A method for preparing independently supported MXenes hydrogel films

Abstract

This invention relates to a method for preparing an independently supported MXenes hydrogel film, comprising the following steps: forming a wet film by vacuum filtration of an MXenes suspension; immersing a filter paper containing the wet film entirely in an acid solution, utilizing hydrated hydrogen ions to induce interlayer confined crosslinking to form a gel structure, and then separating it from the filter paper; and washing the resulting gel film with deionized water until the pH value is close to neutral to obtain an independently supported MXenes hydrogel film. This method does not require the introduction of polymers or second-phase materials, retains the intrinsic conductive network of MXenes, and the resulting gel film possesses a three-dimensional porous structure, excellent mechanical stability and conductivity, making it suitable for applications such as aqueous energy storage, electromagnetic shielding, and flexible electronic devices. It has the advantages of a green process, controllable structure, and suitability for large-scale preparation.

Description

Technical Field

[0001] This invention relates to the field of two-dimensional functional material preparation, specifically to a method for preparing an independently supported MXenes hydrogel film, which belongs to the preparation and application technology of novel conductive gel materials, and is particularly suitable for fields such as aqueous electrochemical energy storage devices, electromagnetic shielding materials, and flexible electronic devices. Background Technology

[0002] Given the widespread attention MXenes materials have received in fields such as flexible electronics, aqueous energy storage, and electromagnetic shielding due to their excellent conductivity, mechanical properties, and abundant surface functional groups, the structural construction and performance regulation of MXenes hydrogel films, as an important form of two-dimensional material assembly, have become a research focus.

[0003] Currently, the construction of independently supported MXenes hydrogel films often relies on the introduction of polymers (such as polyvinyl alcohol and polyacrylamide) or inorganic / organic additives as supporting frameworks or cross-linking bridges. These second-phase materials form composite networks with MXenes nanosheets through hydrogen bonds, electrostatic interactions, or chemical bonds, thereby enhancing their mechanical stability. However, this composite strategy has significant drawbacks: on the one hand, polymers or additives can occupy conductive paths between nanosheets, disrupting the intrinsic conductive network of MXenes and leading to a decrease in overall electron transport performance; on the other hand, the composite assembly process involves complex material selection and proportion control, increasing the difficulty and uncertainty of the process, while the introduction of some organic additives also brings environmental pollution and high cost issues.

[0004] Furthermore, in traditional vacuum filtration processes, the presence of numerous disordered water molecules between MXenes layers results in a loose wet film structure with insufficient interlayer forces, making it difficult to achieve a self-supporting and stable structure independent of the substrate. This structural relaxation phenomenon limits its direct application in flexible, independent devices, necessitating post-processing strengthening or carrier assistance, which further increases system complexity.

[0005] Therefore, current technology urgently needs a simple, green, and controllable preparation strategy to achieve spontaneous confined crosslinking and stable support structure construction of pure-phase MXene nanosheets without compromising their intrinsic properties, thereby promoting their application in advanced devices. This invention addresses these issues by employing the induction mechanism of hydrated hydrogen ions in acid solution to endow MXene films with structural stability and self-supporting capabilities, avoiding the performance sacrifices and process complexities of traditional methods. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a method for preparing an independently supported MXenes hydrogel film, so as to solve the problems of impaired intrinsic conductivity, poor structural stability and complex process of MXenes caused by the reliance on polymer composites in the prior art, thereby realizing the construction of a pure phase, self-supporting and structurally stable MXenes gel film.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In one embodiment of the present invention, a method for preparing an independently supported MXenes hydrogel film is provided, comprising the following steps: 1. Vacuum filter the MXenes suspension until the suspension stops flowing, forming a wet MXenes film on the filter paper; 2. Immerse the entire filter paper with the MXenes wet membrane attached in an acid solution to transform the MXenes wet membrane into an independently supported gel film, and then separate it from the filter paper; 3. The separated gel film is repeatedly washed with deionized water until the pH value is close to neutral to obtain an independently supported MXenes hydrogel film.

[0008] Furthermore, the hydrogen ion concentration of the acid solution in step (2) is not less than 1 mol / L, so as to ensure that the hydrated hydrogen ions can fully enter the MXenes interlayer and achieve effective interlayer confinement crosslinking.

