A method for testing the hydration number of ions across membranes based on non-equilibrium thermodynamics

Abstract

The present invention provides a method for testing the hydration number of ions across membranes based on non-equilibrium thermodynamics. The testing method of the present invention: A membrane is clamped in an H-type electrolytic cell, and different solutions are filled on both sides of the membrane respectively to measure the potential difference across the membrane. Specifically, one side of the electrolytic cell is filled with a mixed solution containing salt and neutral molecules that do not cross the membrane, and the other side of the electrolytic cell is filled only with a salt solution, and the salt concentrations on both sides are the same. An electrochemical workstation is used to test the potential difference across the membrane, and mathematical fitting is performed according to the change of the potential difference with time, so as to obtain the relationship between the potential difference and the hydration number of ions across the membrane, and finally the determination of the hydration number of ions across the membrane is realized. This method can quantify the transmembrane hydration state of ions and is of great significance for studying ion mass transfer mechanisms, selective separation of ions, physicochemical properties of membranes, etc.

Description

Technical Field

[0001] The present invention relates to the technical field of testing methods for ion transmembrane phenomena, and in particular to a method for testing the hydration number of ions across membranes based on non-equilibrium thermodynamics. Background Art

[0002] The hydration number of an ion (i.e., the number of water molecules around the ion) is of great significance for understanding the ion transmembrane process, the selectivity of the membrane, and the behavior of ions in solution. In many applications, such as membrane filtration, electrochemical desalination, selective recovery of high-value metal ions, and other advanced wastewater treatment and resource recovery processes, the interaction between ions and water molecules has an important impact on the performance of the system. To better understand these phenomena, it is crucial to accurately determine the hydration of ions.

[0003] Traditional methods for testing the hydration number of ions mainly rely on femtosecond / mass spectrometry analysis and molecular simulation calculations, but these methods are complex and time-consuming to operate, and require relatively special experimental devices and environments. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for testing the hydration number of ions across membranes based on non-equilibrium thermodynamics. The present invention provides a method that combines non-equilibrium thermodynamics theory with electrochemical signal measurement technology. It can calculate the hydration number of ions across membranes through the change in the potential difference across the membrane under relatively simple experimental conditions, with high accuracy and practicality. This method is mainly applied to fields such as membrane separation technology, electrochemical analysis, and ion hydration research, providing an important theoretical basis for understanding ion behavior during the ion transmembrane process.

[0005] The object of the present invention is to provide a method for testing the hydration number of ions across membranes based on non-equilibrium thermodynamics, comprising the following steps:

[0006] Place the membrane between the first electrolytic cell and the second electrolytic cell of an H-type electrolytic cell equipped with a membrane clip;

[0007] Inject a mixed solution containing salt and neutral molecules that do not pass through the membrane into the first electrolytic cell;

[0008] Inject a salt solution with the same concentration as that in the first electrolytic cell into the second electrolytic cell;

[0009] Set two reference electrodes, place them respectively in Luggin capillaries containing saturated potassium chloride solution, and place them respectively in the first electrolytic cell and the second electrolytic cell;

[0010] Connect an electrochemical workstation to measure the potential difference across the membrane and record the change of the potential difference over time ; The potential difference Perform a linear fit with to obtain the relationship between the ion transmembrane potential difference and time, and calculate the ion transmembrane hydration number according to the following formula:

[0011] ,

[0012] where is the ion transmembrane potential difference, n is the ion transmembrane hydration number, F is the Faraday constant, is the molar volume of water molecules, R is the gas constant, T is the thermodynamic temperature, c i is the concentration of non-membrane-passing neutral molecules in the mixed solution, and S(c 0 ) is the fitting coefficient, and t is the test time.

[0013] In some embodiments of the present invention, the membrane is a cation exchange membrane, an anion exchange membrane, a reverse osmosis membrane, a nanofiltration membrane, a microfiltration membrane or an ultrafiltration membrane.

[0014] In some embodiments of the present invention, the salt solution is one of LiCl, NaCl, KCl, KBr, KI, Na 2 SO 4 , MgCl 2 , CaCl 2 solutions.

[0015] In some embodiments of the present invention, the concentration of the salt solution is 0.01 - 1.00 mol / L.

[0016] In some embodiments of the present invention, the concentration of the salt solution is 0.01 - 0.1 mol / L. Exemplarily, it can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1 mol / L, etc., or any value within any interval between any two values.

[0017] In some embodiments of the present invention, the non-membrane-passing neutral molecules are selected from one or more of glucose, sucrose and urea.

[0018] In some embodiments of the present invention, the concentration of non-membrane-passing neutral molecules in the mixed solution is 0.1 - 2.00 mol / L.

