Lotus root-shaped porous structure carbon-cobalt composite material and preparation method thereof

Abstract

The application belongs to the technical field of wave-absorbing materials, and discloses a lotus root-shaped porous structure carbon-cobalt composite material and a preparation method thereof.The wave-absorbing material maintains the lotus root-shaped porous fiber structure of loofah sponge, and the metal cobalt is loaded on the surface of the loofah sponge carbon in the form of coral cluster structure.The application uses pre-carbonized loofah sponge as a carbon source, cobalt nitrate (cobalt chloride, cobalt sulfate) as a metal salt, dimethyl imidazole as an organic ligand, and deionized water as a solvent, and adopts normal-temperature standing reaction and high-temperature pyrolysis two synthesis processes to prepare the loofah sponge carbon-cobalt wave-absorbing material derived from biomass, and the wave-absorbing material has simple synthesis process, low cost and unique structure.The loofah sponge carbon-cobalt wave-absorbing material prepared by the application meets the requirements of light mass, thin thickness, strong absorption, wide frequency band and the like, and also meets the requirements of green and sustainable development.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing composite materials technology, specifically relating to a lotus root-like porous carbon-cobalt composite material and its preparation method. Background Technology

[0002] Traditional microwave absorbing materials (ferromagnetic metals and their oxides, conductive polymers, and ceramics) can meet the requirements of strong absorption capacity and wide absorption bandwidth, but their preparation processes are often complex and costly, making it difficult to meet the requirements of lightweight and low cost. Therefore, the development of efficient, lightweight, low-cost microwave absorbing materials with excellent absorption performance has become a new research hotspot.

[0003] Studies have found that biomass materials with high cellulose content can serve as excellent precursors for lightweight, inexpensive carbon, such as cotton, wood, bamboo, and corn stalks. Converting biomass materials into biomass-derived carbon requires only a simple carbonization process. Biomass-derived carbon not only possesses the advantages of high dielectric properties, good stability, and low density of carbon materials, but also retains its unique porous network structure. Unfortunately, the single dielectric loss mechanism of carbon materials limits their attenuation ability for electromagnetic waves, while high conductivity also leads to high electromagnetic wave reflection. Therefore, constructing magnetic / carbon composite materials with a dielectric-magnetic dual-loss mechanism can simultaneously optimize impedance matching and improve attenuation capability, making it an effective method for obtaining highly efficient microwave absorbing materials. Metal-organic frameworks (MOFs) have advantages such as high porosity, tunable composition, and diverse structures. Combining MOFs with biomass-derived carbon can obtain magnetic / carbon composite materials uniformly dispersed on biomass-derived carbon, which is a simple and effective method for modifying biomass-derived carbon microwave absorbing materials.

[0004] It can be argued that the reuse of biomass materials with high cellulose content is of great significance for environmental protection and resource recycling, and also provides a sustainable and low-cost method for designing efficient and lightweight microwave absorbing materials. Summary of the Invention

[0005] The purpose of this invention is to provide a lotus root-like porous carbon-cobalt composite material and its preparation method, so as to solve the problems in the prior art mentioned in the background.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention proposes a lotus root-like porous carbon-cobalt composite material, which is composed of a lotus root-like porous fiber structure with coral cluster-like metallic cobalt loaded on the surface.

[0008] This invention also provides a method for preparing a lotus root-like porous carbon-cobalt composite material, comprising the following steps:

[0009] S1. Remove the outer shell and internal structure of the loofah, keeping only the spongy part in the middle. After cleaning with deionized water, put it in a vacuum drying oven and dry at 60℃ for 12 hours.

[0010] S2. Under a nitrogen protective atmosphere, the above-mentioned loofah sponge is pre-carbonized to obtain loofah sponge carbon.

[0011] S3. Add cobalt salt to 40 mL of deionized water and stir and sonicate. After the treatment is completed, take it out to obtain solution A.

[0012] S4. Add dimethylimidazole to 40 mL of deionized water and stir and sonicate. After the treatment is completed, take it out to obtain solution B.

[0013] S5. Stir the solution B thoroughly, add the solution A to the solution B and mix and stir. After stirring, take it out to obtain solution C.

