A liquid dispersion of MXene stabilized by lignin and a preparation method thereof

Abstract

The present invention relates to a method for preparing a liquid dispersion of MXene, comprising: S1, providing an aqueous dispersion of a monolayer or a few-layer MXene; S2, providing a lignin fraction; the preparation method comprising: adding lignin to an organic solvent, stirring and dissolving the lignin, and then centrifuging to obtain a supernatant; first subjecting the supernatant to rotary evaporation to remove most of the organic solvent, and then vacuum drying to obtain a lignin fraction corresponding to the organic solvent; S3, dissolving the lignin fraction in an organic solvent, then adding the aqueous dispersion of the monolayer or few-layer MXene to the organic solution of lignin, stirring for reaction, then centrifuging the product, and repeatedly washing the precipitate with deionized water until the supernatant is clear; S4, separating the precipitate, adding an organic solvent or deionized water to the precipitate, and homogenizing to obtain a MXene organic phase dispersion or aqueous phase dispersion of a predetermined concentration. The present invention can provide a MXene liquid dispersion that can be stably stored.

Description

Technical Field

[0001] The present invention relates to the field of materials technology, and in particular to a liquid dispersion of MXene stabilized by lignin and a preparation method thereof. Background Art

[0002] Two-dimensional MXene materials, namely two-dimensional transition metal carbides, nitrides or carbonitrides, have the general formula M n+1 X n T x (n = 1, 2, 3), where M is a transition metal (such as Ti, Nb, Mo, etc.), X is a carbon or nitrogen element, and T is a surface terminal group (F, -O, -Cl, etc.). Due to its excellent conductivity, mechanical properties, optical properties, and rich surface-tunable functional groups, MXene has become a very promising electrochemical material and flexible wearable material. Currently, MXene is mainly obtained by selectively etching the A phase of the MAX ceramic phase. The rich terminal groups on the MXene surface enable it to be well dispersed in the aqueous phase. However, MXene is unstable in aqueous phase, which has become a major limitation for its subsequent application. Once MXene is dispersed in water, water molecules and dissolved oxygen in the water rapidly oxidize and degrade the MXene into titanium dioxide TiO2 or other transition metal oxides, causing it to lose its excellent properties. Currently, MXene aqueous dispersions can only be prepared and used immediately and cannot be stored stably.

[0003] For example, Chinese Patent Publication No. CN115041027A discloses a method for modifying membranes using MXene nanosheets. The MXene nanosheets are first added to deionized water and ultrasonically dispersed. Subsequently, sodium lignin sulfonate (LS) is added in an amount 60 times the mass of the MXene nanosheets and magnetically stirred at room temperature to obtain a dispersion. The MoS2 dispersion is then added and ultrasonically dispersed for 15 minutes to obtain a MoS2@LS-MXene precursor solution. Finally, the precursor solution is infiltrated onto a commercial polyethersulfone membrane using vacuum-assisted self-assembly at a pressure of 2 bar to construct a MoS2@LS-MXene composite membrane. This method primarily functionalizes the MXene nanosheets with LS. LS itself possesses a large number of sulfonic acid groups and phenolic hydroxyl groups, making the functionalized MXene more hydrophilic. Furthermore, the LS molecules carry a negative charge. When entering the interlayers of the MXene, they electrostatically interact with the similarly negatively charged MXene, expanding the interlayer spacing of the MXene nanosheets. This method uses a large amount of sodium lignin sulfonate (containing hydrophilic sulfonic acid groups), which is mainly used to increase the hydrophilicity and dispersibility of MXene in water. In addition, Chinese Patent Publication No. CN115651219A discloses a method for preparing a MXene-based hydrogel material with a directional pore structure. This method evenly disperses a MXene aqueous dispersion with a water-soluble polymer solution of cellulose, hydroxymethyl cellulose, carboxymethyl cellulose, lignin, and starch to obtain a mixed aqueous dispersion, which is placed in a mold and frozen. The frozen product is placed in a salt solution, subjected to salting-out treatment, and washed to obtain a MXene-based hydrogel material with a directional pore structure. This method mainly uses lignin as a water-soluble polymer gel material, and does not suggest that lignin can increase the dispersibility and stability of MXene in the aqueous phase, nor does it suggest that lignin can be used to increase the dispersibility of MXene in the organic phase.

