Preparation method and application of an antioxidant MXene-based flow electrode material for efficient capacitor defluorination

Abstract

This invention discloses a method for preparing and applying an antioxidant MXene-based flow electrode material capable of highly efficient capacitive defluorination, belonging to the field of water treatment technology. The preparation method includes the following steps: sequentially performing nitrogen doping and cysteine ​​modification on MXene to obtain the antioxidant MXene-based flow electrode material capable of highly efficient capacitive defluorination. The MXene is prepared by Lewis acid molten salt etching. The method of this invention effectively improves the electrochemical performance of the MXene electrode, enhances its conductivity, and improves its antioxidant performance by protecting the terminal groups through cysteine ​​modification. The antioxidant MXene-based flow electrode material prepared by this invention has a high specific surface area, large pore volume, and multiple adsorption sites, enabling specific and efficient adsorption of fluoride ions through ion intercalation and special functional groups at the terminal sites.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method for preparing and applying an antioxidant MXene-based flow electrode material that can achieve efficient capacitive defluorination. Background Technology

[0002] Fluoride ions are common pollutants in water bodies. An intake of 0.5–1.0 mg / L is crucial for dental health and can also stimulate bone cell proliferation, promote the absorption and utilization of phosphorus and calcium, accelerate bone formation, and prevent symptoms such as osteoporosis and bone cavities. However, excessive fluoride intake can lead to fluorosis, causing irreversible demineralization of teeth and bone tissue, and may also cause damage to the kidneys, thyroid, brain, and liver.

[0003] Fluorides are characterized by strong ligand interactions and small radii, readily forming numerous diverse inorganic and organic compounds in plants, soil, air, and rocks. Typically, fluorides are found in groundwater and surface water, primarily originating from the release of fluoride ions from fluoride-containing minerals. Natural activities such as wind, rain, and volcanic eruptions promote the release of fluoride ions into soil and groundwater, accumulating over many years to eventually create high-fluoride groundwater.

[0004] Currently, the main methods for defluoridation include coagulation sedimentation, electrodialysis, ion exchange, membrane separation, and adsorption. However, conventional methods for removing fluoride ions from water all have certain limitations. Based on these common processes, some new technologies have emerged, such as induced crystallization and capacitive deionization (CDI) technology. Capacitive deionization technology, also known as electroadsorption, uses highly conductive electrode materials. Due to its large adsorption capacity, continuous ion removal, and high water recovery rate, it has significant advantages over traditional adsorption methods. When using a flowing electrode, a small voltage is applied only between the two current collectors in the CDI system. The flowing electrode is pumped into the electrode compartment and flows between the ion exchange membrane and the corresponding current collector. Ions in the feed water migrate through the ion exchange membrane, enter the flowing electrode, and are ultimately adsorbed onto the suspended carbon material. CDI devices can continuously desalinate high-salinity feedwater without the need for a typical discharge step. The key to capacitive deionization technology is the selection of electrode materials; materials with high conductivity, large specific surface area, and specific active sites should be chosen.

[0005] Chinese patent document CN113354039A discloses an iron-zirconium co-modified titanium dioxide nanotube electrode and its electroadsorption fluoride removal method. The method includes: 1) pretreating a titanium substrate, using a purified titanium plate as the anode and a copper sheet as the counter electrode, using a mixed solution of 0.10-0.20 mol / L NaF and 10-15 wt% H3PO4 as the electrolyte, applying a voltage of 20-25 V, removing the reacted titanium sheet, rinsing it with deionized water and drying it to obtain a titanium dioxide nanotube electrode sample; 2) heat-treating the sample prepared in step 1) and then cooling it to obtain a shaped titanium dioxide nanotube electrode. The heating rate is 3-5 °C / min, and after heating to 400 °C, it is held at that temperature for 1 h; 3) preparing Fe and Zr precursors and uniformly coating them onto the outer surface of the titanium dioxide nanotube electrode prepared in step 2), and calcining it repeatedly 8-10 times after coating to finally obtain the iron-zirconium co-modified titanium dioxide nanotube electrode. However, traditional defluorination electrode materials have low fluoride adsorption capacity, and their preparation is cumbersome, energy-intensive, and has a low recovery rate. Therefore, there is an urgent need to develop a novel flow electrode that is simple to prepare, highly conductive, environmentally friendly, and reusable, thereby enhancing the selective adsorption of fluoride ions in water.

