Defect state carbon nanotube, preparation method and application

Abstract

The application discloses a kind of defect state carbon nanotubes, preparation method and application, belong to water treatment material technical field, the present application with multi-walled carbon nanotube as carbon base, dicyandiamide is precursor, by high temperature pyrolysis mode makes dicyandiamide etching multi-walled carbon nanotube, obtains defect state carbon nanotube.The defect state carbon nanotube obtained in the application is used as catalyst for free chlorine fenton oxidation process, compared with the widely used single-wavelength ultraviolet light activation technology has the advantages of easy and cheap, reaction efficient etc.And lower catalyst and extremely low oxidant consumption, not only reduce the process operation cost, but also avoid the stability reduction of catalyst due to excessive oxidation of oxidant.The present application has broad application prospect in the field of environmental governance of water body remediation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, in particular to a defective state carbon nanotube, a preparation method and application thereof. BACKGROUND

[0002] With the rapid development of industry, the organic wastewater generated in the industrialization process has threatened the water environment. Advanced oxidation technology is favored because it can efficiently degrade organic pollutants in water by releasing strong oxidizing active species. According to the way of generating active species and the difference of reaction conditions, advanced oxidation technology can be divided into photochemical oxidation, catalytic wet oxidation, sonochemical oxidation, ozone oxidation, electrochemical oxidation, Fenton oxidation, etc.

[0003] Fenton oxidation includes: 1) homogeneous / heterogeneous Fenton (Fenton-like) process based on oxidant activation, and the oxidants include hydrogen peroxide, persulfate, periodate, ozone and free chlorine (HOCl, Cl2 and ClO - ) and the like; 2) in-situ self-Fenton process, including photo-catalytic / electro-catalytic oxidation process, ultrasonic catalysis process, etc.

[0004] In the process of activating hydrogen peroxide, persulfate and ozone to remove organic matter, there are respectively the disadvantages of narrow pH adaptation range, secondary pollution of sulfate and higher toxicity of intermediates than the parent after ozone oxidation, so that it is difficult to degrade and mineralize extremely low concentration organic matter (nm-μm). The Fenton-like process based on free chlorine activation provides multiple protective barriers for water body, such as strong oxidizing species generated by free chlorine decomposition (such as photolysis) for deep mineralization of organic matter, and the residual chlorine after reaction can also play the role of secondary protection, sterilization and disinfection without the need to capture and remove as other oxidants (such as H2O2) after reaction. The main energy input of free chlorine activation is single-wavelength ultraviolet light, but single-wavelength ultraviolet light is high in cost and difficult to obtain in actual use, thereby limiting its popularization and application in actual production. SUMMARY

[0005] To solve the above technical problems, the present application provides a defective state carbon nanotube, a preparation method and application thereof.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A defective state carbon nanotube preparation method, using multi-walled carbon nanotubes as a carbon base and dicyandiamide as a precursor, etching the multi-walled carbon nanotubes by high-temperature pyrolysis of dicyandiamide to obtain a defective state carbon nanotube.

[0008] Further, the defective state carbon nanotube preparation method comprises the following steps:

[0009] (1) adding multi-walled carbon nanotubes and dicyandiamide into anhydrous ethanol, and mixing uniformly under ultrasonic wave to obtain a liquid mixture;

[0010] (2) drying the liquid mixture to obtain a solid mixture;

[0011] (3) grinding the solid mixture into powder;

[0012] (4) pyrolyzing the powder under inert gas protection at high temperature, and obtaining the defective carbon nanotubes after cooling.

[0013] Further, the mass ratio of the multi-walled carbon nanotubes to dicyandiamide is 1:0.5-5.

[0014] Further, the ratio of the use amount of the carbon nanotubes, dicyandiamide and anhydrous ethanol is 0.1-1.0 g:0.1-1.5 g:20 mL.

