A method for preparing a ferroferric oxide-graphene magnetic heterostructure material and application thereof in directional heat conduction composite material

Abstract

The application provides a method for preparing a magnetic heterostructure material of magnetite-graphene and application of the magnetic heterostructure material in a directional heat-conducting composite material, and belongs to the technical field of composite materials. The method comprises the following steps: (1) slowly adding a sodium hydroxide solution into a ferric chloride solution under water bath condition to prepare a ferric hydroxide gel, and sequentially performing drying and aging, centrifugation, cleaning and freeze drying on the gel to obtain a ferrous oxide nanocrystal; (2) adding the ferrous oxide nanocrystal, graphene and dopamine hydrochloride into a Tris buffer solution and fully stirring, and performing multiple centrifugation, cleaning and freeze drying to obtain ferrous oxide-dopamine-graphene; and (3) performing calcination reduction on the ferrous oxide-dopamine-graphene to obtain the magnetic heterostructure material of magnetite-graphene. The magnetic heterostructure material prepared by the method can be applied to the preparation of the directional heat-conducting composite material as a heat-conducting filler, and has the advantages of high operability, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite materials, in particular to a method for preparing a magnetic heterostructure material of magnetite-graphene using a calcination reduction method and application of the magnetic heterostructure material in a directional heat-conducting composite material. BACKGROUND

[0002] Magnetite is a black crystal with magnetism, and graphene is a single-atom layer material with a hexagonal honeycomb crystal lattice of carbon atoms, which has good electrical conductivity and thermal conductivity. The combination of the two to prepare a magnetic heterostructure material of magnetite-graphene has good physical properties and wide application prospects as a composite material.

[0003] The prior art CN109741964 A discloses an iron oxide-polydopamine-graphene composite material, a preparation method thereof and application. However, the iron oxide in the prior art exists in the form of Fe2O3, and according to paragraph 0036, it is recorded that "the iron oxide in the composite material is α-Fe2O3". The iron oxide in the above prior art has no magnetism and is mainly applied to the surface of an electrode.

[0004] The calcination process of the present application is carried out in an argon environment, which is a calcination reduction process. The iron oxide in the present application exists in the form of Fe3O4 and has magnetism. When it is used as a filler of a heat-conducting composite material, the magnetism can be used to prepare a directional heat-conducting material by applying a magnetic field to arrange the fillers directionally.

[0005] Meanwhile, there are also great differences in the preparation processes of the two. In the prior art, iron exists in the form of ions in the solution and is attached to graphene, while in the present application, complete Fe2O3 nanocells are first prepared and then attached to graphene together with polydopamine hydrochloride. SUMMARY

[0006] In view of the deficiencies of the prior art, the present application provides a magnetic heterostructure material of magnetite-graphene and a preparation method thereof. The method uses a calcination reduction method to make the Fe3O4 crystal grow on the surface of graphene in a point-plane three-dimensional structure, which is simple to operate, has good performance and low cost.

[0007] Therefore, in a first aspect, the present application provides a method for preparing a magnetic heterostructure material of magnetite-graphene, comprising:

[0008] (1) preparing Fe2O3 nanocells: slowly adding a sodium hydroxide solution to a ferric chloride solution under water bath conditions to obtain a ferric hydroxide gel, and then sequentially performing drying and aging, centrifugation, washing and freeze-drying on the gel to obtain Fe2O3 nanocells;

[0009] (2) Preparation of Fe2O3-dopamine-graphene: the Fe2O3 nanocrystal, graphene and dopamine hydrochloride prepared in step (1) are added into Tris buffer solution and stirred thoroughly, and then centrifuged, washed and freeze-dried to obtain Fe2O3-dopamine-graphene;

[0010] (3) Preparation of Fe3O4-graphene: the Fe2O3-dopamine-graphene prepared in step (2) is calcined and reduced to obtain Fe3O4-graphene magnetic heterostructure material.

