Hollow ZIF-L frame material and preparation method thereof

Abstract

The invention discloses a hollow ZIF-L framework material and a preparation method thereof. A precursor ZIF material is pre-layered in a synthesis system by adopting a continuous preparation method, precursor dispersion liquid is transferred to a flat hydrophilic substrate to be dried after part of supernate is removed, and the hollow ZIF-L framework material is prepared by utilizing a Marangei effect. The hollow ZIF-L framework material prepared by the method has unique structural characteristics, and can be widely applied to the technical fields of gas adsorption and separation, drug delivery and electrochemistry as a carrier.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and more specifically to a hollow ZIF-L framework material and a preparation method thereof. Background Art

[0002] Metal-organic frameworks (MOFs), as a class of crystalline materials with porous structures, have attracted widespread interest in the field of materials science. Among them, ZIF-L (Zeolitic Imidazolate Framework-L) is a member of the MOFs family with a unique structure and diverse application potential. The synthesis of ZIF-L materials usually adopts a solution synthesis method, in which metal ions and organic ligands combine under appropriate conditions to form a crystal structure. Common metal ions include zinc, cobalt, copper, etc., while organic ligands are usually imidazole compounds such as 2-methylimidazole. By adjusting the synthesis conditions, ZIF-L crystals of different morphologies and sizes can be achieved to meet various application requirements. One of the most notable features of ZIF-L materials is their porous structure. Their crystal structure is similar to that of molecular sieves and consists of continuous porous channels that can accommodate various molecules and ions. In addition, ZIF-L crystals also have highly controllable pore size and porosity. As a porous crystalline material, ZIF-L materials have unique structures and broad application potential. They have shown excellent performance in many fields such as gas adsorption, catalysis, drug delivery and energy storage. However, in practical applications, the sheet structure of ZIF-L materials easily causes stacking, which loses the advantage of high porosity of ZIF-L materials, thereby causing loss of adsorption or performance as a carrier.

[0003] Therefore, a ZIF-L material with a simple preparation method and a hollow structure is needed to solve the problem of performance loss caused by material stacking in multiple fields of application. Summary of the invention

[0004] In view of the above problems in the prior art, the first object of the present invention is to provide a hollow ZIF-L framework material. The hollow ZIF-L framework has a hollow structure, can avoid stacking and performance loss in application, and provide higher mass transfer capacity. The second object of the present invention is to provide a preparation method of a hollow ZIF-L framework material. The method has low cost and forms a target structure by controlling the synthesis conditions.

[0005] In order to achieve the above first object, the present invention adopts the following technical scheme: A hollow ZIF-L framework material presents a framework morphology in which twelve edges are interconnected to form a hollow structure, and each edge is composed of a coordination compound of a metal ion and an organic ligand.

[0006] In order to achieve the above second purpose, the present invention adopts the following technical solutions: A method for preparing a hollow ZIF-L framework material comprises the following steps: dissolving a metal salt and a surfactant in water, adding an organic ligand solution, and mixing the mixture evenly to obtain a precursor reaction liquid of the material; removing the supernatant of the precursor reaction liquid, dripping the remaining mother liquid on a flat hydrophilic substrate, and drying the mixture to obtain the hollow ZIF-L framework material.

[0007] Preferably, the metal salt is one or both of a cobalt salt or a zinc salt.

[0008] Preferably, the organic ligand is 2-methylimidazole.

[0009] Preferably, the surfactant is cetyltrimethylammonium bromide (CTAB), and the molar ratio of CTAB to the metal ion is (1:30) to (1:180).

[0010] Preferably, the molar ratio of metal ions to organic ligands is (1:30) to (1:70).

[0011] Preferably, the volume of the supernatant removed is 50%-85% of the total volume.

