In-situ sampling method for perfluorinated compounds in fresh water, brackish water and salt water
By using COF materials and modified filter membranes in the DGT device, the accuracy problem of perfluorinated compound detection in seawater environment was solved, achieving efficient adsorption and resistance to biofouling, and ensuring the accuracy and stability of the detection results.
Patent Information
- Application Number
- CN202510971781.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-14
- Publication Date
- 2025-10-21
AI Technical Summary
Existing DGT devices face challenges such as high ionic strength, pH fluctuations, and biofouling when used in seawater environments, leading to inaccurate perfluorinated compound detection results.
A DGT device containing covalent organic framework material COF as the adsorbent was designed, combined with a modified filter membrane to inhibit microbial growth. By stacking adsorption membrane, diffusion membrane and filter membrane, a sampling method for perfluorinated compounds suitable for freshwater, brackish water and saline water environments was designed.
It improves the adsorption efficiency and resistance to biofouling of perfluorinated compounds, ensuring the accuracy and stability of test results. The adsorption capacity is much higher than that of the traditional WAX-DGT device, and the test results are basically consistent with those obtained by the grab water sample method.
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Figure CN120820360A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of environmental detection technology, in particular to an in-situ sampling method for perfluorinated compounds in fresh water, brackish water and salt water. Background Art
[0002] Diffusion gradient technology (DGT) is a passive sampling technique used to measure chemical concentrations in the environment. It is used to determine the free dissolved phase concentrations of metal ions and other chemicals in the environment. It is widely used in environmental monitoring and scientific research in freshwater systems such as lakes and rivers. This method provides a measurement that approximates bioavailability because it mimics the biological uptake of these chemicals. The fundamental principle of DGT technology is based on Fick's first law, which states that substances diffuse from areas of high concentration to areas of low concentration. A DGT device consists of a diffusion layer and a binding layer. When the DGT device is placed in the environment to be measured, the target chemical first passes through the diffusion layer and reaches the binding layer (capture layer), where it is captured and immobilized. Because the diffusion process is limited to molecules within the diffusion layer, the influence of water flow on the measurement results is eliminated. By analyzing the chemical content in the binding layer and combining it with diffusion parameters, the concentration of the chemical in the environment can be calculated. To maintain structural stability and prevent external interference, the DGT device also contains one or more layers of support material. These materials do not participate in the capture process of the chemical but provide physical support for the diffusion and binding layers. The entire DGT device is encapsulated in a protective shell to ensure that it is not directly disturbed by external factors (such as water flow, sediment particles, etc.) during actual application.
[0003] Despite its high sensitivity and selectivity, DGT technology faces several limitations and challenges in practical application, particularly in coastal and marine environments. First, the use of DGT devices in the unique environment of seawater requires special consideration of their applicability and limitations. The high ionic strength and pH of seawater place higher demands on the chemical capture layer within the DGT device. For example, the WAX-DGT sampler commonly used by researchers (which utilizes an adsorption membrane containing a weak anion adsorbent resin) is susceptible to adsorption competition when faced with high concentrations of chloride ions and other anions, as well as perfluorinated compounds (PFAs), compromising the effective capture of target compounds. Particularly in high salinity conditions, the adsorption performance of WAX-DGT for PFAs decreases with prolonged in situ sampling. Second, in addition to the impact of the chemical environment, DGT devices can also be susceptible to biofouling during deployment. Prolonged exposure to natural water bodies can lead to the formation of algae or other microorganisms covering the surface of the DGT device, potentially altering its physical properties and potentially inaccurate or distorting monitoring results.
[0004] Therefore, when applying DGT technology to research and monitoring seawater environments, the DGT device must be rationally designed and operated in accordance with specific research objectives and environmental conditions. Furthermore, careful consideration and addressing of the aforementioned challenges are crucial, such as optimizing the selection and preparation of the capture layer, considering the impact of environmental factors on device performance, and implementing measures to reduce biofouling. Designing a DGT device suitable for the detection of perfluorinated compounds in a wide range of freshwater, brackish, and saltwater environments is currently a key research focus. Summary of the Invention
[0005] The purpose of the present invention is to provide an in-situ sampling method for perfluorinated compounds in fresh water, brackish water and salt water, so as to solve the problem that the above-mentioned existing DGT device is easily affected by the salt water environment (ionic strength, pH value, biological fouling, etc.) when directly used for target substance detection in brackish water and salt water environments, resulting in inaccurate detection results.
[0006] To achieve the above objectives, the present invention provides an in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water. The in-situ sampling method is carried out using a DGT device. The DGT device includes a base and an adsorption membrane, a diffusion membrane, and a filter membrane superimposed on the base. After the superposition is completed, the air is exhausted and the upper cover is loaded.
