Regenerative supported metal catalyst for growing single-walled carbon nanotubes and preparation method thereof

Abstract

The invention belongs to the field of catalysts, and provides a regenerated supported metal catalyst for growing a single-walled carbon nanotube and a preparation method of the regenerated supported metal catalyst. Comprising the following steps: growing the SWNTs by taking gases such as CO, CH4, C2H2 and the like as carbon source gases through a CVD (Chemical Vapor Deposition) method on an oxide carrier loaded metal (such as Fe, Co and Ni) catalyst. And then dissolving the metal nanoparticles by using strong acid (such as hydrochloric acid), introducing an alkali precipitator into an acidic leaching solution, and carrying out coordination recombination on metal ions and the carrier magnesium oxide through pH regulation and control to realize reloading of the active components on the surface of the carrier. After the regenerated catalyst is calcined and activated, the SWNTs are grown again under the same CVD condition, and the high-purity SWNTs can be controllably prepared through multiple regeneration and growth processes. According to the scheme, the inherent limitation of single use of the supported metal catalyst is broken through, the yield of the SWNTs is improved, the discharge of acid waste liquid is effectively reduced, and the utilization rate of the metal catalyst is improved.

Description

Technical Field

[0001] The invention belongs to the field of catalysts and relates to a regenerative supported metal catalyst for growing single-walled carbon nanotubes and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Single-walled carbon nanotubes (SWNTs) are quasi-one-dimensional tubular nanomaterials formed by curling a single layer of graphene along a specific spiral angle through a chiral vector. SWNTs have excellent optical, electrical, mechanical and thermal properties, and have great application potential in biomedicine, electronic devices, composite materials, energy storage and other fields.

[0004] Currently, chemical vapor deposition (CVD) is a common method used in industry and laboratories to grow SWNTs on supported metal catalysts. However, in the post-processing process for purifying SWNTs, the metal nanoparticles and SWNTs must be separated through strong acid etching to obtain high-purity SWNTs. This process produces acidic wastewater containing high concentrations of metal cations, causing heavy metal pollution. Furthermore, each catalyst reuse doubles the consumption of metal precursors, resulting in a serious waste of metal resources and a significant increase in industrial production costs.

[0005] Research has disclosed a method and apparatus for producing carbon nanotubes. The method involves recovering the support material and catalyst separately through precipitation, regenerating the catalyst and support in multiple steps, and then re-impregnating them to produce a new catalyst. However, this regeneration method is relatively cumbersome. Furthermore, fresh catalyst and support are added during the regeneration step, increasing the cost of the regeneration process and altering the catalyst composition to some extent.

[0006] Therefore, the industry urgently needs to solve the inherent limitation of supported metal catalysts that they can only be used once, and achieve efficient regeneration of high-purity SWNTs. Summary of the Invention

[0007] To address the above-mentioned issues, the present invention provides a regenerative supported metal catalyst for growing single-walled carbon nanotubes and its preparation method. This invention utilizes an acid-washing-coprecipitation synergistic regeneration method to develop a cyclic regeneration process for the supported metal catalyst, which can then be reused for growing SWNTs. Specifically, a metal catalyst (such as Fe, Co, or Ni) supported on an oxide support is grown via CVD using gases such as CO, CH₄, or C₂H₂ as a carbon source. The metal nanoparticles are then dissolved using a strong acid (such as hydrochloric acid). An alkaline precipitant is introduced into the acidic leachate, and pH control is employed to induce coordination recombination between the metal ions and the magnesium oxide support, achieving re-loading of the active component onto the support surface. After calcination and activation, the regenerated catalyst is used for SWNT growth again under the same CVD conditions. Through multiple regeneration and growth processes, high-purity SWNTs can be prepared. This approach overcomes the inherent limitation of single-use supported metal catalysts, not only increasing SWNT yields but also effectively reducing the discharge of acidic wastewater and improving metal catalyst utilization.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes, comprising: The transition metal salt precursor and the oxide support are mixed uniformly in a solvent, dried, ground, and SWNTs are grown by CVD method to obtain a supported metal catalyst; The supported metal catalyst is dissolved in an acid solution, allowed to stand, the supernatant is filtered, the filtrate is collected, an alkaline solution is added until the metal cations in the solution are completely precipitated, the precipitate is collected, washed, dried, and calcined to obtain a regenerated metal catalyst; SWNTs were grown on regenerated metal catalysts using CVD method; The steps of regenerating the metal catalyst and growing SWNTs on the regenerated metal catalyst using a CVD method are repeated multiple times until the catalyst is unable to grow single-walled carbon nanotubes.

