A composite nanocatalyst, its preparation method and application

Abstract

This invention discloses a novel composite nanocatalyst, its preparation method, and its applications. The novel composite nanocatalyst comprises an Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial, which has a multi-layered core-shell structure, including an Ag material coated with Fe3O4 as the core, and TiO2 layers and MoS2 layers sequentially stacked on the surface of the core from the inside out. The Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst provided by this invention exhibits good dispersibility and can be used for the controllable preparation of carbon nanotubes, contributing to improved conductivity and purity of carbon nanotubes.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube catalysts, specifically to a composite nanocatalyst, its preparation method, and its application, and more specifically to an Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst, its preparation method, and its application. Background Technology

[0002] Carbon nanotubes, as a one-dimensional nanomaterial, possess broad application potential in electronics, energy, and biomedicine due to their unique nanostructure and excellent mechanical, thermal, and electrical properties. To fully leverage the advantages of carbon nanotubes and realize their industrial application, it is urgent to explore methods for improving their structure and performance, such as the controllable growth of carbon nanotubes (controlling properties such as density, length, and chirality), and the controllable enhancement of electrical and thermal conductivity. Since the discovery of carbon nanotubes in 1991, researchers have developed various methods for the controllable preparation of carbon nanotubes, such as chemical vapor deposition (CVD), laser ablation, and arc discharge. CVD has been widely used for the controllable preparation of carbon nanotubes due to its advantages, including simple preparation process, excellent controllability, high purity and reproducibility of carbon nanotubes, low cost, and ease of large-scale mass production. In the research on carbon nanotube preparation, breakthroughs are needed in controlling the number of walls, diameter, length, and conductivity of carbon nanotubes to achieve high yield and high purity.

[0003] Catalyst design is a crucial method for achieving controllable growth of carbon nanotubes (CNTs). The structure of CNTs is inextricably linked to the structure of the catalyst, and regulating catalyst synthesis can fundamentally control the structural growth of CNTs. Common metal catalysts include iron, aluminum, cobalt, tin, nickel, copper, palladium, manganese, molybdenum, gold, silver, chromium, and platinum; non-metal catalysts include boron nitride, silicon carbide, titanium dioxide, alumina, and iron oxide; and co-catalysts include cobalt sulfide, molybdenum sulfide, and sulfur powder. Direct use of metal catalysts may lead to agglomeration and oxidation, reducing catalytic efficiency. Furthermore, directly mixing catalysts and co-catalysts can also reduce catalyst utilization. Therefore, exploring the controllable synthesis of catalysts and co-catalysts is essential. Developing supported metal catalysts is currently the main technique for macroscopically preparing CNTs. However, the preparation methods for supported catalysts still need improvement, and there is an urgent need to find highly efficient supported composite catalysts to enhance the controllable preparation and properties of CNTs. Summary of the Invention

[0004] The main objective of this invention is to provide a composite nanocatalyst, its preparation method, and its application, in order to overcome the shortcomings of the prior art.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] One aspect of the present invention provides a composite nanocatalyst comprising an Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial having a multilayer core-shell structure, comprising an Ag material coated with Fe3O4 as a core, and TiO2 layers and MoS2 layers sequentially stacked on the surface of the core from the inside out.

[0007] Another aspect of the present invention provides a method for preparing the aforementioned composite nanocatalyst, comprising:

[0008] Provide Fe3O4-coated Ag materials;

[0009] A TiO2 layer is coated on the surface of the Fe3O4-coated Ag material to obtain an Ag / Fe3O4 / TiO2 composite material;

[0010] A composite nanocatalyst was prepared by coating the surface of the Ag / Fe3O4 / TiO2 composite material with a MoS2 layer.

[0011] Another aspect of the present invention provides a composite nanocatalyst prepared by the aforementioned preparation method.

[0012] Another aspect of the present invention provides the application of the aforementioned composite nanocatalyst in the preparation of carbon nanotubes.

