ZnO / chitin carbon aerogel composite wave-absorbing material and preparation method thereof

Abstract

The invention belongs to the technical field of wave-absorbing materials, and particularly relates to a ZnO / chitin carbon aerogel composite wave-absorbing material and a preparation method thereof. The method specifically comprises the following steps: adding purified chitin and a zinc oxide dispersion liquid into a mixed solution prepared from sodium hydroxide and urea, and uniformly stirring to obtain a ZnO / chitin aqueous solution; adding epichlorohydrin into the ZnO / chitin aqueous solution, centrifuging, standing at room temperature, heating and aging to obtain ZnO / chitin composite gel; cleaning the ZnO / chitin composite gel to be neutral, and freeze-drying to obtain ZnO / chitin aerogel; and calcining the ZnO / chitin aerogel under the protection of nitrogen, and cooling to obtain the ZnO / chitin carbon aerogel composite wave-absorbing material. The preparation method is low in cost, the indissolvability of chitin is overcome, the problem of impedance mismatch of derived carbon aerogel is solved, and the prepared wave-absorbing material has the characteristics of small thickness and wide frequency band.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, specifically relating to a ZnO / chitin carbon aerogel composite microwave absorbing material and its preparation method. Background Technology

[0002] Currently, with the rapid development of electromagnetic wave communication technology, especially the rapid integration of 5G technology, the virtual reality and smart home industries have flourished, greatly improving people's living standards. However, while electronic devices bring convenience to people's daily lives, they also create a complex electromagnetic environment. Electromagnetic radiation not only affects the normal operation of equipment but also threatens people's health. Electromagnetic wave absorbing materials are receiving increasing attention because they can effectively protect the human body from electromagnetic radiation and ensure the normal operation of equipment.

[0003] Chitin, one of the most abundant and renewable biopolymers on Earth, inherently contains nitrogen and oxygen, providing an opportunity to dope these atoms to prepare defective carbon. Simple carbonization offers a convenient and sustainable method for fabricating porous, nitrogen- and oxygen-doped defective carbon structures, making it a promising candidate for nitrogen-doped carbon aerogels. This discovery opens a new avenue for developing high-performance and sustainable microwave absorbing materials. However, pure chitin is difficult to dissolve, and the excessively high dielectric constant and single composition of its derived carbon aerogels are detrimental to impedance matching. Therefore, its preparation process and absorption performance do not meet practical requirements, necessitating modification.

[0004] To address the low solubility of chitin and the impedance mismatch of its derived carbon aerogels, researchers have proposed numerous modification strategies. One approach is to optimize the chitin solvent, thereby effectively enhancing its dissolution rate. Another is to combine the carbon aerogel with dielectric materials to increase the loss mechanism and enhance its electromagnetic wave attenuation capability. However, current research has revealed limited exploration of the potential properties and applicability of chitin-derived carbon aerogels in microwave absorption.

[0005] Therefore, preparing porous ZnO / CA composite carbon aerogel microwave absorbing materials using a simple and controllable method is one of the effective measures for exploring electromagnetic wave absorbing materials. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of existing technologies, such as the low solubility of chitin and the impedance mismatch caused by the excessively high dielectric of its derived carbon aerogel microwave absorbing materials. The present invention provides a method for preparing ZnO / CA composite microwave absorbing materials. The method is easy to control and has low production cost. The ZnO / CA microwave absorbing materials prepared have the characteristics of thin matching thickness, strong absorption and wide effective absorption bandwidth.

[0007] To address the aforementioned technical problems, this invention discloses a method for preparing a ZnO / chitosan carbon aerogel composite microwave absorbing material, comprising the following steps:

[0008] S1. Add the purified chitin and zinc oxide dispersion to the mixed solution of sodium hydroxide and urea, stir evenly to obtain ZnO / chitin aqueous solution;

[0009] S2. Add epichlorohydrin to the ZnO / chitosan aqueous solution obtained in S1 and centrifuge. Let it stand at room temperature and then age it at a higher temperature to obtain ZnO / chitosan composite gel. Wash the ZnO / chitosan composite gel until it is neutral and freeze-dry it to obtain ZnO / chitosan aerogel.

[0010] S3. The ZnO / chitosan aerogel prepared in S2 is calcined under nitrogen protection and cooled to obtain the ZnO / chitosan carbon aerogel composite microwave absorbing material.

