Core-shell structured ferroferric oxide@lignin nanospheres, preparation method and application thereof

Abstract

This invention discloses core-shell structured iron(III) oxide@lignin nanospheres, their preparation method, and applications. The invention involves uniformly mixing a lignin solution and a monodisperse iron(III) oxide nanoparticle solution, followed by stirring to evaporate the organic solvent, resulting in a monodisperse iron(III) oxide@lignin nanosphere suspension. The core-shell structured iron(III) oxide@lignin nanospheres are then separated using a magnet. This method is simple, requires no cumbersome modification of lignin, operates under mild conditions, and allows for solvent recovery through condensation and liquefaction, aligning with sustainable chemistry principles. It facilitates the large-scale preparation of iron(III) oxide@lignin nanospheres. The prepared iron(III) oxide@lignin nanospheres exhibit excellent dispersibility and uniformity, effectively enhancing the stability of the magnetic nanoparticles. Under an external magnetic field, they display vibrant structural colors, demonstrating significant application potential in advanced optics.

Description

Technical Field

[0001] This invention belongs to the field of biomass composite materials technology, specifically relating to core-shell structured iron(III) oxide@lignin nanospheres, their preparation methods, and applications. Background Technology

[0002] Lignin is a abundant natural polymer found in plants and has wide applications in biomedicine, energy, cosmetics, and construction. Lignin nanospheres, in particular, exhibit good size controllability, antioxidant properties, water dispersibility, and stability, demonstrating significant potential value in natural polymer-based structural color materials. Currently, lignin-based photonic crystals typically require first modifying or fractionating lignin to prepare nanospheres of uniform size, followed by construction using external forces such as centrifugal force. However, controlling the color of photonic crystals necessitates synthesizing a series of nanospheres of different sizes, which hinders their practical application.

[0003] Colloidal photonic crystals made of iron(III) oxide (Fe3O4), with their highly negatively charged surface, have been shown to allow for the creation of photonic crystals of different colors simply by adjusting the distance between particles through a magnetic field, due to their non-dense packing structure and high dispersibility. However, iron(III) oxide exhibits poor chemical and colloidal stability during use or long-term storage, inevitably requiring a protective shell of synthetic polymers or inorganic materials, which contradicts current trends towards sustainability and health. The co-assembly of iron(III) oxide with lignin to prepare core-shell nanospheres not only improves the stability of iron(III) oxide but also enables the controllable construction of lignin-based photonic crystals. Existing methods for preparing iron(III) oxide@lignin nanospheres or other inorganic materials@lignin nanospheres still face technical challenges such as difficulty in controlling the number of cores, poor coating effects, and the need for cumbersome chemical modification of lignin. Therefore, there is an urgent need to develop a simple and green method to achieve efficient and controllable preparation of monodisperse iron(III) oxide@lignin nanospheres, which is of great significance for promoting the research of lignin-based structural color materials in the field of advanced optics. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the primary objective of this invention is to provide a method for preparing core-shell structured iron(III) oxide@lignin nanospheres.

[0005] A simple, mild, and scalable method for preparing core-shell structured iron(III) oxide@lignin nanospheres is disclosed. The method involves a one-pot synthesis of iron(III) oxide with a highly negatively charged surface, followed by assembly using it as the assembly core in a volatile organic solvent / water binary solvent. A simple stirring-evaporation method is then employed to prepare magnetic nanospheres with regular morphology and uniform size. These monodisperse magnetic nanospheres combine the superparamagnetism of iron(III) oxide with the antioxidant properties and high dispersibility of nano-lignin, and can form brightly colored photonic crystals under an external magnetic field.

[0006] Another object of the present invention is to provide core-shell structured iron(III) oxide@lignin nanospheres prepared by the above preparation method.

[0007] Another object of the present invention is to provide the application of the above-mentioned core-shell structured iron(III) oxide@lignin nanospheres in colloidal photonic crystals.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for preparing core-shell structured iron(III) oxide@lignin nanospheres includes the following steps:

[0010] (1) Mix lignin with a binary solvent of organic solvent / water to obtain a lignin solution;

[0011] (2) Mix the monodisperse iron oxide nanoparticle solution with the lignin solution evenly, and then stir to evaporate the organic solvent to obtain an iron oxide@lignin nanosphere suspension. Separate the suspension with a magnet to obtain core-shell structured iron oxide@lignin nanospheres.

