A metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, its preparation method and application.

Abstract

This invention discloses a metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, its preparation method, and its application. Belonging to the field of crystalline materials technology, the chemical formula is [Cr(OH)(SO3)(CO2)(C6H4)], and the ligand is p-sulfobenzoic acid. It is prepared by the following steps: p-sulfobenzoic acid and chromium chloride hexahydrate are ground and mixed to obtain a premix; the premix is ​​heated to 150-250℃ and reacted for 12-144 hours; after the reaction, the product is washed with ethanol, centrifuged, and dried to obtain the chromium-based metal-organic framework material. The obtained chromium-based metal-organic framework material exhibits excellent proton conductivity, with a conductivity reaching 8.54 × 10⁻⁶. ‑3 S·cm ‑1 (98%RH).

Description

Technical Field

[0001] This invention belongs to the field of crystalline material preparation technology, specifically relating to a metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs) are a class of crystalline porous materials composed of metal ions or metal clusters linked to organic ligands via coordination bonds. With their tunable structures, functional diversity, and excellent stability, MOFs have shown great potential in gas adsorption and separation, catalysis, electrochemical energy storage, and proton conduction. In recent years, research on proton-conducting MOFs has become increasingly popular, making the development of solid proton-conducting materials with both high conductivity and high stability crucial. Currently, the mainstream strategies for improving the proton conductivity of MOFs mainly fall into two categories: one is to introduce hydrophilic functional groups (such as -SO3H, -COOH, -PO3H2, etc.) to enhance the adsorption of water molecules and construct a hydrogen bond network; the other is to form continuous hydrogen bond channels through structural design to promote proton migration along the hydrogen bond direction. For example, introducing sulfonic acid groups into MOF channels can provide multiple proton donor and acceptor sites, thereby forming a broad hydrogen bond network within the framework channels and promoting proton transport. However, although many MOF matrices can form highly conductive channels after absorbing moisture, their long-term stability remains a key issue restricting their application.

[0003] For two-dimensional layered MOFs, stability is a particularly prominent issue. Two-dimensional layered MOF structures typically form a two-dimensional network within the layers through metal coordination bonds, while the connections between layers rely solely on weak van der Waals forces or dipole-dipole interactions, lacking strong directional bonding. However, strong interlayer hydrogen bond networks can effectively reinforce the layered structure, preventing delamination or collapse. Utilizing the advantage of sulfonic acids containing a large number of oxygen atoms, while ensuring that some oxygen atoms form coordination bonds, the remaining oxygen atoms can participate in forming strong hydrogen bonds, potentially firmly connecting the layers and significantly improving the structural stability of the material. However, in the existing literature, stable two-dimensional layered Cr-MOF structures with ligands containing both sulfonic and carboxylic acid bifunctional groups simultaneously coordinated with chromium ions have not yet been reported.

[0004] Metal-organic frameworks (MOFs) are typically obtained through a solvothermal route to achieve highly crystalline products. For example, patent CN104672277A reports the construction of bowl-shaped MOFs using DMF as a solvent via a solvothermal reaction; patent CN108440439A uses a mixed solvent system of DMF / benzoic acid / trifluoroacetic acid to prepare MOF materials via a solvothermal method. Although the traditional solvothermal method is a routine approach for preparing high-quality crystals, it still has the following problems:

[0005] (1) The system commonly uses a large amount of organic reagents such as DMF and acetone, which pose safety and environmental risks due to their cost, toxicity and flammability under certain conditions.

[0006] (2) The process is complex, requiring the removal of non-volatile solvents and unreacted raw materials from the channels. Compared with the solvent-free approach, the process is more complicated and the post-processing burden is heavier.

