Two-dimensional bismuth nanosheet and preparation method thereof

Abstract

The invention discloses a two-dimensional bismuth nanosheet and a preparation method thereof, and relates to the technical field of nano materials. The specific preparation process comprises the following steps: mixing bismuth powder serving as a raw material and diethylene glycol serving as a solvent, heating, preserving heat and refluxing to obtain bismuth nano liquid drops; and dropwise adding the bismuth nano liquid into absolute ethyl alcohol for crystallization reaction, controlling the crystallization speed by controlling the temperature of the absolute ethyl alcohol, and separating and purifying to obtain the two-dimensional bismuth nanosheet. According to the preparation method, a liquid metal recrystallization method is introduced into preparation of the bismuth nanosheet for the first time, accurate regulation and control of the morphology and the structure of the bismuth nanosheet are achieved by controlling the crystallization rate, the bismuth nanosheet is of a two-dimensional quadrilateral structure, and it is guaranteed that the thickness of the bismuth nanosheet is thin and uniform. Meanwhile, the two-dimensional bismuth nanosheet can be prepared without a carrier or a substrate or a surfactant, so that the preparation of the self-supporting two-dimensional bismuth nanosheet is realized, and the adverse effect of the surfactant on the performance of the two-dimensional bismuth nanosheet can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of nanomaterials, and in particular to a two-dimensional bismuth nanosheet and a preparation method thereof. Background Art

[0002] Due to their unique surface properties and structural advantages, two-dimensional metal nanomaterials have shown important application prospects in the fields of electrocatalysis, optics and energy conversion. Among them, bismuth nanosheets have become a potential two-dimensional material with their low melting point, layered crystal structure and excellent quasi-metal properties.

[0003] In the prior art, the methods for synthesizing two-dimensional bismuth nanosheets include physical methods and chemical methods. Among them, chemical methods include reduction methods, solvent thermal methods, electrochemical deposition methods, etc. These bottom-up chemical methods for synthesizing bismuth nanosheets usually rely on strong reducing agents, high temperatures and long reaction conditions. Such harsh reaction conditions increase the complexity and cost of preparation. CN104400004A discloses a bismuth metal nanosheet and a preparation method thereof, which uses bismuth nitrate, hexadecyltrimethylammonium bromide and glucose as raw materials to prepare bismuth nanosheets, but the surfactant hexadecyltrimethylammonium bromide needs to be introduced during the preparation process to regulate the morphology of nanomaterials, but the residues of these surfactants will have an adverse effect on the performance of the material and reduce its electrocatalytic or optical properties. In addition, in the process of synthesizing two-dimensional bismuth nanosheets by chemical methods, it is difficult to accurately regulate the morphology and size of two-dimensional bismuth nanomaterials, resulting in a widened size distribution of the resulting material and uneven thickness. Physical methods include exfoliation, hot pressing and vapor deposition. Although the exfoliation method can prepare ultrathin nanosheets, the yield is low and it cannot be separated from the substrate support, which limits the applicability of the product; the bismuth nanosheets prepared by the hot pressing method have uneven temperature and pressure distribution, resulting in large differences in the size of the prepared bismuth nanosheets; the vapor deposition method has problems of poor continuity and uneven size and thickness distribution, and relies on substrate support. The resulting bismuth nanosheets are difficult to support independently, which limits their flexibility in practical applications.

[0004] The low melting point and active chemical properties of bismuth make its growth process less controllable, especially in maintaining the two-dimensional structure and regulating surface defects. Therefore, it is particularly important to develop a preparation method for two-dimensional bismuth nanosheets that can avoid the use of carrier / substrate materials and surfactants and overcome the defects of the existing technology of large thickness, uneven distribution and wide size distribution of bismuth nanosheets. Summary of the invention

[0005] In view of the above-mentioned prior art, the purpose of the present invention is to provide a two-dimensional bismuth nanosheet and a preparation method thereof. The present invention introduces the liquid metal recrystallization method into the preparation process of bismuth nanosheets for the first time, and the obtained two-dimensional bismuth nanosheets have a regular two-dimensional quadrilateral structure with a thickness of 1.1-3.4nm, a length of 0.47±0.20μm, and a width of 0.31±0.12μm. The present invention utilizes the low melting point characteristics of bismuth, first melts the bismuth powder, and then controls the crystallization rate to achieve precise control of the morphology and structure of the bismuth nanosheets, so that the bismuth nanosheets present a two-dimensional quadrilateral structure, and the thickness of the bismuth nanosheets is thin and uniform. The preparation conditions in the present invention are mild, which can effectively reduce energy consumption and finished products, and the two-dimensional bismuth nanosheets can be obtained without relying on surfactants and substrate materials, which not only avoids the adverse effects of surfactants on the performance of two-dimensional bismuth nanosheets, thereby ensuring that the product is more convenient in subsequent processing and application, but also can achieve self-support of bismuth nanosheets. At the same time, the size distribution of the obtained two-dimensional bismuth nanosheets is relatively concentrated. In addition, the process of the present invention is simplified, easy to operate, and does not require special equipment, and can achieve efficient and large-scale preparation of bismuth nanosheets.

