Preparation method of three-dimensional graded porous carbon material

Abstract

The invention relates to a preparation method of a three-dimensional graded porous carbon material, and belongs to the technical field of porous carbon materials. The preparation method comprises the following steps: mixing polyether polyol (R2305) and polymethylene polyphenyl isocyanate (PM200) according to a ratio, heating in a water bath kettle at a constant temperature to form a polyurethane mixed precursor, adding mixed powder of silicone oil, an activating agent and glucose into the precursor, uniformly mixing by mechanical stirring, then adding a catalyst, continuously uniformly stirring, and carrying out vacuum drying to obtain the polyurethane composite material. And finally, adding a certain amount of water as a foaming agent, stirring and standing to form a hardened blank, and carbonizing, activating, pickling and drying to obtain the three-dimensional graded porous carbon. The porous carbon material with the three-dimensional interconnected graded pore structure is prepared by adopting a carbonization-activation one-step method, the pore size and porosity of macropores can be regulated and controlled, the strength of a green body and a carbonized sample is effectively improved, the specific surface area of porous carbon is remarkably increased, the process is simpler, and the efficiency is higher.

Description

Technical Field

[0001] This invention belongs to the field of porous carbon materials technology, specifically relating to a method for preparing three-dimensional hierarchical porous carbon materials. Background Technology

[0002] Hierarchical porous carbon is a novel type of carbon material with a hierarchical pore structure. Compared to ordinary porous carbon, it exhibits higher porosity, larger specific surface area, and superior pore size control, all stemming from its unique hierarchical pore structure. This type of material typically manifests as two-dimensional sheet-like or three-dimensional blocky morphologies. Among them, three-dimensional interconnected hierarchical porous carbon, with its interconnected three-dimensional pore network, high specific surface area, and composite structure containing micropores, mesopores, and macropores, demonstrates outstanding performance in adsorption, electrochemical, and thermal properties, thus holding significant application value in fields such as lithium-sulfur batteries, supercapacitors, and water purification.

[0003] Currently, there are various methods for preparing three-dimensional hierarchical porous carbon, with template method, activation method, and foaming method being the most common. The template method relies on a structure-directing agent (template) to construct pore structures of different sizes and morphologies, and can be divided into hard template method and soft template method. However, this method is costly, and achieving precise control of the pore size requires meticulous control of the template size, which remains technically challenging. The activation method is a commonly used technique for preparing porous carbon, mainly including physical activation and chemical activation. Its principle is to ablate some carbon atoms through an activating agent, forming abundant pores in the carbon framework, thereby increasing the pore volume and specific surface area of ​​the material. However, traditional activation methods (such as using KOH solution) are highly corrosive to equipment, making the collection and subsequent processing of biomass raw materials difficult, and the pore structure is prone to collapse during high-temperature carbonization activation, making it difficult to maintain a complete bulk morphology. In addition, the foaming method is also a technique for preparing three-dimensional hierarchical porous carbon materials. Unlike the previous two, it often uses biomass as a carbon source directly, but the resulting products are often dominated by macropores, with insufficient development of micropores and mesopores, so the specific surface area is usually low. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing high specific surface area three-dimensional hierarchical porous carbon. The aim is to achieve control over the pore size and pore shape of hierarchical porous carbon while reducing production costs, simplifying the production process, and obtaining blocky hierarchical porous carbon with a three-dimensional network structure.

[0005] To achieve the above objectives, the present invention provides a method for preparing a three-dimensional hierarchical porous carbon material, which is carried out according to the following steps:

[0006] First, a polyurethane mixed precursor was prepared using polyether polyol (R2305) and polymethylene polyphenyl isocyanate (PM200). The mixed powder was first added to the polyurethane mixed precursor and mixed evenly by mechanical stirring. Then, a catalyst was added and mixed evenly. The mixture was allowed to stand and foam to form a hardened preform. The hardened preform was carbonized and activated to obtain porous carbon. The porous carbon was washed with water and dried to obtain three-dimensional hierarchical porous carbon.

[0007] Furthermore, the process for preparing the polyurethane mixed precursor is as follows: polyether polyol and polymethylene polyphenyl isocyanate are mixed in a certain proportion and heated in a water bath at a constant temperature; the mass ratio of the added polyether polyol and polymethylene polyphenyl isocyanate is 1:1, the water bath heating temperature is 30℃~50℃, and the heating time is 5min~10min.

