Method and device for determining the diffusion coefficient of charged micropollutants in nanofiltration membranes

Abstract

The application discloses a kind of method and device for determining the diffusion coefficient of charged micro-pollutants in nanofiltration membrane in the field of membrane technology, including setting four-electrode electrochemical system in H-type electrolytic cell, adding micro-pollutant solution to H-type electrolytic cell, using linear sweep voltammetry to analyze micro-pollutant solution to obtain first data.The application tests and analyzes micro-pollutant solution system, micro-pollutant solution and nanofiltration membrane system and different concentration micro-pollutant solution and nanofiltration membrane system based on four-electrode electrochemical system in H-type electrolytic cell, and obtains corresponding solution intrinsic conductance data, system conductance data and open-circuit voltage data, and then determines the intramembrane diffusion coefficient of charged micro-pollutants, the test steps are simple, the data is obtained quickly, and the overall test period is short, the micro-pollutant solution and nanofiltration membrane are replaced and adjusted quickly, the application range is wide, the linear fitting data processing process is simple and effective, and it has good repeatability.

Description

Technical Field

[0001] This invention relates to the field of membrane technology, specifically a method and apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micropollutants. Background Technology

[0002] Organic micropollutants widely present in environmental water bodies are characterized by their wide distribution, diverse types, and high toxicity, seriously threatening the water safety of various organisms in nature. Among many water treatment technologies, nanofiltration technology is expected to become the mainstream technology for micropollutant removal due to its advantages such as high efficiency, stability, and no toxic byproduct generation. However, given the complex interactions between micropollutants and membranes, existing nanofiltration technologies are unable to effectively remove certain specific micropollutants. The lack of understanding of the transmembrane transport mechanism of micropollutants limits the precise structural control and functional orientation design of high-performance micropollutant removal nanofiltration membrane materials, thus restricting further improvements in the ability of nanofiltration membranes to retain micropollutants. To deeply elucidate the mass transfer mechanism of micropollutants across nanofiltration membranes, understanding their intramembrane transport behavior is crucial. The intramembrane diffusion coefficient of a solute reflects the ease of its transmembrane transport and directly affects the separation efficiency and performance of the nanofiltration membrane.

[0003] Existing methods for determining the diffusion coefficient of micropollutants within membranes all have certain limitations. Concentration-driven transmembrane diffusion experiments have long testing cycles, low sensitivity to solutes with low diffusion rates, and are complex and have poor universality when testing different micropollutants. Testing with nuclear magnetic resonance instruments is costly and difficult to meet the diverse testing needs of micropollutants, and the test results are greatly affected by the conductivity of the sample. Testing with electrochemical impedance spectroscopy also has the limitation of long testing cycles and relies on equivalent circuit model assumptions, which may lead to large errors for membrane materials with complex pore structures. Summary of the Invention

[0004] The purpose of this invention is to provide a method and apparatus for determining the diffusion coefficient of charged micro-pollutants within a nanofiltration membrane, thereby solving the problems of long testing cycles, complex testing processes, poor adaptability, and large errors in detection results mentioned above.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a method for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants, comprising the following steps: S1: A four-electrode electrochemical system is set up in an H-type electrolytic cell. A micro-pollutant solution is added to the H-type electrolytic cell. The micro-pollutant solution is analyzed by linear scanning voltammetry to obtain the first data. The first data is fitted to obtain the intrinsic conductivity data of the solution. S2: Install the nanofiltration membrane in the H-shaped electrolytic cell, analyze the micro-pollutant solution and the nanofiltration membrane using linear scanning voltammetry to obtain second data, and fit the second data to obtain the system conductivity data, wherein the nanofiltration membrane is set in the middle of the H-shaped electrolytic cell to divide it into two corresponding electrolytic chambers; S3: The micro-pollutant solution in the H-type electrolytic cell is exported and cleaned. A first micro-pollutant solution is added to one electrolytic chamber of the H-type electrolytic cell, and a second micro-pollutant solution is added to the other electrolytic chamber. Then, the first micro-pollutant solution, the nanofiltration membrane, and the second micro-pollutant solution are analyzed by linear scanning voltammetry to obtain third data. The third data is fitted to obtain open-circuit voltage data, wherein the concentration of the second micro-pollutant solution is greater than the concentration of the first micro-pollutant solution. S4: The diffusion coefficient is calculated based on the intrinsic conductivity data of the solution, the conductivity data of the system, and the open-circuit voltage data of the Nernst equation and the Nernst-Einstein equation.

