Silane-modified mxene, preparation method and application thereof

Abstract

The application discloses a silane modified MXene, a preparation method and application thereof, relates to the technical field of functional material preparation, and adopts a HF etching method to prepare the silane modified MXene by etching MAX powder with in-situ generated hydrofluoric acid through mixing of lithium fluoride and hydrochloric acid. The silane modified MXene builds a'molecular' bridge between two-dimensional materials and organic matters by using the functional groups in silane, and can be stably dispersed in organic phase variable materials. The application provides a preparation method of phase change microcapsules without supercooling and with high enthalpy, mixes organic phase variable core materials containing the silane modified MXene and emulsifier powder, and then adds deionized water to form an emulsion, and adopts a stirring shearing method to form a stable water-in-oil (W / O) microemulsion structure; subsequently, a shell material prepolymer solution is added to perform a polymerization reaction, and phase change microcapsules without supercooling and with high enthalpy are obtained.

Description

Technical Field

[0001] This invention relates to the field of functional materials preparation technology, and in particular to a silane-modified MXene, its preparation method, and its application. Background Technology

[0002] In recent years, due to the depletion of fossil fuels and the energy crisis, energy storage technology has attracted significant attention. Latent heat storage, as a type of energy storage technology, is achieved through phase change materials (PCMs). It can provide latent heat at a constant temperature, offering advantages such as high energy density, compatibility with compact and miniaturized equipment, and the ability to maintain a constant temperature, effectively addressing the problem of energy supply and demand imbalance. It has significant application value and development prospects in solar thermal storage systems, industrial waste heat recovery, phase change energy-saving buildings, air conditioning cold storage systems, heat dissipation for electronic components, and textiles. Paraffin PCMs have received widespread attention due to their high latent heat, wide availability, and broad phase change temperature range; however, direct application of paraffin PCMs presents problems such as flammability, leakage, and large volume changes.

[0003] Supercooling is a significant problem with phase change microcapsules. Paraffin phase change materials encapsulated in tiny sizes can experience supercooling due to poor nucleation. Supercooling refers to a state where the phase change material begins to crystallize only at temperatures far below its phase change temperature. This means that latent heat is only released when the temperature reaches below the supercooling temperature. In practical applications, the release and storage of latent heat require a large temperature difference, which is not conducive to efficient energy storage and can cause unnecessary losses.

[0004] Currently, a common approach is to add nucleating agents to the core material to eliminate capsule supercooling, such as octadecyl alcohol, octadecyl acid, and sodium chloride. However, adding these nucleating agents can have negative effects on the capsules, such as causing capsule depression, adhesion between capsules, and a decrease in enthalpy. Another approach is to use inorganic nanoparticles to eliminate capsule supercooling, such as carbon nanotubes, nano-titanium dioxide, and silver nanoparticles. Nanoparticles, due to their small particle size, large specific surface area, and highly active surface, provide more nucleation sites for the matrix, thus promoting heterogeneous nucleation. However, inorganic nanoparticles generally do not have good compatibility with organic materials, and due to their small particle size and high surface energy, they are in an energy unstable state, leading to uneven dispersion and agglomeration problems when added to phase change materials. Therefore, they cannot act as nucleation sites in microcapsules and cannot promote nucleation, resulting in poor effectiveness in reducing capsule supercooling.

[0005] Therefore, it is necessary to provide a new method to eliminate the problem of undercooling in phase change microcapsules. Summary of the Invention

[0006] To address the shortcomings of existing nucleating agents in eliminating supercooling in phase change microcapsules and affecting their morphology, this invention provides a silane-modified MXene, its preparation method, and its application. The high-performance silane-modified MXene serves as a nucleating agent to eliminate supercooling in phase change microcapsules. Two-dimensional material MXene possesses good thermal stability and tunable surface functional groups. Through silane modification, it can be stably and uniformly dispersed in organic phase change materials, acting as excellent nucleation sites and promoting heterogeneous nucleation. The phase change microcapsules prepared by this invention contain a minimal amount of silane-modified MXene, which acts as a nucleating agent to eliminate supercooling, resulting in good capsule morphology and high enthalpy.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a method for preparing silane-modified MXene, comprising the following steps:

[0009] (1) Disperse MAX powder in a mixed solution of lithium fluoride and hydrochloric acid, heat and stir to etch; after the reaction is complete, wash the precipitate; redisperse the washed precipitate in water, perform ultrasonic peeling under inert gas protection, then centrifuge to collect the stable colloidal dispersion, freeze dry to obtain MXene;

[0010] (2) Take the MXene obtained in step (1) and disperse it in a mixed solution of anhydrous ethanol and water. Perform the first sonication to obtain nano-sized MXene. Add silane coupling agent and perform the second sonication. Heat in an oil bath and stir to obtain a suspension. Centrifuge and wash with anhydrous ethanol to remove unreacted silane coupling agent. Freeze dry to obtain silane-modified MXene.

[0011] Preferably, in the preparation method of the silane-modified MXene, in step (1), the mass ratio of MAX powder to lithium fluoride is 2~4:3~5.

[0012] Preferably, in the preparation method of the silane-modified MXene, MAX is a layered ceramic with excellent ductility, where M represents a transition metal element, A represents elements IIIA and IVA, and X represents carbon / nitrogen elements. The MAX powder is Ti3AlC2 powder.

[0013] Preferably, in the preparation method of the silane-modified MXene, in step (1), the precipitate is washed successively with hydrochloric acid, lithium chloride solution (concentration 3wt%), and water.

[0014] Preferably, in the preparation method of the silane-modified MXene, in step (1), the stirring speed is 150~300 rpm, the stirring time is 36~48 h, the heating temperature is 35~45℃; the centrifugation speed is 5000 rpm, the time is 5~10 min, the washing times are 1~3 times; the ultrasonic power is 600~800 W, and the time is 60~80 min.

[0015] Preferably, in the preparation method of the silane-modified MXene, in step (2), the silane coupling agent is one of n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane. Coupling agents are a class of substances with an amphoteric structure. Some groups in their molecules can react with chemical groups on inorganic surfaces to form chemical bonds; other groups have organophilic properties and can generate strong intermolecular interactions with organic molecules, thereby firmly binding two materials with drastically different properties together. The silane coupling agents specified in this invention contain trimethoxy and triethoxy groups, which hydrolyze during modification to generate trihydroxy groups that undergo co-condensation reactions with the -OH functional groups on the MXene surface. Furthermore, all selected are alkylsilanes, and their carbon functional groups are all long-chain alkanes, exhibiting high chemical similarity to the phase change material to be coated in this invention, thus demonstrating excellent compatibility. The use of alkylsilane modification ensures that nano-sized MXene remains well dispersed in the phase change core material, preventing aggregation and precipitation. Microscopically, MXene can be uniformly distributed within each microcapsule, acting as crystal nuclei and promoting heterogeneous nucleation of the capsules. Macroscopically, this manifests as an increase in capsule crystallization temperature and elimination of supercooling.

[0016] Preferably, in the method for preparing silane-modified MXene, in step (2), the mass ratio of MXene, anhydrous ethanol, water and silane coupling agent is 1.5:158:5:1.

[0017] Preferably, in the preparation method of the silane-modified MXene, in step (2), the power of the first and second ultrasonication is 80~100W, with an interval of 1.5s (the instrument probe works for 1.5s and pauses for 1.5s), the time for the first ultrasonication is 20~30min, and the time for the second ultrasonication is 5~20min; the stirring speed is 250~350rpm, the stirring heating temperature is 60~70℃, and the stirring time is 4~6h; the centrifugation speed is 8000rpm, and the centrifugation time is 15min.

[0018] A silane-modified MXene was prepared according to the above preparation method.

[0019] A method for eliminating supercooling in paraffin-based phase change microcapsules involves adding the aforementioned silane-modified MXene during the microcapsule preparation process.

[0020] A phase change microcapsule, wherein the above-mentioned silane-modified MXene is added to the core material, the phase change microcapsule has no supercooling and has a high enthalpy value of over 190 J / g.

