Pyridine hexacarboxylic acid ligand-based indium-based metal-organic framework material, and preparation method and application thereof

Abstract

The invention discloses an indium-based metal-organic framework material based on a pyridine hexacarboxylic acid ligand as well as a preparation method and application of the indium-based metal-organic framework material, the chemical formula is {[NH2Me2] 2 [In4 (mu2-O) (H6L) 2 (H2O) 2]. 3DMF. 10H2O} n, and H6L is an organic ligand 4, 4 ', 4' '-(pyridine-2, 4, 6-triyl) triisophthalic acid. The material has excellent thermal stability and chemical stability, and due to the frame charge characteristic and the excellent pore structure of the material, the metal organic frame material shows efficient dye selective adsorption and separation performance, can selectively adsorb cationic dye methylene blue MB and repel anionic dye methyl orange MO at the same time. In conclusion, a new design thought is developed for the novel indium-based metal organic framework material based on the pyridine hexacarboxylic acid ligand, and meanwhile, a new candidate is provided for developing a high-efficiency dye wastewater purification material.

Description

Technical Field

[0001] This invention belongs to the field of crystalline materials technology in coordination chemistry, specifically relating to indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. This invention also relates to a method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. Furthermore, this invention relates to the applications of indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. Background Technology

[0002] With the continuous expansion of industrial systems and the rapid development of manufacturing, water pollution has become increasingly severe, posing a key bottleneck to sustainable social development. Organic synthetic dyes, including methylene blue (MB), methyl violet (MV), methyl orange (MO), and malachite green (MG), are widely used in textiles, dyeing and printing, daily chemicals, and plastics processing. The large amounts of dye-containing wastewater generated during their production and application accumulate, posing a serious threat to the water environment. Statistics show that dye wastewater from the textile and dyeing industries alone accounts for approximately 75% of total dye wastewater discharge. These dye molecules are typically structurally stable, highly water-soluble, and highly mobile, making them difficult to remove effectively through conventional physical sedimentation or biodegradation. More concerningly, they can further degrade into aromatic amines in the natural environment. These products are not only difficult to biodegrade but may also enter the human body through water, inducing gene mutations and even cell carcinogenesis, posing a dual threat to ecosystem security and public health.

[0003] Currently, commonly used adsorption materials such as biochar, ion exchange resins, and zeolites, while possessing some adsorption capacity for organic dyes, have limited adsorption capacity and low selectivity, making it difficult to meet the demands for high-efficiency purification. Against this backdrop, developing dye wastewater treatment technologies that combine high efficiency, stability, and environmental compatibility has become an urgent research topic.

[0004] Metal-organic framework (Metal-Organic Framework) Organic Frameworks (MOFs) offer a solution to the aforementioned problems. As a novel porous crystalline material formed by the coordination of metal ions / metal clusters with organic ligands, MOFs have a much higher specific surface area than traditional adsorption materials. Furthermore, they enable precise control of the network structure and the directional design of functional groups, allowing them to adapt to dye molecules with different structures, thus laying the foundation for efficient and selective adsorption.

[0005] Pyridine hexacarboxylic acid ligands possess bifunctional coordination sites, diverse coordination modes, and designability. According to the hard-soft acid-base theory (HSAB), their carboxylic acid oxygen atom readily reacts with hard acid metal ions (such as In). 3+Coordination facilitates the construction of high-performance MOFs. These MOFs typically possess high stability, large specific surface area, and tunable pore environment. In dye adsorption applications, they exhibit high adsorption capacity, rapid kinetics, good selectivity, and excellent regeneration and recycling performance through various synergistic mechanisms such as pore confinement, electrostatic attraction, π-π interactions, and hydrogen bonding, making them highly promising adsorption materials for dye wastewater. Summary of the Invention

[0006] The purpose of this invention is to provide indium-based metal-organic framework (In-MOF) materials based on pyridine hexacarboxylic acid ligands, which solves the problem of poor chemical / thermal stability of existing materials.

[0007] Another object of the present invention is to provide a method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands.

[0008] Another object of the present invention is to provide applications of indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands.

