A chromium phosphonate metal-organic framework material, a solvent-free preparation method thereof, and applications thereof

Abstract

The present invention belongs to the technical field of crystalline materials, and particularly relates to a chromium phosphonate metal organic framework material and a solvent-free preparation method and application thereof. The chemical formula is [Cr(H2BPD) 1.5 The preparation method comprises the following steps: mixing an organic ligand, p-terephthalenediphosphonic acid, with chromium chloride hexahydrate, grinding the mixture, heating the mixture, and, after completion of the reaction, spontaneously cooling the mixture to room temperature. The mixture is repeatedly washed with ethanol until the supernatant is colorless and transparent, and vacuum-dried to obtain a light green chromium phosphonate metal-organic framework material. The chromium phosphonate metal-organic framework material can be used in proton conduction.

Description

Technical Field

[0001] The invention belongs to the technical field of crystalline materials, and particularly relates to a chromium phosphonate metal organic framework material and a solvent-free preparation method and application thereof. Background Art

[0002] Metal-organic frameworks (MOFs), composed of metal ions or metal clusters linked to organic ligands through coordination bonds, are a new class of porous materials. They possess large surface area, high porosity, and tunable pore structures, promising applications in gas adsorption and separation, catalysis, fluorescence, and proton conductivity. Numerous studies have explored how to enhance the proton conductivity of MOFs. Common approaches include introducing acidic guest molecules into the pores of MOFs, which is the most common approach. However, these guest molecules lack interaction with the MOFs, leading to leakage over time. Direct synthesis of MOFs using materials with proton donors (such as acidic groups) as organic ligands is another approach. Therefore, the use of phosphonic acid groups with high proton density could be an attractive approach to synthesize novel MOFs with high proton conductivity.

[0003] Compared to carboxylic acid ligands, phosphonate ligands are more likely to form strong chemical bonds with metal atoms. The chemical stability of phosphonate MOFs generally depends on the valence of the metal ion. Monovalent metal phosphonates are highly soluble, and their solubility decreases with increasing metal valence. Divalent metal phosphonates have lower solubility and can be obtained as single crystals using hydrothermal or solvothermal techniques. However, trivalent and tetravalent metal phosphonates rarely crystallize because they are highly insoluble and tend to precipitate as disordered layered materials. Tetravalent metal phosphonates are insoluble even in strong acid solutions.

[0004] Cr-MOFs generally have good stability, and studies have shown that Cr-MOFs with sulfonic acid groups can exhibit high proton conductivity. However, there are currently no reports on proton conductivity in chromium phosphonate MOFs. Furthermore, there is currently only one reported method for synthesizing the chromium phosphonate framework using a two-step synthesis method: first preparing a chromium-hydrogen-bonded organic framework (Cr-HOF), then heating and dehydrating it to obtain the desired chromium phosphonate MOF. This method is significantly different from the solvent-free synthesis method used in the present invention.

[0005] Although the traditional solvothermal method is a common method for obtaining high-quality crystals, it still has the following shortcomings:

[0006] (1) A large amount of organic reagents, such as N,N-dimethylformamide and acetone, are required during the reaction process. Their cost, toxicity, and flammability make them pose a great safety hazard and easily lead to safety accidents.

[0007] (2) The reaction conditions are harsh. Solvothermal methods usually need to be carried out under high temperature and high pressure, and safety issues cannot be guaranteed.

[0008] (3) After the solvent thermal reaction is completed, a large amount of waste liquid is generated. The production of waste liquid will corrode the equipment and its treatment requires extremely high costs. Summary of the Invention

[0009] In order to solve the above deficiencies and shortcomings of the prior art, the present invention provides a chromium phosphonate metal organic framework material and a solvent-free preparation method and application thereof.

[0010] The present invention is achieved through the following technical solutions:

[0011] A chromium phosphonate metal organic framework material, the chemical formula of which is [Cr(H2BPD) 1.5 ], the ligand is terephthalic acid, and the structural formula is:

[0012] ;

[0013] The chromium phosphonate metal organic framework material has a three-dimensional network structure.

