Composite electrode material and preparation method and application thereof

Abstract

The application discloses a kind of composite electrode materials, the composite electrode material includes carrier and the nano zero-valent iron attached on the carrier;The carrier is sludge-based biochar.This composite electrode material uses sludge as raw material, this method weakens the secondary pollution that sludge can cause to environment, and by the method of making sludge into composite electrode, it is resource utilization, so as to reach the effect of " waste control waste ".The application also discloses a kind of composite electrode, including electrode matrix and the substance attached on the electrode matrix.This composite electrode can expand the applicable range of wastewater pH in electro-Fenton reaction, solve the limitation of wastewater pH to electro-Fenton reaction system.The application also discloses a kind of printing and dyeing wastewater treatment method, in which the printing and dyeing wastewater is treated by electro-Fenton, wherein the cathode of electro-Fenton treatment uses the composite electrode prepared by the application, and the method can improve the reliability of electro-Fenton in treating printing and dyeing wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heterogeneous electro-Fenton treatment of printing and dyeing, and particularly relates to a composite electrode material, a composite electrode, and a preparation method of the composite electrode material and the composite electrode. BACKGROUND

[0002] Organic dyes are widely used in the fields of leather papermaking industry, clothing manufacturing industry, plastic processing industry, etc. Since the dye molecules have stability and are not easy to be degraded, they have high persistence in the environment, and thus have certain harm to humans, aquatic animals, and the natural environment. The treatment methods for organic dye wastewater include physical methods, chemical methods, and biological methods. Among them, the most common treatment method in the physical method is adsorption, which is processed by using a large amount of adsorbent. However, the adsorbent has poor regeneration performance, which greatly increases the treatment cost of the organic dye wastewater. The biological method separates and degrades the chromogenic substances in the wastewater through the flocculation, adsorption and biological degradation of biological bacteria, but due to the limited processing capacity of the biological bacteria, the treated dye wastewater is difficult to meet the discharge standard, and needs to be combined with other processes for treatment, increasing the complexity of the operation.

[0003] The advanced oxidation process (AOPs) in the chemical method is widely used due to its high efficiency in removing refractory organic pollutants. The electro-Fenton technology in the advanced oxidation process (AOPs) is more and more valued in wastewater treatment due to its high efficiency, non-toxicity (environmental protection) of reagents, strong total organic compound mineralization ability in a short time, mild reaction conditions, simple operation and other advantages. The electro-Fenton technology generates H2O2 in situ through electrolysis of water and reacts with divalent iron ions in the solution to generate hydroxyl radicals with strong oxidation to remove pollutants in water. Under the action of electric current, H2O2 is generated in situ at the cathode and reacts with divalent iron ions to generate hydroxyl radicals. The organic matter in the solution is oxidized into carbon dioxide and water, and at the same time, due to the increase of pH during the reaction process, iron hydroxide and other precipitates are also produced. In this treatment process, the acidity and alkalinity (pH value) of the solution has a great influence on the removal of organic matter. When the pH of the wastewater is greater than 3, the iron ions are easily oxidized to form Fe(OH)3 precipitate, and the electro-Fenton reaction cannot proceed smoothly. In order to avoid the precipitation of iron ions in the form of iron hydroxide, it is necessary to maintain the reaction system in an acidic condition, so the electro-Fenton reaction is limited by the pH condition. At the same time, the electro-Fenton reaction needs to add iron ions to the system, and the added iron ions cannot be recovered, which increases the chemical cost of the reaction. Therefore, it has important practical significance to provide an electrode needed for a green and environmentally friendly, low-cost electro-Fenton reaction which is not limited by the pH condition, reduces the use condition, and can recycle and use the iron ions in the system. SUMMARY

[0004] The main purpose of the present application is to provide a composite electrode material and a composite electrode, and the present application also discloses a preparation method of the composite electrode material and the composite electrode, which solves the problem that the iron in the electrode material in the electro-Fenton reaction is easily oxidized to form a precipitate that cannot be recovered, affecting the electro-Fenton reaction.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0006] The present application discloses a composite electrode material, which comprises a carrier and nano zero-valent iron attached to the carrier.

[0007] The carrier is sludge-based biochar.

[0008] Further, in the composite electrode material, the molar ratio of iron elements to carbon elements is 1:1.4-9.8.

[0009] Preferably, the sludge-based biochar is obtained by pyrolysis of residual sludge from water treatment.

[0010] Further, the method comprises at least the following steps:

[0011] Mixing the sludge-based biochar with a solution containing an iron source under a protective atmosphere to obtain a mixture A;

[0012] Reducing the mixture A to obtain a mixture B;

[0013] Drying the mixture B to obtain the composite electrode material.

[0014] Further, the mass ratio of the sludge-based biochar to the iron source is 0.3-2.1:1.

[0015] The iron source is selected from ferrous sulfate or ferric chloride.

