Catalyst for carbon nanotube synthesis, preparation method thereof and carbon nanotube synthesis method
By modifying the metal precursor and forming an aqueous nanodispersion, a catalyst for synthesis of highly activated carbon nanotubes was prepared, which solved the problems of complex catalyst preparation and poor performance in the prior art, and significantly improved the yield and quality of carbon nanotubes.
Patent Information
- Application Number
- CN202311583949.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-24
- Publication Date
- 2025-05-27
AI Technical Summary
The preparation process of existing catalysts for carbon nanotube synthesis is complicated, and the morphology, size and dispersion of catalyst particles are difficult to control, resulting in poor catalytic performance and affecting the controllable synthesis of carbon nanotubes.
By modifying the metal precursor, uniformly dispersed metal nanoparticles were prepared, and dispersed in an aqueous solvent to form an aqueous nanodispersion, coated on a substrate for drying, and prepared a catalyst for synthesis of highly activated carbon nanotubes.
The catalyst activity and catalytic performance are significantly improved, the yield and quality of carbon nanotubes are enhanced, and a novel catalyst preparation method is provided, which solves the problems of complex catalyst preparation and poor performance in the prior art.
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Figure BDA0004569338570000141
Abstract
Description
Technical Field
[0001] The present invention relates to the field of carbon nanotube synthesis, and particularly to a catalyst for carbon nanotube synthesis, a preparation method thereof, and a carbon nanotube synthesis method. Background Art
[0002] Carbon nanotubes have attracted extensive attention from many researchers in various fields such as materials, chemistry, medicine, microelectronics, energy, and catalysis due to their unique structure, excellent mechanical properties, and unique physical and chemical properties.
[0003] The synthesis methods of carbon nanotubes mainly include arc discharge method, laser evaporation method, chemical vapor deposition method, flame method, electrolysis method, template method, hydrothermal method, ion radiation method, ion bombardment growth method, and solar energy method, etc. Among them, the chemical vapor deposition method is also called catalytic cracking method. Because of its advantages such as simple operation, low cost, high yield, and suitability for large-scale production, it is widely used in the preparation of carbon nanotubes. When preparing carbon nanotubes by chemical vapor deposition method, the catalyst for carbon nanotube synthesis assists the cracking of carbon source gas at high temperature. When the carbon content reaches the saturation state, it precipitates on the surface of the catalyst for carbon nanotube synthesis to form carbon nanotubes.
[0004] At present, the conventional coated catalyst for carbon nanotube synthesis is to coat a metal salt solution on the surface of a substrate, and then reduce it to metal particles through processes such as calcination, reduction, and cooling, and then use it for the synthesis of carbon nanotubes. The above catalyst preparation process is complex, and it is difficult to control the morphology, size, dispersion degree, etc. of the catalyst particles. Therefore, it seriously affects the catalytic performance, is not conducive to the controllable synthesis of carbon nanotubes, and limits the synthesis of carbon nanotubes.
[0005] In addition, most of the existing catalysts for carbon nanotube synthesis are in powder form, with insufficient effective contact area for catalysis during the synthesis of carbon nanotubes, low utilization rate, and very limited loading methods for carbon nanotube preparation, which also seriously hinders the development of the carbon nanotube preparation industry.
[0006] Therefore, it is urgent to develop a catalyst for carbon nanotube synthesis that can improve the synthesis effect of carbon nanotubes. Summary of the Invention
[0007] The object of the present invention is to overcome the problems existing in the prior art such as the limitation of carbon nanotube synthesis, and to provide a catalyst for carbon nanotube synthesis, a preparation method thereof, and a method for synthesizing carbon nanotubes. The preparation method of the catalyst for carbon nanotube synthesis provided by the present invention completely changes the preparation method of the catalyst for carbon nanotube synthesis in the prior art, in which an active metal salt solution is directly coated on a substrate. By dispersing the modified metal nanoparticles in an aqueous solvent to form a uniform dispersion, the active metal is controllably and uniformly distributed on the substrate, thereby significantly improving the activity and catalytic performance of the obtained catalyst for carbon nanotube synthesis, and thus greatly increasing the yield and quality of carbon nanotubes.
[0008] To achieve the above object, a first aspect of the present invention provides a preparation method of a catalyst for carbon nanotube synthesis, wherein the method comprises the following steps:
[0009] 1) In the presence of a modifier and a first solvent, contacting a metal precursor with a reducing agent to obtain modified metal nanoparticles;
[0010] 2) Dispersing the modified metal nanoparticles in an aqueous solvent to obtain an aqueous nano-dispersion;
[0011] 3) Coating the aqueous nano-dispersion on a substrate and performing a drying treatment.
