O-PDA-derived Co / N / C composite wave-absorbing agent and preparation method thereof

Abstract

The invention discloses a Co / N / C composite wave absorbing agent derived from o-PDA and a preparation method of the Co / N / C composite wave absorbing agent. According to the method, o-phenylenediamine and Co < 2 + > are subjected to a direct coordination reaction to form a precursor, and the precursor is carbonized after ultrasonic-assisted treatment to obtain the Co / N / C composite wave-absorbing agent rich in defects. The composite wave absorbing agent has excellent microwave absorbing performance, the minimum reflection loss of the composite wave absorbing agent at 10.24 GHz reaches-73.66 dB, the effective absorption bandwidth is 7.04 GHz under the thickness of 2.5 mm, the preparation process is simple, the cost is low, and the composite wave absorbing agent has wide application prospects in the fields of high-frequency communication equipment, stealth technology and the like.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic wave absorbing materials technology, specifically relating to a cobalt / nitrogen / carbon (Co / N / C) composite microwave absorber derived from o-phenylenediamine (o-PDA) and its preparation method. Background Technology

[0002] In recent years, technologies such as artificial intelligence, the Internet of Things, and quantum computing have seen explosive breakthroughs. With the approach of the 6G era, the world is accelerating its deep integration towards intelligence and interconnectivity. However, while these innovations are reshaping industrial landscapes and lifestyles, they are also generating a series of new challenges. The massive deployment of smart devices and the demand for high-frequency communication have led to an increasingly complex electromagnetic spectrum environment. To address this issue, many methods have been tried in recent years, with the most common being the use of electromagnetic wave absorbing materials to neutralize harmful electromagnetic waves through their interaction with magnetic fields.

[0003] In recent years, cobalt nitrate (Co(NO3)2·6H2O) has attracted considerable attention in the field of electrochemistry due to its low cost, high specific capacity, and good cycling performance, and is commonly used as an electrode material. However, cobalt nitrate, as a common cobalt source precursor, has never been reported in the field of electromagnetic wave absorption. This is because pure cobalt nitrate is an ionic compound with extremely poor conductivity, making it difficult to dissipate electromagnetic wave energy through conductivity loss. Furthermore, it lacks an effective magnetic loss mechanism and has weak polarization ability, failing to meet the basic requirements of "incident-loss-impedance matching" for electromagnetic wave absorption. Combining cobalt-based compounds derived from cobalt nitrate with conductive carbon materials to construct composite materials is an important approach for designing novel, highly efficient electromagnetic wave absorbing materials. Existing research shows that the heterojunction interface formed by cobalt-based compounds and carbon materials can significantly enhance charge separation efficiency and dipole polarization effect, thereby improving the electromagnetic wave absorption performance of the material (Jie Li, Peng Miao, Kai-Jie Chen, et al, Highly effective electromagnetic wave absorbing Prismatic Co / C nanocomposites derived from cubic metal-organic framework, Composites Part B: Engineering, Volume 182, 2020, 107613, ISSN 1359-8368, https: / / doi.org / 10.1016 / j.compositesb.2019.107613.).

[0004] In the field of electromagnetic absorption, MOFs synthesized by traditional methods generally face challenges such as excessively large crystals and difficult-to-control morphology, which prevent the formation of nanoscale conductive networks, resulting in weakened dielectric loss and interfacial polarization. High-pressure reactor temperature fields and concentration gradients cause batch-to-batch drift in particle size and defect density, making it difficult to repeat absorption curves. High consumption and difficult recovery of polar solvents such as DMF and NMP, coupled with the energy-intensive processes of 120-220℃ and 12-48h, keep gram-level costs high. Furthermore, batch reactors have space-time yields below 10 g / L. -1 h -1 During scaling up, heat and mass transfer deteriorates, crystals are prone to agglomeration, and there is a lack of continuous green routes; powder post-processing requires ball milling, coating or hot pressing, the process is cumbersome and the risk of interface contamination is high; residual solvents and defects cause the skeleton to absorb moisture, ε′ / ε″ drifts under high temperature and humidity or irradiation, and the performance degrades rapidly; the crystal surface has few functional groups, making it difficult to anchor Fe, Co, Ni and other magnetic nanoparticles in situ, and subsequent impregnation-reduction is easy to destroy the skeleton, making it difficult to achieve magnetic-dielectric synergistic loss, which ultimately hinders the industrialization of "thin, light, wide and strong" microwave absorbing materials (Stock, N.; Biswas, S. Synthesis of Metal-Organic Frameworks (MOFs): Routes to Various MOF Topologies, Morphologies, and Composites. Chem. Rev. 2012, 112(2), 933-969. https: / / doi.org / 10.1021 / cr200304e). Summary of the Invention

