CN112280052B

CN112280052B - Hierarchical pore ZIF-8 material and preparation method and application thereof

Info

Publication number: CN112280052B
Application number: CN202011057409.9A
Authority: CN
Inventors: 奚红霞; 张雪莲; 吴颖; 余仪
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2020-09-30
Filing date: 2020-09-30
Publication date: 2021-08-10
Anticipated expiration: 2040-09-30
Also published as: CN112280052A

Abstract

The invention discloses a multi-level porous ZIF-8 material and a preparation method and application thereof. The method comprises the following steps: (1) adding ZnO into water and stirring; (2) dissolving Zn(CH ₃ CO ₂ ) ₂ ·2H ₂ O in the DMF-aqueous solution, then adding it to step (1) for reaction; (3) 3-sulfopropyltetradecyldimethylbetaine is added to the 2-methylimidazole-DMF solution, and after stirring and dissolving, it is added to step (2) to react; (4) the resulting product is subjected to purification treatment After that, the multi-level porous ZIF-8 material was obtained. The present invention utilizes 3-sulfopropyltetradecyldimethylbetaine as a template agent, which is environmentally friendly and has mild preparation conditions, which is beneficial to practical popularization and use. The prepared material has three-scale pores of micropore-mesoporous-macropore, can be used as a catalyst for CO ₂ cycloaddition reaction, and has the advantages of good catalytic activity, stability, cycle performance and the like.

Description

Hierarchical pore ZIF-8 material and preparation method and application thereof

Technical Field

The invention belongs to the field of preparation of hierarchical pore metal organic frameworks, and particularly relates to a hierarchical pore ZIF-8 material, and a preparation method and application thereof.

Background

With the rapid development of the human industrial society, carbon dioxide (CO)₂) Annual emissions are increasing at an alarming rate, which is also the leading cause of acid rain pollution, global warming. Reacting CO with₂The collected and converted chemicals with high added value (such as methanol, formic acid and cyclic carbonic acid) can not only turn waste into wealth, provide a new way for solving the problem of environmental pollution, but also be an important ring of carbonization industry, and have remarkable economic and social benefits. However, CO₂The bond energy of the medium C-O bond is higher, resulting in CO₂The fixing difficulty is high. In a plurality of CO₂In the fixing method, an epoxy compound is reacted with CO₂The cycloaddition reaction of (a) to produce cyclic carbonates is undoubtedly one of the most attractive, direct and greenest routes. The reaction can realize 100% of atom conversion rate, and the product cyclic carbonate is used as a chemical basic raw material and has wide application in pharmaceutical chemistry and organic synthesis [ Cokoja M, Bruckmeier C, Rieger B, et alal Challenge？[J].Angewandte Chemie International Edition,2011.]。

At present, researchers have been working on CO₂The cycloaddition reaction of (a) has developed a series of homogeneous and heterogeneous catalysts, such as alkali metal halides, ionic liquids, polymers, zeolites and transition metal complexes, etc. Homogeneous catalyst in CO₂The cycloaddition reaction has been studied most extensively, with conversion efficiencies as high as 99%, but still suffers from difficulties in catalyst and product separation and recovery. In comparison, heterogeneous catalysts have the advantage that the catalyst is easily separated from the product and regenerated. Compared with other heterogeneous catalysts, Metal Organic Framework (MOFs) materials show outstanding heterogeneous catalytic performance due to multiple active sites, high specific surface area, modifiable structure and easy functionalization. At the same time, MOFs materials are paired with CO₂The adsorption performance of (2) is higher. These characteristics give MOFs catalysts in CO₂Unique superiority in the chemical fixation field.

