A self-supporting carbon material, a method for preparing the same, and an application thereof

Abstract

The application discloses a kind of self-supporting carbon materials and its preparation method and application, it is related to the technical field of preparation of carbon material, preparation method includes the following steps: S1: paperboard is cut and transferred to high-temperature furnace and is carbonized, then sequentially cooling, washing obtains carbonized paperboard;S2: the carbonized paperboard is activated, washed, dried to obtain self-supporting carbon material, wherein, the carbonized paperboard is activated in S2 including carbonized paperboard is transferred to NH4H2PO4 Solution and is soaked.The application is carbonized by paperboard as raw material to prepare carbon material, utilize the rigidity of paperboard itself, realize the function of self-supporting, to avoid the support of current collector needs the addition of additional adhesive, influence the conductivity and specific surface area of carbon material, and the interface between carbon film and current collector between the interface between carbon film and current collector reduces the performance of porous carbon material.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon material preparation, and in particular to a self-supporting carbon material and a preparation method and application thereof. Background Art

[0002] In recent years, a large number of biomass-derived carbon materials have been synthesized and applied in energy, adsorption and other fields, such as batteries, capacitors, gas adsorption and water purification. However, the complex preparation methods of most biochars and the modification process using expensive modifiers have greatly hindered their large-scale application. At the same time, the carbon films used in most fields are usually prepared by mixing the converted biomass carbon powder with a powdered binder and coating it on a current collector, such as titanium sheet or carbon paper. It is worth noting that in the process of converting biochar into carbon powder, the original unique biological structure of biomass and its derivatives will be destroyed.

[0003] Furthermore, the addition of non-conductive polymer binders such as polyvinylidene fluoride not only significantly reduces the conductivity and specific surface area of ​​the biochar material, but also significantly reduces the performance of the porous carbon material due to the interfacial resistance between the carbon film and the current collector. Furthermore, the current collector used in the coating process is expensive and the preparation process is relatively complex, which greatly increases the cost and cycle time of electrode preparation.

[0004] In view of this, this application is filed. Summary of the Invention

[0005] The purpose of the present invention is to provide a self-supporting carbon material and its preparation method and application. The carbon material is prepared by carbonizing cardboard as a raw material, and the rigidity of the cardboard itself is utilized to achieve the self-supporting function, so as to solve the problem in the prior art that the use of a current collector for support requires the addition of an additional adhesive, which affects the electrical conductivity and specific surface area of ​​the carbon material, the weak adhesion between the carbon film and the current collector, and the increase of the interface resistance between the carbon film and the current collector, thereby reducing the performance of the porous carbon material.

[0006] The present invention is implemented through the following technical solutions: First, an embodiment of the present invention provides a method for preparing a self-supporting carbon material, comprising the following steps:

[0007] S1: After cutting, the cardboard is transferred to a high-temperature furnace for carbonization, and then cooled and cleaned in sequence to obtain carbonized cardboard;

[0008] S2: activating, washing, and drying the carbonized paperboard to obtain a self-supporting carbon material.

[0009] As an optional embodiment, the activation of the carbonized paperboard in S2 includes transferring the carbonized paperboard to an NH4H2PO4 solution for immersion.

[0010] As an optional implementation manner, the carbonization in S1 is the first carbonization, and after the carbonized paperboard is transferred to the NH4H2PO4 solution for soaking in S2, the carbonized paperboard soaked in the NH4H2PO4 solution is further subjected to a second carbonization.

[0011] As an optional implementation, the activation of the carbonized paperboard in S2 further includes washing and drying the carbonized paperboard after the second carbonization for the first time, and then transferring the carbonized paperboard to a H3PO4 solution for immersion.

[0012] As an optional implementation manner, the concentration of the NH4H2PO4 solution is 4-6 mol / L, and the soaking time in the NH4H2PO4 solution is 20-30 h.

[0013] As an optional implementation manner, the concentration of the H3PO4 solution is 2-4 mol / L, and the soaking time in the H3PO4 solution is 6-10 h.

[0014] As an optional embodiment, the temperature of the first carbonization is 350-450° C., and the carbonization time is 2-4 hours;

[0015] The temperature of the second carbonization is 500-700°C, and the carbonization time is 1-3 hours;

[0016] The first carbonization and the second carbonization are both carried out under N2 protection.