[0009] The second aspect of the present invention provides a regenerated supported metal catalyst for growing single-walled carbon nanotubes prepared by the above method.

[0010] The third aspect of the present invention provides applications of the above-mentioned regenerative supported metal catalyst in the fields of electronic devices, biomedicine, energy storage, and composite materials.

[0011] Beneficial effects of the present invention (1) Unlike the traditional process in which the supported metal catalyst is directly discarded after a single use, the present invention uses an impregnation method to regenerate the supported metal catalyst. Without introducing new carriers and metal catalysts, single-walled carbon nanotubes can be successfully regenerated and grown 3-4 times. At the same time, Raman spectroscopy analysis shows that the yield of regenerated single-walled carbon nanotubes is high and the defects are small.

[0012] (2) The preparation process of the present invention is simple, the required raw materials are easy to obtain, and the preparation time is short, which is conducive to mass production.

[0013] (3) The present invention proposes an acid washing-coprecipitation method for regenerating the metal catalyst, which can effectively reduce the discharge of acidic waste liquid and improve the utilization rate of the metal catalyst. After cyclic regeneration and growth, the yield of single-walled carbon nanotubes can be effectively increased.

[0014] (4) The present invention uses oxides such as MgO, SiO2, Al2O3 as catalyst carriers, which have the advantages of easy preparation, low price, good thermal stability, large specific surface area, etc. They can be removed by common reactions with hydrochloric acid or sodium hydroxide, and the regeneration cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0016] Figure 1 Schematic diagram of the reaction device used in the present invention; Figure 2 It is the experimental principle diagram of the present invention; Figure 3 is a Raman spectrum of SWNTs directly grown on the Fe / MgO catalyst in the present invention; Figure 4 This is a Raman spectrum of SWNTs grown again after the Fe / MgO catalyst is regenerated in the present invention. DETAILED DESCRIPTION

[0017] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0018] The present invention uses a high specific surface area oxide carrier (such as MgO, Al2O3, SiO2) to load a transition metal (Fe, Co, Ni, etc.) catalyst, uses CO, CH4, C2H2 and other gases as carbon source gases, grows SWNTs by CVD method, uses strong acid to dissolve the grown supported metal catalyst, and regenerates the metal catalyst by co-precipitation method, and uses the regenerated catalyst to grow SWNTs multiple times.

[0019] (1) Take an appropriate amount of transition metal salt precursor and oxide support and dissolve them in deionized water and stir them evenly. Place the above solution in an oven to dry, and then grind it in a mortar after drying.

[0020] (2) Place the catalyst in a quartz boat, which is placed in the middle of a dual-temperature zone slide-type CVD furnace. Connect the experimental device as required and set the furnace heating program to 20 o C / min, Ar was introduced at a flow rate of 300 sccm to remove the air in the device. After the furnace temperature reached the growth temperature, carbon source gas was introduced at a flow rate of 300 sccm for 30 min. After the reaction was completed, heating was stopped and Ar was introduced until the sample temperature reached room temperature. Ar was turned off and the sample was taken out.

[0021] (3) In a fume hood, place the sample in a 250 ml beaker and add an appropriate amount of hydrochloric acid to completely dissolve it. After standing for a period of time, take the supernatant and filter it. Add alkaline solution to the filtrate until the metal cations in the solution are completely precipitated. Filter the resulting precipitate and wash it to neutrality. After drying in an oven, calcine it in a muffle furnace to obtain a regenerated metal catalyst.