However, most of the traditional MOFs have a microporous structure, if the materials are applied to large-scale industrial catalysis, the mass transfer resistance is increased, the mass transfer rate of substrate molecules is reduced, the large molecular compounds are not beneficial to reach active centers, and the catalytic efficiency is necessarily reduced. As exemplified by Zalomaeva et al [ Zalomaeva O V, Chibiryaev A M, Kovalenko K A, et al₂ over metal–organic framework Cr-MIL-101[J].Journal of catalysis,2013,298:179-185.]It is reported that propylene oxide and phenyl ethylene oxide can be obtained under milder conditions (25 ℃ and 0.8MPa CO) under the synergistic effect of MIL-101(Cr) and a cocatalyst TBAB₂) High efficiency of conversion to the corresponding cyclic carbonate. However, for the more sterically hindered cyclohexane epoxides, the reactivity of the reaction is very low. Park et al [ Babu R, Kathiaikkattill A C, Rosman R, et al, Dual-pore metal for room temperature CO₂ fixation via cyclic carbonate synthesis[J].Green Chemistry,2016,18(1):232-242.]2-amino terephthalic acid and 1, 3, 5-tri (4-carboxyl phenyl) benzene are used as mixed ligands, zinc nitrate is used as metal salt, and the novel micropore-mesopore structure is constructedMOFs catalyst UMCM-1-NH₂Realizes that the catalyst is used under mild conditions (25 ℃ and 1.2MPa CO)₂) The method can efficiently catalyze the synthesis of cyclic carbonate. In contrast to the previous catalytic systems, they indicate UMCM-1-NH₂The hierarchical pore structure in (A) plays a key role in the reactivity. On one hand, the mesoporous structure in the hierarchical pore MOFs effectively promotes the mass transfer process between substrates, and the microporous structure is favorable for the full action of the substrates and catalytic sites. Therefore, an efficient preparation method was developed to introduce larger pores (meso-and/or macro-pores) in microporous MOFs to form a hierarchical porous metal-organic framework (HP-MOFs) for CO promotion₂The catalytic efficiency of the cycloaddition reaction is of critical importance.

At present, the microporous MOFs multi-stage pore-forming strategies mainly comprise five methods, namely an extended ligand method, a mixed ligand method, a post-synthesis modification method, a template-free method and a template-assisted method, which have respective advantages and disadvantages. Template-based methods are commonly used for the manufacture of various HP-MOFs, compared to other methods, and after template removal, hierarchical porous MOFs structures [ Wang C, Liu X, Li W, et al₂ mediated fabrication of hierarchically porous metal-organic frameworks[J].Microporous and Mesoporous Materials,2019,277:154-162.]. Li et al [ Wu Y, Zhou M, Zhang B, et al, amino acid associated with a structural synthesis of a structural immunogenic enzyme frame-8 for an effective citrate removal [ J].Nanoscale,2014,6(2):1105-1112.]A surfactant CTAB (cetyl trimethyl ammonium bromide) is used as a template agent, and alpha-amino acid L-histidine is used as a chelating agent, so that the hierarchical pore ZIF-8 material is successfully prepared in a water phase. Compared with the microporous ZIF-8 material, the prepared hierarchical pore ZIF-8 can efficiently remove inorganic pollutant arsenate in water, and the impurity removal efficiency is about 1.8 times of that of the microporous ZIF-8 material. Recently, Xi et al [ Zhang H, Huo J, Yang H, et al Green and Rapid prediction of microwave powder metals-organic zeolites and sizing of the same growth [ J].Journal of Materials Chemistry A,2019,7(3):1022-1029.]Under the condition of room temperature, a series of hierarchical pore ZIF materials (ZIF-8, ZIF-61 and ZIF-90) are synthesized by using an anionic surfactant Sodium Benzenesulfonate (SBS) as a template agent and DMF as a solvent. The pore structure of the porous pipe can pass throughThe amount of the sodium benzenesulfonate template agent added is finely regulated. However, the types of templating agents reported so far are limited, and the material structure may collapse during the activation process for removing the surfactant from the sample. In addition, template residue may also remain in the final product, blocking the channels. Therefore, it is still a serious challenge to select a simple synthesis route to design and synthesize stable multi-level pore MOFs, so as to avoid the harsh synthesis conditions (high temperature and high pressure), reduce the industrialization cost and environmental pollution, etc.

Disclosure of Invention

The invention aims to provide a hierarchical pore ZIF-8 material and a preparation method and application thereof, the method develops an environment-friendly amphoteric surfactant (3-sulfopropyl tetradecyl dimethyl betaine), the amphoteric surfactant is used as a structure guiding agent based on hydroxyl double metal salt ((Zn, Zn) -HDS), and the hierarchical pore ZIF-8 material with three pore channel structures of micropore-mesopore-macropore can be synthesized under mild conditions, so that the hierarchical pore ZIF-8 material can be used for treating CO₂The catalytic activity of the cycloaddition reaction is effectively improved.

