Stable Pickering emulsion based on chitosan-coated metal organic framework composite material and application of stable Pickering emulsion

Abstract

The invention discloses a stable Pickering emulsion based on a chitosan-coated metal organic framework composite material and application of the stable Pickering emulsion, and relates to the technical field of catalytic synthesis. The method comprises the following steps: firstly, synthesizing a metal organic framework material MIL-101 (Cr) and CS based on chitosan coating, and then preparing a metal organic framework composite material Pd and MIL-101 (Cr) and CS; then, water and n-butyl alcohol are adopted as solvents, the Pd-coated MIL-101 (Cr)-coated CS material is adopted as an excellent emulsifier, and a stable Pd-coated MIL-101 (Cr)-coated CS Pickering emulsion is formed and used for catalyzing the Suzuki reaction. The Pickering emulsion provided by the invention is simple in preparation method, shows ultrahigh catalytic ability in Suzuki reaction, realizes simple and convenient separation and recycling of the catalyst, avoids additional addition of an emulsifier, reduces the reaction cost, improves the product purity, and has a good application prospect in the field of organic catalytic reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic synthesis, and particularly relates to a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material and its application. Background Art

[0002] The Suzuki reaction is a coupling reaction using a transition metal as a catalyst, with aryl or alkenyl boronic acid or boronic acid ester and alkene or haloarene as substrates. Compared with other coupling reactions, the Suzuki reaction has fewer by-products, mild reaction conditions, and certain substrate adaptability and functional group tolerance. The Suzuki reaction can be widely applied in fields such as pharmaceuticals, the electronics industry, and advanced materials. Traditional Suzuki reaction systems have some limitations. For example, homogeneous catalysts are difficult to separate and recycle, resulting in increased costs and possible product contamination; although heterogeneous catalysts are easy to separate, their catalytic activity and substrate contact efficiency need to be improved.

[0003] In the Suzuki reaction, metal Pd nanoparticles are commonly used as catalysts. However, during the catalytic process, metal Pd often undergoes phenomena such as aggregation and auto-oxidation, resulting in problems of low catalytic efficiency and short lifespan.

[0004] An emulsion is a liquid dispersed in another immiscible liquid in the form of droplets. The droplets are called the dispersed phase, and the surrounding liquid is called the continuous phase. Different from emulsions stabilized by traditional surfactants, Pickering emulsions are water-in-oil two-phase emulsions stabilized by solid particles. The difference between Pickering emulsions and traditional emulsions is that traditional emulsions achieve stability by surfactants distributed at the two-phase interface, while Pickering emulsions form a dense interfacial film by small solid particles distributed at the two-phase interface. Compared with traditional emulsions, Pickering emulsions have advantages such as low toxicity and strong stability. Summary of the Invention

[0005] To solve the problems existing in the prior art, one of the purposes of the present invention is to provide a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material. As a catalyst, this Pickering emulsion can improve the catalytic efficiency of the Suzuki reaction, achieve the simple separation and recycling of the catalyst, and avoid the problems caused by the additional addition of emulsifiers.

[0006] To achieve the above invention purpose, the technical solution adopted by the present invention is: a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material, and the Pickering emulsion stabilized by the chitosan-coated metal-organic framework composite material is a Pd@MIL-101(Cr)@CS Pickering emulsion, which is made by mixing the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS with deionized water and n-butanol.

[0007] Further, according to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = (40 - 60) mg: 5 mL; according to the volume ratio, deionized water: n-butanol = (1 - 4):(4 - 1).

[0008] Furthermore, according to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = 50 mg: 5 mL; according to the volume ratio, deionized water: n-butanol = 3:2.

