Narrow chirality distribution single-walled carbon nanotubes and preparation method thereof

Abstract

The present invention belongs to the field of single-walled carbon nanotube preparation, and relates to a single-walled carbon nanotube with a narrow chiral distribution and a preparation method thereof. First, a cobalt-palladium bimetallic layered silicate catalyst is prepared, and then the cobalt-palladium bimetallic layered silicate catalyst is used. With CoPd as the catalytic metal and layered silicate as the growth substrate, the preparation of small-diameter SWNTs with a narrow chiral distribution is achieved at a specific temperature using the atmospheric pressure CVD method. The present invention uses CO as a carbon source, splits out carbon atoms while reducing the metal, and the size of the Co metal nanoparticles reduced from the carrier is small, which is conducive to the enrichment preparation of narrow-chiral SWNTs; layered silicate is used as the catalyst carrier, which has the advantages of easy preparation, good thermal stability, high metal dispersion, etc., and can provide an excellent growth environment for the narrow-chiral growth of SWNTs.

Description

Technical Field

[0001] The present invention belongs to the field of single-walled carbon nanotube preparation, and particularly relates to a single-walled carbon nanotube with a narrow chiral distribution and a preparation method thereof. Background Art

[0002] Single-walled carbon nanotubes (SWNTs) have become an increasingly important component in high-performance nanodevices due to their extraordinary electronic and mechanical properties. For specific applications, SWNTs with well-defined chirality are highly desirable. Based on the efforts of the past two decades, it has been recognized that combining direct synthesis with post-growth sorting is a reliable and effective method for producing pure chiral SWNTs. To improve separation efficiency and reduce processing costs, the starting SWNTs material must have the narrowest possible chiral distribution.

[0003] The chemical vapor deposition (CVD) synthesis method based on solid-supported catalysts has become an attractive method due to its low cost, good controllability, and potential for large-scale synthesis with controlled structures. Researchers have developed various supported catalysts for growing SWNTs with a narrow chiral distribution. In heterogeneous catalysts, the active components are generally composed of Fe, Co, or Ni, which are low-cost and have high SWNTs growth efficiency. However, due to the sintering of metal particles at high reaction temperatures, it is challenging to synthesize SWNTs with a narrow chiral distribution. Therefore, to limit the coalescence of the reducing metal catalyst during the CVD process, there is an urgent need to design a supported catalyst with strong metal-support interaction and high metal dispersion for preparing SWNTs with a narrow chiral distribution. Summary of the Invention

[0004] The purpose of the present invention is to solve the above problems existing in the prior art, and propose a single-walled carbon nanotube with a narrow chiral distribution and a preparation method thereof. The preparation method uses CO as the carbon source for growing SWNTs, Ar as the protective gas, CoPd and layered carbonate as the catalyst and growth substrate respectively, and realizes the preparation of small-diameter SWNTs with a narrow chiral distribution at a specific temperature using atmospheric pressure CVD method.

[0005] The technical solution of the present invention is as follows:

[0006] A preparation method of a single-walled carbon nanotube with a narrow chiral distribution, using a cobalt-palladium double-metal layered silicate catalyst, with CoPd as the catalytic metal and layered silicate as the growth substrate, to prepare SWNTs with a narrow chiral distribution; the steps include:

[0007] (1) Dissolve cobalt nitrate hexahydrate and colloidal silica with a mass ratio of 1∶(0.5 - 2) in deionized water. At the same time, add an appropriate amount of urea, stir evenly, and heat to 170 - 200 °C for 20 - 30 h;

[0008] In step (1), the mass ratio of cobalt nitrate hexahydrate to colloidal silica is 1∶(0.5 - 2). For example, it can be 1∶0.5, 1∶0.8, 1∶1, 1∶1.2, 1∶1.5, 1∶1.8, or 1∶2, etc., but not limited to the listed ratios. Other unlisted ratios within this range are equally applicable;

[0009] The heating temperature is 170 - 200 °C. For example, it can be 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, or 200 °C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable;

[0010] The reaction time is 20 - 30 h. For example, it can be 20 h, 22 h, 24 h, 25 h, 27 h, 28 h, or 30 h, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0011] (2) Wash, dry, and grind the product of step (1) into powder, and calcine it at 700 - 900 °C for 3 - 5 h to obtain a single - metal cobalt catalyst;

[0012] The heating temperature in step (2) is 700 - 900 °C. For example, it can be 700 °C, 750 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 850 °C, or 900 °C, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable;

[0013] The calcination time is 3 - 5 h. For example, it can be calcined for 3 h, 3.2 h, 3.5 h, 3.8 h, 3.9 h, 4 h, 4.1 h, 4.2 h, 4.5 h, or 5 h, etc., but not limited to the listed values. Other unlisted values within this range are equally applicable.

