Porous carbon-based composite wave-absorbing material and preparation method thereof

Abstract

The invention provides a porous carbon-based composite wave-absorbing material and a preparation method thereof, and belongs to the technical field of wave-absorbing materials. Comprising the following steps: 1) performing high-temperature pyrolysis on rape straws in an oxygen-free environment to generate porous carbon; 2) electroplating Ni on the surface of the porous carbon to prepare porous carbon coated Ni; and 3) performing high-temperature oxidation on the porous carbon-coated Ni to obtain the porous carbon-based composite wave-absorbing material, namely the porous carbon-coated Ni / NiO composite wave-absorbing material. According to the preparation method, the porous carbon-coated Ni is prepared by taking the rape straw as a carbon source and adopting an electroplating technology, the finally obtained porous carbon-coated Ni / NiO composite wave-absorbing material is low in density, wide in effective wave-absorbing frequency band and good in wave-absorbing performance, and the preparation method is stable, controllable, simple to operate and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of absorbing materials, and in particular relates to a porous carbon-based composite absorbing material and a preparation method thereof. Background Art

[0002] Electromagnetic waves are widely used in electronic communication technologies such as mobile networks, high-speed processors, radar broadband and satellites due to their unique advantages of wide spectrum. However, the electromagnetic radiation and interference problems caused by electromagnetic wave transmission not only seriously endanger human health, but also affect the durability and normal operation of electronic products. Absorbing materials can convert electromagnetic waves into heat energy or other forms of energy, thereby achieving the purpose of attenuating electromagnetic waves. Therefore, the preparation of excellent absorbing materials with thin thickness, light weight, wide absorption bandwidth and strong absorption capacity has become a current research hotspot.

[0003] Among absorbing materials, carbon materials have excellent chemical stability and electrical conductivity, and their dielectric properties are easy to control. They are ideal dielectric loss absorbing materials, such as carbon nanotubes, graphene, carbon fibers, porous carbon, etc. Among them, biomass porous carbon is widely available, green and sustainable, and the rich pore structure of porous carbon materials can make the incident wave experience multiple reflections and scattering inside the material, which is conducive to microwave absorption; at the same time, the rich solid-air interface in the pore structure strengthens the interface polarization and further enhances the dielectric loss. However, the inherent high electrical conductivity of carbon materials leads to impedance mismatch, making it difficult to achieve efficient electromagnetic absorption performance. Summary of the invention

[0004] The purpose of the present invention is to propose a method for preparing a porous carbon-based composite absorbing material in view of the problems existing in the background technology.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a porous carbon-based composite absorbing material, first pyrolyzing rape straw in an oxygen-free environment to generate porous carbon, then electroplating Ni on the surface of the porous carbon to obtain porous carbon@Ni, and finally heating and oxidizing the porous carbon@Ni to obtain a porous carbon-based composite absorbing material, that is, a porous carbon@Ni / NiO composite absorbing material, the specific steps are as follows:

[0007] Step 1, pre-treating the rape straw, specifically, first cutting the rape straw into sheets, washing and drying, then mixing the sheets of rape straw with a KOH aqueous solution, and magnetically stirring to obtain a mixture; hydrothermally treating the mixture, specifically, placing the mixture in a hydrothermal reactor, treating at a temperature of 150° C. for 2 hours, and then drying at 80° C.;

[0008] Step 2, carbonizing the pretreated rape straw obtained in step 1, wherein the specific carbonization process is: nitrogen environment, heating rate of 5°C / min, carbonization temperature of 800°C, holding time of 1h, and natural furnace cooling; after carbonization, repeatedly washing with 5wt% dilute hydrochloric acid solution and deionized water until neutral, and drying at 80°C to obtain porous carbon based on rape straw;

[0009] Step 3: The porous carbon obtained in step 2 is subjected to surface nickel electroplating treatment using an electroplating device. The specific electroplating operation is as follows: a flexible copper foil horizontally placed at the bottom of a cylindrical plating tank is used as a cathode, a circular nickel plate located directly above and parallel to the cathode is used as an anode, and the positive and negative electrodes are connected to the nickel plate and the copper foil respectively through an electrode clamp and a wire at 55°C and a current density of 15 mA / cm 2 Under the conditions, porous carbon is intermittently electroplated; after the electroplating treatment, the porous carbon is separated from the electroplating solution, washed and dried to obtain porous carbon@Ni;

[0010] Step 4: The porous carbon@Ni obtained in step 3 is transferred into a muffle furnace for high-temperature oxidation treatment. The specific process is: air environment, heating rate of 10°C / min, heat treatment temperature of 450°C, holding time of 5min, cooling method of natural furnace cooling, and finally a porous carbon-based composite absorbing material, i.e., a porous carbon@Ni / NiO composite absorbing material, is obtained.

