Preparation method of lignin composite magnetic microspheres

Abstract

The present invention relates to the technical field of functional materials, in particular to a preparation method of lignin composite magnetic microspheres, which comprises the following steps: preparing modified lignin microspheres, preparing oleic acid-modified Fe3O4@OA magnetic nanoparticles, preparing modified Fe3O4@DMSA nanoparticles, preparing lignin composite magnetic microspheres, and preparing lignin composite magnetic microspheres with a silica shell. The lignin composite magnetic microspheres prepared by this method are monodisperse microspheres with uniform particle size, good dispersibility and not easy to agglomerate. They not only have high magnetic content, fast magnetic response and stable performance, but more importantly, the composite magnetic microspheres have good biocompatibility, low cytotoxicity, low non-specific adsorption and a simple preparation process, and have broad application prospects in clinical testing, diagnostic analysis, biological separation and drug research.

Description

Technical Field

[0001] The present invention relates to the technical field of functional materials, and particularly to a method for preparing lignin composite magnetic microspheres. Background Art

[0002] Magnetic nanomaterials have long been widely concerned and favored by people. Due to their advantages such as strong loading capacity, high magnetic susceptibility, and good biocompatibility, they have important application values in the fields of biotechnology and biomedical engineering.

[0003] Magnetic microspheres are a type of submicron / micron-sized superparamagnetic particles. According to the different materials compounded with magnetic nanoparticles, they can be divided into organic magnetic microspheres and inorganic magnetic microspheres. Organic magnetic microspheres, also known as magnetic polymer microspheres, are generally monodisperse composite microspheres with magnetic properties and specific structures formed by physically or chemically compounding magnetic nanoparticles with polymers. The most common among them are magnetic microspheres compounded with polystyrene. Such microspheres have mature preparation processes and stable properties, and are currently the most commercially successful magnetic microsphere materials. They have good dispersibility and stability in water, and their surfaces can be chemically modified according to different application requirements, and various organic functional groups such as amino, mercapto, hydroxyl, and carboxyl can be introduced to immobilize various guest molecules such as proteins, nucleic acids, and small molecule substances to achieve different uses. And good paramagnetism enables magnetic microspheres to achieve separation and directional movement under the action of an external magnetic field, and can integrate reaction and separation in the analysis process, simplifying the separation and purification process, and being widely used in life science research fields such as nucleic acid extraction, gene sequencing, cell separation, immunoassay, immobilized enzyme, and chiral separation.

[0004] At present, the research and development of composite magnetic microsphere materials mainly focus on synthetic polymer materials derived from fossil resources, such as magnetic microspheres composite with polystyrene microspheres, magnetic microspheres composite with polymethyl methacrylate microspheres, and magnetic microspheres composite with polystyrene copolymer microspheres. There are still some defects in the magnetic microspheres prepared by such schemes in applications, such as toxicity in organisms, poor long-term stability and biocompatibility. And with the continuous exploitation of fossil fuels, there is ultimately a risk of resource shortage. Therefore, choosing natural biomass-based materials to synthesize magnetic microspheres is a good way to solve the above problems. Lignin is a natural polymer material widely existing in nature, with good biocompatibility, degradability, green environmental protection and non-toxicity, and is simple to extract and low in cost. It is estimated that more than 50 million tons of lignin are produced by the pulp and paper industry every year, and only a very small part is utilized, and the others are mainly used for burning to produce energy, which not only causes great waste of resources but also brings heavy pressure to the environment. Therefore, developing new lignin products to improve the comprehensive utilization value of lignin has become the research focus. There are abundant groups on the surface of lignin, which can be combined with target molecules through physical, chemical, hydrogen bond and other interaction forces. The microspheres synthesized from lignin are ideal carriers for loading magnetic nanoparticles.

[0005] Most of the lignin magnetic composites reported at present are synthesized by the in-situ co-precipitation method. Although the steps are simple, there are problems such as easy aggregation of magnetic materials and uneven particle size, which affect the actual application of the materials. Summary of the Invention

[0006] In order to overcome the deficiencies of the above existing problems, the present invention provides a preparation method of lignin composite magnetic microspheres.

