Five-element multi-cage zinc-based organic framework material as well as preparation method and application thereof

Abstract

The invention discloses a five-element multi-cage zinc-based organic framework material and a preparation method and application thereof, the molecular formula of the material is Zn5 (mu-H2O) (1, 2, 4-BTC) 2 (Ad) 4], the material belongs to an R-3c (No.167) space group of a trigonal system, the cell parameters are # imgabs 0 # alpha = beta = 90 degrees, gamma = 120 degrees, and the cell volume is # imgabs 1 #, the material is prepared by taking zinc acetate, adenine and 1, 2, 4-trimellitic anhydride as raw materials, DMF and water as solvents, and the materials are subjected to one-step reaction to obtain the five-element multi-cage zinc-based organic framework material. The material is prepared through solvothermal reaction. The material has the structural characteristics of multiple components, multiple cages and more electronegative sites, has excellent thermal stability and chemical stability, has the ethane and acetylene adsorption capacity greater than that of ethylene under the conditions of 25 DEG C and 1 bar, can realize one-step purification of ethylene in C2 gas, has the propylene adsorption capacity far greater than that of ethylene, can realize separation of MTO (Methanol To Olefin) products, and has good application prospects. The method has a wide application prospect in the fields of one-step purification of ethylene in C2 gas and separation of ethylene from MTO products.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal organic framework materials, and in particular relates to a five-element multi-cage zinc-based organic framework material and a preparation method and application thereof. Background Art

[0002] Metal-organic frameworks (MOFs) are a new class of solid porous materials. They are composed of three-dimensional networks formed by the self-assembly of metal ions or metal clusters and organic ligands through coordination bonds. MOFs have a rich and diverse structure and have shown potential applications in energy gas adsorption and separation, carbon capture and conversion, and heterogeneous catalysis. Consequently, they have garnered extensive research attention over the past two decades. While tens of thousands of MOFs for ethylene and ethane separation have been reported, few five-component multi-cage MOFs have been developed for both the single-step purification of ethylene from C2 gas and the purification of ethylene from MTO products.

[0003] As an emerging porous material, multi-component organic framework materials often use transition metals as basic building blocks, and then introduce multiple organic ligands to try to construct new multi-element MOF materials. Therefore, the structure and preparation of this type of material have received attention from multiple research groups. Summary of the Invention

[0004] The purpose of the present invention is to provide a five-element multi-cage zinc-based organic framework material, and to provide a preparation method and application of the material.

[0005] For the above purpose, the present invention provides a five-element multi-cage zinc-based organic framework material with a molecular formula of Zn5(μ-H2O)(1,2,4-BTC)2(Ad)4], wherein 1,2,4-BTC represents completely deprotonated 1,2,4-benzene trimellitic anhydride, and Ad represents deprotonated adenine; the material belongs to the trigonal crystal system, R-3c (No.167) space group, and the unit cell parameters are: α=β=90°,γ=120°,the unit cell volume is

[0006]

[0007] In the crystal structure of the above-mentioned five-element multi-cage zinc-based organic framework material, there are five crystallographically independent zinc ions, all of which present a tetrahedral coordination geometry. These zinc ions are coordinated with the nitrogen atoms at the N3, N7, and N9 positions of adenine, bridging water molecules, and the three monodentate carboxylic acid oxygen atoms of 1,2,4-benzenetricarboxylic acid, respectively. This coordination mode forms three different zinc-based structural units: mononuclear zinc unit [ZnN2(O2C─)2], binuclear zinc unit [Zn2(Ad)3(O2C─)2], and hexanuclear zinc cluster [Zn6N3(μ-H2O)3(Ad)3(O2C─)6]; these structural units are cross-linked with each other through deprotonated adenine and completely deprotonated 1,2,4-benzenetricarboxylic acid linkers, ultimately forming a three-dimensional network structure. The crystal structure of this material also contains three cages of different sizes: the size is Cage-I, size is The cage-II and the dimensions are Cage-III, Cage-I through The window of is connected to six cage-IIs, and each cage-II is connected to two cage-Is and one cage-III, where the shared window size between cage-II and cage-III is In this crystal structure, the ratio of cage-I, cage-II and cage-III is 1:6:1.

[0008] The preparation method of the penta-element multi-cage zinc-based organic framework material of the present invention is as follows: zinc acetate, adenine and 1,2,4-benzene trimellitic anhydride are added to a mixed solution of N,N-dimethylformamide and deionized water; after the solution is clarified, it is heated at 90-105° C. for 36-48 hours under closed conditions; and cooled to room temperature to obtain the penta-element multi-cage zinc-based organic framework material.

