A two-dimensional structure metal-organic framework material and its preparation method and application

Abstract

The invention discloses a fast and simple preparation method and application of a two-dimensional metal-organic framework material (MOF), which relates to the technical field of two-dimensional MOFs preparation. The method includes doping nickel ions with cobalt ions or zinc ions to form a bimetallic ion precursor, using 2-methylimidazole as a ligand, and reacting at room temperature in a mixed solvent system consisting of methanol and water to form a MOF material with a two-dimensional nanosheet structure. The prepared two-dimensional structural material is calcined in an air atmosphere to obtain its derivative, and the derivative material has obvious electromagnetic response characteristics. The method has the characteristics of being economical, environmentally friendly, safe, efficient, and can be prepared in large quantities.

Description

Technical Field

[0001] The invention relates to a two-dimensional structure metal-organic framework material and a preparation method thereof, and belongs to the technical field of electromagnetic response materials.

[0002] Background

[0003] In recent years, metal organic framework (MOF) materials have shown great potential in electromagnetic protection materials and have received widespread attention at home and abroad. Most MOF materials are crystalline materials with three-dimensional structures. Their derivatives have good electromagnetic response characteristics. The dielectric components and magnetic components in MOF derivative materials are effectively combined to achieve wide-band and high-intensity absorption of electromagnetic waves by the materials. Among them, the two-dimensional metal organic framework (2D-MOF) has a thinner thickness and larger lateral size and surface area than the three-dimensional metal organic framework (3D-MOF). These advantages can increase the unit receiving area of ​​2D-MOF material derivatives for electromagnetic signals, which directly affects the absorption and loss of electromagnetic waves by the material.

[0004] At present, based on 2-methylimidazole organic molecules and metal ions (Co 2+ and Zn 2+ ) respectively prepared ZIF-67 and ZIF-8 both exhibit rhombic dodecahedral three-dimensional structures, which have attracted a certain amount of research attention in the field of electromagnetic wave absorption. However, it is still a major difficulty and challenge in the industry to design 2D-MOF materials containing multiple metals based on 2-methylimidazole and a variety of mixed metal ions using a simple preparation method to achieve absorbing materials with adjustable magnetic component types and diverse properties. Summary of the invention

[0005] The purpose of the present invention is to provide a safe, low-energy, simple and rapid preparation method for a bimetallic MOF material with a two-dimensional structure, so that it has commercial application prospects, and the derivatives of this type of material have unique electromagnetic response characteristics.

[0006] The present invention provides a method for preparing a two-dimensional structured metal-organic framework material, comprising the following steps:

[0007] S1 uniformly mixes methanol, water, nickel chloride hexahydrate, and cobalt chloride hexahydrate according to a preset ratio to obtain a mixed solution A;

[0008] S2, while continuously stirring the mixed solution A, adding a preset amount of 2-methylimidazole methanol solution dropwise to the mixed solution A to obtain a mixed solution B;

[0009] In the mixed solution B, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.05-0.2:1, the total concentration of cobalt and nickel is 0.04-0.16 mmol / ml, and the volume ratio of methanol to water is 2-4:1;

[0010] The metal salt is composed of cobalt chloride and nickel chloride in the mixed solution A;

[0011] S3 centrifuges the mixed solution B, washes and dries the centrifuged product, and obtains a two-dimensional structured metal-organic framework material.

[0012] Preferably, the S1 specifically comprises the following steps:

[0013] First, 10 ml of methanol and 10 ml of water were measured and added to a beaker, and then 0.715 g of nickel chloride hexahydrate and 0.429 g of cobalt chloride hexahydrate were added to the beaker, and dissolved and uniformly mixed by ultrasonic-assisted dissolution to obtain a mixed solution A;

[0014] In step S2, the continuous stirring of the mixed solution A specifically comprises:

[0015] At room temperature, using a magnetic stirrer, uniformly stirring at a rate of 300 rpm for 2 hours, within the 2 hours, completing the dropwise addition of the 2-methylimidazole methanol solution, and after the dropwise addition, continuing to uniformly stir at a rate of 300 rpm for 3 hours;

[0016] In step S2, the preparation method of the 2-methylimidazole methanol solution is: weigh 1.97 grams of 2-methylimidazole into a beaker and add 10 milliliters of methanol, and dissolve it with ultrasound to obtain the 2-methylimidazole methanol solution.