[0011] In S1, the mass ratio of the purified chitin to the zinc oxide dispersion is 1:(0-20); the concentration of the zinc oxide dispersion is 50 wt%.

[0012] In some embodiments of the present invention, the mass ratio of the purified chitin to the zinc oxide dispersion is 1:(5-10).

[0013] In S1, the mass ratio of urea to sodium hydroxide in the mixed solution is 1:(2-3); the concentration of sodium hydroxide in the mixed solution is 2.85 M.

[0014] In S1, the mass-volume concentration of the purified chitin in the mixed solution is 3%.

[0015] In S2, the amount of epichlorohydrin used is 4 mL of epichlorohydrin per 100 g ZnO / chitosan aqueous solution.

[0016] In S2, the centrifugation conditions are: centrifuge temperature 0 to -20 ℃, centrifugation for 5 to 10 min.

[0017] In S2, the time for standing at room temperature is 12 to 36 hours.

[0018] In S2, the aging process is carried out under the following conditions: temperature 0–60 °C, aging time 12–36 h.

[0019] In S2, the freeze-drying conditions are -60 to -80 ℃ and the time is 24 to 72 h.

[0020] In S3, the calcination conditions are as follows: heating rate of 1-3 °C / min, calcination temperature of 600-800 °C, and calcination time of 1-2 h.

[0021] Furthermore, the ZnO / chitosan carbon aerogel composite microwave absorbing material prepared by the above preparation method is also within the scope of protection of this invention.

[0022] Specifically, in some embodiments of the present invention, ZnO / chitin carbon aerogel composite microwave absorbing materials were successfully prepared by the above preparation method. XRD and SEM analysis showed that the composite microwave absorbing material has a porous structure and the surface of the pores is loaded with a large number of ZnO particles. Further analysis of the microwave absorption performance of the composite microwave absorbing material showed that the microwave absorption performance of the composite material can be significantly improved by introducing metal oxides to adjust the microstructure, which proved its application prospects in the field of microwave absorption.

[0023] Beneficial effects:

[0024] First, a ZnO / CA aerogel precursor was prepared by freeze-drying using chitin and ZnO as raw materials, an aqueous solution of sodium hydroxide and urea as solvent, and epichlorohydrin as an auxiliary agent. Then, a porous ZnO / CA composite microwave absorbing material was prepared by carbonization. In this invention, ZnO is used as Zn(OH)4. 2- The form of dissolution disrupts the intermolecular hydrogen bonds of the polymer, increasing the dissolution rate of chitin and providing abundant in-situ nucleation sites. Recarbonizing the freeze-dried ZnO / chitin aerogel produces a more stable 0D / 3D absorbing material with abundant heterointerfaces, a thin matching thickness, and a wide bandwidth. This not only overcomes the poor solubility of chitin but also helps solve the impedance mismatch problem of its derived carbon aerogel. When the matching thickness is 2.09 mm, the filling amount is 40 wt%, and the frequency is 15.84 GHz, the minimum reflection loss (RL) is... min With a wavelength of -45.67 dB and an effective bandwidth (EAB) of 7.52 GHz (10.48 - 18.00 GHz), it is a thin and wide-bandwidth absorbing material. Attached Figure Description

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0026] Figure 1 The X-ray diffraction (XRD) patterns of the KA prepared in Example 1 and the ZnO / CA composite absorbing materials prepared in Examples 2-3 of this invention.

[0027] Figure 2The images show scanning electron microscope (SEM) images of the KA prepared in Example 1 and the ZnO / CA composite absorbing materials prepared in Examples 2 and 3 of this invention.

[0028] Figure 3 The reflection loss curves of the chitin-derived carbon aerogel absorbing material prepared in Example 1 of this invention are shown in the form of a thickness of 1.0–5.5 mm.

[0029] Figure 4 The reflection loss curves of the ZnO / CA composite absorbing material prepared in Example 2 of this invention are shown in the figure with a thickness of 1.0 to 5.5 mm.