[0009] In the above preparation method, the molar ratio of trimellitic anhydride to adenine and zinc acetate is preferably 1:3.5-4.5:4.5-5.5.

[0010] In the above preparation method, the volume ratio of N,N-dimethylformamide to deionized water is preferably 5 to 6:1.

[0011] In the above preparation method, it is further preferred to heat at 95° C. for 48 hours under sealed conditions.

[0012] The present invention also provides the use of the five-element multi-cage zinc-based organic framework material in the one-step purification of ethylene from C2 gas (ethane, ethylene, acetylene) and the separation of ethylene from MTO products.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention uses zinc acetate as a metal source, adenine and 1,2,4-trimellitic anhydride as organic ligands, and N,N-dimethylformamide and deionized water as solvents to prepare a five-element multi-cage zinc-based organic framework material through a solvothermal reaction. The five-element multi-cage zinc-based organic framework material has an inert porous environment and abundant electronegative sites, which can provide more supramolecular bonds and sites. In addition to supramolecular interactions, it also exhibits van der Waals forces. Furthermore, the organic framework material has a multi-cage structure with abundant electronegative sites within the three cages. The π···π interactions enhance the adsorption of acetylene, ethane, and propylene. At 25°C and 1 bar, the adsorption of ethane and acetylene is greater than that of ethylene, enabling the separation and purification of ethylene from C2 gas. The adsorption of propylene is much greater than that of ethylene, enabling the separation and purification of ethylene from MTO products. This material has broad application prospects in the fields of one-step purification of ethylene from C2 gas and separation and purification of ethylene from MTO products. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0016] Figure 2 Schematic diagram of the cage of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0017] Figure 3 This is the powder X-ray diffraction pattern of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0018] Figure 4 This is a thermal analysis diagram of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0019] Figure 5 This is a nitrogen adsorption isotherm diagram of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0020] Figure 6 This is the pore size distribution diagram of the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0021] Figure 7 This is a temperature-dependent adsorption isotherm diagram of acetylene for the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0022] Figure 8 This is a temperature-dependent adsorption isotherm diagram of ethylene for the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0023] Figure 9 This is a temperature-dependent adsorption isotherm diagram of ethane for the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0024] Figure 10 This is a temperature-dependent adsorption isotherm diagram of propylene for the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0025] Figure 11 The Q of the five-element multi-cage zinc-based organic framework material prepared in Example 1 is st picture.

[0026] Figure 12 This is the adsorption isotherm diagram of acetylene, ethylene and ethane of the five-element multi-cage zinc-based organic framework material prepared in Example 1 at 298K.

[0027] Figure 13 This is the adsorption isotherm diagram of ethylene and propylene at 298K for the five-element multi-cage zinc-based organic framework material prepared in Example 1.

[0028] Figure 14 This is the IAST selectivity diagram of the five-element multi-cage zinc-based organic framework material prepared in Example 1 for acetylene / ethylene and ethane / ethylene.

[0029] Figure 15 This is the IAST selectivity diagram of the five-element multi-cage zinc-based organic framework material prepared in Example 1 for propylene / ethylene.

[0030] Figure 16 This is a curve diagram of the penetration experiment of the five-element multi-cage zinc-based organic framework material prepared in Example 1 to C2 mixed gas.

[0031] Figure 17 This is a curve diagram of the penetration experiment of the five-element multi-cage zinc-based organic framework material prepared in Example 1 to the MTO product mixed gas. DETAILED DESCRIPTION

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited to these examples.

