Photo-thermal carbon dioxide adsorbent as well as preparation method and application thereof

Abstract

The invention discloses a photo-thermal carbon dioxide adsorbent as well as a preparation method and application thereof. The photo-thermal carbon dioxide adsorbent is green in production process and wide in raw material source, chitosan which is high in natural abundance and low in price is directly used as a raw material, and the energy consumption in the preparation process is effectively reduced through a composite pore-forming strategy that an activating agent, a pore-forming agent and a nitrogen source are introduced through a one-pot method. The photo-thermal carbon dioxide adsorbent provided by the invention can realize direct carbon capture in normal-temperature air or adsorption separation of CO2 in flue gas, and then realizes zero-carbon desorption under sunlight irradiation, thereby providing a new idea for capture, utilization and storage of carbon dioxide.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture technology, specifically, it relates to a photothermal carbon dioxide adsorbent, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, the concentration of carbon dioxide (CO2) in the atmosphere has reached 420 ppm, leading to frequent extreme weather events such as global warming, glacial melting, and sea-level rise. The international community has begun to take active steps to address climate change, establishing the goal of limiting global warming to well below 1.5°C through the Paris Agreement. To achieve this, the world needs to reduce carbon emissions by 50% by 2030 and achieve net-zero emissions by 2050. Carbon capture, utilization, and storage (CCUS) technology is considered one of the key technologies for achieving carbon neutrality. Capturing carbon from air or flue gas is a crucial link in the CCUS technology chain. Currently, the high cost of carbon capture (accounting for more than 60% of the entire process) is the core issue restricting the further large-scale application of this technology. Among various CO2 capture materials, solid adsorbents are favored by researchers due to their excellent regeneration performance, low energy consumption, and high adsorption capacity, compared to the problems of easily degradable, low-capacity, and highly corrosive nature of amine-based absorbent solvents. However, most solid adsorbents, such as MOFs and molecular sieves, remain in the laboratory or pilot-scale stages due to their high preparation costs, limiting their further large-scale industrial production. While the preparation methods for the most widely used amine-functionalized solid adsorbents are simple, the high temperatures during adsorption and desorption processes still lead to safety issues related to amine pyrolysis, resulting in poor selectivity and cycle performance, as well as high energy consumption. Furthermore, most solid adsorbent products are in powder form and require a molding process before practical application. The adsorption performance and cycle stability of most adsorbent powders decrease significantly after molding, making CO2 adsorbent molding a major challenge. Therefore, developing novel, efficient, low-energy-consumption, environmentally friendly, and low-cost molded CO2 adsorbents is of great significance.

[0003] In industrial CO2 adsorption and separation operations, how to achieve efficient regeneration of the adsorbent is a key factor determining CO2 adsorption technology. Traditional adsorbent materials usually need to be recycled under varying temperature or pressure conditions, that is, adsorbing at room temperature and desorbing when heated, or adsorbing under pressure and desorbing after depressurization, resulting in high energy consumption in the entire adsorption-desorption process and strict requirements on equipment. Therefore, when developing CO2 adsorbents, it is necessary to consider both adsorption selectivity and regeneration performance. The traditional industrial method of regenerating adsorbents by heating and desorption inevitably leads to a large amount of energy loss due to low thermal efficiency, which is not in line with the current concept of green and sustainable development. In recent years, photothermal materials have attracted the attention of researchers because they can fully absorb sunlight and convert it into heat energy. According to the interaction mechanism between light and matter and different heat generation mechanisms, photothermal mechanisms can be divided into three categories: (1) localized plasma heating; (2) non-radiative relaxation; (3) molecular thermal vibration. To reduce the energy consumption of the adsorption-desorption process, it is desirable to introduce light-absorbing components into the solid adsorbent material, which can be converted into heat energy in situ under light conditions to achieve self-thermal desorption. This CO2 adsorption-photo-self-thermal desorption mechanism greatly reduces the energy consumption of the capture process compared with traditional temperature swing and pressure swing adsorption.

