Method for preparing magnetic iron oxide-graphene composite

Abstract

The present invention relates to a method for preparing a magnetic iron oxide-graphene composite, a magnetic iron oxide-graphene composite prepared thereby and a composition for electromagnetic wave shielding including the same, and since graphene is prepared from a stage 1-GIC using FeCl.sub.3, magnetic particles in the form of FeO.sub.x are naturally formed on the surface of graphene during the preparation process. In addition, a magnetic material is formed on the surface of graphene while the defects of graphene are minimized, and thus the magnetic iron oxide-graphene composite prepared according to the present invention can be useful as an electromagnetic wave absorber.

Claims

1. A method for preparing a magnetic iron oxide-graphene composite comprising the steps of: mixing graphite and a halogen salt of iron and heat-treating the same (Step 1); reacting the product of step 1 with a (C.sub.1-20 alkyl) amine (Step 2); washing the product of step 2 (Step 3); subjecting the product of step 3 to a high-speed homogenization (Step 4); and subjecting the product of step 4 to sonication or a high-pressure homogenization (Step 5), wherein the high-speed homogenization of step 4 is carried out by stirring the product of Step 2 at 5000 to 8000 rpm, wherein the high-pressure homogenization of step 5 is carried out by passing the product of step 4 through a high-pressure homogenizer including an inlet, an outlet, and a micro-channel that connects between the inlet and the outlet and has a diameter in a micrometer scale, wherein the product of step 4 is introduced to the inlet of the high-pressure homogenizer under application of a pressure of 500 to 3000 bar and passes through the micro-channel.

2. The method according to claim 1, wherein the halogen salt of iron is FeCl.sub.3, FeCl.sub.2, or a mixture thereof.

3. The method according to claim 1, wherein, in step 1, the weight ratio between graphite and halogen salt of iron is 1:1 to 1:10.

4. The method according to claim 1, wherein the heat treatment is carried out at 300 C. to 400 C.

5. The method according to claim 1, wherein the step 1 is carried out for 24 hours or more.

6. The method according to claim 1, wherein (C.sub.1-20 alkyl) amine is hexylamine, or dodecylamine.

7. The method according to claim 1, wherein the step 2 is carried out at 30 C. to 250 C. for 6 hours or more.

8. The method according to claim 1, wherein the step 4 is carried out for 0.5 to 3 hours.

9. The method according to claim 1, wherein the micro-channel has a diameter of 50 to 300 m.

10. The method according to claim 1, wherein the step 5 is additionally carried out for 2 to 10 times.

11. The method according to claim 1, wherein the iron oxide of the magnetic iron oxide-graphene composite is Fe.sub.3O.sub.4, or Fe.sub.2O.sub.3.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 schematically shows a process in which the interlayer spacing of graphite widens according to the reaction between FeCl.sub.3 and a primary amine in the present invention.

(2) FIG. 2 shows a SEM image of graphite according to an embodiment of the present invention. FIG. 2(a) shows pristine graphite, FIG. 2(b) shows graphite in which FeCl.sub.3 is intercalated, and FIGS. 2(c) and 2(d) graphite treated with dodecylamine and hexylamine, respectively.

(3) FIG. 3 shows the result of Raman analysis (FIG. 3(a)) of graphite according to one embodiment of the present invention.

(4) FIG. 4 shows the result of XRD analysis (FIG. 3(b)) of graphite according to one embodiment of the present invention.

(5) FIG. 5 shows a TEM image (FIG. 5(a)) and a HR-TEM image (FIG. 5(b)) of the magnetic iron oxide-graphene composite according to one embodiment of the present invention.

(6) FIG. 6 shows STEM EDS MAPPING images (FIG. 6(a)) and the result of magnetic confirmation (FIG. 6(b)) of the magnetic iron oxide-graphene composite according to one embodiment of the present invention.

(7) FIG. 7 shows a SEM image of the magnetic iron oxide-graphene composite according to one embodiment of the present invention through the preparation process.

(8) FIG. 8 shows the result of lateral size analysis of the magnetic iron oxide-graphene composite according to one embodiment of the present invention. FIG. 8(a) shows the size distribution, and FIG. 8(b) shows a SEM image.

(9) FIG. 9 shows the result of thickness analysis of the magnetic iron oxide-graphene composite according to one embodiment of the present invention.

(10) FIG. 9(a) shows the result of AFM analysis, and FIG. 9(b) shows the thickness distribution.

(11) FIG. 10 shows the result of EMI shielding efficiency measurement of the magnetic iron oxide-graphene composite according to one embodiment of the present invention. FIGS. 10(a) and 10(b) each show a SEM image of the side view of the film, and FIG. 10(c) shows the result of EMI shielding efficiency measurement according to mass % of the iron oxide-graphene composite.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(12) Hereinafter, preferred examples are presented to aid in understanding of the invention. However, the following examples are provided only for illustrative purposes, and the scope of the present invention is not limited thereto.

EXAMPLE 1

(13) 4 g of pristine graphite and 20 g of FeCl.sub.3 were added to a round bottom flask and mixed, and then the mixture was heat-treated at 337 C. for 3 days (72 hours) in a box furnace. The product was cooled to room temperature and then dispersed in 400 mL of a dodecylamine solution and reacted at 90 C. for 6 hours. After the product was filtered, it was washed with 2 L of 10 rnM HCl/EtOH solution and 500 mL of ethanol with a vacuum filter. Then, the product was dried to prepare graphite intercalated with iron oxide, and the resultant was named FeO.sub.x-GIC.

