Antioxidation method based on pH response type MXenes and application thereof

Abstract

The invention discloses an anti-oxidation method based on pH response type MXenes and application of the anti-oxidation method, and belongs to the technical field of two-dimensional nanomaterials, and the anti-oxidation method specifically comprises the step that in an MXenes suspension, anti-oxidation end capping of MXenes is achieved only by adding a metal ion-polyphenol organic matter complex and controlling the pH value to be 3-6. On the basis, when the MXenes need to be applied, the alkaline solution is added to adjust the pH value to be not smaller than 7, the MXenes maintaining the intrinsic characteristics can be separated out, the whole process is low in cost, the problem that a reducing agent is difficult to remove is solved, the universality is high, and the intrinsic characteristics of the MXenes can be maintained for more than 3 years.

Description

Technical Field

[0001] The present invention belongs to the technical field of two-dimensional nanomaterials, and particularly relates to a pH-responsive MXenes antioxidant method and its application. Background Art

[0002] MXenes refer to a new type of graphene-like two-dimensional transition metal carbides / nitrides, and their basic chemical formula is M n+ 1X n T x (n = 1 - 3), where M is a transition metal (one or more combinations of Sc, Ti, Mo, etc.), X is C or N, and T represents surface functional groups (such as -OH, -F, -O, etc.). MXenes nanosheets have a large specific surface area and unique electronic, mechanical, optical, and magnetic properties, and have good application prospects in energy storage, catalysis, electromagnetic shielding, optoelectronics, sensors, biomedicine, etc. However, the easy oxidation of MXenes during storage is a bottleneck problem, which limits their large-scale synthesis and practical applications.

[0003] MXenes have a large number of defects and edges, and the exposure of a large number of highly active transition metal M atoms causes MXenes to be in a thermodynamically metastable state. Therefore, MXenes are easily oxidized to form oxides of transition metal M and amorphous carbon, resulting in changes in material composition, structural collapse, and rapid deterioration of physical and chemical properties. Improving the antioxidant performance of MXenes is the basis for their large-scale synthesis and application.

[0004] Currently, the methods for improving the antioxidant properties of MXenes are mainly divided into two types: physically isolating oxidants and reducing oxidation kinetics. The physical isolation of oxidants method includes, but is not limited to: low-temperature preservation in inert gas, preservation in organic solutions, surface coating, addition of reducing agents. The method of reducing oxidation kinetics includes, but is not limited to: heat treatment in a reducing or inert atmosphere to obtain a structurally dense MXenes film, synthesis of MXenes in Lewis acid molten salts (>500 °C). Although the above antioxidant methods can effectively prevent the oxidation of MXenes, problems such as high energy consumption caused by low-temperature preservation and high-temperature heat treatment, complex surface coating processes, high costs of organic solvents, and difficulty in removing reducing agents limit the practical applications of the above methods. The preparation and use of MXenes often occur in aqueous solutions, and preservation in aqueous solutions can effectively reduce the material preparation and use costs, which is beneficial to the large-scale production and subsequent practical applications of MXenes. How to improve the antioxidant performance of MXenes in aqueous solutions without damaging their intrinsic physical and chemical properties is extremely urgent. Summary of the Invention

[0005] In view of the above, the object of the present invention is to provide a pH-responsive MXenes antioxidant method and its application, which can achieve low-cost and universal prevention of MXenes oxidation and can maintain the intrinsic properties of MXenes for a long time.

[0006] To achieve the above object of the invention, a pH-responsive MXenes antioxidant method provided by an embodiment includes the following steps: Dissolve divalent or trivalent metal salts and polyphenolic organic compounds in deionized water according to a molar ratio of 1:(0.8 - 1.3) or 1:(1.8 - 2.3) respectively, add an acid solution with the same anion as the metal salt and adjust the pH to 3 - 6, mix and stir the metal salt solution and the polyphenolic organic compound solution to prepare a metal ion-polyphenolic organic compound complex solution; Use an acid solution with the same anion as the metal salt to adjust the pH of the MXenes suspension to the same value as that of the metal ion-polyphenolic organic compound complex solution. Then add the metal ion-polyphenolic organic compound complex and stir evenly, and add a certain amount of polyphenolic organic compound so that the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic compound in the resulting mixed solution is 1:(2 - 2.2) or 1:(3 - 3.2) to achieve antioxidant capping of MXenes; Add an alkaline solution to the mixed solution and adjust the pH to not less than 7, then centrifuge and separate to obtain MXenes that maintain their intrinsic properties.

