Carbon dioxide adsorbent and preparation method thereof

Abstract

The invention provides a carbon dioxide adsorbent and a preparation method thereof, and belongs to the technical field of carbon dioxide capture, utilization and storage. The adsorbent is reduced graphene oxide aerogel modified by carbon quantum dots or ammoniated carbon quantum dots. According to the invention, the carbon quantum dots or ammoniated carbon quantum dots are introduced into the graphene aerogel, so that the adsorbent with high CO2 adsorption capacity is developed.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon dioxide capture, utilization and storage, and specifically relates to a carbon dioxide adsorbent and a preparation method thereof. Background Art

[0002] Carbon dioxide capture, utilization and storage (CCUS) technology has become a key research target in the scientific research field of various countries. This technology aims to separate carbon dioxide from emission sources, and then realize its direct utilization or safe storage, thereby effectively reducing carbon dioxide emissions. It is a key technical approach to achieve low-carbon utilization of fossil energy. Given that carbon dioxide is an abundant and low-cost carbon source, its resource utilization has far-reaching strategic significance for mitigating the greenhouse effect and reducing dependence on fossil energy.

[0003] At present, the main methods for capturing carbon dioxide include solvent absorption, cryogenic separation and adsorption separation. However, solvent absorption and cryogenic separation face challenges such as high energy consumption and high separation costs in practical applications. In contrast, adsorption separation has attracted much attention due to its advantages such as simple equipment, flexible operation, low cost and wide applicable temperature range, and has become a hot topic in current international research.

[0004] Although adsorption separation has significant advantages in the field of carbon dioxide capture, existing solid adsorption materials such as zeolite molecular sieves, metal organic framework materials (MOFs) and porous polymers show good adsorption performance under high pressure, but their adsorption amount and adsorption capacity decrease significantly under low pressure conditions. Therefore, the development of new and efficient solid adsorption materials suitable for low pressure environments is of great significance for expanding the application scope of carbon dioxide capture technology. Summary of the invention

[0005] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an embodiment of the present invention provides a carbon dioxide adsorbent and a preparation method thereof.

[0006] An embodiment of the present invention provides a carbon dioxide adsorbent, wherein the adsorbent is reduced graphene oxide aerogel modified with carbon quantum dots or ammoniated carbon quantum dots.

[0007] The advantages and technical effects brought by the carbon dioxide adsorbent of the embodiment of the present invention are:

[0008] (1) The adsorbent of the embodiment of the present invention contains reduced graphene oxide. Reduced graphene oxide aerogel is a high-strength reduced-oxidation aerogel with a porous structure, high elasticity and strong adsorption properties. It is also called carbon sponge and can be used for the adsorption of CO2 in flue gas.

[0009] (2) The adsorbent of the embodiment of the present invention also contains carbon quantum dots or ammoniated carbon quantum dots loaded on the inner and outer surfaces of the reduced graphene oxide aerogel. Carbon quantum dots (Carbon Quantum Dots, CQDs), also known as carbon dots or carbon nanodots, are a type of zero-dimensional carbon nanomaterials, which are composed of ultrafine, dispersed, quasi-spherical carbon nanoparticles with a particle size of less than 10 nm. After being modified on the reduced graphene oxide aerogel, it can provide abundant adsorption sites, increase the specific surface area of ​​the reduced graphene oxide aerogel, and enhance the adsorption effect of the reduced graphene oxide aerogel on CO2.

[0010] (3) Ammoniated carbon quantum dots can not only enhance the adsorption of CO2 by reduced graphene oxide aerogel, but also provide abundant reactive sites due to their large number of amino (-NH2), primary amino (-NH), and tertiary amino (-N) functional groups. The -NH2 and other functional groups on the aminated carbon quantum dots can react chemically with CO2 to further enhance the adsorption of reduced graphene oxide aerogel and optimize the CO2 adsorption performance.

[0011] According to the carbon dioxide adsorbent described in the embodiment of the present invention, when the adsorbent is reduced graphene oxide aerogel modified by carbon quantum dots, the mass fraction of the carbon quantum dots is 1-20% based on the total mass of the adsorbent being 100%.

[0012] According to the carbon dioxide adsorbent described in an embodiment of the present invention, when the adsorbent is reduced graphene oxide aerogel modified by ammoniated carbon quantum dots, based on the total mass of the adsorbent being 100%, the mass fraction of the carbon quantum dots is 1-20%, and the mass fraction of N is 2-25%.