[0017] As an optional embodiment, S2 further includes washing the carbonized paperboard soaked in the H3PO4 solution for a second time and drying it for a second time to obtain a self-supporting carbon material;

[0018] The first washing comprises ultrasonic cleaning in deionized water to remove residual NH4H2PO4 impurities, and the first drying comprises drying in an oven at a temperature of 70 to 90°C;

[0019] The second washing includes ultrasonic cleaning with deionized water until the pH reaches 6.5-7.5, and then ultrasonic cleaning with anhydrous ethanol. The second drying includes drying in an oven at a temperature of 70-90°C.

[0020] Secondly, an embodiment of the present invention further provides a self-supporting carbon material, which is prepared by the above preparation method.

[0021] Finally, an embodiment of the present invention also provides an application of a self-supporting carbon material, including using the self-supporting carbon material for CO2 capture and brackish water desalination.

[0022] Compared with the prior art, the embodiments of the present invention have the following advantages and beneficial effects:

[0023] 1. The embodiment of the present invention uses a simple process to convert waste cardboard into a self-supporting carbon material without the need for additional binders, thereby making greater use of the active sites of the material, simplifying the preparation process, and significantly reducing costs.

[0024] 2. The self-supporting carbon film prepared in the present invention is made from corrugated paperboard made from municipal solid waste, which is rich in cellulose, soluble starch, and some lignin. This process utilizes carbonization, NH4H2PO4 as a bifunctional activator, and H3PO4 for surface chemical modification. This process achieves synergistic optimization of adsorption performance and surface chemical properties. The N / P-codoped self-supporting carbon material can be prepared through a simple carbonization process combined with activation with the bifunctional NH4H2PO4 activator and surface chemical modification with H3PO4. The interweaving of hemicellulose, lignin, and starch contained in the raw material imparts excellent stability to the entire carbon skeleton. Activation with NH4H2PO4 produces a large specific surface area and achieves N / P-codoping. The material is then further surface-modified with the low-toxic, mild H3PO4 to maintain a high oxygen atom content and further improve the hydrophilicity of the electrode.

[0025] 3. The self-supporting carbon material provided by the embodiment of the present invention can be directly used for CO2 capture and brackish water desalination without the need for additional binders, thereby making greater use of the active sites of the material, simplifying the preparation process, and significantly reducing costs; converting the cardboard waste commonly found in cities into high-performance adsorption materials to achieve resource utilization, and can be applied to air CO2 capture and capacitor deionization fresh water production; adsorbent materials for heavy metals and dyes; supercapacitor electrodes; negative electrode materials in the battery field; and various uses in various water treatment fields in medicine. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0027] Figure 1 Schematic diagram of the preparation process of self-supporting carbon membrane from waste cardboard and its application in CO2 adsorption and CDI brackish water desalination;

[0028] Figure 2 These are the optical photographs and scanning electron microscope images in Example 11;

[0029] in, Figure 2a is an optical photograph of the original waste cardboard PB, Figure 2 b. Figure 2 c and Figure 2 d are SEM images of the original waste cardboard PB at different magnifications;

[0030] Figure 2 e is an optical photograph of Carbonized PB, Figure 2 f. Figure 2 g and Figure 2 h are SEM images of Carbonized PB at different magnifications;

[0031] Figure 2 i is the optical photograph of Activated PB, Figure 2 j. Figure 2 k and Figure 2 l are SEM images of Activated PB at different magnifications;

[0032] Figure 3 is the detection spectrum in Example 11;

[0033] in, Figure 3 a is the XRD patterns of Carbonized PB and Activated PB;

[0034] Figure 3 b is the RM map of Carbonized PB and Activated PB;

[0035] Figure 3 c is the XPS spectra of Carbonized PB and Activated PB;

[0036] Figure 3 d is the N 1s XPS spectrum of activated PB;

[0037] Figure 4 Nitrogen adsorption-desorption isotherms of Carbonized PB and Activated PB materials in Example 11;

[0038] Figure 5 is the pore size distribution diagram of Carbonized PB and Activated PB materials in Example 11;

[0039] Figure 6 CO2 adsorption-desorption isotherms of Carbonized PB and Activated PB materials in Example 11;

[0040] Figure 7The CO2 adsorption stability test results of Activated PB in Example 11;

[0041] Figure 8 The cyclic voltammetry test results of Carbonized PB and Activated PB materials in Example 11;

