites within industrial clusters, it is difficult to effectively deploy wells, and there is also a risk of pollutant spread. Geophysical detection technology is primarily used for geophysical exploration. Recent studies have found that by comparing the electrical and acoustic signals of organic pollutants with those of the surrounding medium, geophysical techniques can be used to detect organic pollutants. This method has minimal disturbance to the aquifer, but has low detection accuracy and is susceptible to interference from signals from other substances, making it difficult to detect and identify low-saturation residual organic pollutants. Tracers are another key technology for the detection and quantification of organic pollutants. Tracers are injected into the aquifer at the contaminated site, and information on the organic pollutant content is obtained by analyzing changes in the tracer's properties. This method has the advantages of low disturbance, wide applicability, and the ability to detect low-saturation residual organic pollutants. Years of research have revealed that conventional tracers currently in use require high solubility in water to maintain good mobility, and a certain solubility in the organic phase to dissolve into it. These two conflicting requirements result in low mass transfer rates for tracers, making them susceptible to heterogeneity in the distribution of organic pollutants and heterogeneity in hydrogeological conditions. Consequently, improved detection accuracy is urgently needed. Therefore, it is imperative to develop a new type of tracer to detect and quantify residual organic pollutants in underground aquifers. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a nano-tracer for detecting and quantifying residual organic pollutants in underground aquifers.

[0005] The technical solution adopted in the present invention is:

[0006] A nano-tracer has carbon black nanoparticles as the core and polyvinyl alcohol polymer chains grafted onto the surface. Signal molecules are loaded onto the surface of the inner carbon black nanoparticles through physical adsorption.

[0007] Preferably, the signal molecule is Nile Red.

[0008] The method for preparing a nanotracer comprises reacting carbon black nanoparticles with 4,4-azobis-4-cyanovaleric acid, mixing the resulting product with polyvinyl alcohol, N,N-dicyclohexyldiimine, and 4-dimethylaminopyridine, reacting to obtain a nanocarrier, and connecting a signal molecule to the nanocarrier to obtain the nanotracer.

[0009] Preferably, the mass ratio of carbon black nanoparticles to 4,4-azobis-4-cyanovaleric acid is 1:0.5-3, and the mass ratio of N,N-dicyclohexyl diimide to 4-dimethylaminopyridine is 5-10:1.

[0010] Preferably, the carbon black nanoparticles have a particle size of 20-50 nm.

[0011] Preferably, the specific steps are as follows:

[0012] Step 1: dissolving carbon black nanoparticles in tetrahydrofuran, adding 4,4-azobis-4-cyanovaleric acid, heating and stirring to react, cooling, washing and separating with tetrahydrofuran, and vacuum drying for later use;

[0013] Step 2: Dissolve the solid prepared in step 1 in dimethyl sulfoxide, add polyvinyl alcohol, and heat and stir until the polyvinyl alcohol is completely dissolved; add N,N-dicyclohexyldiimine and 4-dimethylaminopyridine, react at room temperature, remove unreacted polyvinyl alcohol using an ultrafiltration device, and replace the solvent dimethyl sulfoxide with deionized water by dialysis to obtain a deionized water solution of the nanocarrier;

[0014] Step 3: Add the signal molecule to the deionized water solution of the nanocarrier, protect from light and ultrasound, stir at room temperature to remove the free Nile red, and obtain the deionized water solution of the nanotracer.

[0015] Preferably, in step 1, the heating temperature is 30-80° C., and the stirring time is 12-48 h.

[0016] Preferably, in step 3, a 0.22 μm filter membrane and a PD-10 chromatography column are used to remove free signal molecules in the solution;

[0017] Preferably, the molecular weight cut-off of the ultrafiltration membrane and the dialysis membrane is 100 kD.

[0018] Application of nanotracers in the detection of residual organic pollutants in underground aquifers.

[0019] Preferably, residual organic pollutants in underground aquifers are detected and / or quantified.

[0020] Preferably, a solution containing a nano-tracer is placed upstream of the underground aquifer in the area to be detected, and extraction is performed downstream of the underground aquifer. The concentrations of nano-carriers and signal molecules in the extract are detected, and the concentration changes of the nano-carriers and signal molecules are compared.

