A porous carbonaceous microwave absorbing material, its preparation method and applications

Abstract

This invention belongs to the technical field of electromagnetic wave absorbing materials, specifically relating to a porous carbonaceous microwave absorbing material, its preparation method, and its applications. The porous carbonaceous microwave absorbing material has a size of 10-300 μm, a pore size of 0.5-2 μm, and a specific surface area of ​​200-1000 m². 2 / g, the porous carbonaceous microwave absorbing material is prepared by acidifying, drying and carbonizing tea leaves in sequence; the present invention has good microwave absorption performance, good electromagnetic impedance matching, low reflectivity and higher effective bandwidth.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a porous carbonaceous wave absorbing material, its preparation method, and its applications. Background Technology

[0002] With the rapid development of modern electronic devices and wireless communication technologies, electromagnetic pollution and interference problems are becoming increasingly serious. Developing efficient electromagnetic wave absorbing materials is crucial for effectively addressing these issues. Currently, a wide variety of absorbing materials are available on the market, but most have shortcomings in terms of absorption performance, manufacturing cost, and environmental friendliness. The Ku-band (12.4-18 GHz) has extensive applications in wireless communication, radar detection, and satellite navigation. Therefore, focusing on research into Ku-band absorbing materials can more precisely meet the needs of these specific applications and improve the practical effectiveness of related technologies.

[0003] Carbonaceous microwave absorbing materials prepared from biomass not only possess excellent microwave absorption performance, but their preparation process is also environmentally friendly and cost-effective. However, existing carbonaceous materials often face problems such as uneven pore structure and unstable microwave absorption performance during preparation.

[0004] Chinese patent application publication number CN 113148972 A describes a method for preparing a lightweight, layered, porous carbonaceous microwave absorbing material derived from *Tremella fuciformis* (silver ear fungus). This method utilizes freeze-drying technology to preserve the inherent layered structure and nanoporous structure of *Tremella fuciformis*. However, its process is complex and the pores are not uniform. Chinese patent publication number CN 110482526 B discloses a method for preparing a biomass porous carbon electromagnetic microwave absorbing material using egg white as a precursor. However, this method is costly and time-consuming. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a porous carbonaceous microwave absorbing material, its preparation method and its uses, which has good microwave absorption performance, good electromagnetic impedance matching, low reflectivity and higher effective bandwidth.

[0006] This invention provides a porous carbonaceous microwave absorbing material, wherein the porous carbonaceous microwave absorbing material has a size of 10-300 μm, a pore size of 0.5-2 nm, and a specific surface area of ​​200-1000 m². 2 / g (preferably 566 m) 2 / g), the porous carbonaceous microwave absorbing material is prepared by acidifying, drying and carbonizing tea leaves in sequence.

[0007] Preferably, the tea leaves are green tea.

[0008] This invention provides a method for preparing the porous carbonaceous microwave absorbing material, which is obtained by sequentially acidifying, drying, and carbonizing tea leaves.

[0009] Preferably, the tea leaves are washed before acidification, and then soaked in hot water (the weight ratio of tea leaves to hot water is 1:0.5-10, and the temperature of the hot water is 50-100℃) for 2 hours. After soaking, the tea leaves are dried (preferably at 80℃ for more than 10 hours, such as 12 hours). After washing, the tea leaves are ground to make their size less than 250 μm.

[0010] Preferably, the acid used for acidification is hydrochloric acid, sulfuric acid, or phosphoric acid, with hydrochloric acid being the most preferred.

[0011] Preferably, acidification involves mixing tea leaves with an acid solution, wherein the concentration of the acid solution is 0.1-3 mol / L (preferably 1 mol / L), and the mass ratio of the tea leaves to the acid solution is 1:10-300.

[0012] Preferably, the acidification temperature is 70-160°C.

[0013] Preferably, after acidification and before drying, the tea leaves are rinsed to control the pH of the rinsed tea leaves to be neutral after steeping.

