Bamboo-like carbon nanotube packaged metal catalyst and preparation method thereof

Abstract

The invention discloses a preparation method of a bamboo-like carbon nanotube packaged metal catalyst, which comprises the following steps: carrying out heating reflux treatment on carbon black with dilute acid, washing to neutral, and drying to obtain acid-treated carbon black powder; adding the acid-treated carbon black powder into a glucose aqueous solution, then adding water-soluble metal salt, and ultrasonically mixing uniformly to obtain a metal / carbon chelated black suspension; carrying out hydrothermal reaction on the black suspension at 100-120 DEG C for 8-12 hours, then separating out a black wet solid, washing and drying to obtain black powder, namely the metal-loaded carbon material; and uniformly mixing the black powder and a heteroatom precursor, grinding, and calcining in a tubular furnace under a protective atmosphere to obtain the bamboo-like carbon nanotube packaged metal catalyst. According to the invention, the non-noble metal is completely encapsulated in the carbon nanotube to form a novel composite material with a carbon encapsulated metal structure, so that not only is abundant active sites provided, but also direct contact between metal and oxygen or a solution in a reaction system is effectively prevented, thereby improving the stability and durability of the catalyst.

Description

Technical Field

[0001] The invention belongs to the technical field of metal catalysis, and in particular relates to a metal catalyst encapsulated in bamboo-shaped carbon nanotubes, and a preparation method and application thereof. Background Art

[0002] In the field of metal catalysis technology, such as oxygen reduction reaction (ORR) and advanced oxidation (AOP) technology for water treatment, non-precious metals such as iron, cobalt, nickel, and manganese have broad application prospects due to their advantages such as high catalytic activity and low cost. In addition, many types of metal alloys can be constructed to enhance the synergistic catalytic effect between metals and greatly improve the catalytic activity. However, there are structural instability defects such as easy oxidation, agglomeration, and dissolution on the surface of metal catalysts. The encapsulation of carbon nanotubes can effectively protect the metal from direct contact with oxygen or solution in the reaction system, thereby improving the stability and durability of the catalyst. In addition, modification treatments such as nitrogen doping and sulfur doping of carbon nanotubes can further optimize their electronic structure, enhance the interaction with metals, significantly improve the activity and selectivity of the catalyst, and broaden the application range of non-precious metal catalysts in various catalytic reactions.

[0003] Although carbon nanotube encapsulated metal (M@CNT) catalysts show many advantages, their traditional preparation methods such as graphite arc discharge, laser ablation and chemical vapor deposition, etc., are complex in process and require high equipment, and it is difficult to directly introduce and regulate the loaded metal catalyst. In addition to the above-mentioned traditional methods, the commonly used preparation methods of carbon nanotube encapsulated metal (M@CNT) catalysts are mainly pyrolysis methods. CN118059906A discloses a method for preparing a propane dehydrogenation catalyst with a mixture of carbon nanotube-encapsulated iron and iron carbide as a structure, wherein ferrocene and thiophene are dissolved in ethanol together, ultrasonic dispersion is performed at room temperature, and ferrocene is completely dissolved in the ethanol solution, and then the mixed solution is transferred to a syringe, and then argon gas is introduced into the tubular furnace, and the syringe is placed on the injector, and injected into the tubular furnace at a slow injection rate. After the reaction is completed, it is allowed to stand to room temperature, and the catalyst on the tubular furnace wall is scraped off to obtain a catalyst of multi-walled carbon nanotube-encapsulated iron and iron carbide. However, this method has some potential deficiencies and limitations in practical applications. First, in terms of raw materials, this method relies on the carbon-containing metal organic small molecule ferrocene, which has a relatively high cost, and the synthesis process of ferrocene is relatively complicated, and thiophene needs to be added as an auxiliary agent; secondly, in terms of preparation method, this high-temperature injection method has certain operating difficulties and dangers, and the scraping collection method may have low purity and yield of the catalyst, and intermediate substances and finished products are easy to remain on the tube wall.

