A Pd@UIO66-NH2@COF picoline emulsion based on a core-shell structure and a preparation method and application thereof

Abstract

The application discloses a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure and a preparation method and application thereof, and belongs to the field of catalytic synthesis. The Pd@UIO66-NH2@COF is used as an emulsifier, toluene and water are used as solvents, and a Pd@UIO66-NH2@COF stable Pickering emulsion is formed. The Pd@UIO66-NH2@COF stable Pickering emulsion disclosed by the application has the advantages of simple preparation method and high catalytic capacity and stability in alcohol oxidation-Knoevenagel series reaction.

Description

Technical Field

[0001] This invention belongs to the field of catalytic synthesis technology, specifically relating to a core-shell structure-based Pd@UIO66-NH2@COF Pickering emulsion, its preparation method, and its application. Background Technology

[0002] Metal-organic frameworks (MOFs) are ordered porous crystalline materials formed by coordination bonds between metal ions and organic ligands or clusters. They possess hierarchical structures, permanent porosity, and high specific surface areas. MOFs have been widely used as heterogeneous catalysts, especially those catalysts using MOFs as supports for metal nanoparticles. Covalent organic frameworks (COFs) are novel porous crystalline materials constructed from covalently linked molecular units, possessing high specific surface areas, tunable pore structures, and good structural stability. The uniformly distributed heteroatoms (N) in COFs make them ideal platforms for anchoring Pd species, thereby enhancing metal-support interactions. The interface between MOFs and COFs leads to the formation of micropores and mesopores, which have higher porosity than single MOFs or COFs, thus facilitating maximum contact between reactants, substrates, and active sites, and rapid product separation. Therefore, Pd-doped MOF@COF ternary nanohybrids hold promise as unique, multifunctional heterogeneous catalysts.

[0003] Pickering emulsions are formed by the self-assembly of solid particles at the interface of two immiscible liquids, preventing droplet coalescence and forming numerous water or oil microdroplets, significantly increasing the interfacial area between water and oil. Pickering interfacial catalysis shows broad application prospects in acid-catalyzed transesterification, oxidation, and acetal reactions. Despite recent progress, the construction of pickering emulsions with bifunctional interfaces remains a significant challenge. Compared to traditional emulsions, pickering emulsions offer advantages such as low toxicity and high stability.

[0004] Benzylmalonium derivatives (BMDs) possess superior chemical and biological activities, making them highly applicable in pharmaceuticals, dyes, and pesticides. Therefore, scientists have been dedicated to finding a green, energy-efficient, and economical method for preparing BMDs. While some progress has been made, it remains a significant challenge.

[0005] Tandem reactions have attracted widespread attention due to their alignment with green and environmentally friendly principles, as they eliminate the need for separation and purification of intermediate products. The alcohol oxidation-Knoevenagel tandem reaction requires a catalyst possessing both Pd nanoparticles and basic active sites. Therefore, it is necessary to develop a novel Pd-doped catalyst for catalyzing this type of reaction. Summary of the Invention

[0006] The purpose of this invention is to provide a core-shell structured Pd@UIO66-NH2@COF Pickering emulsion for efficient catalysis of alcohol oxidation-Knoevenagel tandem reactions.

[0007] The technical solution adopted in this invention is: a core-shell structure-based Pd@UIO66-NH2@COF Pickering emulsion, which is a Pickering emulsion prepared using Pd@UIO66-NH2@COF as an emulsifier.

[0008] A method for preparing a core-shell structured Pd@UIO66-NH2@COF pickeril emulsion includes the following steps:

[0009] 1) Disperse ZrCl4 and 2-aminoterephthalic acid in a mixture of N-dimethylformamide and glacial acetic acid, stir evenly, and then put it into a reaction vessel for hydrothermal reaction. After the reaction is completed, cool to room temperature, wash with DMF and ethanol in sequence, and dry under vacuum to obtain UIO66-NH2.

[0010] 2) The UIO66-NH2 obtained in step 1) was dispersed in acetonitrile as the core component. After sonication, pyromellitic methyl ether was added and stirred for 3 h. Then, 1,3,5-tris(4-aminophenyl)benzene was added and stirred for 3 h. Acetic acid was then added to the mixture to initiate polymerization. After aging at room temperature, the mixture was placed in a reactor. After the reaction was completed, the mixture was cooled to room temperature, washed with a large amount of tetrahydrofuran, and dried under vacuum to obtain UIO66-NH2@COF.