[0009] Further, the preparation method of the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS includes the following steps:

[0010] 1) Sequentially add chitosan (CS), Cr(NO3)3·9H2O, terephthalic acid, and 1 wt% acetic acid aqueous solution into a hydrothermal synthesis reactor, mix and stir for 0.5 - 1 h, then place it in an oven at 553 - 593 K for reaction for 8 - 9 h. After the reaction is completed, cool it to room temperature, wash it successively with DMF and methanol, and dry it under vacuum to obtain the precursor MIL-101(Cr)@CS;

[0011] 2) Mix palladium chloride, sodium chloride, and methanol until dissolved, and stir overnight to obtain a sodium chloropalladate solution;

[0012] 3) Mix MIL-101(Cr)@CS and the sodium chloropalladate solution, and disperse them evenly; add sodium borohydride to the methanol solution. Sodium borohydride and methanol release hydrogen gas. Quickly suck the upper layer of liquid with bubbles and add it to the mixed solution of MIL-101(Cr)@CS and sodium chloropalladate, continuously stir for 0.5 - 1 h, wash it with methanol, and dry it under vacuum to obtain the Pd@MIL-101(Cr)@CS material.

[0013] Further, in step 1), according to the mass ratio, CS:Cr(NO3)3·9H2O:terephthalic acid = 1:10:(4 - 5).

[0014] Further, in step 1), the vacuum drying is carried out at 373 K for 12 - 14 h.

[0015] Further, in step 3), the vacuum drying is carried out at 353 K for 6 - 7 h.

[0016] Further, in step 3), according to the solid-liquid ratio, MIL-101(Cr)@CS: sodium chloropalladate solution = 50 mg:(58 - 59) μL; sodium borohydride: methanol = (8.5 - 9.0) mg: 5 mL.

[0017] The second object of the present invention is to provide a method for preparing a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material, comprising the following steps: ultrasonically dispersing the Pd@MIL-101(Cr)@CS material in deionized water, adding n-butanol under stirring conditions, and oscillating for 5-6 min to obtain the Pd@MIL-101(Cr)@CS Pickering emulsion.

[0018] The third object of the present invention is to provide an application of a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material as a catalyst in the Suzuki reaction.

[0019] Furthermore, the method is as follows: take iodobenzene, phenylboronic acid, potassium carbonate and the catalyst in a reaction vessel, and react under the condition of 313-353K for 2-3 h; the catalyst is the Pd@MIL-101(Cr)@CS Pickering emulsion.

[0020] Furthermore, by molar ratio, iodobenzene:phenylboronic acid:potassium carbonate = 1:(1-2):(2-4).

[0021] The beneficial effects of the present invention are:

[0022] The Pd@MIL-101(Cr)@CS Pickering emulsion stabilized by the chitosan-coated metal-organic framework composite material provided by the present invention, compared with the emulsion stabilized by traditional surfactants, the present invention loads Pd nanoparticles into the MOF material MIL-101(Cr)@CS. Due to the large specific surface area and unique pore structure of MIL-101(Cr)@CS, it will inhibit the aggregation of Pd nanoparticles and can evenly distribute the Pd nanoparticles in the pore structure. The Pd@MIL-101(Cr)@CS Pickering emulsion provided by the present invention has a high catalytic efficiency in the Suzuki reaction, solves the problems of poor solubility of the substrates in the reaction system in aqueous solution and low catalyst activity. At the same time, the chitosan-coated MIL-101 composite material has abundant active functional groups such as amino and hydroxyl groups, playing a superior emulsifying role, without the need to introduce other emulsifiers, greatly improving the catalytic environment. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0024] Figure 1It is the PXRD pattern of the Pd@MIL-101(Cr)@CS material in the Pd@MIL-101(Cr)@CS Pickering emulsion of the present invention.

[0025] Figure 2 It is the SEM image of the Pd@MIL-101(Cr)@CS material in the Pd@MIL-101(Cr)@CS Pickering emulsion of the present invention.

[0026] Figure 3 It is the optical microscope photograph of the Pd@MIL-101(Cr)@CS Pickering emulsion formed in the present invention.

[0027] Figure 4 It is the catalytic activity diagram of the Pd@MIL-101(Cr)@CS Pickering emulsion of the present invention for five cycles of catalytic reaction. Detailed implementation manners

[0028] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0029] In the first aspect of the embodiments of the present invention, a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material is provided. The Pickering emulsion stabilized by the chitosan-coated metal-organic framework composite material is a Pd@MIL-101(Cr)@CS Pickering emulsion, which is made by mixing the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS with deionized water and n-butanol.

