Method for detecting sodium ions in ion exchange membranes and applications

Abstract

This invention belongs to the field of nuclear magnetic resonance (NMR) detection technology, specifically relating to a method and application for detecting sodium ions in an ion exchange membrane. The detection method includes: (1) soaking the ion exchange membrane to prepare a polygonal sample with a symmetrical structure and at least 4 sides; winding the sample around a uniform rod; inserting the sample into the bottom of the NMR tube using a screw-in method; removing the rod or leaving it in the NMR tube; (2) placing the NMR tube obtained in step (1) into an NMR spectrometer; tuning and homogenizing the field; adjusting the NMR test parameters; and acquiring the signal. The NMR test parameters include: a 90° pulse width of 10-14 μs; and a power of 60-110 W. The NMR sample prepared by this invention has advantages such as good homogenization, high detection sensitivity, and high spectral resolution during detection, enabling the detection of sodium ions inside the ion exchange membrane bulk phase. 23 Na.

Description

Technical Field

[0001] This invention belongs to the field of nuclear magnetic resonance (NMR) detection technology, specifically relating to a method and application for detecting sodium ions in an ion exchange membrane. Background Technology

[0002] Liquid-state nuclear magnetic resonance (Liquid-State NMR) technology has wide applications in chemistry, materials science, and biomedicine due to its high resolution, ease of operation, and rich information acquisition capabilities. However, ion exchange membranes, as functional materials with unique microphase separation structures, have performance highly dependent on the distribution of ion transport channel networks and hydrophilic and hydrophobic water zones in the solid state. Using traditional dissolved liquid NMR detection methods would disrupt their intrinsic structure, leading to the loss of crucial microstructural information (such as ion cluster size, connectivity, and dynamic behavior). Therefore, how to efficiently characterize the microenvironment and ion transport mechanisms of ion exchange membranes using liquid NMR while maintaining the structural integrity of the membrane material remains a challenge in the current technological field.

[0003] Sodium ions (Na) + Sodium nuclei play a crucial role in life sciences, energy storage (such as sodium-ion batteries), environmental monitoring, and food safety. Accurate detection of their dynamic distribution and coordination state is essential for optimizing material performance. However, sodium nuclei (… 23 Na has a low gyromagnetic ratio (γ) (approximately 1 H (26.5%), and natural abundance (100%) 23 Sodium nuclei exhibit a significant quadrupole moment effect (I=3 / 2), resulting in low NMR signal sensitivity and severe peak broadening. Conventional detection requires high-field instruments (≥500MHz) or signal enhancement techniques such as dynamic nuclear polarization (DNP), greatly limiting its practical applications. Therefore, the detection of sodium ions in ion exchange membranes is of great significance. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is how to detect the NMR signal of sodium ions in an ion exchange membrane, thereby providing a method and application for detecting sodium ions in an ion exchange membrane.

[0005] To address the aforementioned problems, this invention proposes an innovative method based on liquid nuclear magnetic resonance (NMR) technology, enabling efficient detection of sodium ion NMR signals within ion-exchange membranes under non-destructive conditions. By optimizing sample preparation strategies, pulse parameters, and sampling parameters, the method achieves efficient detection of sodium ion NMR signals within ion-exchange membranes. + This method enables precise analysis of the local environment and dynamic behavior of ion exchange membranes. It not only provides a new tool for studying the structure-performance relationship of ion exchange membranes, but also has significant application value in fields such as energy storage and separation membrane development.

[0006] To this end, the present invention provides the following technical solution.

[0007] This invention provides a method for detecting sodium ions in an ion exchange membrane, comprising the following steps:

[0008] (1) After soaking, the ion exchange membrane is made into a polygonal sample with a symmetrical structure and a number of sides not less than 4. The sample is wound around a uniform rod and inserted into the bottom of the NMR tube by screwing. The rod is then removed or left in the NMR tube. It should be explained that: soaking here refers to immersing the ion exchange membrane in a solution; or, for ion exchange membranes used in a liquid environment, this process also belongs to soaking; for example, polygons include quadrilaterals, pentagons, hexagons, etc.; further, polygons also include chamfers and / or rounded corners, etc. The NMR sample prepared by this invention has advantages such as good shimming effect, high detection sensitivity and spectral resolution during detection, and the NMR sample preparation process is simple. When detecting sodium ions in ion exchange membranes, this invention is applicable to ion exchange membranes that will not bend or break when the glass rod is wound. The ion exchange membrane is placed in a regular and orderly manner inside the NMR tube.