[0006] MXenes are a class of two-dimensional transition metal carbides, nitrides, or carbonitrides with excellent electrical conductivity and hydrophilicity. They can form stable colloidal solutions and are currently capable of large-scale production without performance loss. They have been proposed as useful environmental remediation materials, including heavy metal adsorption, pollutant adsorption, and desalination technologies, and are a viable flow electrode material for capacitor defluorination. However, existing MXenes suffer from poor defluorination efficiency and poor oxidation resistance in capacitor defluorination. Therefore, developing an antioxidant MXene-based flow electrode material that can achieve highly efficient capacitor defluorination would be extremely promising. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing and applying an antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination, so as to solve the problems existing in the prior art.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] One of the technical solutions of the present invention: a method for preparing an antioxidant MXene-based flow electrode material capable of achieving efficient capacitor defluorination, comprising the following steps:

[0010] MXene was sequentially subjected to nitrogen doping and cysteine ​​modification to obtain the antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination.

[0011] Nitrogen doping improves the conductivity of MXene. Modifying nitrogen-doped MXene with cysteine ​​allows the terminal groups on the MXene surface to bond with cysteine, forming coordinate and hydrogen bonds. This protects the terminal groups, preventing MXene from being oxidized by oxygen molecules in water and improving its chemical stability. Nitrogen doping and cysteine ​​modification effectively enhance the adsorption capacity of MXene for fluoride ions.

[0012] Further, the nitrogen doping step includes: dispersing the MXene in an ammonium chloride solution, allowing it to stand to form a colloidal precipitation, then aspirating the supernatant, drying the precipitate, and calcining it to obtain nitrogen-doped MXene.

[0013] The above steps involve electrostatically attracting positively charged ammonium salts into the gaps between MXene layers to achieve nitrogen doping of MXene.

[0014] Further, the concentration of the ammonium chloride solution is 1.0–3.0 mol / L; the ratio of MXene to the ammonium chloride solution is 1.0–2.0 g: 30 mL;

[0015] And / or, the calcination temperature is 450–600°C, and the time is 2–4 hours.

[0016] Furthermore, the settling time is 30 to 90 minutes.

[0017] Furthermore, the calcination is carried out under an argon atmosphere.

[0018] Furthermore, the calcination process also includes washing and drying steps for the calcined product, specifically: washing with water 3 to 5 times, and then drying at 40 to 60°C for 8 to 10 hours.

[0019] Further, the cysteine ​​modification step includes: mixing the nitrogen-doped MXene and the cysteine ​​solution, stirring evenly, adding sodium chloride, and continuing to stir (to ensure that the particles are fully wetted) to obtain the antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination.

[0020] Further, the concentration of the cysteine ​​solution is 0.05–1.0 mol / L; the ratio of nitrogen-doped MXene, cysteine ​​solution, and sodium chloride is 100–250 mg: 30 mL: 15–45 mg.

[0021] Furthermore, the stirring time after mixing the nitrogen-doped MXene and cysteine ​​solution is 1-5 hours; the stirring time after adding sodium chloride is 12-24 hours.

[0022] Furthermore, the stirring speed is 50-100 r / min.

[0023] Furthermore, the MXene is prepared by Lewis acid molten salt etching, and the preparation steps include: mixing the MAX precursor with copper chloride, potassium chloride and sodium chloride to obtain a mixed solid powder; soaking the mixed solid powder in anhydrous ethanol and then calcining it to obtain the MXene.

[0024] MXene prepared by Lewis acid molten salt etching using a fluorine-free method has a large number of terminal groups (Cl-, OH-, etc.) on its surface. When mixed with ammonium chloride solution, it can attract more nitrogen between MXene layers through electrostatic attraction with positively charged ammonium ions.

[0025] Furthermore, the molar ratio of the MAX precursor to copper chloride (CuCl2), potassium chloride (NaCl), and sodium chloride (KCl) is 1:3:2:2;

[0026] And / or, the calcination temperature is 700–750°C, and the time is 8–12 h.

[0027] Furthermore, the MAX precursor is Ti3AlC2.

[0028] Furthermore, the ratio of the mixed solid powder to the anhydrous ethanol is 5g:10-20mL.

[0029] Furthermore, the soaking is carried out under vacuum conditions at 25–30°C for 12–24 hours.

[0030] Furthermore, the calcination is carried out under an argon atmosphere.