(14) 0.1 g of the FeO.sub.x-GIC and 0.04 g of PVP were added to water and homogenized at a high speed for 1 hour at 5000 rpm using a high-speed homogenizer (Silverson model L5M mixer). Then, the resultant was sonicated at a frequency of 40 kHz for 30 minutes with an ultrasonic processor to prepare a magnetic iron oxide-graphene composite.

EXAMPLE 2

(15) A magnetic iron oxide-graphene complex was prepared in the same manner as in Example 1 except that hexylamine was used instead of dodecylamine.

EXAMPLE 3

(16) 2.5 g of FeO.sub.x-GIC prepared in Example 1 and 0.5 g of PVP were added to 500 mL of NMP and homogenized at a high speed of 5000 rpm for 1 hour using a high-speed homogenizer (Silverson model L5M mixer).

(17) Then, the solution was fed to the inlet of the high-pressure homogenizer. The high-pressure homogenizer has a structure including an inlet of the raw material, an outlet of the exfoliated product, and a micro-channel that connects between the inlet and the outlet and has a diameter in a micrometer scale. The feed solution was introduced in the inlet while applying a high-pressure of 800 to 1200 bar, and a high shear force was applied while passing through a micro-channel having a diameter of 75 m. The solution recovered from the outlet was again reintroduced to the inlet of the high-pressure homogenizer, and this process was repeated until the number of times the solution passed through the micro-channel reached 5 times, thereby preparing a magnetic iron oxide-graphene composite.

EXPERIMENTAL EXAMPLE 1

(18) In order to confirm the interlayer spacing of graphite after the primary amine treatment, the graphite up to the primary amine treatment of Examples 1 and 2 was confirmed by SEM images, and the results are shown in FIG. 2.

(19) FIG. 2(a) shows pristine graphite, and FIG. 2(b) shows graphite in which FeCl.sub.3 is intercalated. In contrast, it was confirmed that the interlayer spacing of graphite was wider after the primary amine treatment as shown in FIGS. 2(c) and 2(d).

(20) Further, Raman analysis and XRD analysis were performed on each of the above materials, and the results are shown in FIG. 3 and FIG. 4, respectively.

(21) As shown in FIG. 3, the change in the position of D peak occurs because the Fermi energy level is lowered due to the charge transfer of FeCl.sub.3 (acceptor) in graphite (donor). Therefore, it was confirmed that FeCl.sub.3 was properly intercalated between the interlayers of graphite. Furthermore, after the primary amine substitution, it was confirmed that the D peak returned to its original position, and from this, it was confirmed that FeCl.sub.3 was properly surrounded by the primary amine.

(22) In addition, as shown in FIG. 4, the intrinsic peak of the graphite intercalated with FeCl.sub.3 (stage 1) was confirmed, and after the primary amine treatment, the interlayer spacing of the graphite became wider, confirming that the intrinsic peak disappeared.

EXPERIMENTAL EXAMPLE 2

(23) The magnetic iron oxide-graphene composite prepared in Example 1 was analyzed by TEM and HR-TEM, and the results are shown in FIG. 5. As shown in FIG. 5, it was confirmed that graphene having a thickness of about 1 to 5 nm was prepared.

(24) Further, the magnetic iron oxide-graphene composite prepared in Example 1 was analyzed by STEM EDS MAPPING, and whether it exhibited magnetic properties was confirmed and shown in FIG. 6. As shown in FIG. 6(a), it was confirmed that iron oxide was formed on the surface of graphene, and as shown in FIG. 6(b), it was confirmed that the composite exhibited magnetic properties.

EXPERIMENTAL EXAMPLE 3

(25) The magnetic iron oxide-graphene composite prepared in Example 3 was analyzed by SEM image for each preparation step, and the results are shown in FIG. 7.

(26) As shown in FIG. 7, the interlayer spacing of the graphite was widened by the primary amine treatment (DA) (FIG. 7(a)), and it was confirmed that the magnetic iron oxide-graphene composite was formed through the high-speed homogenization (FIG. 7(b)) and high-pressure homogenization (FIG. 7(c)).

EXPERIMENTAL EXAMPLE 4

(27) The average lateral size of the magnetic iron oxide-graphene composite prepared in Example 3 was analyzed by SEM image, and the results are shown in FIG. 8. As shown in FIG. 8, it was confirmed that the average lateral size of the magnetic iron oxide-graphene composite ranged from about 0.5 m to 7 m and that the average size was about 2.38 m.

(28) In addition, the average thickness of the magnetic iron oxide-graphene composite prepared in Example 3 was analyzed by AFM, and the results are shown in FIG. 9. As shown in FIG. 9, it was confirmed that the thickness of the magnetic iron oxide-graphene composite ranged from about 0.5 nm to 15 nm and that the average thickness was about 4 nm. From this, it can be confirmed that the graphene having a small thickness was generally prepared.

EXPERIMENTAL EXAMPLE 5

(29) An appropriate amount of the iron oxide-graphene complex prepared in Example 3 was added to PMMA/Chloroform solution, and the chloroform used as a solvent for 3 to 6 hours at 60 to 75 C. was evaporated, followed by vacuum drying for 12 hours to evaporate the residual chloroform at 60 C. After vacuum drying, a sheet in the form of a film was prepared by pressurizing at 5 MPa and 210 C. for 10 minutes using a hot press, and EMI shielding efficiency was measured. The measurement results are shown in FIG. 10.