[0013] Compared with the prior art, the technical solution of the present invention has at least the following advantages:

[0014] The preparation method provided by this invention involves first preparing Fe3O4-coated Ag material, then loading a TiO2 layer onto its surface, and finally modifying its surface with a thin layer of MoS2 using a solvothermal method to obtain an Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst. This nanocatalyst exhibits good dispersibility and can be used for the controllable preparation of carbon nanotubes. By adjusting the reaction temperature, reaction time, and MoS2 loading, the performance of the obtained composite catalyst can be modified, thereby helping to improve the conductivity and purity of the prepared carbon nanotubes. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 These are XRD patterns of samples obtained in different steps of Example 1 of the present invention;

[0017] Figure 2a This is a SEM image of the Ag / Fe3O4 sample obtained in Example 1 of the present invention;

[0018] Figure 2b This is a SEM image of the Ag / Fe3O4 / TiO2 sample obtained in Example 1 of this invention;

[0019] Figure 2c This is a SEM image of the Ag / Fe3O4 / TiO2 / MoS2 sample obtained in Example 1 of this invention;

[0020] Figure 2d This is a TEM image of the Ag / Fe3O4 / TiO2 / MoS2 sample obtained in Example 1 of the present invention;

[0021] Figure 3a The image shows a SEM image (magnification 5000x) of the product obtained by using the composite nanocatalyst obtained in Example 1 of this invention for the growth of carbon nanotubes.

[0022] Figure 3b The image shows a SEM image (magnification 10000x) of the product obtained by using the composite nanocatalyst obtained in Example 1 of this invention for the growth of carbon nanotubes. Detailed Implementation

[0023] The invention will be more fully understood by reading the following detailed description. However, it should be understood that the detailed description disclosed below is merely exemplary of the invention, which can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as a representative basis for teaching those skilled in the art to employ the invention in different ways in any suitable detailed embodiment.

[0024] As one aspect of the technical solution of the present invention, a composite nanocatalyst includes: Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial, wherein the Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial has a multi-layer core-shell structure, including Fe3O4 coating Ag material as the core, and TiO2 layer and MoS2 layer stacked from the inside to the outside on the surface of the core.

[0025] In some embodiments, the Fe3O4-coated Ag material includes Ag and Fe3O4 coated on the surface of the Ag.

[0026] In some preferred embodiments, the Fe3O4-coated Ag material comprises Fe3O4-coated Ag nanospheres.

[0027] In some preferred embodiments, the diameter of the Fe3O4-coated Ag nanospheres is 180~230 nm.

[0028] In some implementations, the thickness of the TiO2 layer is 30-50 nm.

[0029] In some implementations, the thickness of the MoS2 layer is 5-9 nm.

[0030] In some embodiments, the composite nanocatalyst contains 6-8 wt% Ag, 40-50 wt% Fe3O4, 25-35 wt% TiO2, and 12-18 wt% MoS2.

[0031] As another aspect of the technical solution of the present invention, the preparation method of the aforementioned composite nanocatalyst includes:

[0032] Provide Fe3O4-coated Ag materials;

[0033] A TiO2 layer is coated on the surface of the Fe3O4-coated Ag material to obtain an Ag / Fe3O4 / TiO2 composite material;

[0034] A composite nanocatalyst was prepared by coating the surface of the Ag / Fe3O4 / TiO2 composite material with a MoS2 layer.

[0035] In some embodiments, the Fe3O4-coated Ag material is synthesized by a hydrothermal method.

[0036] In some preferred embodiments, the preparation method of the Fe3O4-coated Ag material includes: mixing an iron source, a silver source and sodium acetate to carry out a hydrothermal reaction to obtain the Fe3O4-coated Ag material.

[0037] In some more preferred embodiments, the iron source includes ferric nitrate.

[0038] In some more preferred embodiments, the silver source includes silver nitrate.

[0039] In some more preferred embodiments, the mass ratio of the iron source, silver source and sodium acetate is 14~18:0.8~1.4:24~32.

[0040] In some more preferred embodiments, the hydrothermal reaction temperature is 180~200°C and the hydrothermal reaction time is 12~24h.

