Cobalt and fluorine single atom co-doped carbon nanotube materials prepared by microwave irradiation and their applications

Abstract

The present invention discloses a cobalt and fluorine single-atom co-doped carbon nanotube material prepared by microwave radiation and its application. The material is prepared by the following method: Step 1: uniformly mixing carbon nanotubes and cobalt chloride to obtain a mixture; adding perfluorooctane to the mixture; and ultrasonically treating the mixture to uniformly disperse the mixture in the perfluorooctane to obtain a uniformly dispersed solution; Step 2: treating the uniformly dispersed solution obtained in Step 1 with microwave radiation to obtain a precursor material; and Step 3: washing the precursor material obtained in Step 2 and drying it to obtain a cobalt and fluorine single-atom co-doped carbon nanotube material. The material prepared by this method has high cobalt and fluorine doping rates, is relatively easy to effectively dope with cobalt single atoms, and exhibits excellent electrochemical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of material chemistry, and in particular to a method for preparing a cobalt single atom and a fluorine single atom co-doped carbon nanotube material by a microwave radiation method and application thereof. Background Art

[0002] As an environmentally friendly oxidant, hydrogen peroxide (H2O2) has been widely used in fields such as bleaching, chemical synthesis and medical disinfection, especially in sewage treatment (typical Fenton reaction) and organic agriculture. At present, up to 95% of H2O2 is produced by industrial-scale anthraquinone oxidation, which not only requires large-scale infrastructure, but also produces a large amount of carbon emissions, and the produced H2O2 needs to be further extracted and purified from organic solvents. These challenges have prompted researchers to develop greener, safer and more efficient methods to continuously generate H2O2. At room temperature, through a two-electron pathway (2e - Direct oxygen reduction to generate H2O2 is a promising alternative method with the characteristics of reducing waste emissions, lowering energy consumption and improving safety. The prepared materials need to break through the inherent tendency of four-electron oxygen reduction to generate water, because the four-electron oxygen reduction process will inevitably inhibit the two-electron oxygen reduction process to generate H2O2. To this end, the development of high 2e - Oxygen reduction-selective electrocatalysts are crucial for efficient hydrogen peroxide production.

[0003] Among currently available electrocatalysts, single-atom catalysts (SACs) have attracted much attention due to their unique unsaturated electronic configuration, maximum atomic utilization, and relatively stable coordination structure. However, single-atom catalysts also have their common disadvantages. On the one hand, the metal single-atom active centers are easily blocked by oxygen-containing intermediates, resulting in severe deactivation of SACs. On the other hand, because single-atom sites generally have high surface energy, they easily agglomerate to form clusters or particles on the surface of the material, making it difficult to achieve high H2O2 yields. Recent studies have found that doping two or more heteroatoms with different electronegativity into the carbon skeleton can effectively regulate the charge distribution of multiple nearby carbon atoms, making them catalytically active for various targeted reactions.

[0004] Zheng Y et al. prepared B, N dual-doped graphene materials. In this material, due to the long-range synergistic effect of B and N, B, N dual-doped graphene has a strong effect on 4e -Oxygen reduction shows high activity and selectivity (Angew. Chem, 2013, 125(11): 3192–3198). Chinese patent document CN111468167A discloses an oxygen reduction electrocatalyst based on a ZIF precursor and nitrogen-doped porous carbon supported by a single cobalt atom and a preparation method thereof, the preparation method comprising the following steps: 1) dissolving cobalt nitrate hexahydrate and zinc nitrate hexahydrate in methanol to obtain solution A, which is set aside; 2) dissolving benzimidazole in methanol to obtain solution B; 3) mixing solution A and solution B and stirring them for 2-3 hours, standing for 24-26 hours, and then washing and drying; 4) calcining the dried product obtained in step 3) at 800-900°C for 1.5-2.5 hours under an inert gas atmosphere to obtain the final product. The preparation process is cumbersome, and the active sites of the prepared material mostly undergo a four-electron oxygen reduction process, which is not conducive to the two-electron oxygen reduction to produce hydrogen peroxide.