[0007] (3) Low yield and poor atom economy make it difficult to meet the needs of large-scale industrialization. Summary of the Invention

[0008] The purpose of this invention is to address the problem of improving the stability and proton conductivity of two-dimensional layered MOFs. By simultaneously coordinating sulfonic acid and carboxylic acid groups with chromium ions, stability is maintained while proton conductivity is improved, thus providing a metal-organic framework material with sulfonic acid and carboxylic acid groups simultaneously coordinated with chromium ions, its preparation method, and applications. This invention employs a solvent-free mechanical milling method to synthesize chromium-based metal-organic framework materials with sulfonic acid and carboxylic acid groups simultaneously coordinated with chromium ions. This method effectively improves the conversion rate of raw materials and the yield of MOFs, and the obtained material exhibits excellent proton conductivity.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, has the chemical formula [Cr(OH)(SO3)(CO2)(C6H4)], with p-sulfobenzoic acid (COOH)C6H4(SO3H) as the ligand, and the structural formula is:

[0011]

[0012] The metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions has a two-dimensional layered structure.

[0013] Furthermore, in the metal-organic framework material where both sulfonic acid and carboxylic acid groups are coordinated with chromium ions, each Cr... 3+ Reacting with two -OH and two -SO3 respectively - The oxygen atom on and the two -COO atoms - The oxygen atoms on the chromium atom coordinate to form an octahedral structure of CrO6; adjacent chromium atoms are connected by hydroxyl oxygen and a -SO3 group. - The two oxygen atoms and -COO -Two oxygen atoms on the top layer are connected to form a {Cr(OH)(SO3)(CO2)} chain extending infinitely along the b-axis. Adjacent {Cr(OH)(SO3)(CO2)} chains are connected by benzene rings, forming a two-dimensional layered structure. A strong hydrogen bond network is formed between the -OH groups and uncoordinated oxygen atoms on the -SO3 groups of adjacent layers, effectively connecting the two-dimensional layered structures into a three-dimensional crystal network. This structure not only enhances the overall stability of the crystal but also provides an efficient channel for proton conduction between layers.

[0014] This invention also provides a method for preparing a metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, comprising the following steps:

[0015] Step 1: Grind and mix p-sulfobenzoic acid and chromium chloride hexahydrate to obtain a premix;

[0016] Step 2: The premixed material is subjected to thermal reaction. After cooling, the product is washed with anhydrous ethanol. After washing, the supernatant is transparent and colorless after centrifugation. The precipitate after centrifugation is collected and vacuum dried at 60-70℃ for 12-16 hours to obtain a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions.

[0017] Furthermore, the premix mentioned in step one is specifically prepared by the following steps: grinding p-sulfobenzoic acid and chromium chloride hexahydrate in a mortar for 15-20 minutes in a reaction vessel to obtain the premix.

[0018] Furthermore, the molar ratio of p-sulfobenzoic acid to chromium chloride hexahydrate is 1:(1~100).

[0019] Furthermore, in step two, the thermal reaction conditions are raised to 150-250℃ and the reaction is carried out for 12-144 hours.

[0020] This invention also provides the application of metal-organic framework materials in which the sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions in proton conductivity.

[0021] Beneficial technical effects of the present invention:

[0022] (1) This invention reports for the first time a chromium-based MOF in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, and successfully synthesizes for the first time a chromium-based metal-organic framework material with p-sulfobenzoic acid (a ligand containing bifunctional groups of sulfonic acid and carboxylic acid) as a ligand.

[0023] (2) In the chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions, -OH forms a strong hydrogen bond network with the uncoordinated oxygen atoms in the -SO3 of the adjacent layer, effectively connecting the layers into a three-dimensional crystal network, which enhances the stability of the material and makes the material have excellent proton conduction performance.

[0024] (3) The present invention adopts a solvent-free preparation process, which directly synthesizes raw materials by grinding and mixing (without solvent) and reacting them with high temperature solid phase (155–250℃), avoiding organic solvent pollution of traditional solvothermal methods. The process is simple, environmentally friendly and has a high yield.