[0009] The first technical solution adopted in this invention is: an indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligands, with the chemical formula {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n H6L is the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid.

[0010] The first technical solution of the present invention is further characterized in that, {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n Its crystal structure belongs to the orthorhombic crystal system. C- 222 Space group 1, cell parameters are: a = 17.3989(9) Å, b = 26.9101(14) Å, c = 26.7316(13) Å; α = β = γ = 90°.

[0011] {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n A minimal asymmetric unit contains four indium ions, two coordinated water molecules, and one μ2-O. 2- and two L 6- ligands, via L 6- The ligands expand to form a two-dimensional layered framework structure.

[0012] Indium ions exist in two forms, In1 and In2, both of which are six-coordinate octahedral. In1 is formed from three different L... 6- The six carboxyl oxygen atoms of the ligand are coordinated in chelate mode, and In2 is bridged by a μ2-O. 2- The oxygen atoms of two coordinated water molecules and those from two different L 6- The three monodentate carboxyl oxygen atoms of the ligand are coordinated.

[0013] The organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid has a rigid structure, and its chemical structure is as follows: .

[0014] The second technical solution adopted in this invention is: a method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. Under sealed conditions, indium nitrate hydrate and the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid are added to a mixed solution of N,N-dimethylformamide and nitric acid aqueous solution, and the mixture is prepared by solvothermal reaction.

[0015] The second technical solution of the present invention is further characterized in that, The molar ratio of the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid to indium nitrate hydrate is 1:1.43–2.86; each 0.5 mL of N,N-dimethylformamide corresponds to 0.95–1.43 mL of nitric acid aqueous solution, wherein the concentration of the nitric acid aqueous solution is 1 mL of HNO3 dissolved in 10 mL of distilled water.

[0016] Indium nitrate hydrate and the organic ligand 4,4',4''-(pyridine-2,4,6-trimethyl)triisophthalic acid were added to the mixed solution, and the mixture was sealed in a borosilicate glass bottle and placed in an oven at 100-120°C for a solvothermal reaction for 4 days.

[0017] The third technical solution adopted in this invention is: the application of indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands, using indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands as adsorbents for selectively adsorbing the cationic dye methylene blue MB.

[0018] The beneficial effects of this invention are as follows: Based on indium-based metal-organic framework materials, their preparation methods, and applications, these materials possess excellent thermal and chemical stability. Benefiting from their framework charge characteristics and superior pore structure, the metal-organic framework materials exhibit highly efficient dye-selective adsorption and separation performance, selectively adsorbing the cationic dye methylene blue (MB) while repelling the anionic dye methyl orange (MO). In summary, this invention opens up new design avenues for novel indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands and also provides new candidates for developing highly efficient dye wastewater purification materials. Attached Figure Description

[0019] Figure 1 This is a two-dimensional structural schematic diagram of the metal-organic framework material of the present invention; Figure 2 This is a diagram of the In1 and In2 ion coordination environments of the metal-organic framework material of this invention; Figure 3 The present invention provides powder X-ray diffraction patterns and single-crystal X-ray diffraction patterns of the metal-organic framework material after immersion in different chemical reagents. Figure 4 This is a thermogravimetric curve test diagram of the metal-organic framework material of the present invention; Figure 5 This is the UV-Vis absorption spectrum of the metal-organic framework material of the present invention for methylene blue MB dye at different times; Figure 6 This is the UV-Vis absorption spectrum of the metal-organic framework material of the present invention for methyl orange (MO) dye at different times; Figure 7 This is a graph showing the adsorption rates of methylene blue (MB) and methyl orange (MO) on the metal-organic framework material of this invention at different times. Figure 8 This is the UV-Vis absorption spectrum of the metal-organic framework material of the present invention for the mixed dyes methylene blue (MB) and methyl orange (MO) at different times. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] This invention provides indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. Two-dimensional metal-organic frameworks were prepared by a solvothermal method by combining the rigid pyridine hexacarboxylic acid ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid with indium nitrate hydrate, such as... Figure 1 As shown, the chemical formula is {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n (H6L represents organic ligands).

