Method for preparing modified multi-walled carbon nanotube anode electrode for soil electroremediation

Abstract

The application discloses a modified multi-walled carbon nanotube anode electrode preparation method for soil electrokinetic remediation, relates to the field of anode preparation in soil electrokinetic remediation technology, and comprises the following steps: preparing a carbon nanotube electrode base material, preparing biochar, preparing a multi-walled carbon nanotube and biochar composite material, preparing an unmodified multi-walled carbon nanotube composite material, preparing an unmodified multi-walled carbon nanotube composite material slurry, preparing a modified multi-walled carbon nanotube electrode material, drying the modified multi-walled carbon nanotube electrode material, preparing a modified multi-walled carbon nanotube electrode material, and placing the modified multi-walled carbon nanotube electrode material into a die casting 10cm*10cm*5cm, dissolving sodium polyacrylate in a 20-layered separate infiltration manner so that the sodium polyacrylate can bond surrounding electrode materials, and forming a square sheet-shaped electrode under the action of pressure. The application uses multi-walled carbon nanotubes and biochar as base materials to prepare an anode electrode, and uses a method of high-temperature loading of chemical formula C6H 11 FeNO7 of ammonium citrate iron to prepare a high-efficiency anode electrode, greatly improves electrocatalytic performance and electrokinetic remediation effect, reduces electrokinetic remediation energy consumption, prolongs electrode service life, and improves heavy metal treatment capacity of contaminated soil.

Description

TECHNICAL FIELD

[0001] The application relates to the field of anode preparation in soil electrokinetic remediation technology, in particular to a preparation method of a modified multi-walled carbon nanotube anode electrode for soil electrokinetic remediation. BACKGROUND

[0002] The electrokinetic remediation technology is a widely used in-situ soil remediation technology, has the characteristics of simple construction process, no secondary pollution and the like in treating contaminated soil, and has been more applied in heavy metal contaminated soil treatment engineering in recent years.

[0003] The process principle of the electrokinetic remediation is that a "cathode-anode-polluted soil-electrolyte" system is constructed, under the action of a direct current or an alternating current electric field, pollutants diffuse through electromigration, electrophoresis and electroosmosis, so that heavy metal ions are transferred to the electrolyte, and the heavy metal ions are removed from the soil.

[0004] The main problems of the anode electrode in the current electrokinetic remediation technology are as follows: the precious metal as the anode is greatly consumed and has a high cost; the graphite anode electrode has weak electrocatalytic ability and low efficiency; the graphite electrode is easily consumed by air, which affects the use cost; and the metal anode electrode causes pollution of the anode electrolyte due to metal deposition, so that the electrokinetic remediation process has the problems of large power consumption and high treatment cost, which restricts the application and popularization of the electrokinetic soil remediation technology.

[0005] For example, the patent with the publication number CN201811340146.5 reports a preparation method of a Co3O4 / graphite felt composite electrode applied to an anodic oxidation system, Co3O4 is loaded on the graphite felt by high-temperature calcination at a certain temperature, the service life of the graphite electrode is prolonged, and high oxidation efficiency is obtained, but there are still problems such as insufficient treatment capacity of the electrode in the electrokinetic remediation, low current efficiency and long remediation time. At present, a new modified electrode needs to be researched for heavy metal contaminated soil, which has small environmental interference, is green and environmentally friendly, and has high economic benefits.

[0006] In response to the defects in the existing heavy metal contaminated soil technology, the existing graphite anode electrode causes a large amount of power consumption in the electrokinetic remediation process, in order to solve the problems of power consumption and remediation effect of the ordinary graphite electrode, the application provides a preparation method of a modified multi-walled carbon nanotube electrode, and the multi-walled carbon nanotube and the biological carbon composite material are used as raw materials to manufacture the electrode, the purpose is to improve the electrokinetic remediation effect, reduce the electrokinetic remediation energy consumption, prolong the service life of the electrode and improve the treatment capacity of the heavy metal in the contaminated soil.

[0007] The anode electrode is manufactured by using the multi-walled carbon nanotube and the biological carbon as the matrix material, and the high-temperature loading chemical formula C6H 11The application discloses a method for preparing a high-efficiency anode electrode by using ammonium citrate ferric iron FeNO7. SUMMARY

[0008] To solve the above technical problems, the application provides the following technical solutions.

[0009] The application discloses a preparation method of a modified multi-walled carbon nanotube anode electrode for soil electrokinetic remediation, and comprises the following steps.

