Preparation method of magnetic carboxyl chitosan microsphere-metal organic framework core-shell structure industrial catalyst

Abstract

The application discloses a kind of preparation methods of magnetic carboxyl chitosan microsphere metal organic framework core-shell structure industrial catalyst, which is prepared by ultrasonic-assisted reverse emulsion polymerization and green crosslinking agent carboxyl chitosan coated ferroferric oxide microspheres, then in-situ growth metal organic framework on the surface of microsphere, then reduce palladium ion in the pore of metal organic framework, and then prepare core-shell structure industrial catalyst with uniform particle size, strong stability, high efficiency, magnetism, reusable.The large specific surface area and pore structure of metal organic framework provide a large number of fixed sites for palladium atoms, increase the contact area and probability of catalyst and reactant, significantly improve the catalytic activity;The method of the application is simple, low cost, green and environment-friendly, and the obtained core-shell structure catalyst has high catalytic efficiency, easy recycling and other advantages, and has great application potential in inorganic chemical industry, organic chemical industry, petroleum chemical industry and environmental purification.

Description

Technical Field

[0001] This invention relates to a method for preparing a magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst, belonging to the field of functional nanomaterial preparation technology. Background Technology

[0002] Chitin is the second most abundant biomass resource in nature. The alkaline polysaccharide obtained after its deacetylation is called chitosan, with the chemical name (1,4)-2-amino-2-deoxy-β-D-glucose. It has advantages such as wide availability, renewability, low cost, good biocompatibility, biodegradability, and non-toxicity, and has wide applications in water treatment, biomedicine, food engineering, textile printing and dyeing and other fields. However, the strong hydrogen bonds between the hydroxyl and amino groups in chitosan molecules make chitosan difficult to dissolve in water and common solvents, and it can only dissolve in acidic solutions. Acidic solutions are volatile, difficult to recover, highly corrosive, pollute the environment, and have certain toxicity to organisms. At the same time, the antibacterial activity of chitosan is easily affected by factors such as molecular weight, degree of deacetylation, and pH, which greatly limits the application of chitosan [Hamedi H, Moradi S, Hudson SM, et al. Chitosan based bioadhesives for biomedical applications: A review. Carbohydrate Polymers, 2022, 282: 119100].

[0003] Carboxylated chitosan is a product of selective oxidation of chitosan through an oxidation system. Its characteristic feature is that some hydroxyl groups at the C6 position are oxidized to carboxyl groups while the remaining functional groups remain unchanged. Carboxylated chitosan possesses unique advantages such as good water solubility, strong chemical reactivity, high biological activity, and safety and hygiene. Furthermore, the carboxylated chitosan molecule contains both carboxyl and amino groups, making it an amphoteric polyelectrolyte. Structurally similar to proteins, it exhibits superior biocompatibility and affinity with the human body. The carboxyl groups (-COOH) in carboxychitosan can protonate the amino groups in its molecules, giving them a positive charge. This allows carboxychitosan to exhibit antibacterial activity under neutral and weakly alkaline conditions, expanding the application range of chitosan [Liao Y, Wang C, Huang C, et al. Robust Cellulose / Carboxymethyl Chitosan Composite Films with High Transparency and Antibacterial Ability for Fresh Fruit Preservation. ACSSustainable Chemistry & Engineering, 2023, 11(15): 5908-5917]. Simultaneously, carboxychitosan contains a large number of carboxyl groups, and the negatively charged carboxyl groups have a strong electrostatic attraction and covalent coordination effect on metal cations. This eliminates the need for surfactants or the introduction of other substances, making it possible for organometallic frameworks to grow directly on the surface of chitosan microspheres. Furthermore, the complete coating of the carboxychitosan molecular chain on the outer layer of the metal particles effectively prevents damage to other matrices by the metal particles.

[0004] Invention patent CN116173914A discloses a biomimetic polymer-encapsulated chitosan magnetic adsorbent, its preparation method and application. The preparation method is relatively complicated, and the resulting composite microspheres have uneven particle size distribution and generally large particle size, resulting in a small specific surface area. At the same time, a large amount of iron oxide is exposed on the surface of the microspheres, which reduces the effective adsorption sites of the material.

[0005] This invention utilizes reverse emulsion polymerization to achieve uniform particle size distribution in the prepared carboxylated chitosan microspheres. Furthermore, the iron oxide (Fe3O4) is completely coated within the microspheres, imparting them with magnetism while effectively preserving attachment sites on the outer surface, ensuring in-situ growth of the metal-organic framework in subsequent steps. This method of directly growing metal-organic frameworks in situ on the surface of chitosan microspheres has been rarely reported previously.

[0006] Currently, the most mature and cost-effective organic "core" materials are mainly composite polymers based on polystyrene (PS). While the microsphere preparation process is mature, polystyrene (PS) is difficult to degrade and recycle, causing a series of environmental pollution problems. [Gongshu Wang, Jiwei Wang, Zhangpei Chen, et al. Metal-organic framework grown in situ on chitosan microspheres as robust host of palladium forheterogeneous catalysis: Suzuki reaction and the p-nitrophenol reduction. International journal of biological macromolecules, 2022, Vol. 206: 232-241]. This invention uses carboxylated chitosan as the "core" layer. Chitosan is a biomass material that is abundant in nature, non-toxic, harmless, biocompatible, and biodegradable, making it an ideal "core" material. Using carboxylated chitosan as the "core" layer avoids the aforementioned problems.