[0014] (3) Mix the single - metal cobalt catalyst and palladium chloride according to the mass ratio of cobalt atoms to palladium atoms of (90 - 110)∶1, impregnate to obtain a CoPd bimetallic layered silicate catalyst. Dry the catalyst and grind it into fine powder, and then calcine it at 300 - 500 °C for 3 - 5 h;

[0015] The mass ratio in step (3) is (90 - 110)∶1. For example, it can be 90∶1, 95∶1, 98∶1, 99∶1, 100∶1, 101∶1, 102∶1, 105∶1, or 110∶1, etc., but not limited to the listed ratios. Other unlisted ratios within this range are equally applicable;

[0016] The temperature is 300 to 500 °C. For example, it can be 300 °C, 350 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 450 °C or 500 °C, etc., but it is not limited to the listed values, and other unlisted values within this range are equally applicable;

[0017] Calcination is carried out for 3 to 5 h. For example, it can be calcined for 3 h, 3.2 h, 3.5 h, 3.8 h, 3.9 h, 4 h, 4.1 h, 4.2 h, 4.5 h or 5 h, etc., but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0018] (4) Place the catalyst calcined in step (3) into a dual-temperature zone sliding rail type CVD furnace. Under an Ar atmosphere, heat it up to 600 to 850 °C, and introduce CO at this temperature to react for 20 to 40 min to obtain SWNTs with a narrow chiral distribution.

[0019] The temperature in step (4) is 600 to 850 °C. For example, it can be 600 °C, 610 °C, 620 °C, 650 °C, 680 °C, 700 °C, 730 °C, 750 °C, 760 °C, 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, 840 °C or 850 °C, etc., but it is not limited to the listed values, and other unlisted values within this range are equally applicable;

[0020] The reaction time is 20 to 40 min. For example, it can be 20 min, 25 min, 28 min, 29 min, 30 min, 31 min, 32 min, 35 min or 40 min, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0021] Compared with traditional catalysts, structural catalysts are good carriers for preparing SWNTs due to their excellent metal dispersion, strong metal-support interaction and adjustable catalytic activity. Among them, layered silicates are a class of minerals containing ideal continuous octahedral and tetrahedral sheets, and layered silicates containing transition metals show excellent catalytic performance in many fields. Under experimental conditions, high metal dispersion and strong metal-support interaction produce metal particles with uniform diameters. It is found through experiments that cobalt layered silicate catalysts can grow SWNTs with a relatively narrow chiral distribution at about 600 to 850 °C. In addition, by adding palladium to form a bimetallic catalyst system, the reduction temperature of metal particles is reduced, the catalytic activity of the catalyst is improved, and the selectivity of the layered silicate catalyst for the chirality of SWNTs is further improved.

[0022] Furthermore, in the step (1), the mass ratio of Co(NO3)2·6H2O to colloidal silica is 1:1.

[0023] The purpose of adding urea in step (1) is to provide an alkaline environment for the hydrothermal reaction. The addition amount of urea can be controlled to be 2 to 3 times the addition amount of Co(NO3)2·6H2O, preferably 2.5 times the mass of the added Co(NO3)2·6H2O.

[0024] Further, in the step (1), the heating temperature is raised to 190 °C and maintained for 24 h.

[0025] Further, in the step (2), washing is carried out by rinsing with water and ethanol.

[0026] Further, in the step (2), calcination is carried out at 800 °C for 4 h.

[0027] Further, in the step (3), the cobalt monometallic catalyst and palladium chloride are mixed according to the mass ratio of cobalt atoms to palladium atoms of 100:1.

[0028] Further, in the step (3), calcination is carried out at 400 °C for 4 h.

[0029] Further, in the step (4), the heating rate is 20 °C / min. When the temperature reaches 600 °C, CO is introduced and the reaction is carried out for 30 min.

[0030] Further, in the step (4), after the reaction is completed, Ar is introduced, heating is stopped and cooling starts. After cooling to room temperature, Ar is turned off, and SWNTs with a narrow chiral distribution are obtained.

[0031] The present invention also protects the SWNTs with a narrow chiral distribution prepared by the above preparation method.