[0010] (1) preparing a carbon nanotube electrode base material: multi-walled carbon nanotube powder is weighed in a 1L beaker and is moistened by using a humidifier device for 1 min, and then the internal static electricity of the multi-walled carbon nanotube electrode is eliminated and the multi-walled carbon nanotube powder is obtained after waiting for 60 min, and is denoted as P1;

[0011] (2) preparing biochar: leaves are placed into an oven, the temperature of the oven is adjusted to evaporate water in the leaves to obtain dried leaves, the dried leaves are crushed and then are placed into a grinding machine to be broken into leaf powder, and the leaf powder is placed into a muffle furnace, the heating time is adjusted to 120 min to 600 DEG C, and the temperature is kept for 120 min, and then the temperature is slowly cooled to room temperature;

[0012] (3) preparing a multi-walled carbon nanotube and biochar composite material: the prepared biochar is placed into a jade grinding tool to be ground to obtain biochar, and then the biochar is slowly placed into a 1L beaker to be mixed with the multi-walled carbon nanotube under stirring to obtain a material, and the material is denoted as P2;

[0013] (4) preparing an unmodified multi-walled carbon nanotube composite material: multi-walled carbon nanotube powder with a chemical formula of C6H 11 ammonium citrate ferric iron FeNO7 with a mass of 15.9 g is placed into a grinding tool to be ground into powder, and then the powder is added into the P2 material for multiple times, and an unmodified multi-walled carbon nanotube material is obtained, and the material is denoted as P3;

[0014] (5) preparing an unmodified multi-walled carbon nanotube composite material turbid liquid: the P3 material is placed into a 1L beaker, ultrapure water is added, and the beaker is sealed and stirred to obtain a turbid liquid;

[0015] (6) preparing an unmodified multi-walled carbon nanotube electrode material: the unmodified multi-walled carbon nanotube composite material turbid liquid is extracted by using a suction filtration device to remove the unmodified multi-walled carbon nanotube composite material, and then the unmodified multi-walled carbon nanotube composite material is washed by using an ammonium citrate ferric iron FeNO7 aqueous solution to obtain an unmodified multi-walled carbon nanotube electrode material, and the material is denoted as material P4; 11

[0016] (7) drying the unmodified multi-walled carbon nanotube electrode material: the material P4 is placed into a sterile vacuum drying box to be dehydrated and dried, and then the material P4 is placed into a grinding tool to be finely ground after being dried; ​

[0017] (8) Preparation of modified multi-walled carbon nanotube electrode material: put the dried material P4 into a vacuum tube furnace for high temperature modification at 600°C to load chemical formula C6H 11 The ammonium citrate iron of FeNO7 further improves the electric dynamic repair ability, and 2g of sodium polyacrylate ground through an 80-mesh sieve is added into the modified multi-walled carbon nanotube electrode material.

[0018] (9) Put the modified multi-walled carbon nanotube electrode material into a die casting of 10cm×10cm×5cm, and dissolve the sodium polyacrylate by a 20-layer separate soaking method to enable it to bond with the surrounding electrode material, and form a square sheet electrode under the action of pressure. Because the carbon nanotube and the biological carbon have strong pressure resistance and are not easy to tear, etc., the electrode material has strong plasticity.

[0019] Preferably, in step (1), the multi-walled carbon nanotube material needs to be treated by humidification to eliminate static electricity, otherwise it cannot effectively contact the biological carbon powder.

[0020] Preferably, in step (2), during the preparation of the biological carbon, the surface of the leaves is dusted and placed in an oven with a temperature setting of 70°C for 1440min. After the leaves are dried, they are put into a crusher and stirred into fine powder, which is convenient for high-temperature preparation of biological carbon. The crushed leaves are put into a muffle furnace for high-temperature sintering. The sintering temperature is 600°C, the temperature is raised at a rate of 5°C / min for 60min to 300°C, and then raised at a rate of 5°C / min for another 60min to 600°C. The temperature is kept constant for 1h, and then decreased to room temperature at the same rate.

[0021] Preferably, in step (4), 15.9g of chemical formula C6H 11 The ammonium citrate iron of FeNO7 is put into the P3 material, 500mL of ultrapure water is added to prepare a turbid liquid, and a magnetic stirrer is used for stirring for 24h and standing for 5h.

[0022] Preferably, in step (7), the oven temperature is adjusted to 120°C for rapid dehydration to dry the material P4, and the material is crushed with a marquise grinding pestle after 360min.