[0011] Further, the concentration of the ferric chloride solution in step (1) is 0.03-0.05 mol / mL, preferably 0.04 mol / mL, the concentration of the sodium hydroxide solution is 0.1-0.12 mol / mL, preferably 0.108 mol / mL, and the volume ratio of the two solutions is 1:1. The water bath heating for preparing the ferric hydroxide gel is performed at 70-80°C, and the speed of adding the sodium hydroxide solution is between 10-20 mL / min.

[0012] Further, the drying and aging in step (1) is performed in a drying oven, and the drying temperature is 90-110°C, and the time is 3-5 days.

[0013] Further, the washing process in step (1) is repeated by centrifugation and washing with deionized water and anhydrous ethanol until the supernatant is neutral, and then the remaining product is collected.

[0014] Further, the freeze-drying process in step (1) is performed by using a vacuum freeze-drying machine, wherein the freezing temperature is ≤-55°C, preferably -60°C, the vacuum pressure is ≤2×10 -3 Pa, preferably 1×10 -3 Pa, and the freeze-drying time is 10-14 hours, preferably 12 h.

[0015] Further, in the mixing and stirring in step (2), the mass ratio of graphene, Fe2O3 nanocrystal and dopamine hydrochloride is 1:(3-5):(3-5), preferably 1:4:4; the pH of the Tris buffer solution is 8.5, and the concentration is 1.2 mg / mL. In the embodiment of the present application, the ratio of the Tris buffer solution to dopamine hydrochloride is 500 mL:1 g.

[0016] Further, the sequence and time of the mixing and stirring process in step (2) are as follows: first, the Fe2O3 nanocrystal and graphene are added into the Tris buffer solution, and then the dopamine hydrochloride is added after the dispersion is complete, and the magnetic stirring is performed under air atmosphere for 11-13 hours, preferably 12 hours.

[0017] Further, in the washing process in step (2), the remaining product is collected after the deionized water is centrifuged and washed until the supernatant is neutral.

[0018] Further, the freeze-drying process in step (2) is performed by a vacuum freeze dryer, wherein the freezing temperature is ≤-55℃, preferably -60℃, the vacuum pressure is ≤2×10 -3 Pa, preferably 1×10 -3 Pa, and the freeze-drying time is 10-14 hours, preferably 12h.

[0019] Further, the calcination reduction process in step (3) is performed by a tube furnace under argon atmosphere, wherein the calcination temperature is ≥450℃, preferably 500℃, and the calcination time is 2-4 hours, preferably 3 hours.

[0020] In the second aspect of the present application, a Fe3O4-graphene magnetic heterostructure material is provided, which is obtained by the preparation method of the present application.

[0021] In the third aspect of the present application, the Fe3O4-graphene magnetic heterostructure material is applied to a directional heat-conducting composite material.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) In the preparation method of the present application, the high-temperature calcination process causes the carbonization of polydopamine to form a carbon shell wrapped on the surface of graphene, and at the same time, the carbonized polydopamine still retains the amino functional group, so that the prepared Fe3O4-graphene magnetic heterostructure material exhibits good hydrophilicity, can form intermolecular hydrogen bonds with specific substrates, effectively reduces structural defects, and enhances the heat conductivity.

[0024] (2) The carbonized dopamine continues to participate in the reduction reaction of Fe2O3, and finally the Fe3O4 nanocrystals grow in situ on the surface of graphene, forming a strong covalent bond between the two instead of physical adsorption, so that the prepared Fe3O4-graphene magnetic heterostructure material has a stable "point-plane" three-dimensional structure.

[0025] (3) The present application prepares a Fe3O4-graphene magnetic heterostructure material with excellent performance by surface modification and calcination reduction. The preparation method is simple to operate, the raw materials are easy to obtain, the cost is low, the preparation period is short, the reaction conditions are mild, and can be applied to multiple composite material technical fields.