[0007] Metal-organic frameworks (MOFs) are porous materials with a framework structure, formed by the continuous self-assembly of metal ions as nodes and organic ligands as connecting bridges. They are characterized by high specific surface area and high porosity, and have wide applications in adsorption, separation, and catalysis. However, their generally small particle size and predominantly powdery nature make them difficult to recycle and reuse, posing a risk of leakage into the environment. Designing a substrate with a larger particle size for MOFs could expand their practical applications; using MOFs as the "shell" layer to prepare core-shell materials is a feasible design approach. In addition, due to the large specific surface area and porosity of metal-organic frameworks, reducing catalytic metals within their channels allows for uniform dispersion of low-particle-size catalysts in the channel space, avoiding catalyst aggregation and increasing the contact area and probability between the catalyst and the reaction substrate, thereby significantly improving catalytic efficiency [Yong-Li Dong; Hao-Ran Liu; Shao-Min Wang; Guo-Wei Guan; Qing-Yuan Yang. Immobilizing Isatin-Schiff Base Complexes in NH2-UiO-66 for Highly Photocatalytic CO2 Reduction. ACS Catalysis, 2023, Vol. 13(4): 2547-2554]. Summary of the Invention

[0008] In view of the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a method for preparing a magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The purpose is to prepare an environmentally friendly core-shell structure nanocomposite microparticle that can effectively enhance the catalytic activity of palladium metal, increase the contact area and probability between palladium catalyst and reactants in the metal-organic framework channels, reduce nanoparticle agglomeration, improve stability and reactivity, and is magnetically recyclable.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a magnetic carboxylated chitosan microsphere@metal-organic framework core-shell structured industrial catalyst involves encapsulating iron oxide microspheres with carboxylated chitosan using an ultrasound-assisted reverse emulsion polymerization method and a green crosslinking agent to obtain magnetic carboxylated chitosan microspheres. Then, a metal-organic framework is grown in situ on the surface of the magnetic carboxylated chitosan microspheres, and finally, palladium ions are reduced into the pores of the metal-organic framework to obtain the final product. The method includes the following steps:

[0011] (1) Dissolve carboxylated chitosan in a 2-4% (v / v) acetic acid solution to prepare a 5-10 mL homogeneous solution with a mass concentration of 0.5-4.5%. Add 50-450 mg of iron oxide powder and let stand to remove air bubbles, which serves as the aqueous phase. Place 50-100 mL of liquid paraffin containing a 2-6% (v / v) nonionic surfactant in a three-necked flask as the oil phase. Add the aqueous phase dropwise to the oil phase at 40-60℃, and then add 0.01 mol / L NaOH solution to adjust the pH of the mixture to 5.4-5.8. Stir continuously at 350-650 r / min using a high-speed shear emulsifier for 0.5-1.5 h. Then add 25-100 mg of green crosslinking agent and react in an ultrasonic oscillator for 2-5 h. The product was centrifuged to remove the upper oil phase, and the crude product was washed 3 to 5 times with petroleum ether and isopropanol, and then dried at 40 to 50°C to obtain magnetic carboxylated chitosan microsphere powder.

[0012] (2) Place 0.4-2.2 g of microsphere powder in a metal ion solution with a concentration of 1-15 mmol / L and treat at 20-30°C for 1-15 min. Use a magnet to separate the microsphere powder from the solution and wash it with anhydrous ethanol 3-4 times. Then add the microsphere powder to an organic ligand solution with a concentration of 1-15 mmol / L and place it in a microwave radiation reactor with a power of 380-600 W at 30-45°C for 2-15 min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0013] (3) Repeat step (2) 1 to 36 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0014] (4) Place 0.32-1.76 g of the magnetic carboxy chitosan@metal-organic framework core-shell structure microsphere powder obtained in step (3) into an ethanol solution containing 30-55 mg of palladium chloride, ultrasonically disperse for 20-30 min, then add 100-300 mg of reducing agent, stir and react at room temperature for 2-3 h, then centrifuge the product, wash with anhydrous ethanol, and vacuum dry to obtain the magnetic carboxy chitosan microsphere@metal-organic framework core-shell structure industrial catalyst.

[0015] Preferably, in step (1), the carboxylated chitosan has a viscosity-average molecular weight of 0.68–1.59 million, a degree of deacetylation ≥92.4%, a C6 carboxylation degree of 50.62–75.31%, and an isoelectric point pH of 4.9–5.3. The structural formula of the carboxylated chitosan is as follows:

[0016]

[0017] Preferably, in step (1), the frequency of the ultrasonic oscillator is 30-45 kHz and the power is 260-800 W.

[0018] Preferably, in step (1), the nonionic surfactant is Span 80 or Tween 80, and the green crosslinking agent is genipin, vanillin, glutamic acid, tartaric acid, malic acid, or maleic acid.

[0019] Preferably, in step (1), the average particle size of the iron oxide is 50-150 nm and the isoelectric point pH is 6.0-6.8.

[0020] Preferably, in step (2), the metal ion solution is an ethanol solution of copper acetate, zinc nitrate or cobalt nitrate; the organic ligand solution corresponding to copper acetate is an ethanol solution of trimesic acid, and the organic ligand solutions corresponding to zinc nitrate and cobalt nitrate are both ethanol solutions of 2-methylimidazole.

[0021] Preferably, in step (4), the reducing agent is glucose, fructose, galactose, maltose, or deoxyribose.

[0022] Preferably, the obtained magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst has a particle size range of 5–25 μm, a Zeta potential of 33.36–45.78 mV, and a monodispersity index of 0.213–0.407.

[0023] By optimizing parameters such as the mass concentration of carboxychitosan in the aqueous phase, the amount of iron oxide added, the ultrasonic power and reaction time in the oil phase, the concentrations of metal ion solution and organic ligand solution, the microwave radiation reaction time and power, the concentration of palladium chloride in ethanol solution, and the amount of reducing agent, a series of core-shell composite microparticles with different particle sizes and catalytic effects can be obtained.

