Graphene composite iron-doped manganese dioxide wave-absorbing agent and preparation method thereof

Abstract

The invention provides a graphene composite iron-doped manganese dioxide wave-absorbing agent and a preparation method thereof, and belongs to the technical field of wave-absorbing agent materials. The iron-doped manganese dioxide composite graphite sheet material is obtained by using a one-step hydrothermal synthesis method, the doping amount of an iron element is less than 2%, the trace iron element is doped into a manganese dioxide lattice to replace the position of a part of the manganese element, and meanwhile, the doping of the iron element can enhance the electromagnetic loss of the composite material; the impedance matching is improved by introducing different contents of iron salts, so that the purpose of enhancing the performance of the wave-absorbing composite material is achieved. The composite material obtained by the method is uniform in fibrous microstructure distribution, so that the interface of the composite material fiber and the graphite nanosheet is more beneficial to electromagnetic wave absorption, and the electromagnetic absorption characteristic is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wave absorbing agent materials, and in particular to a graphene composite iron-doped manganese dioxide wave absorbing agent and a preparation method thereof. Background Art

[0002] Graphene is a material with great potential as an absorber, but due to its extremely weak magnetic loss, graphene alone has very poor absorption performance. Existing technologies combine graphene with other substances to improve impedance matching and achieve even better absorption performance. Manganese dioxide is a material with a strong dielectric response and excellent electromagnetic wave absorption properties. Combining graphene with manganese dioxide can prevent electromagnetic waves from penetrating the composite material due to steric hindrance, slowing their direct penetration. The high dielectric loss of graphene oxide and manganese dioxide can be utilized to significantly reduce the transmitted energy of electromagnetic waves. Patent application number 201710020153.6 discloses a method for preparing a graphene oxide / manganese dioxide composite material. After intercalation and exfoliation of graphite, the composite material is directly prepared in situ using a one-step redox hydrothermal method on the basis of incomplete oxidation. However, the wave absorption performance of the composite material prepared by this method still needs to be improved, and its reflection loss value is not lower than -20dB; the applicant discloses a sea urchin-shaped microstructured manganese dioxide composite graphene nanosheet powder. The one-dimensional manganese oxide in the outer layer of the composite powder can act as an antenna, inducing the generation of microcurrent, which is beneficial to increase the loss of incident electromagnetic waves. At the same time, it can also serve as a transition layer for electromagnetic waves to enter the material interface, which is beneficial to improve impedance matching and facilitate the absorption of electromagnetic waves.

[0003] As we all know, the absorption performance of a material depends on dielectric polarization, conductivity loss, and magnetic resonance. The crystal structure, defects, and morphology of the material can affect the absorption performance by affecting the electromagnetic properties. Manganese dioxide has characteristics such as polycrystalline and is prone to phase change in various ways. Therefore, it can be further optimized. Patent application number 201910981632.3 discloses an iron-doped manganese dioxide composite reduced graphene oxide material. By doping with iron elements, defects are introduced into the crystal to weaken the interaction between zinc ions and the manganese dioxide matrix, making it easier for zinc ions to embed / eject from the matrix, while increasing the carrier concentration in manganese dioxide, thereby obtaining a zinc ion battery positive electrode material with high specific capacity and good cycle stability. However, the patent does not disclose its application in the field of wave absorption, and impurities or incomplete reaction products may be generated during the reaction process, thereby affecting product performance. In addition, the preparation method includes a two-step hydrothermal reaction, which requires precise control of parameters such as time and temperature in each step, and the operation is complicated.

[0004] Therefore, it is of great significance to further develop and optimize composite absorbers and find an absorber with simple preparation method, no impurities and excellent absorbing performance. Summary of the Invention

[0005] The purpose of this application is to provide a graphene composite iron-doped manganese dioxide absorber and a preparation method thereof to solve the problems existing in the above-mentioned background technology.

[0006] The embodiments of the present application can be implemented through the following technical solutions:

[0007] A graphene composite iron-doped manganese dioxide absorber is composed of fibrous MnO2 nanowires uniformly wrapped on the surface of two-dimensional sheet-like GNs, wherein Fe replaces part of the Mn position in the MnO2 lattice, and the content of iron in the composite absorber is greater than 0 and less than 2% by mass.