[0021] A method for preparing the above-mentioned phase change microcapsules includes the following steps:

[0022] (1) Melamine, formaldehyde solution and water are mixed, the pH value is adjusted to alkaline with triethanolamine and stirred to obtain melamine-formaldehyde (MF) prepolymer, which is denoted as solution A; the silane-modified MXene is heated and stirred with organic phase change material to obtain solution B; the emulsifier is dissolved in water and the pH is adjusted to acidic with citric acid to obtain solution C;

[0023] (2) Mix solution B and solution C, heat to perform shear emulsification, then add solution A to carry out polymerization reaction. After the reaction is completed, freeze-dry the resulting emulsion to obtain phase change microcapsules.

[0024] Preferably, in the method for preparing the phase change microcapsules, in step (1), the mass ratio of melamine, formaldehyde solution, and water is 9~15:15~20:60~80. The mass fraction of the formaldehyde solution is 37%.

[0025] Preferably, in the preparation method of the phase change microcapsules, in step (1), the pH value is adjusted to 9.5 with triethanolamine. After adjusting the pH with triethanolamine, the stirring speed is 250~300 rpm, the stirring time is 1~1.5 h, and the stirring temperature is 50℃.

[0026] Preferably, in the preparation method of the phase change microcapsules, in step (1), the organic phase change material is at least one of tetradecane, hexadecane, octadecane, eicosane, docosane and composite paraffin phase change material; the mass ratio of silane-modified MXene to organic phase change material is 0.001~0.005:1; when mixing silane-modified MXene and organic phase change material, the stirring speed is 200~250 rpm, the stirring time is 30~40 min, and the stirring temperature is 60~70℃.

[0027] Preferably, in the method for preparing phase change microcapsules, in step (1), the emulsifier is one or more of the following anionic surfactants: styrene-maleic anhydride (SMA), sodium dodecylbenzene sulfonate (SDBS), sodium alginate, and sodium dodecyl sulfate; the mass ratio of emulsifier to water is 1~4:45~50; and the pH is adjusted to 3.8~4.1 with citric acid.

[0028] Preferably, in the method for preparing phase change microcapsules, in step (2), the heating temperature for shear emulsification is 60~70℃, the shearing speed is 5000~7000rpm, and the shearing time is 0.5h; the polymerization reaction temperature is 75~80℃, and the reaction time is 1~1.5h.

[0029] This invention is the first to propose using silane-modified MXene as a nucleating agent to eliminate the supercooling of paraffin-based phase change microcapsules. The silane-modified MXene of this invention is a two-dimensional sheet material obtained by selectively etching the MAX atom layer with HF solution to remove the atom layer. While traditional MXene materials possess high surface activity and a large specific surface area, making them suitable nucleation sites in phase change materials, their small size, strong surface activity, large density difference with phase change materials, and predominantly hydrophilic and oleophobic properties lead to problems such as uneven dispersion, agglomeration, and precipitation in phase change materials. This invention utilizes the hydrolytic groups of a silane coupling agent to generate siloxanes from inorganic substances. The organic functional groups of silanes combine with organic substances, acting as "molecular bridges" between organic and inorganic materials. Modifying MXene with a silane coupling agent improves its compatibility with organic substances, thus solving the problem of uneven dispersion of MXene in phase change materials. Furthermore, adding a very small amount of silane-modified MXene can eliminate capsule supercooling and also prepare paraffin phase change microcapsules with high enthalpy and no supercooling.

[0030] The present invention discloses the following technical effects:

[0031] 1. This invention uses a silane coupling agent to modify two-dimensional MXene nanosheets in one step. The silane coupling agent has a unique chemical structure that combines inorganic and organic elements, and its functional groups react with the abundant functional groups on the surface of MXene to form a stable cross-linked structure, giving MXene good hydrophobicity and thermal stability. This process is simple, fast, and inexpensive.

