阅读说明：本技术 一种新型稻壳基磁性材料及制备方法和应用 (Novel rice hull-based magnetic material and preparation method and application thereof ) 是由 宋也男 束翔凤 赵振杰 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种新型稻壳基磁性材料及制备方法和应用,材料上属于磁性活性炭,应用上主要针对电磁波屏蔽。该方法以稻壳为碳源,通过水热预处理、脱硅预处理、球磨处理、磁化处理、活化处理和惰性气氛煅烧,得到了针状及多面体状的稻壳基磁性活性炭,电磁波屏蔽性能优异,具有巨大的环保意义与广阔的发展前景。本发明在脱硅预处理后,创新性地引入球磨工艺,将稻壳颗粒进一步研磨至平均粒径为100～1000目。此外,活性炭形成的孔隙和四氧化三铁的规则结构会增强界面极化和多重反射,这将极大促进其电磁波屏蔽性能。实施例的实验结果表明,最佳样品的最小反射率分别可达到-47.61、-51.73、-41.92和-52.14 dB,并且主要集中在C、X和Kμ波段,频宽最宽可达约13 GHz。(The invention discloses a novel rice hull-based magnetic material, a preparation method and application thereof, wherein the material belongs to magnetic activated carbon and is mainly used for shielding electromagnetic waves. The method takes rice hulls as a carbon source, and obtains the acicular or polyhedral rice hull-based magnetic activated carbon through hydrothermal pretreatment, desiliconization pretreatment, ball milling treatment, magnetization treatment, activation treatment and inert atmosphere calcination, so that the method has excellent electromagnetic wave shielding performance, and has great environmental protection significance and wide development prospect. After desiliconization pretreatment, the invention innovatively introduces a ball milling process to further grind the rice hull particles to an average particle size of 100-1000 meshes. In addition, the pores formed by the activated carbon and the regular structure of ferroferric oxide can enhance interface polarization and multiple reflections, which greatly promotes the electromagnetic wave shielding performance of the activated carbon. The experimental results of the examples show that the minimum reflectivity of the best sample can reach-47.61, -51.73, -41.92 and-52.14 dB respectively, and the best sample is mainly concentrated in C, X and K mu wave bands, and the bandwidth can reach about 13 GHz at the widest.)

1. A preparation method of a novel rice hull-based magnetic material is characterized by comprising the following specific steps:

(1) hydrothermal pretreatment:

after coarse washing of rice hulls, uniformly mixing clean rice hulls with deionized water, and then putting the mixture into a reaction kettle, wherein the reaction temperature is 160-200 ℃, the reaction pressure is 0.9-1.3 MPa, and the reaction time is 0.5-2.0 h; cooling the reaction kettle to room temperature, filtering and washing the rice hulls, and drying to obtain the rice hulls subjected to hydrothermal pretreatment; wherein the mass ratio of the rice hulls to the deionized water is 1: 10-30;

(2) desiliconization pretreatment:

fully mixing the rice hull obtained in the step (1) with a strong alkali solution, uniformly mixing, and then putting into a reaction kettle, wherein the reaction temperature is 100-200 ℃, the reaction pressure is 0.9-1.3 MP, and the reaction time is 1.0-4.0 h; cooling the reaction kettle to room temperature, filtering and washing the rice hulls until the pH value is 7-9, and drying to obtain the rice hulls subjected to desiliconization pretreatment; wherein the mass ratio of the rice hulls to the strong alkali solute is 1: 1-5;

(3) ball milling treatment:

putting the rice hulls obtained in the step (2) into a ball milling tank, adding zirconia balls, and carrying out ball milling for 60-120 min to obtain desiliconized rice hull powder with the mesh number of 100-1000 meshes;

(4) magnetization treatment:

uniformly mixing the desiliconized rice hull powder obtained in the step (3), a magnetizing agent and deionized water, and standing for 0.5-2 hours to obtain magnetized desiliconized rice hull powder; wherein the mass ratio of the desiliconized rice hull powder to the magnetizer to the deionized water is 1: 0.2-10;

