Bi2O3 dodecahedral cage material assembled by amorphous nanodots and preparation method thereof

Abstract

The present invention provides a Bi- 2 O 3 Dodecahedral cage material and preparation method thereof. The material is a hollow dodecahedral cage structure with a high surface exposure ratio assembled from bismuth oxide amorphous nanodots of about 10 nm in size. The preparation method comprises: dissolving a certain amount of bismuth nitrate and potassium ferrocyanide in an aqueous solution successively to form a clear solution, adding a certain amount of nitric acid to the above solution while stirring, standing for a period of time at room temperature, centrifugally separating and drying to obtain a precursor material after the reaction is completed; taking a certain amount of precursor material and dispersing it in a certain concentration of KOH aqueous solution, centrifugally separating and drying after the reaction is completed. The material has a large surface atomic exposure ratio, highly active nanodot assembly units, fast conductive edges and a porous structure that accelerates the diffusion of substances. It has a novel structure, low cost, green and environmentally friendly, and broad application prospects; its preparation method is green and mild, simple and easy to control, does not require surfactants, and has high production efficiency.

Description

Technical Field

[0001] The invention belongs to the field of nano material preparation, and in particular relates to a Bi2O3 dodecahedron cage material assembled by amorphous nano dots and a preparation method thereof. Background Art

[0002] Excessive energy consumption and the resulting environmental problems are two major problems facing mankind in the 21st century. The conversion and storage of various new energy sources is a green and environmentally friendly route to alleviate the above crisis. Among them, aqueous rechargeable alkaline batteries are a promising energy storage device. It uses an aqueous electrolyte with faster ion transport characteristics, so it has a high power density; at the same time, it uses a Faraday reaction-type electrode material based on a high theoretical capacity to build a device, so it has a high energy density. In addition, it has many advantages such as high safety, low cost, and environmental friendliness, making it a hot topic of research. However, its actual energy density is low and its cycle stability is poor, which greatly limits its practical application. The root cause of these problems lies in the lack of high-performance electrode materials. After a lot of research, its positive electrode materials, such as nickel / cobalt-based hydroxides, oxides, sulfides, etc., have excellent electrochemical properties. In contrast, its negative electrode materials, such as iron oxide, manganese oxide, bismuth oxide, etc., still show problems such as low capacity, poor rate capability, and poor cycle stability. Therefore, the design and preparation of high-performance negative electrode materials are urgently needed for its practical application.

[0003] In order to solve the above problems of negative electrode materials, it is very important to design a structure with high conductivity, suitable pore structure, highly active assembly unit and higher atomic exposure ratio. The synergy of these structural advantages can simultaneously achieve high conductivity and ion diffusivity of electrode materials to obtain excellent electrochemical performance. However, it is still a major challenge to design and synthesize negative electrode materials with these structural characteristics. The present invention obtains Bi2O3 dodecahedral cage nanomaterials assembled by amorphous nanodots for the first time through the structural inheritance transformation method of bismuth-iron dodecahedral precursors. It has a multi-level structure that is beneficial to electrochemical reactions: highly active nanoparticle assembly units, large specific surface area, highly conductive edges, large cavities, and low crystallinity. These structures work synergistically to effectively improve the electronic conduction, ion transport and atomic utilization of the material during the electrochemical reaction, and ultimately achieve high specific capacity, superior rate and good cycle stability. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a bismuth oxide with novel structure, low cost, green and environmental protection, ultra-high capacity, high rate performance, excellent cycle stability and a preparation method thereof which can be used as a negative electrode material for aqueous alkaline batteries. The preparation method has simple process and is green and environmentally friendly.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] For the first time, a uniform bismuth-containing iron dodecahedron precursor was prepared by liquid phase precipitation method, and then an amorphous nanodot-assembled Bi2O3 dodecahedron cage material was obtained for the first time by alkali-driven structural inheritance transformation, in which the size of the nanodot assembly unit was about 10nm.

[0007] The present invention also provides a method for preparing a Bi2O3 dodecahedral cage material assembled by amorphous nanodots, the specific steps of which are:

[0008] (1) dissolving a certain amount of bismuth nitrate and potassium ferrocyanide in deionized water in sequence, and stirring to form a clear and transparent solution;

[0009] (2) Add a certain amount of nitric acid dropwise to the solution formed in step (1), stir evenly and let stand at room temperature for a period of time. After the reaction is completed, centrifuge the product and dry it in an oven at 60°C. Obtaining precursor materials .

[0010] Should The precursor material is The precursor material containing bismuth iron has a solid dodecahedral structure.

[0011] (3) Take a certain amount of the precursor material obtained in step (2), add it to a KOH solution of a certain concentration, and after the conversion reaction is completed, amorphous nanodots assembled can be obtained. Bi2O3 dodecahedral cage material .

[0012] Preferably, the amount of bismuth nitrate added in step (1) is 0.1-0.5 g, the amount of potassium ferrocyanide added is 0.2-0.7 g, and the volume of deionized water is 100 mL.