[0005] The purpose of this invention is to provide an o-PDA-derived Co / N / C composite microwave absorber and its preparation method. This invention employs a direct coordination-pyrolysis strategy without a metal-organic framework precursor, first using Co… 2+ It forms a small molecule coordination compound with o-phenylenediamine, and then obtains a non-porous, graphitized Co / N / C composite microwave absorber through high-temperature pyrolysis. This avoids the requirements of "framework structure" and "crystal order" in MOF preparation and has the characteristics of simple steps, mild conditions, and controllable defects.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] The preparation method of o-PDA-derived Co / N / C composite microwave absorber includes the following steps:

[0008] Step 1: Cobalt nitrate and o-phenylenediamine are mixed at a molar ratio of 1:4 and dissolved in anhydrous ethanol. The mixture is then sonicated to promote the reaction of Co. 2+ Rapid coordination with o-phenylenediamine to form a uniform Co 2+ -o-PDA coordination complex solution;

[0009] Step 2: The coordination complex solution is rotary evaporated to remove the solvent, and then vacuum dried to obtain the precursor;

[0010] Step 3: The precursor is placed in a tube furnace and carbonized at 600-800°C at a rate of 5-10°C / min under an argon atmosphere to obtain an o-PDA-derived Co / N / C composite microwave absorber.

[0011] Preferably, in step 2, the ultrasonic power is 300-500W.

[0012] Preferably, in step 2, the rotary evaporation conditions are: temperature of 40-50°C and pressure of 0.08-0.1 MPa.

[0013] Preferably, in step 2, the vacuum drying temperature is 60–70°C and the vacuum degree is 10. -2 ~10 -3 Pa, vacuum drying time is 8-10 hours.

[0014] Preferably, in step 3, the carbonization temperature is 600℃ and the carbonization time is 2-3 hours.

[0015] The present invention provides a Co / N / C composite microwave absorber prepared by the above preparation method.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) No MOF precursors are required, simplifying the preparation process and reducing costs;

[0018] (2) Ultrasonic-assisted coordination can achieve atomic-level uniform dispersion of metal ions and ligands, and improve material stability;

[0019] (3) Defect-dominated multi-scale structures (N / O defects, Co / C heterojunctions) synergistically enhance dipole polarization and interface polarization, significantly broadening the absorption bandwidth;

[0020] (4) Lightweight materials (density < 1.5 g / cm³) 3 It can cover 82% of the X / Ku band with a thickness of only 2.5mm, making it suitable for high-frequency communication equipment and stealth technology;

[0021] (5) The present invention utilizes a direct coordination-pyrolysis strategy to achieve atomic-level control of materials. The resulting o-PDA-derived Co / N / C composite microwave absorber has a minimum reflection loss of -73.66dB at 10.24GHz and an effective absorption bandwidth of 7.04GHz (10.96-18GHz) with a thickness of 2.5mm. Attached Figure Description

[0022] Figure 1 The image is a scanning electron microscope image of OPD-Co(600) from Example 1.

[0023] Figure 2 The XPS (C1s, N1s, and Co2p) spectra of OPD-Co(600) from Example 1 are shown.

[0024] Figure 3 The image shows the XRD pattern of OPD-Co(600) from Example 1.

[0025] Figure 4 The image shows the Raman spectrum of OPD-Co(600) from Example 1.

[0026] Figure 5 The microwave absorption performance of OPD-Co(600) in Example 1 is shown.

[0027] Figure 6 The microwave absorption performance of OPD-Co(800) in Example 2 is shown.

