Low-dimensional mixed carbon network based on iron-based MOF and preparation method of low-dimensional mixed carbon network
By using the pyrolysis process in iron-based MOF derivatives to construct a low-dimensional hybrid carbon network of two-dimensional carbon sheets and carbon nanotubes, the problem of poor absorption performance in the prior art is solved, and efficient electron transmission and multi-dimensional transmission are achieved This loss mechanism improves the absorption performance and reflection loss effect.
Patent Information
- Application Number
- CN202411211310.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-30
- Publication Date
- 2024-12-06
AI Technical Summary
The prior art is difficult to construct an efficient low-dimensional hybrid carbon network through simple methods, especially when the pyrolytic MOF derivatives bind to CNTs, it is restricted by factors such as pyrolytic temperature, MOF morphology and structure, and central metal ion type, resulting in absorption. The wave performance is poor.
By combining ferrous salt, zinc salt, 2-methylimidazole and polyvinylpyrolynone to form a hexagonal sheet-like iron-based MOF, high enthalpyricyclone formation ligands and high catalytically active metal carbides during pyrolysis, the high enthalpy formation ligands and high catalytically active metal carbides during pyrolysis , implement a one-step pyrolysis method to build a low-dimensional hybrid carbon network between two-dimensional carbon sheets and carbon nanotubes, adjust the pyrolysis temperature and metal salt ratio to control the length and load of CNTs, generate magnetic Fe particles, and promote magnetoelectric synergistic effects.
At lower matching thickness, efficient electron transmission, multiple loss mechanisms and impedance matching are achieved, the absorption performance is improved, the high reflection loss and wide effective bandwidth are obtained, and it is suitable for microwave absorption field.
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Figure CN119076968A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of wave absorbing materials, and more specifically, relates to a low-dimensional mixed carbon network based on an iron-based MOF and a preparation method thereof. Background Art
[0002] People are vigorously developing efficient microwave absorbing (MA) materials with low density, thin thickness, wide absorption bandwidth and strong reflection loss. Studies have shown that traditional absorbing materials with a single loss mechanism (magnetic loss, dielectric loss, etc.) are difficult to achieve the goal of efficient absorption due to impedance mismatch problems. Therefore, one of the current focuses is to develop new magnetic / dielectric composite materials in which multiple loss mechanisms coexist, and the magnetic permeability and dielectric constant can be adjusted to improve the impedance matching characteristics.
[0003] In recent years, metal-organic frameworks (MOFs) are widely considered to be ideal templates for obtaining metal nanoparticle-decorated porous carbons for the preparation of magnetic / dielectric coupled composites. MOFs are a new class of porous crystalline materials consisting of central metal ions as nodes and organic ligands as bridging components. MOFs have the advantages of large surface area, adjustable porosity, and controllable structure. Therefore, they are widely used in electromagnetic wave absorption, gas storage, catalysis, and medicine. Most MOF pyrolysis derivatives retain the original morphology and porous properties of their parent structures, which is beneficial for microwave absorption (MA) applications. Examples of these MOF derivatives include Fe / C rod-like nanocomposites derived from Fe-based MOFs, Co / C sheet-like nanocomposites derived from Co-based MOFs, and Ni / C spherical nanocomposites derived from Ni-based MOFs. However, how to rationally design and control the morphology of MOF derivatives and understand the relationship between morphology and MA performance require further research.
[0004] Previous studies have shown that assembling or hybridizing different low-dimensional carbon materials to prepare 1D-2D hybrid carbon networks is an effective means to improve the performance of MA, which can be attributed to the synergistic effect of different low-dimensional material components. One-dimensional (1D) carbon structures, such as carbon nanotubes (CNTs), nanorods, and nanowires, are widely used as microwave absorbing (MA) materials due to their excellent properties such as high conductivity and large aspect ratio. Two-dimensional (2D) carbon structures, such as carbon nanosheets and graphene, have the characteristics of low density, large specific surface area, and strong dielectric loss capacity. In addition, carbon nanosheets and graphene can be used as ideal carriers for various nanomaterials. Therefore, the construction of hybrid carbon networks using simple methods has attracted widespread attention. At present, the catalytic mechanism of metal catalysts such as Co and Ni converting carbon sources into CNTs at high temperatures has been gradually reported. However, the low-dimensional hybrid carbon network obtained by pyrolyzing MOF derivatives combined with CNTs is often restricted by factors such as pyrolysis temperature, the morphology and structure of MOF itself, the type of central metal ions, and whether the carbon source is sufficient during pyrolysis. In order to realize nanocomposites with a core of MOFs derivatives and an outer layer of CNTs network, the two-dimensional leaf-like structure ZIF-L can be etched with acetic acid to obtain a thinner sheet structure, which is conducive to the catalytic growth of CNTs, but at the expense of the morphological structure of ZIF-L. Recently, some researchers have introduced additives such as sulfur or melamine to increase the carbon source during pyrolysis, which also promotes the growth of CNTs. However, experimental parameters such as precursor design, additive selection, temperature and atmosphere control make the experimental process too complicated. Therefore, it remains a challenge to realize low-dimensional hybrid carbon networks through simple schemes. Summary of the invention
[0005] In view of the above defects or improvement needs of the prior art, the present invention provides a low-dimensional mixed carbon network based on iron-based MOF and a preparation method thereof, the purpose of which is to construct a low-dimensional mixed carbon network composed of two-dimensional carbon sheets and carbon nanotubes to improve the wave absorbing performance of the material.