[0009] Preferably, the MXenes wet film is immersed in the acid solution for no less than 10 seconds to ensure that the gel network structure is fully and stably formed.

[0010] Optionally, the acid solution may be a sulfuric acid solution, a hydrochloric acid solution, or a mixture of both, to accommodate the chemical stability and crosslinking reaction efficiency of different MXenes systems.

[0011] Furthermore, the MXenes mentioned in step (1) are selected from titanium-based MXenes, vanadium-based MXenes, or niobium-based MXenes to cover the mainstream two-dimensional transition metal carbon / nitride systems.

[0012] Preferably, the MXenes are Ti3C2T. X V2CT X Ti3CNT X Ti2CT X Ti4N3T X or Nb4C3T X T x These represent surface functional groups, such as –OH, –O, or –F.

[0013] Furthermore, the independently supported MXenes hydrogel film has a three-dimensional porous structure, which is beneficial for improving the specific surface area, the number of ion channels, and mechanical flexibility.

[0014] Alternatively, the preparation method does not add polymer crosslinking agents or second-phase support materials throughout the process, ensuring that the resulting film has a pure-phase structure and retains the intrinsic conductive network and physicochemical properties of MXenes to the greatest extent.

[0015] Furthermore, the treatment temperature of the acid solution in step (2) is controlled between 15°C and 35°C to balance reactivity and material stability.

[0016] Preferably, the filtration in step (1) uses a filter membrane with a pore size of 0.2–0.5 μm to improve the uniformity of film formation and separation efficiency.

[0017] Based on the above technical solution, the method for preparing independently supported MXenes hydrogel films of the present invention, through steps such as vacuum filtration film formation, acid solution-induced self-supporting structure formation, and neutralization and shaping in pure water, successfully achieves the formation of a stable three-dimensional structure of pure-phase MXenes nanosheets between layers without introducing a second-phase material. This method not only completely preserves the intrinsic conductive network of MXenes but also significantly improves its mechanical strength and independent support capability, providing effective support for its large-scale green applications in fields such as aqueous electrochemical energy storage, electromagnetic shielding, and flexible electronic devices.

[0018] Specifically, this invention utilizes the negatively charged surface of MXenes nanosheets and leverages the small size and high mobility of hydrated hydrogen ions in acidic solutions to achieve spontaneous embedding between the nanosheet layers. This reduces interlayer spacing and enhances interlayer attraction through electrostatic interactions, thereby forming a stable gel network structure. Compared to traditional techniques relying on polymer crosslinking agents or supporting materials, the MXenes hydrogel film prepared by this invention exhibits significant advantages in terms of electrical conductivity, purity, environmental friendliness, and mechanical properties.

[0019] Furthermore, the process of this invention is simple, the experimental conditions are mild, and there is no need to use toxic reagents or complex equipment, which has good potential for industrial scale-up. The obtained hydrogel film can be prepared in large size and continuously, and is suitable for the construction of advanced devices such as flexible supercapacitors, conductive film materials, and electromagnetic shielding films, providing a new technical path and application foundation for the integrated development of the structure and function of MXenes materials. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the appearance of the independently supported MXenes hydrogel film obtained by crosslinking induced by acid solution in an embodiment of the present invention.

[0021] Figure 2 MXene (Ti3C2T) in this invention X A comparison of the X-ray diffraction (XRD) patterns of the wet film and the gel film (MXene-3M) obtained after acid treatment shows the changes in the interlayer structure before and after acid treatment. Detailed Implementation

[0022] To better understand the technical solution and its implementation effects of the present invention, the preparation method of the independently supported MXenes hydrogel film of the present invention is described in detail below with reference to several specific embodiments. The raw material ratios, processing conditions and characterization results used in these embodiments are all based on experimental verification and can truly reflect the technical features and practical advantages of the present invention.

[0023] It should be understood that these embodiments are only used to illustrate preferred embodiments of the present invention and do not constitute a limitation on the scope of protection of the present invention. For those skilled in the art, various equivalent substitutions, modifications or optimizations made thereto without departing from the spirit and substance of the present invention should be included within the scope of protection of the present invention.

[0024] Example 1: Ti3C2T X Standard preparation process for raw materials This embodiment provides a method using Ti3C2T X A method for preparing independently supported MXene hydrogel films using MXene as a raw material is provided to illustrate the specific implementation process of the technical solution of this invention.

