Preparation process of mesoporous carbon

Abstract

The application discloses a mesoporous carbon preparation process with recyclable silicon source and mesoporous carbon with small pore size and large specific surface area. The mesoporous carbon preparation process comprises the following steps: preparing a silicon template: reacting a fluosilicic acid solution with calcium carbonate, and separating calcium fluoride precipitate and silica sol; the pH of the silica sol is 2-5; the concentration of silicon dioxide in the silica sol is 1-8 wt%; preparing a precursor: dissolving a carbon source and an organic acid in the silica sol, drying, grinding, and carbonizing in an inert atmosphere to obtain a C / Si precursor; the organic acid comprises at least one of oxalic acid, tannic acid, acetic acid and citric acid; removing the silicon template and recycling the silicon source: treating the C / Si precursor with hydrofluoric acid, and performing solid-liquid separation to obtain mesoporous carbon and a fluosilicic acid solution, wherein the fluosilicic acid solution is used for preparing the silicon template. The specific surface area of the mesoporous carbon is greater than 800 m 2 / g, and the pore size is less than 6 nm.

Description

Technical Field

[0001] This invention relates to the field of mesoporous carbon preparation technology, specifically to a silicon-source-recyclable mesoporous carbon preparation process and mesoporous carbon with small pore size and large specific surface area. Background Technology

[0002] Mesoporous carbon, as a material with high specific surface area, strong adsorption capacity, good electrical conductivity, stable chemical properties, and tunable surface chemistry, has broad application potential in catalyst supports, adsorption, hydrogen storage, electrode materials, environmental applications, and medicine. Currently, the preparation process of mesoporous carbon is mostly based on template methods, divided into hard template methods and soft template methods. The advantage of the template method is that the prepared mesoporous carbon has a high specific surface area and uniform pore size with regular arrangement; the disadvantage is that the pore size of the mesoporous carbon is limited by the wall thickness of the template, making it difficult to meet the requirements of special industries such as electrochemical electrode materials (pore size requirements below 6 nm); and a large amount of waste acid and alkali liquid is generated during template removal. Therefore, it is necessary to find a preparation process for mesoporous carbon materials with high specific surface area and uniform pore size that uses inexpensive raw materials, reasonably solves the waste acid and alkali problem, and produces materials with high specific surface area and uniform pore size.

[0003] Patent application CN202010572464.5 discloses a process for rapidly preparing high-purity fluorite through the reaction of fluorosilicic acid and calcium carbonate. This patented technology utilizes the reaction of fluorosilicic acid and calcium carbonate, with the aid of a protective agent, to form calcium fluoride at room temperature. High-purity fluorite powder is then obtained by separating silica from the calcium fluoride. This patented technology does not involve the treatment of silica.

[0004] Patent application CN201711329074.X discloses a method for preparing a mesoporous carbon catalyst. This method uses phenol-aldehyde as the carbon precursor and commercially available silica sol as a hard template agent. The carbon / silicon composite material is prepared through sol-gelation, drying, and carbonization. Then, it is treated with an alkaline solution to simultaneously etch and support the material, and finally dried to obtain an alkaline mesoporous carbon catalyst. This method simplifies the preparation and loading process of mesoporous carbon, but it still generates alkaline waste liquid, and the pore size of the obtained mesoporous carbon is similar to that of silica particles in silica sol, exhibiting a relatively large pore size and a small specific surface area.

[0005] Patent application CN200910152795.7 discloses a method for preparing acrylonitrile polymer-based mesoporous carbon. This method involves adjusting the pH of a silica sol with a particle size of 5–20 nm using ammonia, modifying the silica sol with 2-amidinylpropane, adding a carbon source and emulsifier, followed by carbonization and hydrofluoric acid removal of the silica template to obtain the mesoporous carbon product. The pore size of the mesoporous carbon obtained by this method can be adjusted within the range of 4–45 nm, depending on the size of the silica particles in the silica sol. Synthesizing mesoporous carbon with a pore size below 6 nm requires a strict requirement that the silica template particle size be below 8 nm. Furthermore, the method does not involve the treatment of hydrofluoric acid / fluorosilicic acid wastewater. Summary of the Invention

[0006] This invention provides a silicon-source-recyclable mesoporous carbon preparation process and the corresponding mesoporous carbon, which features high specific surface area, large pore volume, and small pore size. The process boasts a high silicon template recycling rate and a silicon recovery rate exceeding 80%, generating virtually no waste acid or alkali solutions. Furthermore, the high specific surface area, large pore volume, and small pore size of the mesoporous carbon product make it suitable for applications in fields with stringent pore size requirements, such as electrode materials, shape-selective catalysis, and selective adsorption.