[0042] Figure 9 The rate performance test results of Carbonized PB and Activated PB materials in Example 11;

[0043] Figure 10 The charge-discharge test results (1 A / g) of the Carbonized PB and Activated PB materials in Example 11 are shown;

[0044] Figure 11 Impedance test results of Carbonized PB and Activated PB materials in Example 11;

[0045] Figure 12 ion transport evaluation results of Carbonized PB and Activated PB materials in Example 11;

[0046] Figure 13 The stability test results (100 mV / s) of the activated PB material in Example 11 are as follows;

[0047] Figure 14 The test results of Carbonized PB and Activated PB electrode materials in Example 11 at a voltage of 1.2 V;

[0048] Figure 15 The conductivity-time curves of the Carbonized PB and Activated PB electrode materials in Example 11 at a flow rate of 30 mL / min and a 500 mg / L NaCl solution;

[0049] Figure 16 The relationship between the adsorption amount of Carbonized PB and Activated PB electrode materials and time in Example 11;

[0050] Figure 17 The CDI Ragone plots of the Carbonized PB and Activated PB electrode materials in Example 11 and the adsorption amounts at different feed solution concentrations are shown;

[0051] Figure 18This is a comparison of the NaCl adsorption performance of the activated PB electrode material in Example 11 and common biomass-derived carbon;

[0052] Figure 19 Figure 2 shows the stability test results of the activated PB electrode material in Example 11 at 1.2 V, 30 min / L, and 500 mg / L NaCl solution. DETAILED DESCRIPTION

[0053] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0054] Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0055] Currently, plants account for approximately 82.4% of Earth's total biomass, and global agricultural and industrial biomass production has exceeded 10 billion tons. It is well known that paper and paperboard (PPB) products are the most important component of municipal solid waste. According to incomplete statistics from the Food and Agriculture Organization of the United Nations, global PPB sales could reach 425 million tons in 2025, and this figure is expected to continue to increase. Currently, PPB is primarily disposed of worldwide through recycling and landfilling. Recycling and reprocessing generate significant amounts of waste, while biodegradation in landfills can take decades or even longer, and the leachate generated by landfills can cause significant environmental pollution. As a green approach, converting biomass waste into advanced functional carbon-based materials has been widely studied in various fields, including batteries, supercapacitors, gas adsorbents, and water purification. Biomass-converted carbon not only possesses unique physical and chemical properties, such as a loose pore structure, large surface area, rich groups, and strong adsorption capacity, but is also renewable, environmentally friendly, and low-cost. Converting biomass derivatives and their product waste into self-supporting carbon materials through a simple process can not only solve the environmental pollution problem caused by municipal solid waste, but also turn waste into treasure, which can be said to kill two birds with one stone.

[0056] In addition, air purification and water treatment are key technologies for overcoming climate change and the freshwater crisis. According to the World Health Organization, one of the main causes of global climate change is the high concentration of CO2 in the atmosphere, and one of the key technologies to solve this problem is the capture of CO2. In addition, the World Health Organization also pointed out that by 2025, half of the world's population will face a shortage of fresh water resources. Electrochemical deionization (Capacitive deionization, CDI) has become a highly competitive brackish water desalination technology due to its significant advantages such as low energy consumption, low cost, high efficiency, simple operation, and no secondary pollution. Therefore, this patent further applies the self-supporting carbon electrode prepared above to the capture of CO2 in the air and as a CDI electrode for brackish water desalination.

[0057] Since PPB is mainly composed of lignin, cellulose, hemicellulose and soluble starch, it is a typical biomass derivative. Among them, waste cardboard has a typical tough texture, good smoothness and high mechanical strength, and has the potential to be used as a preparation for multifunctional self-supporting electrodes. Therefore, the embodiment of the present invention selects solid waste paperboard (PB) that exists in large quantities in cities as a raw material to prepare self-supporting carbon materials. First, clean, hard, smooth and mechanically strong corrugated cardboard (PB) is selected and cut into small cardboards of a certain length and width. Secondly, the above-mentioned cut cardboard is transferred to a tubular furnace and, under the protection of N2, heated to a suitable temperature at a certain heating rate for carbonization. After natural cooling to room temperature, deionized water is used to remove residual impurities to obtain carbonized cardboard, which is abbreviated as Carbonized PB. Finally, the carbonized paperboard obtained above was transferred to a certain concentration of NH4H2PO4 solution and soaked for a certain period of time before drying. After drying, the paperboard loaded with NH4H2PO4 was transferred to a tube furnace for high-temperature activation to produce more defects on its surface. After it was naturally cooled to room temperature, it was soaked in deionized water to remove residual NH4H2PO4 and other impurities. It was further washed with ethanol and dried. Finally, the self-supporting material obtained above was chemically modified with H3PO4 on the material surface, and then ultrasonically cleaned with deionized water to a pH close to 7, and then ultrasonically cleaned with anhydrous ethanol until almost no fragments fell off, and then transferred to an 80°C oven for drying. The dried material is abbreviated as Activated PB.

