Method for detecting fluorine ions in ion exchange membranes and use thereof

Abstract

The application belongs to the field of nuclear magnetic resonance technology detection, and particularly relates to a method for detecting fluorine ions in an ion exchange membrane and application thereof. The method comprises the following steps: (1) after the ion exchange membrane is soaked to prepare a sample, the sample is wound around a rod, and the sample is loaded into the bottom of a nuclear magnetic tube in a spin-in manner; the shape of the sample is a polygon, and the polygon has a symmetrical structure and a side number not less than 4; (2) the nuclear magnetic tube prepared in the step (1) is placed into a nuclear magnetic resonance spectrometer, a pulse sequence is selected, tuning and shimming are performed, nuclear magnetic resonance test parameters are adjusted, and a signal is collected; the nuclear magnetic resonance test parameters comprise: a 90° pulse width of 9-15 mu s; and a power of 20-55 W. The nuclear magnetic sample obtained by using the specific sample preparation method can detect the structure information in the bulk phase of the ion exchange membrane under the condition of a 90° pulse width of 9-15 mu s and a power of 20-55 W. 19 F, which provides strong support for detecting and analyzing the structure information in the bulk phase of the ion exchange membrane.

Description

Technical Field

[0001] This invention belongs to the field of nuclear magnetic resonance technology detection, specifically relating to a method for detecting fluoride ions in ion exchange membranes and its application. Background Technology

[0002] Ion exchange membranes are thin films prepared using polymer materials as the substrate, typically made of plastics, adhesives, rubber, or other organic polymers. Ion exchange membranes include various functional films, such as optical films, water treatment films, battery separators, and conductive films, and are widely used in optical devices, photovoltaic power generation, wastewater treatment, element enrichment, seawater desalination, fluoride-ion batteries, and other fields in medicine, food, agriculture, and chemicals, showing broad application prospects. The detection of the internal structure, surface morphology, mechanical properties, and electrochemical properties of ion exchange membranes has always been one of the main research hotspots in the field. Currently, the main characterization techniques for ion exchange membranes include thermogravimetric analysis, infrared spectroscopy, Raman spectroscopy, atomic force microscopy, and electron microscopy.

[0003] Liquid-state nuclear magnetic resonance (Liquid-State NMR) has become a core tool for chemical structure characterization and dynamic process research due to its superior resolution (δ≤0.1 ppm), non-destructive detection characteristics, and multidimensional spectral resolution capabilities. However, ion exchange membranes, as key components of energy conversion and storage systems (such as fuel cells and flow batteries), are functional materials with unique microphase separation structures. Their performance is highly dependent on the distribution of ion transport channel networks and hydrophilic and hydrophobic water regions in the solid state. Using traditional dissolved liquid NMR detection methods would destroy 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.

[0004] Fluoride ions (F) - Fluoride (F) is an important anion widely found in nature, with significant applications in environmental monitoring (e.g., drinking water safety, industrial wastewater treatment, soil and air pollution assessment), biomedicine (clinical diagnosis, dentistry, drug analysis), industrial production (semiconductor manufacturing, nuclear industry, fluoride battery electrolytes), and food safety. Liquid nuclear magnetic resonance (NMR) technology is used to detect fluoride ions (F). - The detection of [something] is of great significance in safeguarding public health, environmental protection, and industrial quality control. 19The F nucleus has a spin of I=1 / 2 and high sensitivity. However, in asymmetric electric field gradient environments, such as binding sites in ion exchange membranes or solid electrode interfaces, the spectral peaks are significantly broadened and the resolution decreases, which greatly limits its practical application range. Therefore, there is an urgent need to develop an NMR detection method that can maintain the intrinsic microstructure of ion exchange membrane materials and detect fluoride ions. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is how to detect the NMR signal of fluoride ions in ion exchange membranes while maintaining the intrinsic microstructure of ion exchange membrane materials, thereby providing a method for detecting fluoride ions in ion exchange membranes and its application.

[0006] This invention innovatively provides a method for detecting fluoride ion NMR signals in ion exchange membranes using liquid NMR technology. By optimizing sample processing techniques and pulse sequence design, it achieves, for the first time, the simultaneous and efficient detection of fluoride ion and free-state fluoride ion signals in ion exchange membranes, providing a new method for analyzing the structural performance of ion exchange membranes.