[0006] To achieve the above object, according to one aspect of the present invention, a method for preparing a low-dimensional mixed carbon network based on an iron-based MOF is proposed, comprising the following steps:
[0007] S1, dissolving ferrous salt, zinc salt, 2-methylimidazole and polyvinylpyrrolidone in water to form a mixed solution for compounding, and then centrifugally drying to obtain Fe-ZIF-L with a two-dimensional hexagonal sheet structure;
[0008] S2. Pyrolyzing the precursor iron-based MOF at a temperature of 600-750°C to convert it into a low-dimensional mixed carbon network in which two-dimensional carbon sheets and carbon nanotubes are interconnected.
[0009] As further preferred, the molar ratio of the ferrous salt to the zinc salt is 1:2 to 1:10.
[0010] As further preferred, the molar ratio of ferrous salt to zinc salt is 1:5.
[0011] As further preferred, the concentration of polyvinyl pyrrolidone in the mixed solution is 4 g / L to 7 g / L.
[0012] As further preferred, during compounding, the temperature is 25 to 30° C., and the reaction is carried out for 20 to 24 hours under stirring conditions.
[0013] As a further preference, when the precursor iron-based MOF is pyrolyzed, the pyrolysis time is 2 to 4 hours.
[0014] As a further preference, when the precursor iron-based MOF is pyrolyzed, the heating rate is 2 to 5° C. / min.
[0015] As further preferred, the ferrous salt is ferrous sulfate heptahydrate or ferrous nitrate, and the zinc salt is zinc nitrate hexahydrate or zinc sulfate.
[0016] As a further preference, the precursor iron-based MOF is pyrolyzed at a pyrolysis temperature of 700°C.
[0017] According to another aspect of the present invention, a low-dimensional mixed carbon network is provided, which is prepared by the above-mentioned method for preparing a low-dimensional mixed carbon network based on iron-based MOF.
[0018] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:
[0019] 1. The present invention forms a hexagonal sheet-structured precursor iron-based MOF (Fe-ZIF-L) by compounding ferrous salt, zinc salt, 2-methylimidazole and polyvinylpyrrolidone, and then utilizes a high formation enthalpy ligand carbon source (2-methylimidazole) and a high catalytic activity metal carbide (ferrous salt carbon thermal reduction at high temperature) in the pyrolysis process. Without adding an additional carbon source or setting complicated pyrolysis conditions, the present invention realizes the construction of a low-dimensional mixed carbon network composed of a two-dimensional carbon sheet and a carbon nanotube by controlling the pyrolysis temperature through a one-step pyrolysis method. The construction of these networks promotes efficient electron transmission, high interface polarization, multiple loss mechanisms and impedance matching, thereby improving the wave absorption performance, and achieving higher reflection loss and wider effective bandwidth at a lower matching thickness.
[0020] 2. The present invention effectively controls the length and loading amount of CNTs by adjusting the pyrolysis temperature, thereby obtaining hybrid carbon networks with different structural morphologies. When the pyrolysis temperature is too low, the CNTs loading amount will be too low, and the microwave absorption performance of the mixed carbon network structure will be unsatisfactory; when the pyrolysis temperature is too high, the entire carbon sheet structure will collapse, and the 1D-2D structure cannot be formed, and the microwave absorption performance will decrease. The pyrolysis temperature is designed accordingly to produce a unique 1D-2D mixed carbon network structure. At the same time, magnetic Fe particles are generated during the pyrolysis process, realizing the magnetoelectric synergistic effect, improving the magnetic loss capacity while improving the impedance matching characteristics, and has good development and application prospects in the field of microwave absorption.
