Preparation method and application of NH2-UiO-66 encapsulating sulfamic acid

Abstract

The application discloses a preparation method of NH2-UiO-66 encapsulated sulfamic acid and proton conduction performance thereof. The preparation method of the NH2-UiO-66 encapsulated sulfamic acid is prepared by using a solvothermal reaction of zirconium tetrachloride and 2-amino terephthalic acid, first synthesizing NH2-UiO-66, and then using a dynamic continuous concentration method to encapsulate sulfamic acid into the pores inside the NH2-UiO-66 material. The preparation method has the advantages of simple preparation process, short encapsulation time, obvious improvement of material proton conductivity, high cycle stability, and the like. More importantly, the interaction between the Lewis base group on the MOF and the guest molecules is utilized to successfully introduce a significant number of amphoteric proton carriers in a mild and rapid method, and the test performance can be maintained for a long time.

Description

Technical Field

[0001] This invention belongs to the field of proton exchange membrane material preparation, and relates to a method for preparing NH2-UiO-66 encapsulated aminosulfonic acid and its proton conduction properties. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are considered one of the most promising power sources for future electric vehicles due to their high conversion efficiency, significant power density, cleanliness, and sustainability. The proton exchange membrane, as a core component of PEMFCs, plays a crucial role in proton transport and the barrier function between the anode and cathode electrolytes. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their high porosity, high specific surface area, tunable structure, and modifiability. Effective proton transfer within MOFs can be achieved by encapsulating or grafting with substances such as acids, bases, histamines, triazoles, imidazoles, or ionic liquids to increase proton carriers (acid / base) within the pores, constructing continuous hydrogen bonding pathways, or increasing the proton concentration within the pores. Among the many MOF materials, NH2-UiO-66 is a highly representative amino MOF. Derived from UiO-66, it is based on the connection of Zr-O cluster secondary building blocks (SBUs) with 2-aminoterephthalic acid, exhibiting excellent chemical stability, thermal stability, and ultra-high water stability. The bridging ligands, with different connection methods to the metal, create triangular windows of 0.6 nm and 1.0 nm. The amino groups within the pores exhibit weak basicity or electron-donating properties, meaning that NH2-UiO-66 has the ability to encapsulate acidic or amphoteric molecules to enhance proton transport.

[0003] It has extremely high proton conductivity (σ≥10) -1 In MOF materials with a density of s·cm⁻¹, strongly acidic molecules such as H₂SO₄ and H₃PO₄ are confined within and used as proton sources and carriers. However, these strongly acidic molecules attack metal-ligand bonds / inorganic clusters, disrupting the original MOF structure. Only a very few strongly acid-resistant MOFs or covalent organic frameworks (COFs) meet this condition. Although confining weakly acidic guest molecules or functionalized groups within the pores of MOFs generally results in lower proton conductivity, the MOF framework is not easily disrupted. Therefore, it is necessary to encapsulate as many guest molecules beneficial to proton transport as possible, within the limits of MOF material stability, to enhance proton conductivity. Aminosulfonic acid (H₂NSO₃H, HSA) molecules, which have moderately strong acidity (pKa=1), are dipoles and are typically... + H3NSO3 - It exists in solution in the form of a proton donor (NH4+). 3+ ) and proton acceptor (SO3- It can form a wide network of hydrogen bonds with water molecules or another aminosulfonic acid molecule to achieve efficient proton transport.

[0004] Immersion encapsulation of proton carriers is a simple and effective strategy to enhance the proton conductivity of MOF materials. Currently, MOF materials with excellent proton conductivity are mainly encapsulated with strong, non-volatile acids. This method is only suitable for a small number of highly stable MOF materials and suffers from problems such as long immersion times and easy leakage of the guest molecules. To address this issue, exploring new methods for encapsulating guest molecules and novel proton carriers is crucial. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing NH2-UiO-66 encapsulated aminosulfonic acid and its proton-conducting material. The NH2-UiO-66 material encapsulated with aminosulfonic acid exhibits strong stability, high encapsulation efficiency, high proton conductivity, and good cycle stability.

[0006] This invention provides a method for preparing NH2-UiO-66 encapsulated aminosulfonic acid and its proton-conducting material, the composition and mass percentage content of which are: NH2-UiO-66 16~36% and aminosulfonic acid 64~84%.