[0011] As a preferred embodiment, in step 1, the amount of rapeseed straw flakes used is 3 g, and the KOH aqueous solution contains 3 g KOH and 54 mL deionized water.

[0012] As a preferred embodiment, in step 3, the dimensions of the cylindrical plating tank are: 85 mm in diameter and 100 mm in height.

[0013] As a preferred method, in step 3, the intermittent electroplating method is: start the mechanical stirring device, stir mechanically for 60 seconds, then turn off the mechanical stirring device, let it stand for 45 minutes, then turn on the electroplating switch, electroplate for 30 seconds, repeat this "stirring-electroplating" operation twice, and electroplate for a total of 60 seconds.

[0014] As a preferred embodiment, in step 3, the plating solution consists of 1.68 mol / L NiCl2·H2O, 4 mol / L NH4Cl, 0.5 mol / L H3BO3, and 0.1 g / L porous carbon.

[0015] As a preferred method, the porous carbon is dispersed in the electroplating solution by ultrasonic dispersion at a power of 480 W for 5 minutes.

[0016] The second object of the present invention is to provide a porous carbon-based composite absorbing material obtained by the preparation method.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The raw materials of the present invention are widely available, low in price, and green and environmentally friendly. The product provided by the present invention is simple to prepare, and the preparation method is stable and controllable. The present invention adopts electroplating technology to prepare porous carbon@Ni composite materials. Compared with chemical plating, electroplating technology has the characteristics of relatively simple operation without sensitization and activation, fast coating deposition rate, easy control of plating process, good coating performance, and relatively green and environmentally friendly plating solution, which is of great significance in production practice.

[0019] 2. The present invention uses rape straw, an agricultural waste, as a raw material, and carbonizes it at high temperature in a protective atmosphere, then deposits metal Ni on the porous carbon surface by electroplating technology, and finally obtains a porous carbon@Ni / NiO composite material derived from rape straw by high-temperature oxidation. The composite material prepared by the present invention has the characteristics of low density, wide effective absorption bandwidth, strong wave absorbing ability, etc., which meets the current requirements for wave absorbing materials to be "thin, light, wide, and strong", and has a wide range of application value BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the electroplating device of the present invention.

[0021] Figure 2 The XPS spectra of Examples 1-3 of the present invention, wherein (a) is the full XPS spectrum of Examples 1-3, and (b), (c), and (d) are the Ni 2p spectrum, O 1s spectrum, and C 1s spectrum of Examples 2 and 3, respectively.

[0022] Figure 3 These are SEM images of Examples 1-3 of the present invention, wherein (a), (d), and (g) are SEM images of Example 1, (b), (e), and (h) are SEM images of Example 2, and (c), (f), and (i) are SEM images of Example 3.

[0023] Figure 4 The diagrams are for the wave absorption performance of Examples 1 to 3. (a) is for Example 1, (b) is for Example 2, and (c) is for Example 3. DETAILED DESCRIPTION

[0024] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0025] The embodiment provides a method for preparing a porous carbon-based composite absorbing material, firstly pyrolyzing rape straw in an oxygen-free environment to generate porous carbon, then electroplating Ni on the surface of the porous carbon to obtain porous carbon@Ni, and finally heating and oxidizing the porous carbon@Ni to obtain a porous carbon-based composite absorbing material, i.e., a porous carbon@Ni / NiO composite absorbing material, and the specific steps are as follows:

[0026] Step 1, pre-treating the rape straw, specifically, first cutting the rape straw into sheets, washing and drying, then mixing the sheets of rape straw with a KOH aqueous solution, and magnetically stirring to obtain a mixture; hydrothermally treating the mixture, specifically, placing the mixture in a hydrothermal reactor, treating at a temperature of 150° C. for 2 hours, and then drying at 80° C.;