[0006] As a further aspect of the present invention: the linear scanning voltammetry used in steps S1-S3 is based on a four-electrode electrochemical system consisting of a working electrode, a counter electrode, and two sets of reference electrodes.

[0007] As a further aspect of the present invention: a first micro-contaminant solution is added to the counter electrode and reference electrode side chambers of the H-type electrolytic cell, and a second micro-contaminant solution is added to the working electrode and reference electrode side chambers of the H-type electrolytic cell.

[0008] As a further aspect of the present invention: the working voltage analyzed by the linear scanning voltammetry method in steps S1-S3 is -200mV to 200mV, and the scanning rate is 0.1mV / s to 50mV / s.

[0009] As a further aspect of the present invention, the concentration ratio of the second micro-pollutant solution to the first micro-pollutant solution is 2:1 to 100:1.

[0010] As a further aspect of the present invention: the concentration of the micro-pollutant solution in steps S1 and S2 is 0.01 mmol / L to 10 mmol / L.

[0011] Secondly, the present invention provides an apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants. The apparatus includes an electrolytic cell, a nanofiltration membrane, and four electrodes. Electrolytic chambers of equal volume are arranged on both sides of the electrolytic cell, and the two electrolytic chambers are connected by a central pipe. The electrolytic cell is H-shaped overall. The two electrolytic chambers are used to add and store micro-pollutant solutions. The nanofiltration membrane is detachably installed within the central pipe and is used for solute separation and to isolate the two electrolytic chambers. The four electrodes include a working electrode, a counter electrode, and two sets of reference electrodes. The working electrode and one set of reference electrodes are installed on one side of the electrolytic chamber, and the counter electrode and the other set of reference electrodes are installed on the other side of the electrolytic chamber. The working electrode, counter electrode, and two sets of reference electrodes form a four-electrode electrochemical system.

[0012] As a further aspect of the present invention: the electrode ends of the working electrode and the electrode ends of the counter electrode are both sheet-shaped platinum electrodes and are placed in parallel, and the ends of the working electrode and the counter electrode are arranged on the same horizontal plane.

[0013] As a further aspect of the present invention: the electrode end of the reference electrode is an L-shaped Luggin capillary, and both sets of the L-shaped Luggin capillary of the reference electrodes are installed facing the middle of the pipe, with the ends of the two sets of reference electrodes set on the same horizontal plane.

[0014] As a further aspect of the present invention: the nanofiltration membrane, the sheet-like platinum electrode of the working electrode, and the sheet-like platinum electrode of the counter electrode are arranged in parallel, wherein the area of ​​the nanofiltration membrane is smaller than the area of ​​the sheet-like platinum electrode of the working electrode, and the area of ​​the nanofiltration membrane is smaller than the area of ​​the sheet-like platinum electrode of the counter electrode.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, a four-electrode electrochemical system is used in an H-type electrolytic cell to test and analyze a micro-pollutant solution system, a micro-pollutant solution and nanofiltration membrane system, and micro-pollutant solutions and nanofiltration membrane systems with different concentrations. The corresponding intrinsic conductivity data of the solution, conductivity data of the system, and open-circuit voltage data are obtained, thereby determining the membrane diffusion coefficient of charged micro-pollutants. The testing steps are simple, the data is obtained quickly, the overall testing cycle is short, the micro-pollutant solution and nanofiltration membrane can be replaced and adjusted quickly, and the application range is wide.

[0016] 2. In this invention, the linear fitting data processing is simple and effective, with good repeatability. Through multiple sets of linear scanning voltammetry analysis, and by calculating the diffusion coefficient using the Nernst equation and the Nernst-Einstein equation, the accuracy of the diffusion coefficient obtained for the corresponding nanofiltration membrane is guaranteed. This enables rapid and accurate determination of the diffusion coefficient within the membrane, resulting in good performance. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the method flow of the present invention; Figure 2 This is a schematic diagram of the device structure of the present invention; Figure 3 The present invention is used to determine the linear voltammetric curves of the intrinsic conductivity of salicylic acid, perfluorobutyric acid and ranitidine solutions; Figure 4 Linear voltammetric curves for measuring the conductivity of salicylic acid, perfluorobutyric acid, and ranitidine solutions with the NF270 membrane system in Example 1 of this invention; Figure 5 The linear voltammetric curves for determining the open-circuit voltage of the salicylic acid, perfluorobutyric acid, and ranitidine solutions with the NF270 membrane system in Example 1 of this invention are shown. Figure 6 The linear voltammetric curves for measuring the conductivity of salicylic acid, perfluorobutyric acid, and ranitidine solutions with the NF90 membrane system in Example 2 of this invention are shown. Figure 7 This is a linear voltammetric curve for measuring the open-circuit voltage of a salicylic acid, perfluorobutyric acid, and ranitidine solution in an NF90 membrane system, as shown in Example 2 of this invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Example:

[0020] Please see Figure 1 In this embodiment of the invention, a method for determining the diffusion coefficient within a charged micro-pollutant nanofiltration membrane includes the following steps: S1: A four-electrode electrochemical system is set up in an H-type electrolytic cell. A micro-pollutant solution is added to the H-type electrolytic cell. The micro-pollutant solution is analyzed by linear scanning voltammetry to obtain the first data. The intrinsic conductivity data of the solution is obtained by fitting the first data. The first data are the current and voltage data of the micro-pollutant solution obtained by linear scanning voltammetry. S2: The nanofiltration membrane is installed in an H-shaped electrolytic cell. The micro-pollutant solution and the nanofiltration membrane are analyzed using linear sweep voltammetry to obtain the second data. The second data is fitted to obtain the system conductivity data. The nanofiltration membrane is set in the middle of the H-shaped electrolytic cell to divide it into two corresponding electrolytic chambers. The second data is the current and voltage data obtained by linear sweep voltammetry of the system formed by the micro-pollutant solution and the nanofiltration membrane. S3: The micro-pollutant solution in the H-type electrolytic cell is extracted and cleaned. A first micro-pollutant solution is added to one electrolytic chamber of the H-type electrolytic cell, and a second micro-pollutant solution is added to the other electrolytic chamber. Then, the first micro-pollutant solution, the nanofiltration membrane, and the second micro-pollutant solution are analyzed using linear sweep voltammetry to obtain third data. The open-circuit voltage data is obtained by fitting the third data, where the concentration of the second micro-pollutant solution is greater than the concentration of the first micro-pollutant solution. The third data consists of the current and voltage data obtained by linear sweep voltammetry for the system formed by the first micro-pollutant solution, the second micro-pollutant solution, and the nanofiltration membrane. S4: The diffusion coefficient is calculated based on the intrinsic conductivity data of the solution, the conductivity data of the system, and the open-circuit voltage data, using the Nernst equation and the Nernst-Einstein equation.

[0021] In some embodiments of the present invention, the derivation process for calculating the diffusion coefficient in step S4 is as follows: According to the definition of electrical conductance, , Among them, dielectric conductivity The slope of the linear fitting result of the current-voltage spectrum is used to obtain the intrinsic conductivity of the solution in step S1. The conductivity of the solution-membrane system obtained in step S2 Determine membrane conductivity : , The current-voltage spectrum obtained from the linear sweep voltammetry analysis in step S3 is linearly fitted, and the resulting transverse intercept is the open-circuit voltage. Then the cation transference number It can be represented as: , in, It is Faraday's constant. Let be the ideal gas constant. Absolute temperature and These represent the solutions on the working electrode and counter electrode sides, respectively. The intramembrane diffusion coefficients for positively charged and negatively charged micropollutants can be expressed as follows: and The calculation process is as follows: , , in, The thickness of the active layer of the membrane. For the effective area of ​​the membrane, The charge number of micro-pollutants, This refers to the concentration of micro-pollutants.

[0022] Furthermore, the micro-pollutant is a conventional charged micro-pollutant in the art, and may preferably be one or more of salicylic acid (SA), sulfamethoxazole (SMX), trimethoprim (TMP), perfluorobutyric acid (PFBA), and ranitidine (RN).

[0023] In some embodiments of the present invention, the membrane used in step S2 is immersed in ultrapure water for 24 h to 72 h before the H-type electrolytic cell is installed.

