Preparation method and application of nano-porous core-shell structure metal organic framework material
The nanoporous core-shell structure E-MAF-6 material was constructed by etching MAF-6 by phosphomolybdate, which solved the problems of difficult catalyst recovery and large solvent usage in the prior art, and achieved efficient catalytic reaction between benzaldehyde and malonitrile under mild conditions, improving catalytic efficiency and stability.
Patent Information
- Application Number
- CN202510464842.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-15
- Publication Date
- 2025-08-15
AI Technical Summary
In the prior art, the condensation reaction is usually carried out under a homogeneous system, which has problems such as difficult catalyst recovery and large solvent usage, and there is a lack of a heterogeneous catalyst that is quickly prepared and efficiently stable under mild conditions.
The MAF-6 material was etched at room temperature using phosphomolybdate (PMo12) to construct the E-MAF-6 material with nanoporous core-shell structures. It used its high specific surface area and core-shell structure to expose more active sites to catalyze the Knoevenagel condensation reaction of benzaldehyde and malonitrile.
The condensation reaction between benzaldehyde and malonitrile is efficiently catalyzed at room temperature. The material is circulated stably at room temperature, which improves the catalytic efficiency and increases the contact area between the reactants and the catalyst, and achieves efficient conversion.
Smart Images
Figure CN120479488A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of catalysts, and in particular relates to a preparation method and application of a nanoporous core-shell structured metal organic framework material. Background Art
[0002] The Knoevenagel reaction, as one of the classic methods for constructing C=C double bonds, is a dehydration condensation reaction of aldehydes and ketones with active methylene compounds, which can produce α, β-unsaturated compounds with important application value in organic synthesis. This type of compound is widely used in the preparation of materials such as coumarins and antihypertensive drugs as key intermediates in their synthesis process. It also plays an important role in the development of fine chemicals such as bioactive molecules and functional polymers. Condensation reactions in this field usually occur in a homogeneous system, and generally have problems such as difficult catalyst recovery and large solvent consumption. In order to overcome the limitations of homogeneous catalysis, it is particularly important to design and develop a heterogeneous catalyst that can be quickly prepared under mild conditions and is efficient and stable.
[0003] Metal-organic frameworks (MOFs) possess a high density of uniformly distributed active sites, a unique framework structure, and a regular morphology. They are widely used in a variety of fields, including catalysis, adsorption, and storage. In recent years, numerous reports have demonstrated the excellent catalytic activity of various MOFs in the catalytic Knoevenagel condensation reaction. The fine-tuning of the structure of MOFs has become a key research area. Through precise design, MOFs with diverse morphologies, including nanoparticles, nanosheets, hollow structures, and core-shell structures, can be prepared. Core-shell MOFs, in particular, have attracted considerable attention due to their unique advantages. They not only maintain the inherent high surface area and porous structure of MOFs, but also ensure close interaction between the core and shell, potentially generating synergistic effects. These MOFs can expose more active sites and enhance catalytic efficiency. Their hierarchical pore structure facilitates mass transfer and diffusion of reactants, resulting in significant potential for application in catalysis. The development of MOFs with nanoporous core-shell structures, their rapid and controllable synthesis under mild reaction conditions, and their enhanced accessibility to catalytically active sites are of great research value.
[0004] Chemical etching technology is one of the effective control strategies for MOFs structure. Traditional etching methods often use acid or alkaline solutions, which are prone to over-etching and cause the collapse of the material skeleton. Polyoxometalates (POMs) have good solubility and strong The unique advantages of acidity and abundant electrons allow it to be used as a strong acid etchant at room temperature. The POMs etching strategy enables the rapid construction of core-shell MOFs under mild conditions, increasing the material's specific surface area while providing more accessible active sites, thereby significantly improving the material's catalytic performance. Summary of the Invention
[0005] The present invention aims to address one of the technical problems existing in the prior art. To this end, a simple preparation method and application of a nanoporous core-shell metal-organic framework material for efficiently catalyzing the Knoevenagel condensation reaction are provided. This catalyst is used to catalyze the condensation reaction between benzaldehyde and malononitrile containing an active methylene group, achieving efficient conversion of benzaldehyde.