[0004] Lignin is a natural three-dimensional polymer compound, second only to cellulose in abundance in the plant kingdom. It is composed of three basic structural units: syringylpropane, guaiacylpropane, and p-hydroxyphenylpropane. Lignin's molecular structure contains a rich array of reactive groups, including aromatic rings and aliphatic and aromatic hydroxyl groups. These structures and functional groups give lignin its natural amphiphilic properties. However, lignin is often incinerated as a byproduct of the pulp and papermaking and biomass refining industries to recover heat, resulting in a waste of resources. Summary of the Invention

[0005] (1) Technical issues to be resolved

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a liquid dispersion of MXene stabilized by lignin and a preparation method thereof, which solves the technical problems such as poor dispersion stability of MXene in aqueous phase and difficulty in uniform dispersion in organic phase. The method of the present invention can provide a stable and storable liquid dispersion of MXene, providing technical support for the application of MXene in the fields of electrochemical materials, flexible wearable materials, etc.

[0007] (2) Technical solution

[0008] In a first aspect, the present invention provides a method for preparing a liquid dispersion of MXene, comprising:

[0009] S1. Providing a monolayer or few-layer MXene aqueous dispersion;

[0010] S2. Providing a lignin fraction; the preparation method thereof is as follows:

[0011] The lignin is added to an organic solvent and stirred to dissolve, followed by centrifugation to obtain a supernatant; the supernatant is first concentrated by rotary evaporation to remove most of the organic solvent, and then vacuum dried to obtain a lignin fraction corresponding to the organic solvent;

[0012] S3, dissolving the lignin fraction in S2 in an organic solvent, then adding the monolayer or few-layer MXene aqueous dispersion to the lignin organic solution, stirring the reaction, then centrifuging the product, and repeatedly washing the precipitate with deionized water until the supernatant is clear;

[0013] S4. Separate the precipitate, add an organic solvent or deionized water to the precipitate, and homogenize it to obtain a MXene organic phase dispersion or aqueous phase dispersion of a predetermined concentration.

[0014] According to a preferred embodiment of the present invention, in S1, the monolayer or few-layer MXene is obtained by etching a MAX ceramic phase using HF. Preferably, the MAX ceramic phase is Ti3AlC2 powder.

[0015] According to a preferred embodiment of the present invention, in S1, the preparation method of the aqueous dispersion of the monolayer or few-layer MXene is as follows:

[0016] (1) LiF is added to a hydrochloric acid solution to generate HF acid;

[0017] (2) Then, 300-350 mesh Ti3AlC2 powder was slowly added several times, and the mixture was placed in a 35-42°C water bath and stirred for more than 20 hours. The mixture was centrifuged, the supernatant was removed, and the precipitate was retained;

[0018] (3) repeatedly washing the precipitate with deionized water until the pH value of the supernatant reaches 6-7;

[0019] (4) The product is fully homogenized by adding deionized water to obtain a monolayer or few-layer MXene aqueous dispersion.

[0020] In step (1), the hydrochloric acid solution used is 9 mol / L; in step (2), 0.06 mol of HF acid is used for etching per 1 g of Ti3AlC2 powder, the reaction temperature during the etching process is constant at 40°C in a water bath, and the reaction time is more than 24 hours; after the reaction, the mixture is centrifuged at 3500 rpm for 5 minutes to remove the supernatant and retain the precipitate.

[0021] According to a preferred embodiment of the present invention, in S2, preferably, 1 g of lignin is dissolved with 4 mL of an organic solvent by stirring (300 rpm, 4 h), and then centrifuged at 3500 rpm for 10 min to obtain a supernatant.

[0022] According to a preferred embodiment of the present invention, in S2, the lignin is alkali lignin, kraft lignin, and enzymatic lignin. The three types of lignin are named after their extraction technologies, and they are products produced by three different extraction technologies.

[0023] According to a preferred embodiment of the present invention, in S2, the organic solvent is a commonly used organic solvent, including but not limited to dimethyl sulfoxide, ethanol, N,N-dimethylformamide, methanol, ethylene glycol, aniline, acetic acid, pyridine, chloroform, isopropanol, ethyl acetate, tetrahydrofuran, n-propanol, butanol, dichloromethane, isobutanol, N-methylpyrrolidone, N-methylpyrrolidone, etc.

