Eutectic Solvent-Mediated Fe3O4@C / BC Carbon-Based Catalysts, Their Preparation Methods and Applications

Abstract

This invention relates to a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst, its preparation method, and its application. The method includes: heating a mixture of choline chloride and fumaric acid to form a DES solution; adding ferric chloride to obtain an iron-containing DES solution; adding biomass feedstock to the DES solution for a solvothermal reaction, causing iron ions and fumaric acid to self-assemble in situ on the biomass surface to grow carbon-encapsulated MIL-88A ultracrystals, obtaining a biomass / MIL-88A composite precursor; washing and drying the precursor, followed by high-temperature pyrolysis under an inert atmosphere to obtain a Fe3O4@C / biomass carbon composite material. In the obtained material, carbon-coated Fe3O4 nanoparticles (Fe3O4@C) are dispersed on a biomass-derived porous carbon (BC) framework. Using this Fe3O4@C / biomass carbon composite material for CO2 desorption in alcoholamine-rich solutions significantly improves the desorption capacity and rate, and exhibits excellent cycle stability. The method of this invention is green and environmentally friendly, and the process is simple. The resulting material has broad application prospects in the field of carbon capture.

Description

Technical Field

[0001] This invention relates to a catalyst, specifically a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent, its preparation method and application, as well as the application of this catalyst in the catalytic desorption of CO2 from alcoholamine-rich solutions, belonging to the field of catalyst preparation and CO2 capture technology. Background Technology

[0002] With the increasing severity of global warming, carbon capture, utilization, and storage (CCUS) technology has become one of the key pathways to achieving carbon neutrality. Chemical absorption based on amines is currently the most mature and widely used CO2 capture technology. However, this technology faces challenges in practical applications, including high desorption energy consumption (accounting for approximately 60-70% of the total capture energy) and significant amine degradation losses. Therefore, reducing the CO2 desorption temperature and improving desorption efficiency are crucial for reducing capture costs.

[0003] In recent years, introducing solid catalysts into the CO2 desorption process to accelerate the release of CO2 from amine solutions has become a research hotspot. Catalysts reported in studies include solid acids (such as HZSM-5, SO42-). 2- Materials include iron-based metal oxides (such as TiO2 and WO3), metal oxides, and carbon-based materials. Among these, iron-based metal oxide nanomaterials exhibit good catalytic desorption potential due to their unique electronic structure, excellent proton-coupled electron transfer ability, and environmental friendliness. For example, Fe2O3 and Fe3O4 have been proven to effectively catalyze the desorption of CO2 from alcoholamine-rich solutions. However, these metal oxide nanoparticles have a small specific surface area and are prone to aggregation, resulting in insufficient exposure of active sites and easy leaching of metal components, which affects their catalytic efficiency and recyclability.

[0004] Loading iron-based nanoparticles onto porous carbon materials with high specific surface area can solve the problem of nanoparticle aggregation and utilize the conductivity and adsorption properties of carbon materials, potentially generating a synergistic catalytic effect. Biomass-derived carbon is an ideal carrier material due to its wide availability, tunable structure, and low cost. In existing technologies, metal-organic frameworks (MOFs), such as MIL-88A, composed of iron ions and fumaric acid, are often used as precursors for preparing carbon-coated iron-based nanomaterials. However, conventional methods typically involve first synthesizing MOFs and then physically mixing or secondary loading them with carbon materials, resulting in complex processes. Furthermore, the bonding between MOFs and carbon substrates is mostly physical contact with weak interfacial interactions, making it difficult to fully realize the synergistic effect. Therefore, developing a simple, structurally controllable iron-based biomass carbon composite material with strong interfacial interactions and its preparation method is of great significance for achieving efficient and low-energy-consumption CO2 catalytic desorption. Summary of the Invention

[0005] The purpose of this invention is to provide a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent, its preparation method, and its application. The preparation method is green and environmentally friendly, and the process is simple. The catalyst obtained has a stable structure and excellent catalytic performance. When this catalyst is applied to CO2 desorption in alcoholamine-rich liquids, it can significantly reduce the desorption temperature, improve the desorption efficiency and rate, and effectively reduce the energy consumption of the carbon capture process.