[0007] The functional groups on the surface of MXenes can maintain their structural stability to a certain extent. The transition metal M atoms at the edges and surface defects are usually unstable due to incomplete bonding. These highly active M atoms are prone to nucleate and form transition metal oxide particles when interacting with water and / or oxygen molecules. The present invention first prepares an unsaturated coordinated metal ion-polyphenolic organic compound complex, and uses the metal ions to occupy the positions of the transition metal M atoms at the edges and surface defects for capping. The subsequently added polyphenolic organic compound has two functions: 1. Part of the polyphenolic organic compound can act as an organic ligand. When the solution pH reaches 7 or above, it can form a saturated coordinated solid metal ion-polyphenolic organic compound complex with the unsaturated coordinated metal ion-polyphenolic organic compound complex and is then separated; 2. At the same time, another part of the polyphenolic organic compound acts as a reducing agent, which can effectively remove the dissolved oxygen in the aqueous solution and avoid the oxidation of MXenes by the dissolved oxygen in the water.

[0008] When the molar ratio of divalent or trivalent metal salt to polyphenolic organic matter is less than 1:2 or 1:3, adjusting the pH of the solution with alkali will not enable the complete coordination of the metal ion-polyphenolic organic matter complex to form, which will result in the existence of some incompletely coordinated metal ion-polyphenolic organic matter complexes in the MXenes solution. When the molar ratio of divalent or trivalent metal salt to polyphenolic organic matter is greater than 1:2.2 or 1:3.2, although adjusting the pH of the solution with alkali can transform the metal ion-polyphenolic organic matter complex from incomplete coordination to complete coordination and remove it by centrifugation, after centrifugation, there will still be some polyphenolic organic matter in the MXenes suspension, which will affect the manifestation of the intrinsic properties of MXenes in subsequent applications.

[0009] When the pH of the MXenes suspension is less than 3, MXenes is more likely to be oxidized under strong acidic conditions. Therefore, the pH of the MXenes suspension is restricted to be greater than or equal to 3.

[0010] The intrinsic properties of MXenes include high conductivity, tunable surface chemistry and layered structure. Its rich surface functional groups and fast ion diffusion channels enable it to exhibit high specific capacity and cycle stability in lithium-ion batteries, and at the same time, high power density and long cycle life can be achieved in supercapacitors.

[0011] Preferably, when a divalent metal salt is used, the pH of the divalent metal salt solution and the polyphenolic organic matter solution is adjusted to 4-6.

[0012] Preferably, when a trivalent metal salt is used, the pH of the trivalent metal salt solution and the polyphenolic organic matter solution is adjusted to 5-6.

[0013] Preferably, the polyphenolic organic matter includes catechol or ellagic acid.

[0014] Preferably, the divalent or trivalent metal salt includes iron salt, cobalt salt or nickel salt.

[0015] Preferably, the centrifugation conditions are: the rotation speed is less than 3500 rpm and the time is less than 1 h.

[0016] Preferably, the trivalent metal salt is iron salt, the polyphenolic organic matter is catechol, the pH of the metal ion-polyphenolic organic matter complex is 5, and the molar ratio of iron salt to catechol in the mixed solution is 1:3.05.

[0017] Preferably, the divalent metal salt is nickel salt, the polyphenolic organic matter is catechol, the pH of the metal ion-polyphenolic organic matter complex is 4, and the molar ratio of nickel salt to catechol in the mixed solution is 1:2.05.

[0018] The embodiment also provides an application of MXenes in lithium batteries. The MXenes maintaining the intrinsic properties prepared by the above method are fabricated into a flexible film and used as an electrode of a lithium-ion battery.

[0019] The embodiment also provides an application of MXenes in supercapacitors. The MXenes maintaining the intrinsic properties prepared by the above method are fabricated into a flexible film and used as an electrode of a supercapacitor.

