Preparation method and application of high-wave-absorbing-performance lignin-based porous carbon based on thermal oxidation treatment

Abstract

The invention discloses a preparation method and application of high-wave-absorbing-performance lignin-based porous carbon based on thermal oxidation treatment.The preparation method comprises the steps that firstly, pre-dried lignin is subjected to pyrolysis in a medium-temperature inert environment, a pyrolysis product is placed in a constant-temperature environment to be subjected to thermal oxidation treatment, the treated material is subjected to secondary pyrolysis, and a carbon precursor is obtained; and fully grinding and mixing the obtained carbon precursor and an alkaline activator, and performing high-temperature activation and water washing treatment to obtain the lignin porous carbon material with high wave-absorbing property. The high-performance carbon-based wave-absorbing material is prepared by using bulk waste lignin of biological refining engineering as a raw material through a thermal oxidation treatment method, has the advantages of simple preparation method and excellent material performance, realizes high-value utilization of wastes, and has a wide market application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass functional material manufacturing, and in particular to a preparation method and application of lignin-based porous carbon with high wave absorption performance based on thermal oxygen treatment. Background Art

[0002] Biorefining projects generate large amounts of lignin waste. Due to the limitations of lignin stabilization methods, most waste lignin is used for internal energy recovery as low-value fuel or directly landfilled. However, lignin is difficult to degrade, has a long landfill cycle, and easily contaminates soil and water sources. Direct incineration can exacerbate air pollution. Therefore, developing low-cost, pollution-free processes to effectively convert lignin into functional materials is an urgent problem in current biorefining processes.

[0003] In recent years, while wireless electronic device technology has been widely used, electromagnetic pollution has become increasingly serious. This not only interferes with the normal operation of electronic devices but can also cause irreversible damage to human health. Therefore, the development of inexpensive absorbing materials with excellent microwave absorption properties is of great significance. Currently, common electromagnetic wave absorbing materials mainly include carbon-based materials, silicon-based ceramics, and metal-containing materials. Among them, carbon-based materials have become a research hotspot in the field of microwave absorption due to their advantages such as low mass density, large specific surface area, good chemical stability, adjustable dielectric constant, good conductivity, and low price. Lignin, a waste product from biomass refining, is the most abundant aromatic compound on Earth. Its conversion into an ideal precursor material for carbon-based absorbers has great potential and can also solve the problem of recycling waste lignin.

[0004] However, in the prior art, the carbon-based absorbing material prepared using lignin as raw material has poor absorbing performance and is highly dependent on metal loading to improve its performance. Summary of the Invention

[0005] The present invention aims to address the defects of the prior art and provide a method for preparing and applying lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] In a first aspect, a method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment is provided, characterized in that it comprises the following steps:

[0008] S1: Place the dried lignin raw material into an atmosphere furnace, introduce inert gas, and heat it to a first target temperature at a constant heating rate for constant temperature pyrolysis. After cooling, take it out and grind it into powder;

[0009] S2: placing the powder in a tube furnace at a constant temperature for a period of time for thermal oxidation treatment, with both ends of the tube furnace connected to air;

[0010] S3: placing the sample powder after the thermal oxidation treatment in the center of a tube furnace, heating it to a second target temperature at a constant heating rate under an inert gas atmosphere, and then performing a secondary pyrolysis treatment to obtain a carbon precursor;

[0011] S4: After the carbon precursor and the alkaline activator are fully ground in a certain ratio, they are transferred to the center of a tube furnace and activated at high temperature for a certain period of time under the protection of inert gas. After cooling, the activated product is obtained;

[0012] S5: The activated product is mixed with dilute hydrochloric acid and stirred thoroughly, and then washed with deionized water until the pH value is neutral. The solid matter is dried and ground to obtain lignin-based porous carbon.

[0013] Furthermore, in S1, the heating rate of the atmosphere furnace is 5-10°C / min, the first target temperature is 500-700°C, and the pyrolysis time is 0.5-1.5h.

