Method for preparing graphene electromagnetic shielding film loaded with Fe3O4 particles through rapid Joule heat

Abstract

The invention relates to a method for preparing an efficient electromagnetic shielding graphene film by using a rapid Joule heat technology, and belongs to the technical field of functional materials and application thereof. The method comprises the following steps: firstly, preparing a graphene oxide film through vacuum filtration, then carrying out pre-reduction treatment under the protection of argon, heating the film to 700 DEG C, and carrying out heat preservation for 1 hour so as to remove part of oxygen functional groups; and then, soaking the pre-reduced film in a ferric chloride ethanol solution, introducing a Fe3O4 nanoparticle precursor, and carrying out discharge treatment for 0.1 second under the voltage of 100V through a rapid Joule thermal reduction technology to realize rapid reduction of graphene oxide and doping of Fe3O4 nanoparticles. The finally prepared graphene film shows excellent electromagnetic shielding effectiveness in an X wave band (8-12 GHz), the electromagnetic shielding effectiveness reaches 38 dB, and the electromagnetic shielding effectiveness is improved by 2 dB compared with a sample (36 dB) not doped with Fe3O4. The method has the advantages of being easy and convenient to operate, low in energy consumption and high in reduction efficiency, meanwhile, the synergistic effect of conductivity loss, magnetic loss and dielectric loss is achieved through introduction of the Fe3O4 nanoparticles, the electromagnetic shielding performance of the material is remarkably improved, and the method is suitable for the fields of electromagnetic interference protection of electronic equipment and the like.

Description

Technical Field

[0001] The present invention belongs to the field of graphene materials, and particularly relates to a preparation method of a graphene-based electromagnetic shielding material, and more particularly to a method for preparing a graphene film loaded with Fe3O4 particles by rapid Joule heating technology. Background Art

[0002] With the rapid development of electronic devices, the problem of electromagnetic interference (EMI) has become increasingly serious, causing great impacts on communication, the environment and even human health, which puts forward higher requirements for the demand of high-performance electromagnetic shielding materials. Graphene and its derivatives have shown broad application prospects in the field of electromagnetic shielding due to their excellent electrical conductivity, thermal conductivity and mechanical strength. In particular, graphene oxide (GO), as an oxidized derivative of graphene, has good dispersibility and chemical reactivity, and has become an important candidate in electromagnetic shielding materials. However, due to its oxygen functional groups, the conductivity of graphene oxide is relatively low, which severely restricts its application effect in electromagnetic shielding.

[0003] To solve this problem, a common strategy is to restore its conductivity by reducing graphene oxide. Traditional reduction methods can be divided into two types: chemical reduction method and thermal reduction method. Chemical reduction methods, including using hydrogen, chemical reducing agents, etc., have a complex reduction process of graphene oxide and high costs. Some reducing agents even cause harm to the environment, and the reduction efficiency is low, making it difficult to meet the needs of large-scale applications. The thermal reduction method requires placing graphene oxide in a high-temperature and high-pressure environment for a long time of reduction to remove as many functional groups as possible, which is energy-consuming, time-consuming and laborious. Therefore, exploring a simple, economical and efficient method for reducing graphene oxide has become the focus of current research.

[0004] In recent years, rapid Joule heating reduction technology has attracted attention in the fields of graphene materials, waste plastic recycling and catalyst preparation due to its simple operation, fast reduction speed and high energy efficiency. This technology applies an electric current to a carbon-rich material to generate Joule heat, thereby removing other elements except carbon and reorganizing amorphous carbon to generate graphene-like materials. This method can prepare a large amount of graphene materials and can complete the reaction process in a relatively short time, with great application potential.

[0005] In addition, recent studies have also shown that introducing various nanomaterials into graphene films can significantly improve their electromagnetic shielding performance. Fe3O4 nanoparticles, as a magnetic material, play an important role in electromagnetic shielding materials. Its mechanism of action mainly includes the following aspects:

[0006] First, Fe3O4 nanoparticles enhance the electromagnetic wave absorption ability through the magnetic loss mechanism. In an alternating electromagnetic field, Fe3O4 nanoparticles will undergo natural resonance, eddy current loss, and hysteresis loss, converting electromagnetic wave energy into heat energy. Fe3O4 nanoparticles have a high dielectric constant and can consume electromagnetic wave energy through the dielectric loss mechanism. Interfacial polarization and dipole polarization are its main dielectric loss forms. In addition, the introduction of Fe3O4 nanoparticles can optimize the impedance matching of the material. By adjusting the dielectric constant and magnetic permeability of the material, the reflection of electromagnetic waves on the material surface is reduced, and the probability of electromagnetic waves entering the interior of the material is increased, thereby improving the overall shielding efficiency. The high conductivity of graphene combined with the magnetic loss and dielectric loss characteristics of Fe3O4 realizes the synergistic effect of conductance loss, magnetic loss, and dielectric loss, enabling the material to have excellent electromagnetic shielding performance in a wide frequency range (such as the X-band). The research on the introduction of Fe3O4 nanoparticles has gradually become a hot field of electromagnetic shielding materials.

