Quantitative analysis method for loading amount of carbon nanotubes

Abstract

This invention provides a quantitative analysis method for the loading of carbon nanotubes inside and outside the tube, comprising the following steps: ① placing carbon nanotubes loaded with metal catalyst particles in a tube furnace and evacuating the vacuum; ② annealing and end-sealing; ③ calcining, followed by placing the tubes in a reaction vessel, adding dilute sulfuric acid, heating and stirring to obtain a metal sulfate solution and end-sealed carbon nanotubes loaded with metal catalyst particles; ④ determining the nickel loading inside the carbon nanotubes using IPC-MS technology; ⑤ determining the metal ion content in the metal sulfate solution using EDTA coupling method. This invention, by pre-sealing the carbon nanotubes before detection, prevents leakage of the loaded metal nanoparticles inside the tube, providing a prerequisite for subsequent detection of the loading inside and outside the tube, while improving the detection accuracy of the loading inside and outside the carbon nanotubes. Furthermore, this invention achieves better end-sealing effect by adjusting the annealing temperature and annealing rate to control the rate and extent of the end-sealing reaction.

Description

Technical Field

[0001] This invention relates to the field of methods for detecting elemental content, and specifically to a method for quantitative analysis of the loading inside and outside carbon nanotubes. Background Technology

[0002] Due to their unique structure and properties, carbon nanotubes possess excellent conditions for serving as catalyst supports. By selecting appropriate methods to assemble catalysts inside carbon nanotubes, the performance modulation effect of the carbon nanotube cavity can be utilized to enhance catalytic activity. Most existing technologies employ liquid-phase impregnation to assemble catalysts onto the inner and outer walls of carbon nanotubes; however, the uncertainty of the total amount of precursor solution entering the carbon nanotube makes it impossible to control the final nickel nanoparticle loading within the tube. Currently, inductively coupled plasma mass spectrometry (ICP-MS) or flame atomic absorption spectrometry (FAAS) can detect the total metal loading on carbon nanotubes, but these methods lack selectivity and cannot distinguish the absolute loading on the inner and outer walls. While transmission electron microscopy (TEM) can observe the nickel loading on the inner and outer walls of carbon nanotubes, this method suffers from significant errors. Summary of the Invention

[0003] To address the shortcomings of existing methods for detecting the loading of metal nanoparticles on the inner and outer walls of carbon nanotubes, such as lack of selectivity and low detection accuracy, this invention provides a quantitative analysis method for the loading of carbon nanotubes inside and outside. By pre-sealing the carbon nanotubes before detection, leakage of the loaded metal nanoparticles inside the tube is prevented, providing a prerequisite for subsequent detection of the loading on the inner and outer walls, while simultaneously improving the detection accuracy of the loading. Furthermore, this invention selects to perform the sealing during the annealing of the carbon nanotubes, and by adjusting the annealing temperature and rate, the rate and extent of the sealing reaction are controlled, thereby achieving a better sealing effect.

[0004] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0005] A method for quantitative analysis of the loading capacity inside and outside carbon nanotubes, characterized by comprising the following steps:

[0006] S1: Pretreatment: Carbon nanotubes loaded with metal catalyst particles are placed in a tube furnace and vacuumed; the metal catalyst particles are one of cobalt, nickel, and copper.

[0007] S2: End sealing: Annealing the carbon nanotubes at a temperature of 1200℃~1500℃; introducing carbon source gas into the tube furnace at the beginning of cooling.

[0008] S3: Oxidation and hydrothermal reaction: The carbon nanotubes annealed in step S2 are placed in the atmosphere for calcination, so that the metal catalyst particles loaded on the outer wall of the carbon nanotubes are converted into the oxidized state. Then, they are placed in a reaction vessel and dilute sulfuric acid is added. The mixture is heated and stirred to dissolve the oxidized metal catalyst particles attached to the outer wall of the carbon nanotubes, resulting in a sulfate metal salt solution and capped carbon nanotubes with metal catalyst particles loaded inside the tubes.

[0009] S4: Intratube loading detection: For the capped carbon nanotubes after S3 treatment, the intratube loading of carbon nanotubes was determined by IPC-MS technology.

[0010] S5: External loading detection: For the sulfate metal salt solution after S3 treatment, the content of metal catalyst particles in the sulfate metal salt solution is determined by EDTA coupling method, which is the external loading of carbon nanotubes.