[0014] Furthermore, in S2, the temperature of the thermal oxidation treatment environment in the tube furnace is 330-350° C., and the thermal oxidation treatment time is 1-7 hours.

[0015] Furthermore, in S3, the heating rate of the tubular furnace is 5-10°C / min, the second target temperature is 500-700°C, and the pyrolysis time is 0.5-1.5h.

[0016] Furthermore, in S4, the alkaline activator includes KOH, K2CO3, NaOH, and Na2CO3.

[0017] Furthermore, in S4, the mixing mass ratio of the carbon precursor and the alkaline activator is 1:1-1:4.

[0018] Furthermore, in S4, the heating rate of the tubular furnace is 5-10°C / min, the high temperature activation temperature is 700-900°C, and the activation time is 30-120 min.

[0019] Furthermore, in S1, S3 and S4, nitrogen is used as the inert gas, and the nitrogen flow rate is 100 mL / min.

[0020] In a second aspect, a lignin-based porous carbon is provided, characterized in that it is prepared by the method described in the first aspect.

[0021] In the third aspect, an application of the lignin-based porous carbon described in the second aspect in an electromagnetic wave absorbing material is provided, characterized in that the minimum reflection loss of the lignin-based porous carbon to electromagnetic waves in the frequency range of 2-18 GHz is -31.72 to -58.37 dB, and the effective absorption bandwidth is 3.99 to 5.31 GHz.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention provides a method for preparing highly absorbing lignin-based porous carbon based on thermal oxygen treatment. Lignin, a bulk waste from biorefining projects, is used as a carbon precursor. The lignin-derived carbon-based absorbing material is prepared through thermal oxygen treatment. The material has the advantages of excellent absorbing performance and small optimal matching thickness, thus realizing the high-value utilization of waste lignin.

[0024] 2. The preparation process of the present invention is simple, low-cost, green and environmentally friendly, can realize waste recycling, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 3D and 2D reflection loss diagrams of the porous carbon HLAC-1 in Example 1 of the present invention;

[0026] Figure 2 3D and 2D reflection loss diagrams of the porous carbon HLAC-3 in Example 2 of the present invention;

[0027] Figure 3 3D and 2D reflection loss diagrams of the porous carbon HLAC-5 in Example 3 of the present invention;

[0028] Figure 4 3D and 2D reflection loss diagrams of the porous carbon HLAC-7 in Example 4 of the present invention;

[0029] Figure 5 3D and 2D reflection loss diagrams of the porous carbon HLAC-0 in Comparative Example 1 of the present invention;

[0030] Figure 6 is a nitrogen desorption isotherm diagram of the porous carbon HLAC-5 in Example 3 of the present invention;

[0031] Figure 7 This is a pore size distribution diagram of the porous carbon HLAC-5 in Example 3 of the present invention;

[0032] Figure 8 This is a SEM image of the porous carbon HLAC-5 in Example 3 of the present invention;

[0033] Figure 9The reflection loss curve of the porous carbon HLAC-5 in the thickness range of 1 mm to 5 mm and the impedance matching of the thickness of 1.48 mm in Example 3 of the present invention are shown. DETAILED DESCRIPTION

[0034] In order to deepen the understanding of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0035] Example 1

[0036] The preparation method of lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment is as follows:

[0037] S1: 100.0 g of pre-dried lignin raw material is spread on a stainless steel tray and moved into the center of an atmosphere furnace. The lignin raw materials used include but are not limited to alkali lignin, fractionated lignin, lignin derivatives, and small molecule lignin;

[0038] Under the protection of a nitrogen atmosphere, the gas in the atmosphere furnace was repeatedly extracted three times to ensure that the atmosphere furnace was in an inert atmosphere state; then, the mixture was heated to 600°C at a constant heating rate of 10°C / min and maintained for 30 minutes, and then ground into powder after cooling.

[0039] S2: 10.0 g of the above powder was placed in a 340° C. constant temperature tube furnace for 1 h of thermal oxidation treatment. Both ends of the tube furnace were connected to the air to ensure that the sample powder could fully contact the air.

