Method for detecting chlorine atoms in ion exchange membrane and application

Abstract

The invention belongs to the technical field of nuclear magnetic resonance detection, and particularly relates to a method for detecting 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) putting the nuclear magnetic tube into a nuclear magnetic resonance spectrometer, selecting a pulse sequence, 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 15-22 [mu] s; and the power is 100 to 200W. Test is carried out 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 structural state of the ion exchange membrane is not damaged, and powerful support is provided for detection and analysis of structural information in the ion exchange membrane.

Description

Technical Field

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

[0002] Ion exchange membranes are thin films made from polymer materials, typically plastics, adhesives, rubber, or other organic polymers. They include various functional films, such as optical films, water treatment films, battery separators, and conductive films. They are widely used in optical devices, photovoltaic power generation, wastewater treatment, element enrichment, desalination, lithium-ion batteries, and other fields in medicine, food, agriculture, and the chemical industry, offering broad application prospects. Detecting the internal structure, surface morphology, mechanical properties, and electrochemical performance of ion exchange membranes has long been a major research focus 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 perform quantitative analysis. Due to its precision, accuracy, and ability to penetrate deeply into the interior of a substance without destroying the sample, NMR spectroscopy has become an indispensable analytical tool in a wide range of disciplines, including chemistry, pharmacy, medicine, agriculture, environment, mining, and materials science.

[0004] Nuclear magnetic resonance (NMR) techniques can be categorized as liquid NMR and solid NMR, depending on the state of the material being examined. 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-state NMR can identify the molecular structure of dry solids and study dynamics and intermolecular interactions. Currently, solid-state NMR is widely used to determine the structural information of ion exchange membranes.

[0005] Due to the unique structural properties of ion exchange membranes, dissolution destroys their structural information. Directly rolling or cutting the membrane into NMR tubes results in poor field shimming and ineffective NMR signal detection, unlike solid-state NMR. Therefore, using liquid NMR to detect NMR signals without destroying the membrane structure is relatively rare, especially for detecting NMR signals from low-content heteroatoms in ion exchange membranes.

[0006] Liquid NMR technology has demonstrated unique value in biomedical research (exploration of physiological and pathological mechanisms, drug metabolism and treatment monitoring), materials and chemistry research (research on electrolyte systems and ion transport, catalysis and reaction mechanism analysis), environmental and industrial analysis (water quality and pollution monitoring), etc. by revealing the chemical environment and dynamic behavior of 35Cl. However, ion exchange membranes have special structural properties, and dissolution will destroy the structural information of ion exchange membranes. In addition, due to the spin quantum number (I) = 3 / 2 of 35Cl, the quadrupole moment signal is severely broadened (relaxation is fast), and the resolution is extremely low. In addition, the magnetic gyroscopic ratio (γ) of 3Cl is only 1 Therefore, it is urgent to develop a liquid NMR detection method that can maintain the intrinsic microstructure of ion exchange membrane materials and distinguish 35Cl in different chemical environments 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 nuclear magnetic signals 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 solutions.

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

[0010] (1) preparing a strip sample of the soaked ion exchange membrane, placing the strip sample into the bottom of a nuclear magnetic resonance tube, and preparing a nuclear magnetic resonance tube containing the ion exchange membrane sample; the ion exchange membrane is in the shape of 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, the sample is wrapped around a uniform rod, the sample is loaded into the bottom of a nuclear magnetic tube by screwing, the rod is pulled out or retained in the nuclear magnetic tube, and a nuclear magnetic tube containing the ion exchange membrane sample is prepared; the shape of the ion exchange membrane includes a polygon with a symmetrical structure and a side number of not less than 4; the ion exchange membrane sample is placed in a regular, orderly and uniform state in the nuclear magnetic tube.

[0012] It should be explained that soaking here refers to soaking the ion exchange membrane in a solution; or, if the ion exchange membrane is used in a liquid environment, this process also belongs to soaking. It should be noted that in the sample preparation process, the soaking solution of the ion exchange membrane includes a solution that can dissociate Cl - Compounds that can dissociate Cl - The compound is selected from any one of the following chlorine compounds. The ion exchange membrane soaking solution may be the same as or different from the chloride-containing solution, preferably the same.