[0012] Preferably, the lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, lignin sulfate, and organic solvent lignin; more preferably, the lignin is at least one of alkali lignin and enzymatically hydrolyzed lignin.

[0013] Preferably, the organic solvent in step (1) is at least one of tetrahydrofuran, ethanol, acetone, methanol and N,N-dimethylformamide; more preferably, the organic solvent is at least one of tetrahydrofuran and ethanol.

[0014] Preferably, the ratio of lignin to water in step (1) is (1-4) mg: 1 mL.

[0015] Preferably, the volume ratio of the organic solvent to water in step (1) is 1:1 to 50:1; more preferably, the volume ratio of the organic solvent to water is 4:3.

[0016] Preferably, the method of uniform mixing in steps (1) and (2) is ultrasonic dispersion.

[0017] Preferably, the solvent for the monodisperse iron oxide nanoparticle solution in step (2) is water.

[0018] Preferably, the concentration of the monodisperse iron oxide nanoparticle solution in step (2) is 5-60 mg / mL; more preferably, it is 10 mg / mL.

[0019] Preferably, in step (2), the mass ratio of iron oxide nanoparticles to lignin is 1:(1.5-6).

[0020] Preferably, the stirring and evaporation of organic solvent in step (2) is carried out by mechanical stirring, the stirring speed is 200-800 rpm, the stirring time is 6-18 h, and the organic solvent is basically completely evaporated after stirring.

[0021] Preferably, the monodisperse iron oxide nanoparticle solution in step (2) is prepared by the following method:

[0022] Anhydrous ferric chloride, alkaline organic salt, a polymer containing carboxyl or amino groups with a molecular weight of 6000–20000 g / mol, a reducing agent, water, and an organic solvent are mixed and dissolved. An inorganic alkali is then added and dissolved. A hydrothermal reaction is carried out, and magnetic nanoparticles are obtained by magnetic separation. After washing, they are dispersed in water.

[0023] More preferably, the alkaline organic salt is at least one of anhydrous sodium acetate, anhydrous sodium citrate, and anhydrous sodium succinate; the polymer containing carboxyl or amino groups with a molecular weight of 6000-20000 g / mol is at least one of sodium poly(4-styrenesulfonic acid-conmaleic acid), polyvinylpyrrolidone, and sodium polyacrylate; the reducing agent is at least one of L-ascorbic acid and tauroursodeoxycholic acid; the organic solvent is at least one of ethylene glycol, n-butanol, and butanediol; and the inorganic base is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0024] More preferably, the ratio of anhydrous ferric chloride, alkaline organic salt, polymer containing carboxyl or amino groups with a molecular weight of 6000-20000 g / mol, reducing agent, water, organic solvent and inorganic base is 0.13-0.52 g: 0.6-2.4 g: 0.2-0.8 g: 3-6 mg: 10-60 μL: 8-32 mL: 0.12-0.48 g.

[0025] More preferably, the hydrothermal reaction is carried out at a temperature of 150–250°C for a duration of 6–18 hours.

[0026] More preferably, the monodisperse iron oxide nanoparticle solution in step (2) is prepared by the following method:

[0027] Anhydrous ferric chloride, anhydrous sodium acetate, sodium poly(4-styrenesulfonic acid-conmaleic acid), L-ascorbic acid, water, and ethylene glycol were mixed and dissolved in sequence. Sodium hydroxide was then added and dissolved. A hydrothermal reaction was carried out, and magnetic nanoparticles were obtained by magnetic separation. After washing, the nanoparticles were dispersed in water.

[0028] More preferably, the ratio of anhydrous ferric chloride, anhydrous sodium acetate, sodium poly(4-styrenesulfonic acid-conmaleic acid), L-ascorbic acid, water, ethylene glycol and sodium hydroxide is 0.26g:1.2g:0.4g:4.5mg:20μL:16mL:0.24g.

[0029] More preferably, the washing refers to washing with an ethanol / water mixture and ultrapure water 1 to 5 times respectively.

[0030] More preferably, in the ethanol / water mixture, the volume ratio of ethanol to water is 0.3 to 1.2:1.