[0013] According to the carbon dioxide adsorbent described in the embodiment of the present invention, the ammoniated carbon quantum dots are carbon quantum dots modified with at least one of amino groups, primary amino groups and tertiary amino groups.

[0014] According to the carbon dioxide adsorbent described in an embodiment of the present invention, the reduced graphene oxide aerogel is a composite of reduced graphene oxide, polyethylene imine and chitosan; the mass ratio of the reduced graphene oxide, the polyethylene imine and the chitosan is (1-5):(1-5):(0.05-0.25).

[0015] In addition, an embodiment of the present invention provides a method for preparing a carbon dioxide adsorbent, comprising the following steps:

[0016] S1. The graphene oxide dispersion is subjected to a first hydrothermal reaction at a high temperature to obtain the reduced graphene oxide aerogel;

[0017] S2. mixing the reduced graphene oxide aerogel and the carbon source dispersion to obtain a mixed solution; subjecting the mixed solution to a second hydrothermal reaction at a high temperature to obtain a carbon quantum dot-modified reduced graphene oxide aerogel;

[0018] Optionally, the method further comprises step S3: mixing the carbon quantum dot-modified reduced graphene oxide aerogel and ammonia water to obtain a mixture; and subjecting the mixture to a third hydrothermal reaction at high temperature to obtain ammoniated carbon quantum dot-modified reduced graphene oxide aerogel.

[0019] The advantages and technical effects brought by the preparation method of the embodiment of the present invention are:

[0020] The preparation method of the embodiment of the present invention develops an adsorbent with high CO2 adsorption capacity by introducing carbon quantum dots or ammoniated carbon quantum dots into reduced graphene oxide aerogel.

[0021] According to the preparation method described in the embodiment of the present invention, step S1 specifically includes the following steps:

[0022] S101. The graphene oxide dispersion, the polyethyleneimine solution and the chitosan solution are mixed to obtain a slurry;

[0023] S102. Subjecting the slurry to a first hydrothermal reaction at high temperature to obtain the reduced graphene oxide aerogel.

[0024] According to the preparation method described in the embodiment of the present invention, in step S2, the mass ratio of the reduced graphene oxide aerogel to the carbon source is 1:(5-50).

[0025] According to the preparation method described in the embodiment of the present invention, in step S3, when the mass of the carbon quantum dot-modified reduced graphene oxide aerogel is 0.2 g, 5-15 mL of ammonia water with a mass concentration of 5 wt % is used.

[0026] According to the preparation method described in the embodiment of the present invention, in step S1, the temperature of the first hydrothermal reaction is 180-220°C and the time is 12-24h; and / or, in step S2, the temperature of the second hydrothermal reaction is 150-200°C and the time is 2-8h; and / or, in step S3, the temperature of the third hydrothermal reaction is 160-200°C and the time is 2-5h DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0028] The embodiment of the present invention provides a carbon dioxide adsorbent, wherein the adsorbent is a reduced graphene oxide aerogel modified by carbon quantum dots or ammoniated carbon quantum dots. Preferably, the adsorbent is a reduced graphene oxide aerogel modified by ammoniated carbon quantum dots.

[0029] The adsorbent of the embodiment of the present invention contains reduced graphene oxide. Reduced graphene oxide aerogel, as a high-strength reduced oxide aerogel, has a porous structure, high elasticity and strong adsorption properties, and is also called carbon sponge, which can be used for the adsorption of CO2 in flue gas. In addition, the adsorbent of the embodiment of the present invention also contains carbon quantum dots or ammoniated carbon quantum dots loaded on the inner and outer surfaces of the reduced graphene oxide aerogel. Carbon quantum dots (Carbon Quantum Dots, CQDs), also known as carbon dots or carbon nanodots, are a type of zero-dimensional carbon nanomaterials, which are composed of ultrafine, dispersed, quasi-spherical carbon nanoparticles with a particle size of less than 10nm. After being modified on the reduced graphene oxide aerogel, it can provide abundant adsorption sites, increase the specific surface area of ​​the reduced graphene oxide aerogel, and strengthen the adsorption of CO2 by the reduced graphene oxide aerogel. In addition, ammoniated carbon quantum dots can not only enhance the adsorption of reduced graphene oxide aerogel on CO2, but also provide abundant reactive sites due to their large number of amino (-NH2), primary amino (-NH), and tertiary amino (-N) functional groups. The -NH2 and other functional groups on ammoniated carbon quantum dots can react chemically with CO2 to further enhance the adsorption of reduced graphene oxide aerogel and optimize the CO2 adsorption performance.

