Mhm electrode material and preparation method and application thereof

Abstract

The application provides an MHM electrode material and a preparation method and application thereof, and belongs to the technical field of electrochemical desalination. The MHM electrode material is Ti3C2T x MXene, polystyrene microspheres are treated by a polydien dimethyl ammonium chloride solution, and then are stirred and reacted with Ti3C2T x MXene, and then are subjected to freeze drying and pyrolysis to obtain the MHM electrode material. The Ti3C2T x MXene is constructed into a three-dimensional spherical structure, the stacking problem of traditional MXene layers is avoided, the advantages of the good conductivity, large surface area and excellent mechanical properties of the Ti3C2T MXene are fully exerted, the structural stability, the electrochemical performance and the desalination capacity are significantly improved, the MHM electrode exhibits excellent adsorption capacity, fast ion transmission rate and good cycle stability in a CDI device, and a new idea is provided for CDI material design.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical desalination technology, and particularly relates to an MHM electrode material, its preparation method and application. Background Technology

[0002] Capacitive Deionization (CDI) technology, as a highly efficient and low-energy-consumption electrochemical desalination method, has become one of the important technologies for solving water scarcity and environmental pollution problems since Blair, Murphy, and others proposed the concept of "electrochemical desalination" in the late 1960s. Its core principle is to purify water through ion adsorption and desorption of electrode materials under the action of an electric field. With its advantages of simple operation, low energy consumption, and environmental friendliness, it has shown broad application prospects in seawater desalination, wastewater treatment, and resource recycling. The performance improvement of CDI technology highly depends on the innovation of electrode materials and system optimization. In early research, electrode materials mainly relied on traditional materials such as activated carbon, oxides, and polymers. Although they possessed certain adsorption capabilities, their adsorption capacity and desalination efficiency were limited by their low specific surface area and limited active sites, making it difficult to meet practical needs. Since the 1990s, the emergence of novel carbon materials (such as graphene, carbon nanotubes, and MXene) has provided key support for breakthroughs in CDI technology. These materials, due to their higher specific surface area, excellent conductivity, and abundant surface functional groups, significantly improve ion adsorption rates and capacities, becoming a current research hotspot.

[0003] To further optimize the performance of CDI electrode materials, researchers have explored various dimensions: at the material design level, they have improved ion adsorption and transport efficiency by controlling the microstructure (e.g., increasing specific surface area and constructing porous frameworks) to expose more active sites; at the surface modification level, they have increased surface charge density by controlling the distribution of valence bonds and functional groups to achieve selective adsorption of specific ions; and at the operating condition level, they have optimized parameters such as voltage (e.g., low voltage <1.4V can avoid side reactions in water electrolysis), solution concentration, and flow rate to adapt to different application scenarios. However, existing technologies still have many key problems that urgently need to be solved, restricting the industrial application of CDI technology.

[0004] First, with Ti3C2T x While novel carbon materials, such as MXene, possess high conductivity, their two-dimensional layered structure is prone to stacking due to van der Waals forces and hydrogen bonding, resulting in low specific surface area utilization and obstructed ion transport pathways, thus limiting further improvement in adsorption capacity. At the same time, the two-dimensional structure is prone to interlayer collapse during repeated ion adsorption-desorption cycles, resulting in insufficient stability and rapid degradation of cycling performance, making it difficult to meet long-term operation requirements.

[0005] Secondly, balancing ion selectivity and desalination efficiency remains a challenge. Existing materials have limited selective adsorption capacity for specific ions, and insufficient control over pore structure and surface functional groups results in slow ion migration rates in low-to-medium concentration salt solutions (the main scenarios in actual water treatment), while in high-concentration solutions, the adsorption capacity is limited by electrostatic repulsion between ions, making it impossible to maintain high-efficiency desalination performance over a wide concentration range.

[0006] Secondly, the electrochemical performance of the materials is not sufficiently synergistic. Materials with strong redox activity (such as some metal oxides) can improve adsorption performance through pseudocapacitive mechanisms, but their low conductivity will hinder charge transport; while highly conductive materials (such as pure MXene) can ensure rapid electron conduction, but lack sufficient redox active sites, making it difficult to balance high capacitance characteristics with fast reaction kinetics.

[0007] Furthermore, existing materials exhibit poor adaptability to operating conditions. At low voltages, their adsorption capacity is insufficient, while at high voltages, they are prone to side reactions such as water electrolysis, leading to energy loss and electrode damage. Simultaneously, they are sensitive to fluctuations in salt concentration and struggle to maintain stable performance in complex water environments, limiting their practical application. Therefore, developing CDI electrode materials that combine high adsorption capacity, excellent cycling stability, good ion selectivity, and wide adaptability to operating conditions has become a core requirement for further advancing CDI technology.

[0008] Therefore, this invention proposes an MHM electrode material, its preparation method, and its application. Summary of the Invention

[0009] Due to Ti3C2T x -MXene suffers from low adsorption capacity and insufficient cycling stability due to its dominant interlayer ion adsorption mechanism. Furthermore, materials with strong redox reaction kinetics are limited by their low conductivity, thus restricting CDI performance. This invention proposes an MHM electrode material, its preparation method, and its applications. Through a "three-dimensional porous framework + dual-mechanism synergistic" design strategy, Ti3C2T is constructed using a polystyrene microsphere template method. x -MXene hollow microspheres were used to prepare Ti3C2T x -MXene hollow microspheres (MHM).

