A method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns

Abstract

The present invention provides a method for improving the electromagnetic wave absorption performance of carbon nanohorns. The method comprises placing nitrogen-doped carbon nanohorns in a dielectric barrier discharge generator, introducing an ambient gas for dielectric barrier discharge treatment, and improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns by replacing some carbon atoms with gas atoms and / or enhancing surface defects in the nitrogen-doped carbon nanohorns. This method solves the technical difficulties of increasing the dielectric loss of carbon nanohorns in the prior art, which are low in efficiency and time-consuming. It can rapidly improve the electromagnetic wave absorption performance of carbon nanohorns and has the advantages of safety, reliability, low cost, and simple operation.

Description

Technical Field

[0001] The present invention relates to the field of plasma applications, and more particularly to a method for improving the electromagnetic wave absorption performance of carbon nanohorns. Background Art

[0002] With the development of radar technology and the widespread use of communications equipment, electromagnetic wave pollution is becoming increasingly serious. Electromagnetic wave absorbing materials are often used to reduce this pollution. Among various absorbing materials, carbon nanomaterials, due to their excellent conductivity and high specific surface area, meet the "lightness" and "strength" requirements of "thin, light, wide, and strong," making them widely used in the field of electromagnetic wave absorption.

[0003] As a member of the carbon nanomaterial family, carbon nanohorns have a relatively complete structure and fewer active sites. Therefore, when applied in the field of electromagnetic wave absorption, carbon nanohorns mainly rely on their own conductive network to generate resistive loss to absorb electromagnetic waves. However, a single loss mechanism cannot cope with the complex and changing actual situation. People have tried to modify carbon nanomaterials to increase the dielectric loss mechanism, thereby improving the electromagnetic wave absorption performance and application range. For example, Wu's team annealed graphene oxide at different temperatures and found that 300°C and 2h were the optimal treatment conditions, obtaining a product with an absorption bandwidth of 7.6GHz. Liu's team added urea to a graphene oxide dispersion and successfully doped nitrogen atoms into graphene oxide through a hydrothermal reaction at 180°C for 12h. Although annealing and chemical doping can increase the dielectric loss mechanism of carbon nanomaterials, there are still problems such as cumbersome steps, long time consumption, and the inability to quickly adjust the product's wave absorption performance according to requirements. Summary of the Invention

[0004] In response to the shortcomings of the prior art, one of the objectives of the present invention is to address one or more of the aforementioned problems. For example, one of the objectives of the present invention is to provide a method for improving the electromagnetic wave absorption performance of doped carbon nanohorns that can address the technical difficulties of the prior art in increasing the dielectric loss of carbon nanohorns, such as low efficiency and long processing time.

[0005] On the one hand, the present invention provides a method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns, which can include the following steps: placing the nitrogen-doped carbon nanohorns in a dielectric barrier discharge generator, introducing an atmospheric gas to perform dielectric barrier discharge treatment, and improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns by replacing some carbon atoms with gas atoms and / or by enhancing the surface defects of the nitrogen-doped carbon nanohorns.

[0006] Furthermore, the atmosphere gas may be oxygen, and the oxygen doping amount after oxygen atoms replace carbon atoms may be 2% to 14%.

[0007] Furthermore, the atmosphere gas may be nitrogen, and the total nitrogen doping amount after nitrogen atoms replace carbon atoms may be 1% to 5%.

[0008] Furthermore, the atmosphere gas may be argon, and both Frenkel defects and Schottky defects may be increased by 17% to 40%.

[0009] Furthermore, the nitrogen content of the nitrogen-doped carbon nanohorns may be no greater than 5%.

[0010] Furthermore, the flow rate of the atmospheric gas may be 20 ml / min to 50 ml / min, and the ventilation time before treatment may be 2 min to 5 min.

[0011] Furthermore, the power of the dielectric barrier discharge generator may be 75W to 125W, and the processing time may be 5 minutes to 30 minutes.