[0007] The technical solution adopted by the present invention to solve its technical problems is: a preparation method of lignin composite magnetic microspheres, characterized by including the following steps:

[0008] S1, Prepare modified lignin microspheres. Take a certain amount of lignin microspheres and disperse them in an aqueous solution of PDDA. Stir at room temperature for 0.5 - 3 h and then centrifuge to obtain an aqueous solution of modified lignin microspheres. The surface of the modified lignin microspheres is positively charged;

[0009] S2, Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles. Take a certain amount of FeCl3 and FeCl2 and dissolve them in an appropriate amount of water. At a certain temperature, add an appropriate amount of ammonia water and stir strongly. After reacting for a period of time, add an appropriate amount of oleic acid and continue to stir for a period of time. Then heat up to 80 - 90 °C and cure for 1 - 2 hours. Then use water and ethanol respectively to magnetically separate and wash repeatedly for 3 - 5 times, and dry.

[0010] S3. Prepare modified Fe3O4@DMSA nanoparticles. Disperse oleic acid-modified Fe3O4@OA magnetic nanoparticles in chloroform, add a certain amount of DMSA, heat under reflux at 60 °C for 12 h, and after centrifugal separation, obtain an aqueous dispersion of modified Fe3O4@DMSA nanoparticles;

[0011] S4. Prepare lignin composite magnetic microspheres. Mix an aqueous solution of modified lignin microspheres with a positive surface charge at a certain concentration and an aqueous dispersion of modified Fe3O4@DMSA nanoparticles with a negative surface charge at a certain concentration. After stirring at room temperature for 0.5 - 24 h, due to the mutual attraction of positive and negative charges, the magnetic modified Fe3O4@DMSA nanoparticles are adsorbed on the surface of the modified lignin microspheres, and then through centrifugal separation, magnetic lignin composite magnetic microspheres with iron oxide nanoparticles adsorbed on the surface are obtained;

[0012] S5. Prepare lignin composite magnetic microspheres with a silica shell. Disperse the lignin composite magnetic microspheres in an ethanol solution, add ammonia water to adjust the pH value to 9 - 10, slowly add TEOS to the system, and after reacting at room temperature for 3 - 10 h, a uniform silica layer can be coated on the surface of the lignin composite magnetic microspheres.

[0013] Since lignin is a renewable polycyclic polymer organic matter, it has a wide source, contains rich aromatic ring structures, aliphatic and aromatic hydroxyl groups, and active groups such as quinone groups and contains many negatively charged groups; the presence of such groups also endows lignin microspheres with good charge properties and the ability to be easily modified. Interacting lignin microspheres with uniform particle size and rich negatively charged groups on the surface with polyelectrolytes with opposite charges can form very stable complexes. The complexes further combine with magnetic nanoparticles with opposite charges on the surface. It can greatly enhance the binding ability of the two, enabling more magnetic nanoparticles to bind very firmly to the surface of the composite lignin microspheres. By simply changing the particle size of the lignin microspheres, a series of lignin composite magnetic microspheres with different sizes can be obtained.

[0014] Using biomass resource lignin microspheres to replace traditional polymer microspheres can not only solve the problems of poor toxicity and biocompatibility of magnetic microspheres, but also reduce production costs and improve the comprehensive utilization value of lignin.

[0015] The lignin composite magnetic microspheres prepared by the method of the present invention can be used in life science research fields such as nucleic acid extraction, gene sequencing, cell separation, immunoassay, immobilized enzyme, and chiral separation.

[0016] According to another embodiment of the present invention, it further includes that the particle size of the lignin microspheres described in S1 is 80 - 2000 nm.

[0017] According to another embodiment of the present invention, it further includes that the particle size of the Fe3O4@OA magnetic nanoparticles in S2 is 5-15 nm.

[0018] According to another embodiment of the present invention, it further includes that the concentration of the PDDA aqueous solution in S1 is 3-10 mg / ml.

[0019] According to another embodiment of the present invention, it further includes that the concentration of the modified Fe3O4@DMSA nanoparticle dispersion in S3 is 3-10 mg / ml.

[0020] According to another embodiment of the present invention, it further includes that the mass ratio of the modified Fe3O4@DMSA nanoparticles to the modified lignin microspheres in S4 is 0.1-1.

[0021] According to another embodiment of the present invention, it further includes that the mass ratio of the addition amount of TEOS to the lignin composite magnetic microspheres in S5 is 1-5.

