Method for detecting chlorine atoms in ion exchange membranes and applications thereof

Abstract

The application belongs to the field of nuclear magnetic resonance technology detection, and particularly relates to a detection method for chlorine atoms in an ion exchange membrane and application. The detection method comprises the following steps: (1) preparing a nuclear magnetic tube containing an ion exchange membrane sample; (2) placing the nuclear magnetic tube into a nuclear magnetic resonance spectrometer, selecting a pulse sequence, tuning and homogenizing, adjusting nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters comprise: a 90° pulse width of 15-22 mu s; and a power of 100-200 W. The application is tested under specific nuclear magnetic resonance test parameters, nuclear magnetic signals of chlorine atoms in the ion exchange membrane can be collected on the basis that the structure of the ion exchange membrane is not damaged, and strong support is provided for detecting and analyzing structural information in the ion exchange membrane.

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 chlorine atoms in an ion exchange membrane. 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, lithium-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] Nuclear magnetic resonance spectroscopy (NMR), along with ultraviolet absorption spectroscopy, infrared absorption spectroscopy, and mass spectrometry, is known as the "four spectra." It is one of the most powerful tools for qualitative analysis of the composition and structure of various organic and inorganic substances, and can also be used for quantitative analysis. Due to its precision, accuracy, and ability to penetrate deep into the substance without destroying the sample, NMR spectroscopy is widely used in chemistry, pharmacy, medicine, agriculture, environment, mining, materials science, and other disciplines, becoming an indispensable analytical method.

[0004] Nuclear magnetic resonance (NMR) technology can be divided into liquid NMR and solid NMR based on the state of the substance it detects. Liquid NMR can identify the molecular structure and spatial configuration of liquid or semi-solid samples such as inorganic small molecules, organic compounds, pharmaceutical preparations, biological peptides, and proteins. Solid NMR can identify the molecular structure of dry solids and can also be used to study kinetics and intermolecular interactions. Currently, solid NMR is widely used to detect the structural information of ion exchange membranes.

[0005] Because ion exchange membranes have unique structural properties, dissolving them destroys their structural information. Directly rolling or cutting the ion exchange membrane and loading it into an NMR tube results in poor shimming, preventing the effective detection of NMR signals as with solid-state NMR. Therefore, using liquid NMR to detect the NMR signal of ion exchange membranes without damaging their structure is relatively rare, especially for detecting NMR signals from membranes with low heteroatom content.

[0006] Liquid nuclear magnetic resonance (NMR) technology has demonstrated unique value in revealing the chemical environment and dynamic behavior of 35Cl in fields such as biomedical research (exploration of physiological and pathological mechanisms, drug metabolism and treatment monitoring), materials and chemistry research (study of electrolyte systems and ion transport, catalysis and reaction mechanism analysis), and environmental and industrial analysis (water quality and pollution monitoring). However, ion exchange membranes have special structural properties, and dissolution destroys their structural information. Furthermore, due to its spin quantum number (I) = 3 / 2, 35Cl exhibits severe signal broadening (rapid relaxation) of the quadrupole moment, resulting in extremely low resolution. In addition, the gyromagnetic ratio (γ) of 3Cl is only a small fraction of the total ion exchange membrane. 1 The presence of 9.8% H results in a weak signal intensity. Therefore, there is an urgent need to develop a liquid NMR detection method that can maintain the intrinsic microstructure of ion exchange membrane materials and distinguish between different chemical environments (e.g., 35Cl) for analyzing the microstructural properties of anion exchange membranes. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is how to detect the NMR signal of chlorine atoms in ion exchange membranes, thereby providing a method and application for detecting chlorine atoms in ion exchange membranes.

[0008] To this end, the present invention provides the following technical solution.