[0006] To achieve the above object, the present invention adopts the following technical solutions: In a first aspect of the present invention, a method for preparing a two-dimensional bismuth nanosheet is provided, comprising the following steps: (1) After mixing bismuth powder and diethylene glycol, heating and reflux under an inert atmosphere to obtain bismuth nanodroplets; (2) In an inert atmosphere, bismuth nanodroplets are added to anhydrous ethanol for crystallization reaction. The temperature of the anhydrous ethanol before the reaction is adjusted to 295-345K to control the crystallization rate. After the crystallization reaction is completed, separation and purification are performed to obtain two-dimensional bismuth nanosheets.

[0007] Preferably, in step (1), the particle size of the bismuth powder is in the range of 80-120 mesh and the purity is ≥99.99%.

[0008] Preferably, in step (1), the material-liquid ratio of bismuth powder to diethylene glycol is (100-150) mg: (15-25) mL.

[0009] Preferably, in step (1), the inert atmosphere is an argon atmosphere.

[0010] Preferably, in step (1), the heating method is oil bath heating, the heating temperature is 470-480K, and the insulation reflux time is 15-30min.

[0011] Preferably, in step (2), the inert atmosphere is an argon atmosphere.

[0012] Preferably, in step (2), the material-liquid ratio of bismuth nanodroplets to anhydrous ethanol is (100-150) mg: (200-300) mL.

[0013] Preferably, in step (2), the crystallization reaction ends when the temperature of the reaction system is 340-390K.

[0014] Preferably, in step (2), the specific operation of separation and purification is: after the liquid after the crystallization reaction is completed is allowed to stand, the supernatant is collected, and the supernatant is centrifuged and washed to obtain the two-dimensional bismuth nanosheets.

[0015] Further preferably, the standing time is 36-48 hours, the centrifugal speed is 6000-8000 rpm, the centrifugal time is 5-10 minutes, and the precipitate is washed with anhydrous ethanol.

[0016] The second aspect of the present invention provides two-dimensional bismuth nanosheets prepared by the above method.

[0017] Preferably, the two-dimensional bismuth nanosheet is a regular quadrilateral with a thickness of 1.1-3.4 nm, a length of 0.47±0.20 μm, and a width of 0.31±0.12 μm.

[0018] Beneficial effects of the present invention: The present invention adopts the liquid metal recrystallization method to prepare two-dimensional bismuth nanosheets for the first time. The prepared two-dimensional bismuth nanosheets have a regular two-dimensional quadrilateral structure with a thickness of 1.1-3.4nm, a length of 0.47±0.20μm, and a width of 0.31±0.12μm. The specific preparation method is: using bismuth powder as a raw material and diethylene glycol as a solvent, heating the two to the boiling point of diethylene glycol after mixing and reflux, so that the bismuth powder is completely melted to obtain bismuth nanodroplets; adding the bismuth nanodroplets to anhydrous ethanol in an inert atmosphere to perform a crystallization reaction, and controlling the temperature of the anhydrous ethanol to control the crystallization speed. After the reaction is completed, separation and purification are performed to obtain two-dimensional bismuth nanosheets.