[0007] Preferably, the preparation method of the adsorption film is: The adsorption material is added to the polymerization reaction system of agar gel to obtain a mixture. After the mixture undergoes polymerization reaction, it is cooled and formed into an adsorption film.
[0008] Preferably, the polymerization reaction system of agar gel includes agar monomer and deionized water.
[0009] Preferably, the preparation method of the adsorption film is: Dissolve 0.2 g of agar powder in 10 mL of deionized water and heat in a hot water bath (approximately 80 °C) or a microwave until all the powder is completely dissolved, forming a clear agar solution. Add 2 g (wet weight, depending on particle size) of adsorbent material to the clear agar solution and mix thoroughly to ensure the adsorbent particles are suspended. Immediately, drop the solution evenly and controlled into a preheated mold with a thickness of 0.4 mm. Leave the mold flat at room temperature until the gel has completely cooled and solidified, and the adsorbent material has settled to one side of the gel by gravity. Open the mold and cut the adsorbent gel into circular pieces with a diameter of 2.5 cm. Place the adsorbent film discs in deionized water and then store them in a 0.01 M sodium chloride solution.
[0010] Preferably, the adsorption material is a COF material, and the preparation method of the COF material is: 1,3,5-tris(4-aminophenyl)benzene and 2,5-divinyl-1,4-benzenedicarboxaldehyde were placed in a centrifuge tube, and then acetonitrile was added. Ultrasonication was performed until the solid matter was completely dissolved to obtain a mixed solution. Acetic acid solution was slowly dripped into the mixed solution and mixed thoroughly. After standing at room temperature, the mixture was washed and dried to obtain a COF material.
[0011] Preferably, the preparation method of COF material is: 1,3,5-Tris(4-aminophenyl)benzene (14.05 mg, 0.04 mmol) and 2,5-divinyl-1,4-benzenedicarboxaldehyde (11.07 mg, 0.06 mmol) were placed in a centrifuge tube, and 5 mL of acetonitrile was added. Ultrasonication was performed until the solid matter was completely dissolved. 0.7 mL of 12 M acetic acid solution was slowly added dropwise to the mixture, and the mixture was thoroughly mixed. After standing at room temperature for 72 h, it was washed with ethanol and tetrahydrofuran and dried in a vacuum oven to obtain a yellow powder.
[0012] Preferably, the preparation method of the diffusion membrane is: Agarose is dissolved in deionized water to form a transparent agar solution, and then the agar solution is added dropwise into a mold to cool and solidify, and then cut to obtain a diffusion membrane.
[0013] Preferably, the preparation method of the diffusion membrane is: Dissolve 0.9 g of agar powder in 60 mL of deionized water and heat in a hot water bath (approximately 80 °C) or a microwave until the powder is completely dissolved to form a transparent agar solution. Pour the hot solution dropwise into a preheated mold with a thickness of 0.8 mm in a smooth and controlled manner, then cool it at room temperature to allow it to cool and solidify. Open the mold and cut the agar hydrogel into circles with a diameter of 2.5 cm.
[0014] Preferably, the filter membrane is a polypropylene-based cuprous oxide composite membrane prepared by growing cuprous oxide in a hydrophilic polypropylene membrane through an in-situ synthesis method. The preparation method of the filter membrane is: The hydrophilic polypropylene membrane is immersed in a mixed solution of copper salt, glucose and water, ultrasonically stirred, and then sodium hydroxide solution is added and stirred continuously. Thereafter, the hydrophilic polypropylene after the reaction is transferred to deionized water for cooling, washed until colorless and transparent, and freeze-dried to obtain a filter membrane.
[0015] Preferably, the preparation method of the filter membrane is: On a magnetic thermostatic stirrer, 0.75 g of copper sulfate pentahydrate was dissolved in 200 mL of deionized water. 2.27 g of glucose was added and mixed thoroughly. A hydrophilic polypropylene membrane (0.45 μm pore size, 25 mm diameter), previously rinsed with methanol and deionized water and freeze-dried, was immersed in the solution and sonicated for 4 h to ensure that the divalent copper salt and the reducing agent, glucose, were fully dispersed on the membrane surface and within its pores. The sonicated mixture was stirred at 80 °C on a thermostatic stirrer. Then, 50 mL of 30 g / L sodium hydroxide solution was added. The reaction was stirred at this temperature for 10 min. The membrane was quickly transferred to deionized water and cooled to terminate the reaction. The cooled membrane was rinsed repeatedly with deionized water until the rinse solution was colorless and transparent. The membrane was then freeze-dried and used for later use.