[0012] Preferably, in step 1), the modifier is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, sodium dodecylsulfonate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium metasilicate, and sodium citrate, and more preferably one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium metasilicate.
[0013] Preferably, the reducing agent is one or more of sodium borohydride, ammonia borane, hydrazine hydrate, ascorbic acid, ethylene glycol, glycerol, and hydrogen; more preferably one or more of ammonia borane, sodium borohydride, hydrazine hydrate, and ascorbic acid.
[0014] Preferably, the first solvent is one or more of water, ethanol, methanol, ethylene glycol, and glycerol, and more preferably water.
[0015] Preferably, the metal precursor is a salt and / or complex selected from one or more of Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd, and Pt, and more preferably a salt and / or complex of Co and Mo.
[0016] Preferably, in step 1), the molar ratio of the metal precursor to the reducing agent is 1:1 - 30; more preferably 1:1 - 10.
[0017] Preferably, the weight ratio of the metal precursor to the first solvent is 1:100 - 1000; more preferably 1:200 - 500.
[0018] Preferably, the weight ratio of the metal precursor to the modifier is 1:1 - 10; more preferably 1:2 - 5.
[0019] Preferably, the conditions of the contact include: temperature is 30 - 240 °C, time is 0.2 - 3 h;
[0020] Preferably, the contact is carried out under stirring.
[0021] Preferably, the metal nanoparticles after the modification treatment are one or more of Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd, and Pt.
[0022] Preferably, the metal nanoparticles after the modification treatment are a combination of Co and Mo; more preferably, the molar ratio of Co to Mo is 1:0.05 - 2, and further preferably 1:0.1 - 0.3.
[0023] Preferably, the particle size of the metal nanoparticles after the modification treatment is 1 - 50 nm, more preferably 1 - 10 nm.
[0024] Preferably, in step 2), the aqueous solvent is at least one of water, methanol, ethanol, ethylene glycol, and glycerol, more preferably one or more of water, ethanol, and ethylene glycol.
[0025] Preferably, in step 2), the aqueous solvent is the same as the first solvent.
[0026] Preferably, relative to 1 g of the metal nanoparticles after the modification treatment, the dosage of the aqueous solvent is 100 - 10000 mL, more preferably 500 - 3000 mL.
[0027] Preferably, in step 2), a dispersant and / or a film-forming agent is further added to the aqueous nano-dispersion.
[0028] Preferably, the dispersant is one or more of sodium oleate, sodium stearate, magnesium stearate, aluminum stearate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, cetylammonium bromide, polyether, and polyethylene glycol.
[0029] Preferably, the film-forming agent is one or more of polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl alcohol, collodion, zein, sodium carboxymethyl cellulose, and polyvinyl pyrrolidone.
[0030] Preferably, the weight ratio of the modified metal nanoparticles to the dispersant is 1:0.01 - 10.
[0031] Preferably, the weight ratio of the modified metal nanoparticles to the film-forming agent is 1:0.01 - 10.
[0032] Preferably, in step 3), the material of the substrate is selected from one or more of single-crystalline silicon, silicon dioxide, diamond, zirconia, alumina, magnesia, titanium dioxide, quartz, glass, silicon carbide, silicon nitride, iron, stainless steel, titanium, and molybdenum.
[0033] Preferably, the material of the substrate is selected from one or more of single-crystalline silicon, silicon dioxide, and alumina.
[0034] Preferably, based on the metal nanoparticles, the coating amount of the coating is 0.01 - 100 mg / cm 2 , more preferably 0.01 - 20 mg / cm 2 .
[0035] Preferably, the conditions of the drying treatment include: the drying temperature is 30 - 90 °C, and the drying time is 6 - 24 h.
[0036] The second aspect of the present invention provides a catalyst for carbon nanotube synthesis prepared by the method described in the first aspect of the present invention.
[0037] The third aspect of the present invention provides a method for synthesizing carbon nanotubes, which uses the catalyst for carbon nanotube synthesis described in the second aspect of the present invention.
[0038] Preferably, the method includes: in the presence of an inert gas, catalytically reacting a carbon source gas with the catalyst for carbon nanotube synthesis.
[0039] Preferably, the conditions of the catalytic reaction include: the temperature is 500 - 900 °C, and the time is 0.5 - 3 h.
[0040] Preferably, the carbon source gas is selected from one or more of methane, ethylene, acetylene, ethanol, and propylene.
[0041] Preferably, relative to 0.01 g of the catalyst for carbon nanotube synthesis based on metal nanoparticles, the flow rate of the carbon source gas is 100 - 1000 mL / min.