[0006] To achieve the above objectives, the present invention provides a method for preparing a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent, comprising the following steps: S1. Preparation of iron-containing eutectic solvent: Weigh choline chloride and fumaric acid according to the preset molar ratio, mix them evenly, heat and stir until a clear and transparent eutectic solvent (DES) is formed, add ferric chloride (FeCl3·6H2O) to the obtained eutectic solvent (DES), and continue stirring until a homogeneous and stable iron-containing eutectic solvent is formed. S2. Solvent-thermal in-situ growth of MIL-88A: Biomass powder is added to the iron-containing eutectic solvent in step S1, using the biomass powder as a supporting framework. The mixture is thoroughly mixed and impregnated, and then transferred to a closed reactor for solvothermal reaction. During the reaction, iron ions and fumaric acid self-assemble on the surface and within the pores of the biomass powder to form MIL-88A crystals. At the same time, the eutectic solvent DES swells the biomass powder, dissolves some components, and solvothermal carbonizes it. The resulting ultrathin carbon layer encapsulates the MIL-88A nanocrystals on the biomass framework expanded by the DES solvent, thus obtaining a biomass / MIL-88A composite precursor. S3. High-temperature pyrolysis: After separating, washing, and drying the biomass / MIL-88A composite precursor obtained in step S2, it is placed in a high-temperature tube furnace under inert atmosphere for pyrolysis treatment. During the pyrolysis process, MIL-88A is converted into carbon-coated Fe3O4 nanoparticles, and the biomass is burned into a porous biomass carbon BC framework, finally obtaining a biomass-derived carbon composite material uniformly loaded with Fe3O4@C nanoparticles, namely Fe3O4@C / BC.

[0007] Preferably, in step S1, the molar ratio of choline chloride to fumaric acid is 1:0.25, and the heating temperature is 70~100 ℃.

[0008] Preferably, in step S1, the molar ratio of ferric chloride to fumaric acid is (0.09~0.3):1.

[0009] Preferably, in step S2, the mass ratio of choline chloride to biomass powder is (5~10):1, the solvothermal reaction temperature is 150~190 °C, and the reaction time is 6~12 h; the biomass powder is dried and pulverized biomass raw material.

[0010] Preferably, in step S3, the pyrolysis temperature is 500~900°C and the holding time is 1~3h.

[0011] Preferably, in step S3, the inert atmosphere is nitrogen.

[0012] Preferably, the biomass raw material is one or more of straw, rice husks, sawdust, or corn cobs.

[0013] The present invention also provides a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst, which is prepared by the above preparation method; the catalyst is composed of a porous biomass carbon skeleton and carbon-coated Fe3O4 nanoparticles (Fe3O4@C) uniformly embedded in the skeleton surface and pores.

[0014] The present invention further provides the application of the above-mentioned eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst in the catalytic desorption of CO2 from alcoholamine-rich solutions.

[0015] Preferably, Fe3O4@C / BC carbon-based catalyst is added as a catalyst to a 30wt% monoethanolamine (MEA) rich solution loaded with CO2, and CO2 desorption is catalyzed at 90 °C. The mass fraction of Fe3O4@C / BC carbon-based catalyst in the MEA rich solution is 0.03~0.15wt%.

