A calcium-based metal organic framework material and its preparation method and application in carbon dioxide capture

Abstract

The present invention belongs to the technical field of crystalline materials, and particularly relates to a calcium-based metal-organic framework material, a preparation method thereof, and an application in carbon dioxide capture. A calcium-based metal-organic framework material formed by using 2,5-pyrazinedicarboxylic acid as a ligand and a calcium salt through a solvothermal method is provided. When the calcium-based metal-organic framework material removes guest molecules and adsorbs CO2 molecules, a transformation of the unit cell parameters will occur. The present invention uses acetonitrile as a template agent to construct a metal-organic framework material. Due to the similarity between acetonitrile and CO2 molecules, this MOF has potential applications in CO2 capture.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystalline materials, and in particular relates to a calcium-based metal organic framework material and a preparation method thereof and application in carbon dioxide capture. Background Art

[0002] Human dependence on fossil fuels has led to the emission of carbon dioxide (CO 2 ) is excessively emitted. The continuous increase of carbon dioxide in the atmosphere has led to a series of serious climate problems. Although the amine solution absorption method is still the most mature post-combustion CO 2 Capture technology, but this technology has disadvantages such as high volatility, large-area corrosion of equipment and release of toxic pollutants, and due to its high adsorption enthalpy, it requires a lot of energy for regeneration. Compared with the high energy consumption of chemical absorption, porous adsorption materials have attracted widespread attention as an alternative. They usually have the advantages of fast adsorption kinetics, low regeneration cycle energy, no corrosion to equipment and no release of toxic pollutants. Common physical adsorbents include porous carbon, zeolites, ionic liquids, metal organic frameworks and porous organic polymers.

[0003] In particular, Metal-Organic Frameworks (MOFs), a three-dimensional network structure composed of metal ions and organic ligands connected by coordination bonds, is a type of organic-inorganic hybrid porous material with the characteristics of large specific surface area, high porosity, easy-to-adjust pore structure and performance. Due to these unique advantages, MOFs have been rapidly developed in many fields such as separation, sensing, and catalysis. Ideally, practical adsorbents for capturing trace amounts of carbon dioxide should not only have excellent adsorption properties (e.g., high adsorption capacity / selectivity, low adsorption enthalpy, and resistance to water vapor), but also have excellent stability and recyclability. However, the preparation of such MOFs remains a huge challenge because it is very difficult to achieve these properties simultaneously in MOFs. Therefore, the rational use of the template effect of the solvent to design and modify the pores can effectively achieve CO2. 2 Capture, which will promote the practical application of MOFs materials in the field of carbon capture. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a calcium-based metal organic framework material and a preparation method thereof and application in carbon dioxide capture.

[0005] The present invention is achieved through the following technical solutions:

[0006] A calcium-based metal organic framework material, wherein the calcium-based metal organic framework material is a metal ion Ca 2+ A porous material with a three-dimensional framework structure formed by self-assembly with an organic ligand 2,5-pyrazinedicarboxylic acid;

[0007] The structural formula of 2,5-pyrazinedicarboxylic acid is shown below:

[0008]

[0009] The three-dimensional framework structure is formed by coordination bonds between a one-dimensional calcium chain and nitrogen atoms and oxygen atoms in the ligand; the one-dimensional calcium chain is in a broken line shape and is composed of a number of mononuclear calcium nodes, and each mononuclear calcium node is in an eight-coordinate mode.

[0010] Furthermore, in the three-dimensional framework structure, each mononuclear calcium node is coordinated with two nitrogen atoms and six oxygen atoms from six ligands, respectively. Specifically, the four oxygen atoms come from four different ligands, one nitrogen atom and one oxygen atom come from the same ligand, and another nitrogen atom and one oxygen atom come from another ligand.

