Method and device for determining diffusion coefficient in charged micropollutant nanofiltration membrane

Abstract

The invention discloses a method and a device for determining a diffusion coefficient in a charged micropollutant nanofiltration membrane in the technical field of membranes. The method comprises the following steps: arranging a four-electrode electrochemical system in an H-type electrolytic tank, adding a micropollutant solution into the H-type electrolytic tank, and analyzing the micropollutant solution by adopting linear scanning voltammetry to obtain first data; according to the method, a micro-pollutant solution system, a micro-pollutant solution and nanofiltration membrane system and micro-pollutant solutions and nanofiltration membrane systems with different concentrations are tested and analyzed based on a four-electrode electrochemical system in an H-shaped electrolytic tank, and corresponding solution intrinsic conductivity data, system conductivity data and open-circuit voltage data are obtained; the method has the advantages of simple test steps, fast data acquisition, short overall test period, fast replacement and adjustment of the micropollutant solution and the nanofiltration membrane, wide application range, simple and effective linear fitting data processing process, and good repeatability.

Description

Technical Field

[0001] The invention relates to the field of membrane technology, in particular to a method and a device for measuring the diffusion coefficient of charged micro-pollutants in a nanofiltration membrane. Background Art

[0002] Organic micropollutants, which are widely present in environmental water bodies, are characterized by their wide distribution, diverse species, and high toxicity, posing a serious threat to the water safety of various organisms in nature. Among the many water treatment technologies, nanofiltration is expected to become the mainstream technology for micropollutant removal due to its advantages such as high efficiency, stability, and the lack of toxic byproducts. However, due to the complex interactions between micropollutants and membranes, existing nanofiltration treatment technologies have difficulty in effectively removing some specific micropollutants. The unclear understanding of the transmembrane transport mechanism of micropollutants limits the precise structural control and functional design of high-performance nanofiltration membrane materials for micropollutant removal, and thus restricts further improvement in the nanofiltration membrane's ability to retain micropollutants. To further understand the mass transfer mechanism of micropollutants across nanofiltration membranes, it is crucial to understand their intramembrane transport behavior. 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. The concentration-driven transmembrane diffusion experiment has a long test cycle and low sensitivity to solutes with low diffusion rates. When testing different micropollutants, the test method is complex and has poor universality. Testing based on nuclear magnetic resonance instruments is expensive and difficult to meet the testing needs of a wide variety of micropollutants, and the test results are greatly affected by the conductivity of the sample. Testing based on electrochemical impedance spectroscopy technology also has the limitation of a long test cycle and relies on the assumption of an equivalent circuit model. There may be large errors for membrane materials with complex pore structures. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and device for measuring the diffusion coefficient of charged micropollutants in nanofiltration membranes to solve the above-mentioned problems of long test cycle, complex test process, poor adaptability and large error in test results.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a method for determining the diffusion coefficient of charged micropollutants within a nanofiltration membrane, comprising the following steps:

[0007] S1: setting a four-electrode electrochemical system in an H-type electrolytic cell, adding a micropollutant solution into the H-type electrolytic cell, analyzing the micropollutant solution using linear sweep voltammetry to obtain first data, and fitting the first data to obtain solution intrinsic conductance data;

[0008] S2: installing a nanofiltration membrane in the H-type electrolytic cell, analyzing the micropollutant solution and the nanofiltration membrane using linear sweep voltammetry to obtain second data, and fitting the second data to obtain system conductance data, wherein the nanofiltration membrane is disposed in the middle of the H-type electrolytic cell to separate the cell into two corresponding electrolysis chambers;

[0009] S3: draining and cleaning the micropollutant solution in the H-type electrolytic cell, adding a first micropollutant solution to one electrolysis chamber of the H-type electrolytic cell and adding a second micropollutant solution to the other electrolysis chamber of the H-type electrolytic cell, then analyzing the first micropollutant solution, the nanofiltration membrane, and the second micropollutant solution using linear sweep voltammetry to obtain third data, and fitting the third data to obtain open circuit voltage data, wherein the concentration of the second micropollutant solution is greater than the concentration of the first micropollutant solution;

[0010] S4: Calculating the solution intrinsic conductivity data, system conductivity data, and open circuit voltage data based on the Nernst equation and the Nernst-Einstein equation to obtain a diffusion coefficient.

[0011] As a further solution of the present invention: the linear sweep voltammetry method 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 for analysis.