[0007] This invention provides a method for preparing NH2-UiO-66 encapsulated aminosulfonic acid, comprising the following steps:

[0008] (1) Dissolve zirconium salt and ligand in solvent, add acetic acid and carry out solvothermal reaction to obtain NH2-UiO-66;

[0009] (2) Dissolve aminosulfonic acid in anhydrous methanol, add NH2-UiO-66, stir at 40-50℃ for 1h-3h, and continue stirring at room temperature for 18h-24h. After filtration, activate the obtained product to obtain NH2-UiO-66-encapsulated aminosulfonic acid.

[0010] The zirconium salt mentioned in step (1) is selected from any one of zirconium tetrachloride, basic zirconium tetrachloride, and zirconium nitrate. The organic ligand mentioned in this invention is 2-aminoterephthalic acid.

[0011] In step (1), the solvothermal reaction temperature is 120℃, the reaction time is 24~72 h, and the vacuum drying is carried out at 120℃ for 24 h.

[0012] The mass percentage content in step (2) is: NH2-UiO-66 16~36%, aminosulfonic acid 64~84%.

[0013] The activation process in step (2) is carried out under vacuum conditions.

[0014] The activation temperature is 70-90℃, and the activation time is 10-15 hours.

[0015] Another technical solution of the present invention is to provide a proton-conducting material, comprising NH2-UiO-66 encapsulated aminosulfonic acid prepared by the preparation method described above.

[0016] This invention provides a method for testing the proton conduction performance of NH2-UiO-66 encapsulated aminosulfonic acid, comprising the following steps:

[0017] (1) Place the samples before and after soaking in NH2-UiO-66 with aminosulfonic acid in an 80℃ vacuum drying oven and dry for 12 h. Use a spatula to take 5-10 mg of the dried sample and pour it into the tableting chamber, pressurize to 0.38 Gpa, stabilize for more than 20 seconds, and then remove the sample to compress it into tablets.

[0018] (2) Place the plate on a glass slide, cover it with a gold wire, and fix both ends with insulating glue. Then apply conductive silver paste to the top of the plate and let it stand for half a minute. After the conductive silver paste is completely dry, flip the plate over and repeat the operation. Wrap the ends of the two gold wires covering the top and bottom of the plate with the conductive posts of the square test stage, and then place it in a constant temperature and humidity chamber. Connect it to the square test stage through wires to perform AC impedance testing.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention provides an NH2-UiO-66 encapsulated aminosulfonic acid method that encapsulates aminosulfonic acid using a continuous dynamic concentration encapsulation method. Compared with conventional immersion encapsulation, this method has a shorter preparation time, milder synthesis conditions, higher encapsulation capacity, and significantly improved proton conductivity and good cycle stability of the material.

[0021] 2. The present invention provides an NH2-UiO-66 encapsulation of aminosulfonic acid, which makes the guest less prone to leakage. Compared with MOFs materials that encapsulate low-boiling-point, high-acid molecules, it prolongs the retention time of the proton source guest and can maintain high conductivity for a long time. Attached Figure Description

[0022] Figure 1 This is a comparison chart of NH2-UiO-66 and simulated PXRD in Example 4.

[0023] Figure 2 The image shows a comparison of PXRD values ​​of NH2-UiO-66 after soaking in aminosulfonic acid solutions of different concentrations in Example 4.

[0024] Figure 3 This is a comparison of PXRD values ​​for different heating times when NH2-UiO-66 was soaked in aminosulfonic acid solution in Example 4.

[0025] Figure 4 This is a comparison image of the NH2-UiO-66 before and after soaking in aminosulfonic acid solution in Example 4.

[0026] Figure 5 The image shows an infrared comparison of NH2-UiO-66 before and after immersion in aminosulfonic acid solution in Example 4.

[0027] Figure 6 This is a comparison diagram of saturated N2 adsorption and desorption before and after soaking NH2-UiO-66 in aminosulfonic acid solution in Example 4.

[0028] Figure 7 This is a schematic diagram of the pore distribution before and after immersion in aminosulfonic acid solution in Example 4 of NH2-UiO-66.

[0029] Figure 8 The diagram shows the proton conductivity of NH2-UiO-66 in Example 4.

[0030] Figure 9 This is a proton conductivity diagram of NH2-UiO-66 after soaking in aminosulfonic acid solution in Example 4.

[0031] Figure 10 This is an Arrhenius fitting diagram of NH2-UiO-66 after soaking in aminosulfonic acid solution in Example 4.