[0028] Figure 7 The microwave absorption performance of OPD-Fe(600) is shown in Comparative Example 1.

[0029] Figure 8 The microwave absorption performance of OPD-Fe(800) in Comparative Example 2 is shown.

[0030] Figure 9 The dielectric Cole-Cole diagram of OPD-Co(600) in Example 1 is shown.

[0031] Figure 10 The XRD patterns are those of OPD-Fe(800) (a) in Comparative Example 2 and Bipy-Fe(800) (b) in Comparative Example 3.

[0032] Figure 11 Raman spectra of OPD-Co(800) in Example 2 and OPD / 2-Co(800) in Comparative Example 4.

[0033] Figure 12 The images shown are transmission electron microscope (TEM) and high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images of OPD-Co(600) in Example 1, where a has a magnification of 10000, b has a magnification of 40000, c has a magnification of 80000, d has a magnification of 150000, e has a magnification of 30000, and f is a HAADF-STEM image.

[0034] Figure 13 The infrared spectrum of OPD-Co(600) in Example 1 is shown. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0036] Example 1

[0037] (1) Weigh 2 mmol of cobalt nitrate (Co(NO3)2·6H2O) and 8 mmol of o-PDA, mix them, and dissolve them in 50 mL of anhydrous ethanol. Then, sonicate the solution for 3 minutes at a power of 400 W. The solution turns dark brown and forms Co. 2+ -o-PDA coordination complex solution;

[0038] (2) Co 2+ The -o-PDA coordination complex solution was rotary evaporated at 45 °C and 0.09 MPa to remove the solvent, and then subjected to further evaporation at 65 °C and 5 × 10⁻⁶ MPa. -3 The precursor was obtained by vacuum drying under Pa conditions for 10 hours.

[0039] (3) The precursor was placed in a tube furnace and heated to 600°C at 5°C / min under argon protection. The temperature was maintained for 2 hours and then naturally cooled to obtain the Co / N / C composite microwave absorber, named OPD-Co(600).

[0040] Example 2

[0041] This embodiment is basically the same as embodiment 1, except that (3) 600℃ is replaced with 800℃, and the Co / N / C composite microwave absorber is named OPD-Co(800).

[0042] Comparative Example 1

[0043] This comparative example is basically the same as Example 1, except that (1) cobalt nitrate is replaced with iron nitrate (Fe(NO3)3·9H2O), and the Fe / N / C composite microwave absorber is named OPD-Fe(600).

[0044] Comparative Example 2

[0045] This comparative example is basically the same as Example 2, except that (1) cobalt nitrate is replaced with iron nitrate (Fe(NO3)3·9H2O), and the Fe / N / C composite microwave absorber is named OPD-Fe(800).

[0046] Comparative Example 3

[0047] This comparative example is basically the same as comparative example 2, except that (1) o-PDA is replaced with bipyridine, and the Fe / N / C composite microwave absorber is named Bipy-Fe(800).

[0048] Comparative Example 4

[0049] This comparative example is basically the same as Example 2, except that (1) 2 mmol of cobalt nitrate and 4 mmol of o-PDA were weighed, that is, the molar ratio of cobalt nitrate and o-PDA was 1:2, and the Co / N / C composite microwave absorber was named OPD / 2-Co(800).

[0050] Figure 1 The scanning electron microscope image of OPD-Co(600) in Example 1 shows that it exhibits a porous network structure. This porous structure is beneficial to increasing the specific surface area of ​​the material. Through the mechanism of multiple scattering and interface polarization, it plays a positive role in the absorption and attenuation of electromagnetic waves, which can increase the probability of interaction between the material and electromagnetic waves and help to enhance the absorption performance.