[0006] The preparation steps of a nanoporous core-shell structure metal organic framework material provided by the present invention are as follows:
[0007] A method for preparing a nanoporous core-shell structure metal organic framework material, wherein the nanoporous core-shell structure material is E-MAF-6, which is composed of phosphomolybdic acid (PMo 12 ) is obtained by stirring and etching MAF-6 at room temperature, and the preparation steps are:
[0008] (1) Preparation of POM ethanol solution: Na2MoO4·2H2O was dissolved in water, phosphoric acid was added, and then concentrated hydrochloric acid was added. The solution was transferred to a separatory funnel and ether was added. The bottom ether compound was obtained by the first extraction. Water and concentrated hydrochloric acid were added, and the solution was extracted with ether. The bottom ether compound was obtained by the second extraction. The ether compound was washed with water, and the ether and water were evaporated in a water bath to obtain orange-yellow crystals, which were PMo. 12 ;
[0009] (2) Preparation of MOF colloidal solution: Zn(OH)2 was added to ammonia water to form solution A, 2-ethylimidazole was dissolved in a mixed solvent of methanol and cyclohexane to form solution B, solution A was added to solution B, stirred for reaction, filtered, washed with methanol, and dried to obtain a white powder, namely MAF-6;
[0010] (3) The POM solution was quickly added to the MOF colloidal solution, and the etching reaction was carried out by stirring at room temperature for different times, followed by centrifugation, ethanol washing, and drying to obtain the nanoporous core-shell structure material E-MAF-6.
[0011] Moreover, in step (1), the ratio of Na2MoO4·2H2O to water before extraction is 1:2 (g / mL), the ratio of Na2MoO4·2H2O to phosphoric acid is 10:1 (g / mL), and the ratio of Na2MoO4·2H2O to concentrated hydrochloric acid before extraction is 1:1 (g / mL).
[0012] Moreover, the usage ratio of the Na2MoO4·2H2O to the ether in the first extraction is 1:1.5 (g / mL).
[0013] Moreover, in step (2), in the solution A, the ratio of the amount of Zn(OH)2 to the ammonia water is 0.9 to 1:200 (g / mL), and in the solution A, the ratio of the amount of 2-ethylimidazole to the mixed solvent of methanol and cyclohexane is 1:1 (g / mL).
[0014] Moreover, in step (3), the POM solution is quickly added to the MOF colloidal solution in a volume ratio of 1:1.
[0015] Moreover, the volume ratios of 20 mL of water, 10 mL of concentrated hydrochloric acid and ether added in the second extraction in step (1) are 2:1:1.5-2 respectively.
[0016] Moreover, the stirring time is 1-5h; the mixture is washed with ethanol and centrifuged 3 times at a rotation speed of 10000rpm; the volume ratio of the ether added in the second extraction to the ether added in the first extraction is 1.5-2:3.
[0017] The present invention also provides a catalytic application of the nanoporous core-shell structure metal organic framework material in a condensation reaction, wherein the material is used for the Knoevenagel condensation reaction between benzaldehyde and malononitrile, which is specifically achieved by the following technical solution:
[0018] The nanoporous core-shell structured metal organic framework material is dispersed in tetrahydrofuran (THF) containing benzaldehyde, and then tetrahydrofuran containing malononitrile is added, and the reaction is stirred at room temperature to achieve a condensation reaction through catalysis.
[0019] Moreover, the weight ratio of the nanoporous core-shell structure metal organic framework material to benzaldehyde is 1:40 (g / mL), the weight ratio of the nanoporous core-shell structure metal organic framework material to malononitrile is 20:1, the reaction time is 5-30 minutes, and sampling is performed every 5 minutes.
