Method for preparing hydrophilic monolithic carbon foam and application thereof

Abstract

The application discloses a preparation method and application of hydrophilic monolithic foam carbon, and the hydrophilic monolithic foam carbon is obtained by mixing a copper-nitrogen ligand solution and a phenolic pre-polymer solution and then performing thermal polymerization and pyrolysis; the hydrophilic carbon monomer in the obtained hydrophilic monolithic foam carbon is used for modifying the hydrophobic monolithic foam carbon; when the relative pressure is 0.4, the water vapor adsorption capacity is 155-200 cm 3 g ‑1 The catalyst uses the hydrophilic monolithic foam carbon as a carrier, and transition metal as an active component; the theoretical loading amount of the transition metal is 2.0 wt% and below; and the specific surface area of the catalyst is increased by 12%-25% relative to the hydrophilic monolithic foam carbon carrier 。 The hydrophobic carbon skeleton of the hydrophilic monolithic foam carbon forms a supporting and dispersing effect on the hydrophilic carbon monomer, increases the contact area between the hydrophilic carbon and the metal, forms metal clusters to etch the carbon pore wall during heat treatment, increases the specific surface area of the supported catalyst, and improves the accessibility of active sites. The hydrophilic monolithic foam carbon can realize a kinetic-thermodynamic synergistic filtration process, and improves the gas adsorption and separation performance.

Description

Technical Field

[0001] This invention relates to the field of carbon material preparation technology, specifically to a method for preparing hydrophilic monolithic foamed carbon and its application. Background Technology

[0002] In recent years, carbon foam materials have been widely used in energy storage and conversion, gas adsorption and separation, and environmental protection due to their excellent properties such as wide availability, well-developed porous structure, and tunable surface chemistry. In the field of energy storage and conversion, carbon materials are often used as a support for the functionalization of catalysts for photocatalysis, electrocatalysis, and thermocatalysis. The essence of catalytic reaction is the internal / external diffusion of molecules and their transformation at active sites. The diffusion process controls the kinetics of the reaction, so the precise control of the porous structure of the catalyst is crucial to improving the catalytic reaction rate. However, in the preparation of supported catalysts, the introduction of metals for high-temperature pyrolysis often leads to problems such as metal center embedding and pore blockage (Science, 2022, 377, 204-208). This results in the metal sites being difficult to expose, reactant molecules being unable to diffuse to the sites, or product molecules being unable to diffuse away from the sites, accumulating near the active sites and reducing the catalytic efficiency of the active sites. To solve this problem, a common method is to introduce template agents to increase the porosity of the catalyst. For example, patent CN114984997A discloses a three-dimensional porous carbon nitride-based Zn single-atom photocatalyst, its preparation method, and its application. Specifically, zinc oxide derived from zinc carbonate is used as a hard template and introduced into a melamine polymerization system to obtain a mixture of zinc oxide and melamine monomer. The mixture is then placed in a hydrochloric acid aqueous solution to remove the zinc oxide, forming a porous structure and increasing the exposure of nitrogen-containing sites. This type of method for introducing porous structures typically uses magnesium oxide, zinc oxide, or silica microspheres as hard templates, followed by acid / alkali washing steps to remove the template and form pores. Therefore, the preparation process is relatively cumbersome.

[0003] In the field of gas adsorption and separation, as the requirements for technical performance continue to increase, the structural properties of traditional carbon materials are difficult to meet the needs of practical production applications. For example, the surface of commercial foamed carbon materials or some common resin-derived foamed carbon materials usually lacks hydrophilic functional groups and cannot provide specific adsorption sites, making it difficult to achieve efficient kinetic-thermodynamic synergistic sieving in gas adsorption and separation applications, resulting in poor separation performance. To solve the above problems, Chinese patent CN117619348A discloses a high-efficiency adsorbent for the removal of trace amounts of CO and its preparation and application. Specifically, it prepares an adsorbent by mixing activated carbon powder, active components copper salt and rare earth metal salt, inorganic clay, and dispersant, and extruding them for the purification of trace amounts of CO in the feed gas. However, the composition and preparation method of this adsorbent are relatively complex. In addition, such carbon materials and adsorbents prepared by combining carbon materials and active components are usually in powder form, requiring mechanical means to form granular carbon or monolithic carbon, which will bring additional costs to the separation and recovery in practical applications. Summary of the Invention

