A method for continuously synthesizing iron-doped bamboo-like carbon nanotubes

Abstract

The application discloses a method for continuously synthesizing iron-doped bamboo-shaped carbon nanotubes and belongs to the technical field of nanometer material preparation. The method uses a transition metal compound as a catalyst precursor, uses a tubular furnace as a reactor, uses a gaseous carbon source to bubble an organic solution in which the transition metal compound is dissolved into a high-temperature reaction zone of the reactor, decomposes the transition metal compound into a catalytically active center at high temperature, and uses the active center to catalyze the gaseous carbon source to generate the iron-doped bamboo-shaped carbon nanotubes. The method realizes high gaseous carbon source utilization rate and regulates the tube length and the tube wall thickness of the iron-doped bamboo-shaped carbon nanotubes by controlling the gas flow rate or changing the type of the transition metal compound. The method realizes semi-continuous / continuous production by bubbling through the mechanical continuous automatic feeding method, further reduces the cost, and is beneficial to mass production. In conclusion, the application has the advantages of a short technological process, sustainable feeding for producing the carbon nanotubes, simple operation, cheap and easily available catalyst, high utilization rate, safe and non-toxic carbon source and the like, and has the industrial amplification preparation prospect.

Description

Technical Field

[0001] This invention relates to a method for preparing iron-doped bamboo-like carbon nanotubes, belonging to the field of nanomaterial preparation technology. Background Technology

[0002] In 1991, Sumio Iijima discovered the structure of tubular graphitic carbon. Like graphene, this tubular graphitic carbon consists of sp2-hybridized carbon atoms linked together to form a hexagonal network structure. However, unlike graphene, this tubular graphitic carbon, called carbon nanotubes, is a hollow structural material formed by seamlessly coiling sp2-hybridized carbon atoms at a specific helical angle. Based on the coiling method, carbon nanotubes can be classified into armrest-shaped carbon nanotubes, serrated carbon nanotubes, and hybrid carbon nanotubes. Based on the number of layers, carbon nanotubes can be classified into single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes (DWNTs), and multi-walled carbon nanotubes (MWNTs).

[0003] Carbon nanotubes possess a variety of properties due to their unique structure. For example, they exhibit ultra-high aspect ratio, high tensile strength, and high toughness, making them promising raw materials for the fabrication of ultra-strong fibers, space elevators, and highly elastic armor. Carbon nanotubes also possess excellent biocompatibility, giving them broad prospects in the biomedical field. The walls of carbon nanotubes have sp2 hybridized carbon atoms, unlike graphite. This is due to the curvature of the rolled-up carbon planes, which causes the carbon atoms to deviate from sp2 hybridization and tend towards sp3 hybridization. Electrons inside the tube transfer outwards, and this unique electronic structure inevitably possesses unique electronic conductivity, making them excellent electron transport carriers. Furthermore, the combination of carbon nanotubes with catalysts will produce remarkable electronic properties and catalytic performance.

[0004] Currently, methods for preparing carbon nanotubes include arc discharge, laser evaporation, and chemical vapor deposition. The DC arc discharge method utilizes high-temperature plasma generated by an arc between electrodes under inert gas protection to vaporize carbon on the anode carbon rod, forming carbon nanotubes which are then deposited on the cathode. However, this method easily produces large amounts of graphite fragments and amorphous carbon due to the extremely high temperature of the plasma generated by the electrode discharge, making separation and purification difficult. Laser evaporation uses a laser to evaporate a mixture of graphite and catalyst heated at high temperatures, which is then carried by a gas flow into a low-temperature region where single-walled carbon nanotubes are generated. However, this method requires high temperatures, consumes a lot of energy, and has a low yield. Chemical vapor deposition uses transition metal (Fe, Co, Ni) or their oxide nanoparticles as catalysts and carbon-containing gaseous compounds (methane, ethane, ethylene, etc.) as carbon sources. The gaseous carbon source is introduced at 600-1000℃, and the catalyst is introduced into the high-temperature region through some method (spraying, bubbling, etc.), thereby dehydrogenating the carbon source to form carbon nanotubes. This method has lower temperature requirements and easier product purification compared to arc discharge and laser evaporation methods. However, currently, when using chemical vapor deposition to produce bamboo-like carbon nanotubes, the transition metal catalyst needs to be replenished only after the temperature drops, a time-consuming and inefficient process. Therefore, we designed a device to avoid this intermittent operation. This device introduces the transition metal precursor dissolved in an organic solvent into a high-temperature reaction zone via a bubbler, allowing for continuous addition of the metal precursor and sustained production of bamboo-like carbon nanotubes. Compared to previously reported methods (such as directly pumping an organic solution containing ferrocene or similar complexes into the reactor using a flow pump), this method offers advantages such as high tunability of the gaseous carbon source and transition metal complexes, a wide range of preparation conditions, and significantly reduced energy and manpower consumption, making it promising for industrial-scale production. Summary of the Invention

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

[0006] To achieve the above objectives, the technical solution of this invention is as follows: An iron-based transition metal organometallic 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 organometallic complex, along with the organic solvent, enters the high-temperature reaction zone, reacting to generate iron-doped bamboo-like carbon nanotubes which are deposited on the quartz tube wall. After a specific reaction time, bubbling is stopped, the gaseous carbon source is switched to an inert gas, and the generated carbon nanotubes can be collected from the tube wall after natural cooling. The organic solution of the iron-based transition metal organometallic complex can be continuously introduced into the bubbler to achieve continuous production.