[0017] Preferably, in step S3, the cleaning is performed by washing with methanol, and the drying is performed by vacuum drying.

[0018] The present invention also provides a method for preparing a two-dimensional structured metal-organic framework material, comprising the following steps:

[0019] S1: uniformly mixing methanol, water, nickel chloride hexahydrate and zinc nitrate hexahydrate according to a preset ratio to obtain a mixed solution A;

[0020] S2, while continuously stirring the mixed solution A, adding a preset amount of 2-methylimidazole methanol solution dropwise to the mixed solution A to obtain a mixed solution B;

[0021] In the mixed solution B, the molar ratio of zinc nitrate hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of zinc and nickel is 0.16 mmol / ml, and the volume ratio of methanol to water is 2:1;

[0022] The metal salt is composed of cobalt chloride and nickel chloride in the mixed solution A;

[0023] S3 centrifuges the mixed solution B, washes and dries the centrifuged product, and obtains a two-dimensional structured metal-organic framework material.

[0024] The present invention also provides a two-dimensional metal-organic framework material prepared by the above preparation method, wherein the two-dimensional metal-organic framework material is a multi-fold sheet-like two-dimensional structure of stacked thin layers, with a sheet thickness of less than 1nm and a sheet diameter distribution in the range of 1 to 5μm.

[0025] The present invention also provides an application of a two-dimensional structured metal-organic framework material in electromagnetic wave absorption. The two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tubular furnace and kept at 400 degrees Celsius for 1 hour to obtain a calcined product; the calcined product is mixed with paraffin and then subjected to electromagnetic wave absorption.

[0026] Preferably, the calcined product is mixed with paraffin in a mass ratio of 6:4;

[0027] The present invention also provides an application of a two-dimensional structured metal-organic framework material in electromagnetic wave absorption:

[0028] The two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tube furnace, and then naturally cooled at 400 degrees Celsius for 1 hour to obtain a calcined product;

[0029] The calcined product was mixed with paraffin wax in a mass ratio of 6:4 to form an annular sheet with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm and a thickness of 2.2 mm;

[0030] Electromagnetic parameter testing uses a network analyzer to conduct electromagnetic wave absorption testing in the 2-18GHz frequency band;

[0031] Output electromagnetic parameters using Agilent PNA software according to Nicolson and Ross and Weir algorithm:

[0032] When the thickness is 2 mm, the maximum absorption intensity is -20.06 dB and the maximum absorption width is 4.76 GHz.

[0033] The present invention also provides an application of a two-dimensional structured metal-organic framework material in electromagnetic wave absorption, wherein the two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tubular furnace, and then naturally cooled at 400 degrees Celsius after being kept at that temperature for 1 hour to obtain a calcined product;

[0034] The calcined product was mixed with paraffin wax in a mass ratio of 6:4 to form an annular sheet with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm and a thickness of 2.2 mm;

[0035] Electromagnetic parameter testing uses a network analyzer to conduct electromagnetic wave absorption testing in the 2-18GHz frequency band;

[0036] Output electromagnetic parameters using Agilent PNA software according to Nicolson and Ross and Weir algorithm:

[0037] The absorbers with different thicknesses show resonance absorption peaks in the frequency region of 14.00-14.08GHz. Among them, when the thickness is 3 mm, it shows the maximum absorption intensity, and the corresponding peak value is -18.25dB.

[0038] Compared with the existing related technologies, the present invention has the following significant advantages:

[0039] 1. For the two-dimensional nanosheet structure Co, Ni-ZIF, (1) the reaction environment of the present invention is mild, safe, pollution-free, and low in energy consumption. Under room temperature, the two-dimensional nanosheet is obtained by stirring in a methanol and water mixed solution system; (2) the optimal molar ratio of the two metal ions in the preparation of the two-dimensional nanosheet is selected to be n Co 2+ :nNi 2+ =0.6:1; (3) The optimal volume ratio of the mixed reaction solvent is preferably V 甲醇 :V 水 =2-4:1; (4) Expand the preparation method of Co, Ni-ZIF two-dimensional nanosheets to the preparation and application of Zn, Ni-ZIF two-dimensional nanosheets.