[0030] In some embodiments, when the adsorbent is a reduced graphene oxide aerogel modified with carbon quantum dots, the mass fraction of the carbon quantum dots is 1-20% based on the total mass of the adsorbent as 100%. When the mass fraction of the carbon quantum dots is too low, it is not conducive to enhancing the adsorption of CO2 by the reduced graphene oxide aerogel. When the mass fraction of the carbon quantum dots is too high, the pores of the reduced graphene oxide aerogel may be blocked. In addition, the mass fraction of the reduced graphene oxide aerogel will be too low, which is also not conducive to improving the overall adsorption capacity of the adsorbent.

[0031] In some embodiments, when the adsorbent is a reduced graphene oxide aerogel modified with ammoniated carbon quantum dots, the mass fraction of the carbon quantum dots is 1-20%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, etc., based on the total mass of the adsorbent as 100%, and the mass fraction of N is 2-20%, such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, etc. When the mass fraction of the ammoniated carbon quantum dots is too low, the difference with the mass fraction of the carbon quantum dots is too small, indicating that the degree of ammoniating is too small, which is not conducive to enhancing the adsorption of CO2 by the reduced graphene oxide aerogel. When the mass fraction of the ammoniated carbon quantum dots is too high, the difference with the mass fraction of the carbon quantum dots is too large, indicating that the degree of ammoniating is too large, and the adsorption of the adsorbent will no longer be significantly enhanced.

[0032] In some embodiments, the aminated carbon quantum dots are carbon quantum dots modified with at least one of amino, primary amino, and tertiary amino groups. Functional groups such as -NH2 on the aminated carbon quantum dots can react chemically with CO2, further strengthening the adsorption of reduced graphene oxide aerogels and optimizing the CO2 adsorption performance. It should be noted that the reaction of functional groups such as -NH2 with CO2 is reversible, and CO2 will become -NH2 after desorption, and -NH2 will not be lost.

[0033] In some embodiments, the reduced graphene oxide aerogel is a composite of reduced graphene oxide, polyethylene imine and chitosan. Polyethylene imine and chitosan act as crosslinking agents in the preparation process of reduced graphene oxide aerogel, and polyethylene imine and chitosan undergo crosslinking reactions with functional groups on the surface of graphene oxide to achieve self-assembly of reduced graphene oxide aerogel.

[0034] In some embodiments, the mass ratio of the reduced graphene oxide, the polyethyleneimine and the chitosan is (1-5):(1-5):(0.05-0.25). When the content of polyethyleneimine and chitosan is too low, it is not conducive to the formation of reduced graphene oxide aerogel. When the content of polyethyleneimine and chitosan is too high, it is not conducive to cost reduction and efficiency improvement.

[0035] In addition, an embodiment of the present invention further provides a method for preparing a carbon dioxide adsorbent, comprising the following steps:

[0036] S1. The graphene oxide dispersion is subjected to a first hydrothermal reaction at a high temperature to obtain the reduced graphene oxide aerogel;

[0037] S2. mixing the reduced graphene oxide aerogel and the carbon source dispersion to obtain a mixed solution; subjecting the mixed solution to a second hydrothermal reaction at a high temperature to obtain a carbon quantum dot-modified reduced graphene oxide aerogel;

[0038] Optionally, the method further comprises step S3: mixing the carbon quantum dot-modified reduced graphene oxide aerogel and ammonia water to obtain a mixture; and subjecting the mixture to a third hydrothermal reaction at high temperature to obtain ammoniated carbon quantum dot-modified reduced graphene oxide aerogel.

[0039] When the adsorbent is reduced graphene oxide aerogel modified by carbon quantum dots, the preparation method of the embodiment of the present invention comprises steps S1 and S2. When the adsorbent is reduced graphene oxide aerogel modified by aminated carbon quantum dots, the preparation method of the embodiment of the present invention comprises steps S1, S2 and S3.

