CN104151336A - Preparation method of metal-organic framework compound with hierarchical pore structure - Google Patents

Abstract

The invention belongs to the technical field of nanocomposite materials, in particular to a preparation method of a metal organic framework compound with a hierarchical porous structure. In the present invention, the two-block copolymer self-assembles in a solvent to form a flexible polymer nanowire with a core-shell structure, and obtains a solvent-stabilized polymer nanowire after cross-linking the core; adding metal ions and organic ligands to the nanowire solution, Form a mixed solution; crystallize at room temperature to obtain a metal-organic framework/core-shell polymer nanowire composite; remove the polymer nanowire after calcination, and obtain both the micropores of the MOFs itself and the calcined polymer nanowire shell A hierarchical porous material with small mesoporous pores and large mesopores formed after calcination of the core layer. This kind of hierarchical porous MOFs material combines the advantages of micropores and mesoporous materials, improves the mass transfer rate of MOFs materials, facilitates the entry of larger molecules, and improves its application potential in the fields of catalysis and adsorption.

Description

A kind of preparation method of the metal-organic framework compound of hierarchical pore structure

technical field

The invention belongs to the technical field of nanocomposite materials, and in particular relates to a preparation method of a metal organic framework compound with a hierarchical porous structure.

Background technique

Porous materials, such as molecular sieves, mesoporous silicon, and activated carbon, are a very important class of materials. Due to their huge specific surface area, they are widely used in catalysis, gas adsorption, ion exchange and so on. Metal-organic frameworks (MOFs), a newly emerging organic-inorganic porous material, have attracted extensive attention due to their excellent properties and the controllability of structure and function. MOFs are a class of crystalline materials composed of metal ions and organic ligands. The structures and functions of MOsFs can be obtained according to the selection of metal ions and the synthesis of different organic ligands. It can be applied in the fields of gas storage, separation, detection and catalysis.

The pore size of most MOFs is microporous (less than 2nm), which makes it have a large specific surface area, but it is not conducive to the entry of larger molecules, and its internal mass transfer is also limited, which limits its use in catalysis, storage, etc. , separation, drug delivery and other applications. Therefore, it is very meaningful to prepare mesoporous MOFs, especially hierarchically porous MOFs with both mesoporous and micropores. For example, as reported by Zhou Hongcai et al. (J. Am. Chem. Soc. 2012, 134, 126-129.), surface activity was used as a porogen to generate mesopores. Reports by Bai Junfeng et al. (Crystal Growth & Design, 2010, 10, 2451-2454.) used nano-MOF particles to gather together through van der Waals force to form interstitial mesoporous grains. Yaghi et al. reported (J. Am. Chem. Soc. 2011, 133, 11920-11923.) By adding monofunctional ligands to make crystals have defects to produce mesopores or macropores, etc. However, the removal of surfactants often leads to the collapse of the overall structure, and the use of van der Waals forces and special ligands is specific. Therefore, it is very meaningful to develop a universal method to prepare MOFs with hierarchical porous structure and maintain the stability of MOFs crystal particles.

Contents of the invention

The object of the present invention is to provide a method for preparing hierarchical porous metal organic frameworks (MOFs) that can ensure the stability of the hierarchical porous structure.

The preparation method of the hierarchical porous metal organic framework compound (MOFs) provided by the present invention, the specific steps are:

(1) First, the diblock copolymer self-assembles in a solvent to form a flexible polymer nanowire with a core-shell structure, and then cross-links the core layer of the nanowire; then switch the solvent of the nanowire solution to the solvent required for MOFs crystallization ;

(2) Then, add a metal salt solution and an organic ligand solution to the polymer nanowire solution to form a mixed solution; stand and crystallize at room temperature to obtain a metal-organic framework/core-shell polymer nanowire composite;

(3) Finally, calcine at a certain temperature to remove the polymer nanowires, and obtain both the micropores of the MOF itself, and the small mesopores formed by the calcination of the polymer nanowire shell and the large mesopores formed by the calcination of the core layer. The hierarchical porous material; in addition, the calcined hierarchical porous particles maintain the geometric shape of the crystal particles and ensure the stability of the structure.

Among them, the MOFs are ZIF-8, ZIF-7, ZIF-67, HKUST-1 or CD-MOF-1, here, ZIF-8 means MOFs formed by divalent zinc ions and 2-methylimidazole, ZIF- 67 represents the MOFs formed by divalent cobalt ions and 2-methylimidazole, ZIF-7 represents the MOFs formed by divalent zinc ions and benzimidazole, HKUST-1 represents the MOFs formed by divalent copper ions and trimesic acid , CD-MOF-1 means MOFs formed by monovalent potassium ions and γ-cyclodextrin;

In the present invention, the polymer nanowires are flexible, capable of bending and intertwining; the polymer forming the shell of the nanowires can interact with metal ions, and when metal ions and ligands crystallize to form MOFs, the polymer nanowires It can be well wrapped into MOFs particles, forming particles to maintain the crystal shape, and nanowires run through the coated crystal particles.