[0041] In some more preferred embodiments, the preparation method of the Fe3O4-coated Ag material specifically includes: mixing an iron source with a solvent, adding sodium acetate and a silver source to carry out the hydrothermal reaction, drying, and obtaining Ag / Fe3O4 nanoparticles.

[0042] Furthermore, the solvent includes, but is not limited to, ethylene glycol.

[0043] Furthermore, the mass-to-volume ratio of the iron source to the solvent is 0.81 g: 20 mL.

[0044] Furthermore, the hydrothermal reaction temperature is 180~200℃, and the hydrothermal reaction time is 12~24 h.

[0045] In some embodiments, the preparation method of the composite nanocatalyst includes: coating Ag material with Fe3O4, mixing ammonia water and titanium source to carry out a first reaction, and then calcining to obtain Ag / Fe3O4 / TiO2 composite material.

[0046] In some preferred embodiments, the temperature of the first reaction is room temperature, and the reaction time is 12-24 hours.

[0047] In some preferred embodiments, the titanium source comprises tetrabutyl titanate.

[0048] In some preferred embodiments, the mass ratio of the Fe3O4-coated Ag material, ammonia, and titanium source is 0.8~1.2:2.5~4.5:8~12.

[0049] In some preferred embodiments, the preparation method of the composite nanocatalyst specifically includes: adding ammonia to an ethanol dispersion of Fe3O4-coated Ag material, followed by adding an ethanol dispersion of titanium source, and carrying out the first reaction.

[0050] In some more preferred embodiments, the mass-to-volume ratio of Fe3O4-coated Ag material to ethanol in the ethanol dispersion is 0.8~1.2 g: 720~1080 mL.

[0051] Furthermore, in the ethanol dispersion of the Fe3O4-coated Ag material, the mass-to-volume ratio of the Fe3O4-coated Ag material to ethanol is 1 g:900 mL.

[0052] In some more preferred embodiments, the mass-to-volume ratio of the titanium source to ethanol in the ethanol dispersion is 0.7~1.2 g: 7~12 mL.

[0053] Furthermore, in the ethanol dispersion of the titanium source, the mass-to-volume ratio of the titanium source to ethanol is 1 g: 10 mL.

[0054] In some embodiments, the calcination temperature is 450~500℃ and the calcination time is 2~4h.

[0055] In some embodiments, the method for preparing the composite nanocatalyst includes: mixing Ag / Fe3O4 / TiO2 composite material, molybdenum source and sulfur source to carry out a second reaction to obtain the composite nanocatalyst;

[0056] In some preferred embodiments, the temperature of the second reaction is 160~220°C, and the reaction time is 12~48 h. In this invention, a temperature that is too low or too high is detrimental to molybdenum disulfide loading.

[0057] In some preferred embodiments, the molybdenum source comprises ammonium molybdate.

[0058] In some preferred embodiments, the sulfur source includes thiourea.

[0059] In some preferred embodiments, the mass ratio of the Ag / Fe3O4 / TiO2 composite material, the molybdenum source, and the sulfur source is 0.25~3:1.8:3.8. In this invention, an excessively high or low mass ratio of the Ag / Fe3O4 / TiO2 composite material, the molybdenum source, and the sulfur source is also detrimental to molybdenum disulfide loading.

[0060] In a typical embodiment, the preparation method of the composite nanocatalyst includes the following steps:

[0061] Step 1: Place a beaker containing a mixed solution of Fe(NO3)3·9H2O and ethylene glycol into a water bath and stir at 40°C for 1 hour. Then add anhydrous sodium acetate and silver nitrate, and stir for another hour. Finally, transfer the mixed solution to a 50 mL polytetrafluoroethylene high-pressure reactor and carry out a hydrothermal reaction in a forced-air drying oven at 180~200°C for 12~24 hours. The product is recovered magnetically and then washed 5 times alternately with ethanol and deionized water. It is then dried overnight in a 60°C oven to obtain Fe3O4-coated Ag material (i.e., Ag / Fe3O4 nanoparticles).

