A zinc-based MOF material, a preparation method and application thereof

Abstract

The application belongs to the field of metal-organic framework materials, and relates to a zinc-based MOF material and a preparation method and application thereof. The zinc-based MOF material is prepared from 2,5-thiophene dicarboxylic acid (H2TDA), 1,2-bis (4-pyridine) ethylene (BPE) and zinc acetate dihydrate as raw materials, and a three-dimensional network framework material is obtained. The basic asymmetric unit of the zinc-based MOF material comprises one Zn 2+ , one deprotonated TDA 2‑ ligand molecule, and one coordinated BPE ligand molecule. The synergistic effect of Zn-O and Zn-N coordination bonds improves the stability of the complex. Meanwhile, the uncoordinated sulfur atoms uniformly distributed on the surface of the material pore can form stronger hydrogen bonds and dipole interactions with CO2 molecules, and the material shows strong separation selectivity in the application of CO2 / C2H2 separation. The synthesis method provided by the application is simple, green and efficient.

Description

Technical Field

[0001] This invention belongs to the field of metal-organic framework materials, specifically relating to a zinc-based MOF material, its preparation method, and its application. Background Technology

[0002] Acetylene (C2H2), as one of the most widely used basic raw materials in the petrochemical industry, requires purification as a key process to obtain atomic absorption spectrometry-grade high-purity acetylene (purity ≥99.6%). Currently, industrially, C2H2 is mainly produced by the combustion of natural gas or the thermal cracking of hydrocarbons, inevitably generating a small amount of carbon dioxide (CO2, content approximately 3.2-3.5%) as a major impurity, severely affecting the purity of acetylene products and their subsequent applications. Currently, the mainstream acetylene purification methods in the petrochemical industry mainly include solvent extraction and cryogenic distillation. However, both of these processes generally suffer from high energy consumption, large equipment infrastructure investment, and high operating costs, and their separation efficiency and economic benefits are insufficient to meet the needs of large-scale industrial production. Therefore, developing new acetylene purification technologies with low cost, low energy consumption, and high separation efficiency has significant industrial application value for improving the economics of acetylene production and ensuring the quality of high-purity acetylene products.

[0003] Metal-organic frameworks (MOFs) are novel porous materials formed by the self-assembly of inorganic metal ions and organic ligands. With their advantages such as precisely tunable pore structure and functionalizable surface chemistry, MOFs have become promising candidate materials for achieving efficient gas separation and purification, and have also provided new technical approaches for the purification of C2H2.

[0004] Currently, efficient separation of CO2 / C2H2 mixtures remains a major technical challenge in the design of gas separation materials. The core reason for this challenge lies in the high similarity of the molecular properties of the two gases (such as similar kinetic diameters, polarizabilities, and boiling points), making it difficult for traditional adsorbent materials to achieve efficient separation through size sieving or polarity differences. Existing adsorbents generally suffer from a trade-off between adsorption capacity and separation selectivity, and in complex industrial gas mixtures containing impurities such as ethylene and sulfides, they are highly susceptible to competitive adsorption interference, resulting in poor dynamic separation stability.

[0005] The MOF materials disclosed in earlier applications CN120757789A and CN120665304A for separating C2H2 / CO2 preferentially adsorb C2H2, requiring subsequent desorption and regeneration to obtain high-purity acetylene. However, considering the separation mechanism and practical industrial application requirements, the ideal separation mode for the CO2 / C2H2 mixed system is to preferentially adsorb CO2 and retain C2H2 to directly obtain high-purity acetylene. However, porous materials with this selectivity reported in the literature are extremely rare. The overall performance of existing MOF materials still falls short of the requirements of practical industrial separation, generally exhibiting key problems such as poor water stability, insufficient CO2 adsorption capacity, and low separation selectivity calculated by IAST, making them unsuitable for complex industrial conditions.

[0006] Therefore, designing and preparing novel porous MOFs materials with excellent water stability, high CO2 adsorption capacity and high CO2 / C2H2 separation selectivity has become a core technical problem that urgently needs to be solved in the field of acetylene purification, and has important research significance and application value. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a zinc-based MOF material, its preparation method, and its applications. The zinc-based MOF material is prepared using a mixed ligand strategy. The zinc-based MOF material is prepared from 2,5-thiophene dicarboxylic acid (H2TDA), 1,2-bis(4-pyridine)ethylene (BPE), and zinc acetate dihydrate as raw materials to obtain a three-dimensional network framework material. This material has the ability to separate CO2 / C2H2 binary mixtures, filling the gap in the construction of novel zinc-based metal-organic framework materials using 2,5-thiophene dicarboxylic acid (H2TDA) and 1,2-bis(4-pyridine)ethylene (BPE) as ligands and their application in CO2 / C2H2 separation. The provided synthesis method is simple, green, and efficient.