[0025] The core innovation of this invention lies in the combination of the structural design of a novel chromium-based MOF material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions and the solvent-free synthesis method. This approach simultaneously achieves stability, proton conductivity, and environmental friendliness, providing a new approach for the development of multifunctional MOFs. Attached Figure Description

[0026] Figure 1 XRD results of the metal-organic framework material prepared for the example;

[0027] Figure 2 A schematic diagram of the {Cr(OH)(SO3)(CO2)} chain of the metal-organic framework material prepared for the example;

[0028] Figure 3 A schematic diagram of the bc-planar two-dimensional layered structure of the metal-organic framework material prepared for the example;

[0029] Figure 4 A schematic diagram of the three-dimensional stacked structure of the metal-organic framework material prepared for the example along the c-axis;

[0030] Figure 5 Infrared spectra of the metal-organic framework materials prepared for the examples;

[0031] Figure 6 The SEM and EDS results of the metal-organic framework materials prepared in the examples are shown below. Figure 6 a is a SEM image of the metal-organic framework material prepared in the example; Figure 6 b、 Figure 6 c. Figure 6 d、 Figure 6 e are EDS distribution diagrams for Cr, O, S and C elements, respectively;

[0032] Figure 7 Thermogravimetric analysis results of the metal-organic framework material prepared for the example are shown in the figure.

[0033] Figure 8 XRD results of the metal-organic framework material prepared for the example after being treated under different conditions;

[0034] Figure 9 The figure shows the water vapor adsorption test results of the metal-organic framework material prepared in the example.

[0035] Figure 10Figure showing the change in proton conductivity of the metal-organic framework material prepared for the example as a function of humidity;

[0036] Figure 11 The impedance of the metal-organic framework material prepared for the example changes with temperature at 100% relative humidity.

[0037] Figure 12 The figure shows the activation energy fitting results of the metal-organic framework material prepared for the example. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1

[0040] A solvent-free method for preparing a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions includes the following steps:

[0041] S1. Grind 202.20 mg (1.00 mmol) p-sulfobenzoic acid and 266.50 mg (1.00 mmol) chromium chloride hexahydrate in a mortar for 15 min in a reaction vessel to obtain a premix.

[0042] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 250°C and reacted for 12 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 12 hours to obtain a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions.

[0043] Example 2

[0044] A solvent-free method for preparing a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions includes the following steps:

[0045] S1. Grind 473.15 mg (2.34 mmol) p-sulfobenzoic acid and 3.17 g (11.70 mmol) chromium chloride hexahydrate in a mortar for 20 min in a reaction vessel to obtain a premix.

[0046] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 220°C and reacted for 18 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 60°C for 12 hours to obtain a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions.

[0047] Example 3

[0048] A solvent-free method for preparing a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions includes the following steps:

[0049] S1. Grind 657.15 mg (3.25 mmol) p-sulfobenzoic acid and 17.32 g (65.00 mmol) chromium chloride hexahydrate in a mortar for 20 min in a reaction vessel to obtain a premix.

[0050] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave and heated to 200°C at a rate of 2°C / min for 24 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 65°C for 14 hours to obtain a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions.

[0051] Example 4

[0052] A solvent-free method for preparing a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions includes the following steps:

[0053] S1. Grind 202.2 mg (1.00 mmol) p-sulfobenzoic acid and 26.65 g (100 mmol) chromium chloride hexahydrate in a mortar for 17.5 min in a reaction vessel to obtain a premix.

[0054] S2. The premixed material was transferred to a Teflon-lined stainless steel autoclave, heated to 150°C and reacted for 144 hours. After cooling, the product was washed with anhydrous ethanol. After centrifugation, the supernatant was transparent and colorless. The precipitate after centrifugation was collected and dried under vacuum at 70°C for 16 hours to obtain a chromium-based metal-organic framework material in which sulfonic acid and carboxylic acid groups are simultaneously coordinated with chromium ions.

[0055] The materials obtained in Examples 1-4 have the same structure. The materials obtained in Examples 1-4 were characterized, and the results are as follows:

[0056] Figure 1 The XRD results of the metal-organic framework material prepared for the example are shown. In the freshly prepared sample, the XRD pattern shows high intensity diffraction peaks, indicating that the material has good crystallinity.