[0031] Furthermore, the calcination process further includes washing and drying the calcined product, specifically: first washing with water 3 to 5 times (to remove unreacted substances), then washing with 0.1 mol / L ammonium persulfate solution 3 to 5 times (to remove copper elements displaced by molten salt), then washing with ethanol and pure water 3 times each, and finally vacuum drying at 25 to 30°C for 12 to 24 hours.

[0032] The second technical solution of the present invention: an antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination, prepared according to the above preparation method.

[0033] The third technical solution of the present invention: the application of the above-mentioned antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination in capacitor defluorination.

[0034] Furthermore, the application in capacitor defluorination specifically refers to applying the antioxidant MXene-based flow electrode material to capacitor deionization to remove fluoride ions from water.

[0035] This invention first prepares MXene rich in terminal groups using a fluorine-free method via Lewis acid molten salt etching. Then, it is mixed with ammonium chloride, and through electrostatic attraction with positively charged ammonium ions, the ammonium ions are introduced into the interlayer voids of the MXene, achieving nitrogen doping and thus enhancing the conductivity of the MXene. Subsequently, through bonding with cysteine, coordinate and hydrogen bonds are formed, protecting the terminal groups on the MXene surface, preventing oxidation by oxygen molecules in water, and improving its chemical stability. The method of this invention effectively improves the electrochemical performance of the MXene electrode, enhances its conductivity, and improves its antioxidant properties by protecting the terminal groups through cysteine ​​modification. The antioxidant MXene-based flow electrode material prepared by this invention has a high specific surface area, large pore volume, and multiple adsorption sites, enabling specific and efficient adsorption of fluoride ions through ion intercalation and special functional groups at the terminal sites.

[0036] The preparation method of this invention is simple, and the obtained antioxidant MXene-based flow electrode material has a high adsorption capacity for fluoride ions. It can be used in capacitive deionization technology to achieve efficient removal of fluoride ions from water. Compared with traditional methods, it has great advantages and is suitable for industrial preparation and treatment of actual fluoride-containing wastewater.

[0037] The present invention discloses the following technical effects:

[0038] (1) This invention improves the conductivity of MXene electrode material by nitrogen doping MXene and enhances its chemical stability by using cysteine ​​bonding to protect the surface terminal groups of MXene from oxidation. Finally, a flow electrode material with high conductivity and excellent adsorption performance for fluoride ions is obtained.

[0039] (2) The antioxidant MXene-based flow electrode material of the present invention is based on the ion exchange between fluoride ions and the terminal groups on the surface of the NCMT electrode, the electrostatic attraction of fluoride ions to the MXene sheets through the functional groups on both sides of the terminal, and the redox reaction of titanium atoms in the MXene nanosheets to remove fluoride ions in water. Compared with the traditional capacitive deionization method, the adsorption capacity is greatly improved.

[0040] (3) The antioxidant MXene-based flow electrode material prepared by the present invention has excellent cycling performance. After multiple cycles, it can still achieve a high fluoride removal efficiency. There is no secondary pollution during the process, which is safe, environmentally friendly and energy-efficient.

[0041] (4) The antioxidant MXene-based flow electrode material of the present invention has good ion selectivity and high selectivity for removing fluoride ions, while other common anions in water have no significant effect in the drinking water range.

[0042] (5) The antioxidant MXene-based flow electrode material of the present invention was found to have small mass loss, no toxicity, no secondary pollution problem, and the water quality after treatment met the standards, making it safe and reliable. Attached Figure Description

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 The image shows an SEM image of the antioxidant MXene-based electrode material (0.5NCMT) prepared in Example 1, which can achieve efficient capacitor defluorination. (A) and (B) are images at different magnifications, respectively.

[0045] Figure 2 Infrared spectra of different types of MXene-based flow electrode materials prepared in Example 1 and Comparative Examples 1-2;

[0046] Figure 3 The capacitive defluorination curves of different types of MXene-based flow electrode materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown.

[0047] Figure 4 The capacitance defluorination curves of the antioxidant MXene-based flow electrode material (0.5NCMT) prepared in Example 1 under different initial concentrations of fluoride ion solution conditions;

[0048] Figure 5 The capacitance defluorination curves of the antioxidant MXene-based flow electrode material (0.5NCMT) prepared in Example 1 under different types of interfering ion coexistence conditions;

[0049] Figure 6 The capacitance defluorination curves of the antioxidant MXene-based flow electrode material (0.5NCMT) prepared in Example 1 under different flow rate conditions are shown.

