Preparation method of environment-friendly electromagnetic wave-absorbing aerogel

Abstract

The invention relates to a preparation method of environment-friendly electromagnetic wave-absorbing aerogel. The material is light in weight, high in strength, environment-friendly, safe and environment-friendly. The preparation method comprises the following steps: step 1, preparing a silver nanowire dispersion liquid; 2, KCl particles are added into the silver nanowire dispersion liquid, pectin powder is added after constant-temperature stirring is conducted to be uniform, and constant-temperature stirring continues to be conducted to be uniform; step 3, pouring the solution uniformly stirred in the step 2 into a mold, and then freezing; and step 4, freeze-drying the sample completely frozen in the step 3 to obtain a finished product. The aerogel prepared by the preparation method disclosed by the invention is good in electromagnetic wave absorbing effect and has mechanical properties of light weight and high strength.

Description

Technical Field

[0001] The invention belongs to the technical field of electromagnetic wave absorbing aerogels, and in particular relates to a method for preparing an environmentally friendly electromagnetic wave absorbing aerogel. Background Art

[0002] At present, the main materials on the market are metal micro-powder absorbers, graphite absorbers, silicon carbide absorbers, conductive polymer absorbers, nano absorbers, etc. Aerogel materials have the advantages of high specific surface area, high porosity, nano-scale pores, low density, stable chemical properties, good thermal insulation and excellent electromagnetic absorption performance, but their production cost is high, they are brittle, and some aerogel materials will pollute the environment, or waste residues are easily generated during production to pollute the environment. Chinese patent CN202410556638.7 uses porous aerogel combined with bimetallic MOF to prepare absorbing aerogel by high-temperature carbonization, and introduces a variety of electromagnetic wave loss mechanisms to achieve absorption. Chinese patent CN202311493624.7 uses iron powder to construct a magnetic / electric heterostructure with graphene in the microstructure; the synergistic effect of the porous structure and the heterostructure gives it good absorption performance.

[0003] However, the skeleton of silicon carbide is relatively brittle and may collapse under high load. Iron powder will produce iron ions in an acidic environment, which may decompose or wear during use and enter the ecosystem to affect the environment. Silver nanowires are a new type of nanomaterial with excellent conductivity, high flexibility and other characteristics. The production process is simple, which is conducive to reducing production costs and improving production efficiency. Therefore, by adding silver nanowires to aerogels, aerogels can be given certain electromagnetic absorption properties without causing harm to the environment. Pectin, as a low-cost and abundant polysaccharide, can be extracted from plant cell walls, providing many functions such as mechanical strength and durability for the highly anisotropically arranged porous structure present in natural plant stems. In addition, pectin has the characteristics of good biocompatibility, wide sources and low cost. As a substrate for aerogels, it can give aerogels high mechanical strength and anisotropic porous structures, which has a certain enhancement effect on the electromagnetic absorption properties of aerogels. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing an environmentally friendly electromagnetic wave absorbing aerogel, the purpose of which is to give the aerogel electromagnetic wave absorbing performance, but at the same time not to damage the characteristics of the aerogel such as light weight, high strength, and good mechanical properties, and to solve the disadvantages of the previous finishing method such as complex preparation process, low raw material utilization rate, and environmental pollution. At the same time, it has a significant effect on the electromagnetic wave absorption function, avoiding secondary pollution to the environment caused by the high energy reflected back.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: A method for preparing an environmentally friendly electromagnetic absorbing aerogel comprises the following steps: Step 1, preparing a silver nanowire dispersion; Step 2, add KCl particles to the silver nanowire dispersion, add pectin powder after constant temperature stirring, and continue to stir at constant temperature until uniform; Step 3, pouring the solution stirred evenly in step 2 into a mold, and then freezing; Step 4: freeze-dry the sample completely frozen in step 3.

[0006] The concentration of the silver nanowire dispersion in step 1 is 20 mg / ml-80 mg / ml, and the concentration of the silver nanowire dispersion is preferably 40 mg / ml, which can achieve a better electromagnetic absorption effect while avoiding the waste of raw materials.

[0007] Preferably, the constant temperature stirring in step 2 is constant temperature stirring at 30-40° C. for 3 h to 4 h.

[0008] In step 2, the silver nanowires are treated in a cell ultrasonic disruptor to form a silver nanowire dispersion. The silver nanowires are treated in a cell ultrasonic disruptor for 15 seconds to improve the dispersibility of the silver nanowires, forming a uniform and stable dispersion system, thereby improving the overall electromagnetic absorption performance of the material.

[0009] Preferably, the freezing in step 3 is performed by low-temperature ethanol quick freezing, which can avoid solution sedimentation and facilitate the formation of aerogel with uniform texture.

[0010] The drying temperature in step 4 is -50°C to -60°C and the drying time is 48 hours. Reasonable freeze-drying temperature and time settings facilitate complete drying of the sample.

[0011] It should be pointed out that in the present invention, the electromagnetic absorbing material is prepared by stirring-freezing technology, and there are no specific restrictions and requirements on the material, size, shape, etc. of the substrate. Different choices need to be made according to the specific situation. It can be the pectin powder in the example or other biomass materials.

