A method for preparing carbon microspheres by alkali / urea aqueous solution low-temperature pretreatment of cellulose by a hydrothermal method

Abstract

The present application belongs to the technical field of environmental protection materials, and particularly relates to a method for preparing carbon microspheres by hydrothermal method of cellulose pretreated by alkali / urea aqueous solution at low temperature. The method comprises the following steps: dissolving and pretreating cellulose by alkali / urea solution at low temperature to obtain regenerated cellulose gel; transferring the regenerated cellulose gel to a reaction kettle to perform hydrothermal reaction; naturally cooling the reaction kettle to room temperature; and washing and drying the obtained hydrothermal solid to obtain carbon microspheres. The method effectively reduces the crystallinity and polymerization degree of cellulose, improves the intensity of the hydrothermal reaction process, and forms more stable, uniform and smooth hydrothermal carbon microspheres. The method provides a broad prospect for large-scale and sustainable synthesis of carbon microspheres, which opens up a new way for functional carbon material synthesis by efficient utilization of cellulose. The hydrothermal carbon microspheres prepared by the method have the advantages of environmental friendliness, sustainability and low cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection materials, and particularly relates to a method for preparing carbon microspheres by hydrothermal method from cellulose pretreated at low temperature by alkali / urea aqueous solution. BACKGROUND

[0002] With the rapid growth of the world population and the rapid development of industry, the demand for energy is growing, and energy has gradually become an important material basis for economic development and social progress. Since the industrial revolution, limited reserves of fossil fuels such as oil, coal and natural gas have been rapidly consumed, causing oil prices to rise, restricting social and economic development, and causing a series of environmental problems. Under this severe energy pressure and increasingly prominent environmental pollution background, it is particularly important to find alternative energy sources.

[0003] Carbon materials can be applied to lithium ion batteries, catalyst carriers and other fields due to their good electrical conductivity and thermal conductivity. With the discovery of fullerenes and carbon nanotubes, people have paid more attention to carbon materials, especially spherical carbon materials, which stand out from many carbon materials due to their excellent performance. Compared with non-renewable resources such as coal and pitch as raw materials, polymer-based carbon microspheres are green and renewable, and cause less environmental pollution, so they attract a lot of research and attention.

[0004] At present, the methods commonly used in experimental research to prepare carbon microspheres include template method, arc discharge method and chemical vapor deposition method, etc. The raw materials of these methods mainly come from non-renewable resources such as coal and heavy oil, and the process is complicated, pollutes the environment and has high preparation cost. Based on these shortcomings, researchers are actively seeking new methods for synthesizing carbon microspheres that are more environmentally friendly, energy-saving and sustainable. Among them, the hydrothermal carbonization (HTC) technology with biomass-based precursor has attracted increasing attention. In the reaction process, external heating and the saturation vapor pressure of subcritical water generate system pressure. Compared with traditional thermochemical conversion methods, HTC has low temperature, no limitation on water content of raw materials, low energy consumption, and has become an efficient method for biomass pretreatment and biomass full-component conversion.

[0005] Among biomass raw materials, cellulose is a natural high molecular substance with the largest reserves, the widest distribution and the highest yield in the world. It has the characteristics of wide raw material sources, low price, simple and green preparation process, and low production cost to prepare functional carbon microsphere materials. However, cellulose is a polysaccharide type linear natural high polymer with high degree of polymerization and high crystallinity, which cannot be effectively converted and utilized. On the one hand, the natural network structure formed by lignin and hemicellulose tightly wrapped around cellulose hinders the conversion efficiency of cellulose; on the other hand, the high crystallinity of cellulose itself also limits the effective conversion of cellulose. SUMMARY

[0006] The technical problem to be solved by this invention is to provide a method for preparing carbon microspheres by low-temperature pretreatment of cellulose with alkali / urea aqueous solution via hydrothermal method. This method provides a broad prospect for the large-scale and sustainable synthesis of carbon microspheres and will also open up a new way for the efficient utilization of cellulose to synthesize functional carbon materials.

[0007] This invention is implemented as follows:

[0008] A method for preparing carbon microspheres by low-temperature pretreatment of cellulose with alkali / urea aqueous solution and hydrothermal method is disclosed. The method uses cellulose as raw material, and pretreatment of cellulose with alkali / urea solution at low temperature to obtain regenerated cellulose gel. Then, the regenerated cellulose gel is transferred to a reaction vessel for hydrothermal reaction. After the reaction vessel is naturally cooled to room temperature, the obtained hydrothermal solid is washed and dried to obtain carbon microspheres.

