A MOFs derived gradient porous carbon material, a preparation method and application thereof
By using MOF powder as a precursor for heat treatment, porous carbon materials exhibiting gradient changes from the inside out were prepared, solving the problems of complex preparation and high cost in existing technologies, and realizing the preparation and application of efficient and low-cost gradient porous carbon materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HARBIN ENG UNIV
- Filing Date
- 2023-09-13
- Publication Date
- 2026-06-02
AI Technical Summary
Existing technologies are difficult to efficiently prepare gradient porous carbon materials with specific structure-function characteristics, and the preparation process is complex, costly, and cannot precisely control the pore structure and composition.
Using MOF powder as a precursor, porous carbon materials with a gradient pore structure and framework structure from the inside out are formed through powder forming and heat treatment. The phase separation conditions are controlled by two heat treatments to achieve the gradual change of pore structure.
Gradient porous carbon materials with high specific surface area, high porosity, and high mechanical strength were prepared, which are suitable for material separation and storage and energy storage, simplifying the preparation process and reducing costs.
Smart Images
Figure CN117383542B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of porous carbon materials, and more particularly to a MOF-derived gradient porous carbon material, its preparation method, and its application. Background Technology
[0002] Gradient materials are a class of heterogeneous composite materials whose composition, structure, and properties vary continuously or quasi-continuously along their thickness or length. Gradient materials possess a layered structure, and specific physical properties can be controlled through the combination of these layers, allowing them to perform multiple functions as needed. Gradient porous carbon materials are an important component of gradient materials, referring to carbon materials whose pore size, porosity, and carbon skeleton exhibit gradual gradients along a certain direction. Compared to traditional porous carbon, gradient porous carbon materials demonstrate structural diversity, enabling the integration of multiple functions at a lower cost, thus showcasing novel properties and overcoming the shortcomings of traditional materials. Therefore, gradient porous carbon materials have great application potential and can meet the needs of many special applications, such as efficient molecular / particle identification and sieving, hierarchical catalyst supports, and multifunctional energy storage materials.
[0003] Metal-organic frameworks (MOFs) are a novel type of porous crystalline material formed by the coordination bonds between metal ions and organic ligands, exhibiting excellent structural modifiability. MOF derivatives not only retain the high specific surface area and porosity of their precursors but also allow for heteroatom doping, defect construction, 2D / 1D structures, and carbon coating through high-temperature carbonization or chemical treatment of the precursor MOFs. Therefore, MOF derivatives hold great promise for applications in electrode materials, catalyst supports, supercapacitors, and many other fields. Currently, there are few reports on the preparation of porous carbon materials with regular pore size distributions using metal-organic framework compounds as precursors through calcination.
[0004] Currently, methods for preparing gradient porous carbon materials are still relatively few. They mainly rely on traditional methods for preparing porous carbon materials, combined with other advanced techniques to construct precursors with gradient structures, which are then transformed into gradient porous carbon materials through heat treatment. In existing technologies, the literature (Adv. Funct. Mater. 2019, 29, 1904058) reports a strategy for preparing gradient porous carbon materials using a template method. Polystyrene spheres are used as templates, and resorcinol-formaldehyde sol is used as a carbon source. The binary mixture is treated using ultracentrifugation to obtain a precursor with a gradient mixed structure. After pyrolysis and template removal, porous carbon materials with gradient structures are obtained. For this type of method, how to distribute different templates according to the designed gradient is a significant challenge. In recent years, researchers have developed many new methods to prepare porous carbon materials with functional and structural gradients. Patent CN202010391646.2 first employs a layer-by-layer electrospinning method to construct a polyacrylonitrile nanofiber membrane with a longitudinal gradient distribution of different functional components. Subsequently, after pre-oxidation and carbonization treatments, a carbon nanofiber material with a longitudinal gradient distribution of functional components is prepared. Patent CN201310406562.1 pours different raw materials into a mold in a sequential manner, and then performs directional curing, deep curing, and pyrolysis treatments at different temperatures at different locations within the mold to obtain a porous carbon material with a gradually gradient pore structure. The preparation of gradient porous carbon materials often requires the use of other special methods, such as non-uniform electric or pressure fields and ultracentrifugation, and cannot be obtained directly using conventional methods. However, non-uniform fields are difficult to control, and current technologies cannot precisely prepare gradient porous carbon materials with specific structure-function characteristics. Furthermore, these technologies are complex, require stringent preparation conditions, and are costly to produce, significantly impacting their potential for practical application.