[0050] Figure 7 The capacitance defluorination curves of the antioxidant MXene-based flow electrode material (0.5NCMT) prepared in Example 1 under different applied voltages are shown.

[0051] Figure 8 The graph shows the adsorption performance of fluoride ions after multiple cycles of the antioxidant MXene-based flow electrode material (0.5NCMT) prepared in Example 1.

[0052] Figure 9SEM images of the antioxidant MXene-based electrode material (0.5NCMT) prepared in Example 1, which enables efficient capacitor defluorination, after multiple adsorptions.

[0053] Figure 10 These are antioxidant test images showing the changes in different types of MXene-based flow electrode materials prepared in Example 1 and Comparative Examples 1-2 over time in aqueous solution. Detailed Implementation

[0054] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0055] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0056] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0057] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0058] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0059] As a first aspect of the present invention, the present invention provides a method for preparing an antioxidant MXene-based flow electrode material capable of achieving efficient capacitor defluorination, comprising the following steps:

[0060] MXene was sequentially subjected to nitrogen doping and cysteine ​​modification to obtain the antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination.

[0061] In a preferred embodiment of the present invention, the preparation method includes the following more specific steps:

[0062] (1) Preparation of MXene by Lewis acid molten salt etching: The MAX precursor (Ti3AlC2) was mixed with copper chloride, potassium chloride and sodium chloride to obtain a mixed solid powder; the mixed solid powder was soaked in anhydrous ethanol and then calcined to obtain the MXene (denoted as MS-Ti3C2T). x );

[0063] (2) Nitrogen doping: The MXene was dispersed in an ammonium chloride solution, and after standing to form a colloidal precipitation, the supernatant was aspirated. The precipitate was dried and calcined to obtain nitrogen-doped MXene (denoted as N / MS-Ti3C2T). x );

[0064] (3) Cysteine ​​modification: The nitrogen-doped MXene and cysteine ​​solution were mixed and stirred evenly. Sodium chloride was then added and stirring was continued to obtain the antioxidant MXene-based flow electrode material (denoted as N-Cys / MS-Ti3C2T) that can achieve high-efficiency capacitor defluorination. x ).

[0065] In a preferred embodiment of the present invention, in step (1):

[0066] The molar ratio of the MAX precursor to copper chloride, potassium chloride and sodium chloride is 1:3:2:2;

[0067] The calcination temperature is 700–750℃, and the time is 8–12 hours;

[0068] The ratio of the mixed solid powder to the anhydrous ethanol is 5g:10-20mL;

[0069] The soaking is carried out under vacuum conditions at 25-30°C for 12-24 hours.

[0070] The calcination was carried out under an argon atmosphere;

[0071] After calcination, the product is further subjected to washing and drying steps, specifically: first, it is washed with water 3 to 5 times (to remove unreacted substances), then washed with 0.1 mol / L ammonium persulfate solution 3 to 5 times (to remove copper elements displaced by molten salt), then washed with ethanol and pure water 3 times each, and finally vacuum dried at 25 to 30°C for 12 to 24 hours.

[0072] In a preferred embodiment of the present invention, in step (2):

[0073] The concentration of the ammonium chloride solution is 1.0–3.0 mol / L; the ratio of MXene to the ammonium chloride solution is 1.0–2.0 g: 30 mL.

[0074] The calcination temperature is 450–600℃, and the time is 2–4 hours;

[0075] The settling time is 30 minutes;

[0076] The calcination was carried out under an argon atmosphere;

[0077] The calcination process also includes washing and drying the calcined product, specifically: washing with water 3 to 5 times, and then drying at 40 to 60°C for 8 to 10 hours;

[0078] In a preferred embodiment of the present invention, in step (3):

[0079] The concentration of the cysteine ​​solution is 0.05–0.20 mol / L; the ratio of nitrogen-doped MXene, cysteine ​​solution, and sodium chloride is 100–250 mg: 30 mL: 15–45 mg.

[0080] The stirring time after mixing the nitrogen-doped MXene and cysteine ​​solution is 1 hour; the stirring time after adding sodium chloride is 10-12 hours.

[0081] The stirring speed is 50-100 r / min.

[0082] As a second aspect of the present invention: the present invention provides an antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination, prepared according to the above preparation method.