[0057] Figure 2-4 This is a schematic diagram of the crystal structure of the metal-organic framework material prepared in the example; in the metal-organic framework material in which both sulfonic acid and carboxylic acid groups are coordinated with chromium ions, each Cr 3+ Reacting with two -OH and two -SO3 respectively - The oxygen atom on and the two -COO atoms - The oxygen atoms on the chromium atom coordinate to form an octahedral structure of CrO6; adjacent chromium atoms are connected by hydroxyl oxygen and a -SO3 group. - The two oxygen atoms and -COO - Two oxygen atoms on the top layer are connected to form a {Cr(OH)(SO3)(CO2)} chain extending infinitely along the b-axis. Adjacent {Cr(OH)(SO3)(CO2)} chains are connected by benzene rings, forming a two-dimensional layered structure. A strong hydrogen bond network is formed between the -OH groups and uncoordinated oxygen atoms on the -SO3 groups of adjacent layers, effectively connecting the two-dimensional layered structures into a three-dimensional crystal network. This structure not only enhances the overall stability of the crystal but also provides an efficient channel for proton conduction between layers.

[0058] Figure 5 Infrared spectra of the metal-organic framework materials prepared for the examples; ligands at 1684 cm⁻¹ -1 The C=O stretching vibration peak of the carboxylic acid group that appears at Cr is significantly weakened or disappears in MOF materials, indicating that the carboxylic acid group interacts with Cr. 3+ Coordination formation of Cr-O(COO) - ) key. At 1138 cm -1 With 1118 cm -1 Nearby, the S=O absorption peak of the sulfonic acid group (-SO3H) shows a slight change in position, indicating that the oxygen on the sulfonic acid is involved in coordination. In addition, the uncoordinated sulfonic acid oxygen forms a strong hydrogen bond with the extra-chain hydroxyl group -OH, which enhances the stability of the interlayer structure.

[0059] Figure 6 The SEM and EDS results of the metal-organic framework material prepared for the example are shown. The SEM-EDS images confirm the crystallographic features, showing the morphology and uniform elemental distribution of the material.

[0060] Figure 7 Thermogravimetric analysis (TGA) results of the metal-organic framework material prepared for the example are shown in the figure; the thermal stability of the material in air atmosphere was evaluated by thermogravimetric analysis, such as... Figure 7 As shown, the MOF exhibits almost no significant weight loss before 400℃, indicating that its framework possesses excellent thermal stability. This result demonstrates that the chromium-based metal-organic framework material prepared in this invention exhibits good structural stability over a wide temperature range.

[0061] Figure 8The XRD results of the metal-organic framework (MOF) prepared for this example after treatment under different conditions are shown. For its practical application in proton conduction, the stability of the MOF is crucial. The XRD results show that the MOF's diffraction peak positions and morphology did not change significantly under extreme conditions such as strong acids (HCl, H₂SO₄, H₃PO₄), strong bases (NaOH), boiling water, and long-term water immersion, consistent with the spectra of the freshly prepared sample. This indicates that the material maintains its framework integrity in acidic, alkaline, and high-temperature aqueous environments, exhibiting excellent chemical and structural stability.

[0062] The materials obtained in Examples 1-4 were subjected to proton conductivity tests.

[0063] Approximately 85 mg of MOF powder was placed in a custom mold and heated at approximately 1,000 kg·cm⁻¹. -2 It is pressed under pressure to a size of approximately 0.2 × 0.4 × 1.0 cm. 3 A dense cuboid sample was prepared and tested for 3 minutes. Both ends of the sample were coated with silver paste and connected with wires, then sealed in a double-glazed test chamber. The test temperature was controlled by a constant-temperature water circulation system within the double-glazed jacket. RH was adjusted using a series of saturated saline solutions. Impedance diagrams were obtained using a Zennium Pro electrochemical workstation tuned from 1 Hz to 8 MHz at an AC potential of 100 mV.

[0064] Proton conductivity (σ, S cm) -1 Use the following formula:

[0065] σ = l / (RS)

[0066] Where: l, the distance between the two electrodes, i.e., the sample thickness, 1.0 cm; R, the measured impedance, Ω; S, the cross-sectional area of ​​the sample, 0.2 × 0.4 cm. 2 .

[0067] The activation energy (Ea) was obtained by fitting the proton conductivity data of the material at 100% relative humidity (RH) and a temperature range of 25 to 90°C to the Arrhenius equation.

[0068] ln(σT) = lnA-E a / (k B T)

[0069] Where: T, absolute temperature, K; A, exponential factor; k B Boltzmann constant.