[0005] To address the aforementioned challenges, there is an urgent need to develop a gradient porous carbon material with high specific surface area and porosity, while also being simple to prepare, having controllable structure and composition, and low cost. Summary of the Invention
[0006] To address the existing technical problems, the present invention aims to provide a MOF-derived gradient porous carbon material, its preparation method, and its applications. The gradient porous carbon material uses MOF powder as a precursor, and after powder forming and heat treatment, forms a porous carbon material exhibiting a gradient pore structure and framework structure from the inside out. This porous carbon material possesses high heteroatom doping, high packing density, and high mechanical strength, and has broad application potential in fields such as material separation and storage, and energy storage and conversion.
[0007] The primary objective of this invention is to provide a method for preparing MOF-derived gradient porous carbon materials, characterized by comprising the following steps:
[0008] S1 Weigh a certain amount of organic ligand and metal salt and dissolve them in methanol. Stir until homogeneous to obtain a mixed solution. The mixed solution is then aged, centrifuged and dried to obtain the first MOF precursor.
[0009] S2 The first MOF precursor is processed by powder forming to obtain the second MOF precursor;
[0010] S3 After drying the second MOF precursor, it undergoes a first heat treatment in an inert atmosphere and is kept at a certain temperature to obtain an intermediate material.
[0011] S4 involves subjecting the intermediate material to a second heat treatment under an inert atmosphere and holding it at that temperature to obtain the first carbon material.
[0012] S5 immerses the first carbon material in hydrochloric acid solution, and after washing and drying, obtains MOF-derived gradient porous carbon material.
[0013] Specifically, the molar ratio of the organic ligand to the metal salt in step S1 is (1:1) to (16:1).
[0014] Specifically, the organic ligand in step S1 is selected from at least one of imidazole, 2-methylimidazolium, 4,4'-bipyridine, 2,2'-bipyridine, benzoic acid, and pyrazine; the metal salt is selected from at least one of copper, zinc, nickel, cobalt, or iron metal salts.
[0015] Specifically, the aging time in step S1 is 12 to 24 hours.
[0016] Specifically, the powder forming process in step S2 includes at least one of compression molding, slurry casting, centrifugal molding, and extrusion molding.
[0017] Specifically, in step S3, the temperature of the first heat treatment is 300–700°C, the heating rate of the first heat treatment is 0.5–20°C / min, and the holding time is 0.1–10h.
[0018] Specifically, in step S4, the temperature of the second heat treatment is 650–1200°C, the heating rate of the second heat treatment is 0.5–30°C / min, and the holding time is 0.1–10h.
[0019] Specifically, the inert atmosphere is any one of argon, nitrogen, or helium; the gas flow rate of the inert atmosphere is 1 to 100 mL / min.
[0020] The second objective of this invention is to provide a MOF-derived gradient porous carbon material, prepared using the above-described preparation method; the pore and carbon framework structure of the gradient porous carbon material exhibit a gradual gradient along the inside-out direction; the pore size gradually decreases from the inside to the outside, while the porosity gradually increases; the carbon framework structure gradually becomes finer from the inside to the outside; the pore size ranges from 15 to 300 nm, and the porosity ranges from 10% to 80%.
[0021] The third objective of this invention is to provide an application of the above-mentioned MOFs-derived gradient porous carbon material as a photocatalyst in the photodegradation reaction of organic dyes or as a redox reaction catalyst in zinc-air batteries.