[0024] Compared with existing technologies, the preparation principle and beneficial effects of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst of this invention are reflected in the following aspects:

[0025] 1. This invention utilizes carboxylated chitosan dissolved in acetic acid solution as the aqueous phase and liquid paraffin containing a nonionic surfactant as the oil phase to prepare magnetic carboxylated chitosan core-shell microparticles via ultrasonic oscillation reverse emulsion polymerization. The reverse emulsion polymerization method can produce carboxylated chitosan microspheres with uniform particle size distribution. The water-in-oil structure and the presence of the nonionic surfactant ensure complete spherical coating of magnetic Fe3O4 by the carboxylated chitosan. Furthermore, carboxylated chitosan is abundant, renewable, and highly safe, possessing advantages such as good water solubility, low cost, numerous active groups, and high biocompatibility. The carboxyl, amino, and hydroxyl groups in the carboxylated chitosan molecule can all be coated onto the exterior of nano-Fe3O4 through multiple coordinate bonds to form magnetic carboxylated chitosan core-shell microspheres, exhibiting strong stability, uniform particle size, and easy magnetic recycling. In addition, carboxylated chitosan contains a large number of carboxyl groups. The negatively charged carboxyl groups have a strong electrostatic attraction and covalent coordination effect on metal cations, eliminating the need for surfactants or the introduction of other substances, making it possible for organometallic frameworks to grow directly on the surface of chitosan microspheres.

[0026] 2. In this invention, a carboxylated chitosan aqueous solution is dropwise added to a liquid paraffin oil phase containing a nonionic surfactant. Under the action of an ultrasonic instrument, an ultrasonic reaction is carried out to form microspheres through complexation. In the ultrasonic chemical reaction, the multiple effects of ultrasound, such as dispersion, pulverization, and activation, can promote the homogeneous reaction of substances and the dispersion of nanoparticles. At the same time, ultrasound generates a cavitation effect, in which cavitation bubbles are formed, grow, and collapse in the reaction solution. When the cavitation bubbles collapse, a high temperature of over 5000K and a high pressure of over 200Mpa are generated in a very short time and in a very small space. This provides an energy source for ultrasonic chemical synthesis and greatly accelerates the reaction. Ultrasound activates the coordination and binding of carboxychitosan molecules, surfactants, and nano-Fe3O4. The strong impact and cavitation of ultrasound dissociate water molecules adsorbed on the surface of Fe3O4 particles, forming hydroxyl groups. This increases the active groups on the Fe3O4 particle surface, promoting ultrasonic chemical cross-linking between the nano-Fe3O4 particles, carboxychitosan molecules, and the green cross-linking agent. This results in the formation of magnetic carboxychitosan microspheres with uniform size distribution and high stability. Simultaneously, the pH of the reaction solution (5.4–5.8) is lower than the isoelectric point of Fe3O4 particles (pH = 6.0–6.8), making the Fe3O4 nanoparticles positively charged. This significantly increases the electrostatic attraction and complexation of the positively charged Fe3O4 nanoparticles with the carboxyl and hydroxyl anions in the negatively charged carboxychitosan molecules (isoelectric point pH = 4.9–5.3), thereby greatly improving the dispersibility of the nano-Fe3O4 particles and the efficiency and stability of the externally coated carboxychitosan molecular chains.

[0027] 3. In this invention, magnetic carboxylated chitosan microspheres are treated in a metal ion solution and then separated using a magnet. The microspheres are then added to an organic ligand solution and reacted under microwave irradiation. This yields core-shell structured microspheres with a metal-organic framework (MOF) grown in situ on the surface of the magnetic carboxylated chitosan microspheres. Due to the rapid heating speed of microwave irradiation, the short reaction time, and the good product uniformity, the metal ions and organic ligands can fully contact the active sites on the surface of the magnetic carboxylated chitosan microspheres, significantly accelerating the in-situ growth rate of the MOF. This effectively avoids the occurrence of side reactions and uneven distribution of the MOF caused by prolonged treatment, allowing the MOF to form layer by layer and become stable and uniform on the surface of the magnetic carboxylated chitosan microspheres. This solves the shortcomings of traditional water bath heating reactions, such as long reaction cycles, low reaction rates, easy aggregation of metal ions and organic ligands in the reaction solution, and uneven dispersion leading to micelle nucleation. The magnetic carboxylated chitosan microspheres@MOF core-shell structure obtained by microwave irradiation reaction are stable, small in size, have a large specific surface area, and exhibit enhanced complexation with palladium ions.

[0028] 4. In this invention, a carboxylated chitosan aqueous solution is added dropwise to a liquid paraffin oil phase containing a nonionic surfactant, and then a green crosslinking agent is added to react in an ultrasonic oscillator to form magnetic carboxylated chitosan microspheres. Green crosslinking agents such as genipin, vanillin, glutamic acid, tartaric acid, malic acid, or maleic acid contain a large number of polar groups such as carboxyl, aldehyde, carbonyl, and hydroxyl groups, which can form strong coordination bonds with positively charged nano-Fe3O4 particles. At the same time, the carboxyl and aldehyde groups in the green crosslinking agents can also crosslink with the amino groups of carboxychitosan through multi-site chemical bonds such as amide and Schiff bases. The green crosslinking agents have small molecular weights and good compatibility with carboxychitosan, which helps to crosslink into smaller magnetic carboxychitosan microspheres in ultrasonic reactions. Moreover, the green crosslinking agent molecules contain more polar carboxyl, aldehyde, and carbonyl groups, which increases the content of negatively charged groups on the surface of magnetic carboxychitosan microspheres, significantly enhancing the electrostatic attraction and covalent coordination with positively charged metal ions, which is conducive to the formation of stable magnetic carboxychitosan microspheres@metal-organic framework core-shell structured particles.