[0009] (2) Place the nuclear magnetic tube obtained in step (1) into the nuclear magnetic resonance spectrometer, tune and homogenize it, adjust the nuclear magnetic resonance test parameters, and collect the signal; the nuclear magnetic resonance test parameters include: 90° pulse width of 10~14μs; power of 60~110W.

[0010] The principle of this invention for collecting sodium ion signals in ion exchange membranes using liquid NMR is as follows: after being soaked in a solution, the ion exchange membrane swells. The ion exchange membrane has the characteristic of selectively permeating ions, so that ions and water molecules coexist inside the bulk phase of the ion exchange membrane, forming countless microscopic liquid environments. Therefore, the NMR signal of sodium ions can be detected using liquid NMR.

[0011] Cation exchange membranes possess cation-selective transport properties, allowing Na+ to be transported during the immersion process. + Sodium ions remain inside the membrane phase. In ion exchange membranes, the sodium ion concentration is low, and current technologies typically employ solid-state detection, with liquid detection being rare, making it impossible to detect sodium ions inside the membrane phase. +Accurate analysis is achieved. This invention uses a specially designed sample preparation method to obtain NMR detection samples, and conducts tests under specific NMR test parameters such as a 90° pulse width of 10~14μs and a power of 60~110W. Without damaging the ion exchange membrane structure, it can acquire the NMR signal of sodium ions inside the ion exchange membrane phase, providing strong support for the detection and analysis of the structural information within the ion exchange membrane phase. Conventional liquid NMR sample preparation methods mainly acquire signals from free-state atoms, i.e., sodium ions in the NMR tube solution (located outside the membrane), and cannot detect sodium ion signals on the ion exchange membrane. This invention fabricates the ion exchange membrane into a polygonal sample with a symmetrical structure and at least 4 sides, and sets the NMR test parameters to a 90° pulse width of 10~14μs and a power of 60~110W, which allows for the detection of the NMR signal of sodium ions within the ion exchange membrane phase.

[0012] As an optional implementation, the nuclear magnetic resonance test parameters also include: pulse sequence of zg; relaxation time: 1~5s; number of sampling points: 16k~32k, k is 1024; sampling time: 1~5s; spectral width: 60~120ppm; spectral range: -60ppm~+60ppm; number of accumulations: 8~256.

[0013] Preferably, the spectral width is 60 ppm and the spectral range is -30 ppm to +30 ppm.

[0014] As an optional implementation, the 90° pulse width is 12μs; the power is 77W.

[0015] For example, the 90° pulse width is 10μs, 11μs, 12μs, 13μs or 14μs; the power is 60W, 70W, 80W, 90W or 100W, etc.

[0016] As an optional implementation, the sodium is 23 Na; and / or,

[0017] The ion exchange membrane is a cation exchange membrane; preferably, the ion exchange membrane is derived from a battery.

[0018] After selecting the pulse sequence, select... 23 The Na tuning channel has different resonance frequencies for different nuclides, therefore requiring independent tuning and matching. 23 The tuning channel for Na is on the X channel. This invention detects... 23 For Na, taking a 600MHz resonance spectrometer as an example, the resonance frequency is 158.7MHz. The field strength of the detector and the type of nuclide being measured determine the resonance frequency of the nuclide in the detector. In this field, the resonance frequency can be determined based on the specific type of nuclide and the field strength of the detector.

[0019] Ion exchange membranes can be derived from commercially available ion exchange membranes, such as Fumasep FKS-30, ASTOM NeoseptaCXP-S, Fumasep-E-620(K), Fumasep F-10120-PK, and Fumasep FS-990-PK. Ion exchange membranes can also originate from devices in which ion exchange membranes are installed, such as diaphragms in fuel cells, electrodialysis units, or electrolysis units.

