A method for rapidly preparing high-concentration MXene slurry by low-temperature spray drying

Abstract

The present invention discloses a method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying. The method comprises the following steps: 1. mixing anhydrous ethanol and ethyl acetate to obtain a regulator; 2. adding the regulator to a MXene dispersion and spray drying to obtain a hollow microsphere MXene powder; and 3. adding deionized water to the MXene powder obtained in step 2 to obtain a single-layer MXene slurry. This method reduces the temperature of the spray drying process from 220°C to 90°C by adding ethanol and ethyl acetate as regulators to the MXene dispersion, thereby preventing oxidation of MXene at high temperatures and achieving the preparation of a high-concentration slurry by low-temperature spray drying. The present invention not only effectively solves the problem of easy oxidation and low production efficiency of high-concentration MXene slurry production, but also the prepared high-concentration slurry can be directly used for the preparation of MXene thin films, exhibiting excellent electromagnetic shielding properties.

Description

Technical Field

[0001] The present invention relates to a method for preparing a MXene slurry, and in particular to a method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying. Background Art

[0002] MXene materials have great application potential in many fields, including electrochemical energy storage, electromagnetic shielding, and flexible electronic materials. Currently, in the process of synthesizing MXene materials, the concentration of MXene dispersions is mostly less than 1wt%. Low MXene dispersion concentrations make it difficult to process into high-concentration MXene slurries during actual device production. MXene is easily oxidized in water and oxygen environments. Conventional spray drying requires a high temperature of 220°C for drying (Chemical Communications, 2017, 53(2):400-403.). MXene will oxidize at 220°C, and the surface groups will be damaged, resulting in a decrease in its dispersibility and inability to be processed into MXene slurries. Therefore, preparing high-concentration MXene slurries can effectively slow down the oxidative deterioration of MXene materials. It has the characteristics of being directly applied to MXene device processing without processing, which is of great significance for the large-scale preparation of MXene devices. In previous studies, the applicant found that a semi-solid MXene with a solid content of 19.4 wt% can be obtained by combining high-speed centrifugation (10,000 rpm, 1 hour) with heating evaporation (50°C, 6-8 hours). The semi-solid MXene has good dispersibility in water and can be further processed into MXene slurries of different concentrations according to actual needs (ACS Materials Letters, 2020, 2(12): 1598-1605.), but this process takes a long time. In addition, MXene materials are easily oxidized at high temperatures. Studies have shown that MXene dispersions will oxidize after being stored at room temperature for 6.2 days, and long-term heating and stirring will inevitably cause the MXene material to oxidize (Chemistry of Materials, 2017, 29(11): 4848-4856.). Oxidation will cause serious loss of various properties of MXene materials, a significant decrease in their conductivity, and a corresponding significant reduction in their electromagnetic shielding performance. To address this issue, researchers have freeze-dried MXene dispersions for extended periods of time and then rehydrated them to convert them into semi-solid MXene with a high solid content of 60 wt%. However, this process takes 2 to 3 days and is inefficient (Advanced Science, 2023, 10(19): 2300660). To meet practical application needs, it is crucial to develop an efficient method for converting low-concentration MXene dispersions into high-concentration MXene slurries while preventing MXene oxidation. Summary of the Invention

[0003] In order to solve the problem that the existing high-temperature spray process will cause MXene oxidation in the preparation of high-concentration slurry, and at the same time, the MXene powder obtained by high-temperature spray drying of MXene has a wrinkled flaky structure and poor dispersibility in water, the present invention provides a method for quickly preparing high-concentration MXene slurry by low-temperature spray drying. This method reduces the temperature of the spray drying process from 220°C to 90°C by adding ethanol and ethyl acetate as regulators to the MXene dispersion, thereby preventing the oxidation of MXene at high temperatures and realizing the preparation of high-concentration slurry (20-50%) by low-temperature spray drying. The present invention not only effectively solves the problem of easy oxidation and low preparation efficiency in the production process of MXene high-concentration slurry, but also the prepared high-concentration slurry can be directly used for MXene film preparation, and has excellent electromagnetic shielding properties.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying comprises the following steps:

[0006] Step 1: Preparation of regulator:

[0007] Anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 5:1 to 20:1, and mixed uniformly by magnetic stirring, wherein the magnetic stirring time is controlled to be 1 to 5 minutes and the speed is controlled to be 200 to 800 rpm to obtain a regulator;

[0008] Step 2: Spray drying:

[0009] First, the regulator prepared in step 1 is added to an 8-12 mg / mL MXene dispersion and mixed uniformly by magnetic stirring. The magnetic stirring time is controlled to be 1-5 minutes, the rotation speed is 200-800 rpm, and the volume ratio of MXene dispersion to regulator is 4:1-5:1. Then, the resulting mixture is spray-dried in a spray dryer. After a drying process of 5-7 minutes, a hollow microsphere MXene powder is obtained. The drying temperature is controlled to be 90-92°C, and the feed rate is 800-1000 mL / h.

[0010] Step 3: Preparation of high concentration MXene slurry:

[0011] Within 1 hour after preparation, deionized water was added to the MXene powder obtained in step 2 and mixed evenly by magnetic stirring. The magnetic stirring time was controlled to be 1 to 5 minutes and the rotation speed was controlled to be 200 to 800 rpm to obtain a single-layer MXene slurry with a solid content of 20 to 50 wt%.

[0012] Compared with the prior art, the present invention has the following advantages:

[0013] 1. The droplet drying time of a single spray of the present invention is only about 1 second. At the same time, ethanol and ethyl acetate are added to the MXene dispersion as regulators, which greatly reduces the temperature required for spray drying. Low-temperature dehydration can be achieved at 90°C to obtain MXene powder with a hollow microsphere morphology. This drying temperature is the lowest drying temperature of existing MXene spray drying technology, avoiding oxidation and dispersibility problems caused by high temperature, and saving equipment and heating costs.

[0014] 2. The MXene hollow microsphere powder prepared by the present invention can be well dispersed in water within the aging period (1 hour) and does not contain titanium dioxide components produced by MXene oxidation. It can be dispersed in water with only low-speed stirring, restoring the two-dimensional lamellae morphology of MXene and processing it into MXene slurry. The film processed based on this slurry has a dense layered structure between layers.

[0015] 3. The concentration of the MXene slurry of the present invention can be adjusted in a wide range (20-50 wt%), which solves the problem of producing high-concentration MXene slurry required for application scenarios such as MXene film coating, MXene material 3D printing, and MXene transfer printing.

[0016] 4. The high-concentration MXene slurry of the present invention can be stored for 120 days without being oxidized.

[0017] 5. The slurry of the present invention can be used for coating production of MXene films. The prepared MXene films have good conductivity (>10000S / cm) and excellent electromagnetic shielding performance, and the electromagnetic shielding performance in the X-band can reach 58dB. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart for the preparation of high-concentration MXene slurry;

[0019] Figure 2 The morphology, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) spectra of the MXene powder prepared in Example 1 are shown;

[0020] Figure 3 is the electromagnetic shielding performance of the MXene film prepared in Example 1;

[0021] Figure 4 is the morphology of the MXene powder prepared in Example 4;

[0022] Figure 5 The morphology, XPS and FTIR spectra of the MXene powder prepared in Example 5 are shown;

[0023] Figure 6 is the electromagnetic shielding performance of the MXene film prepared in Example 6;

[0024] Figure 7 This is the electromagnetic shielding performance of the MXene film prepared in Example 7. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0026] The present invention provides a method for rapidly preparing high-concentration MXene slurry by low-temperature spray drying, such as Figure 1 As shown, the method includes the following steps:

[0027] Step 1: Preparation of regulator:

[0028] Anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 5:1 to 20:1, and are uniformly mixed by magnetic stirring for 1 to 5 minutes (200 to 800 rpm) to obtain a regulator.

[0029] In this step, ethanol and ethyl acetate were selected as conditioning agents. These agents can effectively lower the boiling point of the mixed solution, enabling spray drying and dehydration at only 90°C. Furthermore, the introduction of these conditioning agents can effectively protect the surface hydrophilic groups of the MXene.