[0020] Moreover, the volume ratio of benzaldehyde to THF is 1:15, and the amount ratio of malononitrile to THF is 1:4000 (g / mL).
[0021] The advantages and positive effects of the present invention are:
[0022] Compared with the prior art, the present invention utilizes PMo 12 MAF-6 was stirred and etched at room temperature to construct nanoporous core-shell structure E-MAF-6 material. 12 Able to extend inward through the MAF-6 crystal window, and super strong Acidity can etch MAF-6. Leveraging the high specific surface area and core-shell structure of E-MAF-6, the synergistic effect of multiple pores of varying scales exposes more active sites. The basic sites originate from the nitrogen atoms of the imidazole ligands. The high porosity of the E-MAF-6 shell increases the contact area between the reactants and the catalyst, improving mass transfer efficiency and ultimately achieving highly efficient catalysis of the condensation reaction of benzaldehyde and malononitrile.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] (1) The present invention has developed a convenient synthesis method by using PMo 12 Etching MAF-6 constructed a nanoporous core-shell structure E-MAF-6 material, which can increase its specific surface area and expose more active sites.
[0025] (2) In the room temperature catalytic system, the E-MAF-6 material not only achieves efficient conversion of benzaldehyde, but can also be used stably in a cycle, demonstrating its application potential as a green and efficient catalytic Knoevenagel condensation reaction.
[0026] (3) The synthesis and catalysis of the nanomaterials of the present invention are carried out at room temperature, which is simple to operate, highly safe, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 The PXRD pattern of E-MAF-6 provided by the present invention;
[0028] Specifically, the PXRD spectra of E-MAF-6, MAF-6, and simulated MAF-6;
[0029] Figure 2 The SEM image of E-MAF-6 provided by the present invention;
[0030] Specifically, the SEM images of (a) MAF-6 and (b) E-MAF-6;
[0031] Figure 3 HRTEM image of E-MAF-6 provided by the present invention;
[0032] Specifically, the HRTEM images of (a) MAF-6 and (bd) E-MAF-6. DETAILED DESCRIPTION
[0033] The technical solution of the present invention is further described below with reference to the accompanying drawings and specific embodiments.
[0034] Example
[0035] The present invention provides a nanoporous core-shell metal organic framework material, and the preparation method thereof comprises the following steps:
[0036] (1) Preparation of 1 mg / mL POM ethanol solution: Dissolve 20 g of Na2MoO4·2H2O in 40 mL of pure water, add 2 mL of phosphoric acid, then add 20 mL of concentrated hydrochloric acid, transfer to a separatory funnel, add 30 mL of ether, extract to obtain the bottom etherate, add 20 mL of water and 10 mL of concentrated hydrochloric acid, extract with 16 mL of ether, wash the etherate again, and finally evaporate the ether and most of the water in a water bath to obtain orange-yellow crystals, which are PMo 12 ;
[0037] (2) Prepare a 10 mg / mL MOF colloidal solution: Add 0.199 g of Zn(OH)2 to 40 mL of ammonia water to form Solution A. Dissolve 0.38 g of 2-ethylimidazole in a mixed solvent of 30 mL of methanol and 8 mL of cyclohexane to form Solution B. Add Solution A to Solution B with stirring, stir for 1 h, filter, wash with methanol, and dry to obtain a white powder, which is MAF-6.
[0038] (3) Place the MAF-6 colloidal solution in a beaker and add PMo 12 The ethanol solution was stirred to react and obtain a suspension. Five equal portions of suspension C were prepared and etched at room temperature for 1-5 hours, with a stirring interval of 1 hour between each portion. The suspension was centrifuged (10,000 rpm for 1 minute), washed with ethanol, and dried in a vacuum drying oven at 60°C for 5 hours to obtain the nanomaterial (the material etched for 3 hours is labeled E-MAF-6).