[0012] As a further solution of the present invention: a first micropollutant solution is added to the chambers on the counter electrode and reference electrode sides of the H-type electrolytic cell, and a second micropollutant solution is added to the chambers on the working electrode and reference electrode sides of the H-type electrolytic cell.

[0013] As a further solution of the present invention: the linear sweep voltammetry analysis in steps S1-S3 is performed at an operating voltage of -200 mV to 200 mV and a scan rate of 0.1 mV / s to 50 mV / s.

[0014] As a further solution of the present invention: the concentration ratio of the second micropollutant solution to the first micropollutant solution is 2:1 to 100:1.

[0015] As a further solution of the present invention: the concentration of the micropollutant solution in step S1 and step S2 is 0.01 mmol / L to 10 mmol / L.

[0016] In a second aspect, the present invention provides a device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane, the device comprising an electrolytic cell, a nanofiltration membrane and four electrodes, electrolysis chambers of equal volume are arranged on both sides of the electrolytic cell, the electrolysis chambers on both sides are connected by a middle pipe, the electrolytic cell as a whole is H-shaped, and the electrolysis chambers on both sides are used to add and store micropollutant solutions; the nanofiltration membrane is detachably installed in the middle pipe, the nanofiltration membrane is used to separate solutes and isolate the electrolysis chambers on both sides; the four electrodes comprise 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, the counter electrode and the other set of reference electrodes are installed on the other side of the electrolysis chamber, the working electrode, the counter electrode and the two sets of reference electrodes are used to form a four-electrode electrochemical system.

[0017] As a further solution of the present invention: the electrode end of the working electrode and the electrode end 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.

[0018] As a further solution of the present invention: the electrode end of the reference electrode is an L-shaped Luggin capillary, the L-shaped Luggin capillaries of the two sets of reference electrodes are installed toward the middle pipe, and the ends of the two sets of reference electrodes are arranged on the same horizontal plane.

[0019] As a further solution of the present invention: the nanofiltration membrane and the sheet platinum electrode of the working electrode and the sheet platinum electrode of the counter electrode are arranged in parallel, the area of the nanofiltration membrane is smaller than the area of the sheet platinum electrode of the working electrode, and the area of the nanofiltration membrane is smaller than the area of the sheet platinum electrode of the counter electrode.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. In the present invention, a micropollutant solution system, a micropollutant solution and nanofiltration membrane system, and micropollutant solutions and nanofiltration membrane systems of different concentrations are tested and analyzed based on a four-electrode electrochemical system in an H-type electrolytic cell, and the corresponding solution intrinsic conductance data, system conductance data, and open-circuit voltage data are obtained, thereby determining the intramembrane diffusion coefficient of the charged micropollutants. The test steps are simple, the data are obtained quickly, the overall test cycle is short, the micropollutant solution and nanofiltration membrane can be quickly replaced and adjusted, and the application range is wide.

[0022] 2. In the present invention, the linear fitting data processing process is simple and effective, with good repeatability. In multiple sets of linear sweep voltammetry analysis, the diffusion coefficient is calculated by the Nernst equation and the Nernst-Einstein equation, ensuring the accuracy of the diffusion coefficient corresponding to the nanofiltration membrane, and can achieve rapid and accurate determination of the diffusion coefficient within the membrane, with good use effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the method flow of the present invention;

[0024] Figure 2 Schematic diagram of the device structure of the present invention;

[0025] Figure 3 The linear voltammetric curves of the intrinsic conductivity of salicylic acid, perfluorobutyric acid and ranitidine solutions are measured in the present invention;

[0026] Figure 4 The linear voltammetric curves for measuring the conductivity of salicylic acid, perfluorobutyric acid, and ranitidine solutions and the NF270 membrane system in Example 1 of the present invention are shown;

[0027] Figure 5 The linear voltammetric curve for measuring the open circuit voltage of the salicylic acid, perfluorobutyric acid and ranitidine solution and the NF270 membrane system in Example 1 of the present invention;

[0028] Figure 6 The linear voltammetric curves for measuring the conductivity of salicylic acid, perfluorobutyric acid, and ranitidine solutions and the NF90 membrane system in Example 2 of the present invention are shown;

[0029] Figure 7 This is a linear voltammetric curve for measuring the open circuit voltage of the salicylic acid, perfluorobutyric acid and ranitidine solution and the NF90 membrane system in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] Example:

[0032] See also Figure 1 In an embodiment of the present invention, a method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane comprises the following steps:

[0033] S1: Setting a four-electrode electrochemical system in an H-type electrolytic cell, adding a micropollutant solution to the H-type electrolytic cell, analyzing the micropollutant solution using linear sweep voltammetry to obtain first data, and fitting the first data to obtain intrinsic conductivity data of the solution; wherein the first data is corresponding current data and voltage data obtained by linear sweep voltammetry for the micropollutant solution;

[0034] S2: Installing the nanofiltration membrane in an H-shaped electrolytic cell, analyzing the micropollutant solution and the nanofiltration membrane using linear sweep voltammetry to obtain second data, and fitting the second data to obtain system conductance data, wherein the nanofiltration membrane is placed in the middle of the H-shaped electrolytic cell to separate the cell into two corresponding electrolysis chambers; wherein the second data is corresponding current data and voltage data obtained by linear sweep voltammetry for the system formed by the micropollutant solution and the nanofiltration membrane;

[0035] S3: draining and cleaning the micropollutant solution in the H-type electrolytic cell, adding the first micropollutant solution to the electrolysis chamber on one side of the H-type electrolytic cell and the second micropollutant solution to the electrolysis chamber on the other side, then analyzing the first micropollutant solution, the nanofiltration membrane, and the second micropollutant solution using linear sweep voltammetry to obtain third data, fitting the third data to obtain open circuit voltage data, wherein the concentration of the second micropollutant solution is greater than the concentration of the first micropollutant solution; wherein the third data is corresponding current data and voltage data obtained by linear sweep voltammetry for a system formed by the first micropollutant solution, the second micropollutant solution, and the nanofiltration membrane;

[0036] S4: The diffusion coefficient is calculated based on the solution intrinsic conductivity data, system conductivity data and open circuit voltage data based on the Nernst equation and the Nernst-Einstein equation.

[0037] In some embodiments of the present invention, the diffusion coefficient calculation and derivation process in step S4 is as follows:

[0038] According to the definition of conductivity,

[0039]

[0040] The dielectric conductivity G is the slope of the linear fitting result of the current-voltage spectrum, and the intrinsic conductivity G of the solution obtained in step S1 is s and the solution-membrane system conductivity G obtained in step S2 t Calculate the membrane conductance G m :

[0041]

[0042] The current-voltage spectrum obtained by the linear sweep voltammetry analysis in step S3 is linearly fitted, and the obtained intercept is the open circuit voltage V rev , then the cation migration number t + It can be expressed as:

[0043]

[0044] Where F is the Faraday constant, R is the ideal gas constant, T is the absolute temperature, and a w and a rare the solution activities at the working electrode and the counter electrode, respectively. The diffusion coefficients of positively charged and negatively charged micropollutants in the membrane can be expressed as D + With D - , the calculation process is as follows:

[0045]

[0046] Where L is the thickness of the membrane active layer, A is the effective area of the membrane, z is the charge number of the micropollutant, and c is the concentration of the micropollutant.

[0047] Furthermore, the micropollutants are conventional charged micropollutants in the art, and may preferably be one or more of salicylic acid (SA), sulfamethoxazole (SMX), trimethoprim (TMP), perfluorobutyric acid (PFBA), and ranitidine (RN).

[0048] In some embodiments of the present invention, the membrane used in step S2 is soaked in ultrapure water for 24 hours to 72 hours before installing the H-type electrolytic cell.

[0049] Specifically, the present invention tests and analyzes a micropollutant solution system, a micropollutant solution and a nanofiltration membrane system, and micropollutant solutions and nanofiltration membrane systems of different concentrations based on a four-electrode electrochemical system in an H-type electrolytic cell, and obtains corresponding solution intrinsic conductivity data, system conductivity data, and open-circuit voltage data, thereby determining the intra-membrane diffusion coefficient of the charged micropollutants. The test steps are simple, the data is obtained quickly, and the overall test cycle is short. The micropollutant solution and the nanofiltration membrane can be quickly replaced and adjusted. The scope of application is wide, the linear fitting data processing process is simple and effective, and has good repeatability. In multiple sets of linear sweep voltammetry analysis, the diffusion coefficient is calculated by the Nernst equation and the Nernst-Einstein equation, ensuring the accuracy of the diffusion coefficient in the corresponding nanofiltration membrane, and can achieve rapid and accurate determination of the intra-membrane diffusion coefficient, with good use effect.