[0008] The specific technical solution of the present invention is as follows: A zinc-based MOF material with the molecular formula [Zn(TDA)] 2- (BPE)], where Zn represents divalent zinc ions, TDA 2- BPE represents the deprotonated 2,5-thiophene dicarboxylate ligand, and BPE represents 1,2-bis(4-pyridine)ethylene.

[0009] This zinc-based MOF material belongs to the orthorhombic crystal system, space group Aba2. Its unit cell parameters are: axial lengths a = 36.6410 Å, b = 13.6989 Å, c = 16.0105 Å; α = β = γ = 90°; and the unit cell volume is 8036.33 Å. 3 Z=8.

[0010] The fundamental asymmetric unit of this zinc-based MOF material contains one Zn. 2+ 1 deprotonated TDA 2- Ligand molecules, one coordinated BPE ligand molecule; Zn in this crystal structure 2+ The coordination mode is six-coordinated, where four of the coordinated oxygen atoms come from the oxygen atoms of three carboxylic acid ligands, one of which provides two oxygen atoms; the two coordinated nitrogen atoms come from the nitrogen atoms of two 1,2-bis(4-pyridine)ethylene ligands.

[0011] The coordination structure of this material provides a structural basis for the efficient separation of CO2 / C2H2: on the one hand, the synergistic effect of Zn-O and Zn-N coordination bonds endows the framework with excellent water stability and structural rigidity, meeting the requirements of actual industrial conditions; on the other hand, the uncoordinated sulfur atoms uniformly distributed on the pore surface can form stronger hydrogen bonds and dipole interactions with CO2 molecules, achieving preferential adsorption of CO2 while retaining high-purity acetylene, providing structural guarantee for the efficient and selective separation of CO2 / C2H2.

[0012] Furthermore, the inventors also provided a method for preparing the above-mentioned zinc-based MOF material, the specific steps of which are as follows: The carboxylic acid ligand 2,5-thiophene dicarboxylic acid (H2TDA), the regulator 1,2-bis(4-pyridine)ethylene (BPE), and zinc acetate dihydrate were added to a mixed solution of N,N-dimethylformamide (DMF) and water (H2O), and the mixture was sonicated at room temperature. The mixture was then placed in a reaction vessel and stirred at room temperature on a magnetic stirrer. The mixture was then transferred to an oven and heated to 90-110°C, and kept at that temperature for 60-72 hours to obtain the zinc-based MOF material.

[0013] The 2,5-thiophene dicarboxylic acid used has the CAS number 4282-31-9 and its structural formula is shown in Formula I. Formula I.

[0014] The 1,2-bis(4-pyridine)ethylene used has CAS number 13362-78-2 and its structural formula is shown in Formula II. Formula II.

[0015] The molar ratio of 2,5-thiophene dicarboxylic acid, 1,2-bis(4-pyridine)ethylene, and zinc acetate dihydrate is 1:1:2-4.

[0016] The volume ratio of N,N-dimethylformamide (DMF) to water (H2O) in the mixed solution is 1:1.

[0017] The concentration of the 2,5-thiophene dicarboxylic acid in the mixed solution of DMF and H2O is 1.147 g / L; the concentration of the zinc acetate dihydrate in the mixed solution of DMF and H2O is 2.927-5.853 g / L.

[0018] The ultrasonic treatment was performed at 60 Hz for 30 min; the magnetic stirring was performed at 60 Hz for 12 h; and the heating rate in the oven was 10 ℃ / min.

[0019] The zinc-based MOF material prepared in this invention, after being cleaned with DMF, undergoes solvent exchange with methanol and dichloromethane, followed by vacuum removal of organic molecules (the above process is called activation). The resulting material exhibits significant adsorption differences for C2H2 and CO2, demonstrating preferential adsorption of CO2. Based on the Ideal Adsorption Solution Theory (IAST), the separation capability of the CO2 / C2H2 binary mixture is predicted to be approximately 3.71 at 273 K, indicating potential for practical separation.

[0020] Compared with existing technologies, the present invention has the following advantages: (1) The ligands selected in this invention contain nitrogen, oxygen, and sulfur atoms simultaneously, providing abundant polar interaction sites for gas adsorption. Furthermore, the crystal structure is orthorhombic, space group Aba2, with a regular and stable coordination framework, filling the gap in the ligands of 2,5-thiophene dicarboxylic acid (TDA). 2- This fills a gap in the field of CO2 / C2H2 separation by constructing novel zinc-based metal-organic framework complexes using 1,2-bis(4-pyridine)ethylene (BPE) as ligands.