[0019] The present invention utilizes the low melting point characteristic of bismuth, first melts the bismuth powder, and then controls the crystallization rate to achieve precise control of the morphology and structure of the bismuth nanosheets, so that the bismuth nanosheets present a two-dimensional quadrilateral structure, and the thickness of the bismuth nanosheets is thin and uniform. At the same time, the present invention can prepare two-dimensional bismuth nanosheets without the need for a carrier or substrate, and without the need for a surfactant, which not only realizes the preparation of self-supporting two-dimensional bismuth nanosheets, but also avoids the adverse effects of surfactants on the performance of two-dimensional bismuth nanosheets, thereby ensuring that the product is more convenient in subsequent processing and application. At the same time, the size distribution of the obtained two-dimensional bismuth nanosheets is relatively concentrated. In addition, the process of the present invention is simplified, easy to operate, and does not require special equipment, and can achieve efficient and large-scale preparation of bismuth nanosheets. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1: Transmission electron microscopy images of two-dimensional bismuth nanosheets at different scales; (a) is a transmission electron microscopy image of a two-dimensional bismuth nanosheet at 2 μm; (b) is a transmission electron microscopy image of a two-dimensional bismuth nanosheet at 1 μm; (c) is a transmission electron microscopy image of a two-dimensional bismuth nanosheet at 500 nm; Figure 2 : Atomic force microscope image of the two-dimensional bismuth nanosheet prepared in Example 1 and the height cross-sectional analysis image of the line scan; wherein (a) is the atomic force microscope image of the two-dimensional bismuth nanosheet; (b) is Figure 2 (a) is the height cross-section analysis diagram corresponding to the horizontal line scan; (c) is Figure 2 (a) Height cross-section analysis diagram corresponding to the longitudinal line scan; Figure 3 : Statistical graph of size distribution of two-dimensional bismuth nanosheets prepared in Example 1; wherein (a) is a statistical graph of length distribution of two-dimensional bismuth nanosheets; (b) is a statistical graph of width distribution of two-dimensional bismuth nanosheets; Figure 4 : X-ray diffraction pattern of the two-dimensional bismuth nanosheets prepared in Example 1; Figure 5 : X-ray electron spectrum of the two-dimensional bismuth nanosheets prepared in Example 1; Figure 6 : Raman spectrum of the two-dimensional bismuth nanosheets prepared in Example 1; Figure 7 : Transmission electron microscope image of the bismuth nanomaterial prepared in Comparative Example 1; Figure 8 : Transmission electron microscopy image of the bismuth nanomaterial prepared in Comparative Example 2; Fig. 9 : Atomic force microscopy images and line scan height cross-sectional analysis images of the bismuth nanomaterial prepared in Comparative Example 2; wherein (a) is an atomic force microscopy image of the bismuth nanomaterial; (b) is Fig. 9 Height cross-section corresponding to the longitudinal line scan in (a). DETAILED DESCRIPTION

[0021] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0022] In the prior art, two-dimensional metallic bismuth nanomaterials have shown important application prospects in the field of electrocatalysis due to their unique surface properties and structural advantages. Methods for preparing two-dimensional bismuth nanosheets include physical and chemical methods, but the chemical method relies on strong reducing agents, surfactants, and high requirements for reaction conditions, resulting in high preparation costs. At the same time, the chemical method cannot accurately control the morphology and size of bismuth nanosheets. Physical laws rely on substrate support, have low yields, and are difficult to apply industrially.

[0023] Among them, the melting point of bismuth is 271°C. When growing two-dimensional nanosheets on a substrate, due to the high surface energy of liquid bismuth, bismuth tends to form nanospheres, making it difficult to achieve controllable growth of two-dimensional structures. At the same time, during the growth of bismuth nanomaterials, the lower melting point makes bismuth atoms prone to migration and aggregation, which makes it difficult to accurately control the distribution and arrangement of bismuth atoms on the surface, and easily forms various surface defects.

[0024] Based on this, the present invention provides a method for preparing a two-dimensional bismuth nanosheet, which uses a liquid metal recrystallization method to prepare a two-dimensional bismuth nanosheet with uniform thickness and relatively concentrated size distribution. Specifically, bismuth powder is used as a raw material and diethylene glycol is used as a solvent. The two are mixed and heated to the boiling point of diethylene glycol and refluxed to completely melt the bismuth powder to obtain bismuth nanodroplets; the bismuth nanodroplets are added to anhydrous ethanol under an inert atmosphere to perform a crystallization reaction, and the crystallization speed is controlled by controlling the temperature of the anhydrous ethanol. After the reaction is completed, the two-dimensional bismuth nanosheet is obtained by separation and purification.

[0025] Compared with the prior art, in the process of preparing two-dimensional bismuth nanosheets of the present invention, 1) two-dimensional bismuth nanosheets can be prepared without relying on surfactants, thus avoiding the adverse effects of surfactants on the performance of two-dimensional bismuth nanosheets, thereby saving the post-processing process; 2) the preparation of two-dimensional bismuth nanosheets can be completed at a relatively low heating temperature, and no strong reducing agent is required, which significantly reduces energy consumption and production costs; 3) by controlling the temperature of anhydrous ethanol to regulate the thermodynamic and kinetic conditions of the crystallization process, it is ensured that the prepared bismuth nanosheets are regular quadrilaterals with thin and uniform thickness and relatively concentrated size distribution, thus overcoming the defects of the bismuth nanosheets prepared in the prior art, such as wide size distribution and uncontrollable morphology; 4) the preparation process is simplified, easy to operate, and no special equipment is required, so that efficient and large-scale preparation of bismuth nanosheets can be achieved.

