Quantitative analysis method for internal and external loading capacities of carbon nanotubes

Abstract

A quantitative analysis method for internal and external loading capacities of carbon nanotubes. The method comprises the following steps: (1) placing, in a tubular furnace, carbon nanotubes loaded with metal catalyst particles, and vacuumizing same; (2) performing annealing and capping; (3) calcining same, then placing same in a reaction kettle, adding dilute sulfuric acid, and heating same while stirring to obtain a sulfuric acid metal salt solution and capped carbon nanotubes in which metal catalyst particles are loaded; (4) measuring the loading capacity of nickel in the carbon nanotubes by means of IPC-MS technology; and (5) measuring the content of metal ions in the sulfuric acid metal salt solution by means of an EDTA coupling method. Capping the carbon nanotubes in advance before detection prevents metal nano particles loaded in the tubes from leaking, provides prerequisites for subsequent respective detection of the loading capacities in the tubes and on the outer walls, and also improves the detection precision of the internal and external loading capacities of carbon nanotubes. Moreover, the progress rate and extent of the capping reaction are regulated and controlled by adjusting the annealing temperature and rate, thereby achieving a better capping effect.

Description

A quantitative analysis method for the internal and external loading of carbon nanotubes Technical Field

[0001] The present invention relates to the field of element content detection methods, and in particular to a quantitative analysis method for the internal and external loading of carbon nanotubes. Background Art

[0002] Due to the unique structure and properties of carbon nanotubes, they have excellent conditions as catalyst carriers. By selecting a suitable approach to assemble the catalyst inside the carbon nanotubes, the modulation effect of the carbon nanotube lumen on the catalyst performance is utilized to achieve the purpose of improving catalytic activity. Most of the existing technologies use liquid phase impregnation methods to assemble the catalyst on the inner and outer walls of carbon nanotubes. However, the uncertainty of the total amount of precursor solution entering the carbon nanotubes makes it impossible to control the final nickel nanoparticle loading in the tube. Currently, the total amount of metal loading on carbon nanotubes can be detected by plasma mass spectrometry or flame atomic absorption spectrometry, but this detection method is not selective and cannot distinguish the absolute loading on the inner and outer walls of the tube. The nickel loading on the inner and outer walls of the tube can be observed by taking a local transmission electron microscope of the carbon nanotube, but this method has serious errors.

[0003] Summary of the Invention

[0004] To address the problems of existing carbon nanotube loading detection methods, which lack selectivity for metal nanoparticles loaded on the inner and outer walls of the tubes and exhibit low detection accuracy, the present invention provides a quantitative analysis method for the internal and outer loading of carbon nanotubes. By pre-capping the carbon nanotubes prior to detection, this method prevents leakage of metal nanoparticles loaded within the tubes, facilitating subsequent separate detection of the loading on the inner and outer walls of the tubes while also improving the accuracy of the detection of the internal and outer loading of the carbon nanotubes. Furthermore, the present invention performs the capping during the annealing of the carbon nanotubes, regulating the rate and extent of the capping reaction by adjusting the annealing temperature and rate, thereby achieving a more effective capping effect.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A method for quantitatively analyzing the internal and external loading of carbon nanotubes, characterized by comprising the following steps:

[0007] S1: Pretreatment: placing carbon nanotubes loaded with metal catalyst particles in a tube furnace and evacuating the furnace; the metal catalyst particles are one of cobalt, nickel, and copper;

[0008] S2: End-capping: Annealing the carbon nanotubes at a temperature of 1200°C to 1500°C; introducing a carbon source gas into the tube furnace at the beginning of cooling;

[0009] S3: Oxidation and hydrothermal reaction: The carbon nanotubes annealed in step S2 are placed in the air for calcination to convert the metal catalyst particles supported on the outer walls of the carbon nanotubes into an oxidized state. The carbon nanotubes are then placed in a reactor and diluted sulfuric acid is added. The mixture is heated and stirred to dissolve the oxidized metal catalyst particles attached to the outer walls of the carbon nanotubes, thereby obtaining a sulfuric acid metal salt solution and capped carbon nanotubes with the metal catalyst particles supported therein.