[0016] The concentration of the solution containing the iron source is 0.07-0.08 mol·L -1 ;

[0017] Further, the reduction of the mixture A comprises:

[0018] Adding a solution containing a reducing agent to the mixture A and performing a reduction reaction under a protective atmosphere;

[0019] The amount of the solution containing the reducing agent added is 0.03-0.05 L.

[0020] The reducing agent is selected from sodium borohydride or potassium borohydride.

[0021] The time of the reduction reaction is 1.8-2.2 h.

[0022] Preferably, the drying temperature is 58-62 DEG C.

[0023] The application also discloses a composite electrode, comprising an electrode substrate and a substance attached to the electrode substrate.

[0024] The substance comprises at least any one of the composite electrode material and the composite electrode material prepared by the method.

[0025] Further, the electrode substrate is selected from any one of foamed nickel, carbon felt, graphite felt and carbon cloth.

[0026] The electrode material further comprises a conductive agent and a binder.

[0027] The conductive agent is selected from conductive carbon black or acetylene black.

[0028] The binder is selected from polytetrafluoroethylene or polyvinylidene fluoride.

[0029] The mass ratio of the composite electrode material, the conductive agent and the binder in the electrode material is 7.8-8.2:1:1.

[0030] The application also discloses a treatment method of printing and dyeing wastewater based on the composite electrode prepared above, at least comprising the following steps.

[0031] The printing and dyeing wastewater is subjected to electro-Fenton treatment, wherein the cathode adopts the composite electrode prepared above.

[0032] Further, in the electro-Fenton treatment process, the pH of the printing and dyeing wastewater is adjusted to 3-9; preferably, the pH of the printing and dyeing wastewater is adjusted to 3-6.

[0033] The current density is controlled to be 50-150 mA.

[0034] Further, the method further comprises performing aeration operation in the electro-Fenton treatment process.

[0035] Compared with the prior art, the application has the following beneficial effects:

[0036] 1. The composite electrode material disclosed by the application is sludge-based biochar loaded with nano zero-valent iron, i.e. sludge-based biochar loaded with nano zero-valent iron (nZVI / SBC) electrode material is formed by loading nano zero-valent iron on sludge-based biochar, which is used for electro-Fenton reaction in sewage treatment, and iron ions can be recovered after the reaction, thereby avoiding waste of iron ions.

[0037] 2. The main raw material of the composite electrode material disclosed by the application is sludge of a sewage treatment plant, the method weakens secondary pollution of the sludge to the environment, and the sludge is resourceized by the method of manufacturing the sludge into the composite electrode, so that the effect of "waste treatment with waste" is achieved.

[0038] 3. The composite electrode prepared by the application solves the problem that the nano zero-valent iron is easy to gather in water, and the composite electrode is used in the electro-Fenton reaction, which not only serves as a cathode, but also provides an iron source for the electro-Fenton reaction, solves the limitation of wastewater pH on the electro-Fenton reaction system, and expands the applicable range of wastewater pH in the electro-Fenton reaction; at the same time, the composite electrode can be recycled, thereby reducing the cost of printing and dyeing wastewater treatment.

[0039] 4. The composite electrode prepared by the application has good degradation effect on pollutants in printing and dyeing wastewater at different pH values, especially the degradation rate of methylene blue is more than 98% at pH 3-5, the degradation rate of methylene blue is more than 70% under neutral and alkaline conditions, and the degradation rate of pollutants in printing and dyeing wastewater at different pH values by the same composite electrode is almost unchanged in the same time period, thereby having stable degradation capacity, increasing the reliability of electro-Fenton treatment on printing and dyeing wastewater treatment. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The scanning electron microscope image of the composite electrode material provided by the application;

[0041] Figure 2 The XPS full spectrum diagram of the composite electrode material provided by the application;

[0042] Figure 3 The Fe phase diagram of the XPS of the composite electrode material provided by the application;

[0043] Figure 4 The XRD diagram of the composite electrode material provided by the application;

[0044] Figure 5 The relationship diagram between the degradation rate of methylene blue in wastewater at different pH values and time in the electro-Fenton reaction of the composite electrode prepared by the application;

[0045] Figure 6 The relationship diagram between the degradation rate of methylene blue and time in the electro-Fenton reaction of the composite electrode prepared by the application under different current intensities

[0046] Figure 7 The relationship diagram between the degradation rate of methylene blue and time in the electro-Fenton reaction of the composite electrode prepared by the application with different carbon-iron ratios;

[0047] Figure 8The degradation rate of methylene blue and time relationship diagram of the same composite electrode prepared by the application applied in the electro-Fenton reaction. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0049] The application discloses a composite electrode material, which comprises a carrier and nano zero-valent iron attached to the carrier; the carrier is sludge-based biochar.

[0050] In the composite electrode material, the molar ratio of iron elements to carbon elements is 1:1.4-9.8.