[0004] Some pyrolysis methods require carbon-containing organic metal small molecules such as metal phthalocyanines, Prussian blue analogs, or metal organic frameworks, organic polymers, etc. as precursors, and then pyrolyze them with metal salts under the addition of organic linkers to form carbon-protected metal catalysts. However, the cost of these complex organic precursors rich in multiple elements is generally high, and some polluting gases such as sulfides and nitrides will be released during the calcination process. Therefore, the preparation method of existing carbon nanotube encapsulated metal (M@CNT) catalysts is still imperfect. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a bamboo-shaped carbon nanotube encapsulated metal catalyst and a preparation method thereof in view of the deficiencies of the above-mentioned prior art, so as to improve the problems of high cost, low activity and poor stability of the existing metal catalysts.

[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is:

[0007] A method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes comprises the following steps:

[0008] (1) heating and refluxing the carbon black with a dilute acid, washing it to neutrality and then drying it to obtain an acid-treated carbon black powder;

[0009] (2) adding the acid-treated carbon black powder obtained in step (1) to a glucose aqueous solution, then adding a water-soluble metal salt, and mixing by ultrasonication to obtain a metal / carbon chelated black suspension;

[0010] (3) subjecting the black suspension obtained in step (2) to a hydrothermal reaction at 100 to 120° C. for 8 to 12 hours, and then separating the black wet solid, washing and drying, and obtaining a black powder which is the metal-loaded carbon material;

[0011] (4) The black powder obtained in step (3) is mixed with the heteroatom precursor, ground and mixed, and calcined in a tubular furnace under a protective atmosphere to obtain a metal catalyst encapsulated by bamboo-shaped carbon nanotubes.

[0012] According to the above scheme, in step (1), the concentration of carbon black added in dilute acid is in the range of 0.5 to 20 g / L, and the concentration of dilute acid is 3 to 10 mol / L. Preferably, the concentration of carbon black added in dilute acid is in the range of 0.5 to 2 g / L.

[0013] According to the above scheme, in step (1), carbon black is heated and refluxed with hydrochloric acid and dilute nitric acid in turn, and the specific process is: carbon black is added to hydrochloric acid with a concentration of 3 to 10 mol / L, and the added concentration is in the range of 0.5 to 20 g / L, and then heated and refluxed, washed to neutrality, and then added to dilute nitric acid with a concentration of 3 to 10 mol / L, and heated and refluxed for the second time, washed to neutrality, and then dried to obtain acid-treated carbon black powder. The temperature of the heating and reflux treatment is 100 to 120°C, and the heating time is 6 to 10 hours.

[0014] According to the above scheme, the carbon black can be commercial carbon black, such as commercial XC-72 type.

[0015] According to the above scheme, in step (2), the concentration of the glucose aqueous solution is in the range of 0.2 to 0.6 mol / L, and the concentration of the acid-treated carbon black powder added to the glucose aqueous solution is in the range of 1.5 to 6 g / L.

[0016] According to the above scheme, in step (2), the metal mainly refers to one or more of non-precious metals such as Fe, Co, Ni, Mn, etc., and of course, it can also include one or more of trace precious metals such as Pt, Pd, Au, etc. The corresponding water-soluble metal salt can be used to prepare the metal catalyst. The water-soluble metal salt can specifically be one or more of cobalt nitrate, nickel nitrate, manganese nitrate, iron nitrate, etc.

[0017] According to the above scheme, in step (2), the concentration of the water-soluble metal salt added to the glucose aqueous solution is calculated as the concentration of metal ions, which is in the range of 0 to 0.2 mol / L and is not 0.

[0018] According to the above scheme, in step (2), after adding the acid-treated carbon black powder, ultrasonic treatment can also be carried out for 2 to 4 hours; after adding the water-soluble metal salt, ultrasonic treatment is continued for 1 to 2 hours.

[0019] According to the above scheme, in step (4), the heteroatom refers to one or more heteroatoms such as N, S, and P, and the heteroatom precursor can be selected from one or more heteroatoms such as melamine, sulfur, thioacetamide, or phosphoramide, phosphide, etc. The mass ratio of the heteroatom precursor to the black powder is 0 to 10. When the amount of the heteroatom precursor is not 0, the carbon nanotubes are heteroatom-doped carbon nanotubes, and when the amount of the heteroatom precursor is 0, they are ordinary carbon nanotubes.

[0020] According to the above scheme, in step (4), the calcination conditions are: calcination at 600-1000° C. for 0.5-2 h in an Ar atmosphere; preferably, the temperature is increased to the calcination temperature at a heating rate of 3-10° C. / min.