[0025] First, weigh out 30 mg of Ti3C2T X MXene powder was added to an appropriate amount of deionized water to form an MXenes suspension. Subsequently, ultrasonic dispersion was used to fully exfoliate and uniformly disperse the MXenes nanosheets in the aqueous solution, thereby obtaining a stable MXenes suspension system.

[0026] The MXenes suspension was then poured into a vacuum filtration apparatus equipped with an aqueous filter membrane (0.22 μm pore size) for filtration using a vacuum-assisted filtration method. As the filtration process proceeded, water was gradually extracted, and the MXenes nanosheets gradually stacked on the filter paper surface, forming a continuous and dense wet film structure. The filtration process was considered complete when the suspension ceased to flow and the filtrate was essentially filtered out. At this point, a relatively intact MXenes wet film was formed on the filter paper surface.

[0027] Subsequently, the filter paper coated with the MXenes wet film was removed from the filtration device and quickly immersed in a 3 mol / L sulfuric acid solution at room temperature. In this embodiment, the acid solution temperature was approximately 25°C, and the immersion time was 30 seconds. Under the influence of the acid solution, hydrated hydrogen ions in the solution spontaneously entered the interlayer space of the MXenes nanosheets due to the attraction of their negative charge, forming a confined distribution within the interlayer space. Because hydrated hydrogen ions have a small ionic radius, their entry into the interlayer space effectively compresses the MXenes interlayer spacing and enhances the electrostatic interaction between the nanosheets, thereby causing the MXenes wet film to gradually transform into a gel film with a three-dimensional network structure.

[0028] As the gel structure gradually forms, the adhesion between the MXenes membrane layer originally attached to the filter paper surface and the filter paper weakens, and the gel film can be peeled off from the filter paper surface as a whole, thus obtaining a complete and independently supported MXenes gel film.

[0029] The separated MXenes gel film was then removed and rinsed multiple times in deionized water to remove residual acid and excess hydrogen ions. The deionized water was continuously replaced during the rinsing process until the pH of the rinsing solution approached neutral. After thorough rinsing, an independently supported MXenes hydrogel film with good structural stability was obtained.

[0030] The resulting MXenes hydrogel film possesses a complete and continuous self-supporting structure, maintaining a stable morphology even without substrate support. Its macroscopic morphology is as follows: Figure 1 As shown. Results of X-ray diffraction analysis (e.g.) Figure 2 As shown, compared to the original MXenes wet film, its (002) diffraction peak changed from a broad state to a sharper diffraction peak and is located at about 6.3°. This indicates that the interlayer water molecule structure changed from a disordered state to a more ordered monolayer water structure. At the same time, it shows that hydrated hydrogen ions form a confinement effect in the interlayer and enhance the interlayer interaction between nanosheets.

[0031] Therefore, this embodiment can achieve confined cross-linking assembly between MXenes nanosheets without introducing polymer cross-linking agents or second-phase materials through a simple vacuum filtration-acid treatment-water washing process, thereby obtaining an MXenes hydrogel film with a three-dimensional porous structure that can be independently supported.

[0032] Example 2: V2CT X alternative routes for raw materials This embodiment aims to verify the applicability of the preparation method described in this invention to different MXenes material systems, using V2CT as an example. X Independently supported hydrogel films were prepared using MXenes precursors.

[0033] First, weigh out 30 mg of V2CT. X The powder was dispersed in an appropriate amount of deionized water and ultrasonically treated for 10 minutes to promote the exfoliation and uniform dispersion of the nanosheets, forming a stable V2CT. X MXenes suspension.

[0034] The resulting suspension was then poured into a vacuum filtration apparatus equipped with an aqueous filter membrane (0.22 μm pore size), and the vacuum pump was turned on to perform the filtration operation. As the filtration process proceeded, the water in the solution was gradually filtered out. X Nanosheets are deposited on the filter membrane surface to form a wet film. Filtration is considered complete when the flow of the filtrate essentially stops and a uniform black film layer covers the filter membrane surface, yielding V2CT attached to the filter membrane. X Wet film.