[0051] Preferably, the sludge-based biochar is obtained by pyrolysis of water treatment residual sludge, and the method comprises at least the following steps:

[0052] The sludge is collected, i.e., sludge in a municipal sewage treatment plant, and then the collected sludge is placed in a baking oven at a set temperature for baking until a constant weight is obtained, to obtain sludge-based biochar. The baking is stopped, and the sludge-based biochar is taken out. The set temperature ranges from 103 to 107 DEG C.

[0053] The taken-out sludge-based biochar is placed in a crucible, and then the crucible is placed in a pyrolysis furnace at a set heat release temperature for 2.8-3.2 h to obtain the sludge-based biochar. The heat release temperature is set in the range of 580 DEG C to 250 DEG C. In this embodiment, the pyrolysis furnace is a GR.BF box-type high-temperature furnace.

[0054] Secondly, the sludge-based biochar after heat release is placed in a mortar for grinding, and then the ground sludge-based biochar is screened through a 80-120 mesh sieve. The screened sludge-based biochar is used as a carrier for loading of nano zero-valent iron.

[0055] Based on the prepared sludge-based biochar, an electrode composite material is prepared by the following method:

[0056] A reaction container is taken, and protective gas is introduced into the reaction container to make the reaction container an anaerobic environment. A solution containing an iron source is added into the reaction container, and then the sludge-based biochar is added into the reaction container. The reaction container is sealed and placed on a shaking table, so that the reactants and the iron-containing inorganic salt solution are fully mixed and reacted for 3.5-4.5 h to obtain a mixture A.

[0057] Preferably, the mass ratio of the sludge-based biochar to the iron source is 0.3-2.1:1.

[0058] The iron source is selected from ferrous sulfate or ferric chloride;

[0059] The ferric chloride includes ferric chloride hexahydrate and anhydrous ferric chloride;

[0060] Most preferably, ferrous sulfate is used, and the ferrous sulfate is prepared into a ferrous sulfate solution, and the concentration of the ferrous sulfate solution is 0.07-0.08 mol·L -1 , preferably 0.075 mol·L -1 .

[0061] The mixture A is reduced;

[0062] The reaction container containing the mixture A is continuously placed on the shaker, and the protection gas is not stopped from being introduced, and the solution containing the reducing agent is slowly added to the reaction container containing the mixture A at a speed of one drop per second, so as to prevent the reducing agent from being added too fast, so as to cause a dangerous accident due to a violent reaction, and the reaction is ended after 1.8-2.2 h, and after the reaction is ended, the shaker is closed and the introduction of the protection gas into the reaction container is stopped, to obtain the mixture B.

[0063] Preferably, the reducing agent is selected from sodium borohydride or potassium borohydride, and most preferably, the sodium borohydride is selected, and the concentration of the sodium borohydride solution is 0.2-0.4 mol·L -1 , preferably 0.3 mol·L -1 .

[0064] The mixture B is dried;

[0065] Firstly, the mixture B is subjected to suction filtration treatment, so as to prevent the mixture B from being oxidized;

[0066] The suction filtration treatment is to add anhydrous ethanol to the reaction container containing the electrode material for three times of rinsing, and then drying;

[0067] The drying is to place the mixture B after the suction filtration treatment into a vacuum drying oven for drying at a temperature of 58-62℃, to obtain the required electrode material.

[0068] The main raw material of the above preparation method is the sludge of a sewage treatment plant, the sludge is made into a sludge-based biochar, and then the nano zero-valent iron is loaded on the sludge-based biochar to provide an attachment site for the nano zero-valent iron, and then the electrode material is made; the method weakens the secondary pollution to the environment caused by the sludge, and the sludge is made into a composite electrode, so as to achieve the effect of "waste treatment with waste".

[0069] The substance includes the composite electrode material prepared by the above preparation method.

[0070] Preferably, the electrode substrate is selected from any one of foamed nickel, carbon felt, graphite felt and carbon cloth; most preferably foamed nickel is used.

[0071] The electrode material further comprises a conductive agent and a binder;

[0072] The conductive agent is selected from any one of conductive carbon black and acetylene black; most preferably conductive carbon black is used.

[0073] The binder is selected from any one of polytetrafluoroethylene and polyvinylidene fluoride; most preferably polytetrafluoroethylene is used.

[0074] The mass ratio of the composite electrode material, the conductive agent and the binder in the electrode is 7.8-8.2:1:1.

[0075] Based on the preparation method of the composite electrode, at least the following steps are included:

[0076] The electrode substrate is cut into a rectangular block, and then the cut foamed nickel is subjected to surface treatment;

[0077] The surface treatment includes degreasing, oxide layer removal and heat baking;

[0078] The degreasing is that the cut foamed nickel is immersed in an acetone solution, and the oil on the surface of the foamed nickel is removed through ultrasonic action for 20 min;

[0079] The oxide layer removal is that the foamed nickel after degreasing is immersed in a hydrochloric acid solution, and the oxide layer on the surface of the foamed nickel is removed through ultrasonic action for 20 min, and then the foamed nickel after oxide layer removal is washed with clean water;

[0080] The heat baking is that the washed foamed nickel is placed in a vacuum drying oven, and the temperature is set to 60℃ for heat baking for 11.5-12.5 h to obtain a foamed nickel core.