[0009] The method specifically includes the following steps:

[0010] (1) A mixture of sodium hydroxide, urea and distilled water of a certain concentration is placed in a refrigerator at -4℃ to -8℃ to pre-cool it to obtain an alkali / urea solution.

[0011] (2) Add cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature to completely dissolve the cellulose in the alkali / urea aqueous solution to obtain a transparent cellulose solution.

[0012] (3) The transparent cellulose solution obtained in step (2) is precipitated in dilute acetic acid solution, and then washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0013] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) to obtain cellulose gel;

[0014] (5) The cellulose gel obtained in step (4) is mixed with distilled water and placed in a high-temperature reactor for hydrothermal reaction to obtain a hydrothermal carbon mixed solution.

[0015] (6) The hydrothermal carbon mixture obtained in step (5) is filtered and repeatedly washed with ethanol and distilled water until the filtrate becomes clear, and the undried hydrothermal carbon microspheres are obtained.

[0016] (7) The undried hydrothermal carbon microspheres from step (6) are dried to finally obtain the target product, hydrothermal carbon microspheres.

[0017] Furthermore:

[0018] The amount of sodium hydroxide added to the alkali / urea solution in step (1) is 1-20% wt.

[0019] The amount of urea added to the alkali / urea solution in step (1) is 1-20% wt.

[0020] Preferably, in step (1), the amount of sodium hydroxide added to the alkali / urea solution is 16%, and the amount of urea added is 3%.

[0021] The amount of cellulose added in step (1) is 2% to 6% of the mass of the alkali / urea solution.

[0022] The concentration of the dilute acetic acid in step (3) is 0.1 to 0.3 mol / L.

[0023] The mass ratio of the cellulose gel to distilled water in step (5) is 1:1 to 2:1.

[0024] In step (5), the hydrothermal reaction is carried out at a temperature of 200-280°C and a holding time of 4-8 hours.

[0025] The present invention has the following advantages:

[0026] This invention pretreats cellulose with an alkali / urea solution to obtain cellulose gel, and then uses the pretreated cellulose hydrogel as a raw material to directly synthesize hydrothermal carbon microspheres through a hydrothermal reaction. This method effectively reduces the crystallinity and degree of polymerization of cellulose, increases the intensity of the hydrothermal reaction process, and forms more stable, uniform, and smooth hydrothermal carbon microspheres. This method provides broad prospects for the large-scale, sustainable synthesis of carbon microspheres, which will open up a new route for the efficient utilization of cellulose to synthesize functional carbon materials. The hydrothermal carbon microspheres prepared by this method have advantages such as environmental friendliness, sustainability, and low cost, and have great potential application value as catalyst supports, energy storage materials, and soft template agents. Attached Figure Description

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Figure 1 X-ray diffraction patterns of cellulose raw materials and cellulose after pretreatment with different alkali / urea solution ratios: (0-5); where system 0 (0% NaOH and 0% urea), system 1 (0% NaOH and 19% urea), system 2 (3% NaOH and 16% urea), system 3 (7% NaOH and 12% urea), system 4 (13% NaOH and 6% urea) and system 5 (16% NaOH and 3% urea).

[0029] Figure 2 Hydrothermal carbonization paradigm diagram of cellulose feedstock and pretreated cellulose under different alkali / urea solution ratios. 。

[0030] Figure 3 For cellulosic feedstocks and differentCellulose hydrothermal carbon microspheres pretreated with alkali / urea solution Microscopic structure schematic. Figure 1 Detailed Implementation

[0031] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and specific embodiments. Unless otherwise specified in the embodiments, conditions are performed according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0032] Example 1

[0033] (1) A mixed solution of 0g sodium hydroxide, 19g urea and 81g distilled water was placed in a -5℃ refrigerator and frozen for 10h to obtain an alkali / urea solution.

