A method for in-situ rapid growth of CNTs on the surface of MOF array treated with oxyacetylene flame

Abstract

The present invention relates to a method for in-situ rapid growth of CNTs on the surface of a MOF array treated with an oxyacetylene flame. First, a MOF array is prepared on a substrate, which serves as a substrate for CNTs growth and provides a catalyst for CNTs growth. The carbon source for CNTs growth comes from the carbon-containing small molecule gas generated by the pyrolysis of MOF itself and the acetylene remaining from the flame combustion. By regulating the process parameters such as the ratio of carbon source to oxygen, the treatment time, and the distance, the rapid carbonization of the MOF array is achieved and the integrity of the array structure is ensured, and the in-situ rapid growth of CNTs is achieved. In addition, there is good bonding between CNTs and the substrate. Compared with the traditional method of preparing carbon nanocatalytic materials using MOF, the carbon nanocatalytic materials prepared by the process of the present invention maintain array characteristics, which can not only avoid the use of conductive additives in subsequent applications, but also have good stability, large specific surface area, and multiple active sites in the structure; at the same time, CNTs can increase the specific surface area of ​​the carbon nanocatalyst, expose more active sites, and improve conductivity.

Description

Technical Field

[0001] The invention belongs to the technical field of nano-catalytic material preparation, and relates to a method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame. Background Art

[0002] Energy crisis and environmental pollution are still two major problems in today's world's rapid economic development. The development of new and efficient energy storage devices has attracted widespread attention. Fuel cells and metal-air batteries have the advantages of low cost, clean and efficient, environmentally friendly, high capacity, and low operating temperature. Although great progress has been made in oxygen reduction catalysts, the bottleneck that currently affects large-scale commercial applications is the large-scale use of precious metal Pt catalysts. Pt-based catalysts are not only expensive, but also have poor stability and weak resistance to methanol poisoning. The development of non-precious metal oxygen reduction catalysts is of great significance.

[0003] Metal organic framework (MOF) is an organic-inorganic hybrid porous material formed by metal ions or clusters connected to organic compound ligands through coordination bonds. In recent years, nanocarbon materials prepared with MOF as precursor have been widely used in oxygen reduction catalysts. Patent 1 "CN110433861B" obtains cobalt-nitrogen co-doped carbon-based nanomaterials by high-temperature pyrolysis of MOF, which exhibits excellent oxygen reduction catalytic performance under alkaline conditions; however, the carbon-based nanomaterials prepared by this patent are in powder form, and the use of additives and binders in the preparation of electrodes easily causes agglomeration, and the catalyst performance cannot be fully exerted. Patent 2 "CN110787819B" obtains a nitrogen-doped carbon nanotube and nitrogen-doped carbon nanosheet array hybrid structure by pyrolyzing MOF arrays in an atmosphere providing ethanol as a carbon source, and combines it with subsequent selenization treatment to obtain a zinc-air battery catalytic electrode material with good performance; however, this method is complicated and cumbersome, requires multi-step reaction preparation, and the heat treatment process requires a long reaction time and fine control of the process. There is little research on how to quickly prepare efficient catalysts using MOF arrays through simple and efficient methods.

[0004] The present invention will treat the MOF array by oxyacetylene flame, and by adjusting the process parameters such as the ratio of carbon source to oxygen, treatment time, and distance, the rapid carbonization of the MOF array can be achieved, and the in-situ rapid growth of CNTs can be completed at the same time. The method has simple preparation process, easy operation, strong controllability, short CNTs preparation time, and strong versatility, and provides new technology and methods for the growth of CNTs on the surface of MOF arrays and the development of new oxygen reduction catalysts. Summary of the invention

[0005] Technical issues to be solved

[0006] In order to avoid the shortcomings of the prior art, the present invention proposes a method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with an oxyacetylene flame, which overcomes the shortcomings of the traditional method for preparing CNTs on the surface of a MOF array.

[0007] The technical solution provided by the present invention is simple and easy to operate, CNTs grow quickly, have strong universality, good repeatability, and are conducive to large-scale preparation. The prepared CNTs grow in situ on the surface of the MOF array, with randomly distributed growth orientations and good bonding strength with the MOF substrate.

