Preparation method of amino-modified biochar / SiO2 composite aerogel

Abstract

The application belongs to the field of new material preparation, and particularly relates to a preparation method of amino-modified biochar / SiO2 composite aerogel. The application prepares cellulose / SiO2 composite aerogel by taking cellulose as a template and tetraethyl orthosilicate as a silicon source, obtains biochar / SiO2 composite aerogel after high-temperature calcination, and then carries out amino modification on the biochar / SiO2 composite aerogel by using a polymer obtained by cross-linking reaction of 3-glycidoxypropyltrimethoxysilane and diethylenetriamine, to obtain amino-modified biochar / SiO2 composite aerogel. The amino-modified biochar / SiO2 composite aerogel prepared by the application has high selectivity for CO2 adsorption, and the preparation process is simple.

Description

Technical Field

[0001] This invention belongs to the field of new material preparation, and specifically relates to a method for preparing amino-modified biochar / SiO2 composite aerogel. Background Technology

[0002] During urban development, land use, and changes, massive deforestation has reduced the Earth's natural CO2 purification capacity. Emissions from fossil fuel combustion have led to a continuous increase in atmospheric CO2 concentration, exacerbating environmental problems. Therefore, CO2 capture is of great significance for addressing global warming and the greenhouse effect. CO2 capture, utilization, and storage technologies are considered one of the most direct and effective means to rapidly reduce atmospheric CO2 concentration. To date, large-scale CO2 separation processes have primarily relied on liquid amine absorption technology. This involves using aqueous solutions of monoethanolamine, diethanolamine, and methyldiethanolamine for large-scale CO2 capture. Although the absorption process has proven effective in capturing CO2, significant drawbacks remain. The main problems are the corrosiveness of liquid amines, the susceptibility to amine loss during operation, and the energy consumption during regeneration.

[0003] In response to this situation, many foreign institutions have conducted research on other adsorbents and found that solid adsorbents have better adsorption effects. These limitations can be overcome by attaching amine functional groups to solids with high surface area. Among them, aerogels have broad development prospects due to their excellent properties such as low density, high porosity, high specific surface area, low thermal conductivity, and low dielectric constant, as well as their unique structure. Traditional silica aerogels have poor mechanical properties and are brittle, while cellulose aerogels not only combine the excellent properties of traditional aerogels and polymer aerogels, but also have excellent biocompatibility and biodegradability, making them an excellent supporting material for reinforcing silica aerogels. Summary of the Invention

[0004] This invention provides a method for preparing amino-modified biochar / SiO2 composite aerogel, which can be used to adsorb CO2 from the air and has high adsorption and selectivity for CO2.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for preparing amino-modified biochar / SiO2 composite aerogel includes: hydrolyzing cellulose to obtain cellulose nanocrystals with a chiral helical structure, then reacting them with tetraethyl orthosilicate to prepare cellulose / SiO2 composite aerogel; then calcining at high temperature to obtain biochar / SiO2 composite aerogel; finally, amino-modifying the biochar / SiO2 composite aerogel with a polymer obtained by crosslinking 3-glycidyloxypropyltrimethoxysilane and diethylenetriamine to obtain amino-modified biochar / SiO2 composite aerogel.

[0007] Specifically, the following steps are included:

[0008] (1) Concentrated sulfuric acid and distilled water were mixed to prepare a concentrated sulfuric acid aqueous solution. Then, the defatted cotton was placed in the concentrated sulfuric acid aqueous solution and stirred in an oil bath at 45°C for 3 hours. Then, it was poured into ice water and allowed to stand for 12 hours to precipitate. The supernatant was removed, and the lower suspension was centrifuged and purified by dialysis to pH > 2.4 to obtain cellulose nanocrystals (CNCs) with chiral helical structure.

[0009] (2) CNCs with chiral helical structure were mixed with tetraethyl orthosilicate (TEOS), stirred at a constant speed at room temperature, and then the solution was allowed to stand. After removing the supernatant, the lower layer solution was replaced with water and ethanol, and then supercritical dried to obtain cellulose / SiO2 composite aerogel.

[0010] (3) The cellulose / SiO2 composite aerogel was placed in a tube furnace for high-temperature calcination to obtain biochar / SiO2 composite aerogel.