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

[0008] (1) The ion exchange membrane is soaked to prepare a sample. The sample is wound around a rod and inserted into the bottom of the NMR tube by screwing. The rod is then removed or left in the NMR tube. The sample is polygonal in shape, with a symmetrical structure and at least 4 sides. The soaking in step (1) of this invention refers to immersing the ion exchange membrane in a solution; or, the ion exchange membrane used in a liquid environment. Both of these methods belong to the soaking method of this invention. The ion exchange membrane of this invention is prepared into a sample with a polygonal shape, such as a quadrilateral, pentagon, or hexagon. The polygon satisfies the requirement of at least 4 sides and a symmetrical structure. Furthermore, the polygon also includes chamfers and / or rounded corners. This invention has a simple method for preparing NMR samples and has advantages such as good shimming effect, high detection sensitivity, and high spectral resolution when the sample is used for detection. The ion exchange membrane is placed in a uniform, orderly, and regular manner inside the NMR tube. Random and disorderly placement will not yield an effective NMR signal. In detecting fluoride ions, this invention requires that the ion exchange membrane does not bend or break when it is wound around the glass rod.

[0009] (2) Place the nuclear magnetic tube obtained in step (1) into the nuclear magnetic resonance spectrometer, select the pulse sequence, tune and homogenize, adjust the nuclear magnetic resonance test parameters, and acquire the signal; the nuclear magnetic resonance test parameters include: 90° pulse width of 9~15μs; power of 20~55W.

[0010] The principle of this invention for acquiring fluoride ion signals in ion exchange membranes using liquid NMR is as follows: After the ion exchange membrane is soaked in a solution, it swells. Since the ion exchange membrane can selectively transmit ions (such as fluoride), ions and water molecules coexist inside the bulk phase of the ion exchange membrane. That is, ions and water molecules form countless microscopic liquid environments in the ion exchange membrane. Therefore, the NMR signal of fluoride ions in the ion exchange membrane can be successfully detected using liquid NMR.

[0011] Anion exchange membranes possess anion-selective transport properties, allowing F to be transported selectively during the immersion process. - Due to limitations imposed by traditional sample preparation methods, the concentration of fluoride ions inside the ion exchange membrane is low compared to that in the liquid phase. This makes it impossible to accurately measure the concentration of fluoride ions inside the membrane phase using current liquid NMR techniques. - Accurate analysis is achieved. This invention utilizes a specially prepared sample method to obtain NMR detection samples, and tests are performed under specific NMR testing parameters: a 90° pulse width of 9–15 μs and a power of 20–55 W. This allows for the acquisition of NMR signals from fluoride ions within the ion exchange membrane phase without disrupting the membrane's structural state. Conventional liquid NMR sample preparation methods primarily acquire signals from free-state atoms, i.e., fluoride ions in the NMR tube solution (located outside the membrane), failing to detect fluoride ion signals on the ion exchange membrane itself. However, by employing the sample preparation method of this invention and testing under specific NMR testing parameters (90° pulse width 9–15 μs and power 20–55 W), NMR signals from fluoride ions within the ion exchange membrane phase can be detected.

[0012] As an optional implementation, the 90° pulse width is 12μs; the power is 32W.

[0013] For example, the 90° pulse width is 9μs, 10μs, 11μs, 12μs, 13μs, 14μs or 15μs; the power is 20W, 30W, 35W, 40W, 45W or 55W.

[0014] As an optional implementation, the fluorine is 19 F; and / or,

[0015] The ion exchange membrane is an anion exchange membrane; preferably, the ion exchange membrane is derived from a battery.

[0016] The ion exchange membrane includes anion exchange membranes. Several commercial models are listed here, such as Fumasep FAA-3-PK-130 and Fumasep FAAM-PK-75.

[0017] As an optional implementation, the nuclear magnetic resonance testing parameters further include: pulse sequence of zgig; relaxation time: 1~5s; number of sampling points: 32k~128k, where k is 1024; sampling time: 0.3~5s; spectral width: 200~600ppm; spectral range: 100ppm~-500ppm; number of accumulations: 4~256.

[0018] Preferably, the spectral width is 300 ppm and the spectral range is 0 ppm to -300 ppm.

[0019] Different nuclides have different resonance frequencies and require independent tuning and matching. This invention selects a pulse sequence followed by... 19 F-tuning channel, 19 The resonance frequency of fluoride (F) is close to that of hydrogen; therefore, when detecting fluoride ions, the tuning channel is in 1H. The resonance frequency of each nuclide in the detection instrument is related to the field strength of the instrument and the type of nuclide. Taking a 600MHz resonance spectrometer as an example, the resonance frequency is 564.7MHz. Those skilled in the art can determine the resonance frequency based on the specific nuclide and the field strength of the detection instrument.