[0033] Example 1

[0034] 27.4 mg (0.125 mmol) of zinc acetate dihydrate, 6.75 mg (0.05 mmol) of adenine, 4.8 mg (0.025 mmol) of 1,2,4-benzene trimellitic anhydride, 3.25 mL of N,N-dimethylformamide, and 0.6 mL of water were added to a 10 mL glass scintillation vial and ultrasonically shaken at room temperature until clear. The glass scintillation vial was sealed and placed in a 95°C oven for 48 hours and then cooled to room temperature to produce a large amount of colorless cubic crystals, namely a five-element multi-cage zinc-based organic framework material. The structure of the obtained material was characterized by single crystal X-ray diffraction. The molecular formula of the material is Zn5(μ-H2O)(1,2,4-BTC)2(Ad)4], where 1,2,4-BTC represents completely deprotonated 1,2,4-benzene trimellitic anhydride and Ad represents deprotonated adenine. It belongs to the trigonal system, R-3c (No.167) space group, and the unit cell parameters are α=β=90°,γ=120°,the unit cell volume is like Figure 1 As shown, in the crystal structure of this material, there are five crystallographically independent zinc ions, all of which present a tetrahedral coordination geometry. These zinc ions are coordinated with the nitrogen atoms at positions N3, N7, and N9 of adenine, bridging water molecules, and the three monodentate carboxylic acid oxygen atoms of 1,2,4-benzenetricarboxylic acid, respectively. This coordination mode forms three different zinc-based structural units: mononuclear zinc units [ZnN2(O2C─)2], binuclear zinc units [Zn2(Ad)3(O2C─)2], and hexanuclear zinc clusters [Zn6N3(μ-H2O)3(Ad)3(O2C─)6]. These structural units are cross-linked with each other through deprotonated adenine and completely deprotonated 1,2,4-benzenetricarboxylic acid linkers, ultimately forming a complex and precise three-dimensional network structure. Due to the presence of these three secondary building units (SBUs) and two ligands, the framework is classified as a five-element MOF. As Figure 2 As shown, the material's crystal structure contains cages of three different sizes: Cage-I, size is The cage-II and the dimensions are Cage-III. Cage-I through The window of is connected to six cage-IIs, and each cage-II is connected to two cage-Is and one cage-III, where the shared window size between cage-II and cage-III is In this crystal structure, the ratio of cage-I, cage-II and cage-III is 1:6:1.

[0035] The prepared five-element multi-cage zinc-based organic framework material, the material after methanol exchange and the activated material after vacuum heating and degassing at 150°C for 12 hours were characterized by powder X-ray. Figure 3 . Figure 3 It shows that the positions of the diffraction peaks of the three materials in the powder X-ray diffraction pattern are completely consistent with the positions of the diffraction peaks in the powder X-ray diffraction pattern simulated by the structural data obtained by single crystal structure analysis, which shows that the single crystal structure determined by the X-ray diffractometer can well describe the material structure, thereby proving that the large amount of colorless and transparent cubic crystals prepared by the present invention are of high purity and have good chemical stability.

[0036] pass Figure 4 From the thermogravimetric analysis curve, it can be seen that the curve maintains a platform state before 330°C, which means that the material remains stable within this temperature range. Thereafter, the weight begins to decrease until the framework completely collapses at 450°C, indicating that the five-element multi-cage zinc-based organic framework material prepared in this example has good thermal stability.

[0037] In order to confirm the porosity of the five-element multi-cage zinc-based organic framework material obtained above, the N2 adsorption isotherm of the sample was tested at 77K, and a typical "I" type curve was obtained (see Figure 5 ), proving that it is a microporous material, and the adsorption capacity of N2 reaches 316cm 3 g -1 , BET specific surface area is 1220m 2 g -1 , pore volume is 0.50cm 3 g -1 .from Figure 6 From the pore size distribution diagram, we can see that the pore diameter is The pore size is within the range, which is consistent with the pore size calculated crystallographically.

[0038] The adsorption isotherms of the five-element multi-cage zinc-based organic framework material prepared in Example 1 for single components acetylene, ethylene, ethane and propylene at 0-1 bar, 298K and 273K were further tested. The results are shown in Figures 7-10 As can be seen from the figure, the material exhibits the characteristics of better adsorption of acetylene and ethane than ethylene and better adsorption of propylene than ethylene. At 298K, the adsorption of acetylene, ethane and propylene are 101.61cm 3 g -1 (4.54mmol g -1 ), 79.89cm 3 g -1 (3.57mmol g -1 ) and 115.51cm 3 g -1 (5.16mmol g -1 ), which is significantly higher than the ethylene adsorption capacity of 72.85 cm 3 g-1 (3.25mmol g -1 At 273K, acetylene (135cm 3 g -1 )>Acrylic(124cm 3 g -1 )>Ethane(105cm 3 g -1 )>Ethylene(95cm 3 g -1 ) trend, indicating that the affinity of this material to acetylene, ethane and propylene is significantly greater than that to ethylene.

[0039] In order to evaluate the strength of the van der Waals force between the adsorbed ethane and ethylene gases and the five-element multi-cage zinc-based organic framework prepared in Example 1, the adsorption enthalpies (Q) of ethane and ethylene were calculated using the adsorption data of single-component gases at 298 K and 273 K. st ), the adsorption enthalpy at zero point can best reflect the affinity between gas molecules and the material framework. The zero-point adsorption enthalpy of acetylene, ethane, propylene and ethylene are 25.93 kJ mol -1 , 24.71 kJ mol -1 、32.52kJ mol -1 and 23.73 kJ mol -1 (like Figure 11 ), which is consistent with the results of the single-component adsorption isotherm, indicating that the interaction between the material and ethane is indeed stronger than that with ethylene.