[0012] Furthermore, the atmosphere gas may be one or a mixture of oxygen, argon, nitrogen or air.

[0013] Another aspect of the present invention provides a modified nitrogen-doped carbon nanohorn, which can be obtained by modifying the nitrogen-doped carbon nanohorn using the above-mentioned method for improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorn.

[0014] Compared with the prior art, the beneficial effects of the present invention include at least any one of the following:

[0015] (1) The method of the present invention solves the technical problems of low efficiency and long time consumption in the process of increasing the dielectric loss of carbon nanohorns in the prior art, can quickly improve the electromagnetic wave absorption performance of carbon nanohorns, and has the advantages of safety, reliability, low cost, and simple operation process.

[0016] (2) The method of the present invention can shift the reflection loss peak to low frequency or high frequency according to the different atmospheres during the treatment, and can quickly obtain carbon nanohorns that meet different absorption requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects and features of the present invention will become more apparent from the following description in conjunction with the accompanying drawings, in which:

[0018] Figure 1 is a graph showing the oxygen doping amount versus the absolute value of the reflection loss peak;

[0019] Figure 2 is a curve diagram of nitrogen doping amount-reflection loss peak absolute value;

[0020] Figure 3 1 / 4 wavelength graph of reflection loss of the modified nitrogen-doped carbon nanohorn prepared in Example 1;

[0021] Figure 4 Graph showing the reflection loss of the modified nitrogen-doped carbon nanohorns prepared in Example 2;

[0022] Figure 5 Graph showing the reflection loss of the modified nitrogen-doped carbon nanohorns prepared in Example 3;

[0023] Figure 6 This is a Raman spectrum of the modified nitrogen-doped carbon nanohorns prepared in Example 3;

[0024] Figure 7 This is an infrared spectrum of the modified nitrogen-doped carbon nanohorns prepared in Example 3;

[0025] Figure 8 is an isothermal adsorption-desorption curve of the modified nitrogen-doped carbon nanohorns prepared in Example 3;

[0026] Figure 9 Graph showing the reflection loss of the modified nitrogen-doped carbon nanohorns prepared in Example 4;

[0027] Figure 10 is an X-ray photoelectron spectrum of the modified nitrogen-doped carbon nanohorns prepared in Example 4;

[0028] Figure 11 Graph showing the reflection loss of the modified nitrogen-doped carbon nanohorns prepared in Example 5;

[0029] Figure 12 This is a reflection loss diagram of the modified nitrogen-doped carbon nanohorns prepared in Comparative Example 1. DETAILED DESCRIPTION

[0030] Hereinafter, a method for improving the electromagnetic wave absorption performance of carbon nanohorns according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0031] In one aspect, the present invention provides a method for improving the electromagnetic wave absorption performance of carbon nanohorns. In an exemplary embodiment, the method for improving the electromagnetic wave absorption performance of carbon nanohorns may include the following steps:

[0032] S01, placing nitrogen-doped carbon nanohorns in a dielectric barrier discharge (DBD) generator. For example, the nitrogen-doped carbon nanohorns can be placed in a quartz container, which is then placed in a dielectric barrier discharge (DBD) generator.

[0033] S02, introduce atmospheric gas.

[0034] S03, dielectric barrier discharge treatment. The flow rate of the atmosphere gas is set, the dielectric barrier discharge generator is turned on, and the treatment time is controlled to obtain modified nitrogen-doped carbon nanohorns with improved electromagnetic wave absorption performance.