[0026] Among them, the present invention adopts the liquid metal recrystallization method to prepare two-dimensional bismuth nanosheets for the first time. The obtained two-dimensional bismuth nanosheets have a regular two-dimensional quadrilateral structure with a thickness of 1.1-3.4nm, a length of 0.47±0.20μm, and a width of 0.31±0.12μm. The present invention makes full use of the low melting point characteristics of bismuth, first melts the bismuth powder, and then mixes the bismuth nanodroplets with anhydrous ethanol for crystallization reaction. By controlling the temperature of anhydrous ethanol before the reaction, the thermodynamics and kinetics during the crystallization reaction are controlled to form two-dimensional bismuth nanosheets under slow cooling conditions. The use of this precise control technology of thermodynamics and kinetics not only improves the stability of the preparation process, but also significantly improves the consistency and repeatability of the product.

[0027] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0028] The experimental materials used in the embodiments of the present invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0029] Example 1: A method for preparing two-dimensional bismuth nanosheets (1) 120 mg of bismuth powder with a particle size of 100 mesh and a purity of 99.99% was mixed with 20 mL of diethylene glycol, and then heated to 473 K in an oil bath under an argon atmosphere, and refluxed for 20 min to completely melt the bismuth powder to obtain bismuth nanodroplets; (2) Under an argon atmosphere, 120 mg of bismuth nanodroplets were poured into 250 mL of anhydrous ethanol at a temperature of 298 K for crystallization reaction. The crystallization rate was controlled by controlling the temperature of the anhydrous ethanol before the reaction. When the temperature of the reaction system reached 343 K, the crystallization reaction was completed. After the crystallization reaction was completed, the liquid was allowed to stand for 40 hours, the supernatant was separated, and the supernatant was centrifuged at 7000 rpm for 8 minutes. The solid after centrifugation was collected and washed with anhydrous ethanol to obtain a two-dimensional bismuth nanosheet.

[0030] The structure of the prepared two-dimensional bismuth nanosheets was characterized. Figure 1-Figure 6 shown.

[0031] pass Figure 1 and Figure 2 It can be seen that the two-dimensional bismuth nanosheets prepared in the present invention have a regular quadrilateral structure, and the thickness of the two-dimensional bismuth nanosheets is 1.9 nm and the thickness distribution is uniform. The length and width of the two-dimensional bismuth nanosheets prepared in this embodiment are counted, and the size distribution is counted. The results are as follows Figure 3 As shown, through Figure 3It can be seen that the length of the regular quadrilateral two-dimensional bismuth nanosheets is concentrated in the range of 0.15-0.95 μm and the width is concentrated in the range of 0.15-0.45 μm. According to the calculation in the above figure, the length of the obtained two-dimensional bismuth nanosheets is 0.47±0.20 μm and the width is 0.31±0.12 μm. Figure 4 It can be seen that the intensity distribution of the diffraction peak is consistent with the bismuth crystal phase of the standard PDF card (#44-1246), indicating that the sample has a pure bismuth phase with high crystallinity. Figure 5 It can be seen that the X-ray photoelectron spectroscopy test results of the Bi 4f electron binding energy peak of the two-dimensional bismuth nanosheet sample show that the two characteristic peaks are clear and have no offset, indicating that the bismuth in the sample is in a pure metallic state and no characteristic peaks of the oxidation state are observed. Figure 6 It can be seen that the two main peaks appear at 68 and 97 cm⁻¹, corresponding to the characteristic phonon modes of bismuth nanosheets, respectively, verifying its two-dimensional material properties and crystal structure integrity.

[0032] Example 2: A method for preparing two-dimensional bismuth nanosheets (1) 100 mg of bismuth powder with a particle size of 80 mesh and a purity of 99.99% was mixed with 15 mL of diethylene glycol, and heated to 470 K in an oil bath under an argon atmosphere, and refluxed for 15 min to completely melt the bismuth powder to obtain bismuth nanodroplets; (2) Under an argon atmosphere, 100 mg of bismuth nanodroplets were poured into 250 mL of anhydrous ethanol at a temperature of 295 K for crystallization reaction. The crystallization rate was controlled by controlling the temperature of the anhydrous ethanol before the reaction. When the temperature of the reaction system reached 340 K, the crystallization reaction was completed. After the crystallization reaction was completed, the liquid was allowed to stand for 36 hours, and the supernatant was separated. The supernatant was centrifuged at 6000 rpm for 10 minutes, and the solid after centrifugation was collected and washed with anhydrous ethanol to obtain a two-dimensional bismuth nanosheet.