[0014] S6. Immerse the loofah sponge carbon into the solution C, let it stand at room temperature to react, and take out the reaction product after the reaction is completed.

[0015] S7. The reaction product is dried to constant weight and taken out to obtain a carbon / cobalt-metal organic framework for loofah sponge.

[0016] S8. The loofah sponge carbon / cobalt-metal-organic framework is annealed under a nitrogen atmosphere and then removed to obtain the loofah sponge carbon / cobalt microwave absorbing material.

[0017] Preferably, the temperature of the pre-carbonization treatment in S2 is 200-500°C, and the annealing time is 2-6 hours.

[0018] Preferably, the cobalt salt described in S3 is derived from one or more of cobalt nitrate, cobalt chloride, and cobalt sulfate.

[0019] For example, in S3, the molar ratio of cobalt nitrate and dimethylimidazole is 1:n, where n is an integer ranging from 12 to 20.

[0020] Preferably, the mass of the loofah sponge carbon in S6 is 1 to 5 g.

[0021] Preferably, the room temperature standing reaction time in S6 is 4 to 12 hours.

[0022] Preferably, the annealing temperature in S8 is 500-800°C and the annealing time is 2-6 hours.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. This invention uses pre-carbonized loofah sponge as the carbon source, cobalt nitrate (cobalt chloride, cobalt sulfate) as the metal salt, dimethylimidazole as the organic ligand, and deionized water as the solvent. It employs two synthesis processes: room temperature static reaction and high temperature pyrolysis, to prepare a biomass-derived loofah sponge carbon / cobalt microwave absorbing material. This microwave absorbing material has a simple synthesis process, low cost, and unique structure.

[0025] 2. The carbon / cobalt absorbing material for loofah sponge prepared by this invention not only meets the requirements of light weight, thin thickness, strong absorption and wide bandwidth, but also meets the requirements of green and sustainable development. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for preparing a lotus root-like porous carbon-cobalt composite material according to an embodiment of the present invention;

[0027] Figure 2 The XRD spectra of the absorbing materials obtained in Examples 1-3 of this invention are shown below.

[0028] Figure 3 The Raman spectra of the absorbing materials obtained in Examples 1-3 of this invention are shown.

[0029] Figure 4 This is the SEM spectrum of carbon from the loofah sponge in this invention example;

[0030] Figure 5 The image shows the SEM spectrum of the absorbing material prepared in Example 1 of this invention.

[0031] Figure 6 The image shows the SEM spectrum of the absorbing material prepared in Example 2 of this invention.

[0032] Figure 7 The image shows the SEM spectrum of the absorbing material prepared in Example 3 of this invention.

[0033] Figure 8 This is a graph showing the variation of reflection loss with frequency for the absorbing material prepared in Example 1 of this invention at different thicknesses;

[0034] Figure 9 This is a graph showing the variation of reflection loss with frequency for the absorbing material prepared in Example 2 of this invention at different thicknesses;

[0035] Figure 10 This is a graph showing the variation of reflection loss with frequency for the absorbing material prepared in Example 3 of this invention at different thicknesses; Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] This invention provides a method for preparing a lotus root-like porous carbon-cobalt composite material.

[0038] like Figure 1 As shown, Figure 1 This is a flowchart illustrating a method for preparing a lotus root-like porous carbon-cobalt composite material according to an embodiment of the present invention.

[0039] In this embodiment, the preparation method described above includes the following steps:

[0040] Step 1: Remove the outer shell and internal structure of the loofah, keeping only the spongy part in the middle. After cleaning it with deionized water, put it in a vacuum drying oven and dry it at 60℃ for 12 hours.

[0041] Step 2: Under a nitrogen protective atmosphere, the above-mentioned loofah sponge is pre-carbonized to obtain loofah sponge carbon.

[0042] Step 3: Add cobalt salt to 40 mL of deionized water and stir and sonicate. After the treatment is completed, take it out to obtain solution A.

[0043] Step 4: Add dimethylimidazole to 40 mL of deionized water and stir and sonicate. After the treatment is completed, take it out to obtain solution B.

