A kind of π complex hollow MOFs pipe structure adsorbing material and its preparation method and application

Abstract

The application discloses a kind of π complex hollow MOFs pipe structure adsorbing material and its preparation method and application, belong to MOFs adsorbing material technical field.Its preparation steps are:1) metal salt, organic ligand and metal ion are uniformly mixed in monohydric alcohol aqueous solution, heated and reacted, and precursor MOFs are prepared;2) precursor MOFs are mixed with monovalent carboxylic acid aqueous solution, and etching is carried out by hydrothermal reaction, to obtain π complex hollow MOFs pipe structure adsorbing material.The π complex hollow MOFs pipe structure adsorbing material prepared by the application has stable hollow tubular structure, and the micro-morphology can be controlled, and shows high efficient adsorption separation performance to ethane / ethylene mixed gas, and has wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of MOFs adsorption material technology, specifically relating to a π-complexed hollow MOFs tube structure adsorption material, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs), as an emerging type of crystalline porous material, have been widely used in adsorption separation due to their advantages such as high specific surface area, adjustable pore environment, and pore size. Taking the adsorption separation of ethylene / ethane mixtures as an example, since ethylene and ethane have similar molecular sizes and boiling points, traditional cryogenic distillation methods are energy-intensive and have low separation efficiency. Adsorption separation technology using high-performance porous adsorbents is a potential energy-saving separation method to replace traditional cryogenic distillation.

[0003] Adsorbents can be classified into ethane-selective MOFs and ethylene-selective MOFs based on the gases they preferentially adsorb. Ethane-selective MOFs are difficult to optimize in terms of adsorption and separation performance, and their separation efficiency for ethane / ethylene mixtures is relatively low. In contrast, ethylene-selective MOFs have gained popularity due to their excellent C2H4 / C2H6 IAST separation selectivity. However, ethylene-selective MOFs are often unstable in water, acidic, or alkaline solutions, and the synthesized MOF adsorbents have relatively uniform morphologies, failing to adequately meet the industrial demand for diverse morphologies. Summary of the Invention

[0004] The purpose of this invention is to provide a π-complexed hollow MOFs tube structure adsorbent material, its preparation method and application. The obtained MOFs adsorbent material has a stable hollow tube structure and its microstructure can be controlled. It exhibits high-efficiency adsorption and separation performance for ethane / ethylene mixed gas.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing a π-complexed hollow MOF tube structure adsorbent material is provided, comprising the following steps:

[0007] 1) Metal salt, organic ligand and metal ion source are uniformly mixed in a monohydric alcohol aqueous solution and heated to react, thus preparing precursor MOFs;

[0008] 2) The precursor MOFs material obtained in step 1) is mixed with a monocarboxylic acid aqueous solution and etched by hydrothermal reaction to obtain a π-complexed hollow MOFs tube structure adsorbent material.

[0009] According to the above scheme, in step 1), after the reaction is completed, the precursor MOFs are washed and purified to obtain the precursor MOFs.

[0010] According to the above scheme, in step 2), after the hydrothermal reaction is completed, the material is cooled, purified, centrifuged, and dried to obtain the π-complexed hollow MOFs tube structure adsorbent material.

[0011] According to the above scheme, in step 1), the reaction temperature is 50-150℃ and the reaction time is 24-48h.

[0012] According to the above scheme, in step 1), the metal salt is one of aluminum chloride, ferric chloride, ferric acetate, and chromium nitrate.

[0013] According to the above scheme, in step 1), the organic ligand is one of 2-aminoterephthalic acid, 2-hydroxyterephthalic acid, monosodium 2-sulfonic terephthalate, and 2-bromoterephthalic acid.