[0040] 2. For bimetallic MOF-derived two-dimensional electromagnetic absorption materials, (1) the combination of two metal substances can obtain adjustable electromagnetic response behavior, which is beneficial to adjust the electromagnetic wave absorption performance of the material; (2) the air environment is used as the calcination atmosphere to avoid the use of relatively expensive inert gases (argon or nitrogen, etc.), which has the characteristics of economy, environmental protection, and safety.

[0041] 3. The preparation method of the present invention has a simple process, does not require complicated synthesis equipment, and can achieve large-scale mass production.

[0042] 4. The material prepared by the present invention has good electromagnetic response absorption behavior, and the sample is in powder form. It is generally mixed with polymer resin, adhesive, etc. to make a composite material for use. It can be processed into any shape as needed and can also be used as a coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a scanning electron microscope image of the Co, Ni-ZIF-1 sample prepared in Example 1 of the present invention.

[0044] Figure 2 This is a transmission electron microscope image of the Co, Ni-ZIF-1 sample prepared in Example 1 of the present invention.

[0045] Figure 3 This is a scanning electron microscope image of the Zn, Ni-ZIF sample prepared in Example 6 of the present invention.

[0046] Figure 4 This is a transmission electron microscope image of the Zn, Ni-ZIF sample prepared in Example 6 of the present invention.

[0047] Figure 5 This is a scanning electron microscope image of the Co / Ni-1 sample prepared in Comparative Example 1 of the present invention.

[0048] Figure 6 This is a scanning electron microscope image of the Co / Ni-2 sample prepared in Comparative Example 2 of the present invention.

[0049] Figure 7 This is a scanning electron microscope image of the Co / Ni-3 sample prepared in Comparative Example 3 of the present invention.

[0050] Figure 8 This is a scanning electron microscope image of the Co / Ni-4 sample prepared in Comparative Example 4 of the present invention.

[0051] Fig. 9 This is a scanning electron microscope image of the Co / Ni-5 (ZIF-67) sample prepared in Comparative Example 5 of the present invention.

[0052] Fig.10 The electronic photographs are of the Co, Ni-ZIF-1 and Zn, Ni-ZIF samples of the present invention and the Co, Ni-ZIF-D and Zn, Ni-ZIF-D samples after calcination.

[0053] Fig.11 The scanning electron microscope image of the Co, Ni-ZIF-D sample in the present invention is

[0054] Fig.12 The scanning electron microscope image of the Zn, Ni-ZIF-D sample in the present invention is

[0055] Fig.13This is a diagram of the microwave absorption performance of the Co, Ni-ZIF-D sample in the present invention.

[0056] Fig.14 This is a diagram of the wave absorption performance of the Zn,Ni-ZIF-D sample in the present invention. DETAILED DESCRIPTION

[0057] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0058] The present invention is inspired by the high lateral size and high surface area of ​​two-dimensional structural materials, and their high reception rate for electromagnetic waves. We adjusted the proportion of bimetallic ions in the solution, selected a certain proportion of methanol and water as solvents, and then added organic ligands at room temperature. We successfully prepared a type of bimetallic MOF flakes with a two-dimensional structure by stirring, and then used temperature-controlled pyrolysis technology in an air atmosphere to successfully achieve the electromagnetic response performance of the two-dimensional structural material.

