Method for rapidly preparing high-concentration MXene slurry through low-temperature spray drying

Abstract

The invention discloses a method for quickly preparing high-concentration MXene slurry through low-temperature spray drying, which comprises the following steps: 1, mixing absolute ethyl alcohol and ethyl acetate to obtain a regulator; 2, adding a regulator into the MXene dispersion liquid, and performing spray drying to obtain MXene powder of hollow microspheres; thirdly, deionized water is added into the MXene powder obtained in the second step, and single-layer MXene slurry is obtained. According to the method, ethanol and ethyl acetate are added into an MXene dispersion liquid as conditioning agents, and the temperature in the spray drying process is reduced from 220 DEG C to 90 DEG C, so that oxidation of MXene at high temperature is prevented, and preparation of high-concentration slurry through low-temperature spray drying is realized. According to the preparation method, the problems that the MXene high-concentration slurry is easy to oxidize and low in preparation efficiency in the production process are effectively solved, and the prepared high-concentration slurry can be directly used for preparing an MXene film and has an excellent electromagnetic shielding characteristic.

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 such as electrochemical energy storage, electromagnetic shielding, and flexible electronic materials. At present, in the process of synthesizing MXene materials, the concentration of MXene dispersion is mostly less than 1wt%. The low concentration of MXene dispersion is not easy to be processed into high-concentration MXene slurry in the actual device production process. MXene is easily oxidized in water and oxygen environments. Ordinary 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 slurry. Therefore, the preparation of high-concentration MXene slurry can effectively slow down the oxidation and 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 high-speed centrifugation (10,000 rpm, 1 hour) combined with heating evaporation (50 ° C, 6 to 8 hours). The semi-solid MXene has good dispersibility in water and can be 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 MXene materials to oxidize (Chemistry of Materials, 2017, 29 (11): 4848-4856.). Oxidation will cause serious losses in the various properties of MXene materials, and their conductivity will drop significantly, which will correspondingly lead to a significant reduction in their electromagnetic shielding performance. To solve the above problems, some researchers freeze-dried the MXene dispersion for a long time and then rehydrated it to convert it into a semi-solid MXene with a high solid content of 60wt%, but the overall process took 2 to 3 days and was too inefficient (Advanced Science, 2023, 10(19): 2300660.). To meet the needs of practical applications, it is critical 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 high-concentration MXene slurry, but also the prepared high-concentration slurry can be directly used for the preparation of MXene thin films, and has excellent electromagnetic shielding properties.

[0004] The objective 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 the regulator:

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

[0008] Step 2: Spray drying:

[0009] First, the regulator prepared in step 1 is added to 8-12 mg / mL MXene dispersion, and the mixture is evenly mixed 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 obtained mixed solution is spray dried by a spray dryer. After a drying process of 5-7 minutes, a MXene powder of hollow microspheres 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 the mixture was evenly mixed 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 the existing MXene spray drying technology, which avoids oxidation and dispersibility problems caused by high temperature and saves equipment costs 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 only by low-speed stirring, restoring the two-dimensional flaky morphology of MXene and processed 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 (20-50wt%), 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 electrical 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 It is a flow chart of 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;

[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 in conjunction with the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be included in the protection scope of the present invention.

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

[0027] Step 1: Preparation of the 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 are selected as regulators, which can effectively reduce the boiling point of the mixed solution, and spray drying and dehydration can be achieved at only 90° C. On the other hand, the introduction of the regulator can effectively protect the surface hydrophilic groups of 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 8-12 mg / mL MXene dispersion, and the mixture is evenly mixed by magnetic stirring for 1-5 minutes (200-800 rpm), and the volume ratio of MXene dispersion to regulator is controlled to be 4:1-5:1; finally, the obtained mixture is spray dried at 90-92°C in a spray dryer, and after a drying process of 5-7 minutes, a MXene powder of hollow microspheres is obtained.