[0007] A process for preparing mesoporous carbon with a recyclable silicon source includes:

[0008] Preparation of silicon template: A fluorosilicic acid solution is reacted with calcium carbonate to separate calcium fluoride precipitate and silica sol; the pH of the silica sol is 2–5; the concentration of silicon dioxide in the silica sol is 1–8 wt%.

[0009] Precursor preparation: A carbon source and an organic acid are dissolved in silica sol, dried, ground, and carbonized under an inert atmosphere to obtain a C / Si precursor; the organic acid includes at least one of oxalic acid, tannic acid, acetic acid, and citric acid;

[0010] Remove silicon template and recover silicon source: Treat C / Si precursor with hydrofluoric acid, and separate solid and liquid to obtain mesoporous carbon and fluorosilicic acid solution. The fluorosilicic acid solution is used to prepare silicon template.

[0011] This invention utilizes a hard template method to prepare mesoporous carbon. Fluorosilicic acid is used as the silicon source and reacts with calcium carbonate to obtain a silica sol template. The carbon source is then mixed with the silica sol template and carbonized to obtain a carbon / silicon precursor. Hydrofluoric acid is used to remove the silica template, yielding the mesoporous carbon product. The resulting acid waste liquid contains fluorosilicic acid, which can be directly recycled as a silicon source to react with the next batch of calcium carbonate to obtain another silica sol template, thus achieving silicon source recycling. The mesoporous carbon prepared by this process has advantages such as small pore size, large specific surface area, and adjustable pore volume, and the preparation process generates virtually no waste liquid.

[0012] The mesoporous carbon preparation process may further include: reacting the calcium fluoride precipitate with sulfuric acid to generate hydrofluoric acid, which is used to treat the C / Si precursor. That is, the hydrogen fluoride used to remove the silicon template in the process of this invention can be partially or entirely recovered from fluorine resources during the fluorosilicic acid solution recycling process, obtained by hydrolyzing the calcium fluoride precipitate formed by the reaction of calcium carbonate in sulfuric acid. Thus, the process of this invention can simultaneously achieve the recycling of silicon and fluorine, requiring only the addition of calcium carbonate, sulfuric acid, a carbon source, and an organic acid.

[0013] The fluorosilicic acid solution used in the mesoporous carbon preparation process can be obtained from the by-products of the fertilizer industry and / or from the recycling of fluorosilicic acid waste liquid after treating C / Si precursors with hydrofluoric acid.

[0014] In the aforementioned mesoporous carbon preparation process, the silica sol obtained during the preparation of the silicon template is an acidic silica sol with a pH of 2-5 and a silica concentration of 1-8 wt%. The morphology of silica in this acidic silica sol is not fixed, and it is mostly spherical silicon monomers and silicon-oxygen oligomers with a particle size of about 7 nm. Its surface contains abundant silanol groups. After adjusting the pH to alkaline or after drying, the oligomers and silicon monomers polymerize to form silica microspheres with a particle size of about 15 nm that are closely arranged.

[0015] In the aforementioned mesoporous carbon preparation process, during the preparation of the silicon template, the mass ratio of calcium carbonate to water in the reaction system can be 1:2 to 7, with calcium carbonate being in sufficient or excessive amounts relative to fluorosilicic acid. Furthermore, the molar ratio of fluorosilicic acid to calcium carbonate can be 1:3 to 5.

[0016] The carbon source in the aforementioned mesoporous carbon preparation process may include at least one of glucose, sucrose, lactose, maltose, glycine, humic acid, and soluble starch.

[0017] In the aforementioned mesoporous carbon preparation process, during the preparation of the precursor, the mass ratio of the carbon source to the silicon dioxide in the silica sol can be 2 to 9:1.

