A porous carbon / magnetic nanoparticle composite and a preparation method and application thereof

Abstract

The application discloses a kind of porous carbon / magnetic nanoparticle composite and its preparation method and application, the composite described in the application is that shaddock skin powder is mixed with cobalt source, 2,5-dihydroxy p-phenylenediamine terephthalate in solvent, precursor is obtained by hydrothermal reaction, and it is prepared by high-temperature carbonization under inert atmosphere.The morphology, size and graphitization degree of the magnetic nanoparticles in the composite can be effectively controlled by regulating the carbonization temperature in the application, so as to optimize the impedance matching and electromagnetic wave attenuation capacity of the material, and the composite prepared has excellent electromagnetic absorption performance, the minimum reflection loss value (RL min ) can reach-36.93 dB, and the effective absorption bandwidth (EAB) can reach 4.77 GHz, and has wide application prospect in the field of electromagnetic wave absorbing materials.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, and in particular to a porous carbon / magnetic nanoparticle composite, its preparation method, and its application. Background Technology

[0002] With the widespread adoption of fifth-generation (5G) mobile communication technology and the preliminary research into sixth-generation (6G) technology, electronic devices are rapidly developing towards higher frequencies and greater integration. This has led to increasingly serious problems with electromagnetic interference (EMI) and electromagnetic radiation (EMR) pollution. Developing high-performance electromagnetic wave absorbing materials (MAMs) with characteristics of being "thin, light, wide, and strong" has become a research hotspot in materials science and defense technology.

[0003] Carbon-based materials are considered ideal substrates for microwave absorbing materials due to their low density, high specific surface area, excellent electrical conductivity, and chemical stability. Among them, the porous structure within porous carbon materials not only optimizes impedance matching, allowing more electromagnetic waves to enter the material, but also extends the propagation path and enhances energy dissipation through multiple reflections and scattering. However, pure carbon materials lack magnetic loss mechanisms, and their singular dielectric loss often leads to poor impedance matching, limiting further improvements in their microwave absorption performance.

[0004] Metal-organic frameworks (MOFs) are a class of porous crystalline materials composed of metal ions and organic ligands. Using MOFs as precursors, composite materials with magnetic metal nanoparticles uniformly loaded onto a porous carbon matrix can be prepared through high-temperature carbonization. This structure retains the high porosity of MOFs while introducing magnetic loss components, potentially achieving a synergistic enhancement of both dielectric and magnetic losses. However, the high cost and complex fabrication processes of MOF materials limit their large-scale application.

[0005] Biomass (such as grapefruit peel and wheat straw) is a widely available, inexpensive, and environmentally friendly renewable resource. Its inherent microstructure (such as porous and fibrous structures) is preserved after carbonization, making it an ideal precursor for preparing porous carbon materials. Combining MOF-derived magnetic components with biomass-derived carbon holds promise for integrating the advantages of both to prepare low-cost, high-performance microwave absorbing materials. However, effectively combining the two and optimizing electromagnetic parameters and impedance matching through microstructure control and carbonization processes remain critical technical challenges in this field. Summary of the Invention

[0006] To address the aforementioned technical problems in existing technologies, the present invention aims to provide a porous carbon / magnetic nanoparticle composite, its preparation method, and its applications. This invention uses waste biomass grapefruit peel as the carbon source and Co-MOF-74 as the magnetic component precursor. Through a one-step hydrothermal reaction and high-temperature carbonization, a porous carbon / magnetic nanoparticle composite with a unique sea urchin-like morphology is prepared. This composite exhibits excellent impedance matching characteristics and multiple electromagnetic wave loss mechanisms, demonstrating superior microwave absorption performance. The preparation process of this invention is simple, low-cost, environmentally friendly, and easily scalable for mass production.

[0007] The technical solution adopted in this invention is: A method for preparing a porous carbon / magnetic nanoparticle composite includes the following steps: Step 1: Dry the fresh grapefruit peel and then crush it to obtain grapefruit peel powder; Step 2: Add the grapefruit peel powder, cobalt source and 2,5-dihydroxyterephthalic acid prepared in Step 1 to the solvent, disperse them evenly by ultrasonication, transfer them to an autoclave, seal the autoclave and carry out hydrothermal reaction. After the reaction is completed, wash and dry the product to obtain the precursor. Step 3: The precursor prepared in step 2 is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain the porous carbon / magnetic nanoparticle composite.