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] One of the technical solutions of the present invention:

[0012] A method for preparing the above-mentioned MHM electrode material includes the following steps:

[0013] (1) Polystyrene (PS) microspheres were prepared by emulsion polymerization using polyvinylpyrrolidone (PVP) as emulsifier, styrene as monomer, and 2,2'-azobisisobutyronitrile (AIBN) as initiator.

[0014] (2) Ti3C2T2 powder was etched with hydrofluoric acid (HF), and Ti3C2T was obtained by intercalation and exfoliation with dimethyl sulfoxide. x -MXene;

[0015] (3) After treating the polystyrene microspheres with polydimethylammonium chloride (PDDA) solution, they are then reacted with the Ti3C2T x -MXene was reacted with stirring, followed by freeze-drying and pyrolysis to obtain Ti3C2T. x -MXene hollow microspheres are the MHM electrode material.

[0016] Furthermore, in step (1), the reaction temperature of the emulsion polymerization method is 65°C and the time is 16h.

[0017] Further, in step (1), the ratio of polyvinylpyrrolidone, styrene, and 2,2'-azobisisobutyronitrile in the emulsion polymerization method is 5g:55mL:1g.

[0018] Further, in step (3), the polystyrene microspheres and Ti3C2T x The mass ratio of MXene is 10:1.

[0019] Further, in step (3), the ratio of the amount of polystyrene microspheres to the polydienedimethylammonium chloride solution is 0.1 mg:1 mL, and the concentration of the polydienedimethylammonium chloride solution is 5 mg / mL.

[0020] Further, in step (3), the polystyrene microspheres are treated with polydimethylammonium chloride solution for 30 minutes.

[0021] Furthermore, in step (3), the stirring reaction time is 2 hours, the pyrolysis temperature is 500°C, the heating rate is 5°C / min, and the holding time is 2 hours.

[0022] Furthermore, in step (3), the pyrolysis process is carried out in a nitrogen atmosphere.

[0023] Furthermore, in step (2), Ti3C2T xThe preparation process of MXene consists of two steps: etching and exfoliation. MXene etching involves chemically etching the MXene precursor material (such as titanium aluminum carbide) to remove Group A elements or other atomic layers, thereby obtaining the MXene layer. Typical etching methods include acid treatment and fluoride treatment. Exfoliation, on the other hand, involves separating the layers from a multilayer MXene structure to obtain a single-layer or few-layer MXene material. Exfoliation is typically achieved through mechanical exfoliation, ion intercalation exfoliation, and other methods. These methods can effectively remove the MXene layer from the multilayer structure to obtain the desired MXene material. Few-layer MXenes possess excellent mechanical properties, reduce interlayer packing, increase specific surface area and active site density, optimize electron transport paths, improve electron transport performance and conductivity, and enhance their performance in electrochemistry, catalysis, and adsorption.

[0024] The second technical solution of the present invention:

[0025] An MHM electrode material prepared according to the above preparation method has a three-dimensional hollow microsphere structure.

[0026] Technical principle: This invention redesigns Ti3C2T x The MXene structure is constructed as a three-dimensional hollow microsphere, avoiding the stacking problems inherent in layered structures, thus improving the material's stability in water and enhancing cycling stability. Simultaneously, the specific surface area is further increased, maximizing the exposure of active sites on the MXene surface, improving ion transport rates, and enhancing the material's performance in electrochemical testing, such as a significant increase in specific capacitance. This also reduces internal resistance and improves its adsorption performance as a CDI electrode. The three-dimensional structure design will facilitate further doping modification of the material, selectively controlling the pore structure and surface functional groups to achieve more efficient adsorption performance while improving the selectivity of the composite material for specific ions, thereby increasing the deionization efficiency of the CDI device.

[0027] The third technical solution of the present invention:

[0028] An asymmetric capacitive deionization (CDI) device uses the aforementioned MHM electrode material as the negative electrode and activated carbon (AC) as the positive electrode.

[0029] The fourth technical solution of the present invention:

[0030] A brine desalination method employs the aforementioned asymmetric capacitor deionization device to treat NaCl solutions with a salt concentration of 300-1500 mg / L at a voltage of 0.8-1.4 V.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] (1) This invention utilizes the template method and the principle of electrostatic self-assembly to synthesize two-dimensional sheet material Ti3C2T x -MXene is constructed into a three-dimensional hollow microsphere structure of MHM, giving it a regular hollow microsphere structure and a large specific surface area. The carbon skeleton left by the pyrolysis of PS microspheres ensures the stability of the spherical structure and avoids the collapse and stacking of layers that would affect material properties. Its mesoporous structure has a large surface area and pore capacity, providing more adsorption sites and facilitating the diffusion and adsorption of ions on the electrode surface. This invention utilizes Ti3C2T x The MXene is constructed as a three-dimensional spherical structure, which avoids the stacking problem of traditional MXene sheets and fully leverages its advantages such as good conductivity, large surface area and excellent mechanical properties. This significantly improves its structural stability, electrochemical performance and desalination capability. The excellent adsorption capacity, fast ion transport rate and good cycling stability exhibited by the MHM electrode in the CDI device provide new ideas for CDI material design.

[0033] (2) The MHM prepared by this invention has excellent electrochemical performance, with a specific capacitance of 5 mV·s. -1 The scanning rate reached 242 F·g -1 And at 200 mV·s -1 It can still maintain 168 F·g at high scan rates -1 The specific capacitance exhibits good capacitance retention (70%). Furthermore, the galvanostatic charge-discharge curves of MHM show good symmetry, indicating excellent double-layer capacitance behavior and cycling stability. Electrochemical impedance spectroscopy analysis further reveals that MHM has low charge transfer impedance and a fast ion diffusion rate.