[0013] (2) placing the nuclear magnetic resonance tube into a nuclear magnetic resonance spectrometer, selecting a pulse sequence, tuning and shimming, adjusting nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters include: a 90° pulse width of 15 to 22 μs; and a power of 100 to 200 W.

[0014] The present invention utilizes the principle of liquid NMR to collect atomic signals to be measured: An ion exchange membrane swells after being immersed in a solution. Because the exchange membrane selectively transmits ions (such as chlorine), ions and water molecules coexist within the bulk of the ion exchange membrane. This creates countless microscopic liquid environments within the ion exchange membrane. Therefore, liquid NMR can successfully detect the NMR signals of atoms within the ion exchange membrane. The NMR samples prepared using the present method offer advantages such as simple sample preparation, good field shimming, high detection sensitivity, and high spectral resolution.

[0015] The ion exchange membrane has the characteristics of ion selective transmission, which can make Cl - The chlorine atoms stay inside the ion exchange membrane. The concentration of chlorine atoms in the ion exchange membrane is low. The existing nuclear magnetic resonance detection technology is limited by the low signal-to-noise ratio and other problems, and it is impossible to detect the Cl inside the membrane. - The present invention prepares specific NMR test samples and performs tests under specific NMR test parameters. Without destroying the structural state of the ion exchange membrane, the NMR signals of chlorine atoms inside the ion exchange membrane bulk can be collected, 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 made according to the size of the nuclear magnetic tube. For example, the length of the strip sample is 4.5-5.5 cm and the width is 2.5-3.5 mm. For example, polygons include quadrilaterals, pentagons, hexagons, etc. The polygons satisfy that the number of sides is not less than 4 and have a symmetrical structure; polygons also include chamfers and / or rounded corners; the shape of the ion exchange membrane sample is related to its hardness. The present invention preferably winds the ion exchange membrane sample on a uniform rod and uses a screw-in method to load the sample into the bottom of the nuclear magnetic tube, thereby preparing a nuclear magnetic tube containing the ion exchange membrane sample. When the ion exchange membrane is relatively hard and cannot be wound around the nuclear magnetic tube, it is cut into strips and neatly loaded into the bottom of the nuclear magnetic tube. When preparing the sample, the present invention requires that the ion exchange membrane be placed neatly, orderly, and evenly in the nuclear magnetic tube.

[0017] 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; spectral width is 600ppm; spectrum range is: -300ppm to +300ppm, cumulative number of times: 128 to 4096 times.

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

[0019] Preferably, the spectrum width is 200 ppm, and the spectrum 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 embodiment, step (2) further includes adding 5 to 10 μL of a chloride-containing solution before placing the nuclear magnetic resonance tube into the nuclear magnetic resonance spectrometer; the method of the present invention can also simultaneously detect the nuclear magnetic signals of the chlorine atoms inside the ion exchange membrane body and the chlorine atoms outside the membrane body (free state, i.e., the chlorine atoms in the chloride-containing solution in the nuclear magnetic resonance tube), and judge the transport performance of the anion exchange membrane for chlorine atoms based on the difference in chemical shift of the nuclear magnetic signals of the chlorine atoms inside and outside the anion exchange membrane, which provides strong support for the structural performance analysis of the anion exchange membrane, and further provides a new idea for the screening of special functions of anion exchange membranes used in different fields.

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

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

[0024] As an optional embodiment, the chloride includes a compound capable of dissociating Cl - of compounds.

[0025] As an optional embodiment, the chloride includes organic chloride and / or inorganic chloride; and / or, the chloride includes a soluble chloride salt;

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

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

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

[0029] Preferably, the solvent comprises at least one of 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 lock step is further performed before field shimming.