[0083] As a third aspect of the present invention: The present invention provides the application of the above-mentioned antioxidant MXene-based flow electrode material that enables efficient capacitor defluorination in capacitor defluorination.

[0084] The preparation method and application of the antioxidant MXene-based flow electrode of the present invention will be further described below with reference to specific embodiments.

[0085] All raw materials used in the following examples and comparative examples are commercially available products.

[0086] Example 1

[0087] An antioxidant MXene-based flow electrode material (N-Cys / MS-Ti3C2T) capable of achieving efficient capacitor defluorination x The preparation of NCMT (non-NCMT) involves the following steps:

[0088] (1) Preparation of MXene by Lewis acid molten salt etching: 1.125 g of MAX precursor (Ti3AlC2) and 2.380 g of copper chloride were mixed and added to an agate mortar and ground for 10 min. Then, 0.865 g of potassium chloride and 0.675 g of sodium chloride were added to the agate mortar and ground for 20 min to obtain a mixed solid powder. The molar ratio of the four solid materials was 1:3:2:2. The mixed solid powder was then poured into a 10×12 cm corundum crucible, leveled, and 10 mL of anhydrous ethanol was added to immerse the mixed solid powder. The corundum crucible was then immersed in vacuum at 30 °C for 24 h. After immersion, it was calcined at 700 °C for 10 h under an argon atmosphere at a heating rate of 5 °C / min. After cooling, the obtained solid was ground for 10 minutes, washed three times with pure water to remove unreacted substances, then washed five times with 0.1 mol / L ammonium persulfate solution to remove copper displaced by the molten salt. It was then washed three times each with ethanol and pure water, and finally centrifuged. The resulting solid was dried at 25°C under vacuum for 24 hours to obtain MS-Ti3C2T. x .

[0089] (2) Nitrogen doping: 2.0 g MS-Ti3C2T was doped under a nitrogen atmosphere. x The precipitate was added to 30 mL of 1.5 mol / L ammonium chloride solution and allowed to stand for 30 min, resulting in a colloidal precipitation. The supernatant was carefully aspirated, and the remaining precipitate was dried under vacuum at room temperature for 24 h. It was then transferred to a 5 × 6 cm corundum crucible and calcined at 600 °C for 4 h under an argon atmosphere at a heating rate of 5 °C / min. After cooling, the resulting solid was ground for 5 min and washed five times with pure water to remove unreacted impurities. Finally, it was centrifuged, and the resulting solid was dried under vacuum at 40 °C for 10 h to obtain N / MS-Ti3C2T. x .

[0090] (3) Cysteine ​​modification: 250 mg N / MS-Ti3C2T x The solution was added to 30 mL of 0.5 mol / L cysteine ​​solution, stirred at 100 r / min for 1 h at room temperature, and then 30 mg of sodium chloride was added as electrolyte. The mixture was stirred continuously for 24 h to ensure that the particles were fully wetted, thus obtaining the flow electrode material 0.5 NCMT.

[0091] Example 2

[0092] Same as Example 1, except that the 30 mL 0.5 mol / L cysteine ​​solution in step (3) is replaced with 30 mL 0.2 mol / L cysteine ​​solution to obtain the flow electrode material 0.2NCMT.

[0093] Example 3

[0094] Same as Example 1, except that the 30 mL 0.5 mol / L cysteine ​​solution in step (3) is replaced with 30 mL 1.0 mol / L cysteine ​​solution to obtain the flow electrode material 1.0NCMT.

[0095] Comparative Example 1

[0096] Same as Example 1, except that nitrogen doping in step (2) and cysteine ​​modification in step (3) are not performed. The MXene obtained by etching with Lewis acid molten salt in step (1), namely MS-Ti3C2T, is obtained instead. x As a flow electrode material.

[0097] Comparative Example 2

[0098] Same as Example 1, except that the cysteine ​​modification in step (3) is not performed, and the nitrogen-doped MXene-based electrode material obtained in step (2), namely N / MS-Ti3C2T, is used instead. x As a flow electrode material.

[0099] Comparative Example 3

[0100] Same as Example 1, except that nitrogen doping in step (2) is not performed, and 2.0g of MS-Ti3C2T obtained by etching with Lewis acid molten salt in step (1) is directly taken. x The cysteine ​​modification in step (3) was performed to obtain Cys / MS-Ti3C2T x (abbreviated as CMT) is used as a flow electrode material.