[0035] Then, the entire filter membrane, along with the V2CT on it, was... X Carefully remove the wet film and immediately immerse it in a 3 mol / L sulfuric acid aqueous solution, maintaining room temperature (25°C) for 30 seconds. The hydrated hydrogen ions in the acid solution will spontaneously enter V2CT under the influence of electrical potential. X The nanosheets effectively compress the interlayer spacing and enhance interlayer electrostatic interactions, promoting V2CT. X The wet film transforms into a stable gel film structure.

[0036] As acid treatment proceeds, the gel membrane gradually detaches from the filter membrane surface, exhibiting good integrity and self-support. At this point, the obtained V2CT... x The gel film was removed from the acid solution and repeatedly washed in deionized water, with the washing solution being changed each time until the pH value was close to neutral, in order to remove residual acidic components and side ions.

[0037] Ultimately obtained independent support V2CT X The hydrogel film can be freely suspended at room temperature, exhibiting excellent morphological integrity and flexibility. Its macroscopic morphology is similar to that of Ti3C2T in Example 1. X The prepared films were similar. Subsequent XRD analysis showed that V2CT... X The film also showed enhancement and narrowing of the (002) diffraction peak after acid treatment, indicating that hydrated hydrogen ions also play an effective confined crosslinking role in V-based MXenes, demonstrating that the method is universal and reproducible in various MXenes systems.

[0038] In summary, Example 2 further verifies the adaptability of the technical solution of the present invention to different MXenes family members, providing flexibility for material selection and industrial promotion, and has good engineering application potential.

[0039] Example 3: Experiment on optimization of acid treatment time This embodiment aims to investigate the effect of acid treatment time on the structural transformation of MXenes wet films and the final hydrogel film properties, and further verify the correlation between hydrated hydrogen ion-induced crosslinking behavior and treatment time. The experiment used Ti3C2T... X Using MXene as a raw material, and extending the acid treatment time based on Example 1, the structural changes and stability of the resulting hydrogel film were observed.

[0040] First, weigh out 30 mg of Ti3C2T X The powder was ultrasonically dispersed in deionized water to prepare a stable suspension. Subsequently, the suspension was filtered through an aqueous filter membrane (pore size 0.22 μm) using a vacuum filtration method until the liquid was basically dried, and MXene nanosheets formed a continuous and dense wet film on the filter membrane surface.

[0041] Next, the Ti3C2T obtained by filtration... X The wet membrane, along with the filter membrane, was removed as a whole and quickly placed in a 3 mol / L sulfuric acid solution for 2 minutes at room temperature (approximately 25°C) (i.e., four times longer than in Example 1). During this process, hydrated hydrogen ions in the acid continuously migrated into the MXene interlayer, inducing stronger electrostatic contraction and confined stacking between the nanosheets, thereby further enhancing the density and stability of the gel network.

[0042] After treatment, it was observed that the interface between the gel membrane and the filter membrane became looser, and the membrane could be peeled off as a whole without damaging the structure, exhibiting good self-supporting properties. The obtained gel membrane was repeatedly washed in deionized water until the pH of the washing solution stabilized between 6.5 and 7.0, thus obtaining the final independently supported MXenes hydrogel membrane.

[0043] X-ray diffraction (XRD) analysis of the sample showed that the (002) diffraction peak was narrower than that of Example 1, and the peak position shifted slightly to the right to 6.3°. This indicates that the water molecules in the MXene interlayer tended to be arranged in a highly ordered manner from a disordered state, and the interlayer spacing was further reduced, forming a denser and more uniform layered structure.

[0044] Furthermore, the resulting gel film maintained good flexibility and integrity after natural drying, indicating that extending the acid treatment time significantly improved the mechanical stability and interlayer bonding of the film.

[0045] This embodiment demonstrates that appropriately extending the acid treatment time helps enhance the confined cross-linking effect of hydrated hydrogen ions, further improving the density and structural order of the hydrogel film. However, excessively long treatment times should be avoided to prevent potential acid corrosion or functional group damage. Therefore, in practical applications, the treatment time can be rationally adjusted according to the required structural characteristics and material type to optimize film performance.

[0046] Example 4: Comparison of low-concentration acid treatment This embodiment aims to evaluate the effect of hydrogen ion concentration in acid solution on the gel structure formation ability of MXenes, in order to verify the regulatory effect of the acid concentration parameter on the stability and self-supporting properties of the gel network. A low concentration of sulfuric acid solution was used to treat Ti3C2T in the experiment. X The wet film was compared with that of Example 1 (3 mol / L).