[0024] According to a preferred embodiment of the present invention, in S3, depending on the amount of monolayer or few-layer MXene in S1, a certain amount of the lignin fraction produced in step S2 is redissolved in an organic solvent to produce a lignin organic solution. The aqueous dispersion of the monolayer or few-layer MXene is slowly added to the lignin organic solution, stirred at 400 rpm for 5 minutes, and the product is then centrifuged at 3500 rpm for 30 minutes. The precipitate is then repeatedly washed with deionized water until the supernatant is clear, thereby separating the precipitate. Finally, depending on the desired MXene concentration in the liquid phase system, a certain amount of organic solvent or deionized water is added to uniformly disperse the MXene, thereby producing an aqueous or organic phase dispersion of the present invention.

[0025] Preferably, in the aqueous dispersion of MXene, the mass ratio of MXene to lignin is in the range of 1:0.1-5. In the organic dispersion of MXene, the mass ratio of MXene to lignin is in the range of 1:0.1-5.

[0026] According to a preferred embodiment of the present invention, the organic solvent in S2 and the organic solvent in steps S3 and S4 can be the same or different, and preferably the same organic solvent. When the organic solvent is the same, the dispersion and stability of the MXene finally prepared are optimal.

[0027] Lignin is a general term for a large class of substance mixtures. It is a mixture, not a pure substance. Since the lignin fraction is prepared using an organic solvent in step S2, it is equivalent to selectively extracting the lignin, and obtaining a lignin fraction that best matches the selected organic solvent.

[0028] In a second aspect, the present invention relates to a liquid dispersion of MXene, wherein the dispersion medium in the liquid system is water or an organic solvent, and the MXene is prepared by any of the above-mentioned preparation methods.

[0029] (3) Beneficial effects

[0030] (1) The present invention uses lignin to stabilize MXene to prepare an aqueous phase dispersion or an organic phase dispersion of MXene, without the need to use surface chemical modification methods to promote the dispersion of MXene in the liquid phase (especially the organic phase), thus solving the technical problems of harsh chemical modification conditions, long time consumption, and expensive reagents.

[0031] (2) The method of the present invention enables high dispersibility of MXene in the organic phase, resulting in a MXene organic phase dispersion that can be stably stored. The organic phase dispersion can prevent direct contact between MXene and water / oxygen, thereby preventing rapid oxidative degradation of MXene, and provides an effective solution to the problem of oxidative degradation of MXene in liquid phase dispersions.

[0032] Before the present invention was proposed, due to the mismatch between the surface polarity of organic solvents and MXene, MXene and most organic solvents would undergo coagulation at the moment of mixing, and could not be well dispersed, and the purpose of dispersed preservation could not be achieved. The present invention can effectively avoid the coagulation of MXene in organic solvents.

[0033] (3) The method of the present invention makes MXene highly stable in the aqueous phase and not easily oxidized, and can inhibit the degradation rate of MXene in the aqueous phase, thereby obtaining a MXene aqueous dispersion that can be stored relatively stably. The MXene aqueous dispersion does not need to be prepared and used immediately, which broadens the scope of application of the MXene aqueous dispersion in industrial applications and enables the MXene aqueous dispersion to meet the needs of specific process steps.

[0034] The present invention provides technical support for the application of MXene in the fields of electrochemical materials, flexible wearable materials, etc.

[0035] (4) The degradation rate of MXene in the lignin-stabilized MXene aqueous dispersion prepared by the present method is significantly slowed, and the degradation rate is 0.2-0.5 times that of the MXene in the lignin-free MXene aqueous dispersion. MXene in the aqueous dispersion system still has a very slow degradation rate at low concentrations (0.013-0.022 mg / ml) (the lower the concentration, the faster the degradation). After stable storage for 5 days under laboratory conditions, the degradation rate is less than 17%. This shows that the use of lignin can effectively inhibit the degradation rate of MXene in the aqueous phase.

[0036] The MXene organic phase dispersion prepared by the method of the present invention can achieve a clay-like dispersion in an organic solvent (such as ethanol or dimethyl sulfoxide) at room temperature, with a mass concentration of up to 82 mg / ml. Even after 45 days of storage, low concentrations of MXene (0.013-0.022 mg / ml) in the organic dispersion showed no visible coagulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 These are dispersibility photos of the MXene@Lignin aqueous dispersions of Examples 1-3 and the MXene aqueous dispersion of the control group.

[0038] Figure 2 Degradation curves of MXene in the MXene@Lignin aqueous dispersions of Examples 1-3 and the MXene aqueous dispersion of the control group.

