Preparation and application of metal-doped carbon nanotube

Abstract

The invention discloses preparation and application of a metal-doped carbon nanotube, and the preparation method comprises the following steps: firstly mixing a multi-walled carbon nanotube with dicyandiamide, then adding ferric acetylacetonate for doping, and then carrying out high-temperature pyrolysis to obtain the metal-doped carbon nanotube. The obtained metal-doped carbon nanotube is used as a catalyst for a free chlorine Fenton oxidation process, the powder is easy to recover, and the material is stable and free of secondary pollution. Due to the low catalyst dosage, the process operation cost is reduced, and the situation that the stability of the catalyst is reduced due to excessive oxidation of an oxidizing agent is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to the preparation and application of metal-doped carbon nanotubes. Background Art

[0002] Global environmental degradation has been recognized as one of the most important challenges of the 21st century. In particular, the refractory organic pollutants in the water environment have adverse effects on the ecological environment system and may threaten human health.

[0003] In recent years, advanced oxidation technology has been favored because it can release highly oxidizing active species that can efficiently degrade organic pollutants in water. Advanced oxidation technology is based on the use of electricity, light radiation, catalysts and oxidants to produce highly active free radicals in the reaction. Through various interactions between free radicals and organic compounds, macromolecular organic matter in water is oxidized and degraded into small molecules, carbon dioxide and water. According to the different ways of producing active species and reaction conditions, advanced oxidation technology can be divided into photochemical oxidation, catalytic wet oxidation, sonochemical oxidation, ozone oxidation, electrochemical oxidation, Fenton oxidation, etc.

[0004] The Fenton-like process based on free chlorine activation provides multiple protective barriers for water bodies. The strong oxidizing species produced by the decomposition of free chlorine (such as photolysis) are used for the deep mineralization of organic matter. The residual chlorine obtained after the reaction does not need to be captured and removed after the reaction like other oxidants (such as H2O2). It can also play a role in secondary protection and sterilization and disinfection.

[0005] At present, metal catalysts have gradually replaced non-metal-doped catalysts in the field of catalysis due to their advantages such as high activity, high selectivity, stability and controllability. On the one hand, because metal atoms can provide or accept electrons and thus participate in the catalytic cycle, metal-doped catalysts usually have higher activity. At the same time, the presence of metals will also affect the electronic structure and coordination environment of the catalyst, which can improve the selectivity of specific chemical reactions, that is, it can promote the progress of specific pathways among multiple possible reaction pathways. In addition, metal catalysts also show excellent activity and selectivity in many reactions, especially in redox reactions that require high electron transfer.

[0006] Based on this, the present invention designs to dope the defective carbon nanotubes with metals to further improve their catalytic activity. Summary of the invention

[0007] One of the purposes of the present invention is to provide a method for preparing metal-doped carbon nanotubes, comprising the following steps:

[0008] (1) adding multi-walled carbon nanotubes and dicyandiamide to anhydrous ethanol to obtain a primary mixture;

[0009] (2) adding ferric acetylacetonate to the primary mixture and stirring to mix the mixture to obtain a target mixed solution;

[0010] (3) drying the target mixed solution to completely evaporate the water, and grinding the resulting solid mixture into powder;

[0011] (4) High-temperature pyrolysis is performed in an inert gas atmosphere to obtain metal-doped carbon nanotubes after cooling.

[0012] Furthermore, in step (1), the usage ratio of anhydrous ethanol, multi-walled carbon nanotubes and dicyandiamide is 20 mL: 0.2 g: 0.5 g.

[0013] Furthermore, in step (2), the usage ratio of the multi-walled carbon nanotubes, dicyandiamide and ferric acetylacetonate is 0.1-0.5 g: 0.1-1 g: 0.004-0.008 g.

[0014] Furthermore, in step (3), the drying is performed at 50-70° C. for 10-16 hours, preferably at 60° C. for 12 hours.

[0015] Furthermore, in step (4), the high temperature pyrolysis conditions are: high temperature annealing polymerization at 600-1000°C for 1-3 hours, preferably high temperature pyrolysis at 800°C for 2 hours.

