Chitosan-conductive carbon black laminated electrode and preparation method and application thereof

Abstract

The invention discloses a chitosan-conductive carbon black laminated electrode as well as a preparation method and application thereof, and belongs to the field of environment-friendly materials. The method comprises the following steps: activating a carbon felt in a sodium nitrate solution through electrochemical etching to prepare a modified carbon felt carrier; coating a carrier with the precursor solution, vacuumizing, and soaking and strengthening by using a sodium hydroxide-nitrilotriacetic acid trisodium salt monohydrate strengthening solution, so that a stable CS active layer is formed on the surface; sP, polyethyleneimine and dilute sulphuric acid are dissolved in water, and an electrophoresis solution is obtained; carrying out electrophoresis on the electrode with the active layer in an electrophoresis solution to form an SP conductive layer on the surface of the electrode; after a plurality of layers are laminated by multiple times of coating reinforcement-electrophoresis attachment cycle operation, the electrode is placed in a freezing reinforcement solution in isopropanol-glycerol to be frozen for secondary reinforcement, and then the electrode is taken out, unfrozen and cleaned to finally prepare the CS-SP laminated electrode. The electrode material provided by the invention has good electro-adsorption removal performance on heavy metal ions in water.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical removal of heavy metal ions in water, and particularly to a preparation method of a chitosan-conductive carbon black laminated electrode and its application in the electrochemical removal of heavy metal ions. Background Art

[0002] With the development of industry, heavy metal pollution has become an environmental problem that cannot be ignored. Industrial production, mining, and metal processing may all discharge wastewater containing heavy metal ions, threatening the ecosystem and human health. Traditional removal methods such as chemical precipitation and ion exchange have problems such as high cost and secondary pollution. As a new type of water treatment method, the electrochemical treatment technology has attracted attention due to its simple operation and low energy consumption. However, there are still some problems in current research on the electrochemical removal of heavy metal ions in water.

[0003] For example, in the utility model patent "A Double-Layer Double-Anode Electrochemical Device for Removing and Recycling Heavy Metals in Sludge" (Application No.: 201510671976.6), although the device structure design is relatively reasonable, the electrode materials used are stainless steel and alloy, and the actual electro-adsorption deposition removal effect of such materials alone on heavy metal ions is limited; another example is in the paper "Removal and Recycling of Heavy Metals in Water by DC / AC Electrochemical Methods Using Graphene Oxide Electrodes" (doi.10.1021 / acsnano.8b09301), where graphene oxide is used to make the electrode, and the removal effect is good, but materials such as graphene oxide are extremely expensive, restricting their large-scale application. And in the currently reported research, the manufacturing methods of such electrodes mostly rely on high-temperature sintering, and the energy consumption during the manufacturing process is relatively high.

[0004] All in all, it is necessary to develop an electrode material with low cost, low process energy consumption, and good performance for the electrochemical removal of heavy metal ions in water. Summary of the Invention

[0005] The purpose of the present invention is to propose a preparation method of a chitosan CS-conductive carbon black SP laminated electrode and apply it to the electro-adsorption removal of heavy metal ions in water.

[0006] A preparation method of a CS-SP laminated electrode uses electrochemically etched carbon felt as a carrier, prepares a CS active layer with CS, polyvinyl alcohol (PVA), and aminotrimethylenephosphonic acid (ATMP) as active components, and prepares an SP conductive layer with an SP-polyethyleneimine dispersion as an electrophoresis solution; it is prepared by a coating strengthening-electrophoretic attachment lamination method; uses a sodium hydroxide-sodium nitrilotriacetate trihydrate (NTA·3Na) solution as a strengthening solution; after laminating several layers of CS active layers and SP conductive layers, final freezing strengthening is completed in an isopropanol-glycerol freezing strengthening solution; the obtained electrode can achieve efficient electro-adsorption removal of heavy metal ions in water.

