Preparation method of hydrophobically modified MXene film capable of keeping high infrared reflectivity

Abstract

The invention provides a preparation method of a hydrophobic modified MXene film capable of keeping high infrared reflectivity, which comprises the following steps: preparing MXene particles by a wet etching method, and adding dopamine hydrochloride and a water phase; the preparation method comprises the following steps: dissolving C10-12 long-chain alkylamine and fluorine-containing silane in an organic solvent to obtain an organic solvent; uniformly mixing the water phase and the organic phase, standing for layering, and separating the organic phase; the hydrophobic modified MXene film is prepared from the organic phase and the porous base film in a filtering manner. According to the invention, through compounding of long-chain alkylamine and fluorine-containing silane, hydrophobic modification of a two-dimensional metal material MXene is completed, and the modified MXene can have better durability in a humid environment; meanwhile, the compounded hydrophobic modifier greatly retains the infrared characteristic of the MXene, and the infrared reflectivity of the obtained hydrophobic MXene film is reduced slightly, so that the hydrophobic MXene film can be applied to optics conveniently.

Description

Technical Field

[0001] The present invention belongs to the technical field of MXene materials, and in particular relates to a method for preparing a hydrophobically modified MXene film that maintains high infrared reflectivity. Background Art

[0002] MXene is a type of transition metal carbide with a two-dimensional layered structure. Since its discovery in 2011, MXene has attracted much attention in many fields such as energy storage, photothermal conversion, electromagnetic shielding, and sewage treatment due to its excellent electrical, magnetic, optical, and thermal properties.

[0003] Typically, MXene is synthesized from a ceramic material called a MAX phase. The MAX phase has a layered structure of transition metals, carbon, and Group 4 elements (silicon, aluminum, germanium), and by using an etching process with a strong acid such as hydrofluoric acid, only the Group 4 elements are selectively removed, leaving two-dimensional MXene nanoparticles. End groups such as –OH, =O, –F, etc. are formed on the surface of the MXene by reaction in a strong acid aqueous solution, and these functional groups provide hydrophilicity. Therefore, these synthesized MXenes have excellent hydrophilicity and can be used as functional materials by various methods. In addition, by adjusting the composition type and the ratio of transition metals to carbon / nitrogen that constitute them, a two-dimensional MXene with excellent conductivity can be functionally provided.

[0004] However, since the hydrophilic MXene film will also be oxidized by water molecules and oxygen in the air, it will become a metal oxide and lose its inherent excellent properties, making it difficult to store for a long time. In addition, the high boiling point of water and the high energy consumption for water removal are limited in liquid phase methods such as spraying, spin coating, and inkjet printing. The existing MXene hydrophobic modification process usually causes a large change in infrared characteristics due to the addition of too much modified substance, especially the decrease in infrared reflectivity, which limits its application in the field of solar cells and sensors.

[0005] CN115725190A discloses a method for preparing a MXene-based super-hydrophobic photothermal coating, comprising the following steps: S1: mixing Ti3AlC2 with HF, stirring for reaction, and drying after ultrasonic treatment to obtain MXene powder, dispersing the MXene powder in water to obtain a MXene dispersion; S2: blending the MXene dispersion with an ethanol solution of FAS ((triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane), standing for reaction at room temperature to obtain a F-MXene dispersion; S3: adding dopamine, trishydroxymethylaminomethane and ethanol into water, stirring to dissolve and disperse evenly, adding the F-MXene dispersion, stirring and mixing evenly, adjusting the pH value of the system, stirring at a constant temperature to react completely, and filtering and drying to obtain the MXene-based super-hydrophobic photothermal coating.

[0006] CN110171831A discloses a method for preparing a hydrophobic two-dimensional Ti3C2Tx-MXene film, comprising the following steps: S1, preparing Ti3C2T x -MXene: 1) Etching: Add lithium fluoride to hydrochloric acid and stir to dissolve, then add Ti3AlC2 to it and react at 30-40°C. After reacting for 18-30 hours, centrifuge to separate Ti3C2T x -MXene particles and liquid, and repeatedly wash the reactants with deionized water for several times until the pH of the supernatant is 5.5-6.5; 2) Stripping: Add deionized water to the washed precipitate again, and use a vortex mixer to mechanically shake for 20-30 hours, and then centrifuge for 0.5-1.5 hours. After the centrifugation, separate the unetched Ti3AlC2 on the lower layer and the single-layer Ti3C2T x -MXene slurry; S2, preparation of Ti3C2T x -MXene film: for Ti3C2T x -MXene slurry was used for solid-liquid separation, and the Ti3C2T x -MXene nanosheets are deposited on the water filter membrane to prepare Ti3C2Tx-MXene film; S3, prepare the modifier: dissolve the isocyanate and the catalyst in acetone to prepare the modifier; S4, prepare the hydrophobic two-dimensional Ti3C2T x -MXene film: The modifier prepared in step S3 is evenly sprayed on both sides of the film prepared in step S2 with a spray gun, and the film is allowed to react at room temperature for 20 to 30 hours, and then the unreacted modifier is washed clean with acetone to obtain the film.