[0059] The present invention provides a safe, low-energy, simple and rapid preparation method for a bimetallic MOF material with a two-dimensional structure, which has a commercial application prospect, and the derivatives of this type of material have unique electromagnetic response characteristics. The bimetallic nanosheet material with a two-dimensional structure is composed of nickel ions (Ni 2+ ) and cobalt ions (Co 2+ ), a mixed bimetallic ion solution system composed of a certain ratio, and then stirred with an imidazole compound in a methanol and water mixed solution system at room temperature for 3 hours to obtain a two-dimensional sheet Co, Ni-ZIF. In this method, the preferred bimetallic ion molar ratio is n Co 2+ :n Ni 2+ =0.6:1, the preferred volume ratio of methanol to water in the mixed reaction solution is V 甲醇 :V 水 =2-4:1. 2. Using the same preparation method and steps as Co, Ni-ZIF-1, nickel ions (Ni 2+ ) and zinc ions (Zn 2+) are mixed in a certain proportion to form a bimetallic ion system, and stirred and reacted with an imidazole compound in a certain proportion of a mixed solution of methanol and water at room temperature for 3 hours to form a Zn, Ni-ZIF two-dimensional material. 3. The above-prepared two-dimensional structured bimetallic nanosheets Co, Ni-ZIF-1 and Zn, Ni-ZIF are treated in the same way to obtain their responsive absorbing materials. The preferred process is as follows: a certain mass of Co, Ni-ZIF-1 and Zn, Ni-ZIF materials are weighed in a tubular furnace respectively, and the tubular furnace is not sealed. In an air environment, the heating rate is 3°C / min, and the temperature in the furnace is adjusted to 400°C. After keeping warm for 1 hour, the temperature is naturally lowered to obtain Co, Ni-ZIF-D and Zn, Ni-ZIF-D materials with electromagnetic response characteristics. The present invention is further illustrated by examples below:

[0060] Example 1

[0061] The preparation method of the thin-layer two-dimensional nanosheet structure material sample Co, Ni-ZIF of the present invention is as follows:

[0062] First, 10 ml of methanol and 10 ml of water were measured in a 50 ml beaker, and then 0.715 g (3 mmol) of nickel chloride hexahydrate and 0.429 g (1.8 mmol) of cobalt chloride hexahydrate were added to the beaker, respectively, and ultrasonic-assisted dissolution was performed, followed by uniform mixing and stirring (about 300 rpm) at room temperature for 2 hours; during this process, a methanol solution of 2-methylimidazole was prepared, 1.97 g (24 mmol) of 2-methylimidazole was weighed in a beaker and 10 ml of methanol was added for ultrasonic-assisted dissolution; next, the uniform stirring process was continued, and the prepared 2-methylimidazole methanol solution was slowly added dropwise to the above-mentioned mixed metal ion solution, and the stirring reaction was continued for 3 hours, and Co,Ni-ZIF-1 was obtained through centrifugation, methanol washing, vacuum drying and other processes.

[0063] In this embodiment, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of cobalt and nickel is 0.16 mmol / ml, and the volume ratio of methanol to water in the reaction solution is 2:1. Figure 1 and Figure 2 The scanning and transmission electron microscope images of the sample Co, Ni-ZIF-1 show that the prepared Co, Ni-ZIF-1 presents a two-dimensional structure of multi-folded sheets stacked with thin layers. The sheet thickness is less than 1nm and the sheet diameter distribution is in the range of 1 to 5μm. The sheet thickness is thin and the aspect ratio is large, and large holes are formed between the sheets.

[0064] Example 2

[0065] The nickel chloride hexahydrate in Example 1 was changed to 0.358 g (1.5 mmol), the cobalt chloride hexahydrate was changed to 0.215 g (0.9 mmol), and the other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co,Ni-ZIF-2.

[0066] In this embodiment, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.1:1, the total concentration of cobalt and nickel is 0.08 mmol / ml, and the volume ratio of methanol to water in the reaction solution is 2:1. The Co, Ni-ZIF-2 obtained in this case exhibits the same morphological characteristics as Co, Ni-ZIF-1.

[0067] Example 3

[0068] The nickel chloride hexahydrate in Example 1 was changed to 0.179 g (0.75 mmol), the cobalt chloride hexahydrate was changed to 0.103 g (0.45 mmol), and the other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co,Ni-ZIF-3.

[0069] In this embodiment, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.05:1, the total concentration of cobalt and nickel is 0.04mmol / ml, and the volume ratio of methanol to water in the reaction solution is 2:1. The Co,Ni-ZIF-3 obtained in this case exhibits the same morphological characteristics as Co,Ni-ZIF-1.

