A porous carbon-coated iron carbide supported carbon nanotube composite material, its preparation method and application

Abstract

The present invention belongs to the technical field of wastewater treatment. The present invention provides a porous carbon-coated iron carbide supported carbon nanotube composite material, a preparation method and an application thereof. The method comprises the following steps: mixing a ferric chloride solution, a glucose solution and a melamine solution to obtain a mixed solution; mixing the mixed solution and carbon nanotubes, and then sequentially drying and calcining to obtain the porous carbon-coated iron carbide supported carbon nanotube composite material. By performing porous carbon coating and carbon nanotube loading on the iron carbide nanomaterial, the obtained porous carbon-coated iron carbide supported carbon nanotube composite material has advantages such as strong ferromagnetism, high stability and strong reusability. An advanced oxidation system for efficiently removing benzo[a]pyrene in complex sewage is constructed by catalyzing persulfate, providing technical guidance for the deep treatment of benzo[a]pyrene wastewater at low temperature.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and particularly relates to a porous carbon-coated iron carbide supported carbon nanotube composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Benzo[a]pyrene is one of the most toxic strong carcinogens among polycyclic aromatic hydrocarbons, which can damage the internal organs and nervous system of animals, can also change the normal cell cycle, damage DNA, and cause cell carcinogenesis. Benzo[a]pyrene is difficult to be effectively degraded by conventional water treatment technologies (such as filtration, adsorption, disinfection, etc.), and ultimately threatens the environment and human health through the water cycle. Therefore, how to improve the efficient removal rate of benzo[a]pyrene in the water environment has become a problem to be solved.

[0003] In recent years, the advanced oxidation technology based on persulfate has received extensive attention because it can efficiently remove refractory pollutants. Persulfate can be activated to generate strongly oxidizing free radicals such as hydroxyl radicals (·OH) and sulfate radicals (SO4 - ·), and the activation methods include heat, light, microwave, ultrasonic, electrochemistry, plasma, transition metal ions, carbon-based materials, etc. Although ·OH and SO4 - · can react quickly with refractory pollutants in ultrapure water, they are prone to side reactions with organic matter and inorganic ions (Cl - 、NO3 - 、NH4 + 、H2PO4 - etc.) and other substances in sewage, so it is difficult to effectively remove organic pollutants in sewage with complex components. In addition, by modifying the structure and surface functional groups of carbon-based materials, persulfate can be activated to generate non-oxidizing free radicals, for example, direct electron transfer, singlet oxygen, superoxide radicals, etc., so as to achieve the rapid removal of organic pollutants in sewage with complex components. In addition, the modified iron-based materials can also activate persulfate to generate high-valent iron (Fe IV =0) to directly oxidize organic pollutants. Therefore, the activation of persulfate by iron-carbon composite materials to degrade organic pollutants in complex sewage is a current research hotspot.

[0004] Iron carbide nanoparticles can effectively catalyze persulfate to generate oxidizing free radicals to remove refractory organic pollutants in wastewater due to the structure of carbon atoms infiltrating into the iron lattice. However, the agglomeration of nanoparticles leading to a decrease in catalytic efficiency has become a bottleneck problem for iron carbide nanoparticles in wastewater treatment. Porous carbon-dispersed iron carbide nanoparticles can significantly improve the dispersibility, catalytic activity, specific surface area, and stability of iron carbide. However, the porous structure limits the electron transfer rate of surface reactions. The graphene-like structure on the surface of carbon nanotubes can not only improve the electron transfer rate but also activate persulfate to generate non-oxidizing free radicals. However, active sites need to be introduced to enhance the catalytic activity of carbon nanotubes.

[0005] Therefore, providing a porous carbon-coated iron carbide supported carbon nanotube composite material with high stability, strong ferromagnetism, and reusability for the deep treatment of benzo[a]pyrene in wastewater has good prospects. Summary of the Invention

[0006] The object of the present invention is to provide a porous carbon-coated iron carbide supported carbon nanotube composite material and its preparation method for the problems of easy agglomeration of nanoparticle materials in the prior art and low removal efficiency of benzo[a]pyrene in complex wastewater. The preparation method of the present invention is simple. The composite material has high reaction activity, strong stability, and good reuse effect, and can catalytically activate persulfate to efficiently remove benzo[a]pyrene in wastewater under a wide pH range and at a low heating temperature.

[0007] In order to achieve the above invention object, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a porous carbon-coated iron carbide supported carbon nanotube composite material, comprising the following steps:

[0009] 1) Mix a ferric chloride solution, a glucose solution, and a melamine solution to obtain a mixed solution;

[0010] 2) Mix the mixed solution and carbon nanotubes, and then sequentially perform drying and calcination to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material.

[0011] Preferably, in the ferric chloride solution in step 1), the solute is anhydrous ferric chloride, the solvents are anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1-2:1-2; the mass-volume ratio of anhydrous ferric chloride to the solvents is 2-4 g:30-50 mL;

[0012] The glucose solution in step 1) contains glucose, water, and anhydrous ethanol, and the mass-volume ratio of glucose, water, and anhydrous ethanol is 2-4 g:15-25 mL:35-45 mL.