The raw material of the invention is Zn (CH)₃CO₂)₂·2H₂O, ZnO, 2-methylimidazole, 3-sulfopropyl tetradecyl dimethyl betaine (purchased from alatin) and DMF, and under the action of a surfactant 3-sulfopropyl tetradecyl dimethyl betaine as a structure directing agent, the ZIF-8 material rich in various pore channel structures (micropore-mesopore-macropore) is prepared. The larger pore channel structure in the hierarchical pore ZIF-8 material is beneficial to improving CO₂The mass transfer rate of cycloaddition catalytic reaction, wherein the macropores and the mesopores can effectively promote the mass transfer process of the substrate, the micropores can provide a chemical environment which is favorable for the substrate and catalytic active sites to be fully contacted, and secondly, the unsaturated metal sites containing Zn ions in the material effectively provide the catalytic active sites.

The purpose of the invention is realized by the following technical scheme.

A preparation method of a hierarchical pore ZIF-8 material comprises the following steps:

(1) adding ZnO into water, and stirring to obtain suspension A;

(2) adding Zn (CH)₃CO₂)₂·2H₂Adding O into a DMF-water solution, and dissolving by ultrasonic to obtain a solution B;

(3) adding the solution B into the suspension A, stirring, and reacting to obtain a mixed solution C;

(4) adding 2-methylimidazole into DMF, and stirring to obtain a solution D;

(5) adding a template agent into the solution D, and stirring and dissolving to obtain a solution E; the template agent is 3-sulfopropyl tetradecyl dimethyl betaine;

(6) mixing the mixed solution C and the solution E, and stirring for reaction;

(7) washing the product obtained after the reaction in the step (6) with DMF and water, and immersing the product in methanol;

(8) and (5) carrying out suction filtration and drying on the product obtained in the step (7) to obtain the hierarchical pore ZIF-8 material.

Preferably, the stirring time of the step (1), the step (4) and the step (5) is 10 to 15 minutes.

Preferably, the volume ratio of the two in the DMF-water solution in the step (2) is 1:1, the ultrasonic time is 1-5 minutes.

Preferably, the reaction time of the step (3) is 20-24 h; the reaction time in the step (6) is 45-600 seconds.

Preferably, the immersion in methanol in the step (7) is carried out for 24-72 h, and the methanol is replaced every 12 h.

Preferably, the Zn (CH)₃CO₂)₂·2H₂O, ZnO, 2-methylimidazole and 3-sulfopropyltetradecyldimethyl betaine in a molar ratio of 1: 1: (5.8-6.2): (0.12-2.5).

Preferably, the Zn (CH)₃CO₂)₂·2H₂O, ZnO, 2-methylimidazole and 3-sulfopropyltetradecyldimethyl betaine in a molar ratio of 1: 1: 6: 2.

the hierarchical pore ZIF-8 material is prepared by the preparation method.

The hierarchical pore ZIF-8 material is applied to catalyzing CO₂A cycloaddition reaction comprising the steps of:

mixing ZIF-8 material,Mixing tetrabutylammonium bromide as cocatalyst with epichlorohydrin, introducing CO₂A cycloaddition reaction is carried out.

Preferably, the mass ratio of the ZIF-8 material to the cocatalyst tetrabutylammonium bromide to the reactant epichlorohydrin is (0.2-2): 1.61:18.51, the reaction temperature is 50-90 ℃, and the reaction time is 12-24 h.

Preferably, the CO is₂The pressure was 1bar, the reaction time was 24h and the reaction temperature was 80 ℃.

Compared with the prior art, the invention has the following advantages and effects:

(1) the template agent (3-sulfopropyl tetradecyl dimethyl betaine) used by the invention is a common skin care product raw material, is green and environment-friendly, and has no pollution to the environment.

(2) The method for preparing the hierarchical pore ZIF-8 material is simple, the synthesis conditions are mild (normal temperature synthesis), the popularization and the industrial use are facilitated, and the material has rich micropore-mesopore-macropore pore structure and good application prospect for the catalytic reaction of macromolecules.

(3) The hierarchical pore ZIF-8 material prepared by the invention catalyzes CO₂The cycloaddition reaction has mild conditions (80 ℃, 24h, 1bar CO)₂) And the conversion rate of the reaction can reach more than 99 percent.