[0008] A preparation method for preparing the composite absorber described above comprises the following steps:

[0009] S1: mixing 0.05-0.15 parts by weight of an inorganic iron salt, 0.5-1.5 parts by weight of acidified GNs, 10-20 parts by weight of manganese sulfate, and 300-600 parts of water to obtain a mixed solution;

[0010] S2: Add 60-120 parts by weight of potassium permanganate to the mixed solution obtained in S1 and stir evenly;

[0011] S3: subjecting the solution obtained in S2 to a hydrothermal reaction at 180-240°C for 8-20 hours, and cooling to room temperature after the reaction is completed.

[0012] Furthermore, a post-processing step S4 is included, and the post-processing step S4 includes one or more of separation, washing, and drying.

[0013] Furthermore, the inorganic iron salt is selected from one or more of ferric nitrate, ferric chloride and ferrous sulfate.

[0014] Furthermore, the inorganic iron salt is 0.1 parts by weight.

[0015] Furthermore, the particle size of the inorganic iron salt is 100-400 mesh.

[0016] Furthermore, the GNs treated with acid have a flake size of 0.5-3 μm, a single flake thickness of 0.55-3.74 nm, and a flake number of less than 10 layers.

[0017] Furthermore, the acidified GNs are obtained by acidification with concentrated nitric acid having a concentration of 60%-70% for 18-22 hours.

[0018] Furthermore, the S1 specifically includes the following steps:

[0019] S11: adding 0.5-1.5 parts by weight of the acidified GNs to 300-600 parts of water, and stirring to obtain a GNs aqueous dispersion;

[0020] S12: adding 0.05-0.15 parts by weight of an inorganic iron salt and 10-20 parts by weight of manganese sulfate to the GNs aqueous dispersion obtained in S11, and subjecting the mixture to ultrasonic treatment for 30 minutes to obtain a mixed solution.

[0021] Furthermore, the stirring time in S2 is 30 min.

[0022] The embodiments of the present application provide a graphene-composite iron-doped manganese dioxide absorber and a preparation method thereof, which have at least the following beneficial effects: the fibrous MnO2 coating of the composite absorber of the present application is uniform, dense, and impurity-free, with a coating rate of over 95%, greatly improving the electromagnetic absorption efficiency; and the composite absorber is prepared by a one-step hydrothermal method, which, on the one hand, enables trace iron doping, and, on the other hand, simplifies the process, is low-cost, and is easy to implement in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the SEM image of product P1 in Example 1;

[0024] Figure 2 is the SEM image of product P2 in Example 2;

[0025] Figure 3 The XRD patterns of products P1, P2 and P3 in Example 1 and Example 2 are shown in FIG.

[0026] Figure 4 is the XPS total spectrum of product P2 in Example 2;

[0027] Figure 5 is the XPS Fe 2p spectrum of product P2 in Example 2;

[0028] Figure 6 RL reflection loss diagram of product P1 in Example 1;

[0029] Figure 7 This is the RL reflection loss diagram of product P2 in Example 2.

[0030] Figure 8 This is the RL reflection loss diagram of product P3 in Example 3. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0032] The present invention provides a graphene-composite iron-doped manganese dioxide absorber and its preparation method. This invention grows fibrous MnO2 on the surface of graphene nanosheets (GNs) through an in-situ reaction method. Furthermore, a very small amount of iron is doped to further improve the microscopic distribution of the composite material, forming a three-dimensional network structure. Unlike previous composite materials, this invention incorporates a very small amount of iron, with the iron doping amount being greater than 0 and less than 2% by mass. A moderate amount of iron doping can effectively enhance the sample's magnetic permeability and magnetic loss while reducing its dielectric properties. However, excessive iron doping significantly reduces the electromagnetic parameters of the resulting sample, ultimately leading to a decrease in the material's absorption performance. The present invention utilizes a one-step hydrothermal method to simultaneously deposit iron and manganese oxides in the same solvent. The two oxides have significant differences in their precipitation and deposition abilities. The deposition ability of manganese oxide, as shown by the Nernst equation, is much higher than that of iron oxide. Therefore, the composite absorber obtained using the preparation method of the present invention is primarily manganese oxide, with a trace amount of iron doping.