[0081] Preferably, the concentration of the acetone solution is 13.5 mol·L -1 ; the concentration of the hydrochloric acid solution is 0.08-0.12 mol·L -1 ;

[0082] A certain amount of the binder, the composite electrode material, the conductive agent and N-methyl-2-pyrrolidone are taken, the weighed binder is put into a beaker, and the N-methyl-2-pyrrolidone solvent is added to the beaker, and under the action of ultrasonic conditions and a stirring rod, the binder is fully dissolved in the N-methyl-2-pyrrolidone solvent, and after dissolution, the liquid in the beaker is transparent, and a solution G is prepared;

[0083] The composite electrode material and the conductive agent are added to the beaker containing the solution G, and the substances in the beaker are fully mixed using a stirring rod, so that they are in a paste state, and an electrode slurry is obtained;

[0084] The electrode slurry is uniformly coated on the electrode substrate to form an electrode sheet;

[0085] After coating, it is placed in a vacuum drying oven at 58-62 DEG C for 23.5-24.5h for drying treatment, to obtain a composite electrode, i.e. a sludge-based biochar loaded nano zero-valent iron (nZVI / SBC) electrode.

[0086] The application further discloses a treatment method of printing and dyeing wastewater.

[0087] The printing and dyeing wastewater is subjected to electro-Fenton treatment, wherein the cathode in the electro-Fenton treatment is the composite electrode prepared above.

[0088] In the electro-Fenton treatment process, the pH of the printing and dyeing wastewater is adjusted to 3-9, and the current density is controlled to be 50-150 mA; preferably, the pH of the printing and dyeing wastewater is adjusted to 3-6.

[0089] The printing and dyeing wastewater is subjected to aeration operation in the electro-Fenton treatment process, and the specific operation is as follows:

[0090] The aeration head is connected to the aeration pump, and the aeration head is placed near the prepared cathode electrode; air is sent to the vicinity of the cathode motor by the aeration pump, and the air near the cathode is aerated to generate H2O2 in situ.

[0091] The composite electrode is applied to the electro-Fenton treatment of the printing and dyeing wastewater, solves the problem that the nano zero-valent iron is easy to aggregate in water, and solves the problem that the existing cathode electrode is limited by the pH condition of the printing and dyeing wastewater in the electro-Fenton treatment of the printing and dyeing wastewater; the sludge-based biochar loaded nano zero-valent iron is beneficial to the reconstruction of the electro-Fenton system, the reconstructed electro-Fenton system is no longer limited by the pH, and the electro-Fenton treatment of the printing and dyeing wastewater does not need to be kept in an over-acid condition, so that the corrosion of the equipment is avoided, and the service life of the equipment is prolonged.

[0092] The composite electrode material and the preparation method of the composite electrode are further explained and described in combination with the embodiments.

[0093] Example 1

[0094] The embodiment discloses a composite electrode material and a preparation method of the composite electrode, and the method comprises the following steps:

[0095] Preparation of the composite electrode material (nano zero-valent iron loading)

[0096] Collecting sludge in a sewage treatment plant, and then placing the collected sludge in a baking oven with a set temperature of 105°C to bake until the mass of the reactant is constant weight, stopping baking, and taking out the sludge;

[0097] Placing the constant weight sludge taken out in a crucible, and then placing the crucible in a GR.BF box type high temperature furnace with a set pyrogenetic temperature of 500°C for 3h to obtain sludge-based biochar by pyrogenation;

[0098] Secondly, the sludge-based biochar after pyrogenation is placed in a mortar for grinding, and after grinding, it is screened through a 100 mesh sieve, and the screened sludge-based biochar is used as a carrier for loading of nano zero-valent iron.

[0099] Preparation of composite electrode material:

[0100] 2.085g of ferrous sulfate is weighed to prepare a 0.1L solution with a concentration of 0.075mol·L -1 Ferrous sulfate aqueous solution, to obtain ferrous sulfate heptahydrate solution;

[0101] Into the anaerobic bottle containing 100mL of ferrous sulfate aqueous solution with a concentration of 0.075mol·L -1 Ferrous sulfate aqueous solution, nitrogen gas is introduced into the anaerobic bottle to make the anaerobic bottle an anaerobic environment, and then 4.17g of sludge-based biochar is added to the anaerobic bottle, and then the anaerobic bottle is sealed and placed on a shaker, and the shaker works at a speed of 300r to make the sludge-based biochar and the ferrous sulfate heptahydrate solution in the anaerobic bottle fully mix and react for 4h, so that the divalent iron ions are loaded onto the sludge-based biochar to obtain mixture A.