[0024] Specifically, this invention utilizes a four-electrode electrochemical system in an H-type electrolytic cell to test and analyze micro-pollutant solution systems, micro-pollutant solution and nanofiltration membrane systems, and micro-pollutant solutions and nanofiltration membrane systems with different concentrations. It obtains corresponding intrinsic conductivity data of the solution, conductivity data of the system, and open-circuit voltage data, thereby determining the intramembrane diffusion coefficient of charged micro-pollutants. The testing steps are simple, data is obtained rapidly, and the overall testing cycle is short. Changing and adjusting the micro-pollutant solution and nanofiltration membrane is quick, and the invention has a wide range of applications. The linear fitting data processing is simple and effective, exhibiting good repeatability. Multiple sets of linear scanning voltammetry analysis are used, and the diffusion coefficient is calculated using the Nernst equation and the Nernst-Einstein equation, ensuring the accuracy of the diffusion coefficient obtained for the corresponding nanofiltration membrane. This enables rapid and accurate determination of the intramembrane diffusion coefficient, demonstrating good performance.

[0025] Furthermore, the nanofiltration membrane is a conventional nanofiltration membrane in the field, which can be selected from commercial nanofiltration membranes such as NF90 membrane (manufactured by Dow Chemical Company) and NF270 membrane (manufactured by Dow Chemical Company) or conventional self-made nanofiltration membranes such as graphene oxide membrane and MXene membrane.

[0026] As a further aspect of the present invention: the linear scanning voltammetry used in steps S1-S3 is based on a four-electrode electrochemical system consisting of a working electrode, a counter electrode, and two sets of reference electrodes.

[0027] Specifically, the four-electrode electrochemical system, by using a working electrode, a counter electrode, and two sets of reference electrodes, can effectively reduce the error caused by electrode polarization effects and improve the ability to quickly and accurately determine the diffusion coefficient, especially when high resolution and measurement of low-concentration systems are required.

[0028] As a further aspect of the present invention: a first micro-contaminant solution is added to the counter electrode and reference electrode side chambers of the H-type electrolytic cell, and a second micro-contaminant solution is added to the working electrode and reference electrode side chambers of the H-type electrolytic cell.

[0029] As a further aspect of the present invention: the working voltage analyzed by the linear scanning voltammetry method in steps S1-S3 is -200mV to 200 mV, and the scanning rate is 0.1mV / s to 50 mV / s.

[0030] As a further aspect of the present invention, the concentration ratio of the second micro-pollutant solution to the first micro-pollutant solution is 2:1 to 100:1.

[0031] Specifically, the concentration ratio of the second micro-contaminant solution to the first micro-contaminant solution is 2:1 to 100:1 to ensure more accurate and stable data during electrochemical analysis.

[0032] As a further aspect of the present invention: the concentration of the micro-pollutant solution in steps S1 and S2 is 0.01 mmol / L to 10 mmol / L.

[0033] like Figure 2 As shown, an apparatus for determining the diffusion coefficient of charged micro-pollutants within a nanofiltration membrane is disclosed. The apparatus includes an electrolytic cell 1, a nanofiltration membrane 2, and four electrodes. Electrolytic cells 1 are arranged on both sides with equal volumes and connected by a central pipe. The electrolytic cell 1 is H-shaped, and the two electrofiltration chambers are used to add and store micro-pollutant solutions. The nanofiltration membrane 2 is detachably installed in the central pipe and is used for solute separation and to isolate the two electrofiltration chambers. The four electrodes include a working electrode 3, a counter electrode 4, and two sets of reference electrodes 5. The working electrode 3 and one set of reference electrodes 5 are installed on one side of the electrofiltration chamber, and the counter electrode 4 and the other set of reference electrodes 5 are installed on the other side of the electrofiltration chamber. The working electrode 3, the counter electrode 4, and the two sets of reference electrodes 5 form a four-electrode electrochemical system.

[0034] Specifically, a micro-pollutant solution is stored and electrolyzed in two electrolytic chambers of an H-shaped electrolytic cell 1. A central pipe connects the two electrolytic chambers and a nanofiltration membrane is detachably installed in the central pipe. When using linear scanning voltammetry to analyze the micro-pollutant solution, the nanofiltration membrane 2 is not installed in the central pipe, allowing the micro-pollutant solutions in the two electrolytic chambers to be connected, which facilitates fitting and obtaining the intrinsic conductivity data of the solution. In subsequent detection and analysis, the nanofiltration membrane 2 is installed in the central pipe to separate the two electrolytic chambers, allowing the corresponding ions to pass through the nanofiltration membrane to fit and obtain the system conductivity data and open-circuit voltage data, which facilitates the subsequent calculation of the diffusion coefficient.