[0034] (3) Using MHM and activated carbon as electrodes, an asymmetric hybrid CDI device was constructed. The results showed that the MHM electrode achieved a desalination capacity of 35 mg / g for 500 mg / L NaCl solution at 1.2 V, which was significantly higher than that of the traditional two-dimensional Ti3C2T electrode. x The desalination performance of the MXene sheet electrode was demonstrated. Furthermore, the MHM electrode exhibited excellent adsorption performance in the salt concentration range of 100-1500 mg / L, especially in medium-to-high concentration salt solutions above 500-1500 mg / L, where its desalination capacity reached 44-51 mg / g, showing its great potential in treating low-to-medium concentration wastewater. Through long-term adsorption-desorption cycle experiments, the MHM electrode maintained over 90% capacity retention after 155 cycles, demonstrating excellent cycle stability and reversibility. In addition, the MHM electrode exhibited a rapid ion release rate during desorption, further proving its high efficiency and reusability in CDI applications. Attached Figure Description

[0035] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0036] Figure 1 (a) shows the multilayer Ti3C2T obtained in step (2) of Example 1. x SEM image of MXene powder, (b) showing Ti3C2T after exfoliation. x - SEM images of MXene, (c) is the SEM image of PS microspheres obtained in step (1) of Example 1 at 5 μm, and (d) is the SEM image of PS microspheres obtained in step (1) of Example 1 at 1 μm;

[0037] Figure 2 The multilayer Ti3C2T obtained before and after peeling in step (2) of Example 1. x -MXene powder and Ti3C2T x -MXene's XRD pattern;

[0038] Figure 3 The PS microspheres (PS in the figure) obtained in step (1) of Example 1 and the Ti3C2T obtained in step (2) are shown. x -MXene (Ti3C2T in the image) x Zeta potential test results;

[0039] Figure 4 The Ti3C2T obtained in step (3) of Example 1 x SEM images of the @PS complex at 5 μm (a) and 1 μm (b) dimensions;

[0040] Figure 5 The images are SEM images of MHM obtained in step (3) of Example 1 at dimensions of 5 μm (a) and 2 μm (b);

[0041] Figure 6 The Ti3C2T obtained in Example 1 x XRD (a) and FT-IR (b) analysis results of MXene, PS microspheres, MXene@PS and MHM;

[0042] Figure 7 (a) represents Ti3C2T x -MXene (Ti3C2T in the image) x (a) Nitrogen adsorption-desorption curves of MHM and (b) are for PS microspheres (PS in the figure) and Ti3C2T. x -MXene (Ti3C2T in the image)x Pore ​​size analysis and specific surface area of ​​MHM;

[0043] Figure 8 In the middle section, (a) is the CV curve at different scan rates in MHM, (b) is the GCD curve at different current densities, (c) is the electrochemical impedance (EIS) spectrum, and the inset is the high-frequency region;

[0044] Figure 9 The Ti3C2T in Example 1 x Comparison of the electrochemical performance of MXene and MHM, where (a) is 50 mV·s -1 CV curves at scan rate; (b) is 0.5 A·g -1 GCD curves at current density; (c) Electrochemical impedance spectroscopy, with the inset showing the high-frequency region; (d) Comparison of specific capacitance.

[0045] Figure 10 This is a schematic diagram of the MHM / / AC electroadsorption / desorption process;

[0046] Figure 11 This is a schematic diagram of the CDI device adsorption testing system connection.

[0047] Figure 12 Ti3C2T x The saturated adsorption capacity (a) of CDI devices prepared by MXene and MHM at different voltages from 0.6 to 1.6 V, 100-1500 mg·L⁻¹ -1 (b) Test results of saturated adsorption capacity of MHM at different NaCl concentrations;

[0048] Figure 13 The CDI device prepared for MHM was tested at 1.2V, 50mL, and 500mg·L⁻¹. -1 Adsorption-desorption curves in NaCl solution, and desalination capacity test results;

[0049] Figure 14 The CDI device prepared for MHM was tested at 1.2V and 500mg·L⁻¹. -1 Results of desalination cycle stability test after NaCl concentration adsorption for 5 min. Detailed Implementation

[0050] 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.

[0051] 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. Every smaller range between any stated value or intermediate value within a stated range, and 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.

[0052] 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.

[0053] 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 apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0054] 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.

[0055] This invention proposes an MHM electrode material, which is a three-dimensional hollow microsphere structure.

[0056] This invention also proposes a method for preparing the above-mentioned MHM electrode material, comprising the following steps:

[0057] (1) Polystyrene (PS) microspheres were prepared by emulsion polymerization using polyvinylpyrrolidone (PVP) as emulsifier, styrene as monomer, and 2,2'-azobisisobutyronitrile (AIBN) as initiator.

[0058] (2) Ti3C2T2 powder was etched with hydrofluoric acid (HF), and Ti3C2T was obtained by intercalation and exfoliation with dimethyl sulfoxide. x -MXene;

[0059] (3) After treating polystyrene microspheres with a solution of polydimethylammonium chloride (PDDA, a cationic polymer, commonly used as a surfactant, which can be adsorbed onto the surface of particles and add a positive charge to the surface of the object), they are then reacted with Ti3C2T x-MXene was reacted with stirring, followed by freeze-drying and pyrolysis to obtain Ti3C2T. x -MXene hollow microspheres are the MHM electrode material.

[0060] In step (1) of the preferred embodiment of the present invention, the reaction temperature of the emulsion polymerization method is 65°C and the time is 16h.

[0061] In step (1) of the preferred embodiment of the present invention, the ratio of polyvinylpyrrolidone, styrene, and 2,2'-azobisisobutyronitrile in the emulsion polymerization method is 5g:55mL:1g.