[0070] Example 4

[0071] The volume of methanol used to dissolve 2-methylimidazole in Example 1 was changed to 20 ml, and the other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co,Ni-ZIF-4.

[0072] In this embodiment, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of cobalt and nickel is 0.12mmol / ml, and the volume ratio of methanol to water in the reaction solution is 3:1. The Co,Ni-ZIF-4 obtained in this case exhibits the same morphological characteristics as Co,Ni-ZIF-1.

[0073] Example 5

[0074] The volume of methanol used to dissolve 2-methylimidazole in Example 1 was changed to 30 ml, and the other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co,Ni-ZIF-5.

[0075] In this embodiment, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of cobalt and nickel is 0.095 mmol / ml, and the volume ratio of methanol to water in the reaction solution is 4:1. The Co, Ni-ZIF-5 obtained in this case exhibits the same morphological characteristics as Co, Ni-ZIF-1.

[0076] Example 6

[0077] The cobalt chloride hexahydrate in Example 1 was replaced with zinc nitrate hexahydrate, and the added amount was 0.535 g (1.8 mmol), the content of nickel chloride hexahydrate remained unchanged, and the other implementation conditions and steps were exactly the same as in Example 1 to obtain Zn,Ni-ZIF.

[0078] In this embodiment, the molar ratio of zinc nitrate hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of zinc and nickel is 0.16 mmol / ml, and the volume ratio of methanol to water in the reaction solution is 2:1. Figure 3 and Figure 4 The scanning and transmission electron microscope images of the sample Zn, Ni-ZIF in Example 6 are respectively. It can be seen from the figure that the prepared Zn, Ni-ZIF presents a multi-fold two-dimensional structure of stacked layers, with a layer thickness of less than 1nm and a sheet diameter distribution of 1 to 5μm. Its layer size is small and thin, and the holes formed between the layers are small; the Zn, Ni-ZIF obtained in this embodiment and the sample Co, Ni-ZIF-1 in Example 1 both present a two-dimensional thin sheet structure, but due to the different radii of the cobalt and zinc elements in the constituent elements, there are certain differences in the morphological structure. Since zinc and cobalt can be prepared with 2-methylimidazole to prepare ZIF-8 and ZIF-67, they have the same topological structure and show the same morphological characteristics. Using this feature, the preparation of Zn, Ni-ZIF further expands the development of bimetallic two-dimensional nanosheets.

[0079] Comparative Example 1

[0080] The 0.429 g of cobalt chloride hexahydrate in Example 1 was changed to 0 g, that is, only nickel ions existed in the mixed metal ion system. The other implementation conditions and steps were the same as those in Example 1, and a sample Co / Ni-1 was obtained. Figure 5 This is a scanning electron microscope image of sample Co / Ni-1 in Comparative Example 1. It can be seen from the image that the prepared Co / Ni-1 presents a blocky irregular morphology.

[0081] Comparative Example 2

[0082] The 0.429 g of cobalt chloride hexahydrate in Example 1 was changed to 0.143 g, that is, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate was 0.2:1, and the other implementation conditions and steps were the same as those in Example 1 to obtain sample Co / Ni-2. Figure 6 This is a scanning electron microscope image of sample Co / Ni-2 in comparative example 2. It can be seen from the image that the prepared Co / Ni-2 presents a cluster-like irregular morphology.

[0083] Comparative Example 3

[0084] The 0.429 g of cobalt chloride hexahydrate in Example 1 was changed to 0.286 g, that is, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate was 0.4:1, and the other implementation conditions and steps were the same as those in Example 1 to obtain a sample Co / Ni-3. Figure 7 This is a scanning electron microscope image of sample Co / Ni-3 in comparative example 3. It can be seen from the image that the prepared Co / Ni-3 presents a cluster-like irregular morphology.