[0023] Preferably, in step (8), N2 is used to replace the air in the tube furnace, and the temperature rising rate of the vacuum tube furnace is set to 5°C / min, the temperature is raised to 600°C for 120min, and then gradually cooled to room temperature at a rate of 5°C / min after keeping the temperature constant for 120min.

[0024] Preferably, in step (9), the high-temperature modified carbon nanotube electrode material is placed in a die casting of 10 cm*10 cm*5 cm, 0.45 mm thick high-temperature modified carbon nanotube electrode material is laid and 5 mL of ultrapure water is sprayed onto the surface and absorbed, and the laying and wetting of 0.45 mm thick high-temperature modified carbon nanotube electrode material is repeated 20 times until the sodium polyacrylate is completely dissolved by absorbing water; 50 kg of pressure is slowly increased for 15 min, so that the thickness reaches 0.6 cm and is kept for 30 min to absorb water;

[0025] The prepared modified multi-walled carbon nanotube electrode needs to be placed in an oven to evaporate water, and the oven temperature is set to 50 DEG C. It should be noted that too high evaporation temperature will cause the electrode sheet to deform.

[0026] The application also discloses a modified multi-walled carbon nanotube electrode preparation method and application of the electrode.

[0027] The application has the following beneficial effects:

[0028] 1. The application provides a modified multi-walled carbon nanotube electrode, which solves the problem of excessive power loss in the electrokinetic remediation process and improves the treatment effect of heavy metal pollution in contaminated soil.

[0029] 2. The application overcomes the problem of excessive power loss caused by the limitation of current size in the electrokinetic remediation process of the existing electrokinetic remediation electrode, and solves the problem that traditional electrodes, such as carbon rods and graphite electrodes, have a smaller specific surface area than multi-walled carbon nanotube electrodes, and it is difficult to significantly improve the current to promote the migration of heavy metals in contaminated soil as the anode of electrokinetic remediation.

[0030] 3. The application breaks away from the contact area constraint of traditional graphite electrodes, thereby significantly improving the electrokinetic remediation capability.

[0031] 4. The specific surface area of the electrode is the void of the multi-walled carbon nanotube and biocarbon composite material, so that the specific surface area of the composite material is larger, and the composite material increases the contact area of the anode chamber electrolyte in the electrokinetic remediation process due to the large pore size, so that the contact area of the electrode is free from the limitation of the planar area of the original graphite electrode, and the contact area of the modified electrode is larger than the planar area, and the improvement of the contact area depends on the multi-void structure of the multi-walled carbon nanotube and biocarbon composite material. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1This is a schematic diagram of the process for preparing the electrode of the present invention.

[0033] Figure 2 A schematic diagram of a self-made modified multi-walled carbon nanotube electrode;

[0034] Figure 3 The cyclic voltammetry (CV) curves of a modified multi-walled carbon nanotube electrode were obtained by preparing a mixed solution of 0.1 mol / L K3Fe(CN)6 and 0.1 mol / L NaCl, using a saturated calomel electrode as the reference electrode and a silver chloride electrode as the auxiliary electrode.

[0035] Figure 4 Photographs of the fabricated modified multi-walled carbon nanotube electrodes;

[0036] Figure 5 The composite material, consisting of multi-walled carbon nanotubes and bio-carbon, is doped with 15.9 g of a chemical formula C6H. 11 Ferric ammonium citrate catalyst of FeNO7 and scanning electron microscope (FE-SEM) images of high-temperature modification were obtained.

[0037] Figure 6 FE-SEM image of an unmodified multi-walled carbon nanotube and bio-carbon composite material doped with 15.9 g of C6H8FeNO7 catalyst;

[0038] Figure 7 The peaks of the material in the range of 2θ = 18.456° to 67.492° correspond to the crystalline characteristic X-ray diffraction (XRD) image with l / lc = 5.21.

[0039] Figure 8 Its chemical formula is C6H 11 Molecular structure diagram of FeNO7 ferric ammonium citrate, and calculated X-ray powder diffraction peak pattern: Magnetite low-Fe3O4Pmc21:5.93 / 5.93 / 16.75<90.0 / 90.0>Fe3O4;

[0040] Figure 9 The electrode is a modified multi-walled carbon nanotube electrode (modified electrode) and a composite material consisting of unmodified multi-walled carbon nanotubes and bio-carbon (comparative electrode 2). The unmodified multi-walled carbon nanotubes have the chemical formula C6H. 11 FTIR images of FeNO7 ferric ammonium citrate catalyst carbon nanotubes and bio-carbon composites (comparative electrode 3);