[0040] Separation selectivity is an important indicator to measure the separation performance of materials. Figure 12 and 13 The single-component gas adsorption isotherm data of the five-element multi-cage zinc-based organic framework material prepared in Example 1 at 298K were used to calculate the separation selectivity of the material for ethane and ethylene using the ideal adsorption solution theory. Figures 14-15 As shown, the IAST selectivity for an ethane / ethylene volume ratio of 10:90 is 1.26 (1 bar), the IAST selectivity for an acetylene / ethylene volume ratio of 50:50 is 2.05 (1 bar), and the IAST selectivity for a propylene / ethylene volume ratio of 20:50 is 8.41 (1 bar). The calculation of adsorption selectivity provides a good theoretical foundation for actual separation results.

[0041] Figure 16 and Figure 17 Driven by the results of IAST theoretical calculations, the actual separation ability of the five-element multi-cage zinc-based organic framework material prepared in Example 1 for C2 mixed gas and MTO products was verified. The separation was carried out with a volume ratio of acetylene, ethane and ethylene of 1:1:1 and a total flow rate of 1 mL min-1 The volume ratio of propylene, ethylene and helium is 20:50:30, and the total flow rate is 4 mL min -1 The penetration test shows that the material has a good effect in separating ethylene from C2 mixed gas and MTO products. The longer time interval means that the material can effectively separate ethylene and achieve the purpose of one-step purification of ethylene.

Claims

1. A five-element multi-cage zinc-based organic framework material, characterized by: The molecular formula of the material is [Zn5(μ-H2O)(1,2,4-BTC)2(Ad)4], where 1,2,4-BTC represents completely deprotonated 1,2,4-benzene trimellitic anhydride and Ad represents deprotonated adenine; The material belongs to the trigonal crystal system, R-3c (No.167) space group, unit cell parameters: α=β=90°,γ=120°,the unit cell volume is 2. The five-element multi-cage zinc-based organic framework material according to claim 1, characterized in that: The material's crystal structure contains five crystallographically independent zinc ions, all exhibiting a tetrahedral coordination geometry. These zinc ions are coordinated with the nitrogen atoms at positions N3, N7, and N9 of adenine, a bridging water molecule, and the three monodentate carboxylic acid oxygen atoms of 1,2,4-benzenetricarboxylic acid, respectively. This coordination pattern forms three different zinc-based structural units: a mononuclear zinc unit [ZnN2(O2C─)2], a binuclear zinc unit [Zn2(Ad)3(O2C─)2], and a hexanuclear zinc cluster [Zn6N3(μ-H2O)3(Ad)3(O2C─)6]. These structural units are cross-linked through deprotonated adenine and completely deprotonated 1,2,4-benzenetricarboxylic acid linkers, ultimately forming a three-dimensional network structure. The material's crystal structure contains cages of three different sizes: Cage-I, size is The cage-II and the dimensions are Cage-III, Cage-I through The window of is connected to six cage-IIs, and each cage-II is connected to two cage-Is and one cage-III, where the shared window size between cage-II and cage-III is In this crystal structure, the ratio of cage-I, cage-II and cage-III is 1:6:

1.

3. A method for preparing the penta-unit multi-cage zinc-based organic framework material according to claim 1, characterized in that: Zinc acetate, adenine and 1,2,4-benzene trimellitic anhydride are added to a mixture of N,N-dimethylformamide and deionized water. After the solution is clarified, it is heated at 90-105°C for 36-48 hours under closed conditions and cooled to room temperature to obtain a penta-unit multi-cage zinc-based organic framework material.

4. The method for preparing a five-element multi-cage zinc-based organic framework material according to claim 3, characterized in that: The molar ratio of the trimellitic anhydride to adenine and zinc acetate is 1:3.5-4.5:4.5-5.

5.

5. The method for preparing the five-element multi-cage zinc-based organic framework material according to claim 3, characterized in that: The volume ratio of the N,N-dimethylformamide to deionized water is 5-6:

1.

6. The method for preparing a five-element multi-cage zinc-based organic framework material according to claim 3, characterized in that: Heat at 95°C for 48 hours under sealed conditions.

7. Use of the five-element multi-cage zinc-based organic framework material according to claim 1 in the one-step purification of ethylene from C2 gas.

8. Use of the five-element multi-cage zinc-based organic framework material according to claim 1 in separating ethylene from MTO products.

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