[0032] 2. Unlike the traditional nucleating agents currently used in phase change microcapsules, this invention uses silane-modified MXene, a two-dimensional material, as a nucleating agent to eliminate the supercooling of phase change microcapsules. Adding 0.1wt%~0.5wt% of silane-modified MXene can serve as a nucleating agent to eliminate the supercooling of phase change microcapsules, and overcomes the defects of using large amounts of traditional nucleating agents, such as capsule morphology depression and significant reduction in enthalpy.

[0033] 3. The prepared paraffin-based phase change microcapsules have a narrower size distribution, a higher specific surface area, and improved heat transfer efficiency. The encapsulation rate of the phase change microcapsules is over 80%, exhibiting excellent heat storage performance, and can be practically applied in fields such as construction, textiles, and solar thermal storage. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 FT-IR curves of MXene, silane-modified MXene (ODTMS-MXene) from Example 3, and octadecyltrimethoxysilane (ODTMS);

[0036] Figure 2 The images shown are scanning electron microscope (SEM) images of silane-modified MXene before and after ultrasonic fragmentation in Example 3, and energy dispersive spectroscopy (EDS) images before ultrasonic fragmentation. (a) is the SEM image before ultrasonic fragmentation, (b) is the EDS image before ultrasonic fragmentation, and (c) and (d) are the SEM images after ultrasonic fragmentation.

[0037] Figure 3 The transmitted light intensity variation curve of MXene-paraffin dispersion in Example 3 (lasting 24 hours).

[0038] Figure 4 This is a particle size distribution diagram of MXene in Example 3;

[0039] Figure 5 The images shown are scanning electron microscope (SEM) images of the phase change microcapsules in each embodiment. (a) to (h) correspond to the SEM images of Examples 1 to 8.

[0040] Figure 6 The following are DSC curves of phase change microcapsules in each embodiment: (a) C18 microcapsules without nucleating agent; (b) DSC test results of C18 phase change microcapsules with unmodified MXene; (c)~(h) curves correspond to the DSC test results of Examples 3~8.

[0041] Figure 7 The figures (a) to (h) are particle size distribution curves of phase change microcapsules in each embodiment. The curves (a) to (h) correspond to the particle size distribution curves of capsules in Examples 1 to 8, respectively. Detailed Implementation

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0046] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0047] Example 1: A method for preparing phase change microcapsules

[0048] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain an MF prepolymer solution. 72 g of octadecane core material, 6.15 g of styrene-maleic anhydride powder, and 97.5 g of deionized water were added to a reaction vessel and emulsified at 70°C and a shear rate of 12000 rpm for 1 hour to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 90°C for 2 hours of polymerization. After filtration, the mixture was freeze-dried at -60°C for 72 hours to obtain octadecane phase change microcapsules (phase change microcapsules without nucleating agent). The enthalpy value of the octadecane phase change capsules was 179.95 J / g.

[0049] Example 2: A method for preparing phase change microcapsules using MXene as a nucleating agent

[0050] (1) Preparation of MXene:

[0051] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0052] (2) Preparation of phase change microcapsules

[0053] 3.6 g of melamine powder, 6.4 g of 37% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of MXene and 71.64 g of octadecane core material were mixed and added to a beaker. The mixture was stirred in a 60°C water bath for 25 minutes to obtain a mixed core material. 72 g of the mixed core material was mixed with 6.15 g of styrene-maleic anhydride powder dissolved in 97.5 g of deionized water. Citric acid was added to adjust the pH to 4, and the mixture was poured into a reaction vessel. The mixture was emulsified at 70°C and a shear rate of 6000 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1 hour of polymerization. After filtration and freeze-drying at -40℃ for 24 h, octadecane phase change microcapsules (unmodified MX-phase change microcapsules) were obtained with an enthalpy of 164.54 J / g.