[0032] In this step, the drying temperature is preferably set to 90 ° C, and the feed rate is preferably set to 1000 mL / h, which can ensure that the spray droplets can be fully dried at a lower temperature. In the ordinary high-temperature spray drying process, the water in the droplets gradually evaporates, causing the MXene nanosheets to gradually aggregate. Due to the irregular arrangement of MXene nanosheets, the surface is unevenly subjected to capillary forces, and finally wrinkled MXene nanosheets are formed. In addition, the capillary force causes dense stacking between MXene sheets, and the high temperature causes partial loss of hydroxyl groups on the MXene surface, which leads to a decrease in the dispersibility of MXene powder. In contrast, ethanol and ethyl acetate are added as regulators to the droplets of low-temperature spray drying, so that the spray droplets form a temperature gradient during evaporation, and constant turbulence is generated inside the MXene solution through Rayleigh-Bernard convection. As evaporation continues, due to the Marangoni effect, the fluctuating MXene flakes assemble into hollow microspheres on the surface of the droplets, which are assembled from MXene nanosheets and have a diameter of 5 to 10 μm. The regular spherical shell can better resist the compression force during the drying process, and finally obtains a 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 be achieved only 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. If the ethanol content is too high, the MXene dispersion will not form a hollow microsphere structure after drying. If the ethyl acetate content is too high, the prepared MXene microspheres will have poor dispersibility in water. If the ethyl acetate content is too low, the hollow microsphere structure will also fail to 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 shape of a hollow sphere. Due to the retention of the hydrophilic groups on the surface of MXene, the MXene powder can be converted into a MXene slurry by adding deionized water within the aging period (1 hour).

[0037] Example:

[0038] Embodiment 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 mixed evenly by magnetic stirring for 2 minutes (500 rpm) to obtain a regulator.

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

[0041] Step 3: The spray dryer setting parameters are: 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 is in the form of hollow microspheres and has good dispersibility in water within 1 hour after preparation. It can be dispersed in water with only low-speed stirring, without any traces 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 (20wt%) MXene slurry. This slurry is used to prepare MXene film with excellent electromagnetic shielding performance (58dB) ( Figure 3 ).

[0044] Embodiment 2:

[0045] The difference between this embodiment and embodiment 1 is that anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 1:5. The regulator is added to 100 ml of MXene dispersion (10 mg / mL), and the solution is stratified, with MXene in the lower aqueous phase and the regulator in the upper layer.

[0046] Embodiment 3:

[0047] The difference between this example and Example 1 is that 125 mL of MXene dispersion (10 mg / mL) was taken and no other reagents were added. No MXene powder was produced in this example. The MXene dispersion could not be dried into powder at 90°C.

[0048] Embodiment 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 a hollow microsphere morphology ( Figure 4 ), but the powder is insoluble in water and oxidizes.

[0050] Embodiment 5:

[0051] The difference between this embodiment and embodiment 3 is that the drying temperature is set to 220°C. The MXene powder obtained in this embodiment 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] Embodiment 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 (33wt%) MXene slurry. The slurry is used to prepare a MXene film with excellent electromagnetic shielding performance (55dB) ( Figure 6 ).

[0054] Embodiment 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 (50wt%) MXene slurry. The slurry is used to prepare a MXene film with excellent electromagnetic shielding performance (58dB) ( Figure 7 ).

[0056] It can be concluded from the above examples that the method provided by the present invention realizes that the MXene dispersion is converted into MXene powder with good dispersibility through low-temperature spray drying, and then converted into MXene slurry with different concentrations (20-50wt%) through hydration. The MXene film processed by the slurry has excellent electrical conductivity and electromagnetic shielding performance.

Claims

1. A method for rapidly preparing a high-concentration MXene slurry by low-temperature spray drying, characterized in that The method comprises the following steps: Step 1: Preparation of the regulator: Anhydrous ethanol and ethyl acetate are mixed in a volume ratio of 5:1 to 20:1, and mixed evenly by magnetic stirring, and the magnetic stirring time is controlled to be 1 to 5 minutes and the rotation speed is 200 to 800 rpm to obtain a regulator; Step 2: Spray drying: First, the regulator prepared in step 1 is added to 8-12 mg / mL MXene dispersion, and the mixture is evenly mixed 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 obtained mixed solution is spray dried by a spray dryer. After a drying process of 5-7 minutes, a MXene powder of hollow microspheres 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 the mixture was evenly mixed 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 step 2, the hollow microspheres are assembled from MXene nanosheets and have a diameter of 5 to 10 μm.

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