[0004] Carbon spheres are excellent photothermal materials due to their inherent physical and chemical properties. Chitosan carbon spheres, in particular, are micron- to millimeter-sized spherical carbon materials prepared through chemical processing using natural high-molecular-weight chitosan as the carbon source and precursor. In carbon dioxide capture applications, their adsorption performance mainly depends on the alkaline sites provided by the material's own nitrogen source and the microporous structure formed during the activation process. However, the adsorption capacity of such materials is often not ideal, limiting their practical applications. Specifically, micron-sized chitosan carbon spheres prepared by the hydrothermal method, even after subsequent alkali activation treatment, still exhibit limited carbon dioxide adsorption capacity and high bed pressure drop during adsorption due to their low specific surface area and small particle size. Furthermore, this process is complex and energy-intensive, further restricting its potential for large-scale application. In contrast, millimeter-sized chitosan carbon spheres prepared by the droplet molding method have certain advantages in terms of industrial applicability, but still suffer from insufficient specific surface area and low adsorption performance, requiring further optimization and structural control. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a photothermal adsorbent, its preparation method, and its application in carbon dioxide capture. It employs an alkaline solution, a soft template pore-forming agent, and a nitrogen source to synergistically create pores, thus preparing a porous carbon-based adsorbent capable of capturing CO2 from ambient air or flue gas. Leveraging its unique physical and chemical properties, it can effectively convert light energy into heat energy and incorporates endothermic substances in situ or through physical blending, aiming to further achieve a low-energy-consumption CO2 adsorption-photothermal self-desorption process.

[0006] In one aspect, the present invention provides a method for preparing a photothermal carbon dioxide adsorbent, the method comprising the following steps:

[0007] S1: Dissolve chitosan in acid A solution, stir thoroughly until no bubbles are present, to obtain acid A solution containing 1-10 wt% chitosan, and let stand;

[0008] S2: Add the pore-forming agent, nitrogen source, and metal salt to the chitosan acid A solution, stir to fully dissolve in the solution, and let stand at 20-60℃ for 0.5-5 hours;

[0009] S3: Drop the solution that has been allowed to stand in step S2 into an alkaline solution and soak it for aging for 10-30 hours to obtain a spherical gel;

[0010] S4: Take out the spherical gel obtained in step S3, rinse it with water until it is weakly alkaline, and dry it for 5-30 hours to obtain the carbon precursor.

[0011] S5: Place the carbon precursor obtained in step S4 under a protective gas atmosphere, slowly heat it to 600-1000℃, and then keep it at a constant temperature for 0.5-5 hours to obtain porous carbon.

[0012] S6: Wash the porous carbon obtained in step S5 with acid B solution for 1-5 hours, then wash with water until neutral, and dry in a vacuum environment at 100-140°C for 5-15 hours to obtain the photothermal carbon dioxide adsorbent.

[0013] In one or more embodiments, the chitosan has a molecular weight of 25 to 250 kDa.

[0014] In one or more embodiments, acid A is selected from hydrochloric acid, acetic acid, sulfuric acid, nitric acid and acrylic acid, and the concentration of acid A solution is 0.5-5% (w / v); acid B is selected from sulfuric acid, nitric acid and acetic acid, and the concentration of acid B solution is 0.02-2 mol / L.

[0015] In one or more embodiments, in step S2, the pore-forming agent is selected from potassium chloride, sodium chloride, ethanol, zinc chloride, sodium silicate, potassium sulfate, and sodium sulfate, and the concentration added is 0.01 to 0.05 mol / L.

[0016] In one or more embodiments, in step S2, the nitrogen source is selected from urea, melamine, ammonium chloride and potassium nitrate, and the concentration added is 0.01 to 0.05 mol / L;

[0017] In one or more embodiments, in step S2, the metal salt is selected from copper nitrate, ferric nitrate, silver nitrate, and copper acetate, and the concentration added is 0.01 to 0.05 mol / L.

[0018] In one or more embodiments, in step S3, the alkaline solution is selected from solutions of potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium thiosulfate, potassium oxalate, and potassium acetate, with a concentration of 0.02 to 2 mol / L.

[0019] In another aspect, the present invention provides a photothermal carbon dioxide adsorbent prepared according to the method described in any embodiment herein.

[0020] In another aspect, the present invention provides the application of the photothermal carbon dioxide adsorbent according to any embodiment herein in carbon dioxide capture.

[0021] In one or more embodiments, the photothermal carbon dioxide adsorbent is used to capture carbon dioxide from air or other carbon dioxide-containing gas mixtures.

[0022] Preferably, the mixed gas comprises carbon dioxide and at least one selected from hydrogen, carbon monoxide, and methane. More preferably, the mixed gas is CO2-H2, CO2-CO, or CO2-CH4. Even more preferably, the volume percentage of carbon dioxide in the mixed gas is 50%.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The method for preparing photothermal porous carbon-based materials provided by the present invention can be directly formed in one step, avoiding secondary processing of powder; and the production process is green, with a wide range of raw material sources, directly using chitosan with high natural abundance and low price as raw material, which comes from waste such as shrimp, crab, and shells, and is suitable for large-scale production and CO2 capture industrial applications.

