阅读说明：本技术 一种用于mof晶型转变的制备方法 (Preparation method for MOF crystal form transformation ) 是由 桑欣欣 倪才华 石刚 王大伟 夏晓峰 于 2020-05-06 设计创作，主要内容包括：本发明公开了一种用于MOF晶型转变的制备方法。采用离子液体和水的混合溶剂溶解有机配体2-甲基咪唑(HIm),并与Zn无机盐水溶液混合,实现2D MOF向3D MOF的结构转变；所述的离子液体是一种由咪唑阳离子构成的亲水性功能溶剂；所述的2D MOF是一种二维沸石咪唑酯类(ZIF-L),转变成的3D MOF是一种三维沸石咪唑酯类(ZIF-8)。本发明的制备方法不仅可以实现MOF骨架结构的转变,而且能够加速MOF的成核结晶,调控产物形貌,是一种环境友好制备不同结构和形貌沸石咪唑酯类MOF的方法。(The invention discloses a preparation method for MOF crystal form transformation, which is characterized in that a mixed solvent of ionic liquid and water is adopted to dissolve an organic ligand 2-methylimidazole (HIm) and is mixed with a Zn inorganic salt aqueous solution to realize the structural transformation from 2D MOF to 3D MOF, wherein the ionic liquid is a hydrophilic functional solvent formed by imidazole cations, the 2D MOF is two-dimensional zeolite imidazolate (ZIF-L), and the transformed 3D MOF is three-dimensional zeolite imidazolate (ZIF-8).)

1. A preparation method for MOF crystal form transformation, characterized in that: mixing a Zn inorganic salt aqueous solution with a mixed solvent in which an organic ligand 2-methylimidazole is dissolved to realize the structural transformation from 2D MOF to 3D MOF, wherein the MOF is zeolite imidazolate; the mixed solvent consists of ionic liquid and water, wherein cations in the ionic liquid are imidazole cations, and anions in the ionic liquid are Cl^-、Br^-、BF₄ ^-One kind of (1).

2. The preparation method for MOF crystal form transformation according to claim 1, wherein the 2D MOF is ZIF-L, and the 3D MOF is ZIF-8.

3. A preparation method for MOF crystalline transformation according to claim 1, characterized in that: the imidazolium cation is 1-alkyl-3-methylimidazole C_nmim, the 1-alkyl is one of ethyl, butyl, hexyl, octyl and decyl.

4. A preparation method for MOF crystalline transformation according to claim 1, characterized in that: the method mainly comprises the following steps:

preparing Zn inorganic salt into an aqueous solution A for later use;

dissolving 2-methylimidazole HIm in a mixed solvent of water and ionic liquid to form a solution B for later use;

and pouring the solution A into the solution B, stirring and reacting at room temperature, centrifugally separating a product, washing with ethanol, and vacuum-drying at 60 ℃ for 24 hours.

5. A preparation method for MOF crystalline transformation according to claim 1, characterized in that: the mixed solvent of water and ionic liquid contains water: the mass ratio of the ionic liquid is 159: 1-1: 1.

6. a preparation method for MOF crystalline transformation according to claim 1, characterized in that: the Zn to HIm is 1: 4-1: 40.

7. a preparation method for MOF crystalline form transformation according to claim 4, characterized in that: and mixing the solution A and the solution B in equal mass.

8. A preparation method for MOF crystalline transformation according to claim 1, characterized in that: the Zn inorganic salt is one of halide, nitrate and acetate.

Technical Field

The invention belongs to the technical field of coordination chemistry and crystal chemistry, and particularly relates to a preparation method of a metal organic framework, in particular to a preparation method for MOF crystal form transformation.

Background

ZIFs are porous materials which are linked by taking imidazole derivatives as ligands and have similar zeolite framework results, and belong to MOFs containing N heterocycles. Generally comprises imidazole organic ligands and transition metal ions Zn²⁺Through nitrogenAnd atom linkage assembling the formed polymer. Because of large specific surface area, good stability and the like, ZIFs have wide application potential in the aspects of catalysis, adsorption separation and the like. The crystal size, morphology, crystal structure and the like of the ZIFs are regulated and controlled, and the ZIFs have an important effect on changing the performance and functions of the ZIFs.