[0015] Further, in step (2), the drying temperature is 50-70 ℃, and the drying time is 10-16 hours.

[0016] Further, in step (4), the pyrolyzing temperature is 600-1000 ℃, and the pyrolyzing time is 1-3 hours. More preferably, the pyrolyzing temperature is 700-800 ℃.

[0017] A defective carbon nanotube prepared by any one of the above-mentioned defective carbon nanotube preparation methods.

[0018] A method for using the defective carbon nanotube as a catalyst for Fenton oxidation of organic wastewater.

[0019] Further, the application method comprises the following steps:

[0020] (1) adding the defective carbon nanotube catalyst into organic wastewater containing 2,4-dichlorophenol;

[0021] (2) stirring sufficiently to make the catalyst adsorb and desorb the pollutants in equilibrium;

[0022] (3) adding hypochlorous acid or hypochlorite into the water body or introducing chlorine gas to induce a Fenton-like reaction.

[0023] Further, the concentration of 2,4-dichlorophenol in the organic wastewater is 4-6 mg / L; in step (1), the use amount of the defective carbon nanotube catalyst is 0.5-1.0 g / L of wastewater; and in step (3), the free chlorine concentration of the Fenton reaction system is 1.2-2.0 mg / L.

[0024] The beneficial effects of the present application are:

[0025] 1. The preparation process of the defective state carbon nanotube is simple, easy to operate, high in yield and good in repeatability.

[0026] 2. The obtained defective state carbon nanotube can efficiently activate free chlorine and has high oxidation agent utilization rate.

[0027] 3. The defective state carbon nanotube obtained by the application is used as a catalyst in a free chlorine Fenton oxidation process, and has the advantages of being easy to obtain and low in cost compared with the widely used single-wavelength ultraviolet light activation technology, and the reaction is efficient. For example, 0.05 g / L of the modified CNT is used to catalyze 0.2 mM NaClO (the concentration of free chlorine is only 1.6 mg / L) to degrade 5 mg / L of 2,4-dichlorophenol, and more than 90% removal rate can be achieved within 20 min of reaction time. The low catalyst and low oxidant dosage not only reduces the process operation cost, but also avoids the decrease in stability of the catalyst due to excessive oxidation of the oxidant.

[0028] 4. In addition, the non-metal catalyst in the application can also avoid a series of shortcomings of the widely reported metal-based catalysts, such as easy dissolution of metal, high preparation cost of catalyst and deactivation of catalyst due to the formation of metal-chlorine complex.

[0029] In summary, the application has a broad application prospect in the field of environmental governance of water body remediation. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the XPS full spectrum diagram of the defective state carbon nanotube T-D8 prepared in Example 1 of the application and multi-walled carbon nanotubes.

[0031] Figure 2 is the XPS C 1s spectrum diagram of T-D8.

[0032] Figure 3 is the XPS N 1s spectrum diagram of T-D8.

[0033] Figure 4 is the XPS O 1s spectrum diagram of T-D8.

[0034] Figure 5 is the XPS full spectrum diagram of the defective state carbon nanotubes T-D8, T-D7, T-D9 and T-D10 prepared in Example 1 of the application.

[0035] Figure 6 is the C 1s spectrum diagram of the XPS of T-D7, T-D9 and T-D10.

[0036] Figure 7 is the XPS full spectrum diagram of the defective state carbon nanotubes prepared in Examples 1, 5-7 of the application.

[0037] Figure 8is a comparison chart of the rate constant of removing 2,4-dichlorophenol in water and the chemical composition on the catalyst of the defective carbon nanotube T-D8, T-D7, T-D9 and T-D10 prepared by the present application.

[0038] Figure 9 is a comparison chart of the effect of removing 2,4-dichlorophenol in water of the defective carbon nanotube T-D8 prepared by the present application and the comparative examples 1-3. DETAILED DESCRIPTION

[0039] The present application will be further described in conjunction with specific examples in order to facilitate the understanding of the present application, but the present application is not limited by the specific examples.