[0022] (4) Place the regenerated metal catalyst in a quartz boat, place the quartz boat in the middle of a dual-temperature zone slide-type CVD furnace, connect the experimental device as required, and set the furnace heating program to 20 o C / min, Ar was introduced at a flow rate of 300 sccm to remove the air in the device. After the sample temperature reached the growth temperature, carbon source gas was introduced at a flow rate of 300 sccm for 30 min. After the reaction was completed, Ar was introduced, heating was stopped and the temperature was lowered until the sample temperature reached room temperature. Ar was turned off and the sample was taken out.

[0023] (5) The sample is regenerated multiple times according to step (3) and grown according to step (4) until the catalyst is unable to grow single-walled carbon nanotubes.

[0024] Different metal catalysts can affect the growth quality and application performance of single-walled carbon nanotubes. Therefore, the present invention studies the types of transition metals, preferably at least one of Fe, Co, and Ni, to better grow single-walled carbon nanotubes.

[0025] The carrier can improve the dispersion of metal nanoparticles and provide sufficient space for the growth of SWNTs. Therefore, the present invention studies the type of carrier. Preferably, the oxide carrier is selected from at least one of MgO and Al2O3 to better promote the growth of SWNTs.

[0026] In some embodiments, the carbon source gas is selected from at least one of CO, CH4, and C2H2.

[0027] Strong acid can dissolve metal nanoparticles. In order to improve the recovery efficiency of metal nanoparticles, the present invention studies the type of acid. Preferably, the acid solution is a hydrochloric acid solution with a mass concentration of 36%-38% to better dissolve the metal nanoparticles.

[0028] The present invention introduces an alkaline precipitant into the acidic leachate, and through pH control, causes coordination recombination between metal ions and the magnesium oxide carrier, thereby achieving reloading of the active component onto the carrier surface. To this end, the present invention studies the type and dosage of the alkaline precipitant. Preferably, the alkaline solution is NaOH, KOH, or Na2CO3 solution with a molar concentration of 6-8 mol / L to improve the efficiency and effect of reloading the active component onto the carrier surface.

[0029] High-temperature calcination can thermally decompose impurities in the catalyst and thermally decompose the structure of the precipitate to obtain a metal catalyst. In order to improve the regeneration effect of the metal catalyst, the present invention studies the calcination conditions. Preferably, the calcination temperature is 600°C-800°C for 4-6 hours to improve the regeneration effect of the metal catalyst.

[0030] The temperature of the CVD method affects the deposition effect. Therefore, the present invention studies the temperature of the CVD method. Preferably, the temperature of the CVD method is 600°C-800°C, the flow rate of the carbon source gas is 300-400 sccm, and the reaction time is 20-30 min to better achieve the growth of single-walled carbon nanotubes.

[0031] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain rather than limit the present invention.

[0032] Example 1 (1) Take 0.4 g Fe(NO3)3·9H2O and 4 g MgO and dissolve them in deionized water and stir them evenly. The above solution is dried and ground after drying to obtain a supported metal catalyst.

[0033] (2) Place the supported metal catalyst in a quartz boat, which is placed in the middle of a dual-temperature zone slide-type CVD furnace, and connect the experimental device. Set the furnace heating program to 20 oC / min, Ar (argon) is introduced at a flow rate of 300 sccm to remove the air in the device. After the furnace temperature reaches the growth temperature (700 ℃), carbon source gas (CO) is introduced at a flow rate of 300 sccm for 30 minutes. After the reaction is completed, heating is stopped and Ar (argon) is introduced until the sample temperature reaches room temperature. Then Ar (argon) is turned off and the sample is taken out.

[0034] (3) In a fume hood, place the sample in a 250 mL beaker and add 12 mol / L hydrochloric acid to completely dissolve it. After standing for a period of time, take the supernatant and filter it. Add 6 mol / L alkaline solution (NaOH) to the filtrate until the metal cations in the solution are completely precipitated. Filter the resulting precipitate and wash it with deionized water until it is neutral. After drying, calcine it in a muffle furnace at 800 °C for 4 h to obtain a regenerated metal catalyst.