[0029] 5. This invention involves placing magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structures in an ethanol solution of palladium chloride, adding a reducing agent, and conducting a hydrothermal reaction to obtain an industrial catalyst with a magnetic carboxylated chitosan microsphere@metal-organic framework core-shell structure. The hydrothermal method can form ordered aggregates with specific structures and functions, and has advantages such as simple process and controllability. Introducing hydrophilic groups such as carboxyl groups into the carboxylated chitosan molecules improves the biocompatibility and stability of the core-shell composite nanoparticles in aqueous solution, enabling the magnetic carboxylated chitosan microsphere@metal-organic framework core-shell structure industrial catalyst to achieve high-efficiency catalysis, easy magnetic recovery, and other functions. Furthermore, carboxylated chitosan is environmentally friendly, stable, non-toxic, and safe to use. Meanwhile, the pH of the reaction solution (5.4–5.8) is higher than the isoelectric point of carboxychitosan (pH 4.9–5.3), causing the carboxychitosan molecules to exhibit negative charge. This enhances the electrostatic attraction with nano-Fe3O4 particles. Furthermore, the carboxyl, amino, and hydroxyl groups in the carboxychitosan complex with metal ions and organic ligands through chemical cross-linking to form a core-shell structure industrial catalyst with small particle size, uniform distribution, strong stability, and high catalytic activity.

[0030] 6. This invention is green and environmentally friendly, using no toxic chemical reagents. The reducing agents used, such as glucose, fructose, galactose, maltose, or deoxyribose, are commonly used as food additives and are safe and hygienic. Reducing sugar molecules typically contain reducing groups such as aldehydes and hydroxyl groups. Some sugars (such as fructose) do not contain aldehydes but only ketone structures. Because their carbonyl groups are very close to the terminal carbons, they can easily be converted to hemiacetal structures through a hemiketal structure under certain conditions, thus indirectly generating aldehydes and exhibiting good reducing properties. Using reducing sugars to reduce palladium chloride complexed on the surface of magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structures to metallic palladium offers advantages such as fast reduction rate, environmental friendliness, uniform distribution of elemental palladium within the metal-organic framework channels, and strong bonding.

[0031] 7. This invention first uses ultrasound-assisted microemulsion polymerization and a green crosslinking agent to prepare carboxylated chitosan-coated iron oxide microspheres. Then, a metal-organic framework (MOF) is grown in situ on the surface of the magnetic carboxylated chitosan microspheres. Palladium ions are then reduced into the pores of the MOF, resulting in a magnetic carboxylated chitosan microsphere@MOF core-shell structured industrial catalyst with uniform particle size, high stability, high catalytic efficiency, and easily reusable magnetic properties. The large specific surface area of ​​the MOF provides numerous anchoring sites for palladium atoms, increasing the contact area and probability between the catalyst and reactants, and significantly improving catalytic activity. This invention is simple, cost-effective, and environmentally friendly, with broad application prospects in inorganic chemistry, organic chemistry, petrochemicals, and environmental remediation. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst prepared in this invention.

[0033] Figure 2 This is a scanning electron microscope image of the magnetic carboxylated chitosan microspheres in Example 3 of the present invention.

[0034] Figure 3 This is a scanning electron microscope image of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst in Example 3 of the present invention.

[0035] Figure 4 This is a catalytic effect diagram of the core-shell structure industrial catalyst catalyzing the Suzuki coupling reaction in test item 3 of this invention. Figure 4 (a) and the effect diagram of recovery and repeated catalysis (in the figure) Figure 4 (b) in the middle. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following reference embodiments are for illustrative purposes only and do not limit the present invention in any way.

[0037] I. Preparation of Magnetic Carboxylated Chitosan Microspheres@Metal-Organic Framework Core-Shell Structure Industrial Catalysts

[0038] Example 1

[0039] This embodiment prepares a magnetic carboxyl chitosan microsphere@metal-organic framework core-shell structured industrial catalyst according to the following steps:

[0040] (1) Carboxylated chitosan with a viscosity-average molecular weight of 14,800, a degree of deacetylation of 96.4%, a degree of carboxylation at C6 of 53.16%, and an isoelectric point of pH 5.2 was dissolved in a 2% (v / v) acetic acid solution to prepare a 6 mL homogeneous solution with a mass concentration of 0.8%. 100 mg of iron oxide powder with an average particle size of 72 nm and an isoelectric point of pH 6.6 was added and allowed to stand for 24 h to remove bubbles, which was used as the aqueous phase. 90 mL of liquid paraffin containing 2.6% (v / v) of the nonionic surfactant Tween 80 was placed in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 40℃, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.7. The mixture was stirred continuously at 380 r / min for 45 min using a high-speed shear emulsifier. Then, 40 mg of green crosslinking agent tartaric acid was added, and the mixture was reacted in an ultrasonic oscillator with a frequency of 32 kHz and a power of 350 W for 2.5 h. The product was centrifuged to discard the upper oil phase, and the crude product was washed three times successively with petroleum ether and isopropanol. After drying at 45℃, magnetic carboxylated chitosan microsphere powder was obtained.

[0041] (2) Place 0.5g of microsphere powder in a zinc nitrate solution with a molar concentration of 4mmol / L and treat at 20℃ for 5min. Use a magnet to separate the microsphere powder from the solution, and wash it 3 times with anhydrous ethanol. Then add the microsphere powder to an ethanol solution of 2-methylimidazole with a concentration of 6mmol / L, place it in a microwave radiation reactor with a power of 400W and react at 30℃ for 3min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0042] (3) Repeat step (2) 5 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0043] (4) 0.48 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 32 mg palladium chloride, ultrasonically dispersed for 20 min, and then 150 mg of reducing agent galactose was added. The mixture was stirred at room temperature for 2 h, and then the product was centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The final core-shell structure composite microparticles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 6 μm, the Zeta potential was 37.07 mV, and the monodispersity index was 0.381.