[0022] This invention alters the phase separation conditions of a system through two gradient heat treatment temperatures, thereby endowing porous carbon materials with a gradually varying pore structure. Specifically, the porosity, pore size, and specific surface area of the pore structure all gradually change from one end of the porous carbon material to the other. In this invention, the first stage of heat treatment induces the decomposition of MOF precursor particles, causing them to connect and fuse together, transforming into a carbon structure. Then, during the second heat treatment, the released gas gradually diffuses outward from within the carbon structure, resulting in directional solidification and forming a porous carbon material with a gradually varying pore structure from the inside out.
[0023] The present invention has the following advantages and beneficial effects:
[0024] (1) The method for preparing MOFs-derived gradient porous carbon materials provided by the present invention is simple and effective, and does not require an additional non-uniform electric field or pressure field, which can greatly reduce costs, increase yield, and facilitate industrial production.
[0025] (2) By adjusting the MOF precursor, powder forming method and heat treatment process, this invention achieves the adjustment of the internal pore size and skeleton structure of gradient carbon material, while making it exhibit a gradual structural gradient from the inside to the outside.
[0026] (3) The gradient porous carbon material obtained by this invention not only possesses a rich multi-scale porous structure, but also features high specific surface area, high electronic conductivity, high heteroatom doping rate, high packing density, and high mechanical strength. It has great application prospects in the fields of material separation and storage and energy storage and conversion. Attached Figure Description
[0027] Figure 1 This is a schematic diagram of the cross-sectional scanning electron microscope image of the MOFs-derived gradient porous carbon materials prepared in Examples 1-4 of this invention;
[0028] Figure 2 These are scanning electron microscope images of various regions on the cross-section of the carbon material #1 prepared in Example 1 of this invention;
[0029] Figure 3 These are scanning electron microscope images of different regions on the cross-section of the carbon material #2 prepared in Example 2 of this invention;
[0030] Figure 4 These are scanning electron microscope images of various regions on the cross-section of the carbon material #3 prepared in Example 3 of this invention;
[0031] Figure 5 These are scanning electron microscope images of different regions on the cross-section of the carbon material #4 prepared in Example 4 of this invention. Detailed Implementation
[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.
[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.
[0035] In the embodiments of the present invention, there are no special restrictions on the organic ligands and metal salts, all of which are commercially available products. The MOF-derived gradient porous carbon materials prepared in the embodiments of the present invention were all imaged using a Zeiss Gemini 500 scanning electron microscope; porosity data were obtained using mercury intrusion porosimetry; specific surface area was obtained using nitrogen adsorption; and pore size was obtained using a laser particle size analyzer.
[0036] Figure 1 This is a schematic diagram of five regions obtained by scanning electron microscopy (SEM) of the MOFs-derived gradient porous carbon materials in Examples 1-4. The SEM images of the five regions are labeled as I, II, III, II', and III', respectively.
[0037] Example 1
[0038] Step 1: Weigh 1.23g of 2-methylimidazole and 1.12g of Zn(NO3)2·6H2O and dissolve them in 35ml of methanol solvent. Stir well at room temperature and age for 24h. Then, centrifuge at 8000rpm and wash three times with methanol. Finally, dry at 80℃ for 24h to obtain the first Zn-MOF precursor without compaction.
[0039] Step 2: Grind the first Zn-MOF precursor to obtain Zn-MOF powder, and process it using molding technology to obtain a block-shaped second Zn-MOF precursor;
[0040] Step 3: The second Zn-MOF precursor was placed in a vacuum oven and dried at 120°C for 24 hours. Then it was placed in a tube furnace and heated to 650°C at a rate of 10°C / min under a nitrogen atmosphere with a continuous flow rate of 40 mL / min. The temperature was maintained at this temperature for 3 hours to obtain the intermediate material.
[0041] Step 4: Transfer the intermediate material to a ceramic boat, place it in a tube furnace, and heat it to 1000°C at a rate of 10°C / min under a nitrogen atmosphere with a continuous flow rate of 40 mL / min. Hold it at this temperature for 2 hours, cool it to room temperature, and then remove it to obtain the first carbon material that has not undergone acid treatment.