[0054] Example 3: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0055] (1) Preparation of MXene:

[0056] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0057] (2) Silane-modified MXene

[0058] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of octadecyltrimethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0059] (3) Preparation of phase change microcapsules

[0060] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene was mixed with 71.64 g of octadecane core material and added to a beaker. The mixture was stirred in a 60°C water bath for 25 minutes to obtain a mixed core material. 72 g of the mixed core material was mixed with 6.15 g of styrene-maleic anhydride powder dissolved in 97.5 g of deionized water. Citric acid was added to adjust the pH to 4, and the mixture was poured into a reaction vessel. The mixture was emulsified at 70°C and a shear rate of 6500 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1 hour of polymerization. After filtration and freeze-drying at -40℃ for 24 hours, octadecane phase change microcapsules (C18 phase change microcapsules) were obtained with an enthalpy value of 182.39 J / g.

[0061] Example 4: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0062] (1) Preparation of MXene

[0063] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0064] (2) Silane-modified MXene

[0065] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of n-octyltrimethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0066] (3) Preparation of phase change microcapsules

[0067] 3.6 g of melamine powder, 6.4 g of 37% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene was mixed with 71.64 g of eicosane core material and added to a beaker. The mixture was stirred in a 70°C water bath for 25 minutes to obtain a mixed core material. 72 g of the mixed core material was mixed with 6.15 g of styrene-maleic anhydride powder dissolved in 97.5 g of deionized water. Citric acid was added to adjust the pH to 4, and the mixture was poured into a reaction vessel. The mixture was emulsified at 60°C and a shear rate of 7000 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1.5 hours for polymerization. After filtration and freeze-drying at -40℃ for 24 hours, eicosane phase change microcapsules (C20 phase change microcapsules) were obtained with an enthalpy value of 186.92 J / g.

[0068] Example 5: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0069] (1) Preparation of MXene

[0070] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0071] (2) Silane-modified MXene

[0072] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of n-octyltriethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0073] (3) Preparation of phase change microcapsules

[0074] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene and 71.64 g of docosane core material were mixed and added to a beaker. The mixture was stirred in a 75°C water bath for 30 minutes to obtain a mixed core material. 72 g of the mixed core material was dissolved in 97.5 g of deionized water with 6.96 g of sodium alginate powder. Citric acid was added to adjust the pH to 4, and the mixture was poured into a reaction vessel. The mixture was emulsified at 60°C and a shear rate of 7000 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 80°C for 1.5 hours of polymerization. After filtration and freeze-drying at -40℃ for 24 hours, docosane phase change microcapsules (C22 phase change microcapsules) were obtained with an enthalpy value of 195.21 J / g.

[0075] Example 6: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0076] (1) Preparation of MXene

[0077] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0078] (2) Silane-modified MXene

[0079] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of hexadecyltrimethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0080] (3) Preparation of phase change microcapsules

[0081] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene was mixed with 71.64 g of hexadecane core material and added to a beaker. The mixture was stirred in a 65°C water bath for 15 minutes to obtain a mixed core material. 72 g of the mixed core material was mixed with 8.12 g of sodium dodecyl sulfate powder dissolved in 97.5 g of deionized water. Citric acid was added to adjust the pH to 4, and the mixture was poured into a reaction vessel. The mixture was emulsified at 60°C and a shear rate of 6000 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1 hour of polymerization. After filtration and freeze-drying at -40℃ for 24 h, hexadecane phase change microcapsules (C16 phase change microcapsules) were obtained with an enthalpy of 176.24 J / g.

[0082] Example 7: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0083] (1) Preparation of MXene

[0084] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0085] (2) Silane-modified MXene

[0086] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of dodecyltrimethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0087] (3) Preparation of phase change microcapsules

[0088] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene was mixed with 71.64 g of tetradecane core material and added to a beaker. The mixture was stirred in a 50°C water bath for 15 minutes to obtain a mixed core material. 72 g of the mixed core material was dissolved in 97.5 g of deionized water with 8.65 g of sodium dodecylbenzenesulfonate powder. Citric acid was added to adjust the pH to 4, and the solution was poured into a reaction vessel. The mixture was emulsified at 60°C and a shear rate of 6500 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1 hour of polymerization. After filtration and freeze-drying at -40℃ for 24 h, tetradecane phase change microcapsules (C14 phase change microcapsules) were obtained with an enthalpy of 168.48 J / g.