[0042] Through the above technical solution, the inherent method of directly coating an active metal salt solution on a substrate and performing a reduction treatment in the prior art is broken. By first subjecting an active metal to a modification treatment to prepare metal nanoparticles, the modified metal particles can be uniformly dispersed in an aqueous solvent without sedimentation, forming the aqueous nano-dispersion. Such an aqueous nano-dispersion belongs to a colloidal system, and the dispersion state of the metal nanoparticles in the aqueous solvent is uniform and stable, and can stably exist for a long time.
[0043] Compared with the metal salt solution, the morphology, size, etc. of the metal nanoparticles in the aqueous nano-dispersion are more easily controlled, so that the properties of the coating catalyst can be flexibly adjusted according to the purpose. For example, the uniformity and controllability of the dispersion of the metal nanoparticles can be significantly improved during coating, and then a catalyst for carbon nanotube synthesis with uniformly dispersed active components, controllable size and structure can be obtained.
[0044] The active components in the catalyst for carbon nanotube synthesis provided by the present invention are not only uniformly distributed, but also have good adhesion, and can be stacked into various three-dimensional structures for use as needed, which can significantly increase the contact area between the catalyst and the carbon source gas per unit time and per unit reactor volume. Therefore, when preparing carbon nanotubes, the yield and quality of the carbon nanotubes can be greatly improved, providing a new idea for carbon nanotube preparation. Detailed implementation mode
[0045] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.
[0046] The first aspect of the present invention provides a method for preparing a catalyst for carbon nanotube synthesis, wherein the method comprises the following steps:
[0047] 1) In the presence of a modifier and a first solvent, bringing a metal precursor into contact with a reducing agent to obtain modified metal nanoparticles;
[0048] 2) Dispersing the modified metal nanoparticles in an aqueous solvent to obtain an aqueous nano-dispersion;
[0049] 3) Coating the aqueous nano-dispersion on a substrate and performing a drying treatment.
[0050] In a large number of experiments and production practices, the inventors of the present invention found that when preparing a catalyst for carbon nanotube synthesis using the existing method, there are problems such as uneven dispersion of the active metal salt in the solution, difficulty in controlling the distribution of the active metal by coating, and poor quality of the catalyst for carbon nanotube synthesis obtained after reduction treatment, which seriously affect the preparation of carbon nanotubes.
[0051] Based on this, the inventors of the present invention have found through in-depth research that by first modifying the metal precursor of the catalyst for carbon nanotube synthesis to obtain modified metal nanoparticles, a water-phase nano-dispersion that is uniformly dispersed, does not settle, and can stably exist can be obtained when it is dispersed in an aqueous solvent. Then, the water-phase nano-dispersion is used as a coating solution to be coated on a substrate. Thereby, the uniformity of the distribution of the active components in the catalyst for carbon nanotube synthesis prepared and the catalytic activity of the catalyst can be significantly improved, and further the yield and quality of carbon nanotubes can be significantly improved, and thus the present invention is completed.
[0052] Hereinafter, the preparation method of the catalyst for carbon nanotube synthesis will be described in detail first.
[0053] In step 1), in the presence of a modifier and a first solvent, the metal precursor is contacted with a reducing agent to obtain modified metal nanoparticles.
[0054] As described above, different from directly using a salt solution of an active metal for coating in the prior art, in the present invention, the metal precursor is first modified through the above step 1).
[0055] The purpose of the modification treatment here is, firstly, to reduce the metal precursor; secondly, to make the active metal form metal nanoparticles through modification. The modified metal nanoparticles can form a water-phase nano-dispersion when dispersed in an aqueous solvent, so that the metal nanoparticles can be uniformly dispersed and stably exist in the water solvent without aggregation and sedimentation.
[0056] In the present invention, the metal nanoparticles refer to nanoparticles composed of metal atoms or metal ions.
[0057] In the present invention, the water-phase nano-dispersion refers to a dispersion system in which nanoparticles or aggregates are uniformly and stably dispersed in an aqueous solvent.
[0058] In the present invention, after the water-phase nano-dispersion stands for 24 hours and is observed by a transmission electron microscope (TEM), no precipitation and aggregates are found and it is confirmed to be monodisperse nano-metal particles.
[0059] In addition, the inventors have found through experiments that the water-phase nano-dispersion provided by the present invention is still monodisperse metal nanoparticles after being placed for 1 month.
[0060] In step 1), the metal precursor refers to the precursor of the active metal used in the catalyst for carbon nanotube synthesis. It can be salts and / or complexes of active metals commonly used in the art as catalysts for carbon nanotube synthesis, without particular limitation.