[0062] Step 2: The Ag / Fe3O4 nanoparticles obtained in Step 1 were dispersed in ethanol, ammonia was added and ultrasonicated for 1 h, followed by the addition of an ethanol solution of tetrabutyl titanate. The mixture was stirred at room temperature for 12-24 h to carry out the first reaction. The product was magnetically recovered and then washed 5 times alternately with ethanol and deionized water. The product was then dried overnight in a 60°C oven. To improve the crystallinity of the product, it was calcined at 450-500°C for 2-4 h to obtain the Ag / Fe3O4 / TiO2 composite material (i.e., Ag / Fe3O4 / TiO2 nanoparticles).

[0063] Step 3: Add the Ag / Fe3O4 / TiO2 nanoparticles obtained in Step 2 to (NH4)6Mo7O 24The mixture of ·4H2O and CS(NH2)2 was stirred at room temperature for 2 h, and then the mixture was transferred to a 50 mL polytetrafluoroethylene high-pressure reactor and reacted in a forced-air drying oven at 160~220℃ for 12~48 h to obtain Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterials (i.e. Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst).

[0064] As another aspect of the technical solution of the present invention, it relates to the composite nanocatalyst prepared by the aforementioned preparation method.

[0065] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned composite nanocatalyst in the preparation of carbon nanotubes.

[0066] In summary, the composite nanocatalyst provided by this invention utilizes Fe3O4 to coat Ag structures, preventing the oxidation of metal catalysts. TiO2 possesses a tunable nanostructure, providing abundant active sites, which is beneficial for improving catalytic activity and selectively growing carbon nanotubes. Finally, the loading of MoS2 as a co-catalyst enhances the interfacial interaction between the catalyst and the co-catalyst. Furthermore, the sulfur atoms or defect sites on the edges of MoS2 facilitate the generation of oxygen vacancies and effectively prevent the aggregation and growth of catalyst nanoparticles, thereby increasing carbon nanotube yield and achieving controllable growth of carbon nanotubes.

[0067] The present invention is further illustrated below by way of examples, but the invention is not limited to the scope of the examples described. All reagents and raw materials used in the following examples are commercially available, and test methods not specifically specified are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0068] Example 1

[0069] A method for preparing a composite nanocatalyst includes the following steps:

[0070] Step 1: Place a beaker containing a mixed solution of Fe(NO3)3·9H2O (0.81 g) and ethylene glycol (20 mL) into a water bath and stir at 40 °C for 1 h. Then add anhydrous sodium acetate (1.44 g) and silver nitrate (50 mg) and stir for another 1 h. Finally, transfer the mixed solution to a 50 mL polytetrafluoroethylene high-pressure reactor and keep it in a 200 °C forced-air drying oven for 12 h. The product is recovered magnetically and then washed 5 times alternately with ethanol and deionized water. The sample is then dried overnight in a 60 °C oven. The product is labeled Ag / Fe3O4.

[0071] Step 2: Disperse the Ag / Fe3O4 (0.1 g) obtained in Step 1 in ethanol (90 mL), add ammonia (0.4 mL) and sonicate for 1 h, then add tetrabutyl titanate (1 mL) in ethanol (10 mL) solution, stir at room temperature for 24 h, recover the product by magnetic means, and wash it 5 times alternately with ethanol and deionized water. Then dry the sample in a 60℃ oven overnight. In order to improve the crystallinity of the product, calcine it at 450℃ for 2 h. The product is recorded as Ag / Fe3O4 / TiO2.

[0072] Step 3: Add the Ag / Fe3O4 / TiO2 (0.1 g) obtained in Step 2 to 25 mL of (NH4)6Mo7O 24 The composite nanocatalyst, denoted as Ag / Fe3O4 / TiO2 / MoS2, was prepared by stirring in a mixed aqueous solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g) at room temperature for 2 h. The mixture was then transferred to a 50 mL polytetrafluoroethylene high-pressure reactor and kept in a 180 °C forced-air drying oven for 24 h.

[0073] Example 2

[0074] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 160°C forced-air drying oven for 24 hours.