[0022] Single-crystal structure analysis reveals that the metal-organic framework of this invention is {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O}. n Its crystal structure belongs to the orthorhombic crystal system. C-222 Space group 1, cell parameters are: a =17.3989(9) Å, b = 26.9101(14) Å, c = 26.7316(13) Å; α = β = γ = 90°. Specific crystal structure data are shown in Table 1 below: Table 1 {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n Crystal structure data

[0023] Complex {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n Crystal structure analysis shows that its smallest asymmetric unit contains four indium ions, exhibiting two crystallographically independent In... 3+ Center (In1 and In2), two L 6- Ligand, a μ2-O 2- And two coordinated water molecules. Although both In1 and In2 adopt a six-coordinated octahedral geometry, their coordination microenvironments differ significantly. For example... Figure 2 As shown, specifically, the coordination layer at the center of In1 is entirely composed of three different L... 6- The ligand is constructed from six carboxyl oxygen atoms (O1-A, O2, O4-A, O6, O8-A, O9-A), all coordinated in a chelate mode. In contrast, the coordination mode of the In2 center is more complex and diverse: its coordinating atoms originate from a bridging μ2-O. 2- The oxygen atoms of two coordinated water molecules (O5-A, O12-A, O15-A) and three carboxyl oxygen atoms (O3, O7-A, O13-A) from two different ligands are coordinated in a monodentate mode. This multi-component coordination mode, especially μ2-O 2- The presence of [specific element] and the multiple coordination modes of the carboxyl oxygen atoms on the ligands enable the above structural units to serve as effective nodes. Through L [specific method / mechanism]... 6- The regular bridging and extension of ligands, with these nodes interconnected in a two-dimensional plane, ultimately construct the two-dimensional layered framework structure of the complex.

[0024] Among them, the pyridine hexacarboxylic acid ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid has a rigid structure, mainly containing an aromatic benzene ring, a pyridine ring, and a carboxylic acid group, and its chemical structure is as follows:

[0025] This invention provides a method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands. Specifically, the method involves adding indium nitrate hydrate (a metal ion source) and pyridine hexacarboxylic acid ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid to a mixed solution of N,N-dimethylformamide (DMF) and nitric acid aqueous solution (HNO3). The solution is then sealed in a borosilicate glass bottle, and the metal-organic framework material is obtained under solvothermal reaction conditions.

[0026] The molar ratio of the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid to indium nitrate hydrate was 1:1.43–2.86; the solvent N,N-dimethylformamide (DMF) was added in an amount of 0.5 mL, and the nitric acid aqueous solution was HNO3 (… =1:10) The addition amount is 0.95~1.43mL; the mixture is completely sealed and placed in an oven at 100~120℃ for solvothermal reaction for 4 days.

[0027] The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligands provided by this invention has excellent stability and high adsorption performance, and can achieve highly selective adsorption of the cationic dye methylene blue MB.

[0028] The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligands provided by this invention exhibits excellent chemical and thermal stability. Experimental results show that the material retains its structural integrity even after immersion in organic solvents such as ethanol and acetonitrile for 24 hours, and its powder X-ray diffraction (PXRD) pattern is highly consistent with the structure obtained by single-crystal X-ray diffraction (SCXRD). Thermogravimetric analysis shows that the material has a high thermal decomposition temperature of 413℃, indicating its good thermal stability. Benefiting from its framework charge characteristics and highly ordered porous structure, the novel indium-based metal-organic framework material of this invention exhibits highly efficient selective adsorption and separation performance for dye molecules. The material of this invention can selectively adsorb the cationic dye methylene blue (MB) while effectively repelling the anionic dye methyl orange (MO). During the adsorption process, the removal rate of methylene blue reaches 98.74% within 30 minutes, while no significant adsorption behavior was observed for methyl orange, indicating its excellent selective separation capability. In summary, this invention not only provides a new approach for the design of pyridine hexacarboxylic acid ligands in indium-based metal-organic framework materials, but also offers a promising candidate for the development of high-efficiency dye wastewater purification materials, demonstrating good application prospects in environmental pollution control.