[0007] CN112973476A discloses a hydrophobic porous MXene membrane and a preparation method thereof, comprising the following steps: (1) etching a three-dimensional layered MAX with a mixed solution of LiF and HCl, washing, adding water and ultrasonic dispersion to obtain a two-dimensional layered MXene suspension; (2) preparing a low surface energy substance into a hydrolysis solution and mixing it with the two-dimensional layered MXene suspension described in step (1) to undergo a hydrolysis reaction; (3) vacuum filtering the modified MXene solution obtained in step (2) on a porous substrate membrane, and vacuum drying to obtain a hydrophobic porous MXene membrane. The low surface energy substance is selected from hexadecyltrimethyloxysilane, 1H,1H,2H,2H-heptafluorodecyltrimethoxysilane, propyltrimethoxysilane, vinyltrimethoxysilane, and polydimethylsiloxane.

[0008] The above patent imparts hydrophobicity to MXene through a modification method, but the infrared reflectivity of the resulting hydrophobic MXene material inevitably decreases. Summary of the invention

[0009] In order to overcome the significant changes in infrared characteristics during the hydrophobic modification of MXene materials in the prior art, such as the decrease in infrared reflectivity, which limits the application scenarios, the present invention proposes a method for preparing a hydrophobically modified MXene material that maintains high infrared reflectivity. The present invention reduces the hydrophilic characteristics of MXene and provides hydrophobic characteristics by modifying the surface of two-dimensional MXene particles to have hydrophobicity or using ligands with functional groups, and adjusts the modification process so that the hydrophobically modified MXene can maintain a high infrared reflectivity. Specifically, the present invention achieves the above purpose through the following technical solutions:

[0010] A method for preparing a hydrophobically modified MXene film with high infrared reflectivity, comprising the following steps:

[0011] (S1) preparing MXene particles in water by a wet etching method, and adding dopamine hydrochloride to obtain an aqueous phase in which MXene particles are dispersed;

[0012] (S2) dissolving a C10-12 long-chain alkylamine and a fluorine-containing silane in an organic solvent separated from the aqueous phase to obtain an organic phase, wherein the fluorine-containing silane has 3-5 F atoms in its molecular structure;

[0013] (S3) the aqueous phase and the organic phase are mixed evenly to complete the hydrophobic modification of MXene, and the organic phase is separated by standing and stratifying;

[0014] (S4) The organic phase and the porous base membrane are prepared by filtration to obtain a hydrophobically modified MXene film.

[0015] The high infrared reflectivity is that the infrared reflectivity of the hydrophobically modified MXene film is compared with that of the unmodified MXene film, and has an infrared reflectivity retention rate of more than 70%, that is, A1 / A2≥70%, A1 is the infrared reflectivity of the modified MXene film, and A2 is the infrared reflectivity of the unmodified MXene film.

[0016] Furthermore, in step (S1), the wet etching is a mixed treatment of Ti3AlC2 and HF; preferably, the molar ratio of Ti3AlC2 and HF is 1:2-10; the etching temperature is 20-50°C, and the etching time is 10-80h. Preferably, the particle size of the obtained MXene particles is 20-50μm.

[0017] Furthermore, in step (S1), the concentration of MXene particles in the aqueous phase is 1-5 mg / mL, and the concentration of dopamine hydrochloride is 0.03-0.06 g / mL.

[0018] Further, in step (S2), the C10-12 long-chain alkylamine is selected from at least one of amine, undecylamine, and dodecylamine; and the fluorinated silane is selected from at least one of 3,3,3,-trifluoropropyltrimethoxysilane, 3,3,3,-trifluoropropyltriethoxysilane, dimethylmethoxy (3,3,3-fluoropropyl) silane, and methyl (3,3,3-trifluoropropyl) diethoxysilane. The inventor unexpectedly found that the compounding of C10-12 long-chain alkylamine and short-chain fluorinated silane can complete the hydrophobic modification of MXene without excessively affecting the infrared reflectivity of the hydrophobic MXene material.

[0019] Furthermore, in step (S2), the mass ratio of C10-12 long-chain alkylamine to fluorine-containing silane is 3-5:1-2; further, the concentration of C10-12 long-chain alkylamine in the organic phase is 0.1-2 mg / mL.

[0020] Furthermore, in step (S2), the organic solvent is selected from at least one of n-hexanol, butyl acetate, dichloromethane, chloroform and n-hexane.