[0089] Example 8: A method for preparing phase change microcapsules with no supercooling and high enthalpy using silane-modified MXene as a nucleating agent.

[0090] (1) Preparation of MXene

[0091] 3.5 g of lithium fluoride was dissolved in 40 mL of 28 wt% hydrochloric acid solution, and then 2 g of Ti3AlC2 powder was added. The etching reaction was carried out at 38 °C and 300 rpm for 48 h. After the reaction was completed, the mixture was centrifuged (5000 rpm, 10 min). The supernatant was discarded to obtain the precipitate. The precipitate was washed three times with 3 wt% hydrochloric acid solution and lithium chloride solution, and then washed with deionized water until the pH of the solution was >6.0. The centrifugation speed was 5000 rpm for 5 min. The precipitate was redispersed in 150 mL of deionized water and broken up in an ice bath under nitrogen protection for 1 h (power 700 W, working time 1.5 s, pause time 1.5 s). The stable dispersion of the colloid was obtained by centrifugation at 3500 rpm and freeze-dried at -60 °C for 72 h to obtain 1.5 g of MXene.

[0092] (2) Silane-modified MXene

[0093] The MXene prepared in step (1) was directly added to a mixed solution of 195 mL ethanol and 5 mL deionized water. The mixture was disrupted in an ice bath for 30 min using a cell disruptor (output power of 800 W, working time of 1.5 s, and pause time of 1.5 s) to obtain a uniform black dispersion. Then, 1 g of dodecyltriethoxysilane was added and the mixture was disrupted in an ice bath for 15 min using the same parameters. The mixture was then stirred in an oil bath at 65 °C for 5 h while maintaining reflux. Finally, the suspension was centrifuged (8000 rpm, 15 min) to obtain the precipitate, which was washed three times with anhydrous ethanol and freeze-dried for 24 h to obtain silane-modified MXene.

[0094] (3) Preparation of phase change microcapsules

[0095] 3.6 g of melamine powder, 6.4 g of 37 wt% formaldehyde solution, and 31 g of deionized water were added to a flask. The pH was adjusted to 8.5 with 10 wt% triethanolamine solution, and the mixture was stirred in a 50°C oil bath for 1 hour at 250 rpm to obtain the MF prepolymer solution. 0.36 g of silane-modified MXene was mixed with 71.64 g of octadecane core material and added to a beaker. The mixture was stirred in a 60°C water bath for 15 minutes to obtain a mixed core material. 72 g of the mixed core material was dissolved in 97.5 g of deionized water with 8.65 g of sodium dodecylbenzenesulfonate powder. Citric acid was added to adjust the pH to 4, and the solution was poured into a reaction vessel. The mixture was emulsified at 65°C and a shear rate of 7000 rpm for 0.5 hours to form a stable O / W emulsion. The MF prepolymer solution was then added, and the temperature was increased to 75°C for 1 hour of polymerization. After filtration and freeze-drying at -40℃ for 24 hours, octadecane phase change microcapsules (C18 phase change microcapsules) were obtained with an enthalpy value of 180.45 J / g.

[0096] In this embodiment of the invention, a Fourier transform infrared spectroscopy (FT-IR, FT-IR 6600, USA) was used to characterize the functional group structure of silane-modified nanosheets with hydrophobic properties.

[0097] This invention uses scanning electron microscopy (SEM, SU-8200, Japan) to characterize the microstructure of two-dimensional MXene nanosheets with nanoscale dimensions, and to characterize the microstructure of phase change microcapsules.

[0098] This invention uses a stability analyzer (Turbiscan Lab, USA) to characterize the dispersion stability of silane-modified MXene in paraffin cores from various embodiments. The test program was set to a temperature of 50°C, a duration of 24 hours, a scan interval of 1 minute, and a total of 1440 scans.

[0099] The present invention uses a particle size analyzer (Nano-Zs, UK) to characterize the size distribution and average size of phase change microcapsules and MXene nanosheets in each embodiment.

