A preparation method of controllable atomically porous manganese dioxide nanosheets

Abstract

The present invention discloses a method for preparing controllable atomically porous manganese dioxide nanosheets. The method first uses a topological ion substitution method at room temperature to replace some Mn ions in the lamellar structure of MnO2 with Al ions, and then uses a tetramethylammonium ion intercalation and exfoliation method to obtain a dispersion of Mn 1‑x Al x O2 nanosheets. Finally, NaOH is used to etch away the Al atoms in the Mn 1‑x Al x O2 nanosheets to obtain atomically porous manganese dioxide nanosheets. Starting from the perspective of crystal structure design, the present invention can not only achieve controllable drilling at the atomic scale on the surface of metal oxides, but also prepare two-dimensional porous manganese dioxide nanosheet materials with different pore sizes by adjusting the concentration of the NaOH solution, which is expected to further improve the performance of manganese dioxide as a positive electrode catalytic material for lithium-oxygen batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a method for preparing controllable atomically porous manganese dioxide nanosheets. Background Art

[0002] Two-dimensional nanomaterials have advantages such as abundant active sites, large specific surface area, and fast ion diffusion paths, representing an important class of electrochemically energy storage or catalytic electrode materials, and are widely used in fields such as secondary batteries, electrocatalysis, and supercapacitors. Especially in the field of cathode catalyst materials for high-energy-density lithium-oxygen batteries, manganese dioxide is beneficial to enhancing the electrocatalytic performance of the oxygen cathode due to its rich resources, environmental friendliness, diverse crystal structures, and its unique [MnO6] octahedral field effect. However, the limited active sites of traditional MnO2 materials are an important factor restricting its development. In view of the above problems, the improvement strategy of porous manganese dioxide nanosheets can not only provide more active sites for redox reactions, but also improve the ion transport ability of MnO2 nanosheets in the vertical direction, increase the specific surface area, and is conducive to assembling lithium-oxygen battery devices with higher energy and power densities.

[0003] At present, the main methods reported in the literature for preparing porous MnO2 nanosheets are as follows: template method, thermal-induced exfoliation method, electrodeposition method, and hydrothermal method. Among them, the template method requires additives and the preparation process is complex; the thermal-induced exfoliation method requires high-temperature conditions; the electrodeposition method has a low mass loading and low yield, thus limiting its commercial application; the porous MnO2 materials obtained by the hydrothermal method generally have a smaller specific surface area and larger pore size. It can be seen that the above methods all have their limitations to a certain extent, and there is currently no reported method that is simple to prepare and can finely control the porosity of MnO2 nanosheets at the atomic level, which has caused certain limitations to the application and development of porous MnO2 nanosheet materials. Therefore, it is of great significance to develop a new preparation technology for controllably preparing atomically porous MnO2 nanosheets. Summary of the Invention

[0004] The purpose of the present invention is to provide a method that is simple to operate and can prepare two-dimensional porous manganese dioxide nanosheets with controllable sizes at the atomic level.

[0005] In view of the above purpose, the technical solution adopted by the present invention includes the following steps:

[0006] Step 1: Prepare exfoliated Mn 1-x Al x O2 nanosheet dispersion

[0007] Quickly mix an aqueous H2O2 solution with a mass fraction of 30% with an aqueous solution of tetramethylammonium hydroxide at 0.6 mol / L, and quickly add it to a mixed aqueous solution of manganese chloride and aluminum sulfate with a total metal ion concentration of 0.3 mol / L under stirring at room temperature. The volume ratio of the H2O2 aqueous solution, the tetramethylammonium hydroxide aqueous solution, and the mixed aqueous solution of manganese chloride and aluminum sulfate is 1:9:5. After continuing to stir for 24 hours, the resulting product is centrifuged at high speed to obtain the lower-layer precipitate. Subsequently, the lower-layer precipitate is washed with water until neutral, and then centrifuged at low speed to collect the supernatant, which is the exfoliated Mn 1-x Al x O2 nanosheet dispersion, where x = 0.1 - 0.9;

[0008] Step 2: Prepare atomically porous manganese dioxide nanosheets

[0009] Mix the exfoliated Mn 1-x Al x O2 nanosheet dispersion with an aqueous NaOH solution, and stir at room temperature to etch away the Al atoms in the Mn 1- x Al x O2 nanosheets. Centrifuge the resulting product to remove the precipitate, wash it with water until the filtrate is neutral, and then freeze-dry to obtain atomically porous manganese dioxide nanosheets.

