Method for detecting sodium ions in ion exchange membrane and application

Abstract

The invention belongs to the field of nuclear magnetic resonance technology detection, and particularly relates to a detection method for sodium ions in an ion exchange membrane and application. The detection method comprises the following steps: (1) soaking an ion exchange membrane to prepare a polygonal sample with a symmetrical structure and no less than 4 edges, winding the sample on a uniform bar, loading the sample into the bottom of a nuclear magnetic tube by adopting a screw-in manner, and drawing out the bar or retaining the bar in the nuclear magnetic tube; (2) putting the nuclear magnetic tube prepared in the step (1) into a nuclear magnetic resonance spectrometer, tuning, shimming, adjusting nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters comprise that the 90-degree pulse width is 10-14 [mu] s; and the power is 60 to 110W. The nuclear magnetic sample prepared by the method has the advantages of good shimming effect, high detection sensitivity, high spectrogram resolution and the like during detection, and 23Na in a bulk phase of an ion exchange membrane can be detected.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear magnetic resonance technology detection, and in particular relates to a method for detecting sodium ions in an ion exchange membrane and its application. Background Art

[0002] Liquid-State NMR technology has been widely used in fields such as chemistry, materials science, and biomedicine due to its high resolution, ease of operation, and rich information acquisition capabilities. However, as a functional material with a special microphase separation structure, the performance of ion exchange membranes is highly dependent on the ion transport channel network and the distribution of hydrophilic and hydrophobic domains in the solid state. If the traditional soluble liquid NMR detection method is used, its intrinsic structure will be destroyed, resulting in the loss of key microstructural information (such as ion cluster size, connectivity, and dynamic behavior). Therefore, how to use liquid NMR to efficiently characterize the microenvironment and ion transport mechanism of ion exchange membranes while maintaining the structural integrity of the membrane material is still a difficulty in the current technical field.

[0003] Sodium ions (Na+) play a key 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 crucial for optimizing material properties. However, the sodium nucleus ( 23 The gyromagnetic ratio (γ) of Na is low (approximately 1 H) and the natural abundance (100%) 23 The Na nucleus has a significant quadrupole effect (I = 3 / 2), resulting in low NMR signal sensitivity and severe spectral broadening. Conventional detection requires high-field instruments (≥500 MHz) or signal enhancement techniques such as dynamic nuclear polarization (DNP), which greatly limits its practical application. Detecting 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 nuclear magnetic resonance signal of sodium ions in the ion exchange membrane, thereby providing a method and application for detecting sodium ions in the ion exchange membrane.

[0005] To address these issues, the present invention proposes an innovative method based on liquid nuclear magnetic resonance (NMR) technology, enabling efficient and non-destructive detection of sodium ion NMR signals within ion exchange membranes. By optimizing sample preparation strategies, pulse parameters, and sampling parameters, this method enables precise analysis of the local environment and dynamic behavior of Na+ within the ion exchange membrane. This method not only provides a new approach for studying the structure-property relationship of ion exchange membranes, but also has important applications in energy storage, separation membrane development, and other fields.

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

[0007] The present 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 side number of not less than 4. The sample is wrapped around a uniform rod and loaded into the bottom of the nuclear magnetic tube by screwing. The rod is pulled out or retained in the nuclear magnetic tube. It should be explained that soaking here refers to soaking the ion exchange membrane in a solution; or, for an ion exchange membrane 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. The nuclear magnetic sample prepared by the present invention has the advantages of good field uniformity, high detection sensitivity and spectral resolution during detection, and the nuclear magnetic sample preparation process is simple. When detecting sodium ions in the ion exchange membrane, the present invention is suitable for ion exchange membranes that will not bend or break when wrapped around a glass rod. The ion exchange membrane is placed in a regular and orderly manner in the nuclear magnetic tube.

[0009] (2) placing the nuclear magnetic resonance tube obtained in step (1) into a nuclear magnetic resonance spectrometer, tuning and shimming, adjusting the nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters include: a 90° pulse width of 10 to 14 μs; and a power of 60 to 110 W.