[0033] MnO 4- +4H + +3e-=MnO 2(固) +2H2O (standard electrode potential 1.695V);

[0034] Fe 3+ +e - =Fe 2+ (standard electrode potential 0.771V);

[0035] Specifically, the trace iron-doped manganese dioxide / graphene composite absorber prepared by the present invention is composed of fibrous MnO2 nanowires uniformly wrapped on the surface of two-dimensional sheet-like GNs. The coating is uniform, dense and free of impurities, with a coating rate of over 95%. Among them, Fe replaces some of the Mn positions in the MnO2 lattice. Among them, GNs, as typical conductive electromagnetic absorption materials, can allow more electromagnetic waves to enter the material interior and convert some of the electromagnetic wave energy into heat energy. The MnO2 nanostructures distributed on the GNs act as dielectric loss-type electromagnetic wave absorption materials, which can consume electromagnetic waves entering the material interior through interface polarization and dipole relaxation polarization. By replacing some of the Mn positions in the MnO2 lattice, the Fe doping can enhance the dielectric loss of the composite material on the one hand, improve its impedance matching through the introduction of different iron salt contents, and on the other hand, the Fe doping improves the distribution of fine fibers in the microstructure, making the interface between the composite fiber and the graphite nanosheet more conducive to electromagnetic wave absorption. The synergistic effect of the above-mentioned consumption methods greatly improves the electromagnetic wave loss capacity.

[0036] The graphene composite iron-doped manganese dioxide absorber of the present invention is prepared by the following method:

[0037] Step 1: mixing the acidified GNs, an inorganic iron salt, manganese sulfate, and water to obtain a mixed solution; preferably, the acidified GNs and water are first mixed and stirred to obtain a GNs dispersion solution, and then the inorganic iron salt is added to the GNs dispersion solution and subjected to ultrasonic treatment;

[0038] Step 2, adding potassium permanganate to the mixed solution obtained in step 1 and stirring;

[0039] Step 3: transfer the mixed solution obtained in step 2 into a reactor and conduct a one-step hydrothermal reaction. After the reaction is completed, cool it to room temperature, separate, wash and dry it to obtain the product composite absorber.

[0040] In step 1, the amount of GNs added is preferably 0.5 to 1.5 parts by weight, more preferably 0.8 to 1.2 parts by weight, and more preferably 1.0 part by weight;

[0041] The GNs have a flake size of 0.5 to 3 μm, a single flake thickness of 0.55 to 3.74 nm, and a flake number of <10 layers. Preferably, the GNs have a flake size of 1 to 2 μm, a single flake thickness of 0.80 to 2.5 nm, and a flake number of <8 layers.

[0042] The acidified GNs are preferably obtained by acidification with concentrated nitric acid; the concentration of the concentrated nitric acid is preferably 60% to 70%, more preferably 68%; the acidification time is preferably 18 to 22 hours, more preferably 20 hours.

[0043] The addition amount of the inorganic iron salt is preferably 0.05 to 0.15 parts by weight; the inorganic iron salt is preferably one or more of ferric nitrate, ferric chloride and ferrous sulfate, more preferably ferric chloride; the particle size of the inorganic iron salt is preferably 100 to 400 mesh, more preferably 200 to 300 mesh.

[0044] The amount of manganese sulfate added is preferably 10 to 15 parts by weight;

[0045] The water is preferably deionized water, and the addition amount is preferably 300 to 600 parts by weight, more preferably 350 to 550 parts, and more preferably 400 to 500 parts;

[0046] The ultrasonic treatment time in step 1 is preferably 30 min;

[0047] The amount of potassium permanganate added in step 2 is preferably 60 to 90 parts by weight;

[0048] The hydrothermal reaction conditions in step 3 are preferably a temperature of 180 to 240° C. and a reaction time of 8 to 20 hours.

[0049] The present invention has no particular limitation on the separation method, and any separation method well known to those skilled in the art can be used. Those skilled in the art can select and adjust the separation method according to actual production conditions, product requirements and quality requirements. The separation method of the present invention is preferably centrifugal separation.

[0050] The present invention has no particular limitation on the washing method, and any washing method familiar to those skilled in the art may be used. Those skilled in the art may select and adjust the method according to actual production conditions, product requirements, and quality requirements. The number of washing times is preferably 5 times.