[0016] Compared with existing technologies, this invention proposes an integrated process of in-situ self-assembly, biomass pore expansion and reconstruction, and pre-carbonization. Choline chloride acts as a hydrogen bond acceptor to construct a eutectic solvent medium, while fumaric acid serves as both a hydrogen bond donor in the eutectic solvent medium and an organic ligand source. Ferric chloride (FeCl3·6H2O) acts as a metal source. The aforementioned iron-containing eutectic solvent DES is used as the reaction medium. Ferric chloride (FeCl3·6H2O) and fumaric acid undergo in-situ coordination self-assembly in the eutectic solvent DES system to construct a biomass / MIL-88A composite precursor. During the solvothermal process, the eutectic solvent DES provides the iron ions and fumaric acid ligands required for the formation of MIL-88A, and also acts as an extraction solvent to swell and dissolve the biomass powder through organic component decomposition, thus constructing a hierarchical porous biomass carrier structure. This integrated design enables the in-situ nucleation and growth of ultrafine MIL-88A crystals within the expanded internal pores of biomass after DES solvent treatment during solvothermal processes. Furthermore, the dissociated and dissolved organic components in the biomass are solvothermally carbonized and encapsulated into an ultrathin carbon layer on the surface of the MIL-88A particles, rather than through simple physical mixing or surface loading. This achieves highly stable bonding between metal-organic framework (MOF) nanoparticles and the biomass substrate. After precursor pyrolysis, Fe3O4 nanoparticles derived from MIL-88A are uniformly coated by the in-situ generated carbon layer, forming a Fe3O4@C core-shell structure, which is highly dispersed within the biomass-derived porous carbon framework (BC). Based on this unique synergistic interface structure between the Fe3O4@C core-shell structure and the carbon framework, not only is the aggregation of metal oxide nanoparticles effectively prevented, but more importantly, rich heterogeneous interfaces are formed between the carbon coating layer and the Fe3O4 core, and between Fe3O4@C and the external carbon framework.

[0017] The composite material prepared by this invention combines the acidic sites of Fe3O4 with the conductivity of the carbon shell, which protects Fe3O4 from corrosion by alkanolamine solutions. When used for CO2 catalytic desorption, the interfacial synergistic effect between the carbon material and Fe3O4 nanoparticles effectively promotes the proton-coupled electron transfer process, significantly reducing the activation energy of CO2 desorption. Compared with existing catalysts (such as pure Fe3O4, conventional biomass carbon, or simple mixtures), the biomass-derived carbon composite material with uniformly loaded Fe3O4@C nanoparticles of this invention achieves higher CO2 desorption capacity and desorption rate at lower temperatures, effectively reducing the energy consumption of the carbon capture process.

[0018] The process of this invention is green and low-cost. The eutectic solvent used is composed of choline chloride and fumaric acid, which has good biocompatibility and can be recycled. The biomass raw materials of this invention are widely available and inexpensive. The entire preparation process does not require the use of toxic and harmful organic solvents, which meets the requirements of green chemistry. Attached Figure Description

[0019] Figure 1 The X-ray diffraction (XRD) pattern of the Fe3O4@C / biomass carbon composite material prepared in this invention; Figure 2 Scanning electron microscope (SEM) image of the Fe3O4@C / biomass carbon composite material prepared for this invention; Figure 3 Scanning electron microscope (TEM) image of the Fe3O4@C / biomass carbon composite material prepared for this invention; Figure 4 Catalytic desorption curves for blank experiments, comparative examples, and embodiments of the present invention; Figure 5 The catalytic desorption rate curves of blank experiments, comparative examples, and embodiments of the present invention. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments and comparative examples, but the scope of protection of the present invention is not limited to the following embodiments. All reagents used are commercially available analytical grade. Example 1

[0021] A method for preparing a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent includes the following steps: S1. Weigh 11.2g of choline chloride and 2.32g of fumaric acid into a beaker according to the preset molar ratio, mix them evenly, and stir magnetically in an oil bath at 80°C for 30min to form a clear and transparent eutectic solvent (DES). Add 1g of ferric chloride (FeCl3·6H2O) to the obtained eutectic solvent (DES), wherein the molar ratio of ferric chloride (FeCl3·6H2O) to fumaric acid is 0.18:1. Continue stirring for 30min until completely dissolved to form a homogeneous and stable iron-containing eutectic solvent. S2. Add 1.6g of corn cob powder to the iron-containing eutectic solvent in step S1, so that the mass ratio of choline chloride to corn cob powder is 7:1. Use corn cob powder as a supporting framework, mix and impregnate thoroughly, and transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor for solvothermal reaction at 160°C for 12h. During the reaction, iron ions and fumaric acid self-assemble on the surface and in the pores of corn cob powder to form MIL-88A crystals. At the same time, the eutectic solvent DES swells the corn cob powder and dissolves some components and undergoes solvothermal reaction to obtain a biomass / MIL-88A composite precursor. S3. The biomass / MIL-88A composite precursor obtained in step S2 is naturally cooled to room temperature. The resulting solid product is washed repeatedly with ethanol and deionized water 3-5 times until neutral. It is then vacuum dried at 60°C overnight. The above-treated precursor is placed in a quartz boat and placed in a tube furnace. Under nitrogen atmosphere protection, it is heated to 600°C at a heating rate of 5°C / min and held for 2 hours. It is then naturally cooled to room temperature to obtain the Fe3O4@C / biomass carbon composite material, denoted as Fe3O4@C / BC-1. Example 2