[0044] Step 5: Thoroughly stir the solution B, add the solution A to the solution B and mix and stir. After stirring, remove the solution to obtain solution C.

[0045] Step 6: Immerse the loofah sponge carbon in the solution C and let it stand at room temperature for 4-12 hours. After the reaction is complete, take out the reaction product.

[0046] Step 7: Dry the reaction product at 60°C for 24 hours until constant weight, then remove it to obtain the loofah sponge carbon / cobalt-metal-organic framework.

[0047] Step 8: Anneal the loofah sponge carbon / cobalt-metal-organic framework under a nitrogen atmosphere, and remove it to obtain the loofah sponge carbon-cobalt microwave absorbing material.

[0048] In step two, the carbonization temperature is 200–500℃ and the annealing time is 2–6 h; in step three, the cobalt salt is derived from one or more of cobalt nitrate, cobalt chloride, and cobalt sulfate; in step three, the molar ratio of cobalt nitrate to dimethylimidazolium is 1:n, where n is an integer ranging from 12 to 20; in step six, the weight of the loofah sponge carbon is 1–5 g; in step six, the room temperature standing reaction time is 4–12 h; and in step eight, the annealing temperature is 500–800℃ and the annealing time is 2–6 h.

[0049] This example uses loofah sponge as the carbon source and prepares a biomass-derived loofah sponge carbon / cobalt microwave absorbing material through carbonization, room-temperature static reaction, and high-temperature pyrolysis. This absorbing material retains the lotus root-like porous fibrous structure of the loofah sponge, with metallic cobalt loaded onto the carbon surface of the loofah sponge in a coral-like structure. This invention features a simple synthesis process, low cost, and unique structure. The loofah sponge carbon / cobalt microwave absorbing material prepared by this invention meets the requirements of light weight, thin thickness, strong absorption, and wide bandwidth, while also satisfying the requirements of green and sustainable development.

[0050] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention are further described below with reference to embodiments. However, the present invention is not limited to the listed embodiments, but should also include any other known modifications within the scope of the claims of the present invention.

[0051] Example 1

[0052] This implementation case demonstrates a method for preparing a lotus root-like porous carbon-cobalt composite material according to the following steps:

[0053] Step 1: Remove the outer shell and internal structure of the loofah, keeping only the spongy part in the middle. After cleaning it with deionized water, put it in a vacuum drying oven and dry it at 60℃ for 12 hours.

[0054] Step 2: Under a nitrogen protective atmosphere, the above-mentioned loofah sponge is pre-carbonized at a carbonization temperature of 200℃ and an annealing time of 2 hours to obtain loofah sponge carbon.

[0055] Step 3: Stir 1 mmol of cobalt chloride and 40 mL of deionized water for 30 min. After the treatment is completed, remove the solution to obtain solution A.

[0056] Step 4: Stir 12 mmol of dimethylimidazole and 40 mL of deionized water for 30 min, then sonicate for 30 min. After the treatment, remove the solution to obtain solution B.

[0057] Step 5: Stir the solution B thoroughly, add the solution A to the solution B and mix and stir for 30 minutes. After stirring, take it out to obtain solution C.

[0058] Step 6: Immerse 1g of loofah sponge carbon into solution C, let it stand at room temperature for 4 hours, and remove the reaction product after the reaction is completed.

[0059] Step 7: Dry the reaction product at 60°C for 24 hours until constant weight, then remove it to obtain the loofah sponge carbon / cobalt-metal-organic framework.

[0060] Step 8: Anneal the loofah sponge carbon cobalt-metal organic framework under a nitrogen atmosphere at a temperature of 500°C for 2 hours. Remove the material to obtain the loofah sponge carbon / cobalt microwave absorbing material.

[0061] Example 2

[0062] This implementation case demonstrates a method for preparing a lotus root-like porous carbon-cobalt composite material according to the following steps:

[0063] Step 1: Remove the outer shell and internal structure of the loofah, keeping only the spongy part in the middle. After cleaning it with deionized water, put it in a vacuum drying oven and dry it at 60℃ for 12 hours.

[0064] Step 2: Under a nitrogen protective atmosphere, the above-mentioned loofah sponge is pre-carbonized at a carbonization temperature of 300℃ and an annealing time of 4h to obtain loofah sponge carbon.