[0010] The present invention utilizes the principle of liquid nuclear magnetic resonance to collect sodium ion signals in ion exchange membranes: the ion exchange membrane swells after being soaked in a solution. The ion exchange membrane has the characteristic of selectively transmitting ions, so that ions and water molecules coexist inside the bulk of the ion exchange membrane, forming countless microscopic liquid environments in the ion exchange membrane. Therefore, the nuclear magnetic signal of sodium ions can be detected using liquid nuclear magnetic resonance.

[0011] The cation exchange membrane has the characteristics of cation selective transmission, which can make Na + Stay inside the membrane phase. The sodium ion concentration in the ion exchange membrane is low. The existing technology usually uses solid detection, and liquid detection is rare, which cannot realize the Na +Accurate analysis. The present invention adopts a nuclear magnetic resonance detection sample prepared by a specific sampling method, and performs testing under specific nuclear magnetic resonance test parameters such as a 90° pulse width of 10 to 14 μs and a power of 60 to 110 W. On the basis of not destroying the structural state of the ion exchange membrane, the nuclear magnetic resonance signal of the sodium ions inside the ion exchange membrane bulk phase can be collected, providing strong support for the detection and analysis of the structural information inside the ion exchange membrane bulk phase. The signals collected by conventional liquid nuclear magnetic resonance sampling methods are mainly free atoms, that is, sodium ions in the nuclear magnetic resonance tube solution (located outside the membrane body), and the sodium ion signals on the ion exchange membrane cannot be detected. The present invention makes the ion exchange membrane into a polygonal sample with a symmetrical structure and a side number of not less than 4, and sets the 90° pulse width in the nuclear magnetic resonance test parameters to 10 to 14 μs and a power of 60 to 110 W, which can detect the nuclear magnetic resonance signal of the sodium ions in the ion exchange membrane bulk phase.

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

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

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

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

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

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

[0018] After selecting the pulse sequence, the 23Na tuning channel is selected. Different nuclides have different resonant frequencies, so independent tuning and matching are required. The 23Na tuning channel is on the X channel. When detecting 23Na in the present invention, taking a 600MHz resonance spectrometer as an example, the resonant frequency is 158.7MHz. The field strength of the detection instrument and the type of nuclide being detected determine the resonant frequency of the detected nuclide in the detection instrument. The field strength of the detection instrument and the type of nuclide being detected determine the resonant frequency of the detected nuclide in the detection instrument. The resonance frequency can be determined in the art based on the specific nuclide type and the field strength of the detection instrument.

[0019] The ion exchange membrane can be a commercial ion exchange membrane, such as Fumasep FKS-30, ASTOM NeoseptaCXP-S, Fumasep-E-620(K), Fumasep F-10120-PK, and Fumasep FS-990-PK. The ion exchange membrane can also be from a device equipped with an ion exchange membrane, such as a diaphragm in a fuel cell, an electrodialysis device, or an electrolysis device.

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

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

[0022] Preferably, the soaking solution is 0.2-1.0 mol / L.

[0023] The method of the present invention can also simultaneously detect the nuclear magnetic signals of sodium ions inside the ion exchange membrane bulk phase and sodium ions outside the membrane (in a free state). The difference in chemical shifts of the atomic nuclear magnetic signals inside and outside the membrane bulk phase can be used to determine the transport performance of the cation exchange membrane for sodium ions, thereby facilitating the analysis of the structural performance of the cation exchange membrane and its application in different fields.

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

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

[0026] Preferably, when the solvent in the immersion solution includes a deuterated solvent, a field lock step is further performed before field shimming.

[0027] As an optional embodiment, in step (1), the soaking solution contains sodium ions. It should also be noted that, during the sample preparation process, the soaking solution of the ion exchange membrane contains sodium ions that can dissociate Na + The soaking solutions in step (1) and step (2) are the same or different, preferably the same. The present invention has no requirements for the soaking time in step (1), which can allow the ion exchange membrane to swell and contain ions and water molecules inside, such as 2h, 5h, 10h, 15h, 20h, 25h, 30h, etc.

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

[0029] The diameter of the rod is 2 to 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 is a hollow cylinder, meaning it can be an inner lining tube, with a hollow interior where liquid can be added. In this case, a deuterated reagent, such as deuterated water, deuterated DMSO, deuterated chloroform, or other common deuterated reagents, can be added to the hollow center of the rod. This allows for a lock field to accurately locate the chemical shift of the atomic nucleus to be measured, while also preventing the deuterated reagent from affecting the ion exchange membrane structure. Furthermore, since deuterated reagents are relatively expensive, a lock field can be achieved using an inner lining tube, saving on the use of deuterated reagents.