[0027] Step 2, carbonizing the pretreated rape straw obtained in step 1, wherein the specific carbonization process is: nitrogen environment, heating rate of 5°C / min, carbonization temperature of 800°C, holding time of 1h, and natural furnace cooling; after carbonization, repeatedly washing with 5wt% dilute hydrochloric acid solution and deionized water until neutral, and drying at 80°C to obtain porous carbon based on rape straw;

[0028] Step 3: The porous carbon obtained in step 2 is subjected to surface nickel electroplating treatment using an electroplating device. The specific electroplating operation is as follows: a flexible copper foil horizontally placed at the bottom of a cylindrical plating tank is used as a cathode, a circular nickel plate located directly above and parallel to the cathode is used as an anode, and the positive and negative electrodes are connected to the nickel plate and the copper foil respectively through an electrode clamp and a wire at 55°C and a current density of 15 mA / cm 2 Under the conditions, porous carbon is intermittently electroplated; after the electroplating treatment, the porous carbon is separated from the electroplating solution, washed and dried to obtain porous carbon@Ni;

[0029] Step 4: The porous carbon@Ni obtained in step 3 is transferred into a muffle furnace for high-temperature oxidation treatment. The specific process is: air environment, heating rate of 10°C / min, heat treatment temperature of 450°C, holding time of 5min, cooling method of natural furnace cooling, and finally a porous carbon-based composite absorbing material, i.e., a porous carbon@Ni / NiO composite absorbing material, is obtained.

[0030] In some embodiments, in step 1, the amount of rapeseed straw flakes used is 3 g, and the KOH aqueous solution contains 3 g KOH and 54 mL deionized water.

[0031] In some embodiments, in step 3, the dimensions of the cylindrical plating tank are: 85 mm in diameter and 100 mm in height.

[0032] In some embodiments, in step 3, the intermittent electroplating method is: start the mechanical stirring device, stir mechanically for 60 seconds, then turn off the mechanical stirring device, let it stand for 45 minutes, then turn on the electroplating switch, electroplate for 30 seconds, repeat this "stirring-electroplating" operation twice, and electroplate for a total of 60 seconds.

[0033] In some embodiments, in step 3, the plating solution consists of 1.68 mol / L NiCl2·H2O, 4 mol / L NH4Cl, 0.5 mol / L H3BO3, and 0.1 g / L porous carbon.

[0034] In some embodiments, the porous carbon is dispersed in the electroplating solution by ultrasonic dispersion at a power of 480 W for 5 minutes.

[0035] Example 1

[0036] This embodiment provides a method for preparing porous carbon based on rape straw in the preparation of a porous carbon-based composite absorbing material, comprising the following steps:

[0037] Step 1, cut the rape straw into sheets, wash them with deionized water and anhydrous ethanol for 3 times respectively, dry them in an oven at 80°C for 24 hours, then mix 3g of the washed and dried rape straw with a KOH aqueous solution and stir them magnetically to obtain a mixture, wherein the amount of KOH in the KOH aqueous solution is 3g and the amount of DI is 54mL;

[0038] Step 2: subjecting the mixture obtained in step 1 to hydrothermal treatment. The specific process is: placing the mixture in a hydrothermal reactor, treating it at a temperature of 150° C. for 2 hours, and then drying it at 80° C.

[0039] Step 3, carbonizing the sample prepared in step 3 in a nitrogen atmosphere at a carbonization temperature of 800°C for 1 hour at a heating rate of 5°C / min, followed by natural furnace cooling to room temperature;

[0040] Step 4: The sample prepared in step 3 was filtered and washed with deionized water and 5% by mass HCl respectively until neutral, and then dried in an oven at 80° C. for 24 hours to obtain porous carbon derived from rapeseed straw.

[0041] The above-obtained product was tested as follows:

[0042] (1) The morphology of the samples was observed using a scanning electron microscope (SEM).

[0043] (2) The wave absorption performance of the material was tested by a vector network analyzer (Agilent N5224A) using the coaxial method in the frequency range of 2-18 GHz. Test sample preparation: The sample was uniformly dispersed in paraffin wax, accounting for 27% of the total weight, and then pressed into a ring-shaped piece (outer diameter: 7.0 mm, inner diameter 3.04 mm).