[0007] The specific technical solution of the present invention is as follows:

[0008] A preparation method of a CS-SP laminated electrode, characterized in that the steps are as follows:

[0009] (1) Pretreat the carbon fiber felt carrier: Immerse the carbon fiber felt in a sodium nitrate solution for activation by electrochemical etching, and then take it out and wash it with deionized water;

[0010] (2) Prepare the precursor solution: Dissolve chitosan CS, polyvinyl alcohol PVA, aminotrimethylene phosphonic acid ATMP, and glacial acetic acid in hot deionized water and stir to mix to obtain the precursor solution;

[0011] (3) Prepare the strengthening solution: Dissolve sodium hydroxide and trisodium nitrilotriacetate monohydrate in deionized water and stir to mix to obtain the strengthening solution;

[0012] (4) Preliminary loading and strengthening: Coat the precursor solution prepared in step (2) on the carrier prepared in step (1) and evacuate, and then soak and strengthen it in the strengthening solution to obtain an electrode with a chitosan CS layer;

[0013] (5) Prepare the electrophoresis solution: Stir and mix SP and polyethyleneimine in a dilute sulfuric acid solution, and ultrasonically disperse it to obtain the electrophoresis solution;

[0014] (6) Electrophoretically attach the SP layer: Place the electrode with the CS layer prepared in step (4) in the electrophoresis solution to electrophoretically attach the SP layer;

[0015] (7) Prepare the laminated electrode by the coating-electrophoresis lamination method: After repeating steps (4) and (6) several times, a laminated electrode with a chitosan CS layer and an electrocarbon black SP layer is obtained;

[0016] (8) Freezing strengthening: Place the laminated electrode prepared in step (7) in an isopropyl alcohol-glycerol freezing strengthening solution for secondary freezing strengthening, and then take it out, thaw it, wash it with deionized water, and finally obtain the CS-SP laminated electrode.

[0017] In the technical solution of the present invention: In step (1), the concentration of sodium nitrate is 0.5-1 mol / L, the electrochemical system is a two-electrode or three-electrode system, the voltage is a pulsed voltage, the frequency is 50-100 Hz, the voltage range is -12 to 12 V, and the time is 2-4 h.

[0018] In the technical solution of the present invention: In step (2), the mass ratio of CS, PVA, ATMP, glacial acetic acid, and deionized water is (1.5-3):(1-2):(0.5-1):1:100, and the temperature of the deionized water is 95-100 °C.

[0019] In the technical solution of the present invention: in step (3), the mass ratio of sodium hydroxide, nitrilotriacetic acid trisodium salt monohydrate, and deionized water is (3-6):(2-4):100.

[0020] In the technical solution of the present invention: in step (4), the strengthening time for soaking in the strengthening solution is 1-2 h.

[0021] In the technical solution of the present invention: in step (5), the mass ratio of SP, polyethyleneimine, and dilute sulfuric acid is (0.5-1.5):(0.1-0.5):100, and the concentration of the dilute sulfuric acid is 0.01-0.03 mol / L.

[0022] In the technical solution of the present invention: in step (6), the voltage is a pulsed voltage with a frequency of 50-100 Hz, the electrochemical system is a three-electrode system, the electrode with a CS layer is used as the working electrode, the voltage range on the working electrode is -12 to 0 V (relative to the reference electrode), and the electrophoresis time is 15-30 min.

[0023] In the technical solution of the present invention: in step (7), the number of cycles of repeating steps (4) and (6) is 3-6 times

[0024] In the technical solution of the present invention: in step (8), the mass ratio of isopropanol and glycerol is (8-9):(1-2), the freezing temperature is -50 to -30 °C, and the freezing time is 48-72 h.

[0025] In the technical solution of the present invention: the application of the electrode in the removal of heavy metal ions from water by electrochemical adsorption method.

[0026] The experimental conditions and results of the present invention:

[0027] A removal experiment was carried out using simulated wastewater. The simulated wastewater contained Cu 2+ , Ni 2+ , and the concentration of each was 200 ppm. The applied DC potential was -5 V (relative to the reference electrode). The experimental results showed that at 2 h, the removal rates of Cu 2+ , Ni 2+ both exceeded 50%, and at 4 h, the removal rates of Cu 2+ , Ni 2+ both reached over 90%;