[0062] In step (3) of the preferred embodiment of the present invention, the ratio of the amount of polystyrene microspheres to polydimethylammonium chloride solution is 0.1 mg:1 mL, and the concentration of the polydimethylammonium chloride solution is 5 mg / mL.

[0063] In step (3) of the preferred embodiment of the present invention, the polystyrene microspheres are treated with polydimethylammonium chloride solution for 30 minutes.

[0064] In step (3) of the preferred embodiment of the present invention, the stirring reaction time is 2h, the pyrolysis temperature is 500℃, the heating rate is 5℃ / min, and the holding time is 2h.

[0065] In step (3) of the preferred embodiment of the present invention, the pyrolysis process is carried out in a nitrogen atmosphere.

[0066] In step (2) of the preferred embodiment of the present invention, Ti3C2T x The preparation process of MXene consists of two steps: etching and exfoliation. MXene etching involves chemically etching the MXene precursor material (such as titanium aluminum carbide) to remove Group A elements or other atomic layers, thereby obtaining the MXene layer. Typical etching methods include acid treatment and fluoride treatment. Exfoliation, on the other hand, involves separating the layers from a multilayer MXene structure to obtain a single-layer or few-layer MXene material. Exfoliation is typically achieved through mechanical exfoliation, ion intercalation exfoliation, and other methods. These methods can effectively remove the MXene layer from the multilayer structure to obtain the desired MXene material. Few-layer MXenes possess excellent mechanical properties, reduce interlayer packing, increase specific surface area and active site density, optimize electron transport paths, improve electron transport performance and conductivity, and enhance their performance in electrochemistry, catalysis, and adsorption.

[0067] The present invention also proposes an asymmetric capacitive deionization (CDI) device, using the above-mentioned MHM electrode material as the negative electrode and activated carbon (AC) as the positive electrode, to desalinate brine, treating NaCl solutions with a salt concentration of 500-1500 mg / L at a voltage of 0.8-1.4V.

[0068] All raw materials used in the embodiments of this invention were purchased commercially.

[0069] The technical solution of the present invention will be further illustrated by the following embodiments.

[0070] Example 1

[0071] A method for preparing an MHM electrode material includes the following steps:

[0072] (1) Preparation of polystyrene (PS) microspheres

[0073] Measure 5g of polyvinylpyrrolidone (PVP), 55mL of styrene, and 150g of anhydrous ethanol into a three-necked flask. Place the flask in a constant-temperature magnetic water bath with a magnetic stir bar and stir at 500rpm for 30min until the PVP dissolves. Adjust the water bath temperature to 65℃. While the water bath is heating up, measure 1g of 2,2'-azobisisobutyronitrile (AIBN) and 50g of anhydrous ethanol into a beaker and stir until they are evenly mixed. When the water bath temperature reaches 65℃, add the mixture to the three-necked flask. The three-necked flask should be connected to a condenser. After filling with nitrogen, seal the flask tightly and maintain a constant temperature of 65℃ for 16h. The reactant changes from transparent to milky white colloid. Take out the reactant and wash it three times with a mixture of anhydrous ethanol and water by centrifugation. Concentrate to 100mL to obtain PS microspheres, which are then refrigerated for later use.

[0074] (2) Ti3C2T x Preparation of MXene

[0075] (a) Etching: First, measure 20 mL of 50 wt.% HF solution into a polytetrafluoroethylene beaker, then slowly add 1.5 g of Ti3AlC2 (titanium aluminum carbide) powder to the HF solution. The reaction is vigorous, accompanied by the generation of a large number of bubbles. After covering and standing for 30 min, the reaction tends to slow down. Add a magnetic stir bar and seal with a sealing film. Then transfer to a 40℃ constant temperature magnetic water bath and react at 1000 rpm for 24 h. After the reaction is completed, first punch holes in the coating membrane to remove air, then peel off the membrane and wash the mixed solution with deionized water several times. Centrifuge at 6000 rpm until the pH is 6-7. Vacuum filter the washed product through a 0.22 μm filter membrane and dry the filter cake in a vacuum drying oven. This is the multilayer Ti3C2T x -MXene powder;

[0076] (b) Stripping: 0.2g of multilayer Ti3C2T x MXene powder was poured into a glass beaker containing 15 mL of DMSO (dimethyl sulfoxide), a magnetic stir bar was added, and the beaker was sealed with a sealing film. The beaker was then placed in a 25°C constant-temperature magnetic water bath and reacted at 1000 rpm for 24 hours. After the reaction, 30 mL of deionized water was added to the beaker, and the mixture was placed under a cell disruptor and sonicated in an ice-water bath for 30 minutes. The mixture was then centrifuged at 6000 rpm and washed with water 5-6 times to remove DMSO. The resulting Ti3C2T was obtained by vacuum filtration. x -MXene;

[0077] (3) MHM (Ti3C2T) x Preparation of MXene hollow microsphere electrode materials

[0078] Take 0.5 mg of the PS microspheres prepared in step (1), disperse them in 100 mL of deionized water, and stir continuously until uniformly dispersed. Add 5 mL of polydimethylammonium chloride solution (PDDA, concentration 5 mg / mL) and treat for 30 min to make it easier to bind with MXene. Then calculate the mass of MXene to be added based on the mass of PS microspheres added, according to the ratio of PS microspheres:Ti3C2T x -MXene was added to a Ti3C2T dispersion in deionized water at a mass ratio of 10:1. x -MXene (Ti3C2T in deionized water) x (MXene concentration 1 mg / mL) The reaction was stirred continuously for 2 hours. After the reaction, the mixture was washed three times by centrifugation with deionized water and concentrated to less than 50 mL to obtain a powder sample, which is Ti3C2T. x The PS composite was placed in a polytetrafluoroethylene beaker, sealed with film, and frozen for 6 hours. It was then placed in a vacuum freeze dryer and freeze-dried for 48 hours. After freezing, it was placed in a tube furnace and dried at 5°C / min under a nitrogen atmosphere. -1 The heating rate was adjusted to 500℃, and the mixture was pyrolyzed at this temperature for 2 hours. After the reaction was completed and the mixture was cooled, it was taken out as MHM (Ti3C2T). x -MXene hollow microsphere electrode material.