[0022] A method for preparing a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent includes the following steps: S1. Weigh 11.2g of choline chloride and 2.32g of fumaric acid into a beaker according to the preset molar ratio, mix them evenly, and stir magnetically in an oil bath at 80°C for 30min to form a clear and transparent eutectic solvent (DES). Add 0.5g of ferric chloride (FeCl3·6H2O) to the obtained eutectic solvent (DES), wherein the molar ratio of ferric chloride (FeCl3·6H2O) to fumaric acid is 0.0925:1. Continue stirring for 30min until completely dissolved to form a homogeneous and stable iron-containing eutectic solvent. S2. Add 1.12g of corn cob powder to the iron-containing eutectic solvent in step S1, so that the mass ratio of choline chloride to corn cob powder is 10:1. Use rice husk powder as a supporting framework, mix and impregnate thoroughly, and transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor for solvothermal reaction at 180°C for 12h. During the reaction, iron ions and fumaric acid self-assemble on the surface and in the pores of corn cob powder to form MIL-88A crystals. At the same time, the eutectic solvent DES swells the corn cob powder and dissolves some components and undergoes solvothermal reaction to obtain a biomass / MIL-88A composite precursor. S3. The biomass / MIL-88A composite precursor obtained in step S2 is naturally cooled to room temperature. The resulting solid product is washed repeatedly with ethanol and deionized water 3-5 times until neutral. It is then vacuum dried at 60°C overnight. The above-treated precursor is placed in a quartz boat and placed in a tube furnace. Under nitrogen atmosphere protection, it is heated to 600°C at a heating rate of 5°C / min and held for 2 hours. It is then naturally cooled to room temperature to obtain the Fe3O4@C / biomass carbon composite material, denoted as Fe3O4@C / BC-2. Example 3

[0023] A method for preparing a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent includes the following steps: S1. Weigh 11.2g of choline chloride and 2.32g of fumaric acid into a beaker according to the preset molar ratio, mix them evenly, and stir magnetically in an oil bath at 80°C for 30min to form a clear and transparent eutectic solvent (DES). Add 1.6g of ferric chloride (FeCl3·6H2O) to the obtained eutectic solvent (DES), wherein the molar ratio of ferric chloride (FeCl3·6H2O) to fumaric acid is 0.296:1. Continue stirring for 30min until completely dissolved to form a homogeneous and stable iron-containing eutectic solvent. S2. Add 2.24g of corn cob powder to the iron-containing eutectic solvent in step S1, so that the mass ratio of choline chloride to corn cob powder is 5:1. Use corn cob powder as a supporting framework, mix and impregnate thoroughly, and transfer to a polytetrafluoroethylene-lined stainless steel high-pressure reactor for solvothermal reaction at 180°C for 12h. During the reaction, iron ions and fumaric acid self-assemble on the surface and in the pores of corn cob powder to form MIL-88A crystals. At the same time, the eutectic solvent DES swells the corn cob powder and dissolves some components and undergoes solvothermal reaction to obtain a biomass / MIL-88A composite precursor. S3. The biomass / MIL-88A composite precursor obtained in step S2 is naturally cooled to room temperature. The resulting solid product is washed repeatedly with ethanol and deionized water 3-5 times until neutral. It is then vacuum dried at 60°C overnight. The above-treated precursor is placed in a quartz boat and placed in a tube furnace. Under nitrogen atmosphere protection, it is heated to 600°C at a heating rate of 5°C / min and held for 2 hours. It is then naturally cooled to room temperature to obtain the Fe3O4@C / biomass carbon composite material, denoted as Fe3O4@C / BC-3. Example 4

[0024] Rice husks were used instead of corn cobs as biomass raw materials, and the other conditions were the same as in Example 1. The resulting composite material was denoted as Fe3O4@C / BC-4.