In the present invention, the stability of the polymer nanowire is lower than that of the metal organic framework compound.

In the present invention, the hierarchically porous MOFs formed after calcination have a sponge-like structure, and the pores are disordered, connected to each other, and connected to the outside world. the

In step (1), the two-block copolymer is polyethylene glycol-polytetravinylpyridine (PEG- b -P4VP, the polyethylene glycol segment molecular weight is between 2000-20000, poly(4-ethylene basepyridine) with a molecular weight of 3000-20000; the crosslinking agent is 1,4-dibromobutane, and the pyridine ring with a crosslinking degree of 5%-100% is crosslinked.

In step (1), polymer nanowires can be modified to introduce functional groups, nanoparticles or other inorganic components to optimize the functionality of MOFs. For example, functional functional groups—pyridine groups and fluorescent groups can be introduced through the reaction of halogenated hydrocarbons and pyridine rings; Au can be introduced through the exchange of counter ions to introduce chloroauric acid, or ^Ag , AgBr; SiO ₂ was introduced by depositing a thinner SiO ₂ on the surface of the polymer core.

In step (1), the method of switching the solvent includes centrifuging to remove the supernatant and then dissolving, dialysis, and freeze-drying and then dissolving; the solvent is methanol (for ZIF-8, ZIF-67, ZIF-7), Ethanol (for HKUST-1), water (for HKUST-1, CD-MOF-1), DMF (for ZIF-8, ZIF-67, ZIF-7), and their mixed solution ethanol/water (for HKUST- 1) One of. the

In step (2), the concentration of the polymer nanowires in the reaction solution is 0.1 mg/ml-10 mg/ml.

In step (2), the corresponding relationship between the metal salt and the organic ligand is: Zn(NO ₃ ) ₂ or ZnCl ₂ corresponds to 2-methylimidazole (ZIF-8), and Co(NO ₃ ) ₂ corresponds to 2-methyl Imidazole (ZIF-67), Zn(NO ₃ ) ₂ corresponds to benzimidazole (ZIF-7), Cu(NO3) ₂ or Cu(Ac) ₂ corresponds to trimesic acid (HKUST-1), KOH corresponds to γ-ring Dextrin (CD-MOF-1); the concentration of the metal salt in the reaction system is 10mM-150mM, and the concentration of the organic ligand is 10mM-200mM.

In step (2), when the prepared MOFs are CD-MOF-1, the polymer nanowires, KOH, and γ-cyclodextrin all use water as the solvent, and use the method of diffusing an equal volume of methanol into the aqueous solution after mixing to prepare the compound.

In step (2), the standing time is 24 hours-3 days (for ZIF-8, ZIF-67, ZIF-7), 7-14 days (for HKUST-1, CD-MOF-1).

In step (3), the calcination temperature is 150°C-500°C, and the calcination time is 0.5-10 hours; preferably, the calcination temperature is 300-400°C, and the calcination time is 3-4 hours.

The present invention is characterized in that:

1. This method produces MOFs materials with a hierarchical pore structure composed of small mesopores formed after the polymer nanowire shell is calcined, large mesopores formed after the core layer is calcined, and the micropores of the MOFs themselves.

2. Polymer nanowires are added before crystallization to form MOFs. In a single MOFs particle, the polymer nanowires form a network structure that runs through the inside and outside of the MOFs particle. Therefore, the disordered pores formed after calcination, the pores penetrate each other and communicate with the outside world.

3. After calcining to remove the polymer nanowires, the MOFs structure does not collapse, maintains the original crystal shape, and ensures the stability of the hierarchical pore structure.

Description of drawings

Fig. 1 is the field emission scanning electron microscope (a, b) and the high resolution transmission electron microscope (c, d) of the hierarchically porous ZIF-8 product in Example 1.

The nitrogen adsorption and desorption curves of ZIF-8, ZIF-8/nanowire composite, and hierarchical porous ZIF-8 in Fig. 2 Example 1.

Fig. 3 NLDFT pore size distribution diagram of ZIF-8, ZIF-8/nanowire composite, and hierarchically porous ZIF-8 in Example 1.

Fig. 4 is a field emission scanning electron microscope image (a) and a high resolution transmission electron microscope image (b) of the hierarchically porous ZIF-7 product in Example 3.

Fig. 5 is a field emission scanning electron microscope image (a) and a high resolution transmission electron microscope image (b) of the hierarchically porous HKUST-1 product in Example 4.

Detailed ways

The present invention will be further described through examples below, but the embodiments of the present invention are not limited thereto.

Example 1. Preparation of hierarchically porous ZIF-8.