[0035] In some embodiments, the atmosphere gas can be one or a mixture of air, oxygen, nitrogen, or argon. By introducing the atmosphere gas and undergoing dielectric barrier discharge treatment, some of the carbon atoms in the nitrogen-doped carbon nanohorns will be replaced by atmosphere gas atoms. In addition, the dielectric barrier discharge treatment will increase the surface defects of the nitrogen-doped carbon nanohorns, thereby improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns. During the above treatment process, there are differences in the way different atmosphere gases are introduced to improve the absorption performance of the nitrogen-doped carbon nanohorns. For example, air, oxygen, and nitrogen can simultaneously achieve the replacement of carbon atoms by atmosphere atoms and increase the surface defects of the nitrogen-doped carbon nanohorns; for argon, argon does not improve the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns by replacing carbon atoms, but rather improves the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns by increasing the surface defects of the nitrogen-doped carbon nanohorns. Similarly, for a mixed gas, when any one of air, nitrogen, and oxygen is present in the atmosphere gas, the above two methods can be used to improve the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns at the same time.

[0036] In some embodiments, the amount of gas atoms in the atmosphere gas that replace the carbon atoms of the nitrogen-doped carbon nanohorns has an important influence on the improvement of the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns. For example, in some embodiments, if the atmosphere gas is oxygen, the oxygen atoms partially replace the carbon atoms, and the oxygen doping amount is set to 2% to 14%. At this time, the reflection loss peak can be shifted to a low frequency of 0.5 GHz to 1.5 GHz. For example, the oxygen doping amount can be 3% to 13%, 4% to 10%, 6% to 9%, 7% to 8%, or a combination of the above ranges. Figure 1 As shown, Figure 1 The relationship between the angular reflection loss of nitrogen-doped carbon nanotubes after DBD treatment and the amount of oxygen doping is shown. Figure 1 It can be seen that when the oxygen doping level is between 2% and 14%, the nitrogen-doped carbon nanohorns experience significant reflection loss. However, after the oxygen doping level reaches 14%, the reflection loss decreases dramatically. Therefore, the oxygen doping level is set between 2% and 14%. Preferably, the oxygen doping level can be 4%, at which point the reflection loss of the nitrogen-doped carbon nanohorns is maximized, and the nitrogen-doped carbon nanohorns after DBD treatment exhibit the best electromagnetic wave absorption performance.

[0037] In certain embodiments, if the atmosphere gas is nitrogen, nitrogen atoms partially replace carbon atoms, and the total nitrogen doping amount is set to 1% to 5%. Here, the total nitrogen refers to the sum of the nitrogen doping amount in the raw material and the nitrogen that replaces the carbon atoms. In this case, the reflection loss peak can be shifted to a lower frequency of 0.5 GHz to 1.0 GHz. For example, the nitrogen doping amount can be 2% to 4%, 2.5% to 3.6%, 3% to 3.2%, or a combination of the above ranges. Figure 2 As shown, Figure 2 The relationship between the angular reflection loss of nitrogen-doped carbon nanotubes after treatment and the nitrogen doping amount is shown. Figure 2It can be seen that as the nitrogen doping content increases, the reflection loss of the nitrogen-doped carbon nanohorns increases first and then decreases. Within the nitrogen doping range of 1% to 5%, the nitrogen-doped carbon nanohorns exhibit significant reflection loss. Therefore, the nitrogen doping level is set to 1% to 5%. Preferably, the nitrogen doping level is 1% to 3%, and more preferably, 2.5%, as this level achieves the best electromagnetic wave absorption performance for the nitrogen-doped carbon nanohorns after DBD treatment.

[0038] In certain embodiments, when the atmosphere is argon, DBD treatment can increase surface defects in nitrogen-doped carbon nanohorns, thereby improving their electromagnetic wave absorption performance. DBD treatment can increase both Frenkel and Schottky defects in the nitrogen-doped carbon nanohorns by 17% to 40%, and shift the peak reflection loss to lower frequencies by 0.2 GHz to 0.6 GHz.

[0039] In certain embodiments, if the atmosphere is air, since air contains gases such as oxygen, nitrogen, and argon, the gas atoms can replace carbon atoms in the air atmosphere, thereby enhancing the surface defects of the carbon nanohorns. After DBD treatment, the reflection loss peak of the nitrogen-doped carbon nanohorns can be reduced by 10dB to 20dB.