[0032] Advantages of the present invention:

[0033] The present invention prepares a CoPd bimetallic layered silicate catalyst by a hydrothermal method. The growth process is carried out under atmospheric pressure conditions. The catalyst preparation process is simple, the required raw materials are easy to obtain, and the preparation time is short, which is beneficial to realizing the large-scale production of the catalyst;

[0034] The present invention uses CO as a carbon source, splits out carbon atoms while reducing metals, and the size of the Co metal nanoparticles reduced from the support is small, which is beneficial to realizing the enrichment preparation of narrow chiral SWNTs; at the same time, it also expands the application of layered silicates in catalytic synthesis;

[0035] The present invention uses a cobalt-palladium bimetallic layered silicate catalyst, with CoPd as the catalytic metal and layered silicate as the catalyst support. It has the advantages of easy preparation, good thermal stability, high metal dispersion, etc., and can provide an excellent growth environment for the narrow chiral growth of SWNTs. Description of the Drawings

[0036] Figure 1 X-ray diffraction pattern of the CoPd layered silicate catalyst prepared in Example 1 of the present invention;

[0037] Figure 2 Raman spectrum of the product prepared in Example 1 of the present invention;

[0038] Figure 3 Ultraviolet-visible-near-infrared absorption spectrum of the product prepared in Example 1 of the present invention;

[0039] Figure 4 Raman spectrum of the product prepared in Example 2 of the present invention;

[0040] Figure 5 Raman spectrum of the product prepared in Example 3 of the present invention;

[0041] Figure 6 Raman spectrum of the product synthesized at 600 °C of the CoPd porous silica catalyst of Comparative Example 1;

[0042] Figure 7 Raman spectrum of the product synthesized at 750 °C of the CoPd porous silica catalyst of Comparative Example 2;

[0043] Figure 8 Raman spectrum of the product synthesized at 850 °C of the CoPd porous silica catalyst of Comparative Example 3. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] To further understand the present invention, the present invention will be further described in conjunction with the accompanying drawings and embodiments.

[0046] The present invention provides a method for preparing single-walled carbon nanotubes with a narrow chiral distribution, comprising the following steps:

[0047] (1) Take 1.97 g of Co(NO3)2·6H2O, 4.0 - 6.0 g of urea, and 1 - 2 mL of colloidal silica (LUDOX, 50 wt%), dissolve them in deionized water and stir evenly. Place the evenly stirred solution in a hydrothermal reaction vessel, and heat it to 170 - 200 °C for 20 - 30 h;

[0048] (2) Rinse the product of step (1) with water and ethanol, dry it, grind it in a mortar, place the ground powder in a muffle furnace, and calcine it at 700 - 900 °C for 3 - 5 h to obtain a single-metal cobalt catalyst;

[0049] (3) Mix the single-metal cobalt catalyst with 10 - 12 mg of PdCl2 in deionized water. After impregnation, a CoPd bimetallic layered silicate catalyst is obtained. Grind the dried catalyst into fine powder, and then calcine it in a muffle furnace at 300 - 500 °C for 3 - 5 h;

[0050] (4) Take the catalyst calcined in step (3) and place it in a quartz boat. Put the quartz boat in the middle of a dual-temperature zone sliding rail type CVD furnace. Connect the experimental device as required. Set the furnace heating program to 20 °C / min. Pass Ar into the device at a flow rate of 300 sccm to expel the air in the device. After the sample temperature reaches 600 - 850 °C, pass CO into it at a flow rate of 300 sccm for 20 - 40 min. After the reaction ends, pass Ar into it, stop heating and start cooling until the sample temperature reaches room temperature, then turn off Ar, and finally take out the sample, which is the SWNTs with a narrow chiral distribution.

[0051] Example 1

[0052] This example provides a method for preparing single-walled carbon nanotubes with a narrow chiral distribution, including the following steps:

[0053] (1) Take 1.97 g of Co(NO3)2·6H2O, 5.0 g of urea, and 1.4 mL of colloidal silica (LUDOX, 50 wt%), dissolve them in 50 mL of deionized water and stir evenly. Place the evenly stirred solution in a hydrothermal reaction vessel and heat it to 190 °C for 24 h;

[0054] (2) Rinse the product of step (1) with water and ethanol, dry it, grind it in a mortar, place the ground powder in a muffle furnace, and calcine it at 800 °C for 4 h to obtain a single-metal cobalt catalyst;

[0055] (3) Mix the single-metal cobalt catalyst with 11 mg of PdCl2 in 50 mL of deionized water. After impregnation, a CoPd bimetallic layered silicate catalyst is obtained. Grind the dried catalyst into fine powder, and then calcine it in a muffle furnace at 400 °C for 4 h;