[0035] (4) Take the metal catalyst regenerated once above and place it in a quartz boat. Place the quartz boat in the middle of a dual-temperature zone slide-type CVD furnace and connect the experimental device. Set the furnace heating program to 20 o C / min, introduce Ar (argon) at a flow rate of 300sccm to remove the air in the device. After the sample temperature reaches the growth temperature (700℃), introduce carbon source gas (CO) at a flow rate of 300sccm for 30min. After the reaction is completed, introduce Ar (argon), stop heating and start cooling until the sample temperature reaches room temperature, turn off Ar (argon) and take out the sample.

[0036] (5) Take out the sample several times (the number of times that the catalyst can be successfully regenerated and grow single-walled carbon nanotubes is about 3-4 times). Regenerate according to step (3) and grow according to step (4) until the catalyst can no longer grow single-walled carbon nanotubes.

[0037] The Raman spectrum of SWNTs grown directly on Fe / MgO catalyst in Example 1 is shown in FIG. Figure 3 As shown in the Raman spectrum of SWNTs grown again after the Fe / MgO catalyst is regenerated in Example 1, Figure 4 As shown by Figure 3 and Figure 4 The comparison shows that the yield of regenerated single-walled carbon nanotubes is higher and the defects are smaller.

[0038] In this embodiment, the number of times that single-walled carbon nanotubes can be successfully regenerated and grown is 4 times.

[0039] Example 2 The difference from Example 1 is that the transition metal is Co, the oxide carrier is Al2O3, and the carbon source gas is CH4. The specific steps include: (1) Dissolve 0.4 g Co(NO3)2·6H2O and 4 g Al2O3 in deionized water and stir evenly. Dry the solution and grind it to obtain a supported metal catalyst.

[0040] (2) Place the supported metal catalyst in a quartz boat, which is placed in the middle of a dual-temperature zone slide-type CVD furnace, and connect the experimental device. Set the furnace heating program to 20 o C / min, Ar (argon) is introduced at a flow rate of 300 sccm to remove the air in the device. After the furnace temperature reaches the growth temperature (700 ℃), carbon source gas (CH4) is introduced at a flow rate of 300 sccm for 30 minutes. After the reaction is completed, heating is stopped and Ar (argon) is introduced until the sample temperature reaches room temperature. Then Ar (argon) is turned off and the sample is taken out.

[0041] (3) In a fume hood, place the sample in a 250 mL beaker and add 12 mol / L hydrochloric acid to completely dissolve it. After standing for a period of time, take the supernatant and filter it. Add 6 mol / L alkaline solution (NaOH) to the filtrate until the metal cations in the solution are completely precipitated. Filter the resulting precipitate and wash it with deionized water until it is neutral. After drying, calcine it in a muffle furnace at 800 °C for 4 h to obtain a regenerated metal catalyst.

[0042] (4) Take the metal catalyst regenerated once above and place it in a quartz boat. Place the quartz boat in the middle of a dual-temperature zone slide-type CVD furnace and connect the experimental device. Set the furnace heating program to 20 o C / min, introduce Ar (argon) at a flow rate of 300sccm to remove the air in the device. After the sample temperature reaches the growth temperature (700℃), introduce carbon source gas (CH4) at a flow rate of 300sccm for 30min. After the reaction is completed, introduce Ar (argon), stop heating and start cooling until the sample temperature reaches room temperature, turn off Ar (argon) and take out the sample.

[0043] (5) Take out the sample several times (the number of times that the catalyst can be successfully regenerated and grow single-walled carbon nanotubes is about 2-3 times). Regenerate according to step (3) and grow according to step (4) until the catalyst can no longer grow single-walled carbon nanotubes.

