A method for preparing single-walled carbon nanotubes based on fly ash

Abstract

This invention relates to the field of carbon nanotube preparation technology, and particularly to a method for preparing single-walled carbon nanotubes based on fly ash, comprising the following steps: calcining fly ash at 500–900°C for 4–8 hours to obtain modified fly ash; impregnating the modified fly ash in a transition metal salt solution, then drying and grinding to obtain catalyst powder; placing the catalyst powder in a reactor and performing chemical vapor deposition at 700–900°C for 20–50 minutes to obtain single-walled carbon nanotubes. This invention, by modifying fly ash and using it as a catalyst carrier to prepare single-walled carbon nanotubes, can achieve high-value utilization of fly ash. This invention uses inexpensive industrial fly ash as a substrate and inexpensive iron, cobalt, and nickel transition metal salts as metal sources, greatly reducing the production cost of single-walled carbon nanotubes and broadening the channels for their widespread application.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube preparation technology, and in particular to a method for preparing single-walled carbon nanotubes based on fly ash. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Single-walled carbon nanotubes (SUVs) exhibit broad application prospects in energy, battery, biosensing, and nanoelectronics due to their excellent acoustic, optical, electrical, thermal, and mechanical properties. Chemical vapor deposition (CVD) has become the preferred growth method due to its simple process and low cost. Currently, catalysts for preparing SUVs are mainly transition metal catalysts supported on substrates such as magnesium oxide, silica, and alumina.

[0004] Patent CN 116514110 A (publication date: August 1, 2023) discloses a method for preparing single-walled carbon nanotubes. The method involves uniformly mixing a salt solution containing a transition metal with an oxide support, wherein the oxide support is one or more of silicon dioxide, magnesium oxide, and aluminum oxide. One or more of chromium, molybdenum, and tungsten salts are added, followed by ultrasonication for 10-120 minutes, filtration, and calcination to obtain a catalyst. The catalyst is placed in a reactor, and by controlling the growth process parameters, high-purity single-walled carbon nanotubes can be grown in batches. However, the chromium, molybdenum, and tungsten salts introduced in this patent are relatively expensive. Therefore, how to achieve low-cost preparation of single-walled carbon nanotubes remains a problem that urgently needs to be solved. Summary of the Invention

[0005] In view of this, the present invention provides a method for preparing single-walled carbon nanotubes based on fly ash, using industrial solid waste fly ash as a catalyst carrier, which can achieve both low-cost preparation of single-walled carbon nanotubes and high-value utilization of industrial solid waste fly ash.

[0006] This invention provides a method for preparing single-walled carbon nanotubes based on fly ash, comprising the following steps:

[0007] Modified fly ash is obtained by calcining fly ash at 500-900℃ for 4-8 hours.

[0008] Modified fly ash was impregnated in a transition metal salt solution, then dried and ground to obtain catalyst powder;

[0009] The catalyst powder is placed in a reactor and subjected to chemical vapor deposition at 700–900°C for 20–50 minutes to obtain single-walled carbon nanotubes.

[0010] Preferably, the amount of catalyst powder used is 1 to 3 g.

[0011] Preferably, the mass ratio of the modified fly ash to the transition metal salt is 4:1 to 2.

[0012] Preferably, the transition metal in the transition metal salt is one or more of iron, cobalt, and nickel.

[0013] Preferably, the transition metal salt is selected from one of the transition metal nitrates, hydrochlorides, acetates, and sulfates.

[0014] Preferably, the solvent for the transition metal salt solution is selected from one or more of ethanol, deionized water, dichloromethane, acetone, and tetrahydrofuran.

[0015] Preferably, the soaking time is 3 to 6 hours, and the drying temperature is 80 to 130°C.

[0016] Preferably, in the chemical vapor deposition step, the carbon source is carbon monoxide, gas generated from the cracking of carbon-rich waste plastics, or hydrocarbon gas, wherein the hydrocarbon gas is selected from methane, ethylene, or propylene; and the flow rate of the carbon source is 250–350 sccm.

[0017] Preferably, before the chemical vapor deposition step, a heating step is further included in an argon atmosphere, with a heating rate of 15-25°C / min and an argon flow rate of 250-350 sccm.

[0018] Preferably, after the chemical vapor deposition step is completed, the process further includes a cooling step in an argon atmosphere, with an argon flow rate of 250–350 sccm.

[0019] Preferably, the diameter of the single-walled carbon nanotube is 1 to 1.2 nm.