[0026] (4) The Fe3O4-graphene magnetic heterostructure material prepared by the present application has good magnetic and thermal conductivity, and when applied to heat-conducting composite filler, it can realize directional arrangement of the filler by applying a magnetic field or other methods, greatly increasing the thermal conductivity in a certain direction. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the technical solutions in the embodiments of the present application clearer, the accompanying drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the accompanying drawings in the following description are only some embodiments of the present application, and other accompanying drawings can be obtained by those skilled in the art without any creative effort on the basis of these accompanying drawings.

[0028] Figure 1 A scanning electron microscope (SEM) image of the magnetic heterostructure material prepared in Example 1.

[0029] Figure 2 An energy dispersive X-ray spectroscopy (EDS) image of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1.

[0030] Figure 3 An X-ray diffraction (XRD) image of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1.

[0031] Figure 4 XPS spectra of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1, wherein (a) is an XPS wide scan spectrum; (b) is a C 1s peak spectrum; (c) is a N 1s peak spectrum; and (d) is a Fe 2p peak spectrum.

[0032] Figure 5 Magnetic testing of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1.

[0033] Figure 6 A schematic diagram of applying a rotating magnetic field to the process of preparing the composite material in Example 1 to allow the magnetic heterostructure material to be oriented and arranged in polyvinyl alcohol (PVA).

[0034] Figure 7 A planar scanning electron microscope (SEM) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1.

[0035] Figure 8 A cross-sectional scanning electron microscope (SEM) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1.

[0036] Figure 9 A Fourier infrared spectroscopy (FTIR) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1 and polyvinyl alcohol.

[0037] Figure 10 A comparison of the tensile strength of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1 and polyvinyl alcohol.

[0038] Figure 11 The Young's modulus of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1 was compared with that of polyvinyl alcohol.

[0039] Figure 12 The thermogravimetric curve of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1 was compared with that of polyvinyl alcohol. DETAILED DESCRIPTION

[0040] To make the technical problems, technical solutions and advantages to be solved by the present application clearer, the following will be described in detail with reference to the drawings and specific examples.

[0041] The raw materials used in the examples are all commercially available, and the raw materials are easy to obtain. If industrialization is implemented, it can be scaled up by the same proportion.

[0042] Example 1:

[0043] First, 2 mol of ferric chloride and 5.4 mol of sodium hydroxide were added to 50 mL of deionized water, respectively, and after being fully stirred, a ferric chloride solution and a sodium hydroxide solution were prepared;

[0044] (1) Under the condition of heating at 75°C in a water bath, the above-mentioned sodium hydroxide solution was added dropwise into the ferric chloride solution within 5 minutes, and the stirring was continued at this temperature for 5 minutes to prepare a ferric hydroxide gel. The ferric hydroxide gel was placed in a 100°C drying oven for natural aging for 4 days, and was repeatedly centrifuged and washed with deionized water and anhydrous ethanol until the supernatant was neutral. The remaining product was collected and freeze-dried for 12 hours to obtain a ferroferric oxide nanocrystal;

[0045] (2) 2 g of the ferroferric oxide nanocrystal and 0.5 g of graphene were added into 250 mL of Tris buffer solution (1.2 mg / mL, pH=8.5), and after being fully dispersed, 2 g of dopamine hydrochloride was added. The mixture was stirred magnetically under air atmosphere for 12 hours. The mixture solution was centrifuged and washed with deionized water until the supernatant was neutral, and then the remaining product was collected and freeze-dried for 12 hours;

[0046] (3) The product of step (2) was placed in a tube furnace and calcined at 500°C for 3 hours under argon atmosphere to obtain a Fe3O4-graphene magnetic heterostructure material powder sample.

[0047] Figure 1 The scanning electron microscope (SEM) image of the magnetic heterostructure material prepared in Example 1 can be seen that the Fe3O4-graphene heterostructure material is a "point-plane" three-dimensional structure, and a large number of nanoscale crystal cells are attached to the surface of the graphene.

[0048] Figure 2The energy dispersive X-ray spectroscopy (EDS) image of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1 shows that the crystal cell is mainly composed of iron element.