[0008] Furthermore, the cobalt source in step 2 is cobalt acetate tetrahydrate, and the mass ratio of grapefruit peel powder to cobalt source in step 2 is 1:0.5-2.0, preferably 1:1.0.

[0009] Further, the mass ratio of grapefruit peel powder to 2,5-dihydroxyterephthalic acid in step 2 is 1:0.1-0.5, preferably 1:0.3-0.32.

[0010] Furthermore, the temperature of the hydrothermal reaction is 90-120℃, preferably 100-110℃, and the reaction time is 10-24h, preferably 12-15h.

[0011] Further, the solvent in step 2 is an ethanol-water mixture, with a volume ratio of ethanol to water of 1-3:1, preferably 2:1; the volume of the solvent used is 100-200 mL / g based on the mass of the grapefruit peel powder.

[0012] Furthermore, in step 3, the high-temperature carbonization treatment starts from room temperature and increases the temperature at a rate of 2-10℃ / min until the carbonization temperature reaches 600-800℃. The carbonization holding time is 1-4 hours.

[0013] Furthermore, the carbonization temperature is 7 hours, and the carbonization holding time is 2-3 hours.

[0014] The present invention relates to the application of a porous carbon / magnetic nanoparticle composite in the preparation of microwave absorbing materials, wherein the materials are used to absorb electromagnetic waves in the frequency range of 2 to 18 GHz.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The raw material of this invention, pomelo peel, is agricultural waste. It is widely available, inexpensive, and environmentally friendly, thus realizing the high-value utilization of biomass resources.

[0016] 2. This invention utilizes a one-step hydrothermal method to grow Co-MOF-74 in situ on a grapefruit peel carbon precursor, followed by high-temperature carbonization, to obtain a porous carbon / magnetic nanoparticle composite with a unique sea urchin-like morphology. This method is simple, easy to operate, and suitable for large-scale production.

[0017] 3. This invention achieves precise control over the morphology of magnetic nanoparticles, the degree of graphitization of the carbon matrix, and the dielectric / magnetic loss capability in the composite by adjusting the carbonization temperature (preferably 700℃). Under these conditions, the material forms a moderately conductive network and abundant heterogeneous interfaces, achieving optimal impedance matching and the synergistic effect of multiple loss mechanisms (including interface polarization, dipole polarization, conductive loss, and natural resonance).

[0018] 4. The composite absorbing material prepared by this invention has excellent electromagnetic absorption performance. With a thickness of only 1.82 mm, the minimum reflection loss (RLmin) can reach -36.93 dB, and the effective absorption bandwidth (EAB) can reach 4.77 GHz, demonstrating the comprehensive advantages of being "thin, light, wide, and strong". Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the composite materials obtained in Examples 1-3 of this invention.

[0020] Figure 2 This is a scanning electron microscope (SEM) image of the composite material obtained in Example 1 of the present invention.

[0021] Figure 3 This is a scanning electron microscope (SEM) image of the composite material obtained in Example 2 of the present invention.

[0022] Figure 4 This is a scanning electron microscope (SEM) image of the composite material obtained in Example 3 of the present invention.

[0023] Figure 5 The images show the Raman spectra of the composite materials obtained in Examples 1-3 of this invention.

[0024] Figure 6 The image shows the reflection loss (RL) curve of the composite material obtained in Example 1 of this invention.

[0025] Figure 7 The image shows the reflection loss (RL) curve of the composite material obtained in Example 2 of this invention.

[0026] Figure 8 The image shows the reflection loss (RL) curve of the composite material obtained in Example 3 of this invention.

[0027] Figure 9 The image shows the reflection loss (RL) curve of the composite material prepared in Comparative Example 1 of this invention.

[0028] Figure 10 The image shows the reflection loss (RL) curve of the composite material prepared in Comparative Example 2 of this invention.

