A hydroxyl- and carboxyl-modified carbon felt electrode, its preparation method and application

Abstract

The present invention belongs to the technical field of nickel-containing wastewater treatment. The present invention discloses a carbon felt electrode modified with hydroxyl and carboxyl groups, its preparation method and application. The preparation of the porous carbon electrode modified with hydroxyl and carboxyl groups includes the following steps: coating a modifier on the carbon felt to make the carbon felt a modified carbon felt electrode with hydroxyl and carboxyl functional groups modified. Using this electrode as the cathode and the bare carbon felt as the anode, nickel-containing wastewater is treated by an electrochemical reaction under direct current, and metallic nickel is directly recovered on the working electrode. The present invention utilizes the chelating effect of hydroxyl and carboxyl functional groups on nickel ions. Through electrochemical technology, it can not only reduce the content of nickel ions in electroplating wastewater, but also successfully recover nickel. This method is simple to operate, low in cost, has good economic benefits, and can efficiently treat nickel-containing wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical field of nickel-containing wastewater treatment, and particularly relates to a carbon felt electrode modified with hydroxyl and carboxyl groups, a preparation method thereof, and an application thereof. Background Technique

[0002] With the economic development and the deepening of industrialization in China in recent years, the domestic electroplating production industry has achieved great development; the electroplating production industry itself is a highly polluting industry, and the electroplating wastewater generated during its production process contains a large amount of heavy metal ions. For example, the toxic and harmful substances include cadmium, lead, chromium, nickel, copper and other suspended matters. The direct discharge of electroplating wastewater will cause serious harm to the ecological environment. In order to make the electroplating wastewater meet the discharge standards, it is necessary to treat the electroplating wastewater.

[0003] Nickel is a metallic element located in Group VIII of the fourth period of the periodic table. The most common valence states are +2 and +3. In an aqueous solution, it usually appears only in the form of +2 valence ions. Nickel ions with a +3 valence have strong oxidizing properties and will quickly undergo redox reactions with water or acid radical ions in water. Nickel and its compounds will cause very serious pollution to the environment. The main industrial pollution sources of nickel are the wastewater and waste residues discharged from industries such as mining, smelting, and electroplating; the nickel released through the combustion process of petroleum and most coals is the main source of nickel in the atmosphere; the nickel content in the wastewater discharged from the electroplating industry and metal processing is relatively high, reaching dozens to hundreds of milligrams per liter of wastewater. Although nickel is an essential element for the human body, the human demand is very small. The nickel content in the blood of a healthy human body is generally between 0.02 μg / L and 0.05 μg / L. Once it exceeds the standard, it will harm human health. Nickel damages the liver and cardiopulmonary functions of people, leading to severe dermatitis and skin allergies; and the unqualified nickel wastewater discharged into the soil will be absorbed by plants and transferred to the human body through the food chain, causing harm to the human body.

[0004] At present, the treatment methods for nickel-containing wastewater mainly include adsorption method, chemical precipitation method, and bioremediation method. The adsorption method mainly relies on the advantages of the adsorbent such as chemical stability, excellent structure, fast adsorption rate, and large adsorption capacity to treat heavy metal ions. Luo et al. (2016) designed 3D-MnO 2The ion cage is used as an adsorbent to extract lithium, and its adsorption capacity is found to be very high (56.87 mg / g). The chemical precipitation method is relatively common, with less energy consumption and relatively low cost. It usually involves alkaline precipitation or sulfide precipitation. The biological method is widely used and has a high metal adsorption capacity. It mainly uses microorganisms or plants to remove heavy metals through biosorption, accumulation, and enrichment. However, these methods also have obvious disadvantages. The adsorption method is highly dependent on target functional groups, and the design of materials leads to increased costs; the chemical precipitation method consumes a large amount of chemical reagents, and the sludge will cause secondary pollution; the biosorption method has difficulties in screening microbial populations and treating biological materials, and the repair time is long, and the treatment effect is limited by the natural environment. These disadvantages result in the poor application of these methods in actual production. Therefore, with the growing demand for recovering metal resources from water, it is necessary to develop a cheaper, sustainable, and more energy-efficient method to recover metal resources from wastewater.