[0022] The beneficial effects of the present invention are that the lignin composite magnetic microspheres prepared by this method are monodisperse microspheres with uniform particle size, good dispersibility and not easy to agglomerate. They not only have high magnetic content, fast magnetic response and stable performance, but more importantly, the composite magnetic microspheres have good biocompatibility, low cytotoxicity, low non-specific adsorption and simple preparation process, and have broad application prospects in clinical testing, diagnostic analysis, biological separation and drug research. Specific embodiments

[0023] Example 1:

[0024] S1, Prepare modified lignin microspheres:

[0025] Dissolve enzymatic lignin in acetone to prepare a solution with a concentration of 1 mg / ml, heat it to 35 °C, add deionized water dropwise to the system at a dropping rate of 6 ml / min, and the volume ratio of water to acetone is 4:6. After dropping, centrifuge and wash to obtain lignin microspheres with an average particle size of 80 nm. Take 5 g of lignin microspheres and disperse them in 100 ml of PDDA aqueous solution with a concentration of 5 mg / ml, stir at room temperature for 2 h, centrifuge and separate to obtain modified lignin microspheres, and disperse them in an aqueous solution for standby.

[0026] S2, Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0027] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat the reaction system to 70 °C, after reacting for 30 minutes, add 5 ml of oleic acid, and then continue to react for 2 hours, after which the reaction ends. Wash the obtained product with water and ethanol repeatedly through an external magnetic field, and then dry it into powder under vacuum.

[0028] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0029] Prepare modified Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to make a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO and mix evenly, then add it to the above Fe3O4@OA dispersion, heat and reflux at 60 °C for 12 h. After the reaction ends, centrifuge and separate with ethanol 3 times, and finally disperse it in 20 ml of water to obtain a high-concentration water-dispersible modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, prepare a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugation and washing, and disperse them in an aqueous solution for standby.

[0030] S4. Prepare lignin composite magnetic microspheres:

[0031] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, stir at room temperature for 12 h, then centrifuge and separate to remove the upper-layer solution to obtain Fe3O4-modified lignin composite magnetic microspheres;

[0032] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0033] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to make a dispersion with a solid content of 0.5%, add ammonia water to adjust the pH value to 9 - 10, add 1 g of TEOS to the system, after reacting for 5 h, modify a silica layer on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres wrapped with silica with a particle size of 100 nm.

[0034] Example 2:

[0035] S1. Prepare modified lignin microspheres:

[0036] Dissolve enzymatically hydrolyzed lignin in acetone to prepare a solution with a concentration of 2 mg / ml. Heat the solution to 35 °C, and add deionized water dropwise to the system at a dropping rate of 4 ml / min. The volume ratio of water to acetone is 4:6. After the addition is complete, centrifuge and wash to obtain lignin microspheres with an average particle size of 180 nm. Take 5 g of lignin microspheres and disperse them in 100 ml of an aqueous solution of PDDA with a concentration of 5 mg / ml. Stir at room temperature for 2 h, and then centrifuge to obtain modified lignin microspheres, which are dispersed in an aqueous solution for later use.

[0037] S2. Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0038] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat the reaction system to 70 °C, and react for 30 minutes. Then add 5 ml of oleic acid, and continue to react for 2 hours. After the reaction is completed, wash the obtained product with water and ethanol repeatedly under an external magnetic field, and then dry it in vacuum to obtain a powder.

[0039] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0040] Prepare modified Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to prepare a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO, mix evenly, and then add it to the above Fe3O4@OA dispersion. Heat and reflux at 60 °C for 12 h. After the reaction is completed, centrifuge and separate with ethanol 3 times, and finally disperse it in 20 ml of water to obtain a high-concentration water-dispersible modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, prepare a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugations and washings, which are dispersed in an aqueous solution for later use.

[0041] S4. Prepare lignin composite magnetic microspheres:

[0042] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a dispersion of modified Fe3O4@DMSA nanoparticles with a concentration of 5 mg / ml, stir at room temperature for 12 h, and then centrifuge to remove the upper layer solution to obtain Fe3O4-modified lignin composite magnetic microspheres;

[0043] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0044] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to prepare a dispersion with a solid content of 0.5%. Add ammonia water to adjust the pH value to 9 - 10. Add 2 g of TEOS to the system. After reacting for 5 h, a silica layer is modified on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres wrapped with silica with a particle size of 200 nm.

[0045] Example 3:

[0046] S1. Prepare modified lignin microspheres:

[0047] Dissolve enzymatically hydrolyzed lignin in acetone to prepare a solution with a concentration of 5 mg / ml. Heat to 35 °C. Add deionized water dropwise to the system at a dropping rate of 0.25 ml / min. The volume ratio of water to acetone is 4:6. After dropping, centrifuge and wash to obtain lignin microspheres with an average particle size of 450 nm. Take 5 g of lignin microspheres and disperse them in 100 ml of an aqueous PDDA solution with a concentration of 5 mg / ml. Stir at room temperature for 2 h, and then centrifuge to obtain modified lignin microspheres, which are dispersed in an aqueous solution for standby.