[0020] As an optional implementation, step (2) further includes adding 10-100 μL of a fluoride-containing solution before placing the NMR tube into the NMR spectrometer. By placing the fluoride-containing solution into the NMR tube, the NMR signal of fluoride ions outside the ion exchange membrane (in the free state, i.e., fluoride ions in the fluoride-containing solution added to the NMR tube) can be detected using the method of this invention. Since this invention can detect fluoride ion signals inside the ion exchange membrane, the difference in chemical shift of the NMR signals of fluoride atoms inside and outside the membrane can be used to determine the fluoride ion transport performance of the ion exchange membrane, providing a basis for the structural performance analysis of anion exchange membranes, and thus enabling the application of ion exchange membranes in different fields based on their performance.

[0021] As an optional implementation, the fluoride-containing solution comprises a soluble fluoride salt;

[0022] Preferably, the soluble fluoride salt includes at least one of LiF, NaF, and KF.

[0023] As an optional implementation, the concentration of the fluoride-containing solution is 0.2~2.0 mol / L;

[0024] Preferably, the concentration of the fluoride-containing solution is 1.0 mol / L.

[0025] As an optional implementation, the solvent in the fluoride-containing solution includes a deuterated solvent or a non-deuterated solvent;

[0026] Preferably, the solvent includes at least one of methanol, dimethyl sulfoxide (DMSO), chloroform (CHCl3), dichloromethane (CH2Cl2), ethanol, and water;

[0027] Preferably, when the solvent in the fluoride-containing solution includes a deuterated solvent, a field locking process is also included before shimming.

[0028] As an optional implementation, in step (1), the soaking solution is capable of dissociating fluoride ions. It should also be noted that, during sample preparation, the soaking solution of the ion exchange membrane includes components capable of dissociating fluoride ions. - Compounds that can dissociate F. - The solution of the compound is selected from any of the above-mentioned solutions containing fluoride ions. The soaking solution of the ion exchange membrane can be the same as or different from the solution containing fluoride ions, preferably the same. The present invention does not require a soaking time, and allows the ion exchange membrane to swell and contain ions and water molecules inside, for example, 1h, 4h, 8h, 12h, 16h, 24h, 28h, etc.

[0029] As an optional implementation, in step (1), the sample is square in shape. When the sample is square, its length is 3-5 cm. It should be noted that the size of the sample can be selected according to the rod material, as long as it can be wound around the rod material. Square includes square, rectangle, etc.

[0030] As an optional implementation, the diameter of the rod is 2-3 mm; and / or,

[0031] The rod material includes a rubber rod, a glass rod, or a metal rod; and / or,

[0032] 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.

[0033] This invention provides the application of the above-described detection method in the detection of membranes in electrodialysis devices, electrolysis devices, or fuel cells. This application can detect fluoride 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 fluoride ions in an ion exchange membrane provided by the present invention includes (1) preparing a sample by soaking the ion exchange membrane, winding the sample around a rod, inserting the sample into the bottom of a nuclear magnetic resonance (NMR) tube by screwing it in, and removing the rod or leaving it in the NMR tube; the sample is polygonal in shape, the polygon has a symmetrical structure and the number of sides is not less than 4; (2) placing the NMR tube obtained in step (1) into a nuclear magnetic resonance spectrometer, selecting a pulse sequence, tuning and shimming, adjusting the NMR test parameters, and acquiring the signal; the NMR test parameters include: a 90° pulse width of 9~15μs; and a power of 20~55W. The NMR sample obtained by the specific sample preparation method of the present invention has a good shimming effect, high detection sensitivity and spectral resolution, and can detect fluoride ions inside the bulk phase of the ion exchange membrane at a 90° pulse width of 9~15μs and a power of 20~55W. 19 F provides strong support for detecting and analyzing the internal structural information of ion exchange membranes.