[0010] S4: Detection of the internal loading capacity of carbon nanotubes: For the capped carbon nanotubes treated in S3, the internal loading capacity of carbon nanotubes was measured by IPC-MS technology;

[0011] S5: Detection of external loading of carbon nanotubes: For the sulfuric acid metal salt solution after treatment in S3, the content of metal catalyst particles in the sulfuric acid metal salt solution is determined by EDTA coupling method, which is the external loading of carbon nanotubes.

[0012] Furthermore, in step S1, vacuum is applied for 1 to 2 hours to make the vacuum degree in the tube furnace 0.1 MPa. After vacuum application, the tube furnace is sealed for 0.5 to 1 hour.

[0013] Furthermore, in step S2, the heating rate in the tube furnace is controlled at 3-5°C / min, and the holding time is 10-15h.

[0014] Furthermore, in step S2, the cooling step is: cooling to 600°C at a cooling rate of 3-5°C / min, and then cooling to room temperature in the furnace.

[0015] Furthermore, in step S2, the carbon source gas is one or more of acetylene, methane, and ethylene.

[0016] Furthermore, in step S2, the carbon source gas is introduced at a rate of 10 to 20 mL / min for a time period of 2 to 5 minutes.

[0017] Furthermore, in step S3, the concentration of the dilute sulfuric acid is 3.5 mol / L.

[0018] Furthermore, in step S3, the stirring temperature is 80° C. to 100° C.; the stirring time is not less than 6 hours; and the hydrothermal reaction is repeated 2 to 3 times.

[0019] Furthermore, in step S4, the specific operation steps of the IPC-MS technology are:

[0020] S4.1: Extract the capped carbon nanotubes loaded with metal catalyst particles from the tube, add acid and heat to dissolve, and adjust the volume to obtain a test solution;

[0021] S4.2: The test solution in step S4.1 is measured on an inductively coupled plasma mass spectrometer to determine the content of the metal catalyst particles.

[0022] Furthermore, in step S5, the specific operation steps of the EDTA coupling method are:

[0023] S5.1: Prepare pH buffer solution;

[0024] S5.2: Add the pH buffer solution dropwise to the metal sulfate solution to obtain a mixed solution I having a pH value of 8 to 10;

[0025] S5.3: Continuously add the indicator to mixed solution I until mixed solution I changes color, thereby obtaining mixed solution II;

[0026] S5.4: Continue to add EDTA standard solution dropwise to mixed solution II until mixed solution II changes color;

[0027] The molar concentration of the EDTA standard solution is 0.2 mol / L, and the nickel content in the aqueous solution of nickel sulfate is calculated using Formula 1;

[0028] Among them, c EDTA is the molar concentration of EDTA standard solution; v EDTA is the consumed volume of EDTA standard solution; M is the relative mass fraction of metal catalyst; m is the mass of carbon nanotubes initially loaded with metal catalyst particles.

[0029] The beneficial effects of the present invention are as follows:

[0030] 1. The end-capping of carbon nanotubes in this invention prevents nickel nanoparticles from leaking out of the tubes, which could affect the accuracy of detecting the nickel loading within the tubes. End-capping allows for separate detection of nickel loading inside and outside the tubes, enabling a more comprehensive assessment of catalytic performance.