[0049] Figure 3 The X-ray diffraction (XRD) image of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1 shows that the Fe3O4-graphene magnetic heterostructure material has a characteristic peak at 2θ = 26.68°, which corresponds to the (002) crystal face characteristic diffraction peak of graphene; and characteristic diffraction peaks at 2θ = 18.38°, 30.26°, 35.53°, 37.16°, 43.28°, 53.58°, 57.01°, 62.63° and 74.22°, which respectively correspond to the (111), (220), (311), (222), (400), (422), (511), (440) and (530) crystal face characteristic diffraction peaks of Fe3O4. Combined with the SEM image results and the preparation process, it can be known that the Fe3O4-graphene magnetic heterostructure material maintains the lattice structure of graphene, and Fe3O4 nanocrystals are in-situ grown on the surface of graphene.

[0050] Figure 4 The (a) XPS wide scan spectrum, (b) C 1s peak spectrum, (c) N 1s peak spectrum and (d) Fe 2p peak spectrum of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1 are shown in Figure 6. Figure 4 As shown in (a), the Fe 2p characteristic peak appears in the XPS wide scan spectrum of the Fe3O4-graphene magnetic heterostructure material, and the atomic content of Fe is about 4.53%. Further analysis of the C 1s, N 1s and Fe 2p peak spectra of the Fe3O4-graphene magnetic heterostructure material is performed. Figure 4 (b) is the C 1s spectrum of the Fe3O4-graphene magnetic heterostructure material, and after peak fitting, the fitting peaks of C-C bond (284.8 eV), C-N bond (285.4 eV) and C-OH bond (286.7 eV) appear. Figure 4 (c) is the N 1s spectrum of the Fe3O4-graphene magnetic heterostructure material, and after peak fitting, the fitting peaks of -NH- bond (398.6 eV) and -NH2 bond (400.4 eV) appear, indicating that the surface of the Fe3O4-graphene magnetic heterostructure material still contains a large amount of amino functional groups. Figure 4 (d) is the Fe 2p characteristic peak of the Fe3O4-graphene magnetic heterostructure material, and after peak fitting, the fitting peaks of Fe 2p3 / 2 (710.6 eV) and Fe 2p1 / 2 (724.2 eV) appear, which are consistent with the Fe 2p characteristic peak of Fe3O4. 3+The characteristic Fe 2p3 / 2(711.1eV), Fe 2p1 / 2(724.1eV) fitting peaks and satellite peaks Fe 2p3 / 2(714.6eV), Fe 2p1 / 2(727.9eV) of Fe are consistent with the XPS spectrum characteristics of Fe3O4 2+ The characteristic Fe 2p3 / 2(709.7eV), Fe 2p1 / 2(722.6eV) fitting peaks are consistent with the XPS spectrum characteristics of Fe3O4, indicating that Fe3O4 is grown in situ on the surface of graphene. In combination with the analysis of the preparation process of the Fe3O4-graphene magnetic heterostructure material, it can be seen that the dopamine modification layer is carbonized at a high temperature of 500°C to form a carbon shell wrapped around the Fe2O3 crystal cell and the surface of graphene, and acts as a carbon source to participate in the reduction reaction of Fe2O3. At this temperature, Fe2O3 is reduced to Fe3O4 particles attached to the surface of graphene, and finally the Fe3O4-graphene magnetic heterostructure material is prepared.

[0051] Figure 5 The magnetic properties of the Fe3O4-graphene magnetic heterostructure material prepared in Example 1 were tested, and the results are shown in Figures 6a and 6b. Figure 5 (a) It can be seen that the Fe3O4-graphene aqueous solution becomes clear and transparent in a short time, and the Fe3O4-graphene sample in the solution is all aggregated on one side of the magnet; as shown in Figure 6a. Figure 5 (b) As shown in Figure 6b, another appropriate amount of Fe3O4-graphene sample was placed in a microcentrifuge tube, and when the centrifuge tube was close to the magnet, the Fe3O4-graphene sample was all aggregated on one side of the magnet, so that the centrifuge tube was adsorbed on the surface of the magnet. These phenomena show that the Fe3O4-graphene magnetic heterostructure material has very excellent magnetic properties.