[0075] Example 3

[0076] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 200°C forced-air drying oven for 24 hours.

[0077] Example 4

[0078] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 220°C forced-air drying oven for 24 hours.

[0079] Example 5

[0080] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 180°C forced-air drying oven for 12 hours.

[0081] Example 6

[0082] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 180°C forced-air drying oven for 36 hours.

[0083] Example 7

[0084] Compared with Example 1, this embodiment is the same in steps one and two, except that in step three, the product is kept in a 180°C forced-air drying oven for 48 hours.

[0085] Example 8

[0086] Compared with Example 1, steps one and two are the same in this embodiment. The difference is that in step three, the Ag / Fe3O4 / TiO2 (0.025 g) obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0087] Example 9

[0088] Compared with Example 1, steps one and two are the same in this embodiment. The difference is that in step three, the Ag / Fe3O4 / TiO2 (0.05 g) obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0089] Example 10

[0090] Compared with Example 1, steps one and two are the same in this embodiment. The difference is that in step three, the Ag / Fe3O4 / TiO2 (0.2 g) obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0091] Example 11

[0092] Compared with Example 1, steps one and two are the same in this embodiment. The difference is that in step three, the Ag / Fe3O4 / TiO2 (0.3 g) obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0093] Example 12

[0094] Compared with Example 1, this embodiment is the same in steps one and three, except that in step two, the reaction is stirred at room temperature for 12 hours.

[0095] Example 13

[0096] Compared with Example 1, this embodiment is the same in steps one and three, except that in step two, the calcination is carried out at 500°C for 2 hours.

[0097] Example 14

[0098] Compared with Example 1, this embodiment is the same in steps one and three, except that in step two, the calcination is carried out at 450°C for 4 hours.

[0099] Example 15

[0100] Compared with Example 1, this embodiment is the same as Example 1 in steps one and three. The difference is that in step two: the Ag / Fe3O4 (0.08 g) obtained in step one is dispersed in ethanol (90 mL), ammonia (0.4 mL) is added and sonicated for 1 h, and then tetrabutyl titanate (1 mL) in ethanol (10 mL) solution is added.

[0101] Example 16

[0102] Compared with Example 1, this embodiment is the same as Example 1 in steps one and three. The difference is that in step two: the Ag / Fe3O4 (0.1 g) obtained in step one is dispersed in ethanol (90 mL), ammonia (0.4 mL) is added and sonicated for 1 h, and then tetrabutyl titanate (1.2 mL) in ethanol (10 mL) solution is added.

[0103] Comparative Example 1

[0104] Step 1: Place a beaker containing a mixed solution of Fe(NO3)3·9H2O (0.81 g) and ethylene glycol (20 mL) into a water bath and stir at 40 °C for 1 h. Then add anhydrous sodium acetate (1.44 g) and silver nitrate (50 mg) and stir for another 1 h. Finally, transfer the mixed solution to a 50 mL polytetrafluoroethylene high-pressure reactor and keep it in a 200 °C forced-air drying oven for 12 h. The product is recovered magnetically and then washed 5 times alternately with ethanol and deionized water. The sample is then dried overnight in a 60 °C oven. The product is labeled Ag / Fe3O4.

[0105] Step 2: Disperse the Ag / Fe3O4 (0.1 g) obtained in Step 1 in an ethanol (90 mL) solution, add ammonia (0.4 mL) and sonicate for 1 h, then add an ethanol (10 mL) solution containing tetrabutyl titanate (1 mL), stir at room temperature for 24 h, recover the product by magnetic means, and then wash it 5 times alternately with ethanol and deionized water. Then place the sample in a 60℃ oven to dry overnight. In order to improve the crystallinity of the product, calcine it at 450℃ for 2 h. The product is recorded as Ag / Fe3O4 / TiO2.

[0106] Comparative Example 2

[0107] Compared with Example 1, the difference is that in step three, the product is kept in a 140°C forced-air drying oven for 24 hours.

[0108] Comparative Example 3

[0109] Compared with Example 1, the difference is that in step three, the product is kept in a 240°C forced-air drying oven for 24 hours.