[0079] Performance testing

[0080] I. Material Characterization

[0081] The multilayer Ti3C2T obtained in step (2) of Example 1 x SEM image of MXene powder is shown below. Figure 1 (a) Ti3C2T after stripping x -See MXene's SEM image. Figure 1 (b) XRD pattern is shown in Figure 1. Figure 2 It can be seen that the aluminum layer in Ti3AlC2 was removed by acid etching, exhibiting an accordion-like shape, proving that Ti3C2T x Successfully prepared. After exfoliation using dimethyl sulfoxide, Ti3C2T was obtained. x -Mxene, composed of Ti3C2T before and after stripping x -MXene's XRD pattern ( Figure 2 Before peeling, it consisted of multiple layers of Ti3C2T. x -MXene powder, after exfoliation, yields Ti3C2T x As can be seen from the MXene, the 002 peak shows a significant leftward shift, from 9.52° to 6.61°. According to Bragg's equation 2dsin(θ)=nλ (where n represents the reflection order and λ represents the wavelength), this indicates that the interlayer spacing of the MXene material increased to 13.4 Å after exfoliation. This increased interlayer spacing contributes to the improvement of Ti3C2T x When used in CDI applications, MXene can embed or adsorb more ions, thereby improving electrochemical performance and adsorption capacity. It also facilitates subsequent doping modification of the structure, creating more possibilities for its application.

[0082] The PS microspheres (PS shown in the figure) obtained in step (1) of Example 1 and the Ti3C2T obtained in step (2) x -MXene (Ti3C2T in the image) x The zeta potential test results for the sheet are shown below. Figure 3 .

[0083] SEM images of the PS microspheres obtained in step (1) of Example 1 at sizes of 5 μm and 1 μm are shown below. Figure 1 As shown in (c) and (d), the diameter of the prepared PS microspheres is approximately 2 μm.

[0084] The Ti3C2T obtained in step (3) of Example 1 x SEM images of the @PS complex at 5μm and 1μm sizes are shown below. Figure 4 , combined Figure 1 , Figure 3 and Figure 4 It can be seen that Ti3C2T x The potential of MXene was measured to be -29.5 mV, a negative potential, while that of PS microspheres was +25.5 mV, a positive potential. Under electrostatic force, the MXene sheets tightly wrapped around the surface of the PS microspheres, thus synthesizing Ti3C2T. xThe scanning electron microscope (SEM) image of the PS composite shows numerous glossy microspheres bonded together, indicating that it consists of MXene sheets uniformly coated on the surface of PS microspheres. This suggests that the mixture of the two materials, after centrifugation and washing, is a viscous liquid mixture and requires freeze-drying before further pyrolysis.

[0085] SEM images of MHM obtained in step (3) of Example 1 at 5μm and 2μm sizes are shown below. Figure 5 It can be seen that after 48 hours of freeze-drying, Ti3C2T x The @PS composite transforms from a viscous liquid into an aerogel-like powder, easily attracted by electrostatics. It is then pyrolyzed at 500°C in a nitrogen atmosphere. Due to the nitrogen atmosphere, Ti3C2T... x MXene has a pyrolysis temperature of 800-1000℃, so it will not decompose. PS microspheres, on the other hand, will gradually undergo pyrolysis and weight loss, during which the carbon will be enriched and retained, transforming into a spherical carbon framework that supports Ti3C2T. x -MXene sheets maintain a spherical shape. Furthermore, benzene, propylene, and ethylene gases are generated during pyrolysis. These gaseous products are diluted and discharged under a nitrogen atmosphere and absorbed by a tail gas collection device to prevent pollution. After pyrolysis, Ti3C2T x @PS is transformed into MXene hollow microspheres (MHM). SEM images show that MHM are regular spheres with pores on the surface. The pores are caused by the gas released during the pyrolysis of PS microspheres. By carefully observing each sphere, it was found that the edges are darker in color and the middle is lighter in color and has a hollow feel, indicating that PS microspheres are removed by pyrolysis.

[0086] Table 1 shows the EDX energy dispersive spectroscopy results of the MHM obtained in step (3) of Example 1. It can be found that the composition is only Ti3C2T. x The presence of C, O, Ti, and small amounts of F and Al in MXene demonstrates the successful synthesis of hollow MXene microspheres.

[0087] Table 1. EDX spectral analysis results of MHM

[0088]

[0089] The Ti3C2T obtained in Example 1 x The XRD (a) and Fourier transform infrared (FT-IR) (b) analysis results of MXene, PS microspheres, MXene@PS (i.e., the MXene@PS complex obtained in step (3)) and MHM are shown in the figure. Figure 6It can be seen that the 002 characteristic peak of MXene appears in both MXene@PS and MHM, while the characteristic peaks of 10° and 20° of PS microspheres appear once in MXene@PS and then disappear in MHM, indicating the addition and removal of PS microspheres during the MHM synthesis process. Fourier transform infrared spectroscopy (FT-IR) was used to analyze the surface functional group and valence bond distribution of the synthesized materials, and the results showed that Ti3C2T x -MXene at 559 cm -1 The unique peak at this location is the stretching vibration peak of the Ti-O bond, which also appears in MXene@PS and MHM. The CH bond at 3026, 2921, 756, and 698 cm⁻¹ in PS microspheres, and at 1492 cm⁻¹, is also present. -1 The -OH functional group also appears in MXene@PS and disappears in MHM, indicating that PS acts as a template in the material synthesis process, successfully promoting the synthesis of MHM.