[0018] In the aforementioned mesoporous carbon preparation process, during the preparation of the precursor, the molar ratio of the organic acid to the silica in the silica sol can be 0.01 to 0.5:1.

[0019] In the aforementioned mesoporous carbon preparation process, the inert atmosphere is a gaseous atmosphere that does not participate in the reaction, specifically including a nitrogen atmosphere and / or a rare gas atmosphere such as argon.

[0020] In the aforementioned mesoporous carbon preparation process, the carbonization temperature can be 700–850℃, and the time can be 1–2 hours.

[0021] In the aforementioned mesoporous carbon preparation process, during the treatment of the C / Si precursor with hydrofluoric acid, the molar ratio of hydrofluoric acid to silicon dioxide in the C / Si precursor can be 5.5 to 8:1.

[0022] In the aforementioned mesoporous carbon preparation process, the treatment time for treating the C / Si precursor with hydrofluoric acid can be 12–24 hours.

[0023] In the aforementioned mesoporous carbon preparation process, during the treatment of the C / Si precursor with hydrofluoric acid, the hydrofluoric acid can be used to treat the C / Si precursor in the form of an aqueous hydrofluoric acid solution. Furthermore, the mass fraction of hydrofluoric acid in the aqueous hydrofluoric acid solution can be 8% to 15%.

[0024] The present invention also provides mesoporous carbon prepared by the aforementioned mesoporous carbon preparation process. Furthermore, the specific surface area of ​​the mesoporous carbon is greater than 800 m². 2 / g, pore size less than 6nm.

[0025] Compared with the prior art, the beneficial effects of this invention are as follows:

[0026] The hard template used in this invention is a fresh acidic silica sol obtained by reacting fluorosilicic acid with carbonates. The pH of the fresh acidic silica sol is 2-5, and the morphology of the silica in it is not fixed, mostly consisting of spherical silicon monomers and silicon-oxygen oligomers with a particle size of about 7 nm, and their surfaces contain abundant silanol groups. A soluble carbon source and organic acid are directly added to the fresh acidic silica sol without further treatment; the functional groups on the surface of the carbon source condense with the silanol groups on the surface of the silica, restricting the polymerization and growth of silicon-oxygen oligomers and silicon monomers during drying and carbonization, promoting the shrinkage of silica particles, thereby reducing the particle size of silica particles in the C / Si composite to below 6 nm. The mesoporous carbon formed after silicon removal in the C / Si composite obtained by this in-situ condensation and organic acid-assisted pore-forming method has a pore size of below 6 nm.

[0027] The mesoporous carbon prepared by the process of this invention has a high specific surface area, large pore volume, small pore size and uniform distribution, and there is basically no waste acid or alkali solution discharged during the preparation process, and the obtained fluorosilicic acid solution can be recycled.

[0028] The process of this invention is expected to provide a solution to the problem of waste liquid treatment during the large-scale production of mesoporous carbon; and the obtained mesoporous carbon with small pore size and large specific surface area has broad application prospects in catalysis, energy, adsorption and other fields. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process for preparing silicon-source-recyclable mesoporous carbon according to the present invention.

[0030] Figure 2 The N2 physical adsorption isotherm and pore size distribution diagram are shown for the mesoporous carbon prepared in Example 3.

[0031] Figure 3 The N2 physical adsorption isotherm and pore size distribution diagram are shown for the mesoporous carbon prepared in Example 8. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] An example of a silicon-source-recyclable mesoporous carbon preparation process, see [link to relevant documentation]. Figure 1 It may include:

[0034] Preparation of silicon template: A fluorosilicic acid solution reacts with calcium carbonate, and the calcium fluoride solid and silica sol are separated by filtration; the calcium fluoride solid can be reacted with sulfuric acid to form hydrofluoric acid, which can be used to remove the silicon template;

[0035] Precursor preparation: Carbon source and organic acid are dissolved in silica sol to form silicon-carbon composite precursor, which is then dried, ground, and carbonized in an inert atmosphere to obtain C / Si precursor (or silicon / carbon composite material);

[0036] Silicon template removal and silicon source recovery: After the C / Si precursor is crushed, it is soaked in hydrofluoric acid to remove silicon. Solid-liquid separation is performed to obtain mesoporous carbon solid and dilute fluorosilicic acid solution. The dilute fluorosilicic acid solution can be concentrated to form fluorosilicic acid solution for the preparation of silicon template.