[0039] Figure 3 These are dispersibility photos of the MXene@Lignin organic phase (EtOH or DMF or DMSO) dispersions of Examples 4-6 and the MXene organic phase (EtOH or DMF or DMSO) dispersion of the control group.

[0040] Figure 4 Degradation curves of MXene in the organic phase (EtOH or DMF or DMSO) of MXene@Lignin of Examples 1-3. DETAILED DESCRIPTION

[0041] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0042] Example 1

[0043] This embodiment is a method for preparing a MXene aqueous dispersion, which includes:

[0044] (1) Preparation of MXene aqueous dispersion: First, add 1.6 g of lithium fluoride (LiF) to 20 mL of hydrochloric acid solution (15 mL, 12 mol / L HCl; 5 mL, H2O) and stir to mix. Then, slowly add 2.0 g of Ti3AlC2 powder (325 mesh, Carbon-Ukraine) to the system in multiple times, and place it in a 40°C water bath and stir (400 rpm) to react for 24 h. After the reaction, the product is centrifuged (3500 rpm, 5 min) to remove the supernatant, and 40 ml of deionized water is added to repeatedly wash the precipitate until the pH value of the supernatant reaches 6. The precipitated product is added with deionized water and stirred or ultrasonically homogenized to obtain a single-layer or few-layer MXene aqueous dispersion.

[0045] (2) Preparation of lignin fraction: 5.0 g of lignin was added to 20 mL of dimethyl sulfoxide and stirred to dissolve (300 rpm, 4 h). The supernatant was then centrifuged (3500 rpm, 10 min). The supernatant was first subjected to rotary evaporation to remove most of the dimethyl sulfoxide and then vacuum dried to obtain the lignin fraction, which was named lignin-dimethyl sulfoxide.

[0046] (3) Take the lignin fraction Lignin-dimethyl sulfoxide and dissolve it in dimethyl sulfoxide again to obtain a lignin dimethyl sulfoxide solution.

[0047] (4) Preparation of MXene aqueous dispersion: The MXene aqueous dispersion from step (1) was slowly added to the lignin dimethyl sulfoxide solution and the reaction was stirred continuously (400 rpm, 5 min). Subsequently, the product was centrifuged (3500 rpm, 30 min) and the precipitate was repeatedly washed with deionized water until the supernatant was clear.

[0048] (5) Separate the MXene@Lignin precipitate and add 10 mL of deionized water to the precipitate, shaking and dispersing it evenly to obtain a MXene aqueous dispersion, referred to as the MXene@Lignin aqueous dispersion. The MXene@Lignin aqueous dispersion was placed in a 15 mL vial and sealed for subsequent observation and testing.

[0049] Example 2

[0050] The steps and conditions of this example are basically the same as those of Example 1, with the only difference being that the organic solvent used in preparing the lignin fraction in step (2) and re-dissolving the lignin fraction in step (3) is changed to ethanol EtOH.

[0051] Example 3

[0052] The steps and conditions of this example are basically the same as those of Example 1, except that the organic solvent used in preparing the lignin fraction in step (2) and re-dissolving the lignin fraction in step (3) is changed to N,N-dimethylformamide (DMF).

[0053] The dispersion of the MXene aqueous dispersion was compared with that of the MXene@Lignin aqueous dispersions from Examples 1-3. A control group was also prepared using the dispersion of MXene in DMSO (dimethyl sulfoxide). Visual inspection determined the dispersion of the MXene, which exhibited a light green appearance and lacked visible aggregates at low concentrations.

[0054] like Figure 1 As shown in the picture, the dispersibility of the MXene aqueous dispersion and the MXene@Lignin aqueous dispersion of Examples 1-3 are similar, with no obvious difference, indicating that the introduction of lignin does not affect the dispersibility of MXene in water.

[0055] However, compared to the dispersion of MXene directly dispersed in DMSO (control group), the dispersions of MXene aqueous dispersions and MXene@Lignin aqueous dispersions were significantly higher than the dispersion of MXene in DMSO (MXene dispersed in DMSO showed obvious aggregated particles). The MXene dispersions in the aforementioned sample groups had the same initial concentration.