[0102] After the reaction is completed, nitrogen gas is continuously introduced and the anaerobic bottle is still placed on the shaker;

[0103] 0.567g of sodium borohydride is weighed to prepare a 50mL solution with a concentration of 0.3mol·L -1 of sodium borohydride solution, and after preparation, it is slowly added to the anaerobic bottle containing mixture A at a speed of one drop per second to prevent the sodium borohydride solution from being added too fast, causing the reaction to be violent and causing accidents; reaction 2h to obtain mixture B, after the reaction is completed, the shaker is turned off and the nitrogen gas introduced into the anaerobic bottle is stopped.

[0104] Then add excess anhydrous ethanol to the anaerobic bottle containing mixture B and rinse repeatedly three times, then put the solid material obtained after rinsing into a vacuum drying oven and dry at a temperature of 60°C to obtain the required composite electrode material.

[0105] Manufacture of foam nickel core:

[0106] The foam nickel is cut into a rectangular block of 2*3cm, and then the cut foam nickel is surface treated;

[0107] Surface treatment includes degreasing, removing oxide layers, and heat drying;

[0108] Among them, degreasing: the cut nickel foam is immersed in an excess of acetone solution with a concentration of 13.5 mol / L, and then subjected to ultrasonic treatment for 20 minutes to remove the grease from the surface of the nickel foam.

[0109] Oxide removal: Immerse the degreased nickel foam in an excess solution with a concentration of 0.1 mol·L⁻¹. -1 The oxide layer on the surface of the nickel foam is removed by ultrasonic treatment for 20 minutes in a hydrochloric acid solution. Then, the nickel foam with the oxide layer removed is rinsed with water and rinsed repeatedly three times.

[0110] Heat drying: Place the cleaned nickel foam in a vacuum drying oven and heat dry at 60℃ for 12 hours to obtain nickel foam core.

[0111] Electrode preparation

[0112] Weigh out the electrode material, polytetrafluoroethylene (PTFE), and carbon black, wherein the PTFE content is 0.1 g, and the mass ratio of the electrode material, PTFE, and carbon black is 8:1:1.

[0113] Weigh 0.1g of polytetrafluoroethylene and place it in a beaker. Add N-methyl-2-pyrrolidone solvent to the beaker and use a stirring rod to dissolve the polytetrafluoroethylene in the N-methyl-2-pyrrolidone solvent. After dissolution, the liquid in the beaker becomes transparent, resulting in solution G.

[0114] Then, the weighed electrode material and carbon black are added to the beaker containing solution G. The substances in the beaker are mixed with a stirring rod to form a paste, thus obtaining the electrode slurry.

[0115] The electrode slurry was then evenly coated onto the prepared nickel foam core. After coating, the core was placed in a vacuum drying oven at 60°C for 24 hours to dry, thus obtaining the composite electrode.

[0116] In Examples 2-4 below, composite electrodes with different iron to carbon mass ratios were prepared by changing the iron to carbon mass ratios to 1:0.33, 1:0.5, and 1:1, respectively.

[0117] Example 2

[0118] 100 mL of a container with a concentration of 0.075 mol·L⁻¹ -1Nitrogen gas was introduced into the anaerobic bottle containing ferrous sulfate aqueous solution to create an anaerobic environment. Then, 0.689 g of sludge-based biochar was added to the anaerobic bottle. The anaerobic bottle was then sealed and placed on a shaker at 300 rpm to ensure thorough mixing and reaction of the sludge-based biochar and ferrous sulfate heptahydrate solution in the anaerobic bottle for 4 hours. This process allowed ferrous ions to be loaded onto the sludge-based biochar, resulting in mixture A.

[0119] After the reaction was complete, nitrogen gas was continuously introduced and the anaerobic flask remained on the shaker to prepare 50 mL of a 0.3 mol·L⁻¹ solution. -1 Sodium borohydride solution was slowly added to the anaerobic flask containing mixture A at a rate of one drop per second to prevent the sodium borohydride solution from being added too quickly, which could cause a violent reaction and lead to a dangerous accident. After reacting for 2 hours, mixture B was obtained. After the reaction was completed, the shaker was turned off and the nitrogen gas supply to the anaerobic flask was stopped.

[0120] Then, excess anhydrous ethanol was added to the anaerobic flask containing mixture B for rinsing, and the rinsing was repeated three times. The solid material obtained after rinsing was then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the desired composite electrode material.

[0121] Example 3

[0122] Preparation of composite electrode materials:

[0123] 100 mL of a container with a concentration of 0.075 mol·L⁻¹ -1 Nitrogen gas was introduced into the anaerobic bottle containing ferrous sulfate aqueous solution to create an anaerobic environment. Then, 1.043 g of sludge-based biochar was added to the anaerobic bottle. The anaerobic bottle was then sealed and placed on a shaker at 300 rpm to ensure thorough mixing and reaction of the sludge-based biochar and ferrous sulfate heptahydrate solution in the anaerobic bottle for 4 hours. This process allowed ferrous ions to be loaded onto the sludge-based biochar, resulting in mixture A.