[0008] Furthermore, the mechanical stirring is carried out at a speed of 500 r / min to 800 r / min.

[0009] Furthermore, the mixed powder is a mixture of silicone oil, activator and glucose, wherein the activator is sodium citrate, the mass ratio of activator to glucose is (1~1.5):1, and the mass ratio of mixed powder to precursor is (1~3.5):1.

[0010] Furthermore, the amount of catalyst added is 0.1% to 0.5% of the precursor mass, and the catalyst is triethylenediamine (A33) and dibutyltin dilaurate (T-12) in a ratio of (0 to 4):1.

[0011] Furthermore, the foaming process is as follows: add water at a mass of 0.4% to 1.2% of the precursor as a foaming agent, stir thoroughly at a speed of 500 r / min to 800 r / min, and let stand for foaming for 12 h to 24 h.

[0012] Furthermore, the carbonization activation process is as follows: under the protection of argon atmosphere, the hardened blank is carbonized and activated at 700℃~900℃ for 1h~3h, and the heating rate is 4℃ / min~8℃ / min.

[0013] Furthermore, the acid washing involves washing the porous carbon in 1 mol / L dilute hydrochloric acid for 6 to 12 hours; the drying involves drying at 80°C for 12 hours.

[0014] Compared with existing technologies, the features and beneficial effects of this invention are as follows:

[0015] (1) This invention combines foaming and activation methods to obtain porous carbon materials with a three-dimensional interconnected hierarchical pore structure, whose pore structure is controllable and whose preparation process is simple;

[0016] (2) The present invention uses a foaming method to obtain a three-dimensional interconnected macroporous structure. By adjusting the raw material ratio of the foaming method, the pore size and porosity of the macropores can be controlled, which can effectively improve the strength of the green body and the carbonized sample.

[0017] (3) The present invention prepares microporous and mesoporous structures in the pore walls of macropores by chemical activation, enriching the types of pore structures, significantly improving the specific surface area of ​​porous carbon, and can be adjusted by adjusting the content of activator, activation temperature and time;

[0018] (4) The present invention uses sodium citrate as an activator, which is green and safe and can avoid the corrosive effect of commonly used activators such as KOH on experimental equipment;

[0019] (5) The present invention adopts a one-step carbonization-activation method, which performs carbonization and activation simultaneously. Compared with the two-step method, the process is simpler and more efficient.

[0020] (6) The raw materials glucose and sodium citrate in this invention are readily available, and the preparation route does not involve complex chemical reactions or the use of expensive reagents, making this invention easy to organize production and low in cost. Attached Figure Description

[0021] Figure 1 These are SEM images of the macroporous, mesoporous, and microporous structures of the high-specific-area three-dimensional hierarchical porous carbon prepared in Example 4 of the present invention; wherein, (a) is an SEM image of the macroporous structure of the three-dimensional hierarchical porous carbon, (b) is an SEM image of the mesoporous structure of the three-dimensional hierarchical porous carbon, and (c) is an SEM image of the microporous structure of the three-dimensional hierarchical porous carbon.

[0022] Figure 2 The XRD pattern of the high specific surface area three-dimensional hierarchical porous carbon prepared in Example 4 of this invention;

[0023] Figure 3 These are images of samples prepared in Examples 1-6 of this invention after graded porous carbonization with different activator ratios;

[0024] Figure 4 These are SEM images of graded porous carbon with different activator ratios prepared in Examples 1-6 of this invention;

[0025] Figures a-1 and a-2 are SEM images of the hierarchical porous carbon prepared in Example 1.

[0026] Figures b-1 and b-2 are SEM images of the hierarchical porous carbon prepared in Example 2;

[0027] Figures c-1 and c-2 are SEM images of the hierarchical porous carbon prepared in Example 3.

[0028] Figures d-1 and d-2 are SEM images of the hierarchical porous carbon prepared in Example 4;

[0029] Figures e-1 and e-2 are SEM images of the hierarchical porous carbon prepared in Example 5;

[0030] Figures f-1 and f-2 are SEM images of the hierarchical porous carbon prepared in Example 6;

[0031] Figure 5 These are nitrogen adsorption / desorption isotherms of graded porous carbon with different activator ratios prepared in Examples 1-6 of this invention;

[0032] Among them, Figures (a)-(f) correspond to the nitrogen adsorption / desorption isotherms of the hierarchical porous carbon prepared in Examples 1-6, respectively.