[0021] Furthermore, in step (S3), the amount of the aqueous phase and the organic phase is such that the mass ratio of MXene particles to C10-12 long-chain alkylamine is 1:0.1-0.5. The hydrophobic modification is carried out by stirring at 30-50°C for 24-48h.

[0022] Furthermore, in step (S4), the porous base membrane is selected from at least one of polypropylene membrane, polyethylene membrane, PVDF membrane, cellulose acetate membrane, nylon membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane; the pore size of the porous base membrane is 1-50 μm, preferably 5-10 μm.

[0023] The present invention achieves hydrophobic modification of the two-dimensional metal material MXene through the compounding of long-chain alkylamine and fluorine-containing silane, and the modified MXene can have better durability in a humid environment; at the same time, the compounded hydrophobic modifier retains the infrared characteristics of MXene itself to a large extent, and the infrared reflectivity of the obtained hydrophobic MXene film decreases slightly, which is beneficial to its application in optics. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the distribution of MXene in water / ethyl acetate before and after the MXene film modification of Example 1.

[0025] Figure 2 This is a photo of the MXene film prepared in Example 1.

[0026] Figure 3It is the water contact angle of unmodified MXene, modified MXene prepared in Example 1, modified MXene prepared in Example 2, and modified MXene prepared in Example 3.

[0027] Figure 4 The infrared reflectivity of the MXene films prepared in Examples 1-5 was tested.

[0028] Figure 5 This is a scanning electron microscope (SEM) image of the hydrophobic modified MXene film obtained in Example 1.

[0029] Figure 6 This is the X-ray photoelectron spectroscopy (XPS) graph of the hydrophobically modified MXene film obtained in Example 1. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0031] The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0032] Example 1

[0033] (S1) Wet etching Ti3AlC2 powder with LiF and hydrochloric acid in water to obtain MXene particles, preparing 20 mL of a phase-separated dispersion with a MXene concentration of 2 mg / mL, adding 1.2 g of dopamine hydrochloride to obtain an aqueous phase in which MXene particles are dispersed;

[0034] (S2) 4 mg of dodecylamine and 1 mg of 3,3,3,-trifluoropropyltrimethoxysilane were dissolved in 20 mL of butyl acetate to obtain an organic phase;

[0035] (S3) The aqueous phase and the organic phase were stirred at 40 °C for 24 h to complete the hydrophobic modification of MXene, and then allowed to stand and separate the organic phase;

[0036] (S4) The organic phase and a polypropylene membrane with a pore size of 6 μm were prepared by vacuum filtration to obtain a two-dimensional hydrophobically modified MXene film.

[0037] Figure 1 is the distribution of MXene in water / ethyl acetate before and after modification. Before modification, Ti3C2T x MXene is dispersed in an aqueous solution. However, through the interfacial hydrophobic modification reaction, the modified MXene moves to the ethyl acetate organic solvent, which has a lower density than water. After the aqueous phase is removed from below, an organic phase in which the hydrophobically modified MXene is dispersed can be obtained.

[0038] Figure 2This is a photo of the MXene film prepared in Example 1.

[0039] Example 2

[0040] The other conditions were the same as those in Example 1, except that in step (S2), the amount of dodecylamine added was 8 mg, and the amount of 3,3,3,-trifluoropropyltrimethoxysilane added was 2 mg.

[0041] Example 3

[0042] The other conditions were the same as those in Example 1, except that in step (S2), the amount of dodecylamine added was 12 mg, and the amount of 3,3,3,-trifluoropropyltrimethoxysilane added was 3 mg.

[0043] Figure 3 The water contact angles of unmodified MXene, modified MXene obtained in Example 1, modified MXene obtained in Example 2, and modified MXene obtained in Example 32. It can be seen that the contact angle of MXene before modification is less than 90°, which has a clear hydrophilic characteristic; as the amount of hydrophobic modifier increases, the contact angle gradually increases, indicating that the hydrophobicity is enhanced.

[0044] Example 4

[0045] The other conditions were the same as those in Example 1, except that in step (S2), the amount of dodecylamine added was 16 mg, and the amount of 3,3,3,-trifluoropropyltrimethoxysilane added was 4 mg.

[0046] Example 5

[0047] The other conditions were the same as those in Example 1, except that in step (S2), the amount of dodecylamine added was 20 mg, and the amount of 3,3,3,-trifluoropropyltrimethoxysilane added was 5 mg.

[0048] The infrared reflectivity test of the MXene films obtained in Examples 1-5 above was performed, and the results are as follows: Figure 4 After hydrophobic modification, the infrared reflectivity of the MXene film decreased to a certain extent, but maintained a high infrared reflectivity of more than 70%.

[0049] Example 6

[0050] The other conditions are the same as those in Example 1, except that in step (S2), dodecylamine is replaced by an equal mass of quinamine.