[0058] The preparation process is as follows: First, clean, hard, smooth, and mechanically strong corrugated cardboard (PB) is selected and cut into small pieces with a length of 10 cm and a width of 4 cm, respectively. Next, the cut pieces are transferred to a tube furnace and, under nitrogen protection, heated to 350-450°C at a rate of 5°C / min and held there for 2-4 hours. The pieces are then cooled naturally to room temperature and ultrasonically cleaned in deionized water to obtain carbonized PB. Finally, the obtained Carbonized PB was transferred to a 4-6 mol / L NH4H2PO4 solution and soaked for 20-30 h, then transferred to a 70-90°C oven for drying. After drying, the cardboard loaded with NH4H2PO4 was transferred to a tube furnace under N2 protection and heated to 500-700°C at a rate of 5°C / min and kept at this temperature for 1-3 h. After cooling to room temperature, it was transferred to deionized water for ultrasonic cleaning to remove residual NH4H2PO4 and other impurities, and then transferred to a 70-90°C oven for drying. Finally, the dried self-supporting material was transferred to a 2-4 mol / L H3PO4 solution and soaked for 6-10 h. The H3PO4-soaked material was then ultrasonically cleaned with deionized water until the pH was close to 7, then ultrasonically cleaned with anhydrous ethanol and transferred to an 80°C oven for drying. The obtained product was abbreviated as Activated PB.

[0059] The self-supporting carbon film prepared by the embodiment of the present invention is a simple process using urban solid waste corrugated cardboard rich in cellulose, soluble starch and part of lignin as raw materials through carbonization and NH4H2PO4 as a dual-functional activator strategy to achieve synergistic optimization of adsorption performance and surface chemical properties. Among them, the interweaving between lignin, hemicellulose and soluble starch makes the entire structure have good stability, so that it can maintain the stability of the entire frame shape during the carbonization process. Subsequent NH4H2PO4 activation can not only further enhance the defects of the material and thus show a larger active area, but also realize N / P co-doping for surface modification; at the same time, lignin, hemicellulose and starch can also provide rich oxygen-containing groups to make the self-supporting carbon material have good hydrophilicity. Finally, the prepared carbon material can be directly used for CO2 adsorption and brackish water desalination without the need for additional binder, which greatly simplifies the electrode preparation process and reduces costs, while also realizing waste resource utilization. Compared with traditional activators such as KOH and HNO3, the activator NH4H2PO4 used in the embodiments of the present invention is not only mild and inexpensive, but also has less corrosion to instruments and equipment during the material preparation process, thereby reducing its secondary damage to the environment. More importantly, NH4H2PO4 can not only act as an activator to improve the active area of ​​the material, but also achieve N / P co-doping; finally, the obtained material is further surface chemically modified with H3PO4, thereby significantly enhancing the material's wettability. These lay a solid foundation for its further application.

[0060] In order to better demonstrate the significant effects of the embodiments of the present invention, experiments will be conducted below to verify the results.

[0061] Example 1: This embodiment of the present invention provides a method for preparing a self-supporting carbon material, comprising the following:

[0062] First, choose corrugated cardboard (PB, manufacturer: Nine Dragons Paper; composition: cellulose and lignin account for 78~85% and ≤8% of the paper base cellulose respectively, and starch adhesive accounts for 20~28g / m 2, thickness: 2 mm) and cut into small paperboards with a length and width of 10 cm and 4 cm, respectively. The cut paperboards were then transferred to a tube furnace and heated at a rate of 5°C / min to 400°C under nitrogen protection for 3 hours. The paperboards were then cooled to room temperature and ultrasonically cleaned in deionized water to obtain carbonized paperboard, referred to as carbonized PB. The resulting carbonized PB was then immersed in a 4 mol / L NH₄H₂PO₄ solution for 24 hours and then dried in an 80°C oven. After drying, the NH₄H₂PO₄-loaded paperboards were transferred to a tube furnace under nitrogen protection and heated at a rate of 5°C / min to 500°C for 2 hours. After cooling to room temperature, the paperboards were ultrasonically cleaned in deionized water to remove residual NH₄H₂PO₄ and other impurities. The resulting product was then dried in an 80°C oven. The resulting product is referred to as a self-supporting carbon material.