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

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

[0009] (2) Inert gas is introduced to remove air from the reactor, and a heating program is set to heat the reactor to the required temperature;

[0010] (3) Stop the inert gas flow and connect the gas path to the bubbler containing the solution prepared in step (1), and introduce the gas carbon source and hydrogen.

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

[0012] (5) After the reaction, stop the introduction of gaseous carbon source and hydrogen, switch to inert protective gas, and cool naturally to room temperature to obtain iron-doped bamboo-shaped carbon nanotubes.

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

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

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

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

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

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

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

[0020] The beneficial effects of this invention are as follows:

[0021] (1) This method can continuously add an organic solution containing iron-based transition metal organic complexes to the bubbler to achieve continuous production.

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

[0023] (3) The transition metal compounds used in this invention are inexpensive and readily available, thus reducing costs.

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

[0025] (5) The post-processing steps of this method are simple and do not require further acid washing to purify 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-like carbon nanotubes provided by this invention is simple, sustainable, environmentally friendly, and has high catalyst utilization efficiency, and has good prospects for industrial application. Attached Figure Description

[0028] Figure 1 This is a diagram of the reaction apparatus for the preparation method of iron-doped bamboo-like carbon nanotubes of the present invention;

[0029] Among them: 1. Bubbler containing an organic solution containing dissolved iron-based transition metal organic complexes; 2. Quartz reaction tube; 3. Heating zone; 4. Reaction zone; 5. Stopper.

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

[0031] Figure 3 Typical transmission electron microscope image of iron-doped bamboo-like carbon nanotubes obtained in Example 2;

[0032] Figure 4 This is a typical transmission electron microscope image of the iron-doped bamboo-like carbon nanotubes obtained in Example 3;

[0033] Figure 5 Typical transmission electron microscope image of iron-doped bamboo-like carbon nanotubes obtained in Example 4;

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

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

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

[0037] Figure 9 This is a typical transmission electron microscope image of the iron-doped bamboo-like carbon nanotubes obtained in Comparative Example 4.

[0038] Figure 10 This is a typical transmission electron microscope image of the iron-doped bamboo-like carbon nanotubes obtained in Comparative Example 5. Detailed Implementation

[0039] The entire process will be described in detail below through examples, but the scope of the claims of the present invention is not limited to 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 in which metal compounds are dissolved, 2. a quartz reaction tube, 3. a heating zone, 4. a reaction zone, 5. a stopper, a passage for introducing inert protective gas, and a passage for introducing raw material gas (gase carbon source and hydrogen).

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

[0042] The b-path is connected to a bubbler containing an organic solution in which a metal compound has been dissolved. The inlet pipe extends into the organic solution, and the outlet pipe is above the surface of the organic solution inside the bubbler.

[0043] Example 1

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

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

[0046] (3) Cut the reactor into the b channel and introduce CH4 at 120 mL / min and H2 at 40 mL / min, and bubble at room temperature for 3 hours;

[0047] (4) The reactor was switched to channel a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 4.4 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscope (TEM) images of the obtained iron-doped bamboo-like carbon nanotubes are shown below. Figure 2 As shown, the iron-doped bamboo-like carbon nanotubes obtained have a length of 3–10 μm and an average outer diameter of approximately 100 nm.

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

[0049] Example 2

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

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

[0052] (3) Cut the reactor into the b channel and introduce CH4 at 200 mL / min and H2 at 50 mL / min, and bubble at room temperature for 2 hours;

[0053] (4) The reactor was switched to channel a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 6.2 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscope (TEM) images of the obtained iron-doped bamboo-like carbon nanotubes are shown below. Figure 3 As shown. The iron-doped bamboo-like carbon nanotubes obtained have a length of 2–8 μm and an average outer diameter of approximately 80 nm.

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

[0055] Example 3

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

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

[0058] (3) Cut the reactor into the b channel and introduce 400 mL / min of C2H4 and 80 mL / min of H2, and bubble at room temperature for 3 hours;

[0059] (4) The reactor was switched to channel a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 11.3 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscope (TEM) images of the obtained iron-doped bamboo-like carbon nanotubes are shown below.

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

[0061] Example 4

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

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

[0064] (3) Cut the reactor into the b channel and introduce 400 mL / min of C2H4 and 80 mL / min of H2, and bubble at room temperature for 3 hours;

[0065] (4) The reactor was switched to channel a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 7.6 g of iron-doped bamboo-like carbon nanotubes. The transmission electron microscope (TEM) images of the obtained iron-doped bamboo-like carbon nanotubes are shown below. Figure 5 As shown, the iron-doped bamboo-like carbon nanotubes obtained have a length of 3–10 μm, an average outer diameter of about 120 nm, an average thickness of about 13 nm, and a graphite layer with good crystallinity on the tube wall.