[0014] According to the above scheme, in step 1), the monohydric alcohol is one of methanol, ethanol, propanol, and isobutanol. The presence of the monohydric alcohol during the synthesis process can induce MOFs to form rod-like structures. By adjusting the content of the monohydric alcohol in the aqueous solution, rod-like structures with different aspect ratios can be obtained, thereby achieving controllable adjustment of their morphology. The higher the volume percentage of monohydric alcohol in the aqueous solution, the more slender and elongated the resulting rod-like structure will be.

[0015] According to the above scheme, in step 1), the molar ratio of metal salt to organic ligand is 1:1.

[0016] According to the above scheme, in step 1), the molar volume ratio of the metal salt to the monohydric alcohol is 1 mmol: 1-20 mL.

[0017] According to the above scheme, in step 1), the volume ratio of water to monohydric alcohol in the monohydric alcohol aqueous solution is 1 to 10:1.

[0018] According to the above scheme, in step 1), the metal ion in the metal ion source is one of Cu(I), Ag(I), Pt(II), and Pd(II). Preferably, the metal ion source is cuprous chloride, silver tetrafluoroborate, potassium tetrachloroplatinate, and palladium chloride.

[0019] According to the above scheme, in step 1), the molar ratio of metal salt to metal ions is 1:0.1-2; wherein the mass of metal ions loaded onto the adsorbent material accounts for 1-20 wt% of the mass of metal ions fed.

[0020] According to the above scheme, in step 2), the mass-to-volume ratio of the precursor MOF material to the monocarboxylic acid aqueous solution is 100 mg: 5-15 mL.

[0021] According to the above scheme, in step 2), the volume ratio of monocarboxylic acid to water in the monocarboxylic acid aqueous solution is 6:1 to 16. The presence of water during the etching process accelerates MOF nucleation, resulting in more internal defects. As the reaction proceeds, metal salts and organic ligands are largely consumed, the reactant concentration continuously decreases, the growth rate of MOFs slows down, and external defects decrease. Since the monocarboxylic acid preferentially etches the areas with more defects, a hollow MOF tube structure can be obtained.

[0022] According to the above scheme, in step 2), the organic monocarboxylic acid used in the monocarboxylic acid aqueous solution is one of formic acid, acetic acid, propionic acid, butyric acid and lauric acid.

[0023] According to the above scheme, in step 2), the hydrothermal reaction conditions are: 100-120℃, constant temperature reaction for 3-12 hours.

[0024] A π-complexed hollow MOFs tube structure adsorbent material prepared by the above preparation method is provided, wherein the inner diameter of the hollow MOFs tube is 0.3-6 μm and the length is 1-100 μm.

[0025] This invention provides an application of the π-complexed hollow MOFs tube structure adsorbent material prepared by the above method in the adsorption and separation of ethane / ethylene gas.

[0026] According to the above scheme, the conditions for using the adsorbent in adsorption separation are: temperature 0-40℃; operating pressure 0-1 bar.

[0027] The beneficial effects of this invention are:

[0028] 1. This invention provides a method for preparing π-complexed hollow MOFs tube-structured adsorbent materials. During the preparation of precursor MOFs, the presence of monohydric alcohols can induce the formation of rod-shaped structures. By adjusting the content of monohydric alcohols in the aqueous solution, rod-shaped structures with different aspect ratios can be obtained, thus achieving controllable morphology adjustment. The precursor MOFs are then etched using a monocarboxylic acid aqueous solution to obtain a hollow MOFs tube morphology. This stable hollow structure not only improves the mass transfer rate of gas molecules in the adsorbent, facilitating rapid anchoring of gas molecules by the adsorbent, but also provides more exposure sites for metal ions introduced into the adsorbent, synergistically enhancing and improving the π-complexation reaction between ethylene molecules and metal ions. This achieves efficient adsorption and separation of ethane / ethylene, and has significant application prospects.