[0044] Example 2

[0045] This embodiment prepares a magnetic carboxyl chitosan microsphere@metal-organic framework core-shell structured industrial catalyst according to the following steps:

[0046] (1) Dissolve carboxylated chitosan with a viscosity-average molecular weight of 12,400, a degree of deacetylation of 95.3%, a degree of carboxylation at C6 of 61.22%, and an isoelectric point of pH 5.1 in a 3% (v / v) acetic acid solution to prepare an 8 mL homogeneous solution with a mass concentration of 1.5%. Add 200 mg of iron(III) oxide powder with an average particle size of 90 nm and an isoelectric point of pH 6.4 and let stand for 24 h to remove bubbles, which is the aqueous phase. Place 80 mL of liquid paraffin containing 3.8% (v / v) of the nonionic surfactant Tween 80 in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 45℃, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.6. The mixture was stirred continuously at 450 r / min for 60 min using a high-speed shear emulsifier. Then, 60 mg of the green crosslinking agent vanillin was added, and the mixture was reacted in an ultrasonic oscillator with a frequency of 38 kHz and a power of 460 W for 3 h. The product was centrifuged to discard the upper oil phase, and the crude product was washed four times with petroleum ether and isopropanol, respectively. After drying at 45℃, magnetic carboxylated chitosan microsphere powder was obtained.

[0047] (2) Place 0.8 g of microsphere powder in a cobalt nitrate solution with a molar concentration of 8 mmol / L and treat at 25°C for 8 min. Use a magnet to separate the microsphere powder from the solution, and then wash it 3 times with anhydrous ethanol. Then add the microsphere powder to an ethanol solution of 2-methylimidazole with a molar concentration of 8 mmol / L, and place it in a microwave radiation reactor with a power of 460W and react at 35°C for 6 min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0048] (3) Repeat step (2) 10 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0049] (4) 0.96 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 40 mg of palladium chloride, ultrasonically dispersed for 25 min, and then 180 mg of reducing agent maltose was added. The mixture was stirred at room temperature for 2.5 h. The product was then centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The final core-shell structure composite microparticles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 10 μm, the Zeta potential was 35.41 mV, and the monodispersity index was 0.327.

[0050] Example 3

[0051] This embodiment prepares a magnetic carboxyl chitosan microsphere@metal-organic framework core-shell structured industrial catalyst according to the following steps:

[0052] (1) Dissolve carboxylated chitosan with a viscosity-average molecular weight of 0.92 million, a degree of deacetylation of 93.1%, a C6 carboxylation degree of 70.96%, and an isoelectric point pH of 4.9 in a 4% (v / v) acetic acid solution to prepare a 10 mL homogeneous solution with a mass concentration of 2.5%. Add 250 mg of iron oxide powder with an average particle size of 100 nm and an isoelectric point pH of 6.2 and let it stand for 24 h to remove bubbles, which is the aqueous phase. Place 80 mL of liquid paraffin containing 4.5% (v / v) of the nonionic surfactant Span 80 in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 50℃, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.4. The mixture was stirred continuously at 520 r / min for 70 min using a high-speed shear emulsifier. Then, 80 mg of the green crosslinking agent genipin was added, and the mixture was reacted in an ultrasonic oscillator with a frequency of 42 kHz and a power of 650 W for 4 h. The product was centrifuged to discard the upper oil phase, and the crude product was washed five times with petroleum ether and isopropanol, respectively. After drying at 50℃, magnetic carboxylated chitosan microsphere powder was obtained.

[0053] (2) Place 1.5g of microsphere powder in a copper acetate solution with a molar concentration of 8mmol / L and treat at 25°C for 10min. Use a magnet to separate the microsphere powder from the solution, and wash it 4 times with anhydrous ethanol. Then add the microsphere powder to an ethanol solution of trimesic acid with a molar concentration of 12mmol / L, place it in a microwave radiation reactor with a power of 500W and react at 40°C for 10min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0054] (3) Repeat step (2) 18 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0055] (4) 1.22 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 45 mg of palladium chloride and ultrasonically dispersed for 28 min. Then, 240 mg of reducing agent glucose was added, and the mixture was stirred at room temperature for 3 h. The product was then centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The final core-shell structure composite microparticles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 15 μm, the Zeta potential was 44.53 mV, and the monodispersity index was 0.219.

[0056] Example 4

[0057] This embodiment prepares a magnetic carboxyl chitosan microsphere@metal-organic framework core-shell structured industrial catalyst according to the following steps:

[0058] (1) Carboxylated chitosan with a viscosity-average molecular weight of 0.92 million, a degree of deacetylation of 93.1%, a C6 carboxylation degree of 70.96%, and an isoelectric point pH of 4.9 was dissolved in a 4% (v / v) acetic acid solution to prepare a 10 mL homogeneous solution with a mass concentration of 2.5%. 360 mg of iron oxide powder with an average particle size of 120 nm and an isoelectric point pH of 6.1 was added and allowed to stand for 24 h to remove bubbles, which was used as the aqueous phase. 60 mL of liquid paraffin containing 4.5% (v / v) of the nonionic surfactant Span 80 was placed in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 55℃, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.4. The mixture was stirred continuously at 580 r / min for 80 min using a high-speed shear emulsifier. Then, 80 mg of the green crosslinking agent genipin was added, and the mixture was reacted in an ultrasonic oscillator with a frequency of 42 kHz and a power of 650 W for 4.5 h. The product was centrifuged to discard the upper oil phase, and the crude product was washed five times with petroleum ether and isopropanol, respectively. After drying at 50℃, magnetic carboxylated chitosan microsphere powder was obtained.