[0005] The electrocatalyst materials prepared by the above doping process are transferred through two electron paths (2e - ) The efficiency of direct oxygen reduction to generate H2O2 is not high, and the catalyst materials prepared by traditional methods still have the disadvantages of long preparation time, complex operation, easy single atom agglomeration, difficulty in achieving effective doping of Co single atoms, serious raw material loss, and low doping efficiency. It is necessary to further optimize the materials from the preparation method. Summary of the Invention

[0006] The purpose of the present invention is to address the technical defects existing in the prior art and provide a method for preparing carbon nanotube materials co-doped with cobalt single atoms and fluorine single atoms based on microwave radiation method. The preparation process of this method is simple and can achieve instantaneous, ultrafast, high-temperature cooling of the material in a short time.

[0007] Another object of the present invention is to provide a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms prepared by the preparation method, which has the advantages of stability, high efficiency, and large-scale preparation.

[0008] Another object of the present invention is to provide an application of the cobalt single atom and fluorine single atom co-doped carbon nanotube material in the preparation of hydrogen peroxide by two-electron oxygen reduction, which has an excellent catalytic effect.

[0009] The technical solution adopted to achieve the purpose of the present invention is:

[0010] A method for preparing a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms based on microwave radiation comprises the following steps:

[0011] Step 1: uniformly mixing carbon nanotubes and cobalt chloride to obtain a mixture, adding perfluorooctane to the mixture, and performing ultrasonic treatment to uniformly disperse the mixture in the perfluorooctane to obtain a uniformly dispersed solution;

[0012] Step 2, treating the uniformly dispersed solution obtained in step 1 with microwave radiation to obtain a precursor material, which is recorded as CoF2 / Co-F-CNT;

[0013] Step 3: Wash the precursor material obtained in step 2 to remove CoF2, and dry it to obtain a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms, which is recorded as Co-F-CNT.

[0014] In the above technical solution, the ratio of the mass fraction of carbon nanotubes, the mass fraction of cobalt chloride and the volume fraction of perfluorooctane in step 1 is 30:(5-30):(1-2), wherein the unit of the mass fraction is mg and the unit of the volume fraction is mL.

[0015] In the above technical solution, the microwave power of the microwave radiation treatment in step 2 is 280 to 700W.

[0016] In the above technical solution, the time of microwave radiation treatment in step 2 is 10 to 30 minutes.

[0017] In the above technical solution, in step 3, the solution is first washed with hydrochloric acid and then with deionized water. Preferably, the concentration of the hydrochloric acid is 2 mol L -1 .

[0018] In the above technical solution, the drying in step 3 is carried out in an oven at a drying temperature of 50 to 70°C.

[0019] Another aspect of the present invention also includes a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms obtained by the preparation method.

[0020] In the above technical solution, the atomic percentage of cobalt in the carbon nanotube material co-doped with single co-atoms of cobalt and fluorine is 0.2-0.6 at%, preferably 0.4-0.6 at%, and the atomic percentage of fluorine is 3-5 at%.

[0021] Another aspect of the present invention also includes the use of the cobalt single atom and fluorine single atom co-doped carbon nanotube material as a catalyst in the two-electron oxygen reduction to produce hydrogen peroxide.

[0022] In the above technical solution, within the potential range of 0.2 to 0.8 V, the selectivity of the catalyst for H2O2 can reach 85.7%, and the H2O2 yield can reach 18 mol g -1 h -1 .

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. Compared with the traditional carbonization method for preparing metal single-atom doped materials, the microwave irradiation method is fast and efficient, with high raw material utilization and doping rate. It is easier to achieve effective doping of cobalt single atoms, and the carbon nanotubes treated with microwave irradiation can still maintain their typical morphology.

[0025] 2. The high electronegativity of fluorine can more effectively adjust the electronic structure of carbon and solve the shortcomings of doping only single metal atoms.