[0021] 3. The present invention controls the ratio of ferrous salt and zinc salt, and appropriately increases the ratio of zinc salt, which can effectively promote the formation of lightweight porous carbon sheets due to the volatilization of zinc after pyrolysis of the precursor, and promote the growth of CNTs to a certain extent. By controlling the concentration of PVP, the selective adsorption of ions during the nucleation and growth process can be effectively controlled, and the growth of crystals in the direction perpendicular to the (001) crystal plane can be better inhibited, thereby synthesizing a Fe-ZIF-L precursor with a hexagonal sheet structure. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 (a)-(d) are scanning electron micrographs of the precursor Fe-ZIF-L of the embodiment of the present invention and the mixed carbon network obtained at different temperatures;
[0023] Figure 2 (a)-(g) are transmission electron micrographs and elemental maps of the mixed carbon network obtained at 700°C from the precursor Fe-ZIF-L of the embodiment of the present invention;
[0024] Figure 3 are electromagnetic parameters of the hybrid carbon network obtained at different temperatures in the embodiments of the present invention, wherein (a) is the real part of the dielectric constant, (b) is the imaginary part of the dielectric constant, (c) is the dielectric loss tangent, (d) is the real part of the magnetic permeability, (e) is the sum of the imaginary parts of the magnetic permeability, and (f) is the magnetic loss tangent;
[0025] Figure 4 (a)-(c) are respectively the reflection loss contour diagrams of Example 1, Example 2 and the comparative example of the present invention in the thickness range of 1-5 mm, and (d)-(f) are respectively the reflection loss diagrams of Example 1, Example 2 and the comparative example of the present invention in the thickness range of 1-5 mm. DETAILED DESCRIPTION
[0026] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.
[0027] The present invention provides a method for preparing a low-dimensional mixed carbon network based on an iron-based MOF, comprising the following steps:
[0028] S1, dissolving soluble ferrous salt, soluble zinc salt, 2-methylimidazole and polyvinylpyrrolidone (PVP) in an aqueous solution, compounding, stirring for a certain period of time and centrifugally drying to obtain a powdery precursor iron-based MOF, which is a two-dimensional hexagonal sheet-like zeolite imidazolidine framework (Fe-ZIF-L);
[0029] S2. Through a one-step pyrolysis method, the precursor iron-based MOF is pyrolyzed at 600-750°C to convert the precursor into a low-dimensional mixed carbon network in which two-dimensional carbon sheets and carbon nanotubes are interconnected.
[0030] Preferably, in S1, the compounding temperature is 25 to 30° C., and the reaction time is 20 to 24 h under stirring conditions.
[0031] Preferably, in S1, the concentration of PVP in the mixed solution is 4 g / L to 7 g / L.
[0032] Preferably, in S1, the ferrous salt is ferrous sulfate heptahydrate or ferrous nitrate.
[0033] Preferably, in S1, the zinc salt is zinc nitrate hexahydrate or zinc sulfate.
[0034] Preferably, in S1, the molar ratio of ferrous salt to zinc salt is 1:2 to 1:10, more preferably 1:5.
[0035] Preferably, in S2, the pyrolysis temperature is 680-720°C, more preferably 700°C; and the pyrolysis time is 2-4h.
[0036] Preferably, in S2, the heating rate is 2-5°C / min.
[0037] In order to verify the effectiveness of the method of the present invention, the following specific examples are provided:
[0038] Embodiment 1:
[0039] 1) First, 3.2 g PVP and 13.14 g 2-methylimidazole were dissolved in 320 mL deionized water and stirred for 10 minutes, which was recorded as solution A. Then, 0.93 g FeSO4·7H2O and 4.96 g Zn(NO3)2·6H2O (Fe 2+ :Zn 2+ =1:2) was dissolved in another 320 mL of deionized water and stirred for 10 minutes, which was recorded as solution B. Solutions A and B were mixed and stirred continuously at 25°C for 24 hours. After the reaction, the mixture was centrifuged several times with deionized water and anhydrous ethanol. The centrifuged product was dried in an oven at 75°C to obtain the precursor powder Fe-ZIF-L.
[0040] 2) The prepared Fe-ZIF-L powder was placed in a ceramic ark and then transferred to a tube furnace. In a nitrogen environment, the temperature was raised to 600°C at a rate of 2°C / min, the pyrolysis time was 2h, and then naturally cooled. The obtained mixed carbon network sample was named Fe-NC-600.