[0021] When the concentration changes of the nanocarrier and the signal molecule are the same, it is determined that the underground aquifer between the detection points does not contain organic pollutants;

[0022] When the change in the concentration of the signal molecule is greater than the change in the concentration of the nanocarrier, it is determined that the underground aquifer between the detection points contains organic pollutants; preferably, the content of the organic pollutants is calculated based on the difference.

[0023] The advantages and positive effects of the present invention are as follows: the prepared nanotracer colloid has strong stability and a penetration rate of nearly 100% in underground aquifers, making it more accurate when used for detection; it is sensitive to organic pollutants and, when used in conjunction with a dual-point migration model, can accurately detect and quantify residual organic pollutants in underground aquifers, with a saturation detection limit as low as 0.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The process of preparing the nano-tracer obtained in Example 1;

[0025] Figure 2 Characterization results of the nanotracer prepared in Example 1; scanning electron microscopy on the left, atomic force microscopy on the right, and the internal data graph shows the nanotracer particle size distribution;

[0026] Figure 3 Characterization results of the nanotracer prepared in Example 1; a is Raman spectrum analysis, b is infrared spectrum analysis;

[0027] Figure 4 Continuous monitoring of the concentration and particle size of nanotracers in solutions with various ionic strengths;

[0028] Figure 5 Nanotracer static distribution experiment;

[0029] Figure 6 Uniform residual organic pollutant sand column sediment profile curve;

[0030] Figure 7 Penetration curves of nanotracers in sand columns with different residual organic pollutant saturations. The red curve represents the Nile Red signal molecule, and the black curve represents the nanocarrier.

[0031] Figure 8 Key parameters of nanotracer penetration curve and fitting curve of organic pollutant saturation. DETAILED DESCRIPTION

[0032] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0033] The present invention relates to a nano-tracer for detecting and quantifying residual organic pollutants in underground aquifers. This invention addresses the technical shortcomings of traditional tracers in detecting and quantifying residual organic pollutants in underground aquifers, and provides a novel nano-tracer for in-situ, low-disturbance detection and quantification of organic pollutants in underground aquifers. The nano-tracer uses carbon black nanoparticles as its core, with polyvinyl alcohol polymer chains grafted onto its surface to form a strongly hydrophilic structure. Signal molecules are physically adsorbed onto the surface of the inner carbon black nanoparticles and can migrate with the groundwater under the wrapping of the carrier. When the nano-tracer contacts residual organic pollutants, it can release the signal molecules in a targeted manner, while the carrier remains in the aqueous phase. By detecting the ratio of the carrier inventory to the signal molecule inventory in the downstream aqueous phase, the inventory of residual organic pollutants in the tracer's flow path is reflected.

[0034] Carbon black nanoparticles react with 4,4-azobis-4-cyanovaleric acid, and the resulting product is mixed with polyvinyl alcohol, N,N-dicyclohexyldiimide, and 4-dimethylaminopyridine to obtain a nanocarrier. The nanocarrier is connected to a signal molecule to prepare a nanotracer. The preparation path is as follows: Figure 1 shown.

[0035] The specific preparation method is as follows:

[0036] Step 1: Dissolve carbon black nanoparticles in sufficient tetrahydrofuran, add 4,4-azobis-4-cyanovaleric acid, the mass ratio of carbon black nanoparticles to 4,4-azobis-4-cyanovaleric acid is 1:0.5-3, wherein the carbon black nanoparticles have a particle size of 20-50 nm, heat and stir at 30-80° C. for 12-48 hours, wash with tetrahydrofuran after cooling, centrifuge, and vacuum dry for later use.

[0037] Step 2: Take the solid prepared in step 1, dissolve it in sufficient dimethyl sulfoxide, add polyvinyl alcohol, the molecular weight of the polyvinyl alcohol is 5-50kD, and heat and stir until the polyvinyl alcohol is completely dissolved; add N,N-dicyclohexyldiimine and 4-dimethylaminopyridine, wherein the mass ratio of N,N-dicyclohexyldiimine to 4-dimethylaminopyridine is 5-10:1, and the mass ratio of the product of step 1 to 4-dimethylaminopyridine is controlled to be 1:1; react at room temperature, use an ultrafiltration device to remove unreacted polyvinyl alcohol, and replace the solvent dimethyl sulfoxide with deionized water by dialysis. The ultrafiltration membrane and dialysis membrane have a molecular weight cutoff of 100kD to obtain a deionized water solution of the nanocarrier.

