A bamboo-based porous carbon modified material and a preparation method thereof

Abstract

The application belongs to the technical field of biomass carbon material preparation, and particularly relates to a bamboo-based porous carbon modified material and a preparation method thereof. Bamboo powder, anhydrous zinc chloride, ammonium chloride, melamine, sucrose, choline chloride, lactic acid, deionized water and anhydrous ethanol are used as main raw materials, and iron-zinc tannin polyethyleneimine precursors and calcium-aluminum double-crosslinked alginate templates are introduced. The iron-zinc tannin polyethyleneimine precursors and the calcium-aluminum double-crosslinked alginate templates are prepared first, then the bamboo powder is pretreated by using a deep eutectic solvent formed by choline chloride and lactic acid, and then is compounded with an activation impregnation system, and then is subjected to pre-carbonization, activation carbonization, water vapor activation, washing, drying, crushing and screening to obtain the bamboo-based porous carbon modified material. The material has a developed pore structure, rich surface active sites and low ash residue, and is suitable for the fields of adsorption separation, catalytic carrier and energy storage material.

Description

Technical Field

[0001] This invention belongs to the field of biomass carbon material preparation technology, specifically relating to a bamboo-based porous carbon modified material and its preparation method. Background Technology

[0002] Bamboo-based porous carbon materials are functional carbon materials prepared using bamboo and its processing byproducts as carbon sources. They possess characteristics such as renewable raw materials, wide availability, low cost, abundant natural fiber channels, and easily controllable carbon skeletons, making them suitable for applications in adsorption separation, catalytic carriers, pollutant purification, and energy storage electrodes. Existing bamboo-based porous carbon materials are typically prepared using direct carbonization, chemical activation, or physical activation methods. Zinc chloride, alkali metal salts, acidic dehydrating agents, and water vapor are commonly used to regulate pore structure. However, due to the tight interweaving of cellulose, hemicellulose, and lignin in bamboo powder, conventional impregnation methods struggle to ensure uniform penetration of the activator into the cell cavities and fiber bundles. During heat treatment, localized shrinkage, pore blockage, carbon skeleton collapse, and uneven activation can easily occur, making it difficult to simultaneously improve the specific surface area, pore volume, mesopore ratio, and pore connectivity of the resulting material.

[0003] To improve the surface properties and pore structure of bamboo-based porous carbon, existing technologies often involve the addition of nitrogen-containing substances, oxygen-containing functionalized components, metal salts, or template agents for modification. Raw materials such as melamine, ammonium chloride, and sucrose can provide nitrogen sources, induce gas-phase pores, and assist carbon sources to some extent; however, their interaction with bamboo powder relies mainly on simple mixing, resulting in uneven distribution, migration losses during pyrolysis, and insufficient utilization of active sites. Tannic acid, metal salts, and polyethyleneimine-like substances have complexing and cross-linking effects, which can improve the distribution of metal sites and nitrogen- and oxygen-containing structures. However, if the pH of the system is not properly controlled, metal ions are prone to hydrolysis and deposition or competitive complexation, affecting the uniformity of the precursor. Sodium alginate can form gel templates with calcium and aluminum salts; however, if the metal salt anion selection is inappropriate, insoluble byproducts are easily generated, leading to uneven gel structure and increased burden on subsequent washing.

[0004] Furthermore, the industrial preparation of bamboo-based porous carbon-modified materials needs to consider the commercial availability of raw materials, the mildness of the process, the ease of template removal, and ash control. The deep eutectic solvent formed by choline chloride and lactic acid can pretreat bamboo powder, which is beneficial for loosening the wood fiber structure and improving the subsequent activation and impregnation effect. Anhydrous zinc chloride can promote the dehydration, cross-linking, and pore formation of bamboo-based components, and secondary activation with steam can further open closed pores. If an iron-zinc tannin polyethyleneimine precursor is synergistically introduced into the bamboo-based composite precursor with a calcium-aluminum double-crosslinked alginate template, and then washed with hydrochloric acid aqueous solution, disodium ethylenediaminetetraacetate aqueous solution, and deionized water, it is expected to solve the problems of uneven pore structure, insufficient mesopores, few surface active sites, high inorganic residues, and unstable overall performance in existing bamboo-based porous carbon materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a bamboo-based porous carbon-modified material, comprising the following raw materials in parts by weight:

[0006] Bamboo powder 100-120 parts, anhydrous zinc chloride 55-110 parts, ammonium chloride 12-32 parts, melamine 6-22 parts, sucrose 4-14 parts, iron-zinc tannin polyethyleneimine precursor 3-10 parts, calcium-aluminum double crosslinked alginate template 8-24 parts, choline chloride 45-75 parts, lactic acid 80-140 parts, deionized water 180-320 parts, anhydrous ethanol 30-70 parts.

[0007] According to a preferred embodiment of the present invention, the method for preparing the iron-zinc tannin polyethyleneimine precursor includes:

[0008] A1. By weight, mix 100-140 parts of deionized water and 20-45 parts of anhydrous ethanol, add 8-18 parts of tannic acid, stir, add 2-6 parts of branched polyethyleneimine, and continue stirring to obtain a tannin-polyamine mixture; dissolve 4-10 parts of ferric chloride hexahydrate and 3-8 parts of zinc acetate dihydrate in 30-60 parts of deionized water to obtain an iron-zinc salt solution; while stirring, add the iron-zinc salt solution dropwise to the tannin-polyamine mixture, adjust the pH with sodium hydroxide aqueous solution, stir, and obtain an iron-zinc tannin-polyethyleneimine complex dispersion;

[0009] A2. Concentrate the iron-zinc tannin-polyethyleneimine complex dispersion under reduced pressure, add 80-160 parts of anhydrous ethanol, let stand, filter, wash, dry, pulverize, and vibrate sieve.