[0013] Preferably, in the melamine solution in step 1), the solvent is anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1-2:1-2; the mass-volume ratio of melamine to the solvent is 1-3 g:80-120 mL.

[0014] Preferably, the volume ratio of the ferric chloride solution, glucose solution and melamine solution in step 1) is 30-50:50-70:80-120.

[0015] Preferably, the mass ratio of carbon nanotubes in step 2) to anhydrous ferric chloride in step 1) is 0.45-0.55:2-4.

[0016] Preferably, the temperature of the mixing in step 2) is 50-70 °C, and the mixing time is 1-3 h; the drying temperature is 160-200 °C, and the drying time is 10-14 h.

[0017] Preferably, the calcination in step 2) is carried out under a protective atmosphere, the protective atmosphere is nitrogen and / or argon, the calcination temperature is 700-900 °C, the heating rate to the calcination temperature is 4-6 °C / min, and the calcination time is 2-4 h.

[0018] The present invention also provides a porous carbon-coated iron carbide-supported carbon nanotube composite material prepared by the above preparation method.

[0019] The present invention also provides an application of the porous carbon-coated iron carbide-supported carbon nanotube composite material in catalyzing sodium persulfate to remove benzo[a]pyrene in wastewater.

[0020] Preferably, the porous carbon-coated iron carbide-supported carbon nanotube composite material, benzo[a]pyrene solution and sodium persulfate are mixed, and the mixed solution is subjected to a degradation reaction; the concentration of sodium persulfate in the mixed solution is 0.2-3 mmol / L, the pH value of the degradation reaction is 3-11, and the temperature of the degradation reaction is 42-50 °C.

[0021] The beneficial effects of the present invention include the following points:

[0022] 1) By coating porous carbon on iron carbide nanomaterials and supporting carbon nanotubes, the obtained porous carbon-coated iron carbide-supported carbon nanotube composite material has the advantages of strong ferromagnetism, high stability, and strong reusability. An advanced oxidation system for efficiently removing benzo[a]pyrene in complex sewage is constructed by catalyzing persulfate, providing technical guidance for the deep treatment of benzo[a]pyrene in wastewater at low temperature.

[0023] 2) The porous carbon-coated iron carbide supported carbon nanotube composite material obtained by the method of the present invention has strong stability, can be used under a wide pH range, is easy to recycle, and has strong reusability; it can be used for the efficient catalytic activation of sodium persulfate at low temperature for the deep treatment of benzo[a]pyrene-contaminated wastewater, has strong adaptability, high application value, and can efficiently activate sodium persulfate for the deep treatment of polycyclic aromatic hydrocarbon-contaminated wastewater. Description of the Drawings

[0024] Figure 1 SEM image of the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1;

[0025] Figure 2 HR-TEM image of the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1;

[0026] Figure 3 X-ray diffraction pattern of the materials prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0027] Figure 4 Raman spectrum of the materials prepared in Example 1, Comparative Example 1 and Comparative Example 2;

[0028] Figure 5 Electron transfer rate of the reaction between benzo[a]pyrene and persulfate on the surface of the materials in Example 1, Example 2 and Example 3;

[0029] Figure 6 Removal effect of the materials in Example 1, Comparative Example 1 and Comparative Example 2 on benzo[a]pyrene;

[0030] Figure 7 Effect of different reaction temperatures on the removal effect of benzo[a]pyrene by the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1;

[0031] Figure 8 Effect of different pH values on the removal effect of benzo[a]pyrene by the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1;

[0032] Figure 9 Effect of the dosage of sodium persulfate on the removal effect of benzo[a]pyrene by the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1;

[0033] Figure 10 Removal effect of the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1 on benzo[a]pyrene in different sewage. Detailed Embodiments

[0034] The present invention provides a preparation method of a porous carbon-coated iron carbide supported carbon nanotube composite material, which comprises the following steps:

[0035] 1) Mix the ferric chloride solution, glucose solution and melamine solution to obtain a mixed solution;

[0036] 2) Mix the mixed solution and carbon nanotubes, and then successively perform drying and calcination to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material.

[0037] In the ferric chloride solution described in step 1) of the present invention, the solute is preferably anhydrous ferric chloride, the solvent is preferably anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is preferably 1-2:1-2, more preferably 1:1; the mass-volume ratio of anhydrous ferric chloride to the solvent is preferably 2-4 g:30-50 mL, more preferably 2.5-3.5 g:35-45 mL, and even more preferably 3 g:40 mL.

[0038] In the present invention, the glucose solution described in step 1) preferably contains glucose, water and anhydrous ethanol, and the mass-volume ratio of glucose, water and anhydrous ethanol is preferably 2-4 g:15-25 mL:35-45 mL, more preferably 2.5-3.5 g:17-22 mL:37-43 mL, and even more preferably 3 g:20 mL:39-40 mL.

[0039] In the present invention, the glucose solution is preferably prepared by first dissolving glucose in water and then adding anhydrous ethanol to the glucose aqueous solution.