[0063] 1. Influence of activator NH4H2PO4 and activation temperature on material properties during material preparation

[0064] The difference between Examples 2 to 9 and Example 1 is that the NH4H2PO4 concentration (mol / L) and activation temperature (°C) are different, and the other steps are the same. Table 1 is a comparison of the process parameters of Examples 1 to 9:

[0065] Table 1

[0066]

[0067] The self-supporting carbon materials prepared in Examples 1 to 9 were subjected to the following tests:

[0068] (1) CO2 adsorption capacity (mg / g): measured at room temperature (25°C) and standard atmospheric pressure (1 bar);

[0069] (2) Specific capacitance (F / g): obtained by cyclic voltammetry in 1 mol / L NaCl electrolyte solution at a scan rate of 10 mV / s;

[0070] (3) NaCl adsorption capacity (mg / g): The test was completed at a voltage of 1.2 V, a flow rate of 30 mL / min, and a 500 mg / L NaCl solution.

[0071] The test results are shown in Table 2 below:

[0072] Table 2

[0073]

[0074] Combining Tables 1 and 2, it can be seen that in Example 5, the material prepared when the concentration of the activator NH4H2PO4 is 5 mol / L and the activation temperature is 600°C has the highest CO2 adsorption capacity, specific capacitance, and salt adsorption capacity. This is because when the concentration of the activator NH4H2PO4 is 4 mol / L and the activation temperature is 500°C, the material is not fully etched and carbonized, resulting in poor performance. When the concentration of NH4H2PO4 is 6 mol / L and the activation temperature is 700°C, the structure of the material is destroyed, thereby reducing its active area, resulting in low performance of the prepared material. Therefore, from the results obtained from the above optimization of the activator concentration and activation temperature, the material prepared when the NH4H2PO4 concentration and activation temperature are 5 mol / L and 600°C respectively has the best CO2 adsorption capacity, specific capacitance, and salt adsorption capacity.

[0075] 2. Performance of materials prepared at 5 mol / L NH4H2PO4 and activation temperature 600℃ under different H3PO4 concentration modification

[0076] Example 10: This embodiment of the present invention provides a method for preparing a self-supporting carbon material, comprising the following:

[0077] First, choose corrugated cardboard (PB, manufacturer: Nine Dragons Paper; composition: cellulose and lignin account for 78-85% and lignin ≤ 8% respectively in the paper base cellulose, and starch adhesive accounts for 20-28g / m 2 , thickness: 2 mm) and cut into small pieces of cardboard with a length of 10 cm and a width of 4 cm, respectively. Next, the cut pieces were transferred to a tube furnace and heated to 400°C at a rate of 5°C / min under nitrogen protection. The temperature was maintained at 400°C for 3 hours. After cooling naturally to room temperature, the pieces were transferred to deionized water for ultrasonic cleaning to obtain carbonized cardboard, abbreviated as Carbonized PB. Secondly, the Carbonized PB obtained above was transferred to a 5 mol / L NH4H2PO4 solution and soaked for 24 h, then transferred to an 80°C oven for drying. After drying, the cardboard loaded with NH4H2PO4 was transferred to a tube furnace under N2 protection and heated to 600°C at a rate of 5°C / min and kept warm for 2 h. After it was naturally cooled to room temperature, it was transferred to deionized water for ultrasonic cleaning to remove residual NH4H2PO4 and other impurities, and then transferred to an 80°C oven for drying. Finally, the dried self-supporting material was transferred to a 3 mol / L H3PO4 solution and soaked for 8 h. Next, the H3PO4-soaked material was ultrasonically cleaned with deionized water until the pH was close to 7, and then ultrasonically cleaned with anhydrous ethanol again and transferred to an 80°C oven for drying. The obtained product was abbreviated as Activated PB.