[0056] The degradation rates of MXene in aqueous systems in Examples 1-3 were compared, while a MXene aqueous dispersion without lignin was used as a control. The MXene aqueous dispersions in the following groups of samples had the same initial concentration. The degree of oxidative degradation of MXene in aqueous phase was measured by UV-visible spectrophotometry at 770 nm using its initial absorbance (C0) and absorbance after standing for a period of time (C10) at room temperature. t ). The retention rate of MXene is calculated as follows:

[0057]

[0058] The experimental results are as follows Figure 2 As shown. After 5 days of standing in water, the retention rate of MXene decreased to 25%. When the standing time was extended to 12 days, MXene was completely oxidized and degraded, and the retention rate dropped to 0. In Examples 1-3, the retention rates of MXene after 5 days of standing were 83% and 12% respectively.

[0059] The MXene aqueous dispersions prepared in Examples 2-3 showed the best stability and the slowest degradation rate of the MXene contained therein, followed by Example 1. The MXene aqueous dispersion without lignin showed the worst stability, the fastest degradation of the MXene contained therein, and the shortest storage time.

[0060] At the same time, according to experimental statistics, compared with the MXene aqueous dispersion without lignin, the time for complete oxidative degradation of MXene (retention rate reduced to 0) in the MXene aqueous dispersion stabilized with lignin is extended from 12 days to 45 days. This shows that lignin has the effect of significantly inhibiting the oxidative degradation rate of MXene in the aqueous phase, that is, the present invention can produce a MXene aqueous dispersion that can be stably stored.

[0061] Example 4

[0062] This embodiment is a method for preparing a MXene organic phase dispersion, which includes:

[0063] (1) Preparation of MXene aqueous dispersion: First, add 1.6 g of lithium fluoride (LiF) to 20 mL of hydrochloric acid solution (15 mL, 12 mol / L HCl; 5 mL, H2O) and stir to mix. Then, slowly add 2.0 g of Ti3AlC2 powder (325 mesh, Carbon-Ukraine) to the system in multiple times, and place it in a 40°C water bath and stir (400 rpm) to react for 24 h. After the reaction, the product is centrifuged (3500 rpm, 5 min) to remove the supernatant, and 40 ml of deionized water is added to repeatedly wash the precipitate until the pH value of the supernatant reaches 6-7. The precipitated product is added with deionized water and stirred or ultrasonically homogenized to obtain a single-layer or few-layer MXene aqueous dispersion.

[0064] (2) Preparation of lignin fraction: 5.0 g of lignin was added to 20 mL of ethanol and stirred to dissolve (300 rpm, 4 h). The supernatant was then centrifuged (3500 rpm, 10 min). The supernatant was first subjected to rotary evaporation to remove most of the ethanol and then vacuum dried to obtain the lignin fraction, which was named lignin-ethanol.

[0065] (3) Take the lignin fraction Lignin-ethanol and dissolve it in ethanol again to obtain a lignin ethanol solution.

[0066] (4) Preparation of MXene aqueous dispersion: The MXene aqueous dispersion from step (1) was slowly added to the lignin ethanol solution and stirred continuously (400 rpm, 5 min). Subsequently, the product was centrifuged (3500 rpm, 30 min) and the precipitate was repeatedly washed with deionized water until the supernatant was clear.

[0067] (5) Separate the MXene@Lignin precipitate and add 10 mL of ethanol to the precipitate, shaking and dispersing it evenly to obtain a MXene ethanol dispersion, referred to as the MXene@Lignin ethanol dispersion. Place the MXene@Lignin precipitate in a 15 mL vial, seal it, and perform subsequent observation and testing.

[0068] Example 5

[0069] The steps and conditions of this example are basically the same as those of Example 4, except that the organic solvent used in preparing the lignin fraction in step (2) and re-dissolving the lignin fraction in step (3) is changed to N,N-dimethylformamide (DMF).

[0070] Example 6

[0071] The steps and conditions of this example are basically the same as those of Example 4, with the only difference being that the organic solvent used in preparing the lignin fraction in step (2) and re-dissolving the lignin fraction in step (3) is changed to dimethyl sulfoxide (DMSO).

[0072] The dispersion of MXene organic phase (EtOH, DMF, or DMSO) dispersions was compared with the MXene@Lignin organic phase (EtOH, DMF, or DMSO) dispersions of Examples 4-6. The dispersion of MXene in EtOH, DMF, or DMSO served as a control group. Dispersibility was assessed visually. Well-dispersed MXene exhibited a light green color at low concentrations and showed no visible aggregated particles. The MXene dispersions in each sample group had the same initial concentration.