[0012] The silver nanowires used in the present invention are all prepared by ourselves, and the main preparation process is as follows: Step 1, measure 25 ml of ethylene glycol and add it into a beaker, put it into a magnetic rotor and stir it with a magnetic stirrer; Step 2, weigh 0.2 g PVP and slowly and evenly add it to the stirring ethylene glycol; Step 3: After the mixture is evenly dispersed, add 0.25 g of AgNO3, and then add 3.5 g of a solution prepared by dissolving 0.0081 g of ferric chloride hexahydrate in 50 ml of ethylene glycol and continue stirring. Step 4: After stirring evenly, place in a drying oven at 130°C and dry for 5 hours to allow for full reaction; Step 5: After taking out, transfer the solution to a large beaker, add acetone ten times the volume of the original liquid to flocculate the silver nitrate, then pour out the acetone, add an appropriate amount of ethanol to the precipitate to dissolve it. Then centrifuge the solution; Step 6: After centrifugation, pour out the waste liquid and add an appropriate amount of ethanol to centrifuge again, centrifuge three times in total. After ethanol centrifugation, add deionized water and centrifuge three times with the same parameters to wash away the residual ethanol on the surface; Step 7: After centrifugation, the obtained silver nanowires are quickly frozen with liquid nitrogen, and after being completely frozen, they are freeze-dried in a freeze dryer for 48 hours.

[0013] Using a simple stirring-freezing process, silver nanowires can be evenly and densely distributed on the surface and inside of the aerogel, making the surface and internal conductive network of the aerogel dense, increasing the dielectric loss, and increasing the electromagnetic absorption performance of the aerogel. This method is easy to operate, has simple equipment requirements, and is cost-controllable. Pectin aerogel is also green and environmentally friendly, avoiding the disadvantages of traditional electromagnetic absorbing materials that are harmful to the environment.

[0014] In the present invention, the method for testing the electromagnetic absorption performance of aerogel is the coaxial method, and its standard is GJB 5239-2004 "Test method for absorption performance of radio frequency absorbing materials". The main working principle of this method is to put the prepared absorbing material sample into the coaxial test fixture, ensure that the sample is in good contact with the inner and outer conductors of the fixture, and the installation position is accurate, so as to ensure that the electromagnetic wave can be normally incident on the sample and absorbed or reflected. The vector network analyzer transmits the electromagnetic wave signal, the signal is transmitted in the coaxial structure, interacts with the absorbing material, part of the signal is absorbed, and part of the signal is reflected. The vector network analyzer receives and measures the reflected signal and the transmitted signal to obtain parameters such as the reflection coefficient and the transmission coefficient.

[0015] The electromagnetic absorption performance of the aerogel prepared when the concentration of silver nanowire dispersion is 40 mg / ml is -50.55 dB, which is much greater than the -20 dB of commercial electromagnetic absorption materials.

[0016] The beneficial technical effects of the present invention are as follows: 1. The present invention prepares electromagnetic absorbing aerogel with good electromagnetic absorbing performance. The prepared aerogel is light and high-strength, and has good electromagnetic absorbing performance, controllable thickness, and adjustable structure.

[0017] 2. The experimental operation conditions required by the present invention are simple, the energy consumption is low, no expensive equipment is required, the production cost is low, and it has good economic value and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a front view of the aerogel after freeze-drying in Example 1; Figure 2 This is a top view of the aerogel after freeze-drying in Example 1; Figure 3 This is a scanning electron microscope image of the aerogel after freeze-drying in Example 1; Figure 4 is the reflection loss curve of aerogel when the concentration of silver nanowire dispersion is 40 mg / ml; Figure 5 is the reflection loss curve of aerogel when the concentration of silver nanowire dispersion is 20 mg / ml; Figure 6 is the reflection loss curve of aerogel when the concentration of silver nanowire dispersion is 60 mg / ml; Figure 7 The XRD patterns of four aerogels containing different substances; Figure 8 Fourier transform infrared spectra of aerogels when the concentration of silver nanowire dispersion is 40 mg / ml, 20 mg / ml, and 60 mg / ml. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0020] Example 1: Step (1): Prepare a silver nanowire dispersion, use a measuring cylinder to take 20 ml of deionized water into a beaker (50 ml), weigh 800 mg of silver nanowires on an electronic balance and put them into the beaker, and treat them with a cell ultrasonic disruptor for 15 seconds; Step (2): add 74.55 mg KCl particles to the silver nanowire dispersion, stir evenly at 30°, then add 600 mg pectin powder, and continue stirring at 30° for 4 h; Step (3): pour the stirred solution into a mold and freeze it in low-temperature ethanol at -70° for 40 minutes; Step (4): Place the frozen sample in a freeze dryer and freeze dry it at -60° vacuum for 48 hours; The photo of the aerogel after freeze drying is as follows Figure 1 , 2. The internal electron microscope photo is shown in Figure 3 As shown. The electromagnetic wave reflection loss curve was drawn by simulating the electromagnetic wave reflection loss ability of the sample at a thickness of 0.5mm~5mm. The maximum reflection loss value of the aerogel after freeze-drying was measured to reach -50.55dB.