[0016] Preferably, the prepared adsorption membrane, diffusion membrane and composite filter membrane are stacked on the base, the air is exhausted, and the upper cover is loaded to obtain a DGT device, which is placed in a polyethylene sealed bag containing ultrapure water and brought to the site for use.
[0017] Preferably, the DGT device is applied in freshwater areas. The specific application process is: fix the DGT device on a stainless steel column and insert it vertically into the riverbed so that the DGT device extends at least 0.5 m below the water surface and avoids locations with high turbulence to prevent the generation of bubbles.
[0018] Preferably, the DGT device is applied to saltwater areas. The specific application process is: fix the DGT device on a suspended DGT arrangement device so that the DGT device is suspended in water and remains parallel to the water flow direction.
[0019] Therefore, the present invention adopts an in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water using the above structure, which has the following beneficial effects: 1. The present invention utilizes covalent organic framework material COF as the adsorption material, which has the advantages of high specific surface area, easy modification, ordered pore size, and adjustable components, effectively solving the problem of adsorption competition.
[0020] 2. The adsorption material of the present invention can achieve efficient adsorption of perfluorooctanoic acid (PFOA) within a few seconds, with a maximum adsorption capacity exceeding 1000 mg / g (much higher than the maximum adsorption capacity of 165 mg / g of the WAX-DGT sampler). Currently, there is no DGT device based on COF adsorption material.
[0021] 3. The modified filter membrane of the present invention contains cuprous oxide, which has antimicrobial properties. It inhibits the growth and reproduction of microorganisms by releasing copper ions. Copper ions can penetrate microbial cell walls and interfere with intracellular metabolic processes, thereby achieving both bactericidal and antibacterial effects. Treating the filter membrane with cuprous oxide effectively improves its anti-biofouling properties.
[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 The adsorption kinetics of COF materials in low concentration perfluorooctanoic acid (PFOA) solution; Figure 2 The adsorption kinetics of COF materials in high concentration perfluorooctanoic acid (PFOA) solution; Figure 3 is the adsorption isotherm of perfluorooctanoic acid (PFOA) solution on COF material; Figure 4 The adsorption film prepared based on COF material is placed on the DGT base; Figure 5 The adsorption membrane, diffusion membrane and filtration membrane are stacked in sequence on the DGT base; Figure 6 This is the appearance of the complete DGT device. DETAILED DESCRIPTION
[0024] The present invention will be further described below. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the present invention is not limited to this embodiment.
[0025] Example 1
[0026] The preparation method of the adsorption film is as follows: (1) Preparation of COF materials 1,3,5-tris(4-aminophenyl)benzene (14.05 mg, 0.04 mmol) and 2,5-divinyl-1,4-benzenedicarbaldehyde (11.07 mg, 0.06 mmol) were placed in a centrifuge tube, and then 5 mL of acetonitrile was added. Ultrasonication was performed until the solid matter was completely dissolved to obtain a mixed solution. 0.7 mL of 12 M acetic acid solution was slowly added dropwise to the mixed solution and thoroughly mixed. After standing at room temperature for 72 h, it was washed with ethanol and tetrahydrofuran and placed in a vacuum oven to obtain a yellow powder (about 20 mg), which is the COF material.
[0027] (2) Preparation of adsorption film Dissolve 0.2 g of agar powder in 10 mL of deionized water and heat in a hot water bath (approximately 80 °C) or a microwave until all the powder is completely dissolved, forming a clear agar solution. Add 2 g (wet weight, depending on particle size) of adsorbent material to the clear agar solution and mix thoroughly to ensure the adsorbent particles are suspended. Immediately, drop the solution steadily and controlledly into a preheated mold with a thickness of 0.4 mm. Leave the mold flat at room temperature until the gel completely cools and solidifies, allowing the adsorbent material to settle to one side of the gel by gravity. Open the mold to obtain the adsorbent gel, which is then cut into circular adsorption films with a diameter of 2.5 cm. Place the adsorption film discs in deionized water and then store them in 0.01 M sodium chloride solution.
[0028] Example 2
[0029] The preparation method of the diffusion membrane is as follows: Dissolve 0.9 g of agar powder in 60 mL of deionized water and heat in a hot water bath (approximately 80 °C) or a microwave until the powder is completely dissolved to form a transparent agar solution. Pour the hot solution dropwise into a preheated mold with a thickness of 0.8 mm in a smooth and controlled manner, then cool it at room temperature to allow it to cool and solidify. Open the mold and cut the agar hydrogel into circles with a diameter of 2.5 cm.
