Carbon nanofiber composite material deposited on lotus leaf as substrate, and preparation method and application thereof

Abstract

This invention discloses a method for depositing carbon nanofiber composite materials using lotus leaves as a substrate, its preparation, and its application. The method includes the following steps: Cleaned lotus leaves are placed in a catalyst aqueous solution and ultrasonically treated for 20-40 minutes. The solution is then poured into a polytetrafluoroethylene-lined reactor. The catalyst aqueous solution is a mixture of nickel nitrate and thiourea, with a molar ratio of 1:10-15. The total concentration of metal ions in the catalyst aqueous solution is 0.01-0.04 mol / L. The reactor is heated at 170-190℃ for 20-30 hours. After the reaction is complete, the solution is cooled, filtered, and the resulting solid is dried to obtain powder. The powder is placed in a quartz boat, the air is replaced with nitrogen, hydrogen is introduced, and the solution is heated to 430-470℃ for 5-15 minutes to reduce the catalyst. Subsequently, the solution is heated to 600-700℃ for reaction growth, with a single introduction of carbon nanofibers. 2 H 2 and H 2 and control N 2 C 2 H 2 and H 2 The flow rate ratio is 5-7:2-4:2-4. After growing for 20-40 minutes, the target product is obtained. The target product is then cooled.

Description

Carbon nanofiber composite materials deposited on lotus leaf substrates, their preparation methods and applications Technical Field

[0001] This invention relates to the field of electromagnetic wave absorbing materials technology, specifically to a carbon nanofiber composite material deposited on a lotus leaf substrate, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With the rapid development of 5G technology, the use of electronic communication devices is increasing daily. While these devices bring convenience to our lives, the electromagnetic radiation they generate affects our health. Therefore, there is an urgent need to develop electromagnetic wave absorbing materials to address this issue. In recent years, carbon skeletons of plants, animals, or microorganisms obtained through carbonization have become excellent electromagnetic wave absorbers. Furthermore, introducing special structural treatment methods during the preparation process can effectively improve adsorption performance. Pore creation is a common method for optimizing electromagnetic wave (EMW) absorption performance.

[0004] Lotus leaves, as a biomass material, are widely distributed, but their application in electromagnetic wave absorption is not widespread, and their absorption performance is relatively weak. While carbon nanofibers have a wider range of applications in wave absorption due to their strong absorption capacity, their bandwidth is relatively narrow. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a carbon nanofiber composite material deposited on a lotus leaf substrate, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing a carbon nanofiber composite material deposited on a lotus leaf substrate, comprising the following steps:

[0008] After cleaning, the lotus leaves are placed in the catalyst aqueous solution and ultrasonically treated for 20-40 minutes. Then, they are poured into a reaction vessel lined with polytetrafluoroethylene. The catalyst aqueous solution is a mixed aqueous solution of nickel nitrate and thiourea, with a molar ratio of nickel nitrate to thiourea of ​​1:10-15. The total concentration of metal ions in the catalyst aqueous solution is 0.01-0.04 mol / L.

[0009] Heat the reactor at 170-190℃ for 20-30 hours;

[0010] After the reaction is complete, the solution is cooled, filtered, and the resulting solid is dried to obtain a powder.

[0011] The powder was placed in a quartz boat, the air was replaced with nitrogen, hydrogen was introduced into it, and the mixture was heated to 430-470℃ for 5-15 minutes to reduce the catalyst.

[0012] The mixture is then heated to 600-700℃ for reaction growth. C2H2 and H2 are introduced at one time, and the flow rate ratio of N2, C2H2 and H2 is controlled at 5-7:2-4:2-4. After growth for 20-40 minutes, the target product is obtained. The target product is then cooled.

[0013] The role of nickel nitrate is to introduce nickel as a catalyst in the subsequent growth of carbon nanofibers, and to generate nickel sulfide, a dielectric material, after hydrothermal reaction with thiourea, which also helps to improve the microwave absorption performance.

[0014] The purpose of heating the reactor at 170-190℃ is to create a high-pressure environment inside the reactor to promote the reaction of nickel nitrate and thiourea to produce nickel sulfide.

[0015] The purpose of reducing the catalyst is to reduce metallic nickel for the growth of carbon nanofibers in the next process.