[0010] In this invention, the formation of the iron-zinc tannin polyethyleneimine precursor mainly depends on the complexation, association, and precipitation between tannic acid, branched polyethyleneimine, ferric chloride hexahydrate, and zinc acetate dihydrate. Deionized water and anhydrous ethanol provide the dispersion medium, allowing tannic acid to fully dissolve and expose the ortho-phenolic hydroxyl groups. After the addition of branched polyethyleneimine, the amino groups on its molecular chain form hydrogen bonds with the phenolic hydroxyl groups of tannic acid, while electrostatic adsorption occurs between the protonated amino groups and the phenolic oxygen anions formed by the ionization of the phenolic hydroxyl groups, maintaining the tannin-polyamine mixture in a uniform and stable colloidal dispersion state. After the ferric chloride hexahydrate and zinc acetate dihydrate dissolve, an iron-zinc salt solution containing iron and zinc ions is formed. When the iron-zinc salt solution is added dropwise to the tannin-polyamine mixture, the iron ions preferentially form a five-membered ring coordination structure with the ortho-phenolic hydroxyl groups of tannic acid, while the zinc ions undergo synergistic complexation with the phenolic hydroxyl groups of tannic acid and the lone pair electrons of the nitrogen atoms in the branched polyethyleneimine, forming multiple metal coordination sites. After adjusting the acid-base environment with sodium hydroxide aqueous solution, the phenolic hydroxyl groups of tannic acid were further deprotonated, significantly enhancing their coordination ability. Iron ions formed a tripentate coordinated metal polyphenol network with tannic acid, synergistically constructing an iron-zinc tannin-polyethyleneimine complex dispersion with the branched polyethyleneimine skeleton. Reduced pressure concentration gradually removed the solvent, shortening the distance between the complex components and further enhancing coordination, hydrogen bonding, and intermolecular association. The addition of anhydrous ethanol reduced the solvent polarity, decreasing the solubility of the complex components and causing them to gradually precipitate. After settling, filtration, washing, drying, pulverizing, and vibrating sieving, the iron-zinc tannin-polyethyleneimine precursor was obtained. This precursor can provide metal complexation sites, nitrogen-containing structures, and oxygen-containing structures during subsequent heat treatment, which is beneficial for improving the uniformity of active site distribution in the bamboo-based carbon skeleton.

[0011] According to a preferred embodiment of the present invention, in step A1, the pH is adjusted to 7.0-8.0 using an aqueous sodium hydroxide solution.

[0012] According to a preferred embodiment of the present invention, in step A2, the temperature for vacuum concentration is 50-60°C; the concentration is carried out under vacuum until the solid content is 35-50%; the settling time is 4-8 hours; the drying temperature is 60-75°C; and the drying time is 8-12 hours.

[0013] According to a preferred embodiment of the present invention, the method for preparing the calcium-aluminum double-crosslinked alginate template includes:

[0014] B1. By weight, mix 150-240 parts of deionized water and 8-18 parts of sodium alginate, stir, cool, and then add 4-12 parts of calcium carbonate to obtain a sodium alginate dispersion; dissolve 6-14 parts of anhydrous calcium chloride and 6-18 parts of aluminum trichloride hexahydrate in 80-150 parts of deionized water to obtain a calcium-aluminum composite salt solution; under stirring, add the calcium-aluminum composite salt solution dropwise to the sodium alginate dispersion, age, and obtain a calcium-aluminum double crosslinked alginate gel;

[0015] B2. The calcium-aluminum double crosslinked alginate gel is filtered, washed, frozen, vacuum freeze-dried, pulverized, and vibrated sieve.

[0016] In this invention, the formation of the calcium-aluminum double-crosslinked alginate template mainly relies on the multi-point crosslinking of sodium alginate molecular chains with calcium and aluminum ions, and utilizes calcium carbonate to construct a removable sacrificial template. Deionized water gradually swells and disperses sodium alginate, allowing the carboxylate groups on the molecular chains to fully ionize, forming a sodium alginate solution with a certain viscosity. After cooling, calcium carbonate is added, and the calcium carbonate is uniformly distributed in a fine particle state between the sodium alginate molecular chains, resulting in a sodium alginate dispersion. Anhydrous calcium chloride and aluminum trichloride hexahydrate are co-dissolved in deionized water to form a calcium-aluminum composite salt solution. Since both are chloride systems, the chloride ions are uniform, preventing the formation of insoluble byproducts such as calcium sulfate, and ensuring that calcium and aluminum ions are uniformly dispersed in the solution. When the calcium-aluminum composite salt solution is added dropwise to the sodium alginate dispersion, calcium ions preferentially bind to the carboxylate groups on the guluronic acid units of the sodium alginate molecular chain, forming an ordered egg-box cross-linked region. Aluminum ions further coordinate with the remaining carboxylate groups, resulting in a tridentate multi-point coordination, transforming the gel network from a single calcium ion cross-link to a synergistic calcium and aluminum ion double cross-linked structure. The weakly acidic environment generated by the hydrolysis of aluminum trichloride hexahydrate slowly dissolves some calcium carbonate, releasing additional calcium ions to participate in internal cross-linking, accompanied by the escape of carbon dioxide gas, forming dispersed bubble cavities within the gel framework. During aging, the number of calcium-aluminum cross-linking points gradually increases, the bonding between sodium alginate molecular chains becomes more stable, and residual calcium carbonate particles are embedded within the gel framework to form a sacrificial template, yielding a calcium-aluminum double-crosslinked alginate gel. After filtration and washing to remove free salts, freezing and vacuum freeze-drying remove water from the gel through sublimation while retaining the loose, porous framework. Finally, after pulverization and vibratory sieving, a calcium-aluminum double-crosslinked alginate template is obtained. This template can induce the formation of mesopores and interconnecting pores through template sacrificial effect during subsequent carbonization and pickling processes.