[0011] (4) 3-glycidyloxypropyltrimethoxysilane (GPTMS) and diethylenetriamine (DETA) were added to tetrahydrofuran and stirred at 70°C for 4 h. The temperature was then lowered to 25°C and stirred for 25 min. The epoxy groups of GPTMS reacted with the amino groups of DETA to form a highly cross-linked compound network. Then, biochar / SiO2 composite aerogel, ethanol and nitric acid were added and stirred at room temperature. SiO2 and GPTMS underwent a condensation reaction, which grafted the amino groups onto the composite aerogel to obtain amino-modified biochar / SiO2 composite aerogel.

[0012] Preferably, in step (1), the mass ratio of degreased cotton to concentrated sulfuric acid aqueous solution is 1:21; and the molar ratio of concentrated sulfuric acid, distilled water and ice water is 1:3:60.

[0013] Preferably, the volume ratio of CNCs to TEOS in step (2) is 12:(1.8-3.3).

[0014] Preferably, in step (2), the mixture is stirred at room temperature at a constant speed for 1 hour; the solution is then allowed to stand for 24 hours.

[0015] Preferably, the specific conditions for high-temperature calcination in step (3) are: under N2 protection, heating to 450°C and calcining for 6 hours.

[0016] Preferably, the molar ratio of GPTMS, DETA and TEOS is (5-12):(3-4):(8-15).

[0017] To improve CO2 adsorption capacity, the molar ratio of GPTMS, DETA and TEOS is (10-12):4:(8-15); more preferably, the molar ratio of GPTMS, DETA and TEOS is 10:4:15.

[0018] Preferably, the stirring reaction time at room temperature in step (4) is 1 hour.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. Using cellulose as a template, a cellulose / SiO2 composite aerogel was prepared. Cellulose becomes brittle during calcination into biochar; doping with mesoporous silica effectively prevents structural collapse and increases the specific surface area of ​​the material. Simultaneously, cellulose undergoes self-assembly during hydrolysis, forming a chiral helical structure that enhances its CO2 adsorption performance.

[0021] 2. Cellulose is a carbon material, which can achieve the purpose of reducing carbon and producing carbon with carbon.

[0022] 3. Amino modification was performed on the calcined cellulose / SiO2 composite aerogel to enhance the material's adsorption selectivity for CO2. Attached Figure Description

[0023] Figure 1 SEM images of cellulose nanocrystals (CNCs) (a), cellulose / SiO2 composite aerogel (b), biochar / SiO2 composite aerogel (c), and amino-modified biochar / SiO2 composite aerogel (d) in Example 1.

[0024] Figure 2 Nitrogen adsorption-desorption isotherms and pore size distribution diagrams of cellulose nanocrystals (CNCs) (a), cellulose / SiO2 composite aerogel (b), biochar / SiO2 composite aerogel (c), and amino-modified biochar / SiO2 composite aerogel (d) in Example 1.

[0025] Figure 3 The XPS total spectrum (a) and X-ray photoelectron spectra (b, c, d) of the cellulose / SiO2 composite aerogel, biochar / SiO2 composite aerogel, and amino-modified biochar / SiO2 composite aerogel in Example 1 are shown.

[0026] Figure 4 The adsorption curves of CO2, N2 and Ar for Example 2(a), Example 3(b), Comparative Example 1(c) and Example 1(d) are shown.

[0027] Figure 5 Adsorption curves of CO2 for different cellulose nanocrystal structures;

[0028] Figure 6 This is a cyclic diagram of the adsorption kinetics of CO2 on the amino-modified biochar / SiO2 composite aerogel of Example 1. Detailed Implementation

[0029] Example 1

[0030] (1) Add 75 mL (1.38 mol) concentrated sulfuric acid to 75 mL (4.17 mol) distilled water, stir well, and cool to room temperature. Then add 10 g of defatted cotton to the above mixed solution, stir in an oil bath at 45 °C for 3 h, and then pour into 1500 mL (83.4 mol) ice water and let it stand for 12 h to precipitate. Pour off the supernatant, take the lower suspension, centrifuge, and dialyze to purify until the pH value is greater than 2.4 to obtain CNCs with chiral helical structures.

