A fibrous α-type or stalactite δ-type manganese dioxide, a method for preparing the same at low temperature, and an application thereof

Abstract

The present invention discloses a fibrous α-type or stalactite-like δ-type manganese dioxide, a low-temperature preparation method thereof and applications. The preparation method includes the following steps: Prepare a manganese sulfate solution, stir and heat it in a water bath at 70-90 °C, dropwise add a potassium permanganate solution into the manganese sulfate solution. After the dropping is completed, react at 60-90 °C for 60-90 min to obtain a reaction solution; perform solid-liquid separation on the reaction solution, wash the obtained solid phase, and dry the solid phase at 50-70 °C for 6-12 h to obtain δ-type manganese dioxide, and dry it at 50-70 °C for 84-120 h to obtain α-type manganese dioxide; the fibrous α-type manganese dioxide obtains a specific capacitance of 343 F g⁻¹ at a current density of 1 A g⁻¹; the stalactite-like δ-type manganese dioxide obtains a specific capacitance of 586 F g⁻¹ at a current density of 1 A g⁻¹; the obtained product can be used as a supercapacitor, a catalyst, etc.

Description

Technical Field

[0001] The present invention relates to the field of inorganic material synthesis, and particularly relates to fibrous α-type or stalactite-shaped δ-type manganese dioxide, a low-temperature preparation method thereof, and applications thereof. Background Art

[0002] As an important industrial raw material, manganese dioxide has good redox catalytic activity, low toxicity, environmental friendliness, and good economic benefits, and plays an irreplaceable role in fields such as catalysis, metal smelting, and supercapacitors. Manganese dioxide has multiple crystal forms, each showing a different morphology, such as α-MnO 2 , β-MnO 2 , γ-MnO 2 , δ-MnO 2 . All these crystal structures are composed of the common edges, angles, or planes of [MnO 6 , with oxygen atoms at the four corners of the octahedron and Mn atoms in the center. In addition, the connection of [MnO 6 basic units enables MnO 2 to form a variety of tunnel structures, α-MnO 2 (2×2 tunnel structure), γ-MnO 2 (mixed tunnel structure of 2×1 and 1×1), δ-MnO 2 (layered structure). Different types of manganese dioxide can play important roles in different application fields. For example, γ-MnO 2 can be used as the negative electrode material of zinc ion batteries and lithium ion batteries, α-MnO 2 , β-MnO 2 are excellent supercapacitor electrode materials, and δ-MnO 2 is a good precursor for polysulfide sealants. There are many methods for synthesizing manganese dioxide in the laboratory, such as hydrothermal method, low-temperature solid-phase method, sol-gel method, potentiostatic deposition method, etc. There are also many methods for obtaining different crystal forms of manganese dioxide, such as adjusting the ratio of raw materials, the temperature and time of hydrothermal reaction, etc. Moreover, different crystal forms of manganese dioxide can be transformed into each other. Commonly used methods include high temperature, ionic liquid assistance, and metal ion synergistic effects. However, these methods will increase costs and energy consumption. A simple and effective method for manganese dioxide crystal form transformation has always been the focus of research.

[0003] Currently, the common methods for preparing three-dimensional manganese dioxide structures are generally hydrothermal method, catalytic method, template method, etc. The template method requires post-treatment of the template after the reaction, which needs to go through high-temperature calcination or acid-base etching. This not only consumes a large amount of energy, but also the obtained product is prone to agglomeration, resulting in uneven size distribution, and may damage the product morphology or introduce other impurities. The hydrothermal method uses a closed container to generate high pressure at high temperature, enabling the reaction to proceed rapidly. However, due to the limitations of the container volume and reaction temperature, it is generally difficult to scale up production. The catalytic reaction has a long reaction time and requires the use of precious metals as catalysts.

[0004] Chinese Patent Document 202011489595.3 discloses a preparation method of α-MnO2 without pore channels: dissolving a manganese salt in water, then adding a sodium hypochlorite solution, and obtaining amorphous manganese dioxide after standing, suction filtration, washing, and drying; adding the amorphous manganese oxide into water, adding concentrated sulfuric acid, dispersing evenly and then standing for reaction to obtain α-MnO2 without pore channels; a large amount of waste liquid will be generated by using concentrated sulfuric acid in this preparation method, which is not environmentally friendly.