[0048] S2. Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0049] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat the reaction system to 70 °C, after reacting for 30 minutes, add 5 ml of oleic acid, and then continue to react for 2 hours. After the reaction ends, wash the obtained product with water and ethanol repeatedly by applying an external magnetic field, and then dry it in vacuum to form a powder.

[0050] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0051] Prepare modified Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to prepare a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO and mix evenly, then add it to the above Fe3O4@OA dispersion, heat and reflux at 60 °C for 12 h. After the reaction ends, centrifuge and separate with ethanol 3 times, and finally disperse it in 20 ml of water to obtain a high-concentration water-dispersible modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, prepare a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugations and washings, which are dispersed in an aqueous solution for standby.

[0052] S4. Prepare lignin composite magnetic microspheres:

[0053] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a dispersion of modified Fe3O4@DMSA nanoparticles with a concentration of 5 mg / ml. After stirring at room temperature for 12 h, centrifuge and separate to remove the upper solution, obtaining Fe3O4-modified lignin composite magnetic microspheres.

[0054] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0055] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to make a dispersion with a solid content of 0.5%. Add ammonia water to adjust the pH value to 9 - 10. Add 3 g of TEOS to the system. After reacting for 5 h, modify a silica layer on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres encapsulated with silica with a particle size of 500 nm.

[0056] Example 4:

[0057] S1. Prepare modified lignin microspheres:

[0058] Dissolve enzymatic lignin in acetone to prepare a solution with a concentration of 10 mg / ml. Heat up to 35 °C, and add deionized water dropwise to the system at a dropping rate of 0.125 ml / min. The volume ratio of water to acetone is 4:6. After dropping, centrifuge and wash to obtain lignin microspheres with an average particle size of 900 nm. Take 5 g of lignin microspheres and disperse them in 100 ml of an aqueous solution of PDDA with a concentration of 5 mg / ml. Stir at room temperature for 2 h, centrifuge and separate to obtain modified lignin microspheres, which are dispersed in an aqueous solution for standby.

[0059] S2. Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0060] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat up the reaction system to 70 °C. After reacting for 30 minutes, add 5 ml of oleic acid, and then continue to react for 2 h. After the reaction ends, wash the obtained product with water and ethanol repeatedly by applying an external magnetic field, dry it in vacuum to form a powder, and then weigh a certain amount of the powder, 1 g, and disperse it in 100 ml of chloroform.

[0061] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0062] Modifying Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to make a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO, mix well, and then add it to the above Fe3O4@OA dispersion. Heat and reflux at 60 °C for 12 h. After the reaction, centrifuge and separate with ethanol three times, and finally disperse in 20 ml of water to obtain a high-concentration water-dispersed modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, prepare a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugation and washing, and disperse them in an aqueous solution for standby.

[0063] S4. Prepare lignin composite magnetic microspheres:

[0064] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, stir at room temperature for 12 h, then centrifuge and separate to remove the upper solution to obtain Fe3O4-modified lignin composite magnetic microspheres.

[0065] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0066] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to make a dispersion with a solid content of 0.5%, add ammonia water to adjust the pH value to 9 - 10, add 4 g of TEOS to the system, and after reacting for 5 h, modify a silica layer on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres wrapped with silica with a particle size of 950 nm.

[0067] Example 5:

[0068] S1. Prepare modified lignin microspheres:

[0069] Dissolve enzymatically hydrolyzed lignin in acetone to prepare a solution with a concentration of 15 mg / ml, heat to 35 °C, add deionized water dropwise to the system at a dropping rate of 0.65 ml / min, with a volume ratio of water to acetone of 4:6. After dropping, centrifuge and wash to obtain lignin microspheres with an average particle size of 2 μm. Take 5 g of lignin microspheres and disperse them in 100 ml of an aqueous solution of PDDA with a concentration of 5 mg / ml, stir at room temperature for 2 h, centrifuge and separate to obtain modified lignin microspheres, and disperse them in an aqueous solution for standby.

[0070] S2. Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0071] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat the reaction system to 70 °C, after reacting for 30 minutes, add 5 ml of oleic acid, and then continue to react for 2 hours, and the reaction ends. The obtained product is washed repeatedly with water and ethanol by means of an external magnetic field, dried in vacuum to form a powder, and then a certain amount of the powder, 1 g, is weighed and dispersed in 100 ml of chloroform.