[0073] Experimental results Figure 3 As shown. The MXene@Lignin prepared in Examples 4-6 all showed a light green color in EtOH, DMF, or DMSO and had no obvious aggregated particles, while the MXene without lignin could not be evenly dispersed in EtOH, DMF, or DMSO. The solution was nearly colorless and had obvious aggregated particles. This shows that the organic phase dispersion and dispersion stability of the MXene prepared by the present invention are significantly higher than those of the MXene without lignin in the organic phase, making the MXene, which was originally difficult to disperse in the organic phase, uniformly and stably dispersed in the organic phase.

[0074] Will Figure 3 and Figure 1By comparison, the dispersion of MXene@Lignin in the organic phase (EtOH, DMF, or DMSO) is essentially identical to that of MXene or MXene@Lignin in the aqueous phase, with both solutions exhibiting a light green color. This demonstrates that the method of the present invention can effectively disperse MXene in the organic phase, a feat not previously possible, and thus produces a stable and highly dispersed MXene organic phase dispersion.

[0075] The degradation rates of MXene in the organic phase (EtOH or DMF or DMSO) in Examples 4-6 were compared. The degree of oxidative degradation of MXene in the organic phase was measured by UV-visible spectrophotometry at 770 nm to measure its initial absorbance (C0) and the absorbance after standing for a period of time (C0) at room temperature. t ). The retention rate of MXene is calculated according to the formula mentioned above.

[0076] The experimental results are as follows Figure 4 As shown. After standing in the organic phase for 5 days, the retention rates of MXene were 91% (Lignin-DMSO), 95% (Lignin-EtOH), and 99% (Lignin-DMF), respectively, showing a very slow rate of decrease. When the standing time was 45 days, the retention rate of MXene was still higher than 80%, among which the retention rate of the MXene dispersion containing Lignin-DMF was 91%, and no coagulation phenomenon was observed with the naked eye. The above results show that the introduction of lignin not only promotes the dispersibility of MXene in organic solvents, but also has a significant effect on inhibiting the oxidative degradation rate of MXene in the organic phase.

[0077] In addition, compared with the aqueous dispersion of MXene, the degradation rate of MXene stabilized by lignin in the organic phase is slower, the stability is better, and the shelf life is longer. This provides technical support for the industrial application of MXene. The MXene dispersion does not need to be prepared and used immediately, and the organic phase dispersion of MXene can also be produced and sold as a commercial product, thereby extending the life of MXene.

[0078] Comparative Example 1

[0079] This comparative example modified the mixing method in step (4) of Example 1, namely, the lignin dimethyl sulfoxide solution was slowly added dropwise to the MXene aqueous dispersion prepared in step (1). The remaining steps were the same as in Example 1. The experimental results showed that the yield of the MXene@lignin product was significantly lower than that obtained in step (4) of Example 1.

[0080] Comparative Example 2

[0081] This comparative example is based on Example 1, except that the organic solvent used in preparing the lignin fraction in step (2) was changed to DMF. However, in step (3), DMSO was still used to dissolve the lignin fraction prepared in step (2) to obtain a lignin dimethyl sulfoxide solution. All other steps were the same as in Example 1. The experimental results revealed the presence of some aggregated particles in the resulting MXene@lignin aqueous dispersion.

[0082] Comparative Example 3

[0083] This comparative example is based on Example 4, but the organic solvent used is modified. DMF is used as the organic solvent for preparing the lignin fraction in step (2), but ethanol is still used to dissolve the lignin fraction prepared in step (2) in step (3) to obtain a lignin ethanol solution. Step (5) remains unchanged, and the other steps are the same as in Example 4. The experimental results show that a small amount of aggregated particles are present in the resulting MXene@lignin ethanol dispersion.

[0084] The above experimental results show that in the preparation method of the MXene liquid dispersion of the present invention, the mixing method in step (4) must be to add the MXene aqueous dispersion to the lignin organic solvent, and the technical purpose cannot be achieved by reversing the addition and mixing method.