[0038] Step 3: Add a small amount of Nile red signal molecules to the mixed solution prepared in step 2, protect from light and ultrasound, stir at room temperature, use a 0.22 μm filter membrane and a PD-10 chromatography column to remove the free signal molecules in the solution to obtain a deionized aqueous solution of the nanotracer.

[0039] The nanotracer prepared by the above method has strong colloid stability. The surface polyvinyl alcohol polymer chain has a high density of hydroxyl groups, which is a strongly hydrophilic structure. This provides a strong hydrophilic effect for the nanotracer. At the same time, the elastic repulsion of the flexible polyvinyl alcohol polymer chain prevents it from contacting or depositing with porous media such as quartz sand. Therefore, the colloid has good stability and mobility, and the penetration rate in underground aquifers is nearly 100%.

[0040] During use, the nanocarriers within the nanotracer carry signal molecules as they migrate along the groundwater. Diffusion brings the nanotracer into contact with the interface between residual organic pollutants and water. When near the organic pollutant / water interface, the flexible polyvinyl alcohol (PVA) polymer chains fold into the water, exposing the signal molecules adsorbed by the carbon black within the nanocarriers. This creates a stronger interaction between the signal molecules and the organic pollutants, leading to their release into the organic pollutant phase. The released nanocarriers, under the hydrophilic effect of the PVA, return to the main water phase and continue their migration. During testing, extraction is performed downstream of the aquifer, and the concentration changes (C / C0) of the nanocarriers and signal molecules are measured simultaneously. In the absence of organic pollutants, the C / C0 of the nanocarriers and signal molecules should be equal. In the presence of organic pollutants, the C / C0 of the signal molecules is significantly lower than that of the nanocarriers. By fitting the penetration curve, the concentration of organic pollutants along the migration path can be quantified. Experimental validation demonstrates a saturation detection limit as low as 0.6%, demonstrating their effectiveness in detecting and quantifying residual organic pollutants in aquifers.

[0041] When nanotracers are put into practical use, a hydrogeological survey of the contaminated site is first conducted to determine the approximate scope of the pollution source, the permeability coefficient, and the hydrological conditions, and to design tracer placement and sampling points. A vertical well is drilled upstream of the groundwater source to be tested, and the tracer solution is released at different depths based on the hydrogeological information. Samples are then taken at corresponding depths downstream of the source, and the concentrations of nanocarriers and signal molecules are analyzed to determine the concentration of organic pollutants along multiple migration paths. To improve tracer detection accuracy, the distance between the injection and extraction wells can be further reduced based on the test results, and the above sampling and analysis process can be repeated until the distribution of residual organic pollutants is determined.

[0042] The present invention is described below with reference to the accompanying figures. Trichloroethylene, a typical organic pollutant found in contaminated sites, was selected as the research subject. A nanotracer was synthesized and its effectiveness in quantifying residual trichloroethylene in a simulated underground aquifer was investigated through column experiments. The quantitative accuracy of the nanotracer was also studied at various trichloroethylene saturation levels. Experimental methods without specific procedures were performed according to the corresponding product specifications. Unless otherwise specified, all instruments, reagents, and consumables used in the examples are commercially available.

[0043] Example 1: Preparation of Nanotracer

[0044] 3 g of carbon black nanoparticles were dissolved in 120 mL of tetrahydrofuran, 6 g of 4,4-azobis-4-cyanovaleric acid was added and mixed evenly, heated in an oil bath at 70° C. with stirring for 24 h, cooled to reflux, centrifuged, and vacuum dried at 100° C. for 48 h to obtain a solid product 1, which was vacuum dried and set aside.

[0045] Take 200 mg of product 1 and dissolve it in 500 mL of dimethyl sulfoxide, ultrasonically disperse it, add 150 mL of dimethyl sulfoxide solution of polyvinyl alcohol (concentration 40 g / L), mix well, add 2 g of N, N-dicyclohexylcarbodiimide and 0.2 mg of 4-dimethylaminopyridine, seal it and stir at room temperature for 24 hours. After the reaction, use an ultrafiltration device to ultrafilter (ultrafiltration membrane molecular weight cutoff 100 kD) and transfer the ultrafiltrate to a dialysis bag (dialysis bag molecular weight cutoff 100 kD) and dialyze it in deionized water for 5 days to obtain a product 2 solution.