[0056] (4) Place the catalyst calcined in step (3) in a quartz boat, place the quartz boat in the middle of a dual-temperature-zone sliding-rail CVD furnace, connect the experimental device as required, set the furnace heating program to 20 °C / min, introduce Ar at a flow rate of 300 sccm to discharge the air in the device. After the sample temperature reaches 600 °C, introduce CO at a flow rate of 300 sccm for 30 min. After the reaction ends, introduce Ar, stop heating and start cooling until the sample temperature reaches room temperature, close Ar, and finally take out the sample, which is the SWNTs with a narrow chiral distribution.

[0057] Figure 1 XRD pattern of the CoPd layered silicate catalyst prepared in Example 1; Figure 2 Raman spectrum of the product; Figure 3 UV-Vis-NIR absorption spectrum of the product.

[0058] Example 2

[0059] This example provides a method for preparing single-walled carbon nanotubes with a narrow chiral distribution, including the following steps:

[0060] (1) Take 1.97 g of Co(NO3)2·6H2O, 4.0 g of urea and 1 mL of colloidal silica (LUDOX, 50 wt%), dissolve them in deionized water and stir evenly. Place the evenly stirred solution in a hydrothermal reaction vessel and heat it to 170 °C for 30 h.

[0061] (2) Rinse the product of step (1) with water and ethanol, dry it and grind it in a mortar. Place the ground powder in a muffle furnace and calcine it at 700 °C for 5 h to obtain a single-metal cobalt catalyst.

[0062] (3) Mix the single-metal cobalt catalyst with 10 mg of PdCl2 in deionized water. After impregnation, obtain a CoPd bimetallic layered silicate catalyst. Grind the dried catalyst into fine powder, and then calcine it in a muffle furnace at 500 °C for 3 h.

[0063] (4) Place the catalyst calcined in step (3) in a quartz boat, place the quartz boat in the middle of a dual-temperature-zone sliding-rail CVD furnace, connect the experimental device as required, set the furnace heating program to 20 °C / min, introduce Ar at a flow rate of 300 sccm to discharge the air in the device. After the sample temperature reaches 750 °C, introduce CO at a flow rate of 300 sccm for 40 min. After the reaction ends, introduce Ar, stop heating and start cooling until the sample temperature reaches room temperature, close Ar, and finally take out the sample, which is the SWNTs with a narrow chiral distribution.

[0064] As Figure 4 shown, Raman spectrum of the SWNTs with a narrow chiral distribution prepared in Example 2.

[0065] Example 3

[0066] This example provides a method for preparing single-walled carbon nanotubes with a narrow chiral distribution, including the following steps:

[0067] (1) Take 1.97 g of Co(NO3)2·6H2O, 6.0 g of urea and 2 mL of colloidal silica (LUDOX, 50 wt%), dissolve them in deionized water and stir evenly. Place the evenly stirred solution in a hydrothermal reaction vessel and heat it to 200 °C for 20 h;

[0068] (2) Rinse the product of step (1) with water and ethanol, dry it and grind it in a mortar. Place the ground powder in a muffle furnace and calcine it at 900 °C for 3 h to obtain a single-metal catalyst of cobalt;

[0069] (3) Mix the single-metal catalyst of cobalt with 12 mg of PdCl2 in deionized water. After impregnation, obtain a CoPd bimetallic layered silicate catalyst. Grind the dried catalyst into fine powder, and then calcine it in a muffle furnace at 300 °C for 5 h;

[0070] (4) Take the catalyst calcined in step (3) and place it in a quartz boat. Place the quartz boat in the middle of a two-temperature-zone sliding-rail CVD furnace. Connect the experimental device as required. Set the furnace heating program to 20 °C / min. Pass Ar at a flow rate of 300 sccm to discharge the air in the device. After the sample temperature reaches 850 °C, pass CO at a flow rate of 300 sccm for 20 min. After the reaction ends, pass Ar, stop heating and start cooling until the sample temperature reaches room temperature, close Ar, and finally take out the sample, which is the SWNTs with a narrow chiral distribution.

[0071] As Figure 5 shown, it is the Raman spectrum of the SWNTs with a narrow chiral distribution prepared in Example 3.

[0072] Comparative Example 1

[0073] Replace the colloidal silica in Example 1 with an equal amount of porous silica, and the other preparation steps are the same as the experimental process of Example 1.