[0040] It should be noted that the materials used in the present application are commercially available, and in order to clearly describe, only the multi-walled carbon nanotubes used as raw materials in the present application are recorded as multi-walled carbon nanotubes, and the multi-walled carbon nanotubes prepared by the present application are recorded as defective carbon nanotubes,

[0041] Examples 1-4

[0042] The following steps are used to prepare the defective carbon nanotube:

[0043] ① 0.2 g of multi-walled carbon nanotubes (CNT) and 0.5 g of dicyandiamide are added to 20 mL of anhydrous ethanol, and mixed uniformly;

[0044] ② The above mixture is ultrasonically treated for 30 min, and the materials are fully mixed by stirring to obtain a liquid mixture;

[0045] ③ The liquid mixture is placed in an oven and dried at 60℃ for 12 hours to obtain a solid mixture;

[0046] ④ The obtained solid mixture is ground into powder;

[0047] ⑤ The powder is pyrolyzed at high temperature under inert gas protection for 2 hours, the pyrolysis temperature is 800℃, the heating rate is 5℃ / min, and the obtained solid powder is taken out after natural cooling, thereby obtaining the defective carbon nanotube.

[0048] The above defective carbon nanotube is marked as T-D8 (Note: T is the first letter of Tube, and D is the first letter of Defective).

[0049] The above operation is repeated, and the pyrolysis temperature is set to 700, 900 or 1000℃ respectively, and the rest of the conditions remain unchanged, and the prepared defective carbon nanotubes are marked as T-D7, T-D9 and T-D10 respectively.

[0050] The chemical composition of the defective carbon nanotubes prepared in Examples 1-4 and the raw material multi-walled carbon nanotubes used in the present application are analyzed by XPS, and the analysis results are shown in Table 1. Figures 1-6.

[0051] XPS survey spectrum Figure 1 It can be seen that the multi-walled carbon nanotubes as raw materials only contain carbon elements, and no other elements including nitrogen and oxygen elements. After the pyrolysis of dicyandiamide, significant oxygen (O 1s) and nitrogen peaks (N1s) appear, indicating that oxygen and nitrogen elements are doped into the carbon nanotubes. Figure 2 is the high-magnification C1s XPS spectrum of T-D8. From the results, it can be seen that the pyrolyzed carbon nanotubes produce significant defects (black shaded part in the figure, mass fraction of 17.2wt.%). The generation of defects is attributed to the fact that dicyandiamide not only condenses (melamine→C3N4) during pyrolysis, but also releases a large amount of gas (ammonia) at too high a temperature (>650℃), which can take away the carbon source, thereby generating defects. The generation and regulation of the defects are the key points of the present application. In addition, it can be seen that the modified oxygen source forms carbon-oxygen double bonds and single bonds, which is also proved in the O1s high-magnification spectrum in Figure 4 . From the N1s high-magnification XPS spectrum in Figure 3 , it can be seen that the modified nitrogen source and the carbon element form pyridine nitrogen, pyrrole nitrogen, graphite nitrogen and oxidized nitrogen. These foreign nitrogen sources are all brought by the precursor dicyandiamide.

[0052] Figure 5 is the XPS survey spectrum of the catalysts obtained at different temperatures in Examples 1-4. From the characterization, it can be seen that in T-D8, T-D7, T-D9 and T-D10, the modified oxygen element shows similar content, while the nitrogen element gradually decreases with the increase of temperature, which further verifies the above-mentioned point that the nitrogen source precursor dicyandiamide will pyrolyze and release gas at too high a temperature, resulting in nitrogen loss. It is worth noting that in the high-magnification C1s spectrum of Figure 6 , it can be seen that the defects increase with the increase of temperature. The reason is that the increase of temperature leads to the collapse of the C3N4 framework formed by the polymerization of the precursor, the volatilization of unstable chemical components, the generation of defects, and the overall structure of the carbon substrate tends to be stable. However, when the temperature is too high, such as >800℃, the amount of defects is stable or even decreases. The reason is that the precursor dicyandiamide has been pyrolyzed and consumed at 800℃, and the remaining mass is close to zero. From Figure 5 Figure 6 , it can be seen that the pyrolysis temperature is an important parameter for regulating the defects of the carbon nanotube wall.