[0021] (2) In the zinc-based MOF material prepared by the present invention, Zn 2+ The center adopts a six-coordinate configuration, constructing a stable framework through Zn-O (carboxylic acid) and Zn-N (pyridine) coordination bonds. The oxygen and nitrogen atoms on the ligands can form stronger hydrogen bonds and dipole interactions with CO2 molecules, achieving preferential adsorption of CO2. It shows excellent separation selectivity in CO2 / C2H2 separation applications, expands the crystallographic structural data of zinc-based complexes, helps to study their assembly mechanism, and provides structural support and theoretical guidance for industrial-scale production and gas adsorption separation applications.

[0022] (3) The synthesis method provided by the present invention is simple, mild, green and environmentally friendly, and has a high yield. It can not only efficiently prepare the target zinc-based MOF material, but also provide a feasible idea for the design and synthesis of similar functional MOFs materials. It has important value for expanding the application of zinc-based complexes in gas separation, catalysis, fluorescence recognition, optoelectronic materials and other fields. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the coordination mode of zinc ions in the zinc-based MOF material prepared in Example 1; Figure 2 The basic asymmetric structural unit of the zinc-based MOF material prepared in Example 1; Figure 3 This is a schematic diagram of the functionalized channels in the zinc-based MOF material prepared in Example 1; Figure 4 The XRD curve of the zinc-based MOF material prepared in Example 1; Figure 5 The single-component CO2 / C2H2 adsorption curve of the zinc-based MOF material prepared in Example 1 at 273 K; Figure 6 The single-component CO2 / C2H2 adsorption curve of the zinc-based MOF material prepared in Example 1 at 298 K; Figure 7 The zinc-based MOF material prepared in Example 1 under 298 K conditions exhibits the following Q values ​​in a CO2 / C2H2 mixed gas: st Adsorption thermogram; Figure 8 The IAST selectivity of the zinc-based MOF material prepared in Example 1 under CO2 / C2H2 mixed gas (volume ratio of 50:50) at 273 K is shown. Detailed Implementation

[0024] The present invention will be further illustrated below with reference to embodiments, which will help those skilled in the art to further understand the present invention, but will not limit the present invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the instruments and reagents used, unless otherwise specified, can be obtained through normal commercial channels.

[0025] Example 1: A method for preparing a zinc-based MOF material, specifically including the following steps: 2,5-Thiophene dicarboxylic acid, 1,2-bis(4-pyridine)ethylene and zinc acetate dihydrate were fed in a molar ratio of 1:1:2. 3.44 mg of 2,5-thiophene dicarboxylic acid, 3.64 mg of 1,2-bis(4-pyridine)ethylene and 8.78 mg of zinc acetate dihydrate were accurately weighed using an analytical balance and added to a 10 mL glass vial. 3 mL of mixed solvent (DMF and H2O in a 1:1 volume ratio) was added, and the mixture was sonicated at 60 Hz at room temperature for 30 min. The mixture was then placed in a glass vial and stirred at 60 Hz at room temperature for 12 h using a magnetic stirrer. The mixture was then transferred to an oven and heated to 90-110 °C at a rate of 10 °C / min, and held at this temperature for 60-72 h to obtain the zinc-based MOF material with a yield of 47.9%.

[0026] Example 2: A method for preparing a zinc-based MOF material, specifically including the following steps: The reactants 2,5-thiophene dicarboxylic acid, 1,2-bis(4-pyridine)ethylene and zinc acetate dihydrate were fed in a molar ratio of 1:1:4. 3.44 mg of 2,5-thiophene dicarboxylic acid, 3.64 mg of 1,2-bis(4-pyridine)ethylene and 17.56 mg of zinc acetate dihydrate were accurately weighed using an analytical balance and added to a 10 mL glass vial. 3 mL of mixed solvent (DMF and H2O in a 1:1 volume ratio) was added, and the mixture was sonicated at 60 Hz at room temperature for 30 min. The mixture was then placed in a glass vial and stirred at 60 Hz at room temperature for 12 h using a magnetic stirrer. The mixture was then transferred to an oven and heated to 90-110 °C at a rate of 10 °C / min, and held at this temperature for 60-72 h to obtain the zinc-based MOF material with a yield of 56.3%.

[0027] The zinc-based MOF materials prepared in Examples 1 and 2 have the same structure and the molecular formula [Zn(TDA)] 2- (BPE)], where Zn represents divalent zinc ions, TDA 2- BPE represents the deprotonated 2,5-thiophene dicarboxylate ligand, and BPE represents 1,2-bis(4-pyridine)ethylene.