[0010] In the above step 1, preferably x = 0.1 - 0.4.

[0011] In the above step 1, preferably the concentration of Mn 1-x Al x O2 nanosheets in the exfoliated Mn 1-x Al x O2 nanosheet dispersion is 0.05 - 0.15 mg / mL.

[0012] In the above step 1, preferably the rotation speed of high-speed centrifugation is 12000 - 18000 r / min, and the rotation speed of low-speed centrifugation is 3000 - 6000 r / min.

[0013] In the above step 2, preferably the ratio of the concentration of Mn 1-x Al x O2 nanosheets in the exfoliated Mn 1-x Al x O2 nanosheet dispersion to the concentration of NaOH in the aqueous NaOH solution is 1:1 - 5, and the volume ratio of the exfoliated Mn 1-x Al x O2 nanosheet dispersion to the aqueous NaOH solution is 1:0.5 - 2, and the concentration of the aqueous NaOH solution is 0.05 - 0.90 mg / mL.

[0014] In the above step 2, it is preferred to stir at room temperature for 0.5 to 3 hours.

[0015] The beneficial effects of the present invention are as follows:

[0016] In the present invention, at room temperature, the topological ion substitution method is first used to replace part of the Mn ions in the MnO2 lamellar structure with Al ions (the amount of substituted Mn ions can be regulated according to the molar ratio), and then the tetramethylammonium ion intercalation and exfoliation method is used to obtain a dispersion of Mn 1-x Al x O2 nanosheets. Finally, NaOH is used to etch away the Al atoms in the Mn 1-x Al x O2 nanosheets to obtain atomically porous manganese dioxide nanosheets. Through the NaOH alkali etching method, the preparation of atomically ordered porous manganese dioxide nanosheets is realized. This method not only has a simple preparation process, without the need for high temperature and template additives, but also can control the etching of Al atoms by adjusting the reaction time and reaction concentration to obtain manganese dioxide nanosheet materials with different pore size distributions, which is expected to further improve the performance of manganese dioxide as a cathode catalytic material for lithium-oxygen batteries. Description of the Drawings

[0017] Figure 1 It is the X-ray diffraction pattern of the exfoliated Mn 0.9 Al 0.1 O2 nanosheets and atomically porous Mn 0.9 H 0.1 O2 nanosheets in Example 1.

[0018] Figure 2 It is the Raman spectrum of the exfoliated Mn 0.9 Al 0.1 O2 nanosheets and atomically porous Mn 0.9 H 0.1 O2 nanosheets in Example 1.

[0019] Figure 3 It is the X-ray photoelectron spectrum of the exfoliated Mn 0.9 Al 0.1 O2 nanosheets (a) and atomically porous Mn 0.9 H 0.1 O2 nanosheets (b) in Example 1.

[0020] Figure 4 It is the scanning electron microscope photograph of the exfoliated Mn 0.9 Al 0.1 O2 nanosheets (a) and atomically porous Mn 0.9 H 0.1 O2 nanosheets (b) in Example 1.

[0021] Figure 5It is the Mn exfoliated in Example 1 0.9 Al 0.1 O2 nanosheets (a) and atomically porous Mn 0.9 H 0.1 O2 nanosheets (b) TEM images.

[0022] Figure 6 It is the atomically porous Mn 0.9 H 0.1 O2 nanosheets N2 adsorption - desorption isotherm diagram in Example 1.

[0023] Figure 7 It is the atomically porous Mn 0.9 H 0.1 O2 nanosheets pore size distribution diagram in Example 1.

[0024] Figure 8 It is the atomically porous Mn 0.9 H 0.1 O2 nanosheets and non - porous MnO2 nanosheets used as the charge - discharge curve diagram of the lithium - oxygen battery cathode catalyst in Example 1.

[0025] Figure 9 It is the atomically porous Mn 0.9 H 0.1 O2 nanosheets TEM images in Example 2.