[0008] Technical Solution

[0009] A method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame, characterized by the following steps:

[0010] Step 1, preparation of MOF array: soak the substrate in a nitrate aqueous solution for 1 to 6 hours, then add a 2-methylimidazole aqueous solution and stir for 30 to 60 seconds; let the reaction stand at room temperature for 1 to 6 hours; wash the reaction material with water and anhydrous ethanol for multiple times, dry it, and deposit it on the substrate to obtain a MOF array;

[0011] Step 2, preparation of CNTs: adjust the distance between the oxyacetylene gun tip and the substrate surface where the MOF array is grown to 10-50 mm, treat with oxyacetylene flame for 0.5-5 seconds, turn off oxygen and acetylene, cool with air, and grow CNTs on the surface of the MOF array.

[0012] The oxygen flow rate is 0.1-0.5 L / s;

[0013] The acetylene or propane flow rate is 0.1-0.5 L / s.

[0014] The substrate is pretreated by washing the substrate with deionized water, anhydrous ethanol and acetone respectively and drying the substrate in an oven at 50-100° C. for 6-12 hours.

[0015] The substrate includes, but is not limited to, carbon fiber cloth, carbon fiber paper, graphite paper, graphite sheet, carbon / carbon composite material, nickel foam, nickel foil, nickel sheet or copper foam.

[0016] The nitrate is a combination of one or more thereof, including but not limited to cobalt nitrate, nickel nitrate or iron nitrate.

[0017] The MOF array is one of them, including but not limited to Co-MOF, Fe-MOF, Ni-MOF, NiCo-MOF, CoFe-MOF, NiFe-MOF, NiCoFe-MOF.

[0018] The concentration of the nitrate aqueous solution is 0.01-0.10 mol / L.

[0019] The concentration of the 2-methylimidazole aqueous solution is 0.2-0.6 mol / L.

[0020] The drying in step 1 is performed by placing the product in an oven at 50 to 100°C.

[0021] Beneficial Effects

[0022] The present invention proposes a method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with an oxyacetylene flame. The MOF array is rapidly heated by an oxyacetylene flame, and rapid carbonization of the MOF array and in-situ rapid growth of CNTs are simultaneously achieved. This method not only effectively solves the problems of long preparation time and complex process of traditional methods for preparing CNTs on the MOF surface, but also achieves efficient preparation of arrayed carbon nanocatalysts.

[0023] In this process, a MOF array is first prepared on a substrate, which serves as a substrate for CNTs growth and also provides a catalyst for CNTs growth; the carbon source for CNTs growth comes from the carbon-containing small molecule gas produced by the pyrolysis of MOF itself and the remaining acetylene from the flame combustion. In this technical solution, by adjusting the process parameters such as the ratio of carbon source to oxygen, processing time, and distance, not only can the rapid carbonization of the MOF array be achieved and the structural integrity of the array be ensured, but also the in-situ rapid growth of CNTs can be achieved. CNTs grow in-situ on the MOF array substrate, and the growth direction is randomly distributed; in addition, there is good bonding between CNTs and the substrate.

[0024] Compared with the traditional method of using MOF to prepare carbon nanocatalytic materials, the carbon nanocatalytic materials prepared by this process maintain array characteristics, which can not only avoid the use of conductive additives in subsequent applications, but also have good stability, large specific surface area, and multiple active sites; at the same time, CNTs can increase the specific surface area of ​​carbon nanocatalysts, expose more active sites, and improve conductivity. The preparation process of this method is simple, easy to operate, highly controllable, short CNTs preparation time, and strong versatility. The present invention provides new technologies and methods for the growth of CNTs on the surface of MOF arrays and the development of new oxygen reduction catalysts. This material will have broad application prospects in the field of energy storage and conversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 : SEM characterization image of the carbon fiber cloth@Co-MOF array prepared by the present invention;

[0027] Figure 2: SEM characterization image of CNTs grown on the surface of the carbon fiber cloth@Co-MOF array prepared by the present invention;

[0028] Figure 3 : Low-magnification SEM characterization image of CNTs grown on the surface of the carbon fiber cloth@Co-MOF array prepared by the present invention;

