Biomass carbon composite wave-absorbing material and preparation method thereof

Abstract

The invention discloses a biomass carbon composite wave-absorbing material and a preparation method thereof, the material is formed by gathering Fe and Fe3C particles on the surface of biomass carbon, and the surface of the biomass carbon has a porous structure; after adsorbing the ferric salt, the biomass is calcined to generate biomass charcoal, and Fe and Fe3C particles are generated on the surface of the biomass charcoal; the preparation method comprises the following steps: (1) immersing dry biomass into an alkaline solution for pretreatment; (2) immersing the pretreated biomass into a ferric salt solution for adsorption; and (3) calcining the biomass adsorbed with the ferric salt under the protection of inert gas, and generating Fe and Fe3C on the surface of the biomass charcoal. According to the invention, a porous structure is constructed on the surface of biomass through pretreatment, and Fe and Fe3C are introduced on the surface of biomass carbon, so that the wave-absorbing electromagnetic shielding and stability of the material are improved.

Description

Technical Field

[0001] The present invention relates to a wave - absorbing material, and particularly to a biomass - carbon composite wave - absorbing material and a preparation method thereof. Background Art

[0002] Since the 21st century, electronic devices have been widely used in people's life and work. Especially in the 5G era, with the advent of portable and wearable intelligent electronic products, electronic devices are also developing towards high integration, high power, and high precision. However, electromagnetic radiation is generated during the operation of electronic devices, which may not only have a negative impact on the human body but also interfere with external devices.

[0003] Carbon materials have broad application prospects in the field of electromagnetic wave absorption due to their excellent dielectric properties, good composite characteristics, special microstructure, low specific gravity, strong chemical stability, and the advantages of easy use and simple maintenance. However, traditional carbon materials such as graphene and carbon nanotubes have disadvantages such as complex preparation processes and high costs. In recent years, biomass carbon has gradually come into the view of researchers. It has a unique microstructure form and low cost, and is an important part of constructing new wave - absorbing materials. However, the electromagnetic shielding performance and stability of existing biomass - carbon wave - absorbing materials still need to be improved. Summary of the Invention

[0004] Object of the Invention: The first object of the present invention is to provide a biomass - carbon composite wave - absorbing material with high - efficiency electromagnetic shielding performance and strong stability; the second object of the present invention is to provide a preparation method of the biomass - carbon composite wave - absorbing material.

[0005] Technical Solution: The biomass - carbon composite wave - absorbing material described in the present invention is formed by the aggregation of Fe and Fe3C particles on the surface of biomass charcoal, and the surface of the biomass carbon has a porous structure; after the biomass adsorbs iron salts and then is calcined, the biomass generates biomass charcoal, and Fe and Fe3C particles are generated on the surface of the biomass charcoal.

[0006] Preferably, the mass - molar ratio of biomass to iron salt in the biomass adsorbing iron salt is 5g: 50 - 100 mmol (5g of biomass is immersed in 100 mL of an iron salt solution with a concentration of 0.5 - 1.0 mol / L for adsorption). Appropriate adsorption of iron salts will neither damage the porous microstructure on the surface of the biomass nor introduce a magnetic loss mechanism to the biomass, and also has good impedance matching, effectively improving the wave - absorbing performance of the material.

[0007] Preferably, the biomass carbon is Solidago canadensis L. biomass charcoal.

[0008] Solidago virgaurea is an invasive species, and most of its treatments mainly involve direct burning or chemical agent killing. This not only harms the environment but also poses a significant economic cost burden. As a biomass raw material, Solidago virgaurea can not only bring economic benefits at extremely low costs but also have a beneficial impact on the ecological environment. The Solidago virgaurea described herein was collected from the suburbs.

[0009] The preparation method of the biomass carbon composite microwave absorption material described in the present invention includes the following steps:

[0010] (1) Take the dried biomass and immerse it in an alkaline solution for pretreatment;

[0011] (2) Take the pretreated biomass and immerse it in an iron salt solution for adsorption;

[0012] (3) Calcinate the biomass adsorbed with the iron salt under the protection of an inert gas to generate Fe and Fe3C on the surface of the biomass carbon.