[0031] 2. The present invention performs end-capping during the annealing cooling phase, during which the carbon nanotube structure undergoes a certain degree of rearrangement and repair, which helps fill the open ends with carbon atoms generated by acetylene decomposition. Simultaneously, by controlling the annealing temperature and rate, the rate and extent of the end-capping reaction can be regulated, thereby achieving better carbon nanotube end-capping results. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is an XRD characterization diagram of the capped carbon nanotubes after aerobic calcination according to Example 1 of the present invention;

[0033] FIG2( a ) is a TEM image of the uncapped carbon nanotubes described in Example 1 of the present invention;

[0034] FIG2( b ) is a TEM image of the capped carbon nanotubes according to Example 1 of the present invention;

[0035] FIG3 is a comparison of Raman characterization and ID / IG values ​​of uncapped and capped carbon nanotubes at different annealing temperatures according to Example 1 of the present invention;

[0036] FIG4 is a comparison of the specific surface area and out-of-bounds nickel loading of uncapped and capped carbon nanotubes at different annealing temperatures according to Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0038] Example 1

[0039] The metal catalyst particles in this embodiment are nickel. The method for quantitatively analyzing the nickel loading inside and outside the carbon nanotubes includes the following steps:

[0040] S1: Pretreatment: Place the nickel-loaded carbon nanotubes in a tube furnace, evacuate the tube furnace for 1 hour until the vacuum degree in the tube furnace is 0.1 MPa, and exhaust the combustible gas.

[0041] In order to check the air tightness in the furnace, this embodiment continues to seal the furnace for 0.5 hours after vacuuming for 1 hour to check the air tightness in the furnace, so as to ensure the smooth progress of subsequent process steps.

[0042] S2: End-capping: Raise the furnace temperature to 1450°C at a rate of 5°C / min and hold for 12 hours. Then, lower the furnace temperature to 600°C at a rate of 3°C / min and allow the furnace to cool to room temperature. Simultaneously, inject acetylene into the furnace at a rate of 10 mL / min for 2 minutes via a flowmeter to complete the carbon nanotube end-capping stage.

[0043] S3: Oxidation and hydrothermal reaction: The carbon nanotubes annealed in step S2 are placed in the atmosphere and calcined for 3-4 hours to convert the nickel element supported on the outer wall of the carbon nanotubes into an oxidized state. Figure 1 shows the XRD characterization of the capped carbon nanotubes after aerobic calcination. It can be seen from the figure that the carbon nanotubes (capped) after aerobic calcination are composed of carbon nanotube carriers, nickel element supported on the inner wall of the carbon nanotubes, and nickel oxide supported on the outer wall of the carbon nanotubes. The calcined carbon nanotubes are placed in a reactor, and 30 mL of 3.5 mol / L dilute sulfuric acid is added to a constant volume. After heating and stirring at 90°C for 6 hours, a yellow-green nickel sulfate aqueous solution and capped carbon nanotubes with nickel loaded inside the tubes are obtained. The above hydrothermal reaction is repeated 2-3 times to ensure that all the nickel element on the outer wall of the tubes is converted to nickel sulfate.

[0044] S4: Determine the nickel loading in carbon nanotubes by IPC-MS technology. The specific steps are as follows:

[0045] S4.1: Extract the nickel-loaded capped carbon nanotubes in the tube, add acid and heat to dissolve, and adjust the volume to obtain the test solution.

[0046] S4.2: Take the test solution in step S4.1 and measure it on an inductively coupled plasma mass spectrometer to obtain the nickel content.

[0047] S5: Determine the nickel content in the nickel sulfate aqueous solution by EDTA coupling method. The specific steps are as follows:

[0048] S5.1: Weigh ammonium hydroxide and ammonium chloride and prepare a buffer solution with a pH of 10.

[0049] S5.2: Add the buffer solution dropwise to the aqueous solution of nickel sulfate to obtain a mixed solution I with a pH value of 10.

[0050] S5.3: Continue to add murexide indicator dropwise to mixed solution I until mixed solution I turns golden yellow to obtain mixed solution II.

[0051] S5.4: Continue to add EDTA standard solution to mixed solution II until mixed solution II turns violet blue.

[0052] The molar concentration of the EDTA standard solution is 0.2 mol / L, and the nickel content in the nickel sulfate aqueous solution is calculated using Formula 1.

[0053] Among them, c EDTA is the molar concentration of EDTA standard solution; v EDTA is the consumption volume of EDTA standard solution; M Ni is the relative mass fraction of nickel; m is the mass of the initial nickel-loaded carbon nanotubes.