[0034] (2) Add 4g of cellulose (α-cellulose powder purchased from Inokai) to the alkali / urea solution obtained in step (1), and stir rapidly for 5min at room temperature to obtain a transparent cellulose solution;

[0035] (3) The transparent cellulose solution obtained in step (2) is precipitated in 0.1 mol / L dilute acetic acid solution and washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0036] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) at 10,000 rpm for 5 min to obtain cellulose gel;

[0037] (5) The cellulose gel obtained in step (4) is mixed with distilled water at a ratio of 1:1 and placed in a high-pressure reactor. The temperature is set to 200℃ and the holding time is 4h. After the reaction is completed, a hydrothermal carbon mixed solution is obtained.

[0038] (6) Filter the hydrothermal carbon mixture obtained in step (5) using a Buchner funnel and wash it repeatedly with ethanol and distilled water until the filtrate becomes clear, to obtain undried hydrothermal carbon microspheres.

[0039] (7) The undried hydrothermal carbon microspheres obtained in step (6) are dried in a vacuum drying oven at 105°C for 4 hours to finally obtain the target product, hydrothermal carbon microspheres.

[0040] Example 2

[0041] (1) A mixed solution of 3g sodium hydroxide, 16g urea and 81g distilled water was placed in a -5℃ refrigerator and frozen for 10h to obtain an alkali / urea solution.

[0042] (2) Add 4.5g of cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature for 10min to obtain a transparent cellulose solution;

[0043] (3) The transparent cellulose solution obtained in step (2) is precipitated in 0.15 mol / L dilute acetic acid solution and washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0044] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) at 10,000 rpm for 15 min to obtain cellulose gel;

[0045] (5) The cellulose gel obtained in step (4) is mixed with distilled water at a ratio of 1.2:1 and placed in a high-pressure reactor. The temperature is set to 220℃ and the holding time is 5h. After the reaction is completed, a hydrothermal carbon mixed solution is obtained.

[0046] (6) Filter the hydrothermal carbon mixture obtained in step (5) using a Buchner funnel and wash it repeatedly with ethanol and distilled water until the filtrate becomes clear, to obtain undried hydrothermal carbon microspheres.

[0047] (7) The undried hydrothermal carbon microspheres obtained in step (6) are dried in a vacuum drying oven at 105°C for 4 hours to finally obtain the target product, hydrothermal carbon microspheres.

[0048] Example 3

[0049] (1) A mixed solution of 7g sodium hydroxide, 12g urea and 81g distilled water was placed in a -5℃ refrigerator and frozen for 10h to obtain an alkali / urea solution.

[0050] (2) Add 4.8g of cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature for 15min to obtain a transparent cellulose solution;

[0051] (3) The transparent cellulose solution obtained in step (2) is precipitated in 0.2 mol / L dilute acetic acid solution and washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0052] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) at 10,000 rpm for 15 min to obtain cellulose gel;

[0053] (5) The cellulose gel obtained in step (4) is mixed with distilled water at a ratio of 1.5:1 and placed in a high-pressure reactor. The temperature is set to 240℃ and the holding time is 6h. After the reaction is completed, a hydrothermal carbon mixed solution is obtained.

[0054] (6) Filter the hydrothermal carbon mixture obtained in step (5) using a Buchner funnel and wash it repeatedly with ethanol and distilled water until the filtrate becomes clear, to obtain undried hydrothermal carbon microspheres.

[0055] (7) The undried hydrothermal carbon microspheres obtained in step (6) are dried in a vacuum drying oven at 105°C for 4 hours to finally obtain the target product, hydrothermal carbon microspheres.

[0056] Example 4

[0057] (1) A mixed solution of 13g sodium hydroxide, 6g urea and 81g distilled water was placed in a -5℃ refrigerator and frozen for 10h to obtain an alkali / urea solution.

[0058] (2) Add 5.5g of cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature for 20min to obtain a transparent cellulose solution;

[0059] (3) The transparent cellulose solution obtained in step (2) is precipitated in 0.25 mol / L dilute acetic acid solution and washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0060] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) at 10,000 rpm for 20 min to obtain cellulose gel;

[0061] (5) The cellulose gel obtained in step (4) is mixed with distilled water at a ratio of 1.8:1 and placed in a high-pressure reactor. The temperature is set to 260℃ and the holding time is 6h. After the reaction is completed, a hydrothermal carbon mixed solution is obtained.

[0062] (6) Filter the hydrothermal carbon mixture obtained in step (5) using a Buchner funnel and wash it repeatedly with ethanol and distilled water until the filtrate becomes clear, to obtain undried hydrothermal carbon microspheres.