[0014] Furthermore, in the chromium phosphonate metal organic framework material, each chromium atom is connected to the oxygen atoms on the phosphate groups from six different ligands to form an octahedral structure; 2- Each phosphonic acid group in the ligand connects two chromium atoms in a bidentate coordination mode. This connection mode extends infinitely in space to form a one-dimensional chain-like Cr-secondary building unit (Cr-SBU). Adjacent Cr-SBU chains are connected by the benzene ring of the ligand, thereby forming a three-dimensional network structure. In this three-dimensional network structure, there is a one-dimensional acid channel, in which the uncoordinated and ionized P-OH groups on the ligand are distributed.

[0015] The present invention also provides a solvent-free preparation method of the chromium phosphonate metal organic framework material, comprising the following steps:

[0016] The organic ligand p-terephthalic acid and chromium chloride hexahydrate are mixed and ground, and then heated for reaction. After the reaction is completed, the mixture is spontaneously cooled to room temperature and repeatedly washed with ethanol until the supernatant is colorless and transparent. After vacuum drying, a light green chromium phosphonate metal-organic framework material is obtained.

[0017] Furthermore, the molar ratio of the organic ligand terephthalenediphosphonic acid to chromium chloride hexahydrate is 1:1.

[0018] Furthermore, the specific operation of the heating reaction is as follows: using a programmed temperature rising method, setting the heating time to 30 minutes, heating to 150° C., and the reaction time is 24-48 hours.

[0019] Furthermore, the grinding was carried out in a glove box with the humidity controlled at 15-20% and the grinding time was 15 minutes.

[0020] Furthermore, the drying condition is: drying in a vacuum oven at 60° C. for 12 hours.

[0021] The present invention also provides application of the chromium phosphonate metal organic framework material in proton conduction.

[0022] Beneficial technical effects of the present invention:

[0023] The present invention adopts a grinding-solvent-free method to prepare a chromium phosphonate metal-organic framework material. The preparation method does not use an organic solvent, is green and environmentally friendly, and has a simple process. The prepared metal-organic framework crystal material has the advantages of good stability and high proton conductivity, making the MOFs have potential applications in proton conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the XRD result of the material prepared in Example 1;

[0025] Figure 2 Schematic diagram of the coordination structure of the material prepared in Example 1;

[0026] Figure 3 This is a schematic diagram of the pore structure of the material prepared in Example 1;

[0027] Figure 4 This is the infrared spectrum of the material prepared in Example 1;

[0028] Figure 5 The SEM and EDS results of the material prepared in Example 1 are shown;

[0029] Figure 6 This is a graph showing the thermogravimetric test results of the material prepared in Example 1;

[0030] Figure 7 This is the XRD result of the material after high temperature treatment;

[0031] Figure 8 This is a graph showing the impedance test results of the material prepared in Example 1;

[0032] Among them, (a) is the result of impedance variation with temperature at 100% relative humidity;

[0033] (b) Changes of proton conductivity with temperature;

[0034] (c) is the activation energy fitting result;

[0035] (d) shows the change of conductivity with temperature at 80℃. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0037] Example 1

[0038] Terephthalic acid (H4BPD) (238 mg, 1 mmol) and chromium chloride hexahydrate (CrCl3·6H2O) (266 mg, 1 mmol) were weighed and placed in 2 ml glass bottles respectively. The mixture was mixed in a glove box (humidity 15%) and ground in a mortar for 15 minutes. The mixture was then transferred to a 5 ml Teflon-lined stainless steel autoclave. The oven heating time was set to 30 minutes, the temperature was raised to 150°C, and the reaction time was 24 hours. The product was washed with anhydrous ethanol at least three times until the supernatant was colorless after centrifugation. The product was then dried in a vacuum oven at 60°C for 12 hours to obtain the metal-organic framework crystal material.