[0061] For example, the metal precursor can be selected from salts and / or complexes of one or more of Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd, and Pt.
[0062] The inventors of the present invention unexpectedly found during the research process that when preparing the catalyst for carbon nanotube synthesis by the method of the present invention, among the above metal precursors, when using salts and / or complexes of Co and Mo as the metal precursor, significantly better catalytic performance can be achieved compared with other metal precursors.
[0063] Therefore, in a preferred embodiment of the present invention, the metal precursor is a salt and / or complex of Co and Mo. And, more preferably, in the metal precursor, the molar ratio of Co to Mo is 1:0.05 - 2, further preferably 1:0.1 - 0.3, whereby the catalytic performance of the obtained catalyst for carbon nanotube synthesis can be further significantly improved.
[0064] According to the present invention, in step 1), the modifier is used to modify the surface of the nanoparticles, so as to control the size and dispersion of the metal nanoparticles.
[0065] In the present invention, as the modifier, various modifiers commonly used in the art that can achieve the above purposes can be used.
[0066] For example, the modifier can be one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, sodium dodecyl sulfate (SDS), sodium lauryl sulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), sodium metasilicate, and sodium citrate, preferably one or more of polyvinylpyrrolidone, polyethylene glycol, and sodium metasilicate.
[0067] According to the present invention, the dosage of the modifier can be determined according to the amount of the metal precursor. For example, the weight ratio of the metal precursor to the modifier can be 1:1 - 10; preferably 1:2 - 5. By using the modifier within the above dosage range, the modification effect can be further improved.
[0068] In the present invention, there is no particular limitation on the first solvent, and various solvents commonly used in the art can be used. For example, the first solvent can be one or more of water, ethanol, methanol, ethylene glycol, and glycerol, and water is preferably used.
[0069] In addition, in the present invention, the amount of the first solvent is not particularly limited and can be appropriately selected according to the amount of the metal precursor. For example, the weight ratio of the metal precursor to the first solvent can be 1:100-1000, preferably 1:200-500. By limiting the amount of the first solvent to the above range, the modification effect can be further improved.
[0070] According to the present invention, the reducing agent is used to reduce the metal precursor to obtain metal nanoparticles. The type of the reducing agent is not particularly limited and can be various reducing agents conventionally used in the art. For example, the reducing agent can be one or more of sodium borohydride, ammonia borane, hydrazine hydrate, ascorbic acid, ethylene glycol, glycerol and hydrogen, preferably one or more of ammonia borane, sodium borohydride, hydrazine hydrate and ascorbic acid. The above preferred reducing agent is more suitable for the system described in the present application, and can further improve the reduction effect, thereby further improving the dispersion uniformity of the obtained aqueous dispersion and improving the performance of the prepared catalyst.
[0071] In addition, the amount of the reducing agent is not particularly limited and can be a conventional choice in the art. And the amount of the reducing agent can be determined according to the amount of the metal precursor. For example, the molar ratio of the metal precursor to the reducing agent can be 1:30; preferably 1:1-10. By limiting the amount of the reducing agent to the above range, the reduction effect can be further ensured, thereby improving the catalytic performance of the prepared carbon nanotube synthesis catalyst.
[0072] According to the first aspect of the present invention, the contact conditions are not particularly limited, as long as the modification and reduction purposes can be achieved. For example, the contact conditions may include: a temperature of 30-240° C. and a time of 0.2-3 h.
[0073] In addition, in order to improve the modification efficiency and the reduction effect, preferably, the contacting is performed under stirring.
[0074] On the other hand, preferably, through the modification treatment in step 1), the particle size of the modified metal nanoparticles is 1-50 nm, more preferably 1-10 nm. By limiting the particle size of the modified metal nanoparticles to the above range, it is more conducive to improving the catalytic activity of the prepared carbon nanotube synthesis catalyst and significantly improving the preparation efficiency of carbon nanotubes.
[0075] Next, in step 2), the modified metal nanoparticles are dispersed in an aqueous solvent to obtain an aqueous nanodispersion.
[0076] The metal nanoparticles obtained through the modification treatment described in step 1) already have good dispersion properties. Therefore, even when dispersed in an aqueous solvent, they will not aggregate or settle, but can form a water-phase nano-dispersion with a uniform distribution and stable existence.
[0077] The metal nanoparticles correspond to the metal precursors used in step 1). For example, the modified metal nanoparticles are one or more of Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd, and Pt.
[0078] Among them, preferably, the modified metal nanoparticles are a combination of Co and Mo; more preferably, the molar ratio of Co to Mo is 1:0.05 - 2, and further preferably 1:0.1 - 0.3. This can further significantly improve the catalytic performance of the catalyst for carbon nanotube synthesis obtained.