[0005] Chinese Patent Document 201610672452.3 discloses a preparation method of coral-shaped porous δ-MnO 2 by mixing a KMnO 4 solution and a MnSO 4 solution evenly; adjusting the pH value of the mixed solution with dilute hydrochloric acid; transferring the mixed solution with adjusted pH value into a high-pressure reaction kettle; after the high-pressure reaction kettle reacts, cooling and reducing the temperature, washing the obtained product with distilled water until neutral and then washing with absolute ethanol, and then drying in an oven to obtain coral-shaped porous δ-MnO 2 powder; the required reaction temperature and reaction pressure for this reaction are relatively large, and the required cost is relatively high.

[0006] In the absence of any template, surfactant or catalyst, it is currently very difficult to prepare α-MnO2 or δ-MnO 2 . Summary of the Invention

[0007] In order to solve the deficiencies existing in the prior art, the purpose of the present invention is to provide a fibrous α-type or stalactite-shaped δ-type manganese dioxide, its low-temperature preparation method and application. During the post-treatment process of sample synthesis, controlling the drying rate of the sample, α-type manganese dioxide and δ-type manganese dioxide are prepared. The preparation method is simple, reducing the cost and energy consumption of producing different crystal forms of manganese dioxide.

[0008] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0009] A low-temperature preparation method of fibrous α-type or stalactite δ-type manganese dioxide, characterized by comprising the following steps: preparing a manganese sulfate solution, and dropping a potassium permanganate solution into the manganese sulfate solution under stirring and water bath heating conditions; after the dropping is completed, reacting to obtain a reaction solution; performing solid-liquid separation on the reaction solution, washing and drying the obtained solid phase to obtain fibrous α-type manganese dioxide or stalactite δ-type manganese dioxide;

[0010] Among them, the drying conditions of the fibrous α-type manganese dioxide are: drying at 50-70 °C for 84-120 h;

[0011] The drying conditions of the stalactite δ-type manganese dioxide are: drying at 50-70 °C for 6-12 h.

[0012] Preferably, the water bath temperature of the manganese sulfate solution is 60-90 °C.

[0013] Preferably, the reaction conditions are reacting at 60-90 °C for 60-90 min.

[0014] Preferably, the mass ratio of the solute to the solvent of the potassium permanganate solution is 7-10:100.

[0015] Preferably, the mass ratio of the solute to the solvent of the manganese sulfate solution is 6-9:100.

[0016] Preferably, the mass ratio of the solute to the solvent of the potassium permanganate solution is 8:100.

[0017] Preferably, the mass ratio of the solute to the solvent of the manganese sulfate solution is 8:100.

[0018] Preferably, the dropping time of the potassium permanganate solution does not exceed 5 min.

[0019] The present invention also claims to protect fibrous α-type manganese dioxide or stalactite δ-type manganese dioxide prepared by the above method, wherein the specific surface area of the fibrous α-type manganese dioxide is 30-55 m 2 / g, the pore volume is 0.1-0.4 cm 3 / g, and the surface pore diameter is 2-8 nm; the specific surface area of the stalactite δ-type manganese dioxide is 110-130 m 2 / g, the pore volume is 0.3-0.6 cm 3 / g, and the surface pore diameter is 4-12 nm.

[0020] The present invention also claims to protect the application of the fibrous α-type manganese dioxide or stalactite δ-type manganese dioxide in supercapacitors.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The present invention provides a low-temperature preparation method for fibrous α-type or stalactite-like δ-type manganese dioxide. The method uses a simple hydrothermal method, which is fast and effective, has a low temperature, a short reaction time, low cost, low energy consumption, and is stable, reliable, and safe.

[0023] 2) The present invention provides a low-temperature preparation method for fibrous α-type or stalactite-like δ-type manganese dioxide. The raw materials are cheap, widely sourced, easy to store, and can be produced on a large scale.