[0007] Although a large number of studies have focused on the preparation and reduction methods of graphene oxide films, as well as the introduction of nanomaterials, how to reduce graphene oxide aqueous solution through rapid Joule heating technology and introduce Fe3O4 nanoparticles to prepare a film with good electromagnetic shielding performance is still a topic worthy of in-depth discussion. This method is not only simple and efficient but also can enhance the electromagnetic shielding ability of the material while ensuring good conductivity, with great practical application value. Summary of the Invention

[0008] In view of the above problems, the present invention proposes a method for preparing a highly efficient electromagnetic shielding graphene film through rapid Joule heating. By pre-reducing to regulate the conductivity of graphene oxide, combined with the uniform loading of Fe3O4 nanoparticles, instantaneous high temperature is used to simultaneously complete reduction and particle curing, and finally a graphene electromagnetic shielding film with high conductivity, magnetic loss, and dielectric loss characteristics is obtained, improving the shielding efficiency of the material in the X-band.

[0009] The technical solution of the present invention is as follows:

[0010] A method for preparing a highly efficient electromagnetic shielding graphene film through rapid Joule heating, characterized by comprising the following steps:

[0011] 1. Preparation of graphene oxide film

[0012] Prepare a graphene oxide film from a graphene oxide aqueous solution through a suction filtration process, and the concentration of the graphene oxide solution is 2 mg / mL;

[0013] 2. Pre-reduction treatment

[0014] Place the prepared graphene oxide film in a tube furnace. Under the protective environment of argon, the heating rate is 5 °C / h, and pre-reduction treatment is carried out at a temperature of 700 °C for 1 hour; the argon ventilation rate is 200 sccm;

[0015] Take it out after cooling.

[0016] 3. Doping Fe3O4

[0017] Immerse the pre-reduced graphene oxide film in a 0.2 mol / L iron chloride ethanol solution, take it out after soaking for 10 minutes and let it dry naturally

[0018] 4. Rapid Joule heating reduction

[0019] Paste the pre-reduced graphene oxide film on the sample stage with conductive silver paste;

[0020] Put it in an oven and dry it at 60 °C for 30 minutes;

[0021] Put the dried film into a vacuum chamber and connect the electrodes at both ends;

[0022] Set the charging voltage (100 V) and the discharge cut-off time (0.1 s), and start the device to charge the capacitor;

[0023] After charging is completed, start discharging. The sample temperature rises to about 3000 K in a short time and then cools rapidly, and complete reduction of graphene oxide is achieved by using Joule heat.

[0024] 5. Electromagnetic shielding performance test

[0025] Take out the reduced graphene film and perform X-band (8–12 GHz) electromagnetic shielding effectiveness test using a vector network analyzer. The test results show that its shielding effectiveness can reach 38 dB.

[0026] Preferably, the amount of graphene oxide used in the present invention is 20 mg. Too little amount of graphene oxide will cause the obtained graphene film to be thin and fragile, and too much graphene oxide will cause it difficult to separate graphene oxide sheets and water during the suction filtration process, and it is also difficult to complete the suction filtration even with the long-term operation of the vacuum pump.

[0027] Preferably, the pre-reduction temperature of the tube furnace used in the present invention is 700 degrees Celsius. Too low a temperature is difficult to reduce graphene oxide, so that the resistance of the pre-reduced graphene film is too high, and the current of the circuit is too low during subsequent processing. Too high a pre-reduction temperature will lead to increased energy consumption.

[0028] Preferably, the discharge voltage used in the present invention is 100V. Under the experimental conditions of the present invention, when the discharge voltage is lower than 100V, the heat generated by the graphene oxide film is not sufficient to completely remove the oxygen-containing functional groups; when the voltage is higher than 100V, due to the violent discharge process, the graphene film will be damaged.