[0035] As a further aspect of the present invention: the electrode ends of the working electrode 3 and the electrode ends of the counter electrode 4 are both sheet-shaped platinum electrodes and are placed in parallel, and the ends of the working electrode 3 and the counter electrode 4 are arranged on the same horizontal plane.

[0036] Specifically, the ends of the working electrode 3 and the counter electrode 4 are set on the same horizontal plane to ensure the uniformity of the electric field distribution during the electrochemical test and improve the accuracy and reliability of the analysis results.

[0037] As a further aspect of the present invention: the electrode end of the reference electrode 5 is an L-shaped Luggin capillary tube, and the L-shaped Luggin capillary tubes of both sets of reference electrodes 5 are installed facing the middle of the pipe, and the ends of the two sets of reference electrodes 5 are set on the same horizontal plane.

[0038] Specifically, the L-shaped Luggin capillary design of reference electrode 5 effectively reduces the liquid junction potential and improves the accuracy of electrochemical measurements. Both sets of L-shaped Luggin capillary tubes of reference electrode 5 are installed facing the central pipe, ensuring stable contact between the reference electrode and the electrolytic solution and reducing potential fluctuations caused by solution flow or bubble interference. Simultaneously, the ends of both sets of reference electrodes 5 are positioned on the same horizontal plane, maintaining the consistency of potential within the electrolytic chambers on both sides, further improving the reliability and repeatability of electrochemical measurements.

[0039] Furthermore, the two sets of reference electrodes 5 are Ag / AgCl electrodes.

[0040] Specifically, the Ag / AgCl electrode exhibits excellent electrochemical stability and reproducibility, making it suitable for various electrochemical analysis applications. In this invention, using two sets of Ag / AgCl electrodes as reference electrodes 5 further improves the accuracy and reliability of electrochemical measurements.

[0041] As a further aspect of the present invention: the nanofiltration membrane 2 and the sheet-like platinum electrode of the working electrode 3 and the sheet-like platinum electrode of the counter electrode 4 are arranged in parallel, the area of ​​the nanofiltration membrane 2 is smaller than the area of ​​the sheet-like platinum electrode of the working electrode 3, and the area of ​​the nanofiltration membrane 2 is smaller than the area of ​​the sheet-like platinum electrode of the counter electrode 4. Specifically, the nanofiltration membrane 2 is positioned to effectively isolate the solutions in the two electrolysis chambers while allowing molecules to pass through, thus enabling the electromigration of charged micro-pollutants. The sheet-like platinum electrode design of the working electrode 3 and the counter electrode 4 ensures the uniformity of the electric field, which helps to stabilize the electromigration of charged micro-pollutants.

[0042] Example 1:

[0043] In the first embodiment provided by the present invention, the micro-pollutant solution is salicylic acid, perfluorobutyric acid and ranitidine, and the nanofiltration membrane is an NF270 membrane. Please see Figures 3-5 This embodiment provides a method for determining the diffusion coefficients of salicylic acid, perfluorobutyric acid, and ranitidine within an NF270 membrane. The specific steps are as follows: S1: A four-electrode electrochemical system was set up in an H-type electrolytic cell. Linear scanning voltammetry analysis was performed on the micro-pollutant solution, and the intrinsic conductivity of the solution was obtained by data fitting. Figure 2A four-electrode electrochemical system was set up in an H-type electrolytic cell, with the counter electrode being an Ag / AgCl electrode immersed in a 3 M potassium chloride solution. 50 mL of prepared 0.5 mmol / L SA solution was added to each side of the H-type electrolytic cell. Linear sweep voltammetry was used for analysis on an electrochemical workstation, with the test parameters set as follows: onset voltage -200 mV, termination voltage 200 mV, and scan rate 0.5 mV / s. The SA solution was then successively replaced with equal volumes and concentrations of PFBA and RN solutions for analysis. The analytical results are shown below. Figure 3 As shown, based on the slope of the linear fitting results, the intrinsic conductivities of 0.5 mmol / L SA, PFBA and RN solutions were obtained as 0.0986 mS, 0.1420 mS and 0.0046 mS, respectively.