[0042] Step 5: Immerse the first carbon material in a 2 mol / L hydrochloric acid solution, wash it 3 times, and dry it at 80°C to obtain the MOFs-derived gradient porous carbon material prepared in Example 1, which is labeled as carbon material #1.
[0043] The obtained carbon material #1 was cut, and five different observation areas were selected on the cross-section, namely I, II, III, II' and III'. Figure 2 These are scanning electron microscope images of various regions on the cross-section of carbon material #1 prepared in Example 1, wherein from Figure 2 Scanning electron microscopy (SEM) images of various regions reveal that carbon material #1 exhibits a completely fused carbon structure from the inside out, with a gradient in its carbon skeleton and pore structure. SEM images of internal region I show that carbon material #1 displays high carbon skeleton strength and large-sized pores. SEM images of regions II, II', III, and III' show that as the location extends outwards, the carbon skeleton strength decreases, porosity increases, and pore size decreases, exhibiting a gradual structural gradient from the inside out.
[0044] Mercury intrusion porosimetry (MIRP) analysis showed that the porosity of carbon material #1 ranged from 41% to 68%, and the pore size ranged from 17 to 260 nm. Nitrogen adsorption analysis showed that the specific surface area ranged from 615.4 to 630.4 m². 2 / g, the pore structure is fully open.
[0045] Example 2
[0046] Step 1: Dissolve 2.46 g of 4,4'-bipyridine and 2.24 g of Cu(NO3)2 in 70 mL of methanol solvent, stir evenly at room temperature, age for 16 h, centrifuge at 8000 rpm, wash three times with methanol, and then dry at 80 °C for 24 h to obtain the first Cu-MOF precursor without compaction.
[0047] Step 2: Grind the first Cu-MOF precursor to obtain Cu-MOF powder, and then process it by slurry casting to obtain a block-shaped second Cu-MOF precursor;
[0048] Step 3: Place the second Cu-MOF precursor block in a vacuum oven and dry it at 120°C for 24 hours. Then place it in a tube furnace and heat it to 700°C at a rate of 5°C / min under a nitrogen atmosphere with a continuous flow rate of 20 mL / min. Hold it at this temperature for 6 hours to obtain the intermediate material.
[0049] Step 4: Transfer the intermediate material to a ceramic boat, place it in a tube furnace, and heat it to 1200°C at a rate of 5°C / min under a nitrogen atmosphere with a continuous flow rate of 20 mL / min. Hold it at this temperature for 2 hours, cool it to room temperature, and then remove it to obtain the first carbon material that has not undergone acid treatment.
[0050] Step 5: Immerse the first carbon material in a 2 mol / L hydrochloric acid solution, wash it 3 times, and dry it at 80°C to obtain the MOFs-derived gradient porous carbon material prepared in Example 2, which is labeled as carbon material #2.
[0051] The obtained carbon material #2 was cut, and five different observation areas were selected on the cross-section, namely I, II, III, II' and III'. Figure 3 These are scanning electron microscope images of various regions on the cross-section of the carbon material #2 prepared in Example 2 of this study. Figure 3As can be seen in the scanning electron microscope (SEM) images of internal region I, the carbon material exhibits high carbon framework strength and a large-sized pore structure. In the SEM images of regions II, II', III, and III', it can be observed that as the location extends outward, the carbon framework strength decreases, the porosity increases, and the pore size decreases. Therefore, carbon material #2 exhibits a completely fused carbon structure from the inside out, with a gradient-changing carbon framework and pore structure.
[0052] The porosity of carbon material #2, determined by mercury intrusion porosimetry, ranged from 39% to 75%, and the pore size ranged from 15 to 228 nm. Nitrogen adsorption analysis showed a specific surface area ranging from 593.71 to 620.2 m². 2 / g, the pore structure is fully open.