[0021] The carbon nanotube-encapsulated metal catalyst prepared by the above method has metal encapsulated in the carbon nanotube in the form of nanoparticles. The carbon nanotube is bamboo-shaped, the diameter of the carbon nanotube is in the range of 20 to 40nm, the size of the metal nanoparticles is in the range of 20 to 40nm, and the metal nanoparticles are nanoparticles of a single metal or nanoparticles of an alloy.

[0022] The technical concept of the present invention is as follows:

[0023] The present invention uses cheap carbon black (such as commercial carbon black XC-72) as a carbon nanotube precursor for the first time, and through a simple and unique synthesis strategy, completely encapsulates non-precious metals inside carbon nanotubes (CNTs) to form an efficient and stable catalytic structure. The present invention firstly activates the oxygen-containing functional groups of carbon black by acid treatment of carbon black, which is conducive to the subsequent chelation with metals. Then, under the action of ultrasound, metal ions and carbon are self-assembled to form metal-carbon chelates, wherein the reducing glucose can reduce metal ions to metal elements during the hydrothermal process, and this is used as a carbon-coated metal precursor before high-temperature pyrolysis; finally, the carbon-coated metal precursor is evenly mixed with heteroatom precursors such as melamine and then pyrolyzed at high temperature, and the heteroatom-containing gas formed by the pyrolysis of the heteroatom precursor is used to promote the formation of carbon nanotubes and the heteroatom doping of carbon nanotubes, further improving its catalytic activity, and obtaining a carbon nanotube-encapsulated metal catalyst (M@CNT).

[0024] In the bamboo-shaped carbon nanotube-encapsulated metal catalyst of the present invention, metal particles are completely encapsulated inside the bamboo-shaped carbon nanotubes, and the carbon nanotubes are in the shape of bamboo nodes. This structure ensures the high dispersion of metal particles and avoids the agglomeration of metal particles during the catalytic process, thereby enhancing the reaction activity and corrosion resistance of the catalyst. In addition, the carbon nanotubes provide excellent conductivity and a large number of active sites, and the strong interaction between the metal and the carbon nanotubes ensures the excellent catalytic activity of the catalyst.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] First, the present invention successfully encapsulates non-precious metals completely inside carbon nanotubes (CNTs) through a unique synthesis strategy, forming a novel carbon-encapsulated metal structure composite material. This structure not only provides abundant active sites, but also effectively prevents the metal from directly contacting oxygen or solution in the reaction system, thereby improving the stability and durability of the catalyst.

[0027] Secondly, since the present invention reduces the content of precious metals or does not use precious metals, the preparation cost of the catalyst is greatly reduced, which helps to promote the large-scale and extensive application of non-precious metal catalysts in various catalytic reactions.

[0028] Third, the present invention is easy to construct non-precious metal alloys such as iron, cobalt, nickel, and manganese, or to modify trace precious metals such as Pt, Pd, and Au, and can synthesize different metal catalysts. According to the characteristics of each metal, it can be applied to different types of catalytic reactions, greatly improving the catalytic activity. The present invention can also prepare alloys (such as FeCo@N-CNT) by introducing a variety of metal salts. The synergistic effect between the two metals can further significantly improve the activity of the catalyst, and it has shown good catalytic activity and long-term stability in both oxygen reduction reaction (ORR) and water treatment advanced oxidation process (AOP).

[0029] Fourthly, the present invention can perform heteroatom doping on carbon nanotubes through a simple pyrolysis method. For example, doping carbon nanotubes with elements such as N, S, and P can further optimize the electronic structure of carbon nanotubes, enhance the interaction with metals, and improve the activity of the catalyst.

[0030] Fifth, compared with the traditional preparation method of carbon nanotube-encapsulated metal catalysts, the present invention uses low-cost commercial carbon black as a carbon precursor for the first time, without adding any organic solvents. The preparation method is green and simple, pyrolysis does not produce polluting gases, and the product exhibits excellent catalytic activity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a scanning electron microscope image of the bamboo-shaped carbon nanotube-encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1.

[0032] Figure 2 This is a scanning electron microscope image of the bamboo-shaped carbon nanotube-encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2.

[0033] Figure 3 This is a transmission electron microscope image of the bamboo-shaped carbon nanotube-encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1.

[0034] Figure 4 It is the X-ray diffraction spectrum of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT), carbon material (AC) and nitrogen-doped carbon material (N-AC) prepared in Example 1.