[0020] Compared with the prior art, the beneficial effects of the present invention at least include: In the antioxidant of MXenes of the present invention, only by adding a metal ion-polyphenolic organic complex and controlling the pH value to be 3-6, the antioxidant capping of MXenes can be achieved. On this basis, when application is required, by adding an alkaline solution to simply adjust the pH, the MXenes maintaining the intrinsic properties can be separated out. The whole process has low cost, avoids the problem of difficult removal of reducing agents, has strong universality, and enables the intrinsic properties of MXenes to be maintained for more than 3 years. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 It is a flowchart of a pH-responsive MXenes antioxidant method provided by the embodiment; Figure 2 Shows the Raman spectrum comparison diagram of three Ti3C2T x samples in the embodiment: Figure 3 It is the X-ray photoelectron spectroscopy (XPS) full-spectrum comparison diagram of three Ti3C2T x samples provided by the embodiment; Figure 4 It is the high-resolution XPS spectrum comparison diagram of Ti 2p of three Ti3C2T x samples provided by the embodiment; Figure 5 It is the scanning electron microscope (SEM) diagram of Ti3C2T x -original sample provided by the embodiment; Figure 6 It is the SEM diagram of Ti3C2T x -oxidized sample provided by the embodiment; Figure 7The Ti3C2T provided by the embodiment x - SEM image of the regenerated sample; Figure 8 The Ti3C2T provided by the embodiment x - Cross-sectional SEM image of the flexible film of the original sample; Figure 9 The Ti3C2T provided by the embodiment x - Cross-sectional SEM image of the flexible film of the regenerated sample; Figure 10 The Ti3C2T provided by the embodiment x - Electrochemical impedance spectroscopy of the original sample; Figure 11 The Ti3C2T provided by the embodiment x - Electrochemical impedance spectroscopy of the oxidized sample; Figure 12 The Ti3C2T provided by the embodiment x - Electrochemical impedance spectroscopy of the regenerated sample; Figure 13 The Ti3C2T provided by the embodiment x Charge-discharge performance diagram of the flexible film sample as the positive electrode of a lithium battery (lithium sheet as the negative electrode); Figure 14 The Ti3C2T provided by the embodiment x - Charge-discharge performance diagram of the oxidized sample as the positive electrode of a lithium battery (lithium sheet as the negative electrode); Figure 15 The Ti3C2T provided by the embodiment x - Charge-discharge performance diagram of the regenerated flexible film sample as the positive electrode of a lithium battery (lithium sheet as the negative electrode); Figure 16 The Ti3C2T provided by the embodiment x - Original flexible film, Ti3C2T x - Oxidized and Ti3C2T x - Cyclic performance diagram of the three samples of the original flexible film, Ti3C2T Figure 17 The Ti3C2T regenerated after 3 years of anti-oxidation of Ni-catechol provided by the embodiment x - SEM image of the regenerated sample; Figure 18 The Ti3C2T regenerated after 3 years of anti-oxidation of Co-catechol provided by the embodiment x - SEM image of the regenerated sample. Detailed implementation mode

[0023] To make the objectives, technical solutions, and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0024] An antioxidant method for pH-responsive MXenes is provided in the embodiment, as Figure 1 shown, including the following steps: Step 1: Dissolve divalent or trivalent metal salts and polyphenolic organic compounds in deionized water according to a molar ratio of 1:(0.8 - 1.3) or 1:(1.8 - 2.3) respectively. Add an acid solution with the same anion as the metal salt to adjust the pH to 3 - 6. Mix and stir the above metal salt solution and polyphenolic organic compound solution to prepare a metal ion-polyphenolic organic compound complex solution; Among them, when using divalent metal salts, the pH of the divalent metal salt solution and the polyphenolic organic compound solution is adjusted to 4 - 6. When using trivalent metal salts, the pH of the trivalent metal salt solution and the polyphenolic organic compound solution is adjusted to 5 - 6. The polyphenolic organic compounds include catechol or ellagic acid, etc. The divalent or trivalent metal salts include iron salts, cobalt salts, or nickel salts.

[0025] Step 2: Use an acid solution with the same anion as the metal salt to adjust the pH of the MXenes suspension to the same as that of the metal ion-polyphenolic organic compound complex solution. Then add the metal ion-polyphenolic organic compound complex and stir evenly. Add a certain amount of polyphenolic organic compound so that the molar ratio of the divalent or trivalent metal salt to the polyphenolic organic compound in the resulting mixed solution is 1:(2 - 2.2) or 1:(3 - 3.2), realizing the antioxidant capping of MXenes; Step 3: Add an alkaline solution to the mixed solution and adjust the pH to not less than 7, then centrifuge and separate to obtain MXenes maintaining their intrinsic properties.