[0037] Example 1

[0038] (1) First, take 7.5g of calcium carbonate and add it to 15g of water at a mass ratio of 1:2. After mixing, add 11.3g of 30wt% fluorosilicic acid solution. A large number of bubbles are generated during the reaction. After filtration, the filter cake is a mixture of calcium carbonate and calcium fluoride, and the filtrate is a silica sol with a pH of 3.5 and a silica concentration of 5.8wt%.

[0039] (2) Add 3g glucose and 0.45g oxalic acid to silica sol, dry at 110℃ for 6h, grind the resulting block solid into powder, and heat to 700℃ under nitrogen atmosphere for 1h to obtain C / Si precursor.

[0040] (3) Add the C / Si precursor to 24g of 10wt% hydrofluoric acid aqueous solution, let stand for 12h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0041] (4) Add 6g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0042] Example 2

[0043] (1) First, take 7g of calcium carbonate and add it to 35g of water at a mass ratio of 1:5. After mixing, add 8g of 30wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 3.4 and a silica concentration of 2.4wt%.

[0044] (2) Add 2.5g of sucrose and 3g of tannic acid to the silica sol, dry at 110°C for 12h, grind the resulting block solid into powder, and heat to 850°C under a nitrogen atmosphere for 1.5h to obtain the C / Si precursor.

[0045] (3) Add the C / Si precursor to 22g of 10wt% hydrofluoric acid aqueous solution, let stand for 12h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0046] (4) Add 7g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0047] Example 3

[0048] (1) First, take 5g of calcium carbonate and add it to 15g of water at a mass ratio of 1:3. After mixing, add 8g of 30wt% fluorosilicic acid solution, filter, the filter cake is calcium fluoride, and the filtrate is silica sol with pH 2.7 and silica concentration of 4.6wt%.

[0049] (2) Add 8g of sucrose and 0.3g of oxalic acid to silica sol, dry at 110°C for 3h, dry at 160°C for 3h, grind the resulting block solid into powder, and heat to 800°C under nitrogen atmosphere for 1h to obtain C / Si precursor.

[0050] (3) Add the C / Si precursor to 23g of 10wt% hydrofluoric acid aqueous solution, let stand for 18h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0051] (4) Add 5g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0052] Figure 2 The N2 physical adsorption isotherm and pore size distribution diagram are shown for the mesoporous carbon product prepared in this embodiment.

[0053] Example 4

[0054] (1) First, take 11.2g of calcium carbonate and add it to 33.6g of water at a mass ratio of 1:3. After mixing, add 19g of 25wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 3.2 and a silica concentration of 4.0wt%.

[0055] (2) Add 10g of soluble starch and 0.6g of citric acid to silica sol, dry at 110°C for 12h, grind the resulting block solid into powder, and heat to 750°C under nitrogen atmosphere for 1.5h to obtain C / Si precursor.

[0056] (3) Add the C / Si precursor to 40g of 8wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0057] (4) Add 8.4g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0058] Example 5

[0059] (1) First, take 50g of calcium carbonate and add it to 100g of water at a mass ratio of 1:2. After mixing, add 70g of 35wt% fluorosilicic acid solution, filter, the filter cake is calcium fluoride, and the filtrate is silica sol with pH 2.3 and silica concentration of 7.0wt%.

[0060] (2) Add 40g glucose and 10.6g citric acid to silica sol, dry at 160℃ for 12h, grind the resulting block solid into powder, and heat to 850℃ under nitrogen atmosphere for 2h to obtain C / Si precursor.

[0061] (3) Add the C / Si precursor to 200g of 10wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0062] (4) Add 50g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0063] Example 6

[0064] (1) First, take 11.6g of calcium carbonate and add it to 34.8g of water at a mass ratio of 1:3. After mixing, add 16g of 30wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 2.7 and a silica concentration of 4.2wt%.

[0065] (2) Add 4g of sucrose and 0.8g of oxalic acid to the silica sol, dry at 110°C for 12h, grind the resulting block solid into powder, and heat to 700°C under a nitrogen atmosphere for 1h to obtain the C / Si precursor.