[0041] Figure 10 The modified multi-walled carbon nanotube electrode (modified electrode) is used in soil electroremediation processes, while the control electrode consists of unmodified multi-walled carbon nanotubes and a biochar composite material (comparative electrode 2). The unmodified multi-walled carbon nanotubes have the chemical formula C6H. 11Figure of the change curve of the carbon nanotube and biochar composite material of the ammonium citrate iron catalyst of FeNO7 (one-armed electrode 3) with time migration current (I);

[0042] Figure 11 Figure of the EC change curve of the cathode solution and the anode solution in the electrokinetic remediation process;

[0043] Figure 12 Figure of the EC change curve of the five zones (S1, S2, S3, S4, and S5) of the soil in the electrokinetic remediation process;

[0044] Figure 13 Figure of the heavy metal Cu and Zn content change of the five zones (S1, S2, S3, S4, and S5) after the electrokinetic remediation treatment;

[0045] Figure 14 Figure of the pH value change curve of the cathode solution, the anode solution, and the measured pH value in the five zones (S1, S2, S3, S4, and S5). DETAILED DESCRIPTION

[0046] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific embodiments.

[0047] As shown in Figures 1 to 14 , the modified multi-walled carbon nanotube anode electrode preparation method for soil electrokinetic remediation comprises the following steps:

[0048] (1) Prepare the carbon nanotube electrode base material: weigh the multi-walled carbon nanotube powder in a 1L beaker and wet it using a humidifier device for 1 min, eliminate the static electricity inside the multi-walled carbon nanotube electrode and wait for 60 min, obtain the multi-walled carbon nanotube powder, and mark it as P1;

[0049] (2) Prepare the biochar: put the leaves into an oven to adjust the temperature to evaporate the water and obtain dried leaves, crush the leaves and put them into a grinder to break them into leaf powder, put the leaf powder into a muffle furnace to adjust the heating time to 600℃ for 120 min, keep it for 120 min, and slowly cool it to room temperature;

[0050] (3) Prepare the multi-walled carbon nanotube and biochar composite material: put the prepared biochar into a jade grinding tool to grind it into biochar, and then slowly put it into a 1L beaker to mix it evenly with the multi-walled carbon nanotube, and obtain the material marked as P2;

[0051] (4) Preparation of unmodified multi-walled carbon nanotube composite material: weigh 15.9g of C6H 11FeNO7 ammonium citrate iron, a small amount of multiple times into the P2 material after grinding into powder, get unmodified multi-walled carbon nanotube material, recorded as P3;

[0052] (5) preparation of unmodified multi-walled carbon nanotube composite material turbidity: P3 material into a 1L beaker, add ultrapure water and sealed stirring to get turbidity;

[0053] (6) preparation of modified multi-walled carbon nanotube electrode material: the unmodified multi-walled carbon nanotube composite material turbidity through the suction filtration device to extract the chemical formula as C6H 11 FeNO7 ammonium citrate iron aqueous solution, get modified multi-walled carbon nanotube electrode material, recorded as material P4;

[0054] (7) drying of modified multi-walled carbon nanotube electrode material: material P4 into a sterile vacuum drying oven dehydration drying, after drying into a grinding tool for fine grinding;

[0055] (8) preparation of modified multi-walled carbon nanotube electrode material: the dried material P4, into a vacuum tube furnace for high temperature 600 DEG C modification, to load the chemical formula as C6H 11 FeNO7 ammonium citrate iron to improve the ability of electric repair, and take 2g of sodium polyacrylate grinding 80 mesh sieve after adding to the modified multi-walled carbon nanotube electrode material;

[0056] (9) the modified multi-walled carbon nanotube electrode material into the die casting 10 cm x 10 cm x 5 cm, through the 20 layers respectively by the way of infiltration of polyacrylic acid sodium to make it can be bonded around the electrode material, under the action of pressure to form square sheet electrode; because of carbon nanotube and biological carbon pressure resistance, not easy to tear the advantages, make the electrode material has strong plasticity.