[0046] Take 500 mL of product 2 solution, add 20 mg of Nile red solid, sonicate in the dark for 0.5 h, stir in the dark at room temperature for 24 h, filter the solution using a 0.22 μm filter membrane to obtain a deionized aqueous solution of the nanotracer, quantify the nanocarrier concentration using an ultraviolet spectrophotometer, and dilute to 75 mg / L for later use. Use three-dimensional fluorescence spectroscopy to quantify the signal molecule concentration.

[0047] The prepared nanotracer was tested, and its scanning electron microscope and atomic force microscope images were as follows: Figure 2 As shown, the nanotracer is approximately spherical; its infrared spectrum and fluorescence spectrum are shown in Figure 3 As shown, a -CH2- stretching vibration peak appears on the surface of the nanotracer, indicating that polyvinyl alcohol is successfully grafted onto the surface of the carbon black particles; the nanotracer has fluorescence peaks at an excitation wavelength of 576 nm and an emission wavelength of 648 nm, and the fluorescence intensity can be used to quantify the concentration of Nile red in the tracer.

[0048] Example 2: Nanotracer colloid stability

[0049] The nanotracer prepared in Example 1 was prepared into a groundwater solution with a concentration of 25 mg / L. 2 mL of the mixture was placed in a dynamic light scattering analyzer and an ultraviolet spectrophotometer respectively to continuously monitor the particle size and concentration of the nanotracer. The results are shown in FIG. Figure 4 As shown, during the continuous monitoring time of 6 hours, the particle size of the nanotracer was stable and did not agglomerate, and the hydrated particle size was ~135nm; the concentration of the nanotracer was stable and did not settle, and the colloidal stability was good.

[0050] Example 3: Static distribution of nanotracers

[0051] 2 mL of trichloroethylene was added to a 4 mL glass bottle. 2 mL of a 25 mg / L nanotracer groundwater solution was slowly added along the bottle wall. Due to its high density and poor solubility in water, the tracer solution was placed on top and the trichloroethylene on the bottom without mixing or shaking. The solution was kept in the dark for different periods of time and the concentrations of the nanocarrier and signal molecule in the upper aqueous solution were measured. The results are shown in Figure 2. Figure 5 As shown in the static tracing experiment lasting up to 48 hours, the concentration of signal molecules in the aqueous phase gradually decreased, indicating that the signal molecules migrated from the aqueous phase to trichloroethylene; the concentration of nanocarriers in the aqueous phase remained unchanged, indicating that the nanocarriers would not leave the aqueous phase and existed stably in the aqueous phase.

[0052] Example 4: Construction of residual TCE sand column

[0053] A residual TCE sand column was constructed to simulate an underground aquifer. The sand column was dry-packed with quartz sand medium. The sand column was 10 cm long and 1.1 cm in inner diameter. It was packed with 260 μm quartz sand and was shaken several times during the filling process.

[0054] After filling, carbon dioxide gas was introduced into the sand column. The carbon dioxide introduction time was 0.5 h and the gas flow rate was 2 mL / min, so that the air in the pores of the medium was completely replaced by carbon dioxide.

[0055] Prepare simulated groundwater, specifically including 60 mg of magnesium sulfate heptahydrate, 20 mg of potassium nitrate, 36 mg of sodium bicarbonate, 36 mg of calcium chloride, 35 mg of calcium nitrate, and 25 mg of calcium sulfate dihydrate, dissolve them in deionized water, and adjust the volume to 1 L to obtain simulated groundwater with an ionic strength of 3.67 mM.

[0056] Place the sand column vertically, and slowly introduce deionized water from the bottom of the sand column through an injection pump. The injection flow rate of deionized water is 50-100μL / min. After the deionized water is saturated, continue to inject 200PV. Convert the injection liquid into trichloroethylene, and slowly introduce it from the bottom of the sand column through an injection pump. The injection flow rate of trichloroethylene is 20μL / min. After the trichloroethylene is saturated, continue to inject 10PV until the groundwater in the pores is completely replaced by trichloroethylene. Then convert the injection liquid into simulated groundwater, and introduce simulated groundwater at a higher flow rate to flush the trichloroethylene in the pores of the medium. The groundwater injection flow rate is 100-500μL / min. Adjust the introduction time and flow rate of simulated groundwater to obtain sand columns with different residual trichloroethylene saturations. The trichloroethylene content in the effluent is obtained by gas chromatography analysis, and the residual trichloroethylene saturation in the sand column is obtained by trichloroethylene mass balance calculation. The constructed sand column is subjected to sedimentation profile analysis, and the results are as follows. Figure 6 As shown, the residual amount of trichloroethylene in each section of the sand column is close to the calculated value, and the recovery rate is 75%. The residual organic pollutants in the sand column constructed by this method are relatively uniform.