(5) and (3) activating agent treatment:

magnetically stirring the magnetized desiliconized rice hull powder obtained in the step (4), an activating agent and deionized water for 0.5-6 h, uniformly soaking and mixing, standing for 1-8 h, and vacuum drying to obtain a calcination precursor; wherein the mass ratio of the desiliconized rice hull powder to the activating agent to the deionized water is 1-3.0: 0.1-10;

(6) calcining in an inert atmosphere:

putting the calcination precursor obtained in the step (5) into a tube furnace, introducing inert gas, keeping the calcination precursor at 400-800 ℃ for 1-4 h, washing, and carrying out vacuum drying to obtain rice hull-based magnetic activated carbon, namely the novel rice hull-based magnetic material; wherein:

the magnetizer is ferric chloride hexahydrate, ferric nitrate nonahydrate, ferric sulfate hydrate, ferric citrate monohydrate or ferrocene;

the activating agent is zinc chloride, potassium hydroxide, potassium carbonate or phosphoric acid.

2. The method of claim 1, wherein the strong alkaline solution is one of a sodium hydroxide solution and a potassium hydroxide solution.

3. The method of claim 1, wherein the inert gas is one of nitrogen and argon.

4. A novel rice hull-based magnetic material made by the method of claim 1.

5. Use of the novel rice hull-based magnetic material according to claim 4 for shielding electromagnetic waves.

Technical Field

The invention relates to the technical field of functional materials, in particular to a novel rice hull-based magnetic material, a preparation method and application in electromagnetic wave shielding.

Background

1. With the development of 5G (5 th generation mobile network) technology, electromagnetic shielding related problems of various electronic devices, military communication, reconnaissance, anti-reconnaissance and the like are more and more widely regarded. However, in the field of electromagnetic wave shielding at present, the problems of single component of the absorbing material, narrow absorption bandwidth of material performance, low minimum reflectance value, thick coating thickness and the like exist. In view of the above problems, research and development of novel and efficient electromagnetic wave shielding composite materials are urgently needed.

2. Many types of carbon-based materials, including activated carbon/porous carbon, graphene, carbon nanotubes, and carbon nanofibers, have been frequently used to prepare novel electromagnetic wave shielding materials. Among them, the activated carbon material shows a great potential in the aspect of electromagnetic wave shielding because it has a lower density, a larger specific surface area, and an excellent dielectric loss capability. The presence of a large number of pores firstly reduces the density of the absorbing material, secondly improves the impedance matching and forms interface polarization, while producing multiple reflections and scattering, and finally obtains good electromagnetic wave shielding performance. Rice hulls are an agricultural byproduct, consisting mainly of cellulose, lignin, silica and some trace elements. The rice hull, as a biomass activated carbon, has a natural plant fiber structure, and can be calcined at high temperature in the absence of oxygen to prepare a porous carbon layer structure with a rough surface. The rice hull-based activated carbon has rich sources, low material availability, sustainable development characteristic and easy regulation and control of a carbon layer structure. However, the rice hull-based activated carbon is more applied to environment restoration materials, such as adsorption, catalysis, concrete, building thermal insulation materials or energy storage materials, and the huge potential of the activated carbon in the field of electromagnetic wave shielding deserves deeper excavation.

3. The magnetic material is introduced into the rice hull-based activated carbon, so that the defects of high density, high sample loading rate and low dielectric loss of the traditional ferrite material can be overcome, high-efficiency and broadband absorption can be realized, and the electromagnetic wave shielding mechanism is more diversified. However, in the existing literature, the processing technology for the rice hull-based magnetic activated carbon is less optimized, and the morphology regulation related to the structure of the magnetic substance is not deeply researched.

Disclosure of Invention

The invention aims to provide a novel rice hull-based magnetic material, a preparation method and application thereof aiming at the defects of the prior art, and the prepared material has the characteristics of large specific surface area, light weight, high dielectric loss, high magnetic loss and the like and has excellent electromagnetic wave shielding performance.