[0026] Based on the above MXenes antioxidant method, taking Ti3C2T x as a typical representative of MXenes, the following specific examples are carried out to detail the pH-responsive MXenes antioxidant method and the corresponding performance. Among them, the layered Ti3C2T x is prepared by etching Ti3AlC2 with LiF and HCl solutions.

[0027] Example 1

[0028] Select Fe(NO3)3 as the trivalent metal salt, catechol as the polyphenolic organic compound, HNO3 as the acid solution, and NaOH solution as the alkaline solution. Then the corresponding MXenes antioxidant method is: First, Fe(NO3)3 and catechol were separately dissolved in deionized water at a molar ratio of 1:2, and a certain amount of HNO3 was added to adjust the pH of the solution to 5. Then, the two were mixed and stirred to prepare an Fe-catechol complex; then, the pH of the suspension of Ti3C2T x was also adjusted to 5 with HNO3, and the above Fe-catechol complex was added, stirred until homogeneous, and then a certain amount of catechol was added and stirred until homogeneous, so that the molar ratio of Fe(NO3)3 to catechol in the resulting mixed solution was 1:3.05; finally, NaOH solution was added to the mixed solution and the pH was adjusted to 7, and then centrifuged at 3500 rpm for 10 min. The upper layer was the suspension of Ti3C2T x , and the lower layer was the Fe-catechol complex. The Ti3C2T x maintaining its intrinsic properties was separated.

[0029] The freshly prepared Ti3C2T x was labeled as Ti3C2T x -original, and the Ti3C2T x naturally oxidized in aqueous solution for 3 years was labeled as Ti3C2T x -oxidized, and the Ti3C2T x regenerated by antioxidant protection with Fe-catechol organic complex for 3 years and removal of the complex by pH adjustment was labeled as Ti3C2T x -regenerated, collectively referred to as the three samples.

[0030] From the Raman spectrum comparison diagrams of the three samples as Figure 2 shown, all Ti in the oxidized Ti3C2T x was oxidized to TiO2, while the Ti3C2T x protected by Fe-catechol organic complex could still maintain its original functional groups and chemical states, and no TiO2 was formed. From the XPS full spectrum comparison diagrams of the three samples as Figure 3 shown, the oxygen content in the oxidized Ti3C2T x increased significantly, much higher than that in the original Ti3C2T x . Further, as Figure 4 shown, the Ti 2p element in each sample was analyzed. Only a small amount of Ti(iv) existed in the newly prepared and regenerated Ti3C2T x . After 3 years of natural oxidation in the water environment, all Ti in the Ti3C2T x had been oxidized to TiO2.

[0031] Further, SEM characterization was also carried out on the three samples. From Figure 5It can be seen that the newly prepared original Ti3C2T x has a typical two-dimensional layered structure. From Figure 6 it can be seen that after oxidation, Ti3C2T x shows a nanos shuttle-like structure. From Figure 7 it can be seen that Ti3C2T protected by Fe-catechol complex x can still restore the typical two-dimensional layered structure after removing the Fe-catechol complex.

[0032] Furthermore, the newly prepared and regenerated Ti3C2T x was filtered into a film by suction filtration, and the cross-section of the film was characterized by SEM, as shown in Figure 8 and Figure 9 respectively. It can be seen from the cross-section SEM of the two samples that both materials can be filtered into films well and both have good layered structures. After oxidation, Ti3C2T x has all been converted into TiO2 and cannot be filtered into a film. Therefore, the cross-section SEM image of the Ti3C2T x -oxide film is not given here.