[0057] Further, in step (1), the multi-walled carbon nanotube material needs to be treated by humidification to eliminate static electricity, otherwise it cannot be effectively contacted with the biological carbon powder;

[0058] Further, in step (2), during the preparation of biological carbon, the surface of the leaves is dusted and placed in an oven with a temperature of 70 DEG C for 1440 min. After the leaves are dried, they are put into a crusher and crushed into fine powder, which is convenient for high temperature preparation of biological carbon. The crushed leaves are placed in a muffle furnace for high temperature sintering. The sintering temperature is 600 DEG C, the temperature is raised at a rate of 5 DEG C / min for 60 min to 300 DEG C, and then the temperature is raised for another 60 min to 600 DEG C. The temperature is kept constant for 1 h, and then it is reduced to room temperature at the same rate;

[0059] Further, in step (4), 15.9g of the chemical formula C6H 11Ferric ammonium citrate of FeNO7 was added to the P3 material, and 500 mL of ultrapure water was added to make a turbid solution. The solution was stirred with a magnetic stirrer for 24 hours and then allowed to stand for 5 hours.

[0060] Further, in step (7), the oven temperature is adjusted to 120°C to quickly dehydrate and dry material P4. After 360 minutes, it is taken out and crushed with an agate grinding pestle.

[0061] Further, step (8) requires replacing the air inside the tube furnace with N2 and setting the heating rate of the vacuum tube furnace to 5℃ / min, heating to 600℃ for 120min, holding for 120min and then gradually cooling down to room temperature at 5℃ / min.

[0062] Further, in step (9), the high-temperature modified carbon nanotube electrode material is placed inside the die-cast part 10cm×10cm×5cm, a 0.45mm thick high-temperature modified carbon nanotube electrode material is laid, and 5mL of ultrapure water is sprayed onto its surface and absorbed. The 0.45mm thick high-temperature modified carbon nanotube electrode material is laid and wetted 20 times until the sodium polyacrylate is completely absorbed and dissolved.

[0063] Slowly increase the pressure to 50kg for 15 minutes to make it 0.6cm thick, and keep it for 30 minutes to allow it to absorb moisture;

[0064] The moisture in the prepared modified multi-walled carbon nanotube electrodes needs to be evaporated in an oven. The oven temperature should be set to 50°C. It should be noted that excessively high evaporation temperatures can cause deformation of the electrode sheets.

[0065] The present invention also discloses the application of a modified multi-walled carbon nanotube electrode preparation method, which uses the modified multi-walled carbon nanotube electrode as the anode for electrokinetic remediation and ordinary graphite electrode as the cathode to remediate soil contaminated with heavy metals.

[0066] The following describes the morphology and electrochemical characterization of the prepared electrodes, and provides a more detailed description of the embodiments of the present invention in conjunction with the accompanying drawings.

[0067] Figure 2 The prepared electrode pattern is complete. Figure 2 In the diagram, ① represents the height of the modified multi-walled carbon nanotube electrode, which is 10 cm; ② represents the width of the electrode, which is 10 cm; ③ represents the electrode material, which is stacked in layers of 20 (0.45 mm / layer) and pressurized; and ④ represents the electrode thickness, which is 0.6 cm.

[0068] The diameters of its working electrode, reference electrode, and counter electrode are 6 mm, 1 mm, and 1 mm, respectively.

[0069] Figure 3The CV curves of the modified multi-walled carbon nanotube electrode in a 0.1 mol / L K3Fe(CN)6+ 0.1 mol / L NaCl solution are shown. From -4V to 4V, the CV curves maintain sharp angles at both ends and a roughly rectangular shape in the middle, without significant distortion, indicating ideal double-layer capacitance behavior. This suggests high ion and electron reversibility and rapid charge transport. Notably, the curves are almost symmetrical with slight distortion. This slight distortion may be due to pseudocapacitive behavior caused by O doping during the high-temperature modification process.

[0070] Figure 4 The image shows the actual modified multi-walled carbon nanotube electrode, which exhibits good conductivity and heavy metal handling capabilities during subsequent electrokinetic repair processes.

[0071] Figure 5 These are FE-SEM images of the modified multi-walled carbon nanotube electrode at 200 nm and 2 μm, such as... Figure 5 As shown, the multi-walled carbon nanotube electrode material exhibits a distinct porous structure and uniform elemental distribution after high-temperature modification, confirming its chemical formula as C6H. 11 The FeNO7 ferric ammonium citrate catalyst was successfully incorporated into the electrode material, and it can be inferred that it has combined with the material itself with more CN, CH and CO bonds.

[0072] Figure 6 These are FE-SEM images of unmodified multi-walled carbon nanotube electrodes at 200 nm and 1 μm, such as... Figure 6 As shown, carbon nanotube materials and biocarbon materials, due to the lack of high-temperature treatment at 600℃, although possessing certain pore structures, exhibit huge solid inclusions of multi-walled carbon nanotubes and biocarbon materials, severely affecting the overall conductivity of the materials.