[0011] The coordination mode of the ligand is as follows: the N atom at one end of the 2,5-pyrazinedicarboxylic acid ligand is coordinated with a mononuclear calcium node, the two O atoms of the carboxyl group in the ligand bridge the other three mononuclear calcium nodes respectively, and the N atom at the symmetrical position of the ligand and the two O atoms of the carboxyl group are coordinated with the calcium node in another one-dimensional calcium chain in the same coordination mode;

[0012] The three-dimensional framework structure is obtained by infinitely extending and stacking the above coordination mode in space.

[0013] Furthermore, in the three-dimensional framework structure, the bond lengths of the Ca-O bonds are 2.444 Å, 2.457 Å, and 2.465 Å, respectively, and the bond length of the Ca-N bond is 2.605 Å;

[0014] In the three-dimensional framework structure, there is a 14.2 Å*7.6 Å particle along the C-axis. 2 The one-dimensional pores are diamond-shaped and the pore volume is 38%.

[0015] Further, from the perspective of skeleton connection construction, when acetonitrile guest molecules exist in the pores of the calcium-based metal-organic framework material, the crystal structure of the calcium-based metal-organic framework material belongs to the monoclinic system, and the space group is C2 / c , the unit cell parameters are: a = 9.0894(3) Å, b = 16.5853(5) Å, c = 5.8655(2) Å, α = γ= 90 o , β = 92.184(3) o .

[0016] Furthermore, the unit cell parameters of the calcium-based metal organic framework material change after the guest acetonitrile molecule is removed, and the crystal structure still belongs to the monoclinic system, and the space group is still C2 / c , the unit cell parameters are: a = 8.9931(5) Å, b =16.6295(7) Å, c = 5.8713(2) Å, α = γ= 90 o , β = 92.205(5) o ;

[0017] Furthermore, the calcium-based metal organic framework material removes the acetonitrile guest molecule and then adsorbs CO 2 After the molecule changes, the unit cell parameters change, the crystal structure still belongs to the monoclinic system, and the space group is still C2 / c , the unit cell parameters are: a = 8.9035(4)Å, b = 16.6510(8) Å, c = 5.8643(3) Å, α = γ= 90 o , β = 92.082(5) o .

[0018] The present invention also provides a method for preparing the calcium-based metal organic framework material, comprising the following steps:

[0019] Under sealed conditions, 2,5-pyrazinedicarboxylic acid (H 2 PZDC) and calcium salt N , N - dimethylformamide (DMF), acetonitrile (MeCN) and water (H 2 O) in a mixed solution, and the metal-organic framework crystals are obtained via a solvothermal reaction.

[0020] Furthermore, the 2,5-pyrazinedicarboxylic acid (H 2 The molar ratio of PZDC to calcium salt is 1:1, and each 1 mmol of calcium nitrate corresponds to (17.5-24) mL of DMF, (7.5-10) mL of acetonitrile, and (1-3.3) mL of water. The temperature of the thermal reaction is 80°C-100°C, and the reaction time is 6-24 hours.

[0021] The present invention also provides the calcium-based metal organic framework material in CO 2 Capture applications.

[0022] Beneficial technical effects of the present invention:

[0023] The present invention provides a calcium-based metal organic framework material formed by a solvent thermal method using 2,5-pyrazine dicarboxylic acid as a ligand and a calcium salt. The calcium-based metal organic framework material removes guest molecules and adsorbs CO 2 The molecules can undergo framework structure transformation. The present invention uses acetonitrile as a template to construct a metal-organic framework material. 2 The molecular similarity makes this MOF 2 It has potential applications in capture. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The coordination mode diagram of the mononuclear Ca node of the metal organic framework material obtained in Example 1-2;

[0025] Figure 2 This is a schematic diagram of the structure of a one-dimensional calcium chain of the metal organic framework material obtained in Example 1-2;

[0026] Figure 3 The coordination pattern diagram of the ligand of the metal organic framework material obtained in Example 1-2;

[0027] Figure 4 The three-dimensional structure diagram of the metal organic framework material obtained in Example 1-2;