[0051] The present invention has no particular limitation on the drying method, and any drying method well known to those skilled in the art may be used. Those skilled in the art may select and adjust the drying method according to actual production conditions, product requirements, and quality requirements.

[0052] Example 1

[0053] Step (1) placing 150 ml of the aqueous solution in a dry and clean 250 ml beaker, adding 0.3 g of GNs acidified with concentrated nitric acid, and stirring to obtain a GNs dispersion solution; wherein the GNs acidified with concentrated nitric acid are specifically obtained by treating graphene nanosheets with 68% concentrated nitric acid for 20 hours;

[0054] Step (2), adding 0.008 g of ferric chloride hexahydrate (FeCl3·6H2O) and 1.51 g of manganese sulfate (MnSO4) to the above-mentioned dispersed solution, and ultrasonically treating for 30 minutes to obtain a mixed solution containing iron salt and graphite nanosheets;

[0055] Step (3), adding 9.48 g of potassium permanganate (KMnO4) to the mixed solution obtained in step (2) and stirring for 30 minutes;

[0056] Step (4), transferring the solution obtained in step (3) into a reaction kettle, placing the reaction kettle in an oven, and reacting at 200° C. for 16 hours;

[0057] Step (5), after the reaction in step (4) is completed and the temperature is lowered to room temperature, the mixture is repeatedly washed with deionized water for 5 times, centrifuged to obtain a precipitate, and the precipitate is dried to obtain an iron-doped MnO2 / GNs composite absorber, which is recorded as P1.

[0058] The product P1 obtained in this example was subjected to XRD (see Figure 3 ), SEM (see Figure 1 ) and wave absorbing performance (see Figure 6) test, it can be seen that the product P1 morphology is fibrous MnO2 nanowires uniformly wrapped on the surface of two-dimensional flaky GNs, and there are no other impurities in the product. Combined with XRD, no iron element was detected, indicating that the iron element doping amount is less than 2%. In addition, the composite absorber has excellent absorbing performance, and its reflection loss value can reach -30dB at a thickness of 5.7mm, and the maximum bandwidth can reach 5.12GHz at a thickness of 2.2mm.

[0059] Example 2

[0060] Step (1) placing 150 ml of the aqueous solution in a dry and clean 250 ml beaker, adding 0.3 g of GNs acidified with concentrated nitric acid, and stirring to obtain a GNs dispersion solution; wherein the GNs acidified with concentrated nitric acid are specifically obtained by treating graphene nanosheets with 68% concentrated nitric acid for 20 hours;

[0061] Step (2), adding 0.016 g of ferric chloride hexahydrate (FeCl3·6H2O) and 1.51 g of manganese sulfate (MnSO4) to the above-mentioned dispersed solution, and ultrasonically treating for 30 minutes to obtain a mixed solution containing iron salt and graphite nanosheets;

[0062] Step (3), adding 9.48 g of potassium permanganate (KMnO4) to the mixed solution obtained in step (2) and stirring for 30 minutes;

[0063] Step (4), transferring the solution obtained in step (3) into a reaction kettle, placing the reaction kettle in an oven, and reacting at 200° C. for 16 hours;

[0064] Step (5), after the reaction in step (4) is completed and the temperature is lowered to room temperature, the mixture is repeatedly washed with deionized water for 5 times, centrifuged to obtain a precipitate, and the precipitate is dried to obtain an iron-doped MnO2 / GNs composite absorber, which is recorded as P2.

[0065] The product P2 obtained in this example was subjected to XRD (see Figure 3 ), SEM (see Figure 2 ), XPS (see Figure 4 、 Figure 5 ) and wave absorbing performance (see Figure 7 ) test, it can be seen that the product P2 morphology is also fibrous MnO2 nanowires uniformly wrapped on the surface of two-dimensional flaky GNs. The XPS results show that the iron element is successfully doped. Combined with the XRD spectrum, it can be seen that there are no other impurities in the product, and the iron element doping amount is less than 2%. In addition, the composite absorber has excellent absorbing performance, and its reflection loss value can reach -60.7dB at a thickness of 5.7mm, and the maximum bandwidth can reach 5.96GHz at 2.4mm.