[0029] The graphene film has the characteristic of being ultrathin. When observing the cross-section using SEM, the thickness is about 10 micrometers, which is significantly lower than that of graphene electromagnetic shielding films prepared by other methods.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1) The present invention applies the rapid Joule heating technology to the reduction of graphene oxide and the synchronous loading of Fe3O4 nanoparticles. By applying a 100V voltage for capacitive discharge (0.1 second), a high temperature of 3000 - 4000K is instantaneously generated, and the complete reduction of graphene oxide (removing oxygen-containing functional groups) and the in-situ generation of Fe3O4 nanoparticles are completed within milliseconds. Compared with the traditional thermal reduction method (requiring a high temperature above 1000°C and several hours of treatment) or chemical reduction method (relying on toxic reagents), this method shortens the reduction time to 0.1 second, reduces energy consumption by more than 80%, and does not require chemical waste liquid treatment, combining the characteristics of high efficiency and environmental protection.

[0032] 2) Through the uniform doping of Fe3O4 nanoparticles, a multi-mechanism synergistic shielding system of conductance loss (graphene), magnetic loss (natural resonance and eddy current loss of Fe3O4), and dielectric loss (interface polarization and dipole polarization) is constructed.

[0033] 3) Before rapid Joule heating reduction, a pre-reduction process is adopted to optimize the conductivity of graphene oxide, providing a conductive path for subsequent instantaneous high-temperature reduction.

[0034] 4) By soaking in an ethanol solution of ferric chloride (0.2 mol / L) and instantaneous high-temperature curing, uniform distribution of Fe3O4 nanoparticles (20 - 50 nm) between and on the surface of graphene layers (coverage rate 80% - 90%) is achieved, and a strong interfacial bond is formed between the particles and the graphene matrix. Compared with the traditional chemical deposition method, this method avoids the problem of particle agglomeration and enhances the mechanical stability of the material through high-temperature curing. Description of the Drawings

[0035] Figure 1 It is a process flow chart for the preparation of graphene oxide thin film and rapid Joule heating reduction.

[0036] Figure 2 It shows the sample stage of the rapid Joule heat treatment device.

[0037] Figure 3It is the curve corresponding to the temperature and time of the prepared graphene film.

[0038] Figure 4 It is the curve corresponding to the highest temperature and the reaction voltage.

[0039] Figure 5 It is the curve corresponding to the sheet resistance of the graphene film and the treatment voltage.

[0040] Figure 6 It is the electromagnetic shielding test curve of the prepared graphene film. Detailed implementation mode

[0041] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0042] Embodiment 1

[0043] 1. Preparation of graphene oxide thin film

[0044] Take 20 mg of graphene oxide and prepare an aqueous solution with a concentration of 2 mg / mL in 10 mL. Pour the solution into a vacuum filtration device and filter it through a cellulose acetate fiber filter membrane with a pore size of 0.22 μm to prepare a graphene oxide thin film.

[0045] 2. Pre-reduction treatment

[0046] Put the prepared graphene oxide thin film into a tube furnace, introduce argon as the protective gas, and the gas flow rate is 200 sccm. Raise the temperature from room temperature to 700 °C at a heating rate of 5 °C / h and keep it at 700 °C for 1 hour. After the heat preservation is over, turn off the heating power supply and let the tube furnace cool naturally to room temperature.

[0047] 3. Doping of Fe3O4 nanoparticles

[0048] Prepare a 0.2 mol / L ethanol solution of ferric chloride, immerse the pre-reduced graphene oxide thin film in the solution for 10 minutes to ensure that the Fe3O4 precursor is fully adsorbed on the film surface. After taking out the film, let it dry naturally at room temperature.

[0049] 4. Rapid Joule heat reduction

[0050] Fix the graphene oxide film doped with Fe3O4 on the sample stage with conductive silver paste. The distance between the two ends of the sample stage is 2 cm, and the width of the sample is 2.5 cm. Place the sample stage in a forced-air drying oven and dry it at 60 °C for 30 minutes. Subsequently, place the sample stage in a vacuum chamber, connect the electrodes at both ends, set the charging voltage to 100 V, and the discharge time to 0.1 s. Start the device for charging and discharging. The sample temperature rises to about 3000 K in a short time and then cools rapidly to complete the reduction of graphene oxide.

[0051] 5. Performance Testing and Optimization

[0052] Take out the reduced graphene film and use a vector network analyzer to measure its electromagnetic shielding effectiveness in the X-band (8 - 12 GHz). The test results show that the electromagnetic shielding effectiveness of the prepared graphene film is 36 dB.