[0057] Example 5: Detection of residual organic pollutants in aquifers using nanotracers

[0058] The nanotracer prepared in Example 1 was diluted with simulated groundwater to a concentration of 25 mg / L, and the nanotracer solution was converted from a deionized water system to a simulated groundwater system.

[0059] The diluted nanotracer solution was injected into the sand column to simulate the groundwater flow rate of 2 m / d and the flow rate of 58 μL / min, and the effluent was collected.

[0060] The concentration of nanocarriers in the effluent was quantified using an ultraviolet spectrophotometer with a wavelength of 265 nm. The concentration of signal molecules in the effluent was quantified using a three-dimensional fluorescence spectrometer with an excitation wavelength of 576 nm and an emission wavelength of 648 nm.

[0061] The penetration curves of nanocarriers and signal molecules were drawn, and the key parameters of the penetration curves (S part max : the maximum adsorption capacity of residual trichloroethylene for signal molecules). The breakthrough curve fitting was completed using Hydrus 1D software. The hydraulic model was the Van Genuchten-Mualem model. The key parameters were fitted with the trichloroethylene saturation to obtain a calculation method for the quantitative determination of residual organic pollutants by nanotracers suitable for this sand column system.

[0062] Penetration curves of nanotracers in sand columns containing residual organic pollutants and Hydrus fitting analysis:

[0063] (1) Nanotracer in situ tracing experiment

[0064] A 25 mg / L nanotracer groundwater solution was prepared and injected into a sand column with residual organic pollutants at a constant flow rate using a syringe pump. The sand column had a porosity of 0.444 and a pore volume of 4.215 mL. The simulated groundwater flow rate was 2 m / d, and the injection rate was 58.55 μL / min. The effluent was collected using a fully automated sampler. A total of 10 PV of nanotracer was injected, with samples taken every 1 PV. After 10 PV, the solution was converted to background groundwater and injected again for 3 PV. All effluent samples were measured for absorbance at 265 nm using an ultraviolet spectrophotometer to determine the nanocarrier concentration in the sample solution. Fluorescence intensity was measured using a three-dimensional fluorescence spectrometer at an excitation wavelength of 576 nm and an emission wavelength of 648 nm to determine the signal molecule concentration in the sample solution. Penetration curves were then plotted.

[0065] (2) Hydrus fitting analysis of penetration curve

[0066] The Darcy experiment determined that the longitudinal permeability coefficient of the sand column in the column experimental system was 13.403 cm / h, and the longitudinal diffusion coefficient was 0.1909 cm using the Hydrus inversion calculation. The Hydrus hydraulic model is the van Genuchten-Mualem model, with the hydraulic upper boundary condition being a constant flux boundary and the lower boundary condition being a free drainage boundary. The solute transport model is a two-point adsorption model, with the solute upper boundary condition being a constant flux concentration boundary and the lower boundary condition being a zero concentration gradient boundary. The nanocarrier penetration curve data was substituted into the model, and the maximum deposition amount S of the nanotracer in the sand column was obtained by inversion calculation. att max , the signal molecule penetration curve data and S att max Substitute into the model and inversely calculate the maximum amount S of signal molecules dissolved and distributed into the residual trichloroethylene part max Hydrus fitted nanotracer penetration curve correlation coefficient R 2 All are greater than 0.98.

[0067] The sand columns with different organic pollutant residual saturations were tested by the above method to obtain the key fitting parameters of the nanotracer penetration curve corresponding to different organic pollutant saturations, among which S part max The maximum amount of signal molecules that enter trichloroethylene, K part Assign the signal molecule the rate of entry into trichloroethylene, S att max is the maximum deposition amount of nanotracer in the sand column, K att is the deposition rate of the nanotracer in the sand column. The test data are shown in Table 1. The penetration curve is drawn based on the obtained data, as shown in Figure 7 shown.