[0066] (3) Add the C / Si precursor to 40g of 10wt% hydrofluoric acid aqueous solution, let stand for 12h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0067] (4) Add 11.6g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0068] Example 7

[0069] (1) First, take 5.1g of calcium carbonate and add it to 25.5g of water at a mass ratio of 1:5. After mixing, add 8g of 30wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 2.9 and a silica concentration of 3.1wt%.

[0070] (2) Add 4g of soluble starch and 0.5g of tannic acid to silica sol, dry at 110°C for 6h, grind the resulting block solid into powder, and heat to 700°C under argon atmosphere for 1h to obtain C / Si precursor.

[0071] (3) Add the C / Si precursor to 25g of 8wt% hydrofluoric acid aqueous solution, let stand for 12h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0072] (4) Add 6g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0073] Example 8

[0074] (1) First, take 5.5g of calcium carbonate and add it to 11g of water at a mass ratio of 1:2. After mixing, add 12g of 20wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 3.5 and a silica concentration of 4.6wt%.

[0075] (2) Add 2g of sucrose and 0.3g of oxalic acid to the silica sol, dry at 110°C for 4h, dry at 160°C for 4h, grind the resulting block solid into powder, and heat it to 800°C under an argon atmosphere for 1h to obtain the C / Si precursor.

[0076] (3) Add the C / Si precursor to 24g of 10wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0077] (4) Add 6g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0078] Figure 3 The N2 physical adsorption isotherm and pore size distribution diagram are shown for the mesoporous carbon product prepared in this embodiment.

[0079] Example 9

[0080] (1) First, take 5g of calcium carbonate and add it to 15g of water at a mass ratio of 1:3. After mixing, add 8g of 30wt% fluorosilicic acid solution, filter, the filter cake is calcium fluoride, and the filtrate is silica sol with pH 2.7 and silica concentration of 4.6wt%.

[0081] (2) Add 8g of sucrose and 0.3g of oxalic acid to silica sol, dry at 110°C for 3h, dry at 160°C for 3h, grind the resulting block solid into powder, and heat to 800°C under nitrogen atmosphere for 1h to obtain C / Si precursor.

[0082] (3) The calcium fluoride obtained in step 1 was added to a dilute sulfuric acid solution and heated at 70°C. The mixture was then filtered to obtain a hydrofluoric acid solution and a calcium sulfate precipitate. The hydrofluoric acid solution was diluted to obtain 19 g of 10 wt% hydrofluoric acid, with a recovery rate of 95%.

[0083] (4) Add the C / Si precursor to the hydrofluoric acid obtained in step 3, let it stand for 18 hours, filter it, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0084] (5) Add 5g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0085] Example 10

[0086] (1) First, take 5.6g of calcium carbonate and add it to 16.8g of water at a mass ratio of 1:3. After mixing, add 12g of 20wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 3.5 and a silica concentration of 3.6wt%.

[0087] (2) Add 5g of soluble starch and 0.5g of oxalic acid to silica sol, dry at 110°C for 6h, grind the resulting block solid into powder, and heat to 750°C under nitrogen atmosphere for 1.5h to obtain C / Si precursor.

[0088] (3) Add the C / Si precursor to 35g of 8wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0089] (4) Add 8.4g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0090] Example 11

[0091] (1) First, take 5.5g of calcium carbonate and add it to 11g of water at a mass ratio of 1:2. After mixing, add 24g of 10wt% fluorosilicic acid solution, filter, and the filter cake is a mixture of calcium carbonate and calcium fluoride. The filtrate is a silica sol with a pH of 4.1 and a silica concentration of 3.0wt%.

[0092] (2) Add 4g of sucrose and 0.2g of acetic acid to the silica sol, dry at 110°C for 8h, grind the resulting block solid into powder, and heat to 800°C under a nitrogen atmosphere for 1.5h to obtain the C / Si precursor.

[0093] (3) Add the C / Si precursor to 30g of 12wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0094] (4) Add 5.5g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0095] Comparative Example 1

[0096] The difference from Example 3 is that the silicon template used is commercially available silicon dioxide powder, and there is no silicon recycling.

[0097] (1) Weigh 2g of commercially available silica powder with a particle size of 15nm and place it in 30g of water to form a suspension. Add 16g of sucrose and 0.6g of oxalic acid and dissolve completely.