[0028] A CV experiment was carried out using simulated wastewater. Two groups of simulated wastewater contained Cu 2+ , Ni 2+ , respectively, and the concentration of each was 150 ppm. The potential range was -2 to 2 V (relative to the reference electrode). The CV diagram showed that both Cu 2+ , Ni 2+ showed obvious reduction peaks, indicating that Cu 2+ , Ni2+ An electrochemical reduction reaction occurred on the electrode surface.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) In the present invention, the active components are CS, PVA, ATMP, and SP. CS contains a large number of amino and carboxyl active groups, which can itself adsorb and chelate heavy metal ions in large quantities. CS can also self-crosslink to improve the overall strength. PVA, while containing a large number of carboxyl groups, can act as a strengthening agent to crosslink and remove water molecules during subsequent freezing strengthening to form a support framework. ATMP is a chelating agent with multiple negatively charged phosphate groups, which has a strong chelating effect on high-valent metal ions. Its high-efficiency chelating performance can further enhance the metal ion capture ability of the material. There may be an electrostatic interaction between the protonated amino group of ATMP and CS, thereby changing the charge distribution of the system and making the component gelation more uniform, thus increasing the effective specific surface area of the adsorbent. SP is evenly dispersed in the components as a conductive agent, improving the overall conductivity;

[0031] (2) In the present invention, a sodium hydroxide - NTA·3Na solution is used to strengthen the CS layer. The high pH value of the sodium hydroxide solution will deprotonate the protonated amino group of CS, causing CS to gelate, and enhancing the intermolecular hydrogen bond interaction of the hydroxyl groups in PVA, causing PVA to crosslink, improving the mechanical properties and chemical stability. During this process, part of NTA·3Na will remain in the CS layer. NTA·3Na is a chelating agent, and the carboxyl group and secondary amino group on its molecule can effectively chelate metal ions, thereby enhancing the adsorption ability of the material for heavy metals;

[0032] (3) In the present invention, by treating the electrode in isopropanol - glycerol at low temperature, on the one hand, isopropanol will reduce the free water content between PVA molecules, enhancing the hydrogen bond linkage of PVA molecules to improve the mechanical strength. On the other hand, glycerol can enter between PVA molecules to plasticize it to a certain extent, avoiding excessive embrittlement. The freezing process will promote PVA to form an ordered network structure, making the hydrogen bond connection tight, and finally making it have both mechanical strength and chemical stability, enabling it to maintain stability during the electrochemical adsorption process;

[0033] (4) In the present invention, a coating - electrophoresis lamination method is used to prepare a laminated electrode. The CS layer is loaded onto the electrode surface by simple coating and preliminarily strengthened with sodium hydroxide - NTA·3Na, and then a layer of SP is deposited on it by electrophoresis in an electrophoresis solution. After several repeated coating - electrophoresis processes, a stacked layer is formed. The stacked layer is stacked by layer - by - layer composite stacking, which not only improves the strength but also makes SP, as a conductive enhancer, evenly distributed in the material layer by layer, avoiding problems such as insufficient cross - linking reaction and uneven agglomeration of SP caused by simply mixing all components and then coating and strengthening them at one time;

[0034] The present invention prepares an electrode material with good electrical conductivity, electro-adsorption performance, mechanical strength, and electrochemical stability, which can achieve efficient electro-adsorption for removing heavy metal ions in water. The raw materials are environmentally friendly, cheap, and easily available, which can effectively reduce the cost of treating heavy metal ion-polluted water bodies and have strong application and promotion value.

[0035] In the technical solution of the present invention, the purpose of etching is to create as many defect sites and hydrophilic groups as possible on the carbon felt for subsequent processing, so a long-duration pulsed high voltage with positive and negative oscillations is adopted. The purpose of attachment is to electrophoretically adsorb enough conductive carbon black SP in a short time, so a short-duration negative pulsed high voltage is adopted;

[0036] In the actual experiment of removing heavy metal ions, the experimental time is as long as 4h. If a long-duration high voltage is adopted, although the removal rate can be improved, side reactions (such as hydrogen evolution and oxygen evolution) will also be enhanced, generating a large number of bubbles, causing the active substances to peel off and oxidize more quickly. Therefore, a lower voltage is adopted in the examples. Description of the Drawings

[0037] Figure 1 It is the removal effect diagram of Example 1.

[0038] Figure 2 It is the removal effect diagram of Example 2.

[0039] Figure 3 It is the CV test effect diagram of Example 3.

[0040] Figure 4 It is the CV test effect diagram of Example 4.