[0085] Comparative Example 4

[0086] The 0.429 g of cobalt chloride hexahydrate in Example 1 was changed to 0.572 g, that is, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate was 0.8:1. The other implementation conditions and steps were the same as those in Example 1, and a sample Co / Ni-4 was obtained. Figure 8 This is a scanning electron microscope image of sample Co / Ni-4 in comparative example 4. It can be seen from the image that the prepared Co / Ni-4 presents a wrinkled cluster structure morphology.

[0087] Comparative Example 5

[0088] The 0.715 g of nickel chloride hexahydrate in step 1 of Example 1 was changed to 0 g, and the 0.429 g of cobalt chloride hexahydrate was changed to 0.715 g, that is, the mixed metal ion system contained only cobalt ions. The other implementation conditions and steps were the same as those in Example 1, and the sample Co / Ni-5 (ZIF-67) was obtained. Fig. 9 This is a scanning electron microscope image of sample ZIF-67 in comparative example 5. It can be seen from the image that the prepared ZIF-67 presents a regular granular rhombic dodecahedron morphology.

[0089] Comparative Example 6

[0090] The 10 ml of water used to dissolve the cobalt and nickel ions in Example 1 was replaced with 10 ml of methanol, that is, the reaction solution was only methanol. The other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co / Ni-6. After separation and drying, the sample shrank into a dark green block solid.

[0091] Comparative Example 7

[0092] The 10 ml of methanol used to dissolve the cobalt and nickel ions in Example 1 was replaced by 10 ml of water, and the 10 ml of methanol used to dissolve the 2-methylimidazole was replaced by 10 ml of water, that is, the reaction solution was only water. The other implementation conditions and steps were exactly the same as those in Example 1 to obtain Co / Ni-7. After separation and drying, the sample shrank into a dark brown block solid.

[0093] By comparing Examples 1-3 and Comparative Examples 1-5, it can be seen that the present invention prepares a thin sheet-like two-dimensional structure MOF by adjusting the molar ratio of cobalt and nickel ions. By comparing their electron microscope images, it is determined that the optimal metal ion molar ratio is n Co 2+ :nNi 2+ =0.6:1; Comparing Examples 4-5 and Comparative Examples 5-6, the best solvent for preparing Co, Ni-ZIF two-dimensional nanosheet materials is a mixed solution of methanol and water, and the corresponding volume ratio of methanol to water is V 甲醇 :V 水 =2-4:1; Comparing Example 1 and Example 4, the same coordination characteristics of the coordinated metal ions zinc and cobalt 2-methylimidazole in ZIF-8 and ZIF-67 are utilized to develop a MOF having the same thin-sheet two-dimensional structural characteristics.

[0094] Preparation and performance test analysis of absorbing samples:

[0095] Since the samples prepared in Examples 2 and 3 have the same structure and composition as the sample obtained in Example 1; the samples prepared in Comparative Examples 1-4 all shrink into crystal blocks after drying, which is not conducive to the subsequent processing to prepare the absorbing test samples; the present invention only further processes the samples prepared in Examples 1 and 6 to demonstrate their application potential in the field of electromagnetic wave absorption. The steps for preparing the absorbing samples are as follows:

[0096] The sample Co, Ni-ZIF-1 in Example 1 of the two-dimensional nanosheet structure and the sample Zn, Ni-ZIF in Example 6 were placed in an open tube furnace, and then heated to 400 degrees Celsius and kept warm for 1 hour to obtain calcined samples Co, Ni-ZIF-D and Zn, Ni-ZIF-D, respectively. The heating rate was 3 degrees Celsius per minute. Subsequently, Co, Ni-ZIF-D and Zn, Ni-ZIF-D were mixed with paraffin wax to prepare electromagnetic parameter test samples.