[0020] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0021] (1) At present, the recycling and utilization of industrial fly ash is mainly concentrated in the construction industry such as cement and concrete. It has low added value and causes secondary pollution. The comprehensive utilization rate is less than 70%. However, this invention modifies fly ash and uses it as a catalyst carrier to prepare single-walled carbon nanotubes, which can realize the high added value utilization of fly ash.

[0022] (2) In this invention, inexpensive industrial fly ash is used as the base and inexpensive iron, cobalt and nickel transition metal salts are used as the metal source, which greatly reduces the production cost of single-walled carbon nanotubes and broadens the channels for the widespread application of single-walled carbon nanotubes in the future.

[0023] (3) The preparation method of the present invention is simple to operate, has a short reaction time, is economical and efficient, and is conducive to the large-scale production of single-walled carbon nanotubes. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0025] Figure 1 The Raman spectrum of the single-walled carbon nanotubes prepared in Example 1 of this invention;

[0026] Figure 2 This is a transmission electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of the present invention;

[0027] Figure 3 This is a scanning electron microscope image of the single-walled carbon nanotubes prepared in Example 1 of the present invention;

[0028] Figure 4 The Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 1 of this invention is shown below.

[0029] Figure 5 The Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 2 of this invention is shown below.

[0030] Figure 6 The Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 3 of this invention is shown.

[0031] Figure 7 This is the Raman spectrum of the single-walled carbon nanotubes prepared in Comparative Example 4 of this invention. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] As noted in the background section, existing methods for preparing single-walled carbon nanotubes are generally costly. Therefore, this invention provides a method for preparing single-walled carbon nanotubes based on fly ash, comprising the following steps:

[0034] Modified fly ash is obtained by calcining fly ash at 500-900℃ for 4-8 hours.

[0035] Modified fly ash was impregnated in a transition metal salt solution, then dried and ground to obtain catalyst powder;

[0036] The catalyst powder is placed in a reactor and subjected to chemical vapor deposition at 700–900°C for 20–50 minutes to obtain single-walled carbon nanotubes.

[0037] Fly ash's main components are silicon dioxide and aluminum oxide. High-temperature treatment aims to disrupt its glassy network structure, making its surface more porous and increasing its surface area. The increased temperature causes surface moisture to evaporate, exposing more active sites and thus enhancing its adsorption capacity. The inventors discovered that fly ash, after being calcined at 500-900℃ for 4-8 hours, can serve as a catalyst substrate for growing high-purity single-walled carbon nanotubes, while fly ash without this high-temperature treatment grows multi-walled carbon nanotubes.

[0038] This invention only requires uniformly mixing modified fly ash and transition metal salts to obtain catalyst powder. During chemical vapor deposition, the transition metal salts are reduced to metal nanoparticles, while single-walled carbon nanotubes grow under the action of a carbon source. Single-walled carbon nanotube growth can be achieved without prior calcination and reduction of the transition metal salts, thus shortening preparation time and saving energy. Silica and alumina in fly ash are the active components for supporting the growth of single-walled carbon nanotubes. After the transition metal salts are impregnated on their surface, they are reduced to metal nanoparticles under high temperature. The carbon source then decomposes, growing single-walled carbon nanotubes on their surface. Fly ash is inexpensive and readily available, significantly reducing the production cost of single-walled carbon nanotubes and achieving high-value utilization of industrial waste.

[0039] The catalyst powder used in this invention is 1–3 g. If the amount is too large, the carbon source cannot be fully covered by decomposition, resulting in uneven distribution of the grown single-walled carbon nanotubes.

[0040] The mass ratio of modified fly ash to transition metal salt in this invention is 4:1 to 2. This suitable mass ratio ensures that the transition metal salt can be uniformly distributed on the modified fly ash carrier during reduction.

[0041] This invention does not impose any special restrictions on the transition metals in the transition metal salts. Commonly used transition metals in the preparation of single-walled carbon nanotubes in this field can be used. This invention preferably uses one or more of iron, cobalt, and nickel, because the above-mentioned transition metals have relatively good catalytic performance and the raw materials are readily available and inexpensive.

[0042] The transition metal salt of the present invention is selected from one of the nitrates, hydrochlorides, acetates and sulfates of transition metals.

[0043] The present invention does not impose any special restrictions on the solvent of the transition metal salt solution, as long as it can dissolve the selected transition metal salt and is easy to remove. In order to ensure that the modified fly ash and the transition metal salt can be fully and uniformly mixed, the present invention preferably selects one or more of ethanol, deionized water, dichloromethane, acetone, and tetrahydrofuran.

[0044] The preferred impregnation time of the present invention is 3 to 6 hours, because the modified fly ash has a porous structure, and sufficient impregnation time can ensure that the transition metal salt is fully and uniformly loaded inside and on the surface of the fly ash.