[0047] First, weigh out 30 mg of Ti3C2T X The powder is dispersed in an appropriate amount of deionized water and then treated with ultrasound to form a stable MXenes suspension.

[0048] Subsequently, a wet membrane was prepared by vacuum-assisted filtration using an aqueous filter membrane (0.22 μm pore size). The filtration process was controlled until the filtrate was almost completely drained, and a continuous and uniform Ti3C2T layer was formed on the filter membrane surface. X Wet film.

[0049] Next, the filter membrane, along with the MXenes wet membrane attached to it, was removed as a whole and immediately immersed in a prepared 1 mol / L sulfuric acid aqueous solution. The solution was kept at room temperature (approximately 25°C) and soaked for 2 minutes. After the acid treatment, the wet membrane was removed from the acid solution, and the bonding state between it and the filter membrane was observed.

[0050] Experimental results show that under 1 mol / L acid conditions, the MXenes wet membrane can still be transformed into a gel film with a certain degree of integrity, and can be partially peeled off from the filter membrane surface during the cleaning process. However, the peeling process is not as smooth as that of samples treated with high concentration acid (such as Example 1), and slight breakage or adhesion occurs in some edge areas.

[0051] The obtained gel film was repeatedly washed in deionized water until the pH of the washing solution was close to neutral. It was then removed for morphological observation and structural characterization. The obtained film possesses a certain degree of independent support, maintaining a flat state for a short time without substrate support. However, during natural drying, the structure is prone to slight warping and collapse, indicating that the density and stability of its internal interlayer structure are lower than those of the high-concentration acid-treated sample.

[0052] XRD test results show that the (002) diffraction peak after treatment is wider than that of the sample treated with high concentration of acid, and the diffraction angle is slightly lower, indicating that the interlayer hydrated hydrogen ion confinement effect is weak and the interlayer shrinkage is insufficient.

[0053] In summary, this embodiment demonstrates that even a low concentration of acid (1 mol / L) can induce the formation of a certain degree of gel structure in the MXenes wet film, exhibiting partial self-supporting ability. However, the structural stability and density are significantly lower than those of the sample treated with 3 mol / L acid. Therefore, the hydrogen ion concentration in the acid is one of the key parameters affecting the gel network formation efficiency and film performance of this invention, and it is preferably designed within the range of ≥3 mol / L.

[0054] Example 5: Experiment on changing the type of acid This embodiment aims to verify the adaptability of different types of acid solutions to the structural transformation behavior of MXenes wet films, in order to evaluate the universality and flexibility of the method of the present invention in terms of acid selection. The experiment compares the treatment of Ti3C2T with hydrochloric acid solution and sulfuric acid-hydrochloric acid mixed solution. X The effect of the wet film was analyzed and compared with the results of sulfuric acid treatment in Example 1.

[0055] First, weigh out 30 mg of Ti3C2T X The powder was dispersed in 50 mL of deionized water and subjected to ultrasonic treatment for 10 minutes to obtain a stable MXenes suspension.

[0056] Subsequently, the suspension was poured into a vacuum filtration device equipped with a 0.22 μm aqueous filter membrane and filtered under vacuum until the solution flow stopped, forming a uniform and continuous MXenes wet membrane on the filter membrane surface.

[0057] Next, the resulting wet membrane, along with the filter membrane, is immersed in one of the following two sets of acid solutions for treatment: Experimental Group A: 3 mol / L hydrochloric acid solution Experimental Group B: A mixed acid solution obtained by mixing 3 mol / L sulfuric acid and 3 mol / L hydrochloric acid in a 1:1 volume ratio. Both groups of samples were immersed at room temperature (25°C) for 30 seconds, and then the membranes were removed from the acid solution. During the observation, it was found that both hydrochloric acid and mixed acid could effectively promote the structural reorganization of the wet membrane. The gelation rate and membrane removal efficiency were comparable to those of the sulfuric acid treatment group (Example 1), and both could successfully form independent support gel membranes that could be peeled off from the filter membrane as a whole.