[0063] (7) The undried hydrothermal carbon microspheres obtained in step (6) are dried in a vacuum drying oven at 105°C for 4 hours to finally obtain the target product, hydrothermal carbon microspheres.

[0064] Example 5

[0065] (1) A mixed solution of 16g ​​sodium hydroxide, 3g urea and 81g distilled water was placed in a -5℃ refrigerator and frozen for 10h to obtain an alkali / urea solution.

[0066] (2) Add 6g of cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature for 25min to obtain a transparent cellulose solution;

[0067] (3) The transparent cellulose solution obtained in step (2) is precipitated in 0.3 mol / L dilute acetic acid solution and washed repeatedly with distilled water until the solution is neutral to obtain cellulose gel solution (neutral);

[0068] (4) Centrifuge the cellulose gel solution (neutral) obtained in step (3) at 10,000 rpm for 25 min to obtain cellulose gel;

[0069] (5) The cellulose gel obtained in step (4) is mixed with distilled water at a ratio of 2:1 and placed in a high-pressure reactor. The temperature is set to 280℃ and the holding time is 7h. After the reaction is completed, a hydrothermal carbon mixed solution is obtained.

[0070] (6) Filter the hydrothermal carbon mixture obtained in step (5) using a Buchner funnel and wash it repeatedly with ethanol and distilled water until the filtrate becomes clear, to obtain undried hydrothermal carbon microspheres.

[0071] (7) The undried hydrothermal carbon microspheres obtained in step (6) are dried in a vacuum drying oven at 105°C for 4 hours to finally obtain the target product, hydrothermal carbon microspheres.

[0072] Example 6

[0073] The crystallinity content of the sample was analyzed using X-ray diffraction (XRD) (see attached). Figure 2 The crystallinity of cellulose pretreated with different alkali / urea solution ratios was calculated. The peak shapes of cellulose without any treatment (system 0) and cellulose treated with only 19% urea (system 1) were basically the same, with the three strongest peaks located at approximately 14.5°, 16°, and 22.5°, corresponding to the crystallinity of cellulose crystals. The 101 and 002 crystal planes are identical to the type I diffraction pattern of cellulose, proving that urea treatment did not alter the crystal form of cellulose. The three strongest peaks in systems 2, 3, 4, and 5 are located approximately at 12°, 20°, and 22°, respectively, corresponding to the 101 and 002 crystal planes of cellulose. The 002 crystal plane, identical to the type II diffraction pattern of cellulose, confirms that upon the addition of sodium hydroxide, the crystal structure of cellulose changes from crystal form I to crystal form II when it dissolves and reprecipitates. Based on the cellulose height method, the crystallinity of cellulose in each system was calculated to be 78.6%, 75.3%, 62.5%, 51.3%, 46.2%, and 42.5%, respectively. Systems 0 and 1 exhibit higher crystallinity, corresponding to cellulose crystal form I. The crystallinity of systems 2, 3, 4, and 5 decreases with increasing sodium hydroxide content, corresponding to cellulose crystal form II. This conforms to the rule that type II crystallinity is lower than type I crystallinity, and also demonstrates that pretreatment with the alkali / urea system reduces the degree of polymerization of cellulose and improves reaction accessibility. Therefore, in the hydrothermal reaction, cellulose pretreated with alkali / urea is more easily hydrolyzed into glucose. Then, glucose begins to undergo dehydration polymerization to form aromatic compounds and oligosaccharides. When the solution reaches the critical supersaturation concentration, oligomers, aromatic compounds and macromolecules containing carboxylic acid groups are further dehydrated to form crystal nuclei. When the pressure and temperature reach a certain level, the crystal nuclei cross-link and polymerize to form the final carbon microspheres.