[0052] The Fe3O4-graphene magnetic heterostructure material prepared in Example 1 was added to polyvinyl alcohol (PVA) to prepare a Fe3O4-graphene / PVA composite material, and the thermal and mechanical properties of the composite material were tested. The specific steps are as follows:

[0053] (1) An appropriate amount of polyvinyl alcohol was heated and dissolved in deionized water to prepare a polyvinyl alcohol aqueous solution as a substrate for fillers;

[0054] (2) The Fe3O4-graphene magnetic heterostructure material was ultrasonically dispersed in an appropriate amount of deionized water, and then mixed with the polyvinyl alcohol aqueous solution to prepare a Fe3O4-graphene / polyvinyl alcohol mixed solution. The mixed solution was poured into a mold to make the mass fraction of the Fe3O4-graphene magnetic heterostructure material 5wt%;

[0055] (3) An electric turntable was placed between two strong magnets, and the mold was placed in the center of the turntable. A rotating magnetic field was applied, and the rotation speed of the turntable was adjusted to 2r / min. The sample was naturally gelled in the rotating magnetic field at room temperature for 12 hours and then taken out;

[0056] (4) Continue to dry naturally at room temperature to form a film to obtain the Fe3O4-graphene / polyvinyl alcohol composite material.

[0057] The thermal conductivity of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in this example reaches 8.22 W·m -1 ·K -1 , which is 1270% higher than the thermal conductivity of polyvinyl alcohol (0.6 W·m -1 ·K -1 ); the vertical thermal conductivity reaches 0.5 W·m -1 ·K -1 , which is 25% higher than the vertical thermal conductivity of polyvinyl alcohol (0.4 W·m -1 ·K -1 ).

[0058] Figure 6 A schematic diagram of applying a rotating magnetic field to the material of Example 1. Specifically, in step (3), the Fe3O4-graphene / polyvinyl alcohol mixed solution loaded in the mold is placed in an electric rotating disc, and a magnetic field is formed by placing a magnetic field on both sides of the electric rotating disc, and a relative rotating magnetic field is formed by rotating the electric rotating disc. The material is naturally gelled for 12 hours and then removed. Then step (4) is performed.

[0059] Figure 7 A planar scanning electron microscope (SEM) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1. It can be seen that the surface of the material is relatively flat and has no obvious structural defects, indicating that the filler is well dispersed in the substrate.

[0060] Figure 8 A cross-sectional scanning electron microscope (SEM) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1. It can be seen that the Fe3O4-graphene magnetic heterostructure material is closely attached to the substrate, and there are no obvious structural defects in the composite material. This is because the Fe3O4-graphene surface contains hydroxyl and amino functional groups, which can form a hydrogen bond network with the hydroxyl groups on the surface of polyvinyl alcohol, enhancing the interfacial interaction between Fe3O4-graphene and polyvinyl alcohol. In addition, Fe3O4-graphene is arranged in the plane direction in an orderly manner, which is consistent with the direction of the applied surface rotating magnetic field in the experiment.

[0061] Figure 9 A Fourier transform infrared spectrum (FTIR) image of the Fe3O4-graphene / polyvinyl alcohol composite material prepared in Example 1 and polyvinyl alcohol. The Fe3O4-graphene / polyvinyl alcohol composite material has a characteristic absorption peak at 833 cm -1The N-H characteristic peak at the position proves that the ferroferric oxide-graphene contains amino groups; compared with the polyvinyl alcohol material, the center position of the intermolecular hydrogen bond characteristic peak of the ferroferric oxide-graphene / polyvinyl alcohol composite material is 3337 cm -1 Moving to 3291 cm -1 , which indicates that the intermolecular hydrogen bond is formed between the ferroferric oxide-graphene and the polyvinyl alcohol. In combination with the SEM result analysis of the ferroferric oxide-graphene / polyvinyl alcohol composite material, the hydroxyl and amino groups on the surface of the ferroferric oxide-graphene isomer filler can form intermolecular hydrogen bonds with the polyvinyl alcohol, so that the ferroferric oxide-graphene can be closely combined with the polyvinyl alcohol. Therefore, there is no obvious structural defect on the surface and inside of the ferroferric oxide-graphene / polyvinyl alcohol composite material.