[0053] Examples 5-7

[0054] The same steps as in Example 1 were used to prepare the defect state carbon nanotubes, except that only the mass ratio of multi-walled carbon nanotubes (CNT) and dicyandiamide was changed.

[0055] Example 5: 0.2 g of multi-walled carbon nanotubes (CNTs) and 0.1 g of dicyandiamide were added.

[0056] Example 6: 0.2 g of multi-walled carbon nanotubes (CNTs) and 0.5 g of dicyandiamide were added.

[0057] Example 7: 0.2g of multi-walled carbon nanotubes (CNTs) and 1g of dicyandiamide were added.

[0058] XPS analysis was performed on the chemical composition of the defective carbon nanotubes prepared in Examples 5-7. The results are shown in the figure. Figure 7 .

[0059] from Figure 7 It can be seen that the mass ratio has little impact on the formation of defects in the carbon nanotube wall, and good technical results can be achieved with a mass ratio within a reasonable range.

[0060] Application Examples 1-4

[0061] The method for using the defective carbon nanotubes prepared in Examples 1-4 as catalysts for the Fenton oxidation of organic wastewater includes the following steps:

[0062] ① Take 0.05g of defective carbon nanotubes T-D8, T-D7, T-D9 and T-D10 respectively, and add them to 100mL of organic wastewater, wherein the concentration of 2,4-dichlorophenol in the organic wastewater is 5mg / L;

[0063] ② Stir for 30 minutes to allow the catalyst to reach adsorption-desorption equilibrium with the pollutants;

[0064] ③ Add 0.2 mM sodium hypochlorite to induce a Fenton-like reaction;

[0065] ④ Take a 0.5 mL sample at the preset time point and add 0.5 mL of sodium thiosulfate solution (concentration of 1.6 g / L) to the sample to terminate the reaction;

[0066] ⑤ The sample was sent to high performance liquid chromatography to detect the concentration of residual 2,4-dichlorophenol in order to determine the removal efficiency.

[0067] The reaction rates of the defective carbon nanotubes T-D8, T-D7, T-D9 and T-D10 were calculated by measuring the residual 2,4-dichlorophenol concentration, and the defective carbon nanotubes of different degrees were analyzed by XPS spectrum analysis to analyze the relationship between the reaction rate of removing 2,4-dichlorophenol from water and their chemical composition under the same conditions. The results show that the defective carbon nanotubes of activated sodium hypochlorite removing 2,4-dichlorophenol follow the rule of T-D8>T-D7>T-D9>T-D10, which has a good corresponding relationship with their defect content, and has no obvious correlation with other chemical compositions, such as nitrogen-based functional groups (commonly used as reaction sites, pyridine nitrogen, pyrrole nitrogen) and oxygen-based functional groups (commonly used as reaction sites, C=O). The experimental results strongly prove that the defects act as catalytic sites for the activation of free chlorine and the removal of organic matter.

[0068] In the reaction process of preparing the defective carbon nanotube T-D8, the initial concentration and the time concentration of 2,4-dichlorophenol were measured, the time concentration was the residual 2,4-dichlorophenol concentration detected by high performance liquid chromatography after a certain time interval after the start of the reaction, and the detection results are shown in Figure 8 .

[0069] Comparative Example 1

[0070] The same method as in Example 2 above was used, and the defective carbon nanotube T-D8 catalyst was replaced with a multi-walled carbon nanotube. In the reaction process, the initial concentration and the time concentration of 2,4-dichlorophenol were measured, and the detection results are shown in Figure 8 .