Although most studies have focused on the specific morphology and structure of ZIFs, the studies on solvent-induced topological transformation of ZIFs have been very rare, and the transformation of 2D ZIF-L (metal centered Co) to 3D ZIF-67, the modification of the ligand to metal ratio, or the control of the methanol/water volume ratio (CrystEngComm,2015,17, 8212-8215; chem. Eur. J.2017,23,10638-10643) have not been reported so far, the transformation of 2D ZIF-L (metal centered Co) to 3D ZIF-8 has not been known.

The ionic liquid is low-temperature molten salt, has the advantages of non-volatility, strong solubility and the like, is a green solvent, and is widely used for preparing MOF materials. Meanwhile, the ionic liquid has special functionality, for example, the hydrophilicity and hydrophobicity of the ionic liquid can be regulated by regulating the length of an alkyl chain, and the surface tension of a solvent can be improved. Therefore, the ionic liquid is used for preparing the MOF, and has important research significance for replacing volatile organic solvents.

Disclosure of Invention

The invention aims to overcome the defects in the prior art, and provides a preparation method for MOF crystal form conversion, in particular to a green preparation method for converting 2D ZIF-L (metal center Co) into 3D ZIF-8.

The technical scheme is as follows: in order to achieve the purpose, the invention adopts the technical scheme that:

a preparation method for Metal Organic Framework (MOF) crystal form transformation is characterized in that a mixed solvent in which an organic ligand 2-methylimidazole is dissolved is mixed with a Zn inorganic saline solution, so that two-dimensional MOF is transformed into a three-dimensional structure, wherein the MOF is zeolite imidazolate, the 2D MOF is ZIF-L, the 3D MOF is ZIF-8, and the mixed solvent is used for preparing the MOFThe mixed solvent is a mixed solvent of water and ionic liquid, the ionic liquid contains imidazole cation, and the imidazole cation is 1-alkyl-3-methylimidazole (C)_nmim), the 1-alkyl is one of ethyl, butyl, hexyl, octyl and decyl; the anion of the ionic liquid is Cl^-、Br^-、BF₄ ^-One of (1);

further, the preparation method for Metal Organic Framework (MOF) crystal form transformation mainly comprises the following steps:

preparing Zn inorganic salt into aqueous solution A with a certain concentration for later use; dissolving 2-methylimidazole (HIm) in a mixed solvent of water and ionic liquid to form a solution B for later use; pouring the solution A into the solution B, and stirring and reacting for a period of time at room temperature. The product was centrifuged, washed 3 times with ethanol and dried in a vacuum oven at 60 ℃ for 24 hours for testing characterization.

Further, the Zn inorganic salt is one of halide, nitrate, acetate and the like; the Zn to HIm (molar ratio) is 1: 4-1: 40; the solution A and the solution B are mixed in equal mass; the mixed solvent of water and ionic liquid contains water: the ionic liquid (mass ratio) was 159: 1-1: 1.

a preparation method for Metal Organic Framework (MOF) crystal form transformation, which is an environment-friendly preparation method. The addition of the ionic liquid can accelerate the crystallization rate of the MOF, and the morphology of the MOF can be regulated and controlled by changing the type and the addition amount of the ionic liquid.

The preparation method for MOF crystal form transformation provided by the invention has the beneficial effects that the transformation of 2D ZIF-L (metal center Co) to 3D ZIF-8 is regulated and controlled by using a mixed solvent of water and ionic liquid, and compared with the prior art, the preparation method has the following advantages:

(1) the hydrophobic preparation process is green and environment-friendly, and meanwhile, MOF crystallization can be accelerated.

(2) The preparation method of the mixed solvent can realize the topological structure transformation of the MOF, and the appearance of the product is changed accordingly.

Drawings

FIG. 1 is an XRD pattern of comparative example 1 and examples 1-3;

FIG. 2 is an SEM photograph of comparative example 1 and examples 1-3;

FIG. 3 is an XRD pattern for examples 4-5;

FIG. 4 is an SEM photograph of examples 4-5;

fig. 5 is an XRD diagram of three states of a crystal form transition process from 2D MOF to 3D MOF.

Detailed Description

The invention discloses a preparation method for converting a two-dimensional metal organic framework (2D MOF) into a three-dimensional framework (3D MOF). The structure conversion from the 2D MOF to the 3D MOF is realized by adopting a mixed solvent of ionic liquid and water, the ionic liquid is a hydrophilic functional solvent formed by imidazole cations, the 2D MOF is a two-dimensional zeolite imidazolate (ZIF-L), and the converted 3D MOF is a three-dimensional zeolite imidazolate (ZIF-8).

The invention is further described with reference to the following figures and examples.