[0025] (2) This invention introduces a composite pore-forming strategy of activator, pore-forming agent, and nitrogen source in a one-pot process, abandoning the energy-intensive drying method of freeze-drying. It achieves precise control over the surface chemistry and pore structure of materials at the molecular / nanoscale, obtaining millimeter-sized spherical photothermal carbon-based adsorbents with unique microporous-mesoporous three-dimensional pore structure, high specific surface area, and strongly alkaline adsorption sites. Its CO2 adsorption performance and selectivity are superior to conventional porous carbon adsorbents. Moreover, the process flow is more simplified, significantly reducing the adsorbent production cost and carbon emissions.

[0026] (3) Compared to conventional temperature-swing or pressure-swing adsorption-desorption, the photothermal carbon-based adsorbent provided by this invention, through in-situ doping or physical blending after molding in a one-pot method, can achieve direct carbon capture in ambient air or CO2 adsorption and separation in flue gas. The regeneration process utilizes sunlight irradiation, and the original heat-generating surface temperature of the photothermal adsorbent particles reaches over 70°C under the action of its light-absorbing components. Moreover, after solar-heated desorption, its separation and adsorption performance is no different from that in desorption in an 80°C oven. This process converts the driving energy from electrical energy to solar energy, achieving zero carbonization in the desorption process, making the entire adsorption-regeneration cycle more economical and environmentally friendly. Attached Figure Description

[0027] Figure 1 This is a diagram of the photothermal adsorbent particles in Example 1.

[0028] Figure 2 This is the isothermal adsorption curve of the photothermal adsorbent particles in Example 8.

[0029] Figure 3 This is a diagram showing the nitrogen specific surface area after the photothermal adsorbent particles in Example 8 have been re-pored.

[0030] Figure 4 This is the adsorption and separation performance diagram of the photothermal adsorbent particles in Example 8 (CO2:H2 = 1:1).

[0031] Figure 5 This is the adsorption and separation performance diagram of the photothermal adsorbent particles in Example 8 (CO2:CO = 1:1).

[0032] Figure 6 This is the adsorption and separation performance diagram of the photothermal adsorbent particles in Example 8 (CO2:CH4 = 1:1).

[0033] Figure 7 This is the adsorption and separation performance diagram of the photothermal adsorbent particles in Example 8 (CO2:N2 = 1:9).

[0034] Figure 8 This is the adsorption and separation performance diagram of the photothermal adsorbent particles in Example 8 (air, CO2 vol% = 460ppm).

[0035] Figure 9 These are isothermal adsorption curves for each pair of proportions.

[0036] Figure 10 This is a SEM image of the photothermal adsorbent particles from Example 8.

[0037] Figure 11 This is a SEM image of the photothermal adsorbent particles in Comparative Example 2. Detailed Implementation

[0038] In the following embodiments, during the preparation of the photothermal carbon dioxide adsorbent, the carbon precursor after drying the spherical gel is calcined and pyrolyzed at high temperature to obtain carbon spheres. During the pyrolysis of the carbon precursor, the metal elements or group IV elements in the "pore-forming agent" and "activator" can be reduced to atoms and uniformly dispersed in the carbon matrix in the form of nanoparticles or clusters, occupying a certain space. In the subsequent washing step, the pore-forming agent and activator are dissolved and removed, leaving cavities in the spaces they originally occupied, thus forming pores. The "metal salt" (mostly nitrates or acetates) can uniformly generate a framework structure in the spheres, playing a supporting role and serving as a photothermal conversion unit, promoting the absorption of light energy and the generation of heat. The "nitrogen source" provides nitrogen atoms doped on the surface of the carbon spheres, thereby enhancing the adsorbent's adsorption capacity for carbon dioxide.

[0039] In the following embodiments, during the carbon precursor pyrolysis process, "pore formation" can be understood as the use of only one of "pore-forming agent" and "activator", and "re-pore formation" can be understood as the use of both "pore-forming agent" and "activator".

[0040] In the following examples, chitosan was soaked in an alkaline solution to obtain spherical gels. Before drying, if the spherical gels are washed to a weakly alkaline state (pH approximately 9-10), the solutes in the alkaline solution can act as "activators"; if washed to a neutral state (pH approximately 7), the solutes in the alkaline solution do not have an activating effect.