[0073] Figure 7 The figure shows the X-ray diffraction (XRD) image of the modified multi-walled carbon nanotube electrode. After modification at 600℃, the Fe3O4 content in the material exhibits multiple main peaks, accounting for approximately 99%. XRD characterization confirms that the electrode material underwent successful high-temperature modification, transforming the chemical formula C6H... 11 The FeNO7 ferric ammonium citrate catalyst was incorporated into the material, and after high temperature, CN and CO bonds were attached to the electrode material, which enhanced the electrocatalytic effect of the electrode and formed functional groups such as Fe3O4.

[0074] Figure 8 The chemical formula is C6H 11 The molecular structure of FeNO7, specifically ferric ammonium citrate, and the microstructure of Fe3O4 after modification as shown in XRD, reveal that FeNO7 possesses abundant C, H, and O elements, and is rich in hydroxyl, carboxyl, ammonium, and iron ions. Its chemical formula is C6H2O.11 The addition of FeNO7 ferric ammonium citrate, especially at concentrations exceeding 0.1 mol, leads to agglomeration of the nano-zero-valent iron after loading. Agglomeration further affects the catalytic effect when the dosage exceeds 15.9 g.

[0075] Figure 9 The FTIR images of the modified multi-walled carbon nanotube electrode and two comparative electrodes (electrode 2 and electrode 3) show that the main peaks of all three electrodes are visible in the range of 3550–3750 rpm. The difference is that in the range of 1350–1750 rpm, although the modified electrode has a lower CO bond peak height than electrode 2, the peak of electrode 3 is higher than that of the comparative electrode. Furthermore, the modified electrode has a wider bandwidth compared to the other two electrodes in the range of 1000–1750 rpm, and it also shows a significant advantage at the main peak in the range of 3250–3500 rpm, indicating that the chemical formula is C6H4H4. 11 FeNO7 ferric ammonium citrate was successfully loaded onto the target electrode material, forming more CN, CH and CO bonds.

[0076] Figure 10 The results show the current performance of the modified electrode compared to control electrodes 2 and 3 during electrokinetic repair. The experiment shows that although the modified electrode initially showed little difference from the other two electrodes, the current gradually increased during the electrokinetic repair process, creating a difference compared to the other two control electrodes (control electrodes 2 and 3), thus affecting the precipitation of heavy metals and demonstrating the advantages of the modified multi-walled carbon nanotube electrode.

[0077] Figure 11 It refers to the EC values ​​of the anode and cathode fluids in the electro-repair process of modified multi-walled carbon nanotube electrodes. During the electro-repair process, the EC of the cathode fluid continuously increases, thereby enhancing the electro-repair effect.

[0078] Figure 12 The results indicate that the EC values ​​of the five zones (S1, S2, S3, S4, and S5) in the electrokinetic remediation process using modified multi-walled carbon nanotube electrodes first increased and then slowly decreased, which is consistent with the EC changes in contaminated soil during the electrokinetic remediation process.

[0079] Figure 13 Display the total Cu starting from the beginning. 2+ 104.3 mg / kg, Zn 2+ 323.7 mg / kg of Cu in 5 zones 2+ Zn 2+ The distribution of heavy metals decreased significantly after repair. Calculations show that the electrode processing capacity is more than 1.2 times that of electrode 2, and 2-3 times that of ordinary graphite electrodes. Cu 2+ Zn 2+ The maximum efflux levels were 59.89 mg / kg and 48.13 mg / kg, respectively, at 48 h.

[0080] Figure 14 The pH changes of the anolyte, catholyte, and five zones (S1, S2, S3, S4, S5) during electrokinetic remediation using modified multi-walled carbon nanotube electrodes are shown. The continuous pH changes during the electrokinetic remediation process cause the pH of the surrounding soil to decrease, while simultaneously desorbing metal ions from the soil.

[0081] Example 1

[0082] This embodiment provides a method for applying a modified multi-walled carbon nanotube electrode in electro-repair:

[0083] (1) Preparation of contaminated soil: After the yellow brown soil is dug out, it is naturally air-dried for 7 days. Various impurities, plant roots and stems, gravel, etc. are removed. It is passed through a 20-mesh sieve and water is added daily to stir and make it into a thin mud. 0.2852g of CuSO4·5H2O and 0.2838g of ZnO are added dropwise and placed in a 150℃ oven for sintering for 24 hours.