[0025] Comparative Example 1 Except for the absence of biomass raw materials, the remaining steps are the same as in Example 1. That is, the iron-containing DES solution is directly subjected to a solvothermal reaction to obtain MIL-88A precipitate, which is then washed, dried, and pyrolyzed in a nitrogen atmosphere to obtain Fe3O4@C material, denoted as Fe3O4@C.

[0026] Comparative Example 2 Except for the absence of ferric chloride hexahydrate (FeCl3·6H2O) in step S1, the remaining steps are exactly the same as in Example 1, resulting in DES solvent-mediated corn cob-derived carbon material, denoted as BC.

[0027] Comparative Example 3 1 g of ferric chloride hexahydrate (with the same mass as ferric chloride in Example 1) was dissolved in 10 mL of deionized water to form an aqueous solution of FeCl3. 1.6 g of corn cob raw material was impregnated in the FeCl3 aqueous solution, ultrasonically dispersed for 30 min, and allowed to stand for 12 h before the solvent was evaporated. The above precursor was placed in a quartz boat, placed in a tube furnace, and heated to 600°C at a heating rate of 5°C / min under nitrogen atmosphere protection. The temperature was held for 2 h and then naturally cooled to room temperature to obtain the Fe3O4-loaded biomass carbon material obtained by impregnation method, denoted as Fe3O4 / BC.

[0028] Comparative Example 4 0.5 g of ferric chloride hexahydrate and 2.32 g of fumaric acid were dissolved in 50 mL of deionized water. 1.6 g of corn cob raw material was added and ultrasonically dispersed until homogeneous. The mixture was then transferred to a polytetrafluoroethylene-lined stainless steel high-pressure reactor and hydrothermally reacted at 160°C for 12 h. After the reaction, the mixture was allowed to cool naturally to room temperature, washed, and dried to obtain the precursor. The precursor was then heated to 600°C under a nitrogen atmosphere at a heating rate of 5°C / min and held for 2 h to obtain the Fe3O4@C / biomass carbon composite material, denoted as Fe3O4@C&BC.

[0029] Material characterization: X-ray diffraction (XRD) analysis was performed on the Fe3O4@C / BC obtained in the examples, and the results are as follows. Figure 1 As shown, the spectrum shows obvious Fe3O4 characteristic diffraction peaks corresponding to the magnetite standard card, indicating that the iron species exist in the form of Fe3O4 after pyrolysis. The absence of obvious impurity peaks indicates high product purity. SEM and TEM observations were performed on the Fe3O4@C / BC obtained in the examples, and the results are as follows. Figure 2 and Figure 3 As shown, Fe3O4 nanoparticles are uniformly dispersed within a porous biomass carbon framework. High-resolution images reveal a clear core-shell structure, with a Fe3O4 core and a carbon outer shell.

[0030] Catalytic desorption performance test: 100g of a 30wt% monoethanolamine (MEA) aqueous solution was prepared and saturated with CO2 gas to achieve a CO2 loading of 0.60~0.68 mol CO2 / mol MEA, serving as a simulated rich solution. The rich solution was placed in a three-necked flask, and 0.05g of Fe3O4@C / BC catalyst was added. The flask was then placed in a 90°C oil bath and magnetically stirred for desorption. The time was recorded using a stopwatch, and the volume of desorbed CO2 was measured using a wet scrubber. The desorption amount and rate were calculated. A blank group was used as a control without catalyst. The changes in desorption amount and rate were compared. The curves showing the changes in CO2 desorption amount and rate over time are shown below. Figure 4 and 5 As shown in Table 1, the desorption performance test results of the materials in each embodiment and comparative example are shown in Table 1.