[0032] Figure 11 The diagram shows the 7-day cyclic conductivity of NH2-UiO-66 after soaking in aminosulfonic acid solution in Example 4.

[0033] Figure 12 The Nyquist plot is obtained after NH2-UiO-66 was soaked in aminosulfonic acid solution and left for 210 days in Example 4. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] (1) Dissolve ZrCl4 (0.5592 g, 2.4 mmol) and H2BDC-NH2 (0.4348 g, 2.4 mmol) in 60 ml DMF, slowly add 7.2 ml acetic acid, and put the mixed solution into a polytetrafluoroethylene bottle and keep it in an oven at 120℃ for 72 h. After natural cooling, centrifuge, wash the sample with 5 ml pure water and 5 ml anhydrous methanol, and vacuum dry at 120℃ for 24 h to obtain activated NH2-UiO-66 sample.

[0037] (2) Dissolve 0.0291 g of aminosulfonic acid in 20 ml of anhydrous methanol to prepare a 0.3 mol / L solution. Add 100 mg of activated NH2-UiO-66, stir at 45 °C for 2 h, then turn off the heating and continue stirring for 18 h to allow the anhydrous methanol to evaporate. After packaging, filter the solution, wash three times with 3 ml of ethanol, and activate it at 80 °C under vacuum for 12 h to obtain aminosulfonic acid / NH2-UiO-66.

[0038] Example 2

[0039] (1) Dissolve ZrCl4 (0.5592 g, 2.4 mmol) and H2BDC-NH2 (0.4348 g, 2.4 mmol) in 60 ml DMF, slowly add 7.2 ml acetic acid, and put the mixed solution into a polytetrafluoroethylene bottle and keep it in an oven at 120℃ for 48 h. After natural cooling, centrifuge, wash the sample with 5 ml pure water and 5 ml anhydrous methanol, and vacuum dry at 120℃ for 24 h to obtain activated NH2-UiO-66 sample.

[0040] (2) Dissolve 0.0291 g of aminosulfonic acid in 20 ml of anhydrous methanol to prepare a 0.3 mol / L solution. Add 100 mg of activated NH2-UiO-66, stir at 45 °C for 2 h, then turn off the heating and continue stirring for 18 h to allow the anhydrous methanol to evaporate. After packaging, filter the solution, wash three times with 3 ml of ethanol, and activate it at 80 °C under vacuum for 12 h to obtain aminosulfonic acid / NH2-UiO-66.

[0041] Example 3

[0042] (1) Dissolve ZrCl4 (0.2796 g, 1.2 mmol) and H2BDC-NH2 (0.2174 g, 1.2 mmol) in 30 ml DMF, slowly add 3.6 ml acetic acid, put the mixed solution into a polytetrafluoroethylene bottle, and keep it in an oven at 120℃ for 24 h. After natural cooling, centrifuge, wash the sample with 5 ml pure water and 5 ml anhydrous methanol, and vacuum dry at 120℃ for 24 h to obtain activated NH2-UiO-66 sample.

[0043] (2) Dissolve 0.0291 g of aminosulfonic acid in 20 ml of anhydrous methanol to prepare a 0.3 mol / L solution. Add 100 mg of activated NH2-UiO-66 and stir at 45 °C for 1 h, 2 h, or 3 h respectively. Then turn off the heating and continue stirring for 18 h to allow the anhydrous methanol to evaporate. After packaging, filter the solution, wash it three times with 3 ml of ethanol, and activate it at 80 °C under vacuum for 12 h to obtain aminosulfonic acid / NH2-UiO-66.

[0044] Example 4

[0045] (1) Dissolve ZrCl4 (0.2796 g, 1.2 mmol) and H2BDC-NH2 (0.2174 g, 1.2 mmol) in 30 ml DMF, slowly add 3.6 ml acetic acid, put the mixed solution into a polytetrafluoroethylene bottle, and keep it in an oven at 120℃ for 24 h. After natural cooling, centrifuge, wash the sample with 5 ml pure water and 5 ml anhydrous methanol, and vacuum dry at 120℃ for 24 h to obtain activated NH2-UiO-66 sample.

[0046] (2) Sulfamic acid (0.0097 g, 0.0194 g, 0.0291 g, 0.0388 g, 0.0485 g) was dissolved in 20 ml of anhydrous methanol to prepare 0.1 M, 0.2 M, 0.3 M, 0.4 M, and 0.5 M solutions, respectively. 100 mg of activated NH2-UiO-66 was added, and the mixture was stirred at 45 °C for 2 h. The heating was then turned off, and stirring was continued for 18 h to allow the anhydrous methanol to evaporate. After packaging, the mixture was filtered, washed three times with 3 ml of ethanol, and activated at 80 °C under vacuum for 12 h to obtain sulfamic acid / NH2-UiO-66.