[0079] In addition, in step 2), the aqueous solvent is not particularly limited and can be various aqueous solvents commonly used in the art. For example, the aqueous solvent can be at least one of water, methanol, ethanol, ethylene glycol, and glycerol, and is preferably one or more of water, ethanol, and ethylene glycol.
[0080] According to the present invention, the amount of the aqueous solvent is not particularly limited as long as it can disperse the metal nanoparticles and obtain the water-phase nano-dispersion. Moreover, the amount of the aqueous solvent can be selected according to the amount of the metal nanoparticles. For example, relative to 1 g of the modified metal nanoparticles, the amount of the aqueous solvent can be 100 - 10,000 mL, and preferably 500 - 3,000 mL. By using the above amount, not only can the metal nanoparticles be uniformly dispersed, but also the metal nanoparticles can be maintained at a suitable dispersion concentration to ensure the catalytic performance of the catalyst for carbon nanotube synthesis obtained after coating.
[0081] In addition, in the present invention, the aqueous solvent is preferably the same as the first solvent.
[0082] According to the present invention, in step 2), the dispersion can be carried out by various conventional means for dispersion in the art. For example, after mixing the modified metal nanoparticles with the aqueous solvent, stirring can be carried out, etc., as long as a water-phase nano-dispersion in which the metal nanoparticles are uniformly and stably dispersed can be obtained. The dispersion method is a well-known method and will not be elaborated here.
[0083] Furthermore, in step 2), in order to further enhance the dispersion effect and make the metal nanoparticles more uniformly and stably dispersed in the aqueous solvent, preferably, other additives are further added to the water-phase nano-dispersion.
[0084] The auxiliaries may be, for example, a dispersant, a film-forming agent, a stabilizer, an adhesion agent, etc.
[0085] The dispersant can further improve the dispersion performance of the metal nanoparticles in the aqueous solvent.
[0086] As the dispersant, for example, it may be one or more of sodium oleate, sodium stearate, magnesium stearate, aluminum stearate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, cetylammonium bromide, polyether, and polyethylene glycol, and preferably one or more of cetylammonium bromide, polyether, and polyethylene glycol.
[0087] In addition, the dosage of the dispersant can be appropriately selected according to the amount of the modified metal nanoparticles. For example, the weight ratio of the modified metal nanoparticles to the dispersant may be 1:0.01 - 10.
[0088] The film-forming agent can further enhance the adhesion of the aqueous nano-dispersion on the substrate described below and the hardness of the coated catalyst layer, and improve the stability and dispersion of the metal nanoparticles after coating.
[0089] As the film-forming agent, for example, it may be one or more of polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl alcohol, collodion, zein, sodium carboxymethyl cellulose, and polyvinylpyrrolidone, and preferably polyvinyl alcohol.
[0090] In addition, the dosage of the film-forming agent can be appropriately selected according to the amount of the modified metal nanoparticles. For example, the weight ratio of the modified metal nanoparticles to the film-forming agent may be 1:0.01 - 10.
[0091] Next, in step 3), the aqueous nano-dispersion is coated on the substrate and dried.
[0092] According to the present invention, the aqueous nano-dispersion obtained in step 2) can be used as a coating liquid for coating, that is, the aqueous nano-dispersion is coated on the substrate and dried.
[0093] Here, the substrate is not particularly limited and can be substrates of various materials commonly used in the art for preparing catalysts for carbon nanotube synthesis. For example, the material of the substrate can be selected from one or more of materials such as single crystal silicon, silicon dioxide, diamond, zirconia, alumina, magnesia, titanium dioxide, quartz, glass, silicon carbide, silicon nitride, iron, stainless steel, titanium, and molybdenum; preferably, the substrate is selected from one or more of single crystal silicon, silicon dioxide, and alumina.
[0094] In addition, in the present invention, there are no particular limitations on the shape and size of the substrate. For example, the shape of the substrate can be sheet-like, and the size can be 10 - 40 mm × 20 - 60 mm in length and width, and the thickness can be 0.1 - 10 mm.
[0095] In the present invention, the substrate can be pretreated before use. For example, it can be polished, acid etched, hydrophilized, ultrasonically treated, etc. The above treatment methods can be carried out by using the well-known methods in the art and will not be elaborated here.
[0096] On the other hand, for the coating method, there are no particular limitations in the present invention. For example, the coating method can be one or more of spraying, roll coating, spin coating, knife coating, dip coating, slot die coating, inkjet printing, screen printing, 3D printing, and gravure printing, as long as the coating can be uniform. In the present invention, spin coating is preferably used.