[0016] The reaction and growth are carried out at 600-700℃, at which temperature the catalytic activity of metallic nickel is the best. If the temperature is too high, the carbon source decomposes too quickly, and the carbon atoms will wrap around the metallic nickel at a faster rate, causing the catalyst to be "poisoned" and lose its catalytic activity. If the temperature is too low, the carbon source decomposes too slowly, making it difficult to grow carbon nanofibers.

[0017] In some embodiments, the molar ratio of nickel nitrate to thiourea in the catalyst aqueous solution is 1:10-14.

[0018] Preferably, the total concentration of metal particles in the catalyst aqueous solution is 0.01-0.03 mol / L.

[0019] In some embodiments, the ultrasound duration is 25-35 minutes.

[0020] Preferably, the ultrasound time is 30 minutes.

[0021] In some embodiments, after replacing the air with nitrogen, the heating rate is 8-12°C / min.

[0022] In some embodiments, the catalyst is reduced at a temperature of 440-460°C for 8-12 minutes.

[0023] In some embodiments, the flow rates of N2, C2H2, and H2 are 5-7 L / min, 2-4 L / min, and 2-4 L / min, respectively.

[0024] In some embodiments, the reaction growth temperature is 640-660°C.

[0025] Preferably, the growth time is 25-35 minutes.

[0026] Secondly, the present invention provides a composite material for depositing carbon nanofibers on a lotus leaf substrate, which is prepared by the aforementioned preparation method.

[0027] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0028] (1) This invention provides a low-cost, time-saving, and high-performance lotus leaf / carbon nanofiber material with excellent wave absorption properties. This method can solve the problems of high cost and inability to mass-produce samples in existing methods.

[0029] (2) The lotus leaf / carbon nanofiber prepared by this invention has the following advantages: First, the porous structure inside the lotus leaf allows as many electromagnetic waves as possible to enter the material and dissipate them through reflection. Second, the carbon nanofiber has a high dielectric constant, resulting in high dielectric loss. The entire process is low-cost and time-saving, and has good application prospects.

[0030] The porous structure of lotus leaves makes them a potentially excellent microwave absorber, while carbon nanofibers also possess good microwave absorption properties. By depositing carbon nanofibers onto lotus leaves, the advantages of both materials are combined to address their respective shortcomings in microwave absorption. The resulting 3D conductive network allows electrons to move freely along the network. The unique atomic structure and hybridization of carbon materials give them excellent current conductivity, which helps to reduce conduction losses. Furthermore, the residual nickel sulfide is itself a dielectric material, which contributes to dielectric loss. Therefore, the electromagnetic wave absorption performance of the lotus leaf / CNF is improved. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0032] Figure 1 is a scanning electron microscope image obtained in Embodiment 1 of the present invention;

[0033] Figure 2 is a graph showing the electromagnetic wave absorption performance obtained in Embodiment 1 of the present invention;

[0034] Figure 3 is a scanning electron microscope image obtained in Embodiment 2 of the present invention;

[0035] Figure 4 shows the electromagnetic wave absorption performance obtained in Embodiment 2 of the present invention.

[0036] Figure 5 is a scanning electron microscope image obtained in Embodiment 3 of the present invention;

[0037] Figure 6 shows the electromagnetic wave absorption performance obtained in Embodiment 3 of the present invention. Detailed Implementation

[0038] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] The present invention will be further described below with reference to the embodiments.

[0040] Example 1

[0041] A method for preparing carbon nanofiber composite materials deposited on lotus leaf substrates includes the following steps:

[0042] Step 1: Select lotus leaves and wash them multiple times with deionized water and anhydrous ethanol;

[0043] Step 2: Prepare an aqueous solution of catalyst using nickel nitrate and thiourea at a molar ratio of 1:12, with a total concentration of metal particles of 0.02 mol / L in the solution;

[0044] Step 3: Place the lotus leaf into the catalyst solution obtained in Step 2 and sonicate for 30 minutes, then pour it into a reaction vessel lined with polytetrafluoroethylene;

[0045] Step 4: Place the reaction vessel from Step 3 into an oven and heat at 180°C for 24 hours;

[0046] Step 5: Remove the reaction vessel from Step 4 and cool it to room temperature. Then pour the solution in the liner into the vacuum filter and filter it. Place the obtained powder in an oven and keep it at 60°C for 2 hours.