[0050] Furthermore, the nanofiltration membrane is a conventional nanofiltration membrane in this field, and can be selected from commercial nanofiltration membranes such as NF90 membrane (produced by Dow Chemical Company) and NF270 membrane (produced by Dow Chemical Company) or conventional homemade nanofiltration membranes such as graphene oxide membrane and MXene membrane.

[0051] As a further solution of the present invention: the linear sweep voltammetry method 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 for analysis.

[0052] 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 the electrode polarization effect and improve the ability to quickly and accurately determine the diffusion coefficient, especially when high resolution and low-concentration systems are required.

[0053] As a further solution of the present invention: a first micropollutant solution is added to the chambers on the counter electrode and reference electrode sides of the H-type electrolytic cell, and a second micropollutant solution is added to the chambers on the working electrode and reference electrode sides of the H-type electrolytic cell.

[0054] As a further solution of the present invention: Steps S1-S3 use linear sweep voltammetry analysis with an operating voltage of -200 mV to 200 mV and a scan rate of 0.1 mV / s to 50 mV / s.

[0055] As a further solution of the present invention: the concentration ratio of the second micropollutant solution to the first micropollutant solution is 2:1 to 100:1.

[0056] Specifically, the concentration ratio of the second micropollutant solution to the first micropollutant solution is 2:1 to 100:1, ensuring that more accurate and stable data are obtained during the electrochemical analysis process.

[0057] As a further solution of the present invention: the concentration of the micropollutant solution in step S1 and step S2 is 0.01 mmol / L to 10 mmol / L.

[0058] like Figure 2 As shown, a device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane comprises an electrolytic cell 1, a nanofiltration membrane 2 and four electrodes. Electrolysis chambers of equal volume are provided on both sides of the electrolytic cell 1, and the electrolysis chambers on both sides are connected by a central pipe. The electrolytic cell 1 is H-shaped as a whole, and the electrolysis chambers on both sides are used to add and store micropollutant solutions; the nanofiltration membrane 2 is detachably installed in the central pipe, and the nanofiltration membrane 2 is used to separate solutes and isolate the electrolysis chambers on both sides; the four electrodes comprise 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 electrolysis chamber, and the counter electrode 4 and the other set of reference electrodes 5 are installed on the other electrolysis chamber. The working electrode 3, the counter electrode 4 and the two sets of reference electrodes 5 are used to form a four-electrode electrochemical system.

[0059] Specifically, the micro-pollutant solution is stored and electrolytically analyzed in the electrolytic chambers on both sides of the overall H-shaped electrolytic cell 1. The middle pipe connects the electrolytic chambers on both sides. The middle pipe is detachably installed with a nanofiltration membrane. When the micro-pollutant solution is analyzed by linear sweep voltammetry, the nanofiltration membrane 2 is not installed in the middle pipe, so that the micro-pollutant solutions in the electrolytic chambers on both sides are connected, which is convenient for fitting to obtain the intrinsic conductivity data of the solution. In the subsequent detection and analysis process, the nanofiltration membrane 2 is installed in the middle pipe to separate the electrolytic chambers on both sides, allowing the corresponding ions to pass through the nanofiltration membrane to fit the system conductivity data and open circuit voltage data, thereby facilitating the subsequent calculation of the diffusion coefficient.

[0060] As a further solution of the present invention: the electrode end of the working electrode 3 and the electrode end of the counter electrode 4 are both sheet 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.

[0061] Specifically, the ends of the working electrode 3 and the counter electrode 4 are arranged 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.

[0062] As a further solution of the present invention: the electrode end of the reference electrode 5 is an L-shaped Luggin capillary, the L-shaped Luggin capillaries of the two sets of reference electrodes 5 are installed toward the middle pipe, and the ends of the two sets of reference electrodes 5 are arranged on the same horizontal plane.

[0063] Specifically, the L-shaped Luggin capillary design of the reference electrode 5 effectively reduces the liquid junction potential and improves the accuracy of electrochemical measurements. The L-shaped Luggin capillaries of both reference electrodes 5 are installed toward the center of the pipe, ensuring stable contact between the reference electrode and the electrolytic solution and reducing potential fluctuations caused by solution flow or bubble interference. Furthermore, the ends of the two reference electrodes 5 are positioned on the same horizontal plane, maintaining consistency in the potential within the electrolysis chambers on both sides, further improving the reliability and repeatability of electrochemical measurements.