[0072] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0073] Prepare modified Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by the ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to make a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO, mix evenly, and then add it to the above Fe3O4@OA dispersion. Heat and reflux at 60 °C for 12 h. After the reaction ends, centrifuge and separate with ethanol 3 times, and finally disperse it in 20 ml of water to obtain a high-concentration water-dispersible modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml is prepared, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugation and washing, and disperse them in an aqueous solution for standby.

[0074] S4. Prepare lignin composite magnetic microspheres:

[0075] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, stir at room temperature for 12 h, then centrifuge and separate to remove the upper layer solution to obtain Fe3O4-modified lignin composite magnetic microspheres;

[0076] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0077] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to make a dispersion with a solid content of 0.5%, add ammonia water to adjust the pH value to 9 - 10, add 4 g of TEOS to the system, after reacting for 5 h, modify a silica layer on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres wrapped with silica with a particle size of 20 - 50 nm.

[0078] Example 6:

[0079] S1. Prepare modified lignin microspheres:

[0080] Dissolve enzymatically hydrolyzed lignin in acetone to prepare a solution with a concentration of 10 mg / ml. Heat the solution to 35 °C, and add deionized water dropwise to the system at a dropping rate of 0.130 ml / min. The volume ratio of water to acetone is 4:6. After the addition is complete, centrifuge and wash to obtain lignin microspheres with an average particle size of 900 nm. Take 5 g of lignin microspheres and disperse them in 100 ml of an aqueous PDDA solution with a concentration of 5 mg / ml. Stir at room temperature for 2 h, and then centrifuge to obtain modified lignin microspheres, which are dispersed in an aqueous solution for later use.

[0081] S2. Prepare oleic acid-modified Fe3O4@OA magnetic nanoparticles:

[0082] Dissolve 0.2 mol of FeCl3 and 0.1 mol of FeCl2 in 500 ml of water, stir evenly, add ammonia water to adjust the pH value to 10, heat the reaction system to 70 °C, and react for 30 minutes. Then add 5 ml of oleic acid, and continue to react for 2 hours. After the reaction is completed, wash the obtained product with water and ethanol repeatedly under an external magnetic field, and then dry it in vacuum to form a powder. Then weigh a certain amount of the powder, 1 g, and disperse it in 100 ml of chloroform.

[0083] S3. Prepare modified Fe3O4@DMSA nanoparticles:

[0084] Prepare modified Fe3O4@DMSA nanoparticles with a water-dispersible outer layer of DMSA by ligand exchange method. Weigh 1 g of Fe3O4@OA magnetic nanoparticles and disperse them in 100 ml of chloroform to form a Fe3O4@OA dispersion. Dissolve 0.5 ml of DMSA in 100 ml of DMSO, mix evenly, and then add it to the above Fe3O4@OA dispersion. Heat and reflux at 60 °C for 12 h. After the reaction is completed, centrifuge and separate with ethanol 3 times, and finally disperse it in 20 ml of water to obtain a high-concentration water-dispersible modified Fe3O4@DMSA nanoparticle dispersion. After magnetic separation and washing, prepare a modified Fe3O4@DMSA nanoparticle dispersion with a concentration of 5 mg / ml, that is, stir at room temperature for 2 h, and obtain modified Fe3O4@DMSA nanoparticles after multiple centrifugations and washings, which are dispersed in an aqueous solution for later use.

[0085] S4. Prepare lignin composite magnetic microspheres:

[0086] Mix 100 ml of an aqueous solution of modified lignin microspheres with a concentration of 10 mg / ml and 100 ml of a dispersion of modified Fe3O4@DMSA nanoparticles with a concentration of 5 mg / ml, stir at room temperature for 12 h, and then centrifuge to remove the upper layer solution to obtain Fe3O4-modified lignin composite magnetic microspheres;

[0087] S5. Prepare lignin composite magnetic microspheres with a silica shell:

[0088] Disperse 1 g of lignin composite magnetic microspheres in 200 ml of ethanol to prepare a dispersion with a solid content of 0.5%. Add ammonia water to adjust the pH value to 9 - 10. Add 1 g of TEOS to the system. After reacting for 5 h, a silica layer is modified on the surface of the lignin composite magnetic microspheres to obtain lignin composite magnetic microspheres encapsulated with silica with a particle size of 200 nm.

[0089] PDDA is poly(diallyldimethylammonium chloride).

[0090] DMSO is dimethyl sulfoxide.