[0040] In some embodiments, the nitrogen content of the nitrogen-doped carbon nanohorns used in the raw material is no greater than 5%. For example, the nitrogen content of the nitrogen-doped carbon nanohorns used in the raw material can range from 1% to 3.5%, 2% to 3%, 2.5% to 4%, or a combination thereof. Compared to pure carbon nanohorns, the nitrogen-doped nanohorns used in the present invention are raw materials that have a certain number of carbon-nitrogen bonds, resulting in stronger dipole polarization and superior microwave absorption performance.

[0041] In some embodiments, the flow rate of the introduced gas is 20 ml / min to 50 ml / min, and the ventilation time before treatment can be 2 min to 5 min. For example, in certain embodiments, the flow rate of the introduced atmospheric gas can be 25 ml / min to 45 ml / min, and the ventilation time before treatment can be 3 min to 4 min, or the flow rate can be 30 ml / min to 40 ml / min, and the ventilation time before treatment can be 2.5 min to 3.5 min, or a combination of the above ranges.

[0042] In some embodiments, the power of the dielectric barrier discharge generator may be 75W to 125W, and the treatment time may be 5 minutes to 30 minutes. For example, in certain embodiments, the power of the dielectric barrier discharge generator may be 85W to 112W, and the treatment time may be 8 minutes to 25 minutes; or the power may be 92W to 102W, and the treatment time may be 15 minutes to 21 minutes; or the power may be 98W to 100W, and the treatment time may be 17 minutes to 20 minutes, or a combination of the above ranges.

[0043] As described above, the present invention can accurately control the amount of carbon atom replacement by different atmosphere atoms by controlling the power of the DBD generator, the DBD treatment time, the gas flow rate, and the ventilation time before treatment to achieve rapid improvement in the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns. Under the premise of controlling the gas flow rate of the introduced atmosphere gas to 20ml / min to 50ml / min and the ventilation time before treatment to 2min to 5min, preferably, when oxygen is used as the atmosphere gas, the treatment time is 5min to 10min, the power is 75W to 100W, and the oxygen doping amount is 2% to 5%; when nitrogen is used as the atmosphere gas, the treatment time is 10min to 15min, the power is 75W to 100W, and the nitrogen doping amount is 2% to 4%; when argon is used as the atmosphere gas, the treatment time is 5min to 10min, the power is 100W to 125W, and the defect content is 17% to 20%; when air is used as the atmosphere gas, the treatment time is 10min to 15min, the power is 75W to 100W, and the nitrogen doping amount is 2% to 4%. By combining the above-mentioned different powers and different processing times, nitrogen-doped carbon nanohorns with optimal doping and defect levels can be obtained.

[0044] Another aspect of the present invention provides a modified nitrogen-doped carbon nanohorn, which can be obtained by modifying the nitrogen-doped carbon nanohorn using the above-mentioned method for improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorn.

[0045] In order to better understand the present invention, the content of the present invention is further explained below with reference to specific examples, but the content of the present invention is not limited to the following examples.

[0046] Example 1

[0047] (1) Filling nitrogen-doped carbon nanohorns: 50 mg of nitrogen-doped carbon nanohorns were spread flat in a quartz container;

[0048] (2) DBD treatment: Keep the air flowing around the quartz container prepared in step (1), set the DBD power to 75W, and perform DBD treatment for 5 minutes to obtain nitrogen-doped carbon nanohorns modified by air DBD. The obtained product is tested for its absorption performance using the coaxial method, and the reflection loss curve is as follows: Figure 3As shown in the figure, the reflection loss peak is -43.02dB at a thickness of 1.8mm, and the effective absorption bandwidth is 4.4GHz in the range of 2GHz-18GHz. Figure 1 It can be seen from the one-to-one correspondence that the actual thickness corresponds well to the theoretically calculated thickness.