[0029] 2. The preparation process of this invention is simple, and the aspect ratio of the resulting hollow MOF tube structure adsorbent material is controllable and adjustable. The morphology adjustability can meet the requirements of various industrial applications. Attached Figure Description

[0030] Figure 1The images show SEM images of the adsorbent material in the π-complexed hollow MOF tube structure described in Examples 1 and 2 of this invention, and schematic diagrams of the inner diameter of the tube. In (a) and (b), the water-to-alcohol ratio is 30 mL:3 mL, and in (c) and (d), the water-to-alcohol ratio is 30 mL:6 mL.

[0031] Figure 2 The N2 adsorption-desorption isotherms are those of the adsorption materials with π-complexed hollow MOF tube structures described in Examples 3 and 4 of this invention. Pressure: 0–1 bar.

[0032] Figure 3 The image shows the XRD pattern of the adsorption material of the π-complexed hollow MOF tube structure described in Embodiment 3 of the present invention.

[0033] Figure 4 This is a SEM image of the adsorbent material A described in Comparative Example 1 of the present invention.

[0034] Figure 5 The images show single-component adsorption isotherms of the MOFs adsorbent materials prepared in Example 5 and Comparative Example 1 of this invention for ethane and ethylene at 298 K. Pressure: 0–1 bar.

[0035] Figure 6 This is a cyclic adsorption test diagram of ethylene on the adsorbent material with the π-complexed hollow MOF tube structure described in Example 5 of the present invention at 298 K. Pressure: 0-1 bar. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments and accompanying drawings. These embodiments are merely descriptions of preferred embodiments of the present invention, but are not limited to the content described below.

[0037] Example 1

[0038] A method for preparing a π-complexed hollow MOF tube structure adsorbent material is provided, comprising the following steps:

[0039] Add 181 mg of 2-aminoterephthalic acid, 40 mg of silver tetrafluoroborate, 162 mg of ferric chloride, 3 mL of ethanol, and 30 mL of water to a round-bottom flask, and sonicate for 10 min at room temperature. Place the mixture in an oil bath and react at 110 °C for 24 h. Remove the mixture and dry it under vacuum at 80 °C overnight to obtain the precursor MOFs.

[0040] 100 mg of precursor MOFs was added to 10 mL of acetic acid / water (6:10, v:v) mixed solution. The MOFs were sonicated for 5 min to disperse them evenly. The solution was then placed in an oven at 100 °C and etched by hydrothermal reaction for 12 h. After vacuum drying at 80 °C for 10 h, the π-complexed hollow MOFs tube structure adsorbent material was obtained, denoted as Ag(I)@H-MIL-101-NH2-3mL.

[0041] Example 2

[0042] The steps are basically the same as in Example 1, except that the volume of ethanol added is changed to 6 mL, which is recorded as Ag(I)@H-MIL-101-NH2-6mL.

[0043] SEM images of the Ag(I)@H-MIL-101-NH2-3mL material prepared in Example 1 and the Ag(I)@H-MIL-101-NH2-6mL material prepared in Example 2 are shown below. Figure 1 As shown. By Figure 1 It can be seen that the microstructure of the prepared adsorbent material is a hollow tubular structure. From... Figure 1 As shown in (a) and (c), when the water-to-alcohol ratio changes from 30 mL:3 mL to 30 mL:6 mL, the hollow tube structure becomes more slender. By comparing the tube diameter of any of the obtained adsorbent materials with the scale bar in the lower right corner of the SEM scan image, the inner diameters of Ag(I)@H-MIL-101-NH2-3 mL and Ag(I)@H-MIL-101-NH2-6 mL can be estimated to be 1 μm and 2 μm, respectively, with lengths ranging from 1 to 30 μm.

[0044] Example 3

[0045] A method for preparing a π-complexed hollow MOF tube structure adsorbent material is provided, comprising the following steps:

[0046] Add 181 mg of 2-aminoterephthalic acid, 40 mg of silver tetrafluoroborate, 133 mg of aluminum chloride, 6 mL of ethanol, and 30 mL of water to a round-bottom flask, and sonicate for 10 min at room temperature. Place the mixture in an oil bath and react at 110 °C for 24 h. After reaction, remove the mixture and vacuum dry it overnight at 80 °C to obtain the precursor MOFs.

