CN108500282B - Preparation method of carbon-supported metal tungsten nanoparticles - Google Patents

Preparation method of carbon-supported metal tungsten nanoparticles Download PDF

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CN108500282B
CN108500282B CN201810358068.5A CN201810358068A CN108500282B CN 108500282 B CN108500282 B CN 108500282B CN 201810358068 A CN201810358068 A CN 201810358068A CN 108500282 B CN108500282 B CN 108500282B
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tungsten
zinc
carbon
polyoxometallate
metal
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CN108500282A (en
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张超
张梦锐
牛景杨
王敬平
马鹏涛
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Henan University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F9/00—Making metallic powder or suspensions thereof
    • B22F9/16—Making metallic powder or suspensions thereof using chemical processes
    • B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
    • B22F9/20—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds starting from solid metal compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30

Abstract

According to the invention, a zinc-containing zeolite imidazolate framework material is used as a dual reducing agent, poly tungstate with a definite uniform structure loaded in a zeolite imidazolate framework pore passage is used as a precursor, and the precursor is calcined under the protection of inert gas, so that the metal tungsten nanoparticles uniformly loaded in a carbon layer are obtained. The method can synthesize the metal tungsten nano particles with uniform size, and the metal tungsten nano particles are uniformly distributed in the carbon layer with the nano scale. Thereby more effectively improving the stability and the specific surface area of the material. The method has the advantages of simple operation flow, low cost, high purity of the obtained tungsten nano particles and good application value.