[0036] Furthermore, the method of this invention can detect the NMR signal of fluoride ions outside the bulk phase of the ion exchange membrane. Since this invention can detect the fluoride ion signal inside the ion exchange membrane, based on the difference in chemical shift of the NMR signals of fluoride atoms inside and outside the membrane, the transport performance of the ion exchange membrane for fluoride ions can be determined, providing a basis for the structural performance analysis of anion exchange membranes, and thus enabling their application in different fields based on their performance. 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 of the blank group in Example 1 of the present invention;

[0040] Figure 3-4 This is the NMR spectrum obtained from the test in Example 2 of this invention;

[0041] Figure 5 This is a schematic diagram of the ion exchange membrane in the NMR tube of Embodiment 2 of the present invention, referred to as the sample diagram.

[0042] Figure 6 This is a schematic diagram of the ion exchange membrane of Comparative Example 1 of the present invention inside an NMR tube, referred to as the sample diagram.

[0043] Figure 7-8 The NMR spectrum obtained by comparative example 1 of this invention. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] Example 1

[0047] This embodiment provides a method for detecting fluoride ions in an ion exchange membrane, comprising the following steps:

[0048] (1) Immerse the ion exchange membrane (Fumasep FAA-3-PK-130) in a 1 mol / L NaF aqueous solution (the solvent is a non-deuterated reagent) for 4 hours. After taking it out and drying it, cut the ion exchange membrane into a rectangular sample with a size of 5 cm × 3 cm. Then wrap it around a glass rod with a diameter of 3 mm and use a screw-in method to evenly wrap the sample around the bottom of the NMR tube. Then pull out the glass rod.

[0049] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The NMR test parameters include: 90° pulse width of 12μs; power of 32W; pulse sequence of zgig; relaxation time of 1s; number of sampling points of 128k, k is 1024; sampling time of 0.39s; spectral width of 300ppm; spectrum range of 0ppm to -300ppm; number of accumulations of 128; the detection instrument is a 600MHz liquid NMR spectrometer with a resonance frequency of 564.7MHz.

[0050] Figure 2 This is the NMR spectrum of the blank group in this embodiment. The difference between the blank group and Example 1 is that the NMR signal was directly measured after the ion exchange membrane was prepared. From Figure 2 The broad peak at -180 ppm is inherent to the ion exchange membrane itself. 19 The nuclear magnetic resonance signal of F. Figure 1 This is the NMR spectrum of this embodiment, from Figure 1 It can be seen that -119ppm and -180ppm are present in the ion exchange membrane. 19 The nuclear magnetic resonance signal of F, combined with Figure 2The broad peak at -180 ppm is inherent to the ion exchange membrane itself. 19 The NMR signal of F is given, therefore, -119 ppm represents the NMR signal of F ions inside the ion exchange membrane. This indicates that the sample preparation and testing methods of the present invention can obtain NMR signals of F ions inside the ion exchange membrane with high resolution and high signal-to-noise ratio. 19 The nuclear magnetic resonance signal of F.

[0051] Example 2

[0052] This embodiment provides a method for detecting fluoride ions in an ion exchange membrane, comprising the following steps:

[0053] (1) Immerse the ion exchange membrane (same as in Example 1) in a 1 mol / L NaF aqueous solution (non-deuterated reagent) for 4 hours. After removing and drying, cut the ion exchange membrane into regular rectangular samples of 5 cm × 3 cm. Then, wrap the samples around a 3 mm diameter glass rod and screw them in evenly to the bottom of the NMR tube. Remove the glass rod. Add 50 μL of 1 mol / L NaF aqueous solution to the NMR tube. The state of the sample in the NMR tube is shown in the figure. Figure 5 .

[0054] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The NMR test parameters include: 90° pulse width of 12μs; power of 32W; pulse sequence of zgig; relaxation time of 1s; number of sampling points of 128k, k is 1024; sampling time of 0.39s; spectral width of 300ppm; spectrum range of 0ppm to -300ppm; number of accumulations of 128; the detection instrument is a 600MHz liquid NMR spectrometer with a resonance frequency of 564.7MHz.

[0055] See NMR spectrum Figure 3 , Figure 4 This is a magnified view of a portion of the NMR signal. The image shows the interior of the ion exchange membrane. 19 The chemical shift of F is -119 ppm, outside the membrane. 19 The chemical shift of F is -120 ppm, and the broad peak at -180 ppm is inherent to the ion exchange membrane itself. 19 The NMR signal of F. Due to the interior of the ion exchange membrane phase. 19 The movement of F atoms is restricted, thus 19 The shortening of the transverse relaxation time (T2) of F and the broadening of the spectral peak relative to the outside of the membrane indicate that this invention can detect both the interior and exterior phases of the ion exchange membrane. 19 The F-type nuclear magnetic resonance signal has high resolution and signal-to-noise ratio.