[0021] Example 2: The materials used in this example are the same as those in Example 1, but the difference lies in the different parameters of the method steps. The specific method steps of this example are as follows: Step (1): Prepare a silver nanowire dispersion. Use a measuring cylinder to take 20 ml of deionized water into a beaker (50 ml). Weigh 400 mg of silver nanowires on an electronic balance and put them into the beaker. Treat with a cell ultrasonic disruptor for 15 s. Step (2): add 74.55 mg KCl particles to the silver nanowire dispersion, stir evenly at 30°, then add 600 mg pectin powder, and continue stirring at 30° for 4 h; Step (3): Pour the stirred solution into a mold and freeze it in low-temperature ethanol at -70° for 40 min; Step (4): Place the frozen sample in a freeze dryer and freeze dry it at -60°C in a vacuum environment for 48 h; The electromagnetic wave reflection loss curve was drawn by simulating the electromagnetic wave reflection loss ability of the sample at a thickness of 0.5mm~5mm. The maximum reflection loss value of the aerogel after freeze-drying was measured to be -34.06 dB.

[0022] Example 3: The materials used in this example are the same as those in Example 1, but the difference lies in the different parameters of the method steps. The specific method steps of this example are as follows: Step (1): prepare a silver nanowire dispersion, use a measuring cylinder to take 20 ml of deionized water into a beaker (50 ml), weigh 1200 mg of silver nanowires on an electronic balance and put them into the beaker, and treat them with a cell ultrasonic disruptor for 15 seconds; Step (2): add 74.55 mg KCl particles to the silver nanowire dispersion, stir evenly at 30°, then add 600 mg pectin powder, and continue stirring at 30° for 4 h; Step (3): pour the stirred solution into a mold and freeze it in low-temperature ethanol at -70° for 40 minutes; Step (4): Place the frozen sample in a freeze dryer and freeze dry it at -60°C in a vacuum environment for 48 hours; The electromagnetic wave reflection loss curve was drawn by simulating the electromagnetic wave reflection loss ability of the sample at a thickness of 0.5mm~5mm. The maximum reflection loss value of the aerogel after freeze-drying was measured to reach -10.30dB.

[0023] Characterization analysis: Figure 7The XRD patterns of various samples. PA is a pectin aerogel prepared without adding any substance, PA-kcl is a pectin aerogel with only potassium chloride particles added, PA-kcl-4 wt% is a pectin aerogel with 40 mg / ml silver nanowires and potassium chloride particles added, and Pure AgNWs is a silver nanowire prepared by itself. The diffraction peaks of PureAgNWs and PA-kcl-4 wt% at 38.1°, 44.3°, 64.4°, and 77.5° correspond to the (111), (200), (220), and (311) crystal planes, respectively, proving that silver nanowires exist before and after the aerogel synthesis. Figure 8 The Fourier transform infrared spectra of aerogels when the concentration of silver nanowire dispersion is 40 mg / ml, 20 mg / ml, and 60 mg / ml. There are many oxygen-containing functional groups on the surface of aerogels at various concentrations, and the weight of oxygen atoms increases with the increase of silver nanowire concentration.

[0024] Analysis of electromagnetic absorption performance: When the concentration of silver nanowire dispersion is 40 mg / ml, 20 mg / ml, and 60 mg / ml, the reflection loss curves of aerogel are as follows: Figure 4 , Figure 5 , Figure 6 As shown. Figure 4 , Figure 5 , Figure 6 In contrast, as the concentration of silver nanowires increases, the reflection loss value of aerogel increases first and then decreases. Therefore, 40 mg / ml is appropriate.

[0025] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for preparing an environmentally friendly electromagnetic absorbing aerogel, characterized in that: The steps include: Step 1, preparing a silver nanowire dispersion; Step 2, add KCl particles to the silver nanowire dispersion, add pectin powder after constant temperature stirring, and continue to stir at constant temperature until uniform; Step 3, pouring the solution stirred evenly in step 2 into a mold, and then freezing; Step 4: freeze-dry the sample completely frozen in step 3.

2. The method for preparing the environmentally friendly electromagnetic absorbing aerogel according to claim 1, characterized in that: The concentration of the silver nanowire dispersion in step 1 is 20 mg / ml to 80 mg / ml.

3. The method for preparing the environmentally friendly electromagnetic absorbing aerogel according to claim 1, characterized in that: The constant temperature stirring in step 2 is stirring at 30-40° C. for 3 h-4 h.

4. The method for preparing the environmentally friendly electromagnetic absorbing aerogel according to claim 1, characterized in that: In the step 2, the silver nanowires are treated with a cell ultrasonic disruptor to form a silver nanowire dispersion.

5. The method for preparing the environmentally friendly electromagnetic absorbing aerogel according to claim 1, characterized in that: The freezing in step 3 is performed by low-temperature ethanol quick freezing.

6. The method for preparing the environmentally friendly electromagnetic absorbing aerogel according to claim 1, characterized in that: The drying temperature in step 4 is -50°C to -60°C, and the drying time is 48 hours.

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