[0040] The preparation method of the embodiment of the present invention develops an adsorbent with high CO2 adsorption capacity by introducing carbon quantum dots or aminated carbon quantum dots into reduced graphene oxide aerogel. First, the preparation method step S1 of the embodiment of the present invention prepares reduced graphene oxide aerogel by hydrothermal reduction. Secondly, the preparation method step S2 of the embodiment of the present invention can achieve the in-situ growth of carbon quantum dots in reduced graphene oxide aerogel by first mixing the carbon source dispersion and reduced graphene oxide aerogel, so that the carbon source dispersion is evenly filled on the inner and outer surfaces of the reduced graphene oxide aerogel, and then a second hydrothermal reaction is performed, so that the carbon quantum dots are evenly modified on the reduced graphene oxide aerogel, which is better than pre-preparing carbon quantum dots and then doping them on the reduced graphene oxide aerogel. Optionally, the preparation method of the embodiment of the present invention also includes step S3, after the carbon quantum dots are in-situ grown on the reduced graphene oxide aerogel, the carbon quantum dots are aminated, which can provide abundant reactive sites, further strengthen the adsorption of the reduced graphene oxide aerogel, and achieve the optimization of the CO2 adsorption performance of the reduced graphene oxide aerogel.

[0041] In some embodiments, step S1 specifically includes the following steps: S101, mixing graphene oxide dispersion, polyethyleneimine solution, and chitosan solution to obtain slurry; S102, subjecting the slurry to a first hydrothermal reaction at high temperature to obtain the reduced graphene oxide aerogel. The role of adding polyethyleneimine and chitosan to graphene oxide is to act as a crosslinking agent, thereby achieving self-assembly of the reduced graphene oxide aerogel.

[0042] In some embodiments, step S101 specifically includes the following steps: dispersing graphene oxide in water to obtain a graphene oxide dispersion; dissolving polyethyleneimide in a phosphate buffer solution to obtain a polyethyleneimide solution; dissolving chitosan in acetic acid to obtain a chitosan solution; mixing the graphene oxide dispersion, the polyethyleneimine solution, and the chitosan solution to obtain the slurry.

[0043] In some embodiments, the mass ratio of the graphene oxide, the polyethyleneimine and the chitosan is (1-5):(1-5):(0.05-0.25).

[0044] In some embodiments, in step S1, the temperature of the first hydrothermal reaction is 180-220°C, such as 180°C, 190°C, 200°C, 210°C, 220°C, etc., and the time is 12-24h, such as 12h, 14h, 16h, 18h, 20h, 22h, 24h, etc. When the temperature of the first hydrothermal reaction is too low or the time is too short, it is not conducive to hydrothermal reduction to generate reduced graphene oxide aerogel. When the temperature of the first hydrothermal reaction is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0045] In some embodiments, in step S2, the mass ratio of the reduced graphene oxide aerogel to the carbon source is 1:(5-50), such as 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, etc. When the mass ratio of the reduced graphene oxide aerogel to the carbon source is too low, the reduced graphene oxide aerogel is too little, and the carbon quantum dots are too much, which is not conducive to improving the adsorption capacity of the adsorbent as a whole for CO2. When the mass ratio of the reduced graphene oxide aerogel to the carbon source is too high, the reduced graphene oxide aerogel is too much, and the carbon quantum dots are too little, which is not conducive to providing abundant adsorption sites for the reduced graphene oxide aerogel, thereby being not conducive to strengthening the adsorption of CO2 by the reduced graphene oxide aerogel.

[0046] In some embodiments, in step S2, the carbon source is at least one of glycine, lysine, serine, and arginine, etc. The above carbon sources are all suitable for preparing carbon quantum dots by hydrothermal method.

[0047] In some embodiments, in step S2, the temperature of the second hydrothermal reaction is 150-200°C, such as 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., and the time is 2-8h, such as 2h, 4h, 6h, 8h, etc. When the temperature of the second hydrothermal reaction is too low or the time is too short, it is not conducive to the hydrothermal reduction reaction of the carbon source to generate carbon quantum dots. When the temperature of the second hydrothermal reaction is too high or the time is too long, it is not conducive to cost reduction and efficiency improvement.

[0048] In some embodiments, in step S3, when the mass of the carbon quantum dot-modified reduced graphene oxide aerogel is 0.2g, 5mL of ammonia water with a mass concentration of 5wt% is used. The higher the amount of ammonia water added, the more functional groups such as amino groups are introduced, the richer the reaction active sites are, and the more conducive to the adsorption of acidic CO2 gas. However, when ammonia water is added to a certain amount, the reaction active sites tend to be saturated, and the CO2 adsorption effect does not increase significantly if the content of functional groups such as amino groups is continued to increase. It should be noted that this is only an example of the ratio of reduced graphene oxide aerogel and ammonia water, and it is not limited to ammoniaization with such a fixed numerical addition amount.