[0044] (3) XPS test of sample element composition

[0045] Figure 3 (a), (d), and (g) are SEM images of the samples prepared in this example. It can be seen that after activation pretreatment and carbonization treatment, biomass carbon with a porous structure is successfully prepared.

[0046] Figure 4 (a) is the reflection loss value of the absorbing material prepared in this embodiment within the test range of 2-18 GHz. When the thickness of the absorbing coating is 1.5 mm, the minimum value of -22.27 dB is obtained at 15.71 GHz.

[0047] Example 2

[0048] This embodiment provides a method for preparing a porous carbon-based composite absorbing material and a method for preparing a rape straw-derived porous carbon@Ni absorbing material, comprising the following steps:

[0049] Step 1, preparing a plating solution: the plating solution is composed of 1.68 mol / L NiCl2·H2O, 4 mol / L NH4Cl, 0.5 mol / L H3BO3, and 0.1 g / L of the porous carbon based on rape straw obtained in Example 1; the prepared plating solution is ultrasonically treated at a power of 480 W for 5 min to disperse the carbon material;

[0050] Step 2: Use a homemade electroplating device to electroplating nickel on the porous carbon surface. The specific electroplating operation is: a copper foil placed parallel to the bottom of a cylindrical plating tank is used as a cathode, a nickel plate located above and parallel to the cathode is used as an anode, and the positive and negative electrodes are connected to the nickel plate and the copper foil respectively through an electrode clamp and a wire at 55°C and a current density of 15 mA / cm 2 Under the above conditions, the porous carbon based on rape straw obtained in Example 1 was intermittently electroplated. The intermittent electroplating method was as follows: start the mechanical stirring device, stir mechanically for 60 seconds, turn off the mechanical stirring device, let it stand for 45 minutes, then turn on the electroplating switch, electroplate for 30 seconds, repeat this "stirring-electroplating" operation twice, and electroplate for a total of 60 seconds.

[0051] Step 3: The carbon material electroplated in step 2 is filtered and washed with deionized water and anhydrous ethanol, and then dried in an oven at 80° C. for 24 h to obtain porous carbon@Ni.

[0052] The product obtained above was tested, and the test content was exactly the same as in Example 1.

[0053] Figure 2 The XPS spectra of Examples 1-3 show that the peak of metallic nickel appears in the XPS spectrum of Example 2, and the fine spectrum of nickel contains Ni 0 、Ni 2+ 、Ni 3+ 2p 1 / 2 , 2p 3 / 2 orbital peak, indicating that metallic nickel was successfully loaded on the porous carbon.

[0054] Figure 3 (b), (e), and (h) are SEM images of the samples prepared in this example. It can be seen that after electroplating, urchin-shaped Ni is successfully deposited on the porous carbon surface.

[0055] Figure 4 (b) is the reflection loss value of the absorbing material prepared in this embodiment within the test range of 2-18 GHz. When the thickness of the absorbing coating is 1.99 mm, the minimum value of -46.53 dB is obtained at 11.63 GHz. When the thickness of the absorbing coating is 1.58 mm, the maximum absorbing bandwidth is 5.1 GHz.

[0056] Example 3

[0057] This embodiment provides a method for preparing a porous carbon-based composite absorbing material. The prepared product is a rape straw-derived porous carbon @Ni / NiO absorbing material. The preparation method is as follows:

[0058] The sample obtained in Example 2 was oxidized using a muffle furnace, and the oxidation treatment conditions were: oxidation temperature 450° C., holding time 5 min, heating rate 10° C. / min, and natural furnace cooling.

[0059] The product obtained above was tested, and the test content was exactly the same as in Example 1.

[0060] Figure 2 The XPS spectra of Examples 1-3 are compared with the XPS spectra of Examples 2 and 3 and the nickel and oxygen fine spectra. It can be seen that after oxidation, the peak intensity of O element in the XPS spectrum is enhanced, and the Ni 0 The peak of O1s disappeared, and the peak intensity corresponding to the O-Ni bond in the O1s fine spectrum increased, indicating that the metallic nickel was oxidized.