[0014] Preferably, the drying temperature is 70-90°C.

[0015] Preferably, the carbonization temperature is 400-1000℃ (preferably 850℃), and the carbonization is carried out in a carbonization atmosphere, which is nitrogen, argon, hydrogen, or a mixture of the above gases, preferably argon.

[0016] This invention provides an application of the porous carbonaceous microwave absorbing material in absorbing electromagnetic waves.

[0017] The beneficial effect of this invention is that it utilizes a porous structure to reflect and disperse electromagnetic waves, and converts electromagnetic energy into thermal energy through dipole polarization and interface polarization, thereby achieving efficient microwave absorption.

[0018] Specifically, this invention provides an environmentally friendly, low-cost, and efficient method for preparing a lightweight, layered, porous carbonaceous microwave absorbing material derived from green tea. This method mainly utilizes abundant and inexpensive green tea as a precursor for carbon materials. The fibrous structure of green tea itself makes it easier to form a rich pore structure, a large specific surface area, and specific active sites during the carbonization process. These characteristics are retained after carbonization, resulting in a final product with excellent microwave absorption performance and lightweight properties.

[0019] This invention first selects suitable tea leaves and removes minerals and impurities by controlling the acidification time and concentration, while simultaneously regulating the microstructure, such as pore and layered structures. A one-step carbonization process transforms the tea leaves into a carbonaceous microwave absorbing material. By selecting an appropriate temperature, the organic matter in the biomass is fully decomposed while avoiding structural damage to the carbon material caused by excessively high temperatures. At the same time, volatile matter and combustible gases in the biomass are effectively removed, allowing the pore structure and specific surface area of ​​the carbon material to reach an optimal state. The green tea-derived porous carbonaceous microwave absorbing material of this invention absorbs incident electromagnetic waves by converting them into heat energy through the porous structure of the biomass, and reduces echo energy through destructive interference, thus achieving the purpose of electromagnetic wave absorption. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the layered porous carbonaceous microwave absorbing material used in Comparative Example 1 of the present invention.

[0021] Figure 2 This is a scanning electron microscope image of the layered porous carbonaceous microwave absorbing material used in Embodiment 1 of the present invention.

[0022] Figure 3 The microwave absorption performance of the layered porous carbonaceous microwave absorbing materials obtained in Examples 1-4 of the present invention is shown.

[0023] Figure 4 The microwave absorption performance of the layered porous carbonaceous microwave absorbing materials obtained in Comparative Examples 1-4 of this invention is shown.

[0024] Figure 5 The image shows the elemental composition analysis of the layered porous carbonaceous microwave absorbing materials obtained in Examples 1-4 of this invention.

[0025] Figure 6 The images show the Raman analysis results of the layered porous carbonaceous microwave absorbing materials obtained in Examples 1-4 of this invention.

[0026] Figure 7 This is the aperture distribution diagram obtained in Embodiment 1 of the present invention.

[0027] Figure 8 This is a graph showing the adsorption amount under different pressures obtained in Example 1 of the present invention. Detailed Implementation

[0028] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] A method for preparing a green tea-derived porous carbonaceous microwave absorbing material includes the following steps:

[0031] 1. Select green tea as raw material and rinse it thoroughly with distilled water to ensure its purity. After rinsing, place the tea leaves in a tube furnace and dry them at 80 ℃ for 12 hours.

[0032] 2. Grind the dried tea leaves to make their size less than 250 μm.

[0033] 3. Take 2 g of ground tea leaves and heat them in 100 ml of hydrochloric acid (1 mol / L). The specific procedure is as follows: mix the tea leaves with the hydrochloric acid solution in an oil bath, heat to 120 ℃ and maintain for 2 hours.

[0034] 4. After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h.

[0035] 5. The dried tea powder was transferred to a quartz tube furnace for carbonization. The tea was carbonized for 1 h in an argon atmosphere (100 sccm) at 850 ℃ to obtain a green tea-derived porous carbonaceous microwave absorbing material.