[0097] In the present invention, there are no particular limitations on the coating amount of the coating. For example, calculated by the weight of the metal nanoparticles, the coating amount of the coating can be 0.01 - 100 mg / cm 2 (that is, 0.01 - 100 mg of metal nanoparticles are coated on each square centimeter of the substrate), preferably 0.01 - 20 mg / cm 2 . The above coating amount can improve the catalytic performance of the catalyst for carbon nanotube synthesis prepared.
[0098] Then, the coated product is dried. The conditions for the drying treatment are not particularly limited as long as the drying purpose can be achieved. For example, the conditions for the drying treatment include: the drying temperature is 30 - 90 °C, and the drying time is 6 - 24 h.
[0099] The second aspect of the present invention provides a catalyst for carbon nanotube synthesis prepared by the method described in the first aspect above.
[0100] According to the second aspect of the present invention, in the obtained catalyst for carbon nanotube synthesis, the active components on the substrate are uniformly distributed, and the active components have all been fully and uniformly modified, so that the obtained catalyst for carbon nanotube synthesis has stable and uniform catalytic activity, the morphology can be controlled during the preparation process, the size of the active metal particles can be artificially controlled in the modification step of step 1), and the structure can be regulated by the coating treatment of step 3). Therefore, compared with the existing catalysts for carbon nanotube synthesis, its stability and activity are both significantly improved, which is very beneficial to the high-efficiency and high-yield synthesis of carbon nanotubes.
[0101] The third aspect of the present invention provides a method for synthesizing carbon nanotubes, wherein the method uses the catalyst for carbon nanotube synthesis described in the second aspect of the present invention.
[0102] As described above, the catalyst for carbon nanotube synthesis provided by the second aspect of the present invention has a uniform and controllable morphology, and the adhesion of active metal particles to the substrate is strong. Therefore, when the catalyst is used for carbon nanotube synthesis, it can be designed into various three-dimensional structures for use, thereby improving the carbon nanotube synthesis efficiency per unit time and per unit reactor space.
[0103] According to the third aspect of the present invention, the carbon nanotube synthesis method can be carried out by various conventional methods in the art. Except that the catalyst for carbon nanotube synthesis is the catalyst for carbon nanotube synthesis provided by the second aspect of the present invention, other steps can adopt the well-known methods in the art.
[0104] According to a preferred embodiment of the present invention, the catalyst for carbon nanotube synthesis includes: in the presence of an inert gas, catalytic reaction is carried out between a carbon source gas and the catalyst for carbon nanotube synthesis.
[0105] In addition, preferably, the conditions of the catalytic reaction include: the temperature is 500 - 900 °C, and the time is 0.5 - 3 h.
[0106] The inert gas is not particularly limited and can be various inert gases commonly used in the art. Nitrogen is preferably used in the present invention.
[0107] In addition, the carbon source gas is not particularly limited. For example, it can be one or more of methane, ethylene, acetylene, ethanol, and propylene; preferably ethylene and / or propylene.
[0108] In the present invention, the introduction amount of the carbon source gas can be determined according to the usage amount of the catalyst for carbon nanotube synthesis. Preferably, relative to 0.01 g of the catalyst for carbon nanotube synthesis in terms of metal nanoparticles, the introduction amount of the carbon source gas is 100 - 1000 mL / min. By carrying out the reaction within the above catalyst usage range, the carbon nanotube synthesis efficiency can be further improved, the waste of the carbon source gas can be reduced, and the energy consumption can be lowered.
[0109] The present invention will be described in detail below through examples.
[0110] In the following preparation examples, polyvinylpyrrolidone was purchased from Aladdin Biochemical Technology Co., Ltd., and the average molecular weight was 8000;
[0111] The size of the substrate silicon wafer was 20 mm × 40 mm, and the thickness was 1 mm.
[0112] After the aqueous phase nano-dispersion prepared in the following preparation examples was allowed to stand for 24 h, it was observed by transmission electron microscopy (TEM) and confirmed to be monodisperse metal nanoparticles.
