Magnetic nanocomposite and application thereof in dye wastewater treatment

Abstract

The application discloses a kind of magnetic nanocomposite and its application in dye wastewater treatment, belong to water treatment functional material technical field.The magnetic nanocomposite with Fe3O4 Magnetic Nanoparticle as core, successively coats silica layer, graphene nanosheet layer and chitosan crosslinking layer, through the synergistic effect of chitosan liquid ultrasonic modification and graphene nanosheet surface modification, realize efficient adsorption and magnetic separation recovery to dye molecule.The preparation process of the application is mild controllable, environment-friendly, cost moderate, has wide application prospect in printing and dyeing wastewater advanced treatment, industrial dye pollution control field, graphene nanosheet greatly promotes specific surface area and adsorption site, chitosan provides a large number of amino / hydroxyl active groups, three synergies realize high adsorption capacity.Graphene nanosheet is reduced by liquid phase ultrasonic stripping, avoids stacking;Chitosan is modified by ultrasonic and TiO2 is scattered, combination is more firm, material structure is stable, not easy to lose, acid and alkali resistant.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a magnetic nanocomposite and its application in dye wastewater treatment. Background Technology

[0002] Dye wastewater is characterized by high color intensity, high toxicity, complex composition, and poor biodegradability, making it a challenging area for industrial wastewater treatment. Traditional treatment methods, such as coagulation sedimentation, biological methods, and oxidation methods, suffer from drawbacks such as incomplete treatment, high costs, and the potential for secondary pollution. Adsorption methods are widely used due to their simplicity, high efficiency, and wide applicability; however, traditional adsorbents such as activated carbon and resins face challenges in separation and recovery, easy loss, and high regeneration costs.

[0003] Magnetic nano-adsorbents, which can be rapidly separated by a magnetic field, have become a research hotspot. However, pure iron oxide nanoparticles are prone to aggregation, have poor stability, and low adsorption selectivity. Introducing graphene can increase the specific surface area and adsorption sites, but graphene is prone to stacking and has weak binding force with the matrix. Chitosan has abundant amino and hydroxyl groups and strong affinity for dyes, but pure chitosan has low mechanical strength and poor acid resistance. Current technologies lack magnetic nanocomposites that are synergistically modified with graphene nanosheets and chitosan, have stable structures, and balance adsorption and magnetic separation performance, which limits their application in practical dye wastewater treatment. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the purpose of this invention is to provide a magnetic nanocomposite and its application in dye wastewater treatment, so as to solve the problems mentioned in the background art.

[0005] The present invention solves the technical problem by adopting the following technical solution:

[0006] This invention provides a magnetic nanocomposite, wherein the magnetic nanocomposite is based on Fe O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

[0007] Preferably, the specific preparation method of the magnetic nanocomposite is as follows:

[0008] Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise to adjust the pH to 9-11. The mixture was stirred at 80-90℃ for 1-2 hours, followed by magnetic separation and washing, and vacuum drying to obtain Fe. O Magnetic nanoparticles;

[0009] Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, and tetraethyl orthosilicate was added. The mixture was stirred and hydrolyzed at room temperature for 2-3 hours, followed by magnetic separation to obtain SiO₂. @Fe O Composite particles;

[0010] Step 3: SiO @Fe O The composite particles were added to the graphene nanosheet dispersion, ultrasonically dispersed for 30-40 min, stirred at 60-70℃ for 1-1.5 h, and magnetically separated to obtain the graphene nanosheet modified intermediate.

[0011] Step 4: Add the intermediate to the chitosan modification solution, sonicate for 20-30 minutes, add the crosslinking agent, react at 40-50℃ for 1-2 hours, magnetically separate, wash, and dry to obtain the magnetic nanocomposite.

[0012] Preferably, in step one, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 25-28%; the vacuum drying temperature is 50-60℃, and the drying time is 6-8h.

[0013] Preferably, in step two, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 10-15% of the mass of magnetic nanoparticles.