[0031] As an optional embodiment, the ion exchange membrane is an anion exchange membrane; preferably, the ion exchange membrane comes 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 resonant frequencies, so independent tuning and matching are required. The 35Cl tuning channel is on the X channel. Taking the detection instrument as a 600MHz resonance spectrometer as an example, its resonant frequency is 58.8MHz. The resonant frequency of each nuclide in the detection instrument is related to the field strength of the detection instrument and the type of nuclide. The field of this field can determine the resonant 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 be sourced from devices equipped with ion exchange membranes, such as the diaphragms in fuel cells, electrodialysis devices, or electrolysis devices. Unused commercial ion exchange membranes require soaking. There are no specific soaking times, such as 2 hours, 5 hours, 10 hours, 15 hours, 20 hours, or 30 hours, as long as the membrane swells and contains ions and water molecules.

[0035] As an optional embodiment, the shape of the ion exchange membrane is square. When the sample is square, the length is 4 to 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 wrapped around the rod. Square includes square, rectangular, etc.; and / or,

[0036] The diameter of the rod is 2 to 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, that is, the rod can be an inner lining tube, and the hollow interior can be filled with liquid. At this time, deuterated reagents, such as deuterated water, deuterated DMSO, deuterated chloroform and other common deuterated reagents, can be added to the hollow of the rod. This can not only achieve a lock field to accurately locate the chemical shift of the atomic nucleus to be measured, but also avoid the influence of the deuterated reagent on the ion exchange membrane structure. At the same time, since deuterated reagents are relatively expensive, the use of an inner lining tube can achieve a lock field, and the use of deuterated reagents can also be saved.

[0040] 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 chlorine atomic signal of used ion exchange membranes, providing strong support for the analysis of the structure and performance of ion exchange membranes.

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

[0042] 1. The present invention provides a method for detecting chlorine atoms in an ion exchange membrane, comprising: (1) preparing a nuclear magnetic resonance tube containing an ion exchange membrane sample; (2) placing the nuclear magnetic resonance tube into a nuclear magnetic resonance spectrometer, selecting a pulse sequence, tuning, shimming, adjusting nuclear magnetic resonance test parameters, and collecting signals; the nuclear magnetic resonance test parameters include: a 90° pulse width of 15 to 22 μs; a power of 100 to 200 W. The ion exchange membrane has ion selective transmission characteristics, which can make Cl atoms - The chlorine atoms stay inside the membrane phase. The concentration of chlorine atoms in the ion exchange membrane is low. The existing nuclear magnetic resonance detection technology is limited by the low signal-to-noise ratio and other problems, and it is impossible to detect the Cl inside the membrane. - Accurate analysis. After the nuclear magnetic resonance detection sample is made by the present invention, it is tested under specific nuclear magnetic resonance test parameters. On the basis of not destroying the structural state of the ion exchange membrane, the nuclear magnetic signals of the chlorine atoms inside the ion exchange membrane can be collected, providing strong support for the detection and analysis of the structural information inside the ion exchange membrane. The signals collected by the conventional liquid nuclear magnetic sampling method are mainly free atoms, that is, chlorine atoms in the nuclear magnetic tube solution (located outside the membrane body), and the chlorine atom signals on the ion exchange membrane cannot be detected. By adopting the sample preparation method of the present invention and combining it with the detection method of the present invention, the nuclear magnetic signals of chlorine atoms on the ion exchange membrane can be detected.

[0043] This detection method can also be used to detect ion exchange membranes that have been used, providing strong support for their structural performance analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] 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.

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

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

[0047] Figure 3 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

[0048] 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.

[0049] 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.

[0050] Example 1

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

[0052] (1) Ion exchange membrane (anion exchange membrane AMI-7001S) was soaked in 1 mol / L NaCl solution for 24 hours. After removal, it was wiped dry. The ion exchange membrane was cut into a shape of 5 cm long and 3 mm wide. The sample was evenly loaded into the bottom of the NMR tube. The state of the ion exchange membrane in the NMR tube was shown in Fig. Figure 3 The ion exchange membrane is placed neatly and evenly in the nuclear magnetic tube.

[0053] (2) Place the NMR tube in the NMR spectrometer, tune, and homogenize. 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: 32768; sampling time: 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; accumulation times: 3200. The detection instrument is a 600 MHz liquid NMR spectrometer with a resonance frequency of 58.8 MHz.