[0084] (2) Preparation of aged contaminated soil: The contaminated soil was aged at room temperature for 60 days to obtain aged contaminated soil. The aged contaminated soil was placed in a star ball mill and divided into 4 portions of 700g each. The speed was adjusted to 3500r / min for 60 minutes. The soil was then ground through a 100-mesh sieve to obtain the prepared aged contaminated soil. The purpose of this is to simulate the environment of electroplating sludge and other heavy metal contaminated soil.

[0085] EC values ​​of anolyte and catholyte in five zones (S1, S2, S3, S4, S5) were measured during electrokinetic repair using modified multi-walled carbon nanotube electrodes. The EC values ​​of anolyte and catholyte were measured directly, while the EC values ​​of the five zones (S1, S2, S3, S4, S5) were measured after a 10-fold diluted mud-water mixture was centrifuged at 4800 r / min for 15 minutes.

[0086] The pH values ​​of the anolyte, catholyte, and five zones (S1, S2, S3, S4, S5) were measured separately.

[0087] In electrokinetic remediation using modified multi-walled carbon nanotube electrodes as anodes, the pH remained stable for 2000 min before exhibiting a slight change. Under these conditions, Cu... 2+ and Zn 2+ The electrokinetic remediation efficiencies were 83.77% and 87.53%, respectively, and the Cu in the treated soil was... 2+ The concentration was 16.928 mg / kg, Zn 2+The concentration was 40.365 mg / kg, which meets the national first-class standard for heavy metal detection in soil (GB15618-1995). According to the "National Standard of the People's Republic of China for Soil Environmental Quality", the following standards apply: Copper (farmland) ≤ 35 mg / kg; Zinc (farmland) ≤ 100 mg / kg.

[0088] Example 2

[0089] This embodiment uses unmodified multi-walled carbon nanotube electrode materials and unmodified, unloaded multi-walled carbon nanotube electrode materials in electrokinetic repair applications:

[0090] Unmodified multi-walled carbon nanotube electrode material refers to 16g of multi-walled carbon nanotube material and 2g of biochar material thoroughly mixed with the addition of chemical formula C6H. 11 The FeNO7 ferric ammonium citrate catalyst was shaken and mixed well, then added to 500 mL of ultrapure water in a sealed beaker and stirred on a magnetic stirrer for 24 hours until fully mixed. Afterwards, the precipitated product was filtered out, and the chemical formula C6H was removed. 11 The FeNO7 ferric ammonium citrate solution yielded P4, the material described in the invention. Material P4 was then sintered in an 80°C oven for 48 hours. The unmodified, unloaded multi-walled carbon nanotube electrode material consisted of 16g ​​of multi-walled carbon nanotube material and 2g of biochar material, thoroughly mixed and placed in a sealed beaker of 500mL ultrapure water. The mixture was then stirred on a magnetic stirrer for 24 hours until fully homogenized. The slurry was filtered to remove the liquid, and then sintered in an 80°C oven for 48 hours. The modified multi-walled carbon nanotube electrode was used as the working electrode, AgCl as the reference electrode, platinum wire as the auxiliary electrode, and 0.1mol / L K3Fe(CN)6+0.1mol / L NaCl as the electrolyte. CV analysis was performed to study the changes in redox current and to investigate the electrochemical stability of the electrode.

[0091] The two control electrodes prepared in Example 2 showed significantly weaker performance as anodes based on the electrorepair process compared to the modified multi-walled carbon nanotube electrode, with an electrorepair efficiency that was about 23% lower. The highest current of control electrodes 2 and 3 was about 290 mA, and the duration was 2500 min. After 2500 min, the current gradually decreased until it was below 100 mA.