[0035] Figure 5 This is a graph comparing the oxygen reduction activity of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 and commercial platinum carbon.

[0036] Figure 6 This is a stability test chart comparing the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 with commercial platinum carbon.

[0037] Figure 7This is a performance graph of the bamboo-shaped carbon nanotube encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2 and Fe element, ferrous sulfate, and the degradation of the pollutant sulfadiazine by AOP technology under the conditions of no catalyst.

[0038] Figure 8 This is a cycle performance diagram of the bamboo-shaped carbon nanotube encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2 for degrading the pollutant sulfadiazine through the AOP technology. DETAILED DESCRIPTION

[0039] In order to better understand the present invention, the content of the present invention is further described below in conjunction with embodiments, but the present invention is not limited to the following embodiments.

[0040] Example 1

[0041] A method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes, the specific steps are as follows

[0042] (1) Weigh 0.5 g of carbon black into a round-bottom flask, then add 500 mL of 5 mol / L dilute hydrochloric acid, and then place the round-bottom flask in a 100° C. oil bath and heat for 8 h. After the reaction is completed, wash until neutral to obtain a black wet solid;

[0043] (2) The black wet solid obtained in step (1) is placed in a round-bottom flask, and then 500 mL of a 5 mol / L dilute nitric acid solution is added. The round-bottom flask is then placed in a 100° C. oil bath and heated for 8 h. After the reaction is completed, the solid is washed to neutrality, dried, and ground into powder to obtain acid-treated carbon black.

[0044] (3) 30 mg of the acid-treated carbon black obtained in step (2) was weighed and dispersed in 20 ml of a 0.4 mol / L glucose aqueous solution, and ultrasonically treated for 2 h. Then, 2 mmol of ferric nitrate and 2 mmol of cobalt nitrate were added, and the ultrasonic treatment was continued for 1 h to obtain a black dispersion; the black dispersion was then poured into a 50 mL high-pressure reactor, hydrothermally treated at 100° C. for 10 h, and then centrifuged, washed, and dried, and then ground to obtain a black powder.

[0045] (4) The black powder obtained in step (3) and melamine are mixed and ground evenly in a mass ratio of 1:5, and then calcined at 800° C. for 1 h under an Ar atmosphere, and the temperature is raised to 800° C. at a heating rate of 5° C. / min to obtain a metal catalyst encapsulated in bamboo-shaped carbon nanotubes.

[0046] The scanning electron microscopy of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 is as follows Figure 1As shown, the scale in the figure is 200nm. It can be seen from the figure that the iron-cobalt alloy particles are completely encapsulated inside the bamboo-shaped carbon nanotubes. The diameter of the alloy nanoparticles is about 20-60nm, and the diameter of the carbon nanotubes is also about 20-60nm.

[0047] The transmission electron microscopy of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 is as follows Figure 3 As shown in the figure, it can be seen that the iron-cobalt alloy particles are completely encapsulated inside the bamboo-shaped carbon nanotubes, and the diameter of the alloy nanoparticles is about 20 to 40 nm.

[0048] The X-ray diffraction of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 is as follows: Figure 4 As shown, 44.8° and 82.5° are iron-cobalt alloys (Co 3 Fe 7 ), and 25.1° is the characteristic peak of carbon. Among them, the carbon material (AC) is a non-doped non-nanotube carbon material, and the preparation process is different from that of Example 1 in that no iron nitrate and cobalt nitrate are added, and no melamine is added; the nitrogen-doped carbon material (N-AC) is a nitrogen-doped non-nanotube carbon material, and the preparation process is different from that of Example 1 in that no iron nitrate and cobalt nitrate are added. Both of these carbon materials have no added metals, and ultimately cannot form the morphology of nanotubes.

[0049] Application: The experiment was carried out under the control of an electrochemical workstation, and a glassy carbon rotating disk electrode was used to collect signals. A carbon electrode and an Ag / AgCl (3.5M KCl) electrode were used as the counting electrode and the reference electrode, respectively. A mixed suspension prepared by FeCo@N-CNT catalyst and 0.1wt% naphthol ethanol solution in a mass ratio of 1:2000 was added dropwise to the glassy carbon electrode as the working electrode. A standard three-electrode electrochemical system was used to continuously input O 2 The performance of oxygen reduction activity test was obtained by linear voltammetry. The stability test was carried out under the same test environment by chronoamperometry to measure the FeCo@N-CNT catalyst in O 2 Long-term stability in saturated alkaline solution. Methanol solvent was added after 500 cycles as a catalyst corrosion control experiment. The reaction solution was collected by ICP-MS to monitor the Fe and Co metal contents. No iron or cobalt was detected in the solution, indicating that the leaching of metals in the electrocatalytic reaction was negligible.