[0011] Further, in step S1, the vacuum level inside the tubular furnace is 0.1 MPa after being evacuated for 1 to 2 hours, and then the tubular furnace is sealed for 0.5 to 1 hour.

[0012] Furthermore, in step S2, the heating rate inside the tubular furnace is controlled at 3-5℃ / min, and the holding time is 10-15h.

[0013] Further, in step S2, the cooling step is as follows: the temperature is reduced to 600°C at a cooling rate of 3-5°C / min, and then cooled to room temperature with the furnace.

[0014] Further, in step S2, the carbon source gas is one or more of acetylene, methane, and ethylene.

[0015] Further, in step S2, the rate of introduction of the carbon source gas is 10-20 mL / min; the introduction time is 2-5 min.

[0016] Furthermore, in step S3, the concentration of the dilute sulfuric acid is 3.5 mol / L.

[0017] Furthermore, in step S3, the stirring temperature is 80℃~100℃; the stirring time is not less than 6 hours; and the hydrothermal reaction is repeated 2~3 times.

[0018] Furthermore, in step S4, the specific operation steps of the IPC-MS technology are as follows:

[0019] S4.1: Extract the end-capped carbon nanotubes loaded with metal catalyst particles inside the extraction tube, add acid to dissolve them by heating, and make up the volume to obtain the test solution;

[0020] S4.2: Take the test liquid from step S4.1 and perform analysis on an inductively coupled plasma mass spectrometer to determine the content of metal catalyst particles.

[0021] Furthermore, in step S5, the specific operation steps of the EDTA coupling method are as follows:

[0022] S5.1: Prepare pH buffer solution;

[0023] S5.2: Add the pH buffer solution dropwise into the metal sulfate solution to obtain a mixed solution I with a pH value of 8-10;

[0024] S5.3: Continuously add indicator to mixed solution I until mixed solution I changes color to obtain mixed solution II;

[0025] S5.4: Continuously add EDTA standard solution to mixed solution II until mixed solution II changes color;

[0026] The molar concentration of the EDTA standard solution is 0.2 mol / L. The nickel content in the aqueous solution of nickel sulfate is calculated using Formula I.

[0027]

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

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

[0030] 1. In this invention, end-capping the carbon nanotubes prevents nickel nanoparticles from leaking out of the tubes, thus avoiding affecting the accuracy of nickel loading detection. End-capping allows for separate detection of nickel loading inside and outside the tubes, enabling a more comprehensive evaluation of catalytic performance.

[0031] 2. In this invention, end-capping is performed during the annealing and cooling stage. During this stage, the structure of the carbon nanotubes undergoes a certain degree of rearrangement and repair, which helps to fill the open ports with carbon atoms generated from the decomposition of acetylene. Simultaneously, by controlling the annealing temperature and annealing rate, the rate and extent of the end-capping reaction can be controlled, thereby achieving a better carbon nanotube end-capping effect. Attached Figure Description

[0032] Figure 1 The image shows the XRD characterization of the capped carbon nanotubes described in Example 1 of this invention after aerobic calcination.

[0033] Figure 2(a) is a TEM image of the unsealed carbon nanotubes described in Example 1 of the present invention;

[0034] Figure 2 (b) is a TEM image of the capped carbon nanotubes described in Example 1 of the present invention;

[0035] Figure 3 This is a Raman characterization and ID / IG value comparison chart of unsealed and sealed carbon nanotubes at different annealing temperatures according to Example 1 of the present invention.

[0036] Figure 4 This is a comparison chart of the specific surface area and external nickel loading of uncapped and capped carbon nanotubes described in Example 1 of the present invention at different annealing temperatures. Detailed Implementation

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

[0038] Example 1

[0039] In this embodiment, the metal catalyst particles are nickel, and the quantitative analysis method for the nickel loading inside and outside the carbon nanotubes includes the following steps:

[0040] S1: Pretreatment: Place nickel-loaded carbon nanotubes in a tube furnace and evacuate for 1 hour to achieve a vacuum level of 0.1 MPa in the tube furnace, and then remove combustible gases.

[0041] To check the airtightness of the furnace, this embodiment continues to seal the furnace for 0.5 hours after evacuating for 1 hour to check the airtightness, ensuring the smooth progress of subsequent process steps.