[0059] (2) 1.8 g of microsphere powder was placed in a copper acetate solution with a molar concentration of 8 mmol / L and treated at 25°C for 12 min. The microsphere powder was separated from the solution using a magnet and washed 4 times with anhydrous ethanol. Then, the microsphere powder was added to an ethanol solution of trimesic acid with a molar concentration of 10 mmol / L and placed in a microwave radiation reactor with a power of 540 W at 45°C for 12 min. The microsphere powder was then separated using a magnet and washed thoroughly with anhydrous ethanol.

[0060] (3) Repeat step (2) 24 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0061] (4) 1.48 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 50 mg palladium chloride, ultrasonically dispersed for 30 min, and then 260 mg of reducing agent glucose was added. The mixture was stirred at room temperature for 3 h. The product was then centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The final core-shell structure composite microparticles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 22 μm, the Zeta potential was 39.17 mV, and the monodispersity index was 0.286.

[0062] Comparative Example 1 (Refer to Example 3, without using an ultrasonic oscillator)

[0063] This comparative example prepared magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structured industrial catalysts according to the following steps:

[0064] (1) Carboxylated chitosan with a viscosity-average molecular weight of 0.92 million, a degree of deacetylation of 93.1%, a C6 carboxylation degree of 70.96%, and an isoelectric point pH of 4.9 was dissolved in a 4% (v / v) acetic acid solution to prepare a 10 mL homogeneous solution with a mass concentration of 2.5%. 250 mg of iron oxide powder with an average particle size of 100 nm and an isoelectric point pH of 6.2 was added, and the solution was allowed to stand for 24 h to remove air bubbles, serving as the aqueous phase. 80 mL of liquid paraffin containing 4.5% (v / v) of the nonionic surfactant Span 80 was placed in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 50 °C, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.4. The mixture was stirred continuously at 520 r / min using a high-speed shear emulsifier for 70 min. Then, 80 mg of the green crosslinking agent genipin was added, and the hydrothermal reaction was carried out for 4 h. The product was centrifuged to remove the upper oil phase, and the crude product was washed five times with petroleum ether and isopropanol, respectively. After drying at 50°C, magnetic carboxylated chitosan microsphere powder was obtained.

[0065] (2) Place 1.5g of microsphere powder in a copper acetate solution with a molar concentration of 8mmol / L and treat at 25°C for 10min. Use a magnet to separate the microsphere powder from the solution, and wash it 4 times with anhydrous ethanol. Then add the microsphere powder to an ethanol solution of trimesic acid with a molar concentration of 12mmol / L, place it in a microwave radiation reactor with a power of 500W and react at 40°C for 10min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0066] (3) Repeat step (2) 18 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0067] (4) 1.22 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 45 mg of palladium chloride and ultrasonically dispersed for 28 min. Then, 240 mg of reducing agent glucose was added, and the mixture was stirred at room temperature for 3 h. The product was then centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The prepared core-shell structure composite particles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 26 μm, the Zeta potential was 30.28 mV, and the monodispersity index was 0.513.

[0068] Comparative Example 2 (Refer to Example 3, without using a green crosslinking agent)

[0069] This comparative example prepared magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structured industrial catalysts according to the following steps:

[0070] (1) Carboxylated chitosan with a viscosity-average molecular weight of 0.92 million, a degree of deacetylation of 93.1%, a C6 carboxylation degree of 70.96%, and an isoelectric point pH of 4.9 was dissolved in a 4% (v / v) acetic acid solution to prepare a 10 mL homogeneous solution with a mass concentration of 2.5%. 250 mg of iron oxide powder with an average particle size of 100 nm and an isoelectric point pH of 6.2 was added, and the mixture was allowed to stand for 24 h to remove air bubbles, serving as the aqueous phase. 80 mL of liquid paraffin containing 4.5% (v / v) of the nonionic surfactant Span 80 was placed in a three-necked flask as the oil phase. The aqueous phase was added dropwise to the oil phase at 50 °C, and then 0.01 mol / L NaOH solution was added dropwise to adjust the pH of the mixture to 5.4. The mixture was stirred continuously at 520 r / min in a high-speed shear emulsifier for 70 min, and then reacted in an ultrasonic oscillator with a frequency of 42 kHz and a power of 650 W for 4 h. The product was centrifuged to remove the upper oil phase, and the crude product was washed five times with petroleum ether and isopropanol, respectively. After drying at 50°C, magnetic carboxylated chitosan microsphere powder was obtained.

[0071] (2) Place 1.5g of microsphere powder in a copper acetate solution with a molar concentration of 8mmol / L and treat at 25°C for 10min. Use a magnet to separate the microsphere powder from the solution, and wash it 4 times with anhydrous ethanol. Then add the microsphere powder to an ethanol solution of trimesic acid with a molar concentration of 12mmol / L, place it in a microwave radiation reactor with a power of 500W and react at 40°C for 10min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol.

[0072] (3) Repeat step (2) 18 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder.

[0073] (4) 1.22 g of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) was placed in an ethanol solution containing 45 mg of palladium chloride and ultrasonically dispersed for 28 min. Then, 240 mg of reducing agent glucose was added, and the mixture was stirred at room temperature for 3 h. The product was then centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst. The prepared core-shell structure composite particles were tested by a particle size scattering analyzer (DLS), and the average particle size range was 29 μm, the Zeta potential was 27.46 mV, and the monodispersity index was 0.475.

[0074] II. Testing the samples obtained in the above embodiments.

[0075] Test Item 1: Particle size test of core-shell composite microparticles prepared with different masses of the green crosslinking agent genipin.