[0020] As an optional implementation, step (2) further includes adding 5~20μL of soaking solution before placing the NMR tube into the NMR spectrometer, wherein the concentration of the soaking solution is 0.2~2.0mol / L;

[0021] Preferably, the soaking solution is a solution containing sodium ions;

[0022] Preferably, the soaking solution has a concentration of 0.2~1.0 mol / L.

[0023] The method of this invention can also simultaneously detect the NMR signals of sodium ions inside the ion exchange membrane phase and sodium ions outside the membrane (in a free state). By measuring the difference in chemical shift of the NMR signals inside and outside the membrane phase, the transport performance of the cation exchange membrane for sodium ions can be determined, which facilitates the analysis of the structural performance of the cation exchange membrane and its application in different fields.

[0024] As an optional implementation, the solvent in the soaking solution includes a deuterated solvent or a non-deuterated solvent;

[0025] Preferably, the solvent includes at least one selected from water, chloroform (CHCl3), dimethyl sulfoxide (DMSO), dichloromethane (CH2Cl2), methanol, and ethanol;

[0026] Preferably, when the solvent in the soaking solution includes a deuterated solvent, a field locking process is also included before shimming.

[0027] As an optional implementation, in step (1), the soaking solution contains sodium ions. It should also be noted that during sample preparation, the soaking solution of the ion exchange membrane includes components capable of dissociating sodium ions. + The compounds. The soaking solutions in steps (1) and (2) may be the same or different, preferably the same. The present invention does not require a soaking time in step (1), which allows the ion exchange membrane to swell and contain ions and water molecules inside, for example, 2h, 5h, 10h, 15h, 20h, 25h, 30h, etc.

[0028] As an optional implementation, in step (1), the sample is square in shape; and / or,

[0029] The diameter of the rod is 2-3 mm; and / or,

[0030] The rod material includes a rubber rod, a glass rod, or a metal rod; and / or,

[0031] The rod is a hollow cylinder. The rod being a hollow cylinder means it can be a liner tube with a hollow interior to accommodate liquid. In this case, a deuterated reagent, such as deuterated water, deuterated DMSO, or deuterated chloroform, can be added into the hollow rod. This allows for precise field locking to pinpoint the chemical shift of the analyte nucleus while avoiding the influence of the deuterated reagent on the ion exchange membrane structure. Furthermore, since deuterated reagents are expensive, using a liner tube to achieve field locking also reduces the amount of deuterated reagent used.

[0032] When the sample is square, its length is 4-5 cm. It should be noted that the sample size can be selected based on the size of the rod, as long as it can be wound around the rod. Square includes rectangular, rectangular, etc.

[0033] This invention provides the application of the above-described detection method in the detection of membranes in fuel cells, electrodialysis devices, or electrolysis devices. This application can detect sodium ion signals in used ion exchange membranes, providing strong support for the structural performance analysis of ion exchange membranes.

[0034] The technical solution of this invention has the following advantages:

[0035] 1. The method for detecting sodium ions in an ion exchange membrane provided by the present invention includes (1) soaking the ion exchange membrane to prepare a polygonal sample with a symmetrical structure and a number of sides not less than 4, winding the sample around a uniform rod, inserting the sample into the bottom of a nuclear magnetic resonance (NMR) tube by screwing, and removing the rod or leaving it in the NMR tube; (2) placing the NMR tube obtained in step (1) into a nuclear magnetic resonance spectrometer, tuning and shimming, adjusting the NMR test parameters, and acquiring the signal; the NMR test parameters include: a 90° pulse width of 10~14μs; and a power of 60~110W. The NMR sample prepared by the present invention has advantages such as good shimming effect, high detection sensitivity and spectral resolution during detection, and the NMR sample preparation process is simple. When tested with NMR test parameters of 90° pulse width of 10~14μs and power of 60~110W, it can detect the sodium ions inside the bulk phase of the ion exchange membrane. 23 Na provides strong support for detecting and analyzing the internal structural information of ion exchange membranes.