[0009] This invention provides a method for detecting chlorine atoms in an ion exchange membrane, comprising the following steps:

[0010] (1) The soaked ion exchange membrane is made into a strip sample, and the strip sample is inserted into the bottom of an NMR tube to prepare an NMR tube containing the ion exchange membrane sample; the ion exchange membrane is a strip with a length of 4.5-5.5 cm and a width of 2.5-3.5 mm; or,

[0011] The soaked ion exchange membrane is made into a sample, which is then wound onto a uniform rod. The sample is then inserted into the bottom of the NMR tube by a screw-in method. The rod is then removed or left in the NMR tube to prepare an NMR tube containing the ion exchange membrane sample. The shape of the ion exchange membrane includes a polygon with a symmetrical structure and at least 4 sides. The ion exchange membrane sample is placed in a regular, orderly, and uniform manner inside the NMR tube.

[0012] It should be clarified 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 falls under the category of soaking. It should be noted that during sample preparation, the soaking solution for the ion exchange membrane includes substances capable of dissociating Cl-. - Compounds that can dissociate Cl. - The compound is selected from any of the chlorine compounds described below. The soaking solution for the ion exchange membrane may be the same as or different from the chloride-containing solution, preferably the same.

[0013] (2) Place the nuclear magnetic tube into the nuclear magnetic resonance spectrometer, select the pulse sequence, tune and shim the field, adjust the nuclear magnetic resonance test parameters, and acquire the signal; the nuclear magnetic resonance test parameters include: 90° pulse width of 15-22μs; power of 100-200W.

[0014] This invention utilizes the principle of liquid NMR to acquire the signals of the atoms to be measured: After the ion exchange membrane is immersed in a solution, it swells. Because the exchange membrane can selectively transmit ions (e.g., chlorine), ions and water molecules coexist within the bulk phase of the ion exchange membrane. That is, ions and water molecules form countless microscopic liquid environments within the ion exchange membrane. Therefore, liquid NMR can successfully detect the NMR signals of atoms in the ion exchange membrane. The NMR samples prepared using the method of this invention have advantages such as simple sample preparation, good shimming effect, high detection sensitivity, and high spectral resolution.

[0015] Ion exchange membranes possess ion-selective transport properties, allowing Cl to be transported during the immersion process. - Chlorine atoms remain inside the ion exchange membrane phase. The concentration of chlorine atoms in the ion exchange membrane is low, and current NMR detection techniques are limited by low signal-to-noise ratios, making it impossible to detect chlorine atoms inside the membrane. - Accurate analysis is achieved. This invention prepares specific NMR samples and conducts tests under specific NMR parameters. Without damaging the structural state of the ion exchange membrane, it can collect NMR signals of chlorine atoms inside the bulk phase of the ion exchange membrane, providing strong support for the detection and analysis of structural information within the ion exchange membrane.

[0016] It should be noted that the size of the strip sample can be determined according to the size of the NMR tube. For example, the strip sample length is 4.5-5.5 cm and the width is 2.5-3.5 mm. Exemplary polygons include quadrilaterals, pentagons, hexagons, etc., and the polygons must have at least 4 sides and a symmetrical structure. Polygons also include chamfers and / or rounded corners. The shape of the ion exchange membrane sample is related to its rigidity. Preferably, the ion exchange membrane sample is wound around a uniform rod and inserted into the bottom of the NMR tube using a screw-in method, thereby preparing an NMR tube containing the ion exchange membrane sample. When the ion exchange membrane is too rigid to be wound around the NMR tube, it is cut into strips and neatly inserted into the bottom of the NMR tube. During sample preparation, this invention requires the ion exchange membrane to be placed neatly, orderly, and uniformly within the NMR tube.

[0017] 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, where k is 1024; sampling time: 1-5s; spectral width of 600ppm; spectral range of -300ppm to +300ppm; and number of accumulations: 128-4096.

[0018] As an optional implementation, the 90° pulse width is 16–20 μs; the power is 120–190 W;

[0019] Preferably, the spectral width is 200 ppm, and the spectral range is -200 ppm to +100 ppm.

[0020] For example, the 90° pulse width is 16μs, 18μs, 19μs, 20μs, etc.; the power is 120W, 130W, 150W, 170W, 190W, etc.