[0044] S2: The membrane was installed in an H-type electrolytic cell, and linear sweep voltammetry was performed on the micro-pollutant solution-membrane system. The system conductivity was obtained by fitting the results. A commercial NF270 membrane was immersed in ultrapure water for 24 h, and after removal, the active layer surface was placed with the working electrode side facing the connection of the H-type electrolytic cell. To prevent leakage, an O-ring was placed at the connection between the membrane and the H-type electrolytic cell. The four-electrode electrochemical system setup, linear sweep voltammetry analysis parameters, and micro-pollutant solutions were consistent with step S1. The three micro-pollutant solutions and the NF270 membrane system were tested sequentially. The results are as follows: Figure 4 As shown, based on the slope of the linear fitting results, the conductivities of 0.5 mmol / L SA, PFBA and RN solutions with NF270 membrane were 0.0684 mS, 0.1037 mS and 0.0034 mS, respectively.

[0045] S3: After cleaning, add a high-concentration micro-contaminant solution to the working electrode side and a low-concentration solution to the counter electrode side, and perform linear sweep voltammetry analysis. Obtain the open-circuit voltage by fitting the results. Clean the apparatus used in step S2 with ultrapure water and drain the water droplets. Add 50 mL of 0.5 mmol / L SA solution to the working electrode side and 50 mL of 0.05 mmol / L SA solution to the counter electrode side. Set the linear sweep voltammetry analysis parameters as in step S1 and perform the test. After cleaning, replace the SA solutions on both sides with equal volumes and concentrations of PFBA and RN solutions, respectively, and repeat the test steps. The results are as follows... Figure 5 As shown, based on the x-intercept of the linear fitting results, the open-circuit voltages of the SA, PFBA, and RN solutions with the NF270 membrane were obtained as -42.46 mV, -45.85 mV, and -20.17 mV, respectively.

[0046] S4: Based on the results of multiple sets of linear sweep voltammetry analysis, the diffusion coefficient is calculated using the Nernst equation and the Nernst-Einstein equation. The intrinsic conductivity of the three micro-pollutant solutions obtained in step S1 is also calculated. The conductivity of the three micro-pollutant solution-membrane systems obtained in step S2 The membrane conductivity can be obtained separately. The open-circuit voltages of the three micro-pollutant solution-membrane systems obtained through step S3. The cation transfer numbers for the corresponding systems were calculated using the Nernst equation. Furthermore, the diffusion coefficients of the three micropollutants within the membrane were calculated using the Nernst-Einstein equation. The diffusion coefficients of SA, PFBA, and RN within the NF270 membrane were 1.38 × 10⁻⁶. -12 m 2 / s, 1.84×10 -12 m 2 / s and 4.29×10 -13 m 2 / s. The detailed calculation process is as follows: , , , , in, It is Faraday's constant. Let be the ideal gas constant. Absolute temperature and These represent the solution activities on the working electrode and counter electrode sides, respectively. The thickness of the active layer of the membrane (17.92 nm for NF270). The effective area of ​​the membrane (currently 2.01 cm²) 2 ), This is the charge number of the micro-pollutant (approximately 1 for SA, PFBA, and RN). Let be the concentration of micro-pollutants. The intramembrane diffusion coefficients for positively charged and negatively charged micro-pollutants are expressed as follows: and .

[0047] Example 2:

[0048] In the first embodiment provided by the present invention, the micro-pollutant solution is salicylic acid, perfluorobutyric acid and ranitidine, and the nanofiltration membrane is an NF90 membrane. Please see Figures 6-7 This embodiment provides a method for determining the diffusion coefficients of salicylic acid, perfluorobutyric acid, and ranitidine within an NF90 membrane. The specific steps are as follows: S1: A four-electrode electrochemical system was set up in an H-type electrolytic cell. Linear scanning voltammetry analysis was performed on the micro-pollutant solution, and the intrinsic conductivity of the solution was obtained by data fitting. Figure 2 A four-electrode electrochemical system was set up in an H-type electrolytic cell, with the counter electrode being an Ag / AgCl electrode immersed in a 3 M potassium chloride solution. 50 mL of prepared 0.5 mmol / L SA solution was added to each side of the H-type electrolytic cell. Linear sweep voltammetry was used for analysis on an electrochemical workstation, with the test parameters set as follows: onset voltage -200 mV, termination voltage 200 mV, and scan rate 0.5 mV / s. The SA solution was then successively replaced with equal volumes and concentrations of PFBA and RN solutions for analysis. The analytical results are shown below. Figure 3 As shown, based on the slope of the linear fitting results, the intrinsic conductivities of 0.5 mmol / L SA, PFBA and RN solutions were obtained as 0.0986 mS, 0.1420 mS and 0.0046 mS, respectively.