[0036] Furthermore, the method of this invention can simultaneously detect the NMR signals of sodium ions inside the ion exchange membrane phase and sodium ions outside the membrane (in a free state). By analyzing the difference in chemical shifts of the NMR signals inside and outside the membrane phase, the transport performance of the cation exchange membrane for sodium ions can be determined, which facilitates the analysis of the structural performance of the cation exchange membrane and its application in different fields. Attached Figure Description

[0037] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is the NMR spectrum obtained from Example 1 of the present invention;

[0039] Figure 2 This is the NMR spectrum obtained from the test in Example 2 of this invention;

[0040] Figure 3 This is the NMR spectrum obtained from Comparative Example 1 of this invention;

[0041] Figure 4 This is a schematic diagram of the ion exchange membrane in the NMR tube of Embodiment 1 of the present invention, referred to as the sample diagram. Detailed Implementation

[0042] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0043] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0044] Example 1

[0045] This embodiment provides a method for detecting sodium ions in an ion exchange membrane, comprising the following steps:

[0046] (1) Immerse the ion exchange membrane (Fumasep FKS-30) in 0.2 mol / L NaCl aqueous solution (non-deuterated reagent) for 24 h, remove and dry it, cut the ion exchange membrane into regular square samples with a length of 4 cm, and then wrap them around a glass rod with a diameter of 3 mm. Use a screw-in method to evenly wrap the sample around the bottom of the NMR tube, remove the glass rod, and the state of the ion exchange membrane in the NMR tube is shown in the figure. Figure 4 .

[0047] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The instrument is a 600MHz liquid NMR spectrometer, the tuned resonance frequency is 158.7MHz, and the NMR test parameters include: 90° pulse width is 12μs; power is 77W; pulse sequence is zg; relaxation time is 1s; number of sampling points is 32k, k is 1024; sampling time is 1.7s; spectral width is 60ppm; spectrum range is -30ppm to +30ppm; number of accumulations is 16.

[0048] The NMR spectrum obtained in this embodiment is shown below. Figure 1 ,from Figure 1 As can be seen from this, the present invention is able to measure the contents of the ion exchange membrane. 23 The NMR signal of Na has a strong NMR signal at -1.15 ppm, with high spectral resolution and signal intensity.

[0049] Example 2

[0050] This embodiment provides a method for detecting sodium ions in an ion exchange membrane, comprising the following steps:

[0051] (1) Immerse the ion exchange membrane (same as in Example 1) in a 0.2 mol / L NaCl aqueous solution (the solvent is a non-deuterated reagent), take it out and wipe it dry. Cut the ion exchange membrane into a regular square sample with a length of 4 cm, and then wrap it around a glass rod with a diameter of 3 mm. Use a screw-in method to evenly wrap the sample around the bottom of the NMR tube and pull out the glass rod. Add 5 μL of 0.2 mol / L NaCl solution to the NMR tube.

[0052] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The instrument is a 600MHz liquid NMR spectrometer with a tuned resonance frequency of 158.7MHz. The NMR test parameters include: 90° pulse width of 12μs; power of 77W; pulse sequence of zg; relaxation time of 1s; number of sampling points of 32k, k of 1024; sampling time of 1.7s; spectral width of 60ppm; spectrum range of -30ppm to +30ppm; number of accumulations of 128.

[0053] The NMR spectrum obtained in this embodiment is shown below. Figure 2 ,from Figure 2 It can be seen that the sample preparation method of the present invention can not only measure the membrane interior... 23 The NMR signal of Na (chemical shift of -1.15 ppm) can be detected simultaneously with that of sodium ions outside the membrane (inside the NMR tube). 23 The NMR signal of Na (chemical shift of 0.3 ppm). Additionally, due to the internal phase of the ion exchange membrane... 23 The movement of Na atoms is restricted, thus 23 The transverse relaxation time (T2) of Na decreases, resulting in a broadening of the spectral peak relative to the outside of the membrane. The detection method provided by this invention offers a novel analytical testing approach for studying the microstructure performance of ion exchange membranes in various applications. Compared to the spectrum measured after the membrane was rolled and compacted in Comparative Example 1, this method exhibits higher spectral resolution and signal-to-noise ratio.