[0013] Preferably, in step (1), the alkaline solution is a potassium hydroxide or sodium hydroxide solution with a concentration of 1.0 - 3.0 mol / L. Preferably, the pretreatment time is 8 - 15 hours. KOH and NaOH are strong bases, and the cellulose in the biomass will be corroded by KOH, leaving holes. This porous structure greatly increases the number of reflections and scatterings of electromagnetic waves between the incident surface of the biomass carbon material and the cavities, improving the electromagnetic wave absorption performance of the material.

[0014] Preferably, the iron salt is Fe(NO3)3·9H2O.

[0015] Preferably, in step (2), the adsorption time is 24 - 36 hours. During the adsorption process, the iron salt can be adsorbed on the surface of the biomass.

[0016] Preferably, the calcination temperature is 800 - 1400 °C, and the calcination time is 1 - 5 hours. Preferably, the heating rate of the calcination is 5 °C / min. Preferably, the inert protective gas is argon.

[0017] During the calcination process, the biomass undergoes thermochemical conversion to generate biomass. During the pyrolysis process, the iron salt is first pyrolyzed into Fe2O3, and carbon has reducibility. At high temperatures, further reaction between Fe2O3 and carbon produces Fe. Fe is reduced by the biomass carbon on the contact surface at high temperatures to generate Fe3C, introducing a magnetic loss mechanism and effectively regulating the dielectric properties of the composite material, improving the dielectric loss ability and impedance matching characteristics.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) The present invention constructs a porous structure on the surface of biomass through pretreatment, and introduces Fe and Fe₃C on the surface of biomass carbon, improving the wave absorption electromagnetic shielding and stability of the material; (2) When the ratio of biomass to iron is 5 g: 50 mmol, at a matching thickness of 5.0 mm, the RL min value at a frequency of 7.88 GHz is -52.67 dB, and the effective bandwidth is 7.24 GHz (from 9.60 GHz to 16.84 GHz); (3) The preparation method has a simple process, only requiring stirring, soaking, and calcination, so it is suitable for large-scale industrial production; (4) Solidago virgaurea used in this method is an invasive species, which not only has high economic benefits but also plays an important role in environmental protection. Description of the Drawings

[0019] Figure 1 SEM images of Comparative Example 1 (a)-(b), Example 1 (c)-(d), Example 2 (e)-(f) and Comparative Example 2 (g)-(h).

[0020] Figure 2 XRD patterns of Example 1 (BC-Fe1), Example 2 (BC-Fe2) and Comparative Example 2 (BC-Fe3).

[0021] Figure 3 RL values of Comparative Example 1 (a)-(b), Example 1 (c)-(d), Example 2 (e)-(f) and (g)-(h) and the corresponding three-dimensional diagrams. Detailed Embodiments

[0022] The technical solutions of the present invention will be further described below in conjunction with the embodiments.

[0023] Example 1

[0024] The preparation method of the biomass carbon composite wave-absorbing material of the present invention includes the following steps:

[0025] (1) Pretreatment of biomass

[0026] Solidago virgaurea is washed with deionized water to remove surface dust and other impurities until the washing liquid is clear and transparent. The washed Solidago virgaurea is placed in an oven at 60 °C for 24 hours for heat preservation. The dried Solidago virgaurea is immersed in a 1 mol / L KOH solution for 8 hours to achieve the effect of pore formation. After the pore formation is completed, it is washed with deionized water until the washing liquid is neutral, and then dried in an oven at 60 °C for 12 hours.

[0027] (2) Adsorption

[0028] Next, take 5 g of pre-treated Solidago virgaurea and immerse it in a beaker containing 100 mL of 0.5 mol / L Fe(NO3)3·9H2O solution. Finally, seal the beaker with plastic wrap and keep it for 24 hours to completely absorb iron ions. Next, take out the impregnated Solidago virgaurea from the beaker and wash it with deionized water until the washing liquid is neutral. Dry the washed Solidago virgaurea in an oven at 60 °C for 24 hours.