[0054] NMR spectrum see Figure 1 As can be seen from the figure, this embodiment can collect chlorine atom signals. Since the movement of 35Cl atoms inside the ion exchange membrane is restricted, the transverse relaxation time (T2) of 35Cl becomes shorter, the spectrum peak broadens, and the signal becomes weaker.

[0055] Example 2

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

[0057] (1) The ion exchange membrane (same as in Example 1) was soaked in a 1 mol / L NaCl solution, removed and dried, and the ion exchange membrane was cut into a shape of 5 cm in length and 3 mm in width and placed at the bottom of an NMR tube; 5 μL of 1 mol / L NaCl solution was added to the NMR tube.

[0058] (2) Place the NMR tube in the NMR spectrometer, tune, and homogenize. 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: 32768; sampling time: 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; accumulation times: 3200. The detection instrument is a 600 MHz liquid NMR spectrometer with a resonance frequency of 58.8 MHz.

[0059] NMR spectrum see Figure 2 As can be seen from 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 high and its movement rate is fast, its signal is stronger. Therefore, the present 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) Ion exchange membranes were soaked in 1 mol / L NaCl solution, taken out and wiped dry, cut into small segments and directly inserted into the NMR tube. The ion exchange membranes appeared as irregular small segments in the NMR tube, with a length of about 1 cm and a width of 3 mm.

[0063] (2) The NMR tube was placed in an 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: 32768; sampling time: 1.38 s; spectral width of 200 ppm; spectral range of -100 ppm to +100 ppm; accumulation times: 3200 times. Tuning, field shimming, and sampling were performed. The detection 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 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 chlorine atoms in an ion exchange membrane, characterized in that: The following steps are involved: (1) preparing a strip sample of the soaked ion exchange membrane, placing the strip sample into the bottom of a nuclear magnetic resonance tube, and preparing a nuclear magnetic resonance tube containing the ion exchange membrane sample; the ion exchange membrane is in the shape of 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 formed into a sample, the sample is wound on a uniform rod, the sample is loaded into the bottom of a nuclear magnetic resonance tube by screwing, and the rod is withdrawn or retained in the nuclear magnetic resonance tube to prepare a nuclear magnetic resonance tube containing the ion exchange membrane sample; the shape of the ion exchange membrane includes a polygon with a symmetrical structure and a side number of not less than 4; (2) placing the NMR tube into a NMR spectrometer, selecting a pulse sequence, tuning and shimming, adjusting NMR test parameters, and collecting signals; The NMR test parameters include: 90° pulse width of 15 to 22 μs; The power is 100~200W.

2. The detection method according to claim 1, wherein 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; spectral width is 600ppm; spectrum range is: -300ppm to +300ppm, cumulative number of times: 128 to 4096 times.

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

4. The detection method according to claim 1, wherein The step (2) further comprises adding 5 to 10 μL of a chloride-containing solution before placing the NMR tube into the NMR spectrometer; Preferably, the concentration of the chloride-containing solution is 0.5 to 2.0 mol / L; Preferably, the concentration of the chloride-containing solution is 1.0 mol / L.

5. The detection method according to claim 4, characterized in that The chloride includes the chloride that can dissociate Cl - of compounds.

6. The detection method according to claim 5, characterized in that The chloride comprises an organic chloride and / or an inorganic chloride; and / or the chloride comprises a soluble chloride salt; Preferably, the inorganic chloride includes at least one of KCl, NaCl, LiCl, and NH4Cl; Preferably, the organic chloride comprises at least one of tetramethylammonium chloride, tetraethylammonium chloride, hexadecyltrimethylammonium chloride, acyl chloride and sulfonyl chloride.

7. The detection method according to claim 4, characterized in that The solvent in the chloride-containing 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 chloride-containing solution includes a deuterated solvent, a field lock step is further performed before field shimming.

8. The detection method according to claim 1, wherein The ion exchange membrane is an anion exchange membrane; preferably, the ion exchange membrane comes from a battery; and / or, The chlorine atom is 35Cl.

9. The detection method according to claim 1, wherein The ion exchange membrane 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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