[0005] Electrochemistry is a promising and efficient water treatment technology. Specifically, electrochemical recovery is a very clean, versatile, and environmentally compatible technology that recovers metals from wastewater in their most valuable state. It can not only eliminate water pollution problems but also recover valuable metal resources. When an external current is applied, metal ions migrate directionally towards the electrode surface and then accumulate in the electric double layer. After undergoing redox reactions with the electrode, pure metal ions are fixed on the electrode surface or precipitate near the electrode surface, enabling the in-situ enrichment of metal ions and even the formation of metal products. Su et al. (2018) used an electrochemical method to absorb more than 100 mg / g of hexavalent chromium (Cr(VI)) and released Cr ions in their less harmful trivalent form (Cr(III)); Wu et al. (2019) applied an electrochemical method to remove heavy metals with a deposition capacity exceeding 2300 mg / g. However, at present, there are still problems such as low efficiency, high cost, a large amount of sludge generation, and difficulty in recovering nickel metal during the treatment of nickel-containing wastewater. Therefore, how to simply and efficiently treat nickel in wastewater still requires further research. Summary of the Invention

[0006] Aiming at the above deficiencies of the prior art, the purpose of the present invention is to provide a carbon felt electrode modified with hydroxyl and carboxyl groups, its preparation method, and application. The present invention solves the problems of low efficiency, high cost, a large amount of sludge generation, and difficulty in recovering nickel metal during the current treatment of nickel-containing wastewater, and proposes a carbon felt electrode modified with hydroxyl and carboxyl groups, and uses it as a working electrode to provide an electrochemical method for recovering nickel from nickel-containing wastewater.

[0007] The present invention is realized through the following technical solutions:

[0008] A preparation method of a carbon felt electrode modified with hydroxyl and carboxyl groups, comprising the following steps:

[0009] S1. Clean the carbon felt to obtain a pretreated carbon felt;

[0010] S2. Completely dissolve citric acid, sodium hydroxide, potassium dihydrogen phosphate, and calcium oxide in water, adjust the pH of the solution to 6.0 - 8.0, dry, grind, and sieve it, then calcine it at 300 - 700 °C for 1 - 3 h under an inert atmosphere to obtain a modifier;

[0011] Among them, the mass ratio of citric acid, sodium hydroxide, potassium dihydrogen phosphate, and calcium oxide is 150 - 210:1:15 - 30:30 - 50;

[0012] S3. Blend the binder, conductive agent, and the modifier obtained in step S2 with a solvent to obtain a coating material;

[0013] S4. Place the pretreated carbon felt obtained in step S1 into the coating material obtained in step S3, perform ultrasonic blending, and then dry it to a constant weight to obtain a carbon felt electrode modified with hydroxyl and carboxyl groups.

[0014] Preferably, the cleaning method in step S1 is: sequentially clean the carbon felt with ultrapure water, a nitric acid solution with a mass fraction of 2%, ultrapure water, absolute ethanol, and ultrapure water, and then dry it to a constant weight to obtain a pretreated carbon felt.

[0015] Preferably, in step S2, an HAc - NaAc buffer solution is used to adjust the pH.

[0016] Preferably, the binder in step S3 is selected from one of polyvinylidene fluoride, polyvinyl fluoride, and polytetrafluoroethylene - propylene; the conductive agent is selected from one of super carbon powder, conductive graphite, and carbon black; the solvent is selected from one of N - methylpyrrolidone, dimethylacetamide, and methyl ethyl ketone.

[0017] Preferably, the mass ratio of the conductive agent, binder, and modifier in step S3 is 1 - 3:1:2 - 4.