[0098] (2) The solution was dried at 110°C for 3 hours and then at 160°C for 3 hours to obtain a blocky solid. The solid was ground and then heated to 800°C under a nitrogen atmosphere and held for 1 hour to obtain the C / Si precursor.

[0099] (3) Add the C / Si precursor to 20g of 10wt% hydrofluoric acid aqueous solution, let stand for 18h, filter, and the filter cake is the mesoporous carbon product.

[0100] Comparative Example 2

[0101] The difference from Example 8 is that the silicon template used is commercially available silicon dioxide powder, and there is no silicon recycling.

[0102] (1) Weigh 1g of commercially available silica powder with a particle size of 15nm and place it in 16g of water to form a suspension. Add 2g of sucrose and 0.3g of oxalic acid and dissolve completely.

[0103] (2) The solution was dried at 110°C for 4 hours and at 160°C for 4 hours to obtain a blocky solid. The solid was ground and heated to 800°C under an argon atmosphere and held for 1 hour to obtain a C / Si precursor.

[0104] (3) Add the C / Si precursor to 20g of 10wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, and the filter cake is the mesoporous carbon product.

[0105] Comparative Example 3

[0106] (1) First, take 5g of calcium carbonate and add it to 15g of water at a mass ratio of 1:3. After mixing, add 8g of 30wt% fluorosilicic acid solution, filter, and the filter cake is calcium fluoride and the filtrate is silica sol.

[0107] (2) Adjust the pH of the silica sol to 6-8. The silica sol will quickly gel and settle. Dry and grind to obtain silica powder.

[0108] (3) Add silicon dioxide powder to 21g of water, mix evenly, then add 8g of sucrose and 0.3g of oxalic acid; dry at 110℃ for 3h, dry at 160℃ for 3h, grind the resulting block solid into powder, and program the temperature to 800℃ under nitrogen atmosphere and hold for 1h to obtain C / Si precursor.

[0109] (3) Add the C / Si precursor to 23g of 10wt% hydrofluoric acid aqueous solution, let stand for 18h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0110] (4) Add 5g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0111] Comparative Example 4

[0112] The only difference from Example 3 is that after the silica sol is prepared in step (1), its pH is adjusted to 12-13 with ammonia. In this process, the silica sol is still in sol form and no gel precipitation occurs.

[0113] Comparative Example 5

[0114] (1) Take 10g of calcium carbonate and add it to 10g of water. After mixing, add 10g of 40wt% fluorosilicic acid solution, filter, the filter cake is calcium fluoride, and the filtrate is 9.4wt% silica sol.

[0115] (2) Add 16g of sucrose and 0.3g of oxalic acid to silica sol, dry at 110°C for 3h, dry at 160°C for 3h, grind the resulting block solid into powder, and heat to 800°C under nitrogen atmosphere for 1h to obtain C / Si precursor.

[0116] (3) Add the C / Si precursor to 23g of 10wt% hydrofluoric acid aqueous solution, let stand for 18h, filter, recover silicon from the filtrate, and the filter cake is the mesoporous carbon product.

[0117] (4) Add 5g of calcium carbonate to the filtrate to obtain silica sol again and complete the silica cycle.

[0118] Comparative Example 6

[0119] The only difference from Example 8 is that no organic acid is added during the preparation of the precursor in step 2; all other steps are the same.

[0120] Comparative Example 7

[0121] (1) Take 2g of ordered mesoporous silica SBA-15 into 21g of water, add 4g of sucrose and 0.6g of oxalic acid, mix evenly, dry at 110℃ for 4h, dry at 160℃ for 4h, grind the resulting block solid into powder, and heat it to 800℃ under an argon atmosphere and hold for 1h to obtain C / Si precursor.

[0122] (2) Add the C / Si precursor to 24g of 10wt% hydrofluoric acid aqueous solution, let stand for 24h, filter, the filtrate is fluorosilicic acid solution, and the filter cake is mesoporous carbon product.

[0123] Comparative Example 8

[0124] The only difference from Comparative Example 7 is that the solution used for removing silicon from the C / Si precursor is a 1.3 mol / L sodium hydroxide aqueous solution in ethanol, with an ethanol:water mass ratio of 2:1. The filtrate obtained in this comparative example is an aqueous solution of sodium silicate in ethanol.