[0029] (3) Calcination

[0030] Put the Solidago virgaurea adsorbed with Fe(NO3)3 into a tube furnace under argon protection and heat it to 800 °C at a heating rate of 5 °C / min, and keep it for 2 hours.

[0031] Example 2

[0032] On the basis of Example 1, change the concentration of Fe(NO3)3·9H2O to 1.0 mL / L, and keep the other conditions unchanged.

[0033] Comparative Example 1

[0034] On the basis of Example 1, do not perform step (2), and keep the other conditions unchanged.

[0035] Comparative Example 2

[0036] On the basis of Example 1, change the concentration of Fe(NO3)3·9H2O to 1.5 mL / L, and keep the other conditions unchanged.

[0037] Microstructural characterization and phase testing

[0038] Figure 1 (a)-(h) show the SEM images of Comparative Examples (a)-(b) and Examples (c)-(h). From Figure 1 (a)-(b), it can be found that a large number of micron and nano-scale holes are generated on the surface of the stem of Solidago virgaurea after adding KOH in Comparative Example 1. This is because the cellulose in Solidago virgaurea is corroded by the strong base KOH. In Figure 1 (c)-(h), a large number of Fe and Fe3C particles are attached to the carbon-based surface of Solidago virgaurea, and their sizes are also different. As a large number of spherical particles accumulate, the biomass carbon surface becomes very rough. This composite structure composed of a rough surface and holes of different sizes can cause the electromagnetic waves irradiated on the material surface to be reflected and scattered multiple times, so as to achieve the purpose of efficiently attenuating electromagnetic waves. In addition, the boundary between carbon and Fe3C particles often causes strong interfacial polarization, and this interfacial polarization phenomenon enhances the microwave absorption ability of the composite material. In Figure 1(c)-(d) In Example 1, a small amount of Fe3C particles are distributed on the surface of the matrix, and Fe and Fe3C particles endow the composite material with the ability of magnetic loss. With the increase of the addition amount of Fe(NO3)3, the deposition rate of the magnetic component on the matrix increases significantly. Figure 1 (e)-(h). According to Figure 1 (g)-(h), it can be found that a large number of Fe and Fe3C particles in the composite material of Comparative Example 2 aggregate together, almost covering the entire surface of the biomass carbon matrix, which destroys the porous structure for microwave absorption. At the same time, excessive Fe and Fe3C particles will seriously affect the impedance matching and are not conducive to microwave absorption.

[0039] Such as Figure 2 are the XRD patterns of Example 1 (BC-Fe1), Example 2 (BC-Fe2) and Comparative Example 2 (BC-Fe3). Figure 2 It shows that the phases of Example 1, Example 2 and Comparative Example 2 are composed of Fe3C and Fe. During the pyrolysis process, iron nitrate is first pyrolyzed into Fe2O3, and carbon has reducibility. At high temperature, further reaction between Fe2O3 and carbon produces Fe. Fe is reduced by the biomass carbon on the contact surface at high temperature to generate Fe3C, and the presence of Fe and Fe3C will affect the electromagnetic properties and impedance matching characteristics of the composite material.

[0040] Performance test:

[0041] Microwave absorption performance test:

[0042] Test method: The biomass carbon composite material is dispersed in paraffin (25 wt% biomass carbon composite material and 75 wt% paraffin) to form a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm, and an electromagnetic parameter study is carried out using an American Agilent vector network analyzer. The smaller the RL value, the stronger the microwave absorption ability. An RL value lower than -10 dB means that more than 90% of the incident microwaves can be dissipated in the absorber, and the corresponding width of its absorption frequency band is defined as the effective bandwidth (EAB).