[0033] Figure 6 These are pore size distribution curves of graded porous carbon with different activator ratios prepared in Examples 1-6 of this invention;

[0034] Figure 7 These are images of samples prepared by graded porous carbonization at different activation temperatures in Examples 4 and 7-10 of this invention.

[0035] Figure 8 These are SEM images of graded porous carbon with different activation temperatures prepared in Examples 4 and 7-10 of this invention;

[0036] Figures a-1 and a-2 are SEM images of the hierarchical porous carbon prepared in Example 7.

[0037] Figures b-1 and b-2 are SEM images of the hierarchical porous carbon prepared in Example 8;

[0038] Figures d-1 and d-2 are SEM images of the hierarchical porous carbon prepared in Example 4;

[0039] Figures e-1 and e-2 are SEM images of the hierarchical porous carbon prepared in Example 9;

[0040] Figures f-1 and f-2 are SEM images of the hierarchical porous carbon prepared in Example 10;

[0041] Figure 9 These are nitrogen adsorption / desorption isotherms of the graded porous carbon with different activation temperatures prepared in Examples 4 and 7-10 of this invention.

[0042] Among them, Figures (a)-(f) correspond to the nitrogen adsorption / desorption isotherms of the hierarchical porous carbon prepared in Examples 7, 8, 4, 9 and 10, respectively;

[0043] Figure 10These are pore size distribution curves of graded porous carbon prepared at different activation temperatures in Examples 4 and 7-10 of this invention;

[0044] Figure 11 These are images of samples prepared by graded porous carbonization at different activation times in Examples 4 and 11-13 of this invention.

[0045] Figure 12 These are SEM images of graded porous carbon with different activation times prepared in Examples 4 and 11-13 of this invention;

[0046] Figures a-1 and a-2 are SEM images of the hierarchical porous carbon prepared in Example 11.

[0047] Figures b-1 and b-2 are SEM images of the hierarchical porous carbon prepared in Example 12;

[0048] Figures c-1 and c-2 are SEM images of the hierarchical porous carbon prepared in Example 4;

[0049] Figures d-1 and d-2 are SEM images of the hierarchical porous carbon prepared in Example 13;

[0050] Figure 13 These are nitrogen adsorption / desorption isotherms of hierarchical porous carbon prepared with different activation times in Examples 4 and 11-13 of the present invention; wherein, Figures (a)-(d) correspond to nitrogen adsorption / desorption isotherms of hierarchical porous carbon prepared in Examples 11, 12, 4 and 13, respectively.

[0051] Figure 14 This is a pore size distribution curve of the graded porous carbon prepared at different activation times in Examples 4 and 11-13 of the present invention. Detailed Implementation

[0052] The present invention will be described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0053] In this embodiment of the invention, the electron microscope used for scanning the hierarchical porous carbon material is model JSM-6510A;

[0054] The X-ray diffractometer model is X'Pert Pro NPP;

[0055] The thermogravimetric-differential thermal analyzer model is STA449F3Jupiter®;

[0056] Nitrogen adsorption analysis was performed using a NOVA 1000e nitrogen physical adsorber.

[0057] Example 1

[0058] A method for preparing a three-dimensional hierarchical porous carbon material, comprising the following steps:

[0059] This experiment used glucose as the carbon source and trisodium citrate as the activator to prepare hierarchical porous carbon materials by combining polyurethane foaming and activation methods. The typical preparation process is as follows:

[0060] (1) Weigh 20.0 g of polyether polyol (R2305) and polymethylene polyphenyl isocyanate (PM200) respectively, mix them, and heat them in a water bath at a constant temperature of 40℃ for 5 min;

[0061] (2) Weigh out 60 g of sodium citrate and glucose in a 1:1 ratio, mix them evenly, and grind them evenly in a mortar and pestle;

[0062] (3) Add the ground mixed powder and 0.02 g of silicone oil to the heated mixture of polyether polyol (R2305) and polymethylene polyphenyl isocyanate (PM200) while stirring;

[0063] (4) Stir the mixture at a speed of 600-800 r / min until it is uniform, then add 0.02 g of catalyst (T-12) and 0.16 g of foaming agent water, and stir it at the same speed until it is fully mixed. Then stop stirring and let it stand to complete the foaming process to obtain the foamed blank.