[0026] 3. The prepared cobalt single atom and fluorine single atom co-doped carbon nanotube material has high activity, high selectivity and durability, excellent electrochemical performance, simple preparation process, low cost, and easy to achieve industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM of the cobalt single atom and fluorine single atom co-doped carbon nanotube material (Co-F-CNT) prepared in Example 1;

[0028] Figure 2 TEM of the cobalt single atom and fluorine single atom co-doped carbon nanotube material (Co-F-CNT) prepared in Example 1;

[0029] Figure 3 HRTEM image of the double boundary region of the cobalt single atom and fluorine single atom co-doped carbon nanotube material (Co-F-CNT) prepared in Example 1;

[0030] Figure 4 The XRD patterns of the materials in Example 1 and the comparative example are as follows;

[0031] Figure 5 is the XRD pattern of comparative example 4 and the precursor material;

[0032] Figure 6 The XPS graph of the material between Example 1 and the comparative example;

[0033] Figure 7 The XPS graphs of Comparative Example 4 and the precursor material are shown;

[0034] Figure 8 This is a table showing the content of each element in the materials of Example 1 and the comparative example;

[0035] Figure 9 is the Raman graph of the materials between Example 1 and the comparative example;

[0036] Figure 10 Graph showing H2O2 selectivity and electron transfer number n between Example 1 and the comparative example;

[0037] Figure 11Graph showing the change in capacitance and current of the materials in Example 1 and the comparative example with different sample scan rates;

[0038] Figure 12 This is a graph showing the H2O2 yield of materials between Example 1 and the comparative example;

[0039] Figure 13 This is a graph showing the cumulative yield of Co-F-CNTs at -0.04 V for the cobalt single atom and fluorine single atom co-doped carbon nanotube material (Co-F-CNT) prepared in Example 1. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0041] Example 1

[0042] The microwave radiation method is used to prepare a cobalt single atom and a fluorine single atom co-doped carbon nanotube material (Co-F-CNT), which includes the following steps:

[0043] (1) 30 mg of carbon nanotubes and 10 mg of cobalt chloride were mixed to obtain a powdered sample. 1 mL of perfluorooctane was then added to the mixture, and ultrasonic treatment was performed to uniformly disperse the mixture in the solvent.

[0044] (2) treating the uniformly dispersed solution in step (1) with microwave radiation at a microwave power of 400 W for 20 min to obtain a precursor material;

[0045] (3) Finally, use 2 mol L -1 The precursor material obtained in step (2) is treated with hydrochloric acid, washed with a large amount of deionized water, and dried in an oven to finally obtain a fluorine-doped cobalt single-atom carbon nanotube material.

[0046] The scanning electron microscope image of the cobalt single atom and fluorine single atom co-doped carbon nanotube material prepared in this embodiment is as follows: Figure 1 As shown in the transmission electron microscope image Figure 2 As shown by Figure 1 、 2 It can be seen that Co-F-CNT still maintains the typical morphology of carbon nanotubes without obvious structural damage, indicating that microwave treatment does not significantly change the microstructure of carbon nanotubes.

[0047] Figure 3 This is an HRTEM image of the Co-F-CNT double boundary region, where the isolated bright spots marked by white circles represent single Co atoms. It can be confirmed that the Co atoms are uniformly distributed on the Co-F-CNT surface, forming the expected single-atom sites.

[0048] Example 2

[0049] The Co-F-CNT prepared in Example 1 was used to prepare the working electrode:

[0050] 2 mg of Co-F-CNT prepared in Example 1 was dispersed in 990 μL of deionized water and 10 μL of 5 wt% Nafion solution at room temperature (~25°C) by vigorous ultrasonication to form a catalyst ink. 10 μL of the catalyst ink was then dropped onto a rotating ring disk electrode (RRDE) with a theoretical collection efficiency of 37% (disk electrode area of ​​0.2475 cm). 2 , the annular electrode area is 0.1866cm 2 ) to form a uniform catalyst layer.