[0125] Table 1 shows the physical properties, carbonization yield, and silicon recovery rate of the mesoporous carbon products prepared by the processes of each embodiment.

[0126] Table 1

[0127]

[0128] The carbonization yield is 100% of the mass of mesoporous carbon product / the mass of the added carbon source;

[0129] The silicon recovery rate is calculated as: (number of moles of silicon in the filtrate fluorosilicic acid / raw material of the fluorosilicic acid solution) × 100%.

[0130] Table 2 shows the physical properties, carbonization yield, and silicon recovery rate of the mesoporous carbon products prepared by each comparative process.

[0131] Table 2

[0132]

[0133] The carbonization yield is 100% of the mass of mesoporous carbon product / the mass of the added carbon source;

[0134] The silicon recovery rate is calculated as: (number of moles of silicon in the filtrate fluorosilicic acid / raw material of the fluorosilicic acid solution) × 100%.

[0135] Comparing Example 3 with Comparative Example 1, it can be found that under the same conditions, using silica sol obtained from the reaction of fluorosilicic acid and carbonate as a template, the prepared mesoporous carbon has a smaller particle size of 2.5 nm and a larger specific surface area of ​​863 m². 2 / g.

[0136] Comparing Example 8 with Example 3, it can be observed that after reducing the mass ratio of carbon source to silica sol, the specific surface area and pore volume of the prepared mesoporous carbon significantly increased, while the pore size remained below 6 nm. This is because reducing the mass ratio of carbon source to silica sol reduced the amount of carbon source condensed on the silica sol surface, weakening the confinement effect of the carbon source on silicon-oxygen monomers and silicon-oxygen oligomers during drying and carbonization. Furthermore, the reduction in carbon source resulted in a thinner carbon layer in the C / Si composite after carbonization. Consequently, the pore volume, pore size, and specific surface area of ​​the mesoporous carbon product increased to varying degrees.

[0137] Comparing Example 8 with Comparative Example 2, it can be found that after changing the mass ratio of carbon source to silica sol, using commercially available silica powder with a particle size of approximately 15 nm as a template, the mesoporous carbon prepared by the same method shows only a small increase in specific surface area and pore volume, while the pore size remains essentially unchanged. Using the silica sol of this invention as a template makes it easier to adjust the properties of the mesoporous carbon.

[0138] Comparing Example 9 and Example 3, it can be seen that the properties and silicon recovery rates of the mesoporous carbon samples obtained by recovering hydrofluoric acid with calcium fluoride and those obtained by adding hydrofluoric acid are basically the same as those obtained by removing silicon from the solution, proving that the recycling of fluorine resources in this method is feasible.

[0139] Comparing Example 3 with Comparative Examples 3 and 4, it can be observed that by altering the properties of the acidic silica sol and preparing mesoporous carbon using alkaline silica sol or gelled silica powder as templates in the same manner, the specific surface area and pore volume of the mesoporous carbon are significantly reduced, while the pore size is significantly increased. This is because, without the confinement effect of a carbon source, changing the solution pH to neutral or alkaline causes the silicon monomers and silicon-oxygen oligomers in the original acidic silica sol to polymerize into small spheres with a particle size of approximately 15 nm, similar in properties to commercially available silica with a particle size of approximately 15 nm; correspondingly, the mesoporous carbon prepared using either as a template also exhibits similar properties.

[0140] Compared with Comparative Example 5, it can be found that under the same conditions, the pore size of the mesoporous carbon prepared using high-concentration silica sol as a template increases, while the specific surface area and pore volume decrease. Similar to the effect of adjusting the pH of silica sol, when the concentration of silica sol is too high, the silicon monomers and silicon-oxygen oligomers inside spontaneously polymerize to form spherical silica particles. The silica particles that act as templates during dehydration and carbonization become larger. Correspondingly, the pore size of the mesoporous carbon product increases, while the pore volume and specific surface area decrease.