[0085] In addition, the organic solvent used in the preparation of the lignin fraction is preferably consistent with the solvent used to prepare the lignin organic solution. If it is inconsistent, since the lignin is partially dissolved in the organic solvent, it cannot fully react and work. Although a MXene liquid phase dispersion with good dispersibility and stability can be obtained, the dispersibility and stability of the final MXene liquid phase dispersion are not as good as the dispersibility and stability of the product obtained by the method of "the organic solvent used to prepare the lignin fraction is consistent with the solvent used to prepare the lignin organic solution". More preferably, if the separated precipitate MXene@Lignin is made into an organic phase dispersion, the organic solvent used in the organic phase dispersion is preferably the same as the organic solvent used to prepare the lignin fraction. The dispersibility and stability of the MXene organic phase dispersion finally prepared are better, and the dispersion can be stored for a longer time.

[0086] Although the above examples only list the implementation schemes and effects of preparing lignin fractions using EtOH, DMF, or DMSO, and preparing dispersions of MXene@Lignin in organic phases such as EtOH, DMF, or DMSO, those skilled in the art can expect that similar technical effects can be achieved by using other organic solvents such as methanol, ethylene glycol, aniline, acetic acid, pyridine, chloroform, isopropanol, ethyl acetate, tetrahydrofuran, n-propanol, butanol, dichloromethane, isobutanol, N-methylpyrrolidone, N-methylpyrrolidone, etc.

[0087] This method utilizes industrial lignin as a dispersant, successfully dispersing MXene in aqueous or organic solvents without chemical modification. This method effectively inhibits the oxidative degradation of MXene in aqueous phases, improves the dispersion of MXene in organic phases, and inhibits its degradation rate in organic phases. This method is applicable to various liquid dispersions, enhancing the performance of MXene for industrial applications.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a liquid dispersion of MXene, characterized in that: It includes: S1. Providing a monolayer or few-layer MXene aqueous dispersion; S2. Providing a lignin fraction; the preparation method thereof is as follows: The lignin is added to an organic solvent and stirred to dissolve, followed by centrifugation to obtain a supernatant; the supernatant is first concentrated by rotary evaporation to remove most of the organic solvent, and then vacuum dried to obtain a lignin fraction corresponding to the organic solvent; S3, dissolving the lignin fraction in S2 in an organic solvent, then adding the monolayer or few-layer MXene aqueous dispersion to the lignin organic solution, stirring the reaction, then centrifuging the product, and repeatedly washing the precipitate with deionized water until the supernatant is clear; S4. Separate the precipitate, add an organic solvent or deionized water to the precipitate, and homogenize it to obtain a MXene organic phase dispersion or aqueous phase dispersion of a predetermined concentration.

2. The method for preparing a liquid dispersion of MXene according to claim 1, wherein: In S1, single-layer or few-layer MXene is obtained by etching the MAX ceramic phase using HF.

3. The method for preparing a liquid dispersion of MXene according to claim 2, characterized in that: In S1, the MAX ceramic phase is Ti3AlC2 powder.

4. The method for preparing a liquid dispersion of MXene according to claim 1, characterized in that: In S1, the preparation method of the aqueous dispersion of the monolayer or few-layer MXene is as follows: (1) LiF is added to a hydrochloric acid solution to generate HF acid; (2) Then slowly add 300-350 mesh Ti3AlC2 powder several times, place it in a 35-42℃ water bath and stir for more than 20 hours, centrifuge, remove the supernatant, and retain the precipitate; (3) Repeatedly wash the precipitate with deionized water until the pH value of the supernatant reaches 6-7; (4) The product is fully homogenized by adding deionized water to obtain a monolayer or few-layer MXene aqueous dispersion.

5. The method for preparing a liquid dispersion of MXene according to claim 1, wherein: In S2, the lignin is alkali lignin, sulfate lignin and enzymatic lignin.

6. The method for preparing a liquid dispersion of MXene according to claim 1, characterized in that: In S2, the organic solvent is dimethyl sulfoxide, ethanol, N,N-dimethylformamide, methanol, ethylene glycol, aniline, acetic acid, pyridine, chloroform, isopropanol, ethyl acetate, tetrahydrofuran, n-propanol, butanol, dichloromethane, isobutanol, N-methylpyrrolidone or N-methylpyrrolidone.

7. The method for preparing a liquid dispersion of MXene according to claim 1, wherein: The organic solvent used in step S2 is the same as the organic solvent used in steps S3 and S4.

8. A liquid dispersion of MXene, wherein the dispersion medium in the liquid system is water or an organic solvent, and the dispersion is prepared by the preparation method according to any one of claims 1 to 7.

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