Description

Preparation method of carbon-supported metal tungsten nanoparticles
Technical Field
The invention relates to a preparation method of carbon-supported metal tungsten nanoparticles, belonging to the technical field of material synthesis and preparation.
Background
The metal tungsten is a non-ferrous metal, and has the characteristics of high melting point, high hardness, high wear resistance, high electric conductivity and thermal conductivity and the like, so that the metal tungsten is important to be applied to the fields of ores, metallurgy, electronic machinery, high-strength alloy materials and the like. Meanwhile, tungsten, which is a rare metal, is also an important strategic national resource and is an important component of modern high-tech new materials. On the other hand, because of the high boiling point and chemical inertness of the tungsten metal, the tungsten metal also has higher difficulty in synthetic processing, and the application of the tungsten metal is limited. The metallic tungsten particles with smaller particle size can meet the requirements of different fields on the metallic tungsten due to higher specific surface area and attractive size effect, and become a solution for solving the contradiction between the requirement on large-scale use of the metallic tungsten and limited supply of metallic tungsten resources. Therefore, tungsten nanoparticles with smaller nanometer size are synthesized, and the method has wide application prospect.
The preparation of the metallic tungsten nanoparticles which is mainstream at present is divided into a physical method and a chemical method. The physical methods mainly include a ball milling method, a physical vapor deposition method, a plasma method and the like. Due to the process limitation of the ball milling method, the milling body is required to be added in the process of preparing a sample, so that impurities are inevitably introduced; because the metal tungsten is the metal with the highest melting point, the physical vapor deposition method and the plasma method are used for preparing the metal tungsten nano particles, which consumes higher energy and has higher requirements on instruments and equipment. The chemical method mainly includes a redox method and the like. The method takes tungsten sources such as hydrazine tungstate, ammonium paratungstate and the like as raw materials, firstly synthesizes oxides, and obtains purer tungsten nano particles after high-temperature reduction by reductive gas such as hydrogen and the like. However, the method has low yield, and the potential safety hazard is increased by using reducing gases such as hydrogen.
Disclosure of Invention
The invention aims to overcome the blindness and the deficiency of the existing tungsten nanoparticle preparation technology, optimize the size uniformity degree of the metal tungsten nanoparticles, and simultaneously disperse the non-nanoparticles uniformly in the porous loose carbon layer, thereby being beneficial to the further utilization of the non-nanoparticles and being a high-performance composite material.
The polyoxometallate is an oxyacid compound obtained by dehydration condensation of oxyacids of metals such as tungsten, molybdenum, vanadium, niobium, tantalum and the like, and can form polyoxometallate with cations such as common metal ions, ammonium ions and the like. The molecular structure of polyoxometallate and salts thereof can be easily determined by an X-ray single crystal diffraction device. Zeolite imidazolate framework materials (ZIFs) are a series of porous crystalline materials with zeolite structures formed by imidazole organic ligands and transition metals such as zinc, cobalt and the like. The method takes polyoxometallate with a determined molecular structure as a tungsten source, takes a zeolite imidazolate framework material as a reducing agent and a carrier of the metal tungsten nano-particles, and utilizes the space confinement effect of the zeolite imidazolate framework material to conveniently synthesize the metal tungsten nano-particles loaded on the porous carbon layer by a one-step calcination method in a relatively low-temperature environment. The invention has simple synthesis process, easily obtained raw materials, quick reaction and suitability for large-scale production.
The polyoxometallate is added in the process of synthesizing the zeolite imidazole ester framework material, and the polyoxometallate can enter the pore channels due to size benefit, so that the polyoxometallate and zinc ions can be uniformly mixed on a molecular level. Meanwhile, the zeolite imidazolate framework material can be carbonized at high temperature, and the reduction performance of carbon at high temperature reduces zinc ions into metallic zinc. More importantly, since the zinc ion is isolated in the zeolitic imidazolate framework, it is the sole metallic zinc atom after being reduced to metallic zinc. The independent zinc atoms have much higher reducibility than common metal zinc, so that high-valence tungsten in the polymetallic oxygen cluster near the zinc atoms can be reduced into metal tungsten. If the synthesized zeolite imidazolate framework material is mixed with polyoxometallate, because the pore channel window of the zeolite imidazolate framework material is very small, the polyoxometallate cannot enter the pore channel of the zeolite imidazolate framework material and cannot be uniformly mixed with zinc ions on the molecular layer, reduced zinc atoms and surrounding zinc atoms can quickly form common metal zinc under the high-temperature condition, the reduction activity of the common metal zinc is greatly reduced, high-valence tungsten in the polyoxometallate cannot be reduced into metal tungsten, and namely the polyoxometallate cannot be reduced into the metal tungsten. It is noted that although carbon thermodynamically reduces the higher valence tungsten to metallic tungsten, it is actually tungsten carbide rather than metallic tungsten because carbon and tungsten are susceptible to chemical reactions. Therefore, it is impossible to directly reduce the high-valence tungsten into metallic tungsten by using carbon.