[0050] The comparison chart of carbon oxygen reduction activity of bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 and commercial platinum is as follows: Figure 5As shown: the oxygen reduction active solution is a 0.1M KOH solution. It can be seen from the figure that the activity of the catalyst prepared by the present invention is significantly better than that of commercial platinum carbon, and the half-wave potential is 42mV better than that of commercial platinum carbon.

[0051] The stability comparison chart of the bamboo-shaped carbon nanotube encapsulated metal catalyst (FeCo@N-CNT) prepared in Example 1 and commercial platinum carbon is as follows: Figure 6 As shown: From the data in the figure, it can be seen that after 500 cycles at room temperature and then methanol is added and the cycle continues for 1500 cycles, the linear curve of the catalyst prepared by the present invention does not change substantially and is not corroded by methanol, while commercial platinum carbon has obvious attenuation, and the final retention rate is more than 35% ahead of commercial platinum carbon.

[0052] It can be seen that the bamboo-shaped carbon nanotube encapsulated metal catalyst of the present invention is superior to the mainstream commercial Pt / C catalyst in the prior art in terms of key indicators such as starting potential, half-wave potential and limiting current density in oxygen reduction reaction (ORR). In particular, in the long-term stability test, the FeCo@N-CNT catalyst showed extremely low performance decay rate and alcohol corrosion resistance.

[0053] Example 2

[0054] The difference between Example 2 and Example 1 is that cobalt nitrate is not added.

[0055] The scanning electron microscopy of the bamboo-shaped carbon nanotube encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2 is as follows: Figure 2 As shown, the scale in the figure is 200nm. It can be seen from the figure that the iron metal particles are completely encapsulated inside the bamboo-shaped carbon nanotubes, and the diameter of the carbon nanotubes is about 30-40nm.

[0056] Application: 8 mg of sulfadiazine powder was weighed as a pollutant and dissolved in 400 mL of water as the mother liquor to be degraded; then 10 mg of the catalyst prepared in Example 2 was added to the 40 mL mother liquor, and then placed on a constant temperature shaker to form a uniform solution, and 1 mL of 30% mass concentration of H 2 O 2 The degradation process started under stirring, and samples were taken at regular intervals to analyze the pollutant concentration. Three control group experiments were conducted using the same method, with 0 catalyst dosage, 10 mg of ferrous sulfate as the catalyst replacement, and 10 mg of metallic iron as the catalyst replacement.

[0057] The performance curve of the bamboo-shaped carbon nanotube encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2 for degrading the pollutant sulfadiazine is as follows: Figure 7As shown: Fe@N-CNT catalyst can degrade 99% of sulfadiazine within 12 minutes, showing fast and efficient degradation performance compared with catalysts Fe element and ferrous sulfate.

[0058] The cycle performance curve of the bamboo-shaped carbon nanotube encapsulated metal catalyst (Fe@N-CNT) prepared in Example 2 for degrading the pollutant sulfadiazine is as follows: Figure 8 As shown: After three degradation cycles, the pollutant degradation rate is still maintained at 99%.

[0059] It can be seen that the bamboo-shaped carbon nanotube-encapsulated metal catalyst of the present invention can quickly and efficiently adsorb and catalytically degrade pollutants in the advanced oxidation (AOP) technology of water treatment. It can degrade 99% of pollutants (such as sulfadiazine, and also metronidazole, etc.) in aqueous solution within 12 minutes, and remove more than 70% of total organic carbon, showing rapid and efficient catalytic degradation performance.

[0060] Example 3

[0061] The only difference between Example 3 and Example 1 is that the mass of the acidified carbon black is 120 mg.

[0062] Example 4

[0063] The only difference between Example 4 and Example 1 is that cobalt nitrate is replaced by nickel nitrate or manganese nitrate.

[0064] Example 5

[0065] The only difference between Example 5 and Example 1 is that the calcination temperature is 600°C.