The specific technical scheme for realizing the purpose of the invention is as follows:

a preparation method of a novel rice hull-based magnetic material comprises the following specific steps:

(1) hydrothermal pretreatment:

after coarse washing of rice hulls, uniformly mixing clean rice hulls with deionized water, and then putting the mixture into a reaction kettle, wherein the reaction temperature is 160-200 ℃, the reaction pressure is 0.9-1.3 MPa, and the reaction time is 0.5-2.0 h; cooling the reaction kettle to room temperature, filtering and washing the rice hulls, and drying to obtain the rice hulls subjected to hydrothermal pretreatment; wherein the mass ratio of the rice hulls to the deionized water is 1: 10-30;

(2) desiliconization pretreatment:

fully mixing the rice hull obtained in the step (1) with a strong alkali solution, uniformly mixing, and then putting into a reaction kettle, wherein the reaction temperature is 100-200 ℃, the reaction pressure is 0.9-1.3 MP, and the reaction time is 1.0-4.0 h; cooling the reaction kettle to room temperature, filtering and washing the rice hulls until the pH value is 7-9, and drying to obtain the rice hulls subjected to desiliconization pretreatment; wherein the mass ratio of the rice hulls to the strong alkali solute is 1: 1-5;

(3) ball milling treatment:

putting the rice hulls obtained in the step (2) into a ball milling tank, adding zirconia balls, and carrying out ball milling for 60-120 min to obtain desiliconized rice hull powder with the mesh number of 100-1000 meshes;

(4) magnetization treatment:

uniformly mixing the desiliconized rice hull powder obtained in the step (3), a magnetizing agent and deionized water, and standing for 0.5-2 hours to obtain magnetized desiliconized rice hull powder; wherein the mass ratio of the desiliconized rice hull powder to the magnetizer to the deionized water is 1: 0.2-10;

(5) and (3) activating agent treatment:

magnetically stirring the magnetized desiliconized rice hull powder obtained in the step (4), an activating agent and deionized water for 0.5-6 h, uniformly soaking and mixing, standing for 1-8 h, and vacuum drying to obtain a calcination precursor; wherein the mass ratio of the desiliconized rice hull powder to the activating agent to the deionized water is 1-3.0: 0.1-10;

(6) calcining in an inert atmosphere:

putting the calcination precursor obtained in the step (5) into a tube furnace, introducing inert gas, keeping the calcination precursor at 400-800 ℃ for 1-4 h, washing, and carrying out vacuum drying to obtain rice hull-based magnetic activated carbon, namely the novel rice hull-based magnetic material; wherein:

the magnetizer is ferric chloride hexahydrate, ferric nitrate nonahydrate, ferric sulfate hydrate, ferric citrate monohydrate or ferrocene;

the activating agent is zinc chloride, potassium hydroxide, potassium carbonate or phosphoric acid.

The strong alkali solution is one of sodium hydroxide solution and potassium hydroxide solution.

The inert gas is one of nitrogen and argon.

A novel rice hull-based magnetic material prepared by the method. The novel rice hull-based magnetic material is applied to electromagnetic wave shielding.

The invention aims to optimize the treatment process of the rice hull-based magnetic activated carbon, and specifically comprises pore size optimization, surface area expansion and multi-component construction; meanwhile, the detailed exploration is carried out on the morphology of the ferroferric oxide specifically comprising a needle shape or a polyhedron shape. The rice hull treatment generally comprises carbonization and activation, the new ball milling process has higher efficiency than the traditional method, and the even and fine desiliconized rice hull powder and the chemical reagent react more thoroughly. In summary, the rice hull-based magnetic activated carbon in the shape of needle or polyhedron is researched through designing components and optimizing the structure, the synergistic effect between the carbon layer and the magnetic substance is beneficial to improving impedance matching, and the composite material has the characteristics of large specific surface area, light weight, high dielectric loss and magnetic loss and the like, and has excellent electromagnetic wave shielding performance.