[0041] In the following embodiments, the method for plotting the CO2 adsorption isotherm of the photothermal carbon dioxide adsorbent is as follows: The photothermal carbon dioxide adsorbent is placed in a sample tube and dried and degassed at 120°C under a nitrogen atmosphere for 6 hours. The degassed volumetric tube is transferred to the analyzer and immersed in a constant temperature bath. The pressure in the volumetric tube is monitored using software, and several target relative pressure points are set. Pure CO2 is injected into the volumetric tube to bring the internal pressure to each relative pressure point. After gas injection, the pressure will continuously decrease due to sample adsorption until the pressure change is less than a threshold within a set time interval, at which point adsorption equilibrium can be considered reached. The instrument will automatically calculate the adsorption capacity at that pressure point according to the following formula: Adsorption capacity (CO2 Capacity) P i = [(Total molar amount of injected gas) - (Molar amount of gas remaining in the dead volume)] / Sample weight in grams; Finally, by fitting the pressure points (Pi) and the corresponding adsorption amounts as the x and y axes, respectively, a CO2 adsorption isotherm is obtained. The adsorption amount of the photothermal carbon dioxide adsorbent under the conditions of a 0℃ constant temperature bath and 1 bar atmospheric pressure is denoted as P0.

[0042] In the following embodiments, the method for testing the desorption rate of the photothermal carbon dioxide adsorbent is as follows: In the step of plotting the CO2 adsorption isotherm of the photothermal carbon dioxide adsorbent, the adsorption amount P0 of the photothermal carbon dioxide adsorbent under the conditions of 0℃ constant temperature bath and 1 bar atmospheric pressure is measured. Then, after photothermal carbon dioxide adsorbent is subjected to light heating and nitrogen desorption, the adsorption amount P0' of the photothermal carbon dioxide adsorbent after desorption under the conditions of 0℃ constant temperature bath and 1 bar atmospheric pressure is measured. The desorption rate is obtained by the following formula: Desorption rate (%) = P0' / P0. Before testing P0', desorption is required by the desorption device built into the instrument; this desorption step is not required when testing P0.

[0043] In the following embodiments, the adsorption and separation performance of the photothermal carbon dioxide adsorbent was measured by using a breakthrough curve obtained from an external flue gas detector connected to a fixed bed. The specific steps are as follows: (1) Take a fixed bed without loaded particles, and introduce a pre-mixed gas (single or mixed gas components) at a flow rate of 20 mL / min using a mass flow meter. Use a flue gas detector to detect the concentration of each component in the introduced gas. Plot the detection time and the gas component fraction on the x and y axes, respectively, to obtain the breakthrough curves of each gas component, which are used as template curves in the adsorption performance graph; (2) Take 1 g of photothermal adsorbent particles and fill them into the fixed bed. Repeat step (1) to obtain the adsorption performance curves for each gas in the adsorption performance graph. Unless otherwise specified, the adsorption and separation performance of the photothermal carbon dioxide adsorbent was measured at room temperature.

[0044] Example 1

[0045] Weigh 1 g of 50 kDa chitosan and dissolve it in 1% acetic acid solution to prepare a 2 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol sodium chloride and 0.01 mol urea, and stir until fully dissolved to obtain a solution. Let stand at 30℃ for 1 hour, then add the system dropwise to a 0.1 mol / L sodium hydroxide solution. After soaking and aging for 10 hours, remove the spherical gel, wash with water until pH = 9-10, and dry in an oven for 24 hours. Place the dried gel in a porcelain boat and put it in a tube furnace. Under nitrogen protection, heat to 700℃ at 5℃ / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 0.1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120℃ for 12 hours to obtain a photothermal carbon dioxide adsorbent with the appearance of... Figure 1 As shown.

[0046] 20 mg of photothermal carbon dioxide adsorbent was taken and its carbon dioxide adsorption capacity was measured at 0℃ and 1 bar atmospheric pressure. The adsorption capacity of the material was found to be 5.67 mmol / g. 1 g of the material was taken and subjected to a mixed gas atmosphere of 25℃, CO2:CO = 1:1, and a mixed gas flow rate of 20 mL / min. The CO2 breakthrough time tA (time to reach 1% CO2 concentration) was measured to be 435 s, and the CO breakthrough time (time to reach 1% CO concentration) was tB = 10 s. α(tA / tB) = 43. After being blended with silver microspheres of 1 mm radius at a 1:1 mass ratio, and then subjected to solar desorption and nitrogen purging for 6 hours, the CO2 adsorption capacity of the material was measured to be 4.82 mmol / g, with a desorption rate of 85%.

[0047] Example 2

[0048] Weigh 1 g of 100 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, then add 0.02 mol potassium chloride, 0.02 mol melamine, and 0.02 mol ferric nitrate, and stir until fully dissolved. Let stand at 40°C for 2 hours, then dropwise into a 0.5 mol / L sodium hydroxide solution. After soaking and aging for 16 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 6 hours, place in a ceramic boat, and put into a tube furnace. Under nitrogen protection, heat to 700°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 0.5 mol / L sulfuric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0049] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 5.01 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:H2 mixture ratio of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% was 410 s, and the H2 breakthrough time (time for H2 concentration to reach 1%) was t. B =12s, α(tA / tB)=34, after xenon lamp desorption and nitrogen purging for 6 hours, the CO2 adsorption capacity of the material was measured to be 4.3 mmol / g, and the desorption rate was 86%.