[0026] Figure 10 It is the atomically porous Mn 0.9 H 0.1 O2 nanosheets TEM images in Example 3. Detailed implementation manners

[0027] The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0028] Example 1

[0029] Step 1: Prepare an exfoliated Mn 0.9 Al 0.1 O2 nanosheet dispersion

[0030] Quickly mix 33 mL of 30% hydrogen peroxide aqueous solution with 297 mL of 0.6 mol / L tetramethylammonium hydroxide aqueous solution, and quickly add it to 165 mL of a mixed aqueous solution of MnCl2·4H2O and Al2(SO4)3·18H2O with a total metal ion concentration of 0.3 mol / L under stirring at room temperature. The volume ratio of the hydrogen peroxide aqueous solution, tetramethylammonium hydroxide aqueous solution, and the mixed aqueous solution of MnCl2·4H2O and Al2(SO4)3·18H2O is 1:9:5, and the molar ratio of Mn to Al is 9:1. Stir at room temperature for 24 hours, and centrifuge the resulting product at 15,000 r / min. Wash the lower precipitate with water until neutral, and then centrifuge at 5,000 r / min to collect the supernatant, which is the exfoliated Mn 0.9 Al 0.1 O2 nanosheet dispersion. Take 100 mL of the exfoliated Mn 0.9 Al 0.1 O2 nanosheet dispersion and freeze-dry it. Weigh the mass to obtain the concentration of Mn 1-x Al x O2 nanosheets in the dispersion is 0.10 mg / mL.

[0031] Step 2: Preparation of atomically porous manganese dioxide nanosheets

[0032] Add 100 mL of 0.10 mg / mL exfoliated Mn 0.9 Al 0.1 O2 nanosheet dispersion to 200 mL of 0.29 mg / mL NaOH aqueous solution, and slowly stir at room temperature for 1 hour to etch away the Al atoms in the Mn 0.9 Al 0.1 O2 nanosheets. Centrifuge the resulting product at 1,500 r / min to remove the precipitate and collect the supernatant. Wash it with water until the filtrate is neutral and then freeze-dry it to obtain atomically porous manganese dioxide nanosheets (denoted as Mn 0.9 H 0.1 O2 nanosheets).

[0033] The prepared manganese oxide was characterized and tested using an X-ray diffractometer, scanning electron microscope, transmission electron microscope, physical adsorption instrument, X-ray photoelectron spectrometer, and electrochemical workstation. The results are shown in Figures 1 to 8 . As Figure 1 shown, the prepared Mn 0.9 Al 0.1 O2 nanosheets and Mn 0.9 H 0.1 O2 nanosheets have a crystal form of δ-MnO2. Figure 2 From the Raman spectroscopy results, it can be seen that the Mn 0.9 Al 0.1 O2 nanosheets have a peak at 558 cm -1An Al-O vibration peak appears at [specific location], and a Mn-O vibration peak appears at 640 cm -1 [specific location]. After etching with NaOH, the obtained Mn 0.9 H 0.1 O₂ nanosheets show that the Al-O vibration peak disappears, successfully removing Al atoms to form an atomically porous material. And Figure 3 from the X-ray photoelectron spectroscopy, the characteristic peak at 73.5 eV in Al 2p disappears after NaOH etching, further confirming that Al atoms are completely removed. Figure 4 Scanning electron microscope photos show that, compared with Mn 0.9 Al 0.1 O₂ nanosheets, Mn 0.9 H 0.1 O₂ nanosheets can clearly show a porous structure, and Figure 5 transmission electron microscope images further confirm this. It can be seen from the images that Mn 0.9 H 0.1 O₂ nanosheets are significantly porous. The large-size pore diameter is about 100 nm, while the atomic-scale pore diameter is invisible to the naked eye. Furthermore, N₂ adsorption-desorption tests are performed on Mn 0.9 H 0.1 O₂ nanosheets. It can be seen from Figure 6 and Figure 7 that the specific surface area of the atomically porous Mn 0.9 H 0.1 O₂ nanosheets is 630 m 2 / g, and the pore volume is about 3.8 cm 3 / g. The atomically porous Mn 0.9 H 0.1 O₂ nanosheets and non-porous MnO₂ nanosheets are used as the positive electrode catalyst to assemble a lithium-oxygen battery. From Figure 8 the charge-discharge curves, it can be seen that at a current density of 100 mA / g, the charge-discharge voltage plateau difference of the non-porous MnO₂ nanosheets is 1.03 V, while when the atomically porous Mn 0.9 H 0.1 O₂ nanosheets are used as the positive electrode catalyst, the charge-discharge voltage plateau difference is only 0.57 V, a decrease of 0.46 V, further indicating the excellent ORR / OER electrocatalytic performance of the atomically porous Mn 0.9 H 0.1 O₂ nanosheets.