[0030] Specifically, chitosan has good biocompatibility, film-forming property and abundant active groups. When it is compounded with MOF to form a chitosan-coated MOF material, it can improve the performance of MOF in the emulsion. At the same time, chitosan endows the material with an additional emulsifying function, eliminating the need to introduce a new emulsifier and saving production costs, thereby constructing an efficient Pickering emulsion catalytic system for Suzuki reaction. The Pd@MIL-101(Cr)@CS Pickering emulsion stabilized by the chitosan-coated metal-organic framework composite material provided by the present invention is different from the traditional surfactant-stabilized emulsion: the chitosan-coated metal-organic framework MOF material provided by the present invention has a high specific surface area, adjustable pore structure and abundant active sites; in the present invention, Pd is attached to the pores of MIL-101(Cr)@CS, effectively preventing the aggregation of Pd nanoparticles.

[0031] In some feasible embodiments, according to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = (40 - 60) mg: 5 mL; according to the volume ratio, deionized water: n-butanol = (1 - 4):(4 - 1). Preferably, according to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = 50 mg: 5 mL; according to the volume ratio, deionized water: n-butanol = 3:2.

[0032] In some feasible embodiments, the preparation method of the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS includes the following steps:

[0033] 1) Sequentially add chitosan (CS), Cr(NO3)3·9H2O, terephthalic acid, and 1 wt% acetic acid aqueous solution into a hydrothermal synthesis reactor, mix and stir for 0.5 - 1 h, then place it in an oven at 553 - 593 K for reaction for 8 - 9 h. After the reaction is completed, cool it to room temperature, wash it successively with DMF and methanol, and dry it under vacuum to obtain the precursor MIL-101(Cr)@CS;

[0034] 2) Mix palladium chloride, sodium chloride, and methanol until dissolved, and stir overnight to obtain a sodium chloropalladate solution;

[0035] 3) Mix MIL-101(Cr)@CS and the sodium chloropalladate solution and disperse them evenly; add sodium borohydride to the methanol solution. Sodium borohydride and methanol release hydrogen gas. Quickly suck the upper layer of the liquid with bubbles and add it to the mixed solution of MIL-101(Cr)@CS and sodium chloropalladate, continuously stir for 0.5 - 1 h, wash it with methanol, and dry it under vacuum to obtain the Pd@MIL-101(Cr)@CS material.

[0036] Specifically, the present invention first synthesizes the chitosan-coated MIL-101(Cr)@CS material through specific steps, and then prepares the Pd@MIL-101(Cr)@CS material. This material can form a stable Pickering emulsion as an excellent emulsifier and be used to catalyze the Suzuki reaction.

[0037] In some feasible embodiments, in step 1), according to the mass ratio, CS:Cr(NO3)3·9H2O:terephthalic acid = 1:10:(4 - 5). Preferably, CS:Cr(NO3)3·9H2O:terephthalic acid = 1:10:4.2.

[0038] In some feasible embodiments, in step 3), according to the solid-liquid ratio, MIL-101(Cr)@CS:sodium chloropalladate solution = 50 mg:(58 - 59) μL; sodium borohydride:methanol = (8.5 - 9.0) mg:5 mL. Preferably, MIL-101(Cr)@CS:sodium chloropalladate solution = 50 mg:58.82 μL; sodium borohydride:methanol = 8.62 mg:5 mL.

[0039] The second object of the present invention is to provide a method for preparing a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material, comprising the following steps: ultrasonically dispersing the Pd@MIL-101(Cr)@CS material in deionized water, adding n-butanol under stirring conditions, and oscillating for 5 - 6 min to obtain a Pd@MIL-101(Cr)@CS Pickering emulsion.

[0040] Specifically, the method for preparing the Pickering emulsion provided by the present invention is simple, exhibits extremely high catalytic ability in the Suzuki reaction, realizes the simple separation and recycling of the catalyst at the same time, avoids the problems brought by the additional addition of emulsifiers, reduces the reaction cost, improves the product purity, and has good application prospects in the field of organic catalytic reactions.