[0030] Step 2: Spray drying:

[0031] First, set the spray dryer parameters as follows: feed rate 800-1000 mL / h, drying temperature 90-92 °C, nozzle diameter 1 mm, nozzle pressure 1.8-2.2 bar, ventilation volume 300-350 m 3 / h; then, the regulator prepared in step 1 is added to the 8-12 mg / mL MXene dispersion, and the mixture is uniformly mixed by magnetic stirring for 1-5 minutes (200-800 rpm), and the volume ratio of the MXene dispersion to the regulator is controlled to be 4:1-5:1; finally, the resulting mixture is passed through a spray dryer and spray-dried at 90-92°C. After a drying process of 5-7 minutes, a hollow microsphere MXene powder is obtained.

[0032] In this step, the drying temperature is preferably set at 90°C, and the feed rate is preferably set at 1000 mL / h to ensure that the spray droplets are fully dried at a relatively low temperature. During conventional high-temperature spray drying, the water in the droplets gradually evaporates, causing the MXene nanosheets to gradually aggregate. Due to the irregular arrangement of the MXene nanosheets, the capillary forces acting on their surface are uneven, ultimately forming wrinkled MXene nanosheets. Furthermore, capillary forces cause the MXene sheets to form dense stacking, and high temperatures cause a partial loss of hydroxyl groups on the MXene surface, both of which lead to a decrease in the dispersibility of the MXene powder. In contrast, the addition of ethanol and ethyl acetate as modifiers to the droplets during low-temperature spray drying creates a temperature gradient during evaporation, generating constant turbulence within the MXene solution through Rayleigh-Bénard convection. As evaporation continues, due to the Marangoni effect, the fluctuating MXene flakes assemble on the droplet surface into hollow microspheres composed of MXene nanosheets with a diameter of 5 to 10 μm. The regular spherical shell can better resist the compression force during the drying process, and finally obtains hollow spherical MXene powder. Since the morphology structure and surface hydrophilic functional groups of MXene are effectively retained, this makes this MXene powder have excellent dispersibility in water.

[0033] In this step, the above effect can only be achieved when anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 5:1 to 20:1. When the ethanol content is too low, the dispersion cannot be dried and dehydrated at low temperatures. When the ethanol content is too high, the MXene dispersion will not form a hollow microsphere structure after drying. When the ethyl acetate content is too high, the prepared MXene microspheres will have poor dispersibility in water. When the ethyl acetate content is too low, the hollow microsphere structure will also not form.

[0034] Step 3: Preparation of high concentration MXene slurry:

[0035] Within 1 hour after preparation, add 1 to 4 times the mass of deionized water to the MXene powder obtained in step 2 as needed, and mix evenly by magnetic stirring for 1 to 5 minutes (200 to 800 rpm) to obtain a single-layer MXene slurry with different solid contents (20 to 50 wt%).

[0036] In this step, the MXene powder prepared after adding the regulator is in the form of hollow spheres. Due to the retention of the hydrophilic groups on the MXene surface, the MXene powder can be converted into a MXene slurry by adding deionized water within the aging period (1 hour).

[0037] Example:

[0038] Example 1:

[0039] Step 1: Anhydrous ethanol and ethyl acetate were mixed in a volume ratio of 5:1 to a total volume of 25 mL, and the mixture was uniformly mixed by magnetic stirring for 2 minutes (500 rpm) to obtain a regulator.

[0040] Step 2: Add the regulator to 100 mL of MXene dispersion (10 mg / mL). At this time, the solution is in a uniform mixed solution.

[0041] Step 3: Setting parameters of spray dryer: feed rate 1000mL / h, drying temperature 90℃, nozzle diameter 1mm, nozzle pressure 2bar, ventilation volume 330m 3 / h.

[0042] Step 4: The mixed solution obtained in step 2 is spray dried by a spray dryer. After a drying process of about 7 minutes, MXene powder is obtained. The powder has a hollow microsphere morphology and has good dispersibility in water within 1 hour after preparation. It can be dispersed in water with only low-speed stirring. There is no trace of oxidation and the surface functional groups are not damaged ( Figure 2 ).

[0043] Step 5: Add deionized water to the prepared MXene powder at a mass ratio of 1:4 and stir in a magnetic stirring device at 500 rpm for 5 minutes to obtain a high concentration (20 wt%) MXene slurry. This slurry is used to prepare MXene films with excellent electromagnetic shielding performance (58 dB) ( Figure 3 ).