[0092] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A method for preparing a modified multi-walled carbon nanotube anode electrode for soil electroremediation, characterized in that, Includes the following steps: (1) Preparation of carbon nanotube electrode base material: Weigh multi-walled carbon nanotube powder into a 1L beaker and label it as P1; (2) Preparation of biochar: The leaves are placed in an oven and the temperature is adjusted to evaporate the moisture to obtain dried leaves. The leaves are crushed and then put into a grinder to be ground into leaf powder. The leaf powder is then placed in a muffle furnace for high-temperature sintering and then slowly cooled to room temperature. (3) Preparation of multi-walled carbon nanotube and biocarbon composite material: The prepared biocarbon is ground in an agate grinding tool to obtain biocarbon, and then slowly added to a 1L beaker while stirring to mix evenly with multi-walled carbon nanotubes to obtain material denoted as P2. (4) Preparation of unmodified multi-walled carbon nanotube composite materials: Weigh out the chemical formula C6H 11 Ferric ammonium citrate of FeNO7 was ground into powder in a grinding tool and then added to material P2 in small amounts multiple times to obtain unmodified multi-walled carbon nanotube material, denoted as P3. (5) Preparation of turbid liquid of unmodified multi-walled carbon nanotube composite material: P3 material was placed in a 1L beaker, ultrapure water was added and the mixture was sealed and stirred to obtain turbid liquid; (6) Preparation of the multi-walled carbon nanotube electrode material to be modified: The turbid liquid of the unmodified multi-walled carbon nanotube composite material is extracted by a vacuum filtration device to remove the chemical formula C6H that is not attached to the composite material. 11 Aqueous solution of FeNO7 containing ferric ammonium citrate was used to obtain the multi-walled carbon nanotube electrode material to be modified, denoted as material P4. (7) Drying the multi-walled carbon nanotube electrode material to be modified: Place material P4 in a sterile vacuum drying oven for dehydration and drying, and after it is dried, place it in a grinding tool for fine grinding. (8) Preparation of modified multi-walled carbon nanotube electrode material: The dried material P4 was placed in a vacuum tube furnace for high-temperature modification at 600°C, and sodium polyacrylate was weighed, ground through an 80-mesh sieve, and added to the modified multi-walled carbon nanotube electrode material. (9) The modified multi-walled carbon nanotube electrode material is placed inside the die-cast part 10cm×10cm×5cm. Sodium polyacrylate is dissolved by impregnation in 20 layers to make it able to bond the surrounding electrode material and form a square sheet electrode under pressure.

2. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: In step (1), the multi-walled carbon nanotube material is moistened with a humidifier for 1 minute, and static electricity inside the multi-walled carbon nanotube electrode is eliminated for 60 minutes to obtain P1.

3. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: In step (2), during the preparation of biochar, the leaves are dusted and ash removed from the surface and then placed in an oven at 70°C for 1440 min. After drying, the leaves are put into a crusher and crushed into fine powder to facilitate the production of biochar at high temperature. The crushed leaves are then placed in a muffle furnace for high-temperature sintering at 600°C. The temperature is increased by 5°C / min for 60 min to 300°C, and then increased by 60 min to 600°C. The temperature is kept constant for 1 h. After the heat preservation is completed, the temperature is reduced to room temperature at the same rate.

4. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: In step (4), 15.9g of the chemical formula C6H is prepared. 11 Ferric ammonium citrate of FeNO7 was added to the P3 material, and 500 mL of ultrapure water was added to make a turbid solution. The solution was stirred with a magnetic stirrer for 24 hours and then allowed to stand for 5 hours.

5. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: In step (7), the oven temperature is set to 120°C for rapid dehydration to dry material P4. After 360 minutes, the material is taken out and crushed using an agate grinding pestle.

6. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: Step (8) requires replacing the air inside the tube furnace with N2 and setting the heating rate of the vacuum tube furnace to 5℃ / min. The temperature is raised to 600℃ in 120min and held for 120min. Then the temperature is gradually lowered to room temperature at 5℃ / min. 2g of sodium polyacrylate is weighed, ground through an 80-mesh sieve, and mixed evenly and added to the modified multi-walled carbon nanotube electrode material.

7. The method for preparing the modified multi-walled carbon nanotube anode electrode for soil electroremediation according to claim 1, characterized in that: In step (9), the high-temperature modified carbon nanotube electrode material is placed inside the die-cast part (10cm×10cm×5cm), and a 0.45mm thick layer of high-temperature modified carbon nanotube electrode material is laid. 5mL of ultrapure water is sprayed onto its surface and absorbed. The process of laying and wetting 0.45mm thick high-temperature modified carbon nanotube electrode material is repeated 20 times until the sodium polyacrylate completely absorbs and dissolves the water. The pressure is slowly increased by 50kg for 15min to make its thickness reach 0.6cm and is maintained for 30min to allow it to absorb water. The modified multi-walled carbon nanotube electrode is then placed in an oven to evaporate the water. The oven temperature is set to 50℃.

8. The application of an electrode prepared by the method for preparing a modified multi-walled carbon nanotube electrode according to any one of claims 1-7, characterized in that, Modified multi-walled carbon nanotube electrodes were used as the anode for electrokinetic remediation, and ordinary graphite electrodes were used as the cathode to remediate soil contaminated with heavy metals.

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