[0039] Structural characterization:
[0040] The structural characterization of E-MAF-6 obtained in step 3) was performed, and the results were as follows:
[0041] like Figure 1 The PXRD pattern of E-MAF-6 material is shown. Figure 1 The PXRD diffraction spectrum of E-MAF-6 closely matches the experimental and simulated spectra of MAF-6. The characteristic diffraction peak of MAF-6 at 7.4° (2θ) is retained, but its intensity is significantly reduced, indicating that partial etching of the material has caused structural defects, weakening the diffraction signal. Furthermore, a ZnO2 diffraction peak was detected, which is speculated to be derived from the formation of trace ZnO2 crystals due to the partial oxidation of zinc species during the synthesis process.
[0042] like Figure 2 Shown are the SEM images of MAF-6 and E-MAF-6 materials. Figure 2 As can be seen from a, the original MAF-6 is a polyhedral particle with regular shape and uniform size, smooth surface and clear edges. Figure 2b It can be seen that E-MAF-6 still maintains its original polyhedral morphology framework after etching, and discretely distributed nanoscale concave etch pits are formed on its surface. The etching starts from multiple angles on the particle surface and extends inward, eventually forming a nanoporous structure.
[0043] like Figure 3 Shown is the HRTEM image of E-MAF-6 material. Figure 3 From a, we can see that MAF-6 is a typical solid particle structure. Figure 3 As shown in b and c, the etched E-MAF-6 is significantly different from the original MAF-6. It presents a typical core-shell structure, and clear lattice fringes can be observed in the central core region ( Figure 3 d), the interplanar spacing corresponds to the {200} plane of ZnO2.
[0044] In summary, PMo 12 The clusters etched MAF-6 under stirring at room temperature and successfully constructed a nanoporous core-shell structured E-MAF-6 material.
[0045] Experimental Examples
[0046] The present invention also applies the E-MAF-6 prepared above to the Knoevenagel condensation reaction of benzaldehyde and malononitrile.
[0047] The specific method is as follows:
[0048] 0.2 mL of benzaldehyde was dissolved in 3.0 mL of tetrahydrofuran (THF concentration containing benzaldehyde was 0.63 mmol / mL), transferred to a 20.0 mL glass vial, 5.0 mg of E-MAF-6 catalyst was added, and after ultrasonic dispersion, stirring was continued for 30 min. 0.25 g of malononitrile was pre-dissolved in 1.0 mL of tetrahydrofuran (THF concentration containing malononitrile was 3.8 mmol / mL), and then injected into the above system. The reaction was stirred at room temperature, sampled at intervals, filtered with an organic filter membrane, 50 μL of the filtrate was mixed with 550 μL of CDCl3 in a nuclear magnetic resonance tube, and analyzed by nuclear magnetic resonance spectrometer. 1 H NMR characterization analysis. The benzaldehyde conversion efficiency was calculated by quantitatively analyzing the integrated area ratio of the characteristic peaks for aldehyde protons (9.89 ppm) and product olefin protons (7.67 ppm). E-MAF-6 exhibited high catalytic activity in the condensation reaction of benzaldehyde and malononitrile. After just 10 minutes at room temperature, the benzaldehyde conversion reached 97%, and the catalytic efficiency remained at 85% after three cycles. For pristine MAF-6, the benzaldehyde conversion was only 5% after 10 minutes.
[0049] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.