[0054] Comparative Example 1

[0055] This comparative example provides a method for detecting sodium ions in an ion exchange membrane, comprising the following steps:

[0056] (1) Immerse the ion exchange membrane in a 0.2 mol / L NaCl aqueous solution (the solvent is a non-deuterated reagent), take it out and wipe it dry. Roll up and compact the membrane and insert it directly into the NMR tube. Add 5 μL of 0.2 mol / L NaCl aqueous solution (the solvent is a non-deuterated reagent) into the NMR tube. The ion exchange membrane forms an irregular clump in the NMR tube.

[0057] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The instrument used is a 600MHz liquid NMR spectrometer, tuned to a resonance frequency of 158.7MHz. The NMR test parameters include: 90° pulse width of 12μs; power of 77W; pulse sequence of zg; relaxation time of 1s; number of sampling points of 32k, where k is 1024; sampling time of 1.7s; spectral width of 60ppm; spectral range of -30ppm to +30ppm; and 128 accumulations. See the NMR spectrum. Figure 3 ,from Figure 3 It can be seen that this comparative example cannot distinguish between the interior and exterior of the membrane phase. 23 The presence of Na signal, along with broadened spectral peaks and low resolution, indicates that the sample preparation method of this invention is helpful for Na signal detection.

[0058] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for detecting sodium ions in an ion exchange membrane, characterized by, Includes the following steps: (1) After soaking, the ion exchange membrane is made into a polygonal sample with a symmetrical structure and a number of sides of not less than 4. The sample is wound on a uniform rod and inserted into the bottom of the NMR tube by a screwing method. (2) Place the nuclear magnetic tube obtained in step (1) into the nuclear magnetic resonance spectrometer, tune and homogenize it, adjust the nuclear magnetic resonance test parameters, and collect the signal; the nuclear magnetic resonance test parameters include: 90° pulse width of 10~14μs; power of 60~110W.

2. The detection method according to claim 1, characterized in that, The nuclear magnetic resonance test parameters also include: pulse sequence of zg; relaxation time: 1~5s; number of sampling points: 16k~32k, k is 1024; sampling time: 1~5s; spectral width: 60~120ppm; spectrum range: -60ppm~+60ppm; number of accumulations: 8~256.

3. The detection method according to claim 2, characterized in that, The spectral width is 60 ppm, and the spectral range is -30 ppm to +30 ppm.

4. The detection method according to claim 1, characterized in that, The 90° pulse width is 12μs; the power is 77W.

5. The assay of any one of claims 1 to 4, wherein, The sodium is 23 Na; and / or, The ion exchange membrane is a cation exchange membrane.

6. The detection method according to claim 5, characterized in that, The ion exchange membrane is derived from a battery.

7. The method of claim 1, wherein Step (2) further includes adding 5~20μL of soaking solution before placing the NMR tube into the NMR spectrometer. The concentration of the soaking solution is 0.2~2.0mol / L.

8. The detection method according to claim 7, characterized in that, The soaking solution is a solution containing sodium ions; And / or, the concentration of the soaking solution is 0.2~1.0 mol / L.

9. The detection method according to claim 7, characterized in that, The soaking solution includes soluble sodium salts.

10. The detection method according to claim 9, characterized in that, The soluble sodium salt includes at least one of NaCl, Na2SO4, Na2CO3, NaHCO3, CH3COONa, NaOH, and NaNO3.

11. The detection method according to claim 7, characterized in that, The solvent in the soaking solution includes deuterated solvents or non-deuterated solvents.

12. The detection method of claim 11, wherein, The solvent includes at least one of water, chloroform, dimethyl sulfoxide, dichloromethane, methanol, and ethanol.

13. The method of claim 11, wherein, When the solvent in the immersion solution includes a deuterated solvent, a field locking process is also included before shimming.

14. The method of claim 1, wherein, In step (1), the soaking solution contains sodium ions.

15. The method of claim 1, wherein, In step (1), the sample is square in shape; and / or, The diameter of the rod is 2-3 mm; and / or, The rod material includes a rubber rod, a glass rod, or a metal rod; and / or, The rod is a hollow cylinder.

16. The application of the detection method according to any one of claims 1 to 15 in detecting the membrane in a fuel cell, an electrodialysis device, or an electrolysis device.

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