[0053] Example 3
[0054] Step 1: Dissolve 2.46 g of 2,2'-bipyridine and 2.24 g of Zn(NO3)2·6H2O and Cu(NO3)2 in 70 mL of methanol solvent respectively. Stir well at room temperature, age for 12 h, centrifuge at 8000 rpm, wash three times with methanol, and then dry at 80 °C for 24 h to obtain the first ZnCu-MOF precursor without compaction.
[0055] Step 2: Grind the first ZnCu-MOF precursor to obtain ZnCu-MOF powder, and then centrifuge it to obtain a block-shaped second ZnCu-MOF precursor.
[0056] Step 3: The second ZnCu-MOF precursor block was placed in a vacuum oven and dried at 120°C for 24 hours. Then, it was placed in a tube furnace and heated to 400°C at a rate of 20°C / min under a nitrogen atmosphere with a continuous flow rate of 40 mL / min. The temperature was maintained at this temperature for 10 hours to obtain the intermediate material.
[0057] Step 4: Transfer the intermediate material to a ceramic boat, place it in a tube furnace, and heat it to 800°C at a rate of 30°C / min under a nitrogen atmosphere with a continuous flow rate of 40 mL / min. Hold it at this temperature for 10 hours, cool it to room temperature, and then remove it to obtain the first carbon material that has not undergone acid treatment.
[0058] Step 5: Immerse the first carbon material in a 2 mol / L hydrochloric acid solution, wash it 3 times, and dry it at 80°C to obtain the MOFs-derived gradient porous carbon material prepared in Example 3, which is labeled as carbon material #3.
[0059] The obtained carbon material #3 was cut, and five different observation areas were selected on the cross-section, namely I, II, III, II' and III'. Figure 4 These are scanning electron microscope images of various regions on the cross-section of the carbon material #3 prepared in Example 3 of this study. Figure 4 As can be seen in the scanning electron microscope (SEM) images of internal region I, the carbon material exhibits high carbon framework strength and a large-sized pore structure. In the SEM images of regions II, II', III, and III', it can be observed that as the location extends outward, the carbon framework strength decreases, the porosity increases, and the pore size decreases. It is evident that carbon material #3 also exhibits a completely fused carbon structure from the inside out, with a gradient-changing carbon framework and pore structure.
[0060] Mercury intrusion porosimetry (MIRP) analysis showed that the porosity of carbon material #2 ranged from 44% to 79%, and the pore size ranged from 13 to 163 nm. Nitrogen adsorption analysis showed that the specific surface area ranged from 803.5 to 822.1 m². 2 / g, the pore structure is fully open.
[0061] Example 4
[0062] Step 1: Dissolve 4.46 g of 1,3,5-benzenetricarboxylic acid and 2.24 g of Zn(NO3)2·6H2O and Co(NO3)2·6H2O in 70 mL of methanol solvent respectively. Stir well at room temperature, age for 12 h, centrifuge at 8000 rpm, wash three times with methanol, and then dry at 80 °C for 24 h to obtain the first ZnCo-MOF precursor without compaction.
[0063] Step 2: Grind the first ZnCo-MOF precursor to obtain ZnCo-MOF powder, and then extrude it to obtain a block-shaped second ZnCo-MOF precursor.
[0064] Step 3: The second ZnCo-MOF precursor block was placed in a vacuum oven and dried at 120°C for 24 hours. Then, it was placed in a tube furnace and heated to 500°C at a rate of 2°C / min under a nitrogen atmosphere with a continuous flow rate of 80 mL / min. The temperature was maintained at this temperature for 5 hours to obtain the intermediate material.
[0065] Step 4: Transfer the intermediate material to a ceramic boat, place it in a tube furnace, and heat it to 900°C at a rate of 2°C / min under a nitrogen atmosphere with a continuous flow rate of 80 mL / min. Hold it at this temperature for 5 hours, cool it to room temperature, and then remove it to obtain the first carbon material that has not undergone acid treatment.
[0066] Step 5: Immerse the first carbon material in a 2 mol / L hydrochloric acid solution, wash it 3 times, and dry it at 80°C to obtain the MOFs-derived gradient porous carbon material prepared in Example 4, which is labeled as carbon material #4.