[0028] Figure 1 This is a schematic diagram of the coordination mode of zinc ions in the zinc-based MOF material prepared in Example 1, as shown below. Figure 1 As shown in Table 1-3, zinc-based MOF materials belong to the orthorhombic crystal system, space group Aba2, and the basic asymmetric unit of the crystal contains one Zn atom. 2+ 1 deprotonated TDA 2- Ligand molecules, including one coordinated BPE ligand molecule. Zn in this crystal structure. 2+The coordination mode is six-coordinated, where four of the coordinated oxygen atoms come from the oxygen atoms of three carboxylic acid ligands, one of which provides two oxygen atoms; the two coordinated nitrogen atoms come from the nitrogen atoms of two 1,2-bis(4-pyridine)ethylene ligands.

[0029] Figure 2 The basic asymmetric structural unit of the zinc-based MOF material prepared in Example 1. Figure 3 This is a schematic diagram of the functionalized channels in the zinc-based MOF material prepared in Example 1. The H2TDA ligand bridges adjacent Zn groups through its two carboxyl groups. 2+ At the center, a two-dimensional layered framework is constructed in the horizontal direction; while the BPE ligand acts as a pillar, connecting the Zn in the upper and lower layers of the framework through the pyridine nitrogen atoms at both ends. 2+ At the center, the two-dimensional layer is expanded to form a through-hole. For example... Figure 2 , Figure 3 As shown, the ligands 2,5-thiophene dicarboxylic acid, 1,2-bis(4-pyridine)ethylene, and Zn 2+ The mutual coordination yields a three-dimensional channel structure.

[0030] The unit cell parameters are: axial length a = 36.6410 (7) Å, b = 13.6989 (3) Å, c = 16.0105 (3) Å, α = 90°, β = 90°, γ = 90°; the unit cell volume is V = 8036.33 Å. 3 Z=8.

[0031] The single-crystal structure was collected at room temperature using a Bruker Apex2 Smart CXD surface detector. Absorption correction was performed using a graphite monochromator with λ(Mo Kα) of 0.71073 Å and a variable-speed scan at ω⁻²θ using the multiscan program SADABS. The crystal structure was resolved directly using the Sir97 program; the structure of F2 was refined using the full-matrix least squares method with the SHELXL-97 program. Anisotropic refinement was performed on all non-hydrogen atoms. Hydrogen atoms in the organic ligands were generated through geometric symmetry (CH 0.96 Å).

[0032] Figure 4 The XRD patterns of the zinc-based MOF material prepared in Example 1 are shown below. The black curve represents the measured XRD pattern of the synthesized sample, and the red curve represents the simulated XRD pattern based on crystal structure data. It can be seen that the positions and relative intensities of the characteristic diffraction peaks of the synthesized sample are in high agreement with the simulated pattern, and no obvious impurity peaks appear. This indicates that the prepared MOF material has good crystallinity and high phase purity, providing a reliable structural basis for subsequent studies on gas adsorption and separation performance.

[0033] Table 1 Crystal Data .

[0034] Table 2 Typical bond length data for crystals (unit: Å) .

[0035] Table 3 Typical bond angle data for crystals (unit: °) .

[0036] Application Example 1: Detection of the adsorption performance of zinc-based MOF materials for C2H2 and CO2. The specific steps are as follows: 100 mg of the zinc-based MOF material prepared in Example 1 was taken, washed with DMF, and then immersed in fresh chromatographic methanol for solvent exchange (three exchanges, each soaking for 6 hours); under the same operating conditions, the same solvent exchange operation was performed again with fresh chromatographic dichloromethane. The zinc-based MOF material was transferred to an adsorption tube and degassed under vacuum at 100°C for 10 hours to obtain 94.8 mg of activated sample.

[0037] The activated samples were kept at a constant temperature using 0℃ and 25℃ constant temperature water baths, respectively. Under the same conditions, the single-component pressure swing adsorption curves of C2H2 and CO2 were measured sequentially using a JW-BK200 microporous analyzer (pressure range 0-110 kPa). A glass rod was placed in the adsorption tube, which was then installed on the analysis station, and the adsorption curves were measured at 273 K and 298 K. The experimental results are as follows: Figure 5 , 6 As shown, it is evident that the zinc-based MOF material exhibits significant differences in adsorption for the two gases.