[0050] Example 3

[0051] Weigh 1 g of 150 kDa chitosan and dissolve it in a 3% acetic acid solution to prepare a 4 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, then add 0.03 mol ethanol, 0.03 mol ammonium chloride, and 0.03 mol silver nitrate, and stir until fully dissolved. Let stand at 50°C for 3 hours, then add the system dropwise to a 1 mol / L potassium carbonate solution. After soaking and aging for 20 hours, remove the microspheres of gel, wash with water until pH = 9-10, dry in an oven for 6 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 900°C at 5°C / min and hold for 2 hours to obtain porous carbon. Wash the porous carbon with 0.5 mol / L sulfuric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 16 hours.

[0052] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 5.33 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% was 420 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) was t. B =10s, α(tA / tB)=42, after 6h of LED desorption and argon purging, the CO2 adsorption capacity of the material was measured to be 4.69mmol / g, and the desorption rate was 88%.

[0053] Example 4

[0054] Weigh 1 g of 200 kDa chitosan and dissolve it in a 3% acetic acid solution to prepare a 4 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, then add 0.04 mol zinc chloride, 0.04 mol potassium nitrate, and 0.05 mol copper acetate, stirring until fully dissolved. Let stand at 50°C for 3 hours, then dropwise into a 1.5 mol / L sodium hydroxide solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 10 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 900°C at 5°C / min and hold for 3 hours to obtain porous carbon. Wash the porous carbon with 1 mol / L nitric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 20 hours.

[0055] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 4.88 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CO ratio of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured.A The time it takes for the CO2 concentration to reach 1% is 365 seconds, and the CO breakthrough time of the material (the time it takes for the CO concentration to reach 1%) is t. B =12s, α(tA / tB)=28.3, after 6h of desorption by halogen tungsten lamp and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 0.39mmol / g, and the desorption rate was 8%.

[0056] Example 5

[0057] Weigh 1 g of 150 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 5 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol sodium silicate and 0.01 mol urea, and stir until fully dissolved. Let stand at 30°C for 1 hour, then drop the system into a 0.5 mol / L potassium hydroxide solution. After soaking and aging for 16 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 12 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 0.5 mol / L acetic acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 6 hours.

[0058] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 5.24 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:H2 mixture ratio of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% was 395 s, and the H2 breakthrough time (time for H2 concentration to reach 1%) was t. B =12s, α(tA / tB)=32, after being mixed with iron oxide spheres with a radius of 1mm at a mass ratio of 1:1, and then subjected to xenon lamp desorption and nitrogen purging for a total of 6h, the CO2 adsorption capacity of the material was measured to be 4.45mmol / g, and the desorption rate was 85%.

[0059] Example 6

[0060] Weigh 1 g of 200 kDa chitosan and dissolve it in a 3% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, then add 0.01 mol potassium sulfate, 0.01 mol urea, and 0.01 mol ferric nitrate, and stir until fully dissolved. Let stand at 40°C for 2 hours, then dropwise into a 0.5 mol / L potassium bicarbonate solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a ceramic boat, and put into a tube furnace. Under nitrogen protection, heat to 750°C at 5°C / min and hold for 4 hours to obtain porous carbon. Wash the porous carbon with 1.5 mol / L acrylic acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0061] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 4.77 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% is 350 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) is t. B =17s, α(tA / tB)=20, after 6 hours of solar desorption and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 4.102 mmol / g, and the desorption rate was 86%.

[0062] Example 7

[0063] Weigh 1 g of 100 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol sodium sulfate and 0.01 mol urea, stir until fully dissolved, let stand at 50°C for 3 hours, then dropwise into a 1 mol / L potassium thiosulfate solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0064] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 4.82 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:N2 mixture ratio of 1:9 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. AThe time for CO2 concentration to reach 1% is 240s, and the N2 breakthrough time (time for N2 concentration to reach 1%) is t. B =10s, α(tA / tB)=24, after being mixed with crushed black rubber at a mass ratio of 1:1, and then subjected to desorption by halogen tungsten lamp and nitrogen purging for a total of 6 hours, the CO2 adsorption capacity of the material was measured to be 4.58 mmol / g, and the desorption rate was 95%.