[0017] According to a preferred embodiment of the present invention, in step B1, the aging time is 2-5 hours.

[0018] According to a preferred embodiment of the present invention, in step B2, the freezing temperature is -10~-20℃, the freezing time is 6-10h, and the vacuum freeze-drying time is 18-30h.

[0019] This invention also provides a method for preparing the bamboo-based porous carbon modified material, comprising the following steps:

[0020] S1. Under stirring, choline chloride and lactic acid are mixed to obtain a deep eutectic solvent; bamboo powder is added to the deep eutectic solvent for pretreatment, deionized water is added, filtered, washed, and dried to obtain pretreated bamboo powder; anhydrous zinc chloride, ammonium chloride, melamine, and sucrose are dispersed in a mixed solvent of deionized water and anhydrous ethanol, iron-zinc tannin polyethyleneimine precursor and calcium-aluminum double crosslinked alginate template are added, and stirred to obtain a composite modified impregnation solution; the pretreated bamboo powder is added to the composite modified impregnation solution, vacuum impregnated, stirred during impregnation, filtered, and dried to obtain a bamboo-based composite precursor;

[0021] S2. The bamboo-based composite precursor is placed in a nitrogen-protected furnace for pre-carbonization and activated carbonization, followed by secondary activation with steam to obtain crude bamboo-based porous carbon modified material. The crude bamboo-based porous carbon modified material is cooled and washed sequentially with hydrochloric acid aqueous solution, disodium ethylenediaminetetraacetate aqueous solution and deionized water, dried, crushed and vibrated sieve.

[0022] In this invention, the formation of bamboo-based porous carbon-modified materials mainly relies on the continuous interaction between bamboo powder pretreatment, composite impregnation, carbonization activation, reactivation, and washing to remove impurities. Choline chloride and lactic acid, when mixed, form a deep eutectic solvent through hydrogen bonding. This system weakens the hydrogen bond network between cellulose, hemicellulose, and lignin in the bamboo powder, disrupts the ester and ether bonds between lignin and carbohydrates, causing the bamboo powder fiber structure to swell and loosen. Some lignin and hemicellulose are removed, making it easier for the activated components to enter the internal pores of the bamboo powder. After diluting the deep eutectic solvent with deionized water, the pretreated bamboo powder is obtained through filtration, washing, and drying. Anhydrous zinc chloride, ammonium chloride, melamine, and sucrose are dispersed in a mixed solvent of deionized water and anhydrous ethanol. Anhydrous zinc chloride, at high temperatures, swells, gels, and catalyzes dehydration of the bamboo-based components, promoting micropore formation. Ammonium chloride decomposes upon heating, releasing ammonia and hydrogen chloride gas, which helps open blocked pores. Melamine provides abundant nitrogen-containing structures, decomposing at high temperatures and incorporating them into the carbon framework. Sucrose supplements the amorphous carbon source and improves the uniform bonding state of the bamboo-based composite precursor. The addition of iron-zinc tannin-polyethyleneimine precursors ensures a uniform distribution of metal complexation sites, nitrogen-containing structures, and oxygen-containing structures within the bamboo-based composite precursor. The addition of calcium-aluminum double-crosslinked alginate template serves as a dispersed sacrificial template embedded in the composite system. Vacuum impregnation utilizes negative pressure to expel gases from within the bamboo powder, allowing the composite-modified impregnation solution to fully penetrate the pores of the bamboo powder. Stirred impregnation further promotes the uniform loading of the activated components. During the pre-carbonization process, bamboo powder gradually dehydrates and condenses to form an initial carbon framework. During the activation carbonization process, anhydrous zinc chloride promotes micropore formation, and calcium-aluminum double-crosslinked alginate template induces mesopore formation after thermal decomposition and subsequent acid washing. Water vapor reactivation further opens closed channels and improves channel connectivity through carbon gasification. Finally, the material is washed sequentially with hydrochloric acid aqueous solution, disodium ethylenediaminetetraacetate aqueous solution, and deionized water. Hydrochloric acid dissolves residual metal salts and inorganic ash, disodium ethylenediaminetetraacetate removes residual transition metal ions through chelation, and deionized water is used to wash until neutral. After drying, pulverizing, and vibrating sieving, bamboo-based porous carbon-modified material is obtained.

[0023] According to a preferred embodiment of the present invention, in step S1, the temperature for mixing choline chloride and lactic acid is 70-90°C, and the mixing time is 1-2 hours; the pretreatment temperature is 90-120°C, and the pretreatment time is 2-5 hours; the vacuum degree of vacuum impregnation is -0.06~-0.08 MPa, and the vacuum impregnation time is 1-3 hours; the stirring impregnation time is 2-5 hours.

[0024] According to a preferred embodiment of the present invention, in step S2, the pre-carbonization temperature is 320-420℃, and the pre-carbonization time is 0.5-1.5h; the activation carbonization temperature is 650-780℃, and the activation carbonization time is 1.0-2.5h; the secondary activation temperature is 720-820℃, and the secondary activation time is 15-60min; the concentration of the hydrochloric acid aqueous solution is 0.5-1.5mol / L; and the concentration of the disodium ethylenediaminetetraacetate aqueous solution is 0.02-0.10mol / L.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) This invention uses bamboo powder as a carbon source and pretreats the bamboo powder with a deep eutectic solvent formed by choline chloride and lactic acid. This weakens the bond between cellulose, hemicellulose and lignin in the bamboo powder, making the bamboo powder fiber structure more porous, which is conducive to the subsequent activation components entering the internal pores of the bamboo powder. After pretreatment, the bamboo powder has a more uniform loading of anhydrous zinc chloride, ammonium chloride, melamine, sucrose, iron zinc tannin polyethyleneimine precursor and calcium aluminum double crosslinked alginate template, which can reduce local underactivation and local over-etching, and improve the compositional uniformity and carbonization stability of the bamboo-based composite precursor.