[0040] In the melamine solution described in step 1) of the present invention, the solvent is preferably anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is preferably 1-2:1-2, more preferably 1:1; the mass-volume ratio of melamine to the solvent is preferably 1-3 g:80-120 mL, more preferably 1.5-2.5 g:90-110 mL, and even more preferably 2 g:100 mL.

[0041] In the present invention, the melamine solution is preferably prepared by dissolving melamine in the solvent at 55-65 °C and stirring until the melamine solution is colorless.

[0042] In the present invention, the volume ratio of the ferric chloride solution, glucose solution and melamine solution described in step 1) is preferably 30-50:50-70:80-120, more preferably 35-45:55-65:90-110, and even more preferably 40:60:100.

[0043] In the present invention, the mixing time in step 1) is preferably 15-25 min, more preferably 17-22 min, and even more preferably 20 min.

[0044] In the present invention, the mixing in step 1) is preferably adding the ferric chloride solution and glucose solution to the melamine solution.

[0045] In step 2) of the present invention, the mass ratio of carbon nanotubes to anhydrous ferric chloride in step 1) is preferably 0.45 - 0.55:2 - 4, more preferably 0.48 - 0.52:2.5 - 3.5, and still more preferably 0.5:3.

[0046] In the present invention, the temperature of the mixing in step 2) is preferably 50 - 70 °C, more preferably 55 - 65 °C, and still more preferably 60 °C; the mixing time is preferably 1 - 3 h, more preferably 1.5 - 2.5 h, and still more preferably 2 h; the drying temperature is preferably 160 - 200 °C, more preferably 170 - 190 °C, and still more preferably 180 °C; the drying time is preferably 10 - 14 h, more preferably 11 - 13 h, and still more preferably 12 h.

[0047] In the present invention, the dried product is preferably ground into powder before calcination.

[0048] In the present invention, the calcination in step 2) is preferably carried out under a protective atmosphere, and the protective atmosphere is preferably nitrogen and / or argon. The calcination temperature is preferably 700 - 900 °C, more preferably 750 - 850 °C, and still more preferably 800 °C; the heating rate to the calcination temperature is preferably 4 - 6 °C / min, more preferably 4.5 - 5.5 °C / min, and still more preferably 5 °C / min; the calcination time is preferably 2 - 4 h, more preferably 2.5 - 3.5 h, and still more preferably 3 h.

[0049] In the present invention, the calcined product is preferably cooled and ground to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material; the porous carbon-coated iron carbide supported carbon nanotube composite material is a black powder.

[0050] The present invention also provides a porous carbon-coated iron carbide supported carbon nanotube composite material prepared by the preparation method described above.

[0051] The present invention also provides the application of the porous carbon-coated iron carbide supported carbon nanotube composite material in the catalytic removal of benzo[a]pyrene in wastewater by sodium persulfate.

[0052] In the present invention, the porous carbon-coated iron carbide supported carbon nanotube composite material, benzo[a]pyrene solution and sodium persulfate are mixed, and the mixed solution is subjected to a degradation reaction; the concentration of sodium persulfate in the mixed solution is preferably 0.2 - 4 mmol / L, more preferably 1 - 3 mmol / L; the pH value of the degradation reaction is preferably 3 - 11, more preferably 3 - 5; the temperature of the degradation reaction is preferably 42 - 50 °C, more preferably 43 - 45 °C.

[0053] In the present invention, the benzo[a]pyrene solution contains benzo[a]pyrene, acetone and water. In the benzo[a]pyrene solution, the concentration of benzo[a]pyrene is preferably 70 - 85 μmol / L, more preferably 75 - 80 μmol / L, and still more preferably 78 μmol / L; the concentration of acetone is preferably 5 - 6 mol / L, and more preferably 5.4 - 5.5 mol / L.

[0054] The technical solutions provided by the present invention will be described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0055] In the examples and comparative examples, the constant temperature magnetic stirrer is Hangzhou Jingfei Instrument, MS-H.

[0056] Example 1

[0057] Dissolve 3.0 g of anhydrous ferric chloride in 40 mL of solvent (composed of anhydrous ethanol and water with a volume ratio of 1:1), and stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 3.0 g of glucose in 20 mL of water, stir until completely dissolved, and then add 40 mL of anhydrous ethanol and mix evenly to obtain a glucose solution. Add 2.0 g of melamine to a 250 mL beaker containing 100 mL of solvent (composed of anhydrous ethanol and water with a volume ratio of 1:1), place the beaker on a constant temperature magnetic stirrer, and stir at a rate of 50 r / min at 60 °C until the solution is colorless to obtain a melamine solution.

[0058] Add the anhydrous ferric chloride solution and the glucose solution to the melamine solution, stir at a rate of 50 r / min for 20 min, then add 0.5 g of carbon nanotubes, and stir at 60 °C for 2 h to obtain a homogeneous mixture. Dry the mixture in an oven at 180 °C for 12 h to obtain a solid material precursor. Grind the solid material precursor into a powder, load it into a porcelain boat, place it in a tubular furnace, heat it to 800 °C at a rate of 5 °C / min under a N2 atmosphere, keep it at 800 °C for 3 h, and then cool the tubular furnace to room temperature. After the tubular furnace cools, take out the porcelain boat, and grind the black solid in the porcelain boat into powder particles with a particle size of about 1.3 μm to obtain a porous carbon-coated iron carbide-supported carbon nanotube composite material.