(1) Add 10ml (2mg/ml) polymer nanowire solution, 15ml methanol, 25ml Zn(NO ₃ ) ₂ (250mM) methanol solution, and 50ml 2-methylimidazole (250mM) methanol solution into the reaction bottle. Shake well and let stand at room temperature. After 24 hours, a white precipitate was obtained, which was collected by centrifugation, washed twice with methanol, and dried overnight in a vacuum oven to obtain 0.1238 g of a white solid.

(2) The product was put into a muffle furnace and calcined at 350° C. for 4 hours to obtain 0.0915 g of a yellow solid. Field emission scanning electron microscopy, high resolution transmission electron microscopy, and nitrogen adsorption and desorption experimental results of the product are shown in Figures 1, 2, and 3.

Example 2. Preparation of hierarchically porous ZIF-8.

(1) Add 2ml polymer nanowire (2mg/ml) solution, 83ml methanol to the reaction bottle, then add 5ml Zn(NO ₃ ) ₂ · 6H ₂ O (250mM) methanol solution, 10ml 2-methylimidazole (250mM) methanol solution. Shake well and let stand at room temperature. After 24 hours, a white flocculent precipitate was obtained, which was collected by centrifugation, washed twice with methanol, and dried overnight in a vacuum oven to obtain 0.0727 g of a white solid.

(2) The product was put into a muffle furnace, and calcined at 350° C. for 4 hours to obtain 0.0504 g of a yellow solid.

Example 3. Preparation of hierarchically porous ZIF-7.

(1) Add 10ml (2mg/ml) polymer nanowire solution and 15ml methanol to the reaction bottle, then add 25ml Zn(NO ₃ ) ₂ · 6H ₂ O (250mM) methanol solution, 50ml benzimidazole (250mM) methanol solution . Shake well and let stand at room temperature. After 3 days, a white precipitate was obtained, which was collected by centrifugation, washed twice with methanol, and dried overnight in a vacuum oven to obtain 0.3216 g of a white solid.

(2) The product was put into a muffle furnace and calcined at 400°C for 3 hours to obtain 0.2852 g of a white solid. The results of field emission scanning electron microscopy and high resolution transmission electron microscopy of the product are shown in Figure 4.

Embodiment 4, HKUST-1.

(1) Add 10ml (2mg/ml) epipolymer nanowire solution, 40ml ethanol/water (1:1) to the reaction bottle, then add 25ml Cu(NO ₃ ) ₂ ·3H ₂ O (375mM) aqueous solution, 25ml Benzenetricarboxylic acid (250mM) ethanol solution. Shake well and let stand at room temperature. After 3 days, a blue precipitate was obtained, which was collected by centrifugation, washed twice with ethanol, and dried overnight in a vacuum oven to obtain 0.2321 g of a white solid.

(2) The product was put into a muffle furnace and calcined at 300°C for 3 hours to obtain 0.2018 g of a black solid. The results of field emission scanning electron microscopy and high resolution transmission electron microscopy of the product are shown in Figure 5.

Claims (2)

1. a preparation method for multi-stage porous organic frame compound, is characterized in that concrete steps are:

First, di-block copolymer self-assembly in solvent forms the flexible polymer nano wire of nucleocapsid structure, the then stratum nucleare of crosslinking nano line; Again the solvent of nano wire solution is switched to the needed solvent of MOFs crystallization;

Then, in polymer nano rice noodles solution, add metal salt solution and organic ligand solution, form mixing solutions; Crystallization under room temperature, obtains metal organic frame/nucleocapsid structure polymer nano rice noodles mixture;

Finally, calcining, removes polymer nano rice noodles, obtains the micropore of existing MOF self, has again the large mesoporous multilevel hole material forming by after the little mesoporous and stratum nucleare calcining forming after the calcining of polymer nano rice noodles shell;

Wherein, the MOFs of institute is ZIF-8, ZIF-7, ZIF-67, HKUST-1 or CD-MOF-1, here, ZIF-8 represents the MOFs being formed by divalent zinc ion and glyoxal ethyline, ZIF-67 represents the MOFs being formed by divalent cobalt ion and glyoxal ethyline, ZIF-7 represents the MOFs being formed by divalent zinc ion and benzoglyoxaline, and HKUST-1 represents the MOFs that bivalent cupric ion and trimesic acid form, and CD-MOF-1 represents the MOFs being formed by monovalence potassium ion and γ-cyclodextrin;

Described di-block copolymer is polyethylene glycol-four vinyl pyridines, and polyoxyethylene glycol chain segment molecular weight is between 2000-20000, and P4VP molecular weight is between 3000-20000; Linking agent is Isosorbide-5-Nitrae-dibromobutane, and the pyridine ring that crosslinking degree is 5%-100% has been crosslinked.

2. the preparation method of multi-stage porous organic frame compound according to claim 1, is characterized in that described calcining temperature is 150 DEG C-500 DEG C, and calcination time is 0.5 hour-10 hours.