[0064] Furthermore, the two sets of reference electrodes 5 are Ag / AgCl electrodes.

[0065] Specifically, Ag / AgCl electrodes have excellent electrochemical stability and reproducibility and are suitable for a variety of electrochemical analysis applications. In the present invention, using two sets of Ag / AgCl electrodes as reference electrodes 5 can further improve the accuracy and reliability of electrochemical measurements.

[0066] As a further solution of the present invention: the nanofiltration membrane 2 and the sheet platinum electrode of the working electrode 3 and the sheet 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 platinum electrode of the working electrode 3, and the area of the nanofiltration membrane 2 is smaller than the area of the sheet platinum electrode of the counter electrode 4

[0067] Specifically, the nanofiltration membrane 2 is positioned to effectively isolate the solutions within the electrolysis chambers on either side while allowing molecules to pass through, enabling electromigration of charged micropollutants. The platinum sheet design of the working electrode 3 and counter electrode 4 ensures a uniform electric field, facilitating stable electromigration of charged micropollutants.

[0068] Example 1:

[0069] In the first embodiment provided by the present invention, the micropollutant solution is salicylic acid, perfluorobutyric acid and ranitidine, and the nanofiltration membrane is an NF270 membrane;

[0070] See also Figure 3-Figure 5 This embodiment provides a method for determining the diffusion coefficients of salicylic acid, perfluorobutyric acid, and ranitidine in an NF270 membrane. The specific steps are as follows:

[0071] S1: Set up a four-electrode electrochemical system in an H-type electrolytic cell, perform linear sweep voltammetry analysis on the micro-pollutant solution, and obtain the intrinsic conductivity of the solution by data fitting: Figure 2 As shown, a four-electrode electrochemical system is set up in an H-type electrolytic cell, and the counter electrode is an Ag / AgCl electrode immersed in a 3M potassium chloride solution. 50mL of the prepared 0.5mmol / LSA solution is added to each side of the H-type electrolytic cell. The electrochemical workstation uses linear sweep voltammetry analysis, and the test parameters are set to a starting voltage of -200mV, an end voltage of 200mV, and a scan rate of 0.5mV / s. The SA solution is replaced with equal volumes and concentrations of PFBA and RN solutions for analysis. The analysis results are shown in Figure 2. Figure 3 As shown, according to the slopes 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.

[0072] S2: Install the membrane in an H-type electrolytic cell, perform linear sweep voltammetry analysis on the micropollutant solution-membrane system, and fit the results to obtain the system conductivity: Soak the commercial NF270 membrane in ultrapure water for 24 hours. After taking it out, place it at the connection of the H-type electrolytic cell with the active layer facing the working electrode. To prevent leakage, an O-ring is placed at the connection between the membrane and the H-type electrolytic cell. The four-electrode electrochemical system settings, linear sweep voltammetry analysis parameters and micropollutant solutions are consistent with step S1. The three micropollutant solutions and the NF270 membrane system are tested in turn. The results are as follows Figure 4 As shown, according to the slopes of the linear fitting results, the conductivities of the 0.5 mmol / L SA, PFBA and RN solutions and the NF270 membrane system were obtained to be 0.0684 mS, 0.1037 mS and 0.0034 mS, respectively.

[0073] S3: After cleaning, add a high concentration of micropollutant solution to the working electrode side and a low concentration solution to the counter electrode side, perform linear sweep voltammetry analysis, and obtain the open circuit voltage by fitting the results: Use ultrapure water to clean the device used in step S2 and drain the water droplets. Add 50mL of 0.5mmol / L SA solution to the working electrode side and 50mL of 0.05mmol / LSA 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 PFBA and RN solutions of equal volume and concentration, and repeat the test steps. The results are as follows. Figure 5As shown, according to the linear fitting results, the open circuit voltages of SA, PFBA and RN solutions and NF270 membrane systems were obtained as -42.46 mV, -45.85 mV and -20.17 mV, respectively.

