Pd-coated UIO66-NH2-coated COF Pickering emulsion based on core-shell structure as well as preparation method and application of Pd-coated UIO66-NH2-coated COF Pickering emulsion

Abstract

The invention discloses Pd-coated UIO66-NH2-coated COF Pickering emulsion based on a core-shell structure as well as a preparation method and application of the Pd-coated UIO66-NH2-coated COF Pickering emulsion, and belongs to the field of catalytic synthesis. The Pickering emulsion with stable Pd-coated UIO66-NH2-coated COF is formed by adopting Pd-coated UIO66-NH2-coated COF as an emulsifier and toluene and water as solvents at the same time. The Pickering emulsion with stable Pd and UIO66-NH2 and COF, provided by the invention, is simple in preparation method, and shows relatively high catalytic capability and stability in an alcohol oxidation-Knoevenagel cascade reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic synthesis, and specifically relates to a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure, and a preparation method and application thereof. Background Art

[0002] Metal-organic frameworks (MOFs) are ordered porous crystalline materials formed by coordination bonds between metal ions and organic ligands or clusters. They have hierarchical structures, permanent porosity, and high specific surface areas. MOFs have been widely used as heterogeneous catalysts, especially those using MOFs as supports for metal nanoparticles. Covalent organic frameworks (COFs) are a new type of porous crystalline materials constructed from covalently linked molecular units with high specific surface areas, tunable pore structures, and good structural stability. The uniform distribution of heteroatoms (N) in COFs makes them an ideal platform for anchoring Pd species, thereby enhancing metal-support interactions. The interface between MOFs and COFs leads to the generation of micropores and mesopores, which have higher porosity than that of a single MOF or COF, thus facilitating the maximization of contacts between reactants, substrates, and active sites, and rapid separation of products. Therefore, Pd-doped MOF@COF ternary nanohybrids are expected to be unique and multifunctional heterogeneous catalysts.

[0003] Pickering emulsions are formed by the self-assembly of solid particles at the interface of two immiscible liquids, which can prevent the merging of droplets. They form a large number of water or oil droplets, greatly expanding the interfacial area of ​​water and oil. Pickering interfacial catalysis has broad application prospects in acid-catalyzed transesterification, oxidation and acetalization reactions. Despite some recent progress, the construction of Pickering emulsions with dual functional interfaces remains a great challenge. Compared with traditional emulsions, Pickering emulsions have the advantages of low toxicity and strong stability.

[0004] Benzalmalononitrile derivatives (BMDs) have excellent chemical and biological activities, which make them have outstanding applications in medicine, dyes and pesticides. Therefore, scientists have been committed to finding a green, energy-saving and economical method to prepare BMDs. Although some progress has been made in this regard, it is still a huge challenge.

[0005] Tandem reactions have attracted widespread attention because they do not require separation and purification of intermediate products and are in line with the concept of green and environmental protection. The alcohol oxidation-Knoevenagel tandem reaction requires a catalyst with both Pd nanoparticles and alkaline active sites to catalyze it. Therefore, it is necessary to develop a new Pd-doped catalyst to catalyze this type of reaction. Summary of the invention

[0006] The purpose of the present invention is to provide a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure to efficiently catalyze alcohol oxidation-Knoevenagel tandem reaction.

[0007] The technical solution adopted by the present invention is: a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure, which is a Pickering emulsion prepared with Pd@UIO66-NH2@COF as an emulsifier.

[0008] A method for preparing a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure comprises the following steps:

[0009] 1) Dispersing ZrCl4 and 2-aminoterephthalic acid in a mixture of NN-dimethylformamide and glacial acetic acid, stirring evenly, and placing in a reactor for hydrothermal reaction. After the reaction is completed, cooling to room temperature, washing with DMF and ethanol in turn, and vacuum drying to obtain UIO66-NH2;

[0010] 2) Dispersing the UIO66-NH2 obtained in step 1) as a core component in acetonitrile, adding trimesaldehyde to the mixture after ultrasonication and stirring for 3 hours, then adding 1,3,5-tri(4-aminophenyl)benzene and stirring for 3 hours, and then adding acetic acid 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 vacuum dried to obtain UIO66-NH2@COF;

[0011] 3) Add sodium chloropalladate solution to the UIO66-NH2@COF obtained in step 2), mix and disperse evenly, add sodium borohydride to the methanol solution, quickly absorb the upper layer of liquid with bubbles and add it to the mixed solution of UIO66-NH2@COF and sodium chloropalladate, continue stirring for 30 minutes, wash with methanol, and vacuum dry to obtain Pd@UIO66-NH2@COF;

[0012] 4) Toluene and water were added to the Pd@UIO66-NH2@COF obtained in step 3), and the mixture was shaken briefly by hand to obtain a 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 NN-dimethylformamide is 1:4.36.