[0059] Example 2

[0060] Dissolve 2.5 g of anhydrous ferric chloride in 35 mL of solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 2.5 g of glucose in 18 mL of water, stir until completely dissolved, then add 37 mL of anhydrous ethanol and mix evenly to obtain a glucose solution. Add 1.5 g of melamine to a 250 mL beaker containing 90 mL of solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), place the beaker on a constant temperature magnetic stirrer, and stir at a rate of 50 r / min at 57 °C until the solution is colorless to obtain a melamine solution.

[0061] Add the anhydrous ferric chloride solution and the glucose solution to the melamine solution, stir at a rate of 50 r / min for 17 min, then add 0.47 g of carbon nanotubes, and stir at 55 °C for 2.5 h to obtain a homogeneous mixture. Dry the mixture in an oven at 170 °C for 13 h to obtain a solid material precursor. Grind the solid material precursor into a powder, load it into a porcelain boat, place it in a tube furnace, and heat it to 750 °C at a rate of 4.5 °C / min under a N2 atmosphere. After holding at 750 °C for 2.5 h, cool the tube furnace to room temperature. After the tube furnace cools, take out the porcelain boat and grind the black solid in the porcelain boat into powder particles with a particle size of about 1.1 μm to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material.

[0062] Example 3

[0063] Dissolve 3.5 g of anhydrous ferric chloride in 45 mL of solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 3.5 g of glucose in 23 mL of water, stir until completely dissolved, then add 43 mL of anhydrous ethanol and mix evenly to obtain a glucose solution. Add 2.5 g of melamine to a 250 mL beaker containing 110 mL of solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), place the beaker on a constant temperature magnetic stirrer, and stir at a rate of 50 r / min at 61 °C until the solution is colorless to obtain a melamine solution.

[0064] Add the anhydrous ferric chloride solution and the glucose solution to the melamine solution, stir at a rate of 50 r / min for 23 min, then add 0.52 g of carbon nanotubes, and stir at 65 °C for 1.5 h to obtain a homogeneous mixture. Dry the mixture in an oven at 190 °C for 11 h to obtain a solid material precursor. Grind the solid material precursor into a powder, load it into a porcelain boat, place it in a tube furnace, and heat it to 850 °C at a rate of 5.5 °C / min under a N2 atmosphere. After holding at 850 °C for 2.5 h, cool the tube furnace to room temperature. After the tube furnace cools, take out the porcelain boat and grind the black solid in the porcelain boat into powder particles with a particle size of about 1.4 μm to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material.

[0065] Comparative Example 1

[0066] Dissolve 3.0 g of anhydrous ferric chloride in 40 mL of a solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), and stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 3.0 g of glucose in 20 mL of water, stir until completely dissolved, and then add 40 mL of anhydrous ethanol and mix evenly to obtain a glucose solution.

[0067] Stir the anhydrous ferric chloride solution and the glucose solution at a rate of 50 r / min at 60 °C for 2 h to obtain a homogeneous mixture. Dry the mixture in an oven at 180 °C for 12 h to obtain a solid material precursor. Grind the solid material precursor into powder, load it into a porcelain boat, place it in a tubular furnace, and heat it to 800 °C at a rate of 5 °C / min under a N2 atmosphere. After holding at 800 °C for 3 h, cool the tubular furnace to room temperature. After the tubular furnace cools, take out the porcelain boat and grind the solid in the porcelain boat into powder to obtain iron carbide nanoparticles.

[0068] Comparative Example 2

[0069] Dissolve 3.0 g of anhydrous ferric chloride in 40 mL of a solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), and stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 3.0 g of glucose in 20 mL of water, stir until completely dissolved, and then add 40 mL of anhydrous ethanol and mix evenly to obtain a glucose solution. Add 2.0 g of melamine to a 250 mL beaker containing 100 mL of a solvent (composed of anhydrous ethanol and water in a volume ratio of 1:1), place the beaker on a constant temperature magnetic stirrer, and stir at 60 °C until the solution is colorless to obtain a melamine solution.

[0070] Add the anhydrous ferric chloride solution and the glucose solution to the melamine solution, and stir at a rate of 50 r / min at 60 °C for 2 h to obtain a homogeneous mixture. Dry the mixture in an oven at 180 °C for 12 h to obtain a solid material precursor. Grind the solid material precursor into powder, load it into a porcelain boat, place it in a tubular furnace, and heat it to 800 °C at a rate of 5 °C / min under a N2 atmosphere. After holding at 800 °C for 3 h, cool the tubular furnace to room temperature. After the tubular furnace cools, take out the porcelain boat and grind the black solid in the porcelain boat into powder to obtain a porous carbon-coated iron carbide nanomaterial.