[0074] S4: Based on the multiple sets of linear sweep voltammetry analysis results, the diffusion coefficients are calculated using the Nernst equation and the Nernst-Einstein equation: the intrinsic conductivities G of the three micropollutant solutions obtained in step S1. s and the three micropollutant solution-membrane system conductivity G obtained in step S2 t , the membrane conductance G can be obtained respectively m The open circuit voltages V of the three micropollutant solution-membrane systems obtained in step S3 are: rev , use the Nernst equation to calculate the cation migration number t under the corresponding system + The diffusion coefficients of the three micropollutants in the membrane were calculated using the Nernst-Einstein equation. The diffusion coefficients of SA, PFBA, and RN in the NF270 membrane were 1.38×10 -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:

[0075]

[0076] Where F is the Faraday constant, R is the ideal gas constant, T is the absolute temperature, and a w and a r are the working electrode and counter electrode solution activities, L is the thickness of the membrane active layer (17.92 nm for NF270), and A is the effective area of the membrane (2.01 cm for the current system). 2 ), z is the charge number of the micropollutant (approximately 1 for SA, PFBA and RN), and c is the concentration of the micropollutant. The diffusion coefficients of positively charged and negatively charged micropollutants in the membrane are expressed as D + With D - .

[0077] Example 2:

[0078] In the first embodiment provided by the present invention, the micropollutant solution is salicylic acid, perfluorobutyric acid and ranitidine, and the nanofiltration membrane is an NF90 membrane;

[0079] See also Figure 6-Figure 7 This embodiment provides a method for determining the diffusion coefficients of salicylic acid, perfluorobutyric acid, and ranitidine in an NF90 membrane. The specific steps are as follows:

[0080] S1: Set up a four-electrode electrochemical system in an H-type electrolytic cell, perform linear sweep voltammetry analysis on the micro-pollutant solution, and obtain the intrinsic conductivity of the solution by data fitting: Figure 2 As shown, a four-electrode electrochemical system is set up in an H-type electrolytic cell, and the counter electrode is an Ag / AgCl electrode immersed in a 3M potassium chloride solution. 50mL of the prepared 0.5mmol / LSA solution is added to each side of the H-type electrolytic cell. The electrochemical workstation uses linear sweep voltammetry analysis, and the test parameters are set to a starting voltage of -200mV, an end voltage of 200mV, and a scan rate of 0.5mV / s. The SA solution is replaced with equal volumes and concentrations of PFBA and RN solutions for analysis. The analysis results are shown in Figure 2. Figure 3 As shown, according to the slopes 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.

[0081] S2: Install the membrane in an H-type electrolytic cell, perform linear sweep voltammetry analysis on the micropollutant solution-membrane system, and fit the results to obtain the system conductivity: Soak the commercial NF90 membrane in ultrapure water for 24 hours, take it out and place it at the connection of the H-type electrolytic cell with the active layer facing the working electrode. To prevent leakage, an O-ring is placed at the connection between the membrane and the H-type electrolytic cell. The four-electrode electrochemical system settings, linear sweep voltammetry analysis parameters and micropollutant solutions are consistent with step S1, and the three micropollutant solutions and the NF90 membrane system are tested in turn. The results are as follows Figure 6 As shown, according to the slopes of the linear fitting results, the conductivities of the 0.5 mmol / L SA, PFBA and RN solutions and the NF90 membrane system were 0.0447 mS, 0.0623 mS and 0.0031 mS, respectively.

[0082] S3: After cleaning, add a high concentration of micropollutant solution to the working electrode side and a low concentration solution to the counter electrode side, perform linear sweep voltammetry analysis, and obtain the open circuit voltage by fitting the results: Use ultrapure water to clean the device used in step S2 and drain the water droplets. Add 50mL of 0.5mmol / L SA solution to the working electrode side and 50mL of 0.05mmol / LSA 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 PFBA and RN solutions of equal volume and concentration, and repeat the test steps. The results are as follows. Figure 7 As shown, according to the linear fitting results, the open circuit voltages of SA, PFBA and RN solutions and NF90 membrane systems were obtained as -40.07 mV, -47.55 mV and -6.46 mV, respectively.

[0083] S4: Based on the multiple sets of linear sweep voltammetry analysis results, the diffusion coefficients are calculated using the Nernst equation and the Nernst-Einstein equation: the intrinsic conductivities G of the three micropollutant solutions obtained in step S1. s and the three micropollutant solution-membrane system conductivity G obtained in step S2 t , the membrane conductance G can be obtained respectively m The open circuit voltages V of the three micropollutant solution-membrane systems obtained in step S3 are: rev , use the Nernst equation to calculate the cation migration number t under the corresponding system + The diffusion coefficients of the three micropollutants in the membrane were calculated using the Nernst-Einstein equation. The diffusion coefficients of SA, PFBA, and RN in the NF90 membrane were 6.72×10 -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:

[0084]

[0085]

[0086] Where F is the Faraday constant, R is the ideal gas constant, T is the absolute temperature, and a w and a r are the solution activities at the working electrode and counter electrode sides, L is the thickness of the membrane active layer (206.51 nm for NF90), and A is the effective area of the membrane (2.01 cm for the current system). 2 ), z is the charge number of the micropollutant (approximately 1 for SA, PFBA and RN), and c is the concentration of the micropollutant. The diffusion coefficients of positively charged and negatively charged micropollutants in the membrane are expressed as D + With D - .