[0029] After immersing the metal-organic framework material of this invention in chemical reagents of different polarities, the X-ray diffraction patterns of the sample powder are as follows: Figure 3 As shown, the positions of the characteristic peaks remain unchanged, indicating that the material has good chemical stability.

[0030] Thermogravimetric analysis (TGA) was performed on the material under a nitrogen atmosphere in the temperature range of 30℃ to 800℃, and the results are as follows: Figure 4 As shown, the material exhibits a slow weight loss trend before 220℃, corresponding to the removal of free water molecules and DMF molecules from the channels; the material remains stable with no significant weight loss between 220℃ and 400℃; when the temperature exceeds 400℃, the material exhibits a rapid weight loss phenomenon, indicating that its framework structure begins to collapse. This confirms that the material has good thermal stability.

[0031] like Figure 5 As shown, the UV-Vis absorption spectra of the material for methylene blue dye at different times are as follows. It can be clearly observed that the absorbance value drops to 0.122 within the test time range of 0 to 30 min, indicating that the material has excellent adsorption performance for methylene blue dye.

[0032] like Figure 6 As shown, the UV-Vis absorption spectra of the material for methyl orange dye at different times show that the absorbance values ​​do not change significantly within the time range of 0 to 30 min, indicating that the adsorption of methyl orange dye by the material is negligible.

[0033] The adsorption rates of methylene blue and methyl orange dyes on the material at different times are as follows: Figure 7As shown, the adsorption rates at 30 min were 95% and 1.1%, respectively. Therefore, it can be concluded that the material can selectively adsorb the cationic dye methylene blue, but has no adsorption effect on the anionic dye methyl orange.

[0034] like Figure 8 As shown, a competitive adsorption experiment was conducted on the mixed dyes methylene blue and methyl orange. Within a 30-minute test range, the material maintained good adsorption performance for the cationic dye methylene blue, while the absorption peak intensity of methyl orange showed no significant change. This phenomenon indicates that the material can achieve highly efficient and selective adsorption of cationic dyes in the mixed dye system.

[0035] Example 1 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (6.01 mg, 0.020 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 0.95 mL of a (1:10) HNO3 mixture to the bottle and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Then seal the bottle with a lid lined with PTFE and place it in a 100°C oven for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The solution was slowly cooled to room temperature using a controlled rate program to obtain pale yellow, fine needle-like crystals. The resulting crystals were washed three times with DMF (totaling approximately 40 mL) to remove residual impurities, yielding a crystalline sample with a yield of 43.4%.

[0036] Example 2 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (7.28 mg, 0.024 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 1.05 mL of a (1:10) HNO3 mixture to the bottle and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Then seal the bottle with a lid lined with PTFE and place it in a 105°C oven for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The solution was slowly cooled to room temperature using a controlled rate program to obtain small, light yellow, spherical crystals. The resulting crystals were washed three times with DMF (approximately 40 mL in total) to remove residual impurities, yielding a crystalline sample with a yield of 41.6%.

[0037] Example 3 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (8.55 mg, 0.028 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 1.16 mL of a (1:10) HNO3 mixture to the bottle and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Seal the bottle with a lid lined with PTFE and place it in a 110°C oven for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The solution was slowly cooled to room temperature using a controlled rate program to obtain light yellow tetragonal crystals. The resulting crystals were washed three times with DMF (approximately 40 mL in total) to remove residual impurities, yielding a high-purity crystal sample with a yield of 83.1%.

[0038] Example 4 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (9.81 mg, 0.032 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 1.23 mL of a (1:10) HNO3 mixture to the bottle and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Seal the bottle with a lid lined with PTFE and place it in a 115°C oven for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The solution was slowly cooled to room temperature using a controlled rate program to obtain light yellow, finely clustered crystals. The resulting crystals were washed three times with DMF (totaling approximately 40 mL) to remove residual impurities, yielding a crystalline sample with a yield of 37.4%.