[0065] Step 3: Stir 1 mmol of cobalt nitrate and 40 mL of deionized water for 30 min. After the treatment is completed, remove the solution to obtain solution A.

[0066] Step 4: Stir 16 mmol of dimethylimidazole and 40 mL of deionized water for 30 min, sonicate for 30 min, remove after treatment, and obtain solution B.

[0067] Step 5: Stir the solution B thoroughly, add the solution A to the solution B and mix and stir for 30 minutes. After stirring, take it out to obtain solution C.

[0068] Step 6: Immerse 3g of loofah sponge carbon into solution C, let it stand at room temperature for 8 hours, and remove the reaction product after the reaction is completed.

[0069] Step 7: Dry the reaction product at 60°C for 24 hours until constant weight, then remove it to obtain the loofah sponge carbon / cobalt-metal-organic framework.

[0070] Step 8: Anneal the loofah sponge carbon / cobalt-metal-organic framework under a nitrogen atmosphere at a temperature of 700°C for 4 hours. Remove the material to obtain the loofah sponge carbon / cobalt microwave absorbing material.

[0071] Example 3

[0072] This implementation case demonstrates a method for preparing a lotus root-like porous carbon-cobalt composite material according to the following steps:

[0073] Step 1: Remove the outer shell and internal structure of the loofah, keeping only the spongy part in the middle. After cleaning it with deionized water, put it in a vacuum drying oven and dry it at 60℃ for 12 hours.

[0074] Step 2: Under a nitrogen protective atmosphere, the above-mentioned loofah sponge is pre-carbonized at a carbonization temperature of 500℃ and an annealing time of 6 hours to obtain loofah sponge carbon.

[0075] Step 3: Stir 1 mmol of cobalt sulfate and 40 mL of deionized water for 30 min. After the treatment is completed, remove the solution to obtain solution A.

[0076] Step 4: Stir 20 mmol of dimethylimidazole and 40 mL of deionized water for 30 min, then sonicate for 30 min. After the treatment, remove the solution to obtain solution B.

[0077] Step 5: Stir the solution B thoroughly, add the solution A to the solution B and mix and stir for 30 minutes. After stirring, take it out to obtain solution C.

[0078] Step 6: Immerse 5g of loofah sponge carbon into solution C, let it stand at room temperature for 12 hours, and remove the reaction product after the reaction is completed.

[0079] Step 7: Dry the reaction product at 60°C for 24 hours until constant weight, then remove it to obtain the loofah sponge carbon / cobalt-metal-organic framework.

[0080] Step 8: Anneal the loofah sponge carbon / cobalt-metal-organic framework under a nitrogen atmosphere at a temperature of 800°C for 6 hours. Remove the material to obtain the loofah sponge carbon / cobalt microwave absorbing material.

[0081] The lotus root-like porous carbon-cobalt composite material prepared in Examples 1-3 was tested.

[0082] Based on the test results, the following conclusions are drawn:

[0083] The X-ray diffraction (XRD) patterns of the samples in Examples 1-3 are shown below. Figure 2 As shown, the diffraction peaks at 44.4°, 51.6°, and 76.1° correspond to the (111), (200), and (220) crystal planes of cobalt (PDF#01-1255), respectively, while the broad diffraction peak near 26° corresponds to graphitic carbon. This indicates that the microwave absorbing material is composed of cobalt and carbon.

[0084] The Raman spectra of samples from Examples 1-3 are as follows: Figure 3 As shown. Raman spectroscopy is used to evaluate the degree of graphitization and defect properties of carbon-based materials. Example 1-3 samples I... D / I G The ratios were 0.698, 0.847, and 0.887, respectively. This indicates that as the pyrolysis temperature increases, the graphitization degree of the microwave absorbing material decreases and the defects increase.