Claims
1. A method for preparing a nanoporous core-shell structure metal organic framework material, characterized by: The nanoporous core-shell structure material is E-MAF-6, which is composed of phosphomolybdic acid (PMo 12 ) is obtained by stirring and etching MAF-6 at room temperature, and the preparation steps are: (1) Preparation of POM ethanol solution: Na2MoO4·2H2O was dissolved in water, phosphoric acid was added, and then concentrated hydrochloric acid was added. The solution was transferred to a separatory funnel and ether was added. The bottom ether compound was obtained by the first extraction. Water and concentrated hydrochloric acid were added, and the solution was extracted with ether. The bottom ether compound was obtained by the second extraction. The ether compound was washed with water, and the ether and water were evaporated in a water bath to obtain orange-yellow crystals, which were PMo. 12 ; (2) Preparation of MOF colloidal solution: Zn(OH)2 was added to ammonia water to form solution A, 2-ethylimidazole was dissolved in a mixed solvent of methanol and cyclohexane to form solution B, solution A was added to solution B, stirred for reaction, filtered, washed with methanol, and dried to obtain a white powder, namely MAF-6; (3) The POM solution was quickly added to the MOF colloidal solution, and the etching reaction was carried out by stirring at room temperature for different times, followed by centrifugation, ethanol washing, and drying to obtain the nanoporous core-shell structure material E-MAF-6.
2. The method for preparing the nanoporous core-shell metal organic framework material according to claim 1, characterized in that: In step (1), the ratio of Na2MoO4·2H2O to water before extraction is 1:2 (g / mL), the ratio of Na2MoO4·2H2O to phosphoric acid is 10:1 (g / mL), and the ratio of Na2MoO4·2H2O to concentrated hydrochloric acid before extraction is 1:1 (g / mL).
3. The method for preparing the nanoporous core-shell metal organic framework material according to claim 1, characterized in that: The ratio of the amount of Na2MoO4·2H2O to the amount of ether used in the first extraction is 1:1.5 (g / mL).
4. The method for preparing a nanoporous core-shell metal organic framework material according to claim 1, characterized in that: In step (2), in the solution A, the ratio of Zn(OH)2 to ammonia water is 0.9 to 1:200 (g / mL), and in the solution A, the ratio of 2-ethylimidazole to a mixed solvent of methanol and cyclohexane is 1:1 (g / mL).
5. The method for preparing the nanoporous core-shell metal organic framework material according to claim 1, characterized in that: In step (3), the POM solution is quickly added to the MOF colloidal solution in a volume ratio of 1:
1.
6. The method for preparing the nanoporous core-shell metal organic framework material according to claim 3, characterized in that: The volume ratios of 20 mL of water, 10 mL of concentrated hydrochloric acid and diethyl ether added in the second extraction in step (1) are 2:1:1.5-2 respectively, and the volume ratio of diethyl ether added in the second extraction to that added in the first extraction is 1.5-2:
3.
7. The method for preparing a nanoporous core-shell metal organic framework material according to claim 4, characterized in that: The stirring time is 1-5 hours; the mixture is washed with ethanol, centrifuged 3 times at a rotation speed of 10,000 rpm, a centrifugal time of 1 minute, and dried at a temperature of 60° C. for 5 hours.
8. A nanoporous core-shell metal organic framework material for catalytic application in condensation reactions, characterized by: The nanoporous core-shell structure metal-organic framework material is prepared by the preparation method of the nanoporous core-shell structure metal-organic framework material according to any one of claims 1 to 7, wherein the nanoporous core-shell structure metal-organic framework material is dispersed in tetrahydrofuran (THF) containing benzaldehyde, and then tetrahydrofuran containing malononitrile is added, and the reaction is stirred at room temperature to achieve a condensation reaction through catalysis.
9. The catalytic application of the nanoporous core-shell metal organic framework material in condensation reaction according to claim 8, characterized in that: The weight ratio of the nanoporous core-shell structure metal organic framework material to benzaldehyde is 1:40 (g / mL), the weight ratio of the nanoporous core-shell structure metal organic framework material to malononitrile is 20:1, the reaction time is 5-30 minutes, and sampling is performed every 5 minutes.
10. The catalytic application of the nanoporous core-shell metal organic framework material in condensation reaction according to claim 9, characterized in that: The volume ratio of benzaldehyde to THF is 1:15, and the amount ratio of malononitrile to THF is 1:4000 (g / mL).