[0019] In some embodiments of the present invention, the concentration of non-membrane-passing neutral molecules in the mixed solution is 0.1 - 1.00 mol / L. Exemplarily, it can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.00 mol / L, etc.

[0020] In some embodiments of the present invention, the reference electrode is an Ag / AgCl electrode or a calomel electrode.

[0021] The device of the H-type electrolytic cell used in the present invention includes: an electrochemical workstation, a first electrolytic cell and a second electrolytic cell connected to the electrochemical workstation. The first electrolytic cell and the second electrolytic cell are arranged opposite to each other. The electrolytic cell device further includes a membrane clip connecting the first electrolytic cell and the second electrolytic cell. The membrane clip is used to fixedly hold the membrane. A first Luggin capillary is arranged in the first electrolytic cell. The tip of the first Luggin capillary extends out of the first electrolytic cell and extends to the first side of the membrane clip. A second Luggin capillary is arranged in the second electrolytic cell. The tip of the second Luggin capillary extends out of the second electrolytic cell and extends to the second side of the membrane clip. A working electrode and a working sensing electrode extend into the first Luggin capillary. The first electrolytic cell is connected to the electrochemical workstation through the working electrode and the working sensing electrode. A reference electrode and a counter electrode extend into the second Luggin capillary. The second electrolytic cell is connected to the electrochemical workstation through the reference electrode and the counter electrode. The first electrolytic cell is filled with a mixed solution of salt and neutral molecules that do not pass through the membrane. The second electrolytic cell is filled with a salt solution having the same concentration as that in the first electrolytic cell.

[0022] The above technical solution of the present invention has the following advantages compared with the prior art:

[0023] This method can monitor the change of the potential difference on both sides of the membrane in real time through the electrochemical workstation, simplifies the experimental process, saves time and cost, and avoids the complex experimental conditions required by the traditional method. The present invention does not require complex pretreatment of the sample, directly obtains data through electrochemical measurement, is easy to operate, has strong applicability, has a wide application prospect, and can be applied to fields such as membrane separation, electrochemical desalination, and water treatment to help optimize membrane materials, improve battery performance, and water treatment efficiency, etc. Description of the Drawings

[0024] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in combination with the drawings, wherein,

[0025] Figure 1 is a schematic diagram of the device for testing the transmembrane potential difference of ions in the present invention.

[0026] Figure 2 is a fitting relationship diagram of the transmembrane potential difference of ions and time in the present invention.

[0027] Figure 3 is Li in Examples 1 to 3 of the present invention + , Na + , K + Test results of transmembrane hydration numbers across different membranes. Detailed Description of the Invention

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the exemplified embodiments are not intended to limit the present invention.

[0029] Example 1:

[0030] This example provides a method for measuring the hydration number of ions across a membrane based on non-equilibrium thermodynamics. The specific steps are as follows:

[0031] (1) A commercialized ASTOM CMX cation exchange membrane is clamped between two electrolytic cells of an H-type electrolytic cell with a single-sided electrolytic cell volume of 50 mL (a conventional H-type electrolytic cell in the art) to form a first electrolytic cell and a second electrolytic cell;

[0032] (2) A mixed solution of 0.1 mol / L LiCl solution and 1 mol / L glucose is added to the first electrolytic cell; 0.1 mol / L LiCl solution is added to the second electrolytic cell;

[0033] (3) Two Ag / AgCl electrodes are placed in Luggin capillaries containing saturated potassium chloride solution and placed on both sides of the membrane respectively;

[0034] (4) The working electrode clamp and the working sensing electrode clamp of the electrochemical workstation are connected to the Ag / AgCl electrode of the first electrolytic cell, and the counter electrode clamp and the reference electrode clamp are connected to the Ag / AgCl electrode of the second electrolytic cell (as Figure 1 shown), measure the potential difference across the membrane, and record the change of this potential difference with time;

[0035] (5) Through mathematical fitting, obtain the relationship between the ion transmembrane potential difference and time , and calculate the hydration number of the ions across the membrane according to the intercept of this relationship.

[0036] The schematic diagram of the device for testing the ion transmembrane potential difference in Example 1 is as Figure 1 shown, and the hydration number of Li + obtained in step (5) is approximately 6.01, and the result is as Figure 3 shown.

