A method for preparing pomegranate-shaped molybdenum carbide / carbon MoC / C nanoparticles

Abstract

A method for preparing pomegranate-shaped molybdenum carbide / carbon (MoC / C) nanocomposite particles, using pyrrole and phosphomolybdic acid as raw materials, and preparing a pomegranate-shaped MoC / C nanocomposite material with an average particle size of about 70 nanometers through in-situ polymerization and subsequent magnesium thermal reaction, wherein 3-5 nm MoC nanocrystals are embedded in an amorphous carbon matrix. The preparation method is simple to operate, and the reaction temperature can be significantly reduced by adjusting the solution ratio and thermal reaction strategy. The preparation process is simple, easy to control, and has good repeatability, and can achieve large-scale production. The MoC / C nanoparticles prepared by the present invention have uniform size and high phase purity, and can be used as a potential catalyst and absorber material for hydrogen evolution reaction.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a method for preparing a pomegranate-shaped molybdenum carbide / carbon MoC / C nanocomposite material. Background Art

[0002] Transition metal carbides are one of the most promising types of materials for new functional fields. For example, they have the advantages of high catalytic activity, high stability, and flexible preparation methods when used as electrocatalysts for hydrogen evolution reaction in water electrolysis; and strong microwave loss capability when used as absorber materials. Molybdenum carbide has attracted attention due to its Pt-like electronic structure, chemical stability, low cost, and good conductivity. The composition, crystal phase, and structure of the prepared molybdenum carbide nanomaterials, which are prepared by adjusting the reaction conditions and precursors during the synthesis process, have a decisive influence on their performance.

[0003] Generally, carbide synthesis is achieved through carbonization reaction at high temperature. For example, molybdenum salt is used as a precursor, gaseous carbon (hydrocarbon gas) or solid carbon (biochar, etc.) is used as a carbon source, and carbon reduction reaction is generally carried out at high temperature with the assistance of hydrogen to obtain molybdenum carbide. Gaseous carbon sources have very high requirements for experimental conditions and preparation processes, and there are certain safety hazards in operation. Solid carbon sources have solid-solid interface reactions, the reaction products have poor uniformity, and the specific surface area is low, which will have a certain impact on the performance of molybdenum carbide.

[0004] In addition, magnesium thermal reduction has been shown to synthesize carbides at temperatures <700°C. Magnesium metal can react with carbon to form magnesium carbide, which undergoes solid-state metathesis with metal oxides to form metal carbides. Therefore, magnesium thermal reduction can achieve the synthesis of molybdenum carbide nanomaterials with high specific surface area and uniform composition at lower temperatures. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a pomegranate-shaped molybdenum carbide / carbon MoC / C nanocomposite material, and to prepare a pomegranate-shaped MoC / C nanocomposite material at low temperature, wherein the particle size of the composite material is 40-70 nanometers, wherein 3-5 nanometer MoC particles are uniformly dispersed in an amorphous carbon matrix to form a pomegranate-shaped microstructure. The composite material prepared by the method will have great application prospects and advantages in electrocatalysis and microwave absorption.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing pomegranate-shaped molybdenum carbide / carbon MoC / C nanoparticles, characterized in that it comprises the following steps:

[0008] 1) Add 420 μl of pyrrole solution into 20 ml of anhydrous ethanol and stir thoroughly;

[0009] 2) Add 1.2 mmol of phosphomolybdic acid into 100 ml of distilled water and stir thoroughly to form a yellow solution;

[0010] 3) Add the solution obtained in step 1 to the solution in step 2 to gradually form a black mixed dispersion, and stir at room temperature for 12 hours;

[0011] 4) The mixed dispersion obtained in step 3 is centrifuged and washed several times with deionized water and ethanol solution until the supernatant is clear, and then dried in a vacuum drying oven at 60° C. to obtain a black product A;

[0012] 5) Mixing the product A obtained in step 4 with magnesium powder and sodium chloride in a mass ratio of 1:1:5, heating and keeping the temperature, to obtain product B;

[0013] 6) The product B obtained in step 5 is treated with an aqueous hydrochloric acid solution to remove magnesium oxide and other soluble by-products, and the insoluble products are collected by centrifugation and dried to obtain a black powder which is a pomegranate-like MoC / C nanocomposite material.