[0047] Step 6: Place the dried powder from Step 5 into a quartz boat, push it into a CVD tube furnace, introduce nitrogen gas to purge the gas inside the tube, heat to 450°C at a heating rate of 10°C / min, then introduce H2 at a rate of 0.3 L / min, hold at 450°C for 10 min to reduce the catalyst, then heat to 600°C, introduce C2H2 and H2 at once, and control the flow rates of N2, C2H2 and H2 to be 6 L / min, 3 L / min and 3 L / min respectively. After growing for 30 min, turn off C2H2 and H2, and cool to room temperature under N2 protection, then remove the sample.

[0048] Step 7: Mix the sample prepared in Step 6 with paraffin to prepare lotus leaf / CNF / paraffin material for electromagnetic wave absorption.

[0049] To perform measurements, the electromagnetic wave absorption performance of lotus leaf / CNF / paraffin materials was characterized using a vector network analyzer (Agilent Technologies N5244A) in the 2-18 GHz range.

[0050] The sample achieved a minimum reflection loss of -67.65 dB at 12.7 GHz, and when the thickness was reduced to 2.07 mm, the effective bandwidth reached 5.9 GHz, covering almost the entire Ku band (12.1-18 GHz).

[0051] Figure 1 is a scanning electron microscope image obtained in Embodiment 1 of the present invention. Figure 2 is a graph showing the electromagnetic wave absorption performance obtained in Embodiment 1 of the present invention.

[0052] Example 2

[0053] A method for preparing carbon nanofiber composite materials deposited on lotus leaf substrates includes the following steps:

[0054] Step 1: Select lotus leaves and wash them multiple times with deionized water and anhydrous ethanol;

[0055] Step 2: Prepare an aqueous solution of catalyst using nickel nitrate and thiourea at a molar ratio of 1:12, with a total concentration of metal particles of 0.02 mol / L in the solution;

[0056] Step 3: Place the lotus leaf into the catalyst solution obtained in Step 2 and sonicate for 30 minutes, then pour it into a reaction vessel lined with polytetrafluoroethylene;

[0057] Step 4: Place the reaction vessel from Step 3 into an oven and heat at 180°C for 24 hours;

[0058] Step 5: Remove the reaction vessel from Step 4 and cool it to room temperature. Then pour the solution in the liner into the vacuum filter and filter it. Place the obtained powder in an oven and keep it at 60°C for 2 hours.

[0059] Step 6: Place the dried powder from Step 5 into a quartz boat, push it into a CVD tube furnace, introduce nitrogen gas to purge the gas inside the tube, heat to 450°C at a heating rate of 10°C / min, then introduce H2 at a rate of 0.3 L / min, hold at 450°C for 10 min to reduce the catalyst, then heat to 650°C, introduce C2H2 and H2 at once, and control the flow rates of N2, C2H2 and H2 to be 6 L / min, 3 L / min and 3 L / min respectively. After growing for 30 min, turn off C2H2 and H2, and cool to room temperature under N2 protection, then remove the sample.

[0060] Step 7: Mix the sample prepared in Step 6 with paraffin to prepare lotus leaf / CNF / paraffin material for electromagnetic wave absorption.

[0061] To perform measurements, the electromagnetic wave absorption performance of lotus leaf / CNF / paraffin materials was characterized using a vector network analyzer (Agilent Technologies N5244A) in the 2-18 GHz range.

[0062] Figure 3 is a scanning electron microscope image obtained in Embodiment 2 of the present invention. Figure 4 is a graph showing the electromagnetic wave absorption performance obtained in Embodiment 2 of the present invention.

[0063] Example 3

[0064] A method for preparing carbon nanofiber composite materials deposited on lotus leaf substrates includes the following steps:

[0065] Step 1: Select lotus leaves and wash them multiple times with deionized water and anhydrous ethanol;

[0066] Step 2: Prepare an aqueous solution of catalyst using nickel nitrate and thiourea at a molar ratio of 1:12, with a total concentration of metal particles of 0.02 mol / L in the solution;

[0067] Step 3: Place the lotus leaf into the catalyst solution obtained in Step 2 and sonicate for 30 minutes, then pour it into a reaction vessel lined with polytetrafluoroethylene;

[0068] Step 4: Place the reaction vessel from Step 3 into an oven and heat at 180°C for 24 hours;

[0069] Step 5: Remove the reaction vessel from Step 4 and cool it to room temperature. Then pour the solution in the liner into the vacuum filter and filter it. Place the obtained powder in an oven and keep it at 60°C for 2 hours.