[0074] As Figure 6 shown is the Raman spectrum of the synthesized product. Due to the weak anchoring effect of porous silica on nanoparticles, it is found through the Raman spectrum that SWNTs cannot grow well within the growth temperature range of 600 °C.

[0075] Comparative Example 2

[0076] Replace the colloidal silica in Example 2 with an equal amount of porous silica, and the other preparation steps are the same as those in the experimental process of Example 1.

[0077] As Figure 7 shown in the Raman spectrum of the synthesized product, due to the weak anchoring effect of porous silica on nanoparticles, it is found through the Raman spectrum that SWNTs cannot grow well in the growth temperature range of 750 °C.

[0078] Comparative Example 3

[0079] Replace the colloidal silica in Example 3 with an equal amount of porous silica, and the other preparation steps are the same as those in the experimental process of Example 1.

[0080] As Figure 8 shown in the Raman spectrum of the synthesized product, due to the weak anchoring effect of porous silica on nanoparticles, it is found through the Raman spectrum that it cannot grow well into SWNTs in the growth temperature range of 850 °C.

[0081] In summary, through the comparative analysis of the Raman spectra of the products in Examples 1-3 and Comparative Examples 1-3, it can be judged that when using porous silica instead of alternating silica for synthesis, SWNTs cannot grow well in the growth temperature range of 600-850 °C.

[0082] The above description is only the preferred embodiment of the present invention and is not a limitation of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, modification, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing single-walled carbon nanotubes with a narrow chiral distribution, characterized in that, Using a cobalt-palladium double-metal layered silicate catalyst, with CoPd as the catalytic metal and layered silicate as the growth substrate, single-walled carbon nanotubes with a narrow chiral distribution are prepared; The steps include: (1) Dissolve cobalt nitrate hexahydrate and colloidal silica with a mass ratio of 1∶(0.5 - 2) in deionized water, and at the same time add an appropriate amount of urea, stir evenly, and heat to 170 - 200 °C and maintain for 20 - 30 h; (2) Wash, dry and grind the product of step (1) into powder, and calcine it at 700 - 900 °C for 3 - 5 h to obtain a single-metal cobalt catalyst; (3) Mix the single-metal cobalt catalyst and palladium chloride according to the mass ratio of cobalt atoms to palladium atoms of (90 - 110)∶1, impregnate to obtain a CoPd double-metal layered silicate catalyst, dry the catalyst and grind it into fine powder, and then calcine it at 300 - 500 °C for 3 - 5 h; (4) Place the catalyst calcined in step (3) in a dual-temperature zone sliding rail type CVD furnace, under an Ar atmosphere, heat up to 600 - 850 °C, and introduce CO to react for 20 - 40 min at this temperature to obtain single-walled carbon nanotubes with a narrow chiral distribution.

2. The method for preparing a single-walled carbon nanotube with a narrow chiral distribution according to claim 1, characterized in that, In step (1), the mass ratio of Co(NO3)2·6H2O to colloidal silica is 1∶1.

3. The method for preparing a single-walled carbon nanotube with a narrow chiral distribution according to claim 1, wherein, In step (1), heat to 190 °C and maintain for 24 h.

4. The method for preparing a single-walled carbon nanotube with a narrow chiral distribution according to claim 1, characterized in that, In step (2), wash by rinsing with water and ethanol.

5. The method for preparing single-walled carbon nanotubes with a narrow chiral distribution according to claim 1, characterized in that, In step (2), calcine at 800 °C for 4 h.

6. The preparation method of the single-walled carbon nanotubes with a narrow chiral distribution according to claim 1, characterized in that, In step (3), the single-metal cobalt catalyst and palladium chloride are mixed according to the mass ratio of cobalt atoms to palladium atoms of 100∶1.

7. The method for preparing a single-walled carbon nanotube with a narrow chiral distribution according to claim 1, characterized in that, In step (3), calcine at 400 °C for 4 h.

8. The method for preparing a single-walled carbon nanotube with a narrow chiral distribution according to claim 1, characterized in that, In step (4), the heating rate is 20 °C / min. When the temperature reaches 600 °C, introduce CO to react for 30 min.

9. The method for preparing single-walled carbon nanotubes with a narrow chiral distribution according to claim 1, characterized in that, In step (4), after the reaction, introduce Ar, stop heating and start cooling. After cooling to room temperature, close Ar, and single-walled carbon nanotubes with a narrow chiral distribution are obtained.

10. Single-walled carbon nanotubes with a narrow chiral distribution prepared by the preparation method according to any one of claims 1 - 9.

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