[0029] Figure 4 : High-magnification SEM characterization image of CNTs grown on the surface of the carbon fiber cloth@Co-MOF array prepared by the present invention; DETAILED DESCRIPTION

[0030] The present invention will now be further described with reference to the embodiments and the accompanying drawings:

[0031] Embodiment 1:

[0032] 1. Substrate pretreatment: The carbon fiber cloth substrate was cleaned with deionized water, anhydrous ethanol and acetone respectively and dried in a 60°C oven for 12 hours;

[0033] 2. Preparation of MOF array: Prepare a 0.05 mol / L Co(NO3)2 aqueous solution, and then soak the carbon fiber cloth substrate in the above solution for 1 hour; prepare a 0.4 mol / L 2-methylimidazole aqueous solution, and then quickly add it to the Co(NO3)2 solution and stir rapidly for 30 seconds; let it stand for 1 hour at room temperature, take out the sample, wash it with water and anhydrous ethanol several times, put it in a 60°C oven to dry, and deposit the Co-MOF array on the carbon fiber cloth substrate;

[0034] 3. Preparation of CNTs: The carbon fiber cloth substrate with the Co-MOF array grown on it was placed on the mold surface. The distance between the oxyacetylene gun tip and the sample surface was 10 mm. The flow rates of oxygen (0.2 L / s) and acetylene (0.2 L / s) were adjusted to control the oxyacetylene flame. After 0.5 s of oxyacetylene flame treatment, the oxygen and acetylene were turned off and the sample was cooled with air to grow CNTs on the surface of the Co-MOF array.

[0035] Embodiment 2:

[0036] 1. Substrate pretreatment: The graphite paper substrate was cleaned with deionized water, anhydrous ethanol and acetone respectively and dried in an oven at 70°C for 10 hours;

[0037] 2. Preparation of MOF array: Prepare a 0.08 mol / L Co(NO3)2 aqueous solution, and then soak the graphite paper substrate in the above solution for 3 hours; prepare a 0.6 mol / L 2-methylimidazole aqueous solution, and then quickly add it to the Co(NO3)2 solution and stir rapidly for 60 seconds; let the reaction stand at room temperature for 3 hours, take out the sample, wash it with water and anhydrous ethanol several times, put it in a 70°C oven to dry, and deposit it on the graphite paper substrate to obtain a Co-MOF array;

[0038] 3. Preparation of CNTs: The graphite paper substrate with the Co-MOF array grown on it was placed on the mold surface. The distance between the oxyacetylene gun tip and the sample surface was 20 mm. The flow rates of oxygen (0.4 L / s) and acetylene (0.3 L / s) were adjusted to control the oxyacetylene flame. After 2 seconds of oxyacetylene flame treatment, the oxygen and acetylene were turned off and the sample was cooled with air to grow CNTs on the surface of the Co-MOF array.

[0039] Embodiment 3:

[0040] 1. Substrate pretreatment: The nickel foam substrate was cleaned with deionized water, anhydrous ethanol and acetone respectively and dried in an oven at 80°C for 12 hours;

[0041] 2. Preparation of MOF array: Prepare a 0.02 mol / L Co(NO3)2 aqueous solution, and then soak the nickel foam substrate in the above solution for 6 hours; prepare a 0.2 mol / L 2-methylimidazole aqueous solution, and then quickly add it to the Co(NO3)2 solution and stir rapidly for 60 seconds; let it stand for 6 hours at room temperature, take out the sample, wash it with water and anhydrous ethanol several times, put it in an 80°C oven to dry, and deposit the Co-MOF array on the nickel foam substrate;

[0042] 3. Preparation of CNTs: Place the nickel foam substrate with the Co-MOF array grown on the mold surface, with the distance from the oxyacetylene gun tip to the sample surface being 15 mm, and adjust the flow rates of oxygen (0.3 L / s) and acetylene (0.4 L / s) to control the oxyacetylene flame; after treating with the oxyacetylene flame for 3 seconds, turn off the oxygen and acetylene, and cool with air to grow CNTs on the surface of the Co-MOF array.