[0065] Example 8

[0066] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 4 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol sodium silicate and 0.01 mol urea, and stir until fully dissolved. Let stand at 50°C for 3 hours, then dropwise add the system to a 1 mol / L potassium hydroxide solution and soak for 24 hours. Remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0067] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 6.22 mmol / g. 1 g of the material was tested at 25 °C in an air atmosphere with a flow rate of 250 mL / min (CO2 concentration of 460 ppm), and the CO2 breakthrough time t was measured. A The time for CO2 concentration to reach 1% was 7650s. After blending with EVA microspheres with a radius of 1mm at a mass ratio of 1:1, and then undergoing xenon lamp desorption and nitrogen purging for a total of 6 hours, the CO2 adsorption capacity of the material was measured to be 6.22 mmol / g, and the desorption rate was 100%.

[0068] 20 mg of photothermal carbon dioxide adsorbent was used for testing, and the following adsorption isotherms, nitrogen specific surface area diagrams after pore reconstruction, adsorption separation performance diagrams under CO2:H2 = 1:1 mixed gas atmosphere, CO2:CO = 1:1 mixed gas atmosphere, CO2:CH4 = 1:1 mixed gas atmosphere, CO2:N2 = 1:9 mixed gas atmosphere, and air atmosphere were plotted respectively. Figures 2-8 As shown; Figure 7 and Figure 8 The adsorption curves for gases other than carbon dioxide were not plotted. The photothermal carbon dioxide adsorbent was taken and its appearance was observed using SEM (scanning electron microscopy), as shown in the following figures. Figure 10As shown.

[0069] After passing through the composite pore system, the photothermal carbon dioxide adsorbent forms numerous pores inside, which... Figure 3 It can be seen that the photothermal carbon dioxide adsorbent in this embodiment exhibits good adsorption performance for nitrogen, surface area per unit mass, and pore volume-width distribution. Figures 4-8 It can be seen that the photothermal carbon dioxide adsorbent of this embodiment has a significant adsorption and separation effect on carbon dioxide in a 1:1 mixture of carbon dioxide and hydrogen, carbon monoxide or methane, a 1:9 mixture of carbon dioxide and nitrogen, and carbon dioxide in the air.

[0070] Example 9

[0071] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol zinc chloride and 0.01 mol urea, stir until fully dissolved, let stand at 50°C for 3 hours, then dropwise into a 1 mol / L potassium hydroxide solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0072] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 5.12 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:N2 mixture ratio of 1:9 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% is 260s, and the N2 breakthrough time (time for N2 concentration to reach 1%) is t. B =13s, α(tA / tB)=20, after being mixed with silver microspheres with a radius of 1mm at a mass ratio of 1:1, and then subjected to xenon lamp desorption and nitrogen purging for a total of 6h, the CO2 adsorption capacity of the material was measured to be 4.86mmol / g, and the desorption rate was 92%.

[0073] Comparative Example 1

[0074] No pore-forming agents or metal salts were added during the preparation of the photothermal adsorbent material in this comparative example.

[0075] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol urea and stir until fully dissolved. Let stand at 50°C for 3 hours, then dropwise into a 1 mol / L potassium hydroxide solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0076] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 3.48 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% was 285 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) was t. B =14s, α(tA / tB)=20, after 6 hours of xenon lamp desorption and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 1.15 mmol / g, and the desorption rate was 33%.

[0077] Comparative Example 2

[0078] No nitrogen source, pore-forming agent, or metal salt was added during the preparation of the photothermal adsorbent material in this comparative example.

[0079] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, and then let stand at 50℃ for 3 hours. Add the system dropwise to a 1 mol / L potassium hydroxide solution and soak for 24 hours. Remove the microspheres, wash with water until pH 9–10, dry in an oven for 3 hours, place in a ceramic boat, and then place in a tube furnace. Under nitrogen protection, heat to 800℃ at 5℃ / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120℃ for 12 hours.

[0080] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 3.01 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. AThe time for CO2 concentration to reach 1% was 320 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) was t. B =20s, α(tA / tB)=16, after 6h of xenon lamp desorption and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 1.11mmol / g, and the desorption rate was 37%.

[0081] Take the photothermal carbon dioxide adsorbent and observe its appearance using SEM (scanning electron microscope), as follows: Figure 11 As shown. By Figure 10 and Figure 11 As can be seen, the photothermal carbon dioxide adsorbent in this comparative example has significantly fewer pores on its surface and a smaller pore width compared to the photothermal carbon dioxide adsorbent in Example 8.

[0082] Comparative Example 3

[0083] This comparative example uses glucose, concentrated hydrochloric acid, and ferric nitrate as the main materials for preparing the photothermal adsorbent.