[0031] The core-shell structured iron(III) oxide@lignin nanospheres prepared by the above method.

[0032] Application of core-shell structured iron(III) oxide@lignin nanospheres prepared by the above method in colloidal photonic crystals.

[0033] This invention uses monodisperse superparamagnetic nanoparticles as the core and utilizes the self-assembly behavior of lignin in an organic solvent / water binary system. A simple stirring and volatilization method is used to grow lignin with magnetic nanoparticles as the core, avoiding the occurrence of multinucleation or agglomeration, to obtain monodisperse iron(III) oxide@lignin nanospheres. The lignin as a shell can effectively improve the colloidal and chemical stability of the magnetic nanoparticles.

[0034] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0035] (1) This invention provides a method for preparing iron oxide@lignin nanospheres, which does not require complicated modification of lignin, has the advantages of simple process and mild conditions, and can recover solvent by condensation and liquefaction, which is in line with the concept of sustainable chemistry and is easy to realize the large-scale preparation of iron oxide@lignin nanospheres.

[0036] (2) In the process of coating lignin with iron oxide nanoparticles, the present invention differs from the traditional preparation method of lignin nanospheres (solvent-antisolvent method) by using a stirring method to evaporate the solvent. In the coating reaction process, no additional antisolvent needs to be introduced, thereby avoiding the occurrence of multinucleation or aggregation of magnetic nanoparticles.

[0037] (3) The iron oxide@lignin nanospheres prepared by the present invention have excellent dispersibility and uniformity, and effectively improve the stability of magnetic nanoparticles. They can exhibit beautiful structural colors under the action of an external magnetic field and have great application prospects in the field of advanced optics. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope image of the iron(II) oxide@lignin nanospheres prepared by the method in Example 1.

[0039] Figure 2 This is a transmission electron microscope (TEM) image of the iron(III) oxide@lignin nanospheres prepared by the method in Example 1.

[0040] Figure 3 This is a particle size distribution diagram of the iron(III) oxide@lignin nanospheres prepared by the method in Example 1.

[0041] Figure 4 The image shows the hysteresis loop diagrams of the iron oxide nanoparticles and iron oxide@lignin nanospheres prepared by the method in Example 1.

[0042] Figure 5 This is a photographic image of the photonic crystal of the iron(III) oxide@lignin nanospheres prepared by the method in Example 1 under the action of a magnetic field.

[0043] Figure 6 This is a scanning electron microscope image of the iron(II) oxide@lignin nanospheres prepared by the method in Example 2.

[0044] Figure 7 This is a scanning electron microscope image of the iron(II) oxide@lignin nanospheres prepared by the method in Example 3.

[0045] Figure 8 The particle size distributions are for the iron oxide nanoparticles and iron oxide@lignin nanospheres prepared by the methods in Examples 4-6.

[0046] Figure 9 The image shows a scanning electron microscope (SEM) image of the iron(III) oxide@lignin nanospheres prepared by the method in Comparative Example 1.

[0047] Figure 10 The image shows a scanning electron microscope (SEM) image of the iron(III) oxide@lignin nanospheres prepared by the method in Comparative Example 2. Detailed Implementation

[0048] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0049] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0050] Example 1

[0051] A method for preparing core-shell structured iron(III) oxide@lignin nanospheres includes the following steps:

[0052] (1) 0.26 g anhydrous ferric chloride, 1.2 g anhydrous sodium acetate, 0.4 g sodium poly(4-styrenesulfonic acid-conmaleic acid) (purchased from Aladdin, catalog number P107093), 4.5 mg L-ascorbic acid, and 20 μL ultrapure water were sequentially added to 16 mL of ethylene glycol and stirred with a magnetic stirrer (600 rpm) until completely dissolved. Then, 0.24 g sodium hydroxide was added, and stirring was continued at the same stirring speed until completely dissolved. The resulting solution was transferred to a 25 mL hydrothermal reactor and reacted at 190 °C for 9 h. After cooling to room temperature, the obtained magnetic nanoparticles were separated by magnetism and washed three times with 15 mL of ethanol / ultrapure water mixed solvent (volume ratio 1:1) and 15 mL of ultrapure water, respectively, to obtain 125 mg of iron(III) oxide nanoparticles, which were finally dispersed in 12.5 mL of ultrapure water.