[0051] Electrochemical tests were performed using the working electrode:

[0052] Electrochemical experiments were conducted in an electrolyte saturated with 0.1 M KOH and O2 using a CHI760E electrochemical workstation. Platinum (Pt) foil and Ag / AgCl (saturated KCl aqueous solution) were used as counter and reference electrodes, respectively. Throughout the test, the working electrode rotated at 1600 rpm, and the ring electrode was set at a constant potential of 1.5 V / RHE to detect the generated H2O2.

[0053] In the potential range of 0.2-0.8 V, the selectivity for H2O2 can reach 85.7%. After 30 minutes of reaction, the H2O2 yield is 18 mol g -1 h -1 .

[0054] The electrochemical properties of other materials were characterized using the same electrochemical test, and the results are shown in the following comparative examples.

[0055] Comparative Example 1

[0056] The microwave radiation method for preparing cobalt single atom-doped carbon nanotube material, denoted as Co-CNT, is basically the same as the method in Example 1, except that perfluorooctane is not added in step (1).

[0057] The Co-CNT prepared in this comparative example has a selectivity of 75.7% for H2O2 in the potential range of 0.2-0.8 V. After 30 min of reaction, the H2O2 yield is 11 mol g -1 h -1 .

[0058] Comparative Example 2

[0059] The microwave radiation method for preparing fluorine-doped carbon nanotube material, denoted as F-CNT, is basically the same as the method in Example 1, except that cobalt chloride is not added in step (1).

[0060] The F-CNT prepared in this comparative example has a selectivity of 78.9% for H2O2 in the potential range of 0.2-0.8 V. After 30 min of reaction, the H2O2 yield is 14 mol g -1 h -1 .

[0061] Comparative Example 3

[0062] The microwave radiation method for treating carbon nanotube materials, referred to as CNTs, is basically the same as the method in Example 1, except that cobalt chloride and perfluorooctane are not added in step (1).

[0063] The CNTs prepared in this comparative example have a selectivity of 74.3% for H2O2 in the potential range of 0.2-0.8 V. After 30 min of reaction, the H2O2 yield is 5 mol g -1 h -1 .

[0064] Comparative Example 4

[0065] The conventional carbonization method for preparing cobalt and fluorine co-doped carbon nanotube material, denoted as Co-F-CNT-700, includes the following steps:

[0066] (1) The same precursor as in Example 1, namely, cobalt chloride, perfluorooctane and carbon nanotubes were mixed and annealed in a conventional tube furnace at 700° C. for 3 h in an argon atmosphere.

[0067] (2) Washing the material obtained in step (1) with hydrochloric acid and drying in an oven to obtain Co-F-CNT-700 prepared by the traditional carbonization method.

[0068] The H2O2 yield of Co-F-CNT-700 prepared in this comparative example is 4 mol g -1 h -1 .

[0069] Figure 4 The following are XRD patterns of the materials from Example 1 and Comparative Examples 1-3. In this figure, we can see that the diffraction peak of the Co-F-CNT material is broader than that of the others, indicating that cobalt and fluorine doping slightly distorts the crystal structure of the carbon nanotubes. Other than this, the samples do not exhibit any other characteristic crystalline peaks.

[0070] exist Figure 5It can be observed that there are four diffraction peaks at 26.8°, 34°, 39.2° and 52.1° in the XRD spectrum of the intermediate product CoF2 / Co-F-CNT, which correspond to the (110), (200), (111) and (211) planes of CoF2, respectively, confirming that CoF2 is formed after the precursor is treated with microwaves. The XRD spectrum of Co-F-CNT-700 in the figure is the same as that of the comparative examples 1-3, and there are no other crystal characteristic peaks.

[0071] Figure 6 It can be clearly seen from the XPS spectrum that the Co-F-CNT material prepared in Example 1 contains Co, F, C, and O elements; the Co-CNT material prepared in Comparative Example 1 contains Co, C, and O elements; the F-CNT material prepared in Comparative Example 2 contains F, C, and O elements; and the CNTs material prepared in Comparative Example 3 contains only C and O elements.