[0124] After the reaction was complete, nitrogen gas was continuously introduced and the anaerobic flask remained on the shaker to prepare 50 mL of a 0.3 mol·L⁻¹ solution. -1 A sodium borohydride solution with a concentration of 0.3 mol·L⁻¹ was slowly added drop by drop at a rate of one drop per second to 50 mL of an anaerobic flask containing mixture A. -1 Sodium borohydride solution was added to prevent it from being added too quickly, which could cause a violent reaction and potentially lead to a dangerous accident. The electrode material was obtained after 2 hours of reaction. After the reaction was completed, the shaker was turned off and the nitrogen gas was stopped from being introduced into the anaerobic flask.

[0125] Then, anhydrous ethanol was added to the anaerobic flask containing mixture B for rinsing, and the rinsing was repeated three times. The solid material obtained after rinsing was then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the desired composite electrode material.

[0126] Example 4

[0127] Preparation of composite electrode materials:

[0128] 100 mL of a container with a concentration of 0.075 mol·L⁻¹ -1 Nitrogen gas was introduced into the anaerobic bottle containing ferrous sulfate aqueous solution to create an anaerobic environment. Then, 2.085 g of sludge-based biochar was added to the anaerobic bottle. The anaerobic bottle was then sealed and placed on a shaker at 300 rpm to ensure thorough mixing and reaction of the sludge-based biochar and ferrous sulfate heptahydrate solution in the anaerobic bottle for 4 hours. This process allowed ferrous ions to be loaded onto the sludge-based biochar, resulting in mixture A.

[0129] After the reaction was complete, nitrogen gas was continuously introduced and the anaerobic flask remained on the shaker to prepare 50 mL of a 0.3 mol·L⁻¹ solution. -1 A sodium borohydride solution was slowly added to the anaerobic flask containing mixture A at a rate of one drop per second to prevent the sodium borohydride solution from being added too quickly, which could cause a violent reaction and lead to a dangerous accident. The composite electrode material was obtained after 2 hours of reaction. After the reaction was completed, the shaker was turned off and the nitrogen gas supply to the anaerobic flask was stopped.

[0130] Then, excess anhydrous ethanol was added to the anaerobic flask containing mixture B for rinsing, and the rinsing was repeated three times. The solid material obtained after rinsing was then placed in a vacuum drying oven and dried at 60°C for 12 hours to obtain the desired composite electrode material.

[0131] The electrode materials prepared in Examples 1-4 were characterized at the microscopic level, with the composite electrode material obtained in Example 1 being a typical example.

[0132] See Figure 1 and Figure 2 The figure is a scanning electron microscope image of the composite electrode material prepared in Example 1, which mainly reflects the surface microstructure of the composite electrode material. Figure 2 The image shows a full spectrum scan of the composite electrode material, revealing the presence of Si in addition to C, N, and O on its surface. This is because sludge-based biochar, generated from pyrolysis of sludge, contains Si. Simultaneously, the presence of Fe is clearly observed in the full spectrum scan, demonstrating that Fe is loaded onto the sludge-based biochar, indicating that sludge-based biochar successfully supports nano-zero-valent iron.

[0133] Referring to Figure 3 The figure is a narrow spectrum of Fe element in full spectrum scanning of the composite electrode material, all lines in the figure are iron elements of the composite electrode material, it can be understood from the figure that the composite electrode material appears a peak of zero-valent iron at a binding energy of 706.68 eV, which indicates that the zero-valent iron is successfully loaded on the sludge-based biochar, and Fe2p3 / 2 and Fe2p1 / 2 peaks appear at binding energies of 710.14 eV, 713.45 eV and 723.72 eV, which is because the oxidation of the composite electrode material is inevitable during the placement process, and the composite electrode material contains nZVI is verified from the narrow spectrum of Fe element in full spectrum scanning of the composite electrode material.

[0134] Referring to Figure 4 The figure is an XRD diffraction pattern of the composite electrode material, it can be understood from the figure that there is a diffraction peak at an angle 2θ=44.7°, which indicates the presence of Fe, and indicates that nZVI is loaded on the sludge-based biochar, and nZVI / SBC is successfully obtained, the content reflected by the above detection data is consistent with the content reflected in Figure 4 , and the composite electrode material contains nZVI is further verified.

[0135] The present application sets up an electro-Fenton experimental device based on the above composite electrode, which is used to install the composite electrode prepared by the present application on the cathode in the device, simulate the treatment of printing and dyeing wastewater, and test the effect of the composite electrode prepared by the present application.

[0136] The device comprises a stabilized DC power supply, a cathode, an anode, a magnetic stirrer, an aeration pump, an aeration head, a magnetic stirring rotor, a wire and a beaker.