[0049] In some embodiments, in step S3, the temperature of the third hydrothermal reaction is 160-200°C, such as 160°C, 170°C, 180°C, 190°C, 200°C, etc., and the time is 2-5h, such as 2h, 3h, 4h, 5h, etc.

[0050] Classically, the method for preparing the carbon dioxide adsorbent according to the embodiment of the present invention comprises the following steps:

[0051] S1. Preparation of reduced graphene oxide aerogel.

[0052] S100. Graphene oxide (GO) was prepared by a modified Hummers method.

[0053] 40-60 mL of concentrated sulfuric acid (98 wt%), 5.0-10.0 g of potassium persulfate and 5.0-10.0 g of phosphorus pentoxide are sequentially added into a round-bottom flask, and stirred vigorously to obtain a clear solution; after heating to 80±2° C. in a water bath, 4.0-8.0 g of natural graphite powder is added to react for 3-8 hours, and after the reaction is completed, the mixture is cooled to room temperature, and 100-300 mL of deionized water is added to slowly dilute the mixture; the reactant is filtered, washed to neutrality, and dried at 40-60° C. for 12-24 hours to obtain a graphite pre-oxide.

[0054] Weigh 100-180 mL of concentrated sulfuric acid and add it to a round-bottom flask, add 3.0-8.0 g of the above-mentioned graphite pre-oxide under stirring, then add 13.0-20.0 g of potassium permanganate in small amounts and multiple times, stir to react, and strictly control the temperature within 20° C.; then add 3.0 g of sodium nitrate, react in a water bath at 35±2° C. for 1-4 hours; add 200-500 mL of deionized water to dilute, and continue to react in a water bath at 35±2° C. for 1-4 hours; add 3-20 mL of hydrogen peroxide with a mass fraction of 35wt%, and wait until the brown reaction liquid suddenly changes to bright yellow, so as to obtain graphite oxide.

[0055] 50-200 mL of 10 vol% dilute hydrochloric acid is added to the graphite oxide, fully stirred, and then washed with deionized water until neutral to obtain graphene oxide.

[0056] S101. Add the above-mentioned graphene oxide to 100-500mL deionized water, stir for 30-60min, ultrasonically disperse for 1-2h, and then centrifuge at 1000-5000rpm for 10-30min to remove the precipitate to obtain a stably dispersed graphene oxide dispersion with a concentration of 1-2g / L, and adjust the pH of the graphene oxide dispersion to 7.0 using NaOH with a concentration of 0.1-1mol / L.

[0057] A polyethyleneimine solution was prepared by dissolving 100-500 mg of polyethyleneimine in 100-500 mL of PBS (phosphate buffered saline, pH=7.0).

[0058] 100-500 mg of chitosan is added into 100-500 mL of 1% acetic acid, dissolved and stirred to prepare a chitosan solution.

[0059] S102. Preparation of reduced graphene oxide aerogel by hydrothermal reduction method.

[0060] Add polyethyleneimine solution and chitosan solution to graphene oxide dispersion, with the volume ratio of graphene oxide dispersion: polyethyleneimine solution: chitosan solution being (1-5):(1-5):(0.1-0.5), stir thoroughly for 30-60 minutes, then put into a stainless steel autoclave lined with polytetrafluoroethylene, perform hydrothermal reduction at 180-220°C for 12-24 hours, take out the product, cool it naturally, and wash it 3 times with deionized water to obtain reduced graphene oxide aerogel.

[0061] S2. Preparation of carbon quantum dot modified reduced graphene oxide aerogel.

[0062] Add glycine to a beaker, and then add deionized water, the mass ratio of glycine to water is (10-5):(3-1), and stir thoroughly to make the glycine completely dispersed in the aqueous solution to form a uniform suspension; then, transfer the suspension to a 25mL polytetrafluoroethylene liner, and put the reduced graphene oxide aerogel prepared in step S1, then put it into a hydrothermal reactor and seal it, heat it at 150-200°C for 2-8h, and after the reactor is naturally cooled to room temperature, obtain the carbon quantum dot-modified reduced graphene oxide aerogel, wash it with deionized water 3 times, and put it back into the polytetrafluoroethylene liner.

[0063] S3. Amination of carbon quantum dots to prepare reduced graphene oxide aerogel modified with amination carbon quantum dots.