[0044] Example 2:

[0045] This example differs from Example 1 in that anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 1:5. The conditioning agent is added to 100 ml of MXene dispersion (10 mg / mL). At this point, the solution is stratified, with the MXene in the lower aqueous phase and the conditioning agent in the upper phase.

[0046] Example 3:

[0047] This example differs from Example 1 in that 125 mL of MXene dispersion (10 mg / mL) was used without adding any other reagents. No MXene powder was produced in this example. The MXene dispersion could not be dried to powder at 90°C.

[0048] Example 4:

[0049] The difference between this embodiment and embodiment 1 is that the drying temperature is set to 220°C. The MXene powder prepared in this embodiment still has the morphology of hollow microspheres ( Figure 4 ), but the powder is insoluble in water and oxidizes.

[0050] Example 5:

[0051] The difference between this example and example 3 is that the drying temperature is set to 220°C. The MXene powder obtained in this example is in the form of wrinkled flakes, has poor dispersibility in water, and cannot be restored to a two-dimensional flake morphology. After testing, the MXene powder was oxidized and the surface functional groups were lost ( Figure 5 ).

[0052] Example 6:

[0053] The difference between this embodiment and embodiment 1 is that the prepared MXene powder is added with deionized water at a mass ratio of 1:2 and stirred in a magnetic stirring device at 500 rpm for 5 minutes to obtain a high concentration (33 wt%) MXene slurry. This slurry is used to prepare a MXene film with excellent electromagnetic shielding performance (55 dB) ( Figure 6 ).

[0054] Example 7:

[0055] The difference between this embodiment and embodiment 1 is that the prepared MXene powder is added with deionized water at a mass ratio of 1:1, and stirred in a magnetic stirring device at 500 rpm for 5 minutes to obtain a high concentration (50 wt%) MXene slurry. This slurry is used to prepare a MXene film with excellent electromagnetic shielding performance (58 dB) ( Figure 7 ).

[0056] The above examples demonstrate that the method provided by this invention allows for the conversion of a MXene dispersion into a well-dispersed MXene powder via low-temperature spray drying, which is then converted into MXene slurries of varying concentrations (20-50 wt%) via hydration. The resulting MXene films exhibit excellent electrical conductivity and electromagnetic shielding properties.

Claims

1. A method for rapidly preparing high-concentration MXene slurry by low-temperature spray drying, characterized in that The method comprises the following steps: Step 1: Preparation of regulator: Anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 5:1 to 20:1, and mixed uniformly by magnetic stirring, wherein the magnetic stirring time is controlled to be 1 to 5 minutes and the speed is controlled to be 200 to 800 rpm to obtain a regulator; Step 2: Spray drying: First, the regulator prepared in step 1 is added to an 8-12 mg / mL MXene dispersion and mixed uniformly by magnetic stirring. The magnetic stirring time is controlled to be 1-5 minutes, the rotation speed is 200-800 rpm, and the volume ratio of MXene dispersion to regulator is 4:1-5:

1. Then, the resulting mixture is spray-dried in a spray dryer. After a drying process of 5-7 minutes, a hollow microsphere MXene powder is obtained. The drying temperature is controlled to be 90-92°C, and the feed rate is 800-1000 mL / h. Step 3: Preparation of high concentration MXene slurry: Within 1 hour after preparation, deionized water was added to the MXene powder obtained in step 2 and mixed evenly by magnetic stirring. The magnetic stirring time was controlled to be 1 to 5 minutes and the rotation speed was controlled to be 200 to 800 rpm to obtain a single-layer MXene slurry with a solid content of 20 to 50 wt%.

2. The method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying according to claim 1, characterized in that In step 2, the spray dryer parameters are set as follows: feed rate 800-1000 mL / h, drying temperature 90-92 ° C, nozzle diameter 1 mm, nozzle pressure 1.8-2.2 bar, ventilation volume 300-350 m 3 / h.

3. The method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying according to claim 1, characterized in that In the second step, the hollow microspheres are assembled from MXene nanosheets and have a diameter of 5 to 10 μm.

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