[0078] The difference between Example 11 and Example 12 and Example 10 is that the concentration of the H3PO4 solution is different, and the other steps remain unchanged. Table 3 is a comparison of the process parameters of Example 10 to Example 12:

[0079] Table 3

[0080]

[0081] The Activated PB prepared in Example 10, Example 11 and Example 12 were subjected to performance tests. The test results are shown in Table 4 below:

[0082] Table 4

[0083]

[0084] Combining Tables 3 and 4, it can be seen that the self-supporting materials obtained at a fixed activator NH4H2PO4 concentration of 5 mol / L and an activation temperature of 600°C were further chemically modified with H3PO4 at different concentrations. From the presented results, in Example 11, when the surface was chemically modified with 3 mol / L H3PO4, it had the highest CO2 adsorption capacity, specific capacitance, and NaCl adsorption capacity. This is because the low concentration of 2 mol / L H3PO4 failed to fully etch the material, while the high concentration of 4 mol / L H3PO4 reduced the active area of ​​the material, resulting in low performance. Therefore, when the raw material is carbonized and activated with NH4H2PO4, and then chemically modified with 3 mol / L H3PO4, the performance of the material can be further improved.

[0085] Combining Tables 2 and 4, we can see that after carbonization, activation of the raw materials with 5 mol / L NH₄H₂PO₄ at 600°C, and further chemical modification of the resulting self-supporting material with 3 mol / L H₃PO₄, can further enhance the material's CO₂ adsorption capacity, specific capacitance, and NaCl adsorption capacity. Therefore, the following examination focuses on the self-supporting material (activated PB) obtained by carbonizing the waste cardboard in Example 11 (Carbonized PB) and further treating it with 5 mol / L NH₄H₂PO₄ and 3 mol / L H₃PO₄.

[0086] Figure 1 This is a process flow chart of preparing a high-oxygen-content self-supporting carbon material using solid waste cardboard (PB) that exists in large quantities in cities as raw materials through carbonization, NH4H2PO4 activation and H3PO4 surface chemical modification processes, and its use in CO2 capture and CDI brackish water desalination in an embodiment of the present invention.

[0087] Figure 2The optical photographs and scanning electron microscope images of the original waste cardboard PB, carbonized cardboard Carbonized PB and activated cardboard Activated PB in Example 11 are shown. Figure 2 It can be seen that the optical photograph (2a) and SEM images (2b~d) of the original PB show that its surface is rough and is composed of a large number of fibers and adhesives interwoven with each other, which lays a solid foundation for the preparation of self-supporting materials. Furthermore, the optical photograph (2e) and SEM images (2f~h) of the carbonized PB show that its entire skeleton remains intact after carbonization, and the melting of the adhesive under high temperature conditions reduces the cracks on the surface. Finally, the carbonized PB is activated with NH4H2PO4 and modified with H3PO4, and the corresponding optical photographs and SEM images are shown in Figures (2i~l). It can be clearly observed that the black color of the sample deepens after activation, and obvious etching marks appear on the surface. At the same time, its structure is interwoven with fragmented carbon and fibrous structures, thereby maintaining the stability of its carbon skeleton.

[0088] Figure 3 The carbonized PB and activated PB spectra in Example 11 are shown in FIG. Figure 3 The XRD spectrum shown in a shows that the prepared carbon material is relatively pure, and compared with Carbonized PB, Activated PB has more defects. RM spectrum ( Figure 3 b) The ratio of the D-band to G-band intensity of the material is also significantly higher for Activated PB than for Carbonized PB, which further confirms that Activated PB has higher defects and is expected to exhibit a higher specific surface area. Figure 3 The XPS spectrum presented in c shows that the oxygen content in the carbonized PB and the PB activated by NH4H2PO4 and modified by H3PO4 is not much different, both maintaining above 25%. This indicates that the loss of oxygen content can be minimized after carbonization, activation by NH4H2PO4 and modification by H3PO4, which greatly enhances the hydrophilicity of the self-supporting carbon material. At the same time, it can be clearly observed from the XPS spectrum that N / P is successfully doped after activation by NH4H2PO4 and modification by H3PO4. Figure 3 d) shows that there are pyridinic-N, pyrrolic-N and graphitized-N in the material. The presence of these different types of nitrogen helps to improve the conductivity of the material.