[0011] 3) Add sodium chloropalladium solution dropwise to the UIO66-NH2@COF obtained in step 2), mix and disperse evenly, add sodium borohydride to methanol solution, quickly pick up the upper layer of liquid with bubbles and add it to the mixture of UIO66-NH2@COF and sodium chloropalladium, stir continuously for 30 min, wash with methanol, and vacuum dry to obtain Pd@UIO66-NH2@COF;

[0012] 4) Add toluene and water to the Pd@UIO66-NH2@COF obtained in step 3), and shake gently by hand to obtain Pd@UIO66-NH2@COF Pickering emulsion.

[0013] Furthermore, in step 1), the molar ratio of ZrCl4:2-aminoterephthalic acid is 1:1.

[0014] Furthermore, in step 1), the volume ratio of glacial acetic acid to N,N-dimethylformamide is 1:4.36.

[0015] Furthermore, in step 1), the stirring condition is 30 min, and the hydrothermal reaction condition is 393 K for 24 h.

[0016] Furthermore, in step 2), the mass of UIO66-NH2 is 100 mg, and the volume of acetonitrile is 20 mL.

[0017] Furthermore, in step 2), the molar ratio is pyromellitic methyl ester: 1,3,5-tris(4-aminophenyl)benzene = 1:1.

[0018] Furthermore, in step 2), the volume of acetic acid is 0.5 mL, and the aging time is 6 h.

[0019] Furthermore, in step 2), the reaction conditions are 343K for 48h.

[0020] Furthermore, in step 3), UIO66-NH2@COF: sodium chloropalladium solution 20mg: 46μL.

[0021] Furthermore, in step 4), the volume ratio of toluene to water is 1:1.

[0022] The present invention relates to the application of a core-shell structure-based Pd@UIO66-NH2@COF Pickering emulsion in the catalytic alcohol oxidation-Knoevenagel tandem reaction.

[0023] Further, the method is as follows: Benzyl alcohol, potassium carbonate and catalyst are reacted in an emulsion system of toluene and water at 353 K for 2 h, and then malononitrile is added and reacted for 1 h. The catalyst is Pd@UIO66-NH2@COF.

[0024] In the Pd@UIO66-NH2@COF Pickering emulsion of this invention, Pd nanoparticles provide active sites for the selective oxidation of the alcohol in the first step, while UIO66-NH2 and COF provide base sites to catalyze the Knoevenagel condensation reaction in the second step, thus synergistically catalyzing the tandem reaction. The reaction formula is as follows:

[0025]

[0026] The beneficial effects of this invention are as follows: This invention uses UIO66-NH2, which has good stability and porous structure, as the core component. A COF shell component is grown through aldehyde-amine condensation to form a core-shell structured material, UIO66-NH2@COF. Pd@UIO66-NH2@COF is then prepared via a simple capillary impregnation reduction method. In this invention, Pd nanoparticles provide active sites for the selective oxidation of alcohols in the first step, while UIO66-NH2 and COF provide base sites to catalyze the second step, Knoevenagel condensation reaction, forming a bifunctional Pickering emulsion. Dispersing Pd@UIO66-NH2@COF in the emulsion system significantly increases the contact area between the substrate and the catalyst, improving catalytic efficiency. Furthermore, after five cycles, Pd@UIO66-NH2@COF maintains high catalytic activity, exhibiting high stability and recyclability. The Pd@UIO66-NH2@COF of this invention demonstrates excellent catalytic performance in the alcohol oxidation-Knoevenagel tandem reaction for the preparation of BMDs. Attached Figure Description

[0027] Figure 1 This is an optical microscope image of the formed Pd@UIO66-NH2@COF Pickering emulsion.

[0028] Figure 2 This is the PXRD pattern of the Pd@UIO66-NH2@COF material in the Pd@UIO66-NH2@COF Pickering emulsion of the present invention.

[0029] Figure 3 This is a TEM image of the Pd@UIO66-NH2@COF material in the Pd@UIO66-NH2@COF Pickering emulsion of the present invention.