[0045] The drying temperature of this invention is preferably 80-130°C, and is appropriately selected based on the principle of removing solvent without affecting catalyst performance. This invention does not impose any special restrictions on this.

[0046] In the chemical vapor deposition step of this invention, the carbon source is carbon monoxide, gas generated from the pyrolysis of carbon-rich waste plastics, or hydrocarbon gas, wherein the hydrocarbon gas is selected from methane, ethylene, or propylene; the flow rate of the carbon source is preferably 250–350 sccm. When gas generated from the pyrolysis of carbon-rich waste plastics is used as the carbon source, the utilization rate of waste resources can be further improved.

[0047] Before the chemical vapor deposition step, the present invention also includes a heating step under an argon atmosphere, with a heating rate of 15-25°C / min and an argon flow rate of 250-350 sccm. This is to remove air and to avoid reactions that occur under heating conditions, which would result in lower purity of the grown single-walled carbon nanotubes.

[0048] After the chemical vapor deposition step, the present invention further includes a cooling step in an argon atmosphere with an argon flow rate of 250-350 sccm to ensure that single-walled carbon nanotubes do not grow under cooling conditions, thus ensuring that the prepared single-walled carbon nanotubes have high purity.

[0049] The single-walled carbon nanotubes prepared by the above method have a diameter of 1 to 1.2 nm and a narrow diameter distribution. Moreover, the above method is low in cost and simple in steps, and has good prospects for industrial application.

[0050] The technical solution of the present invention will be further described below with reference to specific embodiments. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased on the market.

[0051] Example 1

[0052] This embodiment provides a method for preparing single-walled carbon nanotubes based on fly ash, including the following steps:

[0053] (1) Modify industrial fly ash by calcining it in a muffle furnace at 700°C for 6 hours;

[0054] (2) Dissolve 4g of modified fly ash and 1g of cobalt nitrate in 150mL of ethanol, mix evenly, impregnate for 4 hours, dry the above solution in an oven at 120℃ and grind it into powder to obtain the catalyst.

[0055] (3) Take 2g of catalyst powder and put it into a quartz boat. Place the quartz boat in the middle of a high-temperature vacuum sliding tube furnace, connect the gas path, start the device, set the furnace temperature to 20℃ / min, and introduce Ar at a flow rate of 300sccm to remove the air in the device until the temperature reaches 800℃. Pull the furnace to the quartz tube on the side where the catalyst powder is placed and heat it. After the furnace temperature reaches 800℃ and stabilizes, turn off Ar and introduce carbon monoxide at a flow rate of 300sccm. After maintaining the reaction temperature and gas flow rate for 35 minutes, turn off carbon monoxide first, introduce Ar, pull the furnace to the other side, stop the heating program and start cooling until the temperature on the side where the sample is placed reaches room temperature. Then turn off Ar and finally take out the quartz boat to obtain the single-walled carbon nanotube sample.

[0056] Figure 1 The Raman spectrum of the single-walled carbon nanotubes prepared in this embodiment shows that at 166 cm⁻¹... -1 The presence of the characteristic RBM peak of single-walled carbon nanotubes indicates the formation of single-walled carbon nanotubes, while I G / I D The value was 28.17, indicating that the prepared single-walled carbon nanotubes had few defects and were of high quality.

[0057] Figure 2 The image shows a transmission electron microscope (TEM) image of the single-walled carbon nanotubes prepared in this embodiment. As can be seen from the image, the diameter of the single-walled carbon nanotubes is about 1.1 nm.

[0058] Figure 3 The image shows a scanning electron microscope (SEM) image of the single-walled carbon nanotubes prepared in this embodiment. As can be seen from the image, the prepared single-walled carbon nanotubes have a high density and uniform distribution, which clearly demonstrates the successful growth of single-walled carbon nanotubes.

[0059] Example 2

[0060] The difference from Example 1 is that industrial fly ash was modified by calcining it at 650°C for 8 hours in a muffle furnace.

[0061] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.04 nm.

[0062] Example 3

[0063] The difference compared to Example 1 is that industrial fly ash was modified by calcining it at 900°C for 6 hours in a muffle furnace.

[0064] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.15 nm.

[0065] Example 4

[0066] The difference compared to Example 1 is that nickel nitrate is used instead of cobalt nitrate.

[0067] The single-walled carbon nanotubes prepared in this embodiment have a diameter of 1.2 nm.

[0068] Example 5

[0069] The difference compared to Example 1 is that cobalt nitrate is replaced with ferric nitrate.

[0070] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.15 nm.

[0071] Example 6

[0072] The difference from Example 1 is that methane is used instead of carbon monoxide.