[0014] Preferably, the preparation method of the graphene nanosheet dispersion in step three is as follows: add graphene oxide to deionized water, exfoliate with ultrasonic power of 600~700W for 1~2h, add ascorbic acid for reduction, centrifuge and wash to obtain a graphene nanosheet dispersion with a concentration of 1~2mg / mL.

[0015] Graphene nanosheets significantly increase specific surface area and adsorption sites, while chitosan provides a large number of amino / hydroxyl active groups; the three work synergistically to achieve high adsorption capacity. Graphene nanosheets are reduced by liquid-phase ultrasonic exfoliation to avoid stacking; chitosan is ultrasonically modified and combined with TiO₂. It disperses and binds more firmly, resulting in a stable material structure that is not easily lost and is resistant to acids and alkalis.

[0016] Preferably, the preparation method of the chitosan modified solution in step four is as follows: dissolve chitosan in a 1-2% acetic acid solution, stir until completely dissolved, and add nano-TiO₂. The mixture was treated with ultrasonic power of 400-500W for 20-30 minutes to obtain a chitosan modified solution with a mass fraction of 2-3%.

[0017] Preferably, in step four, the crosslinking agent is a glutaraldehyde solution with a mass fraction of 2-3%, and the added volume is 5-8% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 350-450W.

[0018] Preferably, the drying conditions for step four are: vacuum freeze drying, temperature -40~-50℃, time 12~16h.

[0019] This invention also provides an application of magnetic nanocomposite in dye wastewater treatment. The magnetic nanocomposite is added to dye-containing wastewater, and adsorption is carried out at room temperature with shaking for 30-60 minutes. The solid and liquid are separated by an external magnetic field, and the saturated material is desorbed and regenerated for recycling.

[0020] Preferably, the dyes include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.2~0.5 g / L; and the wastewater pH is 4~10.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention uses Fe O @SiO The graphene nanosheets and chitosan core-shell structure, with a silica layer enhancing stability, graphene nanosheets significantly increasing specific surface area and adsorption sites, and chitosan providing a large number of amino / hydroxyl active groups, work synergistically to achieve high adsorption capacity. The graphene nanosheets are reduced by liquid-phase ultrasonic exfoliation to avoid stacking; chitosan is ultrasonically modified and combined with TiO₂. It exhibits stronger dispersion and binding, resulting in a stable material structure that is less prone to loss and resistant to acids and alkalis. Its rapid magnetic response allows for solid-liquid separation within 10 seconds using an external magnetic field, solving the problem of difficult recovery of traditional adsorbents. Even after 10 cycles, the adsorption retention rate remains ≥85%, demonstrating excellent regeneration performance. The preparation process is mild, environmentally friendly, and requires no high temperature or high pressure, making it suitable for large-scale production. It possesses high-efficiency removal capabilities for various dyes, has a wide pH range, and offers significant advantages in the deep treatment of dye wastewater. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This embodiment describes a magnetic nanocomposite, wherein the magnetic nanocomposite uses Fe... O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

[0025] The specific preparation method of the magnetic nanocomposite in this embodiment is as follows:

[0026] Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise to adjust the pH to 9-11. The mixture was stirred at 80-90℃ for 1-2 hours, followed by magnetic separation and washing, and vacuum drying to obtain Fe. O Magnetic nanoparticles;

[0027] Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, and tetraethyl orthosilicate was added. The mixture was stirred and hydrolyzed at room temperature for 2-3 hours, followed by magnetic separation to obtain SiO₂. @Fe O Composite particles;

[0028] Step 3: SiO @Fe O The composite particles were added to the graphene nanosheet dispersion, ultrasonically dispersed for 30-40 min, stirred at 60-70℃ for 1-1.5 h, and magnetically separated to obtain the graphene nanosheet modified intermediate.

[0029] Step 4: Add the intermediate to the chitosan modification solution, sonicate for 20-30 minutes, add the crosslinking agent, react at 40-50℃ for 1-2 hours, magnetically separate, wash, and dry to obtain the magnetic nanocomposite.

[0030] In step one of this embodiment, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 25-28%; the vacuum drying temperature is 50-60℃, and the drying time is 6-8h.