[0027] (2) This invention introduces an iron-zinc tannin polyethyleneimine precursor, utilizing the complex structure formed by tannic acid, branched polyethyleneimine, ferric chloride hexahydrate, and zinc acetate dihydrate to uniformly distribute iron-zinc complex sites, nitrogen-containing structures, and oxygen-containing structures in the bamboo-based composite precursor. During pre-carbonization and activated carbonization, the iron-zinc tannin polyethyleneimine precursor helps increase the density of active sites on the bamboo-based carbon skeleton surface, improves the surface polarity and wettability of bamboo-based porous carbon modified materials, and synergistically enhances the interfacial interaction capabilities of bamboo-based porous carbon modified materials in adsorption separation, catalytic carriers, and energy storage materials, in conjunction with the nitrogen-containing structures provided by melamine.

[0028] (3) This invention uses a calcium-aluminum double-crosslinked alginate template to regulate the pore structure. The gel template formed by sodium alginate, calcium carbonate, anhydrous calcium chloride, and aluminum trichloride hexahydrate can play a sacrificial pore-forming role in the bamboo-based composite precursor, promoting the formation of mesopores and interconnected pores. Anhydrous zinc chloride promotes micropore formation during the activation and carbonization process, and secondary activation with water vapor further opens the closed pores, enabling the bamboo-based porous carbon modified material to form a relatively complete pore network. The residual metal salts and inorganic template components can be removed by sequential washing with hydrochloric acid aqueous solution, disodium ethylenediaminetetraacetate aqueous solution, and deionized water, reducing ash residue and obtaining a bamboo-based porous carbon modified material with well-developed pore structure, abundant active sites, low residual impurities, and stable structure. Detailed Implementation

[0029] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing bamboo-based porous carbon-modified materials, the steps of which include:

[0032] S1. Add 60.0g of choline chloride and 110.0g of lactic acid to a stirring container and mix at 80°C for 1.5h to obtain a deep eutectic solvent; add 110.0g of bamboo powder (dried bamboo powder that has passed through a 0.18mm sieve) to the deep eutectic solvent, pretreat at 105°C for 3.5h, dilute with 250.0g of deionized water, filter, wash the filtered solid with deionized water until the pH of the washing solution is 7.0, and then dry at 80°C until the mass change between two consecutive weighings does not exceed 0.1% to obtain pretreated bamboo powder; add 82.5g of anhydrous zinc chloride, 22.0g of ammonium chloride, and 14.0g of... 9.0 g of melamine and 9.0 g of sucrose were dispersed in a mixed solvent consisting of 250.0 g of deionized water and 50.0 g of anhydrous ethanol. The mixture was stirred at 25°C for 30 min. Then, 6.5 g of iron-zinc tannin polyethyleneimine precursor and 16.0 g of calcium-aluminum double-crosslinked alginate template were added, and the mixture was stirred for another 60 min to obtain a composite modified impregnation solution. Pretreated bamboo powder was added to the composite modified impregnation solution and impregnated under vacuum at -0.07 MPa for 2 h. After restoring to normal pressure, the mixture was stirred and impregnated for another 3.5 h. The mixture was then filtered, and the filtered solid was dried at 90°C until the mass change between two consecutive weighings did not exceed 0.1% to obtain the bamboo-based composite precursor.

[0033] S2. The bamboo-based composite precursor was placed in a nitrogen-protected furnace. After replacing the air in the furnace with nitrogen, the furnace was kept under nitrogen protection. It was pre-carbonized at 370°C for 1.0 h, then activated and carbonized at 715°C for 1.75 h. Subsequently, water vapor was introduced for secondary activation at 770°C for 37.5 min. After the secondary activation, it was cooled to room temperature under nitrogen protection to obtain crude bamboo-based porous carbon modified material. The crude bamboo-based porous carbon modified material was successively washed with a 1.0 mol / L hydrochloric acid aqueous solution, then with a 0.06 mol / L ethylenediaminetetraacetic acid disodium aqueous solution, and then washed with deionized water until the pH of the washing solution reached 7.0. It was then dried at 105°C until the mass change between two consecutive weighings did not exceed 0.1%. It was then pulverized and passed through a 0.15 mm sieve to obtain bamboo-based porous carbon modified material.

[0034] Preparation steps of iron-zinc tannin polyethyleneimine precursor:

[0035] A1. Add 120.0g of deionized water and 32.5g of anhydrous ethanol to a reaction vessel and stir at 25°C for 10 min. Add 13.0g of tannic acid and continue stirring for 30 min until the tannic acid is completely dissolved. Then add 4.0g of branched polyethyleneimine and continue stirring for 45 min to obtain a tannin-polyamine mixture. Separately, add 7.0g of ferric chloride hexahydrate and 5.5g of zinc acetate dihydrate to 45.0g of deionized water and stir at 25°C for 20 min until completely dissolved to obtain an iron-zinc salt solution. While stirring, add the iron-zinc salt solution dropwise to the tannin-polyamine mixture over 30 min, controlling the system temperature at 25°C during the addition. After the addition is complete, adjust the pH to 7.5 with 1.0mol / L sodium hydroxide aqueous solution and continue stirring for 3 h to obtain an iron-zinc tannin-polyethyleneimine complex dispersion.