[0101] Test Example 1

[0102] Characterization of flow electrode materials

[0103] Figure 1 SEM images of the antioxidant MXene-based electrode material (0.5NCMT) prepared in Example 1, which enables efficient capacitor defluorination, are shown. (A) and (B) are images at different magnifications. Figure 1 It can be seen that the prepared 0.5NCMT electrode material exhibits a typical multilayer accordion structure of MXene materials, with large interlayer spacing and a two-dimensional lamellar structure. Under magnification, cysteine ​​particles can be clearly observed in N / MS-Ti3C2T x The uniform doping on the material surface proves that 0.5NCMT was successfully prepared.

[0104] Figure 2 The infrared spectra of the flow electrode materials prepared in Examples 1 and 1-2 are shown below. Figure 2It can be known that MS-Ti3C2T x The material is 1398cm -1 Ti-O peaks were observed at 3100 cm⁻¹. -1 An OH peak was observed at the point, indicating typical MS-Ti3C2T x MXene was successfully prepared; after nitrogen doping, it showed significant improvement at 3400 cm⁻¹. -1 A sharp NH peak was observed at 990 cm⁻¹. -1 The observation of N-Ti peaks at this location indicates that N / MS-Ti3C2T x Preparation was successful; and after compounding with cysteine ​​particles, it can be processed at 670 cm⁻¹. -1 The observation of Ti-S peaks indicates that Ti atoms in MXene coordinate with S atoms in cysteine, proving the successful preparation of NCMT electrode material.

[0105] Application Example 1

[0106] This application example is used to examine the performance of the flow electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 in the field of capacitor defluorination. The specific process and results are as follows:

[0107] Using 30±0.2 mL of mobile electrode material as the electrode in the FCDI system, a peristaltic pump was controlled to adjust the electrode material flow rate to 40 mL / min. A constant voltage of 1.2 V was applied between the graphite manifolds to form an electroadsorption defluorination assembly. A 10 mg / L sodium fluoride aqueous solution (calculated as F-) was used as simulated wastewater, with a treatment volume of 50 mL, in a 100 mL beaker. The capacitive defluorination data of the mobile electrode material were obtained, such as... Figure 3 As shown. Analysis yielded MS-Ti3C2T x N / MS-Ti3C2T x The removal efficiencies of CMT, 0.2NCMT, 0.5NCMT and 1.0NCMT for fluoride ions at 60 min, CMT, MS-Ti3C2T x and N / MS-Ti3C2T x The fluoride removal efficiencies of the three MXenes were all below 90% (61.5%, 66.4%, and 88.5%, respectively), failing to meet the acceptable level of the national standard (<1.0 mg / L). However, the fluoride removal efficiencies of 0.2NCMT, 0.5MTPA, and 1.0NCMT reached 92.6%, 98.1%, and 94.3%, respectively, successfully removing conventionally concentrated fluoride wastewater to below the national standard. This demonstrates that after nitrogen doping and cysteine ​​modification, a suitable loading can significantly enhance the fluoride ion adsorption capacity of MXene, showing potential for practical application in the removal of fluoride ions from water.

[0108] Application Example 2

[0109] This application example examines the capacitive defluorination performance of the antioxidant MXene-based flow electrode material prepared in Example 1 under different initial concentrations of fluoride ion solution. The specific process and results are as follows:

[0110] Using 30±0.2 mL of mobile electrode material as the electrode in the FCDI system, a peristaltic pump was controlled to adjust the flow rate of the mobile electrode material to 40 mL / min. A constant voltage of 1.2 V was applied between the graphite manifolds to form an electroadsorption defluorination assembly. Capacitive defluorination was performed using 5, 10, 30, 50, and 100 mg / L sodium fluoride aqueous solutions (calculated as F⁻) as simulated wastewater, with a treatment volume of 50 mL in each 100 mL beaker. The capacitive defluorination data of the mobile electrode material were obtained, such as... Figure 4 As shown, sodium fluoride aqueous solutions with initial concentrations of 5, 10, 30, 50, and 100 mg / L were subjected to electroadsorption for 120 min, and the fluoride concentrations were reduced to 0.15, 0.32, 5.33, 13.56, and 22.27 mg / L, respectively. This indicates that the 0.5 NCMT electrode prepared in Example 1 can achieve short-time and efficient removal of fluoride ions from aqueous solutions and has a wide applicable range of concentration gradients.