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

[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 of trimesaldehyde:1,3,5-tris(4-aminophenyl)benzene is 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 48 hours.

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

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

[0022] The invention discloses an application of a core-shell structure-based Pd@UIO66-NH2@COF Pickering emulsion in catalyzing an alcohol oxidation-Knoevenagel tandem reaction.

[0023] Furthermore, the method is as follows: benzyl alcohol, potassium carbonate and a catalyst are taken, reacted at 353K for 2 hours in an emulsion system of toluene and water, and then malononitrile is added to react for 1 hour, and the catalyst is Pd@UIO66-NH2@COF.

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

[0025]

[0026] The beneficial effects of the present invention are as follows: the present invention uses UIO66-NH2 with good stability and porous structure as the core component, grows the COF shell component through aldehyde amine condensation, forms a material UIO66-NH2@COF with a core-shell structure, and prepares Pd@UIO66-NH2@COF by a simple capillary impregnation reduction method. In the present invention, Pd nanoparticles provide active sites for the selective oxidation of alcohol in the first step, and UIO66-NH2 and COF provide base sites to catalyze the Knoevenagel condensation reaction in the second step to form a Pickering emulsion with dual functions. The present invention disperses Pd@UIO66-NH2@COF into the emulsion system, which can greatly increase the contact area between the substrate and the catalyst and improve the catalytic efficiency. In addition, after 5 cycle tests, Pd@UIO66-NH2@COF still maintains a high catalytic activity and has high stability and recyclability. The Pd@UIO66-NH2@COF of the present invention has excellent catalytic performance in the preparation of BMDs by alcohol oxidation-Knoevenagel tandem reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an optical microscope photograph 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 the 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 DESCRIPTION

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

[0032] 1. Synthesis of UIO66-NH2 powder

[0033] Disperse ZrCl4 (0.0995 g) and 2-aminoterephthalic acid (0.0773 g) in a mixture of 43.6 mL NN-dimethylformamide and 10 mL glacial acetic acid, stir for 30 min, put into a reactor, and react at 393 K in an oven for 24 h. After the reaction is completed, cool to room temperature, wash with DMF and ethanol in turn, and dry in a vacuum oven at 353 K for 12 h to obtain UIO66-NH2 for later use.

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

[0035] 100 mg UIO66-NH2 powder was dispersed in 20 mL acetonitrile as the core component. After ultrasonic treatment for 20 min, 0.0162 g of trimesaldehyde was introduced into the mixture. After stirring for 3 h, 0.0352 g 1,3,5-tris(4-aminophenyl)benzene was added to the mixture. The mixture was stirred for 3 h, and 0.5 mL 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 vial, add 46 μL of sodium chloropalladate solution to it, mix and disperse evenly, add 8.6 mg of sodium borohydride to 4 mL of methanol solution, quickly absorb the upper layer of liquid with bubbles and add it to the mixture of UIO66-NH2@COF and sodium chloropalladate, continue stirring for 30 minutes, wash with methanol, and vacuum dry to obtain Pd@UIO66-NH2@COF material.

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

[0039] 20 mg of Pd@UIO66-NH2@COF was placed in a vial, 2 mL of toluene and 2 mL of water were added thereto, and the mixture was simply shaken by hand to prepare a Pd@UIO66-NH2@COF Pickering emulsion.

[0040] (II) Testing

[0041] Figure 1 This is an optical microscope photo of the formed Pd@UIO66-NH2@COF Pickering emulsion. It can be seen that the Pickering emulsion droplets stabilized by Pd@UIO66-NH2@COF are evenly dispersed and uniform in size.

[0042] Figure 2This is the PXRD pattern of Pd@UIO66-NH2@COF material in 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 is the TEM image of Pd@UIO66-NH2@COF material in Pd@UIO66-NH2@COF Pickering emulsion, which further indicates the successful incorporation of Pd nanoparticles and the successful synthesis of UIO66-NH2@COF core-shell structure.