[0036] The pore size distribution and adsorption amount data of the absorbing material obtained in Example 1 are as follows: Figure 7-8 As shown. The porous carbonaceous microwave absorbing material has a size of 10-300 μm, a pore size of 0.5-2 nm, and a specific surface area of ​​200-1000 m². 2 / g.

[0037] Examples 2-4

[0038] The difference between Example 2 and Example 1 is that the carbonization temperature in step 4 is changed to 650 ℃. The difference between Example 3 and Example 1 is that the carbonization temperature in step 4 is changed to 750 ℃. The difference between Example 4 and Example 1 is that the carbonization temperature in step 4 is changed to 950 ℃.

[0039] By controlling the carbonization time, the graphitization degree of porous carbonaceous microwave absorbing materials can be effectively adjusted, thereby optimizing the impedance matching effect of the composite microwave absorbing agent and improving its electromagnetic wave loss.

[0040] Comparative Example 1

[0041] A method for preparing a green tea-derived porous carbonaceous microwave absorbing material includes the following steps:

[0042] 1. Select green tea as raw material and rinse it thoroughly with distilled water to ensure its purity. After rinsing, place the tea leaves in a tube furnace and dry them at 80 ℃ for 12 hours.

[0043] 2. Grind the dried tea leaves to make their size less than 250 μm.

[0044] 3. Take 2g of ground tea leaves and heat them in 100ml of sulfuric acid (1 mol / L). The specific procedure is as follows: mix the tea leaves with the sulfuric acid solution in an oil bath, heat to 120℃ and maintain for 2 hours.

[0045] 4. After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h.

[0046] 5. The dried tea powder was transferred to a quartz tube furnace for carbonization. The tea was carbonized for 1 h in an argon atmosphere (100 sccm) at 650 ℃ to obtain a green tea-derived porous carbonaceous microwave absorbing material.

[0047] Comparative Example 2

[0048] A method for preparing a green tea-derived porous carbonaceous microwave absorbing material includes the following steps:

[0049] 1. Select green tea as raw material and rinse it thoroughly with distilled water to ensure its purity. After rinsing, place the tea leaves in a tube furnace and dry them at 80 ℃ for 12 hours.

[0050] 2. Grind the dried tea leaves to make their size less than 250 μm.

[0051] 3. Take 2g of ground tea leaves and heat them in 100ml of phosphoric acid (1 mol / L). The specific procedure is as follows: mix the tea leaves with the phosphoric acid solution in an oil bath, heat to 120℃ and maintain for 2 hours.

[0052] 4. After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h.

[0053] 5. The dried tea powder was transferred to a quartz tube furnace for carbonization. The tea was carbonized for 1 hour in an argon atmosphere (100 sccm) at 650 °C to obtain a green tea-derived porous carbonaceous microwave absorbing material.

[0054] Comparative Example 3

[0055] A method for preparing a green tea-derived porous carbonaceous microwave absorbing material includes the following steps:

[0056] 1. Select green tea as raw material and rinse it thoroughly with distilled water to ensure its purity. After rinsing, place the tea leaves in a tube furnace and dry them at 80 ℃ for 12 hours.

[0057] 2. Grind the dried tea leaves to make their size less than 250 μm.

[0058] 3. Place 2g of ground tea leaves in a quartz tube furnace for carbonization. Carbonize the tea leaves for 1 hour in an argon atmosphere (100 sccm) at 850 ℃.

[0059] 4. Take 2g of carbonized tea leaves and heat them in 100ml of hydrochloric acid (1 mol / L). The specific procedure is as follows: mix the tea leaves with the hydrochloric acid solution in an oil bath, heat to 120℃ and maintain for 2 hours.

[0060] 5. After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product. Dry it at 80 ℃ for 12 h to obtain green tea-derived porous carbonaceous microwave absorbing material.