[0054] In order to verify the effect of end-capping on the detection accuracy of nickel loading on the inner and outer walls of carbon nanotubes, the following control experiments were also conducted in this example:

[0055] S1: Calcinate the uncapped carbon nanotubes in air for 3-4 hours to convert the loaded nickel into nickel oxide. The nanotubes are then placed in a reactor and 30 mL of 3.5 mol / L dilute sulfuric acid is added. Heat and stir at 90°C for 6 hours to obtain a yellow-green aqueous solution of nickel sulfate and uncapped carbon nanotubes. Repeat this hydrothermal reaction 2-3 times to ensure that all nickel oxide on the carbon nanotubes is converted into nickel sulfate.

[0056] S2: Determine the nickel content in the nickel sulfate aqueous solution by EDTA coupling method. The specific steps are as follows:

[0057] S2.1: Weigh ammonium hydroxide and ammonium chloride and prepare a buffer solution with a pH of 10.

[0058] S2.2: Add the buffer solution dropwise to the aqueous solution of nickel sulfate to obtain a mixed solution I with a pH value of 10.

[0059] S2.3: Continuously add murexide indicator to the mixed solution I until the mixed solution I turns golden yellow to obtain a mixed solution II.

[0060] S2.4: Continue to add EDTA standard solution dropwise to mixed solution II until mixed solution II turns violet-blue.

[0061] The molar concentration of the EDTA standard solution is 0.2 mol / L, and the nickel content in the nickel sulfate aqueous solution is calculated using Formula 1.

[0062] Among them, c EDTA is the molar concentration of EDTA standard solution; v EDTA is the consumption volume of EDTA standard solution; M Ni is the relative mass fraction of nickel; m is the mass of the initial nickel-loaded carbon nanotubes.

[0063] FIG2(a) and (b) are SEM images of the uncapped and capped carbon nanotubes, respectively, according to this embodiment. As shown in the figure, a black passivation layer appears at the end of the capped carbon nanotube, indicating that the acetylene was introduced during annealing to achieve a good capping effect in this embodiment.

[0064] FIG3 is a Raman characterization and ID / IG value comparison diagram of the uncapped and capped carbon nanotubes described in this embodiment at different annealing temperatures. It can be seen from the figure that the ID / IG value of the uncapped carbon nanotubes is significantly higher than that of the capped carbon nanotubes, which means that the uncapped carbon nanotubes have lower crystallinity and more defects.

[0065] Figure 4 compares the specific surface area and external nickel loading of uncapped and capped carbon nanotubes at different annealing temperatures described in this example. As shown, for uncapped carbon nanotubes, it is impossible to separately measure the nickel loading inside and outside the tubes; only the total nickel loading on the carbon nanotubes can be measured. However, for capped carbon nanotubes, the ratio of internal to external nickel loading increases with increasing annealing temperature, with the optimal capping effect achieved at approximately 1400°C.

[0066] Example 2

[0067] The difference between this embodiment and embodiment 1 is that the metal catalyst particles are cobalt. The quantitative analysis method of the cobalt loading inside and outside the carbon nanotubes is different from the quantitative analysis method in embodiment 1 only in that the pH buffer solution and indicator components in step S5 are different, and the remaining steps are consistent with embodiment 1.

[0068] Example 3

[0069] The difference between this embodiment and embodiment 1 is that the metal catalyst particles are copper. The quantitative analysis method of the copper loading inside and outside the carbon nanotubes is different from the quantitative analysis method in embodiment 1 only in that the pH buffer solution and indicator components in step S5 are different, and the remaining steps are consistent with embodiment 1.

[0070] The embodiments described are preferred implementations of the present invention, but the present invention is not limited to the above implementations. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention are within the scope of protection of the present invention.

