Method for macroscopically preparing three-dimensional hollow ZIF-L nano frame

Abstract

The invention discloses a method for macroscopically preparing a three-dimensional hollow ZIF-L nano frame. According to the preparation method, a ZIF synthesis solution with surfactant regulation and control is selected, and the three-dimensional hollow ZIF-L nano-frame with uniform morphology can be prepared after mother liquor is dripped to a hydrophobic membrane and naturally air-dried. The process is simple, the raw materials are cheap and easy to obtain, the synthesized ZIF-L nano-frame is uniform in size, the preparation method can realize single-batch gram-level preparation, and large-scale production and application of the material are facilitated.

Description

Technical Field

[0001] The invention relates to a method for preparing a three-dimensional hollow ZIF-L nanoframe in large quantities, belonging to the technical field of nano material preparation. Background Art

[0002] Metal-organic frameworks (MOFs) are porous multifunctional materials composed of inorganic building blocks connected by organic linkers. Zeolitic imidazolate frameworks (ZIFs) are a subclass of the metal-organic framework (MOF) family, consisting of planar tetrahedral metal ion nodes and imidazole ligands. ZIF-L is a member of the ZIF family. It has strong chemical stability and can maintain its structural integrity and functionality over a wide range of temperatures and pH, which enables it to work stably in various environments. Its structure is controllable and can be adjusted and changed by selecting different metals and organic ligands to achieve different properties and functions. Due to these unique properties, it is widely used in many fields such as gas separation, catalysis, and energy conversion.

[0003] However, the traditional ZIF-L morphology is a two-dimensional nanosheet, and the two-dimensional structure usually has a small pore size and area, which limits its ability in applications such as adsorption, separation and storage. In contrast, the three-dimensional structure usually has a richer pore structure and a larger specific surface area, which can accommodate more molecules and ions. Furthermore, the hollow structure can provide a large amount of surface area to contact the substance to be adsorbed, thereby increasing the efficiency and capacity of adsorption separation. Therefore, if a three-dimensional hollow ZIF-L can be prepared and the large-scale preparation of three-dimensional hollow ZIF-L can be achieved, it will have a broader application prospect. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing three-dimensional hollow ZIF-L nanoframes in large quantities.

[0005] The technical solution to achieve the purpose of the present invention is as follows: A method for preparing three-dimensional hollow ZIF-L nanoframes in large quantities, comprising: Step 1, dissolving a transition metal salt and a surfactant in deionized water, adding the solution to the ligand solution, stirring for a period of time to obtain a mixed solution of the three, and settling at room temperature; Step 2, remove the supernatant and drop the mother solution onto the hydrophobic membrane; Step 3: After the droplets are dried, the sample on the hydrophobic film is scraped off and ground to obtain a ZIF-L nanoframe powder sample.

[0006] Furthermore, in step 1, the transition metal salt is one or both of zinc salt and cobalt salt, the surfactant is hexadecyltrimethylammonium bromide, and the ligand is 2-methylimidazole.

[0007] Furthermore, in step 1, the molar ratio of the surfactant to the metal ion is (1:30) to (1:180); the molar ratio of the transition metal salt to 2-methylimidazole is (1:30) to (1:70).

[0008] Furthermore, in step 1, the stirring time is 5 to 60 min.

[0009] Furthermore, in step 2, the amount of supernatant removed is 50% to 85% of the total volume; and the amount of mother solution added per square centimeter of hydrophobic membrane is 160 μL to 200 μL.

[0010] Furthermore, in step 2, the hydrophobic film is any one of a polypropylene film, a polyethylene terephthalate film, a polyimide film, and a polytetrafluoroethylene film.

[0011] Furthermore, in step 3, the drying time is 18h-24h.

[0012] Compared with the prior art, the present invention has the following advantages: (1) The present invention realizes the preparation of three-dimensional hollow ZIF-L nanoframes.

[0013] (2) The present invention can prepare three-dimensional hollow ZIF-L nanoframes in large quantities, and grams of ZIF-L nanoframes can be prepared at one time.

[0014] (3) The process of the present invention is simple and the steps are easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a scanning electron microscope image of the ZIF-L nanoframe prepared in Example 1.

[0016] Figure 2 This is a scanning electron microscope image of the ZIF-67 nanocube prepared in Comparative Example 1.

[0017] Figure 3 Schematic diagram of the synthesis method.

