Method for continuously synthesizing iron-doped bamboo-like carbon nanotubes

Abstract

The invention discloses a method for continuously synthesizing an iron-doped bamboo-like carbon nanotube, and belongs to the technical field of nano material preparation. According to the method, a transition metal compound is used as a catalyst precursor, a tubular furnace is used as a reactor, an organic solution in which the transition metal compound is dissolved is bubbled and brought into a high-temperature reaction area of the reactor by using a gas carbon source, and the transition metal compound is decomposed at high temperature to generate a catalytic active center; and the active center catalyzes a gas carbon source to generate the iron-doped bamboo-like carbon nanotube. The high gas carbon source utilization rate and the regulation and control of the tube length and the tube wall thickness of the iron-doped bamboo-like carbon nano tube are realized by controlling the gas flow rate or changing the types of transition metal compounds and the like; and semi-continuous / continuous production can be realized by bubbling through a mechanical continuous automatic feeding method, so that the cost is further reduced, and large-scale preparation is facilitated. In conclusion, the method has the advantages of being short in technological process, capable of continuously feeding to produce the carbon nanotubes, simple to operate, cheap and easily available in catalyst, high in utilization rate, safe and non-toxic in carbon source and the like, and has industrial amplification preparation prospects.

Description

Technical Field

[0001] The invention relates to a method for preparing iron-doped bamboo-shaped carbon nanotubes, belonging to the technical field of nano material preparation. Background Art

[0002] In 1991, Sumio Iijima discovered the structure of tubular graphite carbon. Like graphene, this tubular graphite carbon is composed of sp2 hybridized carbon atoms connected to form a hexagonal network structure. However, unlike graphene, this tubular graphite carbon, called carbon nanotubes, is a hollow structure material formed by seamless curling of sp2 hybridized carbon atoms at a certain spiral angle. According to the different curling methods, carbon nanotubes can be divided into armrest-type carbon nanotubes, zigzag carbon nanotubes, and hybrid carbon nanotubes. According to the number of layers, carbon nanotubes can be divided into single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), and multi-walled carbon nanotubes (MWNTs).

[0003] Carbon nanotubes have many properties due to their unique structure. For example, carbon nanotubes have ultra-high aspect ratio, high tensile strength, and high toughness, which makes carbon nanotubes promising to become raw materials for preparing super-strong fibers, space elevators, and highly elastic armor; carbon nanotubes have good biocompatibility, which gives them broad development prospects in the biomedical field; the walls of carbon nanotubes have sp2 hybridized carbon atoms that are different from graphite, which is due to the curling of the carbon plane of the carbon nanotube to produce a certain curvature. This curved carbon plane causes the carbon atoms to deviate from sp2 hybridization and tend to sp3 hybridization, and the electrons in the tube will transfer to the outside of the tube. This specific electronic structure must have specific electronic conduction properties, such as being a good electron transport carrier. If carbon nanotubes are compounded with catalysts, they will produce wonderful electronic properties and catalytic properties.

[0004] So far, the preparation methods of carbon nanotubes include arc discharge method, laser evaporation method, chemical vapor deposition method, etc. The DC arc method is to use the high-temperature plasma generated by arcing between electrodes under the condition of inert gas protection to gasify the carbon on the anode carbon rod to generate carbon nanotubes and deposit them on the cathode. Due to the extremely high temperature of the plasma generated by the discharge between the electrodes, this method is easy to produce a large amount of graphite fragments and amorphous carbon, etc., which are difficult to separate and purify. The laser evaporation method uses laser to evaporate the high-temperature heated graphite and catalyst mixture, and flows into the low-temperature zone under the drive of air flow to generate single-walled carbon nanotubes in the low-temperature zone, but this method requires high temperature conditions, consumes a lot of energy and has low yield. The chemical vapor deposition method uses transition metal (Fe, Co, Ni) or its oxide nanoparticles as catalysts, carbon-containing gaseous compounds (methane, ethane, ethylene, etc.) as carbon sources, passes the gaseous carbon source at 600-1000°C, and introduces the catalyst into the high-temperature zone by some means (spraying, bubbling, etc.) to dehydrogenate the carbon source to generate carbon nanotubes. Compared with arc discharge method and laser evaporation method, this method has lower temperature requirements and the product is easier to purify. However, at present, when using chemical vapor deposition to produce bamboo-shaped carbon nanotubes, when the transition metal catalyst is consumed, it is necessary to wait for the temperature to drop before adding the catalyst again. This intermittent operation process not only takes a lot of time, but also reduces production efficiency. Therefore, we designed a device to avoid intermittent operation. The device is to introduce the transition metal precursor dissolved in the organic solvent in the bubbler into the high-temperature reaction zone in the form of steam by passing the carbon source gas into the bubbler. The metal precursor can be continuously added to the bubbler to continuously produce bamboo-shaped carbon nanotubes. Compared with other methods reported previously (such as the method of synthesizing bamboo-shaped carbon nanotubes by directly pumping an organic solution dissolved in ferrocene and other complexes into a reactor through a flow pump), our method of producing bamboo-shaped carbon nanotubes has the advantages of high adjustable denaturation of gas carbon source and transition metal complexes and a wide range of preparation conditions, and this method greatly reduces the consumption of energy and human resources, and has the prospect of industrial scale-up preparation. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing iron-doped bamboo-shaped carbon nanotubes which is uninterrupted, has simple equipment, is easy to operate and has high catalyst utilization efficiency.