[0073] The single-walled carbon nanotubes prepared in this embodiment have a diameter of 1.2 nm.

[0074] Example 7

[0075] Compared with Example 1, the difference is that carbon monoxide was passed through at a flow rate of 320 sccm, and the reaction temperature and gas flow rate were maintained for 25 minutes.

[0076] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.1 nm.

[0077] Example 8

[0078] The difference compared to Example 1 is that the furnace temperature (chemical vapor deposition temperature) is 700°C.

[0079] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.05 nm.

[0080] Example 9

[0081] The difference compared to Example 1 is that the furnace temperature (chemical vapor deposition temperature) is 900°C.

[0082] The diameter of the single-walled carbon nanotubes prepared in this embodiment is 1.15 nm.

[0083] Comparative Example 1

[0084] The difference compared to Example 1 is that the industrial fly ash was not modified by high-temperature calcination.

[0085] Figure 4The Raman spectrum of the carbon nanotubes prepared in Comparative Example 1 shows that no characteristic RBM peak of single-walled carbon nanotubes appears, indicating that high-quality single-walled carbon nanotubes cannot be grown from fly ash that has not been modified by high-temperature calcination.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that industrial fly ash was modified by calcining it at 700°C for 3 hours in a muffle furnace.

[0088] Figure 5 The Raman spectrum of the carbon nanotubes prepared in Comparative Example 2 shows that the characteristic RBM peak of single-walled carbon nanotubes did not appear in the Raman spectrum. The calcination time was less than 6 hours, the calcination was insufficient, the fly ash modification was unsuccessful, and high-quality single-walled carbon nanotubes could not be grown.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that industrial fly ash was modified by calcining it at 400°C for 6 hours in a muffle furnace.

[0091] Figure 6 The Raman spectrum of the carbon nanotubes prepared in Comparative Example 3 shows that no characteristic RBM peak of single-walled carbon nanotubes appeared. The calcination temperature was too low, which prevented the glass network structure on the surface of fly ash from being destroyed and the active sites from being exposed, thus making it impossible to grow high-quality single-walled carbon nanotubes.

[0092] Comparative Example 4

[0093] Compared with Example 1, the difference is that industrial fly ash was modified by calcining it in a muffle furnace at 1000°C for 6 hours.

[0094] Figure 7 The Raman spectrum of the carbon nanotubes prepared in Comparative Example 4 shows that no characteristic RBM peak of single-walled carbon nanotubes appeared. The calcination temperature was too high, which caused the pores of the fly ash to collapse or become blocked, the active components to sinter, the surface area to decrease, the adsorption performance of the fly ash to be reduced, and high-quality single-walled carbon nanotubes could not be grown.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes based on fly ash, characterized in that, Includes the following steps: Modified fly ash is obtained by calcining fly ash at 500-900℃ for 4-8 hours. Modified fly ash was impregnated in a transition metal salt solution, then dried and ground to obtain catalyst powder; The catalyst powder is placed in a reactor and subjected to chemical vapor deposition at 700–900°C for 20–50 minutes to obtain single-walled carbon nanotubes.

2. The method as described in claim 1, characterized in that, The amount of catalyst powder used is 1-3g.

3. The method as described in claim 1, characterized in that, The mass ratio of the modified fly ash to the transition metal salt is 4:1 to 2.

4. The method as described in claim 1, characterized in that, The transition metal salt is selected from one of the nitrates, hydrochlorides, acetates, and sulfates of transition metals.

5. The method as described in claim 1, characterized in that, The solvent for the transition metal salt solution is selected from one or more of ethanol, deionized water, dichloromethane, acetone, and tetrahydrofuran.

6. The method as described in claim 1, characterized in that, The soaking time is 3 to 6 hours, and the drying temperature is 80 to 130°C.

7. The method as described in claim 1, characterized in that, In the chemical vapor deposition step, the carbon source is carbon monoxide, gas generated from the cracking of carbon-rich waste plastics, or hydrocarbon gas, wherein the hydrocarbon gas is selected from methane, ethylene, or propylene; the flow rate of the carbon source is 250–350 sccm.

8. The method as described in claim 1, characterized in that, Before the chemical vapor deposition step, a heating step is also included in the argon atmosphere, with a heating rate of 15-25°C / min and an argon flow rate of 250-350 sccm.

9. The method as described in claim 8, characterized in that, After the chemical vapor deposition step is completed, a cooling step is also included in an argon atmosphere with an argon flow rate of 250–350 sccm.

10. The method as described in claim 1, characterized in that, The diameter of the single-walled carbon nanotubes is 1 to 1.2 nm.

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