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

[0045] Here’s how:

[0046] 20 mg of Pd@UIO66-NH2@COF core-shell material was added to a 10 mL three-necked reaction vessel, followed by 1.0 mmol of benzyl alcohol, 0.7 mmol of K2CO3, 2 mL of toluene and 2 mL of water. O2 was introduced at 353 K for 2 h, and then 3.0 mmol of malononitrile was added 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 experimental results of the catalytic performance of Pd@UIO66-NH2@COF Pickering emulsion for the tandem reaction were detected by GC. As the reaction proceeded, the yield of the reaction gradually increased. When the reaction was carried out for 3 hours, the yield of BMDs had reached 99%.

[0048] (II) Recycling of Pd@UIO66-NH2@COF Pickering Emulsion

[0049] After the reaction, the reaction mixture was separated from Pd@UIO66-NH2@COF by centrifugal filtration, and then washed with ethanol, filtered, and dried to recover Pd@UIO66-NH2@COF material.

[0050] The specific operation of the cyclic experiment was as follows: the recycled 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] The experimental results are as follows Figure 4As shown in the figure, after five cycles, the activity of the catalyst did not decrease significantly, and the recovered catalyst could still stably form a Pickering emulsion, indicating that the Pd@UIO66-NH2@COF in the Pickering emulsion can be recycled as a catalyst for the alcohol oxidation-Knoevenagel reaction.

Claims

1. A Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure, characterized in that: The Pd@UIO66-NH2@COF Pickering emulsion is a Pickering emulsion prepared by using Pd@UIO66-NH2@COF as an emulsifier.

2. The method for preparing a Pd@UIO66-NH2@COF Pickering emulsion based on a core-shell structure according to claim 1, characterized in that: The steps include: 1) Dispersing ZrCl4 and 2-aminoterephthalic acid in a mixture of NN-dimethylformamide and glacial acetic acid, stirring evenly, and placing in a reactor for hydrothermal reaction. After the reaction is completed, cooling to room temperature, washing with DMF and ethanol in turn, and vacuum drying to obtain UIO66-NH2; 2) Dispersing the UIO66-NH2 obtained in step 1) as a core component in acetonitrile, adding trimesaldehyde to the mixture after ultrasonication and stirring for 3 hours, then adding 1,3,5-tri(4-aminophenyl)benzene and stirring for 3 hours, and then adding acetic acid 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 vacuum dried to obtain UIO66-NH2@COF; 3) Add sodium chloropalladate solution to the UIO66-NH2@COF obtained in step 2), mix and disperse evenly, add sodium borohydride to the methanol solution, quickly absorb the upper layer of liquid with bubbles and add it to the mixed solution of UIO66-NH2@COF and sodium chloropalladate, continue stirring for 30 minutes, wash with methanol, and vacuum dry to obtain Pd@UIO66-NH2@COF; 4) Toluene and water were added to the Pd@UIO66-NH2@COF obtained in step 3), and the mixture was shaken briefly by hand to obtain a Pd@UIO66-NH2@COF Pickering emulsion.

3. The preparation method according to claim 2, characterized in that: In step 1), the molar ratio of ZrCl4:2-aminoterephthalic acid is 1:

1.

4. The preparation method according to claim 2, characterized in that: In step 1), the stirring condition is 30 minutes, and the hydrothermal reaction condition is 393K hydrothermal reaction for 24 hours.

5. The preparation method according to claim 2, characterized in that: In step 2), the molar ratio of trimesaldehyde to 1,3,5-tris(4-aminophenyl)benzene is 1:

1.

6. The preparation method according to claim 2, characterized in that: In step 2), the reaction conditions are 343K for 48 hours.

7. The preparation method according to claim 2, characterized in that: In step 3), UIO66-NH2@COF: sodium chloropalladate solution 20 mg: 46 μL.

8. The preparation method according to claim 2, characterized in that: In step 4), by volume ratio, toluene: water = 1:

1.

9. Use of the core-shell structured Pd@UIO66-NH2@COF Pickering emulsion according to claim 1 in catalyzing alcohol oxidation-Knoevenagel tandem reaction.

10. The use according to claim 9, characterized in that: The method is as follows: benzyl alcohol, potassium carbonate and a catalyst are taken, reacted for 2 hours at 353K in an emulsion system of toluene and water, and then malononitrile is added to react for 1 hour, wherein the catalyst is the Pd@UIO66-NH2@COF Pickering emulsion described in claim 1.

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