[0004] Addressing the technical challenges of precise structural control and application of porous carbon foam materials in key fields, this invention aims to leverage the structural advantages of carbon foam materials and enhance their potential for application in critical areas by controlling the inherent properties of the materials themselves. This invention discloses a method for preparing and applying hydrophilic monolithic carbon foam. By introducing functional hydrophilic components into the cross-linked structure of monolithic carbon foam microspheres and performing surface chemical modification, hydrophilic monolithic carbon foam was successfully prepared. Metal-doped catalysts derived from carbon materials often exhibit a decrease in specific surface area during preparation. This is due to the weak interaction between the metal and the support, leading to metal migration and aggregation into large particles that block pores, or catalytic graphitization of the carbon matrix resulting in pore closure. The original hydrophobic monolithic foamed carbon of this invention possesses a rich mesoporous-macroporous structure. The stacked carbon microspheres support and disperse the hydrophilic carbon monomers, increasing the contact area between the hydrophilic carbon monomers and metal ions. The hydrophilic carbon monomers dispersed on the microspheres provide abundant hydrophilic sites, enhancing the interaction between the metal and the support. During heat treatment, metal clusters are formed, etching the hydrophobic carbon framework modified with hydrophilic components, increasing the specific surface area of ​​the derived catalyst, and promoting the loading and exposure of active metal species. Furthermore, the abundant hydrophilic functional groups of the hydrophilic monolithic foamed carbon itself constitute specific adsorption sites, enabling a kinetic-thermodynamic synergistic sieving process and improving gas adsorption and separation performance. Moreover, the monolithic structure of the hydrophilic monolithic foamed carbon provides advantages for the construction of self-supporting catalysts and the development of high-performance adsorbents.

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

[0006] A method for preparing hydrophilic monolithic foamed carbon includes the following steps:

[0007] S1 dissolves the copper salt in deionized water and the nitrogen-containing ligand in an organic solvent, mixing them thoroughly while stirring to obtain a copper-nitrogen-containing ligand solution;

[0008] S2 dissolves resorcinol and sodium carbonate in deionized water, then adds formaldehyde aqueous solution, and stirs at 25-50℃ to carry out prepolymerization reaction to obtain phenolic prepolymer solution;

[0009] The molar ratio of resorcinol, copper ions and nitrogen-containing ligands added is 1:0.03:0.05 to 1:0.3:0.5; the molar ratio of resorcinol, formaldehyde and sodium carbonate added is 1:1:0.001 to 1:5:0.01.

[0010] S3 adds a copper-nitrogen-containing ligand solution to a phenolic prepolymer solution and continues stirring until homogeneous. Then, it is placed in an oven for thermal polymerization to obtain a carbon precursor.

[0011] S4 pyrolyzes the carbon precursor in an inert atmosphere at a temperature of 450–1000℃, followed by acid washing, water washing, and drying to obtain hydrophilic monolithic foamed carbon. The hydrophilic monolithic foamed carbon contains hydrophilic carbon monomers dispersed in a framework formed by the three-dimensional stacking of carbon microspheres. At a relative pressure of 0.4, the water vapor adsorption capacity is 155–200 cm⁻¹. 3 g -1 .

[0012] The copper salt solution is one or more of copper chloride, copper iodide, and copper bromide, with a concentration of 0.001–0.01 mol / L. Further, the copper salt is copper chloride.

[0013] The nitrogen-containing organic ligand solution is a solution of bipyridine propylene glycol, bipyridine ethanol, or o-phenanthroline ethanol, with a concentration of 0.005–0.05 mol / L. Further, the nitrogen-containing organic ligand solution is a solution of bipyridine ethanol.

[0014] The temperature of the thermal polymerization reaction is 70–120°C.

[0015] The present invention also provides an integrally supported catalyst, wherein the catalyst uses hydrophilic integral foam carbon obtained by the method as a support and a transition metal as an active component; the transition metal is one or more of iron, cobalt and nickel, and the theoretical loading of the transition metal (mass ratio of metal to hydrophilic integral carbon) is 2.0 wt% or less; the specific surface area of ​​the catalyst is increased by 12%-25% relative to the hydrophilic integral foam carbon support.

[0016] The preparation method of the monolithic supported catalyst includes the following steps: preparing a transition metal salt solution, using the hydrophilic monolithic foam carbon as a carrier, loading the active metal component into the hydrophilic monolithic foam carbon by impregnation, and pyrolyzing it in an inert atmosphere to obtain a catalyst with a more developed porous structure (increased specific surface area).

[0017] Solvents for preparing transition metal salt solutions include one or more of deionized water and ethanol.

[0018] Transition metal salt solutions include nitrates, and more specifically, nickel nitrate solutions.

[0019] The pyrolysis temperature is 700–900℃, the pyrolysis time is 0.5–3h, and the inert atmosphere during the pyrolysis process is argon or nitrogen.