[0041] The third object of the present invention is to provide an application of a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material as a catalyst in the catalytic Suzuki reaction.

[0042] Specifically, the Pickering emulsion Pd@MIL-101(Cr)@CS stabilized by the chitosan-coated metal-organic framework composite material provided by the present invention is different from the traditional surfactant-stabilized emulsion. Pd is attached in the pores of MIL-101(Cr)@CS, effectively preventing the aggregation of Pd nanoparticles. Pd(0) undergoes an oxidative addition reaction with the haloarene to generate a Pd(II) complex, then undergoes a transmetalation reaction with the activated boric acid to generate a Pd(II) complex, and finally undergoes reductive elimination to generate the product and Pd(0). Due to the interfacial effect, the Pd@MIL-101(Cr)@CS Pickering emulsion provided by the present invention exhibits extremely high catalytic ability as a catalyst in the Suzuki reaction, can improve the catalytic efficiency of the Suzuki reaction, realizes the simple separation and recycling of the catalyst at the same time, avoids the problems brought by the additional addition of emulsifiers, reduces the reaction cost, improves the product purity, and has good application prospects in the field of organic catalytic reactions.

[0043] In some feasible embodiments, the method is as follows: take iodobenzene, phenylboronic acid, potassium carbonate and the catalyst in a reaction vessel, and react at 313 - 353 K for 2 - 3 h; the catalyst is the Pd@MIL-101(Cr)@CS Pickering emulsion.

[0044] In some feasible embodiments, by molar ratio, iodobenzene: phenylboronic acid: potassium carbonate = 1:(1 - 2):(2 - 4). Preferably, iodobenzene: phenylboronic acid: potassium carbonate = 1:1.5:3.

[0045] Example 1 Pickering emulsion of Pd@MIL-101(Cr)@CS stabilized by chitosan-coated metal-organic framework composite

[0046] (I) Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0047] The method includes the following steps:

[0048] 1. Preparation of chitosan-coated metal-organic framework composite (Pd@MIL-101(Cr)@CS material)

[0049] 1.1) Add chitosan (CS) (0.12 g), Cr(NO3)3·9H2O (1.2 g, 0.003 mol), terephthalic acid (0.498 g, 0.003 mol), and 30 mL of 1 wt% aqueous acetic acid solution (accurately pipette 1.47 mL of 99.5% glacial acetic acid with a pipette gun and make up to 30 mL with deionized water to obtain 1 wt% aqueous acetic acid solution) into an 80 mL hydrothermal synthesis reactor, mix and stir for 0.5 h, place the reactor in an oven at 573 K for reaction for 8 h, cool to room temperature after the reaction, wash three times with DMF first, then wash three times with methanol, and finally place it in a vacuum drying oven and dry at 373 K for 12 h to obtain the precursor MIL-101(Cr)@CS.

[0050] 1.2) Accurately weigh 0.12 g of palladium chloride solid and 0.044 g of sodium chloride solid, pour them into a 10 mL glass bottle, then add 4 mL of methanol to the glass bottle, heat slightly until completely dissolved, and stir overnight to obtain a 0.17 mol / L brown sodium chloropalladate solution.

[0051] 1.3) Accurately weigh 50 mg of MIL-101(Cr)@CS and place it in a 5 mL glass bottle. Accurately pipette 58.82 μL of 0.17 mol / L sodium chloropalladate solution into the glass bottle in multiple portions to make the solution more evenly dispersed. Accurately weigh 8.62 mg of sodium borohydride solid and add it to 5 mL of methanol solution. Sodium borohydride reacts with methanol to release hydrogen. Quickly suck the upper layer of liquid with bubbles and add it to the glass bottle, continue to stir for 0.5 h, and the final solution is black. Then wash three times with methanol, and finally place it in a vacuum drying oven at 353 K and dry for 6 h to obtain black crystals, which is the Pd@MIL-101(Cr)@CS material.