[0071] Comparative Example 3

[0072] Dissolve 3.0 g of anhydrous ferric chloride in 40 mL of solvent (composed of anhydrous ethanol and water with a volume ratio of 1:1), and stir until completely dissolved to obtain an anhydrous ferric chloride solution. Dissolve 3.0 g of glucose in 20 mL of water, stir until completely dissolved, and then add 40 mL of anhydrous ethanol and mix evenly to obtain a glucose solution. Add a mixture of 50 mL of anhydrous ethanol and 50 mL of water to a 250 mL beaker.

[0073] Add the anhydrous ferric chloride solution and the glucose solution to the mixture of anhydrous ethanol and water, stir at a rate of 50 r / min for 20 min, then add 0.5 g of carbon nanotubes, and stir at 60 °C for 2 h to obtain a homogeneous mixture. Dry the mixture in an oven at 180 °C for 12 h to obtain a solid material precursor. Grind the solid material precursor into powder, load it into a porcelain boat, place it in a tube furnace, heat it to 800 °C at a rate of 5 °C / min under a N2 atmosphere, keep it at 800 °C for 3 h, and then cool the tube furnace to room temperature. After the tube furnace cools, take out the porcelain boat, grind the black solid in the porcelain boat into powder to obtain an iron carbide supported carbon nanotube material.

[0074] Characterize the materials of Example 1, Comparative Example 1 - 3.

[0075] The SEM image of the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1 is as Figure 1 shown. It can be seen from Figure 1 that the surface of the porous carbon-coated iron carbide supported carbon nanotube composite material has a large number of porous structures and carbon nanotubes are attached.

[0076] The HR-TEM image of the porous carbon-coated iron carbide supported carbon nanotube composite material of Example 1 is as Figure 2 shown. It can be known from Figure 2 that the porous carbon-coated iron carbide supported carbon nanotube composite material is a porous carbon-coated iron carbide structure, which can disperse iron carbide nanoparticles well.

[0077] The X-ray crystal diffraction patterns of the materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are as Figure 3 shown. It can be seen from Figure 3It can be seen that on the surface of the material in Example 1, there are mainly iron carbide phase (Fe3C, JCPDS: 35-0072), ferrous carbide phase (Fe2C, JCPDS: 37-0999), iron nitride phase (Fe3N, JCPDS: 50-0958) and graphite phase (Graphite, JCPDS: 41-1487). On the surface of the material in Comparative Example 1, there are mainly iron carbide phase (Fe3C, JCPDS: 35-0072) and carbon phase (Carbon, JCPDS: 26-1080). On the surface of the material in Comparative Example 2, there are mainly iron carbide phase (Fe3C, JCPDS: 35-0072), iron nitride phase (Fe3N, JCPDS: 50-0958) and graphite phase (Graphite, JCPDS: 41-1487).

[0078] The Raman spectra of the materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 are as Figure 4 shown. Figure 4 The ID / IG value in the Raman spectrum can reflect the defect degree of the material. The surface defect degree of the material in Example 1 (I D / I G = 2.59) is much greater than that in Comparative Example 1 (I D / I G = 1.03), Comparative Example 2 (I D / I G = 1.33), and the value in the literature of Comparative Example 3 (I D / I G = 1.01 - 1.10).

[0079] The linear sweep voltammetry was used to compare the electron transfer rates of the reaction between benzo(a)pyrene and persulfate on the surfaces of the materials in Example 1, Comparative Example 1 and Comparative Example 2. The prepared 0.5% Nafion membrane solution and the catalytic material were ultrasonically treated for 2 h at an ultrasonic power of 150 W and then titrated onto the glassy carbon to ensure a coverage concentration of 0.3 mg / cm 3 . As the working electrode, AgCl as the reference electrode, and a carbon rod as the auxiliary electrode, a solution containing 3 mmol / L sodium persulfate, 0.078 mmol / L benzo[a]pyrene and 5.4 mol / L acetone was used as the electrolyte, and the electron transfer rate of the reaction occurring on the material surface was tested using linear sweep voltammetry (LSV) on a CHI660E electrochemical workstation (Shanghai Chenhua). The results are as Figure 5 shown. From Figure 5It can be seen that the peak current of the reaction between sodium persulfate and benzo[a]pyrene on the material surface in Example 1 is the largest, indicating that the number of electrons gained and lost at the same time during the reaction is the largest, and thus the electron transfer rate is the fastest. These results show that adding a nitrogen source (melamine) during the synthesis of Fe3C nanomaterials can increase the crystal form of the iron carbide phase, and new iron nitride phase and graphene phase are added; adding carbon nanotubes can add a part of the iron carbide phase; introducing nitrogen source (melamine) and carbon nanotubes at the same time can increase the defect sites on the material surface. Introducing iron nitride phase, iron carbide phase and graphene phase into Fe3C nanomaterials will improve the catalytic activity of Fe3C as a persulfate catalyst, and the newly introduced graphene phase can greatly improve the electron transfer efficiency of the material. The large increase in defect sites makes the porous carbon-coated iron carbide supported carbon nanotube composite material have extremely high catalytic activity, which helps to improve the efficiency of treating refractory organic pollutants in wastewater.