[0090] In CDI systems, the specific surface area and pore size distribution of the electrode directly affect its adsorption performance. A larger surface area and appropriate pore size structure can improve the adsorption capacity and rate of the electrode, thereby increasing the deionization efficiency of the CDI system. Therefore, the Ti3C2T in Example 1 was obtained through BET testing. x Nitrogen adsorption-desorption curves, specific surface area, and pore size distribution of MXene, PS microspheres, and MHM are shown in the figure. Figure 7 (a) represents MHM and Ti3C2T x -MXene nitrogen adsorption-desorption curves, (b) is Ti3C2T x -MXene (Ti3C2T in the image) x Pore ​​size analysis and specific surface area analysis of PS microspheres (PS in the figure) and MHM. The adsorption-desorption curves show that MHM exhibits a typical type IV isotherm and an H3 type hysteresis loop, indicating that the pore size distribution is mainly mesoporous. (This is achieved by analyzing the pore size and specific surface area of ​​Ti3C2T...) x -MXene is constructed as a three-dimensional spherical structure with a specific surface area of ​​8.9 m². 2 / g increased to 59m 2 / g, pore volume reaches 0.15cm³ 3 / g, the pore size is basically distributed between 2-10nm mesopores. Mesoporous structures have a large surface area and pore capacity, which can provide more adsorption sites. This means that the material has a larger electrochemically active specific surface area, which is conducive to the diffusion and adsorption of ions on the electrode surface, improving the ion transport rate of the electrode and the desalination efficiency when used as a CDI electrode.

[0091] II. Electrochemical Characterization

[0092] Using a salt solution containing 1M NaCl as the electrolyte, platinum sheet electrodes and Ag / AgCl were used as the counter and reference electrodes, respectively. Cyclic voltammetry (CV), cyclic voltammetry (GCD), and electrochemical osmosis (EIS) methods were employed for testing. Electrochemical signal feedback was used to analyze the capacitance and resistance properties of the materials, thereby providing a more comprehensive understanding of the material's characteristics under electrochemical conditions. This revealed the electrochemical behavior of the newly prepared electrode material, providing important experimental data and theoretical basis for the design and optimization of CDI systems. By measuring its cyclic voltammetry (CV), the shape and characteristics of the CV curves were analyzed to understand the redox behavior, electrochemical active surface area, capacitance characteristics, and electrolyte transport and ion diffusion performance of the MHM material prepared in Example 1.

[0093] Figure 8 The electrochemical performance analysis of MHM is shown in (a) CV curves at different scan rates; (b) GCD curves at different current densities; and (c) electrochemical impedance spectroscopy. The inset shows the high-frequency region.

[0094] Depend on Figure 8 As can be observed in (a), the area under the curve increases with increasing scan rate, and the curve gradually approaches a spindle shape from a quasi-rectangular shape. This is because with increasing scan rate, the number of current signals corresponding to the scanned potential per unit time increases, resulting in polarization of the CV curve and a decrease in the calculated specific capacitance. In contrast, the CV curves of MHM are mostly quasi-rectangular in shape, with a large integral area, indicating a large current density at a specific potential, high conductivity, and thus, efficient charge transport. The specific capacitance calculated from the CV curve is within 5 mV·s. -1 At a scan rate of 242 F·g, MHM can achieve this. -1 The capacitance, even as the scan rate gradually increases to 200 mV·s -1 At that time, it still had 168 F·g -1 The capacitance exhibits an excellent 70% capacitance retention. Furthermore, a pair of weak redox peaks can be observed in the CV curve of the MHM at -0.2V and -0.6V. This indicates that at these potentials, ion transport on the electrode material is no longer a simple electric double-layer adsorption (EDL), but rather exhibits pseudocapacitive behavior involving redox phenomena, proving that Na… + Insertion and deintercalation occur during this process, which is beneficial for the design of future CDI devices, improving their adsorption capacity and efficiency for ions in salt solutions.

[0095] Constant current charge-discharge curves are valuable for assessing important performance indicators such as capacitance, energy density, charge-discharge efficiency, and cycle stability. These indicators are crucial for evaluating the application potential of materials in energy storage and conversion devices such as supercapacitors and lithium-ion batteries. The integral area of ​​a single charge-discharge curve can be used to measure the capacitance and rate performance of a material, and the symmetry of the curve can indicate whether the material exhibits good double-layer capacitance behavior. The GCD curves of MHM at different current densities (…) Figure 8 As can be seen in (b), the charge-discharge time decreases with increasing current density, but the charge-discharge curve still maintains a symmetrical shape. At 0.5 A·g -1 At a current density, its single charge-discharge process lasts up to 500 s, demonstrating that the material has high capacitance and energy density. The long charge-discharge process also indicates its strong cycle stability, maintaining stable performance in multiple charge-discharge cycles, proving its potential as a CDI electrode in terms of stability.