[0018] Preferably, the ultrasonic conditions in step S4 are: ultrasonic for 5 - 15 min at a frequency of 40 kHz, and perform static deposition treatment after ultrasonic treatment.

[0019] The present invention also protects the carbon felt electrode modified with hydroxyl and carboxyl groups prepared by the preparation method.

[0020] The present invention also protects the application of the carbon felt electrode modified with hydroxyl and carboxyl groups in the preparation of a nickel - containing wastewater treatment agent. The application method is as follows:

[0021] Using the electrodeposition technique, with a carbon felt electrode modified with hydroxyl and carboxyl groups as the working electrode, an unmodified carbon felt electrode as the counter electrode, and nickel-containing wastewater as the electrolyte, the working electrode and the counter electrode are jointly placed in the electrolyte and electrically connected using a DC power supply. Electrodeposition is carried out at a potential of 3 - 6V for 1 - 2h to deposit nickel on the surface of the carbon felt electrode modified with hydroxyl and carboxyl groups.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention utilizes the chelation of nickel ions by hydroxyl and carboxyl functional groups. Through electrochemical technology, it can not only reduce the content of nickel ions in electroplating wastewater but also successfully recover nickel. The results show that the carbon felt electrode modified with hydroxyl and carboxyl groups of the present invention can recover about 72% of the metallic nickel in nickel wastewater.

[0024] 2. The present invention uses a calcined material to modify the carbon felt electrode and uses the modified electrode as the cathode. Carbon felt is a very cheap carbon material suitable for large-scale applications; moreover, the electrochemical reduction technology adopted by the present invention has a rapid reaction, is green and environmentally friendly, and will not cause secondary pollution.

[0025] 3. The present invention first cleans the carbon felt material to sequentially remove the reducing substances and organic substances attached to the surface of the carbon felt. Then, citric acid, sodium hydroxide, potassium dihydrogen phosphate, and calcium oxide are jointly calcined. After calcination, substances such as calcium phosphate, calcium citrate, and sodium citrate can be generated. Calcium ions can perform ion exchange with nickel ions. Hydroxyl groups are provided by alkaline substances such as sodium hydroxide and calcium oxide, and carboxyl groups are brought by citric acid. Hydroxyl and carboxyl groups can chelate with nickel ions, thereby achieving the purpose of recovering metallic nickel and effectively solving the problems of low efficiency, high cost, generation of a large amount of sludge, and difficulty in recovering nickel metal during the current stage of treating nickel-containing wastewater. Description of the Drawings

[0026] Figure 1 It is a graph showing the change of nickel ion removal rate with time when the carbon felt electrode modified with hydroxyl and carboxyl groups prepared in Example 1 of the present invention is electrolyzed in a nickel solution.

[0027] Figure 2 In (a) and (b), they are respectively the scanning electron microscope (SEM) and X-ray energy spectrum analysis (EDS) characterization diagrams of nickel deposited on the working electrode after the carbon felt electrode modified with hydroxyl and carboxyl groups prepared in Example 1 of the present invention is electrolyzed in a nickel solution for 2h.

[0028] Figure 3 It is the X-ray photoelectron spectroscopy (XPS) characterization diagram of nickel deposited on the working electrode after the carbon felt electrode modified with hydroxyl and carboxyl groups prepared in Example 1 of the present invention is electrolyzed in a nickel solution for 2h. Detailed Embodiments

[0029] The specific embodiments of the present invention will be described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention. The experimental methods described in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0030] Example 1

[0031] A preparation method of a carbon felt electrode modified with hydroxyl and carboxyl groups comprises the following steps:

[0032] (1) Cut the carbon felt into sheets of 1.7×2.2 cm and put them into a beaker. Add ultrapure water and ultrasonically clean for 5 min. After taking out, rinse with ultrapure water 5 times; then put the carbon felt into a beaker containing a 2% nitric acid solution and ultrasonically clean for 5 min to remove the reducing substances attached to the surface of the carbon felt. After taking out, rinse with ultrapure water 5 times; finally, put the carbon felt sheet into a beaker containing anhydrous ethanol and ultrasonically clean for 5 min to remove the organic substances attached to the surface of the carbon felt. After taking out, rinse with ultrapure water 5 times; put the treated carbon felt into a blast drying oven and dry at 100 °C for 6 h until the weight does not change and becomes shiny after removing impurities to obtain pretreated carbon felt;

[0033] (2) Weigh 3.0 g of citric acid, 0.0146 g of sodium hydroxide, 0.3585 g of potassium dihydrogen phosphate and 0.6334 g of calcium oxide with an electronic balance into a 100 mL beaker. Add 30 mL of ultrapure water and stir evenly with a glass rod. After the medicines are completely dissolved, add HAc-NaAc buffer solution to adjust the pH of the solution to 7.0. Put the beaker into a blast drying oven, set the temperature to 60 °C, and dry thoroughly for 36 h until the weight does not change to remove the moisture in the sample;

[0034] Put the dried sample into a mortar and grind it thoroughly. Sieve it through a 100-mesh sieve to obtain particles of 0.15 mm. Put the sieved sample into a boat and calcine it in a tube furnace at 500 °C for 2 h. The protective gas is argon and the heating rate is 10 °C / min to obtain a modifier;

[0035] (3) Pipette 10 mL of N-methylpyrrolidone (NMP) into a 50 mL beaker. Weigh 0.2 g of polyvinylidene fluoride (PVDF) with an electronic balance and put it into the beaker. Then put a rotor and stir for 1 h to completely dissolve PVDF in NMP to prepare a 2% PVDF by mass. Weigh 0.375 g of super carbon powder and 0.5 g of the calcined material with an electronic balance and put them into the 2% PVDF by mass and stir for 3.5 h to prepare a coating material;

[0036] (4) Place the pretreated carbon felt from step (1) into a 50 mL beaker containing the coating material. Place the beaker in an ultrasonic cleaner and ultrasonicate for 10 min to allow the coating material to fully penetrate into the interior of the carbon felt. Then remove the beaker and let it stand for 5 min to allow the coating material to deposit and adhere to the carbon felt. After standing, take out the carbon felt and place it in a petri dish. Place the petri dish in a vacuum drying oven, set the temperature to 60 °C, and vacuum dry for 4.5 h until the weight of the carbon felt no longer changes, obtaining a carbon felt electrode modified with hydroxyl and carboxyl groups.

[0037] Example 2

[0038] A method for preparing a carbon felt electrode modified with hydroxyl and carboxyl groups, comprising the following steps:

[0039] (1) Cut the carbon felt into pieces of 1.7×2.2 cm and place them in a beaker. Add ultrapure water and ultrasonically clean for 5 min. After taking it out, rinse it 5 times with ultrapure water; then place the carbon felt in a beaker containing a 2% nitric acid solution and ultrasonically clean for 5 min to remove the reducing substances attached to the surface of the carbon felt. After taking it out, rinse it 5 times with ultrapure water; finally, place the carbon felt pieces in a beaker containing absolute ethanol and ultrasonically clean for 5 min to remove the organic substances attached to the surface of the carbon felt. After taking it out, rinse it 5 times with ultrapure water; place the treated carbon felt in a blast drying oven and dry it at 100 °C for 6 h until the weight does not change and it becomes shiny after removing impurities, obtaining the pretreated carbon felt;

[0040] (2) Weigh 2.19 g of citric acid, 0.0146 g of sodium hydroxide, 0.438 g of potassium dihydrogen phosphate, and 0.73 g of calcium oxide in a 100 mL beaker. Add 30 mL of ultrapure water and stir evenly with a glass rod. After the chemicals are completely dissolved, add the HAc-NaAc buffer solution to adjust the pH of the solution to 6.0. Place the beaker in a blast drying oven, set the temperature to 60 °C, and fully dry for 36 h until the weight does not change to remove the moisture in the sample;