[0111] Application Example 3

[0112] This application example is used to examine the capacitive defluorination performance of the antioxidant MXene-based flow electrode material prepared in Example 1 under different types of interfering ions. The specific process and results are as follows:

[0113] Using 30±0.2 mL of flowing electrode material as the electrode in the FCDI system, a peristaltic pump was controlled to adjust the flow rate of the flowing electrode material to 40 mL / min. A constant voltage of 1.2 V was applied between the graphite manifolds to form an electroadsorption defluorination assembly. A 50 mg / L sodium fluoride aqueous solution (as F...) was used... - (Calculation) To simulate wastewater, different types of interfering ions (Cl-, NO3-) were added at the same molar concentration (50 mg / L). - SO4 2- PO4 3- The process volume was 50 mL, carried out in a 100 mL beaker, and the capacitive defluorination data of the flow electrode material was obtained, such as... Figure 5 As shown. At the same concentration of interfering ions and fluoride ions, even PO4, which has the greatest interference with the selective adsorption of fluoride ions, [is affected]. 3- Under coexisting conditions, the 0.5 NCMT flow electrode still achieves a fluoride ion removal efficiency of over 50%, while the Cl- electrode, which has minimal interference with the selective adsorption of fluoride ions, remains effective. - Under the coexistence conditions, the NCMT electrode can remove fluoride ions at an efficiency of up to 80%, proving that the NCMT electrode has excellent selective fluoride ion removal performance.

[0114] Application Example 4

[0115] This application example is used to investigate the capacitive defluorination performance of the antioxidant MXene-based flow electrode material prepared in Example 1 under different flow rate conditions. The specific process and results are as follows:

[0116] Using 30±0.2 mL of flowing electrode material as the electrode in the FCDI system, a constant voltage of 1.2 V was applied between the graphite current collectors to form an electro-adsorption defluorination assembly. A 10 mg / L sodium fluoride aqueous solution (as F...) was used... - To simulate wastewater for capacitive defluorination, multiple experiments were conducted by controlling a peristaltic pump to adjust the flow rate of the mobile electrode material to 20, 30, 40, 50, and 60 mL / min. The simulated wastewater volume was 50 mL, and the experiments were carried out in 100 mL beakers. The capacitive defluorination data of the mobile electrode material were obtained. Figure 6 As shown, within the flow rate range of 20-40 mL / min, the fluoride ion removal efficiency gradually increases with increasing flow rate. However, as the test flow rate exceeds 40 mL / min, the fluoride ion removal efficiency decreases instead of increasing. Considering both energy consumption and fluoride removal efficiency, 40 mL / min is selected as the optimal flow rate for the 0.5 NCMT flow electrode.

[0117] Application Example 5

[0118] This application example is used to examine the capacitive defluorination performance of the antioxidant MXene-based flow electrode material prepared in Example 1 under different applied voltages. The specific process and results are as follows:

[0119] Using 30±0.2 mL of flowing electrode material as the electrode in the FCDI system, a peristaltic pump was controlled to adjust the flow rate of the flowing electrode material to 40 mL / min. A constant voltage was applied between the graphite manifolds to form an electroadsorption defluorination assembly. A 10 mg / L sodium fluoride aqueous solution (as F...) was used... - To simulate wastewater for capacitive defluorination, multiple sets of experiments were conducted by applying constant voltages of 0.4, 0.8, 1.0, 1.2, and 1.6 V between graphite current collectors. The simulated wastewater volume was 50 mL, and the experiments were carried out in 100 mL beakers. The capacitive defluorination data of the flow electrode material were obtained. Figure 7As shown, at voltages of 0.4, 0.8, 1.0, 1.2, and 1.6 V, the 0.5 NCMT flow electrode can remove sodium fluoride ions from an initial concentration of 10 mg / L to 4.65, 3.45, 2.34, 0.74, and 0.45 mg / L within 60 min, respectively. This demonstrates that the removal capacity of the NCMT flow electrode gradually increases with increasing applied voltage. Considering that both 1.2 V and 1.6 V can remove fluoride ions to below 1.0 mg / L (an acceptable level), and that 1.2 V results in lower energy consumption, 1.2 V is chosen as the optimal operating voltage for the 0.5 NCMT flow electrode.