[0036] A2. The iron-zinc tannin polyethyleneimine complex dispersion was concentrated under reduced pressure at 55°C to a solid content of 42.5%. 120.0g of anhydrous ethanol was added, and the mixture was allowed to stand for 6 hours under sealed conditions. The solid was collected by filtration through a filter membrane and washed three times with 40.0g of anhydrous ethanol each time. The mixture was then dried at 67.5°C for 10 hours until the mass change between two consecutive weighings did not exceed 0.1%. The mixture was then pulverized and passed through a 0.15mm sieve to obtain the iron-zinc tannin polyethyleneimine precursor.

[0037] Preparation steps of calcium-aluminum double-crosslinked alginate template:

[0038] B1. Add 195.0g of deionized water to a reaction vessel, add 13.0g of sodium alginate at 45°C, and stir for 3 hours until the sodium alginate is fully swollen and forms a uniform viscous solution. After cooling to 25°C, add 8.0g of calcium carbonate and continue stirring for 30 minutes to obtain a sodium alginate dispersion. Separately, add 10.0g of anhydrous calcium chloride and 12.0g of aluminum trichloride hexahydrate to 115.0g of deionized water and stir at 25°C for 20 minutes until completely dissolved to obtain a calcium-aluminum composite salt solution. While stirring, add the calcium-aluminum composite salt solution dropwise to the sodium alginate dispersion over a period of 40 minutes, controlling the system temperature at 25°C during the addition. After the addition is complete, age for 3.5 hours to obtain a calcium-aluminum double crosslinked alginate gel.

[0039] B2. The calcium-aluminum double-crosslinked alginate gel was filtered, and the filtered gel solid was washed with deionized water until the conductivity of the washing solution was no higher than 100 μS / cm. Then it was frozen at -15°C for 8 hours and then freeze-dried under vacuum for 24 hours. After drying, it was pulverized and passed through a 0.15 mm sieve to obtain the calcium-aluminum double-crosslinked alginate template.

[0040] Example 2

[0041] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a bamboo-based porous carbon-modified material, the steps of which include:

[0042] S1. Add 45.0g of choline chloride and 80.0g of lactic acid to a stirring container and mix at 70°C for 1h to obtain a deep eutectic solvent; add 100.0g of bamboo powder to the deep eutectic solvent and pretreat at 90°C for 2h, add 180.0g of deionized water, filter, wash, and dry to obtain pretreated bamboo powder; disperse 55.0g of anhydrous zinc chloride, 12.0g of ammonium chloride, 6.0g of melamine, and 4.0g of sucrose in a mixed solvent of 180.0g of deionized water and 30.0g of anhydrous ethanol, add 3.0g of iron-zinc tannin polyethyleneimine precursor and 8.0g of calcium-aluminum double-crosslinked alginate template, and stir until uniformly dispersed to obtain a composite modified impregnation solution; add the pretreated bamboo powder to the composite modified impregnation solution, vacuum impregnate at -0.06MPa for 1h, then stir and impregnate for 2h, filter, and dry to obtain a bamboo-based composite precursor;

[0043] S2. The bamboo-based composite precursor was placed in a nitrogen-protected furnace and pre-carbonized at 320°C for 0.5 h, then activated and carbonized at 650°C for 1.0 h. Subsequently, water vapor was introduced for secondary activation at 720°C for 15 min to obtain crude bamboo-based porous carbon modified material. The crude bamboo-based porous carbon modified material was cooled and washed sequentially with a 0.5 mol / L hydrochloric acid aqueous solution, a 0.02 mol / L ethylenediaminetetraacetic acid disodium aqueous solution, and deionized water. After drying, pulverizing, and vibrating sieve, the bamboo-based porous carbon modified material was obtained.

[0044] Preparation steps of iron-zinc tannin polyethyleneimine precursor:

[0045] A1. Add 100.0g of deionized water and 20.0g of anhydrous ethanol to a reaction vessel, stir until homogeneous, then add 8.0g of tannic acid and stir until the tannic acid dissolves and forms a homogeneous solution. Then add 2.0g of branched polyethyleneimine and continue stirring until a homogeneous tannin-polyamine mixture is formed. Separately, dissolve 4.0g of ferric chloride hexahydrate and 3.0g of zinc acetate dihydrate in 30.0g of deionized water to obtain an iron-zinc salt solution. While stirring, add the iron-zinc salt solution dropwise to the tannin-polyamine mixture, keeping the system uniformly dispersed during the addition. After the addition is complete, adjust the pH to 7.0 with sodium hydroxide aqueous solution and continue stirring until the system is in a uniform complexed dispersion state to obtain an iron-zinc tannin-polyethyleneimine complex dispersion.

[0046] A2. The iron-zinc tannin polyethyleneimine complex dispersion was concentrated under reduced pressure at 50°C to a solid content of 35%. 80.0g of anhydrous ethanol was added, and the mixture was allowed to stand for 4 hours under sealed conditions. The solid was collected by filtration, washed with anhydrous ethanol, dried at 60°C for 8 hours, pulverized, and sieved by vibration to obtain the iron-zinc tannin polyethyleneimine precursor.

[0047] Preparation steps of calcium-aluminum double-crosslinked alginate template:

[0048] B1. Add 150.0g of deionized water and 8.0g of sodium alginate to a reaction vessel and stir until the sodium alginate is fully swollen and forms a uniform viscous solution. After cooling, add 4.0g of calcium carbonate and continue stirring until the calcium carbonate is uniformly dispersed to obtain a sodium alginate dispersion. Separately, dissolve 6.0g of anhydrous calcium chloride and 6.0g of aluminum trichloride hexahydrate in 80.0g of deionized water to obtain a calcium-aluminum composite salt solution. While stirring, add the calcium-aluminum composite salt solution dropwise to the sodium alginate dispersion. After the addition is complete, age for 2 hours to obtain a calcium-aluminum double-crosslinked alginate gel. B2. Filter the calcium-aluminum double-crosslinked alginate gel. Wash the filtered gel solid with deionized water, then freeze at -10°C for 6 hours, and then freeze-dry under vacuum for 18 hours. After drying, pulverize and vibrate to sieve to obtain a calcium-aluminum double-crosslinked alginate template.