[0052] 2. Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0053] 2.1) Activation treatment of Pd@MIL-101(Cr)@CS material: Take a certain amount of Pd@MIL-101(Cr)@CS material and vacuum dry it at 353K for 12h under heating conditions.

[0054] 2.2) Weigh 50mg of the activated Pd@MIL-101(Cr)@CS material and ultrasonically disperse it in 3mL of deionized water to obtain a Pd@MIL-101(Cr)@CS dispersion. Under stirring conditions, add 2mL of n-butanol to the Pd@MIL-101(Cr)@CS dispersion and oscillate for 3min to prepare a Pd@MIL-101(Cr)@CS Pickering emulsion.

[0055] (II) Detection

[0056] Figure 1 is the powder X-ray diffraction (PXRD) pattern of the synthesized Pd@MIL-101(Cr)@CS material. Figure 1 It shows that the Pd@MIL-101(Cr)@CS material has good crystallinity during the synthesis process.

[0057] Figure 2 is the SEM image of the synthesized Pd@MIL-101(Cr)@CS material. Figure 2 It shows that chitosan is uniformly coated on MIL-101.

[0058] Figure 3 is the optical microscope photograph of the formed Pd@MIL-101(Cr)@CS Pickering emulsion. Figure 3 It can be seen that the droplets of the Pd@MIL-101(Cr)@CS-stabilized Pickering emulsion are uniformly dispersed and of uniform size.

[0059] Example 2 Application of Pd@MIL-101(Cr)@CS Pickering emulsion in catalytic Suzuki reaction

[0060] The reaction formula is as follows:

[0061]

[0062] (I) The method is as follows:

[0063] Add 5mL of the Pd@MIL-101(Cr)@CS Pickering emulsion prepared in Example 1 to a 10mL three-neck reaction vessel, and then successively add 1mmol of iodobenzene, 1.5mmol of phenylboronic acid, and 3mmol of K2CO3, and react at 333K for 2h.

[0064] The yield of the product was monitored by gas chromatography. During the progress of this reaction, the experimental results of the catalytic performance of the Pd@MIL-101(Cr)@CS Pickering emulsion-catalyzed reaction were detected by GC. As the reaction proceeded, the yield of this reaction gradually increased. When the reaction proceeded for 2 h, the yield of this reaction had reached 99%, and the conversion rate was 99%.

[0065] (II) Recyclability of the catalyst in the Suzuki reaction.

[0066] After the reaction was completed, centrifugation and filtration were carried out to separate the reaction mixture from Pd@MIL-101(Cr)@CS, and it was washed with methanol, filtered, and dried to recover the Pd@MIL-101(Cr)@CS material.

[0067] Specific operation of the recycling experiment: The recycled Pd@MIL-101(Cr)@CS material was used to prepare Pd@MIL-101(Cr)@CS Pickering emulsion again according to the method of Example 1 and catalyze the Suzuki reaction according to the method of (I) of this example at 333 K for 2 h.

[0068] Figure 4 is the catalytic activity diagram of the Pd@MIL-101(Cr)@CS Pickering emulsion for five cycles of catalytic reactions. From Figure 4 it can be seen that after five cycles of the reaction, the catalyst still maintained good catalytic activity.

[0069] Example 3 Influence of the addition amount of Pd@MIL-101(Cr)@CS material on the Suzuki reaction (I) Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0070] The method includes the following steps:

[0071] 1. Preparation of chitosan-coated metal-organic framework composite material (Pd@MIL-101(Cr)@CS material)

[0072] Same as Example 1.

[0073] 2. Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0074] 2.1) Activation treatment of Pd@MIL-101(Cr)@CS material: Take a certain amount of Pd@MIL-101(Cr)@CS material and vacuum dry it at 353 K for 12 h under heating conditions.

[0075] 2.2) Weigh 20 mg - 80 mg of the activated Pd@MIL-101(Cr)@CS material respectively, and ultrasonically disperse it in 3 mL of deionized water to obtain a Pd@MIL-101(Cr)@CS dispersion. Under stirring conditions, add 2 mL of n-butanol to the Pd@MIL-101(Cr)@CS dispersion, and oscillate for 3 min to prepare 5 mL of Pickering emulsions with different Pd@MIL-101(Cr)@CS addition amounts respectively.