[0047] 100 mg of precursor MOFs was added to 10 mL of acetic acid / water (6:10, v:v) mixed solution, and sonicated for 5 min to disperse the MOFs evenly. Then, the solution was placed in an oven at 100 °C for hydrothermal etching for 12 h, and vacuum dried at 80 °C for 10 h to obtain the π-complexed hollow MOF tube structure adsorbent material, denoted as Ag(I)@H-MIL-101-NH2.

[0048] The XRD pattern of the Ag(I)@H-MIL-101-NH2 material prepared in this embodiment is shown below. Figure 3 As shown in the figure, the characteristic peaks of the adsorbent synthesized by the method of the present invention match the standard peaks well, indicating the successful synthesis of the adsorbent. It also shows that the adsorbent has high phase purity and stable chemical structure.

[0049] Example 4

[0050] The steps are basically the same as in Example 3, except that the silver tetrafluoroborate added is replaced with an equimolar amount of cuprous chloride, and the resulting material is denoted as Cu(I)@H-MIL-101-NH2.

[0051] The N2 isotherms of the Ag(I)@H-MIL-101-NH2 material prepared in Example 3 and the Cu(I)@H-MIL-101-NH2 material prepared in Example 4 were measured using a Bestar adsorption analyzer (Beijing) in a constant-temperature liquid nitrogen bath at 77K. Their N2 adsorption-desorption curves are shown below. Figure 2 As shown, the curve exhibits a large hysteresis loop, indicating the presence of hollow structures in both materials. This demonstrates the successful etching of the rod-shaped material using a monocarboxylic acid aqueous solution, proving that the invented method can successfully synthesize adsorbents with hollow tube structures. Calculations using the BET equation yielded specific surface areas of 398 m² for both the Ag(I)@H-MIL-101-NH₂ and Cu(I)@H-MIL-101-NH₂ adsorbents. 2 / g and 340m 2 / g. A comparison of the specific surface areas of the two adsorbents shows no significant difference, indicating that changing the type of metal ion introduced has little impact on the specific surface area of ​​the adsorbent material. Therefore, we should select the metal ion with the best separation performance for the optimized adsorbent material to improve and enhance the adsorption and separation effect of the desired adsorbent on the ethane / ethylene mixture.

[0052] Example 5

[0053] A method for preparing a π-complexed hollow MOF tube structure adsorbent material is provided, comprising the following steps:

[0054] Add 268 mg of monosodium 2-sulfonic terephthalate, 40 mg of silver tetrafluoroborate, 162 mg of ferric chloride, 6 mL of ethanol, and 30 mL of water to a round-bottom flask, and sonicate for 10 min at room temperature. Place the mixture in an oil bath and react at 110 °C for 24 h. After reaction, remove the mixture and dry it under vacuum at 80 °C overnight to obtain the precursor MOFs.

[0055] 100 mg of precursor MOFs was added to 10 mL of acetic acid / water (6:10, v:v) mixed solution, and sonicated for 5 min to disperse the MOFs evenly. Then, the solution was placed in an oven at 100 °C for hydrothermal etching for 12 h, and vacuum dried at 80 °C for 10 h to obtain the π-complexed hollow MOF tube structure adsorbent material, denoted as Ag(I)@H-MIL-101-SO3.

[0056] Comparative Example 1

[0057] In this comparative example, adsorbent material A (Ag(I)@MIL-101-SO3) and adsorbent material B (H-MIL-101-SO3) were prepared by the following methods, and the adsorption and separation performance of different materials was investigated.