[0070] The results are as follows Figure 9-12 Show: Figure 9The graph shows the water vapor adsorption curve. The adsorption capacity increases significantly with increasing relative humidity (RH), reaching approximately 60 cm⁻¹ at 95% RH. 3 ·g -1 This result indicates that the material has good hydrophilicity and can adsorb a large number of water molecules between layers, which is conducive to the formation of a continuous hydrogen bond network. Figure 10 The figure shows the relationship between proton conductivity and relative humidity. It can be seen that the conductivity increases significantly with increasing humidity, from 3.40 × 10⁻⁶. -7 S·cm -1 (33%RH) increased to 8.54×10 -3 S·cm -1 (98%RH), from Figure 9 It can be seen that as humidity gradually increases, the adsorption of water molecules can increase the density of the hydrogen bond network between layers, making proton migration easier and the conductivity gradually increases. Figure 11 The Nyquist plot shows the AC impedance spectra at different temperatures under 100% RH conditions. The Nyquist plot exhibits a typical semi-circular curve, indicating that the system resistance decreases with increasing temperature, while the conductivity increases. Figure 12 The activation energy E is obtained by linear fitting of the Arrhenius curve. a The value is approximately 0.28 eV, indicating that proton conduction follows the Grotthuss mechanism (E... a <0.4 eV), meaning that protons hop forward between layers in this material via a network of hydrogen bonds.

Claims

1. A metal-organic framework material in which both sulfonic acid and carboxylic acid groups are simultaneously coordinated to chromium ions, characterized in that: The chemical formula is [Cr(OH)(SO3)(CO2)(C6H4)], the ligand is p-sulfonic acid (COOH) C6H4(SO3H), and the structural formula is: ； In the metal organic framework material, the sulfonic acid and the carboxylic acid group are simultaneously coordinated with the chromium ion, and have a two-dimensional layered structure. In the metal-organic framework material in which the sulfonic acid and the carboxylic acid group simultaneously coordinate with the chromium ion, each Cr 3+ is coordinated with two -OH, two -SO3 - and two -COO - oxygen atoms, respectively, to form a CrO6 octahedral structure; adjacent chromium atoms are connected by two oxygen atoms of the hydroxyl oxygen, one -SO3 - and two oxygen atoms of -COO - to form {Cr(OH)(SO3)(CO2)} chains extending infinitely along the b axis, and adjacent {Cr(OH)(SO3)(CO2)} chains are connected by benzene rings to form a two-dimensional layered structure; a strong hydrogen bond network is formed between the two-dimensional layered structures by -OH and the uncoordinated oxygen atoms of -SO3 groups of adjacent layers to connect the two-dimensional layered structures into a three-dimensional crystal network.

2. A method of preparing a metal-organic framework material having both sulfonic and carboxylic groups coordinated to chromium ions as claimed in claim 1, characterized in that: The method comprises the following steps: Step one: grinding and mixing p-sulfonic acid and chromium chloride hexahydrate to obtain a premix; Step two: performing thermal reaction on the premix, washing the product with anhydrous ethanol after cooling, collecting the precipitate after centrifugation, and vacuum drying the precipitate at 60-70°C for 12-16h to obtain the chromium-based metal organic framework material in which the sulfonic acid and the carboxylic acid group are simultaneously coordinated with the chromium ion.

3. The method of claim 2, wherein the method further comprises: The premix in step one is prepared by the following steps: grinding p-sulfonic acid and chromium chloride hexahydrate in a mortar for 15-20min in a reaction kettle to obtain the premix.

4. The method of claim 2, wherein the method further comprises: The molar ratio of the p-sulfonic acid to the chromium chloride hexahydrate is 1:(1-100).

5. The method for preparing a metal-organic framework material with sulfonic acid and carboxylic acid groups simultaneously coordinated with chromium ions according to claim 2, characterized in that: In step two, the thermal reaction condition is to heat to 150-250°C and react for 12-144h.

6. Application of the metal organic framework material in which the sulfonic acid and the carboxylic acid group are simultaneously coordinated with the chromium ion to proton conduction.

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