[0072] Figure 7 The XPS spectrum of the material Co-F-CNT-700 prepared in Comparative Example 4 shows the presence of Co and O elements. Figure 8 From the element content of each material, it can be seen that the material Co-F-CNT-700 contains only trace amounts of Co and F elements or almost no Co and F elements.

[0073] Figure 9 The Raman spectrum of Co-F-CNT shows that I D / I G The band intensity ratio is greater than that of other samples, indicating that its carbon skeleton introduces more defects.

[0074] Figure 10 The H2O2 selectivity and electron transfer number n are shown in the figure. In the potential range of 0.2 to 0.8 V vs. RHE, Co-F-CNT has the highest selectivity for H2O2, reaching 85%, which is significantly higher than other catalysts. The electron transfer number of Co-F-CNT in this potential range is close to 2, which is always the best in the entire test potential range. This shows that Co-F-CNT has a 2e selectivity for H2O2 as the product. - The ORR pathway was dominant.

[0075] Figure 11 The corresponding graph of capacitance current changing with the scanning rate of different samples can be used to obtain the double layer capacitance value of the catalyst (C dl ), it can be seen from the figure that Co-F-CNT has the highest C dl The value is 9.79mF cm -2 , which is significantly higher than that of other samples, and the electrochemically active surface area is related to the double layer capacitance (C dl), which shows that Co-F-CNT can expose more active sites.

[0076] Figure 12 It shows that Co-F-CNT has the highest H2O2 yield of about 18 mol g -1 h -1 and 90% Faradaic current efficiency.

[0077] Figure 13 This indicates that the H2O2 yield of Co-F-CNT is quite constant and stable within 20 h. After 20 h of catalysis, the cumulative concentration of H2O2 reaches 5.2 g L -1 .

[0078] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms based on microwave radiation, characterized in that: The following steps are involved: Step 1: uniformly mixing carbon nanotubes and cobalt chloride to obtain a mixture, adding perfluorooctane to the mixture, and performing ultrasonic treatment to uniformly disperse the mixture in the perfluorooctane to obtain a uniformly dispersed solution; Step 2, treating the uniformly dispersed solution obtained in step 1 with microwave radiation to obtain a precursor material, which is recorded as CoF2 / Co-F-CNT; Step 3: Wash the precursor material obtained in step 2 to remove CoF2, and dry it to obtain a carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms, which is recorded as Co-F-CNT.

2. The preparation method according to claim 1, wherein In step 1, the ratio of the mass fraction of carbon nanotubes, the mass fraction of cobalt chloride and the volume fraction of perfluorooctane is 30:(5-30):(1-2), wherein the unit of the mass fraction is mg and the unit of the volume fraction is mL.

3. The preparation method according to claim 1, wherein The microwave power of the microwave radiation treatment in step 2 is 280-700 W.

4. The preparation method according to claim 1, wherein The microwave radiation treatment time in step 2 is 10 to 30 minutes.

5. The preparation method according to claim 1, wherein In step 3, the mixture is first washed with hydrochloric acid and then with deionized water. The concentration of the hydrochloric acid is 2 mol L -1 .

6. The preparation method according to claim 1, wherein The drying in step 3 is carried out in an oven at a drying temperature of 50-70°C.

7. A carbon nanotube material co-doped with cobalt single atoms and fluorine single atoms obtained by the preparation method according to claim 1.

8. The cobalt single atom and fluorine single atom co-doped carbon nanotube material according to claim 7, characterized in that: The atomic percentage of cobalt is 0.2 to 0.6 at%, and the atomic percentage of fluorine is 3 to 5 at%.

9. Use of the cobalt single atom and fluorine single atom co-doped carbon nanotube material according to claim 7 as a catalyst in two-electron oxygen reduction to produce hydrogen peroxide.

10. The use according to claim 9, characterized in that In the potential range of 0.2-0.8 V, the selectivity of the catalyst for H2O2 can reach 85.7%, and the H2O2 yield can reach 18 mol g -1 h -1 .

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