[0033] Furthermore, the impedance spectra of Ti3C2T x -original, Ti3C2T x -oxide and Ti3C2T x -regenerated three samples were measured, as shown in Figure 10 , Figure 11 , Figure 12 respectively. It can be seen from the impedance spectra that the charge transfer resistances of Ti3C2T x -original, Ti3C2T x -oxide and Ti3C2T x -regenerated are 50 Ω, 154000 Ω and 70 Ω respectively. The original Ti3C2T x itself has excellent conductivity and shows a small charge transfer resistance on the impedance spectrum. Ti3C2T x is oxidized to form TiO2, which will greatly reduce its conductivity. Correspondingly, its charge transfer resistance increases. Therefore, the greater the charge transfer resistance of Ti3C2T x , the higher the degree of oxidation of the material. It can be seen that the charge transfer resistance of the regenerated Ti3C2T protected by Fe-catechol x is still very small, indicating that it is hardly oxidized. The above results are consistent with the conclusions obtained from the Raman spectra ( Figure 2 ), XPS spectra ( Figure 3 and Figure 4 ) and SEM images ( Figure 5 , Figure 6 , Figure 7 ) of the three samples.

[0034] Application Example 1 Filter the Ti3C2T x - pristine and Ti3C2T x - regenerated samples into flexible films. Filter the Ti3C2T x - oxidized sample is fully mixed with a binder and a conductive agent and then coated on a copper foil to prepare an electrode. Use the above flexible film and the electrode with the copper foil as the current collector as the positive electrode of a lithium-ion battery (the lithium sheet is the negative electrode), and test its lithium storage performance. From Figure 13 , Figure 14 , Figure 15 it can be seen that Ti3C2T x - pristine and Ti3C2T x - regenerated have excellent rate performance. When the charging current increases from 1 A / g to 5 A / g, the charge-discharge specific capacity changes little, and during the entire rate performance test, the Coulomb efficiency of the material changes little. Then, regarding the rate performance of Ti3C2T x - oxidized, as the charging current increases, its charge-discharge specific capacity decreases rapidly, showing poor rate performance, which is related to the sharp increase in the charge transfer resistance after the material is oxidized.

[0035] Application Example 2 Filter the Ti3C2T x - pristine and Ti3C2T x - regenerated samples into flexible films. Filter the Ti3C2T x - oxidized sample is fully mixed with a binder and a conductive agent and then coated on nickel foam to prepare an electrode. Use the above flexible film and the electrode with nickel foam as the carrier and current collector as the electrode of a supercapacitor, and test the cyclic performance by measuring the voltammetric curves of each sample at a scan rate of 100 mV / s. The results are as Figure 16 shown. After 20,000 cycles, the capacity retention rates of Ti3C2T x - pristine and Ti3C2T x - regenerated samples are 98.5% and 98.0% respectively. While the capacity retention rate of the Ti3C2T x - oxidized sample drops from the initial 100% to 67.0%. The above results indicate that Ti3C2T protected by Fe-catechol x , after removing Fe-catechol, can still maintain the intrinsic properties of Ti3C2T x . While Ti3C2T without Fe-catechol protection x is severely oxidized, resulting in a sharp decline in its capacity retention rate.

[0036] Example 2

[0037] When the divalent metal salt is selected as NiCl2, the polyphenolic organic compound is selected as catechol, the acid solution is selected as HCl, and the alkaline solution is selected as KOH solution, the corresponding MXenes antioxidant method is as follows: First, NiCl2 and catechol are separately dissolved in deionized water according to a molar ratio of 1:1, and a certain amount of HCl is added to adjust the pH of the solution to 4, and then mixed and stirred to prepare a Ni-catechol complex; then, the pH of the suspension of Ti3C2T x is also adjusted to 4 with HCl, and then the above Ni-catechol complex is added, stirred until homogeneous, and then a certain amount of catechol is added and stirred until homogeneous, so that the molar ratio of NiCl2 to catechol in the obtained mixed solution is 1:2.05; finally, KOH solution is added to the mixed solution and the pH is adjusted to 7, and then centrifuged at 3500 rpm for 10 min. The upper layer is the Ti3C2T x suspension, and the lower layer is the Ni-catechol complex, and the Ti3C2T x maintaining its intrinsic properties is separated.

[0038] The Ti3C2T x -regenerated sample that has been antioxidant-capped with the Ni-catechol complex for 3 years is characterized, and the SEM image as shown in Figure 17 is obtained. By analysis, Figure 17 it can be seen that the Ni-catechol complex also has an effective antioxidant effect on Ti3C2T x .