[0044] Example 3 The difference from Example 1 is that the growth temperature is 800° C. The specific steps include: (1) Take 0.4 g Fe(NO3)3·9H2O and 4 g MgO and dissolve them in deionized water and stir them evenly. The above solution is dried and ground after drying to obtain a supported metal catalyst.

[0045] (2) Place the supported metal catalyst in a quartz boat, which is placed in the middle of a dual-temperature zone slide-type CVD furnace, and connect the experimental device. Set the furnace heating program to 20 o C / min, Ar (argon) is introduced at a flow rate of 300 sccm to remove the air in the device. After the furnace temperature reaches the growth temperature (800 ℃), carbon source gas (CO) is introduced at a flow rate of 300 sccm for 30 minutes. After the reaction is completed, heating is stopped and Ar (argon) is introduced until the sample temperature reaches room temperature. Then Ar (argon) is turned off and the sample is taken out.

[0046] (3) In a fume hood, place the sample in a 250 mL beaker and add 12 mol / L hydrochloric acid to completely dissolve it. After standing for a period of time, take the supernatant and filter it. Add 6 mol / L alkaline solution (NaOH) to the filtrate until the metal cations in the solution are completely precipitated. Filter the resulting precipitate and wash it with deionized water until it is neutral. After drying, calcine it in a muffle furnace at 800 °C for 4 h to obtain a regenerated metal catalyst.

[0047] (4) Take the metal catalyst regenerated once above and place it in a quartz boat. Place the quartz boat in the middle of a dual-temperature zone slide-type CVD furnace and connect the experimental device. Set the furnace heating program to 20 o C / min, introduce Ar (argon) at a flow rate of 300sccm to remove the air in the device. After the sample temperature reaches the growth temperature (800℃), introduce carbon source gas (CO) at a flow rate of 300sccm for 30min. After the reaction is completed, introduce Ar (argon), stop heating and start cooling until the sample temperature reaches room temperature, turn off Ar (argon) and take out the sample.

[0048] (5) Take out the sample several times (the number of times that the catalyst can be successfully regenerated and grow single-walled carbon nanotubes is about 3-4 times). Regenerate according to step (3) and grow according to step (4) until the catalyst can no longer grow single-walled carbon nanotubes.

[0049] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes, characterized in that: include: The transition metal salt precursor and the oxide support are mixed uniformly in a solvent, dried, ground, and SWNTs are grown by CVD method to obtain a supported metal catalyst; The supported metal catalyst is dissolved in an acid solution, allowed to stand, the supernatant is filtered, the filtrate is collected, an alkaline solution is added until the metal cations in the solution are completely precipitated, the precipitate is collected, washed, dried, and calcined to obtain a regenerated metal catalyst; SWNTs were grown on regenerated metal catalysts using CVD method; The steps of regenerating the metal catalyst and growing SWNTs on the regenerated metal catalyst using a CVD method are repeated multiple times until the catalyst is unable to grow single-walled carbon nanotubes.

2. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The transition metal is selected from at least one of Fe, Co and Ni.

3. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The oxide carrier is selected from at least one of MgO, Al2O3, and SiO2.

4. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The carbon source gas is selected from at least one of CO, CH4, and C2H2.

5. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The acid solution is a hydrochloric acid solution with a mass concentration of 36%-38%.

6. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The alkaline solution is NaOH, KOH or Na2CO3 solution, and the molar concentration is 6-8 mol / L.

7. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The calcination temperature is 600°C-800°C, and the calcination time is 4-6 hours.

8. The method for preparing a regenerative supported metal catalyst for growing single-walled carbon nanotubes according to claim 1, wherein: The temperature of the CVD method is 600-800° C., the flow rate of the carbon source gas is 300-400 sccm, and the reaction time is 20-30 minutes.

9. A regenerated supported metal catalyst for growing single-walled carbon nanotubes prepared by the method according to any one of claims 1 to 8.

10. Use of the regenerated supported metal catalyst according to claim 9 in the fields of electronic devices, biomedicine, energy storage, and composite materials.

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