[0030] Figure 4 This is a catalytic activity diagram of the Pd@UIO66-NH2@COF Pickering emulsion of the present invention undergoing five cycles of catalytic reaction. Detailed Implementation

[0031] Example 1: A method for preparing a core-shell structure-based Pd@UIO66-NH2@COF Pickering emulsion (I) is as follows:

[0032] 1. Synthesis of UIO66-NH2 powder

[0033] ZrCl4 (0.0995 g) and 2-aminoterephthalic acid (0.0773 g) were co-dispersed in a mixture of 43.6 mL N,N-dimethylformamide and 10 mL glacial acetic acid. After stirring for 30 min, the mixture was placed in a reaction vessel and reacted in an oven at 393 K for 24 h. After the reaction was completed, the mixture was cooled to room temperature, washed successively with DMF and ethanol, and then vacuum dried in an oven at 353 K for 12 h to obtain UIO66-NH2 for later use.

[0034] 2. Synthesis of UIO66-NH2@COF core-shell material

[0035] 100 mg of UIO66-NH2 powder was dispersed in 20 mL of acetonitrile as the core component. After sonication for 20 min, 0.0162 g of trimesin was introduced into the mixture. After stirring for 3 h, 0.0352 g of 1,3,5-tris(4-aminophenyl)benzene was added to the mixture, and stirring was continued for 3 h. Then, 0.5 mL of glacial acetic acid was added to the mixture. After aging at room temperature for 6 h, the mixture was placed in a reactor and reacted at 343 K for 48 h to obtain UIO66-NH2@COF core-shell material.

[0036] 3. Synthesis of Pd@UIO66-NH2@COF

[0037] Take 20 mg of UIO66-NH2@COF and put it into a small bottle. Add 46 μL of sodium chloropalladium solution and mix and disperse evenly. Add 8.6 mg of sodium borohydride to 4 mL of methanol solution. Quickly pick up the liquid with bubbles on the upper layer and add it to the mixture of UIO66-NH2@COF and sodium chloropalladium. Stir continuously for 30 min, wash with methanol, and vacuum dry to obtain Pd@UIO66-NH2@COF material.

[0038] 4. Preparation of Pd@UIO66-NH2@COF Pickering emulsion

[0039] Place 20 mg of Pd@UIO66-NH2@COF into a small vial, add 2 mL of toluene and 2 mL of water, and simply shake by hand to prepare Pd@UIO66-NH2@COF Picklein emulsion.

[0040] (II) Testing

[0041] Figure 1 This is an optical microscope image of the formed Pd@UIO66-NH2@COF Picklern emulsion. It can be seen that the Pd@UIO66-NH2@COF stable Picklern emulsion droplets are uniformly dispersed and of uniform size.

[0042] Figure 2The image shows the PXRD pattern of Pd@UIO66-NH2@COF material in the Pd@UIO66-NH2@COF Pickering emulsion, indicating that the Pd@UIO66-NH2@COF material has good crystallinity during the synthesis and preparation process.

[0043] Figure 3 This is a TEM image of Pd@UIO66-NH2@COF material in a Pickering emulsion, further demonstrating the successful incorporation of Pd nanoparticles and the successful synthesis of the UIO66-NH2@COF core-shell structure.

[0044] Example 2 Catalytic function of Pd@UIO66-NH2@COF Pickering emulsion for alcohol oxidation-Knoevenagel tandem reaction (I) The Pd@UIO66-NH2@COF Pickering emulsion prepared in Example 1 was used as a catalyst to catalyze the alcohol oxidation-Knoevenagel tandem reaction.

[0045] The method is as follows:

[0046] 20 mg of Pd@UIO66-NH2@COF core-shell material was added to a 10 mL three-necked reaction vessel, followed by the sequential addition of 1.0 mmol benzyl alcohol, 0.7 mmol K2CO3, 2 mL toluene, and 2 mL water. The mixture was reacted at 353 K with O2 for 2 h, followed by the addition of 3.0 mmol malononitrile for 1 h to generate benzylidene malononitrile derivatives (BMDs). The yield of the product was monitored by gas chromatography (GC).

[0047] During the reaction, the catalytic performance of Pd@UIO66-NH2@COF Pickering emulsion on the tandem reaction was detected by GC. As the reaction proceeded, the yield gradually increased, and the yield of BMDs reached 99% after 3 hours of reaction.