[0053] (2) Take 90 mg of alkali lignin and place it in a 100 mL beaker. Add 70 mL of tetrahydrofuran / ultrapure water binary solvent (volume ratio 4:3) and sonicate for 5 min until the alkali lignin is completely dissolved to obtain a lignin solution.

[0054] (3) Add 2 mL of the iron oxide nanoparticle dispersion obtained in step (1) to the lignin solution obtained in step (2), sonicate for 5 min to completely disperse it, and then stir continuously at 400 rpm for 6 h with a mechanical stirrer. After the tetrahydrofuran in the mixture has completely evaporated, separate it with a magnet to obtain iron oxide@lignin nanospheres.

[0055] Figure 1 This is a scanning electron microscope image of the iron(II) oxide@lignin nanospheres prepared in Example 1 of the present invention. Figure 2 This is a transmission electron microscope (TEM) image of the iron(II) oxide@lignin nanospheres prepared in Example 1 of this invention. Figure 3 This is a particle size distribution diagram of the iron(III) oxide@lignin nanospheres prepared in Example 1 of the present invention. Figure 4 The image shows the hysteresis loop diagrams of the iron oxide nanoparticles and iron oxide@lignin nanospheres prepared by the method in Example 1 of this invention. Figure 5 This is a photographic image of the photonic crystal of the iron(III) oxide@lignin nanospheres prepared by the method in Example 1 of this invention under the influence of a magnetic field. Figure 1 and Figure 2It can be seen that the iron(III) oxide@lignin nanospheres prepared by the method of the present invention have uniform size and regular morphology, and the iron(III) oxide nanoparticles are uniformly coated with lignin. As shown in Figure 3, the average size of the iron(III) oxide@lignin nanospheres prepared in Example 1 of the present invention is 183.7 nm, and the polydispersity index is only 0.059. Figure 4 It is evident that the magnetite@lignin nanospheres prepared in this invention retain superparamagnetism even after lignin coating. Under the influence of a common strong magnet, the magnetite@lignin nanospheres prepared in this invention can be assembled into brightly colored structural color materials, and the magnetic strength can be controlled by changing the distance between the magnet and the sample, thereby obtaining… Figure 5 .

[0056] Example 2

[0057] A method for preparing core-shell structured iron(III) oxide@lignin nanospheres is basically the same as the preparation method in Example 1, except that the lignin raw material in Example 2 is enzymatically hydrolyzed lignin.

[0058] Figure 6 This is a scanning electron microscope image of the iron(III) oxide@lignin nanospheres prepared in Example 2 of the invention. Testing showed that the iron(III) oxide@lignin nanospheres prepared in Example 2 were of uniform size and regular morphology, and the iron(III) oxide nanoparticles were uniformly coated with lignin, showing no significant change compared to Example 1.

[0059] Example 3

[0060] A method for preparing core-shell structured iron(III) oxide@lignin nanospheres is basically the same as the preparation method in Example 1, except that the organic solvent in Example 3 is ethanol.

[0061] Figure 7 This is a scanning electron microscope image of the iron(III) oxide@lignin nanospheres prepared in Example 3 of the invention. Testing showed that the iron(III) oxide@lignin nanospheres prepared in Example 3 were of uniform size and regular morphology, and the iron(III) oxide nanoparticles were uniformly coated with lignin, showing no significant change compared to Example 1.

[0062] Examples 4-6

[0063] A method for preparing core-shell structured iron(III) oxide@lignin nanospheres is basically the same as the preparation method in Example 1, except that by adjusting the amount of lignin used in the preparation process (30, 60, 120 mg), core-shell structured iron(III) oxide@lignin nanospheres of different sizes were prepared.

[0064] Figure 8The particle size distributions are shown for the iron(III) oxide nanoparticles and iron(III) oxide@lignin nanospheres prepared by the methods in Examples 4-6. Testing revealed that the iron(III) oxide@lignin nanospheres obtained in Examples 4-6 were all larger than the iron(III) oxide nanoparticles, and their size increased with increasing initial lignin concentration.