[0084] 0.72 g NaMoO4, 5.89 g glucose, and 20 mg ferric nitrate were dispersed in 57.5 mL of deionized water, ultrasonically dispersed, and stirred to obtain a homogeneous solution A. 2.5 mL of concentrated hydrochloric acid (12 mol / L) was added dropwise to solution A, and stirred to obtain a homogeneous solution B. Solution B was then transferred to a hydrothermal reactor and kept at 180 °C for 6 h. After washing, the solution was freeze-dried for 35 h to obtain a carbon sphere precursor. The carbon sphere precursor was placed in a tube furnace and annealed at 800 °C for 2 h under an argon atmosphere at a heating rate of 5 °C / min. It was then annealed at 300 °C for 2 h under an air atmosphere at a heating rate of 1 °C / min to obtain carbon spheres. The carbon spheres were dispersed in an ammonia solution and magnetically stirred for 12 h. After washing and drying, porous carbon sphere photothermal material was obtained.

[0085] 20 mg of the photothermal carbon dioxide adsorbent was taken and its carbon dioxide adsorption capacity was measured at 0 °C and 1 bar atmospheric pressure. The adsorption capacity of the material was found to be 0 mmol / g. 1 g of the material was taken and subjected to a mixed gas atmosphere at 25 °C, with a CO2:CH4 ratio of 1:1 and a gas flow rate of 20 mL / min. The CO2 breakthrough time t of the material was measured. A The time for CO2 concentration to reach 1% is 0s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) is t. B =0s.

[0086] Comparative Example 4

[0087] No pore-forming agent was added during the preparation of the photothermal adsorbent material in this comparative example.

[0088] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, add 0.01 mol urea and 0.01 mol ferric nitrate, and stir until fully dissolved. Let stand at 50°C for 3 hours, then dropwise into a 1 mol / L potassium hydroxide solution. After soaking and aging for 24 hours, remove the microspheres, wash with water until pH = 9-10, dry in an oven for 3 hours, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0089] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 3.35 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% is 250 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) is t. B =17s, α(tA / tB)=14, after xenon lamp desorption and nitrogen purging for 6 hours, the CO2 adsorption capacity of the material was measured to be 2.95mmol / g, and the desorption rate was 88%.

[0090] Comparative Example 5

[0091] No nitrogen source, pore-forming agent, metal salt or activator was added during the preparation of the photothermal adsorbent material in this comparative example.

[0092] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand for 2 hours, and then let stand at 50°C for 3 hours. Add the solution dropwise to a 1 mol / L potassium hydroxide solution and soak for 24 hours. Remove the microspheres of gel, wash with water until pH = 7, place in an oven, dry for 3 hours, then place in a porcelain boat and put into a tube furnace. Under nitrogen protection, heat to 800°C at 5°C / min and hold for 1 hour to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 hours, then wash with water until neutral, and dry in a vacuum oven at 120°C for 12 hours.

[0093] 20 mg of the photothermal carbon dioxide adsorbent was taken and its carbon dioxide adsorption capacity was measured at 0 °C and 1 bar atmospheric pressure. The adsorption capacity of the material was found to be 0 mmol / g. 1 g of the material was taken and subjected to a mixed gas atmosphere at 25 °C, with a CO2:CH4 ratio of 1:1 and a gas flow rate of 20 mL / min. The CO2 breakthrough time t of the material was measured.A The time for CO2 concentration to reach 1% is 0s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) is t. B =0s.

[0094] Comparative Example 6

[0095] No nitrogen source, metal salt, or activator was added during the preparation of the photothermal adsorbent material in this comparative example.

[0096] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand, add 0.01 mol of sodium silicate, and let stand at 50℃ for 3 h. Then, dropwise add the system into a 1 mol / L potassium hydroxide solution and soak for aging for 16 h. Remove the microspheres, wash with water until pH = 7, dry in an oven for 3 h, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800℃ at 5℃ / min and hold for 1 h to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 h, wash with water until neutral, and dry in a vacuum oven at 120℃ for 12 h.

[0097] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 2.27 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% was 170 s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) was t. B =21s, α(tA / tB)=8, after 6 hours of xenon lamp desorption and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 0.636 mmol / g, and the desorption rate was 28%.

[0098] Comparative Example 7

[0099] No pore-forming agents, metal salts, or activators were added during the preparation of the photothermal adsorbent material in this comparative example.

[0100] Weigh 1 g of 200 kDa chitosan and dissolve it in a 2% acetic acid solution to prepare a 3 wt% chitosan solution. Stir until no bubbles appear, let stand, add 0.01 mol urea, and let stand at 50℃ for 3 h. Then, dropwise add the system into a 1 mol / L potassium hydroxide solution and soak for aging for 24 h. Remove the microspheres, wash with water until pH = 7, dry in an oven for 3 h, place in a porcelain boat, and put into a tube furnace. Under nitrogen protection, heat to 800℃ at 5℃ / min and hold for 1 h to obtain porous carbon. Wash the porous carbon with 1 mol / L hydrochloric acid for 3 h, wash with water until neutral, and dry in a vacuum oven at 120℃ for 12 h.