The present invention is described in further detail below by way of implementation but is not limited to the present invention, and various modifications and improvements can be made in accordance with the basic idea of the present invention without departing from the scope of the invention.
The invention relates to a method for preparing carbon-supported metal tungsten nanoparticles based on reduction of polyoxometallate, which is characterized in that the polyoxometallate is used as a tungsten source and is prepared by carbonization reduction with a zinc-containing zeolite imidazolate framework material.
Preferably, the method comprises the following steps of dissolving polyoxometallate and zinc salt, adding an imidazole ligand solution after the polyoxometallate and the zinc salt are dissolved, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
Preferably, the method comprises the following steps of dissolving polyoxometallate in an imidazole ligand solution, adding zinc salt, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
Preferably, the method comprises the following steps of adding the imidazole ligand into a mixed solution of oxometallate and zinc salt, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
Preferably, the carbonization temperature ranges from about 800 ℃ to about 1200 ℃ to obtain the carbon-supported metal tungsten nanoparticles.
Preferably, the molar ratio of the polyoxometallate to the zinc salt is 1: 10-200; the concentration range of the polyoxometallate dissolved in water is as follows: 2.525 to 25.25 mmol/L.
Preferably, the carbonization is carried out under the protection of inert gas, the carbonization process comprises the steps of heating the zeolite imidazole ester framework material to obtain a carbon layer, reducing zinc ions by the carbon layer to obtain metal zinc, reducing high-valence tungsten in polyoxometallate into metal tungsten by the metal zinc, simultaneously oxidizing the metal zinc, reducing the oxidized metal zinc by the carbon layer again, and then volatilizing under the heating condition to only leave tungsten nanoparticles loaded in the carbon layer.
Preferably, the tungsten source is a soluble polytungstate of any molecular size consistent with the pore size of the zeolitic imidazolate framework material.
The invention provides a preparation method of carbon-supported metal tungsten nanoparticles, which utilizes the characteristics of a dual reducing agent of a zinc-containing zeolite imidazole ester framework material. According to the invention, poly tungstate with a definite uniform structure loaded in a zeolite imidazole ester framework pore channel is used as a precursor, and metal tungsten nano particles uniformly loaded in a carbon layer are obtained by calcining under the protection of inert gas. The method can synthesize the metal tungsten nano particles with uniform size, and the metal tungsten nano particles are uniformly distributed in the carbon layer with the nano scale. Thereby more effectively improving the stability and the specific surface area of the material. The method has the advantages of simple operation flow, low cost, high purity of the obtained non-nano particles and good application value.
The invention has the following advantages:
1. and obtaining tungsten nano-particles which have uniform particle sizes and are loaded in the porous carbon layer through one-step calcination. Compared with the existing chemical synthesis scheme, the implementation scheme is convenient to implement, and is more efficient, energy-saving and high in purity compared with the existing physical synthesis scheme.
2. The method is carried out on the basis of conventional tubular furnace calcination, is simple to operate and easy to repeat, and realizes industrial application.
Drawings
FIG. 1 is K5BW12O40·xH2O (hereinafter abbreviated BW)12Shown) sample (BW) loaded on ZIF-8 channels12@ ZIF), K alone5BW12O40·xH2Fourier transform infrared spectra of the O sample and the ZIF-8 sample alone prove K5BW12O40·xH2O was successfully complexed with ZIF-8.
FIG. 2 is BW12@ ZIF cleaning solution, ZIF-8 sample cleaning solution alone, 2-methylimidazole solution and K5BW12O40 xH2Uv-vis absorption spectrum of O solution. Proves that the carrier loaded on the ZIF-8 pore channel can not be dissolved into the solution.
FIG. 3 is BW12Comparison of @ ZIF, ZIF-8 alone sample with ZIF-8 crystallography data simulated X-ray powder diffraction data. The demonstrated loading did not disrupt the structure and pore channels of ZIF-8.
FIG. 4 is BW12And comparing the X-ray powder diffraction spectrum of the calcined sample of the @ ZIF with the standard peak of the metal tungsten. Figure 4 corresponds to the features of the diffraction peaks of metallic tungsten, no other phases being found, indicating a higher purity of the product.
FIG. 5 is BW12The @ ZIF samples were compared by scanning electron microscope (left) before calcination and by transmission electron microscope (right) after calcination. The metal tungsten nano-particles obtained by the method are uniform in size and uniformly loaded in the carbon layer, and the ZIF-8 framework is proved to retain a nano-scale carbon particle structure after calcination.
Detailed Description
The present invention is described in further detail below by way of implementation but is not limited to the present invention, and various modifications and improvements can be made in accordance with the basic idea of the present invention without departing from the scope of the invention.
Example 1:
(1) weighing zinc nitrate and polyoxometallate in certain mass, adding a proper amount of distilled water, and stirring until the zinc nitrate and the polyoxometallate are completely dissolved.
(2) Weighing a certain mass of 2-methylimidazole, adding distilled water, and stirring until the 2-methylimidazole is completely dissolved.
(3) Mixing the two solutions, stirring vigorously for 30min, standing for precipitation, centrifuging, washing with distilled water, methanol and ethanol for several times, and vacuum drying overnight.
(4) And (3) placing the dried powder in a porcelain boat, calcining in a tubular furnace by taking argon as protective gas, washing a sample by using distilled water, and drying in vacuum to obtain the carbon-supported metal tungsten nano-particles.