[0041] Place the dried sample in a mortar and grind it thoroughly. Pass it through a 100-mesh sieve to obtain particles of 0.15 mm. Place the sieved sample in a boat and calcine it in a tube furnace at 300 °C for 3 h. The protective gas is argon, and the heating rate is 5 °C / min to obtain the modifier;

[0042] (3) Pipette 10 mL of N-methylpyrrolidone (NMP) into a 50 mL beaker. Weigh 0.1 g of polyvinylidene fluoride (PVDF) and place it in the beaker. Then place a rotor and stir for 1 h to completely dissolve PVDF in NMP, preparing a 1% PVDF by mass. Weigh 0.1 g of super carbon powder and 0.4 g of the calcined material, place them in the 1% PVDF by mass and stir for 3.5 h to prepare the coating material;

[0043] (4) Place the pretreated carbon felt from step (1) into a 50 mL beaker containing the coating material. Place the beaker in an ultrasonic cleaner and ultrasonicate for 10 min to allow the coating material to fully penetrate into the interior of the carbon felt. Then take out the beaker and let it stand for 5 min to allow the coating material to deposit and adhere to the carbon felt. After standing, take out the carbon felt and place it in a petri dish. Place the petri dish in a vacuum drying oven, set the temperature to 60 °C, and vacuum dry for 4.5 h until the weight of the carbon felt no longer changes, obtaining a carbon felt electrode modified with hydroxyl and carboxyl groups.

[0044] Example 3

[0045] A method for preparing a carbon felt electrode modified with hydroxyl and carboxyl groups, comprising the following steps:

[0046] (1) Cut the carbon felt into pieces of 1.7×2.2 cm and put them into a beaker. Add ultrapure water and ultrasonicate for 5 min. After taking out, rinse with ultrapure water 5 times; then put the carbon felt into a beaker containing a nitric acid solution with a mass fraction of 2%, ultrasonicate for 5 min to remove the reducing substances attached to the surface of the carbon felt. After taking out, rinse with ultrapure water 5 times; finally, put the carbon felt pieces into a beaker containing absolute ethanol, ultrasonicate for 5 min to remove the organic substances attached to the surface of the carbon felt. After taking out, rinse with ultrapure water 5 times; put the treated carbon felt into a blast drying oven, dry at 100 °C for 6 h until the weight does not change and becomes shiny after removing impurities, obtaining the pretreated carbon felt;

[0047] (2) Weigh 3.066 g of citric acid, 0.0146 g of sodium hydroxide, 0.219 g of potassium dihydrogen phosphate, and 0.438 g of calcium oxide in a 100 mL beaker. Add 30 mL of ultrapure water and stir evenly with a glass rod. After the drugs are completely dissolved, add HAc-NaAc buffer solution to adjust the pH of the solution to 8.0. Place the beaker in a blast drying oven, set the temperature to 60 °C, and fully dry for 36 h until the weight does not change to remove the moisture in the sample;

[0048] Put the dried sample into a mortar and grind it thoroughly. Pass it through a 100-mesh sieve to obtain particles of 0.15 mm. Put the sieved sample into a boat and calcine it in a tube furnace at 700 °C for 1 h. The protective gas is argon, and the heating rate is 5 °C / min to obtain the modifier;

[0049] (3) Pipette 10 mL of N-methylpyrrolidone (NMP) into a 50 mL beaker. Weigh 0.2 g of polyvinylidene fluoride (PVDF) using an electronic balance and put it into the beaker. Then place a rotor and stir for 1 h until the PVDF is completely dissolved in NMP, obtaining PVDF with a mass fraction of 2%. Weigh 0.6 g of super carbon powder and 0.4 g of the calcined material, put them into the PVDF with a mass fraction of 2% and stir for 3.5 h to obtain the coating material;