[0096] Electrochemical impedance spectroscopy (EIS) is used to study the interfacial properties of electrochemical systems. By applying AC signals at different frequencies and measuring the response, information about electrode surface reactions, electrolyte transport, and interfacial impedance can be obtained. It reflects the process and resistance of ion diffusion and transport from the material surface to the interior, elucidating the electrochemical behavior between the electrode and electrolyte, and is an important tool for studying electrode process kinetics. The EIS spectra of MHM (Metalloma Hydrocarbons) are... Figure 8 As can be seen in (c), the slope in the low-frequency region is almost vertical, indicating rapid diffusion of ions at the electrode interface. In the high-frequency region, there are two small semicircles, which is different from the typical EIS curve of a high-frequency semicircle (charge transfer) and a low-frequency sloping line (diffusion). This may be due to the construction of the hollow microsphere structure, which leads to a new charge transfer interface layer and interlayer transport process. This reveals the rapid ion diffusion and extremely low conduction resistance of the material, which will result in lower energy loss when used as a CDI electrode.

[0097] In Example 1, Ti3C2T x The electrochemical performance comparison results of MXene and MHM are shown in [link to table]. Figure 9 , of which (a) 50 mV·s -1 CV curve at scan rate; (b) 0.5 A·g -1 (c) GCD curve at current density; (d) Electrochemical impedance spectroscopy, with the inset showing the high-frequency region; (e) Specific capacitance comparison plot. (The text then abruptly shifts to a different topic: "By using Ti3C2T...") x A comparison of the various electrochemical properties of MXene and MHM shows that the two-dimensional layered structure of Ti3C2T... x After MXene was constructed into a three-dimensional hollow spherical structure, its various electrochemical properties were significantly improved. At 50 mV·s -1In the CV curves, MHM has a larger integral area and more obvious redox peaks, proving that the structural stability of MHM is superior to that of Ti3C2T. x -MXene and MHM also exhibit good ion insertion / extraction properties in NaCl solution, and the specific capacitance calculated from the CV curve is higher than that of Ti3C2T. x The MXene content is high, and its capacity retention is better as the scan rate increases. The charge / discharge time of MHM in the GCD plot is also better than that of Ti3C2T. x - MXene is longer, and the semicircle and horizontal intercept of the MHM in the high-frequency region of EIS are also shorter, representing higher capacitance and energy density, as well as lower energy loss.

[0098] III. Assembly and Adsorption Performance Testing of CDI Unit

[0099] (1) Assembly and testing of CDI device

[0100] Based on the aforementioned characterization of the microstructure, valence bonds, and functional groups of MHM material, as well as the detection of its electrochemical performance, a preliminary assessment of MHM's comprehensive performance has been made: it possesses a high specific surface area and abundant surface active sites, exhibiting excellent electrochemical performance, high charge capacity, fast ion transport rate, and strong structural stability. To test its adsorption performance as a CDI electrode material, a flexible, independent MHM membrane (membrane electrode) was prepared using polytetrafluoroethylene (PTFE) as a binder to adsorb cations via pseudocapacitive behavior as the CDI negative electrode. Similarly, an AC membrane electrode was prepared to adsorb anions via double-layer capacitance behavior as the CDI positive electrode. To ensure that the MHM membrane electrode could be fully utilized and to achieve its full performance, the mass of AC was controlled to be 1.3 times that of MHM. An asymmetric hybrid CDI device was assembled to reduce the charge transport resistance between the two electrodes, achieving efficient adsorption and improving desalination performance. When a voltage was applied, the MHM membrane negative electrode adsorbed Na. + AC anodes adsorb Cl in the salt water - Conversely, when the positive and negative electrodes of the device are directly connected and the CDI device is in a short-circuit state, the adsorbed Na... + From the negative electrode, it is released into the brine, thus realizing Na + Electroadsorption / desorption, see the schematic diagram of the MHM / / AC electroadsorption / desorption process. Figure 10 .

[0101] (2) Connection and operation of CDI device

[0102] See the connection diagram of the CDI device adsorption testing system. Figure 11 The CDI device is powered by a DC regulated power supply, and is also connected to a brine solution and a peristaltic pump, which operates at a rate of 20 mL / min. -1The target salt solution is pumped into the CDI device and then flows back into the salt solution beaker. The conductivity meter probe is inserted below the surface of the salt solution to monitor and record the changes in the conductivity of the salt solution in real time, reflecting the process of ion adsorption by the CDI device.

[0103] After connecting the CDI testing system, an "activation" operation is required before starting the adsorption experiment. First, check for short circuits by directly connecting the device to a power source and applying 1.2V. Without salt solution flowing through, observe the current display on the DC power supply screen. If a number is displayed, it indicates a short circuit in the CDI device, such as slight contact between the positive and negative electrodes. In this case, disassemble the device, troubleshoot the electrode contact issue, and reinstall it. Then, without applying voltage, continuously flow approximately 1L of deionized water through the CDI device to fully immerse the electrodes and acclimate them to the liquid environment, preparing them for subsequent adsorption performance testing.

[0104] (3) CDI adsorption performance test results

[0105] Various parameters in the CDI test have a certain impact on the adsorption performance, such as the applied voltage and the concentration of the adsorbed salt solution. Therefore, the adsorption performance of this CDI electrode under different system parameters was tested. Within a voltage range of 0.6-1.6V, increments of 0.2V were set at a voltage of 500 mg·L⁻¹. -1 NaCl solution, for Ti3C2T in Example 1 x -MXene (Ti3C2T in the image) x The Ti3C2T (layer) and MHM were tested separately at different voltages from 0.6 to 1.6V. x saturated adsorption capacity (a) of MXene and MHM, 100-1500 mg·L⁻¹ -1 The saturated adsorption capacity (b) of MHM at different NaCl concentrations is shown in the figure. Figure 12 .