[0058] The resulting gel film was then thoroughly washed in deionized water until the pH of the washing solution was close to neutral, thus obtaining the final independently supported MXenes hydrogel film.

[0059] The comparison results are as follows: Morphological observation: The gel films obtained from the three acid treatment groups (sulfuric acid, hydrochloric acid, and mixed acid) all exhibited good structural integrity and self-supporting ability; Structural analysis (XRD): The (002) diffraction peaks of the three samples showed significant shrinkage and narrowing, indicating that different acid species can induce hydrated hydrogen ions to enter the interlayer and form confined crosslinks; Flexibility and mechanical performance: The mixed acid-treated samples exhibited slightly better mechanical strength than those treated with a single acid, suggesting that the multi-acid system may further optimize the interlayer configuration.

[0060] This embodiment demonstrates that, in addition to sulfuric acid, hydrochloric acid and sulfuric acid-hydrochloric acid mixtures are also suitable for the self-supporting construction strategy of MXenes hydrogel films described in this invention, exhibiting good compatibility and practicality. Therefore, in practical applications, different types of inorganic acids can be selected for treatment based on requirements such as equipment material, cost control, or system stability, further enhancing the process flexibility and promotional value of this invention.

[0061] In summary, through the systematic verification of Examples 1 to 5, it can be clearly demonstrated that the preparation method of the independently supported MXenes hydrogel film proposed in this invention has good versatility, controllability and practicality.

[0062] This method does not rely on polymer crosslinking agents or second-phase support materials. It achieves confined crosslinking and the construction of a self-supporting gel structure between MXenes nanosheets through simple vacuum filtration, acid induction, and water washing, preserving the intrinsic electrical conductivity and layered structure characteristics of MXenes materials. Furthermore, it can be used with MXenes materials in different metal systems (such as Ti3C2T). X V2CT X Different types of acid solutions (such as sulfuric acid, hydrochloric acid and their mixtures) and acid treatment parameters (time, concentration) have all been shown to be well adapted to the technical solution of this invention.

[0063] The resulting MXenes hydrogel films generally possess characteristics such as structural integrity, three-dimensional porosity, self-support, and flexibility, which can meet the key requirements for integrated structural and functional materials in fields such as aqueous electrochemical energy storage, electromagnetic shielding, and flexible electronic devices.

[0064] The preparation method of the present invention has the advantages of being green, simple to operate, low in cost, and stable in performance. It is suitable for large-scale continuous production and has broad prospects for technology promotion and industrial application.

Claims

1. A method for preparing an independently supported MXenes hydrogel film, characterized in that, Includes the following steps: (1) Vacuum filter the MXenes suspension until the suspension stops flowing and a wet MXenes film is formed on the filter paper; (2) Immerse the entire filter paper with the MXenes wet film attached in an acid solution to transform the MXenes wet film into an independently supported gel film and separate it from the filter paper; (3) The separated gel film is repeatedly washed with deionized water until the pH value is close to neutral to obtain an independently supported MXenes hydrogel film.

2. The preparation method according to claim 1, characterized in that, The hydrogen ion concentration of the acid solution in step (2) is not less than 1 mol / L.

3. The preparation method according to claim 1 or 2, characterized in that, The MXenes wet film is immersed in the acid solution for no less than 10 seconds.

4. The preparation method according to claim 1, characterized in that, The acid solution is a sulfuric acid solution, a hydrochloric acid solution, or a mixture thereof.

5. The preparation method according to claim 1, characterized in that, The MXenes mentioned in step (1) are selected from titanium-based MXenes, vanadium-based MXenes, or niobium-based MXenes.

6. The preparation method according to claim 5, characterized in that, The MXenes are Ti3C2T x V2CT x Ti3CNT x Ti2CT x Ti4N3T x or Nb4C3T x T x It represents surface functional groups.

7. The preparation method according to claim 1, characterized in that, The independently supported MXenes hydrogel film obtained in step (3) has a three-dimensional porous structure.

8. The preparation method according to claim 1, characterized in that, The method does not add polymer crosslinking agents or second-phase support materials.

9. The preparation method according to claim 1, characterized in that, The acid solution in step (2) is processed at a temperature of 15°C to 35°C.

10. The preparation method according to claim 1, characterized in that, The filtration in step (1) uses a filter membrane with a pore size of 0.2–0.5 μm.

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