The invention has the following advantages:

1. the rice hull-based activated carbon has rich sources, low material availability, sustainable development characteristic and easy regulation and control of a carbon layer structure.

2. The ball milling process is innovatively introduced, and the rice hulls are ground to be more uniform and fine, so that the rice hulls are fully contacted with chemical reagents, and a good foundation is provided for subsequent reactions.

3. The rice hull-based magnetic activated carbon compounded ferroferric oxide particles belong to a regular needle-like or polyhedral shape and have novelty.

4. By adjusting the ratio of the magnetizing agent to the activating agent, the composition and microstructure of the composite material can be flexibly controlled.

5. The pores formed by the activated carbon and the regular structure of ferroferric oxide can enhance multi-interface polarization, the dielectric property and the magnetic property are both good, and a multiple loss mechanism is generated, so that the electromagnetic wave shielding property of the material is greatly promoted.

Drawings

FIG. 1 is an X-ray diffraction pattern of materials prepared in examples 1 and 2 of the present invention;

FIG. 2 is a plot of the nitrogen adsorption and desorption isotherms for the materials prepared in examples 1 and 2 of the present invention;

FIG. 3 is a field emission scanning electron microscope image of materials prepared in examples 1 and 2 of the present invention;

FIG. 4 is a graph showing the electromagnetic wave shielding performance of the materials obtained in examples 1 and 2 of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples and accompanying drawings.

Example 1

(1) Hydrothermal pretreatment: after 10 g of rice hulls are roughly washed, the clean rice hulls and deionized water are taken according to the mass ratio of 1:20, the mixture is uniformly mixed and then placed into a reaction kettle with the volume of 1L, the reaction temperature is 180 ℃, the reaction pressure is 1.1 MPa, and the reaction time is 1.0 h. Cooling the reaction kettle to room temperature, filtering and washing the rice hulls, and drying to obtain the rice hulls subjected to hydrothermal pretreatment;

(2) desiliconization pretreatment: and (2) fully mixing the rice hulls obtained in the step (1) with a sodium hydroxide solution with the volume of 200ml and the solute mass fraction of 15 wt%, uniformly mixing, putting into a reaction kettle with the volume of 1L, and keeping the reaction temperature at 120 ℃, the reaction pressure at 1.1 MP and the heat preservation time at 2.0 h. Cooling the reaction kettle to room temperature, filtering and washing the rice hulls until the pH value is about 8, and drying to obtain the rice hulls subjected to desiliconization pretreatment;

(3) ball milling treatment: putting the rice hulls obtained in the step (2) into a ball milling tank, adding zirconia balls, and carrying out ball milling for 90 min to obtain desiliconized rice hull powder with the average particle size of 325 meshes;

(4) magnetization treatment: selecting ferric chloride hexahydrate as a magnetizer, uniformly mixing 1.0 g of the desiliconized rice hull powder obtained in the step (3), 0.8 g of the magnetizer and 10.0 ml of deionized water, and standing for 1 h to obtain magnetized desiliconized rice hull powder;

(5) and (3) activating agent treatment: and (3) selecting zinc chloride as an activating agent, magnetically stirring 1.0 g of the magnetized desiliconized rice hull powder obtained in the step (4), 1.0 g of the activating agent and 10.0 ml of deionized water for 4 hours, uniformly soaking and mixing, standing for 6 hours, and drying in vacuum to obtain a calcination precursor.

(6) Calcining in an inert atmosphere: and (5) placing the calcination precursor obtained in the step (5) into a tube furnace, introducing nitrogen gas, keeping the temperature at 600 ℃ for 2 h, washing, and drying in vacuum to obtain the rice hull-based magnetic activated carbon.