[0053] Example 2

[0054] 1. Preparation of Graphene Oxide Film

[0055] Take 20 mg of graphene oxide and prepare an aqueous solution with a concentration of 2 mg / mL in 10 mL. Prepare the graphene oxide film through a vacuum filtration device.

[0056] 2. Pre-Reduction Treatment

[0057] Place the graphene oxide film in a tube furnace, introduce argon for protection, and the gas flow rate is 200 sccm. Increase the temperature to 500 °C at a heating rate of 5 °C / h and hold for 1 hour at 500 °C. After the holding period, turn off the heating power supply and let the tube furnace cool naturally to room temperature.

[0058] 3. Doping with Fe3O4 Nanoparticles

[0059] Immerse the pre-reduced graphene oxide film in a 0.2 mol / L iron chloride ethanol solution for 10 minutes, take it out and let it dry naturally at room temperature.

[0060] 4. Rapid Joule Heating Reduction

[0061] Fix the film on the sample stage with conductive silver paste, place it in a forced-air drying oven and dry it at 60 °C for 30 minutes. Subsequently, place the sample stage in a vacuum chamber, connect the electrodes, set the charging voltage to 100 V, and the discharge time to 0.1 s. Start the device for charging and discharging to complete the reduction process.

[0062] 5. Performance Testing

[0063] The test results show that due to the relatively low pre-reduction temperature, the reduction degree of graphene oxide is insufficient, resulting in a large resistance of the film and a significant decrease in the electromagnetic shielding effectiveness, which is only 28 dB.

[0064] Example 3

[0065] 1. Preparation of graphene oxide film

[0066] Take 20 mg of graphene oxide and prepare an aqueous solution with a concentration of 2 mg / mL in 10 mL. Prepare the graphene oxide film through a vacuum filtration device.

[0067] 2. Prereduction treatment

[0068] Put the graphene oxide film into a tubular furnace, introduce argon for protection, and the gas flow rate is 200 sccm. Raise the temperature to 1000 °C at a heating rate of 5 °C / h and hold for 1 hour at 1000 °C. After the holding ends, turn off the heating power supply and let the tubular furnace cool naturally to room temperature.

[0069] 3. Doping with Fe3O4 nanoparticles

[0070] Immerse the prereduced graphene oxide film in a 0.2 mol / L iron chloride ethanol solution for 10 minutes, take it out and let it dry naturally at room temperature.

[0071] 4. Rapid Joule heating reduction

[0072] Fix the film on the sample stage with conductive silver paste and dry it in a forced-air drying oven at 60 °C for 30 minutes. Subsequently, put the sample stage into a vacuum chamber, connect the electrodes, set the charging voltage to 100 V, and the discharge time to 0.1 second. Start the device for charging and discharging to complete the reduction process.

[0073] 5. Performance testing

[0074] The test results show that although the prereduction temperature is relatively high and the reduction degree of graphene oxide is good, the energy consumption increases significantly, and the electromagnetic shielding effectiveness is 36 dB, which is equivalent to that of Example 1.

[0075] Example 4

[0076] 1. Preparation of graphene oxide film

[0077] Take 20 mg of graphene oxide and prepare an aqueous solution with a concentration of 2 mg / mL in 10 mL. Prepare the graphene oxide film through a vacuum filtration device.

[0078] 2. Prereduction treatment

[0079] Put the graphene oxide film into a tubular furnace, introduce argon for protection, and the gas flow rate is 200 sccm. Raise the temperature to 700 °C at a heating rate of 5 °C / h and hold for 1 hour at 700 °C. After the holding ends, turn off the heating power supply and let the tubular furnace cool naturally to room temperature.

[0080] 3. Doping with Fe3O4 nanoparticles

[0081] The pre-reduced graphene oxide film was immersed in a 0.2 mol / L iron chloride ethanol solution for 10 minutes, and then taken out and air-dried at room temperature.

[0082] 4. Rapid Joule heating reduction

[0083] The film was fixed on the sample stage with conductive silver paste and dried in a forced-air drying oven at 60 °C for 30 minutes. Subsequently, the sample stage was placed in a vacuum chamber, the electrodes were connected, the charging voltages were set to 60 V, 100 V, and 120 V respectively, and the discharge time was 0.1 s. The device was started for charging and discharging to complete the reduction process.

[0084] 5. Performance testing

[0085] The test results showed that when the charging voltage was 100 V, the electromagnetic shielding effectiveness was the best, reaching 36 dB; when the voltage was 60 V, the reduction was insufficient and the shielding effectiveness decreased to 30 dB; when the voltage was 120 V, due to the too violent discharge process, part of the film was damaged and the shielding effectiveness was 34 dB.