[0065] Comparative Example 1

[0066] A method for preparing iron(III) oxide@lignin nanospheres includes the following steps:

[0067] (1) 0.26 g anhydrous ferric chloride, 1.2 g anhydrous sodium acetate, 0.4 g sodium poly(4-styrenesulfonic acid-conmaleic acid) (purchased from Aladdin, catalog number P107093), 4.5 mg L-ascorbic acid, and 20 μL ultrapure water were sequentially added to 16 mL of ethylene glycol and stirred with a magnetic stirrer (600 rpm) until completely dissolved. Then, 0.24 g sodium hydroxide was added, and the mixture was stirred at the same stirring speed until completely dissolved. The resulting solution was transferred to a 25 mL hydrothermal reactor and reacted at 190 °C for 9 h. After cooling to room temperature, the obtained magnetic nanoparticles were separated by magnetism and washed three times with 15 mL of ethanol / ultrapure water mixed solvent (volume ratio 1:1) and 15 mL of ultrapure water, respectively, and finally dispersed in 12.5 mL of ultrapure water.

[0068] (2) Take 90 mg of alkali lignin and place it in a 100 mL beaker. Add 40 mL of tetrahydrofuran solution and sonicate for 5 min until the alkali lignin is completely dissolved to obtain a lignin solution.

[0069] (3) Add 2 mL of the iron oxide nanoparticle dispersion obtained in step (1) to the lignin solution obtained in step (2), sonicate for 5 min to disperse it completely, then add 60 mL of ultrapure water at a rate of 4 mL / min, and stir continuously at 400 rpm for 6 h. After the tetrahydrofuran in the mixture has completely evaporated, separate it with a magnet to obtain iron oxide@lignin nanospheres.

[0070] Figure 9 This is a scanning electron microscope (SEM) image of the iron(III) oxide@lignin nanospheres prepared by the method in Comparative Example 1. Figure 9 As can be seen, compared with Example 1, the coating effect of the iron(III) oxide@lignin nanospheres prepared by self-assembly with the addition of antisolvent in the solvent is poor, with multinucleation and aggregation. This indicates that monodisperse core-shell structured iron(III) oxide@lignin nanospheres cannot be prepared under the condition of introducing antisolvent. The reason is that with the addition of antisolvent, local lignin molecules are induced to preferentially and spontaneously nucleate, and combine with nearby iron(III) oxide nanoparticles during the assembly process, thereby forming multinucleated nanospheres.

[0071] Comparative Example 2

[0072] A method for preparing iron(III) oxide@lignin nanoparticles includes the following steps:

[0073] (1) 0.26 g anhydrous ferric chloride, 1.2 g anhydrous sodium acetate, 0.4 g sodium poly(4-styrenesulfonic acid-conmaleic acid) (purchased from Aladdin, catalog number P107093), 4.5 mg L-ascorbic acid, and 20 μL ultrapure water were sequentially added to 16 mL of ethylene glycol and stirred with a magnetic stirrer (600 rpm) until completely dissolved. Then, 0.24 g sodium hydroxide was added, and the mixture was stirred at the same stirring speed until completely dissolved. The resulting solution was transferred to a 25 mL hydrothermal reactor and reacted at 190 °C for 9 h. After cooling to room temperature, the obtained magnetic nanoparticles were separated by magnetism and washed three times with 15 mL of ethanol / ultrapure water mixed solvent (volume ratio 1:1) and 15 mL of ultrapure water, respectively, and finally dispersed in 12.5 mL of ultrapure water.

[0074] (2) Take 90 mg of alkali lignin and place it in a 100 mL beaker. Add 70 mL of tetrahydrofuran / ultrapure water binary solvent (volume ratio 4:3) and sonicate for 5 min until the alkali lignin is completely dissolved to obtain a lignin solution.

[0075] (3) Add 2 mL of the iron oxide nanoparticle dispersion obtained in step (1) to the lignin solution obtained in step (2), sonicate for 5 min to make it completely dispersed, and then place it under an exhaust fan for 36 h. After the tetrahydrofuran in the mixture has completely evaporated, separate it with a magnet to obtain iron oxide@lignin nanoparticles.