[0031] In step two of this embodiment, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 10-15% of the mass of magnetic nanoparticles.

[0032] The preparation method of the graphene nanosheet dispersion in step three of this embodiment is as follows: graphene oxide is added to deionized water, ultrasonically exfoliated at a power of 600~700W for 1~2 hours, ascorbic acid is added for reduction, and the mixture is centrifuged and washed to obtain a graphene nanosheet dispersion with a concentration of 1~2 mg / mL.

[0033] In step four of this embodiment, the preparation method of the chitosan modified solution is as follows: dissolve chitosan in a 1-2% acetic acid solution, stir until completely dissolved, and add nano-TiO₂. The mixture was treated with ultrasonic power of 400-500W for 20-30 minutes to obtain a chitosan modified solution with a mass fraction of 2-3%.

[0034] In step four of this embodiment, the crosslinking agent is a glutaraldehyde solution with a mass fraction of 2-3%, and the added volume is 5-8% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 350-450W.

[0035] The drying conditions for step four in this embodiment are: vacuum freeze drying, temperature -40~-50℃, time 12~16h.

[0036] This embodiment describes the application of a magnetic nanocomposite in the treatment of dye wastewater. The magnetic nanocomposite is added to the dye-containing wastewater, and adsorption is carried out at room temperature with shaking for 30-60 minutes. The solid and liquid are separated by an external magnetic field, and the saturated material is desorbed and regenerated for recycling.

[0037] The dyes in this embodiment include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.2~0.5 g / L; and the pH of the wastewater is 4~10.

[0038] Example 1

[0039] This embodiment describes a magnetic nanocomposite, wherein the magnetic nanocomposite uses Fe... O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

[0040] The specific preparation method of the magnetic nanocomposite in this embodiment is as follows:

[0041] Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise to adjust the pH to 9. The mixture was stirred at 80°C for 1 hour, followed by magnetic separation and washing, and vacuum drying to obtain Fe. O Magnetic nanoparticles;

[0042] Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, and tetraethyl orthosilicate was added. The mixture was stirred and hydrolyzed at room temperature for 2 hours, followed by magnetic separation to obtain SiO₂. @Fe O Composite particles;

[0043] Step 3: SiO @Fe O The composite particles were added to the graphene nanosheet dispersion, ultrasonically dispersed for 30 min, stirred at 60 °C for 1 h, and magnetically separated to obtain the graphene nanosheet modified intermediate.

[0044] Step 4: Add the intermediate to the chitosan modification solution, sonicate for 20 min, add crosslinking agent, react at 40℃ for 1 h, magnetically separate, wash, and dry to obtain magnetic nanocomposite.

[0045] In step one of this embodiment, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 25%; the vacuum drying temperature is 50℃ and the drying time is 6h.

[0046] In step two of this embodiment, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 10% of the mass of magnetic nanoparticles.

[0047] The preparation method of the graphene nanosheet dispersion in step three of this embodiment is as follows: graphene oxide is added to deionized water, ultrasonically exfoliated at 600W for 1 hour, ascorbic acid is added for reduction, and the mixture is centrifuged and washed to obtain a graphene nanosheet dispersion with a concentration of 1 mg / mL.

[0048] In step four of this embodiment, the preparation method of the chitosan modified solution is as follows: dissolve chitosan in a 1% acetic acid solution, stir until completely dissolved, and add nano-TiO₂. The mixture was treated with an ultrasonic power of 400W for 20-30 minutes to obtain a chitosan modified solution with a mass fraction of 2%.

[0049] In step four of this embodiment, the crosslinking agent is glutaraldehyde solution with a mass fraction of 2%, and the added volume is 5% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 350W.

[0050] The drying conditions for step four in this embodiment are: vacuum freeze drying, temperature -40℃, time 12h.

[0051] This embodiment describes the application of a magnetic nanocomposite in the treatment of dye wastewater. The magnetic nanocomposite is added to the dye-containing wastewater, and adsorption is carried out at room temperature with shaking for 30 minutes. The solid and liquid are separated by an external magnetic field, and the saturated material is desorbed and regenerated for reuse.