[0100] The present invention uses a DSC instrument (METTLER-DSC3, Switzerland) to characterize the phase change temperature point and the heat storage enthalpy of the phase change microcapsules in each embodiment.

[0101] The FT-IR curves of MXene, silane-modified MXene (ODTMS-MXene) from Example 3, and octadecyltrimethoxysilane (ODTMS) are shown below. Figure 1 ;

[0102] Example 3: Scanning electron microscopy (SEM) images of silane-modified MXene before and after ultrasonic disruption, and energy dispersive spectroscopy (EDS) image before ultrasonic disruption are shown in the figure. Figure 2 (a) is the SEM image before ultrasonic fragmentation, (b) is the energy spectrum image before ultrasonic fragmentation, and (c) and (d) are the SEM images after ultrasonic fragmentation.

[0103] Example 3: Transmitted light intensity variation curve of MXene-paraffin dispersion (lasting 24 hours) is shown in the figure. Figure 3 ;

[0104] The particle size distribution diagram of MXene in Example 3 is shown below. Figure 4 ;

[0105] Scanning electron microscope images of the phase change microcapsules in each embodiment are shown below. Figure 5 (a) to (h) correspond to the SEM images of Examples 1 to 8;

[0106] The DSC curves of the phase change microcapsules in each embodiment are shown below. Figure 6 (a) C18 microcapsules without nucleating agent; (b) DSC test results of C18 phase change microcapsules with unmodified MXene; (c)~(h) curves corresponding to the DSC test results of Examples 3~8;

[0107] The particle size distribution curves of the phase change microcapsules in each embodiment are shown in the figure. Figure 7 The curves (a) to (h) correspond to the capsule particle size distribution curves of Examples 1 to 8, respectively.

[0108] Experimental Results Analysis

[0109] The infrared spectrum of MXene shows that at 3450 cm⁻¹ -1 and 1384cm -1 The peak corresponds to the stretching vibration peak of the OH bond: 1633 cm⁻¹ -1 Corresponding to the tensile vibration of the C=O bond; at 555 cm -1 The peak corresponds to the stretching vibration of the Ti-O bond. The infrared spectrum of octadecyltrimethoxysilane shows a peak at 2918 cm⁻¹. -1 and 2855 cm -1The peak corresponds to the stretching vibrations of -CH3 and -CH2-. 1435 cm⁻¹ -1 1081 cm -1 This corresponds to the bending vibration of the CH bond and the absorption of Ti-O. The infrared spectrum of ODTMS-MXene shows a value at 2917 cm⁻¹. -1 2849 cm -1 The peak corresponds to the stretching vibrations of -CH3 and -CH2-, at 1467 cm⁻¹. -1 The stretching vibration corresponding to the CH bond occurs at 720 cm⁻¹. -1 The peak represents the tensile vibration of Si-O-Ti generated after successful grafting of ODTMS and MXene, indicating that the MXene modification was successful.

[0110] Electron microscopy images of MXene show that after ultrasonic fragmentation, MXene forms sheet-like structures with a size of tens of nanometers. These structures have a small size and a high specific surface area, which can serve as good nucleation sites in microcapsules and reduce capsule supercooling.

[0111] The light intensity change curve obtained from the dispersion stability test shows that the maximum error of the light intensity change curve within 0~24h is within 0.5%, indicating that the silane-modified MXene has good hydrophobicity, is uniformly dispersed in the paraffin core material, and has no agglomeration or sedimentation.

[0112] The particle size distribution curve of the modified MXene shows that the size distribution of the modified MXene is between 50 nm and 100 nm, with an average particle size of 80 nm. The particle size distribution is concentrated and consistent with the size in the electron micrograph, which can serve as a good nucleation site in the microcapsule.

[0113] Electron microscopy images of the phase change microcapsules in Examples 1, 3-8 show that the prepared phase change microcapsules with different core materials all exhibit regular spherical shapes, smooth and dense surfaces, uniform particle size, and no adhesion or agglomeration between capsules. In Example 2, the capsules containing unmodified MXene showed shell material impurities, indicating that the unmodified MXene was unevenly dispersed in the phase change material and exhibited agglomeration. This agglomeration affected the polymerization of the shell material at the oil-water interface, resulting in poor capsule encapsulation.