[0137] The beaker is used to contain simulated printing and dyeing wastewater, in the experiment, the content of methylene blue in the printing and dyeing wastewater is 0.1 g / L, and the content of methylene blue in the printing and dyeing wastewater is detected in the experiment to analyze the functional effect of the composite electrode prepared by the present application.

[0138] The beaker is placed on the magnetic stirrer, and the magnetic stirring rotor is placed in the beaker, so that the simulated printing and dyeing wastewater in the beaker is fully mixed and the reaction rate is accelerated through the cooperation of the magnetic stirrer and the magnetic stirring rotor.

[0139] The cathode is connected to the negative electrode of the stabilized DC power supply through the wire, and the anode is connected to the positive electrode of the stabilized DC power supply through the wire, and the cathode and the anode are placed in the beaker.

[0140] Among them, the cathode is a sludge-based biochar loaded nano zero-valent iron (nZVI / SBC) electrode, and the anode is a platinum sheet electrode.

[0141] The aeration head is connected to the aeration pump through the conduit, and then is placed in the beaker and located at the position of the cathode to provide oxygen for the reaction.

[0142] The device is powered by a stabilized DC power supply, so that the cathode and anode in the beaker carry out the electro-Fenton effect, and then degrade methylene blue in printing and dyeing wastewater.

[0143] Six comparative experimental groups are set up in the simulation experiment, and the pH of the printing and dyeing wastewater in the six comparative experimental groups is 3 to 9 in turn, and four beakers are set up in each experiment. Then the composite electrode prepared in the example is installed on the cathode in the experiment, that is, the pH of the printing and dyeing wastewater in the experimental group is 3, and the cathode in the four beakers is the composite electrode prepared in Example 1-Example 4, and the other five experimental groups are the same. During the experiment, the current intensity of the stabilized DC power supply is adjusted, that is, the current intensity is adjusted to 50 mA, 100 mA, 150 mA and 200 mA respectively, and the degradation rate of methylene blue in the printing and dyeing wastewater in the beaker is observed. The data obtained by simulation experiment are shown in Figures 3-8 .

[0144] Referring to Figure 5 , the figure reflects the degradation efficiency of the composite electrode on methylene blue in printing and dyeing wastewater in wastewater with different pH, and it can be understood from the figure that: the composite electrode prepared in the application can degrade methylene blue in printing and dyeing wastewater in wastewater with pH of 3-9, and the degradation rate is more than 70% in wastewater with pH of 3-9 after 180 min, the degradation rate of methylene blue in wastewater with pH of 3-6 is more than 90%, the degradation rate of methylene blue in wastewater with pH of 3-5 reaches the highest value of 98%, and in wastewater with pH of 5, not only the degradation rate of methylene blue is high, but also the time spent is less. In the subsequent degradation process, the degradation rate is stable and unchanged, thereby verifying that the composite electrode prepared in the application used as the cathode of electro-Fenton reaction can make the electro-Fenton reaction have a wider pH range. Although the removal rate of methylene blue under the condition of pH of 7 and 9 is not as good as that under acidic and weakly acidic conditions, the removal rate can also reach more than 70%, realizing the further expansion of the pH range of electro-Fenton.

[0145] Referring to Figure 6The figure reflects the degradation rate of methylene blue in printing and dyeing wastewater by the composite electrode under different current intensities. The current intensity has a certain influence on the degradation of methylene blue. In the electro-Fenton degradation process, with the increase of the current intensity, the degradation effect of methylene blue is significantly enhanced. Under the conditions of an initial concentration of 0.1 g / L, a pH of 5, and a mass ratio of iron to carbon of 1:1, when the current density is 50 mA, the degradation rate of methylene blue is 85.65% within 180 min. When the current density increases to 150 mA, the degradation effect of methylene blue can reach almost 100%. The increase of the current can improve the generation efficiency of hydrogen peroxide, and then improve the generation of hydroxyl radicals, thereby indicating that the increase of the current intensity of the composite electrode prepared by the application can significantly enhance the degradation effect of methylene blue, and the current intensity reaches the peak at 150 mA.

[0146] Referring to Figure 7 The figure reflects the degradation rate of methylene blue in printing and dyeing wastewater by the composite electrode under different iron-carbon ratios. It can be understood from the figure that the degradation rate of the composite electrode with an iron-carbon ratio of 1:2 in the electro-Fenton experiment > the degradation rate of the composite electrode with an iron-carbon ratio of 1:1 in the electro-Fenton experiment > the degradation rate of the composite electrode with an iron-carbon ratio of 2:1 in the electro-Fenton experiment > the degradation rate of the composite electrode with an iron-carbon ratio of 3:1 in the electro-Fenton experiment. The phenomenon is due to the fact that a higher carbon content can produce more hydrogen peroxide, and the hydrogen peroxide is decomposed into hydroxyl radicals faster to react with iron ions. Moreover, the degradation rate of the composite electrode with an iron-carbon ratio of 1:2 in the electro-Fenton experiment is optimal.