[0013] Preferably, the amount of nitric acid added in step (2) is 200 to 1000 μL.

[0014] Preferably, the concentration of the KOH aqueous solution in step (3) is 0.5% to 1%, and the mass of the precursor material is 50-100 mg.

[0015] In the present invention, a bismuth-iron precursor with a solid dodecahedral structure is first prepared, and then the precursor itself is used as a template and a reactant to perform an ion exchange reaction in an alkaline solution, and finally a dodecahedron assembled with amorphous nanodots that inherits the structural characteristics of the precursor is converted. During the conversion reaction, the ions in the outermost layer of the dodecahedral precursor first react with the hydroxide ions in the solution to form a densely packed shell assembled with nanodots. Subsequently, the external hydroxide diffuses inwardly while the internal bismuth ions diffuse outwardly through the shell to react, so that the shell plays a role in controlling the transport of substances. Since the large-sized hydroxide ions are slightly slower than the bismuth ions in transport, a dodecahedral cage material assembled with nanodots is finally obtained for the first time.

[0016] During the preparation process, the synthesis and conversion conditions of the precursor play a key role in the formation of the final product structure. During the preparation of the precursor, whether nitric acid is added to start the reaction and the amount of nitric acid added will affect the morphology and structure of the precursor. Secondly, the amount of precursor added, the reaction concentration of KOH, and the order of addition of the two during the conversion process have a great influence on the structure of the final nanomaterial. Excessive precursor will lead to incomplete conversion reaction, generating a core-shell structure with bismuth oxide as the outer shell and the core of the precursor as the core. Excessive high concentration of KOH will accelerate the conversion reaction and cause the collapse of the structure. Adding KOH directly to the aqueous solution of the precursor will cause the structure to break up, generate nanoparticles, and fail to obtain the target structure.

[0017] The above technical solution adopted by the present invention, as an example but not a limitation, has the following beneficial effects compared with the prior art:

[0018] 1. The present invention prepares for the first time a bismuth oxide dodecahedron cage material assembled by amorphous nanodots, which has a novel structure, low cost, and is green and environmentally friendly, does not require additional templates, surfactants, and complex post-processing, and has high production efficiency.

[0019] 2. The room temperature co-precipitation and structural inheritance transformation methods used in the preparation process of the present invention are simple, easy to control, efficient and stable, and can be extended to the construction of other similar multi-level assembled hollow nanomaterials.

[0020] 3. The bismuth oxide dodecahedral cage material assembled by amorphous nanodots prepared by the present invention has broad application prospects in rechargeable aqueous alkaline batteries. This is due to the unique multiple synergistic structural advantages of the material: the highly active amorphous ultra-small nanodot assembly unit has more exposed atoms on the surface, thus greatly accelerating the Faraday reaction rate and improving the utilization rate of atoms; the stacking assembly of nanoparticles brings a larger specific surface area and rich pore structure, which is conducive to rapid electrochemical reactions; the directional dense edges can effectively accelerate the electron transmission during the electrochemical reaction; the large cavity structure can temporarily store electrolyte, which is conducive to the rapid diffusion of electrolyte ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a SEM photograph of the precursor material obtained in Example 2 at a magnification of 2 um.

[0022] Figure 2 This is a SEM photograph of the Bi2O3 dodecahedral cage assembled by amorphous nanodots obtained in Example 2 at a magnification of 2um.

[0023] Figure 3 This is a SEM photograph of the Bi2O3 dodecahedral cage assembled by amorphous nanodots obtained in Example 2 at a magnification of 1 um.

[0024] Figure 4 TEM photo of the Bi2O3 dodecahedron cage obtained in Example 2 at a multiple of 10 nm

[0025] Figure 5 This is the XRD spectrum of the Bi2O3 dodecahedral cage assembled by nanodots obtained in Example 2. DETAILED DESCRIPTION

[0026] The technical solution of the Bi2O3 dodecahedron cage assembled by amorphous nanodots provided by the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. The advantages and features of the present invention will become more apparent with the following description.

[0027] Example 1

[0028] (1) Dissolve 0.4 g of bismuth nitrate and 0.6 g of potassium ferrocyanide in 100 mL of deionized water, and stir to form a clear and transparent solution;

[0029] (2) 800 μL of nitric acid was added dropwise to the stirred clear solution. After the addition was completed, the mixture was allowed to react at room temperature for 2 h. After the reaction was completed, the product was separated by centrifugation, washed three times with water and ethanol, and then dried in an oven at 60° C.;

[0030] (3) Take 100 mg of the precursor material obtained in step (2), add it to 50 mL of an aqueous solution containing 1 g of KOH, and stir the reaction for 2 h to obtain a Bi2O3 dodecahedral cage nanomaterial assembled by amorphous nanodots.