[0050] (4) Put the pretreated carbon felt from step (1) into a 50 mL beaker containing the coating material. Place the beaker in an ultrasonic cleaner and ultrasonicate for 10 min to allow the coating material to fully penetrate into the interior of the carbon felt. Then take out the beaker and let it stand for 5 min to allow the coating material to deposit and adhere to the carbon felt. After standing, take out the carbon felt and put it into a petri dish. Place the petri dish in a vacuum drying oven, set the temperature to 60 °C, and vacuum dry for 4.5 h until the weight of the carbon felt no longer changes, obtaining a carbon felt electrode modified with hydroxyl and carboxyl groups.

[0051] In Examples 1 - 3 of the present invention, carbon felt electrode materials modified with hydroxyl and carboxyl groups capable of efficiently recovering nickel are prepared, and the effects are parallel. Below, taking the carbon felt electrode material modified with hydroxyl and carboxyl groups in Example 1 as an example for research, the specific research methods and results are as follows:

[0052] Research method:

[0053] The electro-deposition method for nickel-containing wastewater is as follows: Use a bare carbon felt with a size of 1.7×2.2 cm and a carbon felt electrode material modified with hydroxyl and carboxyl groups as the anode and cathode respectively, and fix them on the electrolytic cell. Pipette 30 mL of a Ni 2+ solution with a concentration of 300 mg / L and 1 mL of HAc-NaAc buffer solution into a 50 mL beaker, place a rotor, and use a function / arbitrary waveform generator DG1000Z as the power supply device. First, rinse the working electrode with ultrapure water, and then deposit nickel on the working electrode to obtain the deposited metallic nickel;

[0054] The Ni 2+ solution to be deposited is a solution obtained by dissolving nickel sulfate hexahydrate in water, where the concentration of nickel element is 300 mg / L, and divalent nickel is the main component;

[0055] The counter electrode and the working electrode are a bare carbon felt and a functional carbon felt modified with hydroxyl and carboxyl groups clamped by platinum electrode clips respectively.

[0056] Adjust the mode of the function / arbitrary waveform generator to the DC mode, and adjust the voltage to 5.5 V. Using this as the power supply, place the beaker in a water bath, heat it in the water bath at 55 °C, adjust the rotation speed to 300 rpm, electrolyze for 2 h. After the electrolysis starts, take 0.1 mL of the electrolyte as a sample every 30 min (including 0 h), and measure the Ni in it by ICP-MS 2+ concentration.

[0057] The following experiments were used to verify the present invention:

[0058] Figure 1 is a graph showing the change of nickel ion removal rate with time. It is a characterization graph of the removal rate of nickel during electrolysis under the application of a 5.5 V DC external voltage. It can be seen from the graph that as the electrolysis time increases, the removal rate of Ni 2+ gradually increases, and after 30 min, the precipitation rate of Ni 2+ becomes slower than before. This is because during the electrolysis process, the concentration of Ni 2+ continually decreases. We can see from the graph that the remaining nickel ions in the electrolyte at 0 min, 30 min, 60 min, 90 min, and 120 min are 287.520 mg / L, 44.748 mg / L, 10.232 mg / L, 5.486 mg / L, and 1.658 mg / L respectively. Thus, it can be found that at a DC voltage of 5.5 V, the removal rate of nickel ions in the solution reaches 99.42%, and the recovery rate of metallic nickel is 71.5%.

[0059] Figure 2 (a) and 2(b) are the scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS) characterization graphs of the nickel deposited on the working electrode after the carbon felt electrodes modified with hydroxyl and carboxyl groups are electrolyzed in the nickel solution for 2 h. Figure 2 (a) shows that at a DC voltage of 5.5 V, many micron-sized heavy metal particles are deposited on the surface of the carbon felt, Figure 2 (b) shows that a lot of heavy metal nickel is deposited on the carbon felt electrode, Figure 2 and the small white dots in (b) are all nickel.