[0091] DMSA is dimercaptosuccinic acid.

[0092] TEOS is tetraethyl orthosilicate.

[0093] FeCl2 is ferrous chloride.

[0094] FeCl3 is ferric chloride.

[0095] Preferably, the particle size of the lignin microspheres described in S1 is 80 - 2000 nm.

[0096] Preferably, the particle size of the Fe3O4@OA magnetic nanoparticles described in S2 is 5 - 15 nm.

[0097] Preferably, the concentration of the PDDA aqueous solution described in S1 is 3 - 10 mg / ml, and the more preferred concentration is 5 mg / ml.

[0098] Preferably, the concentration of the modified Fe3O4@DMSA nanoparticle dispersion described in S3 is 3 - 10 mg / ml, and the more preferred concentration is 5 mg / ml.

[0099] Preferably, the mass ratio of the modified Fe3O4@DMSA nanoparticles to the modified lignin microspheres described in S4 is 0.1 - 1.

[0100] Preferably, the mass ratio of the addition amount of TEOS to the lignin composite magnetic microspheres described in S5 is 1 - 5.

[0101] The above description is illustrative rather than restrictive to the present invention. Those of ordinary skill in the art understand that many modifications, variations or equivalents can be made without departing from the spirit and scope defined by the appended claims, and all of them will fall within the protection scope of the present invention.

Claims

1. A method for preparing lignin composite magnetic microspheres, characterized in that, It includes the following steps: S1. Prepare modified lignin microspheres. Take a certain amount of lignin microspheres and disperse them in an aqueous solution of PDDA. After stirring at room temperature for 0.5 - 3 h, perform centrifugal separation to obtain an aqueous solution of modified lignin microspheres. The surface of the modified lignin microspheres is positively charged; S2. Prepare oleic acid - modified Fe3O4@OA magnetic nanoparticles. Take a certain amount of FeCl3 and FeCl2 and dissolve them in an appropriate amount of water. At a certain temperature, add an appropriate amount of ammonia water and stir strongly. After reacting for a period of time, add an appropriate amount of oleic acid and continue to stir for a period of time. Then heat up to 80 - 90 °C for ripening for 1 - 2 h. Then, use water and ethanol respectively, and perform magnetic separation and washing repeatedly for 3 - 5 times, and then dry; S3. Prepare modified Fe3O4@DMSA nanoparticles. Disperse the oleic acid - modified Fe3O4@OA magnetic nanoparticles in chloroform, add a certain amount of DMSA, and heat - reflux at 60 °C for 12 h. After centrifugal separation, obtain an aqueous - dispersed modified Fe3O4@DMSA nanoparticle dispersion; S4. Prepare lignin - composite magnetic microspheres. Mix an aqueous solution of modified lignin microspheres with a certain concentration and a dispersion of modified Fe3O4@DMSA nanoparticles with a certain concentration and a negatively charged surface at room temperature and stir for 0.5 - 24 h. Through the attraction of positive and negative charges, the magnetic modified Fe3O4@DMSA nanoparticles are adsorbed on the surface of the modified lignin microspheres. Then, through centrifugal separation, obtain magnetic lignin - composite magnetic microspheres with magnetite nanoparticles adsorbed on the surface; S5. Prepare lignin - composite magnetic microspheres with a silica shell. Disperse the lignin - composite magnetic microspheres in an ethanol solution, add ammonia water to adjust the pH value to 9 - 10, and slowly add TEOS to the system. After reacting at room temperature for 3 - 10 h, a uniform silica layer can be coated on the surface of the lignin - composite magnetic microspheres; The particle size of the lignin microspheres described in S1 is 80 - 2000 nm; The particle size of the Fe3O4@OA magnetic nanoparticles described in S2 is 5 - 15 nm; The concentration of the modified Fe3O4@DMSA nanoparticle dispersion described in S3 is 3 - 10 mg / ml; The mass ratio of the modified Fe3O4@DMSA nanoparticles to the modified lignin microspheres described in S4 is 0.1 - 1; The PDDA is poly(diallyldimethylammonium chloride), and the DMSA is dimercaptosuccinic acid.

2. The method for preparing lignin composite magnetic microspheres according to claim 1, characterized in that, The concentration of the PDDA aqueous solution described in S1 is 3 - 10 mg / ml.

3. The method for preparing lignin composite magnetic microspheres according to claim 1, characterized in that, The mass ratio of the addition amount of TEOS to the lignin - composite magnetic microspheres described in S5 is 1 - 5.