[0058] (1) Preparation of adsorption materials:

[0059] Adsorbent A: Add 268 mg of monosodium 2-sulfonic acid terephthalate, 40 mg of silver tetrafluoroborate, 162 mg of ferric chloride, 23 mL of DMF, and 1 mL of acetic acid to a round-bottom flask. Sonicate the mixture at room temperature for 10 min. Place the mixture in an oil bath and react at 110 °C for 24 h. Remove the mixture and vacuum dry it at 80 °C for 10 h to obtain the π-complexed MOF adsorbent, denoted as Ag(I)@MIL-101-SO3.

[0060] Adsorbent B: 268 mg of monosodium 2-sulfonic acid terephthalate, 162 mg of ferric chloride, 23 mL of DMF, and 1 mL of acetic acid were added to a round-bottom flask. The mixture was sonicated at room temperature for 10 min. The mixture was then placed in an oil bath and reacted at 110 °C for 24 h. After removal, it was vacuum dried overnight at 80 °C to obtain precursor MOFs. 100 mg of precursor MOFs was added to 10 mL of acetic acid / water (6:10, v:v) mixed solution, sonicated for 5 min to disperse the MOFs evenly, etched in an oven at 100 °C for 12 h, and vacuum dried at 80 °C for 10 h to obtain hollow MOF adsorbent material, denoted as H-MIL-101-SO3.

[0061] (2) Characterization:

[0062] The morphology and structure of adsorbent material A were characterized using SEM (Sequencing Electron Microscopy). Figure 4 As shown, the adsorbent material exhibits a regular octahedral structure, which can be compared with... Figure 1 and Figure 4 It can be observed that the presence of monohydric alcohols during the material preparation process can indeed induce the MIL-101 series adsorbents to form a rod-shaped morphology.

[0063] (3) Ethane / ethylene adsorption separation performance test:

[0064] The adsorbent material was degassed under vacuum at 150℃ for 10 h to obtain the activated adsorbent. Single-component adsorption tests of ethane and ethylene were performed on Ag(I)@H-MIL-101-SO3, adsorbent A, and adsorbent B using a Bestar adsorption analyzer (Beijing) at 298 K and 1 bar, respectively, to obtain single-component adsorption isotherms for different samples.

[0065] like Figure 5 As shown, the adsorption capacities of Ag(I)@H-MIL-101-SO3, a π-complexed hollow MOF tube structure adsorbent in Example 3, for ethylene and ethane were 2.62 mmol / g and 1.22 mmol / g, respectively. Adsorbent A had adsorption capacities of 2.64 mmol / g and 1.83 mmol / g, and adsorbent B had adsorption capacities of 1.99 mmol / g and 1.62 mmol / g. The adsorption isotherms of ethane and ethylene for the first two adsorbent materials were fitted using the Dual-Site Langmuir (DSL) equation, and for adsorbent B, the Langmuir-Freundlich (LF) equation was used. The calculated C2H4 / C2H6 IAST values ​​for Ag(I)@H-MIL-101-SO3, Ag(I)@MIL-101-SO3, and H-MIL-101-SO3 were 11.95, 3.44, and 1.37, respectively.

[0066] Compared to adsorbent B, the adsorbent Ag(I)@H-MIL-101-SO3, obtained by introducing metallic Ag(I) into the adsorbent material, exhibits a significant increase in its adsorption capacity for ethylene. This results in a nearly 9-fold increase in the C2H4 / C2H6 IAST selectivity of Ag(I)@H-MIL-101-SO3, indicating that the metal ions introduced into the adsorbent undergo a strong π-complexation reaction with ethylene molecules. Similarly, compared to adsorbent A, the hollow-structured adsorbent Ag(I)@H-MIL-101-SO3, obtained after etching with a monocarboxylic acid aqueous solution, also shows a nearly 3.5-fold increase in selectivity. This demonstrates that the hollow tube structure material described in this invention can significantly improve the adsorption capacity of the material for ethylene molecules, thereby significantly enhancing the C2H4 / C2H6 IAST separation selectivity of the adsorbent. In summary, the π-complexed hollow MOF tube structure adsorbent material obtained by introducing metal ion active sites into the adsorbent material and etching it with a monocarboxylic acid aqueous solution can preferentially adsorb ethylene molecules in ethane / ethylene mixed gases and exhibits a high ethylene adsorption capacity. Furthermore, the adsorbent material prepared in this invention possesses superior C2H4 / C2H6 IAST separation selectivity, enabling efficient separation of ethane / ethylene mixed gases, and is expected to become an alternative adsorbent for industrial separation of mixed gases using traditional methods.