Claims

1. A quantitative analysis method for the internal and external loading of carbon nanotubes, characterized in that: The following steps are involved: S1： Pretreatment: placing carbon nanotubes loaded with metal catalyst particles in a tube furnace and evacuating the tube furnace; the metal catalyst particles are one of cobalt, nickel and copper; S2: Capping: Annealing the carbon nanotubes, setting the annealing temperature to 1200°C to 1500°C; passing carbon source gas into the tube furnace when cooling begins; S3: oxidation and hydrothermal reaction: placing the carbon nanotubes annealed in step S2 in the air for calcination to convert the metal catalyst particles loaded on the outer wall of the carbon nanotubes into an oxidized state; then placing the carbon nanotubes in a reaction kettle and adding dilute sulfuric acid, heating and stirring to dissolve the oxidized metal catalyst particles attached to the outer wall of the carbon nanotubes, and obtaining a sulfuric acid metal salt solution and capped carbon nanotubes loaded with metal catalyst particles in the tubes; S4: Detection of the internal loading of the carbon nanotubes: For the capped carbon nanotubes treated in S3, the internal loading of the carbon nanotubes is measured by IPC-MS technology; S5: Detection of the external loading of the carbon nanotubes: For the metal sulfate solution after the treatment in S3, the content of the metal catalyst particles in the metal sulfate solution is determined by the EDTA coupling method, which is the external loading of the carbon nanotubes.

2. The quantitative analysis method according to claim 1, characterized in that In step S1, the vacuum is evacuated for 1 to 2 hours to make the vacuum degree in the tube furnace 0.1 MPa. After the vacuum is evacuated, the tube furnace is sealed for 0.5 to 1 hour.

3. The quantitative analysis method according to claim 1, characterized in that: In step S2, the heating rate in the tube furnace is controlled at 3-5°C / min, and the insulation time is 10-15h.

4. The quantitative analysis method according to claim 1, characterized in that: In step S2, the cooling step is: cooling to 600°C at a cooling rate of 3-5°C / min, and then cooling to room temperature in the furnace.

5. The quantitative analysis method according to claim 1, characterized in that: In step S2, the carbon source gas is one or more of acetylene, methane, and ethylene.

6. The quantitative analysis method according to claim 1, characterized in that: In step S2, the carbon source gas is introduced at a rate of 10 to 20 mL / min for a period of 2 to 5 min.

7. The quantitative analysis method according to claim 1, characterized in that: In step S3, the concentration of the dilute sulfuric acid is 3.5 mol / L.

8. The quantitative analysis method according to claim 1, characterized in that: In step S3, the stirring temperature is 80°C to 100°C; the stirring time is not less than 6 hours; and the hydrothermal reaction is repeated 2 to 3 times.

9. The quantitative analysis method according to claim 1, characterized in that: In step S4, the specific operation steps of the IPC-MS technology are: S4.1: extracting the capped carbon nanotubes loaded with metal catalyst particles in the tube, adding acid and hot dissolving, and fixing the volume to obtain a test solution; S4.2: The test solution in step S4.1 is measured on an inductively coupled plasma mass spectrometer to measure the content of the metal catalyst particles.

10. The quantitative analysis method according to claim 1, characterized in that: In step S5, the specific operation steps of the EDTA coupling method are: S5.1: Prepare pH buffer solution; S5.2: dropping the pH buffer solution into the metal sulfate solution to obtain a mixed solution I with a pH value of 8 to 10; S5.3: Continuously add the indicator to the mixed solution I until the mixed solution I changes color, thereby obtaining a mixed solution II; S5.4: Continue to add EDTA standard solution to mixed solution II until mixed solution II changes color; The molar concentration of the EDTA standard solution is 0.2 mol / L, and the nickel content in the aqueous solution of nickel sulfate is calculated using Formula 1; Among them, c EDTA is the molar concentration of EDTA standard solution; v EDTA is the consumed volume of EDTA standard solution; M is the relative mass fraction of metal catalyst; m is the mass of carbon nanotubes initially loaded with metal catalyst particles.

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