[0080] Effect of different materials in Application Example 1 on activating sodium persulfate to remove benzo[a]pyrene

[0081] Add 50 mL of benzo[a]pyrene solution with a concentration of 78 μmol / L into a conical flask. The benzo[a]pyrene solution contains 5.4 mol / L of acetone, and the solvent is ultrapure water. Adjust the pH value of the benzo[a]pyrene solution to 3 with 0.5 mol / L hydrochloric acid solution and 0.5 mol / L NaOH solution. Add 80 mg of the composite material in Example 1 into the benzo[a]pyrene solution, shake it at a rate of 200 r / min at room temperature for 20 min in a constant temperature oscillator, then add sodium persulfate with a concentration of 0.2 mmol / L (0.2 mM), and start the degradation reaction after raising the temperature to 35 °C. Take 0.5 mL of samples at 5 min, 15 min, 30 min, 60 min, and 90 min after degradation, add them into 0.5 mL of methanol, filter through a 0.22 μm polytetrafluoroethylene (PTFE) filter head, and then use a high performance liquid chromatography mass spectrometer (Agilent 1290 Infinity Ⅱ LC - Agilent 6400 MS) to detect the content of benzo[a]pyrene in the samples.

[0082] Replace the material in Example 1 with the materials in Comparative Example 1, Comparative Example 2, and Comparative Example 3, and conduct tests according to the same method above. The effects of the materials in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 on removing benzo[a]pyrene are as Figure 6 shown, Figure 6 Among them, -20 to 0 min is the adsorption time, and 0 to 90 min is the degradation time.

[0083] From Figure 6It can be seen that the degradation rate of benzo[a]pyrene by 0.2 mM sodium persulfate at 35°C is less than 5%. The materials in Example 1, Comparative Example 1, and Comparative Example 2 had weak adsorption effects on benzo[a]pyrene within 20 min, which were 11.3%, 17.1%, and 13.6% respectively. After adding sodium persulfate oxidant, within 90 min, the degradation rate of benzo[a]pyrene by the material in Example 1 activating sodium persulfate at 35°C could reach 99.5%, while the degradation rates of benzo[a]pyrene by the materials in Comparative Example 1 and Comparative Example 2 activating sodium persulfate at 35°C were 57% and 58% respectively. Due to the high acetone concentration of 5.4 mol / L and its ability to · OH and SO4 ·- react quickly, benzo[a]pyrene was mainly degraded by non-oxidative free radicals or direct electron transfer pathways. The results showed that the material in Example 1 activating the sodium persulfate oxidation system at a lower heating temperature could efficiently repair benzo[a]pyrene pollution in water bodies containing organic matter. Using the method of porous carbon-coated iron carbide nanomaterials and carbon nanotube loading to prepare composite iron carbide-based materials could significantly improve the performance of iron carbide, porous carbon, and carbon nanotubes in activating sodium persulfate to generate non-oxidative free radicals or direct electron transfer pathways, and enhance the application prospects of iron carbide-based materials.

[0084] Effect of reaction temperature on the removal of benzo[a]pyrene by porous carbon-coated iron carbide loaded with carbon nanotubes composite activating sodium persulfate

[0085] Add 50 mL of benzo[a]pyrene solution with a concentration of 78 μmol / L to a conical flask. The benzo[a]pyrene solution contains 5.4 mol / L of acetone, the solvent is ultrapure water, and the pH value of the benzo[a]pyrene solution is adjusted to 3. Add 80 mg of the composite material in Example 1 to the benzo[a]pyrene solution, shake it at room temperature in a constant temperature oscillator for 20 min, then add sodium persulfate with a concentration of 0.2 mmol / L, and start the degradation reaction after raising the temperature to 45°C. Take 0.5 mL of samples at 5 min, 15 min, 30 min, 60 min, and 90 min after degradation, add them to 0.5 mL of methanol, filter through a 0.22 μm PTFE filter head, and then use a high performance liquid chromatograph to detect the content of benzo[a]pyrene in the samples.

[0086] Change the reaction temperature to 25°C, 30°C, 35°C, and 40°C respectively, and keep other conditions the same as the above method. Compare the effects of different reaction temperatures on the removal of benzo[a]pyrene by the material in Example 1 activating the sodium persulfate system. The results are as Figure 7 shown.

[0087] From Figure 7It can be seen that under the condition of 45 °C, the removal rate of benzo[a]pyrene reached 99.7% at 90 min, while at 25 °C, 30 °C, 35 °C and 40 °C, the removal rates of benzo[a]pyrene at 90 min were 77.1%, 80.7%, 81.2% and 88.7% respectively. The results show that within the range of 25 - 45 °C, increasing the temperature can significantly promote the removal effect of the porous carbon-coated iron carbide supported carbon nanotube composite on benzo[a]pyrene by catalyzing sodium persulfate, and the removal rate of benzo[a]pyrene slightly increases or hardly changes after exceeding 45 °C. Moreover, the material of the present invention can still maintain good stability after thermal energy injection, is not easy to age, and can significantly improve the performance of activating persulfate to degrade pollutants compared with conventional iron-carbon materials, thus enhancing the application value of iron carbide-based nanomaterials.