[0028] Figure 5 XRD patterns of the crystal obtained in Example 1-2, the crystal after removing the guest molecules and the crystal after carbon dioxide adsorption;

[0029] Figure 6 This is a thermal stability analysis diagram of the metal organic framework material obtained in Example 1-2 before and after degassing;

[0030] Figure 7 The N of the metal organic framework material obtained in Example 1-2 at 77K 2 The adsorption isotherms of CO at 195K 2 Adsorption isotherms of

[0031] Figure 8 The adsorption isotherms of carbon dioxide and nitrogen of the metal organic framework material obtained in Example 1-2 at 298 and 313 K;

[0032] Fig. 9 The simulated flue gas (CO) with different humidity of the metal organic framework material obtained in Example 1-2 2 :N 2 =4:96) penetration test result diagram;

[0033] Fig.10 For CO 2 Schematic diagram of single crystal structure analysis of the crystal after gas adsorption. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with examples, but the present invention is not limited to the following examples.

[0035] Example 1

[0036] Weigh the commercially available ligand H 2 PZDC (0.3 mmol) and Ca(NO 3 ) 2 ·4H 2 O (0.3 mmol) or CaCl 2 (0.3mmol) was placed in a 20 mL glass vial, 7.2 mL of DMF solution, 3 mL of acetonitrile solution and 1 mL of water were added, and then the vial was sealed and placed in an ultrasonicator for 5 minutes at room temperature. o C oven for 24 hours. After the reaction, the oven was turned off and the solid particles in the vial were collected by filtration after cooling to room temperature. Then, they were washed with DMF and acetonitrile (5 mL × 3) in sequence. Under the microscope, light yellow transparent strip crystals [Ca(PZDC)(MeCN)] were obtained (yield: 98%, based on H 2 PZDC ligand).

[0037] Example 2

[0038] Weigh the commercially available ligand H 2 PZDC (2.0 mmol) and Ca(NO 3 ) 2 ·4H 2 O (2.0 mmol / L) or CaCl 2 (2.0mmol) was placed in a 100 mL round-bottom flask, and 35 mL of DMF, 15 mL of acetonitrile solution and 2 mL of water were added. The flask was then sealed and placed in an ultrasonicator for 5 minutes at room temperature. o C oil bath and stirred for 6 hours. After the reaction was completed, the oil bath was closed and cooled to room temperature. The solid powder obtained in the flask was collected by centrifugal filtration and then washed with DMF and acetonitrile (5 mL × 3) in sequence. White powder crystals [Ca(PZDC)(MeCN)] were obtained under a microscope (yield: 95%, based on H 2 PZDC ligand).

[0039] The results are the same, see below for details:

[0040] (1) Determination of crystal structure:

[0041] Single crystals of suitable size were selected and data were collected using a PANalytical X'Pert PRO high-resolution powder diffractometer at 293 K. Data were collected using a Cu-K α (λ = 1.5406 Å) target ray. The absorption correction of the data was completed using SCALE3 ABSPACK software. The crystal structure was solved by the direct method using the SHELXTL-97 program. First, the coordinates of all non-hydrogen atoms were determined by the difference function method and the least squares method, and the positions of hydrogen atoms were obtained by the theoretical hydrogenation method, and then the crystal structure was refined using SHELXTL-97. The crystallographic data are shown in Table 1. The first column of data is the crystal structure data obtained in Example 1-2, the second column is the crystal structure data after removing the guest molecule (immersing the single crystal in acetonitrile solvent, changing the solvent every 12 hours, and degassing at 200°C for 12 hours under vacuum conditions after three days of replacement), and the third column is the crystal structure data after removing the guest molecule and then adsorbing carbon dioxide.

[0042] Table 1 Crystallographic data of metal organic framework materials

[0043]

[0044] The structure of the calcium-based metal organic framework material is shown in Figure 1-4 shown.