[0031] Table 1. Comparison of CO2 desorption performance of different materials in MEA rich liquid The results show that the Fe3O4@C / biomass carbon composite materials prepared in the embodiments of the present invention all exhibit excellent desorption performance, with a 40%~47% increase in desorption capacity and a 165~182% increase in desorption rate compared to the blank group, which is significantly better than the comparative examples. Although Comparative Example 1 has a Fe3O4@C coating structure, it lacks a biomass carbon skeleton support, resulting in easy particle aggregation, fewer pore structures, and lower performance than the examples; Comparative Example 2 only has a carbon support skeleton without Fe3O4 nanoparticles, resulting in limited active sites and lower performance than the examples; Comparative Example 3 uses a traditional impregnation method, resulting in uneven distribution of Fe3O4 particles, significantly lower performance than the examples, and the Fe3O4 particles lack a carbon layer coating, making it easy for Fe elements to leach out and resulting in poor cycle stability. Comparative Example 4 used a hydrothermal method to load MIL-88A nanoparticles onto biomass, followed by pyrolysis to form a biomass carbon-derived catalyst supported on Fe3O4@C. However, due to the rapid nucleation rate of MIL-88A crystallization in aqueous solution, some MIL-88A crystals precipitated quickly and were not loaded onto the surface of the biomass carbon material. Some Fe3O4@C particles were only physically mixed with the porous biomass carbon material, resulting in performance lower than the example. Comparative analysis indicates that the uniformly dispersed structure obtained by the DES-mediated in-situ growth coupled with pyrolysis carbonization strategy is crucial for improving CO2 catalytic desorption performance.

[0032] Effect of desorption capacity on catalytic performance: Using the material prepared in Example 1 as the catalyst, 0.03 g, 0.05 g, 0.1 g and 0.15 g of catalyst were added to 100 g of 30 wt% MEA rich solution, and CO2 desorption tests were conducted at 90 °C. The results are shown in Table 2.

[0033] Table 2. Percentage increase in CO2 desorption capacity compared to blank at different catalyst addition levels. The results show that, even with a low addition of 0.03 wt%, the catalytic desorption capacity and desorption rate can still reach 39% and 165% of the blank, respectively, after adding the catalyst of the present invention. This proves that the catalyst can effectively desorb at a low temperature of 90°C. The addition of a low mass fraction can achieve a significant improvement in catalytic desorption performance and has energy-saving potential.

[0034] Cyclic stability test: Using the material from Example 1 as the catalyst, five cycles of desorption experiments were conducted. After each desorption, the catalyst was recovered by centrifugation and used directly for the next desorption without regeneration. The initial maximum desorption rate was 0.537 mmol CO2 mol. -1 MEA s -1After 5 cycles, the maximum desorption rate was 0.522 mmol CO2 mol. -1 MEA s -1 The decrease was only 2.8%, indicating that the material has excellent cycling stability. This is attributed to the protective effect of the carbon shell on the Fe3O4 core, preventing it from being corroded and lost in the alkanolamine solution.

[0035] The superiority of the technical solution of this invention stems from the following collaborative mechanism: (1) Multifunctionality of eutectic solvent (DES): Choline chloride / fumaric acid DES serves both as a solvent to dissolve biomass components, disrupt their crystalline structure, and form a multi-level porous biomass-derived carrier, and as a ligand (fumaric acid) required for the synthesis of MIL-88A. After the addition of FeCl3·6H2O, Fe... 3+ Pre-coordinated with fumaric acid in DES lays the foundation for subsequent MOF growth.

[0036] (2) Advantages of in-situ growth: During the solvothermal process, MIL-88A grows in situ on the surface of biomass. The oxygen-containing functional groups (-OH and -COOH) on the surface of biomass can serve as nucleation sites, inducing uniform growth of MIL-88A crystals and avoiding particle agglomeration caused by individual nucleation in the solution.

[0037] (3) Pyrolysis conversion mechanism: During high-temperature pyrolysis, the organic ligands in MIL-88A carbonize to form a coating layer, Fe 3+ It is reduced to Fe3O4, and at the same time, biomass carbonization forms a porous framework; the MIL-88A-derived carbon layer can effectively prevent the migration and agglomeration of Fe3O4 particles during the pyrolysis process, and finally obtain a uniformly dispersed core-shell structure.