[0064] (5) The billet was activated at 800 °C under argon atmosphere protection, with a heating rate of 8 °C / min, and held at that temperature for 2 hours;

[0065] (6) The carbonized sample was acid washed in 1 mol / L dilute hydrochloric acid for 6 h, then washed with distilled water until neutral, and dried in an oven at 80 ℃ for 12 h to finally obtain high specific surface area three-dimensional hierarchical porous carbon, and the sample was named H1T800S2; where “H” represents the ratio of activator to glucose, “T” represents the activation temperature, and “S” represents the activation time.

[0066] Example 2

[0067] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 1 in that the ratio of sodium citrate to glucose in this example is 1.1:1, while other steps remain unchanged. The obtained sample is named H1.1T800S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0068] Example 3

[0069] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 1 in that the ratio of sodium citrate to glucose in this example is 1.2:1, while other steps remain unchanged. The obtained sample is named H1.2T800S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0070] Example 4

[0071] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 1 in that the ratio of sodium citrate to glucose in this example is 1.3:1, while other steps remain unchanged. The obtained sample is named H1.3T800S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0072] Figure 1 These are SEM images of the macroporous, mesoporous, and microporous structures of the high-specific-surface-area three-dimensional hierarchical porous carbon prepared in this embodiment. The images show a significant macroporous structure in the sample. Figure 1 (a) This is mainly due to the skeleton formed during the polyurethane foaming process. In addition, a certain number of mesopores also exist in the material. Figure 1 (b) , whose formation can be attributed to the pyrolysis and pore-forming effect of sodium citrate at high temperatures. Further from Figure 1 (c) As can be seen, the sample generated a large number of micropores after KOH activation. These micropores, together with mesopores, significantly increased the specific surface area of ​​the material. In summary, this sample successfully constructed a hierarchical pore structure containing micropores, mesopores, and macropores. Figure 2 The XRD pattern of the large specific surface area three-dimensional hierarchical porous carbon prepared in this embodiment is shown. Two broadened diffraction peaks appear at approximately 26° and 44°, indicating that the carbon material is mainly amorphous. Furthermore, no other crystalline phase characteristic peaks appear in the pattern, indicating that the carbonized product is a pure carbon phase and the organic components in the raw material have been completely decomposed.

[0073] Example 5

[0074] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 1 in that the ratio of sodium citrate to glucose in this example is 1.4:1, while other steps remain unchanged. The obtained sample is named H1.4T800S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0075] Example 6

[0076] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 1 in that the ratio of sodium citrate to glucose in this example is 1.5:1, while other steps remain unchanged. The obtained sample is named H1.5T800S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0077] Table 1 shows the nitrogen adsorption physical parameters, bulk density, and porosity of the hierarchical porous carbon prepared in Examples 1-6.

[0078]