[0020] The present invention also provides a gas separation method, which uses the hydrophilic monolithic foamed carbon as an adsorbent for the separation of low-concentration CO2.

[0021] The beneficial effects of this invention are:

[0022] The hydrophilic monolithic foamed carbon prepared by the method of this invention involves uniformly introducing a hydrophilic precursor into the hydrophobic foamed carbon precursor framework. During in-situ pyrolysis, the hydrophilic component modifies the hydrophobic monolithic foamed carbon, significantly enhancing the surface hydrophilicity of the foamed carbon material. Furthermore, the monolithic macroscopic molding effect further expands the application possibilities of the foamed material.

[0023] Utilizing the "umbrella effect," a synergistic effect is formed between the hydrophilic carbon monomers and the hydrophobic foam carbon microspheres. On one hand, the framework formed by the accumulation of hydrophobic carbon microspheres disperses the hydrophilic carbon monomers, increasing the contact between metal ions and the hydrophilic carbon monomers. On the other hand, the hydrophilic carbon monomers grown on the hydrophobic carbon microspheres provide hydrophilic sites (containing nitrogen or oxygen hydrophilic functional groups) that interact strongly with metal ions, capturing and anchoring them. During heat treatment, the formed clusters etch the framework, creating a more developed porous structure. Compared with the support itself (hydrophilic monolithic foam carbon), the specific surface area increases by about 25%, effectively exposing the active sites during the reaction and promoting the internal and external diffusion of reactants and products during the catalytic reaction, thus accelerating the kinetic process.

[0024] The hydrophilic monolithic foam carbon can be directly used as a gas separation adsorbent. Because the pore walls of the hydrophilic monolithic foam carbon contain abundant hydrophilic sites that act as specific adsorption sites, it can generate kinetic and thermodynamic synergistic adsorption of specific gas molecules from multiple components, increasing the gas adsorption capacity and extending the breakthrough time by up to 1.5 times. Attached Figure Description

[0025] Figure 1Optical photographs of hydrophobic monolithic foamed carbon and its pure resin polymer precursor, and hydrophilic monolithic foamed carbon and its resin polymer precursor modified with hydrophilic component precursor.

[0026] Figure 2 The image shows the morphology of hydrophilic monolithic foam carbon.

[0027] Figure 3 This is the water vapor adsorption isotherm diagram of hydrophilic monolithic foamed carbon at 298K.

[0028] Figure 4 Nitrogen adsorption isotherms at 77 K for hydrophilic monolithic foam carbon and nickel-hydrophilic monolithic foam carbon (metal loading of 1 wt% and 2 wt%).

[0029] Figure 5 A comparison chart showing the change in specific surface area between hydrophilic monolithic foamed carbon and nickel-hydrophilic monolithic foamed carbon (metal loading of 1wt% and 2wt%).

[0030] Figure 6 The image shows the water vapor adsorption isotherm of hydrophobic monolithic foamed carbon at 298 K.

[0031] Figure 7 The diagram shows the CO2 penetration performance of hydrophilic and hydrophobic monolithic foamed carbon. Detailed Implementation

[0032] The present invention will be described in detail below through some representative examples. It should be understood that the following examples are merely illustrative and should not be construed as limiting the protection of this invention. Any technical solutions implemented based on the content described in this invention should be covered within the protection scope of this invention.

[0033] Comparative Example 1

[0034] Preparation of hydrophobic monolithic foamed carbon: 3g resorcinol and 5mg sodium carbonate were dissolved in deionized water, and a 37% formaldehyde aqueous solution was added. The mixture was stirred at 45℃ for 2 hours to pre-crosslink the resorcinol and formaldehyde, obtaining a phenolic prepolymer solution. The solution was then placed in a 90℃ oven for polymerization for 24 hours. The carbon precursor was pyrolyzed in an argon atmosphere at 500℃ to obtain the hydrophobic monolithic foamed carbon material.

[0035] Example 1

[0036] 1. Preparation of hydrophilic monolithic foamed carbon: 1 g of 4,4-bipyridine was dissolved in 2.5 mL of ethanol, and 0.8 g of copper chloride dihydrate was dissolved in 2.5 mL of deionized water. The mixture was thoroughly mixed. 3 g of resorcinol and 5 mg of sodium carbonate were dissolved in deionized water, and 37% formaldehyde aqueous solution was added. The mixture was stirred at 45 °C for 2 h to pre-crosslink resorcinol and formaldehyde, obtaining a phenolic prepolymer solution. A copper-nitrogen ligand solution was added to the phenolic prepolymer solution, and the mixture was stirred until homogeneous. The mixture was then placed in a 90 °C oven for polymerization for 24 h. The carbon precursor was pyrolyzed in an argon atmosphere at 500 °C, followed by acid washing with 4M nitric acid, water washing until neutral, and drying to obtain hydrophilic monolithic foamed carbon A.