[0029] Figure 11 The image shows the reflection loss (RL) curve of the composite material prepared in Comparative Example 3 of this invention.

[0030] Figure 12 The image shows the reflection loss (RL) curve of the composite material prepared in Comparative Example 4 of this invention.

[0031] Figure 13 The image shows the reflection loss (RL) curve of the composite material prepared in Comparative Example 5 of this invention. Detailed Implementation

[0032] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] The tube furnace used in this embodiment of the invention is model OTF-1200X, and the vector network analyzer is model N5244A. The room temperature mentioned in this embodiment of the invention refers to 25-30℃.

[0034] Example 1: Preparation of porous carbon / magnetic nanoparticle composite Co-CCP-600 (1) Wash the fresh grapefruit peel with deionized water, dry it at 60°C to constant weight, pulverize it and pass it through a 100-mesh sieve to obtain grapefruit peel powder.

[0035] (2) Weigh 0.5 g of the grapefruit peel powder prepared in step (1) and add it to a mixed solution of 50 mL ethanol and 25 mL deionized water. Disperse the mixture by sonication for 15 min. Then add 0.5 g of cobalt acetate tetrahydrate (Co(OAc)2·4H2O) and 0.16 g of 2,5-dihydroxyterephthalic acid, and continue sonicating for 15 min to ensure complete dissolution and dispersion. Transfer the mixed solution to a 100 mL stainless steel autoclave lined with polytetrafluoroethylene and react at 100 °C for 12 h. After the reaction is complete, allow it to cool naturally to room temperature. Wash the product three times each with ethanol and deionized water, and dry it under vacuum at 70 °C for 12 h to obtain the precursor.

[0036] (3) The precursor prepared in step (2) was placed in a tube furnace and heated to 600°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 2 h. It was then naturally cooled to room temperature to obtain a porous carbon / magnetic nanoparticle composite, denoted as Co-CCP-600.

[0037] Example 2: Preparation of porous carbon / magnetic nanoparticle composite Co-CCP-700 (1) The preparation of grapefruit peel powder is the same as in Example 1.

[0038] (2) The preparation of the precursor is the same as in Example 1.

[0039] (3) The precursor prepared in step (2) was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 2 h. It was then naturally cooled to room temperature to obtain a porous carbon / magnetic nanoparticle composite, denoted as Co-CCP-700.

[0040] Example 3: Preparation of porous carbon / magnetic nanoparticle composite Co-CCP-800 (1) The preparation of grapefruit peel powder is the same as in Example 1.

[0041] (2) The preparation of the precursor is the same as in Example 1.

[0042] (3) The precursor prepared in step (2) is placed in a tube furnace and heated to 800°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 2 h. It is then naturally cooled to room temperature to obtain a porous carbon / magnetic nanoparticle composite, denoted as Co-CCP-800.

[0043] Comparative Example 1: Preparation of Co / C composite material without grapefruit peel activation (1) The preparation steps of the precursor are the same as in Example 1, but grapefruit peel powder is not added.

[0044] (2) The prepared precursor was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere. After calcination for 2 h, it was naturally cooled to room temperature to obtain the Co / C composite material.

[0045] Comparative Example 2: Preparation of Fe-MOF-74 (1) The preparation of grapefruit peel powder is the same as in Example 1.

[0046] (2) The preparation of the precursor was the same as in Example 1, except that "cobalt acetate tetrahydrate (Co(OAc)2·4H2O) was replaced with an equal molar amount of iron acetate", and all other conditions remained the same; (3) The precursor prepared in step (2) was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 2 h. It was then naturally cooled to room temperature to obtain a porous carbon / magnetic nanoparticle composite, denoted as Fe-MOF-74.

[0047] Comparative Example 3: Preparation of Zn-MOF-74 (1) The preparation of grapefruit peel powder is the same as in Example 1.