[0062] Figure 10 The tensile strength of the ferroferric oxide-graphene / polyvinyl alcohol composite material prepared in Example 1 is compared with that of the polyvinyl alcohol. It can be seen that the tensile strength of the ferroferric oxide-graphene / polyvinyl alcohol composite material is stronger than that of the polyvinyl alcohol.

[0063] Figure 11 The Young's modulus of the ferroferric oxide-graphene / polyvinyl alcohol composite material prepared in Example 1 is compared with that of the polyvinyl alcohol. It can be seen that the ferroferric oxide-graphene / polyvinyl alcohol composite material has a very outstanding Young's modulus compared with the polyvinyl alcohol.

[0064] Figure 12 The thermal gravimetric curves of the ferroferric oxide-graphene / polyvinyl alcohol composite material prepared in Example 1 are compared with those of the polyvinyl alcohol. It can be seen that the ferroferric oxide-graphene / polyvinyl alcohol composite material has good thermal stability, and the change trend of the thermal gravimetric curve is basically the same as that of the polyvinyl alcohol. However, the temperature at which the weight of the ferroferric oxide-graphene / polyvinyl alcohol composite material tends to be stable is higher than that of the polyvinyl alcohol.

[0065] Example 2

[0066] First, 4 mol of ferric chloride and 11 mol of sodium hydroxide were added to 100 mL of deionized water, respectively, and after being fully stirred, a ferric chloride solution and a sodium hydroxide solution were prepared;

[0067] (1) Under the condition of heating at 80°C water bath, the above-mentioned sodium hydroxide solution was added dropwise into the ferric chloride solution within 10 minutes, and the stirring was continued at this temperature for 10 minutes, to prepare a ferric hydroxide gel; the ferric hydroxide gel was placed in a 100°C drying oven for natural aging for 4 days, and was repeatedly centrifuged and washed with deionized water and anhydrous ethanol until the supernatant was neutral, and the remaining product was collected and freeze-dried for 12 hours to obtain a ferroferric oxide nanocrystal;

[0068] (2) 4 g of the ferric trioxide nanocrystal and 1 g of graphene were added into 500 mL of Tris buffer (1.2 mg / mL, pH = 8.5), and 4 g of dopamine hydrochloride was added after the mixture was dispersed thoroughly. The mixture was stirred magnetically for 13 hours under air atmosphere. The mixture solution was centrifuged and washed with deionized water until the supernatant was neutral, and then the remaining product was collected and freeze-dried for 14 hours;

[0069] (3) The product of step (2) was placed into a tube furnace and calcined at 460°C for 4 hours under argon atmosphere to obtain a sample of the ferric trioxide-graphene magnetic heterostructure material powder.

[0070] The ferric trioxide-graphene magnetic heterostructure material prepared in Example 2 was dispersed in a polyvinyl alcohol aqueous solution and a magnetic field was applied to obtain a ferric trioxide-graphene / polyvinyl alcohol composite material by the same method as in Example 1.

[0071] According to the test, the tensile strength of the ferric trioxide-graphene / polyvinyl alcohol composite material prepared in Example 2 was 43.27 MPa, the Young's modulus was 2.59 GPa, the in-plane thermal conductivity was 8.17 W·m -1 ·K -1 , and the vertical thermal conductivity was 0.5 W·m -1 ·K -1 .