[0076] (II) Suzuki reaction catalyzed by Pd@MIL-101(Cr)@CS Pickering emulsion

[0077] Add 5 mL of Pickering emulsions with different Pd@MIL-101(Cr)@CS addition amounts into a 10 mL three-neck reaction vessel respectively, and then add 1 mmol of iodobenzene, 1.5 mmol of phenylboronic acid and 3 mmol of K2CO3 in sequence, and react at 333 K for 2 h. Monitor the product yield by gas chromatography, and the results are shown in Table 1.

[0078] Table 1 Influence of different Pd@MIL-101(Cr)@CS addition amounts on Suzuki reaction

[0079]

[0080] It can be seen from Table 1 that different addition amounts of Pd@MIL-101(Cr)@CS have a great influence on the reaction. When the dosage of Pd@MIL-101(Cr)@CS is 20 mg, the catalytic efficiency is only 41.4%. As the dosage of Pd@MIL-101(Cr)@CS increases, the reaction substrate fully contacts with Pd@MIL-101(Cr)@CS in the emulsion system, and the catalytic efficiency is significantly improved. When the addition amount of Pd@MIL-101(Cr)@CS is 50 mg, the yield has reached 99.9%. When it continues to increase to 80 mg, the yield is still above 99%. At the same time, the reaction time is not significantly shortened. Therefore, it is not necessary to add too much Pd@MIL-101(Cr)@CS to avoid waste. To save costs, the present invention preferably uses a solid-liquid ratio of Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = (40 - 60) mg: 5 mL. More preferably, the solid-liquid ratio is Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = 50 mg: 5 mL.

[0081] Example 4 Influence of water-oil ratio of emulsion system on Suzuki reaction (I) Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0082] The method includes the following steps:

[0083] 1. Preparation of chitosan-coated metal-organic framework composite material (Pd@MIL-101(Cr)@CS material)

[0084] Same as Example 1.

[0085] 2. Preparation of Pd@MIL-101(Cr)@CS Pickering emulsion

[0086] 2.1) Activation treatment of Pd@MIL-101(Cr)@CS material: Take a certain amount of Pd@MIL-101(Cr)@CS material and vacuum dry it at 353K for 12h under heating conditions.

[0087] 2.2) Weigh 50mg of the activated Pd@MIL-101(Cr)@CS material and ultrasonically disperse it in deionized water to obtain a Pd@MIL-101(Cr)@CS dispersion. Under stirring conditions, add n-butanol to the Pd@MIL-101(Cr)@CS dispersion and oscillate for 3min to prepare 5mL of Pd@MIL-101(Cr)@CS Pickering emulsions with different water-oil ratios. The sum of the volumes of deionized water and n-butanol is 5mL, and the volume ratios are shown in Table 2.

[0088] (II) Pd@MIL-101(Cr)@CS Pickering emulsion catalyzed Suzuki reaction

[0089] Add 5mL of Pd@MIL-101(Cr)@CS Pickering emulsions with different water-oil ratios to a 10mL three-neck reaction vessel respectively, and then add 1mmol of iodobenzene, 1.5mmol of phenylboronic acid and 3mmol of K2CO3 in sequence, and react at 333K for 2h. Monitor the product yield by gas chromatography, and the results are shown in Table 2.

[0090] Table 2 Influence of different water-oil ratios in the emulsion system on the Suzuki reaction

[0091]

[0092] It can be seen from Table 2 that different water-oil ratios in the emulsion system have a great influence on the Suzuki reaction. When the water-oil ratio of the emulsion is deionized water:n-butanol = 3:2, the final yield after 2 hours is 99.9%, and a well-dispersed and stable Pickering emulsion can be observed under an optical microscope. When there is too much water phase or oil phase in the emulsion, it will lead to poor emulsion formation state, low droplet dispersion degree, easy demulsification and coagulation, thus reducing the stability of the system and affecting the catalytic effect. Therefore, in the present invention, it is preferred that the volume ratio of deionized water:n-butanol = 3:2.