[0097] Fig.10The electron photos of Co, Ni-ZIF and Zn, Ni-ZIF before and after calcination at 400℃ in air atmosphere show that all samples are in powder form before and after calcination. Due to the difference in composition elements, Co, Ni-ZIF and Zn, Ni-ZIF show different colors, Co, Ni-ZIF is yellow, Zn, Ni-ZIF is light green, and their respective calcination products also show different colors. Fig.11 and Fig.12 The following are the scanning electron microscope images of Co, Ni-ZIF-D and Zn, Ni-ZIF-D. It can be seen from the figure that the samples of Co, Ni-ZIF and Zn, Ni-ZIF retain their original skeleton structure after calcination, and many nanoparticles are formed on the surface of the thin layer nanosheets, and there are many gaps between the particles. The electromagnetic parameters of the sample Co, Ni-ZIF-D are calculated and analyzed to draw a schematic diagram of the absorption performance as shown in the figure. Fig.13 As shown in the figure, it can be seen that Co and Ni-ZIF-D both show certain electromagnetic response characteristics under different calculated thicknesses. When the thickness is 2 mm, the maximum absorption intensity is -20.06 dB and the maximum absorption width is 4.76 GHz. Fig.14 The reflection loss diagram of the sample Zn,Ni-ZIF-D at different thicknesses is shown. It can be seen from the figure that at different thicknesses, obvious resonance absorption peaks appear in the frequency region of 14.00-14.08GHz. When the thickness is 3 mm, the maximum reflection loss value is -18.25dB, and the maximum absorption of electromagnetic waves by the sample does not change with the change of frequency, indicating that Zn,Ni-ZIF-D has unique electromagnetic response characteristics.

[0098] The electromagnetic reflection loss values ​​in the case analysis are derived from the calculation of electromagnetic parameters, which are tested using a network analyzer (VNA, N5245A, Agilent, USA) in the 2-18 GHz frequency band. The mass ratio of sample Co, Ni-ZIF-D and sample Zn, Ni-ZIF-D to paraffin is 6:4. All samples are pressed into standard ring holes (inner diameter: 3.04 mm, outer diameter 7.00 mm) by the same mold to maintain the certainty of the geometric shape. The thickness of all rings is maintained at 2.2 mm. Agilent PNA software automatically outputs relevant electromagnetic parameters according to the Nicolson and Ross and Weir algorithm.

[0099] The present invention is based on the ZIF-67 and ZIF-8 metal organic framework material composition framework as the premise of the idea, and constructs a metal organic framework material with a two-dimensional sheet structure by doping mixed metal ion nickel. In this process, the ratio of mixed metal ions is optimized, and a mixed solution of water and methanol is used as a reaction solvent, so that the prepared material finally presents a two-dimensional nanosheet structure. By calcining in an air environment, its excellent potential as an electromagnetic wave absorbing material is demonstrated. The preparation method of the present invention is simple in process and low in cost, and the synthesis can be expanded by adjusting the amount of raw materials, which is suitable for industrial production.

[0100] The above-mentioned examples are merely examples for clearly explaining the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes can be made based on the description. It is not necessary and impossible to list all the embodiments here. However, these obvious changes or modifications derived from the spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a two-dimensional metal-organic framework material, It is characterized in that The following steps are involved: S1 uniformly mixes methanol, water, nickel chloride hexahydrate, and cobalt chloride hexahydrate according to a preset ratio to obtain a mixed solution A; S2, while continuously stirring the mixed solution A, adding a preset amount of 2-methylimidazole methanol solution dropwise to the mixed solution A to obtain a mixed solution B; In the mixed solution B, the molar ratio of cobalt chloride hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.05-0.2:1, the total concentration of cobalt and nickel is 0.04-0.16 mmol / ml, and the volume ratio of methanol to water is 2-4:1; The metal salt is composed of cobalt chloride and nickel chloride in the mixed solution A; S3 centrifuges the mixed solution B, washes and dries the centrifuged product, and obtains a two-dimensional structured metal-organic framework material.

2. A method for preparing a two-dimensional metal-organic framework material according to claim 1, It is characterized in that The S1 specifically includes the following steps: First, 10 ml of methanol and 10 ml of water were measured and added to a beaker, and then 0.715 g of nickel chloride hexahydrate and 0.429 g of cobalt chloride hexahydrate were added to the beaker, and dissolved and uniformly mixed by ultrasonic-assisted dissolution to obtain a mixed solution A; In step S2, the continuous stirring of the mixed solution A specifically comprises: At room temperature, using a magnetic stirrer, uniformly stirring at a rate of 300 rpm for 2 hours, within the 2 hours, completing the dropwise addition of the 2-methylimidazole methanol solution, and after the dropwise addition, continuing to uniformly stir at a rate of 300 rpm for 3 hours; In step S2, the preparation method of the 2-methylimidazole methanol solution is: weigh 1.97 grams of 2-methylimidazole into a beaker and add 10 milliliters of methanol, and dissolve it with ultrasound to obtain the 2-methylimidazole methanol solution.