[0018] Figure 4 This is a scanning electron microscope image of the ZIF-L two-dimensional nanosheet prepared in Comparative Example 2.

[0019] Figure 5 This is a scanning electron microscope image of the ZIF-L two-dimensional nanosheet prepared in comparative example 3.

[0020] Figure 6 The XRD patterns of the samples prepared in Example 1 and Comparative Example 4 are shown below.

[0021] Figure 7 This is a scanning electron microscope image of the sample prepared in Comparative Example 4.

[0022] Figure 8 This is a diagram of the on-site preparation of Example 1 and Comparative Example 4. DETAILED DESCRIPTION

[0023] In order to better understand the technical content of the present invention, specific embodiments are given as follows.

[0024] Combination Figure 3 The method for preparing three-dimensional hollow ZIF-L nanoframes in large quantities according to the present invention comprises the following steps: Step 1, dissolving a transition metal nitrate and a surfactant in deionized water, adding the solution to the ligand solution, stirring for a period of time to obtain a mixed solution of the three, and settling at room temperature; Step 2, remove the supernatant and drop the mother solution onto the hydrophobic membrane; Step 3: After the droplets are dried, the sample on the hydrophobic film is scraped off and ground to obtain a ZIF-L nanoframe powder sample. Implementation Example 1

[0025] 1) Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 540 mmol of 2-methylimidazole to 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0026] 2) Remove the supernatant and use a pipette to transfer the mother solution at room temperature, and transfer 160 μL each time onto a 1 cm2 polypropylene hydrophobic membrane.

[0027] 3) After the droplets are dried, the sample on the polypropylene hydrophobic film is scraped off and ground to obtain a powder sample (such as Figure 8 ), weighed, about 1.2g, proving that gram-scale production is achievable.

[0028] Figure 1 This is a scanning electron microscope image of the sample prepared in Example 1. Figure 1 It can be seen that the sample morphology is a framework morphology with twelve edges interconnected to form a hollow structure. Each edge is composed of a coordination compound of metal ions and organic ligands, and the morphology is regular and evenly distributed. Implementation Example 2

[0029] 1) Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 540 mmol of 2-methylimidazole to 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0030] 2) Remove the supernatant and use a pipette to transfer the mother solution at room temperature, and apply 200 μL of the mother solution onto a 1 cm2 polypropylene hydrophobic membrane each time.

[0031] 3) After the droplets dried, the sample on the polypropylene hydrophobic film was scraped off and ground. Scanning electron microscopy confirmed that the sample morphology was a framework morphology with twelve edges interconnected to form a hollow structure, indicating that a three-dimensional hollow nanoframe sample can still be obtained by increasing the amount of droplets added. Implementation Example 3

[0032] 1) Dissolve 10 mmol of zinc nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 540 mmol of 2-methylimidazole to 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0033] 2) Remove the supernatant and use a pipette to transfer 200 μL of the stock solution onto a 1 cm2 hydrophobic polyethylene terephthalate membrane at room temperature.

[0034] 3) After the droplets dried, the sample on the polyethylene terephthalate hydrophobic film was scraped off and ground. Scanning electron microscopy confirmed that the sample morphology was a framework morphology with twelve edges interconnected to form a hollow structure, indicating that a three-dimensional hollow nanoframe sample can still be obtained by replacing the polyethylene terephthalate hydrophobic membrane and increasing the amount of droplets added. Comparative Example 1

[0035] Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 540 mmol of 2-methylimidazole into 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0036] The supernatant was removed, the remaining mother liquor was centrifuged in a high-speed centrifuge, and washed three times with anhydrous ethanol.

[0037] The centrifuged samples were placed in a vacuum drying oven at 60°C for 24 h.

[0038] Figure 2 The scanning electron microscope image of the sample prepared in Comparative Example 1 is shown in FIG. Figure 2 It can be seen that the sample morphology is a nanocube, which means that the sample prepared by conventional methods cannot obtain a three-dimensional hollow nanoframe morphology but a nanocube morphology. Comparative Example 2

[0039] Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 80 mmol of 2-methylimidazole into 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0040] The supernatant was removed, the remaining mother liquor was centrifuged in a high-speed centrifuge, and washed three times with anhydrous ethanol.

[0041] The centrifuged samples were placed in a vacuum drying oven at 60°C for 24 h.