[0031] Example 2

[0032] (1) Dissolve 0.25 g of bismuth nitrate and 0.3 g of potassium ferrocyanide in 100 mL of deionized water, and stir to form a clear and transparent solution;

[0033] (2) 400 μL of nitric acid was added dropwise to the stirred clear solution. After the addition was completed, the reaction was allowed to stand at room temperature for 2 h. After the reaction was completed, the product was centrifuged and separated. After washing with water and ethanol three times, the product was dried in an oven at 60° C. to obtain a precursor material. Figure 1 This is a SEM photograph of the precursor material obtained in Example 2 at a magnification of 2 um. As can be seen from the figure, the precursor is a dodecahedral structure with a smooth surface.

[0034] (3) Take 100 mg of the precursor material obtained in step (2), add it to 50 mL of an aqueous solution containing 0.5 g of KOH, and stir the reaction for 2 h to obtain a Bi2O3 dodecahedral cage nanomaterial assembled by amorphous nanodots.

[0035] Figure 2 The Bi2O3 dodecahedron cage assembled by the amorphous nanodots obtained in Example 2 is Multiples of 2um SEM photo of the converted material. As can be seen from the figure, the structural characteristics of the precursor are inherited, and the surface becomes rough due to the distribution of nanodot particles.

[0036] Figure 3 The Bi2O3 dodecahedron cage assembled by the amorphous nanodots obtained in Example 2 is Multiples of 1um The SEM photo shows that the damaged part has a hollow structure inside.

[0037] Figure 4 The Bi2O3 dodecahedron cage obtained in Example 2 At multiples of 10nm TEM image. As can be seen from the image, the dodecahedral cage is assembled from nanodots of about 10 nm in size.

[0038] Figure 5 This is the XRD spectrum of the Bi2O3 dodecahedron cage assembled by nanodots obtained in Example 2. The spectrum consists of two large mantou peaks, indicating that the material is an amorphous structure.

[0039] Example 3

[0040] (1) Dissolve 0.1 g of bismuth nitrate and 0.2 g of potassium ferrocyanide in 100 mL of deionized water, and stir to form a clear and transparent solution;

[0041] (2) 500 μL of nitric acid was added dropwise to the stirred clear solution. After the addition was completed, the mixture was allowed to react at room temperature for 2 h. After the reaction was completed, the product was separated by centrifugation, washed three times with water and ethanol, and then dried in an oven at 60° C.;

[0042] (3) Take 50 mg of the precursor material obtained in step (2), add it to 50 mL of aqueous solution containing 0.5 g of KOH, and stir the reaction for 2 h to obtain a Bi2O3 dodecahedral cage nanomaterial assembled by amorphous nanodots.

[0043] The reagents used in the present invention are all purchased from Sinopharm Chemical Reagent Co., Ltd., among which bismuth nitrate, AR (Shanghai test), ≥99.0%; potassium ferrocyanide, AR (Shanghai test), ≥99.5%; nitric acid, AR (Shanghai test), 65.0-68.0%; potassium hydroxide, AR (Shanghai test), ≥85%; anhydrous ethanol, AR (Shanghai test), ≥99.7%. The instruments used in the present invention are all conventional chemical instruments.

[0044] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by any person skilled in the art based on the above disclosed technical contents shall be regarded as equivalent effective embodiments and shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a Bi2O3 dodecahedral cage material assembled by amorphous nanodots, characterized in that: The specific preparation steps are: (1) dissolving a certain amount of bismuth nitrate and potassium ferrocyanide in deionized water in sequence, and stirring to form a clear and transparent solution; (2) adding a certain amount of nitric acid dropwise to the solution formed in step (1), stirring evenly and then standing at room temperature for a period of time, centrifuging and separating the product after the reaction is completed, and drying in an oven at 60° C. to obtain a precursor material; (3) taking a certain amount of the precursor material obtained in step (2), adding it to a KOH solution of a certain concentration, and after the conversion reaction is completed, a Bi2O3 dodecahedral cage material assembled by amorphous nanodots can be obtained; The amount of bismuth nitrate added in step (1) is 0.1-0.5 g, the amount of potassium ferrocyanide added is 0.2-0.7 g, and the volume of deionized water is 100 mL; the concentration of the KOH aqueous solution in step (3) is 0.5%-1%, and the mass of the precursor material in step (2) is 50-100 mg.

2. The method for preparing the Bi2O3 dodecahedral cage material assembled by amorphous nanodots according to claim 1, characterized in that: The amount of nitric acid added in step (2) is 200-1000 μL.

3. A precursor material obtained according to the preparation method according to any one of claims 1-2, characterized in that: The precursor material is a solid dodecahedral structure with uniform size.

4. A Bi2O3 dodecahedral cage material assembled by amorphous nanodots obtained by the preparation method according to any one of claims 1-2, characterized in that: The material is a hollow dodecahedral cage structure assembled from 10nm-sized bismuth oxide amorphous nanodots.

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