[0113] Preparation Examples 1 - 3
[0114] 1) Modification treatment:
[0115] Dissolve the modifier and reducing agent in water (the dosages of the modifier and reducing agent are shown in Table 1 relative to 15 mL of water), then transfer them into a three-necked flask, heat in a water bath at 25 °C for 10 min, while performing magnetic stirring at a rotation speed of 1000 rpm. After that, add the metal precursor (the dosage of the metal precursor is shown in Table 1 relative to 15 mL of water), continue stirring for 0.5 h, then perform centrifugation, collect the solid phase, and wash the obtained solid phase with distilled water 5 times to obtain modified metal nanoparticles;
[0116] 2) Dispersion treatment:
[0117] Mix and stir the modified metal nanoparticles obtained in step 1) with water. The amount of water used is 1000 mL relative to 1 g of the modified metal nanoparticles to obtain an aqueous nano-dispersion;
[0118] 3) Coating and drying:
[0119] Coat the aqueous nano-dispersion obtained by the dispersion treatment method in step 2) on the washed silicon wafer by spin coating. Among them, based on the metal nanoparticles, the coating amount is 0.1 mg / cm 2 , and then vacuum dry the coated silicon wafer at 60 °C for 10 hours to obtain the catalyst C1 - C3 for carbon nanotube synthesis.
[0120] The specific parameters of Preparation Examples 1 - 3 are shown in Table 1 below:
[0121] Table 1
[0122]
[0123] Preparation Example 4
[0124] Carry out according to the method of Preparation Example 1, except that
[0125] In step 1), the precursor is replaced with cobalt dichloride hexahydrate and ammonium molybdate tetrahydrate with the same molar amount (that is, the total molar amount of cobalt dichloride hexahydrate and ammonium molybdate tetrahydrate is the same as that of cobalt dichloride hexahydrate in Preparation Example 1), and the Co:Mo molar ratio is 1:0.15. The particle size of the obtained nano-metal particles is 4.2 nm.
[0126] Obtain catalyst C4.
[0127] Preparation Example 5
[0128] Carry out according to the method of Preparation Example 1, except that
[0129] In step 2), polyethylene glycol is further added to the aqueous nanodispersion. The addition amount of polyethylene glycol is 200 mg relative to 1 L of the aqueous nanodispersion.
[0130] Catalyst C5 is obtained.
[0131] Comparative Preparation Example 1
[0132] 1) Cobalt dichloride hexahydrate (2 mmol / L) is dissolved in water to obtain a coating solution. The dosage of cobalt dichloride hexahydrate is 5 mL relative to 15 mL of water.
[0133] 2) The coating solution obtained in step 1) is coated on the washed silicon wafer according to the method described in step 3) of Example 1, so that the coating amount is 0.1 mg / cm 2 , and the coated silicon wafer is vacuum dried at 60 °C for 10 hours.
[0134] 3) The coated catalyst supported on the silicon wafer is reduced in a gas stream of 600 standard cubic centimeters per minute of argon and 400 standard cubic centimeters per minute of hydrogen at 800 °C for 5 minutes, and then naturally cooled to 25 °C.
[0135] Catalyst D1 is obtained.
[0136] Example
[0137] 1) The porcelain boat containing the catalyst for carbon nanotube synthesis is transferred into a CVD tube furnace. The temperature inside the furnace is set to 700 °C, and the heating rate is 20 °C / min. At the same time, nitrogen purging is carried out, and the nitrogen flow rate is 700 mL / min.
[0138] 2) After the temperature is raised to 700 °C, the nitrogen flow rate is reduced to 300 mL / min, and ethylene gas is introduced. The introduction amount of ethylene gas is 300 mL / min, and the reaction is carried out for 0.5 h.
[0139] 3) After the reaction is completed, the ethylene gas is turned off, and nitrogen is continuously introduced for cooling. The flow rate is 700 mL / min. After cooling to 25 °C, all gases are turned off, and the carbon nanotubes are collected and the mass of the obtained carbon nanotubes is weighed.
[0140] According to the above method, carbon nanotubes are synthesized using catalysts C1 - C5 and D1 prepared from Preparation Examples 1 - 5 and Comparative Preparation Example 1 respectively.
[0141] The yield of carbon nanotubes prepared by each catalyst (i.e., the mass of carbon nanotubes obtained relative to 1 g of the catalyst (calculated based on the metal therein)) is calculated, and the results are shown in Table 2 below:
[0142] Table 2
[0143] Catalyst C1 C2 C3 C4 C5 D1 Yield of carbon nanotubes 13.2 11.9 10.2 17.5 18.8 7.5
[0144] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.
Claims
1. A preparation method of a catalyst for carbon nanotube synthesis, characterized in that, the method comprises the following steps: 1) In the presence of a modifier and a first solvent, contacting a metal precursor with a reducing agent to obtain modified metal nanoparticles; 2) Dispersing the modified metal nanoparticles in an aqueous solvent to obtain an aqueous nano-dispersion; 3) Coating the aqueous nano-dispersion on a substrate and performing a drying treatment.