[0048] (2) The preparation of the precursor was the same as in Example 1, except that “cobalt acetate tetrahydrate (Co(OAc)2·4H2O) was replaced with an equal molar amount of zinc acetate”, and all other conditions remained the same. (3) The precursor prepared in step (2) was placed in a tube furnace and heated to 700°C at a heating rate of 5°C / min under a nitrogen atmosphere and calcined for 2 h. It was then naturally cooled to room temperature to obtain a porous carbon / magnetic nanoparticle composite, denoted as Zn-MOF-74.

[0049] Comparative Example 4: Preparation of Glucose-Co-MOF-74 The preparation method of Comparative Example 4 was repeated in Example 2, except that "the addition of grapefruit peel powder was omitted and grapefruit peel powder was replaced with the same mass of glucose in step (2)", and the other conditions remained unchanged, and glucose-Co-MOF-74 was finally obtained.

[0050] Comparative Example 5: Preparation of Bamboo Powder-Co-MOF-74 The preparation method of Comparative Example 5 was repeated in Example 2, except that "the addition of grapefruit peel powder was omitted and the grapefruit peel powder in step (2) was replaced with bamboo powder of the same mass". All other conditions remained the same, and bamboo powder-Co-MOF-74 was finally obtained.

[0051] Example 4: Phase and morphology characterization of the composite material 1. XRD elemental analysis The X-ray diffraction (XRD) patterns of Co-CCP samples prepared at different carbonization temperatures were analyzed. The XRD patterns of the composites in Examples 1-3 are shown below. Figure 1A broad, diffuse peak appeared at approximately 25.9° in all samples, corresponding to the (002) crystal plane of graphitized carbon, confirming that the grapefruit peel biomass precursor was successfully transformed into an amorphous or microcrystalline carbon substrate during heat treatment. For the high-temperature annealed samples, three significant diffraction peaks appeared at approximately 44.2°, 51.5°, and 75.8°, belonging to the (111), (200), and (220) crystal planes of metallic cobalt, respectively. At 600°C, the spectrum mainly consisted of diffuse peaks of amorphous carbon, with no obvious metallic phase characteristic peaks observed, indicating that although Co-MOF-74 underwent thermal decomposition at this point, the cobalt component was still embedded in the carbon framework in the form of highly dispersed ultrafine clusters or amorphous particles. After the temperature increased to 700°C, diffraction peaks of metallic Co began to appear, but the peak shape was relatively broad and the intensity was low. This peak broadening phenomenon indicates that the metal composition maintains a fine grain size. When the temperature is further increased to 800°C, the characteristic peaks of Co become sharper and stronger, indicating that the metal atoms undergo violent rearrangement and aggregation under high temperature, resulting in a significant increase in grain size.

[0052] 2. Scanning electron microscopy analysis The microstructure of the composite materials prepared in Examples 1-3 was observed using a scanning electron microscope, and the results are as follows: Figure 2-4 As shown. Figure 2 The results show that at a lower carbonization temperature (600℃), the cobalt nanoparticles are smaller in size and more scattered in distribution. Figure 3 The composite material exhibits a unique sea urchin-like morphology, with cobalt nanoparticles uniformly anchored on porous carbon sheets, forming abundant heterogeneous interfaces. Figure 4 The results show that at high temperatures, cobalt nanoparticles agglomerate, their particle size increases, their morphology becomes more rounded, and their sea urchin-like structure weakens.

[0053] 3. Raman spectroscopy analysis The composite materials prepared in Examples 1-3 were analyzed using Raman spectroscopy, and the results are as follows: Figure 5 As shown. All samples were at approximately 1350 cm. -1 and 1580 cm -1 The D and G bands of the carbon material are shown. The intensity ratios (Iᴅ / Iɢ) of the D band to the G band are 1.20 (600℃), 0.89 (700℃), and 0.71 (800℃), respectively, indicating that the degree of graphitization of the material increases and defects decrease with increasing carbonization temperature.

[0054] Example 5: Electromagnetic wave absorption performance test of composite materials The composite materials obtained in Examples 1-3 and Comparative Examples 1-5 were mixed with paraffin wax at a mass ratio of 3:7 and pressed into coaxial ring-shaped samples with an outer diameter of 7 mm and an inner diameter of 3.04 mm. The complex permittivity and complex permeability in the frequency range of 2-18 GHz were tested using a vector network analyzer, and the reflection loss (RL) was calculated according to transmission line theory. The results are shown below. Figure 6-13 As shown.