[0066] Example 6

[0067] The only difference between Example 6 and Example 1 is that melamine is replaced by an equal mass of other heteroatom precursors such as thioacetamide or phosphoramide.

[0068] Example 7

[0069] The only difference between Example 7 and Example 1 is that the mass of commercial carbon black is 2 to 5 g.

[0070] In summary, compared with traditional catalysts, the bamboo-shaped carbon nanotube-encapsulated metal catalyst provided by the present invention exhibits more excellent catalytic activity and stability in oxygen reduction reaction (ORR) and advanced oxidation reaction (AOP) of water treatment, has low cost, and has a wide range of applications.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and changes without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes, characterized in that: The steps include: (1) heating and refluxing the carbon black with a dilute acid, washing it to neutrality and then drying it to obtain an acid-treated carbon black powder; (2) adding the acid-treated carbon black powder obtained in step (1) to a glucose aqueous solution, then adding a water-soluble metal salt, and mixing by ultrasonication to obtain a metal / carbon chelated black suspension; (3) subjecting the black suspension obtained in step (2) to a hydrothermal reaction at 100 to 120° C. for 8 to 12 hours, separating the black wet solid, washing and drying it to obtain a black powder, which is the metal-loaded carbon material; (4) The black powder obtained in step (3) is mixed with the heteroatom precursor, ground and mixed, and calcined in a tubular furnace under a protective atmosphere to obtain a metal catalyst encapsulated by bamboo-shaped carbon nanotubes.

2. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: In step (1), the concentration of carbon black added in the dilute acid is in the range of 0.5 to 20 g / L, and the concentration of the dilute acid is 3 to 10 mol / L; the temperature of the heating reflux treatment is 100 to 120° C., and the heating time is 6 to 10 hours.

3. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: In step (1), carbon black is heated and refluxed with hydrochloric acid and dilute nitric acid in turn. The specific process is as follows: carbon black is added to hydrochloric acid with a concentration of 3 to 10 mol / L and the added concentration is in the range of 0.5 to 20 g / L. After heating and reflux treatment, it is washed to neutrality and then added to dilute nitric acid with a concentration of 3 to 10 mol / L. After a second heating and reflux treatment, it is washed to neutrality and then dried to obtain acid-treated carbon black powder.

4. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: The carbon black is commercial carbon black; the corresponding water-soluble metal salt is used to prepare the metal catalyst, and the metal mainly refers to one or more of the non-precious metals Fe, Co, Ni, and Mn; the heteroatom refers to one or more of N, S, and P, and the heteroatom precursor is selected from one or more of melamine, sulfur, thioacetamide or phosphoramide, and phosphide.

5. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 4, characterized in that: The metal also includes one or more of the noble metals Pt, Pd, and Au.

6. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: In step (2), the concentration of the glucose aqueous solution is in the range of 0.2 to 0.6 mol / L, the concentration of the acid-treated carbon black powder in the glucose aqueous solution is in the range of 1.5 to 6 g / L; the concentration of the water-soluble metal salt in the glucose aqueous solution is in the range of 0 to 0.2 mol / L and is not 0, calculated based on the concentration of metal ions.

7. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: In step (4), the mass ratio of the heteroatom precursor to the black powder is 0 to 10; when the amount of the heteroatom precursor is not 0, the carbon nanotubes are heteroatom-doped carbon nanotubes, and when the amount of the heteroatom precursor is 0, they are undoped carbon nanotubes.

8. The method for preparing a metal catalyst encapsulated by bamboo-shaped carbon nanotubes according to claim 1, characterized in that: In step (4), the calcination conditions are: calcination at a temperature of 600-1000° C. for 0.5-2 h in an Ar atmosphere; wherein the temperature is increased to the calcination temperature at a heating rate of 3-10° C. / min.

9. The metal catalyst encapsulated by bamboo-shaped carbon nanotubes prepared by the method of claim 1, characterized in that: The metal is encapsulated in the carbon nanotube in the form of nanoparticles. The carbon nanotube is in the shape of bamboo nodes and has a diameter in the range of 20 to 60 nm. The metal nanoparticles are nanoparticles of a single metal or nanoparticles of an alloy, and the carbon nanotube is a heteroatom-doped carbon nanotube or an undoped carbon nanotube.

10. Use of the metal catalyst encapsulated by the bamboo-shaped carbon nanotubes according to claim 9 in oxygen reduction reaction or advanced oxidation for water treatment.

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