[0048] (II) Reuse of Pd@UIO66-NH2@COF Picklein Emulsion

[0049] After the reaction was completed, the reaction mixture was centrifuged and filtered to separate it from Pd@UIO66-NH2@COF. The separated Pd@UIO66-NH2@COF mixture was washed with ethanol, filtered, and dried. The Pd@UIO66-NH2@COF material was recovered.

[0050] The specific operation of the cycle experiment: The recovered Pd@UIO66-NH2@COF material was used to prepare the Pickering emulsion-catalyzed alcohol oxidation-Knoevenagel reaction again, and the reaction was carried out at 353K for 3h.

[0051] Experimental results are as follows Figure 4As shown, after five cycles of the cyclic experiment, the catalyst activity did not decrease significantly, and the recovered catalyst could still stably form a Pickering emulsion. This indicates that Pd@UIO66-NH2@COF in the Pickering emulsion can be recycled as a catalyst for the alcohol oxidation-Knoevenagel reaction.

Claims

1. Use of a Pd@UIO66-NH2@COF Pickering emulsion based on core-shell structure in catalyzing alcohol oxidation-Knoevenagel tandem reaction, characterized in that, The Pd@UIO66-NH2@COF Pickering emulsion is a Pickering emulsion prepared by taking Pd@UIO66-NH2@COF as an emulsifier, and the Pd@UIO66-NH2@COF Pickering emulsion is a catalyst. The preparation method of the Pd@UIO66-NH2@COF Pickering emulsion based on the core-shell structure comprises the following steps: 1) ZrCl4 and 2-amino terephthalic acid are dispersed in a mixed solution of N-N-dimethylformamide and glacial acetic acid, and after being uniformly stirred, they are put into a reaction kettle for hydrothermal reaction. After the reaction is completed, it is cooled to room temperature, and then sequentially washed with DMF and ethanol, and vacuum dried to obtain UIO66-NH2. 2) The UIO66-NH2 obtained in step 1) is dispersed in acetonitrile, and after being ultrasonically treated, 1, 3, 5-tris(4-aminophenyl) benzene is added thereto and stirred for 3 h, and then acetic acid is added to initiate polymerization. After being aged at room temperature, it is put into a reaction kettle for reaction. After the reaction is completed, it is cooled to room temperature, washed with tetrahydrofuran, and vacuum dried to obtain UIO66-NH2@COF. 3) A sodium chloropalladate solution is added dropwise to the UIO66-NH2@COF obtained in step 2), and sodium borohydride is added to a methanol solution. The upper liquid with bubbles is quickly taken and added to the mixture of UIO66-NH2@COF and sodium chloropalladate. After continuous stirring for 30 min, it is washed with methanol and vacuum dried to obtain Pd@UIO66-NH2@COF. 4) Toluene and water are added to the Pd@UIO66-NH2@COF obtained in step 3), and Pd@UIO66-NH2@COF Pickering emulsion is prepared by shaking by hand.

2. Use according to claim 1, characterized in that, In step 1), the molar ratio of ZrCl4 to 2-amino terephthalic acid is 1:

1.

3. Use according to claim 1, characterized in that, In step 1), the stirring condition is 30 min, and the hydrothermal reaction condition is 393 K for 24 h.

4. Use according to claim 1, characterized in that, In step 2), the molar ratio of trimesyl formaldelhyde to 1, 3, 5-tris(4-aminophenyl) benzene is 1:

1.

5. The use according to claim 1, characterized in that, In step 2), the reaction condition is 343 K for 48 h.

6. Use according to claim 1, characterized in that, In step 3), the molar ratio of UIO66-NH2@COF to sodium chloropalladate solution is 20 mg:46 μL.

7. Use according to claim 1, characterized in that, In step 4), the volume ratio of toluene to water is 1:

1.

8. The use according to claim 1, characterized in that, The method is as follows: benzyl alcohol, potassium carbonate and catalyst are taken, and the emulsion system of toluene and water is reacted at 353 K for 2 h, and then malononitrile is added and reacted for 1 h. The catalyst is Pd@UIO66-NH2@COF Pickering emulsion.

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