[0033] Example 3: A method for preparing two-dimensional bismuth nanosheets (1) 150 mg of bismuth powder with a particle size of 120 mesh and a purity of 99.99% was mixed with 25 mL of diethylene glycol, and heated to 480 K in an oil bath under an argon atmosphere, and refluxed for 25 min to completely melt the bismuth powder to obtain bismuth nanodroplets; (2) Under an argon atmosphere, 150 mg of bismuth nanodroplets were poured into 250 mL of anhydrous ethanol at a temperature of 345 K for crystallization reaction. The crystallization rate was controlled by controlling the temperature of the anhydrous ethanol before the reaction. When the temperature of the reaction system reached 390 K, the crystallization reaction was completed. After the crystallization reaction was completed, the liquid was allowed to stand for 48 hours, the supernatant was separated, and the supernatant was centrifuged at 8000 rpm for 5 minutes. The solid after centrifugation was collected and washed with anhydrous ethanol to obtain a two-dimensional bismuth nanosheet.

[0034] Comparative Example 1: The difference between this comparative example and Example 1 is that in step (2), the temperature of anhydrous ethanol before the crystallization reaction is 255K.

[0035] The electron microscope image of the bismuth nanomaterial prepared in this comparative example is as follows Figure 7 As shown. Figure 7 It can be seen that when the temperature of anhydrous ethanol before the crystallization reaction is low, the prepared bismuth nanomaterial is in the shape of nanospheres. It can be seen that when the temperature of anhydrous ethanol before the crystallization reaction is too low, the prepared bismuth nanomaterial cannot have a sheet structure.

[0036] Comparative Example 2: The difference between this comparative example and Example 1 is that in step (2), the temperature of anhydrous ethanol before the crystallization reaction is 350K.

[0037] The structural characterization of the bismuth nanomaterial obtained in this comparative example is as follows: Figure 8-Figure 9 As shown, through Figure 8 and Fig. 9 It can be seen that although the bismuth nanomaterial obtained in this comparative example presents a sheet structure, its morphology is irregular and there is a certain degree of agglomeration. At the same time, the thickness of the bismuth nanomaterial is 5.8nm. It can be seen that when the temperature of anhydrous ethanol before the crystallization reaction is too high, the bismuth nanomaterial obtained is a sheet structure, but its thickness is much higher than that of the present application and has an irregular morphology. Therefore, the temperature of anhydrous ethanol before the crystallization reaction is too high to achieve accurate control of the morphology and structure of the bismuth nanosheet.

[0038] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing two-dimensional bismuth nanosheets, characterized in that: The following steps are involved: (1) After mixing bismuth powder and diethylene glycol, heating and reflux under an inert atmosphere to obtain bismuth nanodroplets; (2) In an inert atmosphere, bismuth nanodroplets are added to anhydrous ethanol for crystallization reaction. The temperature of the anhydrous ethanol before the reaction is adjusted to 295-345K to control the crystallization rate. After the crystallization reaction is completed, separation and purification are performed to obtain two-dimensional bismuth nanosheets.

2. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (1), the particle size of the bismuth powder is in the range of 80-120 mesh and the purity is ≥99.99%.

3. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (1), the material-liquid ratio of bismuth powder to diethylene glycol is (100-150) mg: (15-25) mL.

4. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (1), the inert atmosphere is argon atmosphere, the heating temperature is 470-480K, and the reflux time is 15-30min.

5. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (2), the material-liquid ratio of bismuth nanodroplets and anhydrous ethanol is (100-150) g: (200-300) mL.

6. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (2), when the temperature of the reaction system is 340-390K, the crystallization reaction is completed.

7. The method for preparing the two-dimensional bismuth nanosheets according to claim 1, characterized in that: In step (2), the specific operation of separation and purification is: after the liquid after the crystallization reaction is completed is allowed to stand, the supernatant is collected, and the two-dimensional bismuth nanosheets are obtained by centrifugation and washing.

8. The method for preparing the two-dimensional bismuth nanosheets according to claim 7, characterized in that: The standing time is 36-48h, the centrifugal speed is 6000-8000rpm, and the centrifugal time is 5-10min.

9. The two-dimensional bismuth nanosheet prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The two-dimensional bismuth nanosheet has a thickness of 1.1-3.4 nm, a length of 0.47±0.20 μm, and a width of 0.31±0.12 μm.

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