[0016] The second object of the present invention is to provide the use of the above metal-doped carbon nanotubes as catalysts in catalytic degradation of organic wastewater.

[0017] The application method comprises the following steps:

[0018] (1) adding metal-doped carbon nanotubes as catalysts into organic wastewater containing 4-p-chlorophenol;

[0019] (2) Stirring thoroughly to allow the catalyst to achieve adsorption and desorption equilibrium of pollutants;

[0020] (3) Add hypochlorous acid to the water to induce a Fenton-like reaction.

[0021] Furthermore, the concentration of 4-p-chlorophenol in the organic wastewater is 8 to 12 mg / L; in step (1), the amount of metal-doped carbon nanotubes is 20 to 80 mg / L; and in step (3), the free chlorine concentration of the Fenton reaction system is 6 to 10 mg / L.

[0022] The present invention uses hypochlorous acid as an oxidant to activate metal-doped carbon nanotubes to degrade 4-parachlorophenol in water. While reducing the toxicity of 4-parachlorophenol, secondary pollution of byproducts can be avoided, which is beneficial to the stability of the system; and in the process of drug degradation in water, the metal-based catalyst has a high catalytic activity, can effectively promote the reaction, reduce the energy demand of the reaction, and increase the reaction rate. The metal-based catalyst has good stability and durability, can be used multiple times, and reduces the cost and waste generation. The metal-based catalyst can also achieve efficient reaction conversion at a lower temperature and pressure, saving energy and cost.

[0023] When the diameter of carbon nanotubes is 3-15nm, the removal performance of 4-p-chlorophenol is the best. Under this diameter, the molecular curvature is the largest, the removal effect is the best, and the pseudo-first-order reaction kinetic constant reaches 0.048min -1 The performance of the catalyst in removing organic pollutants is also quite superior to that of the reported carbon-based catalysts that do not contain metal or contain metal to activate hypochlorous acid to remove organic pollutants.

[0024] The present invention has the following advantages

[0025] (1) The preparation steps of metal-doped carbon nanotubes are simple, the modification process is green and environmentally friendly, and the base materials are completely converted into valuable catalysts.

[0026] (2) The obtained metal-doped carbon nanotubes can efficiently activate free chlorine and have a high oxidant utilization rate.

[0027] (3) The metal-doped carbon nanotubes obtained by the present invention are used as catalysts in the free chlorfenton oxidation process. The powder is easy to recycle, and the material is stable and has no secondary pollution. The lower catalyst dosage not only reduces the process operation cost, but also avoids the catalyst from being degraded in stability due to excessive oxidation of the oxidant.

[0028] In summary, the present invention has broad application prospects in the field of environmental management of water body restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The Raman spectra of metal-doped multi-walled carbon nanotubes with different diameters.

[0030] Figure 2 Comparison of the effects of metal-doped multi-walled carbon nanotubes activating hypochlorous acid to remove 4-p-chlorophenol from water.

[0031] Figure 3 This is a comparison chart of the effects of metal-doped multi-walled carbon nanotubes with different tube diameters in activating hypochlorous acid to remove 4-p-chlorophenol in water in Example 1 and a pseudo-first-order rate constant fitting chart.

[0032] Figure 4Figures a and b are the hypochlorous acid attenuation effect diagrams of metal-doped multi-walled carbon nanotubes with different diameters activated in systems with and without pollutants, respectively. Figure a is without pollutants, and figure b is with 10 mg / L p-chlorophenol added. DETAILED DESCRIPTION

[0033] The preferred embodiments of the present invention will be described in detail below in conjunction with examples. It should be understood that the following examples are provided only for the purpose of illustration and are not intended to limit the scope of the present invention. Those skilled in the art may make various modifications and substitutions to the present invention without departing from the purpose and spirit of the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0035] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0036] Examples 1-3

[0037] The method for metal doping multi-walled carbon nanotubes comprises the following steps:

[0038] (1) Add 0.2 g of multi-walled carbon nanotubes with different diameters (the diameters are 3-15 nm, 20-30 nm, and 60-100 nm) and 0.5 g of dicyandiamide to 20 mL of anhydrous ethanol and mix them evenly;

[0039] (2) adding 0.006 g of ferric acetylacetonate to the above mixed solution and stirring to make the materials fully mixed;

[0040] (3) Place the material in an oven and dry at 60°C for 12 hours until the anhydrous ethanol is completely evaporated;

[0041] (4) grinding the obtained solid mixture into powder;

[0042] (5) The powder is pyrolyzed at high temperature for 2 hours under the protection of inert gas, the pyrolysis temperature is 800° C., and the heating rate is 5° C. / min. The obtained solid powder is taken out after being cooled, and the metal-doped carbon nanotubes are obtained.