[0141] Comparing Example 8 and Comparative Example 6, it can be observed that without the addition of organic acids to assist in pore formation during the preparation of the precursor, the pore size of the resulting mesoporous carbon is significantly increased, while the specific surface area and pore volume are significantly decreased. This is because the organic acids accelerate the condensation of hydroxyl groups during the dissolution of the carbon source in the silica sol, making the pre-oxidation process of the carbon source before carbonization more complete, and intensifying the shrinkage of silica during the dehydration process of the silica sol, thus assisting the carbonization process of the carbon source. Furthermore, the decomposition of organic acids at high temperatures generates gas, which also plays a role in assisting pore formation, increasing the specific surface area and pore volume. If oxalic acid is not added, the carbonization yield of the mesoporous carbon product decreases, the pore size increases, and correspondingly, its specific surface area and pore volume decrease.

[0142] Comparing Example 8 with Comparative Examples 7 and 8, it can be seen that using ordered mesoporous silica SBA-15 as a template can yield mesoporous carbon with a pore size of less than 6 nm. However, this method generates waste liquid from silicon removal, which is either fluorosilicic acid or sodium silicate solution. It is difficult to re-prepare the template SBA-15 using these two types of waste liquid. The mesoporous carbon prepared by this method can maintain a pore size of 2–6 nm, and the preparation process achieves silicon template recycling, generating virtually no waste liquid.

[0143] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A process for preparing mesoporous carbon with a recyclable silicon source, characterized in that, include: Preparation of silicon template: A fluorosilicic acid solution is reacted with calcium carbonate to separate calcium fluoride precipitate and silica sol; the pH of the silica sol is 2-5; The concentration of silica in the silica sol is 1-8 wt%; Precursor preparation: A carbon source and an organic acid are dissolved in silica sol, dried, ground, and carbonized under an inert atmosphere to obtain a C / Si precursor; the organic acid includes at least one of oxalic acid, tannic acid, acetic acid, and citric acid; Remove silicon template and recover silicon source: Treat C / Si precursor with hydrofluoric acid, and separate solid and liquid to obtain mesoporous carbon and fluorosilicic acid solution. The fluorosilicic acid solution is used to prepare silicon template.

2. The process for preparing mesoporous carbon according to claim 1, characterized in that, The mesoporous carbon preparation process further includes: reacting the calcium fluoride precipitate with sulfuric acid to generate hydrofluoric acid, which is used to treat the C / Si precursor.

3. The mesoporous carbon preparation process according to claim 1, characterized in that, The fluorosilicic acid solution used in the mesoporous carbon preparation process is obtained by recycling fluorosilicic acid waste liquid from the fertilizer industry and / or after treating C / Si precursors with hydrofluoric acid.

4. The process for preparing mesoporous carbon according to claim 1, characterized in that, In the process of preparing silicon templates, the mass ratio of calcium carbonate to water in the reaction system is 1:2~7, the amount of calcium carbonate relative to fluorosilicic acid is just sufficient or excessive, and the molar ratio of fluorosilicic acid to calcium carbonate is 1:3~5.

5. The process for preparing mesoporous carbon according to claim 1, characterized in that, The carbon source includes at least one of glucose, sucrose, lactose, maltose, glycine, humic acid, and soluble starch.

6. The process for preparing mesoporous carbon according to claim 1, characterized in that, During the preparation of the precursor, the mass ratio of the carbon source to the silicon dioxide in the silica sol is 2~9:

1.

7. The process for preparing mesoporous carbon according to claim 1, characterized in that, During the preparation of the precursor, the molar ratio of the organic acid to the silica in the silica sol is 0.01~0.5:

1.

8. The process for preparing mesoporous carbon according to claim 1, characterized in that, The inert atmosphere is a nitrogen atmosphere; The carbonization temperature is 700~850℃, and the time is 1~2 h.

9. The process for preparing mesoporous carbon according to claim 1, characterized in that, During the treatment of C / Si precursors with hydrofluoric acid: The molar ratio of hydrofluoric acid to silica in the C / Si precursor is 5.5~8:1; The processing time is 12~24 hours; In the process of treating C / Si precursors with hydrofluoric acid, the hydrofluoric acid is used in the form of an aqueous solution of hydrofluoric acid, with a mass fraction of 8% to 15%.

10. The process for preparing mesoporous carbon according to any one of claims 1 to 9, characterized in that, The specific surface area of ​​the mesoporous carbon is greater than 800 m². 2 / g, pore size less than 6 nm.

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