[0064] Add 1-20 mL of 1-5 wt% ammonia water to the polytetrafluoroethylene liner of step S2, put it into a hydrothermal kettle and seal it, perform hydrothermal reaction at 160-200° C. for 2-5 hours, cool it and dry it at room temperature to obtain graphene aerogel modified with aminated carbon quantum dots.

[0065] The present invention is described in detail below with reference to embodiments.

[0066] Example 1

[0067] A carbon dioxide adsorbent is a reduced graphene oxide aerogel modified by aminated carbon quantum dots, wherein the total mass of the adsorbent is 100%, the mass fraction of the carbon quantum dots is 18%, the mass fraction of N is 6%, and the remainder is reduced graphene oxide aerogel. The reduced graphene oxide aerogel is a composite of reduced graphene oxide, polyethylene imine and chitosan, and the mass ratio of reduced graphene oxide, polyethylene imine and chitosan is 1:3:0.1.

[0068] The preparation method of the carbon dioxide adsorbent is as follows:

[0069] S1. Preparation of reduced graphene oxide aerogel.

[0070] S100, graphene oxide (GO) was prepared using the improved Hummers method.

[0071] 50mL of concentrated sulfuric acid, 8.0g of potassium persulfate, and 8.0g of phosphorus pentoxide were added to a round-bottom flask in sequence, and stirred vigorously to obtain a clear solution; 4.0g of natural graphite powder was added after heating to 80°C in a water bath to react for 5h, and after the reaction was completed, it was cooled to room temperature and slowly diluted with 200mL of deionized water; the reactant was filtered, washed to neutrality, and dried at 60°C for 12h to obtain graphite pre-oxide. 140mL of concentrated sulfuric acid was weighed and added to a round-bottom flask, 3.0g of the above graphite pre-oxide was added under stirring, and then 18.0g of potassium permanganate was added in small amounts and several times, stirred to react, and the temperature was strictly controlled within 20°C; then 3.0g of sodium nitrate was added, and the reaction was carried out in a water bath at 35°C for 2h; 300mL of deionized water was added to dilute, and the reaction was continued in a water bath at 35°C for 2h; 10mL of hydrogen peroxide with a mass fraction of 35wt% was added, and the brown reaction solution was suddenly changed to bright yellow, and graphite oxide was obtained. 100 mL of 10 vol% dilute hydrochloric acid was added to the graphite oxide, the mixture was fully stirred, and then washed with deionized water until neutral to obtain graphene oxide (GO).

[0072] S101. Prepare GO dispersion, PEI solution and CS solution.

[0073] The above graphene oxide (GO) was added to 100 mL of deionized water, stirred for 30 min, ultrasonically dispersed for 2 h, and then centrifuged at 4000 rpm for 10 min to remove the precipitate (the precipitate was mainly unreacted graphite raw materials and multilayer GO, and the single-layer GO was basically not separated at 4000 rpm) to obtain a GO dispersion with a concentration of 2 g / L and a pH of 7.0 was adjusted using 0.5 mol / L NaOH. 200 mg of polyethyleneimine (PEI) was dissolved in 100 mL of PBS (phosphate buffered saline, pH = 7.0) to prepare a PEI solution with a concentration of 2 g / L. 100 mg of chitosan (CS) was added to 100 mL of 1% acetic acid, dissolved and stirred to prepare a CS solution with a concentration of 1 g / L.

[0074] S102. Preparation of reduced graphene oxide aerogel by hydrothermal reduction method.

[0075] PEI solution and CS solution were added to GO dispersion with a volume ratio of GO dispersion: PEI solution: CS solution of 1:3:0.2. The mixture was stirred for 30 min and then placed in a stainless steel autoclave lined with polytetrafluoroethylene for hydrothermal reduction at 200 °C for 12 h. The product was taken out and cooled naturally and washed with deionized water for 3 times to obtain rGO-PEI-CS composite, i.e., reduced graphene oxide aerogel.

[0076] S2. Preparation of carbon quantum dot modified reduced graphene oxide aerogel.

[0077] Add glycine to a beaker, and then add deionized water, the mass ratio of glycine to water is 2:5, stir thoroughly to make glycine completely dispersed in the aqueous solution to form a uniform suspension, and the mass ratio of reduced A graphene oxide aerogel to glycine is 1:10; then, transfer the suspension to a 25mL polytetrafluoroethylene liner, and put it into the reduced graphene oxide aerogel prepared in step S102, then put it into a hydrothermal kettle and seal it, heat it at 180°C for 4h, wait for the reactor to cool naturally to room temperature, and obtain carbon quantum dot-modified reduced graphene oxide aerogel, wash it with deionized water 3 times, and put it back into the polytetrafluoroethylene liner.