[0038] Figure 7 The CO2 / C2H2 mixed gas Q for the zinc-based MOF material prepared in Example 1 st The heat of adsorption, Q of CO2, over the entire adsorption range. st The values ​​are all significantly higher than those for C2H2, indicating a stronger interaction between the material and CO2 molecules, and a superior adsorption affinity for CO2. Among them, the Q value for CO2... st The continuously increasing trend indicates a synergistic effect in the CO2 adsorption process of the material, and a relatively uniform energy distribution at the adsorption sites. Meanwhile, the Q of C2H2... st The curve exhibits a characteristic of first rising and then falling due to the significant energy inhomogeneity of its adsorption sites, with steric hindrance and weakly interacting sites dominating at high adsorption levels. This significant difference in adsorption heat provides a clear thermodynamic basis for the efficient separation of CO2 / C2H2 mixed systems using this material.

[0039] Figure 8The IAST selectivity of the zinc-based MOF material prepared in Example 1 for a CO2 / C2H2 mixed gas (volume ratio 50:50) at 0°C is shown in the figure. Based on the ideal adsorption solution theory, its IAST selectivity is calculated to be 3.71. In the low-pressure region (<20 kPa), the IAST selectivity decreases slightly with increasing pressure. This is because at low adsorption levels, C2H2 molecules preferentially occupy some of the matched high-energy sites, resulting in a relatively high initial adsorption rate, which temporarily weakens the adsorption advantage of CO2. As the pressure further increases (>20 kPa), the synergistic effect of the material on CO2 adsorption gradually becomes apparent, with the CO2 adsorption rate significantly exceeding that of C2H2. The selectivity continues to increase with pressure, eventually stabilizing at 3.71 in the 100-120 kPa range. These results indicate that the material exhibits good CO2 preferential adsorption selectivity for the CO2 / C2H2 mixed system under normal pressure conditions, demonstrating potential for practical separation applications.

[0040] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above. Those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of the present invention.

Claims

1. A zinc-based MOF material, characterized in that, The molecular formula of this material is [Zn(TDA)] 2- (BPE)], where Zn represents divalent zinc ions, TDA 2- BPE represents the deprotonated 2,5-thiophene dicarboxylate ligand, and BPE represents 1,2-bis(4-pyridine)ethylene.

2. The zinc-based MOF material according to claim 1, characterized in that, The zinc-based MOF material belongs to the orthorhombic crystal system, space group Aba2, with the following unit cell parameters: axial lengths a = 36.6410 Å, b = 13.6989 Å, c = 16.0105 Å; α = β = γ = 90°; and a unit cell volume of 8036.33 Å. 3 Z=8; The fundamental asymmetric unit contains one Zn. 2+ 1 deprotonated TDA 2- Ligand molecules, one coordinated BPE ligand molecule; Zn in this crystal structure 2+ The coordination mode is six-coordinated, where four of the coordinated oxygen atoms come from the oxygen atoms of the three carboxylic acid ligands, and two of the coordinated nitrogen atoms come from the nitrogen atoms of the two 1,2-bis(4-pyridine)ethylene ligands.

3. The method for preparing the zinc-based MOF material according to claim 1 or 2, characterized in that, The specific steps are as follows: 2,5-thiophene dicarboxylic acid ligand, 1,2-bis(4-pyridine)ethylene and zinc acetate dihydrate are added to a mixed solution of N,N-dimethylformamide and water, and ultrasonically treated at room temperature; the mixture is placed in a reaction vessel, stirred at room temperature on a magnetic stirrer, and then transferred to an oven and heated to 90-110℃ for 60-72 h to obtain the zinc-based MOF material.

4. The method for preparing the zinc-based MOF material according to claim 3, characterized in that, The molar ratio of 2,5-thiophene dicarboxylic acid, 1,2-bis(4-pyridine)ethylene and zinc acetate dihydrate is 1:1:2-1:1:

4.

5. The method for preparing the zinc-based MOF material according to claim 3, characterized in that, The volume ratio of N,N-dimethylformamide to water in the mixed solution is 1:

1.

6. The method for preparing the zinc-based MOF material according to claim 3, characterized in that, The concentration of the 2,5-thiophene dicarboxylic acid in the mixed solution of N,N-dimethylformamide and water was 1.147 g / L.

7. The method for preparing the zinc-based MOF material according to claim 3, characterized in that, The concentration of the zinc acetate dihydrate in a mixed solution of N,N-dimethylformamide and water is 2.927-5.853 g / L.

8. The method for preparing the zinc-based MOF material according to claim 3, characterized in that, The ultrasonic treatment was performed at 60 Hz for 30 min; the magnetic stirring was performed at 60 Hz for 12 h; and the heating rate in the oven was 10 ℃ / min.

9. The application of the zinc-based MOF material according to claim 1 in CO2 / C2H2 separation.

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