[0041] Figure 5 It is the removal effect diagrams of Comparative Examples 1-2. Detailed Embodiments

[0042] The following further illustrates the present invention in conjunction with examples, but the protection scope of the present invention is not limited thereto.

[0043] Example 1

[0044] (1) Pretreat the carbon fiber felt carrier: Immerse the carbon fiber felt in a 0.5 mol / L sodium nitrate solution, apply a pulsed voltage of -10 to 10V, a frequency of 50Hz, and a time of 4h to electrochemically etch and activate it, and then take it out and wash it with deionized water.

[0045] (2) Prepare the precursor solution: The mass ratio of CS, PVA, ATMP, glacial acetic acid, and deionized water is 3:2:0.5:1:100, and the temperature of the deionized water is 99°C.

[0046] (3) Preparation of the strengthening solution: The mass ratio of sodium hydroxide, trisodium nitrilotriacetate monohydrate, and deionized water is 3:2:100, and they are stirred and mixed.

[0047] (4) Preliminary loading and strengthening: The CS precursor solution prepared in step (2) is coated on the carrier prepared in step (1) and vacuumed, and then it is immersed in the strengthening solution for 1 h.

[0048] (5) Preparation of the electrophoresis solution: The mass ratio of SP, polyethyleneimine, and dilute sulfuric acid is 1:0.3:100, the concentration of the dilute sulfuric acid is 0.01 mol / L, they are stirred and mixed, and then ultrasonically dispersed.

[0049] (6) Electrophoretic attachment of the SP layer: It is carried out in a three-electrode system. The electrode with the CS layer is used as the working electrode, the voltage is a pulsed voltage, the frequency is 50 Hz, the voltage range on the working electrode is -12 to 0 V (relative to the reference electrode), and the electrophoresis time is 15 min.

[0050] (7) Preparation of the laminated electrode by the coating-electrophoresis lamination method: Steps (4) and (6) are repeated 3 times in a cycle.

[0051] (8) Freezing strengthening: In freezing strengthening, the mass ratio of isopropanol to glycerol is 8:2, the freezing temperature is -30 °C, the freezing time is 72 h, and then it is taken out, thawed, and washed with deionized water to finally obtain the CS-SP laminated electrode.

[0052] (9) Electro-adsorption for removing Cu 2+ ion experiment

[0053] Specifically, the CS-SP laminated electrode is used as the working electrode, the platinum-coated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode, and the respective electrodes are connected to an electrochemical workstation.

[0054] When using the CS-SP laminated electrode to remove heavy metal ions, a DC potential of -5 V (relative to the reference electrode) is applied to the electrode.

[0055] The removal experiment is carried out using simulated wastewater. The heavy metal ion in the simulated wastewater is Cu 2+ , with a concentration of 200 ppm and a composition of CuSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 400 ppm.

[0056] The experimental results show that the removal rate of Cu reaches 64.09% at 2 h, and the removal rate of Cu reaches 90.09% at 4 h. 2+ 2+ 2+ The removal rate reaches 90.09%.

[0057] The removal experiment is carried out using simulated wastewater. The heavy metal ion in the simulated wastewater is Ni 2+, with a concentration of 200 ppm and a composition of NiSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 500 ppm.

[0058] The experimental results show that at 2 h, the Ni 2+ removal rate reaches 56.62%, and at 4 h, the Ni 2+ removal rate reaches 93.3%.

[0059] Example 2

[0060] (1) Pretreat the carbon fiber felt carrier: Immerse the carbon fiber felt in a 1 mol / L sodium nitrate solution, apply a pulsed voltage of -12 to 12 V with a frequency of 100 Hz for 3 h to electrochemically etch and activate it, and then take it out and wash it with deionized water.

[0061] (2) Prepare the precursor solution: The mass ratio of CS, PVA, ATMP, glacial acetic acid, and deionized water is 2:1:1:1:100, and the temperature of the deionized water is 95 °C.

[0062] (3) Prepare the strengthening solution: The mass ratio of sodium hydroxide, trisodium nitrilotriacetate monohydrate, and deionized water is 6:3:100, and stir and mix them.

[0063] (4) Preliminary loading and strengthening: Coat the CS precursor solution prepared in step (2) on the carrier prepared in step (1) and evacuate, and then immerse it in the strengthening solution for 1 h.