[0049] Example 2

[0050] (1) Filling nitrogen-doped carbon nanohorns: 50 mg of nitrogen-doped carbon nanohorns were spread flat in a quartz container;

[0051] (2) Introducing atmospheric gas and reacting: Nitrogen gas was introduced into the quartz container prepared in step (1) at a flow rate of 50 ml / min for 2 min. The gas flow rate was maintained, and the DBD power was set to 100 W. DBD treatment was performed for 20 min to obtain nitrogen-doped carbon nanohorns modified by nitrogen DBD. The nitrogen doping level was 3.3%. The obtained product was tested for its absorption performance using the coaxial method. The reflection loss curve is shown in FIG. Figure 4 As shown, at a thickness of 1.8mm, the peak reflection loss is -36.71dB, and the effective absorption bandwidth is 4.37GHz in the 2GHz-18GHz range. In particular, the nitrogen DBD-modified nitrogen-doped carbon nanohorns increases the nitrogen content of the nanohorns, enhancing the dielectric loss capacity caused by their dipole polarization, thereby shifting the reflection loss peak toward higher frequencies, meeting high-frequency absorption requirements.

[0052] Example 3

[0053] (1) Filling nitrogen-doped carbon nanohorns: 50 mg of nitrogen-doped carbon nanohorns were spread flat in a quartz container;

[0054] (2) Introducing atmospheric gas and reacting: Argon gas was introduced into the quartz container prepared in step (1) at a flow rate of 50 ml / min for 2 min. The gas flow rate was maintained, and the DBD power was set to 100 W. The DBD treatment was performed for 10 min to obtain nitrogen-doped carbon nanohorns modified by argon DBD. The obtained product was tested for its absorption performance using the coaxial method. The reflection loss curve is shown in FIG. Figure 5 As shown in the figure, the reflection loss peak is -18.55dB when the thickness is 1.4mm, and the effective absorption bandwidth is 4.3GHz in the range of 2GHz-18GHz. In particular, the reflection loss peak of the argon DBD modified nitrogen-doped carbon nanohorn moves to low frequency. Figure 6 It can be seen that the I D / I G is 0.97, indicating that its graphitization degree is very low, that is, the defect content increases; Figure 7 It can be seen that the main bonds connecting the samples are still carbon-carbon bonds and carbon-nitrogen bonds, indicating that no new elements have been introduced. Figure 8 Showing BET is 235.72m2 / g, which means that the sample has excellent defect content. The increased defects enhance the defect-induced polarization of the sample, thereby improving the absorption performance.

[0055] Example 4

[0056] (1) Filling nitrogen-doped carbon nanohorns: 30 mg of nitrogen-doped carbon nanohorns were spread flat in a quartz container;

[0057] (2) Introduction of atmospheric gas and reaction: High-purity oxygen was introduced into the quartz container prepared in step (1) at a flow rate of 20 ml / min for 2 minutes. The gas flow rate was maintained, and the DBD power was set to 75 W. DBD treatment was performed for 5 minutes to obtain nitrogen-doped carbon nanohorns modified by oxygen DBD. The oxygen doping level was 4%. The obtained product was tested for its absorption performance using the coaxial method. The reflection loss curve is shown in FIG. Figure 9 As shown in the figure, the reflection loss peak is -42.95dB when the thickness is 2.6mm, and the effective absorption bandwidth is 4.14GHz in the range of 2GHz-18GHz. In particular, the reflection loss peak of the oxygen DBD modified nitrogen-doped carbon nanohorn moves to low frequency, which can meet the low-frequency absorption requirements. Figure 10 As shown in FIG. 3 , oxygen is successfully doped into the nitrogen-doped nanohorns, and the oxygen doping amount is 13.39%.