[0079] Figure 3 These are sample images of graded porous carbon carbon prepared in Examples 1-6 after carbonization with different proportions of activator. As can be seen from the images, as the amount of activator increases, although the graded porous carbon can still maintain its solid shape, the solid gradually becomes brittle and its strength gradually decreases. Figure 4 These are SEM images of hierarchical porous carbon prepared in Examples 1-6 with different activator ratios. The images show that the hierarchical porous carbon has a well-developed pore structure. The macropore framework has a loose, porous, honeycomb-like morphology, with interconnected pores and thin, intact pore walls. Furthermore, it was found that the shape and size of the macropores changed with increasing activator dosage. As the activator dosage increased, the uniformity of the pore structure improved, the interconnectivity of the pores increased, and the pore walls became thinner. Figure 4 (ae)). When too much activator is added, the uniformity of the pore structure decreases, the pore size increases, the structural connectivity deteriorates, and even filamentous structures appear in the pore walls. Figure 4 (f)). Figure 5 These are nitrogen adsorption / desorption isotherms of fractionated porous carbon prepared in Examples 1-6 with different activator ratios; from Figure 5 As shown in (af), the N2 adsorption-desorption curves of samples H1T800S2, H1.3T800S2, H1.4T800S2, and H1.5T800S2 are a combination of Type I and Type IV. The curves show a gradual increase in the low-pressure region (P / P0 < 0.01), with the H1.4T800S2 curve almost touching the x-axis. These characteristics are consistent with the initial shape of a Type I curve, indicating the presence of numerous microporous structures within the sample. Subsequently, a weak hysteresis loop appears in the relative pressure range of P / P0 = 0.3–0.9, and this hysteresis loop is of Type H4, indicating the presence of mesoporous layered structures in the sample. Finally, upon reaching the saturation pressure region (P / P0 > 0.99), adsorbate aggregation occurs, causing the curve to rise at the end, similar to the end characteristic of a Type I curve, further indicating the presence of abundant microporous structures in the sample. Figure 6The figures show the pore size distribution curves of the graded porous carbon prepared in Examples 1-6 with different activator ratios. As can be seen from the figures, the samples contain a large number of micropores and a certain number of mesopores. The micropore diameter is approximately 1-3 nm, while the mesopore diameter is mainly concentrated between 15-25 nm. With the increase of the activator ratio, the number of micropores and mesopores increases significantly. When the ratio of sodium citrate to glucose is 1.3:1, the number of micropores and mesopores reaches its maximum. Further increasing the ratio reduces the number of micropores and mesopores. This is because when the amount of Na3C6H5O7 exceeds a certain level, the amount of carbon source is insufficient to support the formation of the carbon framework, and the decreased pore stability actually reduces the number of pores in the sample. This indicates that Na3C6H5O7 has a strong activating and pore-forming effect, and the prepared porous carbon simultaneously possesses a three-level pore structure of micropores, mesopores, and macropores. Table 1 shows the nitrogen adsorption physical parameters, bulk density, and porosity of graded porous carbon with different activator ratios. As can be seen from the table, with the increase of the activator ratio, the pore volume, specific surface area, and porosity of the porous carbon all show a trend of first increasing and then decreasing, while the bulk density shows the opposite trend. When the ratio of sodium citrate to glucose is 1.3:1, the pore volume, specific surface area, and porosity of the material all reach their maximum values, while the bulk density drops to its minimum. As the activator ratio continues to increase, the pore volume and specific surface area of ​​the porous carbon decrease significantly, the porosity also decreases accordingly, and the bulk density increases accordingly.

[0080] Example 7

[0081] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the activation temperature in this example is 700℃, while other steps remain unchanged. The obtained sample is named H1.3T700S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0082] Example 8

[0083] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the activation temperature in this example is 750℃, while other steps remain unchanged. The obtained sample is named H1.3T750S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0084] Example 9

[0085] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the activation temperature in this example is 850℃, while other steps remain unchanged. The obtained sample is named H1.3T850S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0086] Example 10

[0087] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the activation temperature in this example is 900℃, while other steps remain unchanged. The obtained sample is named H1.3T900S2; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0088] Table 2 shows the nitrogen adsorption physical parameters, bulk density, and porosity of hierarchical porous carbon prepared at different activation temperatures in Examples 4 and 7-10 of this invention.

[0089]

[0090] Figure 7 The figures show the carbonized samples of hierarchical porous carbon prepared at different activation temperatures. As can be seen from the figures, the hierarchical porous carbon prepared at different activation temperatures can all maintain their original solid morphology, indicating that the activation temperature has no significant effect on the stability of its solid morphology. However, as the activation temperature increases, the strength and density of the samples gradually decrease. Figure 8 These are SEM images of hierarchical porous carbon prepared at different activation temperatures in Examples 4 and 7-10. As can be seen from the figures, the hierarchical porous carbon prepared at different activation temperatures can all maintain a complete macroporous structure. This is because its macroporous structure is mainly formed by polyurethane foaming. Increasing the activation temperature can only increase the carbonization degree of the skeleton, but cannot change its macroporous structure. Figure 9 The figures show the adsorption / desorption curves of porous carbon and nitrogen gases prepared at different activation temperatures in Examples 4 and 7-10. The figures reveal that the adsorption / desorption curves of some samples are not closed, indicating that most of the pores in these samples are flexible micropores. The adsorption / desorption curves of the five samples exhibit a weak hysteresis loop at relative pressures P / P0 = 0.1–0.9, and no obvious adsorption saturation plateau is observed near the saturation pressure (P / P0 > 0.99). This indicates that the hysteresis loop type is H4, and also suggests that the pore structure is not very regular. Figure 9 (c) The curve rises significantly at the saturation pressure region (P / P0 > 0.99), indicating adsorbate aggregation in the sample, similar to the end characteristic of a type I curve. This proves the presence of abundant microporous structures in the sample. It also shows that sodium citrate has the best ability to form micropores at 800℃. Figure 10The figures show the pore size distribution curves of hierarchical porous carbon prepared in Examples 4 and 7-10 at different activation temperatures. As can be seen from the figures, all five samples contain a large number of micropores and a certain number of mesopores, with the micropore size mainly distributed around 1-3 nm. With increasing activation temperature, the number of both micropores and mesopores initially increases and then decreases, reaching its maximum at 800℃. Further increases in activation temperature lead to a gradual decrease in the number of micropores. Table 2 shows the nitrogen adsorption physical parameters, bulk density, and porosity of hierarchical porous carbon at different activation temperatures. As the table shows, with increasing activation temperature, the pore volume, specific surface area, and porosity of the porous carbon all exhibit a trend of first increasing and then decreasing, while the bulk density shows the opposite trend of first decreasing and then increasing. When the activation temperature is 800℃, the pore volume and specific surface area of ​​the material reach their maximum values, 0.463 cc / g and 629.187 m² / g, respectively. Simultaneously, the porosity reaches its highest value, while the bulk density decreases to its lowest. When the activation temperature continues to rise, the pore volume, specific surface area, and porosity all decrease significantly. This is because the activation effect of sodium citrate decreases above 800℃, and the stability of the pore structure deteriorates at high temperatures, leading to a decrease in specific surface area, pore volume, and porosity. This indicates that 800℃ is the optimal activation temperature for this hierarchical porous carbon, at which point the activator effect is optimal.