[0064] (5) Prepare the electrophoresis solution: The mass ratio of SP, polyethyleneimine, and dilute sulfuric acid is 1.5:0.5:100, the concentration of the dilute sulfuric acid is 0.03 mol / L, stir and mix them, and then ultrasonically disperse them.

[0065] (6) Electrophoretically attach the SP layer: Conduct it in a three-electrode system. The electrode with the CS layer serves as the working electrode, the voltage is a pulsed voltage with a frequency of 100 Hz, the voltage range on the working electrode is -10 to 0 V (relative to the reference electrode), and the electrophoresis time is 25 min.

[0066] (7) Prepare the laminated electrode by the coating-electrophoresis lamination method: Repeat steps (4) and (6) for 5 cycles.

[0067] (8) Freeze strengthening: In freeze strengthening, the mass ratio of isopropanol to glycerol is 9:1, the freezing temperature is -50 °C, and the freezing time is 48 h. Then take it out, thaw it, wash it with deionized water, and finally obtain the CS-SP laminated electrode.

[0068] (9) Electro-adsorption removal of Ni 2+ ion experiment

[0069] Specifically, the CS-SP laminated electrode is used as the working electrode, the platinum-plated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Connect the respective electrodes to an electrochemical workstation.

[0070] When using the CS-SP laminated electrode to remove heavy metal ions, a DC potential of -5V (relative to the reference electrode) is applied to the electrode.

[0071] Use simulated wastewater for the removal experiment. The heavy metal ion in the simulated wastewater is Cu 2+ , with a concentration of 200 ppm and a composition of CuSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 500 ppm.

[0072] The experimental results show that the removal rate of Cu reaches 65.17% at 2 h 2+ and reaches 95.36% at 4 h. 2+ The experimental results show that the removal rate of Cu reaches 95.36% at 4 h.

[0073] Use simulated wastewater for the removal experiment. The heavy metal ion in the simulated wastewater is Ni 2+ , with a concentration of 200 ppm and a composition of NiSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 500 ppm.

[0074] The experimental results show that the removal rate of Ni reaches 61.49% at 2 h 2+ and reaches 91.48% at 4 h. 2+ The experimental results show that the removal rate of Ni reaches 91.48% at 4 h.

[0075] Example 3

[0076] (1) Preparation of the CS-SP laminated electrode

[0077] The electrode preparation method in Example 3 of the present invention is the same as that in Example 1.

[0078] (2) CV test of Cu 2+ ions

[0079] Specifically, the CS-SP laminated electrode is used as the working electrode, the platinum-plated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Connect the respective electrodes to an electrochemical workstation.

[0080] When using the CS-SP laminated electrode to test CV, the potential range applied to the electrode is -1 to 1V (relative to the reference electrode), and the scan rate is 5 mV / s.

[0081] Use simulated wastewater for the CV test. The heavy metal ion in the simulated wastewater is Cu 2+ , with a concentration of 300 ppm and a composition of CuSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 500 ppm.

[0082] The experimental results show that obvious oxidation-reduction peaks appear, and the oxidation-reduction peak potential conforms to that of Cu 2+ , confirming that Cu 2+ has undergone an electrochemical reaction on the electrode surface.

[0083] Example 4

[0084] (1) Preparation of the CS-SP laminated electrode

[0085] The method for preparing the electrode in Example 4 of the present invention is the same as that in Example 2.

[0086] (2) CV test of heavy metal ions

[0087] Specifically, the CS-SP laminated electrode is used as the working electrode, the platinum-plated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Connect the respective electrodes to an electrochemical workstation.

[0088] When using the CS-SP laminated electrode to test CV, the potential range applied to the electrode (relative to the reference electrode) is -1.5 to 1.5 V, and the scanning rate is 5 mV.

[0089] Use simulated wastewater for CV testing. The heavy metal ion in the simulated wastewater is Ni 2+ , with a concentration of 100 ppm and a composition of NiSO4; the remaining supporting electrolyte has a composition of Na2SO4 with a concentration of 500 ppm.

[0090] The experimental results show that obvious oxidation-reduction peaks appear, and the oxidation-reduction peak potential conforms to that of Ni 2+ , confirming that Ni 2+ has undergone an electrochemical reaction on the electrode surface.