[0076] Particle size, zeta potential, and monodispersity index were measured using dynamic light scattering (DLS), with each sample tested three times. Core-shell composite microparticles obtained by adding different masses of the green crosslinking agent genipin according to the method of Example 3, and core-shell composite microparticles of Comparative Example 1, were dispersed at a mass concentration of 0.1% in a 2% acetic acid (v / v) solution and ultrasonically dispersed for 30 min to obtain five nano-dispersion test samples. The test results are shown in Table 1.

[0077] Table 1. DLS test results of core-shell composite microparticles with different qualities of green crosslinking agent genipin

[0078]

[0079] As shown in Table 1, the core-shell composite microparticles prepared by ultrasonic oscillation with different masses of the green crosslinking agent genipin in this invention have smaller particle size, more uniform size, lower monodispersity coefficient, and stronger stability. Compared with the core-shell composite microparticles with an average particle size of 26 μm obtained without ultrasonic oscillation, the core-shell composite microparticles with different masses of the green crosslinking agent genipin added by ultrasonic oscillation have an average particle size of about 15-20 μm. The nanoparticle size is significantly reduced and the distribution is uniform. This indicates that under ultrasonic-assisted reaction, the stability and chemical activity of magnetic carboxylated chitosan microspheres are significantly improved, enhancing the electrostatic attraction and complexation with the metal-organic framework, which is beneficial to the electrostatic adsorption and reduction of palladium ions, thereby forming a stable core-shell structure industrial catalyst.

[0080] Test Item 2: Scanning Electron Microscopy Analysis of Core-Shell Structure Industrial Catalysts

[0081] The microstructure of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst was analyzed by scanning electron microscopy. Two nano-dispersion samples were taken: the first and second samples were the magnetic carboxylated chitosan microspheres obtained according to step (1) in Example 3 and the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalysts obtained according to steps (1) to (3), respectively. The test results are shown in [reference to relevant documentation]. Figure 2 and Figure 3 .

[0082] from Figure 2 It can be seen that the magnetic carboxylated chitosan microspheres exhibit a regular spherical shape and a relatively smooth surface. Most of the nanospheres are approximately 4–12 μm in size, indicating that the carboxylated chitosan is tightly coated on the exterior of the Fe3O4 nanoparticles through chemical cross-linking and coordination via a green cross-linking agent, forming stable core-shell microspheres. Magnetic carboxylated chitosan microspheres are prepared by combining metal ions and organic ligands through electrostatic attraction and complexation to form a metal-organic framework (MOF), followed by in-situ reduction of palladium particles within the MOF pores. (See Metal-Organic Framework Core-Shell Structure Industrial Catalysts). Figure 3 The entire system exhibits good dispersion stability, with individual composite particles displaying regular spheres of a core-shell structure. Furthermore, the surface of the composite particles is clearly coated with a relatively thick layer of metal-organic framework and palladium. The average particle size distribution of the core-shell structured industrial catalyst is 12–15 μm, indicating that the present invention has prepared a core-shell structured industrial catalyst with small particle size, uniform distribution, strong stability, and high reactivity.

[0083] Test Item 3: Test of Suzuki Coupling Reaction Catalyzed by Magnetic Carboxylated Chitosan Microspheres@Metal-Organic Framework Core-Shell Structure Industrial Catalyst

[0084] 40 mg of magnetic carboxylated chitosan microspheres@metal-organic framework core-shell catalyst, 2 mmol of iodobenzene, 2.4 mmol of phenylboronic acid, 4 mmol of potassium carbonate, and 8 mL of ethanol aqueous solution were added to a round-bottom flask and stirred in a 60 °C oil bath for 90 min. After cooling to room temperature, the mixture was extracted three times with dichloromethane, dried over anhydrous sodium sulfate, and then purified by column chromatography to obtain the product. The catalytic efficiency of the magnetic carboxylated chitosan microspheres@metal-organic framework core-shell catalyst for the Suzuki coupling reaction was expressed by calculating the product yield.

[0085] Depend on Figure 4 As shown in Figure (a), the core-shell structured industrial catalyst disclosed in this invention exhibits catalytic activity for the Suzuki coupling reaction. Furthermore, to a certain extent, the reaction yield increases with the gradual increase in palladium addition (Examples 1, 2, and 3). Example 4 had the highest palladium addition, but the actual reaction yield was lower than that of Example 3. This is because the palladium addition exceeded the maximum loading capacity of the core-shell structure, causing palladium to agglomerate to a certain extent, reducing the actual catalyst surface area participating in the reaction. The catalytic effect of Comparative Example 1, which did not use an ultrasonic oscillator, was significantly lower than that of the examples.

[0086] The core-shell structured industrial catalyst disclosed in this invention was also tested for recovery and repeated catalytic performance. Figure 4 As shown in Figure (b), the results of five repeated catalytic experiments demonstrate that the catalyst has reusable efficacy. The catalyst prepared according to the parameters of Example 3 still exhibited a catalytic effect with a product yield of over 90% after five experiments. The reusability of Comparative Example 1, which did not use an ultrasonic oscillator, was significantly lower than that of the Example.

[0087] Test Item 4: Stability Test of Core-Shell Structure Industrial Catalysts

[0088] Core-shell composite microparticle samples from Comparative Example 2, Example 2, and Example 3 were taken and dispersed in 2% acetic acid (v / v) solution at a mass concentration of 0.4%. 10 mL of each dispersion sample was placed in a 20 mL vial, sealed, and left at room temperature for 14 days. The average particle size and Zeta potential of the nanoparticles were measured at specified time points, and the appearance changes of each sample were compared. The test results are shown in Table 2.

[0089] Table 2. Changes in particle size and potential of core-shell composite microparticles before and after 14 days of settling.