[0120] Application Example 6

[0121] This application example is used to examine the capacitive defluorination performance of the antioxidant MXene-based flow electrode material prepared in Example 1 under multiple cycle experiments. The specific process and results are as follows:

[0122] Using 30±0.2 mL of flowing electrode material as the electrode in the FCDI system, a peristaltic pump was controlled to adjust the flow rate of the flowing electrode material to 40 mL / min. A constant voltage of 1.2 V was applied between the graphite manifolds to form an electroadsorption defluorination assembly. A 10 mg / L sodium fluoride aqueous solution (as F...) was used... - The simulated wastewater (50 mL) was used for the electro-adsorption defluorination process. After one electro-adsorption defluorination experiment, the circulating water in the FCDI system was drained, and a new simulated fluoride-containing wastewater of the same concentration was added as the next cycle for electro-adsorption defluorination. The results are as follows. Figure 8 As shown, after 20 cycles of defluorination experiments, the 0.5NCMT flow electrode still maintained a high removal efficiency of over 85%, demonstrating that the 0.5NCMT flow electrode has excellent cyclic defluorination performance and chemical stability.

[0123] Figure 9 The images shown are SEM images of the antioxidant MXene-based electrode material prepared in Example 1 after multiple (20 cycles) adsorption processes. Figure 9 It can be seen that the 0.5NCMT flow electrode still has a two-dimensional sheet structure and the structure is intact, indicating that it has chemical stability and antioxidant properties in aqueous solution, and has good recycling performance when used for defluorination of capacitors.

[0124] Test Example 2

[0125] Antioxidant performance test of flow electrode material

[0126] Figure 10These are images showing the antioxidant properties of different types of MXene-based flow electrode materials prepared in Examples 1 and Comparative Examples 1-2 over time in aqueous solution. The concentration of the electrode materials in the aqueous solution was 0.1 mg / L, and the test temperature was 25°C. Figure 10 It can be seen that the MS-Ti3C2T of Comparative Example 1 x After being stored in water for only 60 days, the solution gradually became transparent, indicating that the pure MS-Ti3C2T x It lacks antioxidant capacity; Comparative Example 2 N / MS-Ti3C2T x After being stored in water for 120 days, the solution remained mostly transparent, indicating that N / MS-Ti3C2T x Most of it had been oxidized; while the 0.5NCMT in Example 1 remained dark black after being stored in water for 120 days, indicating that 0.5NCMT exhibited good chemical stability.

[0127] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing an antioxidant MXene-based flow electrode material capable of achieving efficient capacitor defluorination, characterized in that, Includes the following steps: MXene was sequentially subjected to nitrogen doping and cysteine ​​modification to obtain the antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination. The nitrogen doping step includes: dispersing the MXene in an ammonium chloride solution, allowing it to stand to form a colloidal precipitation, then aspirating the supernatant, drying the precipitate, and calcining it to obtain nitrogen-doped MXene; The concentration of the ammonium chloride solution is 1.0~3.0 mol / L; the ratio of MXene to the ammonium chloride solution is 1.0~2.0 g:30 mL; The calcination temperature is 450~600 ℃, and the time is 2~4 h; The cysteine ​​modification step includes: mixing the nitrogen-doped MXene and cysteine ​​solution, stirring evenly, adding sodium chloride, and continuing to stir to obtain the antioxidant MXene-based flow electrode material that can achieve efficient capacitor defluorination. The concentration of the cysteine ​​solution is 0.05~1.0 mol / L; the ratio of nitrogen-doped MXene, cysteine ​​solution, and sodium chloride is 100~250 mg:30 mL:15~45 mg.

2. The preparation method according to claim 1, characterized in that, The stirring time after mixing the nitrogen-doped MXene and cysteine ​​solution is 1-5 h; the stirring time after adding sodium chloride is 12-24 h.

3. The preparation method according to claim 1, characterized in that, The MXene was prepared by Lewis acid molten salt etching. The preparation steps included: mixing the MAX precursor with copper chloride, potassium chloride and sodium chloride to obtain a mixed solid powder; soaking the mixed solid powder in anhydrous ethanol and then calcining it to obtain the MXene.

4. The preparation method according to claim 3, characterized in that, The molar ratio of the MAX precursor to copper chloride, potassium chloride, and sodium chloride is 1:3:2:2; And / or, the calcination temperature is 700~750 ℃, and the time is 8~12 h.

5. An antioxidant MXene-based flow electrode material capable of achieving efficient capacitor defluorination, prepared by the method described in any one of claims 1-4.

6. The application of the antioxidant MXene-based flow electrode material as described in claim 5, which enables efficient capacitor defluorination, in capacitor defluorination.

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