[0147] Referring to Figure 8 The figure reflects the relationship between the cycle number, the degradation rate of methylene blue and the time of the same composite electrode prepared by the application applied in the electro-Fenton reaction. From left to right in the figure, the degradation rate of methylene blue by the same composite electrode applied in the electro-Fenton reaction for the first 180 min, the degradation rate of methylene blue by the composite electrode for the subsequent 180 min of continuous use for the second time, and the degradation rate of methylene blue by the composite electrode for the subsequent 180 min of continuous use for the fifth time are shown. It can be understood from the figure that the degradation rate of methylene blue by the nZVI / SBC electro-Fenton body reaction of the same electrolytic plate after five continuous reactions only decreases by 0.65%, and the degradation rate is maintained above 98.5%. After multiple uses, part of the zero-valent iron loaded on the sludge-based biochar is consumed in the reaction process, resulting in a slight decrease in the degradation rate. The results show that the nZVI / SBC electro-Fenton system has good stability, and the electrode prepared by the application has good stability.

[0148] It can be clearly understood from the analysis of the experimental data that the degradation rate of methylene blue in the printing and dyeing wastewater is not less than 85% by the composite electrode prepared in the printing and dyeing wastewater in the range of pH 3-6, wherein the degradation rate of methylene blue can reach 99.55% by the composite electrode prepared by the iron and carbon ratio of 1:2 in the printing and dyeing wastewater under the conditions of pH 5 and current intensity 150 mA within 3 hours. After 5 times of cycle reaction, the degradation rate of methylene blue by the electro-Fenton reaction using the composite electrode prepared in the application as the electrode is still maintained to be more than 98.9%, that is, the composite electrode prepared in the application, that is, the sludge-based biochar loaded with nano zero-valent iron (nZVI / SBC) electrode, can expand the pH range of the wastewater in the electro-Fenton reaction and also increase the effect of the electro-Fenton reaction on the treatment of the printing and dyeing wastewater.

[0149] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A composite electrode material, characterized by, The composite electrode material comprises a carrier and nano zero-valent iron attached to the carrier; The carrier is sludge-based biochar; The molar ratio of iron element to carbon element is 1:2; The composite electrode material is used as a cathode of an electro-Fenton reaction to treat printing and dyeing wastewater; During the treatment of printing and dyeing wastewater by the electro-Fenton reaction, the pH of the printing and dyeing wastewater is adjusted to 3-9.

2. The composite electrode material of claim 1, wherein, In the composite electrode material, the sludge-based biochar is obtained by pyrolysis of residual sludge from water treatment.

3. A method for producing the composite electrode material according to claim 1 or 2, characterized by, The method comprises at least the following steps: Mixing sludge-based biochar and a solution containing an iron source in a protective atmosphere to obtain a mixture A; Reducing the mixture A to obtain a mixture B; Drying the mixture B to obtain the composite electrode material.

4. The method of claim 3, wherein the composite electrode material is prepared by a process comprising: The mass ratio of the sludge-based biochar to the iron source is 0.3-2.1:1; The iron source is selected from ferrous sulfate heptahydrate or ferric chloride; The concentration of the solution containing the iron source is 0.07-0.08 mol L -1 .

5. The method of claim 3, wherein the composite electrode material is prepared by a process comprising: The reduction of the mixture A comprises: Adding a solution containing a reducing agent to the mixture A and performing a reduction reaction in a protective atmosphere; The amount of the solution containing the reducing agent added is 0.03-0.05 L; The reducing agent is selected from sodium borohydride or potassium borohydride; The time of the reduction reaction is 1.8-2.2 h; The drying temperature is 58-62℃.

6. A composite electrode characterized by, An electrode body and a substance attached to the electrode body; The substance comprises at least any one of the composite electrode material of claim 1 or 2 or the composite electrode material prepared by the method of claim 3 or 4.

7. The composite electrode of claim 6, wherein The electrode body is selected from any one of foamed nickel, carbon felt, graphite felt and carbon cloth; The electrode material further comprises a conductive agent and a binder; The conductive agent is selected from conductive carbon black or acetylene black; The binder is selected from polytetrafluoroethylene or polyvinylidene fluoride; The mass ratio of the composite electrode material, the conductive agent and the binder in the electrode material is 7.8-8.2:1:

1.

8. A method for treating printing and dyeing wastewater, characterized by, At least the following steps are included: Electro-Fenton treatment of printing and dyeing wastewater, wherein the cathode uses the composite electrode of claim 6.

9. The method for treating printing and dyeing wastewater according to claim 8, characterized in that, During the electro-Fenton treatment, the pH of the printing and dyeing wastewater is adjusted to 3-6; The current density is controlled to be 50-150 mA.

10. The method for treating printing and dyeing wastewater according to claim 9, characterized in that, The method further comprises an aeration operation during the electro-Fenton treatment.

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