[0074] Example 6

[0075] Elemental composition analysis of the samples was performed using energy-dispersive spectroscopy (EDS) (see attached). Figure 2 (See Table 1). The effect of pretreatment with different alkali / urea solution ratios on the hydrothermal carbonization of cellulose was investigated by elemental analysis. Figure 2 This paper presents a hydrothermal carbonization paradigm for cellulose pretreated with different alkali / urea solution ratios in a 220℃ high-pressure reactor for 5 hours. The reaction types of cellulose during hydrothermal carbonization at different alkali / urea solution ratios are qualitatively determined by the arrows and directional extension. Starting with untreated cellulose (system 0), and using pretreated cellulose with different alkali / urea solution ratios as the endpoints, principal vectors are established by connecting the start and end points sequentially. Vector decomposition is then performed along the three different arrow directions representing dehydration, decarboxylation, and demethylation. Longer subvectors indicate more vigorous reactions of that type during carbonization. Figure 2 It can be seen that the reaction type remained unchanged before and after the alkali / urea solution pretreatment; the main difference lay in the intensity of the reaction. From... Figure 3 It can be seen from the data that the O / C and H / C ratios in the hydrothermal carbon both decrease continuously with the increase of the sodium hydroxide ratio. From the direction vector, it can be seen that the main reactions are decarboxylation and dehydroxylation.

[0076] Table 1 Yield and elemental analysis of hydrothermal carbon microspheres

[0077]

[0078] Cellulose gels treated with different alkali / urea solution ratios were used to synthesize carbon microspheres via a hydrothermal method. Elemental analysis and yield calculations were performed. Table 1 details the elemental analysis data of the carbon microspheres prepared by the hydrothermal method from cellulose treated with different alkali / urea solution ratios. Compared with the control group (system 0), the cellulose treated with different alkali / urea solution ratios showed no significant changes in O / C and H / C values. However, as the sodium hydroxide ratio in the pretreatment gradually increased, the C content also showed an increasing trend, while the O / C and H / C values ​​decreased accordingly. This is because as the degree of cellulose degradation increases, the crystallinity and degree of polymerization decrease significantly, which enhances the dehydroxylation and carboxylation reactions, leading to the removal of H and O elements and a relative increase in the C content. Further analysis of the changes in the recovery rate of hydrothermal carbon microspheres and the C element recovery rate during the hydrothermal process revealed that the yield of hydrothermal carbon microspheres prepared from pretreated cellulose decreased compared to the raw cellulose as the sodium hydroxide concentration increased. This is because the increased sodium hydroxide concentration leads to a decrease in the crystallinity and degree of polymerization of cellulose. During the hydrothermal process, most of the cellulose can be hydrolyzed into glucose, which undergoes dehydration and polymerization to form aromatic compounds. The aromatic compounds and macromolecules containing carboxylic acid groups further dehydrate to form crystal nuclei. The crystal nuclei cross-link and polymerize to form the final carbon microspheres. However, the hydrothermal carbon microspheres synthesized by glucose have a lower yield than those synthesized by cellulose. This is because many side reactions occur during the dehydration and polymerization of glucose, while most of the cellulose undergoes direct aromatization.

[0079] Example 7

[0080] Physical characterization of the samples was performed using scanning electron microscopy (see attached image). Figure 3 ). Figure 3 (0) refers to hydrothermal carbon microspheres synthesized from cellulose raw materials through a hydrothermal reaction; Figure 3 In the diagrams 1), 2), 3), 4), and 5), carbon microspheres were synthesized from cellulose gels obtained by pretreatment of cellulose under different alkali / urea solution ratios via a hydrothermal method.

[0081] from ​As can be seen, the carbon microspheres obtained from the cellulose raw material pretreated in System 1 are basically consistent in morphology, because urea has almost no effect on the crystallinity of cellulose and only plays an auxiliary role in the pretreatment process. The morphology of the hydrothermal carbon microspheres obtained from System 2 pretreatment is only slightly different from that of System 1, because the content of sodium hydroxide added is small and the urea ratio is the main solvent, so only a small part of the hydrogen bonds of cellulose are broken, and the difference in carbon microsphere morphology is not obvious. The size distribution of carbon microspheres in Systems 0 to 2 is 2 to 200 nm; the formed hydrothermal carbon microspheres are tightly aggregated. From System 3 onwards, the particle size of hydrothermal carbon microspheres changes significantly, with a size distribution of 1 to 2 μm; because under low temperature conditions, the small molecules of urea can prevent the large molecules of cellulose from getting close to each other, and the increase in sodium hydroxide content allows more and more hydroxide ions to penetrate into the amorphous and crystalline regions of cellulose, producing a violent swelling and dissolution effect, thereby breaking the hydrogen bonds between and within cellulose molecules, and enhancing the degree of cellulose hydrolysis during the hydrothermal process. With further increases in the sodium hydroxide ratio, the particle size of carbon microspheres in systems 4 and 5 can reach 3–20 μm, and the morphology of the hydrothermal carbon microspheres becomes more uniform and smooth. This is because the alkali / urea solution disrupts the intramolecular and intermolecular hydrogen bonds in the cellulose structure, transforming cellulose from crystal form I to crystal form II. The degree of crystallinity and polymerization of cellulose is significantly reduced, with sodium hydroxide playing a major role. During the hydrothermal reaction, cellulose with lower crystallinity and polymerization is more easily hydrolyzed into monosaccharides. Finally, the monosaccharides undergo dehydration, condensation, polymerization, and aromatization reactions to form the final carbon microspheres.