[0091] Example 11

[0092] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the carbonization activation holding time in this example is 1 hour, while other steps remain unchanged. The obtained sample is named H1.3T800S1; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0093] Example 12

[0094] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the carbonization activation holding time in this example is 1.5 h, while other steps remain unchanged. The obtained sample is named H1.3T800S1.5; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0095] Example 13

[0096] A method for preparing a three-dimensional hierarchical porous carbon material differs from Example 4 in that the carbonization activation holding time in this example is 2.5 h, while other steps remain unchanged. The obtained sample is named H1.3T800S2.5; where "H" represents the ratio of activator to glucose, "T" represents the activation temperature, and "S" represents the activation time.

[0097] Table 3 shows the physical parameters, bulk density, and porosity of the graded porous carbon and nitrogen adsorption materials prepared in Examples 4, 11-13 of this invention with different activation times.

[0098]

[0099] Figure 11 These are images of samples of hierarchical porous carbon after carbonization at different activation times. As can be seen from the images, with the increase of activation time, the shape of hierarchical porous carbon gradually changes from a complete solid form to broken blocks or even powder, and the strength decreases sharply. This indicates that the increase of activation time will significantly affect the solid form of hierarchical porous carbon. Figure 12 These are SEM images of the graded porous carbons prepared in Examples 4 and 11-13 with different activation times. As shown in the images, the samples contain many loose, uneven macropores with a honeycomb-like surface structure, forming a three-dimensional interconnected porous structure. With prolonged activation time, the degree of pore structure completion decreases. This is because sodium citrate over-activates the raw materials, causing the pores to become loose. Furthermore, when the activation time is too long, the macroporous structure disappears because the solid morphology cannot be maintained. Figure 13 The figures show nitrogen adsorption / desorption isotherms for graded porous carbon with different activation times prepared in Examples 4 and 11-13. As can be seen from the figures, the adsorption / desorption curves of the samples are not closed, indicating that most of the pores in the samples are flexible micropores. After gas adsorption, the pore size shrinks, making it difficult for the gas to escape during desorption, thus causing the curves to not close. The adsorption curves of all samples are basically similar, showing a gentle upward trend in the relatively low pressure range (P / P0 < 0.1), and a weak H1-type hysteresis loop appearing at relative pressures P / P0 = 0.1~0.8. The adsorption amount increases steadily at P / P0 = 0.1~0.4, indicating that N2 molecules are adsorbed on the inner surface of the mesopores. The adsorption amount is significant around P / P0 = 0.4~0.8, indicating the presence of small mesopore sizes in the samples. Figure 14The figures show the pore size distribution curves of the graded porous carbon prepared in Examples 4 and 11-13 with different activation times. As can be seen from the figures, all samples contain a large number of micropores and a certain number of mesopores, with the mesopore size ranging from 1 to 3 nm. With increasing activation time, the number of micropores and mesopores increases, reaching its maximum when the holding time is 2 hours. However, when the holding time is too long, sodium citrate can over-activate the carbon, gradually reducing the integrity of the pore structure, causing the macropore structure to disappear, reducing the sample strength, and making it difficult to maintain a solid state, thus severely limiting its performance and applications. Table 3 shows the nitrogen adsorption physical parameters of the graded porous carbon with different activation times. As can be seen from the table, with increasing activation time, the specific surface area, pore volume, and porosity of the samples all show a trend of first increasing and then decreasing. When the holding time is 2 hours, the pore volume, specific surface area, and porosity of the samples reach their maximum, at 0.463 cc / g, 629.187 m³ / g, and 629.187 m³ / g, respectively. 2 / g and 94.26%.