[0110] Comparative Example 4

[0111] Compared with Example 1, the difference is that in step three, the product is kept in a 180°C forced-air drying oven for 6 hours.

[0112] Comparative Example 5

[0113] Compared with Example 1, the difference is that in step three, the product is kept in a 180°C forced-air drying oven for 54 hours.

[0114] Comparative Example 6

[0115] Compared with Example 1, the difference lies in step three: 0.01 g of Ag / Fe3O4 / TiO2 obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0116] Comparative Example 7

[0117] Compared with Example 1, the difference lies in step three: 0.4 g of Ag / Fe3O4 / TiO2 obtained in step two is added to (NH4)6Mo7O 24 In a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g).

[0118] Comparative Example 8

[0119] Compared with Example 1, the difference is that step three is omitted, and step two involves directly adding the Ag / Fe3O4 (0.1 g) obtained in step one to (NH4)6Mo7O. 24 The composite nanocatalyst, denoted as Ag / Fe3O4 / MoS2, was prepared by stirring a mixed solution of 4H2O (0.18 g) and CS(NH2)2 (0.38 g) at room temperature for 2 h. The mixture was then transferred to a 50 mL polytetrafluoroethylene high-pressure reactor and kept in a 180 °C forced-air drying oven for 24 h.

[0120] Comparative Example 9

[0121] Compared with Example 1, the difference is that in step two, the reaction is stirred at room temperature for 6 hours.

[0122] Comparative Example 10

[0123] Compared with Example 1, the difference is that in step two, the reaction is stirred at room temperature for 30 hours.

[0124] Comparative Example 11

[0125] Compared with Example 1, this embodiment is the same as Example 1 in steps one and three. The difference is that in step two: the Ag / Fe3O4 (0.25g) obtained in step one is dispersed in ethanol (90 mL), ammonia (0.4 mL) is added and sonicated for 1 h, and then tetrabutyl titanate (1 mL) in ethanol (10 mL) solution is added.

[0126] Comparative Example 12

[0127] Compared with Example 1, this embodiment is the same as Example 1 in steps one and three. The difference is that in step two: the Ag / Fe3O4 (0.1 g) obtained in step one is dispersed in ethanol (90 mL), ammonia (0.4 mL) is added and sonicated for 1 h, and then tetrabutyl titanate (0.5 mL) in ethanol (10 mL) solution is added.

[0128] Catalyst structure and property testing

[0129] The experimental procedure is as follows:

[0130] The products of different steps of the catalyst prepared in Example 1 were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM); the catalyst prepared in Example 1 was examined by transmission electron microscopy (TEM); the carbon nanotubes synthesized from the catalyst prepared in Example 1 were measured by SEM; the resistivity and Raman spectra of the carbon nanotubes prepared in Examples 1-10 and Comparative Example 1 were examined, and the intensity ratio of the G peak to the D peak (IG / ID) was calculated to evaluate their purity.

[0131] The experimental results are as follows:

[0132] (1) Structural analysis of nanocomposites prepared in different steps in Example 1:

[0133] like Figure 1 As shown, from Figure 1 As can be seen from 'a', all diffraction peaks for Ag / Fe3O4 are attributed to the orthorhombic Fe3O4 phase (PDF#75-1609) and the cubic Ag phase (PDF#04-0783). From... Figure 1As can be seen from b in the figure, after loading the TiO2 nanoshell, the characteristic peaks of anatase TiO2 are clearly visible (PDF#21-1272). From Figure 1 As can be seen from 'c', the characteristic peaks of other substances are weakened after loading MoS2, and the characteristic peak of hexagonal MoS2 appears at around 15° (PDF#37-1492). XRD data indicate the successful preparation of Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst.