Drawings

FIG. 1 is a wide angle X-ray diffraction pattern of ZIF-8 materials prepared in examples 1-6 of the present invention.

FIG. 2 is a scanning electron micrograph of a hierarchical pore ZIF-8 material prepared according to example 2/3/5/6 of the present invention.

FIG. 3 is an SEM image (a) and an EDS energy spectrum (b) of a multi-well ZIF-8 material prepared in example 5 of the present invention.

FIG. 4 is a thermogravimetric plot of a hierarchical pore ZIF-8 material prepared in accordance with example 2/5 of the present invention.

FIG. 5 is N of a hierarchical pore ZIF-8 material prepared in example 2/3/5/6₂Adsorption-desorption isotherm diagram.

FIG. 6 is a graph of the full pore size distribution calculated from a DFT model for the hierarchical pore ZIF-8 material prepared in example 2/3/5/6.

FIG. 7Catalyzing CO for ZIF-8 materials₂Graph of the effect of the performance of the cycloaddition reaction.

FIG. 8 is a graph showing the effect of reaction temperature on the catalytic performance of the ZIF-8 material prepared in example 5 of the present invention.

FIG. 9 is a graph showing the effect of catalytic reaction time on the catalytic performance of ZIF-8 prepared in example 5 of the present invention.

FIG. 10 is a hierarchical pore ZIF-8 material catalyzed CO prepared in example 5₂Nuclear magnetic spectrum of cycloaddition reaction result (conversion rate)>99％)。

Detailed Description

The invention is further described below with reference to the drawings and examples, but the scope of the invention as claimed is not limited to the scope of the examples.

Example 1

Dissolving 0.081g ZnO in 1ml deionized water, and stirring for 10 minutes to obtain a suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂Dissolving O in 2ml of DMF-deionized water (v/v ═ 1:1) solution, and carrying out ultrasonic treatment for 1 minute to obtain solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 20 hours to obtain a mixed solution C; dissolving 0.476g of 2-methylimidazole in 9ml of DMF, and stirring for 10 minutes to obtain a solution D; adding 3-sulfopropyl tetradecyl dimethyl betaine 0.364g into the solution D, and continuously stirring for 10 minutes to obtain a solution E; and mixing and stirring the mixed solution C and the solution E at room temperature, carrying out suction filtration after reacting for 45 seconds, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying for 24 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying for 10 hours at 100 ℃ to obtain a hierarchical pore ZIF-8 material which is marked as a sample A1.

Example 2

Dissolving 0.081g ZnO in 1ml deionized water, stirring for 11 minutes to obtain suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂Dissolving O in 2ml of DMF-deionized water (v/v ═ 1:1) solution, and carrying out ultrasonic treatment for 1 minute to obtain solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 20 hours to obtain a mixed solution C; dissolving 0.476g of 2-methylimidazole in 9ml of DMF, and stirring for 10 minutes to obtain a solution D; adding 0.045g of 3-sulfopropyl tetradecyl dimethyl betaine into the solution D, and continuously stirring for 10 minutes to obtain a solution E; mixing ofMixing and stirring the mixed solution C and the solution E at room temperature, carrying out reaction for 60 seconds, then carrying out suction filtration, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying the product for 24 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying at 100 ℃ for 10 hours to obtain a hierarchical pore ZIF-8 material which is marked as a sample A2.

Example 3

Dissolving 0.081g ZnO in 1ml deionized water, stirring for 12 minutes to obtain suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂Dissolving O in 2ml of DMF-deionized water (v/v ═ 1:1) solution, and carrying out ultrasonic treatment for 3 minutes to obtain solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 22h to obtain a mixed solution C; dissolving 0.500g of 2-methylimidazole in 9ml of DMF, and stirring for 12 minutes to obtain a solution D; adding 3-sulfopropyl tetradecyl dimethyl betaine 0.182g into the solution D, and stirring for 12 minutes to obtain a solution E; and mixing and stirring the mixed solution C and the solution E at room temperature, carrying out reaction for 120 seconds, then carrying out suction filtration, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying the product for 48 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying at 110 ℃ for 11 hours to obtain a hierarchical pore ZIF-8 material which is marked as a sample A3.