[0038] (4) Desorption catalytic mechanism: The Lewis acidic sites of Fe3O4 can activate the CN bond in the alkanolamine-CO2 product, promoting CO2 desorption; the carbon shell has good electrical and thermal conductivity, which helps electron transfer and heat transfer; the porous carbon skeleton provides abundant mass transfer channels. The three work together to significantly reduce the desorption activation energy.

[0039] In summary, this invention provides a green, simple, and controllable method for preparing Fe3O4@C / biomass carbon composite materials. The resulting material exhibits excellent catalytic activity and stability in CO2 desorption in alcohol amine-rich solutions, and has broad prospects for industrial application.

[0040] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent, characterized in that, Includes the following steps: S1. Preparation of iron-containing eutectic solvent: Weigh choline chloride and fumaric acid according to the preset molar ratio, mix them evenly, heat and stir until a clear and transparent eutectic solvent is formed, add ferric chloride (FeCl3·6H2O) to the obtained eutectic solvent, and continue stirring until a homogeneous and stable iron-containing eutectic solvent is formed. S2. Solvent-thermal in-situ growth of MIL-88A: Biomass powder is added to the iron-containing eutectic solvent in step S1, using the biomass powder as a supporting framework. The mixture is thoroughly mixed and impregnated, and then transferred to a closed reactor for solvothermal reaction. During the reaction, iron ions and fumaric acid self-assemble on the surface and in the pores of the biomass powder to form MIL-88A crystals. At the same time, the eutectic solvent swells the biomass powder, dissolves some components, and solvothermal carbonizes it. The resulting ultrathin carbon layer encapsulates the MIL-88A nanocrystals on the biomass framework expanded by DES solvent, thus obtaining a biomass / MIL-88A composite precursor. S3. High-temperature pyrolysis: After separating, washing, and drying the biomass / MIL-88A composite precursor obtained in step S2, it is placed in a high-temperature tube furnace under inert atmosphere for pyrolysis treatment. During the pyrolysis process, MIL-88A is converted into carbon-coated Fe3O4 nanoparticles, and the biomass is burned into a porous biomass carbon BC framework, finally obtaining a biomass-derived carbon composite material uniformly loaded with Fe3O4@C nanoparticles, namely Fe3O4@C / BC.

2. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 1, characterized in that, In step S1, the molar ratio of choline chloride to fumaric acid is 1:0.25, and the heating temperature is 70~100 ℃.

3. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 2, characterized in that, In step S1, the molar ratio of ferric chloride to fumaric acid is (0.09~0.3):

1.

4. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 2, characterized in that, In step S2, the mass ratio of choline chloride to biomass powder is (5~10):1, the solvothermal reaction temperature is 150~190 °C, and the reaction time is 6~12h; the biomass powder is dried and pulverized biomass raw material.

5. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 4, characterized in that, In step S3, the pyrolysis temperature is 500~900°C, and the holding time is 1~3h.

6. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 4, characterized in that, In step S3, the inert atmosphere is nitrogen.

7. The method for preparing a eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 4, characterized in that, The biomass raw material is one or more of straw, rice husks, sawdust, or corn cobs.

8. A eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst, characterized in that, The catalyst is prepared by the preparation method according to any one of claims 1-7; the catalyst is composed of a porous biomass carbon skeleton and carbon-coated Fe3O4 nanoparticles (Fe3O4@C) uniformly embedded on the surface and in the pores of the skeleton.

9. The application of the Fe3O4@C / BC carbon-based catalyst mediated by a eutectic solvent as described in claim 8 in the catalytic desorption of CO2 from alcoholamine-rich solutions.

10. The application of the eutectic solvent-mediated Fe3O4@C / BC carbon-based catalyst according to claim 9 in the catalytic desorption of CO2 from alcoholamine-rich solutions, characterized in that, The Fe3O4@C / BC carbon-based catalyst was added to a 30wt% monoethanolamine (MEA)-rich solution loaded with CO2, and the desorption of CO2 was catalyzed at 90 °C. The mass fraction of the Fe3O4@C / BC carbon-based catalyst in the MEA-rich solution was 0.03~0.15wt%.

Images