[0052] The dyes in this embodiment include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.2 g / L; and the wastewater pH is 4.

[0053] Example 2

[0054] This embodiment describes a magnetic nanocomposite, wherein the magnetic nanocomposite uses Fe... O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

[0055] The specific preparation method of the magnetic nanocomposite in this embodiment is as follows:

[0056] Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise to adjust the pH to 11. The reaction was stirred at 90°C for 2 hours, followed by magnetic separation and washing, and vacuum drying to obtain Fe. O Magnetic nanoparticles;

[0057] Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, tetraethyl orthosilicate was added, and the mixture was stirred and hydrolyzed at room temperature for 3 hours. SiO₂ was then obtained by magnetic separation. @Fe O Composite particles;

[0058] Step 3: SiO @Fe O The composite particles were added to a graphene nanosheet dispersion, ultrasonically dispersed for 40 min, stirred at 70 °C for 1.5 h, and magnetically separated to obtain the graphene nanosheet modified intermediate.

[0059] Step 4: Add the intermediate to the chitosan modification solution, sonicate for 30 min, add crosslinking agent, react at 50℃ for 2 h, magnetically separate, wash, and dry to obtain magnetic nanocomposite.

[0060] In step one of this embodiment, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 28%; the vacuum drying temperature is 60℃ and the drying time is 8h.

[0061] In step two of this embodiment, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 15% of the mass of magnetic nanoparticles.

[0062] The preparation method of the graphene nanosheet dispersion in step three of this embodiment is as follows: graphene oxide is added to deionized water, ultrasonically exfoliated at 700W for 2 hours, ascorbic acid is added for reduction, and the mixture is centrifuged and washed to obtain a graphene nanosheet dispersion with a concentration of 2 mg / mL.

[0063] In step four of this embodiment, the preparation method of the chitosan modified solution is as follows: dissolve chitosan in a 2% acetic acid solution, stir until completely dissolved, and add nano-TiO₂. The mixture was treated with an ultrasonic power of 500W for 30 minutes to obtain a chitosan modified solution with a mass fraction of 3%.

[0064] In step four of this embodiment, the crosslinking agent is glutaraldehyde solution with a mass fraction of 3%, and the added volume is 8% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 450W.

[0065] The drying conditions for step four in this embodiment are: vacuum freeze drying, temperature -50℃, time 16h.

[0066] This embodiment describes the application of a magnetic nanocomposite in the treatment of dye wastewater. The magnetic nanocomposite is added to the dye-containing wastewater, and adsorption is carried out at room temperature with shaking for 60 minutes. The solid and liquid are separated by an external magnetic field, and the saturated material is desorbed and regenerated for recycling.

[0067] The dyes in this embodiment include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.5 g / L; and the pH of the wastewater is 4-10.

[0068] Example 3

[0069] This embodiment describes a magnetic nanocomposite, wherein the magnetic nanocomposite uses Fe... O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

[0070] The specific preparation method of the magnetic nanocomposite in this embodiment is as follows:

[0071] Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and ammonia was added dropwise under nitrogen protection to adjust the pH to 10. The mixture was stirred at 85°C for 1.5 h, magnetically separated and washed, and then vacuum dried to obtain Fe. O Magnetic nanoparticles;

[0072] Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, and tetraethyl orthosilicate was added. The mixture was stirred and hydrolyzed at room temperature for 2.5 h, followed by magnetic separation to obtain SiO₂. @Fe O Composite particles;

[0073] Step 3: SiO @Fe O The composite particles were added to a graphene nanosheet dispersion, ultrasonically dispersed for 35 min, stirred at 65 °C for 1.2 h, and magnetically separated to obtain the graphene nanosheet modified intermediate.

[0074] Step 4: Add the intermediate to the chitosan modification solution, sonicate for 25 min, add crosslinking agent, react at 45℃ for 1.2 h, magnetically separate, wash, and dry to obtain magnetic nanocomposite.

[0075] In step one of this embodiment, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 26%; the vacuum drying temperature is 55℃ and the drying time is 7h.