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

[0033] The present invention provides the application of the above-mentioned detection method to the detection of diaphragms in fuel cells, electrodialysis devices, or electrolysis devices. This application can detect the sodium ion signal of used ion exchange membranes, providing strong support for the analysis of the structure and performance of ion exchange membranes.

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

[0035] 1. The method for detecting sodium ions in an ion exchange membrane provided by the present invention comprises: (1) preparing a polygonal sample having a symmetrical structure and a side number of not less than 4 after soaking the ion exchange membrane, winding the sample on a uniform rod, loading the sample into the bottom of a nuclear magnetic resonance tube by a screw-in method, and extracting the rod or retaining it in the nuclear magnetic resonance tube; (2) placing the nuclear magnetic resonance tube prepared in step (1) into a nuclear magnetic resonance spectrometer, tuning and shimming, adjusting nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters include: a 90° pulse width of 10 to 14 μs; and a power of 60 to 110 W. The nuclear magnetic resonance sample prepared by the present invention has the advantages of good field uniformity effect, high detection sensitivity and spectral resolution during detection, and the nuclear magnetic resonance sample preparation process is simple. When tested under the nuclear magnetic resonance test parameters: 90° pulse width of 10 to 14 μs; power of 60 to 110 W, 23Na inside the ion exchange membrane bulk phase can be detected, providing strong support for detecting and analyzing structural information inside the ion exchange membrane bulk phase.

[0036] Furthermore, the method of the present invention can also simultaneously detect the nuclear magnetic resonance signals of sodium ions inside the ion exchange membrane bulk phase and sodium ions outside the membrane (in a free state). The transport performance of the cation exchange membrane for sodium ions can be judged by the difference in chemical shifts of the atomic nuclear magnetic signals inside and outside the membrane bulk phase, which facilitates the analysis of the structural properties of the cation exchange membrane and its application in different fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

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

[0040] Figure 3 This is the nuclear magnetic spectrum obtained by testing comparative example 1 of the present invention;

[0041] Figure 4 This is the state of the ion exchange membrane in Example 1 of the present invention in the nuclear magnetic tube, referred to as the sample schematic diagram. DETAILED DESCRIPTION

[0042] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0043] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0044] Example 1

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

[0046] (1) Ion exchange membrane (Fumasep FKS-30) was immersed in 0.2 mol / L NaCl aqueous solution (solvent is non-deuterated reagent) for 24 h. After removal, it was wiped dry. The ion exchange membrane was cut into regular square samples with a length of 4 cm. Then, it was wound on a glass rod with a diameter of 3 mm. The sample was evenly wrapped around the bottom of the NMR tube by screwing it out. The glass rod was pulled out. The state of the ion exchange membrane in the NMR tube was shown in Fig. Figure 4 .

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

[0048] The nuclear magnetic spectrum obtained by the test in this example is shown in Figure 1 ,from Figure 1 It can be seen from the figure that the present invention can measure the nuclear magnetic signal of 23Na inside the ion exchange membrane body. The signal has a strong nuclear magnetic signal at -1.15ppm, and the spectrum resolution and signal intensity are both high.

[0049] Example 2

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

[0051] (1) The ion exchange membrane (same as in Example 1) was immersed in a 0.2 mol / L NaCl aqueous solution (the solvent was a non-deuterated reagent), removed and dried, and the ion exchange membrane was cut into a regular square sample with a length of 4 cm. The sample was then wrapped around a glass rod with a diameter of 3 mm. The sample was evenly placed at the bottom of the NMR tube by screwing it inward, and the glass rod was removed. 5 μL of 0.2 mol / L NaCl solution was added to the NMR tube.