The rice hull-based magnetic activated carbon (needle-shaped) prepared in example 1 was subjected to a performance test, specifically, it was mixed with paraffin wax, the sample ratio was 50%, and an electromagnetic wave shielding performance test experiment was performed using a vector network analyzer (VNA, AV 3672B-S). The experimental result shows that as shown in figure 1, the XRD pattern of example 1 is consistent with the characteristic peaks of PDF #65-3107, which indicates that the ferroferric oxide crystal phase 20 exists^o~30 ^oThe broad peak of (a) represents the carbon phase; as shown in fig. 2a, an embodiment1, the specific surface area is 941.98m after nitrogen adsorption and desorption isothermal test²(ii)/g; as shown in fig. 3a, the micro-morphology of example 1 is micron-sized needle-like particles; as shown in FIG. 4a, the minimum reflectance of example 1 is-52.137, -41.918, -51.733 and-47.614 dB at 1.669, 2.002, 2.393 and 3.000 mm thickness, respectively, and is mainly concentrated in C, X and K μ bands, and the bandwidth can reach about 13 GHz at the widest.

Example 2

(1) Hydrothermal pretreatment: after 10 g of rice hulls are roughly washed, the clean rice hulls and deionized water are taken according to the mass ratio of 1:20, the mixture is uniformly mixed and then placed into a reaction kettle with the volume of 1L, the reaction temperature is 180 ℃, the reaction pressure is 1.1 MPa, and the heat preservation time is 1.0 h. Cooling the reaction kettle to room temperature, filtering and washing the rice hulls, and drying to obtain the rice hulls subjected to hydrothermal pretreatment;

(2) desiliconization pretreatment: and (2) fully mixing the rice hulls obtained in the step (1) with a sodium hydroxide solution with the volume of 200ml and the solute mass fraction of 15 wt%, uniformly mixing, putting into a reaction kettle with the volume of 1L, and keeping the reaction temperature at 120 ℃, the reaction pressure at 1.1 MP and the heat preservation time at 2.0 h. Cooling the reaction kettle to room temperature, filtering and washing the rice hulls until the pH value is about 8, and drying to obtain the rice hulls subjected to desiliconization pretreatment;

(3) ball milling treatment: putting the rice hulls obtained in the step (2) into a ball milling tank, adding zirconia balls, and carrying out ball milling for 90 min to obtain desiliconized rice hull powder with the average particle size of 325 meshes;

(4) magnetization treatment: selecting ferric chloride hexahydrate as a magnetizer, uniformly mixing 1.0 g of the desiliconized rice hull powder obtained in the step (3), 0.6 g of the magnetizer and 10.0 g of deionized water, and standing for 1 h to obtain magnetized desiliconized rice hull powder;

(5) and (3) activating agent treatment: and (3) selecting zinc chloride as an activating agent, magnetically stirring 1.0 g of the magnetized desiliconized rice hull powder obtained in the step (4), 2.0 g of the activating agent and 10.0 g of deionized water for 4 hours, uniformly soaking and mixing, standing for 6 hours, and drying in vacuum to obtain a calcination precursor.

(6) Calcining in an inert atmosphere: and (5) placing the calcination precursor obtained in the step (5) into a tube furnace, introducing nitrogen gas, keeping the temperature at 600 ℃ for 2 h, washing, and drying in vacuum to obtain the rice hull-based magnetic activated carbon.

The rice hull-based magnetic activated carbon (polyhedral) prepared in example 2 was subjected to a performance test, specifically, an electromagnetic wave shielding performance test experiment was performed using a vector network analyzer (VNA, AV36 3672B-S) by mixing it with paraffin wax at a sample ratio of 50%. The experimental result shows that as shown in figure 1, XRD of example 2 is consistent with characteristic peaks of PDF #65-3107, which indicates that a ferroferric oxide crystal phase 20 exists^o~30 ^oThe broad peak of (a) represents the carbon phase; as shown in FIG. 2b, the nitrogen adsorption-desorption isothermal test of example 2 gave a specific surface area of 892.74 m²(ii)/g; as shown in fig. 3b, the micro-topography of example 2 is micro-scale polyhedral particles; as shown in fig. 4b, the minimum reflectance of example 2 was-59.534 and-61.273 dB at 1.870 and 2.001 mm thickness, respectively, and was mainly concentrated in the K μ band.