[0068] Table 1 Key fitting parameters of nanotracer penetration curves corresponding to different organic pollutant saturations

[0069]

[0070]

[0071] (3) Relationship between key parameters and organic pollutant saturation

[0072] The penetration curves in each set of experiments were calculated by Hydrus inversion to obtain S att max , K att 、S part max , K part , where S partmax It is a parameter directly related to the residual trichloroethylene in the pores of the medium. The inversion calculation results in S part max Plot the trichloroethylene saturation of the corresponding experimental group, and the results are as follows Figure 8 As shown, S part max There is a linear relationship between the concentration and the saturation of trichloroethylene, which proves that the nanotracer can accurately detect and quantify the saturation of residual organic pollutants in aquifers.

[0073] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A nano-tracer, characterized in that: Carbon black nanoparticles are used as the core, polyvinyl alcohol polymer chains are grafted onto the surface, and signal molecules are loaded onto the surface of the inner layer of carbon black nanoparticles through physical adsorption.

2. The nanotracer according to claim 1, characterized in that: The signal molecule is Nile Red.

3. A method for preparing the nanotracer according to claim 1 or 2, characterized in that: Carbon black nanoparticles are reacted with 4,4-azobis-4-cyanovaleric acid, and the resulting product is mixed with polyvinyl alcohol, N,N-dicyclohexyldiimide, and 4-dimethylaminopyridine to obtain a nanocarrier after the reaction. After the signal molecule is connected to the nanocarrier, a nanotracer is obtained.

4. The method for preparing the nano-tracer according to claim 3, characterized in that: The mass ratio of carbon black nanoparticles to 4,4-azobis-4-cyanovaleric acid is 1:0.5-3, and the mass ratio of N,N-dicyclohexyl diimide to 4-dimethylaminopyridine is 5-10:1 Preferably, the carbon black nanoparticles have a particle size of 20-50 nm.

5. The method for preparing the nano-tracer according to claim 3 or 4, characterized in that: The specific steps are as follows: Step 1: dissolving carbon black nanoparticles in tetrahydrofuran, adding 4,4-azobis-4-cyanovaleric acid, heating and stirring to react, cooling, washing and separating with tetrahydrofuran, and vacuum drying for later use; Step 2: Dissolve the solid prepared in step 1 in dimethyl sulfoxide, add polyvinyl alcohol, and heat and stir until the polyvinyl alcohol is completely dissolved; add N,N-dicyclohexyldiimine and 4-dimethylaminopyridine, react at room temperature, remove unreacted polyvinyl alcohol using an ultrafiltration device, and replace the solvent dimethyl sulfoxide with deionized water by dialysis to obtain a deionized water solution of the nanocarrier; Step 3: Add the signal molecule to the deionized water solution of the nanocarrier, protect from light and ultrasound, stir at room temperature to remove the free Nile red, and obtain the deionized water solution of the nanotracer.

6. The method for preparing the nano-tracer according to claim 5, characterized in that: In step 1, the heating temperature is 30-80° C., and the stirring time is 12-48 hours.

7. The method for preparing the nano-tracer according to claim 5, characterized in that: In step 3, a 0.22 μm filter membrane and a PD-10 chromatography column were used to remove free signal molecules in the solution; Preferably, the molecular weight cut-off of the ultrafiltration membrane and the dialysis membrane is 100 kD.

8. Use of the nanotracer according to claim 1 or 2 in the detection of residual organic pollutants in underground aquifers.

9. The use according to claim 8, characterized in that: Detection and / or quantification of residual organic pollutants in underground aquifers.

10. The use according to claim 8, characterized in that: A solution containing a nano-tracer is placed upstream of the underground aquifer in the area to be tested, and extracted downstream of the underground aquifer. The concentrations of nano-carriers and signal molecules in the extract are detected, and the changes in the concentrations of nano-carriers and signal molecules are compared. When the concentration changes of the nanocarrier and the signal molecule are the same, it is determined that the underground aquifer between the detection points does not contain organic pollutants; When the change in the concentration of the signal molecule is greater than the change in the concentration of the nanocarrier, it is determined that the underground aquifer between the detection points contains organic pollutants; preferably, the content of the organic pollutants is calculated based on the difference.

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