Porous carbon nanomaterials, preparation method, and electromagnetic shielding film

Abstract

The present invention relates to the technical field of electromagnetic shielding technology, and discloses a porous carbon nanomaterial, a preparation method, and an electromagnetic shielding film; the preparation method of the porous carbon nanomaterial is to use iron citrate and phytic acid as carbon sources, add an activator, and obtain porous carbon through carbonization; the porous carbon and a nano-metal precursor are obtained through hydrothermal reduction. The porous carbon nanomaterial provided by the present invention uses iron citrate and phytic acid as raw materials, assisted by adding an activator, and adopts a direct carbonization method to prepare a porous carbon material with a large number of micropores inside, and its specific surface area and pore size can also be regulated by controlling the amount of the activator. Then, by utilizing the microporous structure and high specific surface area of the porous polymer, the nano-metal precursor is subjected to hydrothermal reduction to achieve the loading of a nano-metal with an ultra-high content, and effectively prevent the aggregation of nanoparticles, thereby achieving a nano-content of more than 40 wt%.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic shielding, and specifically, to porous carbon nanomaterials, preparation methods, and electromagnetic shielding films. Background Art

[0002] The sensitivity to electromagnetic waves is increasing day by day, which requires new wave-absorbing materials to develop in the directions of thin thickness, low density, wide frequency band, and strong absorption. To develop new wave-absorbing materials that meet the requirements of "thin, light, wide, and strong", current research mainly focuses on wave-absorbing materials with different materials, different components (various nanomaterials), and different structures (chiral materials). However, the development of wave-absorbing materials mainly relies on the absorption of electromagnetic waves by a certain structure or component, lacking comprehensive consideration and design of the absorption of structure and component. Based on this, to achieve the purpose of "thin, light, wide, and high", it is necessary to follow the design concept and research idea of compounding multiple wave-absorbing mechanisms, combine the internal relationship between the microstructure, components, and functions of the material, construct a design idea that combines component and structure wave absorption, and develop new materials that integrate multiple wave-absorbing mechanisms.

[0003] Porous materials and nanomaterials have received increasing attention as new wave-absorbing materials. Porous carbon nanomaterials have been widely studied as adsorption materials, hydrogen storage materials, capacitor materials, and catalytic carriers for polymer electrolyte membrane fuel cells due to their unique structures and physicochemical properties. Combining porous carbon materials with nanomaterials and applying them to the field of electromagnetic shielding can design and develop metal-based filled conductive polymer composites with the wave-absorbing effect of structure and material coupling. It should be noted that the commonly used metal fillers can be conductive metals such as copper and silver, or magnetic metals such as ferrites. The electrical conductivity of common metal silver itself is generally greater than 10 5 S / cm, but the electrical conductivity of its corresponding metal particles or powders decreases as the particle size becomes smaller, generally less than 10 -3 S / cm. Only by adding a large amount of metal fillers can such composites meet the conductivity and electromagnetic shielding performance requirements of the application environment and functions; therefore, the metal-based filled composites that lose the advantage of light weight do not meet the standards of "light, thin, wide, and strong" for new electromagnetic shielding materials. At the same time, in the composite material, due to the increase in the content of the filler, the compatibility and dispersibility between the polymer and the metal-based filler are also a difficult problem. Summary of the Invention

[0004] <Technical problems to be solved by the present invention>

[0005] To solve the problems existing in the prior art that the electromagnetic shielding material has a large specific gravity due to the large amount added to meet the performance requirements, and the compatibility and dispersibility between the polymer and the metal-based filler are affected.

[0006] <Technical solution adopted by the present invention>

[0007] In view of the above technical problems, the object of the present invention is to provide a porous carbon nanomaterial, a preparation method, and an electromagnetic shielding film. The porous carbon nanomaterial provided by the present invention uses iron citrate and phytic acid as raw materials, assisted by adding an activator, and adopts a direct carbonization method to prepare a porous carbon material with a large number of micropores inside. The specific surface area and pore size can also be regulated by controlling the amount of the activator. Then, by utilizing the microporous structure and high specific surface area of the porous polymer, the nano-metal precursor is hydrothermally reduced to achieve the loading of ultra-high content nano-metals, and effectively prevent the aggregation of nano-particles, thereby achieving a nano-content of more than 40 wt%.

[0008] The specific content is as follows:

[0009] First, the present invention provides a preparation method of a porous carbon nanomaterial, using iron citrate and phytic acid as carbon sources, adding an activator, and obtaining porous carbon through carbonization; the porous carbon and the nano-metal precursor are hydrothermally reduced to obtain a porous carbon nanomaterial.

[0010] Second, the present invention provides a porous carbon nanomaterial obtained by the aforementioned preparation method.

[0011] Third, the present invention provides an electromagnetic shielding film, which is characterized in that it is obtained by blending and forming a porous carbon nanomaterial, PVDF, and a solvent.