[0056] Comparative Example 1

[0057] This comparative example provides a method for detecting fluoride ions in an ion exchange membrane, comprising the following steps:

[0058] (1) The ion exchange membrane (same as in Example 1) was immersed in a 1 mol / L NaF aqueous solution (non-deuterated reagent) for 4 hours. After removal and drying, the ion exchange membrane was cut into regular rectangular samples with dimensions of 5 cm × 3 cm. After rolling, the samples were cut into uniform segments (approximately 0.3 cm in length) and directly loaded into the bottom of the NMR tube. 50 μL of 1 mol / L NaF aqueous solution was added to the NMR tube. The state of the sample in the NMR tube is shown in the figure. Figure 6 .

[0059] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The NMR test parameters include: 90° pulse width of 12μs; power of 32W; pulse sequence of zgig; relaxation time of 1s; number of sampling points of 128k, k is 1024; sampling time of 0.39s; spectral width of 300ppm; spectrum range of 0ppm to -300ppm; number of accumulations of 128; the detection instrument is a 600MHz liquid NMR spectrometer with a resonance frequency of 564.7MHz.

[0060] See NMR spectrum Figure 7 , Figure 8 yes Figure 7 A magnified view of a portion of the NMR signal, inside the ion exchange membrane. 19 The signal of F overlapped significantly with that outside the membrane, resulting in multiple sets of peak signals and broadened spectral peaks. This further demonstrates the superiority of the sample preparation and testing methods of this invention.

[0061] 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 of detecting fluoride ions in an ion exchange membrane, characterized by, Includes the following steps: (1) The ion exchange membrane is soaked to make a sample, the sample is wound around a rod, and the sample is inserted into the bottom of the NMR tube by screwing in. The rod is then pulled out or left in the NMR tube. The sample is polygonal in shape, the polygon has a symmetrical structure and the number of sides is not less than 4. (2) Place the nuclear magnetic tube obtained in step (1) into the nuclear magnetic resonance spectrometer, select the pulse sequence, tune and shim, adjust the nuclear magnetic resonance test parameters, and acquire the signal; The nuclear magnetic resonance test parameters include: a 90° pulse width of 9-15 μs; The power is 20~55W.

2. The method of claim 1, wherein, The 90° pulse width is 12μs; the power is 32W.

3. The method of claim 1, wherein, said fluorine is 19 F; and / or, The ion exchange membrane is an anion exchange membrane.

4. The method of claim 3, wherein, The ion exchange membrane is derived from a battery.

5. The method according to any one of claims 1 to 4, characterized in that, The nuclear magnetic resonance testing parameters also include: pulse sequence of zgig; relaxation time: 1~5s; number of sampling points: 32k~128k, k is 1024; sampling time: 0.3~5s; spectral width: 200~600ppm; spectrum range: 100ppm~-500ppm; number of accumulations: 4~256.

6. The method of claim 5, wherein, The spectral width is 300 ppm, and the spectral range is 0 ppm to -300 ppm.

7. The method according to any one of claims 1-4 or 6, characterized in that, Step (2) further includes adding 10-100 μL of a fluoride ion-containing solution before placing the nuclear magnetic resonance tube into the nuclear magnetic resonance spectrometer; The fluoride-containing solution includes soluble fluoride salts.

8. The method of claim 7, wherein, The soluble fluoride salt includes at least one of LiF, NaF, and KF.

9. The method of claim 7, wherein, The concentration of the fluoride-containing solution is 0.2~2.0 mol / L.

10. The method of claim 9, wherein, The concentration of the fluoride-containing solution is 1.0 mol / L.

11. The method of claim 7, wherein, The solvent in the fluoride-containing solution includes deuterated solvents or non-deuterated solvents.

12. The method of claim 11, wherein, The solvent includes at least one of dimethyl sulfoxide, chloroform, methanol, dichloromethane, ethanol, and water; And / or, when the solvent in the fluoride-containing solution includes a deuterated solvent, a field locking process is also included before shimming.

13. The method of claim 1, wherein, In step (1), the sample is square in shape.

14. The method of claim 1, wherein, 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.

15. The application of the method according to any one of claims 1 to 14 in detecting the membrane in an electrodialysis device, an electrolysis device, or a fuel cell.

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