[0006] In order to achieve the above object, the technical scheme of the present invention is as follows: an iron-based transition metal organic complex is used as a catalyst precursor, dissolved in an organic solution and placed in a bubbler. A gaseous carbon source and hydrogen are introduced into the bubbler, and the transition metal organic complex enters the high-temperature reaction zone together with an organic solvent, reacts to generate iron-doped bamboo-shaped carbon nanotubes and deposits them on the quartz tube wall. After a specific reaction time, bubbling is stopped, and the gaseous carbon source is switched to an inert gas. The carbon nanotubes generated after natural cooling can be collected from the tube wall, and the organic solution of the iron-based transition metal organic complex can be continuously introduced into the bubbler to achieve continuous production.

[0007] A method for synthesizing iron-doped bamboo-shaped carbon nanotubes, the method comprising the following steps:

[0008] (1) dissolving a certain amount of an iron-based transition metal organic complex in an organic solution;

[0009] (2) introducing inert gas to remove air from the reactor, and setting a temperature increase program to raise the reactor temperature to the desired temperature;

[0010] (3) stopping the introduction of the inert gas, connecting the gas line to the bubbler containing the solution prepared in step (1), and introducing the gaseous carbon source and hydrogen;

[0011] (4) start bubbling and react for a specific time;

[0012] (5) After the reaction, the introduction of the carbon source and hydrogen gas is stopped, and the inert protective gas is switched to the inert protective gas, and the mixture is naturally cooled to room temperature to obtain iron-doped bamboo-shaped carbon nanotubes.

[0013] In the above technical solution, further, all reaction tubes of the tubular furnace are made of quartz material and have an outer diameter of 50 mm.

[0014] In the above technical solution, further, the inert gas is any one of argon, helium and nitrogen.

[0015] In the above technical solution, further, the flow rate of the inert gas is 100 to 4000 mL / min.

[0016] In the above technical solution, further, the carbon source is any one of carbon-containing low-boiling point organic matter such as methane, ethane, propane, ethylene, propylene, etc.

[0017] In the above technical solution, further, the flow rate of the gaseous carbon source is 80-4000 mL / min, the flow rate of hydrogen is 40-400 mL / min, and the reaction pressure is normal pressure.

[0018] In the above technical solution, further, the heating rate of the heating zone where the reaction occurs is 2-20°C / min, the reaction temperature is 600-1250°C, and an organic solution that dissolves the iron-based transition metal organic complex can be continuously added to achieve continuous production.

[0019] In the above technical solution, further, the metal precursor is an iron-based transition metal organic complex, such as triethylferro (TEF), ethylferrocene, ferrocene, etc.

[0020] The beneficial effects of the present invention are:

[0021] (1) The method can continuously add an organic solution dissolving an iron-based transition metal organic complex into the bubbler to achieve continuous production.

[0022] (2) This method has high catalyst utilization efficiency. The amount of catalyst bubbled into the reactor each time is constant, and the quality of the obtained carbon tubes is uniform.

[0023] (3) The transition metal compound used in the present invention is cheap and readily available, thus reducing costs.

[0024] (4) The device used in this method is simple and easy to operate.

[0025] (5) The post-processing steps of this method are simple and no further acid washing is required to purify the carbon nanotubes.

[0026] (6) The carbon source used in this method is cheap, widely available, and non-toxic.

[0027] In summary, the method for preparing iron-doped bamboo-shaped carbon nanotubes provided by the present invention has simple process, sustainable production, green environmental protection, high catalyst utilization efficiency, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A diagram of a reaction device for the method for preparing iron-doped bamboo-shaped carbon nanotubes of the present invention;

[0029] Wherein: 1. a bubbler containing an organic solution in which an iron-based transition metal organic complex is dissolved, 2. a quartz reaction tube, 3. a heating zone, 4. a reaction zone, 5. a stopper;

[0030] Figure 2 This is a typical high-resolution transmission electron microscopy image of the iron-doped bamboo-shaped carbon nanotubes obtained in Example 1;

[0031] Figure 3 This is a typical transmission electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Example 2;