[0086] Example 5

[0087] 1. Preparation of graphene oxide film

[0088] Take 20 mg of graphene oxide and prepare an aqueous solution with a concentration of 2 mg / mL in 10 mL. The graphene oxide film was prepared by a vacuum filtration device.

[0089] 2. Pre-reduction treatment

[0090] The graphene oxide film was placed in a tube furnace, and argon was introduced for protection at a flow rate of 200 sccm. The temperature was raised to 700 °C at a heating rate of 5 °C / min and held at 700 °C for 1 hour. After the holding period, the heating power was turned off and the tube furnace was allowed to cool naturally to room temperature.

[0091] 3. Doping with Fe3O4 nanoparticles

[0092] Prepare a 0.2 mol / L iron chloride ethanol solution, immerse the pre-reduced graphene oxide film in the solution for 10 minutes to ensure that the Fe3O4 precursor is fully adsorbed on the film surface. After taking out the film, it was air-dried at room temperature.

[0093] 4. Rapid Joule heating reduction

[0094] Fix the graphene oxide film doped with Fe3O4 on the sample stage with conductive silver paste. The distance between the two ends of the sample stage is 2 cm, and the width of the sample is 2.5 cm. Place the sample stage in a forced-air drying oven and dry it at 60 °C for 30 minutes. Subsequently, place the sample stage in a vacuum chamber, connect the electrodes at both ends, set the charging voltage to 100 V, and the discharge time to 0.1 s. Start the device for charging and discharging to complete the reduction process.

[0095] 5. Performance Testing

[0096] Take out the reduced graphene film and use a vector network analyzer to test its electromagnetic shielding effectiveness in the X-band (8 - 12 GHz). The test results show that the electromagnetic shielding effectiveness of the prepared graphene film is 38 dB, which is 2 dB higher than that of the sample without Fe3O4 doping (36 dB), proving the enhancing effect of the introduction of Fe3O4 nanoparticles on the electromagnetic shielding performance. The above-described embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the principle scope of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-efficiency electromagnetic shielding graphene film by rapid Joule heating, characterized in that: The steps include: (1) preparing a graphene oxide film: a graphene oxide aqueous solution with a concentration of 2 mg / mL was formed on a cellulose acetate fiber filter membrane with a pore size of 0.22 μm by vacuum filtration to form an initial graphene oxide film; (2) Pre-reduction treatment: placing the graphene oxide film in a tubular furnace protected by inert gas, heating it to 500-1000° C. at a heating rate of 5° C. / h, and keeping the temperature for 1-5 hours to obtain a pre-reduced graphene film; (3) Doping with Fe3O4 nanoparticles: The pre-reduced graphene film is immersed in ferric chloride ethanol solution to make Fe 3+ The precursor is uniformly adsorbed on the film surface and between layers; (4) Rapid Joule thermal reduction: The doped film is fixed on the sample stage of the vacuum chamber, and a 100 V voltage is applied to discharge the capacitor, which instantly generates high temperature and simultaneously completes the complete reduction of graphene oxide and the in-situ generation of Fe3O4 nanoparticles; (5) A graphene electromagnetic shielding film with a thickness of 8 to 12 μm is obtained, whose electromagnetic shielding effectiveness in the X-band is 36 to 38 dB and whose conductivity is 400 S / m.

2. The method according to claim 1, characterized in that A graphene oxide film was prepared by vacuum filtration using a graphene oxide solution as a raw material, and the concentration of the graphene oxide solution was 2 mg / mL.

3. The method according to claim 1, characterized in that The film is pre-reduced in a tubular furnace under inert gas protection, with a pre-reduction temperature of 500-1000°C, a heating rate of 5°C / h, a holding time of 1-5 hours, preferably 700°C.

4. The method according to claim 1, characterized in that: The pre-reduced graphene oxide film is immersed in a ferric chloride ethanol solution, wherein the concentration of the ferric chloride ethanol solution is 0.2 mol / L.

5. The method according to claim 1, characterized in that The graphene oxide film was reduced under vacuum conditions using the rapid Joule heating method. During the rapid Joule heating process, the sample temperature rose to 3000K-4000K, the duration was 0.1 second, and the charging voltage was 100V.

6. The method according to claim 1, characterized in that The prepared graphene film has good electrical conductivity, with an electrical conductivity of 400S / m.

7. The method according to claim 1, characterized in that The electromagnetic shielding effectiveness of the prepared graphene film in the X-band (8-12GHz) is 36dB-38dB.

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