[0014] The average particle size of the MoC / C nanoparticles is 70 nanometers, and the microstructure thereof is pomegranate-shaped, that is, MoC particles of 3 to 5 nanometers are uniformly dispersed in an amorphous carbon matrix.

[0015] In the step 5, the temperature is raised to 550-700° C., the heating rate is 5-10° C. / min, and the insulation time is 4-8 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The present invention uses pyrrole solution and phosphomolybdic acid as precursors, forms a nano-spherical structure through in-situ polymerization, and prepares pomegranate-shaped MoC / C nanoparticles with uniform size by combining subsequent magnesium thermal reaction. The prepared nanocomposite particles have an average particle size of 70 nanometers, uniform size, and no impurities. The entire preparation process is simple in steps, easy to operate, and has good repeatability.

[0018] The dosage of molybdenum salt has an important regulatory effect on the product composition, and the use of solid carbon source in the carbonization process can reduce the deposited carbon produced during the carbonization process, which is beneficial to regulating the active surface area of ​​MoC.

[0019] Compared with the prior art, the reaction temperature of the present invention is relatively low, thus greatly reducing energy consumption.

[0020] In summary, the molybdenum source and carbon source used in the present invention are both common reagents, and the preparation process is simple, easy to control, and has good repeatability, and can achieve large-scale production. At the same time, the product has high purity and uniform and controllable size, and the active material MoC nanoparticles are uniformly dispersed in the amorphous carbon matrix, which is beneficial to increase the active surface area. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Scanning electron microscopy and low-magnification transmission electron microscopy images of MoC / C nanoparticles;

[0022] Figure 2 This is a high-magnification transmission electron microscopy image of MoC / C nanoparticles;

[0023] Figure 3 This is the X-ray diffraction pattern of MoC / C nanoparticles. DETAILED DESCRIPTION

[0024] The invention is further described below with reference to the accompanying drawings and embodiments.

[0025] The molybdenum carbide (MoC) nanoparticles of the invention use pyrrole and phosphomolybdic acid as raw materials, and prepare pomegranate-shaped MoC / C nanoparticles through magnesium thermal reaction.

[0026] Example 1

[0027] 400 μl of pyrrole solution was added to 20 ml of anhydrous ethanol and stirred to form a mixed solution A; 1.2 mmol of phosphomolybdic acid was added to 100 ml of distilled water and stirred to form a yellow solution B; the mixed solution A was added dropwise to the mixed solution B to form a black mixed dispersion, and stirred at room temperature for 12 hours; the obtained product was centrifuged and washed several times with a mixed solution of deionized water and ethanol until the supernatant was clear, and then dried in a vacuum drying oven at 60°C overnight to obtain a black product A; the obtained product A was mixed with magnesium powder and sodium chloride in a mass ratio of 1:1:5, and the temperature was increased to 650°C at a heating rate of 5°C / min and kept for 6 hours, then cooled naturally to room temperature, and then treated with a hydrochloric acid aqueous solution to remove magnesium oxide and other soluble byproducts. The insoluble product was collected by centrifugation and dried to obtain a black powder as MoC / C nanoparticles. The MoC / C nanoparticles are shown in FIG. 1 and FIG. 2 ; the d value and relative intensity of the diffraction peak thereof are consistent with the d value and relative intensity listed in the PDF standard card (89-2868) of MoC, as shown in FIG. 3 .