[0101] 20 mg of the photothermal carbon dioxide adsorbent was tested at 0 °C and 1 bar atmospheric pressure to determine its carbon dioxide adsorption capacity, which was found to be 1.35 mmol / g. 1 g of the material was tested at 25 °C in an atmosphere with a CO2:CH4 mixture of 1:1 and a gas flow rate of 20 mL / min; the CO2 breakthrough time t was then measured. A The time for CO2 concentration to reach 1% is 100s, and the CH4 breakthrough time (time for CH4 concentration to reach 1%) is t. B =20s, α(tA / tB)=5, after 6h of xenon lamp desorption and nitrogen purging, the CO2 adsorption capacity of the material was measured to be 1.25mmol / g, and the desorption rate was 26%.

[0102] The isothermal adsorption curves of the photothermal carbon dioxide adsorbents in Comparative Examples 1–7 are as follows: Figure 9 As shown, by Figure 2 and Figure 9 It is evident that, under the same pressure, the adsorption performance of the photothermal carbon dioxide adsorbents in Comparative Examples 1 to 7 is lower than that of the photothermal carbon dioxide adsorbent in Example 8.

[0103] Table 1: Material Parameters for Examples and Comparative Examples

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[0105]

[0106] Table 2: Process parameters and results parameters for the examples and comparative examples

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[0108]

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a photothermal carbon dioxide adsorbent, characterized in that, The method includes the following steps: S1: Dissolve chitosan in acid A solution, stir thoroughly until no bubbles are present, to obtain acid A solution containing 1-10 wt% chitosan, and let stand; S2: Add the pore-forming agent, nitrogen source, and metal salt to the chitosan acid A solution, stir to fully dissolve in the solution, and let stand at 20-60°C. S3: Drop the solution that has been allowed to stand in step S2 into an alkaline solution and soak it for aging for 10-30 hours to obtain a spherical gel; S4: Take out the spherical gel obtained in step S3, rinse it with water until it is weakly alkaline, and dry it for 5-30 hours to obtain the carbon precursor. S5: Place the carbon precursor obtained in step S4 under a protective gas atmosphere, slowly heat it to 600-1000℃, and then keep it at a constant temperature for 0.5-5 hours to obtain porous carbon. S6: Wash the porous carbon obtained in step S5 with acid B solution for 1-5 hours, then wash with water until neutral, and dry in a vacuum environment at 100-140°C for 5-15 hours to obtain the photothermal carbon dioxide adsorbent.

2. The method according to claim 1, characterized in that, The molecular weight of the chitosan is 25–250 kDa.

3. The method according to claim 1, characterized in that, Acid A is selected from hydrochloric acid, acetic acid, sulfuric acid, nitric acid and acrylic acid, and the concentration of acid A solution is 0.5-5% (w / v); acid B is selected from sulfuric acid, nitric acid and acetic acid, and the concentration of acid B solution is 0.02-2 mol / L.

4. The method according to claim 1, characterized in that, In step S2, the pore-forming agent is selected from potassium chloride, sodium chloride, ethanol, zinc chloride, sodium silicate, potassium sulfate and sodium sulfate, and the addition concentration is 0.01 to 0.05 mol / L.

5. The method according to claim 1, characterized in that, In step S2, the nitrogen source is selected from urea, melamine, ammonium chloride and potassium nitrate, and the concentration added is 0.01 to 0.05 mol / L.

6. The method according to claim 1, characterized in that, In step S2, the metal salt is selected from copper nitrate, ferric nitrate, silver nitrate and copper acetate, and the concentration added is 0.01 to 0.05 mol / L.

7. The method according to claim 1, characterized in that, In step S3, the alkaline solution is selected from solutions of potassium hydroxide, potassium carbonate, potassium bicarbonate, potassium thiosulfate, potassium oxalate, and potassium acetate, with a concentration of 0.02–2 mol / L.

8. A photothermal carbon dioxide adsorbent, characterized in that, The photothermal carbon dioxide adsorbent is prepared by the method according to any one of claims 1-7.

9. The application of the photothermal carbon dioxide adsorbent according to claim 8 in carbon dioxide capture.

10. The application according to claim 9, characterized in that, The photothermal carbon dioxide adsorbent is used to capture carbon dioxide from air or other carbon dioxide-containing gas mixtures.

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