[0076] In step two of this embodiment, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 12.5% ​​of the mass of magnetic nanoparticles.

[0077] The preparation method of the graphene nanosheet dispersion in step three of this embodiment is as follows: graphene oxide is added to deionized water, ultrasonically exfoliated at a power of 65W for 1.5h, ascorbic acid is added for reduction, and the mixture is centrifuged and washed to obtain a graphene nanosheet dispersion with a concentration of 1.5mg / mL.

[0078] In step four of this embodiment, the chitosan-modified solution is prepared as follows: chitosan is dissolved in a 1.5% acetic acid solution and stirred until completely dissolved; then nano-TiO₂ is added. The mixture was treated with ultrasonic power of 450W for 25 minutes to obtain a chitosan modified solution with a mass fraction of 2.5%.

[0079] In step four of this embodiment, the crosslinking agent is glutaraldehyde solution with a mass fraction of 2.5%, and the added volume is 6.5% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 400W.

[0080] The drying conditions for step four in this embodiment are: vacuum freeze drying, temperature -45℃, time 14h.

[0081] This embodiment describes the application of a magnetic nanocomposite in the treatment of dye wastewater. The magnetic nanocomposite is added to the dye-containing wastewater, and adsorption is carried out at room temperature with shaking for 45 minutes. The solid and liquid are separated by an external magnetic field, and the saturated material is desorbed and regenerated for recycling.

[0082] The dyes in this embodiment include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.35 g / L; and the wastewater pH is 6.

[0083] Scale settings

[0084] Comparative Example 1: Same as Example 3, but without the addition of graphene nanosheet dispersion.

[0085] Comparative Example 2: Same as Example 3, but without the addition of chitosan modification solution.

[0086] Comparative Example 3: Same as Example 3, but graphene nanosheets were replaced with unreduced graphene oxide.

[0087] Comparative Example 4: Same as Example 3, but without the addition of nano-TiO2 to the chitosan-modified solution. And it was not subjected to ultrasonic treatment.

[0088] Comparative Example 5: Same as Example 3, but without SiO2 treatment. To cover.

[0089] Comparative Example 6: Same as Example 3, but without the use of glutaraldehyde crosslinking.

[0090] Performance testing

[0091] The saturated adsorption capacity (mg / g), magnetic response time (s), adsorption retention rate (%) after 10 cycles, and water dispersion stability (h) of samples from Examples 1-3 and Comparative Examples 1-6 were tested. The results are shown in Table 1 below:

[0092] sample Saturated adsorption capacity (mg / g) Magnetic response time (s) Retention rate (%) after 10 cycles Water dispersion stability (h) Example 1 218.4 12 89.2 72 Example 2 223.7 10 90.5 78 Example 3 229.6 8 92.3 84 Comparative Example 1 145.3 9 71.6 36 Comparative Example 2 152.8 8 73.2 42 Comparative Example 3 176.5 15 78.4 48 Comparative Example 4 184.2 11 80.5 53 Comparative Example 5 169.7 22 68.9 29 Comparative Example 6 191.3 10 75.8 61

[0093] The performance test results above show that:

[0094] Example 3 showed the best performance, with a saturated adsorption capacity of 229.6 mg / g, a magnetic response of only 8 s, a cycle retention rate of 92.3%, and stable water dispersion for 84 h. Comparative Examples 1 (without graphene) and 2 (without chitosan) showed significantly lower performance, demonstrating that the synergistic effect of both is indispensable. Comparative Examples 3-6 lacked reduction, ultrasound, and SiO2, respectively. Coating and cross-linking both lead to a significant reduction in adsorption, stability, and cycleability, confirming the necessity and superiority of the process steps in this invention. Only the raw materials obtained by using the specific process of this invention have the most significant multi-performance effects, and other methods are not as effective as those of this invention.