[0042] S2: End-sealing: The furnace temperature is raised to 1450℃ at a heating rate of 5℃ / min and held for 12 hours; then the furnace temperature is lowered to 600℃ at a cooling rate of 3℃ / min, and then cooled to room temperature with the furnace. While cooling, acetylene is injected into the furnace at a rate of 10mL / min for 2 minutes using a flow meter to complete the end-sealing stage of the carbon nanotubes.

[0043] S3: Oxidation and hydrothermal reaction: The carbon nanotubes after annealing in step S2 are placed in the atmosphere for calcination for 3-4 hours, so that the nickel element supported on the outer wall of the carbon nanotubes is converted into an oxidized state. Figure 1The image shows the XRD pattern of capped carbon nanotubes after aerobic calcination. It can be seen from the image that the capped carbon nanotubes after aerobic calcination consist of a carbon nanotube carrier, elemental nickel loaded on the inner wall of the carbon nanotubes, and nickel oxide loaded on the outer wall of the carbon nanotubes. The calcined carbon nanotubes were placed in a reaction vessel, and 30 mL of 3.5 mol / L dilute sulfuric acid was added. After heating and stirring at 90 °C for 6 h, a yellow-green aqueous solution of nickel sulfate and capped carbon nanotubes loaded with nickel were obtained. The above hydrothermal reaction was repeated 2–3 times to ensure that all elemental nickel on the outer wall of the tubes was converted to nickel sulfate.

[0044] S4: The nickel loading inside carbon nanotubes was determined using IPC-MS technology. The specific steps are as follows:

[0045] S4.1: Extract the nickel-loaded capped carbon nanotubes from the tube, add acid to dissolve them by heating, and make up the volume to obtain the test solution.

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

[0047] S5: The nickel content in an aqueous solution of nickel sulfate was determined by EDTA coupling method. The specific steps are as follows:

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

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

[0050] S5.3: Continuously add ammonium purpurate indicator to mixed solution I until mixed solution I turns golden yellow, thus obtaining mixed solution II.

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

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

[0053]

[0054] Among them, c EDTA v is the molar concentration of the EDTA standard solution; EDTA M represents the volume of EDTA standard solution consumed. Ni denoted as the relative mass fraction of nickel; m is the initial mass of the nickel-loaded carbon nanotubes.

[0055] To verify the impact of end capping on the accuracy of nickel loading detection on the inner and outer walls of carbon nanotubes, the following comparative experiment was also conducted in this embodiment:

[0056] S1: Uncapped carbon nanotubes are calcined in the atmosphere for 3–4 hours, converting the supported nickel to nickel oxide. The resulting solution is then placed in a reaction vessel, and 30 mL of 3.5 mol / L dilute sulfuric acid is added. The mixture is heated and stirred at 90°C for 6 hours to obtain a yellow-green aqueous solution of nickel sulfate and uncapped carbon nanotubes. This hydrothermal reaction is repeated 2–3 times to ensure that all nickel oxide on the carbon nanotubes is converted to nickel sulfate.

[0057] S2: The nickel content in an aqueous solution of nickel sulfate was determined by EDTA coupling method. The specific steps are as follows:

[0058] S2.1: Weigh out ammonium hydroxide and ammonium chloride and prepare a buffer solution with a pH of 10.

[0059] S2.2: Add the buffer solution dropwise into the aqueous solution of nickel sulfate to obtain mixed solution I with a pH of 10.

[0060] S2.3: Continuously add ammonium purpurate indicator to mixed solution I until mixed solution I turns golden yellow, thus obtaining mixed solution II.

[0061] S2.4: Continuously add EDTA standard solution to mixed solution II until mixed solution II turns violet blue.

[0062] The EDTA standard solution has a molar concentration of 0.2 mol / L. The nickel content in the aqueous solution of nickel sulfate is calculated using Formula I.

[0063]

[0064] Among them, c EDTA v is the molar concentration of the EDTA standard solution; EDTA M represents the volume of EDTA standard solution consumed. Ni denoted as the relative mass fraction of nickel; m is the initial mass of the nickel-loaded carbon nanotubes.

[0065] Figure 2 (a) and (b) are SEM images of the unsealed and sealed carbon nanotubes described in this embodiment, respectively. As shown in the figure, a black passivation layer appears at the end of the sealed carbon nanotube, indicating that the acetylene purging during annealing in this embodiment achieved a good sealing effect.

[0066] Figure 3 The figure shows the Raman characterization and ID / IG value comparison of uncapped and capped carbon nanotubes at different annealing temperatures in this embodiment. It can be seen from the figure that the ID / IG value of uncapped carbon nanotubes is significantly higher than that of capped carbon nanotubes, which indicates that the uncapped carbon nanotubes have lower crystallinity and more defects.