[0106] Depend on Figure 12 In (a), it can be found that Ti3C2T x Due to unavoidable sheet stacking issues, MXene exhibits low desalination capacity when fabricated as a membrane electrode, but this capacity suddenly increases to 26 mg·g at 1.4 V. -1 This may be because the increased voltage triggers water electrolysis or redox reactions on the electrode surface, generating more active sites and instantly increasing the adsorption capacity until it reaches the saturation limit. Therefore, further increasing the voltage will not increase the adsorption capacity further, and the adsorption amount may even decrease significantly due to irreversible damage to the electrode. However, when MXene is constructed into hollow microspheres (MHM), its adsorption capacity is significantly improved, reaching a maximum of 35 mg·g at 1.2V. -1The desalination capacity decreases as the voltage continues to rise. This may be due to side reactions that occur when the voltage increases, such as the electrolysis of water (hydrogen evolution or oxygen evolution reaction), which consume electrical energy and reduce the effective current available for ion adsorption, leading to a decrease in capacity. Secondly, high voltage may also damage the double layer structure at the electrode-solution interface, weakening the electric field's ability to adsorb ions.

[0107] Depend on Figure 12 In (b), it can be observed that the overall trend of desalination increases with increasing concentration, reaching 500 mg·L⁻¹. -1 When the adsorption capacity reaches near saturation, even with further increases in salt solution concentration, the desalination rate shows no significant improvement. The MHM membrane electrode operates within the range of 100-300 mg / L. -1 The ion adsorption capacity is only 5.6-11.8 mg·g. -1 When the concentration is increased to 500 mg·L -1 At the above values, the ion adsorption capacity reached 44-51 mg·g. -1 The capacity was significantly increased. The concentration reached 500 mg / L. -1 When the concentration increases, the adsorption capacity of the HCDI device reaches its maximum and does not change with the further increase of concentration, indicating that the CDI device (i.e., HCDI device) prepared with MHM has great potential in treating low-concentration wastewater.

[0108] The adsorption and desorption of the HCDI device can be visually represented by the change curve of the solution conductivity. The adsorption time of the HCDI device was recorded at 20 min, 1.2 V voltage, 50 mL, and 500 mg·L⁻¹. -1 Adsorption-desorption curves in NaCl solution and desalination capacity test results are shown below. Figure 13 As can be seen from the extreme desalination capacity test, the SAC (salt saturated adsorption capacity) of the HCDI device gradually increases with the progress of the test, indicating that the adsorption performance of the CDI device is gradually released during the test. Furthermore, the adsorption rate shows a trend from fast to slow, with the fastest adsorption rate reaching 2.4 mg·g⁻¹. -1 ·min -1 The highest desalination capacity reached 47.5 mg / g. -1 During desorption, the curve rises almost linearly, indicating that the Na adsorbed at the electrode... + Instantaneous desorption indicates that MHM affects Na + It has a fast capacitive adsorption rate, strong reversibility, and great potential for recycling.

[0109] To further investigate its cycling stability, the adsorption time was shortened to 5 min and the desorption time to 3 min for adsorption-desorption cycle testing at 1.2 V and 500 mg·L⁻¹. -1 The results of the desalination cycle stability test for NaCl concentration adsorption for 5 min are shown below. Figure 14 The results showed that the MHM electrode maintained excellent capacity retention after multiple cycles of testing, with an adsorption capacity of 30 mg·g⁻¹. -1 After approximately 155 cycles, the capacity retention rate remained above 90%, indicating that MHM exhibits good adsorption capacity and capacity retention rate overall.

[0110] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method of preparing an MHM electrode material, characterized by, Comprise the following steps: (1) by emulsion polymerization method, with polyvinylpyrrolidone as emulsifier, styrene as monomer, 2,2'-azobis isobutyronitrile as initiator, polystyrene microspheres are prepared; (2) Ti3AlC2 powder is etched by hydrofluoric acid, and Ti3C2T is obtained by intercalation and exfoliation with dimethyl sulfoxide x -MXene; (3) the polystyrene microspheres are immersed in a polydien dimethyl ammonium chloride solution for treatment, and then combined with the Ti3C2T x MXene stirring reaction, freeze-drying and pyrolysis to obtain Ti3C2T x MXene hollow microspheres, which are the MHM electrode material; The MHM electrode material is a three-dimensional hollow microsphere structure; In step (3), the polystyrene microspheres are mixed with Ti3C2T x The mass ratio of MXene is 10:

1. In step (3), the ratio of the use amount of polystyrene microspheres to polydiallyldimethylammonium chloride solution is 0.1 mg:1 mL, and the concentration of polydiallyldimethylammonium chloride solution is 5 mg / mL; In step (3), the stirring reaction time is 2h; the pyrolysis condition is: heating to 500℃ at a heating rate of 5℃ / min, and the holding time at this temperature is 2h; In step (1), the reaction temperature of the emulsion polymerization method is 65℃, and the time is 16h; In step (3), the pyrolysis process is carried out under nitrogen atmosphere; In step (3), the polystyrene microspheres are treated with polydiallyldimethylammonium chloride solution for 30min.

2. An MHM electrode material, characterized in that, Prepared by the preparation method of the MHM electrode material of claim 1.

3. An asymmetric capacitive deionization device, characterized by, The MHM electrode material of claim 2 is used as a negative electrode, and activated carbon is used as a positive electrode.

4. A method of desalinating saltwater, characterized by, The asymmetric capacitive deionization device of claim 3 is used to treat NaCl solution with a salt concentration of 500-1500mg / L at a voltage of 0.8-1.4V.

Images