[0090]

[0091] As shown in Table 2, the core-shell composite microparticles in Comparative Example 2, without the addition of a green crosslinking agent, exhibited a significant increase in average particle size within 14 days, along with noticeable sedimentation and agglomeration, resulting in poor stability. In contrast, the core-shell composite microparticles in Examples 2 and 3 showed minimal agglomeration, minimal particle size variation, and strong stability. Therefore, this invention first uses ultrasound-assisted reverse emulsion polymerization and a green crosslinking agent to prepare carboxylated chitosan-coated iron oxide microspheres. Then, a metal-organic framework is grown in situ on the surface of the magnetic carboxylated chitosan microspheres. Finally, the electrostatic attraction and reduction of palladium ions within the pores of the metal-organic framework effectively enhances the stability of the core-shell structured industrial catalyst in solution.

[0092] In summary, carboxylated chitosan-coated iron oxide microspheres were prepared via ultrasound-assisted reverse emulsion polymerization and a green crosslinking agent. A metal-organic framework (MOF) was then grown in situ on the surface of the magnetic carboxylated chitosan microspheres. Palladium ions were subsequently reduced into the pores of the MOF, resulting in a core-shell structured industrial catalyst with uniform particle size, high stability, high catalytic efficiency, magnetic properties, and reusability. This invention is simple, cost-effective, and environmentally friendly. The obtained core-shell structured catalyst exhibits advantages such as high catalytic efficiency and easy magnetic recovery, thus demonstrating its potential for large-scale application.

[0093] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structured industrial catalyst, characterized in that: The core-shell structured industrial catalyst is prepared by encapsulating carboxylated chitosan with iron oxide microspheres using an ultrasound-assisted reverse emulsion polymerization method and a green crosslinking agent to obtain magnetic carboxylated chitosan microspheres. Then, a metal-organic framework is grown in situ on the surface of the magnetic carboxylated chitosan microspheres, and palladium ions are reduced within the pores of the metal-organic framework. The specific steps include: (1) Dissolve carboxychitosan in acetic acid solution with a volume concentration of 2-4% to prepare a homogeneous solution with a mass concentration of 0.5-4.5% (5-10 mL). Add 50-450 mg of iron oxide powder and let stand to remove air bubbles as the aqueous phase. Place 50-100 mL of liquid paraffin containing 2-6% nonionic surfactant in a three-necked flask as the oil phase. Add the aqueous phase solution dropwise to the oil phase at 40-60℃, and then add NaOH solution to adjust the pH of the mixture to 5.4-5.

8. Stir continuously for 0.5-1.5 h at 350-650 r / min using a high-speed shear emulsifier. Then add 25-100 mg of green crosslinking agent and react in an ultrasonic oscillator for 2-5 h. Centrifuge the product to discard the upper oil phase, and then wash the crude product with petroleum ether and isopropanol 3-5 times in sequence. Dry at 40-50℃ to obtain magnetic carboxychitosan microsphere powder. (2) Place 0.4-2.2 g of microsphere powder in a metal ion solution with a concentration of 1-15 mmol / L and treat at 20-30°C for 1-15 min. Use a magnet to separate the microsphere powder from the solution, and wash with anhydrous ethanol 3-4 times. Then add the microsphere powder to an organic ligand solution with a concentration of 1-15 mmol / L and place it in a microwave radiation reactor with a power of 380-600 W at 30-45°C for 2-15 min. Then use a magnet to separate the microsphere powder and wash it thoroughly with anhydrous ethanol. (3) Repeat step (2) 1 to 36 times to obtain in-situ grown metal-organic frameworks. Then, the product is vacuum dried at 60°C to obtain magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure powder. (4) Place 0.32-1.76 g of the magnetic carboxy chitosan microspheres@metal-organic framework core-shell structure powder obtained in step (3) into an ethanol solution containing 30-55 mg of palladium chloride, ultrasonically disperse for 20-30 min, then add 100-300 mg of reducing agent, stir at room temperature for 2-3 h, then centrifuge the product, wash with anhydrous ethanol, and vacuum dry to obtain the magnetic carboxy chitosan microspheres@metal-organic framework core-shell structure industrial catalyst; In step (1), the carboxychitosan has a viscosity-average molecular weight of 0.68–1.59 million, a degree of deacetylation ≥92.4%, a C6 carboxyl degree of 50.62–75.31%, and an isoelectric point pH of 4.9–5.

3. The structural formula of the carboxychitosan is as follows: In step (1), the nonionic surfactant is Span 80 or Tween 80; the green crosslinking agent is genipin, vanillin, glutamic acid, tartaric acid, malic acid or maleic acid.

2. The preparation method according to claim 1, characterized in that: In step (1), the frequency of the ultrasonic oscillator is 30-45kHz and the power is 260-800W.

3. The preparation method according to claim 1, characterized in that: In step (1), the average particle size of the iron oxide is 50-150 nm and the isoelectric point pH is 6.0-6.

8.

4. The preparation method according to claim 1, characterized in that: In step (2), the metal ion solution is an ethanol solution of copper acetate, zinc nitrate or cobalt nitrate; the organic ligand solution corresponding to copper acetate is an ethanol solution of pyromellitic acid, and the organic ligand solutions corresponding to zinc nitrate and cobalt nitrate are both ethanol solutions of 2-methylimidazole.

5. The preparation method according to claim 1, characterized in that: In step (4), the reducing agent is glucose, fructose, galactose, maltose or deoxyribose.

6. A magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structured industrial catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. The core-shell structured industrial catalyst according to claim 6, characterized in that: The magnetic carboxylated chitosan microspheres@metal-organic framework core-shell structure industrial catalyst has a particle size range of 5–25 μm, a Zeta potential of 33.36–45.78 mV, and a monodispersity index of 0.213–0.407.

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