[0085] Scanning electron microscopy (SEM) images of the loofah sponge carbon in the examples and the samples from Examples 1-3 are shown below. Figure 4-7 As shown, the carbon from the loofah sponge retains the lotus root-like porous fibrous structure of the loofah sponge, and its surface exhibits a smooth, grooved appearance. In Example 1, the cobalt on the surface of the loofah sponge carbon is clearly dispersed and independent, with no tendency to connect into sheets. In Example 2, the cobalt on the surface of the loofah sponge carbon is dispersed, but its independence is poor, forming a continuous coral-like structure. In Example 3, the cobalt on the surface of the loofah sponge carbon is dispersed and interconnected, forming a distinct coral-like cluster structure. This can be explained by the fact that as the pyrolysis temperature increases, the reduction of cobalt ions is promoted, and the generated cobalt attracts each other, interconnecting into sheets.

[0086] To evaluate the electromagnetic wave absorption performance of the loofah sponge carbon / cobalt absorbing material, its reflection loss value can be calculated based on transmission line theory. Concentric rings (outer diameter 7.00 mm, inner diameter 3.04 mm, thickness 2.00 mm) were prepared from 40 wt% loofah sponge carbon / cobalt absorbing material and 70 wt% paraffin wax. The electromagnetic wave absorption performance of the samples was measured and calculated using a vector network analyzer. The reflection loss versus frequency curve of the samples is shown in the figure below. Figure 8-10 As shown.

[0087] from Figure 8 It can be seen that Example 1 has almost no electromagnetic wave absorption performance. From Figure 9 It can be seen that, with a matching thickness of 2.61 mm, Example 2 exhibits an optimal reflection loss of -60.81 dB, and with a matching thickness of 1.68 mm, the effective absorption bandwidth is 5.56 GHz. From... Figure 10 It can be seen that, with a matching thickness of 1.38 mm, Example 3 exhibits the best reflection loss of -54.93 dB and an effective absorption bandwidth of 3.90 GHz. From the above experimental results, it can be seen that Example 2 possesses excellent electromagnetic wave absorption performance with high absorption intensity, wide absorption bandwidth, and low thickness.

[0088] As can be seen from the test results of the above embodiments, the present invention successfully prepared a low-cost, lightweight porous cobalt carbon-cobalt absorbing material from a loofah sponge by loading a coral-like cobalt structure onto its surface after carbonization pretreatment.

[0089] A lotus root-like porous carbon-cobalt composite material was prepared using loofah sponge as a lightweight and inexpensive carbon source. This preparation process is simple, low-cost, and features a unique structure. Sample 2 exhibits optimal overall microwave absorption performance; at a thickness of 2.61 mm, the maximum absorption intensity reaches -60.81 dB, and at a matched thickness of 1.68 mm, the effective absorption bandwidth is 5.56 GHz. Therefore, the prepared biomass-derived loofah sponge carbon-cobalt microwave absorbing material is an ideal lightweight and environmentally friendly microwave absorbing material.

[0090] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a lotus root-like porous structure carbon-cobalt composite material, characterized in that: It includes, in sequence, an inseparable set of processes: ​ S1. Pretreatment of loofah sponge: Remove the outer shell and seeds, wash with water and vacuum dry at 60℃ for 12h; S2, nitrogen atmosphere, low temperature pre-carbonization at 200-500℃ for 2-6h to prepare rigid lotus root porous carbon framework; S3. Dissolve cobalt nitrate in 40 mL of deionized water to obtain solution A; S4, dissolve dimethylimidazole in an equal volume of 40 mL of deionized water to obtain solution B, with a molar ratio of cobalt nitrate to dimethylimidazole of 1:12-20; S5. Slowly add solution A to solution B and mix to obtain a homogeneous precursor solution; S6, 1-5g of loofah sponge carbon is immersed in the mixed solution and left to stand at room temperature for 4-12 hours to grow ZIF-67 in situ in a thick layer; S7, dried at 60℃ to constant weight to obtain carbon / ZIF-67 intermediate; Annealing with S8 and nitrogen at 500-800℃ for 2-6 hours induces cross-linking of cobalt particles to form a continuous coral cluster magnetic network.

2. A lotus root-shaped porous carbon-cobalt composite material prepared by the method for preparing lotus root-shaped porous carbon-cobalt composite material according to claim 1, characterized in that: The composite material consists of a lotus root-like porous fiber structure with coral-like metallic cobalt loaded on its surface.

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