[0040] S3: The sample after thermal oxidation treatment was placed in the center of a tube furnace, and heated to 600°C at a constant heating rate of 10°C / min under a nitrogen atmosphere and maintained at this temperature for 60 min for secondary thermal deoxidation treatment to obtain a carbon precursor.

[0041] S4: The carbon precursor and KOH were fully ground in a mass ratio of 1:3, transferred to the center of a tube furnace, and heated to 800°C at a heating rate of 10°C / min under the protection of a nitrogen atmosphere and maintained for 90 min. After cooling, an activated product was obtained.

[0042] S5: The activated product is mixed with dilute hydrochloric acid, stirred thoroughly, and allowed to stand. The solid matter is then filtered out and repeatedly washed with deionized water until the pH value of the washed liquid is neutral. The solid matter is dried to obtain a lignin-based porous carbon material, which is labeled HLAC-1.

[0043] Example 2

[0044] A lignin-based porous carbon with high microwave absorption performance based on thermal oxidation treatment and a preparation method thereof. In step S2, the thermal oxidation treatment time is set to 3 hours, and the remaining steps are the same as in Example 1. The obtained lignin-based porous carbon material is labeled as HLAC-3.

[0045] Example 3

[0046] A lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment and a preparation method thereof. In step S2, the thermal oxygen treatment time is set to 5 hours, and the remaining steps are the same as in Example 1. The obtained lignin-based porous carbon material is labeled as HLAC-5.

[0047] Example 4

[0048] A lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment and a preparation method thereof. In step S2, the thermal oxygen treatment time is set to 7 hours, and the remaining steps are the same as in Example 1. The obtained lignin-based porous carbon material is labeled as HLAC-7.

[0049] Comparative Example 1

[0050] A method for preparing lignin porous carbon, the specific steps are as follows:

[0051] S1: 100.0 g of pre-dried lignin raw material is spread on a stainless steel tray and moved into the center of an atmosphere furnace. The lignin raw materials used include but are not limited to alkali lignin, fractionated lignin, lignin derivatives, and small molecule lignin;

[0052] Under the protection of a nitrogen atmosphere, the gas in the atmosphere furnace was repeatedly extracted three times to ensure that the atmosphere furnace was in an inert atmosphere state; then, the mixture was heated to 600°C at a constant heating rate of 10°C / min and maintained for 30 minutes, and then ground into powder after cooling.

[0053] S2: The sample powder was placed in the center of a tube furnace, and heated to 600°C at a constant heating rate of 10°C / min under a nitrogen atmosphere and maintained at that temperature for 60 min for a secondary thermal deoxidation treatment to obtain a carbon precursor.

[0054] S3: The carbon precursor and KOH were fully ground in a mass ratio of 1:3, transferred to the center of a tube furnace, and heated to 800°C at a heating rate of 10°C / min under the protection of a nitrogen atmosphere and maintained for 90 min. After cooling, an activated product was obtained.

[0055] S4: The activated product is mixed with dilute hydrochloric acid and stirred thoroughly and allowed to stand. The solid matter is then filtered out and repeatedly washed with deionized water until the pH value of the washed liquid is neutral. The solid matter is dried to obtain a lignin-based porous carbon material, which is labeled as HLAC-0.

[0056] The electromagnetic parameter tests were performed on the lignin-based porous carbon materials prepared in Examples 1-4 and Comparative Example 1:

[0057] The dielectric constant and magnetic permeability of the absorbing material were tested using a coaxial method using a vector network. The prepared lignin-based porous carbon was mixed with paraffin wax at a mass ratio of 2:8 at 60°C. Hollow rings with an inner diameter of 3.07 mm, an outer diameter of 7.00 mm, and a thickness of 2 mm were formed in a specific metal mold. The electromagnetic parameters of the concentric rings were measured using an N5230C vector network analyzer in the 2-18 GHz frequency range. The reflection loss (RL) value can be calculated using transmission line theory:

[0058]

[0059] Where Z0 represents the inherent impedance of free space, Z in Represents the input impedance of the absorber. ε r (ε r =ε'-jε") represents the complex dielectric constant, μ r (μ r =μ'-jμ") represents the complex magnetic permeability, f is the frequency of the electromagnetic wave, d is the thickness of the absorbing material, and c is the speed of the electromagnetic wave in free space. The smaller the value of RL, the better the absorbing performance of the absorbing material.