[0021] As an optional implementation, step (2) further includes adding 5-10 μL of chloride-containing solution before placing the NMR tube into the NMR spectrometer. The method of the present invention can also simultaneously detect the NMR signals of chlorine atoms inside the ion exchange membrane and chlorine atoms outside the membrane (free state, i.e., chlorine atoms in the chloride-containing solution in the NMR tube). Based on the difference in chemical shift of the NMR signals of chlorine atoms inside and outside the anion exchange membrane, the transport performance of the anion exchange membrane for chlorine atoms can be determined, providing strong support for the structural performance analysis of anion exchange membranes, and thus providing a new approach for screening the special functions of anion exchange membranes used in different fields.

[0022] Preferably, the concentration of the chloride-containing solution is 0.5–2.0 mol / L;

[0023] Preferably, the concentration of the chloride-containing solution is 1.0 mol / L.

[0024] As an optional implementation, the chloride includes a component capable of dissociating Cl. - Compounds.

[0025] As an optional implementation, the chloride includes organic chlorides and / or inorganic chlorides; and / or, the chloride includes soluble chloride salts;

[0026] Preferably, the inorganic chloride includes at least one of KCl, NaCl, LiCl, and NH4Cl;

[0027] Preferably, the organochlorine includes at least one of tetramethylammonium chloride, tetraethylammonium chloride, hexadecyltrimethylammonium chloride, acyl chloride, and sulfonyl chloride.

[0028] As an optional implementation, the solvent in the chloride-containing solution includes a deuterated solvent or a non-deuterated solvent;

[0029] Preferably, the solvent includes at least one selected from water, chloroform (CHCl3), dimethyl sulfoxide (DMSO), dichloromethane (CH2Cl2), methanol, and ethanol;

[0030] Preferably, when the solvent in the chloride-containing solution includes a deuterated solvent, a field locking process is also included before shimming.

[0031] As an optional implementation, the ion exchange membrane is an anion exchange membrane; preferably, the ion exchange membrane is derived from a battery; and / or,

[0032] The chlorine atom is 35Cl.

[0033] It should be noted that after selecting the pulse sequence, the 35Cl tuning channel is selected. Different nuclides have different resonance frequencies, therefore they need to be tuned and matched independently. The 35Cl tuning channel is on the X channel. Taking a 600MHz resonance spectrometer as an example, its resonance frequency is 58.8MHz. The resonance frequency of each nuclide in the detection instrument is related to the field strength of the detection instrument and the type of nuclide. Those skilled in the art can determine the resonance frequency based on the specific nuclide and the field strength of the detection instrument.

[0034] Ion exchange membranes can be commercially available, such as Fumasep FAA-3-PK-130 and Sustainion X37-50 Grade T. They can also come from devices that incorporate ion exchange membranes, such as diaphragms in fuel cells, electrodialysis units, or electrolysis units. When the ion exchange membrane is a commercially available model and has not been used, it needs to be soaked first. The soaking time is not specifically limited, and can be anything from 2 hours to 30 hours, as long as it allows the membrane to swell and contains ions and water molecules.

[0035] As an optional implementation, the ion exchange membrane is square in shape, and 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 rod material, as long as it can be wound around the rod. Square includes squares, rectangles, etc.; and / or,

[0036] The diameter of the rod is 2-3 mm; and / or,

[0037] The rod material includes a rubber rod, a glass rod, or a metal rod; and / or,

[0038] The rod is a hollow cylinder.

[0039] The rod is a hollow cylinder, meaning 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 saves on the amount of deuterated reagent used.

[0040] 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 chlorine atom signals in used ion exchange membranes, providing strong support for the structural performance analysis of ion exchange membranes.