[0045] Figure 1 The coordination mode diagram of the mononuclear Ca node of the metal organic framework material obtained in Example 1-2 shows that each mononuclear calcium node is in an eight-coordinate mode, coordinated by two nitrogen atoms and six oxygen atoms from six ligands, specifically, four oxygen atoms come from four different ligands, one nitrogen atom and one oxygen atom come from the same ligand, and another nitrogen atom and one oxygen atom come from another ligand; the mononuclear calcium nodes form a one-dimensional calcium chain in a broken line by bridging carboxylic acid oxygen atoms, as shown in FIG. Figure 2 .

[0046] Figure 3 The coordination mode diagram of the ligand of the metal organic framework material obtained in Example 1-2 shows that the coordination mode of the ligand is as follows: the N atom at one end of the 2,5-pyrazinedicarboxylic acid ligand is coordinated with a mononuclear calcium node, the two O atoms of the carboxyl group in the ligand bridge the other three mononuclear calcium nodes respectively, and the N atom at the symmetrical position in the ligand and the two O atoms of the carboxyl group are coordinated with the calcium node in another one-dimensional calcium chain in the same coordination mode;

[0047] The three-dimensional framework structure is obtained by infinitely extending and stacking the above-mentioned single-core Ca nodes and the coordination mode of the ligands in space, as shown in detail. Figure 4In the three-dimensional framework structure, the bond lengths of Ca-O are 2.444 Å, 2.457 Å and 2.465 Å, respectively, and the bond length of Ca-N is 2.605 Å; along the C-axis, there is a 14.2 Å*7.6 Å 2 The one-dimensional pores are diamond-shaped and the pore volume is 38%.

[0048] Characterization of materials:

[0049] The materials obtained in Example 1-2 were characterized by X-ray diffraction and thermogravimetric analysis. Figure 5 The XRD patterns of the crystals obtained in Example 1-2, the crystals after removing the guest molecules and the crystals after carbon dioxide adsorption; Figure 5 It can be seen that the single crystal was synthesized into a pure phase, and XRD confirmed the relationship between the guest molecule before and after removal and the adsorbed CO 2 The structure after that has not changed.

[0050] Figure 6 The thermal stability analysis diagram of the metal organic framework material obtained in Example 1-2 before and after degassing is shown; it can be found that the thermal stability of the structure of the metal organic framework material remains unchanged before and after vacuum heating degassing, and the collapse temperature remains at 470° C. At the same time, it also proves that the solvent molecules in the guest-free phase pores after heating degassing are completely removed.

[0051] (2) Gas adsorption test characterization

[0052] Figure 7 is the N of the metal organic framework material obtained in Example 1-2 at 77K 2 The adsorption isotherms of CO at 195K 2 The adsorption isotherm.

[0053] Depend on Figure 7 It can be seen that the metal has a frame at 77K to N 2 There is no adsorption, which is due to the pore limitation at 77K, which prevents nitrogen molecules from entering the pores; 2 The adsorption amount can be used to calculate the specific surface area of ​​the framework: S BET =517.77 m 2 g -1 .

[0054] Figure 8 The adsorption isotherms of the metal organic framework material obtained in Example 1-2 for carbon dioxide and nitrogen at 298 and 313 K. Figure 8 It can be seen that the metal organic framework material is subjected to CO at 298K and 40mbar. 2The adsorption capacity is about 2.7 mmol, about 4.2 mmol at normal pressure; CO at 313K, 40 mbar 2 The adsorption capacity is about 1.8 mmol, and about 4.0 mmol at normal pressure; it proves its ability to capture CO in a gas power plant environment. 2 ability.