[0051] from Figure 2 As can be seen from the three XPS spectra of C1s, N1s, and Co 2p, the C1s spectrum of OPD-Co(600) shows CC / C=C (~285eV, carbon skeleton), CO (~286eV, oxygen-containing functional groups), and C=O (~287eV, oxidized carbon) peaks. These functional groups introduce dipole polarization, which helps dielectric loss. The N1s spectrum has CN (~398.5eV, pyridine / pyrrole N) and C=N (~400eV, graphite / quaternary N) peaks. N doping optimizes the carbon electronic structure and enhances dielectric loss and interface polarization. The Co 2p spectrum shows the main peaks of Co2p3 / 2 and Co2p1 / 2, as well as satellite peaks, indicating the presence of metallic Co (Co) 0 ) and oxidized Co (Co 2+ / Co 3+ In this material, metallic Co contributes magnetic loss, while oxidized Co assists in dielectric loss, working synergistically to regulate microwave absorption performance. Overall, the material achieves "dual loss" by adjusting dielectric loss through C / N doping and by relying on the synergistic magnetic-dielectric loss of Co's multiple valence states. The elemental states are related to the 600℃ carbonization process, providing chemical structural support for performance optimization.

[0052] Figure 3 The XRD pattern of OPD-Co(600) in Example 1 shows that OPD-Co(600) is a composite material composed of a low-crystallinity carbon matrix and highly dispersed or low-crystallinity cobalt species. This structural feature gives the material suitable impedance matching and multiple loss mechanisms in terms of electromagnetic parameters.

[0053] Figure 4The Raman spectrum of OPD-Co(600) from Example 1 shows that ID / IG = 1.146, indicating numerous carbon structural defects and low graphitization. These defects act as dipole polarization centers, enhancing dielectric loss; the low graphitization provides more interfaces, promoting interfacial polarization. The carbonization process (600℃) did not fully graphitize the carbon, and the retained defect structure provides a basis for microwave absorption. The absorption function is achieved through the synergistic effect of carbon defects and multi-element losses.

[0054] The carbonization temperature and the choice of metal ions also affect the microwave absorbing material. Figures 5-8 It can be seen that: OPD-Co(600) has a reflection loss of -73.66dB and an effective absorption bandwidth of 7.04GHz; OPD-Co(800) has a reflection loss of -62.41dB and an effective absorption bandwidth of 5.64GHz; OPD-Fe(600) has a reflection loss of -65.16dB and an effective absorption bandwidth of 6.72GHz; and OPD-Fe(800) has a reflection loss of -52.32dB and an effective absorption bandwidth of 5.48GHz. In summary, low-temperature treatment (600℃) is significantly better than high-temperature treatment (800℃), and Co-based materials are generally superior to Fe-based materials. This indicates that lowering the treatment temperature and using Co can simultaneously enhance absorption intensity and broaden the effective frequency band. Therefore, a carbonization temperature of 600℃ and cobalt-based materials are the most suitable choices.

[0055] from Figure 9 It can be seen that the Cole-Cole diagram of OPD-Co(600) presents a single relaxation arc (Debye type) that is approximately semicircular, with the center slightly offset below the real axis, indicating that there is a dielectric loss mechanism dominated by dipole polarization in the system, accompanied by a weak background of conductivity loss. The arc radius is large and the span covers ε′≈4-8, corresponding to strong polarization intensity and narrow relaxation time distribution. The excellent electromagnetic wave dissipation capability comes from this efficient dielectric polarization process. The low-temperature treatment at 600℃ retains abundant defects / interfaces, which not only provides sufficient polarization centers, but also avoids relaxation peak broadening or excessive formation of conductivity paths caused by high-temperature agglomeration. Thus, while maintaining good impedance matching, the imaginary peak value is maintained, achieving the dual maximization of absorption intensity and effective bandwidth.

[0056] Figure 10In the image, (a) represents OPD-Fe(800) and (b) represents Bipy-Fe(800). A comparison reveals that Bipy-Fe(800) exhibits sharp Fe3O4 / γ-Fe2O3 crystalline phase peaks, while OPD-Fe(800) only retains a broad bulge. After pyrolysis at 800℃, both follow two paths: "highly crystalline magnetic oxide" and "amorphous Fe-C composite," respectively. This implies that the former retains magnetic-dielectric synergy, while the latter relies on defect polarization for absorption. The ligand rigidity and pyrolysis path allow for switching between crystalline and amorphous phases, thereby controlling the final electromagnetic loss mechanism. XRD results suggest that the amorphous structure of OPD-Fe(800) leads to richer defect polarization and multiple interface relaxations, typically resulting in broader and stronger absorption at thinner thicknesses. While the crystalline magnetite of Bipy-Fe(800) provides magnetic loss, its larger particle size and limited interfaces make it prone to impedance mismatch. Therefore, under the same filling amount and thickness conditions, OPD-Fe(800) is expected to have better microwave absorption performance than Bipy-Fe(800). Therefore, o-PDA is preferred as the organic ligand.

