Preparation method of graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material

Abstract

A method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material, the invention relates to the field of preparation of composite materials for electromagnetic wave radiation absorption and protection. The invention aims to solve the technical problems that the existing graphene materials have poor impedance matching performance, narrow wave absorption band, and weak absorption performance when used alone. Method: synthesize MOF precursor; prepare MOF-derived nitrogen-doped carbon-coated cobalt phosphide nanoparticle composite materials; compound the above materials with reduced graphene oxide to prepare graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide composite materials. The product of the invention has excellent wave absorption performance, and has strong absorption and wide effective absorption band performance at low filling amount and thin thickness. The graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared by the method of the invention is applied to the field of electromagnetic wave radiation absorption materials.

Description

Technical Field

[0001] The invention relates to the field of preparation of composite materials for absorbing and protecting electromagnetic wave radiation. Background Art

[0002] At present, graphene materials have been widely used in the preparation of absorbing materials. Graphene materials have excellent dielectric properties, large dielectric constant values, and significantly decrease with increasing frequency, which manifests as dispersion phenomenon. Therefore, they have important application prospects in the field of electromagnetic wave absorption and protection. However, due to the high dielectric constant, pure graphene materials often have impedance mismatch when used as absorbers, and cannot fully exert their loss capacity for electromagnetic waves, and the absorption band is narrow. These problems limit its application in the field of absorbing materials. Therefore, it is necessary to introduce some substances that adjust impedance matching and increase dielectric loss performance to synthesize composite materials with graphene materials to obtain good absorbing performance. Summary of the invention

[0003] The present invention aims to solve the technical problems that the existing graphene material has poor impedance matching performance, narrow absorption band and weak absorption performance when used alone, and provides a method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material.

[0004] A method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material, which is carried out according to the following steps:

[0005] Step 1: evenly disperse MOF in anhydrous ethanol, add a methanol solution of cobalt salt, stir and mix, then centrifuge to separate precipitate A, wash precipitate A, and dry;

[0006] Step 2, dispersing the precipitate A obtained in step 1 in anhydrous ethanol, adding an ethanol solution of melamine and an ethanol solution of phytic acid in sequence, stirring and mixing, and then ultrasonically treating in an ultrasonic cleaning machine, and then centrifuging and separating the precipitate B, washing the precipitate B, and drying;

[0007] Step 3: placing the precipitate B obtained in step 2 into a tubular furnace and calcining to obtain a powder material, namely, a nitrogen-doped carbon nanocage-coated cobalt phosphide material;

[0008] Step 4: uniformly dispersing the powder material obtained in step 3 in anhydrous ethanol, then adding it to the aqueous dispersion of graphite oxide, and then placing it in an ultrasonic cleaning machine for ultrasonic treatment, and then stirring, and then freeze-drying to obtain a precursor material;

[0009] Step 5: Place the precursor material obtained in step 4 into a tubular furnace and calcine to obtain a powder product, which is the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material. The preparation is complete.

[0010] The present invention utilizes the large surface area and excellent dielectric properties of graphene to load nitrogen-doped carbon nano cages and cobalt phosphide structures on the sheets. Cobalt phosphide has strong electrochemical activity and has abundant defect vacancies inside, which can bring a large number of dipole polarization sites. At the same time, the nitrogen-doped carbon nano cage-coated cobalt phosphide structure forms a large number of heterogeneous interfaces, introduces interface polarization, and significantly enhances dielectric loss performance. The reduced graphene oxide sheets form an efficient conductive network, which is conducive to increasing the conductivity loss of the composite material, and improves the impedance matching of the composite material, so that the electromagnetic wave loss capacity of the material can be fully utilized.

[0011] The beneficial effects of the present invention are:

[0012] The graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared by the method of the present invention has strong electrochemical activity and rich defects in the cobalt phosphide nanoparticles; the nitrogen-doped carbon nanocage structure is a nitrogen-doped amorphous carbon with low crystallinity, and a rich interface is formed between it and the cobalt phosphide nanoparticles; the graphene is reduced graphite oxide, and its sheet has rich defect sites. In terms of morphology, the nitrogen-doped carbon nanocage-coated cobalt phosphide structure is attached to the reduced graphene oxide sheet. The reduced graphene oxide sheet provides an efficient conductive network, which brings a large dielectric constant to the entire composite material. At the same time, the rich defect sites on its sheet constitute polarization sites to enhance the polarization loss performance of the material; the large number of interfaces formed by the nitrogen-doped amorphous carbon and the cobalt phosphide and the defect sites inside it will become the center of dipole polarization and interface polarization to enhance the electromagnetic wave loss capacity. The most important thing is that this structure improves the impedance matching of reduced graphene oxide, so that the loss capacity of the composite material can be fully utilized, and finally achieves excellent absorbing performance. The prepared graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material has a maximum absorption intensity of -67.5dB and a maximum effective absorption band of 7GHz. At the same time, the preparation process is simple, safe and fast, and is expected to be put into practical application.