[0047] Performance testing:

[0048] 1. Frame Structure Analysis

[0049] The activated NH2-UiO-66 sample prepared in step (1) of Example 4 was continuously scanned using graphite monochromatic copper target X-rays (λ=1.5406 Å) in the range of 5° to 50° at a step size of 0.02° / min and a speed of 5° / min. The scanned results were compared with the single-crystal simulated powder diffraction pattern on Mercury software. The comparison of the two spectra showed that the peak positions of the activated NH2-UiO-66 sample prepared in step (1) of Example 4 were completely consistent with those of the single-crystal simulated powder diffraction pattern, and there were no extra diffraction impurities. This indicates that the activated NH2-UiO-66 sample synthesized in this step is pure NH2-UiO-66. The powder diffraction comparison pattern is shown in [reference needed]. Figure 1 .

[0050] 2. Optimal Encapsulation Concentration Analysis

[0051] Aminosulfonic acid was encapsulated in aminosulfonic acid solutions of different concentrations according to the specific steps in Example 4. Diffraction patterns were obtained after testing. Figure 2As shown in the figure, the crystallinity of activated NH2-UiO-66 gradually decreases with the increase of aminosulfonic acid concentration. Impurities appear in the diffraction peaks after the aminosulfonic acid concentration is greater than 0.3 mol / L. In order to maintain the stability and purity of the activated NH2-UiO-66 sample during the encapsulation of aminosulfonic acid, 0.3 mol / L was selected as the optimal encapsulation concentration.

[0052] 3. Optimal Packaging Time Analysis

[0053] The effect of different heating times was investigated in a 0.3 mol / L aminosulfonic acid solution according to the specific steps in Example 3. Diffraction patterns were obtained after the tests. Figure 3 As shown in the figure, impurities appear in the powder diffraction pattern as the heating time increases. Therefore, a heating time of 2 hours is recommended.

[0054] 4. Infrared analysis

[0055] Two samples from Example 4, before and after immersion in 0.3 mol / L aminosulfonic acid solution (e.g., NH2-UiO-66), were compared. Figure 4 After drying at 80℃ for 1 day, infrared testing was performed, and the infrared spectrum is shown below. Figure 5 As shown, at 1002 cm -1 and 1064 cm -1 The stretching vibration peak of O=S=O is at 1215 cm⁻¹. -1 A new peak appeared, which can be attributed to the vibration of the CS bond. 3300 cm⁻¹ -1 The bimodal absorption of primary amines changed to a single-peak absorption of secondary amines, and the blue shift occurred at 3147 cm⁻¹. -1 Therefore, it can be inferred that aminosulfonic acid readily combines with the primary amine group on the activated NH2-UiO-66 to form new chemical bonds and extensive hydrogen bonds.

[0056] 5. BET specific surface area analysis

[0057] The specific surface area of ​​the samples was tested using an adsorption-desorption experiment based on saturated nitrogen. Before the gas adsorption experiment, two samples from Example 4, before and after soaking in 0.3 mol / L aminosulfonic acid solution (NH2-UiO-66), were deeply activated: 100 mg of sample was weighed and solvent-exchanged with 10 ml of anhydrous methanol at room temperature for three days, with the solvent changed every 8 hours (10 ml × 12 times). The supernatant was then removed by centrifugation, and the resulting sample was activated in a 120℃ vacuum drying oven for 24 h. Finally, it was activated again at 120℃ for 6 h on a BET instrument to completely remove anhydrous methanol molecules from the sample. The fully activated sample was then tested for adsorption of saturated nitrogen at 77 K. The saturated nitrogen adsorption-desorption results are as follows: Figure 6 , 7As shown, at 77 K and 1 standard atmosphere, the saturated nitrogen adsorption capacity of the two samples before and after immersion in aminosulfonic acid solution was 210.75 cm⁻¹. 3 / g and 301.61 cm 3 / g, and the surface areas of the two samples were evaluated by computer fitting of the adsorption-desorption results, which were 642.23m². 2 / g and 899.54 m 2 / g. The total test pore volume for the two samples was 0.3277 cm³. 3 / g and 0.4690 cm 3 / g. In contrast, the total amount of N2 adsorbed, the specific surface area, and the pore volume of the NH2-UiO-66 sample after soaking in aminosulfonic acid solution were significantly reduced, confirming that a large number of aminosulfonic acid molecules exist inside the pores of the NH2-UiO-66 sample.