[0037] 2. Preparation of nickel-hydrophilic monolithic foamed carbon catalyst: Prepare 2 mol L... -1 A nickel nitrate solution was used to impregnate a hydrophilic monolithic carbon material with an active metal component, the loading of which was 1 wt%. The mixture was then pyrolyzed at 900 °C for 1 h under an argon atmosphere to obtain nickel-hydrophilic monolithic foamed carbon (metal loading 1 wt%) B.

[0038] The structures of hydrophilic monolithic foamed carbon A and nickel-hydrophilic monolithic foamed carbon (metal loading 1 wt%) prepared in Example 1 were characterized as follows:

[0039] Depend on Figure 1 It is known that introducing hydrophilic precursor components into hydrophobic foam carbon precursors can yield a uniform composite polymer. After pyrolysis, a hydrophilic overall foam carbon with a stable overall structure is obtained. Figure 2 The image shows a scanning electron microscope (SEM) image of hydrophilic monolithic foamed carbon A. The absence of a prismatic morphology of the hydrophilic carbon component demonstrates that the hydrophilic carbon component is composited with hydrophobic carbon microspheres, and the hydrophilic carbon monomers are uniformly dispersed within the three-dimensional framework of the stacked hydrophobic carbon microspheres. Figure 3 The water vapor adsorption results show that the hydrophilic monolithic foam carbon A exhibits a high water vapor adsorption capacity induced by its high surface hydrophilicity when the relative humidity is less than 40% RH. The water vapor adsorption capacity at 40% RH is 164 cm⁻¹. 3 g -1 At 100% RH humidity, the water vapor adsorption capacity is 245 cm³. 3 g -1 This indicates that the surface of the hydrophilic monolithic foam carbon A has abundant hydrophilic sites, which serve as specific sites for gas adsorption, improving adsorption and separation performance. Simultaneously, the abundant hydrophilic sites uniformly dispersed within the three-dimensional framework of hydrophobic carbon microspheres exhibit strong interactions with metal ions, effectively anchoring and dispersing them. Figure 4 It is known that, using hydrophilic monolithic foamed carbon A as a carrier, the prepared supported nickel-nickel-hydrophilic monolithic foamed carbon (metal loading 1 wt%) B exhibits a trend of increasing specific surface area and improved porosity; Figure 5It is known that the specific surface area of ​​catalyst B is 24% higher than that of support A, meaning that while introducing active sites, the high accessibility of the active sites can be maintained. Furthermore, from... Figure 6 and Figure 7 It is known that, compared with hydrophobic monolithic foam carbon, hydrophilic monolithic foam carbon A has abundant hydrophilic sites that act as CO2-specific adsorption sites, resulting in a longer CO2 breakthrough time (extending the breakthrough time by 1.5 times), higher adsorption capacity, and good sieving performance for CO2 / N2 adsorption and separation.

[0040] Example 2

[0041] In Example 1, the loading of transition metal nickel relative to the support was changed to 2 wt%. The remaining steps, including the synthesis of the catalyst nickel-hydrophilic monolithic foamed carbon (2 wt% metal loading), were the same as in Example 1. The material was named nickel-hydrophilic monolithic foamed carbon (2 wt% metal loading) C, and its specific surface area increase was 13.5% (e.g., Figure 4 (as shown in Figure 5).

[0042] Example 3

[0043] In Example 1, the transition metal 2 was replaced with cobalt, and the metal loading relative to the support was changed to 1 wt%. The remaining steps, including the synthesis of the cobalt-hydrophilic monolithic foam carbon (1 wt% metal loading), were the same as in Example 1. The material was named cobalt-hydrophilic monolithic foam carbon (1 wt% metal loading) D, with a specific surface area increase of 7.5%.

[0044] Example 4

[0045] In Example 1, the transition metal in step 2 was replaced with iron, and the metal loading relative to the support was changed to 1 wt%. The remaining steps, including the synthesis of the catalyst iron-hydrophilic monolithic foamed carbon (1 wt% metal loading), were the same as in Example 1. The material was named iron-hydrophilic monolithic foamed carbon (1 wt% metal loading) E, and its specific surface area increased by 17.5%.