[0072] Comparative Example 1

[0073] The heterostructure material was prepared by the same method as in Example 1, except that the calcination atmosphere in step (3) was air. The obtained product was subjected to magnetic test as shown in FIG. 1, and was placed into a transparent centrifugal tube and dispersed with water. When the centrifugal tube was placed close to a magnet, the liquid in the centrifugal tube did not change obviously. Therefore, it can be illustrated that the ferric trioxide crystal cannot be reduced sufficiently by calcination in air atmosphere, and the obtained heterostructure material has no magnetism. Figure 5

[0074] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which shall be covered within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.​

Claims

1. A method for preparing a magnetic heterostructure material of magnetite-graphene, characterized in that, It comprises the following steps: (1) Preparation of Fe2O3 nanocrystals: sodium hydroxide solution is slowly added to ferric chloride solution under water bath condition to prepare ferric hydroxide gel, and the gel is sequentially subjected to drying aging, centrifugation, washing and freeze drying to obtain Fe2O3 nanocrystals; (2) Preparation of Fe2O3-dopamine-graphene: Fe2O3 nanocrystals, graphene and dopamine hydrochloride prepared in step (1) are added into Tris buffer solution and fully stirred, and then subjected to centrifugation, washing and freeze drying to obtain Fe2O3-dopamine-graphene; (3) Preparation of Fe3O4-graphene: Fe2O3-dopamine-graphene prepared in step (2) is subjected to calcination reduction to obtain Fe3O4-graphene magnetic heterostructure material.

2. The method of claim 1, wherein, In step (1), the concentration of ferric chloride solution is 0.03-0.05 mol / mL, the concentration of sodium hydroxide solution is 0.1-0.12 mol / mL, and the volume ratio of the two solutions is 1:1; the water bath heating for preparing ferric hydroxide gel is performed at 70-80℃; and the speed of adding sodium hydroxide solution is between 10-20 mL / min.

3. The method of claim 1, wherein, In step (1), the drying aging is performed in a drying oven, the drying temperature is 90-110℃, and the time is 3-5 days. In step (1), the centrifugation and washing are performed by repeatedly centrifuging and washing with deionized water and anhydrous ethanol until the supernatant is neutral, and then the remaining product is collected. And / or, the freezing and drying process in step (1) is performed by a vacuum freeze dryer, wherein the freezing temperature is ≤-55℃, the vacuum pressure is ≤2×10 -3 Pa, and the freeze drying time is 10-14 hours.

4. The method of claim 1, wherein, In step (2), the mass ratio of graphene, Fe2O3 nanocrystals and dopamine hydrochloride in the mixing and stirring is 1:(3-5):(3-5); the pH of Tris buffer solution is 8.5, and the concentration is 1.2 mg / mL.

5. The method of claim 1, wherein, In step (2), the sequence and time of the mixing and stirring process are as follows: first, Fe2O3 nanocrystals and graphene are added into Tris buffer solution, then dopamine hydrochloride is added after the dispersion is complete, and the magnetic stirring is performed for 11-13 hours under air atmosphere.

6. The method of claim 1, wherein, In step (2), the centrifugation and washing are performed with deionized water until the supernatant is neutral, and then the remaining product is collected. And / or, the freezing and drying process in step (2) is performed by a vacuum freeze dryer, wherein the freezing temperature is ≤-55℃, the vacuum pressure is ≤2×10 -3 Pa, and the freeze drying time is 10-14 hours.

7. The method of claim 1, wherein, In step (3), the calcination reduction is performed by using a tube furnace to calcine Fe2O3-dopamine-graphene under argon atmosphere, wherein the calcination temperature is ≥450℃, and the calcination time is 2-4 hours.

8. The method of claim 7, wherein, In step (3), the calcination temperature is 500℃, and the calcination time is 3 hours.

9. Fe3O4-graphene magnetic heterostructure material prepared by the method of any one of claims 1 to 8.

10. Application of Fe3O4-graphene magnetic heterostructure material of claim 9 in directional heat-conducting composite material.

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