[0028] Example 2

[0029] 350 μl of pyrrole solution was added to 20 ml of anhydrous ethanol and stirred to form a mixed solution A; 1.2 mmol of phosphomolybdic acid was added to 100 ml of distilled water and stirred to form a yellow solution B; the mixed solution A was added dropwise to the mixed solution B to form a black mixed dispersion, and stirred at room temperature for 12 hours; the obtained product was centrifuged and washed several times with a mixed solution of deionized water and ethanol until the supernatant was clear, and then dried in a vacuum drying oven at 60°C overnight to obtain a black product A; the obtained product A was mixed with magnesium powder and sodium chloride in a mass ratio of 1:1:5, and the temperature was increased to 650°C at a heating rate of 5°C / min and kept for 6 hours, then cooled naturally to room temperature, and then treated with a hydrochloric acid aqueous solution to remove magnesium oxide and other soluble byproducts. The insoluble product was collected by centrifugation and dried to obtain a black powder as MoC / C nanoparticles. The d value and relative intensity of its diffraction peak are consistent with the d value and relative intensity listed in the PDF standard card of MoC (89-2868), indicating that it is MoC / C nanoparticles.

[0030] Example 3

[0031] 450 μl of pyrrole solution was added to 20 ml of anhydrous ethanol and stirred to form a mixed solution A; 1.2 mmol of phosphomolybdic acid was added to 100 ml of distilled water and stirred to form a yellow solution B; the mixed solution A was added dropwise to the mixed solution B to form a black mixed dispersion, and stirred at room temperature for 12 hours; the obtained product was centrifuged and washed several times with a mixed solution of deionized water and ethanol until the supernatant was clear, and then dried in a vacuum drying oven at 60°C overnight to obtain a black product A; the obtained product A was mixed with magnesium powder and sodium chloride in a mass ratio of 1:1:5, and the temperature was increased to 650°C at a heating rate of 5°C / min and kept for 6 hours, then cooled naturally to room temperature, and then treated with a hydrochloric acid aqueous solution to remove magnesium oxide and other soluble byproducts. The insoluble product was collected by centrifugation and dried to obtain a black powder as MoC / C nanoparticles. The d value and relative intensity of its diffraction peak are consistent with the d value and relative intensity listed in the PDF standard card of MoC (89-2868), indicating that it is MoC / C nanoparticles.

[0032] Figure 1 Scanning and low-magnification transmission electron micrographs of the MoC / C nanoparticles prepared in the present invention show that the average particle diameter is 70 nanometers.

[0033] Figure 2 This is a high-magnification transmission electron micrograph of carbonized MoC / C nanoparticles, indicating that the MoC grain size is 3~5 nanometers.

[0034] Figure 3 This is the X-ray diffraction pattern of MoC / C nanoparticles, indicating that their phase purity is high.

Claims

1. A method for preparing pomegranate-shaped molybdenum carbide / carbon MoC / C nanoparticles, characterized in that: The following steps are involved: 1) Add 350~450μl of pyrrole solution into 20ml of anhydrous ethanol and stir thoroughly; 2) Add 1.2 mmol of phosphomolybdic acid into 100 ml of distilled water and stir thoroughly to form a yellow solution; 3) Add the solution obtained in step 1 to the solution in step 2 to gradually form a black mixed dispersion, and stir at room temperature for 12 hours; 4) The mixed dispersion obtained in step 3 is centrifuged and washed several times with deionized water and ethanol solution until the supernatant is clear, and then dried in a vacuum drying oven at 60° C. to obtain a black product A; 5) Mixing the product A obtained in step 4 with magnesium powder and sodium chloride in a mass ratio of 1:1:5, heating and keeping the temperature, to obtain product B; 6) treating the product B obtained in step 5 with an aqueous hydrochloric acid solution to remove magnesium oxide and other soluble by-products, collecting the insoluble products by centrifugation, and drying to obtain a black powder as a pomegranate-like MoC / C nanocomposite material; In the step 5, the temperature is raised to 550-700° C., the heating rate is 5-10° C. / min, and the insulation time is 4-8 hours.

2. The method for preparing a pomegranate-shaped molybdenum carbide / carbon MoC / C nanoparticle according to claim 1, characterized in that: The average particle size of the MoC / C nanoparticles is 70 nanometers, and the microstructure thereof is pomegranate-shaped, that is, MoC particles of 3 to 5 nanometers are uniformly dispersed in an amorphous carbon matrix.

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