[0051] Comparative Example 1

[0052] The other conditions were the same as those in Example 3, except that in step (S2), only 15 mg of dodecylamine was added.

[0053] Comparative Example 2

[0054] The other conditions were the same as those in Example 3, except that in step (S2), only 15 mg of 3,3,3,-trifluoropropyltrimethoxysilane was added.

[0055] Comparative Example 3

[0056] The other conditions are the same as those in Example 3, except that in step (S2), dodecylamine is replaced with an equal mass of hexadecylamine.

[0057] Comparative Example 4

[0058] The other conditions are the same as those in Example 3, except that in step (S2), 3,3,3-trifluoropropyltrimethoxysilane is replaced with an equal mass of tridecafluorooctyltriethoxysilane.

[0059] Figure 5 The scanning electron microscope (SEM) was used to observe and analyze the microstructure of the MXene film after the surface modification reaction prepared in Example 1. From the analysis of the image, it can be seen that after the surface modification reaction, the MXene still maintains a two-dimensional layered structure. Figure 6 The results of using X-ray photoelectron spectroscopy to observe and analyze the composition of the MXene film after the surface modification reaction in Example 1 show that after the surface modification reaction, functional groups containing N elements are attached to the MXene and N-Ti covalent bonds are formed.

[0060] The hydrophobicity and infrared reflectivity retention rate of the MXene films obtained in the above examples and comparative examples were tested, and the results are shown in Table 1 below.

[0061] Table 1 MXene film performance test

[0062]

[0063]

Claims

1. A method for preparing a hydrophobically modified MXene film with high infrared reflectivity, characterized in that: The following steps are involved: (S1) preparing MXene particles in water by a wet etching method, and adding dopamine hydrochloride to obtain an aqueous phase in which MXene particles are dispersed; (S2) dissolving a C10-12 long-chain alkylamine and a fluorinated silane in an organic solvent separated from the aqueous phase to obtain an organic phase, wherein the fluorinated silane has 3-5 F atoms in its molecular structure; (S3) the aqueous phase and the organic phase are mixed evenly to complete the hydrophobic modification of MXene, and the organic phase is separated by standing and stratifying; (S4) The organic phase and the porous base membrane are prepared by filtration to obtain a hydrophobically modified MXene film.

2. The preparation method according to claim 1, characterized in that: The high infrared reflectivity is that the infrared reflectivity of the hydrophobically modified MXene film is compared with that of the unmodified MXene film, and has an infrared reflectivity retention rate of more than 60%; the infrared reflectivity retention rate A=A1 / A2, A≥70%, A1 is the infrared reflectivity of the modified MXene film, and A2 is the infrared reflectivity of the unmodified MXene film.

3. The preparation method according to claim 1, characterized in that: In step (S1), the wet etching is a mixed treatment of Ti3AlC2 and HF; preferably, the molar ratio of Ti3AlC2 and HF is 1:2-10; the etching temperature is 20-50°C, and the etching time is 10-80h; preferably, the particle size of the obtained MXene particles is 20-50μm.

4. The preparation method according to claim 1, characterized in that: In step (S1), the concentration of MXene particles in the aqueous phase is 1-5 mg / mL, and the concentration of dopamine hydrochloride is 0.03-0.06 g / mL.

5. The preparation method according to claim 1, characterized in that: In step (S2), the C10-12 long-chain alkylamine is selected from at least one of amine, undecylamine and dodecylamine; the fluorine-containing silane is selected from at least one of 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, dimethylmethoxy (3,3,3-fluoropropyl) silane and methyl (3,3,3-trifluoropropyl) diethoxy silane.

6. The preparation method according to claim 1, characterized in that: In step (S2), the mass ratio of C10-12 long-chain alkylamine to fluorine-containing silane is 3-5:1-2; further, the concentration of C10-12 long-chain alkylamine in the organic phase is 0.1-2 mg / mL.

7. The preparation method according to claim 1, characterized in that: In step (S2), the organic solvent is selected from at least one of n-hexanol, butyl acetate, dichloromethane, chloroform and n-hexane.

8. The preparation method according to claim 1, characterized in that: In step (S3), the amount of aqueous phase and organic phase is such that the mass ratio of MXene particles to C10-12 long-chain alkylamine is 1:0.1-0.5; and the hydrophobic modification is carried out by stirring at 30-50°C for 24-48h.

9. The preparation method according to claim 1, characterized in that: In step (S4), the porous base membrane is selected from at least one of polypropylene membrane, polyethylene membrane, PVDF membrane, cellulose acetate membrane, nylon membrane, polytetrafluoroethylene membrane, and polyethersulfone membrane; the pore size of the porous base membrane is 1-50 μm, preferably 5-10 μm.

10. A hydrophobically modified MXene film, characterized in that: The method is prepared according to any one of claims 1 to 9.

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