[0013] The graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared by the method of the present invention is applied to the field of electromagnetic wave radiation absorbing materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is the XRD spectrum of the graphene-supported nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1;

[0015] Figure 2 TEM photo of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 (500 nm);

[0016] Figure 3 This is a SEM photo of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 (10 μm);

[0017] Figure 4 The Raman spectrum of the graphene-supported nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1;

[0018] Figure 5 This is a graph showing the variation of electromagnetic parameters of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 with frequency;

[0019] Figure 6 This is a test curve diagram of the wave absorbing performance of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 as a function of frequency. DETAILED DESCRIPTION

[0020] Specific implementation method 1: This implementation method is a method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material, which is carried out according to the following steps:

[0021] Step 1: evenly disperse MOF in anhydrous ethanol, add a methanol solution of cobalt salt, stir and mix, then centrifuge to separate precipitate A, wash precipitate A, and dry;

[0022] Step 2, dispersing the precipitate A obtained in step 1 in anhydrous ethanol, adding an ethanol solution of melamine and an ethanol solution of phytic acid in sequence, stirring and mixing, and then ultrasonically treating in an ultrasonic cleaning machine, and then centrifuging and separating the precipitate B, washing the precipitate B, and drying;

[0023] Step 3: placing the precipitate B obtained in step 2 into a tubular furnace and calcining to obtain a powder material, namely, a nitrogen-doped carbon nanocage-coated cobalt phosphide material;

[0024] Step 4: uniformly dispersing the powder material obtained in step 3 in anhydrous ethanol, then adding it to the aqueous dispersion of graphite oxide, and then placing it in an ultrasonic cleaning machine for ultrasonic treatment, and then stirring, and then freeze-drying to obtain a precursor material;

[0025] Step 5: Place the precursor material obtained in step 4 into a tubular furnace and calcine to obtain a powder product, which is the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material. The preparation is complete.

[0026] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the MOF in step 1 is a commercial Co-based MOF. The rest is the same as specific embodiment 1.

[0027] Specific embodiment 3: This embodiment differs from specific embodiment 1 or 2 in that the methanol solution of cobalt salt in step 1 is prepared with cobalt nitrate hexahydrate and methanol, wherein the concentration of cobalt nitrate is 0.1-0.5 mol / L. Others are the same as specific embodiment 1 or 2.

[0028] Specific embodiment 4: This embodiment differs from Specific embodiments 1 to 3 in that the mass molar ratio of MOF to cobalt salt in step 1 is 0.2 g:0.45 mmol. The rest is the same as Specific embodiments 1 to 3.

[0029] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: in step 2, the amount of precipitate A is 0.1 g to 0.5 g, the amount of melamine is 0.25 g to 1.25 g, and the amount of phytic acid reagent is 1 mL to 5 mL. Other aspects are the same as those of specific embodiments 1 to 4.

[0030] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that: the stirring and mixing time in step 2 is 0.5h to 1h, the ultrasonic treatment time is 0.5h to 1h; the precipitate B is washed 2 to 3 times with anhydrous ethanol; the drying temperature is 50℃ to 70℃, and the drying time is 6h to 12h. Others are the same as specific embodiments 1 to 5.

[0031] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that: in step 3, the calcination atmosphere is a mixed gas of argon and hydrogen, or the calcination atmosphere is hydrogen, the heating rate is controlled to be 3 to 5°C / min, the calcination temperature is 500 to 800°C, and the holding time is 6 to 8h. Others are the same as specific embodiments 1 to 6.

[0032] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that: the aqueous dispersion of graphite oxide in step 4 is prepared from graphite oxide and water; the amount of graphite oxide used is 0.255 g to 1.275 g, and the amount of powder material used is 0.1 g to 0.5 g. Other aspects are the same as those of specific embodiments 1 to 7.

[0033] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that: in step 4, the ultrasonic treatment is controlled for 1 to 3 hours, the ultrasonic frequency is 40 KHz, and then stirring is performed for 12 to 24 hours. The rest is the same as specific embodiments 1 to 8.