[0076] Figure 10 This is a scanning electron microscope (SEM) image of the iron(III) oxide@lignin nanospheres prepared by the method in Comparative Example 2. Figure 10 As can be seen, compared with Example 1, the iron(III) oxide@lignin nanoparticles prepared without stirring during solvent evaporation exhibited cross-linking and aggregation. This indicates that even omitting the continuous stirring process of the lignin solution and iron(III) oxide nanoparticles, monodisperse core-shell structured iron(III) oxide@lignin nanospheres cannot be prepared. The reason is that the lack of stirring prevents the magnetic nanoparticles from maintaining good dispersion throughout the assembly process, leading to cross-linking and aggregation between the lignin shells.

[0077] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing core-shell structured iron(III) oxide@lignin nanospheres, characterized in that, Includes the following steps: (1) Mix lignin with a binary solvent of organic solvent / water to obtain a lignin solution; (2) Mix the monodisperse iron oxide nanoparticle solution with the lignin solution evenly, and then stir to evaporate the organic solvent to obtain an iron oxide@lignin nanosphere suspension. Separate the suspension with a magnet to obtain core-shell structured iron oxide@lignin nanospheres. The monodisperse iron oxide nanoparticle solution in step (2) is prepared by the following method: anhydrous ferric chloride, alkaline organic salt, a polymer containing carboxyl or amino groups with a molecular weight of 6000-20000 g / mol, a reducing agent, water and an organic solvent are mixed and dissolved in sequence, an inorganic base is added and dissolved, hydrothermal reaction is carried out, magnetic nanoparticles are obtained by magnetic separation, and after washing, they are dispersed in water. The alkaline organic salt is at least one of anhydrous sodium acetate, anhydrous sodium citrate, and anhydrous sodium succinate; the polymer containing carboxyl or amino groups with a molecular weight of 6000-20000 g / mol is at least one of sodium poly(4-styrenesulfonic acid-conmaleic acid), polyvinylpyrrolidone, and sodium polyacrylate; the reducing agent is at least one of L-ascorbic acid and tauroursodeoxycholic acid. The organic solvent in step (1) is at least one of tetrahydrofuran, ethanol, acetone, methanol and N,N-dimethylformamide; the volume ratio of the organic solvent and water in step (1) is 1:1 to 50:

1.

2. The method for preparing core-shell structured iron(III) oxide@lignin nanospheres according to claim 1, characterized in that, In step (2), the mass ratio of iron oxide nanoparticles to lignin is 1:(1.5-6). The lignin in step (1) is at least one of alkali lignin, enzymatically hydrolyzed lignin, lignin sulfate, and organic solvent lignin.

3. The method for preparing core-shell structured iron(III) oxide@lignin nanospheres according to claim 1, characterized in that, The ratio of lignin to water in step (1) is (1-4) mg: 1 mL; The concentration of the monodisperse iron oxide nanoparticle solution in step (2) is 5–60 mg / mL.

4. The method for preparing core-shell structured iron(III) oxide@lignin nanospheres according to claim 1, characterized in that, The stirring and evaporation of organic solvent in step (2) is carried out by mechanical stirring, with a stirring speed of 200-800 rpm and a stirring time of 6-18 h.

5. The method for preparing core-shell structured iron(III) oxide@lignin nanospheres according to claim 1, characterized in that, The lignin in step (1) is at least one of alkali lignin and enzymatically hydrolyzed lignin; the organic solvent is at least one of tetrahydrofuran and ethanol.

6. The method for preparing core-shell structured iron(III) oxide@lignin nanospheres according to claim 1, characterized in that, The organic solvent is at least one of ethylene glycol, n-butanol, and butanediol; the inorganic base is at least one of sodium hydroxide, potassium hydroxide, and lithium hydroxide. The ratio of anhydrous ferric chloride, alkaline organic salt, a polymer containing carboxyl or amino groups with a molecular weight of 6000–20000 g / mol, reducing agent, water, organic solvent, and inorganic base is 0.13–0.52 g: 0.6–2.4 g: 0.2–0.8 g: 3–6 mg: 10–60 µL: 8–32 mL: 0.12–0.48 g; The hydrothermal reaction is carried out at a temperature of 150–250 °C for a duration of 6–18 h.

7. A core-shell structured iron(III) oxide@lignin nanosphere prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the core-shell structured iron(III) oxide@lignin nanospheres as described in claim 7 in colloidal photonic crystals.

Images