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

[0053] The nuclear magnetic spectrum obtained by the test in this example is shown in Figure 2 ,from Figure 2 It can be seen that the sample preparation method of the present invention can not only measure the nuclear magnetic signal of 23Na in the membrane (chemical shift is -1.15ppm), but also measure the nuclear magnetic signal of 23Na outside the membrane (sodium ions in the nuclear magnetic tube) (chemical shift is 0.3ppm). In addition, due to the limited movement of 23Na atoms inside the ion exchange membrane bulk, the transverse relaxation time (T2) of 23Na is shortened, and the spectrum peak is widened relative to the outside of the membrane. The detection method provided by the present invention provides a new analytical test method for the study of the microstructure performance of ion exchange membranes applied to different scenarios, which has a high spectrum resolution and signal-to-noise ratio compared to the spectrum measured after the membrane is curled and compacted in Comparative Example 1.

[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) The ion exchange membrane was immersed in a 0.2 mol / L NaCl aqueous solution (the solvent was a non-deuterated reagent), taken out and wiped dry, and the membrane was rolled and compacted and directly inserted into the NMR tube. 5 μL of a 0.2 mol / L NaCl aqueous solution (the solvent was a non-deuterated reagent) was added to the NMR tube. The ion exchange membrane appeared as irregular clumps in the NMR tube.

[0057] (2) Place the NMR tube in the NMR spectrometer, tune and homogenize the field. The detection 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: 1s; number of sampling points: 32k, k is 1024; sampling time: 1.7s; spectral width of 60ppm; spectral range: -30ppm to +30ppm; cumulative number of times: 128 times. NMR spectrum is shown in Figure 3 ,from Figure 3 It can be seen that this comparative example cannot distinguish the 23Na signals inside and outside the membrane phase, and the spectrum peak is broadened and the resolution is low, indicating that the sample preparation method of the present invention is helpful for Na signal detection.

[0058] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for detecting sodium ions in an ion exchange membrane, characterized in that: The following steps are involved: (1) After soaking, the ion exchange membrane is made into a polygonal sample with a symmetrical structure and a side number of not less than 4, the sample is wrapped around a uniform rod, and the sample is placed into the bottom of the nuclear magnetic tube by screwing; (2) placing the nuclear magnetic resonance tube obtained in step (1) into a nuclear magnetic resonance spectrometer, tuning and shimming, adjusting the nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters include: a 90° pulse width of 10 to 14 μs; The power is 60~110W.

2. The detection method according to claim 1, wherein The NMR test parameters also include: pulse sequence zg; relaxation time: 1 to 5s; number of sampling points: 16k to 32k, k is 1024; sampling time: 1 to 5s; spectrum width: 60 to 120ppm; spectrum range: -60ppm to +60ppm, cumulative number of times: 8 to 256 times; Preferably, the spectrum width is 60 ppm and the spectrum range is -30 ppm to +30 ppm.

3. The detection method according to claim 1, wherein The 90° pulse width is 12μs; the power is 77W.

4. The detection method according to any one of claims 1 to 3, characterized in that: The sodium is 23Na; and / or, The ion exchange membrane is a cation exchange membrane; preferably, the ion exchange membrane comes from a battery.

5. The detection method according to claim 1, wherein The step (2) further comprises adding 5 to 20 μL of soaking solution before placing the NMR tube into the NMR spectrometer, wherein the concentration of the soaking solution is 0.2 to 2.0 mol / L; Preferably, the soaking solution is a solution containing sodium ions; Preferably, the concentration of the soaking solution is 0.2-1.0 mol / L.

6. The detection method according to claim 5, characterized in that The soaking solution includes a soluble sodium salt; Preferably, the soluble sodium salt includes at least one of NaCl, Na2SO4, Na2CO3, NaHCO3, CH3COONa, NaOH, and NaNO3.

7. The detection method according to claim 6, characterized in that The solvent in the soaking solution includes a deuterated solvent or a non-deuterated solvent; Preferably, the solvent comprises at least one of water, chloroform, dimethyl sulfoxide, dichloromethane, methanol, and ethanol; Preferably, when the solvent in the immersion solution includes a deuterated solvent, a field lock step is further performed before field shimming.

8. The detection method according to claim 1, wherein In the step (1), the soaking solution contains sodium ions.

9. The detection method according to claim 1, wherein In the step (1), the sample is in a square shape; and / or, The diameter of the rod is 2 to 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.

10. Use of the detection method according to any one of claims 1 to 9 in detecting a diaphragm in a fuel cell, an electrodialysis device or an electrolysis device.

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