[0070] Step 6: Place the dried powder from Step 5 into a quartz boat, push it into a CVD tube furnace, introduce nitrogen gas to purge the gas inside the tube, heat to 450°C at a heating rate of 10°C / min, then introduce H2 at a rate of 0.3 L / min, hold at 450°C for 10 min to reduce the catalyst, then heat to 700°C, introduce C2H2 and H2 at once, and control the flow rate ratio of N2, C2H2 and H2 to be 6 L / min, 3 L / min and 3 L / min respectively. After growing for 30 min, turn off C2H2 and H2, and cool to room temperature under N2 protection, then remove the sample.

[0071] Step 7: Mix the sample prepared in Step 6 with paraffin to prepare lotus leaf / CNF / paraffin material for electromagnetic wave absorption.

[0072] To perform measurements, the electromagnetic wave absorption performance of lotus leaf / CNF / paraffin materials was characterized using a vector network analyzer (Agilent Technologies N5244A) in the 2-18 GHz range.

[0073] Figure 5 is a scanning electron microscope image obtained in Example 3 of the present invention. Figure 6 is a graph showing the electromagnetic wave absorption performance obtained in Example 3 of the present invention.

[0074] Table 1 shows the electromagnetic wave absorption performance of the lotus leaf / CNF / paraffin materials in Examples 1-3, illustrating the corresponding minimum EMW RL and maximum EAB. As can be seen from the table, the electromagnetic wave absorption performance of the lotus leaf / CNF / paraffin materials in the three examples is greater than 10 dB in the 2-18 GHz range, proving that they can absorb 90% of electromagnetic waves, indicating their potential application value.

[0075] In Example 1, all values ​​are greater than those in other examples, indicating that the lotus leaf / CNF / paraffin material grown at 600℃ under nitrogen atmosphere protection produces more interfaces due to the lotus leaf structure. Furthermore, the grown CNF exhibits strong conductivity, allowing some electromagnetic waves to enter the material interior and be fully absorbed by the porous structure when incident on the material surface, while the other part is reflected on the material surface, ultimately achieving optimal electromagnetic wave absorption performance.

[0076] Table 1 Electromagnetic wave absorption properties of lotus leaf / CNF / paraffin materials

[0077]

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanofiber composite material deposited on a lotus leaf substrate, characterized in that: The process includes the following steps: After cleaning, lotus leaves are placed in a catalyst aqueous solution and ultrasonically treated for 20-40 minutes. The solution is then poured into a polytetrafluoroethylene-lined reactor. The catalyst aqueous solution is a mixture of nickel nitrate and thiourea, with a molar ratio of 1:10-15. The total concentration of metal ions in the catalyst aqueous solution is 0.01-0.04 mol / L. The reactor is heated at 170-190℃ for 20-30 hours. After the reaction is complete, the solution is cooled, filtered, and the resulting solid is dried to obtain powder. The powder is placed in a quartz boat, and after replacing the air with nitrogen, hydrogen is introduced. The boat is heated and held at 430-470℃ for 5-15 minutes to reduce the catalyst. The solution is then heated to 600-700℃ for reaction growth, with C2H2 and H2 introduced simultaneously, and the flow rate ratio of N2, C2H2, and H2 controlled at 5-7:2-4:2-4. After growth for 20-40 minutes, the target product is obtained and cooled.

2. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: In the aqueous solution of the catalyst, the molar ratio of nickel nitrate to thiourea is 1:10-14.

3. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 2, characterized in that: In the aqueous solution of the catalyst, the total concentration of metal particles is 0.01-0.03 mol / L.

4. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: The ultrasound session lasted 25-35 minutes.

5. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: After replacing the air with nitrogen, the heating rate is 8-12℃ / min.

6. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: The catalyst is reduced at a temperature of 440-460℃ for 8-12 minutes.

7. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: The flow rates of N2, C2H2 and H2 are 5-7 L / min, 2-4 L / min and 2-4 L / min, respectively.

8. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 1, characterized in that: The reaction growth temperature is 640-660℃.

9. The method for preparing carbon nanofiber composite material deposited on a lotus leaf substrate according to claim 8, characterized in that: The growth time is 25-35 minutes.

10. A composite material for depositing carbon nanofibers on a lotus leaf substrate, characterized in that: It is prepared by any one of the preparation methods described in claims 1-9.

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