[0057] from Figure 11 As can be seen, both Raman spectra exhibit typical carbon-based characteristics. The D / G ratio of OPD / 2-Co(800) (Comparative Example 4) is 1.04, indicating a moderate defect density and a high degree of graphitization. In contrast, the D / G ratio of OPD-Co(800) (Example 2) is 1.079, showing a significantly increased defect concentration and smaller graphite domain size. The richer the defects, the stronger the interfacial polarization and conductivity loss. Therefore, OPD-Co(800) is expected to outperform OPD / 2-Co(800) in electromagnetic absorption performance.

[0058] Figure 12 OPD-Co(600) was subjected to transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Under low magnification TEM, OPD-Co(600) appeared as a sheet-like substrate. Figure 12 (a, 12b) The carbon matrix contains numerous nanoscale pores and particles. This porous structure increases the specific surface area, promotes interfacial polarization loss, and enhances energy decay efficiency. High-magnification TEM reveals disordered or short-range ordered structures within the carbon matrix. Figure 12 c, 12d, 12e), and the lattice fringes of cobalt-based particles. The nanoscale effect of cobalt particles induces magnetic moment disorder, enhances magnetic loss, and strengthens interfacial polarization. HAADF-STEM dark-field image ( Figure 12 In f), the bright spot corresponds to the cobalt-rich region. The uniformly dispersed cobalt particles form a conductive network that contributes to conductivity loss and also maintains good impedance matching by avoiding agglomeration.

[0059] Figure 13It can be seen that the infrared spectrum of OPD-Co(600) is dominated by the characteristic Co-O peak of Co3O4, supplemented by a broad C=C peak of graphitized carbon and a small amount of weak signals from surface hydroxyl and carbonyl groups, showing an overall characteristic of metal oxide dominance and weakened residual carbon skeleton. At 600℃, the unique functional group structure of cobalt-based materials increases the interfaces formed between cobalt and surrounding groups, and the interfacial polarization loss is synergistically enhanced; the defect structure makes electron scattering and relaxation more frequent, enhancing the conductivity loss. Strong absorption is achieved in a wide frequency range (such as 2-18 GHz), and the absorption effect is even better in the mid-to-low frequency range due to the dominance of dipole and interfacial polarization.

Claims

1. A method for preparing an o-PDA-derived Co / N / C composite microwave absorber, characterized in that, Includes the following steps: Step 1: Cobalt nitrate and o-phenylenediamine are mixed at a molar ratio of 1:4 and dissolved in anhydrous ethanol. The mixture is then sonicated to promote the reaction of Co. 2+ Rapid coordination with o-phenylenediamine to form a uniform Co 2+ -o-PDA coordination complex solution; Step 2: The coordination complex solution is rotary evaporated to remove the solvent, and then vacuum dried to obtain the precursor; Step 3: Place the precursor in a tube furnace and carbonize it at a rate of 5~10℃ / min to 600~800℃ under an argon atmosphere to obtain the o-PDA-derived Co / N / C composite microwave absorber.

2. The preparation method according to claim 1, characterized in that, In step 2, the ultrasonic power is 300~500 W.

3. The preparation method according to claim 1, characterized in that, In step 2, the rotary evaporation conditions are: temperature 40~50℃ and pressure 0.08~0.1 MPa.

4. The preparation method according to claim 1, characterized in that, In step 2, the vacuum drying temperature is 60~70℃, and the vacuum degree is 10. -2 ~10 -3 Pa, vacuum drying time is 8~10 hours.

5. The preparation method according to claim 1, characterized in that, In step 3, the carbonization temperature is 600℃ and the carbonization time is 2~3h.

6. The Co / N / C composite microwave absorber prepared by any one of the preparation methods according to claims 1 to 5.

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