[0060] Figure 3 After the carbon felt electrodes modified with hydroxyl and carboxyl groups are electrolyzed in the nickel solution for 2 h, the chemical properties of the metallic nickel deposited on the working electrode are analyzed by X-ray photoelectron spectroscopy (XPS). As shown in the figure, Ni2p 3 / 2 appearing at 856.30 eV and 860.73 eV, and Ni2p 1 / 2 appearing at 873.82 eV indicate that the nickel deposited on the working electrode is zero-valent nickel, accounting for 71.5%. Ni2p 1 / 2 appearing at 879.93 eV indicates that the nickel deposited on the working electrode is Ni(OH) 2 , accounting for 28.5%.

[0061] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, these changes and variations are also intended to be included.

Claims

1. A preparation method of a hydroxyl- and carboxyl-modified carbon felt electrode, characterized in that, it comprises the following steps: S1. Clean the carbon felt to obtain a pretreated carbon felt; S2. Completely dissolve citric acid, sodium hydroxide, potassium dihydrogen phosphate and calcium oxide in water, adjust the pH of the solution to 6.0 - 8.0, after drying, grinding and sieving, calcine at 300 - 700 °C for 1 - 3 h under an inert atmosphere to obtain a modifier; wherein, the mass ratio of citric acid, sodium hydroxide, potassium dihydrogen phosphate and calcium oxide is 150 - 210:1:15 - 30:30 - 50; S3. Blend the binder, conductive agent and the modifier in step S2 with a solvent together to obtain a coating material; S4. Place the pretreated carbon felt in step S1 into the coating material in step S3, carry out ultrasonic blending, and then dry to constant weight to obtain a hydroxyl- and carboxyl-modified carbon felt electrode; the binder in step S3 is selected from one of polyvinylidene fluoride, polyvinyl fluoride, and polyperfluoroethylene; the conductive agent is selected from one of super carbon powder, conductive graphite, and carbon black; the solvent is selected from one of N-methylpyrrolidone, dimethylacetamide, and methyl ethyl ketone.

2. The preparation method of a hydroxyl- and carboxyl-modified carbon felt electrode according to claim 1, characterized in that, the cleaning method in step S1 is: clean the carbon felt successively with ultrapure water, a nitric acid solution with a mass fraction of 2%, ultrapure water, absolute ethanol, and ultrapure water, and then dry to constant weight to obtain a pretreated carbon felt.

3. The preparation method of a hydroxyl- and carboxyl-modified carbon felt electrode according to claim 1, characterized in that, HAc-NaAc buffer solution is used to adjust the pH in step S2.

4. The preparation method of a hydroxyl- and carboxyl-modified carbon felt electrode according to claim 1, characterized in that, the mass ratio of the conductive agent, binder and modifier in step S3 is 1 - 3:1:2 - 4.

5. The preparation method of a hydroxyl- and carboxyl-modified carbon felt electrode according to claim 1, characterized in that, the ultrasonic conditions in step S4 are: ultrasonic at a frequency of 40 kHz for 5 - 15 min, and carry out static deposition treatment after ultrasonic treatment.

6. A hydroxyl- and carboxyl-modified carbon felt electrode prepared by the preparation method according to any one of claims 1 - 5.

7. An application of the hydroxyl- and carboxyl-modified carbon felt electrode according to claim 6 in the treatment of nickel-containing wastewater and nickel recovery, characterized in that, the application method is: Adopt the electroplating technology, use the hydroxyl- and carboxyl-modified carbon felt electrode as the working electrode, the unmodified carbon felt electrode as the counter electrode, the nickel-containing wastewater as the electrolyte, place the working electrode and the counter electrode into the electrolyte together, and electrically connect them with a DC power supply, and carry out electroplating at a potential of 3 - 6 V for 1 - 2 h to deposit nickel on the surface of the hydroxyl- and carboxyl-modified carbon felt electrode.

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