[0061] Comparative Example 4

[0062] A method for preparing a porous carbonaceous microwave absorbing material includes the following steps:

[0063] 1. Select laver as raw material and rinse it thoroughly with distilled water to ensure its purity. After rinsing, place the tea leaves in a tube furnace and dry them at 80 ℃ for 12 hours.

[0064] 2. Grind the dried laver to reduce its size to less than 250 μm.

[0065] 3. Take 2g of ground laver and heat it in 100ml of hydrochloric acid (1 mol / L). The specific procedure is as follows: mix the laver with the hydrochloric acid solution in an oil bath, heat to 120℃ and maintain for 2 hours.

[0066] 4. After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h.

[0067] 5. The dried laver powder was transferred to a quartz tube furnace for carbonization. The laver was carbonized for 1 h in an argon atmosphere (100 sccm) at 850 ℃ to obtain a porous carbonaceous microwave absorbing material.

[0068] The absorption performance of Examples 1-4 and Comparative Examples 1-4 is as follows: Figure 3-4As shown, it can be seen that the reflectivity of Example 1 and Comparative Examples 1-4 is significantly lower than that of the other examples. Among them, the absorption performance of Example 1 is better than that of the other examples. At the 13.5 GHz frequency point, its minimum reflectivity reaches -47.1 dB and its effective bandwidth (reflectivity R < -10 dB) reaches 4.7 GHz.

[0069] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of protection of this application is limited to these examples; within the framework of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of one or more embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0070] One or more embodiments in this application are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments in this application should be included within the protection scope of this application.

Claims

1. A porous carbonaceous microwave absorbing material, characterized in that, The porous carbonaceous microwave absorbing material has a size of 10-300 μm, a pore size of 0.5-2 nm, and a specific surface area of ​​200-1000 m². 2 / g, the preparation method of the porous carbonaceous microwave absorbing material includes the following steps: 1) Select green tea as raw material and rinse it thoroughly with distilled water to ensure the purity of the raw material; after rinsing, put the tea leaves into a tube furnace and dry them at 80 ℃ for 12 h. 2) Grind the dried tea leaves to reduce their size to less than 250 μm; 3) Take 2 g of ground tea leaves and heat them in 100 ml of 1 mol / L hydrochloric acid. The specific procedure is as follows: mix the tea leaves with the hydrochloric acid solution in an oil bath, heat to 120 ℃ and keep it for 2 hours. 4) After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h. 5) The dried tea powder was transferred to a quartz tube furnace for carbonization treatment; the tea was carbonized in an argon atmosphere at 850 ℃ for 1 h with an argon flow rate of 100 sccm to obtain a green tea-derived porous carbonaceous microwave absorbing material.

2. A method for preparing the porous carbonaceous microwave absorbing material as described in claim 1, characterized in that, Includes the following steps: 1) Select green tea as raw material and rinse it thoroughly with distilled water to ensure the purity of the raw material; after rinsing, put the tea leaves into a tube furnace and dry them at 80 ℃ for 12 h. 2) Grind the dried tea leaves to reduce their size to less than 250 μm; 3) Take 2 g of ground tea leaves and heat them in 100 ml of 1 mol / L hydrochloric acid. The specific procedure is as follows: mix the tea leaves with the hydrochloric acid solution in an oil bath, heat to 120 ℃ and keep it for 2 hours. 4) After acid treatment, rinse the product repeatedly with deionized water until its pH value reaches 7 to ensure the purity and neutrality of the product, and dry it at 80 ℃ for 12 h. 5) The dried tea powder was transferred to a quartz tube furnace for carbonization treatment; the tea was carbonized in an argon atmosphere at 850 ℃ for 1 h with an argon flow rate of 100 sccm to obtain a green tea-derived porous carbonaceous microwave absorbing material.

3. The use of the porous carbonaceous microwave absorbing material as described in claim 1 in absorbing electromagnetic waves.

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