[0041] The technical solution of this invention has the following advantages:

[0042] 1. This invention provides a method for detecting chlorine atoms in an ion-exchange membrane, comprising (1) preparing a nuclear magnetic resonance (NMR) tube containing an ion-exchange membrane sample; (2) placing the NMR tube into a nuclear magnetic resonance (NMR) 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 15–22 μs; and a power of 100–200 W. The ion-exchange membrane has ion-selective transport characteristics, allowing chlorine atoms to be detected during the immersion process. - Chlorine atoms remain inside the membrane phase. The concentration of chlorine atoms in ion exchange membranes is low, and current NMR detection techniques are limited by low signal-to-noise ratios, making it impossible to detect chlorine atoms inside the membrane. - Accurate analysis is achieved. After preparing the NMR sample according to this invention, testing is performed under specific NMR parameters. Without damaging the ion exchange membrane structure, the NMR signal of chlorine atoms inside the ion exchange membrane can be acquired, providing strong support for the detection and analysis of the internal structure of the ion exchange membrane. Conventional liquid NMR sample preparation methods mainly acquire signals from free-state atoms, namely chlorine atoms in the NMR tube solution (located outside the membrane), and cannot detect chlorine atom signals on the ion exchange membrane. Using the sample preparation method of this invention combined with the detection method of this invention, the NMR signal of chlorine atoms on the ion exchange membrane can be detected.

[0043] This detection method can also be used to detect ion exchange membranes already in use, providing strong support for their structural performance analysis. Attached Figure Description

[0044] 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.

[0045] Figure 1 This is the NMR spectrum obtained from Example 1 of the present invention;

[0046] Figure 2 This is the NMR spectrum obtained from the test in Example 2 of this invention;

[0047] Figure 3 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

[0048] 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.

[0049] 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.

[0050] Example 1

[0051] This embodiment provides a method for detecting chlorine atoms in an ion exchange membrane, comprising the following steps:

[0052] (1) Immerse the ion exchange membrane (AMI-7001S anion exchange membrane) in a 1 mol / L NaCl solution for 24 hours. After removing and drying, cut the ion exchange membrane into a length of 5 cm and a width of 3 mm. Evenly pack the sample into the bottom of the NMR tube. The state of the ion exchange membrane inside the NMR tube is shown in the figure. Figure 3 The ion exchange membranes are neatly and uniformly placed inside the NMR tube.

[0053] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The NMR test parameters include: 90° pulse width of 18 μs; power of 150 W; pulse sequence of zg; relaxation time of 1 s; number of sampling points of 32768; sampling time of 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; and number of accumulations of 3200. The instrument used is a 600 MHz liquid NMR spectrometer with a resonance frequency of 58.8 MHz.

[0054] See NMR spectrum Figure 1 As can be seen from the figure, this embodiment can collect chlorine atom signals. Due to the restricted movement of 35Cl atoms inside the ion exchange membrane, the transverse relaxation time (T2) of 35Cl is shortened, the spectral peak is broadened, and the signal is weakened.

[0055] Example 2

[0056] This embodiment provides a method for detecting chlorine atoms in an ion exchange membrane, comprising the following steps:

[0057] (1) Immerse the ion exchange membrane (same as in Example 1) in 1 mol / L NaCl solution, take it out and wipe it dry, cut the ion exchange membrane into a length of 5 cm and a width of 3 mm, and put it into the bottom of the NMR tube; add 5 μL of 1 mol / L NaCl solution into the NMR tube.

[0058] (2) Place the NMR tube into the NMR spectrometer, tune and shim it. The NMR test parameters include: 90° pulse width of 18 μs; power of 150 W; pulse sequence of zg; relaxation time of 1 s; number of sampling points of 32768; sampling time of 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; and number of accumulations of 3200. The instrument used is a 600 MHz liquid NMR spectrometer with a resonance frequency of 58.8 MHz.

[0059] See NMR spectrum Figure 2 As shown in the figure, two chlorine atom signals can be detected. The low-field signal (i.e., the peak on the left) is the NMR signal of 35Cl inside the membrane, and the high-field signal (i.e., the peak on the right) is the NMR signal of 35Cl outside the membrane. Because the content of 35Cl outside the membrane is higher and its movement rate is faster, its signal is stronger. This invention can simultaneously detect the NMR signals of 35Cl inside and outside the membrane.