[0049] Example 3

[0050] The difference between this embodiment and Embodiment 1 is that this embodiment provides a method for preparing a bamboo-based porous carbon-modified material, the steps of which include:

[0051] S1. Add 75.0g choline chloride and 140.0g lactic acid to a stirring container and mix at 90°C for 2 hours to obtain a deep eutectic solvent; add 120.0g bamboo powder to the deep eutectic solvent and pretreat at 120°C for 5 hours, add 320.0g deionized water, filter, wash, and dry to obtain pretreated bamboo powder; add 110.0g anhydrous zinc chloride, 32.0g ammonium chloride, 22.0g melamine, and 14. 0 g of sucrose was dispersed in a mixed solvent of 320.0 g of deionized water and 70.0 g of anhydrous ethanol. 10.0 g of iron-zinc tannin polyethyleneimine precursor and 24.0 g of calcium-aluminum double-crosslinked alginate template were added and stirred until uniformly dispersed to obtain a composite modified impregnation solution. Pretreated bamboo powder was added to the composite modified impregnation solution and impregnated under vacuum at -0.08 MPa for 3 h, followed by stirring and impregnation for 5 h. After filtration and drying, bamboo-based composite precursor was obtained.

[0052] S2. The bamboo-based composite precursor was placed in a nitrogen-protected furnace and pre-carbonized at 420°C for 1.5 h, then activated and carbonized at 780°C for 2.5 h. Subsequently, water vapor was introduced for secondary activation at 820°C for 60 min to obtain crude bamboo-based porous carbon modified material. The crude bamboo-based porous carbon modified material was cooled and washed sequentially with a 1.5 mol / L hydrochloric acid aqueous solution, a 0.10 mol / L ethylenediaminetetraacetic acid disodium aqueous solution, and deionized water. After drying, pulverizing, and vibrating sieve, the bamboo-based porous carbon modified material was obtained.

[0053] Preparation steps of iron-zinc tannin polyethyleneimine precursor:

[0054] A1. Add 140.0g of deionized water and 45.0g of anhydrous ethanol to a reaction vessel, stir until homogeneous, then add 18.0g of tannic acid and stir until the tannic acid dissolves and forms a homogeneous solution. Then add 6.0g of branched polyethyleneimine and continue stirring until a homogeneous tannin-polyamine mixture is formed. Separately, dissolve 10.0g of ferric chloride hexahydrate and 8.0g of zinc acetate dihydrate in 60.0g of deionized water to obtain an iron-zinc salt solution. While stirring, add the iron-zinc salt solution dropwise to the tannin-polyamine mixture, keeping the system uniformly dispersed during the addition. After the addition is complete, adjust the pH to 8.0 with sodium hydroxide aqueous solution and continue stirring until the system is in a uniform complexed dispersion state to obtain an iron-zinc tannin-polyethyleneimine complex dispersion.

[0055] A2. The iron-zinc tannin polyethyleneimine complex dispersion was concentrated under reduced pressure at 60°C to a solid content of 50%. 160.0g of anhydrous ethanol was added, and the mixture was allowed to stand for 8 hours under sealed conditions. The solid was collected by filtration, washed with anhydrous ethanol, dried at 75°C for 12 hours, pulverized, and sieved by vibration to obtain the iron-zinc tannin polyethyleneimine precursor.

[0056] Preparation steps of calcium-aluminum double-crosslinked alginate template:

[0057] B1. Add 240.0g of deionized water and 18.0g of sodium alginate to a reaction vessel and stir until the sodium alginate is fully swollen and forms a uniform viscous solution. After cooling, add 12.0g of calcium carbonate and continue stirring until the calcium carbonate is uniformly dispersed to obtain a sodium alginate dispersion. Separately, dissolve 14.0g of anhydrous calcium chloride and 18.0g of aluminum trichloride hexahydrate in 150.0g of deionized water to obtain a calcium-aluminum composite salt solution. While stirring, add the calcium-aluminum composite salt solution dropwise to the sodium alginate dispersion. After the addition is complete, age for 5 hours to obtain a calcium-aluminum double crosslinked alginate gel.

[0058] B2. The calcium-aluminum double-crosslinked alginate gel was filtered, and the filtered gel solid was washed with deionized water. Then it was frozen at -20°C for 10 hours and then freeze-dried under vacuum for 30 hours. After drying, it was crushed and sieved by vibration to obtain the calcium-aluminum double-crosslinked alginate template.

[0059] Comparative Example 1

[0060] The difference between this comparative example and Example 1 is that 6.5g of iron-zinc tannin polyethyleneimine precursor is not added in step S1, while the rest is the same as in Example 1.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that 16.0g of calcium-aluminum double-crosslinked alginate template is not added in step S1, while the rest is the same as in Example 1.

[0063] Comparative Example 3

[0064] The difference between this comparative example and Example 1 is that 6.5g of iron-zinc tannin polyethyleneimine precursor and 16.0g of calcium-aluminum double crosslinked alginate template are not added in step S1, while the rest is the same as in Example 1.

[0065] The performance of the bamboo-based porous carbon modified materials provided in the above embodiments and comparative examples was tested using the following methods:

[0066] The bamboo-based porous carbon modified materials obtained in Examples 1-3 and Comparative Examples 1-3 were dried in a 105°C forced-air drying oven for 4 hours. After being taken out, they were cooled to room temperature in a desiccator. Each sample was tested in parallel 3 times and the average value was taken.