[0091] Comparative Example 1

[0092] (1) Preparation of the electrode

[0093] Specifically, instead of performing the coating-electrophoresis lamination in steps (2) to (7), CS, PVA, ATMP glacial acetic acid, SP, PEI, and dilute sulfuric acid are directly added to deionized water at 95 °C and simply mixed, then coated on the carrier, and then soaked and strengthened with a sodium hydroxide-nitrilotriacetic acid trisodium salt monohydrate strengthening solution for 2 h. Finally, step (8) is performed for freeze strengthening to obtain the electrode.

[0094] (2) Experiment on electroadsorption removal of Cu 2+ ion

[0095] Specifically, the electrode prepared above is used as the working electrode, the platinum-plated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Connect the respective electrodes to an electrochemical workstation.

[0096] When using the said electrode to remove heavy metal ions, the potential applied to the electrode is -5V (relative to the reference electrode).

[0097] Use simulated wastewater for the removal experiment. The heavy metal ion in the simulated wastewater is Cu 2+ , with a concentration of 100 ppm and the composition being CuSO4; the remaining supporting electrolyte composition is Na2SO4 with a concentration of 500 ppm.

[0098] The experimental results show that the removal rate of Cu 2+ is lower than 30% at 2 h, and the removal rate of Cu 2+ is lower than 65% at 4 h.

[0099] The comparison effect shows that: compared with Example 1, the simple mixing process does not form an ordered stacked structure, which leads to uneven and insufficient distribution of the active substance and the conductive substance, and further leads to a decrease in the removal rate of Cu 2+ compared with Example 1.

[0100] Comparative Example ②

[0101] (1) Prepare the electrode

[0102] Specifically, except for not adding ATMP in step (2) and not adding nitrilotriacetic acid trisodium salt monohydrate in step (3), other conditions are the same as in Example 2.

[0103] (2) Electro-adsorption removal of Ni 2+ ion experiment

[0104] Specifically, the above-prepared electrode is used as the working electrode, the platinum-plated titanium mesh is used as the counter electrode, and the saturated calomel electrode is used as the reference electrode. Connect the respective electrodes to an electrochemical workstation.

[0105] When using the said electrode to remove heavy metal ions, the potential applied to the electrode is -5V (relative to the reference electrode).

[0106] Use simulated wastewater for the removal experiment. The heavy metal ion in the simulated wastewater is Ni 2+ , with a concentration of 100 ppm and the composition being NiSO4; the remaining supporting electrolyte composition is Na2SO4 with a concentration of 500 ppm.

[0107] The experimental results show that the removal rate of Ni 2+ is lower than {35% at 2 h, and the removal rate of Ni 2+ is lower than 60% at 4 h.

[0108] The comparison effect shows that: compared with Example 2, two chelating agents are removed, and CS and PVA will lose effective adsorption groups during the cross-linking strengthening process. Without the supplementation of chelating agents to enhance the adsorption capacity, the material for Cu2+ The removal rate decreased compared with that of Example 1.

[0109] Comparative Example 3

[0110] (1) Preparation of the electrode

[0111] Specifically, the steps were the same as those in Example 1, but sodium hydroxide was removed from the components of the strengthening solution in step (3), and step (8) was removed. After direct drying, it was used for the experiment.

[0112] (2) Stability experiment

[0113] Specifically, the prepared electrode above was used as the working electrode, the platinum-coated titanium mesh was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode. Each electrode was connected to an electrochemical workstation.

[0114] When using the electrode to remove heavy metal ions, a potential of -5V (relative to the reference electrode) was applied to the electrode.

[0115] A stability experiment was carried out using simulated wastewater. The heavy metal ion in the simulated wastewater was Ni 2+ , with a concentration of 50 ppm and the component being NiSO4; the remaining supporting electrolyte component was Na2SO4 with a concentration of 500 ppm.

[0116] The experimental results showed that: compared with Example 1 and Example 2, a large amount of foam dissolved on the electrode surface at 2 h during the experiment in Comparative Example 3, a large amount of flocculants appeared in the water at 4 h, and the color of the water sample was yellowish-brown and turbid.