[0041] Embodiment 2:
[0042] 1) First, 3.2 g PVP and 13.14 g 2-methylimidazole were dissolved in 320 mL deionized water and stirred for 10 minutes, which was recorded as solution A. Then, 0.93 g FeSO4·7H2O and 4.96 g Zn(NO3)2·6H2O (Fe 2+ :Zn 2+ =1:5) was dissolved in another 320 mL of deionized water and stirred for 10 minutes, which was recorded as solution B. Solutions A and B were mixed and stirred continuously at 27°C for 24 hours. After the reaction, the mixture was centrifuged several times with deionized water and anhydrous ethanol. The centrifuged product was dried in an oven at 75°C to obtain the precursor powder Fe-ZIF-L.
[0043] 2) The prepared Fe-ZIF-L powder was placed in a ceramic ark and then transferred to a tube furnace. In a nitrogen environment, the temperature was raised to 700°C at a rate of 3°C / min, the pyrolysis time was 2h, and then naturally cooled. The obtained mixed carbon network sample was named Fe-NC-700.
[0044] Embodiment 3:
[0045] 1) First, 3.2 g PVP and 13.14 g 2-methylimidazole were dissolved in 320 mL deionized water and stirred for 10 minutes, which was recorded as solution A. Then, 0.93 g FeSO4·7H2O and 4.96 g Zn(NO3)2·6H2O (Fe 2+ :Zn 2+=1:5) was dissolved in another 320 mL of deionized water and stirred for 10 minutes, which was recorded as solution B. Solutions A and B were mixed and stirred continuously at 27°C for 24 hours. After the reaction, the mixture was centrifuged several times with deionized water and anhydrous ethanol. The centrifuged product was dried in an oven at 75°C to obtain the precursor powder Fe-ZIF-L.
[0046] 2) The prepared Fe-ZIF-L powder was placed in a ceramic ark and then transferred to a tube furnace. In a nitrogen environment, the temperature was raised to 750°C at a rate of 3°C / min, the pyrolysis time was 2h, and then naturally cooled. The obtained mixed carbon network sample was named Fe-NC-750.
[0047] Embodiment 4:
[0048] In the precursor synthesis, only the PVP mass was changed to 3.84 g and the molar ratio of iron salt to zinc salt was changed to Fe 2+ :Zn 2+ =1:10, other conditions being the same.
[0049] Comparative Example:
[0050] 1) First, 3.2 g PVP and 13.14 g 2-methylimidazole were dissolved in 320 mL deionized water and stirred for 10 minutes, which was recorded as solution A. Then, 0.93 g FeSO4·7H2O and 4.96 g Zn(NO3)2·6H2O (Fe 2+ :Zn 2+ =1:5) was dissolved in another 320 mL of deionized water and stirred for 10 minutes, which was recorded as solution B. Solutions A and B were mixed and stirred continuously at 25°C for 26 hours. After the reaction, the mixture was centrifuged several times with deionized water and anhydrous ethanol. The centrifuged product was dried in an oven at 75°C to obtain the precursor powder Fe-ZIF-L.
[0051] 2) The prepared Fe-ZIF-L powder was placed in a ceramic ark and then transferred to a tube furnace. In a nitrogen environment, the temperature was raised to 800°C at a rate of 4°C / min, the pyrolysis time was 3h, and then naturally cooled. The obtained mixed carbon network sample was named Fe-NC-800.
[0052] The samples after pyrolysis at different temperatures were tested by scanning electron microscopy, transmission electron microscopy and electromagnetic parameters.
[0053] Figure 1The following are scanning electron microscope images of the precursor Fe-ZIF-L and the mixed carbon network obtained by pyrolysis at different temperatures. It can be seen that the length and loading of CNTs at different pyrolysis temperatures, when the pyrolysis temperature is 700℃, it can be most clearly observed that CNTs and carbon nanosheets form a 1D-2D mixed carbon network. When the pyrolysis temperature is 800℃, the carbon sheet structure collapses and cannot form a 1D-2D structure.
[0054] Figure 2 TEM image and elemental map of Fe-NC-700. The hexagonal sheet structure of Fe-NC-700 can be clearly observed, with many elongated CNTs growing on its surface. At the same time, the black particle shadows at the ends of the CNTs show lattice spacings of about 0.20nm and 0.24nm, corresponding to the (110) crystal plane of metallic Fe and the (210) crystal plane of Fe3C, respectively, which proves the presence of Fe and Fe3C nanoparticles with high catalytic activity. These interwoven mixed carbon networks are beneficial to improving the conductive loss of the sample and thus improving the microwave absorption performance. The elemental map results of Fe-NC-700 show that C, N, O and Zn elements are uniformly dispersed throughout the nanosheet. However, the iron element is obviously unevenly distributed and partially clustered, which is highly consistent with the bright spots in the HADDF image, indicating that iron is mainly distributed in the sample in the form of small iron clusters.