[0034] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: in step 5, the calcination atmosphere is a mixed gas of argon and hydrogen, or the calcination atmosphere is hydrogen, the heating rate is controlled to be 3 to 5°C / min, the calcination temperature is 500 to 800°C, and the holding time is 3 to 6h. Others are the same as specific embodiments 1 to 9.

[0035] The content of the present invention is not limited to the content of the above-mentioned embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0036] Embodiment 1:

[0037] The present embodiment provides a method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material, which is carried out according to the following steps:

[0038] Step 1: Disperse 0.2 g ZIF-67 in 50 mL anhydrous ethanol, add methanol solution of cobalt salt, stir and mix for 1.5 h, stir at 400 r / min, then centrifuge to separate precipitate A at 6000 r / min, wash precipitate A three times with anhydrous ethanol, and dry at 60 °C for 8 h;

[0039] The methanol solution of cobalt salt is prepared by using cobalt nitrate hexahydrate and 30 mL of methanol, wherein the concentration of cobalt nitrate is 0.15 mol / L;

[0040] Step 2: Disperse 0.2 g of the precipitate A obtained in step 1 in 50 mL of anhydrous ethanol, add an ethanol solution of melamine and an ethanol solution of phytic acid in sequence, stir and mix for 30 min at a stirring rate of 400 r / min, then perform ultrasonic treatment in an ultrasonic cleaning machine for 30 min at an ultrasonic frequency of 40 KHz, then centrifuge to separate the precipitate B, wash the precipitate B three times with anhydrous ethanol, and control the temperature to dry at 60 ° C for 6 h;

[0041] The ethanol solution of melamine is prepared from 0.5 g of melamine and 150 mL of anhydrous ethanol;

[0042] The ethanol solution of phytic acid was prepared by 2 mL of phytic acid reagent and 80 mL of anhydrous ethanol;

[0043] Step 3, 0.2 g of the precipitate B obtained in step 2 is placed in a tubular furnace and calcined. The calcination atmosphere is a mixed gas of argon and hydrogen, and the mixed volume ratio of argon to hydrogen is 50:1. The heating rate is controlled to be 5°C / min, the calcination temperature is 650°C, and the holding time is 6h to obtain a powder material, that is, a nitrogen-doped carbon nanocage-coated cobalt phosphide material;

[0044] Step 4: Disperse 0.2 g of the powder material obtained in step 3 uniformly in 20 mL of anhydrous ethanol, then add it to the aqueous dispersion of graphite oxide, and then put it into an ultrasonic cleaning machine for ultrasonic treatment for 1.5 h at an ultrasonic frequency of 40 KHz, and then stir for 12 h at a stirring speed of 400 r / min, and then freeze-dry to obtain a precursor material;

[0045] Aqueous dispersion of graphite oxide was prepared by mixing 0.255 g of graphite oxide with 200 mL of water;

[0046] Step 5. Place the precursor material obtained in step 4 into a tubular furnace for calcination. The calcination atmosphere is a mixture of argon and hydrogen. The mixed volume ratio of argon to hydrogen is 50:1. The heating rate is controlled to be 5°C / min, the calcination temperature is 650°C, and the insulation time is 4h to obtain a powder product, which is a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material. The preparation is completed.

[0047] Preparation of test samples:

[0048] The graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 was mixed with paraffin, with a mass fraction of 4% for the powder material, heated to 75°C to melt the paraffin, mixed evenly and then cooled to room temperature to obtain a block sample, placed the block in a mold, and pressed out a coaxial ring sample with an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a height of 2 mm to 3 mm.

[0049] The graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 was tested.

[0050] The XRD spectrum of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 is as follows: Figure 1 As shown, the diffraction peak of cobalt phosphide is obvious and can correspond to the standard PDF card 89-2747. At the same time, the bun peak of amorphous nitrogen-doped carbon is not obvious because it is covered by the strong peak.

[0051] TEM photo of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 is shown in Figure 2 (500nm) as shown; Example 1 prepared graphene loaded nitrogen-doped carbon nanocage coated cobalt phosphide absorbing material SEM photo as shown Figure 3 (10μm); from the figure, it can be seen that the nitrogen-doped carbon nanocages encapsulated cobalt phosphide are in the form of small spheres and are evenly distributed on the graphene sheets.