[0012] Preferably, the flat hydrophilic substrate is selected from any one of silicon wafer, glass, quartz, stainless steel, aluminum alloy and ceramic.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention provides a hollow ZIF-L framework material, which can effectively avoid the problems of stacking and performance loss that are easy to occur in ZIF-L materials. At the same time, the present invention provides a method for preparing a hollow ZIF-L framework material, which adjusts the parameters in the synthesis process of the ZIF material so that the ZIF-L precursor is affected by the concentration change of the crystallization unit during the synthesis process to change the crystallization habit, and the ZIF material is dissociated and secondary grown to successfully form a hollow framework structure; the preparation method avoids the commonly used etchants and cumbersome pore-making methods, and is economical and efficient; the hollow ZIF-L framework material is prepared through a continuous preparation process, and a high synthesis efficiency can be obtained to achieve continuous large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A scanning electron microscope image of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0015] Figure 2 A transmission electron microscope image of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0016] Figure 3 The XRD pattern of the hollow ZIF-L framework material obtained in Example 1 is shown.

[0017] Figure 4 A scanning electron microscope image of the nanocubes obtained in Comparative Example 1 is shown.

[0018] Figure 5 A scanning electron microscope image of the two-dimensional nanosheet obtained in Comparative Example 2 is shown.

[0019] Figure 6 A scanning electron microscope image of the two-dimensional nanosheets obtained in Comparative Example 3 is shown. DETAILED DESCRIPTION

[0020] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments and drawings. It should be understood by those skilled in the art that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0021] Embodiment 1: A method for preparing a hollow ZIF-L framework material comprises the following steps: Weigh 1 mmol of cobalt nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; Weigh 54 mmol of 2-methylimidazole and dissolve it in 70 mL of deionized water to obtain solution 2; Solution 1 was added to solution 2 and stirred for 20 min to obtain mixed solution 3; The mixed solution 3 was allowed to stand for 24 h, and 70 mL of the upper solution was removed to obtain mother solution 4; Four drops of the mother solution were added onto a silicon wafer and dried to obtain the Co-ZIF-L hollow framework material.

[0022] Figure 1 and Figure 2 The scanning electron microscope and transmission electron microscope images of the samples obtained in Example 1 are shown in FIG. Figure 1 and Figure 2 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.

[0023] Figure 3 This is the XRD diagram of the sample obtained in Example 1. From the crystal structure of the sample, it can be known that it is Co-ZIF-L.

[0024] Embodiment 2: A method for preparing a hollow ZIF-L framework material comprises the following steps: Weigh 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; Weigh 54 mmol of 2-methylimidazole and dissolve it in 70 mL of deionized water to obtain solution 2; Solution 1 was added to solution 2 and stirred for 20 min to obtain solution 3; Solution 3 was allowed to stand for 24 h, and 70 mL of the upper solution was removed to obtain mother solution 4; Four drops of the mother solution were added to a silicon wafer and dried to obtain a Zn-ZIF-L hollow framework material. Scanning electron microscopy showed that a hollow ZIF-L framework material could also be obtained by replacing the metal salt with zinc nitrate hexahydrate. Embodiment three:

[0025] A method for preparing a hollow ZIF-L framework material comprises the following steps: 1) Weigh 0.5 mmol of cobalt nitrate hexahydrate, 0.5 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; 2) Weigh 54 mmol of 2-methylimidazole and dissolve it in 70 mL of deionized water to obtain solution 2; 3) Add solution 1 to solution 2 and stir for 20 min to obtain solution 3; 4) Let solution 3 stand for 24 h, remove 70 mL of the upper solution, and obtain mother solution 4; 5) Four drops of the mother solution were added to the silicon wafer and dried to obtain the Co / Zn-ZIF-L hollow framework material. Scanning electron microscopy showed that when the metal salt was replaced with half cobalt nitrate hexahydrate and half zinc nitrate hexahydrate, the hollow ZIF-L framework material could still be obtained. Comparative Example 1:

[0026] 1) Weigh 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; 2) Weigh 54 mmol of 2-methylimidazole and dissolve it in 70 mL of deionized water to obtain solution 2; 3) Add solution 1 to solution 2 and stir for 20 min to obtain solution 3; 4) Let solution 3 stand for 24 h, remove 70 mL of the upper solution, and obtain mother solution 4; 5) Centrifuge the mother solution 4 in a high-speed centrifuge and wash it three times with anhydrous ethanol;

[0027] 6) Dry the centrifuged sample in a vacuum drying oven at 60°C for 24 hours.