[0046] Example 5

[0047] The pyrolysis temperature in Example 1 is changed to 600℃, and the remaining steps 1 and 2, including the synthesis of materials and catalysts, are the same as in Example 1.

[0048] Example 6

[0049] In Example 1, the bipyridine ethanol organic solution was replaced with an o-phenanthroline ethanol solution. The remaining steps 1 and 2, including the synthesis of materials and catalysts, were the same as in Example 1.

[0050] Conclusion: This invention further expands the understanding of the relationship between surface hydrophilicity and the preparation of supported catalysts. Using a monolithic foamed carbon with a highly hydrophilic surface as a support, the hydrophilic carbon monomers are uniformly cross-linked on the hydrophobic carbon microsphere stacked framework. This serves as an anchoring point for the efficient loading of metal ions. During heat treatment, the reduction and migration of metal ions etch the carbon walls, achieving the introduction of active sites while maintaining their accessibility and the diffusion of reactant / product molecules, which is beneficial for improving catalyst performance. When using hydrophilic monolithic foamed carbon material as a support for supported catalysts, with a metal loading between 0.5-2 wt%, the specific surface area of ​​the derived metal-carbon catalyst increases, and the porosity change rate exhibits a volcanic trend.

[0051] Furthermore, because the hydrophilic components modify the hydrophobic carbon microsphere framework, creating abundant hydrophilic sites for CO2 adsorption, the hydrophilic monolithic carbon material itself can generate thermodynamic and kinetic synergistic effects, enhancing gas adsorption and separation efficiency. The hydrophilic monolithic foamed carbon developed in this invention is expected to inspire the development of high-performance supported catalysts and efficient gas sieving adsorbents, expanding the application of foamed carbon in catalysis and adsorption.

Claims

1. A monolithically supported catalyst, characterized in that: The catalyst uses hydrophilic monolithic foamed carbon as a support and a transition metal as the active component. The transition metal is one or more of iron, cobalt, and nickel, and the theoretical loading of the transition metal is 2.0 wt% or less. The specific surface area of ​​the catalyst is increased by 12%-25% relative to the hydrophilic monolithic foamed carbon support. The method for preparing the hydrophilic monolithic foamed carbon is characterized by comprising the following steps: S1 dissolves the copper salt in deionized water and the nitrogen-containing ligand in an organic solvent, mixing them thoroughly while stirring to obtain a copper-nitrogen-containing ligand solution; S2 dissolves resorcinol and sodium carbonate in deionized water, then adds formaldehyde aqueous solution, and stirs at 25~50 ℃ to carry out prepolymerization reaction to obtain phenolic prepolymer solution; The molar ratio of added resorcinol, copper ions and nitrogen-containing ligands is 1:0.03:0.05~1:0.3:0.5; the molar ratio of added resorcinol, formaldehyde and sodium carbonate is 1:1:0.001~1:5:0.

01. S3. Add the copper-nitrogen-containing ligand solution to the phenolic prepolymer solution, continue stirring until homogeneous, and place it in an oven for thermal polymerization to obtain the carbon precursor. S4 pyrolyzes the carbon precursor in an inert atmosphere at a temperature of 450–1000 °C, followed by acid washing, water washing, and drying to obtain hydrophilic monolithic foamed carbon. The hydrophilic monolithic foamed carbon contains hydrophilic carbon monomers dispersed in a framework formed by the three-dimensional stacking of carbon microspheres. At a relative pressure of 0.4, the water vapor adsorption capacity is 155–200 cm⁻². 3 g -1 .

2. The monolithic supported catalyst as described in claim 1, characterized in that: The copper salt solution is one or more of copper chloride, copper iodide, and copper bromide, with a concentration of 0.001~0.01 mol / L.

3. The monolithic supported catalyst as described in claim 1, characterized in that: The nitrogen-containing organic solution is a solution of bipyridine propylene glycol, bipyridine ethanol, or o-phenanthroline ethanol, with a concentration of 0.005~0.05 mol / L.

4. The monolithic supported catalyst as described in claim 1, characterized in that: The temperature of the thermal polymerization reaction is 70~120 ℃.

5. A method for preparing the monolithic supported catalyst according to claim 1, characterized in that: The process includes the following steps: preparing a transition metal salt solution, using the hydrophilic monolithic foam carbon as a carrier, loading the active metal component into the hydrophilic monolithic foam carbon by impregnation, and then pyrolyzing it in an inert atmosphere.

6. The method for preparing the monolithic supported catalyst as described in claim 5, characterized in that: The pyrolysis temperature is 700~900℃, the pyrolysis time is 0.5~3 h, and the inert atmosphere during the pyrolysis process is argon or nitrogen.

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