[0114] The DSC test results of Examples 3-8 show that the phase change microcapsules with silane-modified MXene exhibited a coverage rate of over 80% based on enthalpy calculations, and the supercooling was eliminated in all cases. These results indicate that the addition of the modified MXene nucleating agent did not negatively impact the capsule performance. In Examples 1-2, both the capsules without nucleating agents and those with unmodified MXene nucleating agents exhibited supercooling.

[0115] The particle size test results of Examples 1-8 show that the average particle size of the prepared capsules is about 1-5 μm. The capsules are small in size, have a higher specific surface area, and have higher heat transfer efficiency.

[0116] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a silane-modified MXene, characterized by, The method comprises the following steps: (1) dispersing MAX powder in a mixed solution of lithium fluoride and hydrochloric acid, and etching by heating and stirring; after the reaction is completed, washing the precipitate; redispersing the washed precipitate in water, and performing ultrasonic peeling under the protection of inert gas; then, centrifugally collecting a stable colloidal dispersion, and obtaining MXene by freeze-drying; (2) dispersing the MXene obtained in step (1) in a mixed solution of anhydrous ethanol and water, performing first ultrasonic treatment to obtain nanoscale MXene; adding a silane coupling agent, and performing second ultrasonic treatment; heating in an oil bath while stirring and maintaining reflux to obtain a suspension; removing unreacted silane coupling agent, and obtaining silane-modified MXene by freeze-drying; In step (2), the silane coupling agent is one of n-octyltrimethoxysilane, n-octyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane. In step (2), the power of the first ultrasonic treatment and the second ultrasonic treatment is 80-100 W, with an interval of 1.5 s; the first ultrasonic treatment is performed for 20-30 min; the second ultrasonic treatment is performed for 5-20 min; and the interval of 1.5 s is that the instrument probe is ultrasonically treated for 1.5 s and is paused for 1.5 s.

2. The method for preparing silane-modified MXene according to claim 1, characterized in that, In step (1), the mass ratio of the MAX powder to lithium fluoride is 2-4:3-5.

3. The method for preparing silane-modified MXene according to claim 1, characterized in that, In step (1), the precipitate is washed with hydrochloric acid, a lithium chloride solution, and water in sequence. 4.The method of claim 1, wherein the silane-modified MXene is prepared by the method of claim 1. In step (2), the mass ratio of the MXene, anhydrous ethanol, water, and the silane coupling agent is 1.5:158:5:

1.

5. A silane-modified MXene, characterized in that, The silane-modified MXene is prepared by the method according to any one of claims 1-4.

6. A method for eliminating supercooling of paraffin-based phase change microcapsules, characterized by, The silane-modified MXene is added in the preparation of microcapsules.

7. A phase change microcapsule characterized by, The silane-modified MXene is added in the core material.

8. A method of producing the phase change microcapsules of claim 7, characterized by, The method comprises the following steps: (1) mixing melamine, a formaldehyde solution, and water, adjusting the pH value to alkaline by triethanolamine, and stirring to obtain a melamine-formaldehyde prepolymer, denoted as solution A; The silane-modified MXene according to claim 5 is mixed with an organic phase change material by heating and stirring to obtain solution B; an emulsifier is dissolved in water, and the pH value is adjusted to 3.8-4.1 by citric acid to obtain solution C; the emulsifier is one or more of styrene-maleic anhydride, sodium dodecylbenzenesulfonate, sodium alginate, and sodium dodecyl sulfate; (2) mixing solution B and solution C, performing shearing emulsification by heating, then adding solution A, and performing a polymerization reaction; after the reaction is completed, the obtained emulsion is freeze-dried to obtain phase change microcapsules.

9. The method of claim 8, wherein the microcapsules are phase change microcapsules. In step (1), the mass ratio of melamine, the formaldehyde solution, and water is 9-15:15-20:60-80.

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