[0043] The metal-doped carbon nanotubes obtained from multi-walled carbon nanotubes with a tube diameter of 3 to 15 nm are marked as CD-D1, the metal-doped carbon nanotubes obtained from multi-walled carbon nanotubes with a tube diameter of 20 to 30 nm are marked as CD-D2, and the metal-doped carbon nanotubes obtained from multi-walled carbon nanotubes with a tube diameter of 60 to 100 nm are marked as CD-D3.

[0044] Depend on Figure 1 It can be seen that at 1350cm -1 The defect peak D of graphite carbon can be observed near 1580 cm-1 and 2670cm -1 Graphitization peaks G and G' can be observed near the D / I G As the tube diameter decreases, it increases, since the D band corresponds to the vibration caused by the dispersion defect (sp 3 bond carbon), and the G band comes from the in-plane vibration of the graphite wall (sp 2 bond carbon), so I D / I G The change in sp 2 The smaller the diameter of the tube, the greater the curvature. D / I G The larger it is, the stronger its electron conduction ability is.

[0045] Comparative Example 1

[0046] The method for preparing metal-free doped multi-walled carbon nanotubes comprises the following steps:

[0047] (1) Add 0.2 g of multi-walled carbon nanotubes with a diameter of 3 to 15 nm and 0.5 g of dicyandiamide to 20 mL of anhydrous ethanol and mix them evenly;

[0048] (2) Place the material in an oven and dry at 60°C for 12 hours until the anhydrous ethanol is completely evaporated;

[0049] (3) grinding the obtained solid mixture into powder;

[0050] (4) The powder is pyrolyzed at high temperature for 2 hours under the protection of inert gas, the pyrolysis temperature is 800° C., and the heating rate is 5° C. / min. The obtained solid powder is taken out after being cooled, and metal-free doped carbon nanotubes (CD) are obtained.

[0051] Unmodified multi-walled carbon nanotubes (with a tube diameter of 3 to 15 nm), non-metal-doped carbon nanotubes (CD) and metallic carbon nanotubes (CD-D1, CD-D2, CD-D3) were taken as catalysts and added into 4-p-chlorophenol organic wastewater with a total volume of 50 mL and a concentration of 10 mg / L at a rate of 0.05 g / L, and stirred for 30 minutes to allow the catalyst to achieve adsorption and desorption equilibrium for the pollutants; after equilibrium, 1 mM hypochlorous acid was added, the reaction timing was started, 1 mL of the sample was taken at a preset time point and added into 0.5 mL of sodium thiosulfate solution (with a concentration of 1.6 g / L) to terminate the reaction; the sample was subjected to high performance liquid chromatography to detect the residual 4-p-chlorophenol concentration to determine the removal efficiency.

[0052] Depend on Figure 2It can be seen that CD-D1 exhibits very strong catalytic activity. The removal rates of hypochlorous acid activated by carbon nanotubes and CD precursors are 30% and 60% respectively, while the degradation of pollutants by hypochlorous acid and CD-D1 alone is only 30% and 10%. The removal rate of 4-p-chlorophenol by CD-D1 / hypochlorous acid system is as high as 100%, and the reaction rate constant of this system is 0.048min -1 , which shows considerable advantages in the metal-based material activated hypochlorous acid removal system for organic pollutants reported in existing literature.