[0030] Example 3
[0031] The filter membrane is prepared by growing cuprous oxide in a hydrophilic polypropylene membrane through an in-situ synthesis method to form a polypropylene-based cuprous oxide composite membrane. The preparation method of the filter membrane is as follows: On a magnetic thermostatic stirrer, 0.75 g of copper sulfate pentahydrate was dissolved in 200 mL of deionized water. 2.27 g of glucose was added and mixed thoroughly. A hydrophilic polypropylene membrane (0.45 μm pore size, 25 mm diameter), previously rinsed with methanol and deionized water and freeze-dried, was immersed in the solution and sonicated for 4 h to fully disperse the divalent copper salt and reducing agent glucose on the surface and in the pores of the polypropylene membrane. The sonicated mixture was stirred at 80 °C on a thermostatic stirrer. Then, 50 mL of 30 g / L sodium hydroxide solution was added and stirred at this temperature for 10 min. The polypropylene membrane was then quickly transferred to deionized water to cool and terminate the reaction. The cooled polypropylene membrane was repeatedly rinsed with deionized water until the rinse solution was colorless and transparent. The membrane was then freeze-dried to obtain a filter membrane for later use.
[0032] Example 4
[0033] The adsorption membrane, diffusion membrane and filtration membrane prepared in Examples 1-3 were stacked on the base in sequence, the air was exhausted, and the upper cover was installed to obtain a DGT device. The DGT device was placed in a polyethylene sealed bag containing a small amount of deionized water and brought to the site for use. The appearance and assembly process of the DGT device are shown in the attached Figure 4 –6.
[0034] Example 5
[0035] The DGT device prepared in Example 4 was applied to a freshwater area. The specific application process was as follows: Two DGT devices were deployed at a sampling site downstream of a representative PFAS-contaminated river (salinity 0.95 ± 0.07 PSU). The DGT devices were mounted on stainless steel poles and inserted vertically into the riverbed, extending at least 0.5 m below the water surface and avoiding areas of high turbulence to prevent air bubble formation. The DGT devices were recovered after 14 days of exposure. After recovery, the device surfaces were carefully inspected, and no significant biofouling was found on any of the DGT devices. The DGT devices were rinsed with deionized water, placed in polyethylene bags, and refrigerated. Laboratory pretreatment and sample testing were completed within one week. Simultaneously, two surface water samples were collected from the river (0.5 m below the water surface) at the DGT device site. The polypropylene (PP) bottles used for collection had been rinsed with sample water and cleaned with solvent. All river water samples were refrigerated, transferred to the laboratory, and immediately stored at -20°C. Laboratory pretreatment and sample testing were completed within one week. The results showed that the PFOA concentrations measured by the two DGTs were 21,520 and 21,393 ng / L, respectively; the PFOA concentrations obtained by the grab water sampling method were 26,594 and 20,567 ng / L, respectively. The average concentration measured by the DGTs was 91% of the average concentration measured by the grab water sampling method, meeting the error tolerance requirements, demonstrating that the DGT device of the present invention is capable of in situ determination of PFOA concentration in water.
[0036] Example 6
[0037] The DGT device prepared in Example 4 was applied to saltwater areas. The specific application process was as follows: Two DGT devices were deployed at a sampling site in a typical PFAS-contaminated bay (salinity 14.37 ± 3.92 PSU). The DGT devices were fixed to a suspended DGT device, suspended in the water (at least 0.5 m below the surface) and parallel to the current. The DGT devices were recovered after 14 days of exposure. After DGT recovery, the device surfaces were carefully inspected, revealing no significant biofouling on any of the DGT devices. The DGT devices were rinsed with deionized water, placed in polyethylene bags, and refrigerated. Laboratory pretreatment and sample testing were completed within a week. Simultaneously, two surface water samples were collected from the river (0.5 m below the surface) at the DGT device site. The polypropylene (PP) bottles used were rinsed with sample water and then cleaned with solvent. All river water samples were refrigerated, transferred to the laboratory, and immediately stored at -20°C. Laboratory pretreatment and sample testing were completed within a week. The results showed that the PFOA concentrations measured by the two DGTs were 2295.0 and 2893.9 ng / L, respectively; the PFOA concentrations obtained by the grab water sampling method were 2438.6 and 2558.1 ng / L, respectively. The average concentration measured by the DGTs was 104% of the average concentration measured by the grab water sampling method, meeting the error requirements, demonstrating that the DGT device of the present invention is capable of in situ determination of PFOA concentration in water.