[0058] Example 5

[0059] (1) Filling nitrogen-doped carbon nanohorns: 50 mg of nitrogen-doped carbon nanohorns were spread flat in a custom quartz container;

[0060] (2) Introducing atmospheric gas and reacting: Nitrogen gas was introduced into the quartz container prepared in step (1) at a flow rate of 50 ml / min for 2 min. The gas flow rate was maintained, and the DBD power was set to 75 W. DBD treatment was performed for 5 min to obtain nitrogen-doped carbon nanohorns modified by nitrogen DBD. The nitrogen doping content at this time was 2.5%. The obtained product was tested for its absorption performance using the coaxial method. The reflection loss curve is shown in FIG. Figure 11 As shown, when the thickness is 2.8 mm, the reflection loss peak is -47.72 dB, and the effective absorption bandwidth is 3.72 GHz in the range of 2 GHz to 18 GHz.

[0061] Comparative Example 1

[0062] (1) Filling nitrogen-doped carbon nanohorns: 30 mg of nitrogen-doped carbon nanohorns were spread flat in a quartz container;

[0063] (2) Introduction of atmospheric gas and reaction: High-purity oxygen was introduced into the quartz container prepared in step (1) at a flow rate of 20 ml / min for 2 min. The gas flow rate was maintained, and the DBD power was set to 100 W. The DBD treatment was performed for 10 min to obtain nitrogen-doped carbon nanohorns modified by oxygen DBD. At this time, the oxygen doping level was 15.2%. The obtained product was tested for its absorption performance using the coaxial method. The reflection loss curve is shown in FIG. Figure 12 As shown, the peak reflection loss reaches -17.94 dB at a thickness of 1.4 mm. Due to the oxygen doping concentration exceeding 14%, the absorption performance of the treated nitrogen-doped carbon nanohorns is poor, with an effective absorption bandwidth of 4 GHz in the 2 GHz-18 GHz range. In particular, oxygen DBD-modified nitrogen-doped carbon nanohorns significantly reduce the application thickness.

[0064] Although the present invention has been described above with reference to the exemplary embodiments, it will be apparent to those skilled in the art that various modifications and variations may be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined in the claims.

Claims

1. A method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns, characterized in that: The following steps are involved: The nitrogen-doped carbon nanohorns are placed in a dielectric barrier discharge generator and subjected to dielectric barrier discharge treatment after the atmospheric gas is introduced. The electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorns is improved by replacing some carbon atoms in the nitrogen-doped carbon nanohorns with gas atoms and / or by enhancing the surface defects of the nitrogen-doped carbon nanohorns.

2. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to claim 1, characterized in that: The atmosphere gas is oxygen, and the oxygen doping amount after oxygen atoms replace carbon atoms is 2% to 14%.

3. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to claim 1, characterized in that: The atmosphere gas is nitrogen, and the total nitrogen doping amount after nitrogen atoms replace carbon atoms is 1% to 5%.

4. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to claim 1, characterized in that: When the atmosphere gas is argon, the Frenkel defects and Schottky defects both increase by 17% to 40%.

5. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to any one of claims 1 to 4, characterized in that: The nitrogen content of the raw material nitrogen-doped carbon nanohorns is no more than 5%.

6. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to any one of claims 1 to 4, characterized in that: The gas flow rate of the atmospheric gas is 20 ml / min to 50 ml / min, and the ventilation time before treatment is 2 min to 5 min.

7. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to any one of claims 1 to 4, characterized in that: The power of the dielectric barrier discharge generator is 75W to 125W, and the processing time is 5 minutes to 30 minutes.

8. The method for improving the electromagnetic wave absorption performance of nitrogen-doped carbon nanohorns according to any one of claim 1, characterized in that: The atmosphere gas is one or a mixture of oxygen, argon, nitrogen or air.

9. A modified nitrogen-doped carbon nanohorn, characterized in that: The nitrogen-doped carbon nanohorn is obtained by modifying the nitrogen-doped carbon nanohorn by the method for improving the electromagnetic wave absorption performance of the nitrogen-doped carbon nanohorn according to any one of claims 1 to 8.

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