[0024] 3) The present invention provides a low-temperature preparation method for fibrous α-type or stalactite-like δ-type manganese dioxide, which can prepare fibrous α-type or stalactite-like δ-type manganese dioxide with high purity and good crystallinity. The specific surface area of the fibrous α-type manganese dioxide is 30 - 55 m 2 / g, the pore volume is 0.1 - 0.4 cm 3 / g, the surface pore diameter is 2 - 8 nm, and a specific capacitance of 343 Fg -1 is obtained at a current density of 1 Ag -1 ; the specific surface area of the stalactite-like δ-type manganese dioxide is 110 - 130 m 2 / g, the pore volume is 0.3 - 0.6 cm 3 / g, the surface pore diameter is 4 - 12 nm, and a specific capacitance of 586 Fg -1 is obtained at a current density of 1 Ag -1 ; the obtained product can be directly applied to various required fields, such as supercapacitors, catalysts, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some schematic diagrams of the embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0026] Figure 1 XRD of the α-type manganese dioxide prepared in Example 1;

[0027] Figure 2 XRD of the δ-type manganese dioxide prepared in Example 1;

[0028] Figure 3 SEM of the α-type manganese dioxide prepared in Example 1;

[0029] Figure 4 SEM of the δ-type manganese dioxide prepared in Example 1;

[0030] Figure 5Cyclic voltammogram curves of δ-MnO₂ prepared in Example 1 at different scanning rates;

[0031] Figure 6 Galvanostatic charge-discharge curves of δ-MnO₂ prepared in Example 1 at different current densities;

[0032] Figure 7 Cyclic voltammogram curves of a two-electrode system assembled with δ-MnO₂ prepared in Example 1 as the positive and negative electrodes at different scanning rates;

[0033] Figure 8 Galvanostatic charge-discharge curves of a two-electrode system assembled with δ-MnO₂ prepared in Example 1 as the positive and negative electrodes at different current densities;

[0034] Figure 9 Cyclic voltammogram curves of α-MnO₂ prepared in Example 1 at different scanning rates;

[0035] Figure 10 Galvanostatic charge-discharge curves of α-MnO₂ prepared in Example 1 at different current densities;

[0036] Figure 11 Cyclic voltammogram curves of a two-electrode system assembled with α-MnO₂ prepared in Example 1 as the positive and negative electrodes at different scanning rates;

[0037] Figure 12 Galvanostatic charge-discharge curves of a two-electrode system assembled with α-MnO₂ prepared in Example 1 as the positive and negative electrodes at different current densities;

[0038] Figure 13 Nitrogen adsorption and desorption curves of δ-MnO₂ and α-MnO₂ prepared in Example 1. Detailed implementation manners

[0039] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further elaborates on the present invention in conjunction with embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0040] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased through market channels or synthesized from raw materials purchased through market channels.

[0041] Example 1

[0042] A low-temperature preparation method for fibrous α-MnO₂ or stalactite-like δ-MnO₂, comprising the following steps:

[0043] Dissolve 6 g of manganese sulfate in 100 g of deionized water to prepare a manganese sulfate solution, stir, and heat in a water bath at 80 °C; dissolve 7 g of potassium permanganate in 100 g of deionized water to prepare a potassium permanganate solution, and drop it into the manganese sulfate solution. The dropping is completed in 2 min, and then react at 60 °C for 90 min to obtain a reaction solution, and then carry out solid-liquid separation, and wash the obtained solid phase;

[0044] Dry a part of the solid phase product at 60 °C for 6 h to obtain stalactite-shaped δ-manganese dioxide;

[0045] Dry the remaining solid phase product at 60 °C for 84 h to obtain fibrous α-manganese dioxide.

[0046] Example 2

[0047] A low-temperature preparation method of fibrous α-manganese dioxide or stalactite-shaped δ-manganese dioxide, comprising the following steps:

[0048] Dissolve 7 g of manganese sulfate in 100 g of deionized water to prepare a manganese sulfate solution, stir, and heat in a water bath at 80; dissolve 8 g of potassium permanganate in 100 g of deionized water to prepare a potassium permanganate solution, and drop it into the manganese sulfate solution. The dropping is completed in 3 min, and then react at 70 °C for 80 min to obtain a reaction solution, and then carry out solid-liquid separation, and wash the obtained solid phase;

[0049] Dry a part of the solid phase product at 60 °C for 7 h to obtain stalactite-shaped δ-manganese dioxide;

[0050] Dry the remaining solid phase product at 60 °C for 96 h to obtain fibrous α-manganese dioxide.