[0030] Figure 5 The reflection loss curves of the ZnO / CA composite absorbing material prepared in Example 3 of this invention are shown in the figure with a thickness of 1.0 to 5.5 mm. Detailed Implementation

[0031] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0032] This invention provides a method for preparing a ZnO / chitosan carbon aerogel composite microwave absorbing material, comprising the following steps: [here]

[0033] S1. Dissolve the purified chitin and nano zinc oxide dispersion in a mixed aqueous solution of sodium hydroxide and urea, and stir until homogeneous to obtain a ZnO / chitin aqueous solution; wherein the mass ratio of urea to sodium hydroxide in the mixed aqueous solution is 1:(2-3); wherein the concentration of sodium hydroxide is 2.85 M and the concentration of urea is 0.69 M; and the mass ratio of zinc oxide dispersion (50 wt% dispersion) to purified chitin is 1:(0-20).

[0034] S2. Epichlorohydrin was added dropwise and centrifuged, then allowed to stand at room temperature and dried to obtain the ZnO / chitosan composite gel; wherein the amount of epichlorohydrin (4 mL per 100 g ZnO / chitosan aqueous solution) added was 4-12 mL; the centrifuge temperature was 0--20 ℃, the centrifugation time was 5-10 min, the gel was allowed to stand at room temperature for 12-36 h, and the oven temperature was 0-60 ℃ for aging for 12-36 h.

[0035] S3. The ZnO / chitosan composite gel is washed with deionized water until neutral, and then freeze-dried to obtain ZnO / chitosan aerogel; wherein the freeze-drying temperature is -60 to -80 ℃ and the time is 24 to 72 h.

[0036] S4. The ZnO / chitosan aerogel is calcined under nitrogen protection and then cooled in the furnace to obtain the ZnO / CA composite material. The heating rate is 2–3 °C / min, the calcination temperature is 700–800 °C, and the calcination time is 1–2 h.

[0037] Example 1:

[0038] This embodiment provides a method for preparing chitin carbon aerogel (CA) microwave absorbing material, including the following steps:

[0039] First, 6 g of purified chitin was dispersed in 200 ml of sodium hydroxide and urea aqueous solution with a mass ratio of sodium hydroxide to urea of ​​11:4, 2.85 M sodium hydroxide and 0.69 M urea. After ultrasonic stirring for 10 min, the mixture was stirred for another 10 min under ice-water mixing to ensure uniform distribution of the sample. The mixture was then frozen for 24 h to prepare a pure chitin aqueous solution with a chitin content of 3%.

[0040] Then, the chitin aqueous solution was taken out and stirred in an ice-water bath until it became fluid. 8 mL of epichlorohydrin was added dropwise and stirred for 10 min, followed by centrifugation for 5 min. The purified sample after centrifugation was poured into a mold, allowed to stand at room temperature for 24 h, aged at 60℃ for 24 h, removed from the mold, soaked and washed until neutral, and freeze-dried for 48 h to obtain chitin aerogel.

[0041] Finally, the chitin aerogel was heated to 700 °C at a rate of 2 °C / min under a nitrogen atmosphere and calcined for 1 h. After the calcination was completed, it was cooled to obtain the chitin carbon aerogel microwave absorbing material, denoted as KA.

[0042] Example 2:

[0043] This embodiment provides a method for preparing a ZnO / CA composite microwave absorbing material, including the following steps:

[0044] First, take 6 g of purified chitin and 0.6 g of zinc oxide dispersion (50 wt% dispersion), disperse them in 200 ml of sodium hydroxide and urea aqueous solution, the mass ratio of sodium hydroxide to urea in the aqueous solution is 11:4, sodium hydroxide 2.85 M, urea 0.69 M, ultrasonically stir for 10 min, then stir for 10 min under ice water mixing to make the sample uniformly distributed, and freeze for 24 h to prepare a chitin / ZnO aqueous solution with a chitin content of 3% and a ZnO content of 0.15%.

[0045] Then, the chitosan / ZnO aqueous solution was removed and stirred in an ice-water bath until it became fluid. 8 mL of epichlorohydrin was added dropwise while stirring for 10 min, followed by centrifugation for 5 min. The purified sample was poured into a mold, allowed to stand at room temperature for 24 h, aged at 60 ℃ for 24 h, removed from the mold, soaked and washed until neutral, and freeze-dried for 48 h to obtain ZnO / chitosan aerogel.

[0046] Finally, the ZnO / chitosan aerogel was heated to 700 °C at a rate of 2 °C / min under a nitrogen atmosphere and calcined for 1 h. After the calcination was completed, it was cooled to obtain the ZnO / CA composite carbon aerogel microwave absorbing material, denoted as ZA-1.