[0055] Penetration test

[0056] The breakthrough experiment was carried out by imitating industrial separation conditions, and CO 2 :N 2 =4:96 mixed gas experiment, before the experiment, the metal organic framework was placed in the filling column, degassed by vacuum heating, and after the degassing was completed, the mixed gas controlled by the mass flow meter was turned on for experiment. After the gas passed through the column, it entered the mass spectrometer for gas composition and content analysis. The penetration experiment with different humidity was set by adjusting the flow meter parameters. The results are shown in Fig. 9 , it can be found that for every 360 mg of sample, CO 2 The penetration time was kept at 55 min, and the adsorption amount was basically the same as the static adsorption amount at 40 mmbar. Although the relative humidity was increased to 75%, the CO adsorption of the metal organic framework 2 The collection performance has not decreased.

[0057] (3) CO 2 Adsorption mechanism

[0058] CO 2 The crystals after gas adsorption were further analyzed for single crystal structure. Fig.10 As shown, the CO adsorbed by the material of the present invention 2 The position of the molecule is the position of the acetonitrile molecule.

Claims

1. A calcium-based metal-organic framework material, characterized in that: The calcium-based metal organic framework material is based on metal ions Ca 2+ A porous material with a three-dimensional framework structure formed by self-assembly with an organic ligand 2,5-pyrazinedicarboxylic acid; The structural formula of 2,5-pyrazinedicarboxylic acid is shown below: ； The three-dimensional framework structure is formed by coordination bonds between a one-dimensional calcium chain and nitrogen atoms and oxygen atoms in the ligand; the one-dimensional calcium chain is in a broken line shape and is composed of a number of mononuclear calcium nodes, each of which is in an eight-coordinate mode; From the perspective of skeleton connection construction, when acetonitrile guest molecules exist in the pores of the calcium-based metal-organic framework material, the crystal structure of the calcium-based metal-organic framework material belongs to the monoclinic system, and the space group is C2 / c , the unit cell parameters are: a =9.0894(3)Å, b=16.5853(5)Å, c=5.8655(2)Å, α = γ= 90 o , β =92.184(3) o .

2. The calcium-based metal organic framework material according to claim 1, characterized in that: In the three-dimensional framework structure, the bond lengths of Ca-O bonds are 2.444Å, 2.457Å, and 2.465Å, respectively, and the bond length of Ca-N bond is 2.605Å; In the three-dimensional framework structure, there is a one-dimensional pore with a size of 14.2Å*7.6Å along the C-axis direction. The pore shape is diamond and the pore volume is 38%.

3. The calcium-based metal organic framework material according to claim 1, characterized in that: The unit cell parameters of the calcium-based metal organic framework material change after removing the guest acetonitrile molecule, and the crystal structure still belongs to the monoclinic system, and the space group is still C2 / c , the unit cell parameters are: a =8.9931(5)Å, b=16.6295(7)Å, c=5.8713(2)Å, α = γ= 90 o , β =92.205(5) o .

4. The calcium-based metal organic framework material according to claim 1, characterized in that: The unit cell parameters of the calcium-based metal organic framework material change after the acetonitrile guest molecule is removed and then the CO2 molecule is adsorbed, and the crystal structure still belongs to the monoclinic system, and the space group is still C2 / c , the unit cell parameters are: a =8.9035(4)Å, b=16.6510(8)Å, c=5.8643(3)Å, α = γ= 90 o , β =92.082(5) o .

5. A method for preparing a calcium-based metal organic framework material as claimed in any one of claims 1 to 2, characterized in that: The steps include: Under sealed conditions, 2,5-pyrazinedicarboxylic acid and calcium salt are reacted in a mixed solution of DMF, acetonitrile and water via a solvothermal reaction to obtain the crystal of the metal-organic framework.

6. The method for preparing a calcium-based metal organic framework material according to claim 5, characterized in that: The molar ratio of the 2,5-pyrazinedicarboxylic acid to the calcium salt is 1:1, and each 1 mmol of calcium nitrate corresponds to (17.5-24) mL of DMF, (7.5-10) mL of acetonitrile, and (1-3.3) mL of water. The thermal reaction temperature is 80° C.-100° C., and the reaction time is 6-24 hours.

7. Use of the calcium-based metal organic framework material as described in any one of claims 1 to 2 in CO2 capture.

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