[0071] Comparative Example 2

[0072] The same method as in Example 2 above was used, but no defective carbon nanotube T-D8 catalyst was added. In the reaction process, the initial concentration and the time concentration of 2,4-dichlorophenol were measured, and the detection results are shown in Figure 8 .

[0073] Comparative Example 3

[0074] The same method as in Example 2 above was used, but no sodium hypochlorite was added. In the reaction process, the initial concentration and the time concentration of 2,4-dichlorophenol were measured, and the detection results are shown in Figure 8 .

[0075] From Figure 3It can be seen that free chlorine (sodium hypochlorite) in the water body cannot spontaneously degrade 2,4-dichlorophenol, and thus needs the activation of a catalyst to play the role of oxidative degradation and purification of the water body by free chlorine; and the catalyst (T-D8) alone cannot remove the organic matter in the water body; when the catalyst of the defective carbon nanotube of the application and sodium hypochlorite are added at the same time, the concentration of 2,4-dichlorophenol is significantly reduced, and the concentration decay has exceeded 90% at 20 min of reaction. Under the same conditions, the existing multi-walled carbon nanotube activated free chlorine shows considerable inertia in removing 2,4-dichlorophenol. The above experimental results show that the defective nanotube proposed in the application has a good technical effect in activating sodium hypochlorite to remove organic pollutants in the water body.

[0076] The above only describes the preferred embodiments of the application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the application, and these improvements and refinements are also within the protection scope of the application.

Claims

1. A method for applying defect-state carbon nanotubes, characterized in that, The defective carbon nanotubes were used as a catalyst in the Fenton oxidation of organic wastewater. The method for preparing the defective carbon nanotubes is as follows: Using multi-walled carbon nanotubes as a carbon substrate and dicyandiamide as a precursor, defect-state carbon nanotubes are obtained by etching multi-walled carbon nanotubes with dicyandiamide through high-temperature pyrolysis; the process includes the following steps: (1) Add multi-walled carbon nanotubes and dicyandiamide to anhydrous ethanol, and mix them evenly by ultrasonication to obtain a liquid mixture; (2) The liquid mixture is dried to obtain a solid mixture; (3) Grind the solid mixture into powder; (4) The powder is pyrolyzed at high temperature under inert gas protection, and the defective carbon nanotubes are obtained after cooling; the high temperature of pyrolysis is 600-1000℃ and the pyrolysis time is 1-3 hours. The mass ratio of the multi-walled carbon nanotubes to dicyandiamide is 1:0.5 to 5.

2. The method for applying defect-state carbon nanotubes according to claim 1, characterized in that, The ratio of carbon nanotubes, dicyandiamide, and anhydrous ethanol is 0.5–1.5 g: 2–3 g: 100 mL.

3. The method for applying defect-state carbon nanotubes according to claim 1, characterized in that, In step (2), the drying temperature is 50-70℃ and the drying time is 10-16 hours.

4. The method for applying defective carbon nanotubes according to claim 1, characterized in that, The defective carbon nanotubes are used as a catalyst in the Fenton oxidation of organic wastewater, which includes the following steps: (1) Add defective carbon nanotube catalyst to organic wastewater containing 2,4-dichlorophenol; (2) Stir thoroughly to allow the catalyst to reach an adsorption-desorption equilibrium with the pollutants; (3) Add hypochlorous acid or chlorine gas to the water to induce a Fenton-like reaction.

5. The method for applying defective carbon nanotubes according to claim 4, characterized in that, The concentration of 2,4-dichlorophenol in the organic wastewater is 4-6 mg / L; in step (1), the amount of defective carbon nanotube catalyst used is 0.5-1.0 g / L of wastewater; in step (3), the concentration of free chlorine in the Fenton reaction system is 1.2-2.0 mg / L.

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