[0047] Example 3:

[0048] This embodiment provides a method for preparing a ZnO / CA composite microwave absorbing material, including the following steps:

[0049] First, 6 g of purified chitin and 1.2 g of zinc oxide dispersion (50 wt%) were dispersed in 200 ml of sodium hydroxide and urea aqueous solution. The mass ratio of sodium hydroxide to urea in the aqueous solution was 11:4, with 2.85 M sodium hydroxide and 0.69 M urea. After ultrasonic stirring for 10 min, the mixture was stirred for 5 min under ice-water mixing to ensure uniform distribution of the sample. The solution was then frozen for 24 h to prepare a chitin / ZnO aqueous solution with a chitin content of 3% and a ZnO content of 0.3%.

[0050] Then, the chitosan / ZnO aqueous solution was removed and stirred in an ice-water bath until it became fluid. 8 mL of epichlorohydrin was added dropwise while stirring for 15 min, followed by centrifugation for 10 min. The purified sample was poured into a mold, allowed to stand at room temperature for 24 h, aged at 60 ℃ for 24 h, removed from the mold, soaked and washed until neutral, and freeze-dried for 48 h to obtain ZnO / chitosan aerogel.

[0051] Finally, the ZnO / chitosan aerogel was heated to 700 °C at a rate of 2 °C / min under a nitrogen atmosphere and calcined for 1 h. After the calcination was completed, it was cooled to obtain the ZnO / CA composite carbon aerogel microwave absorbing material, denoted as ZA-2.

[0052] Performance testing:

[0053] 1. The phase structure of the KA prepared in Example 1 and the ZnO / CA composite microwave absorbing materials prepared in Examples 2 and 3 were analyzed by XRD.

[0054] Figure 1 The XRD patterns of the KA prepared in Example 1 and the ZnO / CA composite absorbing materials prepared in Examples 2-3 are shown below. Figure 1As shown, ZnO / CA is mainly composed of ZnO and chitin-derived carbon. The main diffraction peaks are located at 31.61, 34.33, 36.09, 47.36 and 56.31, 62.64, 66.03, 67.63, 68.73, 72.36, 76.58, 81.10, 89.18 °, which belong to ZnO, respectively. The (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), (202), (104) and (203) crystal planes of (JCPDS No. 79-0208) showed the formation of graphitized carbon at 25 °, indicating that the ZnO / CA composite material was successfully synthesized.

[0055] 2. The microstructure of the KA prepared in Example 1 and the ZnO / CA composite microwave absorbing materials prepared in Examples 2 and 3 were analyzed by SEM.

[0056] Figure 2 The images shown are SEM images of the carbon aerogel absorbing materials prepared in Examples 1-3. Figure 2 (a, d) are SEM images at different CA magnifications; Figure 2 (b, e) are SEM images of ZA-1 at different magnifications; Figure 2 (c, f) are SEM images of ZA-2 at different magnifications. For example... Figure 2 As shown in (a, d), CA has a unique pore structure, consisting of a large number of macropores, mesopores, and mesopores. Figure 2 (b, e) are SEM images of ZA-1 at different magnifications. The carbonized aerogel has uneven pore diameters and smooth pore surfaces. Figure 2 In the image (c, f), we see SEM images of ZA-2 at different magnifications. The ZnO / CA obtained by loading ZnO particles inherits the porous structure of chitin carbon aerogel, with a large number of ZnO particles loaded on the pore surface. This unique porous structure reduces reflected electromagnetic waves, improves impedance matching, and constructs a three-dimensional conductive network that facilitates multiple reflections and scattering of incident electromagnetic waves, promoting electron migration. Furthermore, loading ZnO particles allows for control of the ZnO content to regulate the dielectric, further enhancing the material's attenuation capability.

[0057] 3. The electromagnetic parameters of the sample are analyzed using a vector network analyzer, and its absorption performance is then calculated.

[0058] Figure 3 The reflection loss curves of the chitin carbon aerogel absorbing material prepared in Example 1 at thicknesses of 1.0–5.5 mm are shown. Figure 4The reflection loss curves of the ZnO / CA composite absorbing material prepared in Example 2 at thicknesses of 1.0–5.5 mm; Figure 5 The reflection loss curves of the ZnO / CA composite absorbing material prepared in Example 3 at thicknesses of 1.0–5.5 mm are shown.