[0028] Figure 4 This is the scanning electron microscope image of the sample prepared in Comparative Example 1. Figure 4It can be seen that the sample morphology is a nanocube, which means that the samples prepared by conventional methods can only obtain a nanocube morphology but not a three-dimensional hollow nanoframe morphology. Comparative Example 2:

[0029] 1) Weigh 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; 2) Weigh 8 mmol 2-methylimidazole and dissolve it in 70 mL deionized water to obtain solution 2; 3) Add solution 1 to solution 2 and stir for 20 min to obtain solution 3; 4) Let solution 3 stand for 24 h, remove 70 mL of the upper solution, and obtain mother solution 4; 5) Centrifuge the mother solution 4 in a high-speed centrifuge and wash three times with anhydrous ethanol;

[0030] 6) Dry the centrifuged sample in a vacuum drying oven at 60°C for 24 hours.

[0031] Figure 5 This is a scanning electron microscope image of the sample prepared in Comparative Example 2. Figure 5 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, the obtained product has a two-dimensional nanosheet morphology rather than a nanocube morphology.

[0032] Comparative Example 3: 1) Weigh 1 mmol of zinc nitrate hexahydrate and 0.006 mmol of CTAB and dissolve them in 10 mL of deionized water to obtain solution 1; 2) Weigh 8 mmol 2-methylimidazole and dissolve it in 70 mL deionized water to obtain solution 2; 3) Add solution 1 to solution 2 and stir for 20 min to obtain solution 3; 4) Let solution 3 stand for 24 h, remove 70 mL of the upper solution, and obtain mother solution 4; 5) Add the mother solution dropwise onto the silicon wafer.

[0033] Figure 6 This is the scanning electron microscope image of the sample prepared in Comparative Example 3. Figure 6 It can be seen that the sample morphology is still a two-dimensional nanosheet, indicating that the ratio of cobalt nitrate hexahydrate and 2-methylimidazole ligand is not within the appropriate range, and no three-dimensional hollow ZIF-L nanoframe can be obtained when it is dropped on a silicon wafer.

Claims

1. A hollow ZIF-L framework material, characterized in that: The material presents a framework morphology in which twelve edges are interconnected to form a hollow structure, and each edge is composed of a coordination compound of metal ions and organic ligands.

2. A method for preparing the hollow ZIF-L framework material according to claim 1, characterized in that: The metal salt and the surfactant are dissolved in water, and the organic ligand solution is added and mixed evenly to obtain the precursor reaction liquid of the material. The supernatant of the precursor reaction liquid is removed, and the remaining mother liquid is dripped on a flat hydrophilic substrate, and the hollow ZIF-L framework material is obtained after drying.

3. The method according to claim 2, characterized in that The metal salt is one or both of cobalt salt and zinc salt.

4. The method according to claim 2, characterized in that The organic ligand is 2-methylimidazole.

5. The method according to claim 2, characterized in that The surfactant is hexadecyltrimethylammonium bromide, and the molar ratio of the surfactant to the metal ion is (1:30) to (1:180).

6. The method according to claim 2, characterized in that The molar ratio of metal ions to organic ligands is (1:30)~(1:70).

7. The method according to claim 2, characterized in that The volume of the supernatant removed is 50%-85% of the total volume.

8. The method according to claim 2, characterized in that The flat hydrophilic substrate is selected from any one of silicon wafer, glass, quartz, stainless steel, aluminum alloy and ceramic.

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