2. The preparation method according to claim 1, wherein, in step 1), the modifier is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyethylene glycol, sodium dodecylsulfonate, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium metasilicate and sodium citrate, preferably one or more of polyvinylpyrrolidone, polyethylene glycol and sodium metasilicate; preferably, the reducing agent is one or more of sodium borohydride, ammonia borane, hydrazine hydrate, ascorbic acid, ethylene glycol, glycerol and hydrogen; more preferably one or more of ammonia borane, sodium borohydride, hydrazine hydrate and ascorbic acid; preferably, the first solvent is one or more of water, ethanol, methanol, ethylene glycol and glycerol, more preferably water; preferably, the metal precursor is a salt and / or complex of one or more selected from Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd and Pt, more preferably a salt and / or complex of Co and Mo.
3. The preparation method according to claim 1 or 2, wherein, in step 1), the molar ratio of the metal precursor to the reducing agent is 1:1 - 30; preferably 1:1 - 10; preferably, the weight ratio of the metal precursor to the first solvent is 1:100 - 1000; preferably 1:200 - 500; preferably, the weight ratio of the metal precursor to the modifier is 1:1 - 10; preferably 1:2 - 5; preferably, the conditions of the contact include: the temperature is 30 - 240 °C and the time is 0.2 - 3 h; preferably, the contact is carried out under stirring.
4. The preparation method according to any one of claims 1 - 3, wherein, the modified metal nanoparticles are one or more of Fe, Co, Mo, Ni, Cu, Ag, Au, Ru, Rh, Pd and Pt; preferably, the modified metal nanoparticles are a combination of Co and Mo; more preferably, the molar ratio of Co to Mo is 1:0.05 - 2, further preferably 1:0.1 - 0.3; preferably, the particle size of the modified metal nanoparticles is 1 - 50 nm, more preferably 1 - 10 nm.
5. The preparation method according to any one of claims 1 - 3, wherein, in step 2), the aqueous solvent is at least one of water, methanol, ethanol, ethylene glycol and glycerol, preferably one or more of water, ethanol and ethylene glycol; preferably, in step 2), the aqueous solvent is the same as the first solvent; Preferably, with respect to 1 g of the surface-modified metal nanoparticles, the amount of the aqueous solvent is 100 - 10,000 mL, more preferably 500 - 3,000 mL.
6. The preparation method according to any one of claims 1 - 3, wherein, in step 2), a dispersant and / or a film-forming agent is further added to the aqueous nano-dispersion; Preferably, the dispersant is one or more of sodium oleate, sodium stearate, magnesium stearate, aluminum stearate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, cetylammonium bromide, polyethers, and polyethylene glycol; Preferably, the film-forming agent is one or more of polyvinyl formal, polyvinyl acetal, polyvinyl butyral, polyvinyl alcohol, collodion, zein, sodium carboxymethyl cellulose, and polyvinyl pyrrolidone; Preferably, the weight ratio of the surface-modified metal nanoparticles to the dispersant is 1:0.01 - 10; Preferably, the weight ratio of the surface-modified metal nanoparticles to the film-forming agent is 1:0.01 - 10.
7. The preparation method according to any one of claims 1 - 3, wherein, in step 3), the material of the substrate is selected from one or more of single-crystalline silicon, silicon dioxide, diamond, zirconia, alumina, magnesia, titanium dioxide, quartz, glass, silicon carbide, silicon nitride, iron, stainless steel, titanium, and molybdenum; Preferably, the material of the substrate is selected from one or more of single-crystalline silicon, silicon dioxide, and alumina; Preferably, based on the metal nanoparticles, the coating amount of the coating is 0.01-100 mg / cm 2 , more preferably 0.01-20 mg / cm 2 ; Preferably, the conditions of the drying treatment include: the drying temperature is 30 - 90 °C, and the drying time is 6 - 24 h.
8. A catalyst for carbon nanotube synthesis prepared by the method according to any one of claims 1 - 7.
9. A method for synthesizing carbon nanotubes, characterized in that, the method for synthesizing carbon nanotubes uses the catalyst for carbon nanotube synthesis according to claim 8.
10. The method for synthesizing carbon nanotubes according to claim 9, wherein, the method includes: in the presence of an inert gas, a carbon source gas is subjected to a catalytic reaction with the catalyst for carbon nanotube synthesis; Preferably, the conditions of the catalytic reaction include: the temperature is 500 - 900 °C, and the time is 0.5 - 3 h; Preferably, the carbon source gas is selected from one or more of methane, ethylene, acetylene, ethanol, and propylene; Preferably, with respect to 0.01 g of the catalyst for carbon nanotube synthesis in terms of metal nanoparticles, the flow rate of the carbon source gas is 100 - 1,000 mL / min.