[0012] <Beneficial effects achieved by the present invention>

[0013] (1) The present invention uses iron citrate and phytic acid as direct carbon sources, adopts a direct carbonization method to prepare a hierarchical microporous carbon material. The preparation method is simple and low-cost, and the porous carbon has a large specific surface area. Phytic acid contains six phosphate groups, and the phosphate group forms a -P-O-C- bond with the carbon skeleton matrix, effectively preventing the collapse of the carbon skeleton during high-temperature carbonization; at the same time, the phosphate compounds generated during the carbonization of phytic acid can also play a role in activating pore formation.

[0014] (2) The porous carbon prepared by the present invention has a large number of micropores inside, and at the same time, its specific surface area and pore size can be regulated. Its specific surface area can reach 904 m 2 / g, and the average pore size is 3.41 nm. The porous structure has the advantage of light weight on the one hand, and on the other hand, the influence on the electromagnetic parameters shows that the real part of the dielectric constant becomes smaller and the loss increases, which is beneficial to the impedance matching of the absorbing material and helps with energy loss, and is beneficial to adjusting the electromagnetic parameters of the material. Description of the drawings

[0015] Figure 1 It is the microscopic morphology diagram of the porous carbon in Example 1;

[0016] Figure 2It is the finished product diagram of the porous carbon nanomaterial in Example 1;

[0017] Figure 3 It is the electromagnetic shielding data diagram of Example 1. Specific embodiments

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0019] <Technical solution>

[0020] First, the present invention provides a preparation method of a porous carbon nanomaterial. Using ferric citrate and phytic acid as carbon sources, an activator is added, and porous carbon is obtained through carbonization; the porous carbon and a nano-metal precursor are hydrothermally reduced to obtain a porous carbon nanomaterial.

[0021] In the present invention, the activator includes ammonium chloride and potassium carbonate. The compound of ammonium chloride and potassium carbonate is used as an activator and a pore-forming agent to produce a porous carbon material with a high specific surface area with interconnected pores through activation. Ammonium chloride will completely decompose into NH3 and HCl during the carbonization process, which can be used as a pore-forming agent to obtain disordered and defective carbon; in addition, high temperature can promote the further decomposition of potassium carbonate to generate CO2, thereby increasing the porosity of the carbon material and finally achieving the effect of increasing the specific surface area and uniform pores of the porous carbon.

[0022] In the present invention, the nano-metal precursor includes a nano-silver precursor and / or an Fe3O4 precursor.

[0023] In the present invention, the nano-silver precursor is silver acetate; the Fe3O4 precursor is FeCl3·6H2O.

[0024] In the present invention, the nano-silver precursor and the porous carbon are subjected to a first hydrothermal treatment to obtain an intermediate; the intermediate and the Fe3O4 precursor are subjected to a second hydrothermal treatment to obtain a porous carbon nanomaterial. In the present invention, by separately loading the nano-precursors on the porous carbon, it is possible to avoid the agglomeration of nano-particles caused by the mutual coating of the two particles during the reduction process.

[0025] In the present invention, the porous carbon obtained through carbonization is ground and then placed in 0.5 mol / L sulfuric acid and treated at 75-90 °C for 20-28 h.

[0026] In the present invention, the mass ratio of ferric citrate, phytic acid, and the activator is 3-6:1-3:10-15; and / or, the mass ratio of the porous carbon to the nano-metal precursor is 1-3:0.1-0.5.

[0027] In the present invention, the carbonization conditions are as follows: under an inert atmosphere, drying treatment is carried out at 100-150°C, and then maintaining at 850-950°C for 1.5-4 h.

[0028] Second, the present invention provides a porous carbon nanomaterial obtained by the aforementioned preparation method.

[0029] Third, the present invention provides an electromagnetic shielding film obtained by blending and forming a porous carbon nanomaterial, PVDF, and a solvent.

[0030] <Example>

[0031] Example 1

[0032] This example provides an electromagnetic shielding film, including the following steps:

[0033] (1) Preparation of porous carbon

[0034] Step 1: Weigh 4 g of ferric citrate and 2 g of phytic acid and place them in an agate mortar. Then weigh 8 g of ammonium chloride and 4 g of potassium carbonate and place them in the same agate mortar. Grind for 2 h until fine powder is obtained and the above two substances are mixed evenly to obtain a mixed powder.

[0035] Step 2: Disperse the mixed powder in 95% ethanol, sonicate for 4 h to further mix it evenly. After rotary evaporation to remove the solvent, place it in a vacuum dryer at 80°C for 12 h.

[0036] Step 3: Transfer the mixed powder to a crucible, put it into a tubular furnace, under N2 protection, first dry at 120°C for 1 h, then maintain at 900°C for 2 h, and the heating rate is 5°C / min.

[0037] Step 4: Grind the burned sample into powder again (for 5 min), and then boil it in 0.5 mol / L H2SO4 at 80°C for 24 h (with gentle stirring).

[0038] Step 5: Wash with ethanol until neutral, filter by suction, and dry at 80°C for 8 h.