[0039] Example 2

[0040] Terephthalic acid (H4BPD) (238 mg, 1 mmol) and chromium chloride hexahydrate (CrCl3·6H2O) (266 mg, 1 mmol) were weighed and placed in 2 ml glass bottles respectively. The mixture was mixed in a glove box (humidity 20%) and ground in a mortar for 15 minutes. The mixture was then transferred to a 5 ml Teflon-lined stainless steel autoclave. The oven heating time was set to 30 minutes, the temperature was raised to 150°C, and the reaction time was 24 hours. The product was washed with anhydrous ethanol at least three times until the supernatant was colorless after centrifugation. The product was then dried in a vacuum oven at 60°C for 12 hours to obtain the metal-organic framework crystal material.

[0041] Example 3

[0042] Terephthalic acid (H4BPD) (238 mg, 1 mmol) and chromium chloride hexahydrate (CrCl3·6H2O) (266 mg, 1 mmol) were weighed and placed in 2 ml glass bottles respectively. The mixture was mixed in a glove box (humidity 15%) and ground in a mortar for 15 minutes. The mixture was then transferred to a 5 ml Teflon-lined stainless steel autoclave. The oven heating time was set to 30 minutes, the temperature was raised to 150°C, and the reaction time was 48 hours. The product was washed with anhydrous ethanol at least three times until the supernatant was colorless after centrifugation. The product was then dried in a vacuum oven at 60°C for 12 hours to obtain the metal-organic framework crystal material.

[0043] The characterization data of the materials obtained in Examples 1-3 are the same.

[0044] A powder of suitable size was obtained from Example 1, and data were collected at 173 K using a PANalytical X'Pert PRO high-resolution powder diffractometer. Data were collected using Cu-Kα target radiation monochromatized by a graphite monochromator. Absorption correction of the data was performed using SCALE3ABSPACK software. The crystal structure was solved by a direct method using the SHELXTL-97 program. The coordinates of all non-hydrogen atoms were first determined using the difference function method and the least squares method, and the hydrogen atom positions were obtained using the theoretical hydrogenation method. The crystal structure was then refined using SHELXTL-97.

[0045] The molecular formula of this material is Cr(H2BPD)1.5, and the molecular weight is 406. From the perspective of skeleton connection construction, the crystal structure of this metal-organic framework belongs to the isometric crystal system and the space group is P21 / c.

[0046] Characterization and analysis results of materials:

[0047] Figure 1 The XRD comparison diagram of the metal organic framework prepared in Example 1 and the XRD of the data fitting show that the characteristic peaks of the two are completely consistent, indicating that the chromium phosphonate metal organic framework material is successfully prepared.

[0048] Figure 2 The coordination structure diagram of the chromium phosphonate metal organic framework material shows that: in the chromium phosphonate metal organic framework material, each chromium atom is connected to the oxygen atoms on the phosphate groups from six different ligands to form an octahedral structure; H2BDP 2- Each phosphonic acid group in the ligand connects two chromium atoms in a bidentate coordination mode. The above connection mode extends infinitely in space to form a one-dimensional chain-like Cr-secondary building unit (Cr-SBU). Adjacent Cr-SBU chains are connected by the benzene ring of the ligand, thereby forming a three-dimensional network structure.

[0049] Figure 3 The figure is a schematic diagram of the three-dimensional structure of the chromium phosphonate metal organic framework material. In the three-dimensional network structure, there is a one-dimensional acid channel, in which the uncoordinated and ionized P-OH groups on the ligand are distributed.

[0050] Figure 4 is the infrared spectrum of the chromium phosphonate metal organic framework material, located at 1203, 1160 and 1078 cm -1 The three new energy bands in the structure indicate that the oxygen atoms in P=O and PO are successfully coordinated with chromium.

[0051] Figure 5The SEM and EDS images of the chromium phosphonate metal organic framework material show that the prepared metal organic framework crystals have a block structure and a uniform particle size distribution.

[0052] Figure 6 is a thermogravimetric curve of the chromium phosphonate metal organic framework material, Figure 7 This is the XRD result of the material after high-temperature treatment, which shows that the prepared metal-organic framework crystal has good thermal stability and can still maintain the stability of the framework at 420°C.