[0067] Figure 4 The figure shows a comparison of the specific surface area and nickel loading at different annealing temperatures for unsealed and sealed carbon nanotubes described in this embodiment. As shown, for unsealed carbon nanotubes, the nickel loading inside and outside the tube cannot be detected separately; only the total nickel loading on the carbon nanotube can be measured. In contrast, for sealed carbon nanotubes, the ratio of nickel loading inside and outside the tube increases with increasing annealing temperature, with the optimal sealing effect observed at an annealing temperature of around 1400°C.

[0068] Example 2

[0069] The difference between this embodiment and Example 1 is that the metal catalyst particles are cobalt. The quantitative analysis method for the cobalt loading inside and outside the carbon nanotubes is different from that in Example 1, except that the pH buffer solution and indicator components in step S5 are different. All other steps are the same as in Example 1.

[0070] Example 3

[0071] The difference between this embodiment and Example 1 is that the metal catalyst particles are copper. The quantitative analysis method for the copper loading inside and outside the carbon nanotubes is different from that in Example 1, except that the pH buffer solution and indicator components in step S5 are different. All other steps are the same as in Example 1.

[0072] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. 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 shall fall within the protection scope of the present invention.

Claims

1. A method for quantitative analysis of the loading capacity inside and outside carbon nanotubes, characterized in that, Includes the following steps: S1： Pretreatment: Carbon nanotubes loaded with metal catalyst particles are placed in a tube furnace and a vacuum is drawn; the metal catalyst particles are one of cobalt, nickel, and copper. S2: End sealing: Annealing the carbon nanotubes at a temperature of 1200℃~1500℃; introducing carbon source gas into the tube furnace at the beginning of cooling. S3: Oxidation and hydrothermal reaction: The carbon nanotubes annealed in step S2 are placed in the atmosphere for calcination, so that the metal catalyst particles loaded on the outer wall of the carbon nanotubes are converted into the oxidized state; then they are placed in a reaction vessel and dilute sulfuric acid is added, heated and stirred to dissolve the oxidized metal catalyst particles attached to the outer wall of the carbon nanotubes, so as to obtain a metal salt sulfate solution and a capped carbon nanotube with metal catalyst particles loaded inside the tube. S4: Intratube loading detection: For the capped carbon nanotubes after S3 treatment, the intratube loading of carbon nanotubes was determined by IPC-MS technology. S5: External loading detection: For the sulfate metal salt solution after S3 treatment, the content of metal catalyst particles in the sulfate metal salt solution is determined by EDTA coupling method, which is the external loading of carbon nanotubes.

2. The quantitative analysis method according to claim 1, characterized in that, In step S1, the vacuum level inside the tubular furnace is 0.1 MPa for 1 to 2 hours. After vacuuming, the tubular 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 inside the tubular furnace is controlled at 3-5℃ / min, and the holding time is 10-15h.

4. The quantitative analysis method according to claim 1, characterized in that, In step S2, the cooling step is as follows: the temperature is reduced to 600°C at a cooling rate of 3-5°C / min, and then cooled to room temperature along with 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 rate of introduction of the carbon source gas is 10-20 mL / min; the introduction time is 2-5 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℃~100℃; the stirring time is not less than 6 hours; and the hydrothermal reaction is repeated 2~3 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 as follows: S4.1: Extract the end-capped carbon nanotubes loaded with metal catalyst particles inside the extraction tube, add acid to dissolve them by heating, and make up the volume to obtain the test solution; S4.2: Take the test liquid from step S4.1 and perform analysis on an inductively coupled plasma mass spectrometer to determine the content of 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 as follows: S5.1: Prepare pH buffer solution; S5.2: Add the pH buffer solution dropwise into the metal sulfate solution to obtain a mixed solution I with a pH value of 8-10; S5.3: Continuously add indicator to mixed solution I until mixed solution I changes color to obtain mixed solution II; S5.4: Continuously 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. The nickel content in the aqueous solution of nickel sulfate is calculated using Formula I. Among them, c EDTA v is the molar concentration of the EDTA standard solution; EDTA denoted as , where is the volume of EDTA standard solution consumed; M is the relative mass fraction of the metal catalyst; and m is the initial mass of the carbon nanotubes loaded with the metal catalyst particles.

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