[0078] S3. Amination of carbon quantum dots to prepare reduced graphene oxide aerogel modified with amination carbon quantum dots.

[0079] The mass of the reduced graphene oxide aerogel modified with carbon quantum dots in the polytetrafluoroethylene liner of step S2 is 0.2 g. 5 mL of 5 wt% ammonia water is added to the polytetrafluoroethylene liner of step S2, and the mixture is placed in a hydrothermal kettle for sealing, and subjected to a hydrothermal reaction at 200° C. for 2 h, and then dried at room temperature after cooling to obtain the reduced graphene oxide aerogel modified with aminated carbon quantum dots.

[0080] Example 2

[0081] The difference between this embodiment and embodiment 1 is that in step S3, when the carbon quantum dots are aminated, 9 mL of 5 wt% ammonia water is added. Based on the total mass of the adsorbent as 100%, the mass fraction of the carbon quantum dots is 18%, and the mass fraction of N is 8%.

[0082] Example 3

[0083] The difference between this embodiment and embodiment 1 is that in step S3, when the carbon quantum dots are aminated, 15 mL of 5 wt% ammonia water is added. Based on the total mass of the adsorbent as 100%, the mass fraction of the carbon quantum dots is 18%, and the mass fraction of N is 13%.

[0084] Example 4

[0085] The difference between this embodiment and embodiment 1 is that in step S3, when the carbon quantum dots are aminated, 21 mL of 5 wt% ammonia water is added. Based on the total mass of the adsorbent as 100%, the mass fraction of the carbon quantum dots is 18%, and the mass fraction of N is 19%.

[0086] Example 5

[0087] The difference between this embodiment and embodiment 1 is that in step S3, when the carbon quantum dots are aminated, 27 mL of 5 wt% ammonia water is added. Based on the total mass of the adsorbent as 100%, the mass fraction of the carbon quantum dots is 18%, and the mass fraction of N is 20%.

[0088] Example 6

[0089] The difference between this embodiment and embodiment 4 is that in step S2, the mass ratio of reduced graphene oxide aerogel and glycine is 1:1, and the mass fraction of carbon quantum dots in the obtained adsorbent is 1%, and the mass fraction of N is 8%.

[0090] Example 7

[0091] The difference between this embodiment and embodiment 4 is that in step S2, the mass ratio of reduced graphene oxide aerogel to glycine is 1:13, and in the obtained adsorbent, the mass fraction of carbon quantum dots is 20%, and the mass fraction of N is 25%.

[0092] Example 8

[0093] The difference between this embodiment and embodiment 4 is that step S3 is omitted, and the obtained adsorbent is reduced graphene oxide aerogel modified with carbon quantum dots. Taking the total mass of the adsorbent as 100%, the mass fraction of the carbon quantum dots is 18%.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that steps S2-S3 are omitted, and the adsorbent obtained is reduced graphene oxide aerogel.

[0096] Performance Test:

[0097] The CO2 adsorption capacity of the adsorbents obtained in each embodiment and comparative example was tested using a specific surface area analyzer under low pressure (<200 kPa) and 298 K. The specific test results are shown in Table 1.

[0098] Table 1. Evaluation results of the adsorption performance of the adsorbents prepared in various embodiments and comparative examples for CO2

[0099] <![CDATA[CO2 adsorption capacity (mg / g)]]> Example 1 73.7 Example 2 89.2 Example 3 104.5 Example 4 122.6 Example 5 122.9 Example 6 30.4 Example 7 146.5 Example 8 19.6 Comparative Example 1 13.1

[0100] From the data in Table 1, it can be seen that the number of effective adsorption sites of the reduced graphene oxide aerogel without carbon quantum dots in Comparative Example 1 is small, and the CO2 adsorption performance is poor. Compared with the reduced graphene oxide aerogel directly prepared by the hydrothermal reduction method in Comparative Example 1, the reduced graphene oxide aerogel with carbon quantum dots added in Example 8 has significantly improved CO2 adsorption, indicating that the introduction of carbon quantum dots is conducive to increasing the specific surface area of ​​the reduced graphene oxide aerogel, thereby increasing the adsorption sites of CO2, thereby improving the CO2 adsorption performance.