[0031] (2) Take 12 mL of CNCs and 2 mL of (0.0089 mol) TEOS and mix them. Stir at a constant speed for 1 h at room temperature, then let the solution stand for 24 h. After the solution separates into layers, remove the supernatant and replace the lower layer with ethanol and water. Then dry it with supercritical carbon dioxide to obtain cellulose / SiO2 composite aerogel.

[0032] (3) The cellulose / SiO2 composite aerogel was placed in a tube furnace and calcined at N2 and 450℃ for 6 hours to obtain biochar / SiO2 composite aerogel.

[0033] (4) 1.24 mL (0.0045 mol) of GPTMS and 0.3 mL (0.0027 mol) of DETA were reacted in tetrahydrofuran and stirred at 70 °C for 4 h. The temperature was then lowered to 25 °C and stirred for 25 min. Then the biochar / SiO2 composite aerogel obtained in step (3), ethanol and nitric acid were added and stirred at 25 °C for 1 h to obtain amino-modified biochar / SiO2 composite aerogel.

[0034] Figure 1 The images shown are SEM images of cellulose nanocrystals (CNCs) (a), cellulose / SiO2 composite aerogel (b), biochar / SiO2 composite aerogel (c), and amino-modified biochar / SiO2 composite aerogel (d) in this embodiment. Figure 1 Layered structures were observed in (a)-(d). The entire structure consists of distinctly stacked strips, exhibiting an orderly and undulating arrangement, indicating that the CNCs, after self-assembly, possess a chiral helical structure with orderly layer arrangement. The orderly arranged pore structure improves the adsorption capacity of the composite aerogel to a certain extent, thereby enhancing the adsorption efficiency.

[0035] Figure 2The diagram shows the specific surface area and pore size distribution of cellulose nanocrystals (CNCs) (a), cellulose / SiO2 composite aerogel (b), biochar / SiO2 composite aerogel (c), and amino-modified biochar / SiO2 composite aerogel (d) in this embodiment. The specific surface area of ​​the cellulose nanocrystals (CNCs) is 182 m². 2 ·g -1 The pore size is 9.8539 nm; the specific surface area of ​​the cellulose / SiO2 composite aerogel is 176 m². 2 ·g -1 The pore size is 9.6874 nm; the specific surface area of ​​the biochar / SiO2 composite aerogel is 292 m². 2 ·g -1 The pore size is 9.1562 nm; the specific surface area of ​​the amino-modified biochar / SiO2 composite aerogel is 287 m². 2 ·g -1 The aperture is 8.9986 nm.

[0036] Figure 3 The XPS total spectrum (a) and X-ray photoelectron spectra (b, c, d) of the cellulose / SiO2 composite aerogel, biochar / SiO2 composite aerogel, and amino-modified biochar / SiO2 composite aerogel in this embodiment are shown below. Figure 3 (c) It can be seen that the C-Si bond indicates that Si has been successfully incorporated into the material. Figure 3 The presence of CN in (d) indicates that amino groups were successfully grafted onto the composite aerogel material.

[0037] Example 2

[0038] (1) Add 75 mL (1.38 mol) concentrated sulfuric acid to 75 mL (4.17 mol) distilled water, stir well, and cool to room temperature. Then add 10 g of defatted cotton to the above mixed solution, stir in an oil bath at 45 °C for 3 h, and then pour into 1500 mL (83.4 mol) ice water and let it stand for 12 h to precipitate. Pour off the supernatant, take the lower suspension, centrifuge, and dialyze to purify until the pH value is greater than 2.4 to obtain CNCs with chiral helical structures.

[0039] (2) Take 12 mL of CNCs and 3.3 mL (0.0149 mol) of TEOS and mix them. Stir at a constant speed for 1 h at room temperature, then let the solution stand for 24 h. After the solution separates into layers, remove the supernatant and replace the lower layer with ethanol and water. Then dry it with supercritical carbon dioxide to obtain cellulose / SiO2 composite aerogel.

[0040] (3) The cellulose / SiO2 composite aerogel was placed in a tube furnace and calcined at N2 and 450℃ for 6 hours to obtain biochar / SiO2 composite aerogel.