[0134] To investigate the microstructure of the prepared catalyst, the catalyst prepared in Example 1 was characterized by SEM. Figure 2a It can be seen that for Ag / Fe3O4, the material surface is rough, the size is relatively uniform, the dispersion is good, and the diameter is approximately 200 nm. From Figure 2b It can be seen that the material diameter increases after being coated with TiO2, the surface is relatively smooth, and the dispersion is good. The thickness of the TiO2 layer is approximately 40 nm. Figure 2c It can be seen that thin-layered MoS2 nanosheets are uniformly dispersed on the surface of the TiO2 shell, and the thickness of the MoS2 layer is approximately 7 nm. From... Figure 2d The TEM images also show that the present invention has successfully prepared a multi-shell nanocatalyst with a diameter of about 320 nm.

[0135] In the composite nanocatalyst of Example 1, the mass content of Ag was 7.7 wt%, the mass content of Fe3O4 was 46.2 wt%, the mass content of TiO2 was 30.8 wt%, and the mass content of MoS2 was 15.3 wt%.

[0136] (2) Structural analysis of the carbon nanotubes prepared in Example 1:

[0137] The catalysts obtained in the examples were used to prepare carbon nanotubes. The preparation process was as follows: 1g of catalyst was added to a quartz boat, the quartz boat was placed in a CVD reactor, and the temperature was raised to 1100℃ at a rate of 10℃ / min under argon protection. Then the argon gas was stopped and replaced with ethylene (carbon source gas) and hydrogen (etching gas). The reaction was carried out for 1 hour to obtain carbon nanotubes.

[0138] Figure 3a and Figure 3b The images shown are SEM images of carbon nanotubes grown using the composite nanocatalyst obtained in Example 1, with magnifications of 5000 and 10000. It can be seen that the prepared carbon nanotubes are dense one-dimensional linear structures, proving the successful growth of carbon nanotubes.

[0139] (3) Performance testing and analysis of carbon nanotubes prepared using composite nanocatalysts from the examples and comparative examples:

[0140] Table 1 shows the performance test results (Raman and conductivity tests) of carbon nanotubes prepared using composite nanocatalysts in the examples and comparative examples. The purity of the sample was evaluated by the intensity ratio of the G peak to the D peak (IG / ID) in the Raman spectrum.

[0141] Table 1. Performance test results of carbon nanotubes prepared using composite nanocatalysts from the examples and comparative examples.

[0142] Example 1 35.9 30 Example 2 24.7 20 Example 3 27.3 22 Example 4 21.4 19 Example 5 32.0 25 Example 6 33.4 26 Example 7 24.5 21 Example 8 19.6 19 Example 9 28.6 23 Example 10 29.5 24 Example 11 25.1 20 Example 12 22.3 17 Example 13 26.3 20 Example 14 24.6 18 Example 15 21.7 16 Example 16 24.1 19 Comparative Example 1 15.5 16 Comparative Example 2 14.1 13 Comparative Example 3 16.2 14 Comparative Example 4 13.6 11 Comparative Example 5 14.5 10 Comparative Example 6 15.0 13 Comparative Example 7 14.7 12 Comparative Example 8 12.3 9 Comparative Example 9 15.3 14 Comparative Example 10 13.9 13 Comparative Example 11 14.8 13 Comparative Example 12 15.5 14

[0143] As can be seen from Table 1, the Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst prepared under the conditions of the catalyst in Example 1 exhibits the best conductivity and purity. Therefore, this invention can further improve the conductivity and purity of the prepared carbon nanotubes by adjusting the reaction temperature, reaction time, and MoS2 loading during the preparation process of the composite nanocatalyst.

[0144] In summary, the embodiments of the present invention provide a method for preparing a composite nanocatalyst Ag / Fe3O4 / TiO2 / MoS2. A stepwise synthesis method is employed, firstly, an Ag / Fe3O4 substrate template is prepared using a hydrothermal method, then a TiO2 layer is coated onto its surface, and finally, a thin layer of MoS2 is modified onto its surface using a solvothermal method. The present invention also provides the Ag / Fe3O4 / TiO2 / MoS2 composite nanocatalyst obtained by the above preparation method for the synthesis of carbon nanotubes. Experimental results show that preparing multi-shell nanocomposite catalysts by combining different types of catalysts can effectively promote the generation of oxygen vacancies and effectively prevent the aggregation and growth of catalyst nanoparticles. By adjusting the reaction temperature, reaction time, and MoS2 loading, the conductivity and purity of the prepared carbon nanotubes can be effectively improved.