[0032] Figure 4 A typical transmission electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Example 3;

[0033] Figure 5 This is a typical transmission electron micrograph of the iron-doped bamboo-shaped carbon nanotubes obtained in Example 4;

[0034] Figure 6 A typical scanning electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Comparative Example 1;

[0035] Figure 7 A typical scanning electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Comparative Example 2;

[0036] Figure 8 This is a typical transmission electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Comparative Example 3;

[0037] Fig. 9 A typical transmission electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Comparative Example 4;

[0038] Fig.10 This is a typical transmission electron microscope image of the iron-doped bamboo-shaped carbon nanotubes obtained in Comparative Example 5. DETAILED DESCRIPTION

[0039] The whole process is described in detail below by way of examples, but the scope of the claims of the present invention is not limited by these examples.

[0040] In the following examples, the reactor is as follows Figure 1 As shown, it includes 1. a bubbler containing an organic solution containing dissolved metal compounds, 2. a quartz reaction tube, 3. a heating zone, 4. a reaction zone, 5. a stopper, a passage for introducing inert protective gas, and b passage for introducing raw material gas (gaseous carbon source and hydrogen).

[0041] The reactor is a closed hollow structure; the reactor includes a heating zone arranged on the periphery of the reactor, a passage a for introducing inert protective gas is provided on one side of the reactor, and a passage b for introducing gaseous carbon source and hydrogen is provided; and a gas outlet is provided on the other side of the reactor.

[0042] The b passage is connected to a bubbler containing an organic solution in which metal compounds are dissolved, an air inlet pipeline penetrates into the organic solution, and an air outlet pipeline is above the liquid level of the organic solution inside the bubbler.

[0043] Example 1

[0044] (1) Dissolve 5 g of ferrocene in 200 mL of ethanol to form a solution and place it in a bubbler;

[0045] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0046] (3) The reactor was cut into channel b, and 120 mL / min CH4 and 40 mL / min H2 were introduced for bubbling at room temperature for 3 hours;

[0047] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 4.4 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscopy of the obtained iron-doped bamboo-like carbon nanotubes was as follows: Figure 2 As shown. The length of the obtained iron-doped bamboo-shaped carbon nanotubes is 3 to 10 μm, and the average outer diameter of the tube is about 100 nm.

[0048] The average tube thickness is about 14 nm.

[0049] Example 2

[0050] (1) Dissolve 5 g of ferrocene in 300 mL of methanol to form a solution and place it in a bubbler;

[0051] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0052] (3) The reactor was cut into channel b, and 200 mL / min CH4 and 50 mL / min H2 were introduced for bubbling at room temperature for 2 hours;

[0053] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 6.2 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscopy of the obtained iron-doped bamboo-like carbon nanotubes was as follows: Figure 3 The obtained iron-doped bamboo-shaped carbon nanotubes are 2 to 8 μm long and have an average outer diameter of about 80 nm.

[0054] The average tube thickness is about 7 nm.

[0055] Example 3

[0056] (1) Dissolve 5 g of ferrocene in 300 mL of acetonitrile to form a solution and place it in a bubbler;

[0057] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 850°C at a rate of 5°C / min;

[0058] (3) The reactor was cut into channel b, and 400 mL / min of C2H4 and 80 mL / min of H2 were introduced for bubbling at room temperature for 3 hours;

[0059] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 11.3 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscopy of the obtained iron-doped bamboo-like carbon nanotubes was as follows:

[0060] Figure 4 The obtained iron-doped bamboo-shaped carbon nanotubes have a length of 5 to 15 μm, an average outer diameter of about 200 nm, and an average thickness of about 15 nm.

[0061] Example 4

[0062] (1) Dissolve 2 g of ferrocene in 300 mL of acetone to form a solution and place it in a bubbler;

[0063] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0064] (3) The reactor was cut into channel b, and 400 mL / min of C2H4 and 80 mL / min of H2 were introduced for bubbling at room temperature for 3 hours;

[0065] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 7.6 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscopy of the obtained iron-doped bamboo-like carbon nanotubes was as follows: Figure 5 The obtained iron-doped bamboo-shaped carbon nanotubes are 3 to 10 μm long, with an average outer diameter of about 120 nm, an average thickness of about 13 nm, and a graphite layer with good crystallinity as the tube wall.

[0066] Comparative Example 1

[0067] (1) Dissolve 5 g of ferrocene in 200 mL of ethanol to form a solution;

[0068] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0069] (3) The reactor was cut into channel b, 120 mL / min of CH4 and 40 mL / min of H2 were introduced, and the solution prepared in step 1 (1) was introduced into the reactor at a rate of 0.1-1 mL / min using a flow pump for reaction for 3 h;

[0070] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 5.2 g of iron-doped bamboo-shaped carbon nanotubes. The scanning electron microscopy of the obtained carbon nanotubes was as follows: Figure 6The obtained carbon tubes are in the shape of curved tubes with uneven diameters of about 50 to 1000 nm. Compared with Example 1, it is proved that the bubbling method is helpful to form iron-doped bamboo-shaped carbon nanotubes.