[0089] Figures 4 to 7 They are the nitrogen adsorption-desorption isotherms, pore size distribution, CO2 adsorption-desorption isotherms of Carbonized PB and Activated PB in Example 11, and the CO2 adsorption stability test of Activated PB. Figure 4 The N2- adsorption / desorption curves show that Activated PB has a higher nitrogen adsorption capacity than Carbonized PB and thus exhibits a larger specific surface area. Further pore size distribution ( Figure 5 ) indicates that activated PB possesses a coexistent structure of micropores, mesopores, and macropores, making it a typical self-supporting material with hierarchical pores. The data in Table 5 further demonstrate that carbonization, activation with NH₄H₂PO₄, and modification with H₃PO₄ significantly improve the specific surface area and pore structure of PB, laying a solid foundation for its application.

[0090] Table 5

[0091]

[0092] Figure 6 The CO2 capture capacity test was conducted at room temperature and one atmosphere. From the test results, it can be seen that Activated PB has a very strong CO2 adsorption capacity (127.18 mg / g), and the adsorption and desorption curves can overlap well, indicating that it has good adsorption / desorption stability. The CO2 adsorption capacity of PB that has only been carbonized is only 33.54 mg / g. In other words, the CO2 capture capacity of the activated PB has increased by 3.7 times, further indicating that carbonization, NH4H2PO4 activation and H3PO4 modification of PB is an effective strategy. Furthermore, the stability test of Activated PB shows that its CO2 enrichment capacity can still be maintained at more than 93% after the 5th cycle ( Figure 7 ), and then there is no significant decay again, indicating that it has good stability.

[0093] Figures 8-13 Cyclic voltammetry, rate performance, charge-discharge (1 A / g), impedance, ion transport, and stability tests were performed on the Carbonized PB and Activated PB in Example 11. All electrochemical tests were performed in 1 mol / L NaCl solution. Figures 8-10 The test results show that Activated PB has a higher ion storage capacity, thus exhibiting a higher specific capacitance, and also has good rate performance. Figure 11 The electrochemical impedance spectroscopy (EIS) test results show that, compared with Carbonized PB, Activated PB has a smaller arc radius in the high-frequency region and a higher slope in the low-frequency region, indicating that Activated PB has better conductivity. Figure 12The ion transport performance evaluation showed that the activated PB had a smaller impedance coefficient, indicating that it had good charge transport performance, which was beneficial to reducing energy loss. Figure 13 The capacity of the activated PB electrode can be maintained above 96% after 5000 cycles at a scan rate of 100 mV / s, indicating that it has good stability, laying the foundation for its application in CDI brackish water desalination.

[0094] from Figure 14-16 It can be seen that compared with Carbonized PB, Activated PB has a faster salt adsorption rate and higher salt adsorption capacity, and it also has good adsorption and regeneration performance, which is mainly attributed to its natural self-supporting structure, good conductivity, high specific surface area and excellent hydrophilicity. Furthermore, under different NaCl feed concentrations, Activated PB also showed a higher adsorption capacity than Carbonized PB electrode ( Figure 17 ), which confirms that the carbonized PB has obvious advantages after further NH4H2PO4 activation and H3PO4 modification. Figure 18 The performance of Activated PB in CDI brackish water desalination is compared with the currently reported biomass carbon electrodes. The results show that the original self-supporting structure, high specific surface area, good conductivity and hydrophilicity of Activated PB enable it to exhibit unique CDI performance. Figure 19 As shown in the figure, after 50 continuous adsorption / desorption cycles, the adsorption capacity of the activated PB electrode can still be maintained above 94%, while the charge efficiency loss is maintained below 5%, further confirming that the activated PB electrode has excellent regeneration performance and low energy loss.

[0095] 3. Comparison of corrugated cardboard parameters and derived self-supporting carbon material performance produced by mainstream domestic corrugated cardboard manufacturers (all thickness 2mm)

[0096] Table 6 shows the performance test results of activated PB produced by the corrugated cardboard manufacturer according to the preparation method of Example 11, including the following performance tests:

[0097] (1) The self-supporting performance of the materials was evaluated by continuous ultrasonication at a frequency of 60 kHz for 1 h.