[0043] Such as Figure 3 (a) and (b) show that although Comparative Example 1 has a porous structure, its microwave absorption ability is still not satisfactory, and it has the minimum RL (RL min ) value of -2.73 dB at a matching thickness of 1.5 mm and a frequency of 14.52 GHz.

[0044] At Figure 3 (c) and (d), Example 1 has excellent microwave absorption ability and realizes strong microwave absorption in a multi-band from 5.72 GHz to 18.00 GHz. For example, when the matching thickness is 2.5 mm, it has an RL min value of -36.26 dB at 16.76 GHz.

[0045] As Figure 3 Example 2 shown in (e) and (f) has an RL of -52.67 dB at 7.88 GHz with a matching thickness of 5.0 mm. min In addition, it has a wide EAB from 9.60 GHz to 16.84 GHz, almost covering the entire X and Ku bands.

[0046] As Figure 3 shown in (g) and (h), the microwave absorption performance of Comparative Example 2 has decreased significantly, mainly for the following two reasons:

[0047] (1) The porous structure is damaged: A large number of Fe and Fe3C particles in Comparative Example 2 aggregate together, almost covering the entire surface of the biomass carbon matrix. This situation destroys the original porous structure used for microwave absorption, and the porous structure plays an important role in the absorption of electromagnetic waves. It can cause the electromagnetic waves irradiated on the material surface to be reflected and scattered multiple times. After the porous structure is damaged, the attenuation ability of the material to electromagnetic waves is significantly reduced.

[0048] (2) The impedance matching is seriously affected: Excessive Fe and Fe3C particles will seriously affect the impedance matching of the material. In microwave absorbing materials, good impedance matching characteristics are one of the key factors for achieving efficient microwave absorption. When the impedance matching is poor, the electromagnetic waves cannot effectively enter the material interior to be absorbed, but will be reflected on the material surface, resulting in a significant decrease in the microwave absorption performance of the material. In Comparative Example 2, the situation of no effective bandwidth occurs.

Claims

1. A biomass carbon composite wave-absorbing material, characterized in that, It is formed by the aggregation of Fe and Fe3C particles on the surface of biomass carbon, and the surface of the biomass carbon has a porous structure; after the biomass adsorbs iron salt and is calcined, the biomass generates biomass carbon, and Fe and Fe3C particles are generated on the surface of the biomass carbon.

2. The biomass carbon composite wave-absorbing material according to claim 1, characterized in that The mass molar ratio of biomass to iron salt in the biomass adsorbing iron salt is 5 g: 50 - 100 mmol.

3. The biomass carbon composite wave-absorbing material according to claim 1, characterized in that, The biomass carbon is Solidago canadensis biomass carbon.

4. A method for preparing the biomass carbon composite wave-absorbing material according to any one of claims 1 to 3, characterized in that, It includes the following steps: (1) Take the dried biomass and immerse it in an alkaline solution for pretreatment; (2) Take the pretreated biomass and immerse it in an iron salt solution for adsorption; (3) Calcinate the biomass adsorbed with iron salt under the protection of inert gas to generate Fe and Fe3C on the surface of the biomass carbon.

5. The preparation method of the biomass carbon composite wave-absorbing material according to claim 4, wherein The calcination temperature is 800 - 1400 °C, and the calcination time is 1 - 5 hours.

6. The preparation method of the biomass carbon composite wave-absorbing material according to claim 4, wherein, The heating rate of the calcination is 5 - 20 °C / min.

7. The preparation method of the biomass carbon composite wave-absorbing material according to claim 4, wherein The alkaline solution is a potassium hydroxide or sodium hydroxide solution with a concentration of 1.0 - 3.0 mol / L.

8. The preparation method of the biomass carbon composite wave-absorbing material according to claim 7, characterized in that, The pretreatment time is 8 - 15 hours.

9. The preparation method of the biomass carbon composite wave-absorbing material according to claim 4, characterized in that, The adsorption time is 24 - 36 hours.

10. The preparation method of the biomass carbon composite wave-absorbing material according to claim 4, characterized in that, The iron salt is Fe(NO3)3·9H2O.

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