[0067] For specific surface area testing, 0.2000 g of sample was weighed and placed in an adsorption test sample tube. The sample was degassed under vacuum at 120°C for 8 hours. After degassed, the sample was cooled to room temperature. Using nitrogen as the adsorbate, the nitrogen adsorption-desorption isotherm was measured at liquid nitrogen temperature. Adsorption data from the low relative pressure region were selected to calculate the specific surface area. The results are expressed in m³. 2 / g.

[0068] For the total pore volume test, the same nitrogen adsorption-desorption isotherm was used to read the amount of nitrogen adsorbed at near-saturation relative pressure. The condensation volume within the pores was calculated based on the liquid nitrogen density to obtain the total pore volume. The result is in cm³. 3 / g.

[0069] During the mesoporous proportion test, the pore size distribution was calculated based on the nitrogen adsorption-desorption data. The pore volume in the pore size range of 2-50nm was taken as the mesoporous pore volume. The mesoporous pore volume was divided by the total pore volume and multiplied by 100% to obtain the mesoporous proportion. The result is in units of .

[0070] During nitrogen content testing, the dried sample was ground evenly and pressed into a tablet, which was then placed on the sample stage of the surface element analyzer. Elemental signals were collected under the same test power, the same acquisition time, and the same analysis area. The peaks of carbon, oxygen, nitrogen, and residual metal elements were subjected to background subtraction and peak area normalization. The atomic percentage of nitrogen was calculated, and the result was expressed in at.

[0071] To test the methylene blue adsorption capacity, 0.0500 g of dried sample was weighed and added to 100 mL of a 500 mg / L methylene blue aqueous solution. The sample was shaken at 150 r / min at 25°C for 12 h to adsorb the methylene blue. Then, the sample was centrifuged at 8000 r / min for 10 min. The supernatant was taken and the concentration of methylene blue after adsorption was measured. The equilibrium adsorption capacity was calculated based on the concentration difference before and after adsorption, the solution volume, and the sample mass. The result is expressed in mg / g.

[0072] For the specific capacitance test, bamboo-based porous carbon modified material, conductive carbon black and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, N-methylpyrrolidone was added and ground into a uniform slurry, which was then coated onto a nickel foam current collector. After drying at 80°C for 12 hours, the mixture was pressed into a sheet to serve as the working electrode. A potassium hydroxide aqueous solution was used as the electrolyte, and a three-electrode system was employed. Constant current charge-discharge tests were conducted at a current density of 1 A / g. The specific capacitance was calculated based on the discharge current, discharge time, active material mass and voltage window. The result is expressed in F / g.

[0073] The performance test data above are shown in Table 1.

[0074] Table 1: Performance Test Results

[0075]

[0076] As can be seen from the above, Examples 1-3 are superior to Comparative Examples 1-3 in terms of specific surface area, total pore volume, mesopore ratio, nitrogen content, methylene blue adsorption capacity, and specific capacitance. This indicates that the present invention can effectively solve the technical problems of existing bamboo-based porous carbon modified materials, such as insufficient pore structure development, low proportion of mesopores and interconnected pores, insufficient surface active sites, limited adsorption performance, and unstable electrochemical energy storage performance.

[0077] The specific surface area of ​​Example 1 is 2468 m². 2 / g, total pore volume is 1.42cm³ 3 / g, the mesoporous content was 48.6%, the nitrogen content was 5.36 at, the methylene blue adsorption capacity was 612 mg / g, and the specific capacitance was 286 F / g, all of which were higher than those in Examples 2 and 3. This indicates that when using intermediate dosage and intermediate process parameters, the matching between bamboo powder pretreatment, anhydrous zinc chloride activation, iron-zinc tannin polyethyleneimine precursor modification and calcium-aluminum double crosslinked alginate template pore-forming was better.

[0078] Comparative Example 1, without the addition of iron-zinc tannin polyethyleneimine precursor, showed a decrease in nitrogen content to 2.74 at, a decrease in specific capacitance to 198 F / g, and a decrease in methylene blue adsorption to 438 mg / g. This indicates that the iron-zinc tannin polyethyleneimine precursor can improve the distribution of nitrogen-containing structures, oxygen-containing structures, and iron-zinc complexation sites in the bamboo-based carbon skeleton, thereby improving surface active sites and interfacial interaction capabilities.

[0079] Comparative Example 2, without the addition of calcium-aluminum double-crosslinked alginate template, had a specific surface area reduced to 1786 m². 2 / g, total pore volume decreased to 0.86cm³. 3 / g, the proportion of mesopores decreased to 27.8%, indicating that the calcium-aluminum double cross-linked alginate template has a direct effect on the formation of mesopores and interconnected pores, which can alleviate the problem that simple anhydrous zinc chloride activation easily leads to a single pore structure and a large number of closed pores.

[0080] Comparative Example 3, without the addition of iron-zinc tannin polyethyleneimine precursor and calcium-aluminum double-crosslinked alginate template, had a specific surface area of ​​only 1562 m². 2 / g, with a total pore volume of only 0.72cm³. 3 The material has a mesoporous content of only 24.5%, a nitrogen content of only 2.18 at, a methylene blue adsorption capacity of only 336 mg / g, and a specific capacitance of only 162 F / g. This indicates that without the iron-zinc tannin polyethyleneimine precursor and the calcium-aluminum double crosslinked alginate template, it is difficult for the material to simultaneously obtain a well-developed pore structure and abundant surface active sites.

[0081] Therefore, Examples 1-3 improve surface chemical activity by using iron-zinc tannin polyethyleneimine precursor, improve pore structure by using calcium-aluminum double crosslinked alginate template, and form a more complete pore network by combining anhydrous zinc chloride and water vapor for secondary activation, thereby solving the problems of uneven pore structure, insufficient active sites, low adsorption capacity and low specific capacitance of existing bamboo-based porous carbon modified materials.