[0042] Figure 4 The scanning electron microscope image of the sample prepared in Comparative Example 2 is shown in FIG. Figure 4 It can be seen from the figure that the sample morphology is a two-dimensional nanosheet, indicating that when the ratio of the transition metal salt to the ligand is not within the appropriate range, a three-dimensional hollow nanoframe morphology cannot be obtained but a two-dimensional nanosheet morphology is obtained. Comparative Example 3

[0043] 1) Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 80 mmol of 2-methylimidazole to 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0044] 2) Remove the supernatant and use a pipette to transfer the mother solution at room temperature, and transfer 160 μL each time onto a 1 cm2 polypropylene hydrophobic membrane.

[0045] 3) After the droplets are dried, the sample on the polypropylene hydrophobic film is scraped off and ground to obtain two-dimensional leaf-shaped ZIF-L nanosheets.

[0046] Figure 5 The scanning electron microscope image of the sample prepared in Comparative Example 3 is shown in FIG. Figure 5 It can be seen that the sample morphology is still a two-dimensional nanosheet, indicating that when the ratio of cobalt nitrate hexahydrate and 2-methylimidazole ligand is not within the appropriate range, even if it is dropped on the hydrophobic membrane, a three-dimensional hollow morphology of ZIF-L nanoframe cannot be obtained. Comparative Example 4

[0047] 1) Dissolve 10 mmol of cobalt nitrate hexahydrate and 0.06 mmol of hexadecyltrimethylammonium bromide in 100 mL of deionized water and stir evenly. Add 540 mmol of 2-methylimidazole to 700 mL of deionized water and stir evenly. Mix and stir the two for 1 hour and let stand at room temperature for 24 hours.

[0048] 2) Remove the supernatant and use a pipette to transfer the mother solution at room temperature, each time transferring 10 μL onto a 1 cm2 silicon wafer. Experiments have shown that the silicon wafer surface cannot withstand a larger amount of dripping.

[0049] 3) After the droplets are dried, the sample on the silicon wafer is scraped off and ground to obtain a small amount of three-dimensional hollow ZIF-L nanoframe powder sample (such as Figure 8 ), after weighing, the obtained three-dimensional hollow ZIF-L nanoframe is only at the milligram level.

[0050] Figure 6 The XRD patterns of the samples prepared in Example 4 and Example 1 are as follows: Figure 6 It can be seen that the crystal structure of the sample does not change when it is dropped on different substrates.

[0051] Figure 7 The scanning electron microscope image of comparative example 4 is shown in FIG. Figure 7 It can be seen that a three-dimensional hollow nanoframe structure can also be obtained by dropping it on a silicon wafer.

[0052] Depend on Figure 8 It can be seen that dripping on a hydrophobic membrane can achieve large-scale (gram-level) preparation, while dripping on a silicon wafer (hydrophilic substrate) instead of a hydrophobic membrane cannot achieve large-scale preparation.

Claims

1. A method for preparing three-dimensional hollow ZIF-L nanoframes in large quantities, characterized in that: include: Step 1, dissolving a transition metal salt and a surfactant in deionized water, adding the solution to the ligand solution, stirring for a period of time to obtain a mixed solution of the three, and settling at room temperature; Step 2, remove the supernatant and drop the mother solution onto the hydrophobic membrane; Step 3: After the droplets are dried, the sample on the hydrophobic film is scraped off and ground to obtain a ZIF-L nanoframe powder sample.

2. The method according to claim 1, characterized in that In step 1, the transition metal salt is one or both of zinc salt and cobalt salt, the surfactant is hexadecyltrimethylammonium bromide, and the ligand is 2-methylimidazole.

3. The method according to claim 1, characterized in that In step 1, the molar ratio of the surfactant to the metal ion is (1:30) to (1:180); the molar ratio of the transition metal salt to 2-methylimidazole is (1:30) to (1:70).

4. The method according to claim 1, wherein: In step 1, the stirring time is 5 to 60 min.

5. The method according to claim 1, characterized in that In step 2, the amount of supernatant removed is 50% to 85% of the total volume; the amount of mother solution added per square centimeter of hydrophobic membrane is 160 μL to 200 μL.

6. The method according to claim 1, characterized in that In step 2, the hydrophobic film is any one of a polypropylene film, a polyethylene terephthalate film, a polyimide film, and a polytetrafluoroethylene film.

7. The method according to claim 1, characterized in that In step 3, the drying time is 18h-24h.

8. A three-dimensional hollow ZIF-L nanoframe prepared by the method according to any one of claims 1 to 7, characterized in that: It has a three-dimensional hollow structure.

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