[0098] (2) CO2 adsorption capacity (mg / g) was measured at room temperature (25°C) and standard atmospheric pressure (1 bar);

[0099] (3) The specific capacitance (F / g) was obtained by cyclic voltammetry in 1 mol / L NaCl electrolyte solution at a scan rate of 10 mV / s.

[0100] (4) The NaCl adsorption capacity (mg / g) was tested at a voltage of 1.2 V, a flow rate of 30 mL / min, and a 500 mg / L NaCl solution.

[0101] Table 6

[0102]

[0103] As can be seen from Table 6, no significant fragmentation occurred in the corrugated cardboards from different manufacturers after ultrasonic treatment with a high-power ultrasonic instrument, indicating that the material synthesized by this method has good self-supporting properties. Further, the CO2 capture performance, electrochemical ion storage capacity, and NaCl adsorption capacity can all be kept stable. This result shows that although the content of paper-based cellulose (including cellulose and lignin) and starch adhesive in the precursor corrugated cardboard for preparing self-supporting carbon materials is different, it does not affect the self-supporting properties and CO2 capture and brackish water desalination performance of the material.

[0104] 4. Performance comparison of corrugated cardboards of different thicknesses (taking Nine Dragons Paper as an example: the cellulose and lignin contents in the paper base cellulose are 78-85% and ≤8% respectively, and the starch adhesive dosage is 20-28g / m 2 )

[0105] Table 7 shows the performance test results of activated PB prepared by the preparation method of Example 11 using corrugated cardboards of different thicknesses:

[0106] Table 7

[0107]

[0108] As shown in Table 7, no significant fragmentation was observed in the self-supporting materials obtained by ultrasonication of corrugated cardboard with thicknesses increasing from 2 mm to 7 mm, indicating the excellent stability of the self-supporting carbon materials synthesized from waste corrugated cardboard of varying thicknesses. Further performance testing revealed that CO adsorption, electrochemical ion capture, and NaCl adsorption all showed an increasing trend with increasing thickness. This is attributed to the increase in active sites in the synthesized self-supporting materials.

[0109] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a self-supporting carbon material, characterized in that: The following steps are involved: S1: After cutting, the cardboard is transferred to a high-temperature furnace for carbonization, and then cooled and cleaned in sequence to obtain carbonized cardboard; S2: activating, washing, and drying the carbonized paperboard to obtain a self-supporting carbon material; The activation of the carbonized paperboard in S2 includes transferring the carbonized paperboard to an NH4H2PO4 solution for immersion; The carbonization in S1 is the first carbonization. After the carbonized paperboard is transferred to the NH4H2PO4 solution for immersion in S2, the carbonized paperboard soaked in the NH4H2PO4 solution is further subjected to a second carbonization. The activation of the carbonized paperboard in S2 further includes washing and drying the carbonized paperboard after the second carbonization for the first time, and then transferring the carbonized paperboard to a H3PO4 solution for immersion; The concentration of the NH4H2PO4 solution is 4-6 mol / L, and the soaking time in the NH4H2PO4 solution is 20-30 h; The concentration of the H3PO4 solution is 2-4 mol / L, and the soaking time in the H3PO4 solution is 6-10 hours; The temperature of the first carbonization is 350-450°C, and the temperature of the second carbonization is 500-700°C.

2. The method for preparing a self-supporting carbon material according to claim 1, wherein: The first carbonization time is 2 to 4 hours; the second carbonization time is 1 to 3 hours.

3. The method for preparing a self-supporting carbon material according to claim 1, wherein: The first carbonization and the second carbonization are both carried out under N2 protection.

4. The method for preparing a self-supporting carbon material according to claim 1, wherein: S2 further includes washing the carbonized paperboard soaked in the H3PO4 solution for a second time and drying it for a second time to obtain a self-supporting carbon material; The first washing comprises ultrasonic cleaning in deionized water to remove residual NH4H2PO4 impurities, and the first drying comprises drying in an oven at a temperature of 70 to 90°C; The second washing includes ultrasonic cleaning with deionized water until the pH reaches 6.5-7.5, and then ultrasonic cleaning with anhydrous ethanol. The second drying includes drying in an oven at a temperature of 70-90°C.

5. A self-supporting carbon material, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 4.

6. A use of a self-supporting carbon material prepared by the method for preparing a self-supporting carbon material according to any one of claims 1 to 4, characterized in that: The invention also includes using the self-supporting carbon material for CO2 capture and brackish water desalination.

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