Example 4

Dissolving 0.081g ZnO in 1ml deionized water, and stirring for 13 minutes to obtain a suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂Dissolving O in 2ml of DMF-deionized water (v/v ═ 1:1) solution, and carrying out ultrasonic treatment for 4 minutes to obtain solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 24 hours to obtain a mixed solution C; dissolving 0.493g of 2-methylimidazole in 9ml of DMF, and stirring for 14 minutes to obtain a solution D; adding 3-sulfopropyl tetradecyl dimethyl betaine 0.364g into the solution D, and continuously stirring for 14 minutes to obtain a solution E; and mixing and stirring the mixed solution C and the solution E at room temperature, carrying out reaction for 180 seconds, then carrying out suction filtration, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying the product for 48 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying at 120 ℃ for 11 hours to obtain a hierarchical pore ZIF-8 material which is marked as a sample A4.

Example 5

Dissolving 0.081g ZnO in 1ml deionized water, and stirring for 14 minutes to obtain a suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂O in 2ml DMF-deionized water (v/v ═ v1:1) carrying out ultrasonic treatment on the solution for 4 minutes to obtain a solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 24 hours to obtain a mixed solution C; dissolving 0.493g of 2-methylimidazole in 9ml of DMF, and stirring for 14 minutes to obtain a solution D; adding 0.727g of 3-sulfopropyl tetradecyl dimethyl betaine into the solution D, and continuously stirring for 14 minutes to obtain a solution E; and mixing and stirring the mixed solution C and the solution E at room temperature, carrying out reaction for 300 seconds, carrying out suction filtration, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying for 60 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying for 11 hours at 120 ℃ to obtain a hierarchical pore ZIF-8 material which is marked as a sample A5.

Example 6

Dissolving 0.081g ZnO in 1ml deionized water, and stirring for 15 minutes to obtain a suspension A; 0.220g of Zn (CH)₃CO₂)₂·2H₂Dissolving O in 2ml of DMF-deionized water (v/v ═ 1:1) solution, and carrying out ultrasonic treatment for 5 minutes to obtain solution B; mixing the solution B with the suspension A, and reacting and stirring at room temperature for 24 hours to obtain a mixed solution C; dissolving 0.509g of 2-methylimidazole in 9ml of DMF, and stirring for 15 minutes to obtain a solution D; adding 3-sulfopropyl tetradecyl dimethyl betaine 0.909g into the solution D, and continuing stirring for 15 minutes to obtain a solution E; and mixing and stirring the mixed solution C and the solution E at room temperature, carrying out suction filtration after reacting for 600 seconds, washing the obtained product with DMF (dimethyl formamide) and deionized water, purifying for 72 hours by using methanol, carrying out suction filtration, and carrying out vacuum drying for 12 hours at 120 ℃ to obtain a hierarchical pore ZIF-8 material which is marked as a sample A6.

The hierarchical pore ZIF-8 material prepared according to the examples was analyzed, and the analysis results are shown in the accompanying drawings.

X-ray powder diffraction analysis of (mono) hierarchical porous ZIF-8

The crystal structures of the samples A1-A6 synthesized in examples 1 to 6 according to the invention were characterized by means of an X-ray polycrystal diffractometer model D8-ADVANCE (Bruker, Germany). As can be seen from FIG. 1, the samples prepared in examples 1-6 have distinct characteristic diffraction peaks and relative intensities that match well with the microporous ZIF-8 material reported in the literature (Lee Y R, Jang M S, Cho H Y, et al, ZIF-8: A composition of synthesis methods [ J ]. Chemical Engineering Journal,2015,271: 276-); when the synthesis conditions such as the molar ratio of the 3-sulfopropyltetradecyldimethyl betaine template to Zn are changed, the samples A1-A6 have similar and identical PXRD spectra, and the diffraction peaks are not obviously changed, which indicates that the ZIF-8 material can be synthesized by adopting the synthesis conditions of the examples 1-6.