[0095] Graphene nanosheets significantly increase specific surface area and adsorption sites, while chitosan provides a large number of amino / hydroxyl active groups; the three work synergistically to achieve high adsorption capacity. Graphene nanosheets are reduced by liquid-phase ultrasonic exfoliation to avoid stacking; chitosan is ultrasonically modified and combined with TiO₂. It disperses and binds more firmly, resulting in a stable material structure that is not easily lost and is resistant to acids and alkalis.

[0096] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0097] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A magnetic nanocomposite, characterized in that, Magnetic nanocomposites with Fe O Magnetic nanoparticles form the core, sequentially coated with SiO₂ An insulating layer, a graphene nanosheet modified layer, and a chitosan cross-linked functional layer form a core-shell structure.

2. The magnetic nanocomposite according to claim 1, characterized in that, The specific preparation method of magnetic nanocomposites is as follows: Step 1: Add FeCl •6H O, FeSO •7H O was dissolved in deionized water, and under nitrogen protection, ammonia was added dropwise to adjust the pH to 9-11. The mixture was stirred at 80-90℃ for 1-2 hours, followed by magnetic separation and washing, and vacuum drying to obtain Fe. O Magnetic nanoparticles; Step 2: Add Fe O Magnetic nanoparticles were dispersed in an ethanol-water mixture, and tetraethyl orthosilicate was added. The mixture was stirred and hydrolyzed at room temperature for 2-3 hours, followed by magnetic separation to obtain SiO₂. @Fe O Composite particles; Step 3: SiO @Fe O The composite particles were added to the graphene nanosheet dispersion, ultrasonically dispersed for 30-40 min, stirred at 60-70℃ for 1-1.5 h, and magnetically separated to obtain the graphene nanosheet modified intermediate. Step 4: Add the intermediate to the chitosan modification solution, sonicate for 20-30 minutes, add the crosslinking agent, react at 40-50℃ for 1-2 hours, magnetically separate, wash, and dry to obtain the magnetic nanocomposite.

3. The magnetic nanocomposite according to claim 1, characterized in that, In step one, FeCl •6H O, FeSO •7H The molar ratio of O is 2:1; the mass fraction of ammonia is 25-28%; the vacuum drying temperature is 50-60℃, and the drying time is 6-8h.

4. The magnetic nanocomposite according to claim 1, characterized in that, In step two, the volume ratio of the ethanol-water mixture is 4:1; the amount of tetraethyl orthosilicate added is Fe. O 10-15% of the mass of magnetic nanoparticles.

5. A magnetic nanocomposite according to claim 1, characterized in that, The preparation method of graphene nanosheet dispersion in step three is as follows: add graphene oxide to deionized water, exfoliate with ultrasonic power of 600~700W for 1~2h, add ascorbic acid for reduction, centrifuge and wash to obtain graphene nanosheet dispersion with a concentration of 1~2mg / mL.

6. The magnetic nanocomposite according to claim 1, characterized in that, The preparation method of the chitosan modified solution in step four is as follows: dissolve chitosan in a 1-2% acetic acid solution, stir until completely dissolved, and add nano-TiO₂. The mixture was treated with ultrasonic power of 400-500W for 20-30 minutes to obtain a chitosan modified solution with a mass fraction of 2-3%.

7. A magnetic nanocomposite according to claim 1, characterized in that, In step four, the crosslinking agent is a glutaraldehyde solution with a mass fraction of 2-3%, and the added volume is 5-8% of the volume of the chitosan-modified liquid; the ultrasonic treatment power is 350-450W.

8. A magnetic nanocomposite according to claim 1, characterized in that, Step four drying conditions are: vacuum freeze drying, temperature -40~-50℃, time 12~16h.

9. The application of the magnetic nanocomposite of any one of claims 1 to 8 in the treatment of dye wastewater, characterized in that, The magnetic nanocomposite was added to the dye-containing wastewater and adsorbed by shaking at room temperature for 30-60 minutes. The solid and liquid were separated by an external magnetic field. The saturated material was desorbed and regenerated for recycling.

10. The application according to claim 9, characterized in that, The dyes include methylene blue, rhodamine B, methyl orange, and acid red G; the dosage is 0.2~0.5 g / L; and the pH of the wastewater is 4~10.