[0051] Example 3

[0052] A low-temperature preparation method of fibrous α-manganese dioxide or stalactite-shaped δ-manganese dioxide, comprising the following steps:

[0053] Dissolve 8 g of manganese sulfate solution in 100 g of deionized water to prepare a manganese sulfate solution, stir, and heat in a water bath at 80 °C; dissolve 9 g of potassium permanganate in deionized water to prepare a potassium permanganate solution, and drop it into the manganese sulfate solution. The dropping is completed in 4 min, and then react at 80 °C for 70 min to obtain a reaction solution, and then carry out solid-liquid separation, and wash the obtained solid phase;

[0054] Dry a part of the solid phase product at 60 °C for 10 h to obtain stalactite-shaped δ-manganese dioxide;

[0055] Dry the remaining solid phase product at 60 °C for 108 h to obtain fibrous α-manganese dioxide.

[0056] Example 4

[0057] A low-temperature preparation method of fibrous α-type or stalactite-like δ-type manganese dioxide, comprising the following steps:

[0058] Dissolve 9 g of manganese sulfate in 100 g of deionized water to prepare a manganese sulfate solution, stir and heat in a water bath at 80 °C; dissolve 10 g of potassium permanganate in 100 g of deionized water to prepare a potassium permanganate solution, and drop it into the manganese sulfate solution. The dropping ends in 5 min, and then react at 90 °C for 60 min to obtain a reaction solution. Subsequently, perform solid-liquid separation and wash the obtained solid phase;

[0059] Dry a part of the solid-phase product at 60 °C for 12 h to obtain stalactite-like δ-type manganese dioxide;

[0060] Dry the remaining solid-phase product at 60 °C for 120 h to obtain fibrous α-type manganese dioxide.

[0061] Example 5

[0062] Mix the δ-type manganese dioxide prepared in Example 1, polyvinylidene fluoride, and conductive agent acetylene black in a mass ratio of 8:1:1, drop 400 μL of N-methylpyrrolidone solution, mix evenly to form a paste, coat it on a 1 cm × 1 cm nickel foam, with a loading amount of 4 mg and dry at 60 °C to obtain an electrode sheet as the working electrode. Use a mercury-mercuric oxide electrode as the reference electrode and a platinum sheet as the counter electrode, and assemble a three-electrode working system with 1 mol / L KOH as the electrolyte. In the voltage range of -0.2 to 0.6 V, obtain a specific capacitance of 586 F / g at a current density of 1 A / g. -1 of -1 specific capacitance.

[0063] Example 6

[0064] Mix the δ-type manganese dioxide prepared in Example 1, polyvinylidene fluoride, and conductive agent acetylene black in a mass ratio of 8:1:1, drop 400 μL of N-methylpyrrolidone solution, mix evenly to form a paste, coat it on a 1 cm × 1 cm nickel foam, with a loading amount of 4 mg and dry at 60 °C to obtain electrode sheets as the positive and negative electrodes respectively. Assemble a two-electrode working system with 1 mol / L KOH as the electrolyte. The maximum energy density and power density achieved by this assembled system are 17.8 Wh / kg -1 and 0.2 W / kg -1 .

[0065] Example 7

[0066] The α-manganese dioxide obtained in Example 1, polyvinylidene fluoride, and conductive agent acetylene black were mixed at a mass ratio of 8:1:1, 400 μL of N-methylpyrrolidone solution was added dropwise, and the mixture was uniformly mixed to form a paste. The paste was coated on a 1 cm × 1 cm nickel foam, with a loading amount of 4 mg, and dried at 60 °C to obtain an electrode sheet as the working electrode. Using a mercury / mercuric oxide electrode as the reference electrode and a platinum sheet as the counter electrode, 1 mol / L -1 KOH was used as the electrolyte to assemble a three-electrode working system. In the voltage range of -0.2 to 0.6 V, a specific capacitance of 343 F / g was obtained at a current density of 1 A / g -1 -1 .