(II) SEM image of room temperature synthesis of hierarchical pore ZIF-8 material

The samples prepared in example 2 (a in fig. 2), example 3 (b in fig. 2), example 5 (c in fig. 2), and example 6 (d in fig. 2) were subjected to morphology characterization using a JSM-6330F type scanning electron microscope (JEOL, japan). FIG. 2 shows that the synthesized sample consists of nanoparticles with a nearly spherical shape, all of which are relatively uniform in size, about 60nm in diameter, and smaller than particles of a material synthesized by a solvothermal method, as reported in the literature (Tran U P N, Le K A, Phan N T S. expanding Applications of Metal-Organic Frameworks: Zeolite Imidazolate Framework ZIF-8as an effective Heterogeneous Catalyst for the Knoevenagel Reaction [ J ]. Acs Catalysis,2011,1(2): 120-; in addition, small nanocrystals are randomly packed together, which can form rich mesoporous and macroporous structures.

FIG. 3 is an SEM image (a) and an EDS energy spectrum (b) of a sample prepared in example 5, and it can be seen from FIG. 3 and Table 1 that the surfactant material added during the synthesis of the hierarchical pore ZIF-8 material has been washed away and the template residue does not remain in the final product, resulting in the clogging of the pores; and no collapse of the structure occurred after removal of the templating agent, which is consistent with the results of FIG. 1 xrd.

TABLE 1

Thermogravimetric analysis of (III) hierarchical pore ZIF-8 materials

The thermal stability of the samples prepared in examples 2 and 5 was examined by using a TG 209 thermogravimetric analyzer (Netzsch) at a heating rate of 10 ℃/min (room temperature-900 ℃) under a nitrogen atmosphere. Fig. 4 shows that the synthesized sample does not significantly decrease at 450 ℃ and has good thermal stability.

(IV) channel Properties

By usingASAP2460 specific surface pore size distribution (Micro, USA) characterizes the pore structure of the sample prepared in example 2/3/5/6, and the results are shown in Table 2. As can be seen from Table 2, the BET specific surface areas of the prepared materials were 1411, 1399, 1446, and 1374m².g^-1Wherein the specific surface area of the mesopores of sample A5 was the highest and was 260m².g^-1. Ratio of mesopore volume to micropore volume (V)_meso/V_micro) 0.51, 0.83, 1.18 and 0.84, respectively, sample A5 having the largest V_meso/V_microThe values indicate that the mesoporous structure in the material is more.

TABLE 2

FIG. 5 is a N representation of a hierarchical pore ZIF-8 material prepared in accordance with example 2/3/5/6 of the present invention₂Adsorption-desorption isotherm diagram. As can be seen, examples 2/3/5/6 all showed similar adsorption isotherms, showing a type I adsorption isotherm at low relative pressures, with a significant increase in adsorption with increasing relative pressure, indicating the presence of abundant micropores; at a relative pressure P/P₀An obvious adsorption hysteresis loop (H4) appears after the concentration is approximately equal to 0.8, which indicates that the material contains a mesoporous structure.

Fig. 6 is a DFT full pore size distribution diagram showing that the hierarchical pore ZIF-8 material prepared in example 2/3/5/6 includes mesopores and larger macropores, mainly distributed at 6-100nm, in addition to a large number of micropores, which confirms that the prepared ZIF-8 material has a micropore-mesopore-macropore structure.

(V) ZIF-8 materials for CO catalysis₂Effect of the Properties of the cycloaddition reaction

Reaction conditions are as follows: the catalyst was ZIF-8 material prepared in example 2/5 (100mg), tetrabutylammonium bromide as a cocatalyst (161.2mg) and epichlorohydrin as a reactant (20mmol) in a mass ratio of 1:1.61:18.51 in terms of CO₂The pressure was 1bar, the reaction time was 24h and the reaction temperature was 80 ℃. After the reaction, the conversion of the reactant was measured by means of a nuclear magnetic resonance spectrometer (AVANCE III HD 600M, Bruker, Germany)

FIG. 7 is a graph showing the effect of catalytic performance of microporous ZIF-8 materials synthesized by hydrothermal synthesis (specifically, synthetic method references: Lee Y R, Jang M S, Cho H Y, et al. ZIF-8: A composition of synthesis methods [ J ]. Chemical Engineering Journal,2015,271:276- & 280.) and the hierarchical porous ZIF-8 material prepared in example 2/5 of the present invention. FIG. 7 shows that the catalytic efficiency of the hierarchical pore ZIF-8 synthesized by the present invention is higher and the conversion can be as high as 99% compared to microporous ZIF-8 (FIG. 10). This is probably due to the meso-macroporous structure in the synthesized material, which promotes the transfer of reactants and products in the pore channels, increasing the mass transfer rate.