[0093] It is easily understood by those skilled in the art that, on the premise of no conflict, the above-mentioned advantageous means can be freely combined and superimposed. The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application. The above is only the preferred implementation manner of the present application. It should be noted that for those of ordinary skill in the technical field of the present application, several improvements and modifications can be made without departing from the technical principle of the present application, and these improvements and modifications should also be regarded as within the protection scope of the present application.

Claims

1. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material, characterized in that The Pickering emulsion stabilized by the chitosan-coated metal-organic framework composite material is the Pd@MIL-101(Cr)@CS Pickering emulsion, which is prepared by mixing the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS with deionized water and n-butanol.

2. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to claim 1, wherein, According to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = (40 - 60) mg: 5 mL; according to the volume ratio, deionized water: n-butanol = (1 - 4):(4 - 1); preferably, according to the solid-liquid ratio, Pd@MIL-101(Cr)@CS: the volume sum of deionized water and n-butanol = 50 mg: 5 mL; according to the volume ratio, deionized water: n-butanol = 3:

2.

3. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to claim 1, wherein, The preparation method of the chitosan-coated metal-organic framework composite material Pd@MIL-101(Cr)@CS includes the following steps: 1) Sequentially add chitosan CS, Cr(NO3)3·9H2O, terephthalic acid, and 1 wt% acetic acid aqueous solution into a hydrothermal synthesis reactor, mix and stir for 0.5 - 1 h, then place it in an oven at 553 - 593 K for reaction for 8 - 9 h. After the reaction is completed, cool it to room temperature, wash it successively with DMF and methanol, and dry it under vacuum to obtain the precursor MIL-101(Cr)@CS; 2) Mix palladium chloride, sodium chloride, and methanol until dissolved, and stir overnight to obtain a sodium chloropalladate solution; 3) Mix MIL-101(Cr)@CS and the sodium chloropalladate solution and disperse them evenly; add sodium borohydride into the methanol solution. Sodium borohydride and methanol release hydrogen gas. Quickly suck the upper layer of liquid with bubbles and add it to the mixed solution of MIL-101(Cr)@CS and sodium chloropalladate, continuously stir for 0.5 - 1 h, wash it with methanol, and dry it under vacuum to obtain the Pd@MIL-101(Cr)@CS material.

4. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to claim 1, wherein In step 1), according to the mass ratio, CS:Cr(NO3)3·9H2O:terephthalic acid = 1:10:(4 - 5).

5. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite according to claim 1, wherein, In step 1), the vacuum drying is carried out at 373 K for 12 - 14 h; in step 3), the vacuum drying is carried out at 353 K for 6 - 7 h.

6. A Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to claim 1, wherein, In step 3), according to the solid-liquid ratio, MIL-101(Cr)@CS: sodium chloropalladate solution = 50 mg:(58 - 59) μL; sodium borohydride: methanol = (8.5 - 9.0) mg: 5 mL.

7. A method for preparing a Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to any one of claims 1-6, characterized in that, The method includes the following steps: ultrasonically disperse the Pd@MIL-101(Cr)@CS material in deionized water, add n-butanol under stirring conditions, and oscillate for 5 - 6 min to prepare the Pd@MIL-101(Cr)@CS Pickering emulsion.

8. Application of the Pickering emulsion stabilized by a chitosan-coated metal-organic framework composite material according to any one of claims 1 - 6 as a catalyst in the catalytic Suzuki reaction.

9. The application according to claim 8, characterized in that, The method is as follows: Take iodobenzene, phenylboronic acid, potassium carbonate and a catalyst in a reaction vessel, and react under the condition of 313 - 353K for 2 - 3h; the catalyst is the Pd@MIL-101(Cr)@CS Pickering emulsion described in any one of claims 1 - 6.

10. The application according to claim 9, wherein By molar ratio, iodobenzene:phenylboronic acid:potassium carbonate = 1:(1 - 2):(2 - 4).

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