[0087] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane, characterized in that: The following steps are involved: S1: setting a four-electrode electrochemical system in an H-type electrolytic cell, adding a micropollutant solution into the H-type electrolytic cell, analyzing the micropollutant solution using linear sweep voltammetry to obtain first data, and fitting the first data to obtain solution intrinsic conductance data; S2: installing a nanofiltration membrane in the H-type electrolytic cell, analyzing the micropollutant solution and the nanofiltration membrane using linear sweep voltammetry to obtain second data, and fitting the second data to obtain system conductance data, wherein the nanofiltration membrane is disposed in the middle of the H-type electrolytic cell to separate the cell into two corresponding electrolysis chambers; S3: draining and cleaning the micropollutant solution in the H-type electrolytic cell, adding a first micropollutant solution to one electrolysis chamber of the H-type electrolytic cell and adding a second micropollutant solution to the other electrolysis chamber of the H-type electrolytic cell, then analyzing the first micropollutant solution, the nanofiltration membrane, and the second micropollutant solution using linear sweep voltammetry to obtain third data, and fitting the third data to obtain open circuit voltage data, wherein the concentration of the second micropollutant solution is greater than the concentration of the first micropollutant solution; S4: Calculating the solution intrinsic conductivity data, system conductivity data, and open circuit voltage data based on the Nernst equation and the Nernst-Einstein equation to obtain a diffusion coefficient.

2. The method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 1, wherein: The linear sweep voltammetry method 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 for analysis.

3. The method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 2, wherein: A first micropollutant solution is added to the chambers on the counter electrode and reference electrode sides of the H-type electrolytic cell, and a second micropollutant solution is added to the chambers on the working electrode and reference electrode sides of the H-type electrolytic cell.

4. The method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 3, wherein: The linear sweep voltammetry analysis in steps S1-S3 is performed at a working voltage of -200 mV to 200 mV and a scan rate of 0.1 mV / s to 50 mV / s.

5. The method for determining the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 3, wherein: The concentration ratio of the second micro-pollutant solution to the first micro-pollutant solution is 2:1 to 100:

1.

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

7. A device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane, applied to the method according to any one of claims 1 to 6, characterized in that: The device comprises: An electrolytic cell, wherein electrolytic chambers of equal volume are provided on both sides of the electrolytic cell, and the electrolytic chambers on both sides are connected by a central pipe. The electrolytic cell is generally H-shaped, and the electrolytic chambers on both sides are used to add and store micropollutant solutions; A nanofiltration membrane, which is detachably mounted in the middle pipe and is used for solute separation and isolation of the electrolysis chambers on both sides; Four electrodes, including 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, the counter electrode and the other set of reference electrodes are installed on the other side of the electrolysis chamber, and the working electrode, counter electrode and two sets of reference electrodes are used to form a four-electrode electrochemical system.

8. The device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 7, characterized in that: The electrode end of the working electrode and the electrode end of the counter electrode are both sheet-shaped platinum electrodes and are placed in parallel. The ends of the working electrode and the counter electrode are arranged on the same horizontal plane.

9. The device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 7, characterized in that: The electrode end of the reference electrode is an L-shaped Luggin capillary. The L-shaped Luggin capillaries of the two sets of reference electrodes are installed toward the middle pipe, and the ends of the two sets of reference electrodes are arranged on the same horizontal plane.

10. The device for measuring the diffusion coefficient of charged micropollutants in a nanofiltration membrane according to claim 8, characterized in that: The nanofiltration membrane and the sheet platinum electrode of the working electrode and the sheet platinum electrode of the counter electrode are arranged in parallel. The area of the nanofiltration membrane is smaller than the area of the sheet platinum electrode of the working electrode, and the area of the nanofiltration membrane is smaller than the area of the sheet platinum electrode of the counter electrode.

Images