[0082] In summary, this invention characterized the changes in crystallinity of cellulose under different ratios of alkaline / urea aqueous solutions and the elemental analysis and morphological structure of hydrothermal carbon microspheres. The dehydration and deoxygenation reactions of cellulose pretreated with different ratios of alkaline / urea aqueous solutions were enhanced to a certain extent during the hydrothermal process. Scanning electron microscopy results showed that the hydrothermal carbon microspheres were uniform, smooth spherical particles with a relatively orderly arrangement, and their particle size increased with decreasing crystallinity.

[0083] X-ray diffraction patterns show a significant decrease in the crystallinity of cellulose pretreated with alkali / urea. Elemental analysis reveals that cellulose pretreated with alkali / urea solution underwent more vigorous dehydrogenation and deoxygenation reactions during hydrothermal treatment compared to untreated cellulose, resulting in more stable hydrothermal carbon microspheres. Scanning electron microscopy (SEM) analysis shows that the hydrothermal carbon microspheres prepared from cellulose pretreated with alkali / urea solution are uniform, smooth, and relatively ordered spherical particles. System 5 (16% sodium hydroxide and 3% urea) showed the best technical performance: it exhibited the most significant reduction in crystallinity and degree of polymerization; elemental analysis showed more pronounced and vigorous dehydrogenation and deoxygenation reactions, resulting in more stable hydrothermal carbon microspheres; and SEM analysis revealed a more uniform and smooth morphology of the carbon microspheres.

[0084] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An application of carbon microspheres prepared by a hydrothermal method using cellulose pretreatment with alkali / urea aqueous solution at low temperature, characterized in that: The applications refer to their use as catalyst supports, energy storage materials, or as soft template agents. The preparation method of the carbon microspheres includes: using cellulose as a raw material, pretreating the cellulose with an alkali / urea solution at low temperature to obtain regenerated cellulose gel; then transferring the regenerated cellulose gel to a reaction vessel for hydrothermal reaction; after the reaction vessel naturally cools to room temperature, washing and drying the obtained hydrothermal solid to obtain carbon microspheres; the method specifically includes the following steps: (1) A mixture of sodium hydroxide, urea and distilled water of a certain concentration is placed in a refrigerator at -4℃ to -8℃ to pre-cool it to obtain an alkali / urea solution; (2) Add cellulose to the alkali / urea solution obtained in step (1) and stir rapidly at room temperature to completely dissolve the cellulose in the alkali / urea aqueous solution to obtain a transparent cellulose solution. (3) The transparent cellulose solution obtained in step (2) is precipitated in dilute acetic acid solution, and then repeatedly washed with distilled water until the solution is neutral to obtain cellulose gel solution; (4) Centrifuge the cellulose gel solution obtained in step (3) to obtain cellulose gel; (5) The cellulose gel obtained in step (4) is mixed with distilled water and placed in a high-temperature reactor for hydrothermal reaction to obtain a hydrothermal carbon mixed solution. (6) The hydrothermal carbon mixture obtained in step (5) is filtered and repeatedly washed with ethanol and distilled water until the filtrate becomes clear, and the undried hydrothermal carbon microspheres are obtained. (7) The undried hydrothermal carbon microspheres from step (6) are dried to finally obtain the target product, hydrothermal carbon microspheres; in: In step (1), the amount of sodium hydroxide added to the alkali / urea solution is 16%wt, and the amount of urea added is 3%wt. The amount of cellulose added in step (2) is 2% to 6% of the mass of the alkali / urea solution; The mass ratio of the cellulose gel to distilled water in step (5) is 1:1 to 2:1; In step (5), the hydrothermal reaction is carried out at a temperature of 200-280℃ and a holding time of 4-8h.

Images