[0061] Figure 3 (c), (f), and (i) are SEM images of the samples prepared in this example. It can be seen that short-term low-temperature oxidation does not cause significant changes in the morphology of metallic nickel.

[0062] Figure 4 (c) is the reflection loss value of the absorbing material prepared in this embodiment within the test range of 2-18 GHz. When the thickness of the absorbing coating is 1.98 mm, a minimum value of -52.09 dB is obtained at 12.73 GHz, and a maximum absorbing bandwidth of 5.1 GHz is obtained.

[0063] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a porous carbon-based composite absorbing material, characterized in that: First, rape straw is pyrolyzed in an oxygen-free environment to generate porous carbon, and then Ni is electroplated on the surface of the porous carbon to obtain porous carbon@Ni. Finally, the porous carbon@Ni is heated and oxidized to obtain a porous carbon-based composite absorbing material, namely, a porous carbon@Ni / NiO composite absorbing material. The specific steps are as follows: Step 1, pre-treating the rape straw, specifically, first cutting the rape straw into sheets, washing and drying, then mixing the sheets of rape straw with a KOH aqueous solution, and magnetically stirring to obtain a mixture; hydrothermally treating the mixture, specifically, placing the mixture in a hydrothermal reactor, treating at a temperature of 150° C. for 2 hours, and then drying at 80° C.; Step 2, carbonizing the pretreated rape straw obtained in step 1, wherein the specific carbonization process is: nitrogen environment, heating rate of 5°C / min, carbonization temperature of 800°C, holding time of 1h, and natural furnace cooling; after carbonization, repeatedly washing with 5wt% dilute hydrochloric acid solution and deionized water until neutral, and drying at 80°C to obtain porous carbon based on rape straw; Step 3: The porous carbon obtained in step 2 is subjected to surface nickel electroplating treatment using an electroplating device. The specific electroplating operation is as follows: a flexible copper foil horizontally placed at the bottom of a cylindrical plating tank is used as a cathode, a circular nickel plate located directly above and parallel to the cathode is used as an anode, and the positive and negative electrodes are connected to the nickel plate and the copper foil respectively through an electrode clamp and a wire at 55°C and a current density of 15 mA / cm 2 Under the conditions, porous carbon is intermittently electroplated; after the electroplating treatment, the porous carbon is separated from the electroplating solution, washed and dried to obtain porous carbon@Ni; Step 4: The porous carbon@Ni obtained in step 3 is transferred into a muffle furnace for high-temperature oxidation treatment. The specific process is: air environment, heating rate of 10°C / min, heat treatment temperature of 450°C, holding time of 5min, cooling method of natural furnace cooling, and finally a porous carbon-based composite absorbing material, i.e., a porous carbon@Ni / NiO composite absorbing material, is obtained.

2. The method for preparing a porous carbon-based composite absorbing material according to claim 1, characterized in that: In step 1, the amount of rape straw flakes used is 3 g, and the KOH aqueous solution contains 3 g KOH and 54 mL deionized water.

3. The method for preparing a porous carbon-based composite absorbing material according to claim 1, characterized in that: In step 3, the dimensions of the cylindrical plating tank are: 85 mm in diameter and 100 mm in height.

4. The method for preparing a porous carbon-based composite absorbing material according to claim 1, characterized in that: In step 3, the intermittent electroplating method is: start the mechanical stirring device, stir mechanically for 60 seconds, then turn off the mechanical stirring device, let it stand for 45 minutes, then turn on the electroplating switch, electroplate for 30 seconds, repeat this "stirring-electroplating" operation twice, and electroplate for a total of 60 seconds.

5. The method for preparing a porous carbon-based composite absorbing material according to claim 1, characterized in that: In step 3, the plating solution consists of 1.68 mol / L NiCl2·H2O, 4 mol / L NH4Cl, 0.5 mol / L H3BO3, and 0.1 g / L porous carbon.

6. The method for preparing a porous carbon-based composite absorbing material according to claim 5, characterized in that: The porous carbon was dispersed in the electroplating solution by ultrasonic dispersion at a power of 480 W for 5 min.

7. A porous carbon-based composite absorbing material obtained by the preparation method according to any one of claims 1 to 6.

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