[0145] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0146] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. The application of a composite nanocatalyst in the preparation of carbon nanotubes, characterized in that, The composite nanocatalyst is an Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial. The Ag / Fe3O4 / TiO2 / MoS2 composite nanomaterial has a multi-layer core-shell structure, including Fe3O4 coating Ag material as the core, and TiO2 layer and MoS2 layer stacked from the inside to the outside on the surface of the core. The Fe3O4 coating Ag material includes Ag and Fe3O4 coating the surface of the Ag.

2. The application according to claim 1, characterized in that: The Fe3O4-coated Ag material includes Fe3O4-coated Ag nanospheres.

3. The application according to claim 2, characterized in that: The diameter of the Fe3O4-coated Ag nanospheres is 180~230 nm.

4. The application according to claim 1, characterized in that: The thickness of the TiO2 layer is 30~50 nm.

5. The application according to claim 1, characterized in that: The thickness of the MoS2 layer is 5~9 nm.

6. The application according to claim 1, characterized in that: The composite nanocatalyst contains 6-8 wt% Ag, 40-50 wt% Fe3O4, 25-35 wt% TiO2, and 12-18 wt% MoS2.

7. The application according to claim 1, characterized in that, The preparation method of the composite nanocatalyst includes: Provide Fe3O4-coated Ag materials; A TiO2 layer is coated on the surface of the Fe3O4-coated Ag material to obtain an Ag / Fe3O4 / TiO2 composite material; A composite nanocatalyst was prepared by coating the surface of the Ag / Fe3O4 / TiO2 composite material with a MoS2 layer.

8. The application according to claim 7, characterized in that: The Fe3O4-coated Ag material was synthesized by a hydrothermal method.

9. The application according to claim 8, characterized in that: The preparation method of the Fe3O4-coated Ag material includes: mixing an iron source, a silver source and sodium acetate to carry out a hydrothermal reaction to obtain the Fe3O4-coated Ag material.

10. The application according to claim 9, characterized in that: The iron source includes ferric nitrate.

11. The application according to claim 9, characterized in that, The silver source includes silver nitrate.

12. The application according to claim 9, characterized in that, The mass ratio of the iron source, silver source and sodium acetate is 14~18:0.8~1.4:24~32.

13. The application according to claim 9, characterized in that, The hydrothermal reaction temperature is 180~200℃, and the hydrothermal reaction time is 12~24 h.

14. The application according to claim 7, characterized in that, include: Fe3O4-coated Ag material, ammonia, and titanium source were mixed to carry out a first reaction, followed by calcination to obtain Ag / Fe3O4 / TiO2 composite material.

15. The application according to claim 14, characterized in that: The temperature of the first reaction was room temperature, and the reaction time was 12-24 h.

16. The application according to claim 14, characterized in that: The titanium source includes tetrabutyl titanate.

17. The application according to claim 14, characterized in that: The mass ratio of Fe3O4-coated Ag material, ammonia, and titanium source is 0.8~1.2:2.5~4.5:8~12.

18. The application according to claim 14, characterized in that: The calcination temperature is 450~500℃, and the calcination time is 2~4 h.

19. The application according to claim 7, characterized in that, include: A composite nanocatalyst was prepared by mixing Ag / Fe3O4 / TiO2 composite material, molybdenum source and sulfur source to carry out a second reaction.

20. The application according to claim 19, characterized in that, The temperature of the second reaction is 160~220℃, and the reaction time is 12~48 h.

21. The application according to claim 19, characterized in that, The molybdenum source includes ammonium molybdate.

22. The application according to claim 19, characterized in that, The sulfur source includes thiourea.

23. The application according to claim 19, characterized in that, The mass ratio of the Ag / Fe3O4 / TiO2 composite material, the molybdenum source, and the sulfur source is 0.25~3:1.8:3.8.

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