[0049] S2: The membrane was installed in an H-type electrolytic cell, and linear sweep voltammetry was performed on the micro-pollutant solution-membrane system. The system conductivity was obtained by fitting the results. A commercial NF90 membrane was immersed in ultrapure water for 24 h, and after removal, the active layer surface was placed with the working electrode side facing the connection of the H-type electrolytic cell. To prevent leakage, an O-ring was placed at the connection between the membrane and the H-type electrolytic cell. The four-electrode electrochemical system setup, linear sweep voltammetry analysis parameters, and micro-pollutant solutions were consistent with step S1. The three micro-pollutant solutions and the NF90 membrane system were tested sequentially. The results are as follows: Figure 6 As shown, based on the slope of the linear fitting results, the conductivities of 0.5 mmol / L SA, PFBA and RN solutions with NF90 membranes were 0.0447 mS, 0.0623 mS and 0.0031 mS, respectively.

[0050] S3: After cleaning, add a high-concentration micro-contaminant solution to the working electrode side and a low-concentration solution to the counter electrode side, and perform linear sweep voltammetry analysis. Obtain the open-circuit voltage by fitting the results. Clean the apparatus used in step S2 with ultrapure water and drain the water droplets. Add 50 mL of 0.5 mmol / L SA solution to the working electrode side and 50 mL of 0.05 mmol / L SA solution to the counter electrode side. Set the linear sweep voltammetry analysis parameters as in step S1 and perform the test. After cleaning, replace the SA solutions on both sides with equal volumes and concentrations of PFBA and RN solutions, respectively, and repeat the test steps. The results are as follows... Figure 7 As shown, based on the x-intercept of the linear fitting results, the open-circuit voltages of the SA, PFBA, and RN solutions with the NF90 membrane were obtained as -40.07 mV, -47.55 mV, and -6.46 mV, respectively.

[0051] S4: Based on the results of multiple sets of linear sweep voltammetry analysis, the diffusion coefficient is calculated using the Nernst equation and the Nernst-Einstein equation. The intrinsic conductivity of the three micro-pollutant solutions obtained in step S1 is also calculated. The conductivity of the three micro-pollutant solution-membrane systems obtained in step S2 The membrane conductivity can be obtained separately. The open-circuit voltages of the three micro-pollutant solution-membrane systems obtained through step S3. The cation transfer numbers for the corresponding systems were calculated using the Nernst equation. Furthermore, the diffusion coefficients of the three micropollutants within the membrane were calculated using the Nernst-Einstein equation. The diffusion coefficients of SA, PFBA, and RN within the NF90 membrane were 6.72 × 10⁻⁶. -12 m 2 / s, 5.26×10 -12 m 2 / s and 2.94×10 -13 m 2 / s. The detailed calculation process is as follows: , , , , in, It is Faraday's constant. Let be the ideal gas constant. Absolute temperature and These represent the solution activities on the working electrode and counter electrode sides, respectively. The thickness of the active layer of the membrane (206.51 nm for NF90). The effective area of ​​the membrane (currently 2.01 cm²) 2 ), This is the charge number of the micro-pollutant (approximately 1 for SA, PFBA, and RN). Let be the concentration of micro-pollutants. The intramembrane diffusion coefficients for positively charged and negatively charged micro-pollutants are expressed as follows: and .