[0039] Example 5 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (11.07 mg, 0.037 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 1.35 mL of a (1:10) HNO3 mixture to the bottle, and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Seal the bottle with a lid lined with PTFE and place it in an oven at 118°C for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The temperature was slowly lowered to room temperature using a controlled rate program, resulting in a light yellow, fine crystalline slag. The obtained crystals were washed three times with DMF (totaling approximately 40 mL) to remove residual impurities, yielding a crystalline sample with a yield of 46.5%.

[0040] Example 6 Accurately weigh ligand P56 (8.20 mg, 0.014 mmol) and indium nitrate hydrate (12.04 mg, 0.040 mmol) and place them in a 25 mL borosilicate glass bottle. Add 0.5 mL of DMF and 1.43 mL of a (1:10) HNO3 mixture to the bottle and sonicate for 15 minutes to ensure thorough dispersion of the reactants. Then seal the bottle with a lid lined with PTFE and place it in a 120°C oven for 96 hours. After the reaction is complete, measure the temperature at 6°C·h⁻¹. -1 The solution was slowly cooled to room temperature using a controlled rate program to obtain light yellow, square-shaped crystals. The resulting crystals were washed three times with DMF (totaling approximately 40 mL) to remove residual impurities, yielding a crystalline sample with a yield of 43.9%.

Claims

1. An indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligands, characterized in that, Chemical formula: {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n H6L is the organic ligand 4,4',4''-(pyridine-2,4,6-triyl) triisophthalic acid.

2. The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligand as described in claim 1, characterized in that, The {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n Its crystal structure belongs to the orthorhombic crystal system. C-222 Space group 1, cell parameters are: a = 17.3989(9) Å, b = 26.9101(14) Å, c = 26.7316(13) Å; α = β = γ = 90°.

3. The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligand as described in claim 1, characterized in that, The {[NH2Me2]2[In4(μ2-O)(H6L)2(H2O)2]·3DMF·10H2O} n A minimal asymmetric unit contains four indium ions, two coordinated water molecules, and one μ2-O. 2- and two L 6- ligands, via L 6- The ligands expand to form a two-dimensional layered framework structure.

4. The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligand as described in claim 3, characterized in that, The indium ions exist in two forms, In1 and In2, both belonging to the six-coordinate octahedral configuration. In1 is composed of indium ions from three different L... 6- The six carboxyl oxygen atoms of the ligand are coordinated in chelate mode, and In2 is bridged by a μ2-O. 2- The oxygen atoms of two coordinated water molecules and those from two different L 6- The three monodentate carboxyl oxygen atoms of the ligand are coordinated.

5. The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligand as described in claim 1, characterized in that, The organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid has a rigid structure, and its chemical structure is as follows: 。 6. The method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands as described in claim 1, characterized in that, Under sealed conditions, indium nitrate hydrate and the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid are added to a mixed solution of N,N-dimethylformamide and nitric acid aqueous solution, and the mixture is prepared by a solvothermal reaction.

7. The method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands as described in claim 6, characterized in that, The molar ratio of the organic ligand 4,4',4''-(pyridine-2,4,6-triyl)triisophthalic acid to indium nitrate hydrate is 1:1.43 to 2.86; each 0.5 mL of N,N-dimethylformamide corresponds to 0.95 to 1.43 mL of nitric acid aqueous solution, wherein the concentration of the nitric acid aqueous solution is 1 mL of HNO3 dissolved in 10 mL of distilled water.

8. The method for preparing indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands as described in claim 6, characterized in that, Indium nitrate hydrate and the organic ligand 4,4',4''-(pyridine-2,4,6-trimethyl)triisophthalic acid were added to the mixed solution, which was then sealed in a borosilicate glass bottle and placed in an oven at 100-120°C for a solvothermal reaction for 4 days.

9. Application of indium-based metal-organic framework materials based on pyridine hexacarboxylic acid ligands, characterized in that, The indium-based metal-organic framework material based on pyridine hexacarboxylic acid ligands as described in any one of claims 1 to 8 is used as an adsorbent for selectively adsorbing the cationic dye methylene blue MB.

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