3. A method for preparing a two-dimensional metal-organic framework material according to claim 1, It is characterized in that In the step S3, the cleaning is performed by washing with methanol, and the drying is performed by vacuum drying.

4. A method for preparing a two-dimensional metal-organic framework material, It is characterized in that The following steps are involved: S1: uniformly mixing methanol, water, nickel chloride hexahydrate and zinc nitrate hexahydrate according to a preset ratio to obtain a mixed solution A; S2, while continuously stirring the mixed solution A, adding a preset amount of 2-methylimidazole methanol solution dropwise to the mixed solution A to obtain a mixed solution B; In the mixed solution B, the molar ratio of zinc nitrate hexahydrate to nickel chloride hexahydrate is 0.6:1, the molar ratio of the total amount of metal salt to 2-methylimidazole is 0.2:1, the total concentration of zinc and nickel is 0.16 mmol / ml, and the volume ratio of methanol to water is 2:1; The metal salt is composed of cobalt chloride and nickel chloride in the mixed solution A; S3 centrifuges the mixed solution B, washes and dries the centrifuged product, and obtains a two-dimensional structured metal-organic framework material.

5. A two-dimensional metal-organic framework material obtained by the preparation method according to any one of claims 1 to 4, It is characterized in that The two-dimensional structured metal-organic framework material is a multi-folded sheet-like two-dimensional structure with stacked thin layers, a sheet thickness of less than 1 nm, and a sheet diameter distribution within the range of 1 to 5 μm.

6. Application of the two-dimensional metal-organic framework material prepared by the preparation method according to any one of claims 1 to 4 in electromagnetic wave absorption, Features: The two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tube furnace and kept at 400 degrees Celsius for 1 hour to obtain a calcined product; The calcined product is mixed with paraffin wax and then subjected to electromagnetic wave absorption.

7. The use according to claim 6, Features: The mixing ratio of the calcined product and paraffin is 6:4 by mass.

8. Application of the two-dimensional metal-organic framework material prepared by the preparation method according to any one of claims 1 to 3 in electromagnetic wave absorption, Features: The two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tube furnace, and then naturally cooled at 400 degrees Celsius for 1 hour to obtain a calcined product; The calcined product was mixed with paraffin wax in a mass ratio of 6:4 to form an annular sheet with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm and a thickness of 2.2 mm; Electromagnetic parameter testing uses a network analyzer to conduct electromagnetic wave absorption testing in the 2-18GHz frequency band; Output electromagnetic parameters using Agilent PNA software according to Nicolson and Ross and Weir algorithm: When the thickness is 2 mm, the maximum absorption intensity is -20.06 dB and the maximum absorption width is 4.76 GHz.

9. Application of the two-dimensional metal-organic framework material prepared by the preparation method according to claim 4 in electromagnetic wave absorption, Features: The two-dimensional structured metal-organic framework material is heated to 400 degrees Celsius in an open tube furnace, and then naturally cooled at 400 degrees Celsius for 1 hour to obtain a calcined product; The calcined product was mixed with paraffin wax in a mass ratio of 6:4 to form an annular sheet with an inner diameter of 3.04 mm, an outer diameter of 7.00 mm and a thickness of 2.2 mm; Electromagnetic parameter testing uses a network analyzer to conduct electromagnetic wave absorption testing in the 2-18GHz frequency band; Output electromagnetic parameters using Agilent PNA software according to Nicolson and Ross and Weir algorithm: The absorbers with different thicknesses show resonance absorption peaks in the frequency region of 14.00-14.08GHz. Among them, when the thickness is 3 mm, it shows the maximum absorption intensity, and the corresponding peak value is -18.25dB.

Images