[0117] The comparison effect showed that: after removing sodium hydroxide from the strengthening solution, CS and PVA were not effectively crosslinked, the strength decreased, and at the same time, the freezing step in isopropanol-glycerol was not carried out, resulting in the water molecules in PVA not being removed and replaced, and PVA not condensing to form a network structure. Eventually, the mechanical properties and chemical stability were poor, and a large amount of PVA and CS on the electrode surface were dissolved out, and an oxidation reaction may have occurred.

Claims

1. A preparation method of a chitosan-conductive carbon black laminated electrode, characterized in that, The steps are as follows: (1) Pretreat the carbon fiber felt carrier: Immerse the carbon fiber felt in a sodium nitrate solution and activate it by electrochemical etching, then take it out and wash it; (2) Prepare the precursor solution: Dissolve chitosan, polyvinyl alcohol, aminotrimethylphosphonic acid, and glacial acetic acid in deionized water at 80 - 100 °C and stir to mix to obtain the precursor solution; (3) Prepare the strengthening solution: Dissolve sodium hydroxide and trisodium nitrilotriacetate monohydrate in deionized water and stir to mix to obtain the strengthening solution; (4) Preliminary loading and strengthening: Coat the precursor solution prepared in step (2) on the carrier prepared in step (1) and evacuate, then immerse it in the strengthening solution for strengthening to obtain an electrode with a chitosan layer; (5) Prepare the electrophoresis solution: Stir and mix conductive carbon black and polyethyleneimine in a dilute sulfuric acid solution, and ultrasonically disperse it to obtain the electrophoresis solution; (6) Electrophoretically attach a conductive carbon black layer: Place the electrode with a chitosan layer prepared in step (4) in the electrophoresis solution to electrophoretically attach a conductive carbon black layer; (7) Prepare a laminated electrode by the coating - electrophoresis lamination method: After repeating steps (4) and (6) several times, obtain a laminated electrode with a chitosan layer and a conductive carbon black layer; (8) Freeze - strengthening: Place the laminated electrode prepared in step (7) in the freeze - strengthening solution of isopropanol - glycerol for secondary freeze - strengthening, then take it out, thaw it, wash it with deionized water, and finally obtain a chitosan - conductive carbon black laminated electrode.

2. The preparation method according to claim 1, wherein: In step (1), the concentration of the sodium nitrate solution is 0.5 - 1 mol / L; the electrode system used for electrochemical etching activation is a three - electrode system, the voltage is a pulsed voltage, the frequency is 50 - 100 Hz, the voltage range is - 12 - 12 V, and the time is 2 - 4 h.

3. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of chitosan, polyvinyl alcohol, aminotrimethylphosphonic acid, glacial acetic acid, and deionized water is (1.5 - 3):(1 - 2):(0.5 - 1):1:

100.

4. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of sodium hydroxide, trisodium nitrilotriacetate monohydrate, and deionized water is (3 - 6):(2 - 4):

100.

5. The preparation method according to claim 1, wherein: In step (4), the soaking time for strengthening in the strengthening solution is 1 - 2 h.

6. The preparation method according to claim 1, wherein: In step (5), the mass ratio of the conductive carbon black layer, polyethyleneimine, and dilute sulfuric acid is (0.5 - 1.5):(0.1 - 0.5):100, and the concentration of the dilute sulfuric acid is 0.01 - 0.03 mol / L.

7. The preparation method according to claim 1, characterized in that: In step (6), the voltage used for electrophoresis is a pulsed voltage, the frequency is 50 - 100 Hz; the electrochemical system used for electrophoresis is a three - electrode system, the electrode with a CS layer is used as the working electrode, the voltage range on the working electrode is - 12 - 0 V, and the electrophoresis time is 15 - 30 min.

8. The preparation method according to claim 1, characterized in that: In step (7), the number of cycles of repeating steps (4) and (6) is 3 - 6 times; In step (8), the mass ratio of isopropanol and glycerol is (8 - 9):(1 - 2), the freezing temperature is - 50 - - 30 °C, and the freezing time is 48 - 72 h.

9. A chitosan-conductive carbon black laminated electrode, characterized in that, Prepared by the method according to any one of claims 1 - 8.

10. Application of the electrode according to claims 1 - 9 in the removal of heavy metal ions in water by the electrochemical adsorption method.

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