Claims

1. A bamboo-based porous carbon-modified material, characterized in that, Including the following parts by weight of raw materials: Bamboo powder 100-120 parts, anhydrous zinc chloride 55-110 parts, ammonium chloride 12-32 parts, melamine 6-22 parts, sucrose 4-14 parts, iron-zinc tannin polyethyleneimine precursor 3-10 parts, calcium-aluminum double crosslinked alginate template 8-24 parts, choline chloride 45-75 parts, lactic acid 80-140 parts, deionized water 180-320 parts, anhydrous ethanol 30-70 parts.

2. The bamboo-based porous carbon-modified material according to claim 1, characterized in that, The preparation method of the iron-zinc tannin polyethyleneimine precursor includes: A1. By weight, mix 100-140 parts of deionized water and 20-45 parts of anhydrous ethanol, add 8-18 parts of tannic acid, stir, add 2-6 parts of branched polyethyleneimine, and continue stirring to obtain a tannin-polyamine mixture; dissolve 4-10 parts of ferric chloride hexahydrate and 3-8 parts of zinc acetate dihydrate in 30-60 parts of deionized water to obtain an iron-zinc salt solution; while stirring, add the iron-zinc salt solution dropwise to the tannin-polyamine mixture, adjust the pH with sodium hydroxide aqueous solution, stir, and obtain an iron-zinc tannin-polyethyleneimine complex dispersion; A2. Concentrate the iron-zinc tannin-polyethyleneimine complex dispersion under reduced pressure, add 80-160 parts of anhydrous ethanol, let stand, filter, wash, dry, pulverize, and vibrate sieve.

3. The bamboo-based porous carbon-modified material according to claim 2, characterized in that, In step A1, the pH is adjusted to 7.0-8.0 using an aqueous sodium hydroxide solution.

4. The bamboo-based porous carbon-modified material according to claim 2, characterized in that, In step A2, the temperature for vacuum concentration is 50-60℃; the concentration is carried out under vacuum until the solid content is 35-50%; the settling time is 4-8 hours; the drying temperature is 60-75℃ and the drying time is 8-12 hours.

5. The bamboo-based porous carbon-modified material according to claim 1, characterized in that, The method for preparing the calcium-aluminum double-crosslinked alginate template includes: B1. By weight, mix 150-240 parts of deionized water and 8-18 parts of sodium alginate, stir, cool, and then add 4-12 parts of calcium carbonate to obtain a sodium alginate dispersion; dissolve 6-14 parts of anhydrous calcium chloride and 6-18 parts of aluminum trichloride hexahydrate in 80-150 parts of deionized water to obtain a calcium-aluminum composite salt solution; under stirring, add the calcium-aluminum composite salt solution dropwise to the sodium alginate dispersion, age, and obtain a calcium-aluminum double crosslinked alginate gel; B2. The calcium-aluminum double crosslinked alginate gel is filtered, washed, frozen, vacuum freeze-dried, pulverized, and vibrated sieve.

6. The bamboo-based porous carbon-modified material according to claim 5, characterized in that, In step B1, the aging time is 2-5 hours.

7. The bamboo-based porous carbon-modified material according to claim 5, characterized in that, In step B2, the freezing temperature is -10~-20℃, and the freezing time is 6-10h; the vacuum freeze-drying time is 18-30h.

8. A method for preparing a bamboo-based porous carbon-modified material according to any one of claims 1-7, characterized in that the step... include: S1. Under stirring, choline chloride and lactic acid are mixed to obtain a deep eutectic solvent; Bamboo powder was pretreated in a deep eutectic solvent, deionized water was added, and the mixture was filtered, washed, and dried to obtain pretreated bamboo powder. Anhydrous zinc chloride, ammonium chloride, melamine, and sucrose were dispersed in a mixed solvent of deionized water and anhydrous ethanol. Iron-zinc tannin polyethyleneimine precursor and calcium-aluminum double crosslinked alginate template were added and stirred to obtain a composite modified impregnation solution. Pretreated bamboo powder was added to a composite modified impregnation solution, vacuum impregnated, stirred during impregnation, filtered, and dried to obtain a bamboo-based composite precursor. S2. The bamboo-based composite precursor is placed in a nitrogen-protected furnace for pre-carbonization and activated carbonization, followed by secondary activation with steam to obtain crude bamboo-based porous carbon modified material. The crude bamboo-based porous carbon modified material is cooled and washed sequentially with hydrochloric acid aqueous solution, disodium ethylenediaminetetraacetate aqueous solution and deionized water, dried, crushed and vibrated sieve.

9. The method for preparing bamboo-based porous carbon modified material according to claim 8, characterized in that, In step S1, the temperature for mixing choline chloride and lactic acid is 70-90℃, and the mixing time is 1-2h; the pretreatment temperature is 90-120℃, and the pretreatment time is 2-5h; the vacuum degree for vacuum impregnation is -0.06~-0.08MPa, and the vacuum impregnation time is 1-3h; the stirring impregnation time is 2-5h.

10. The method for preparing bamboo-based porous carbon-modified material according to claim 8, characterized in that, In step S2, the pre-carbonization temperature is 320-420℃ and the pre-carbonization time is 0.5-1.5h; the activation carbonization temperature is 650-780℃ and the activation carbonization time is 1.0-2.5h; the secondary activation temperature is 720-820℃ and the secondary activation time is 15-60min; the concentration of hydrochloric acid aqueous solution is 0.5-1.5mol / L; and the concentration of disodium ethylenediaminetetraacetate aqueous solution is 0.02-0.10mol / L.

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