[0060] Comparative Example 1

[0061] This comparative example provides a method for detecting chlorine atoms in an ion exchange membrane, comprising the following steps:

[0062] (1) Immerse the ion exchange membrane in a 1 mol / L NaCl solution, take it out, wipe it dry, cut it into small segments and insert it directly into the NMR tube. The ion exchange membrane is in the NMR tube in the form of irregular small segments, with a length of about 1 cm and a width of 3 mm.

[0063] (2) The NMR tube was placed in the NMR spectrometer. The NMR test parameters included: 90° pulse width of 18 μs; power of 150 W; pulse sequence of zg; relaxation time of 1 s; number of sampling points of 32768; sampling time of 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; number of accumulations of 3200. After tuning and shimming, sampling was performed. The instrument was a 600 MHz liquid NMR spectrometer with a resonance frequency of 58.8 MHz. No NMR signal of 35Cl was obtained after sampling.

[0064] 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 a chlorine atom in an ion exchange membrane, characterized by, Includes the following steps: (1) The soaked ion exchange membrane is made into a strip sample, and the strip sample is inserted into the bottom of an NMR tube to prepare an NMR tube containing the ion exchange membrane sample; the ion exchange membrane is a strip with a length of 4.5-5.5 cm and a width of 2.5-3.5 mm; or, The soaked ion exchange membrane is made into a sample, which is then wound around a uniform rod. The sample is then inserted into the bottom of an NMR tube by a screw-in method. The rod is then removed or left in the NMR tube to prepare an NMR tube containing the ion exchange membrane sample. The shape of the ion exchange membrane includes a polygon with a symmetrical structure and at least 4 sides. (2) Place the nuclear magnetic tube into the nuclear magnetic resonance spectrometer, select the pulse sequence, tune and shim the field, adjust the nuclear magnetic resonance test parameters, and acquire the signal; The nuclear magnetic resonance test parameters include: a 90° pulse width of 15~22μs; The power is 100~200W.

2. The detection method according to claim 1, characterized in that, The nuclear magnetic resonance testing 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: 600ppm; spectral range: -300ppm~+300ppm; number of accumulations: 128~4096.

3. The detection method according to claim 2, characterized in that, 90° pulse width is 16~20μs; power is 120~190W; and / or, The spectral width is 200 ppm, and the spectral range is -100 ppm to +100 ppm.

4. The method of claim 1, wherein, Step (2) further includes adding 5-10 μL of chloride-containing solution before placing the NMR tube into the NMR spectrometer.

5. The detection method according to claim 4, characterized in that, The chloride includes a compound capable of dissociating Cl - and / or, The concentration of the chloride-containing solution is 0.5~2.0 mol / L.

6. The detection method according to claim 5, characterized in that, The chloride includes organic chlorides and / or inorganic chlorides; and / or, the chloride includes soluble chloride salts; and / or, The concentration of the chloride-containing solution is 1.0 mol / L.

7. The detection method according to claim 6, characterized in that, The solvent in the chloride-containing solution includes deuterated solvents or non-deuterated solvents; and / or, The inorganic chloride includes at least one selected from KCl, NaCl, LiCl, and NH4Cl; and / or, The organochlorine includes at least one of tetramethylammonium chloride, tetraethylammonium chloride, hexadecyltrimethylammonium chloride, acyl chloride, and sulfonyl chloride.

8. The detection method according to claim 7, wherein the solvent comprises at least one selected from water, chloroform, dimethyl sulfoxide, dichloromethane, methanol, and ethanol; and / or, When the solvent in the chloride-containing solution includes a deuterated solvent, a field locking process is also included before shimming.

9. The method of claim 1, wherein, The ion exchange membrane is an anion exchange membrane; and / or, The chlorine atom is 35Cl.

10. The detection method according to claim 9, characterized in that, The ion exchange membrane 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; and / or, The ion exchange membrane is derived from a battery.

11. The application of the detection method according to any one of claims 1 to 10 in detecting the membrane in a fuel cell, an electrodialysis device, or an electrolysis device.

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