[0052] The Raman spectrum of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 is as follows: Figure 4 As shown in the figure, it can be seen that the D peak (1587.6 cm -1 ) and G peak (1355.0cm -1 The intensity ratio I D / I G The D peak is mainly caused by the lattice motion away from the center of the Brillouin zone. It is a defect peak, reflecting the disorder of the graphene sheet. 2g The phonon produces the G peak, which is the carbon sp 2 The characteristic peaks of the structure reflect its symmetry and degree of crystallinity.D / I G Indicates the disorder of graphene. This indicates that there are many defects in the material and the crystallinity of carbon is very low.

[0053] The electromagnetic parameter test curve of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 is as follows: Figure 5 As shown in the figure, there are sharp resonance peaks on the real and imaginary curves of the dielectric constant, which is caused by polarization, indicating that the material has strong dielectric loss. The real and imaginary values ​​of the magnetic permeability are small, remaining near 1 and 0 respectively, indicating that the material basically does not show magnetic loss characteristics; the test curve of the absorption performance of the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material prepared in Example 1 varies with frequency as shown in the figure below. Figure 6 As shown, curve 1 represents 1.0mm thickness, curve 2 represents 1.5mm thickness, curve 3 represents 2.14mm thickness, curve 4 represents 2.71mm thickness, curve 5 represents 3.0mm thickness, curve 6 represents 3.5mm thickness, and curve 7 represents 4.0mm thickness. It shows excellent wave absorption performance at 1-18GHz and 2-4mm thickness. The effective absorption bandwidth at 2-4mm thickness almost covers 6-18GHz frequency, and the maximum absorption intensity is achieved near 2.14mm thickness.

Claims

1. A method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material, characterized in that It proceeds as follows: Step 1: Disperse MOF uniformly in anhydrous ethanol, add a methanol solution of cobalt salt, stir and mix, then centrifuge to separate precipitate A, wash precipitate A, and dry; Step 2, dispersing the precipitate A obtained in step 1 in anhydrous ethanol, adding an ethanol solution of melamine and an ethanol solution of phytic acid in sequence, stirring and mixing, and then ultrasonically treating in an ultrasonic cleaning machine, and then centrifuging and separating the precipitate B, washing the precipitate B, and drying; Step 3: placing the precipitate B obtained in step 2 into a tubular furnace and calcining to obtain a powder material, namely, a nitrogen-doped carbon nanocage-coated cobalt phosphide material; Step 4: uniformly dispersing the powder material obtained in step 3 in anhydrous ethanol, then adding it to the aqueous dispersion of graphite oxide, and then placing it in an ultrasonic cleaning machine for ultrasonic treatment, and then stirring, and then freeze-drying to obtain a precursor material; Step 5: Place the precursor material obtained in step 4 into a tubular furnace and calcine to obtain a powder product, which is the graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material. The preparation is complete.

2. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that The MOF in step 1 is a commercial Co-based MOF.

3. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 1, the methanol solution of the cobalt salt is prepared by using cobalt nitrate hexahydrate and methanol, wherein the concentration of the cobalt nitrate is 0.1-0.5 mol / L.

4. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 1, the mass molar ratio of MOF to cobalt salt is 0.2 g:0.45 mmol.

5. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 2, the amount of precipitate A is 0.1 g to 0.5 g, the amount of melamine is 0.25 g to 1.25 g, and the amount of phytic acid reagent is 1 mL to 5 mL.

6. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that The stirring and mixing time in step 2 is 0.5h~1h, and the ultrasonic treatment time is 0.5h~1h; the precipitate B is washed 2~3 times with anhydrous ethanol; the drying temperature is 50℃~70℃, and the drying time is 6h~12h.

7. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 3, the calcination atmosphere is a mixed gas of argon and hydrogen, or the calcination atmosphere is hydrogen, the heating rate is controlled at 3 to 5°C / min, the calcination temperature is 500 to 800°C, and the insulation time is 6 to 8h.

8. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that The aqueous dispersion of graphite oxide in step 4 is prepared by graphite oxide and water; the amount of graphite oxide used is 0.255g to 1.275g, and the amount of powder material used is 0.1g to 0.5g.

9. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 4, the ultrasonic treatment is controlled for 1 to 3 hours, and the ultrasonic frequency is 40 KHz; and then stirring is performed for 12 to 24 hours.

10. The method for preparing a graphene-loaded nitrogen-doped carbon nanocage-coated cobalt phosphide absorbing material according to claim 1, characterized in that In step 5, the calcination atmosphere is a mixed gas of argon and hydrogen, or the calcination atmosphere is hydrogen, the heating rate is controlled at 3 to 5° C. / min, the calcination temperature is 500 to 800° C., and the insulation time is 3 to 6 hours.

Images