[0067] Example 8

[0068] The α-manganese dioxide obtained in Example 1, polyvinylidene fluoride, and conductive agent acetylene black were mixed at a mass ratio of 8:1:1, 400 μL of N-methylpyrrolidone solution was added dropwise, and the mixture was uniformly mixed to form a paste. The paste was coated on a 1 cm × 1 cm nickel foam, with a loading amount of 4 mg, and dried at 60 °C to obtain electrode sheets as the positive and negative electrodes respectively. Using 1 mol / L -1 KOH as the electrolyte to assemble a two-electrode working system. The maximum energy density and power density achieved by this assembled system were 17.8 Wh / kg -1 and 0.2 W / kg -1 .

[0069] Comparative Example 1

[0070] A low-temperature preparation method of manganese dioxide includes the following steps:

[0071] Dissolve 6 g of manganese sulfate in 100 g of deionized water to prepare a manganese sulfate solution, stir, and heat in a water bath at 80 °C; dissolve 7 g of potassium permanganate in 100 g of deionized water to prepare a potassium permanganate solution, and add it dropwise into the manganese sulfate solution. The dropping ends in 2 min, and then react at 60 °C for 90 min to obtain a reaction solution. Subsequently, solid-liquid separation is carried out, and the obtained solid phase is washed;

[0072] The solid-phase product is dried at 60 °C for 24 h to obtain manganese dioxide with poor crystallization, and stalactite-like δ-manganese dioxide cannot be obtained.

[0073] Comparative Example 2

[0074] A low-temperature preparation method of manganese dioxide includes the following steps:

[0075] ​Dissolve 6 g of manganese sulfate in 100 g of deionized water to prepare a manganese sulfate solution, stir, and heat it in a water bath at 80 °C; dissolve 7 g of potassium permanganate in 100 g of deionized water to prepare a potassium permanganate solution, and drop it into the manganese sulfate solution. The dropping is completed in 2 min, and then react at 60 °C for 90 min to obtain a reaction solution. Subsequently, perform solid-liquid separation and wash the obtained solid phase.

[0076] Dry the solid phase product at 60 °C for 48 h to obtain manganese dioxide with poor crystallization, and fibrous α-manganese dioxide cannot be obtained.

[0077] Detect the two different crystal forms of manganese dioxide prepared in Example 1 with a BET specific surface area analyzer, and the specific data are shown in Table 1.

[0078] Table 1 Detection results of the surface properties of two different crystal forms of manganese dioxide

[0079] Sample <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Pore diameter (nm) <![CDATA[δ-MnO 2 > 121.140 0.331 6.148 <![CDATA[α-MnO 2 > 46.433 0.117 4.128

[0080] As mentioned above, the above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A low-temperature preparation method for obtaining different crystal forms of manganese dioxide by controlling the drying time, characterized in that, it comprises the following steps: Prepare a manganese sulfate solution, and under stirring and water bath heating conditions, dropwise add a potassium permanganate solution into the manganese sulfate solution. After the dropping is completed, react to obtain a reaction solution; perform solid-liquid separation on the reaction solution, wash and dry the obtained solid phase to obtain fibrous α-type manganese dioxide or stalactite-like δ-type manganese dioxide; When the drying condition is drying at 50-70°C for 6-12 hours, stalactite-like δ-type manganese dioxide is obtained; When the drying condition is drying at 50-70°C for 84-120 hours, fibrous α-type manganese dioxide is obtained; The water bath temperature of the manganese sulfate solution is 70-90°C; The reaction condition is reacting at 60-90°C for 60-90 minutes.

2. The low-temperature preparation method according to claim 1, characterized in that, the mass ratio of the solute to the solvent of the potassium permanganate solution is 7-10:

100.

3. The low-temperature preparation method according to claim 1, characterized in that, the mass ratio of the solute to the solvent of the manganese sulfate solution is 6-9:

100.

4. The low-temperature preparation method according to claim 1, characterized in that, the mass ratio of the solute to the solvent of the potassium permanganate solution is 8:

100.

5. The low-temperature preparation method according to claim 1, characterized in that, the mass ratio of the solute to the solvent of the manganese sulfate solution is 8:

100.

6. The low-temperature preparation method according to claim 1, characterized in that, the dropping time of the potassium permanganate solution does not exceed 5 minutes.

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