[0053] Depend on Figure 3 As shown in Figure a, the removal rate of pollutants by multi-walled carbon nanotubes doped with metal Fe with different diameters increases as the diameter decreases. The removal rates of 4-p-chlorophenol within 60 minutes are 100%, 70%, and 50%, respectively. This may be because the smaller the diameter of the carbon nanotube, the greater the molecular curvature. The increased molecular curvature adjusts the electronic properties of the carbon material, produces a stronger interfacial electric field, and makes the active sites more residing, which can better activate the oxidant to produce free radicals, so that the pollutants are further degraded. Figure 3 From b, we can see that the pseudo-first-order rate constants for pollutant removal are 0.048, 0.012, and 0.007 min -1 , which further reflects that the greater the curvature of the molecule, the better the effect of removing pollutants.

[0054] The concentration of free chlorine was detected by DPD colorimetric method. A phosphate buffer solution was prepared by dissolving 30g Na2HPO4-12H2O, 23g KH2PO4 and 0.4g EDTA-2Na in 500mL deionized water. A N,N-diethyl-p-phenylenediamine sulfate (DPD) solution was prepared by adding 0.1g EDTA-2Na and 1mL H2SO4 to 500mL deionized water. Then 0.55g DPD was added to the above mixed solution and mixed thoroughly. To determine free chlorine, 0.05g / L metal-doped carbon nanotube catalysts with different diameters and 1mM oxidant were added to 50mL deionized water for reaction. Samples were taken at set points. 3mL phosphate buffer solution, 1mL DPD solution and 5mL sample solution were mixed within 1min, and the product of red chlorinated DPD was measured at 515nm using a spectrophotometer.

[0055] Depend on Figure 4 From a, we can see that without adding pollutants, the catalyst has poor attenuation effect on the oxidant. CD-D1, which has the best pollutant removal, attenuates free chlorine by only 70%, while CD-D2 and CD-D3 attenuate the oxidant by only 30%. Figure 4In the system with pollutants added in b, the catalyst's ability to attenuate the oxidant is greatly enhanced, and the CD-D1 catalyst's attenuation of free chlorine reaches 100%. This shows that the synergistic effect of the catalyst, oxidant and pollutant system can enhance the attenuation of the oxidant through direct electron transfer, and the pollutant degradation efficiency can be significantly improved by constructing a nano-confined system. The catalytic reaction pathway gradually changes from singlet oxygen to direct electron transfer pathway, which significantly improves the degradation efficiency of electron-rich pollutants and the utilization rate of oxidants, thereby achieving efficient degradation of organic pollutants.

Claims

1. A method for preparing metal-doped carbon nanotubes, characterized in that: The following steps are involved: (1) adding multi-walled carbon nanotubes and dicyandiamide into anhydrous ethanol to obtain a primary mixture; (2) adding ferric acetylacetonate to the primary mixture and stirring to mix the mixture to obtain a target mixed solution; (3) drying the target mixed liquid to completely evaporate the water, and grinding the resulting solid mixture into powder; (4) High-temperature pyrolysis is performed in an inert gas atmosphere, and metal-doped carbon nanotubes are obtained after cooling.

2. The preparation method according to claim 1, characterized in that In step (1), the usage ratio of anhydrous ethanol, multi-walled carbon nanotubes and dicyandiamide is 20 mL: 0.2 g: 0.5 g.

3. The preparation method according to claim 2, characterized in that In step (2), the usage ratio of the multi-walled carbon nanotubes, dicyandiamide and ferric acetylacetonate is 0.1-0.5 g: 0.1-1 g: 0.004-0.008 g.

4. The preparation method according to claim 1, characterized in that In step (3), the drying is carried out at 50 to 70 o C drying for 10~16 hours.

5. The preparation method according to claim 4, characterized in that In step (3), the drying is carried out at 60 o C dry for 12 hours.

6. The preparation method according to claim 1, characterized in that In step (4), the high temperature pyrolysis conditions are: at 600-1000 o C high temperature annealing polymerization for 1 to 3 hours.

7. The preparation method according to claim 6, characterized in that In step (4), the high temperature pyrolysis conditions are: at 800 o C for 2 hours.

8. Use of the metal-doped carbon nanotubes prepared by the preparation method according to any one of claims 1 to 7 as a catalyst in catalytic degradation of organic wastewater.

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