[0041] (4) 2.8 mL (0.01 mol) of GPTMS and 0.44 mL (0.00397 mol) of DETA were reacted in tetrahydrofuran and stirred at 70 °C for 4 h. Then the temperature was lowered to 25 °C and stirred for 25 min. Then the biochar / SiO2 composite aerogel obtained in step (3), ethanol and nitric acid were added and stirred at 25 °C for 1 h to obtain amino-modified biochar / SiO2 composite aerogel.

[0042] Example 3

[0043] (1) Add 75 mL (1.38 mol) concentrated sulfuric acid to 75 mL (4.17 mol) distilled water, stir well, and cool to room temperature. Then add 10 g of defatted cotton to the above mixed solution, stir in an oil bath at 45 °C for 3 h, and then pour into 1500 mL (83.4 mol) ice water and let it stand for 12 h to precipitate. Pour off the supernatant, take the lower suspension, centrifuge, and dialyze to purify until the pH value is greater than 2.4 to obtain CNCs with chiral helical structures.

[0044] (2) Take 12 mL of CNCs and 1.8 mL (0.008 mol) of TEOS and mix them. Stir at a constant speed for 1 h at room temperature, then let the solution stand for 24 h. After the solution separates into layers, remove the supernatant, replace the lower layer with ethanol and water, and then dry it with supercritical carbon dioxide to obtain cellulose / SiO2 composite aerogel.

[0045] (3) The cellulose / SiO2 composite aerogel was placed in a tube furnace and calcined at N2 and 450℃ for 6 hours to obtain biochar / SiO2 composite aerogel.

[0046] (4) 3.3 mL (0.012 mol) of GPTMS and 0.44 mL (0.00397 mol) of DETA were reacted in tetrahydrofuran and stirred at 70 °C for 4 h. Then the temperature was lowered to 25 °C and stirred for 25 min. Then the biochar / SiO2 composite aerogel obtained in step (3), ethanol and nitric acid were added and stirred at 25 °C for 1 h to obtain amino-modified biochar / SiO2 composite aerogel.

[0047] Comparative Example 1

[0048] (1) Add 75 mL (1.38 mol) concentrated sulfuric acid to 75 mL (4.17 mol) distilled water, stir well, and cool to room temperature. Then add 10 g of defatted cotton to the above mixed solution, stir in an oil bath at 45 °C for 3 h, and then pour into 1500 mL (83.4 mol) ice water and let it stand for 12 h to precipitate. Pour off the supernatant, take the lower suspension, centrifuge, and dialyze to purify until the pH value is greater than 2.4 to obtain CNCs with chiral helical structures.

[0049] (2) Take 12 mL of CNCs and 2 mL of (0.0089 mol) TEOS and mix them. Stir at a constant speed for 1 h at room temperature, then let the solution stand for 24 h. After the solution separates into layers, remove the supernatant and replace the lower layer with ethanol and water. Then dry it with supercritical carbon dioxide to obtain cellulose / SiO2 composite aerogel.

[0050] (3) The cellulose / SiO2 composite aerogel was placed in a tube furnace and calcined at N2 and 450℃ for 6 hours to obtain biochar / SiO2 composite aerogel.

[0051] (4) 4.66 mL (0.0267 mol) of APTMS was stirred and reacted with the biochar / SiO2 composite aerogel obtained in step (3), ethanol and nitric acid at 60 °C for 24 h. After the reaction was completed, the mixture was filtered, washed with toluene and ethanol, and dried at 100 °C for 24 h to obtain amino-modified biochar / SiO2 composite aerogel.

[0052] Figure 4 The figures show the adsorption curves of CO2, N2, and Ar for Examples 2(a), 3(b), Comparative Example 1(c), and 1(d). As can be seen from the figures, the adsorption capacity of the amino-modified biochar / SiO2 composite aerogel for CO2 is much greater than that for N2 and Ar, indicating that it has good CO2 adsorption selectivity. The amino-modified biochar / SiO2 composite aerogel of Example 1 has the highest CO2 adsorption performance, at 3.31 mmol / g. Comparative Example 1, which uses APTMS to aminate the biochar / SiO2 composite aerogel, achieves an adsorption capacity of 2.78 mmol / g, demonstrating that using GPTMS and DETA for amino modification results in superior adsorption performance of the composite aerogel.