[0039] Example 3

[0040] When the divalent metal salt is selected as CoSO4, the polyphenolic organic compound is selected as catechol, the acid solution is selected as H2SO4, and the alkaline solution is selected as NaOH solution, the corresponding MXenes antioxidant method is as follows: First, CoSO4 and catechol are separately dissolved in deionized water according to a molar ratio of 1:1, and H2SO4 is added respectively to adjust the pH of the solution to 4.5, and the two are mixed and stirred to prepare a Co-catechol complex; then, the pH of the suspension of Ti3C2T x is also adjusted to 4.5 with H2SO4, and then the above Co-catechol complex is added, stirred until homogeneous, and then a certain amount of catechol is added and stirred until homogeneous, so that the molar ratio of CoSO4 to catechol in the obtained mixed solution is 1:2.1; finally, NaOH solution is added to the mixed solution and the pH is adjusted to 7, and then centrifuged at 3500 rpm for 10 min. The upper layer is the Ti3C2T x suspension, and the lower layer is the Co-catechol complex, and the Ti3C2T x maintaining its intrinsic properties is separated.

[0041] Characterize the Ti3C2T x -regenerated samples capped with Co-catechol complex after 3 years of antioxidant treatment, and obtain the SEM images as shown Figure 18 below. By analysis Figure 18 it can be obtained that the Co-catechol complex also has an effective antioxidant effect on Ti3C2T x .

[0042] The specific embodiments described above have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above is only the most preferred embodiment of the present invention and is not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A pH-responsive MXenes-based antioxidant method, characterized in that, Comprising the following steps: Dissolve divalent or trivalent metal salts and polyphenolic organic compounds in deionized water according to a molar ratio of 1:(0.8 - 1.3) or 1:(1.8 - 2.3) respectively. Add an acid solution with the same anion as the metal salt to adjust the pH to 3 - 6. Mix and stir the metal salt solution and the polyphenolic organic compound solution to prepare a metal ion-polyphenolic organic compound complex solution; Use an acid solution with the same anion as the metal salt to adjust the pH of the MXenes suspension to the same value as that of the metal ion-polyphenolic organic compound complex solution. Then add the metal ion-polyphenolic organic compound complex and stir evenly. Add a certain amount of polyphenolic organic compound so that the molar ratio of divalent or trivalent metal salt to polyphenolic organic compound in the resulting mixed solution is 1:(2 - 2.2) or 1:(3 - 3.2), realizing the antioxidant capping of MXenes; Add an alkaline solution to the mixed solution and adjust the pH to not less than 7, then centrifuge and separate to obtain MXenes maintaining their intrinsic properties.

2. The pH-responsive MXenes-based antioxidant method according to claim 1, wherein When using a divalent metal salt, the pH of the divalent metal salt solution and the polyphenolic organic compound solution is adjusted to 4 - 6.

3. The pH-responsive MXenes-based antioxidant method according to claim 1, wherein When using a trivalent metal salt, the pH of the trivalent metal salt solution and the polyphenolic organic compound solution is adjusted to 5 - 6.

4. The pH-responsive MXenes-based antioxidant method according to any one of claims 1 to 3, characterized in that, The polyphenolic organic compound includes catechol or ellagic acid.

5. The pH-responsive MXenes-based antioxidant method according to any one of claims 1-3, characterized in that, The divalent or trivalent metal salt includes iron salt, cobalt salt or nickel salt.

6. The antioxidant method based on pH-responsive MXenes according to claim 1, wherein, The centrifugation conditions are: the rotation speed is less than 3500 rpm and the time is less than 1 h.

7. The antioxidant method based on pH-responsive MXenes according to claim 5, characterized in that, The trivalent metal salt is iron salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 5, and the molar ratio of iron salt to catechol in the mixed solution is 1:3.

05.

8. The pH-responsive MXenes-based antioxidant method according to claim 5, wherein The divalent metal salt is nickel salt, the polyphenolic organic compound is catechol, the pH of the metal ion-polyphenolic organic compound complex is 4, and the molar ratio of nickel salt to catechol in the mixed solution is 1:2.

05.

9. Application of MXenes in lithium batteries, characterized in that, The MXenes maintaining their intrinsic properties prepared by the method according to any one of claims 1 - 8 are made into a flexible film and used as an electrode for a lithium-ion battery.

10. Application of MXenes in supercapacitors, characterized in that, The MXenes maintaining their intrinsic properties prepared by the method according to any one of claims 1 - 8 are made into a flexible film and used as an electrode for a supercapacitor.

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