[0039] (2) Loading Ag by solvothermal reduction method

[0040] Step 1: Weigh 1 g of silver acetate and 0.1 g of porous carbon and pour them into a 100 m beaker, then add 30-50 ml of ethylene glycol (EG), and stir for 30 min;

[0041] Step 2: Transfer the solution to a 100 ml reaction kettle, put it into a muffle furnace, and react at 150°C for 5 h;

[0042] Step 3: Filter by suction, wash with ethanol until neutral, and then dry at 70°C.

[0043] (3) Loading Fe3O4 by solvothermal reduction method

[0044] Step 1: Weigh 1.35 g of FeCl3·6H2O, 3.6 g of anhydrous sodium acetate and 0.4 g of silver-loaded porous carbon. Measure 1 ml of polyethylene glycol (PEG-400) and add it to 30 - 50 ml of ethylene glycol (EG). Pour the mixture into a 100 ml beaker and stir for 15 min;

[0045] Step 2: Transfer the solution from Step 1 to a reaction kettle, place it in a muffle furnace, set the temperature to 170 °C, and react for 12 h;

[0046] Step 3: After the reaction is completed, pour out the upper layer of EG, rinse with ethanol, and let it stand for 3 h until the sample completely precipitates at the bottom of the beaker;

[0047] Step 4: Use a magnet to attract at the bottom of the beaker, pour out the upper layer of ethanol, repeat 2 times, and dry (60 - 80 °C).

[0048] (4) Film formation

[0049] Dissolve 1 g of PVDF in 15 ml of DMF, stir until completely dissolved, then remove the rotor, add 0.4 g of porous carbon-Ag-Fe x O y , ultrasonicate for 5 - 10 min, and pour it into a petri dish with a diameter of 7 cm and dry it at 80 °C to form a film.

[0050] <Comparative example>

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that silver acetate, FeCl3·6H2O, and anhydrous sodium acetate are all mixed in ethylene glycol and treated by hydrothermal reaction (170 °C, 12 h).

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that ammonium chloride and potassium carbonate are not added.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that it does not include Step 4 in (1).

[0057] <Test example>

[0058] Microtopography

[0059] Taking the porous carbon prepared in Example 1 as the sample, observe its microscopic morphology, and the results are as Figure 1 shown.

[0060] Specific surface area and pore size

[0061] Taking the porous carbon prepared in Example 1 as a sample, its specific surface area and pore size were measured, and the results are shown in Table 1.

[0062] Table 1 Specific Surface Area and Pore Size of Porous Carbon

[0063]

[0064] Sample diagram

[0065] Figure 2 It is the porous carbon nanomaterial prepared in Example 1.

[0066] Electromagnetic shielding effectiveness

[0067] Taking the electromagnetic shielding films prepared in Example 1 and Comparative Examples 1-3 as samples, the electromagnetic shielding effectiveness of the samples was measured, and the measurement results are shown in Table 2. The electromagnetic shielding data of Example 1 are as Figure 3 shown.

[0068] Table 2 Electromagnetic Shielding Effectiveness of Films

[0069] Sample Film thickness (mm) SET (dB) Example 1 0.131 64.2 Comparative Example 1 0.129 42.7 Comparative Example 2 0.133 35.2 Comparative Example 3 0.130 56.3

[0070] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a porous carbon nanomaterial, characterized in that, Using ferric citrate and phytic acid as carbon sources, an activator is added, and porous carbon is obtained through carbonization; the porous carbon and a nano-metal precursor are hydrothermally reduced to obtain a porous carbon nano-material; the nano-metal precursor includes a nano-silver precursor and / or an Fe3O4 precursor; the nano-silver precursor and the porous carbon are subjected to a first hydrothermal treatment to obtain an intermediate; the intermediate and the Fe3O4 precursor are subjected to a second hydrothermal treatment to obtain the porous carbon nano-material.

2. The preparation method of the porous carbon nanomaterial according to claim 1, characterized in that, The activator includes ammonium chloride and potassium carbonate.

3. The preparation method of the porous carbon nanomaterial according to claim 1, characterized in that, The nano-silver precursor is silver acetate; the Fe3O4 precursor is FeCl3·6H2O.

4. The preparation method of the porous carbon nanomaterial according to claim 1, characterized in that, The porous carbon obtained through carbonization is ground and then placed in 0.5 mol / L sulfuric acid and treated at 75 - 90 °C for 20 - 28 h.

5. The preparation method of the porous carbon nanomaterial according to any one of claims 1 to 4, characterized in that, The mass ratio of ferric citrate, phytic acid, and the activator is 3 - 6:1 - 3:10 - 15; and / or, the mass ratio of the porous carbon to the nano-metal precursor is 1 - 3:0.1 - 0.

5.

6. The preparation method of the porous carbon nanomaterial according to any one of claims 1 to 4, characterized in that, The carbonization conditions are as follows: under an inert atmosphere, it is dried at 100 - 150 °C and then maintained at 850 - 950 °C for 1.5 - 4 h.

7. A porous carbon nano-material obtained by the preparation method according to any one of claims 1 to 6.

8. An electromagnetic shielding film, characterized in that, It is obtained by blending and forming a film from the porous carbon nano-material according to claim 7, PVDF, and a solvent.

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