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for determining the diffusion coefficient within a nanofiltration membrane for charged micropollutants, characterized in that, Includes the following steps: S1: A four-electrode electrochemical system is set up in an H-type electrolytic cell. A micro-contaminant solution is added to the H-type electrolytic cell. The micro-contaminant solution is analyzed using linear sweep voltammetry to obtain first data. The first data is fitted to obtain the intrinsic conductivity data of the solution. A first micro-contaminant solution is added to the counter electrode and reference electrode side chambers of the H-type electrolytic cell, and a second micro-contaminant solution is added to the working electrode and reference electrode side chambers of the H-type electrolytic cell. The four electrodes include a working electrode, a counter electrode, and two sets of reference electrodes. The working electrode and one set of reference electrodes are installed on one side of the electrolytic chamber, and the counter electrode and the other set of reference electrodes are installed on the other side of the electrolytic chamber. The working electrode, counter electrode, and two sets of reference electrodes are used to form a four-electrode electrochemical system. The first data are the corresponding current and voltage data obtained by linear sweep voltammetry using the micro-contaminant solution. S2: Install the nanofiltration membrane in the H-shaped electrolytic cell, analyze the micro-pollutant solution and the nanofiltration membrane using linear scanning voltammetry to obtain second data, and fit the second data to obtain the system conductivity data. The nanofiltration membrane is set in the middle of the H-shaped electrolytic cell to separate two corresponding electrolytic chambers. The second data is the current data and voltage data obtained by linear scanning voltammetry of the system formed by the micro-pollutant solution and the nanofiltration membrane. S3: The micro-pollutant solution in the H-type electrolytic cell is exported and cleaned. A first micro-pollutant solution is added to one electrolytic chamber of the H-type electrolytic cell, and a second micro-pollutant solution is added to the other electrolytic chamber. Then, the first micro-pollutant solution, the nanofiltration membrane, and the second micro-pollutant solution are analyzed by linear scanning voltammetry to obtain third data. The third data is fitted to obtain open-circuit voltage data, wherein the concentration of the second micro-pollutant solution is greater than the concentration of the first micro-pollutant solution. S4: The diffusion coefficient is calculated based on the intrinsic conductivity data of the solution, the conductivity data of the system, and the open-circuit voltage data of the Nernst equation and the Nernst-Einstein equation.

2. The method for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 1, characterized in that: The linear scanning voltammetry used in steps S1-S3 is based on a four-electrode electrochemical system consisting of a working electrode, a counter electrode, and two sets of reference electrodes.

3. The method for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 2, characterized in that: The working voltage for the linear scanning voltammetry analysis in steps S1-S3 is -200 mV to 200 mV, and the scanning rate is 0.1 mV / s to 50 mV / s.

4. The method for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 1, characterized in that: The concentration ratio of the second micro-pollutant solution to the first micro-pollutant solution is 2:1 to 100:

1.

5. The method for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 1, characterized in that: In steps S1 and S2, the concentration of the micro-pollutant solution is 0.01 mmol / L to 10 mmol / L.

6. An apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micropollutants, applied to the method described in any one of claims 1-5, characterized in that: The device includes: An electrolytic cell is provided with electrolytic chambers of equal volume on both sides of the electrolytic cell. The two electrolytic chambers are connected by a central pipe. The electrolytic cell is H-shaped as a whole. The two electrolytic chambers are used to add and store micro-pollutant solutions. A nanofiltration membrane is detachably installed inside the central pipe. The nanofiltration membrane is used for solute separation and to isolate the two electrolysis chambers on both sides. The four electrodes include a working electrode, a counter electrode, and two sets of reference electrodes. The working electrode and one set of reference electrodes are installed on one side of the electrolysis chamber, and the counter electrode and the other set of reference electrodes are installed on the other side of the electrolysis chamber. The working electrode, counter electrode, and two sets of reference electrodes are used to form a four-electrode electrochemical system.

7. The apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 6, characterized in that: The working electrode and the counter electrode are both sheet-shaped platinum electrodes placed in parallel, and the ends of the working electrode and the counter electrode are arranged on the same horizontal plane.

8. The apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micro-pollutants according to claim 6, characterized in that: The electrode end of the reference electrode is an L-shaped Luggin capillary. Both sets of L-shaped Luggin capillary tubes of the reference electrodes are installed facing the middle of the pipe, and the ends of the two sets of reference electrodes are set on the same horizontal plane.

9. The apparatus for determining the diffusion coefficient within a nanofiltration membrane for charged micropollutants according to claim 7, characterized in that: The nanofiltration membrane, the sheet-like platinum electrode of the working electrode, and the sheet-like platinum electrode of the counter electrode are arranged in parallel. The area of ​​the nanofiltration membrane is smaller than the area of ​​the sheet-like platinum electrode of the working electrode, and the area of ​​the nanofiltration membrane is smaller than the area of ​​the sheet-like platinum electrode of the counter electrode.

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