[0088] Application Example 3 Influence of pH value on the removal of benzo[a]pyrene by activating sodium persulfate with porous carbon-coated iron carbide supported carbon nanotube composite

[0089] Add 50 mL of benzo[a]pyrene solution with a concentration of 78 μmol / L into a conical flask. The benzo[a]pyrene solution contains 5.4 mol / L of acetone, the solvent is ultrapure water, and the pH value of the benzo[a]pyrene solution is adjusted to 3. Add 80 mg of the composite material of Example 1 into the benzo[a]pyrene solution, shake it at room temperature in a constant temperature oscillator for 20 min, then add sodium persulfate with a concentration of 0.2 mmol / L, and start the degradation reaction after heating the temperature to 45 °C. Take 0.5 mL of samples at 5 min, 15 min, 30 min, 60 min and 90 min after degradation, add them into 0.5 mL of methanol, filter through a 0.22 μm PTFE filter head, and then use a high performance liquid chromatograph to detect the content of benzo[a]pyrene in the samples.

[0090] Adjust the pH value to 5, 7, 9 and 11 respectively, and keep other conditions the same as the above method. Compare the influence of different pH values on the effect of the material of Example 1 activating the sodium persulfate system to remove benzo[a]pyrene. The results are as Figure 8 shown.

[0091] It can be seen from Figure 8 that the removal rates of benzo[a]pyrene by the porous carbon-coated iron carbide supported carbon nanotube composite catalyzing the sodium persulfate system are 100%, 100%, 98.9%, 99.2% and 97.6% under the conditions of pH values of 3, 5, 7, 9 and 11 respectively. The results show that the iron carbide-based material can have good activity under a wide range of acid-base conditions, has a good removal effect on benzo[a]pyrene, has a wide pH application range, and is beneficial to practical applications.

[0092] Application Example 4 Influence of Sodium Persulfate Dosage on the Removal of Benzo[a]pyrene by Activating Sodium Persulfate with Porous Carbon-Coated Iron Carbide Supported Carbon Nanotube Composite

[0093] Add 50 mL of benzo[a]pyrene solution with a concentration of 78 μmol / L into a conical flask. The benzo[a]pyrene solution contains 5.4 mol / L of acetone, and the solvent is ultrapure water. Add 80 mg of the composite material of Example 1 into the benzo[a]pyrene solution, shake it at room temperature in a constant temperature oscillator for 20 min, then add sodium persulfate with a concentration of 0.2 mmol / L, and start the degradation reaction after raising the temperature to 45 °C. Since the process of the composite material of Example 1 catalyzing the degradation of benzo[a]pyrene by PS is not affected by pH, there is no need to adjust the pH during the reaction process. Take 0.5 mL of samples at 5 min, 15 min, 30 min, 60 min, and 90 min after degradation respectively, add them into 0.5 mL of methanol, filter through a 0.22 μm PTFE filter head, and then use a high performance liquid chromatograph to detect the content of benzo[a]pyrene in the samples.

[0094] Change the dosage concentrations of sodium persulfate to 2 mM, 3 mM, 5 mM, and 10 mM respectively, and keep other conditions the same as the above method. Compare the influence of the dosage of the oxidant sodium persulfate on the effect of removing benzo[a]pyrene in the system of activating sodium persulfate with the material of Example 1. The results are as Figure 9 shown.

[0095] As Figure 9 can be seen, after 20 min of adsorption, the adsorption rates of the porous carbon-coated iron carbide supported carbon nanotube composite for benzo[a]pyrene are 36.5%, 35.2%, 42.4%, 38.6%, and 36.9% respectively. When the dosages of the oxidant sodium persulfate are 0.2 mM, 2 mM, 3 mM, 5 mM, and 10 mM respectively, the degradation rates of benzo[a]pyrene after 30 min of degradation are 84.5%, 90%, 100%, 72.5%, and 74% respectively. The results show that when the dosage of sodium persulfate is in the range of 0.2 - 3 mM, with the increase of the dosage of sodium persulfate, the degradation rate of benzo[a]pyrene can be correspondingly improved; however, when the dosage of sodium persulfate is in the range of 3 - 5 mM, the degradation rate of benzo[a]pyrene decreases significantly. This is because sodium persulfate is adsorbed onto the surface active sites of the material and is activated by the porous carbon-coated iron carbide supported carbon nanotube composite under low heating conditions to generate a non-radical path for the degradation of benzo[a]pyrene; when the concentration of sodium persulfate exceeds 3 mM, most of the surface active sites of the material are occupied by sodium persulfate, which affects the adsorption and reaction of benzo[a]pyrene on the material surface, thus resulting in a decrease in the degradation rate of benzo[a]pyrene.