[0053] Comparative Example 2

[0054] Compared with Example 1, the reaction conditions of step (1) were changed: the mixture was heated in a water bath at 40°C for 7 days, while the other steps were the same as in Example 1.

[0055] Compared to Example 1, the cellulose nanocrystals supporting the amino-modified biochar / SiO2 composite aerogel prepared in Comparative Example 2 did not form a chiral helical structure. Figure 5 It is known that the chiral helical structure of cellulose is beneficial to increasing the adsorption capacity of CO2 by the composite aerogel.

[0056] Figure 6This is a cyclic adsorption kinetic diagram of CO2 adsorption by the amino-modified biochar / SiO2 composite aerogel of Example 1. At room temperature, after four adsorption cycles, the adsorption efficiency of the composite aerogel for CO2 decreased by only 10%, indicating that the composite aerogel material has good thermal stability.

Claims

1. A method for preparing amino-modified biochar / SiO2 composite aerogel, characterized in that, The preparation method includes: hydrolyzing cellulose to obtain cellulose nanocrystals with a chiral helical structure, then reacting them with tetraethyl orthosilicate to prepare cellulose / SiO2 composite aerogel; then calcining at high temperature to obtain biochar / SiO2 composite aerogel; finally, using a polymer obtained by crosslinking 3-glycidyloxypropyltrimethoxysilane and diethylenetriamine to amide-modify the biochar / SiO2 composite aerogel to obtain amino-modified biochar / SiO2 composite aerogel; the preparation method of the cellulose nanocrystals includes the following steps: mixing concentrated sulfuric acid and distilled water to prepare a concentrated sulfuric acid aqueous solution, then placing defatted cotton into the concentrated sulfuric acid aqueous solution, stirring in an oil bath at 45°C for 3 hours, then pouring it into ice water and allowing it to stand for 12 hours to precipitate, then removing the supernatant, centrifuging the lower suspension, and dialysis purification to pH > 2.4 to obtain cellulose nanocrystals.

2. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 1, characterized in that, Includes the following steps: (1) Cellulose nanocrystals were mixed with tetraethyl orthosilicate and stirred at a constant speed at room temperature. The solution was then allowed to stand, and the supernatant was removed. The lower layer solution was replaced with water and ethanol as solvents, and then dried by supercritical drying to obtain cellulose / SiO2 composite aerogel. (2) The cellulose / SiO2 composite aerogel was placed in a tube furnace for high-temperature calcination to obtain biochar / SiO2 composite aerogel. (3) 3-glycidyloxypropyltrimethoxysilane and diethylenetriamine were added to tetrahydrofuran and stirred at 70°C for 4 h. The temperature was then lowered to 25°C and stirred for 25 min. Biochar / SiO2 composite aerogel, ethanol and nitric acid were added and stirred at room temperature to obtain amino-modified biochar / SiO2 composite aerogel.

3. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 1, characterized in that, The mass ratio of degreased cotton to concentrated sulfuric acid aqueous solution is 1:21; the molar ratio of concentrated sulfuric acid, distilled water and ice water is 1:3:

60.

4. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 2, characterized in that, In step (1), the volume ratio of cellulose nanocrystals to tetraethyl orthosilicate is 12:(1.8-3.3).

5. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 2, characterized in that, In step (1), stir at room temperature at a constant speed for 1 hour; let the solution stand for 24 hours.

6. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 2, characterized in that, The specific conditions for high-temperature calcination in step (2) are: under N2 protection, heat to 450℃ and calcinate for 6 hours.

7. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 2, characterized in that, The molar ratio of 3-glycidyloxypropyltrimethoxysilane, diethylenetriamine and tetraethyl orthosilicate is (5-12):(3-4):(8-15).

8. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 7, characterized in that, The molar ratio of 3-glycidyloxypropyltrimethoxysilane, diethylenetriamine and tetraethyl orthosilicate is (10-12):4:(8-15).

9. The method for preparing amino-modified biochar / SiO2 composite aerogel according to claim 2, characterized in that, The stirring reaction time at room temperature in step (3) is 1 hour.

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