[0043] The beneficial effects of the present invention are further obtained from the accompanying drawings:

[0044] Figure 1 This is a low-magnification SEM characterization image of the carbon fiber cloth@Co-MOF array prepared by the present invention, from which it can be clearly seen that a large number of Co-MOF nanosheets grow vertically on the surface of the carbon fiber; the surface of the nanosheet is smooth and the interior is a solid structure.

[0045] Figure 2This is a high-magnification SEM characterization image of the carbon fiber cloth@Co-MOF array prepared by the present invention, from which it can be clearly seen that the thickness of the nanosheets is about 200-500nm, the nanosheets support each other to form an array, and the array height is about 5μm.

[0046] Figure 3 This is a low-magnification SEM characterization image of CNTs grown on the surface of the carbon cloth@Co-MOF array prepared in the present invention. It can be seen that after the Co-MOF array is treated with oxyacetylene flame, the nanosheets are carbonized and the surface becomes rough, but the complete array structure can still be maintained.

[0047] Moreover, the high-magnification SEM characterization image of CNTs grown on the surface of the carbon cloth @ Co-MOF array prepared by the present invention ( Figure 4 ) It can be observed that a large number of CNTs grow in situ and uniformly on the surface of Co-MOF nanosheets, and the growth direction is randomly distributed.

[0048] The present invention provides a method for in-situ rapid growth of CNTs on the surface of a MOF array by oxyacetylene flame treatment. The technical solution provided by the present invention is to simultaneously achieve efficient carbonization of MOF and in-situ rapid growth of CNTs by oxyacetylene flame treatment, thereby obtaining uniform growth of CNTs on MOF nanosheets. The technical solution is simple to operate, has a controllable process, high preparation efficiency, and strong universality, and has broad prospects in the field of efficient preparation of CNTs and their catalytic application.

[0049] The technical solution of the present invention is not limited to the specific implementation methods listed above, and various changes can be made. That is, all other embodiments obtained according to the claims and description of the present invention application belong to the protection scope of the present invention.

Claims

1. A method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame, characterized in that Here are the steps: Step 1, preparation of MOF array: soak the substrate in a nitrate aqueous solution for 1-6 h, then add a 2-methylimidazole aqueous solution and stir for 30-60 s; let the reaction stand at room temperature for 1-6 h; wash the reaction material with water and anhydrous ethanol for multiple times, dry it, and deposit it on the substrate to obtain a MOF array; Step 2, preparation of CNTs: adjust the distance between the oxyacetylene gun tip and the substrate surface on which the MOF array is grown to 10-50 mm, use oxyacetylene flame treatment for 0.5-5 s, turn off oxygen and acetylene, cool with air, and grow CNTs on the surface of the MOF array; The oxygen flow rate is 0.1~0.5 L / s; The acetylene flow rate is 0.1~0.5 L / s; The MOF array is one of Co-MOF, Fe-MOF, Ni-MOF, NiCo-MOF, CoFe-MOF, NiFe-MOF, and NiCoFe-MOF.

2. The method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame according to claim 1, characterized in that: The substrate is pretreated by washing the substrate with deionized water, anhydrous ethanol and acetone respectively and drying the substrate in an oven at 50-100° C. for 6-12 h.

3. The method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame according to claim 1 or 2, characterized in that: The substrate is carbon fiber cloth, carbon fiber paper, graphite paper, graphite sheet, carbon / carbon composite material, foamed nickel, nickel foil, nickel sheet or foamed copper.

4. The method for in-situ rapid growth of CNTs on the surface of a MOF array by oxyacetylene flame treatment according to claim 1, characterized in that: The nitrate is one or more of cobalt nitrate, nickel nitrate and iron nitrate.

5. The method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame according to claim 1, characterized in that: The concentration of the nitrate aqueous solution is 0.01-0.10 mol / L.

6. The method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame according to claim 1, characterized in that: The concentration of the 2-methylimidazole aqueous solution is 0.2-0.6 mol / L.

7. The method for in-situ rapid growth of CNTs on the surface of a MOF array by treating it with oxyacetylene flame according to claim 1, characterized in that: The drying in step 1 is carried out by placing the product in an oven at 50-100°C.

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