[0058] 6. AC Impedance Testing and Analysis

[0059] The sample impedance and proton conductivity are related to the amino groups on the framework, the aminosulfonic acid in the pores, water molecules, and the hydrogen bonds formed by these three. Two samples (20 mg each from Example 4, before and after immersion in 0.3 mol / L aminosulfonic acid solution) were separately compressed into tablets using a micro-tablet. The tablets were then subjected to impedance analysis using an XK-CTS80Z thermo-humidifier and a Solartron S1-1260 and S1-1296 EIS impedance analyzer. The analytical results are as follows: Figure 8 , 9 As shown, the conductivity of the activated NH2-UiO-66 sample at 70℃ and 98%RH is 3.24 × 10⁻⁶. -5 The conductivity of the sample encapsulated with NH2-UiO-66 and containing aminosulfonic acid reached 0.172 S / cm at 90℃ and 98%RH, which is 10 times that of the activated NH2-UiO-66 sample. 5 The activation energy obtained by least squares fitting is 0.38 eV, as shown below. Figure 10 As shown, this confirms that a large number of aminosulfonic acid molecules and water molecules within the pores form a long-range ordered hydrogen bond network, which plays a very important role in proton transport. Samples of NH2-UiO-66 encapsulated with aminosulfonic acid from Examples 1 and 2 were tested under the same conditions, and the conductivity was 0.168 S / cm and 0.170 S / cm, respectively.

[0060] 7. Stability Analysis

[0061] A good material not only needs outstanding performance but also good stability and cycleability to ensure its long-term use and storage. The sample from Example 4, after being soaked in a 0.3 mol / L aminosulfonic acid solution, was continuously tested for 7 days at 98% humidity and 90°C. The test results are as follows... Figure 11 As shown, its conductivity decreased by only 2%, which is almost negligible. Subsequently, XRD diffraction was performed on the compressed tablet after testing, and the diffraction pattern was found to be basically consistent with that before the test, proving that the main framework was not damaged and the cycling performance was excellent. Later, the NH2-UiO-66 sample from Experiment 4, which had been placed in an open system at room temperature for 210 days, was immersed in a 0.3 mol / L aminosulfonic acid solution and subjected to AC impedance testing again. The test results are shown below. Figure 12 The study found that even after the sample was left exposed for 210 days, the proton conductivity still reached 0.160 S / cm, demonstrating the material's excellent stability.

[0062] In summary, NH2-UiO-66 encapsulated with aminosulfonic acid using this method exhibits very high proton conductivity, excellent cycling performance and stability, and the preparation process is simple, easy to operate, and has a short encapsulation time for aminosulfonic acid, resulting in a significant improvement in conductivity. It has great potential in the preparation of novel proton exchange membranes.

[0063] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. Use of NH2-UiO-66 encapsulating sulfamic acid in the preparation of a proton-conducting material, characterized in that, The preparation method of the NH2-UiO-66 encapsulating sulfamic acid comprises the following steps: (1) dissolving a zirconium salt and a ligand in a solvent, and then performing a solvothermal reaction after adding acetic acid to obtain NH2-UiO-66; (2) dissolving sulfamic acid in anhydrous methanol, adding NH2-UiO-66, stirring at 40-50 DEG C for 1h-3h, continuing to stir at room temperature for 18h-24h, filtering the obtained product, and activating the product to obtain NH2-UiO-66 encapsulating sulfamic acid, wherein the activation temperature is 70-90 DEG C, the activation time is 10-15h, and the activation process is performed under vacuum.

2. Use according to claim 1, characterized in that, The zirconium salt in step (1) is any one selected from the group consisting of zirconium tetrachloride, basic zirconium tetrachloride and zirconium nitrate.

3. Use according to claim 1, characterized in that, The solvothermal reaction temperature in step (1) is 120-140 DEG C, the reaction time is 24-72h, and the vacuum drying temperature is 110-120 DEG C, and the vacuum drying time is 12-24h.

4. Use according to claim 1, characterized in that, In step (2), the mass percentage content is: NH2-UiO-66 16-36%, and sulfamic acid 64-84%.

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