[0101] Compared with the reduced graphene oxide aerogel directly prepared by the hydrothermal reduction method in Comparative Example 1, the reduced graphene oxide aerogel with added aminated carbon quantum dots in Examples 1-7 has significantly increased CO2 adsorption. This is because the CO2 adsorption is related to the adsorption sites on the aerogel surface and the degree of ammoniation of the carbon quantum dots. Examples 1-7 can further enhance the CO2 adsorption effect of the reduced graphene oxide aerogel by modifying the aminated carbon quantum dots on the reduced graphene oxide aerogel.

[0102] Compared with the reduced graphene oxide aerogel modified with carbon quantum dots in Example 8, the reduced graphene oxide aerogel with aminated carbon quantum dots added in Examples 1-7 has significantly improved CO2 adsorption capacity. This indicates that the introduction of amino groups has a significant effect on improving the CO2 adsorption performance of reduced graphene oxide aerogel.

[0103] In addition, Examples 1-4 show that the higher the amount of ammonia water added, the more functional groups such as amino groups are introduced, the richer the reactive sites are, and the more conducive to the adsorption of acidic CO2 gas. Examples 4-5 show that when 5wt% ammonia water is added to a certain amount, the reactive sites tend to be saturated, and the CO2 adsorption effect does not increase significantly when the content of functional groups such as amino groups is further increased.

[0104] In the present invention, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0105] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A carbon dioxide adsorbent, characterized in that: The adsorbent is carbon quantum dots or ammoniated carbon quantum dots modified reduced graphene oxide aerogel.

2. The carbon dioxide adsorbent according to claim 1, characterized in that When the adsorbent is reduced graphene oxide aerogel modified by carbon quantum dots, the mass fraction of the carbon quantum dots is 1-20% based on the total mass of the adsorbent being 100%.

3. The carbon dioxide adsorbent according to claim 1, characterized in that When the adsorbent is reduced graphene oxide aerogel modified by aminated carbon quantum dots, based on the total mass of the adsorbent being 100%, the mass fraction of the carbon quantum dots is 1-20%, and the mass fraction of N is 2-25%.

4. The carbon dioxide adsorbent according to claim 1, characterized in that The aminated carbon quantum dots are carbon quantum dots modified with at least one of amino groups, primary amino groups, and tertiary amino groups.

5. The carbon dioxide adsorbent according to any one of claims 1 to 4, characterized in that: The reduced graphene oxide aerogel is a composite of reduced graphene oxide, polyethylene imine and chitosan; the mass ratio of the reduced graphene oxide, the polyethylene imine and the chitosan is (1-5):(1-5):(0.05-0.25).

6. The method for preparing a carbon dioxide adsorbent according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. The graphene oxide dispersion is subjected to a first hydrothermal reaction at a high temperature to obtain the reduced graphene oxide aerogel; S2. mixing the reduced graphene oxide aerogel and the carbon source dispersion to obtain a mixed solution; subjecting the mixed solution to a second hydrothermal reaction at a high temperature to obtain a carbon quantum dot-modified reduced graphene oxide aerogel; Optionally, the method further comprises step S3: mixing the carbon quantum dot-modified reduced graphene oxide aerogel and ammonia water to obtain a mixture; and subjecting the mixture to a third hydrothermal reaction at high temperature to obtain ammoniated carbon quantum dot-modified reduced graphene oxide aerogel.

7. The preparation method according to claim 6, characterized in that: Step S1 specifically includes the following steps: S101. The graphene oxide dispersion, the polyethyleneimine solution and the chitosan solution are mixed to obtain a slurry; S102. Subjecting the slurry to a first hydrothermal reaction at high temperature to obtain the reduced graphene oxide aerogel.

8. The preparation method according to claim 6, characterized in that: In step S2, the mass ratio of the reduced graphene oxide aerogel to the carbon source is 1:(5-50).

9. The preparation method according to claim 6, characterized in that: In step S3, when the mass of the carbon quantum dot-modified reduced graphene oxide aerogel is 0.2 g, 5-15 mL of ammonia water with a mass concentration of 5 wt % is used.

10. The preparation method according to claim 6, characterized in that: In step S1, the temperature of the first hydrothermal reaction is 180-220°C and the time is 12-24h; and / or, in step S2, the temperature of the second hydrothermal reaction is 150-200°C for 2-8h; and / or, in step S3, the temperature of the third hydrothermal reaction is 160-200°C, The time is 2-5h.