[0066] Example 3

[0067] Step (1) placing 150 ml of the aqueous solution in a dry and clean 250 ml beaker, adding 0.3 g of GNs acidified with concentrated nitric acid, and stirring to obtain a GNs dispersion solution; wherein the GNs acidified with concentrated nitric acid are specifically obtained by treating graphene nanosheets with 68% concentrated nitric acid for 20 hours;

[0068] Step (2), adding 0.024 g of ferric chloride hexahydrate (FeCl3·6H2O) and 1.51 g of manganese sulfate (MnSO4) to the above-mentioned dispersed solution, and ultrasonically treating for 30 minutes to obtain a mixed solution containing iron salt and graphite nanosheets;

[0069] Step (3), adding 9.48 g of potassium permanganate (KMnO4) to the mixed solution obtained in step (2) and stirring for 30 minutes;

[0070] Step (4), transferring the solution obtained in step (3) into a reaction kettle, placing the reaction kettle in an oven, and reacting at 200° C. for 16 hours;

[0071] Step (5), after the reaction in step (4) is completed and the temperature is lowered to room temperature, the mixture is repeatedly washed with deionized water for 5 times, centrifuged to obtain a precipitate, and the precipitate is dried to obtain an iron-doped MnO2 / GNs composite absorber, which is recorded as P3.

[0072] The product P3 obtained in this example was subjected to XRD (see Figure 3 ), and wave absorbing performance (see Figure 8 ) test, it can be seen that there are no other impurities in the product, and the iron content is less than 2%. The composite absorber has excellent absorbing performance. It can be clearly observed that the reflection loss value of product P3 can reach -35.5dB at a thickness of 5.5mm, and the maximum bandwidth can reach 5.2GHz at a thickness of 2.1mm.

[0073] The above is a detailed introduction to the specific implementation methods of the present application. For those skilled in the art, several improvements and modifications can be made to the present application without departing from the principles of the present application. These improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A graphene composite iron-doped manganese dioxide absorber, characterized in that: The composite absorber is composed of fibrous MnO2 nanowires uniformly wrapped on the surface of two-dimensional sheet-like GNs, wherein Fe replaces part of the Mn position in the MnO2 lattice, and the content of iron in the composite absorber is greater than 0 and less than 2% by mass percentage.

2. A preparation method for preparing the wave absorbing agent according to claim 1, characterized in that: The following steps are involved: S1: mixing 0.05-0.15 parts by weight of an inorganic iron salt, 0.5-1.5 parts by weight of acidified GNs, 10-20 parts by weight of manganese sulfate, and 300-600 parts of water to obtain a mixed solution; S2: Add 60-120 parts by weight of potassium permanganate to the mixed solution obtained in S1 and stir evenly; S3: subjecting the solution obtained in S2 to a hydrothermal reaction at 180-240°C for 8-20 hours, and cooling to room temperature after the reaction is completed.

3. The preparation method according to claim 2, characterized in that The method further includes a post-processing step S4, which includes one or more of separation, washing, and drying.

4. The preparation method according to claim 2, characterized in that The inorganic iron salt is selected from one or more of ferric nitrate, ferric chloride and ferrous sulfate.

5. The preparation method according to claim 2, characterized in that The inorganic iron salt is 0.1 parts by weight.

6. The preparation method according to claim 4, characterized in that The particle size of the inorganic iron salt is 100-400 meshes.

7. The preparation method according to claim 2, characterized in that The GNs treated by acidification have a flake size of 0.5-3 μm, a single flake thickness of 0.55-3.74 nm, and a flake number of less than 10 layers.

8. The preparation method according to claim 7, characterized in that The acidified GNs are obtained by acidification with concentrated nitric acid having a concentration of 60% to 70% for 18 to 22 hours.

9. The preparation method according to claim 2, characterized in that The S1 specifically includes the following steps: S11: adding 0.5-1.5 parts by weight of the acidified GNs to 300-600 parts of water, and stirring to obtain a GNs aqueous dispersion; S12: adding 0.05-0.15 parts by weight of an inorganic iron salt and 10-20 parts by weight of manganese sulfate to the GNs aqueous dispersion obtained in S11, and subjecting the mixture to ultrasonic treatment for 30 minutes to obtain a mixed solution.

10. The preparation method according to claim 2, characterized in that The stirring time in S2 is 30 min.

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