[0096] Application Example 5 Effect of Porous Carbon-Coated Iron Carbide Supported Carbon Nanotube Composite on Activating Sodium Persulfate to Remove Benzo[a]pyrene in Different Sewage

[0097] Add 50 mL of benzo[a]pyrene solution with a concentration of 78 μmol / L into a conical flask. The benzo[a]pyrene solution contains 5.4 mol / L of acetone, and the solvent is ultrapure water. Add 80 mg of the composite material of Example 1 into the benzo[a]pyrene solution, shake it at room temperature in a constant temperature oscillator for 20 min, then add sodium persulfate with a concentration of 5 mmol / L, and start the degradation reaction after raising the temperature to 45 °C. Since the process of the composite material of Example 1 catalyzing the degradation of benzo[a]pyrene by PS is not affected by pH, it is not necessary to adjust the pH during the reaction process. Take 0.5 mL of samples at the time points of 5 min, 15 min, 30 min, 60 min, and 90 min after degradation, add them into 0.5 mL of methanol, and filter through a 0.22 μm PTFE filter head. Finally, use a high performance liquid chromatograph to detect the content of benzo[a]pyrene in the samples.

[0098] Prepare 50 mL of benzo[a]pyrene solution with a concentration of 78 μM using the actual wastewater from the secondary sedimentation tank of papermaking wastewater, the secondary sedimentation tank of printing and dyeing wastewater, and the final sedimentation tank in the wastewater treatment plant of Zhejiang Huachuan Industry Group Co., Ltd. Other conditions are the same as the above method. Compare the effects of different water bodies on the removal effect of benzo[a]pyrene by the persulfate activation system of the material of Example 1. The results are as Figure 10 shown, and the pure water is the ultrapure water in the above method.

[0099] As Figure 10 can be seen, the removal rates of benzo[a]pyrene by the porous carbon-coated iron carbide-supported carbon nanotube composite material of Example 1 in different wastewaters within 20 min are 50.2% (final sedimentation tank), 35.2% (papermaking secondary sedimentation tank), and 32.4% (printing and dyeing secondary sedimentation tank), respectively. After adding sodium persulfate, at 90 min of degradation, the removal rates of benzo[a]pyrene by the persulfate activation system (45 °C) of the porous carbon-coated iron carbide-supported carbon nanotube composite material under different actual wastewater conditions are 100% (final sedimentation tank), 100% (papermaking secondary sedimentation tank), and 97.7% (printing and dyeing secondary sedimentation tank), respectively. The results show that the persulfate activation system with low temperature (45 °C) of the porous carbon-coated iron carbide-supported carbon nanotube composite material of the present invention can be used to catalytically degrade benzo[a]pyrene in actual industrial wastewater with complex components, and has good application value.

[0100] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. Application of a porous carbon-coated iron carbide supported carbon nanotube composite in catalytic removal of benzo[a]pyrene in wastewater by sodium persulfate, characterized in that, Preparation method of porous carbon-coated iron carbide supported carbon nanotube composite material, comprising the following steps: 1) Mix ferric chloride solution, glucose solution and melamine solution to obtain a mixed solution; 2) Mix the mixed solution and carbon nanotubes, and then successively carry out drying and calcination to obtain a porous carbon-coated iron carbide supported carbon nanotube composite material; In the ferric chloride solution in step 1), the solute is anhydrous ferric chloride, the solvents are anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1-2:1-2; the mass-volume ratio of anhydrous ferric chloride to the solvents is 2-4 g:30-50 mL; The glucose solution contains glucose, water and anhydrous ethanol, and the mass-volume ratio of glucose, water and anhydrous ethanol is 2-4 g:15-25 mL:35-45 mL; In the melamine solution in step 1), the solvents are anhydrous ethanol and water, and the volume ratio of anhydrous ethanol to water is 1-2:1-2; the mass-volume ratio of melamine to the solvents is 1-3 g:80-120 mL; The volume ratio of the ferric chloride solution, glucose solution and melamine solution in step 1) is 30-50:50-70:80-120; In step 2), the mass ratio of carbon nanotubes to anhydrous ferric chloride in step 1) is 0.45-0.55:2-4; Mix the porous carbon-coated iron carbide supported carbon nanotube composite material, benzo[a]pyrene solution and sodium persulfate, and carry out a degradation reaction on the mixed solution; the benzo[a]pyrene solution contains benzo[a]pyrene, acetone and water.

2. The application according to claim 1, characterized in that, The temperature of mixing in step 2) is 50-70 °C, and the mixing time is 1-3 h; the drying temperature is 160-200 °C, and the drying time is 10-14 h.

3. The application according to claim 2, characterized in that, The calcination in step 2) is carried out under a protective atmosphere, the protective atmosphere is nitrogen and / or argon, the calcination temperature is 700-900 °C, the heating rate to the calcination temperature is 4-6 °C / min, and the calcination time is 2-4 h.

4. The application according to claim 3, characterized in that, The concentration of sodium persulfate in the mixed solution is 0.2-3 mmol / L, the pH value of the degradation reaction is 3-11, and the temperature of the degradation reaction is 42-50 °C.

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