(VI) catalyzing CO by using reaction temperature to hierarchical porous ZIF-8 material₂Effect of the Properties of the cycloaddition reaction

Reaction conditions are as follows: the catalyst was ZIF-8 material (100mg) prepared in example 5, tetrabutylammonium bromide (161.2mg) as a cocatalyst and epichlorohydrin (20mmol) as a reactant in a mass ratio of 1:1.61:18.51 in terms of CO₂The pressure is 1bar, the reaction time is 24h, and the reaction temperature is 50-90 ℃. After the reaction, the conversion of the reactants was measured by nuclear magnetic resonance spectroscopy (AVANCE III HD 600M, Bruker, Germany).

FIG. 8 is a graph showing the effect of reaction temperature on the catalytic performance of the hierarchical pore ZIF-8 prepared in example 5 of the present invention. Fig. 8 shows that the conversion of the reactants increases with increasing reaction temperature, and that the conversion can be as high as 99% at a temperature of 80 ℃.

(VII) catalyzing CO by using reaction time on hierarchical porous ZIF-8 material₂Effect of the Properties of the cycloaddition reaction

Reaction conditions are as follows: the catalyst was ZIF-8 material (100mg) prepared in example 5, tetrabutylammonium bromide (161.2mg) as a cocatalyst and epichlorohydrin (20mmol) as a reactant in a mass ratio of 1:1.61:18.51 in terms of CO₂The pressure is 1bar, the reaction temperature is 80 ℃, and the reaction time is 12-28 h. After the reaction, the conversion of the reactants was measured by nuclear magnetic resonance spectroscopy (AVANCE III HD 600M, Bruker, Germany).

FIG. 9 is a graph of the effect of reaction time on the catalytic performance of the hierarchical pore ZIF-8 prepared in example 5 of the present invention. As can be seen from the graph, the conversion of the reactant increased as the reaction time increased. When the reaction time reaches 24 hours, the conversion rate can reach about 99 percent, which can be attributed to the fact that the sufficient contact time of reactants and the catalyst is increased along with the increase of the reaction time, the reaction is facilitated, and the conversion rate is improved.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be regarded as equivalent replacements within the scope of the present invention.

Claims

1. a preparation method of multi-level hole ZIF-8 material, is characterized in that, comprises the steps:

(1) Add ZnO to water and stir to obtain suspension A;

(2) Add Zn(CH ₃ CO ₂ ) ₂ ·2H ₂ O into the DMF-water solution, and ultrasonically dissolve to obtain solution B;

(3) Add solution B to suspension A, stir, and obtain mixed solution C after the reaction;

(4) 2-methylimidazole was added to DMF and stirred to obtain solution D;

(5) adding the templating agent to solution D, stirring and dissolving to obtain solution E; the templating agent is 3-sulfopropyltetradecyldimethylbetaine;

(6) Mix the mixed solution C and the solution E, and stir the reaction;

(7) washing the product obtained after the reaction in step (6) with DMF and water, and then immersing it in methanol;

(8) Suction filtration and drying of the product obtained in step (7) to obtain a multi-stage porous ZIF-8 material;

The molar ratio of Zn(CH ₃ CO ₂ ) ₂ ·2H ₂ O, ZnO, 2-methylimidazole and 3-sulfopropyltetradecyldimethylbetaine is 1:1: (5.8-6.2): (0.12-2.5).

2. The method according to claim 1, characterized in that: the stirring time in step (1), step (4), and step (5) is 10-15 minutes; the DMF-water solution in step (2) The volume ratio of DMF to water is 1:1, and the sonication time is 1-5 minutes.

3 . The method according to claim 1 , wherein the reaction time of step (3) is 20-24 h; the reaction time of step (6) is 45 to 600 seconds. 4 .

4 . The method according to claim 1 , wherein the immersion time in methanol in step (7) is 24-72 h, and the methanol is replaced every 12 h. 5 .

The method according to claim 1, characterized in that: the Zn(CH ₃ CO ₂ ) ₂ ·2H ₂ O, ZnO, 2-methylimidazole, 3-sulfopropyltetradecyldimethyl beet The molar ratio of base is 1:1:6:2.