[0066] Comparative Example 1

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

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

[0069] (3) Switch the reactor to the b channel, introduce CH4 at 120 mL / min and H2 at 40 mL / min, and use a flow pump to introduce the solution prepared in step (1) into the reactor at a rate of 0.1-1 mL / min for 3 hours;

[0070] (4) The reactor was switched to channel a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 5.2 g of iron-doped bamboo-like carbon nanotubes. The scanning electron microscope (SEM) images of the obtained carbon nanotubes are shown below. Figure 6As shown, the prepared carbon nanotubes are curved tubular in shape with uneven diameters, ranging from approximately 50 to 1000 nm. A comparison with Example 1 demonstrates that the bubbling method is beneficial for forming iron-doped bamboo-like carbon nanotubes.

[0071] Comparative Example 2

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

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

[0074] (7) Cut the reactor into the b channel and introduce CH4 at a rate of 120 mL / min. Bubble at room temperature for 3 hours.

[0075] (8) The reactor was switched to pathway a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The mixture was allowed to cool naturally, yielding 4.2 g of carbon spheres with a diameter of approximately 400 nm. (Scanning electron microscopy results are shown below.) Figure 7 As shown. A comparison with Example 1 demonstrates that hydrogen helps form iron-doped bamboo-like carbon nanotubes.

[0076] Comparative Example 3

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

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

[0079] (3) Cut the reactor into the b channel and introduce CH4 at 120 mL / min and H2 at 40 mL / min, and bubble at room temperature for 3 hours;

[0080] (4) The reactor was switched to pathway a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The mixture was allowed to cool naturally, yielding 4.6 g of amorphous carbon. Transmission electron microscopy (TEM) results are shown below. Figure 8 As shown in Example 1, organic solvents such as ethanol facilitate the formation of iron-doped bamboo-like carbon nanotubes.

[0081] Comparative Example 4

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

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

[0084] (3) Cut the reactor into the b channel and introduce CH4 at 120 mL / min and H2 at 40 mL / min, and bubble at room temperature for 3 hours;

[0085] (4) The reactor was switched to pathway a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The mixture was allowed to cool naturally, yielding 5.2 g of amorphous carbon. Transmission electron microscopy (TEM) results are shown below. Figure 9 As shown. A comparison with Example 1 demonstrates that transition metal-organic complexes such as ferrocene facilitate the formation of iron-doped bamboo-like carbon nanotubes.

[0086] Comparative Example 5

[0087] (1) Dissolve 5g of ethyl ferrocene in 200mL of ethanol to form a solution and put it into a bubbler;

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

[0089] (3) Cut the reactor into the b channel and introduce CH4 at 120 mL / min and H2 at 40 mL / min, and bubble at room temperature for 3 hours;

[0090] (4) The reactor was switched to pathway a, and an inert protective gas Ar was introduced at a flow rate of 150 mL / min. The reactor was allowed to cool naturally, yielding 4.6 g of iron-doped bamboo-like carbon nanotubes with a diameter of approximately 80 nm and a length of approximately 3-10 μm. Transmission electron microscopy (TEM) images are shown below. Figure 10 As shown in Example 1, comparison with Example 1 demonstrates that other iron-based transition metal organometallic complexes, such as ethyl ferrocene, also contribute to the formation of iron-doped bamboo-like carbon nanotubes.

Claims

1. A method for continuous synthesis of iron-doped bamboo-like carbon nanotubes, characterized in that, The method includes the following steps: (1) Dissolve the transition metal precursor in an organic solvent; (2) Inert protective gas is introduced into the reactor, and the temperature is simultaneously increased to the required temperature. (3) Stop the inert protective gas flow and continuously bubble the gaseous carbon source and hydrogen through the organic solution of the dissolved metal precursor prepared in step (1). The metal precursor enters the reactor along with the gaseous carbon source. The metal precursor is an iron-based transition metal organic complex. (4) Control the specific gas flow rate, reaction time, and reaction temperature; (5) After a specific reaction time, stop the introduction of carbon gas and hydrogen gas, switch to inert protective gas, and cool down naturally to obtain iron-doped bamboo-shaped carbon nanotubes. The flow rate of the inert protective gas is 100~4000 mL / min; The flow rate of the gaseous carbon source is 80~4000 mL / min, the flow rate of the hydrogen gas is 40-400 mL / min, and the reaction pressure is atmospheric pressure; The heating zone where the reaction occurs has a heating rate of 2~20 ℃ / min and a reaction temperature of 600~1250 ℃. An organic solution for dissolving transition metal compounds is continuously added to achieve continuous production. The metal precursor is selected from triethylferric, ethylferrocene, and ferrocene.

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

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

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

5. The method for synthesizing iron-doped bamboo-like 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.

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