[0034] Example 2

[0035] In step 2 of this example, 100 mL of 0.10 mg / mL exfoliated Mn 0.9 Al 0.1The O2 nanosheet dispersion was added to 200 mL of an aqueous NaOH solution with a concentration of 0.15 mg / mL, and slowly stirred at room temperature for 1 hour to etch away the Al atoms in the MnAlO2 nanosheets. The other steps were the same as in Example 1, and MnHO2 nanosheets were obtained, as shown in... 0.9 Al 0.1 atoms in the MnAlO2 nanosheets. The other steps were the same as in Example 1, and MnHO2 nanosheets were obtained, as shown in... 0.9 H 0.1 O2 nanosheets, as shown in Figure 9 .

[0036] Example 3

[0037] In step 2 of this example, 100 mL of the exfoliated MnAlO2 nanosheet dispersion with a concentration of 0.10 mg / mL was added to 200 mL of an aqueous NaOH solution with a concentration of 0.73 mg / mL, and slowly stirred at room temperature for 1 hour to etch away the Al atoms in the MnAlO2 nanosheets. The other steps were the same as in Example 1, and MnHO2 nanosheets were obtained, as shown in... 0.9 Al 0.1 atoms in the MnAlO2 nanosheets. The other steps were the same as in Example 1, and MnHO2 nanosheets were obtained, as shown in... 0.9 Al 0.1 atoms in the MnAlO2 nanosheets. The other steps were the same as in Example 1, and MnHO2 nanosheets were obtained, as shown in... 0.9 H 0.1 O2 nanosheets, as shown in Figure 10 .

Claims

1. A preparation method of controllable atomically porous manganese dioxide nanosheets, characterized in that The preparation method includes the following steps: Step 1: Prepare exfoliated Mn 1-x Al x O2 nanosheet dispersion Quickly mix an aqueous H2O2 solution with a mass fraction of 30% with an aqueous solution of tetramethylammonium hydroxide at 0.6 mol / L, and quickly add it to a mixed aqueous solution of manganese chloride and aluminum sulfate with a total metal ion concentration of 0.3 mol / L under stirring at room temperature. The volume ratio of the H2O2 aqueous solution, the tetramethylammonium hydroxide aqueous solution, and the mixed aqueous solution of manganese chloride and aluminum sulfate is 1:9:

5. After continuing to stir for 24 hours, subject the resulting product to high-speed centrifugation to obtain the lower-layer precipitate. Subsequently, wash the lower-layer precipitate with water until it is neutral, and then collect the supernatant by low-speed centrifugation to obtain a dispersed solution of exfoliated Mn 1-x Al x O2 nanosheets, where x = 0.1 - 0.9; Step 2: Prepare atomically porous manganese dioxide nanosheets The exfoliated Mn 1-x Al x O₂ nanosheet dispersion is mixed with an aqueous NaOH solution and stirred at room temperature to etch away the Mn 1-x Al x atoms in the O₂ nanosheets. The product is centrifuged to remove the precipitate, washed with water until the filtrate is neutral, and freeze-dried to obtain atomically porous manganese dioxide nanosheets.

2. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 1, wherein: In step 1, x = 0.1 - 0.

4.

3. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 1, wherein: In Step 1, the exfoliated Mn 1-x Al x concentration of Mn 1-x Al x O2 nanosheets in the dispersion is 0.05 - 0.15 mg / mL.

4. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 1, wherein: In step 1, the rotation speed of high-speed centrifugation is 12000 - 18000 r / min, and the rotation speed of low-speed centrifugation is 3000 - 6000 r / min.

5. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 3, wherein: In step 2, the stripped Mn 1-x Al x Mn in O2 nanosheet dispersion 1-x Al x The concentration ratio of O2 nanosheets to NaOH in the NaOH aqueous solution is 1:1-5. 1-x Al x The mixing volume ratio of the O2 nanosheet dispersion and the NaOH aqueous solution is 1:0.5-2.

6. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 5, wherein: In step 2, the concentration of the NaOH aqueous solution is 0.05 - 0.90 mg / mL.

7. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 1, characterized in that: In step 2, stir at room temperature for 0.5 - 3 hours.

8. The preparation method of the controllable atomically porous manganese dioxide nanosheets according to claim 1, wherein: In step 2, the rotation speed of centrifuging the product is 1000 - 3000 r / min.

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