[0071] Comparative Example 2

[0072] (5) Dissolve 5 g of ferrocene in 200 mL of ethanol to form a solution and place it in a bubbler;

[0073] (6) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0074] (7) The reactor was cut into channel b and CH4 was introduced at 120 mL / min for bubbling at room temperature for 3 h;

[0075] (8) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 4.2 g of carbon spheres with a diameter of about 400 nm. Figure 7 Compared with Example 1, it is proved that hydrogen is helpful to form iron-doped bamboo-shaped carbon nanotubes.

[0076] Comparative Example 3

[0077] (1) Dissolve 5 g of ferrocene in 200 mL of cyclohexane to form a solution and place it in a bubbler;

[0078] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0079] (3) The reactor was cut into channel b, and 120 mL / min CH4 and 40 mL / min H2 were introduced for bubbling at room temperature for 3 hours;

[0080] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 4.6 g of amorphous carbon. The transmission electron microscopy results are as follows: Figure 8 Compared with Example 1, it is proved that organic solvents such as ethanol are helpful to form iron-doped bamboo-like carbon nanotubes.

[0081] Comparative Example 4

[0082] (1) Dissolve 5 g of ferric nitrate in 200 mL of ethanol to form a solution and place it in a bubbler;

[0083] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0084] (3) The reactor was cut into channel b, and 120 mL / min CH4 and 40 mL / min H2 were introduced for bubbling at room temperature for 3 hours;

[0085] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 5.2 g of amorphous carbon. The transmission electron microscopy results are as follows: Fig. 9 Compared with Example 1, it is proved that transition metal organic complexes such as ferrocene are helpful to form iron-doped bamboo-shaped carbon nanotubes.

[0086] Comparative Example 5

[0087] (1) Dissolve 5 g of ethylferrocene in 200 mL of ethanol to form a solution and place it in a bubbler;

[0088] (2) Connect the reactor to passage a, introduce 150 mL / min of inert protective gas Ar, and raise the temperature to 900°C at a rate of 5°C / min;

[0089] (3) The reactor was cut into channel b, and 120 mL / min CH4 and 40 mL / min H2 were introduced for bubbling at room temperature for 3 hours;

[0090] (4) The reactor was cut into a channel, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The temperature was naturally lowered to obtain 4.6 g of iron-doped bamboo-shaped carbon nanotubes with a diameter of about 80 nm and a length of about 3-10 μm. The transmission electron microscopy results were as follows: Fig.10 Compared with Example 1, it is proved that other iron-based transition metal organic complexes such as ethylferrocene can also help to form iron-doped bamboo-shaped carbon nanotubes.

Claims

1. A method for continuously synthesizing iron-doped bamboo-shaped carbon nanotubes, characterized in that: The method comprises the following steps: (1) dissolving a transition metal precursor with an organic solvent; (2) introducing an inert protective gas into the reactor and simultaneously raising the temperature to the desired temperature; (3) stopping the inert protective gas, and continuously bubbling the gaseous carbon source and hydrogen through the organic solution prepared in step (1) in which the metal precursor is dissolved, so that the metal precursor enters the reactor along with the gaseous carbon source; the metal precursor is an iron-based transition metal organic complex; (4) Controlling specific gas flow rate, reaction time and reaction temperature; (5) After a specific reaction time, the introduction of the carbon source and hydrogen gases is stopped, and the inert protective gas is switched to obtain the iron-doped bamboo-shaped carbon nanotubes by natural cooling.

2. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The reactor is a tubular furnace, and the reaction tube used is made of quartz material with an outer diameter of 50 mm.

3. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The inert protective gas is any one of argon, helium and nitrogen.

4. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The flow rate of the inert protective gas is 100-4000 mL / min.

5. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The carbon source is a carbon-containing low-boiling-point organic matter selected from any one of methane, ethane, propane, ethylene and propylene.

6. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The flow rate of the gaseous carbon source is 80-4000 mL / min, the flow rate of hydrogen is 40-400 mL / min, and the reaction pressure is normal pressure.

7. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The organic solvent is selected from any one of methanol, ethanol, ethylene glycol, acetonitrile and acetone.

8. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The heating rate of the heating zone where the reaction occurs is 2-20°C / min, the reaction temperature is 600-1250°C, and an organic solution for dissolving the transition metal compound can be continuously added to achieve continuous production.

9. The method for synthesizing iron-doped bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The metal precursor is selected from triethylferrocene, ethylferrocene and ferrocene.

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