[0038] Test example 4 mg of COF material prepared in Example 1 was placed in 40 mL of 50 ng / mL PFOA solution (low concentration), and 16 mg of COF material was placed in 40 mL of 400 ng / mL PFOA solution (high concentration). Three replicate experiments and one control experiment (no COF material) were set up. The samples were shaken on a shaker, and a certain volume of solution was collected at 0, 1, 5, 10, 30, 60, 180, and 1320 min, and the PFOA concentration in the solution was measured using a liquid chromatography-triple quadrupole instrument. The adsorption kinetics of PFOA by COF material were obtained, as shown in Figure 2. Figure 1 (low concentration) and Figure 2 (High concentration). The results show that under low concentration conditions, the adsorption rate of PFOA by COF material reaches 80% within 5 minutes, and the adsorption rate reaches 95% after 60 minutes, which is close to the adsorption equilibrium ( Figure 1 ); Under high concentration conditions, the adsorption rate of PFOA by COF material reached 95% within 5 minutes, close to the adsorption equilibrium ( Figure 2). In summary, the COF material prepared in the test example has excellent adsorption performance for PFOA and can reach adsorption equilibrium in a relatively short time. Prepare 20 mL of PFOA solution with concentrations of 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, 300, and 500 mg / L, add 6 mg of COF material, set up three groups of repeated experiments and one group of control experiments (without COF material). After shaking on a shaker for 24 hours, collect a certain volume of solution and use a liquid chromatography-triple quadrupole coupling instrument to determine the concentration of PFOA in the solution. From Figure 3 It can be seen that the adsorption capacity of PFOA by COF material increases with the increase of PFOA concentration in the solution. The Langmuir model fitting predicts that the maximum adsorption capacity of PFOA by COF material can reach 1078 mg / g.
[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.
Claims
1. An in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water, characterized by: The in-situ sampling method is carried out using a DGT device, which includes a base and an adsorption membrane, a diffusion membrane and a filter membrane superimposed on the base. After the superposition is completed, the air is exhausted and the upper cover is loaded.
2. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 1, characterized in that: The preparation method of the adsorption film is as follows: The adsorption material is added to the polymerization reaction system of agar gel to obtain a mixture. After the mixture undergoes polymerization reaction, it is cooled and formed into an adsorption film.
3. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 2, characterized in that: The polymerization reaction system of agar gel includes agar monomer and deionized water.
4. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 2, characterized in that: The adsorption material is COF material, and the preparation method of COF material is as follows: 1,3,5-tris(4-aminophenyl)benzene and 2,5-divinyl-1,4-benzenedicarboxaldehyde are placed in a centrifuge tube, acetonitrile is added, and ultrasonication is performed until all the solid substances are dissolved to obtain a mixed liquid, acetic acid solution is slowly dripped into the mixed liquid to fully mix, and the mixture is allowed to stand at room temperature, washed, and dried to obtain the COF material.
5. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 1, characterized in that: The preparation method of the diffusion membrane is as follows: Agarose is dissolved in deionized water to form a transparent agar solution, and then the agar solution is added dropwise into a mold to cool and solidify, and then cut to obtain a diffusion membrane.
6. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 1, characterized in that: The filter membrane is a polypropylene-based cuprous oxide composite membrane prepared by growing cuprous oxide in a hydrophilic polypropylene membrane through an in-situ synthesis method. The preparation method of the filter membrane is as follows: The hydrophilic polypropylene membrane is immersed in a mixed solution of copper salt, glucose and water, ultrasonically stirred, and then sodium hydroxide solution is added and stirred continuously. Thereafter, the hydrophilic polypropylene after the reaction is transferred to deionized water for cooling, washed until colorless and transparent, and freeze-dried to obtain a filter membrane.
7. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, or salt water according to any one of claims 2 to 6, characterized in that: The prepared adsorption membrane, diffusion membrane and filter membrane are stacked on the base, the air is exhausted, and the upper cover is loaded to obtain a DGT device. The DGT device is placed in a polyethylene sealed bag containing ultrapure water and brought to the site for use.
8. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 7, characterized in that: The DGT device is applied in freshwater areas. The specific application process is: fix the DGT device on a stainless steel column and insert it vertically into the riverbed, so that the DGT device extends at least 0.5 m below the water surface and avoids locations with high turbulence to prevent the generation of bubbles.
9. The in-situ sampling method for perfluorinated compounds in fresh water, brackish water, and salt water according to claim 7, characterized in that: The DGT device is applied in saltwater areas. The specific application process is: fix the DGT device on a suspended DGT arrangement device, hang the device on an ocean buoy, and make the DGT device suspended in the water and parallel to the water flow direction.