[0100] In summary, this invention enables the preparation of three-dimensional hierarchical porous carbon with high specific surface area. By controlling the amount of sodium citrate added as an activator, the number of mesopores can be controlled, thereby increasing the specific surface area of ​​the material. Simultaneously, adjusting the activation temperature and time can improve the material's hardness. With increasing activator ratio, although the hierarchical porous carbon retains its solid shape, the solid gradually becomes more brittle, and its strength gradually decreases. The number of micropores and mesopores increases significantly, reaching its maximum when the ratio of sodium citrate to glucose is 1.3:1. With increasing activation temperature, the prepared hierarchical porous carbon maintains a complete macropore, micropore, and mesopore structure, and the number of pores initially increases and then decreases. With prolonged activation time, the degree of pore structure completion initially increases and then decreases. When the holding time is 2 hours, the sample exhibits the highest number of micropores and mesopores, and the best macropore structure completion. Therefore, based on the above results, when the ratio of sodium citrate to glucose is 1.3:1, the activation temperature is 800℃, and the activation time is 2h, the prepared hierarchical porous carbon has good mechanical strength and optimal hierarchical pore structure.

[0101] In summary, this invention enables the successful preparation of three-dimensional hierarchical porous carbon materials with uniform pore distribution, adjustable pore size, and high porosity. This method utilizes inexpensive raw materials, involves few process steps, is easily controlled, exhibits good repeatability, and requires no complex or expensive specialized equipment, resulting in low fixed asset investment and promising application prospects.

Claims

1. A method for preparing a three-dimensional hierarchical porous carbon material, characterized in that, Follow these steps: First, a polyurethane mixed precursor was prepared using polyether polyol and polymethylene polyphenyl isocyanate. Mixed powder was added to the polyurethane mixed precursor and mixed evenly by mechanical stirring. Then, a catalyst was added and mixed evenly. The mixture was allowed to stand and foam to form a hardened preform. The hardened preform was carbonized and activated to obtain porous carbon. The porous carbon was washed with water and dried to obtain three-dimensional hierarchical porous carbon.

2. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The process for preparing the polyurethane mixed precursor is as follows: polyether polyol and polymethylene polyphenyl isocyanate are mixed in a certain proportion and heated in a water bath at a constant temperature; the mass ratio of polyether polyol to polymethylene polyphenyl isocyanate is 1:1, the water bath heating temperature is 30℃~50℃, and the heating time is 5min~10min.

3. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The mechanical stirring is carried out at a speed of 500 r / min to 800 r / min.

4. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The mixed powder is a mixture of silicone oil, activator and glucose. The activator is sodium citrate. The mass ratio of activator to glucose is (1~1.5):

1. The mass ratio of mixed powder to precursor is (1~3.5):

1.

5. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The catalyst is added at a rate of 0.1% to 0.5% of the precursor mass, and the catalyst is triethylenediamine and dibutyltin dilaurate in a ratio of (0 to 4):

1.

6. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The foaming process is as follows: add water at a mass of 0.4% to 1.2% of the precursor as a foaming agent, stir thoroughly at a speed of 500 r / min to 800 r / min, and let it stand for foaming for 12 h to 24 h.

7. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The carbonization activation process is as follows: under the protection of argon atmosphere, the hardened blank is carbonized and activated at 700℃~900℃ for 1h~3h, and the heating rate is 4℃ / min~8℃ / min.

8. The method for preparing a three-dimensional hierarchical porous carbon material according to claim 1, characterized in that, The acid washing involves washing the porous carbon in 1 mol / L dilute hydrochloric acid for 6 to 12 hours; the drying involves drying at 80°C for 12 hours.

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