[0053] In order to obtain the proton conductivity of the chromium phosphonate metal organic framework, the following method was used for testing:

[0054] Approximately 90 mg of metal organic framework powder was placed in a custom mold under a pressure of 1000 kg cm -2 The result was a rectangular parallelepiped (about 0.2 × 0.4 × 1.0 cm) 3 ) of the sample to be tested. Place the two planes of the sample (0.2×0.4 cm 2 ) is fixed to a silver wire with silver conductive glue and sealed in a double-walled glass chamber. The temperature is controlled by temperature-controlled circulating water in the interlayer of the double-layer glass chamber. The humidity in the glass chamber is controlled by a series of saturated saline solutions. The impedance diagram of the sample to be tested is then measured using an electrochemical workstation, with the frequency range set to 1 Hz to 8 MHz and the AC potential set to 100 mV. Its proton conductivity is calculated as: L / RS (L = 1 cm, R is the impedance of the sample to be tested). The results are shown in Figure 2. Figure 8 Figure 8a shows that the conductivity of the prepared metal organic framework crystal can reach 1.44×10 −2 S / cm, which can reach 2.42×10 at 90℃ − 2 S cm −1 Figure 8b shows that the material's proton conductivity improves with increasing temperature, exhibiting even higher proton conductivity at high temperatures. Figure 8b demonstrates excellent temperature stability of the proton conductivity, indicating that the material can maintain its excellent proton conductivity over a wide temperature range. This stability is critical for high-temperature applications, particularly in devices such as proton exchange membrane fuel cells. Figure 8c shows that the activation energy for proton conduction is only 0.1 eV, indicating that protons conduct very easily in this material. A low activation energy is a key factor in its rapid proton conduction. Generally, the lower the activation energy, the easier protons migrate through the material, resulting in better conductivity. Figure 8d shows that the material's proton conductivity remains unchanged for at least 100 hours at 90°C and 100% relative humidity, showing no significant degradation, demonstrating the material's excellent long-term stability. This long-term stability is crucial for sustained operation in practical applications.

Claims

1. A solvent-free preparation method of a chromium phosphonate metal organic framework material, characterized in that: The steps include: The organic ligand p-terephthalic acid and chromium chloride hexahydrate are mixed and ground, and then heated to react. After the reaction is completed, the mixture is cooled to room temperature, and repeatedly washed with ethanol until the supernatant is colorless and transparent. After vacuum drying, a light green chromium phosphonate metal organic framework material is obtained; The chemical formula of the chromium phosphonate metal organic framework material is [Cr(H2BPD) 1.5 ], the ligand is terephthalic acid, and the structural formula is: ； The chromium phosphonate metal organic framework material has a three-dimensional network structure; In the chromium phosphonate metal organic framework material, each chromium atom is connected to the oxygen atoms on the phosphate groups from six different ligands to form an octahedral structure; 2- Each phosphonic acid group in the ligand connects two chromium atoms in a bidentate coordination mode. This connection mode extends infinitely in space to form a one-dimensional chain-like Cr-secondary building block unit (Cr-SBU). Adjacent Cr-SBU chains are connected by the benzene rings of the ligand, forming a three-dimensional network structure. In the three-dimensional network structure, there is a one-dimensional acid channel, in which the uncoordinated and ionized P-OH groups on the ligand are distributed.

2. The solvent-free preparation method of the chromium phosphonate metal organic framework material according to claim 1, characterized in that: The molar ratio of the organic ligand terephthalenediphosphonic acid to chromium chloride hexahydrate is 1:

1.

3. The solvent-free preparation method of the chromium phosphonate metal organic framework material according to claim 1, characterized in that: The specific operation of the heating reaction is as follows: using a programmed temperature rising method, setting the heating time to 30 minutes, heating to 150° C., and the reaction time is 24-48 hours.

4. The solvent-free preparation method of the chromium phosphonate metal organic framework material according to claim 1, characterized in that: The grinding was carried out in a glove box with the humidity controlled at 15-20% and the grinding time was 15 minutes.

5. The solvent-free preparation method of the chromium phosphonate metal organic framework material according to claim 1, characterized in that: Drying conditions: drying in a vacuum oven at 60°C for 12 hours.

6. Use of the chromium phosphonate metal organic framework material prepared by the preparation method according to claim 1 in proton conduction.

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