[0055] from Figure 7 As can be seen, the Co-CCP-700 of Example 2 exhibits the best absorption performance, achieving a minimum reflection loss RLmin of -36.93 dB and an effective absorption bandwidth (RL < -10 dB) of 4.77 GHz with a thickness of only 1.82 mm. Figure 6 and Figure 8 It can be seen that the Co-CCP-600 of Example 1 has poor absorption performance due to incomplete carbonization, resulting in weak conductivity and polarization loss. Although the Co-CCP-800 of Example 3 has a high degree of graphitization, its excessively high conductivity leads to impedance mismatch, and the urchin-like structure is destroyed, resulting in a decrease in absorption performance compared to Example 2. Figure 9 It can be seen that the microwave absorption performance of the Co / C composite material without grapefruit peel in Comparative Example 1 is much worse than that in Example 2. This proves that the grapefruit peel-derived porous carbon skeleton plays a key role in constructing a unique microstructure and optimizing impedance matching.

[0056] from Figures 10-11 It can be seen that the minimum reflection loss RLmin of Fe-MOF-74 in Comparative Example 2 and Zn-MOF-74 in Comparative Example 3 are significantly lower than those in Example 2, indicating that the metal selection of the porous carbon / magnetic nanoparticle composite has a significant impact on the microwave absorption performance.

[0057] Additionally from Figures 12-13 It can be seen that the absorption performance of glucose-Co-MOF-74 and bamboo powder-Co-MOF-74 is much worse than that of Example 2, which proves that the choice of different biomass has a significant impact on the optimization of impedance matching.

[0058] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a porous carbon / magnetic nanoparticle composite, characterized in that, Includes the following steps: Step 1: Dry the fresh grapefruit peel and then crush it to obtain grapefruit peel powder; Step 2: Add the grapefruit peel powder, cobalt source and 2,5-dihydroxyterephthalic acid prepared in Step 1 to the solvent, disperse them evenly by ultrasonication, transfer them to an autoclave, seal the autoclave and carry out hydrothermal reaction. After the reaction is completed, wash and dry the product to obtain the precursor. Step 3: The precursor prepared in step 2 is subjected to high-temperature carbonization treatment under an inert atmosphere to obtain the porous carbon / magnetic nanoparticle composite.

2. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 1, characterized in that, The cobalt source mentioned in step 2 is cobalt acetate tetrahydrate, and the mass ratio of grapefruit peel powder to cobalt source in step 2 is 1:0.5-2.0, preferably 1:1.

0.

3. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 1, characterized in that, The mass ratio of grapefruit peel powder to 2,5-dihydroxyterephthalic acid in step 2 is 1:0.1-0.5, preferably 1:0.3-0.

32.

4. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 1, characterized in that, The temperature of the hydrothermal reaction is 90-120℃, preferably 100-110℃, and the reaction time is 10-24h, preferably 12-15h.

5. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 1, characterized in that, The solvent mentioned in step 2 is an ethanol-water mixture, with a volume ratio of ethanol to water of 1-3:1, preferably 2:1; the volume of the solvent used is 100-200 mL / g based on the mass of the grapefruit peel powder.

6. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 1, characterized in that, In step 3, the high-temperature carbonization process starts from room temperature and increases the temperature at a rate of 2-10℃ / min until the carbonization temperature reaches 600-800℃. The carbonization holding time is 1-4 hours.

7. The method for preparing a porous carbon / magnetic nanoparticle composite as described in claim 6, characterized in that, The carbonization temperature is 7 hours, and the carbonization holding time is 2-3 hours.

8. A porous carbon / magnetic nanoparticle composite prepared by any one of the methods described in claims 1-7.

9. The application of the porous carbon / magnetic nanoparticle composite as described in claim 8 in the preparation of microwave absorbing materials, characterized in that, The material is used to absorb electromagnetic waves in the frequency range of 2 to 18 GHz.

Images