[0059] Depend on Figure 3 As can be seen, when the thickness of KA (the chitin carbon aerogel absorbing material prepared in Example 1) is 1.50 mm, RL min The value is -12.40 dB, and the EAB value is 4.56 GHz (13.44-18.00 GHz).

[0060] Depend on Figure 4 It can be seen that the RL of ZA-1 (the ZnO / CA composite absorbing material prepared in Example 2) min The EAB value is significantly improved compared to KA, and the RL value is significantly improved when the matching thickness is 2.09 mm. min The absorption value is -45.67 dB at 15.84 GHz, and the EAB value is 7.52 GHz (10.48-18.00 GHz). The improved absorption performance is attributed to strong electromagnetic attenuation and good impedance matching characteristics. The porous structure increases the interfacial polarization of the material and improves its impedance matching characteristics. The moderate conductivity provides strong conductive loss, significantly dissipating electromagnetic waves.

[0061] from Figure 5 It is evident that the microwave absorption performance of ZA-2 (the ZnO / CA composite absorbing material prepared in Example 3) decreases significantly with increasing ZnO content. When the matching thickness is 5.0 mm, the RL... min The value is -13.88 dB, while the EAB value at 3.5 mm is 2.32 GHz (8.56–10.88 GHz). Clearly, the sample's RL... min The EAB value initially increases and then decreases with increasing ZnO content. This is because changes in the metal oxide content alter the sample's microstructure, directly affecting the material's dielectric loss and impedance matching. Conversely, when the metal oxide content is zero, the sample's dielectric constant is too high, leading to impedance mismatch. Therefore, the metal oxide content significantly impacts electromagnetic parameters, and a suitable dielectric material contributes to excellent microwave absorption performance. ZnO / CA composite microwave absorbing materials exhibit excellent electromagnetic wave absorption performance, meeting the requirements of "thin, light, wide, and strong" for microwave absorbing materials.

[0062] This invention provides a ZnO / chitin carbon aerogel composite microwave absorbing material and its preparation method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing a ZnO / chitin carbon aerogel composite wave-absorbing material, characterized in that, Comprising the following steps: S1. adding a purified chitin and zinc oxide dispersion liquid into a mixed solution prepared by sodium hydroxide and urea, stirring uniformly to obtain a ZnO / chitin aqueous solution; S2. adding epichlorohydrin to the ZnO / chitin aqueous solution obtained in S1 and centrifuging, standing at room temperature, and aging at elevated temperature to prepare a ZnO / chitin composite gel; washing the ZnO / chitin composite gel to neutral, and freeze-drying to obtain a ZnO / chitin aerogel; S3. calcining the ZnO / chitin aerogel prepared in S2 under nitrogen protection, and cooling to obtain the ZnO / chitin carbon aerogel composite wave-absorbing material.

2. The production method according to claim 1, characterized by, In S1, the mass ratio of the purified chitin and zinc oxide dispersion liquid is 1:(0-20); the concentration of the zinc oxide dispersion liquid is 50 wt%.

3. The production method according to claim 1, characterized by, In S1, the mass ratio of urea to sodium hydroxide in the mixed solution is 1:(2-3); the concentration of sodium hydroxide in the mixed solution is 2.85 M.

4. The method of claim 1, wherein, In S1, the mass-volume concentration of the purified chitin in the mixed solution is 3%.

5. The preparation method according to claim 1, characterized in that, In S2, the amount of epichlorohydrin used is 4 mL per 100 g of ZnO / chitin aqueous solution.

6. The method of claim 1, wherein, In S2, the centrifugation is performed under the following conditions: centrifuge temperature 0-20℃, centrifugation time 5-10 min.

7. The preparation method according to claim 1, characterized in that, In S2, the aging at elevated temperature is performed under the following conditions: temperature 0-60℃, aging time 12-36 h.

8. The method of claim 1, wherein, In S2, the freeze-drying is performed under the following conditions: temperature -60--80℃, time 24-72 h.

9. The method of claim 1, wherein, In S3, the calcination is performed under the following conditions: heating rate 1-3℃ / min, calcination temperature 600-800℃, calcination time 1-2 h.

10. The ZnO / chitin carbon aerogel composite wave-absorbing material prepared by the preparation method of any one of claims 1-9.

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