[0060] In Example 1, the lignin porous carbon absorbing material HLAC-1 subjected to thermal oxidation treatment for 1 hour was tested and calculated based on electromagnetic parameters to obtain 3D and 2D reflection loss diagrams as shown in FIG. Figure 1 As shown. The minimum reflection loss value RL of the lignin-based porous carbon material HLAC-1 under the matching thickness of 1.79mm min =-41.79dB.

[0061] In Example 2, the lignin porous carbon absorbing material HLAC-3 subjected to thermal oxidation treatment for 3 hours was tested and calculated based on electromagnetic parameters to obtain 3D and 2D reflection loss diagrams as shown in FIG. Figure 2 As shown. The minimum reflection loss value RL of the lignin-based porous carbon material HLAC-3 under the matching thickness of 4.79mm min =-51.93dB.

[0062] In Example 3, the lignin porous carbon absorbing material HLAC-5 subjected to thermal oxidation treatment for 5 hours was tested and calculated based on electromagnetic parameters to obtain 3D and 2D reflection loss diagrams as shown in FIG. Figure 3 As shown. The minimum reflection loss value RL of the lignin-based porous carbon material HLC-5 is 1.48 mm thick. min =-58.37dB.

[0063] In Example 4, the lignin porous carbon absorbing material HLAC-7 subjected to thermal oxidation treatment for 7 hours was tested and calculated based on electromagnetic parameters to obtain 3D and 2D reflection loss diagrams as shown in FIG. Figure 4 As shown. The minimum reflection loss value RL of the lignin-based porous carbon material HLAC-7 under the matching thickness of 1.82mm min =-41.50dB.

[0064] In Comparative Example 1, the lignin porous carbon absorbing material HLAC-0 without thermal oxidation treatment was tested and calculated based on electromagnetic parameters to obtain the 3D and 2D reflection loss diagrams as shown in FIG. Figure 5 As shown. The minimum reflection loss value RL of the lignin-based porous carbon material HLAC-0 under the matching thickness of 1.82mm min =-31.72dB.

[0065] It can be seen that HLAC-5 has the best wave absorption performance, HLAC-0 has the worst wave absorption performance, the lignin-based porous carbon material that has been thermally oxygenated has better wave absorption effect than that that has not been thermally oxygenated, and the best wave absorption effect can be obtained by thermally oxygenating for 5 hours.

[0066] Then, the pore structure parameters of the above-mentioned lignin-based porous carbon samples HLAC-1, HLAC-3, HLAC-5, HLAC-7, and HLAC-0 were analyzed.

[0067] Table 1 shows the pore structure parameters of the lignin-based porous carbon samples HLAC-1, HLAC-3, HLAC-5, HLAC-7, and HLAC-0 prepared in Examples 1-4 and Comparative Example 1.

[0068] Table 1

[0069]

[0070] Take HLAC-5 for nitrogen desorption test and pore size measurement, Figure 1 、 2The nitrogen desorption isotherm and pore size distribution of lignin-based porous carbon HLAC-5 are shown in the figure. The isotherms show a combination of Type I and Type IV, and a distinct hierarchical pore structure is present. This hierarchical pore structure overcomes the absorption limitations of single-scale pores by physically extending the wave propagation path, optimizing impedance matching, and inducing multiple interferences. This significantly enhances the multiple reflection and scattering effects of electromagnetic waves, thereby improving electromagnetic wave absorption.