[0055] Figure 3 The electromagnetic parameters of the mixed carbon network obtained by pyrolysis at different temperatures in the frequency range of 2-18 GHz. It can be seen that the ε′ and ε″ of all samples show an overall downward trend, which indicates the existence of the classic frequency dispersion phenomenon. With the increase of pyrolysis temperature, the ε′ and ε″ of all samples also increase, which indicates that higher pyrolysis temperature can lead to higher dielectric loss capacity. The complex magnetic permeability μ′ and μ″ both increase with the increase of pyrolysis temperature. The main reason is that when the pyrolysis temperature increases, more Fe 2+ Reduction generates Fe nanoparticles. And, tanδ ε The value is significantly greater than tanδ μ values, which indicates that dielectric loss is the main electromagnetic wave absorption mechanism.
[0056] Figure 4The reflection loss contour map and reflection loss map of the mixed carbon network obtained by pyrolysis at different temperatures in the thickness range of 1-5mm. It can be seen that Fe-NC-700 has better microwave absorption performance than Fe-NC-600, while the microwave absorption performance of Fe-NC-800 decreases due to the collapse of the carbon sheet structure. Among them, when the matching thickness is 1.6mm, the RL of Fe-NC-700 at 16.05GHz is the lowest, which is -37.67dB; when the matching thickness is 1.67mm, the EAB is the largest, which is 5.0GHz. By adjusting the thickness of the sample, the EAB of Fe-NC-700 can cover the frequency region of 14.25GHz (3.75-18GHz), and is effective in the C band (4-8GHz), X band (8-12GHz) and Ku band (12-18GHz). It is particularly worth mentioning that in the frequency region covering about 10.0 GHz (8-18 GHz), the absorption performance of Fe-NC-700 reaches more than 99% (-20 dB).
[0057] It can be seen from the above results that the present invention, by utilizing high formation enthalpy ligand carbon sources and high catalytic activity metal carbides during the pyrolysis process, realizes the construction of low-dimensional mixed carbon networks composed of two-dimensional carbon sheets and carbon nanotubes through only a one-step pyrolysis method. The construction of these networks promotes efficient electron transmission, high interface polarization, multiple loss mechanisms and impedance matching, thereby improving the absorbing performance and achieving higher reflection loss and wider effective bandwidth at a lower matching thickness.
[0058] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.
Claims
1. A method for preparing a low-dimensional mixed carbon network based on iron-based MOF, It is characterized in that The steps include: S1, dissolving ferrous salt, zinc salt, 2-methylimidazole and polyvinylpyrrolidone in water to form a mixed solution for compounding, and then centrifugally drying to obtain Fe-ZIF-L with a two-dimensional hexagonal sheet structure; S2. Pyrolyzing the precursor iron-based MOF at a temperature of 600-750°C to convert it into a low-dimensional mixed carbon network in which two-dimensional carbon sheets and carbon nanotubes are interconnected.
2. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that The molar ratio of the ferrous salt to the zinc salt is 1:2 to 1:
10.
3. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 2, It is characterized in that The molar ratio of ferrous salt to zinc salt is 1:
5.
4. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that The concentration of polyvinyl pyrrolidone in the mixed solution is 4 g / L to 7 g / L.
5. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that During compounding, the temperature is 25-30°C and the reaction is carried out under stirring for 20-24 hours.
6. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that When the precursor iron-based MOF is pyrolyzed, the pyrolysis time is 2 to 4 hours.
7. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that When the precursor iron-based MOF is pyrolyzed, the heating rate is 2 to 5°C / min.
8. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to claim 1, It is characterized in that The ferrous salt is ferrous sulfate heptahydrate or ferrous nitrate, and the zinc salt is zinc nitrate hexahydrate or zinc sulfate.
9. The method for preparing a low-dimensional mixed carbon network based on an iron-based MOF according to any one of claims 1 to 8, It is characterized in that The precursor iron-based MOF was pyrolyzed at a temperature of 700°C.
10. A low-dimensional mixed carbon network, It is characterized in that The low-dimensional mixed carbon network is prepared by the method for preparing the iron-based MOF according to any one of claims 1 to 9.