[0067] The obtained carbon material #4 was cut, and five different observation areas were selected on the cross-section, namely I, II, III, II' and III'. Figure 5 These are scanning electron microscope images of various regions on the cross-section of the carbon material #4 prepared in Example 4 of this study. Figure 5 As can be seen in the scanning electron microscope (SEM) images of internal region I, the carbon material exhibits high carbon framework strength and a large pore structure. In the SEM images of regions II, II', III, and III', it can be observed that as the location extends outward, the carbon framework strength decreases, the porosity increases, and the pore size decreases. It is evident that carbon material #4 also exhibits a completely fused carbon structure from the inside out, with a gradient-changing carbon framework and pore structure.
[0068] Mercury intrusion porosimetry (MIRP) analysis showed that the porosity of carbon material #2 ranged from 34% to 72%, and the pore size ranged from 20 to 284 nm. Nitrogen adsorption analysis showed that the specific surface area ranged from 386.7 to 438.9 m². 2 / g, the pore structure is fully open.
[0069] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.
Claims
1. A method for preparing MOF-derived gradient porous carbon materials, characterized in that, Includes the following steps: S1 Weigh a certain amount of organic ligand and metal salt and dissolve them in methanol. Stir until homogeneous to obtain a mixed solution. Then, age, centrifuge and dry the mixed solution to obtain the first MOF precursor. S2 The first MOF precursor is subjected to powder forming process to obtain the second MOF precursor; S3 After drying the second MOF precursor, it undergoes a first heat treatment in an inert atmosphere and is kept at a certain temperature to obtain an intermediate material. S4 The intermediate material is subjected to a second heat treatment in an inert atmosphere and kept at that temperature to obtain the first carbon material; S5 The first carbon material was immersed in hydrochloric acid solution, and after washing and drying, MOFs-derived gradient porous carbon material was obtained. In step S1, the organic ligand is selected from at least one of imidazole, 2-methylimidazolium, 4,4'-bipyridine, 2,2'-bipyridine, benzoic acid, and pyrazine; the metal salt is selected from at least one of copper, zinc, nickel, cobalt, or iron metal salts; the molar ratio of the organic ligand to the metal salt is (1:1) to (16:1); and the aging time in step S1 is 12 to 24 hours.
2. The method for preparing MOFs-derived gradient porous carbon materials according to claim 1, characterized in that, The powder forming process described in step S2 includes at least one of compression molding, slurry casting, centrifugal molding, and extrusion molding.
3. The method for preparing MOFs-derived gradient porous carbon materials according to claim 1, characterized in that, In step S3, the temperature of the first heat treatment is 300–700 °C, the heating rate of the first heat treatment is 0.5–20 °C / min, and the holding time is 0.1–10 h.
4. The method for preparing MOFs-derived gradient porous carbon materials according to claim 1, characterized in that, In step S4, the temperature of the second heat treatment is 650–1200 °C, the heating rate of the second heat treatment is 0.5–30 °C / min, and the holding time is 0.1–10 h.
5. The method for preparing MOFs-derived gradient porous carbon materials according to claim 1, characterized in that, The inert atmosphere is any one of argon, nitrogen, or helium; the gas flow rate of the inert atmosphere is 1 to 100 mL / min.
6. A MOF-derived gradient porous carbon material, characterized in that, The material is prepared by the method described in any one of claims 1 to 5; the pores and carbon skeleton structure of the gradient porous carbon material have a gradual gradient along the direction from the inside to the outside; the pore size gradually decreases from the inside to the outside, and the porosity gradually increases; the carbon skeleton structure gradually becomes thinner from the inside to the outside; the pore size ranges from 15 to 300 nm, and the porosity ranges from 10 to 80%.
7. The application of the MOFs-derived gradient porous carbon material as described in claim 6 as a photocatalyst in the photodegradation of organic dyes or as a redox reaction catalyst in zinc-air batteries.