[0037] Example 2:

[0038] This example provides a method for measuring the hydration number of ions across a membrane based on non-equilibrium thermodynamics. The specific steps are as follows:

[0039] (1) A commercialized Fumatech FKS-PET-75 cation exchange membrane is clamped between two electrolytic cells of an H-type electrolytic cell with a single-sided electrolytic cell volume of 50 mL to form a first electrolytic cell and a second electrolytic cell;

[0040] (2) Add a mixed solution of 0.1 mol / L NaCl solution and 1 mol / L glucose to the first electrolytic cell; add 0.1 mol / L NaCl solution to the second electrolytic cell;

[0041] (3) Place two Ag / AgCl electrodes in Luggin capillaries containing saturated potassium chloride solution and place them on both sides of the membrane respectively;

[0042] (4) Connect the working electrode clamp and the working sensing electrode clamp of the electrochemical workstation to the Ag / AgCl electrode of the first electrolytic cell, and connect the counter electrode clamp and the reference electrode clamp to the Ag / AgCl electrode of the second electrolytic cell (as Figure 1 shown), measure the potential difference across the membrane, and record the change of this potential difference with time;

[0043] (5) Through mathematical fitting, obtain the relationship between the ion transmembrane potential difference and time , and calculate the ion transmembrane hydration number according to the intercept of this relationship.

[0044] The schematic diagram of the device for testing the ion transmembrane potential difference in Example 1 is as Figure 1 shown. The hydration number of Na + obtained in step (5) is approximately 4.86, and the results are as Figure 3 shown.

[0045] Example 3:

[0046] This example provides a method for determining the ion transmembrane hydration number based on non-equilibrium thermodynamics, and the specific steps are as follows:

[0047] (1) Sandwich a commercial Nafion 211 cation exchange membrane between two electrolytic cells of an H-type electrolytic cell with a unilateral electrolytic cell volume of 50 mL to form a first electrolytic cell and a second electrolytic cell;

[0048] (2) Add a mixed solution of 0.1 mol / L KCl solution and 1 mol / L glucose to the first electrolytic cell; add 0.1 mol / L KCl solution to the second electrolytic cell;

[0049] (3) Place two Ag / AgCl electrodes in Luggin capillaries containing saturated potassium chloride solution and place them on both sides of the membrane respectively;

[0050] (4) Connect the working electrode and the working sensing electrode of the electrochemical workstation to the Ag / AgCl electrode of the first electrolytic cell, connect the counter electrode and the reference electrode to the Ag / AgCl electrode of the second electrolytic cell, measure the potential difference across the membrane, and record the change of this potential difference with time;

[0051] (5) Through mathematical fitting, the relationship between the transmembrane potential difference of ions and time is obtained. According to the intercept of the relational expression, the transmembrane hydration number of the ions is calculated.

[0052] The schematic diagram of the device for testing the transmembrane potential difference of ions in Example 1 is as Figure 1 shown. The K + hydration number is approximately 3.92, and the result is as Figure 3 shown.

[0053] Obviously, the above examples are only for illustration and are not limitations on the implementation. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementations here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics, characterized in that: The following steps are involved: The membrane is placed between a first electrolytic cell and a second electrolytic cell of an H-type electrolytic cell provided with a membrane clamp; injecting a mixed solution containing salt and neutral molecules that do not cross the membrane into the first electrolytic cell; injecting a salt solution having the same concentration as that in the first electrolytic cell into the second electrolytic cell; Two reference electrodes are provided and placed in Luggin capillaries containing saturated potassium chloride solution, respectively, and are placed in the first electrolytic cell and the second electrolytic cell, respectively; Connect to an electrochemical workstation to measure the potential difference across the membrane , and record the potential difference Changes over time ; The potential difference and Linear fitting was performed to obtain the relationship between the ion transmembrane potential difference and time, and the ion transmembrane hydration number was calculated according to the following formula: ， in, is the ion potential difference across the membrane, n is the ion transmembrane hydration number, F is Faraday's constant, is the molar volume of a water molecule, R is the gas constant, T is the thermodynamic temperature, c i is the concentration of membrane-penetrating neutral molecules in the mixed solution, S(c0) is the fitting coefficient, t is the test time; the salt solution is one of LiCl, NaCl, KCl, KBr, KI, Na2SO4, MgCl2, and CaCl2 solutions.

2. A method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 1, characterized in that: The membrane is a cation exchange membrane, an anion exchange membrane, a reverse osmosis membrane, a nanofiltration membrane, a microfiltration membrane, and an ultrafiltration membrane.

3. The method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 1, characterized in that: The concentration of the salt solution is 0.01-1.00 mol / L.

4. The method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 3, characterized in that: The concentration of the salt solution is 0.01-0.1 mol / L.

5. The method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 1, characterized in that: The neutral molecules that do not pass through the membrane are selected from one or more of glucose, sucrose and urea.

6. The method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 1, characterized in that: The concentration of membrane-independent neutral molecules in the mixed solution is 0.1~2.00 mol / L.

7. A method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 6, characterized in that: The concentration of membrane-independent neutral molecules in the mixed solution is 0.1~1.00 mol / L.

8. The method for testing the ion transmembrane hydration number based on non-equilibrium thermodynamics according to claim 1, characterized in that: The reference electrode is a Ag / AgCl electrode or a calomel electrode.

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