[0071] Take HLAC-5 for electron microscopy scanning, Figure 3 This is a SEM image of the lignin-based porous carbon HLAC-5 absorber. Microstructural characterization clearly reveals an irregular porous carbon structure on the surface of the activated sample, with abundant and dense small pores. This increases the number of heterogeneous interfaces and effectively improves interfacial polarization. This enhanced interfacial polarization of lignin-based porous carbon significantly improves its absorption performance by enhancing the conversion efficiency of electromagnetic energy to thermal energy, optimizing impedance matching, and synergizing multiple loss mechanisms.

[0072] like Figure 4 As shown in the figure, the impedance matching value of the HLAC-5 material with a thickness of 1.48 mm is close to 1. The closer the impedance matching value of the absorbing material is to 1, the better the matching degree of the microwave absorbing material is, which is a decisive factor in judging high-performance microwave absorbing materials.

[0073] Through Examples 1-4 and Comparative Example 1, it can be seen that the lignin porous carbon based on thermal oxidation treatment in the present invention has good electromagnetic wave absorption performance. By reasonably controlling the thermal oxidation treatment time to about 5h, the absorption performance of the porous carbon can be effectively controlled, and the RL min =-58.37dB (>99.999% absorption), thereby obtaining a high-performance porous carbon absorbing material with practical application significance.

[0074] The above specific implementation methods are only for illustrating the technical concept and structural features of the present invention, and the purpose is to enable relevant persons familiar with this technology to implement them accordingly. However, the above content does not limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment, characterized in that: The steps include: S1: Place the dried lignin raw material into an atmosphere furnace, introduce inert gas, and heat it to the first target temperature at a constant heating rate for constant temperature pyrolysis. After cooling, take it out and grind it into powder; S2: placing the powder in a tube furnace at a constant temperature for a period of time for thermal oxidation treatment, with both ends of the tube furnace connected to air; S3: placing the sample powder after the thermal oxidation treatment in the center of a tube furnace, heating it to a second target temperature at a constant heating rate under an inert gas atmosphere, and then performing a secondary pyrolysis treatment to obtain a carbon precursor; S4: After the carbon precursor and the alkaline activator are fully ground in a certain ratio, they are transferred to the center of a tube furnace and activated at high temperature for a certain period of time under the protection of inert gas. After cooling, the activated product is obtained; S5: The activated product is mixed with dilute hydrochloric acid and stirred thoroughly, and then washed with deionized water until the pH value is neutral. The solid matter is dried and ground to obtain lignin-based porous carbon.

2. The method for preparing a lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In S1, the heating rate of the atmosphere furnace is 5-10°C / min, the first target temperature is 500-700°C, and the pyrolysis time is 0.5-1.5h.

3. The method for preparing a lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In S2, the temperature of the thermal oxidation treatment environment in the tube furnace is 330-350° C., and the thermal oxidation treatment time is 1-7 hours.

4. The method for preparing a lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In S3, the heating rate of the tubular furnace is 5-10°C / min, the second target temperature is 500-700°C, and the pyrolysis time is 0.5-1.5h.

5. The method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In said S4, the alkaline activator includes KOH, K2CO3, NaOH, and Na2CO3.

6. The method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In the above-mentioned S4, the mixing mass ratio of the carbon precursor and the alkaline activator is 1:1-1:

4.

7. The method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In the step S4, the heating rate of the tubular furnace is 5-10° C. / min, the high-temperature activation temperature is 700-900° C., and the activation time is 30-120 min.

8. The method for preparing lignin-based porous carbon with high microwave absorption performance based on thermal oxygen treatment according to claim 1, characterized in that: In S1, S3 and S4, nitrogen is used as the inert gas, and the nitrogen flow rate is 100 mL / min.

9. A lignin-based porous carbon, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. Use of the lignin-based porous carbon as claimed in claim 9 in an electromagnetic wave absorbing material, characterized in that: The minimum reflection loss of the lignin-based porous carbon to electromagnetic waves in the frequency range of 2-18 GHz is -31.72 to -58.37 dB, and the effective absorption bandwidth is 3.99 to 5.31 GHz.

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