[0067] (4) Stability performance test:

[0068] After testing the separation performance of the adsorbent Ag(I)@H-MIL-101-SO3, we further investigated its stability. Using a Bestar adsorption analyzer (Beijing), we conducted five ethylene adsorption-desorption cycles at 298 K and 1 bar. The results are as follows: Figure 6 As shown, after five adsorption cycles, the adsorption capacity of the adsorbent for ethylene did not decrease significantly, indicating that the adsorbent prepared by the method of this invention maintains a stable chemical structure and pore size structure throughout the adsorption process, which has a significant advantage compared to other adsorbent materials.

[0069] It must be emphasized that the above examples are merely illustrative of the present invention and are not intended to completely limit the implementation. Those skilled in the art can make other variations based on the above description. It is neither possible nor necessary to provide examples for all implementations here, but obvious variations derived therefrom still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a π-complexed hollow MOF tube structure adsorbent material, characterized in that, Includes the following steps: 1) Metal salt, organic ligand and metal ion source are uniformly mixed in a monohydric alcohol aqueous solution and heated to react, thereby preparing precursor MOFs; wherein: the molar volume ratio of metal salt to monohydric alcohol is 1 mmol: 1~20 mL; in the monohydric alcohol aqueous solution, the volume ratio of water to monohydric alcohol is 1~10:1; 2) The precursor MOFs material obtained in step 1) is mixed with a monocarboxylic acid aqueous solution and etched by hydrothermal reaction to obtain a π-complexed hollow MOFs tube structure adsorbent material; wherein: in the monocarboxylic acid aqueous solution, the volume ratio of monocarboxylic acid to water is 6:1~16.

2. The preparation method according to claim 1, characterized in that, In step 1), the reaction temperature is 50~150℃ and the reaction time is 24~48 h.

3. The preparation method according to claim 1, characterized in that, In step 1), the metal salt is one of aluminum chloride, ferric chloride, ferric acetate, and chromium nitrate; the organic ligand is one of 2-aminoterephthalic acid, 2-hydroxyterephthalic acid, monosodium 2-sulfonic terephthalate, and 2-bromoterephthalic acid; and the metal ion in the metal ion source is one of Cu(I), Ag(I), Pt(II), and Pd(II).

4. The preparation method according to claim 1, characterized in that, In step 1), the monohydric alcohol is one of methanol, ethanol, propanol and isobutanol.

5. The preparation method according to claim 1, characterized in that, In step 1), the molar ratio of metal salt to organic ligand is 1:1; the molar ratio of metal salt to metal ion source is 1:0.1~2.

6. The preparation method according to claim 1, characterized in that, In step 2), the monocarboxylic acid is one of formic acid, acetic acid, propionic acid, butyric acid, and lauric acid.

7. The preparation method according to claim 1, characterized in that, In step 2), the hydrothermal reaction conditions are: 100~120℃, constant temperature reaction for 3~12 h.

8. A π-complexed hollow MOFs tube structure adsorbent material prepared by the preparation method according to any one of claims 1-7, characterized in that, In the π-complexed hollow MOFs tube structure adsorption material, the inner diameter of the hollow MOFs tube is 0.3~6 µm and the length is 1~100 µm.

9. The application of the π-complexed hollow MOFs tube structure adsorbent material as described in claim 8 in the adsorption and separation of ethane / ethylene gas.

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