(5) The carbon-supported metal tungsten nano-particles are prepared on the basis of obtaining a porous and loose carbon layer structure by carbonizing zeolite imidazole ester at high temperature.
The zeolite imidazolate framework material ZIF-8 is a crystal material with uniform pore channels, polyoxometallate is added in the process of synthesizing the zeolite imidazolate framework material, and the polyoxometallate is wrapped in the pore channels of the ZIF-8, so that the polyoxometallate can be uniformly mixed on a molecular layer. ZIF-8 can be carbonized at high temperature, and the carbon layer has reducibility, so that zinc ions in the original ZIF-8 can be reduced into metal zinc, and the metal zinc further reduces metal oxygen clusters containing tungsten polyoxometallate into tungsten nano-particles. Due to the low boiling point of metallic zinc (about 900 ℃), it gradually volatilizes during calcination, eventually leaving metallic tungsten nanoparticles encapsulated in the carbon layer.
(6) In the synthesis, the molar ratio of the polyoxometallate to the metal zinc is as follows: 1: 10-200
(7) The mol ratio of ZIF-8 to polyoxometallate loaded in the pore channel is as follows: 2.5: 1
The polyoxometallate is taken as a tungsten source material and is selected from one of the following materials: keggin type K5BW12O40·xH2O、Na3PW12O40·xH2O, vacancy Keggin type K7PW11O39·xH2O、Na9PW9O34·xH2O, Dawson vacancy type K12[H2P2W12O48]·xH2O, and the like. The zeolite imidazole ester framework structure adopts zinc nitrate and 2-methylimidazoleAnd (4) synthesizing oxazole. The solvent is selected from one or a mixture of solvents with different volume ratios of the following solvents: distilled water, methanol, and ethanol.
Example 2: 6g (20.02mmol) of zinc nitrate and 3.083g (1.01mmol) of K5BW12O40·xH2Dissolving O in 40ml of distilled water in sequence, and continuously stirring; then 112g (1.366mol) of 2-methylimidazole is weighed, and 400ml of distilled water is added to be stirred until the solution is completely dissolved; mixing the above two solutions, stirring vigorously for 30min, standing for precipitation, centrifuging, washing with distilled water, methanol and ethanol for several times, and vacuum drying at 65 deg.C overnight to obtain white powder.
Weighing 0.3g of dry powder, placing in a porcelain boat, calcining in a tube furnace by taking argon as protective gas, starting to heat from 30 ℃ to 80 ℃, fully discharging air (the air flow is 60ml/min) for 150min, heating to 500 ℃, then heating to 1000 ℃, heating at the rate of 5 ℃/min, and keeping at the temperature for 3 h. Washing the sample with distilled water and vacuum drying to obtain the carbon-supported metal tungsten nano-particles.
Example 3: weighing 0.3g of white powder synthesized in the example 1, placing the white powder in a porcelain boat, calcining the white powder in a tube furnace by taking argon as protective gas, raising the temperature from 30 ℃ to 200 ℃ and keeping the temperature for 2 hours, then keeping the temperature for 3 hours at 700 ℃, finally carbonizing the white powder for 3 hours at 1200 ℃ (the heating rate is 5 ℃/min), and naturally cooling the white powder. Washing the sample with distilled water and vacuum drying to obtain the carbon-supported metal tungsten nano-particles.
Example 4: weighing 0.3g of white powder synthesized in the example 1, placing the white powder in a porcelain boat, calcining the white powder in a tubular furnace by taking argon as protective gas, introducing air into the tubular furnace for 2 hours, raising the temperature from 30 ℃ to 1000 ℃ and keeping the temperature for 3 hours (the temperature raising rate is 5 ℃/min), and naturally cooling. Washing the sample with distilled water and vacuum drying to obtain the carbon-supported metal tungsten nano-particles.
Example 5: 6g (20.02mmol) of zinc nitrate and 2.976g (1.01mmol) of Na3PW12O40·xH2Dissolving O in 40ml of distilled water in sequence, and continuously stirring; then 112g (1.366mol) of 2-methylimidazole is weighed, and 400ml of distilled water is added to be stirred until the solution is completely dissolved; then mixing the two solutionsMixing, stirring vigorously for 30min, standing for precipitation, centrifuging, washing with distilled water, methanol and ethanol for several times, and vacuum drying at 65 deg.C overnight to obtain white powder.
Weighing 0.3g of white powder, placing the white powder in a porcelain boat, calcining the white powder in a tubular furnace by taking argon as protective gas, introducing air into the tubular furnace for 2 hours, raising the temperature from 30 ℃ to 200 ℃ and keeping the temperature for 3 hours, then keeping the temperature for 4 hours at 900 ℃, finally carbonizing the white powder for 2 hours at 1200 ℃ (the heating rate is 5 ℃/min), and naturally cooling the white powder. Washing the sample with distilled water and vacuum drying to obtain the carbon-supported metal tungsten nano-particles.
Example 6: 6g (20.02mmol) of zinc nitrate and 1.233g (0.404mmol) of K5BW12O40·xH2Dissolving O in 40ml of distilled water in sequence, and continuously stirring; then 112g (1.366mol) of 2-methylimidazole is weighed, and 400ml of distilled water is added to be stirred until the solution is completely dissolved; mixing the above two solutions, stirring vigorously for 30min, standing for precipitation, centrifuging, washing with distilled water, methanol and ethanol for several times, and vacuum drying at 65 deg.C overnight to obtain white powder.
Weighing 0.3g of dry powder, placing the dry powder in a porcelain boat, calcining the powder in a tube furnace by taking argon as protective gas, firstly heating the powder from 30 ℃ to 200 ℃ and keeping the temperature for 4 hours, then keeping the temperature for 12 hours at 900 ℃, finally carbonizing the powder for 2 hours at 1200 ℃ (the heating rate is 5 ℃/min), and naturally cooling the powder. Washing the sample with distilled water and vacuum drying to obtain the carbon-supported metal tungsten nano-particles.

Claims (7)

1. A method for preparing carbon-supported metal tungsten nanoparticles based on reduction of polyoxometallate is characterized in that polyoxometallate is used as a tungsten source and is prepared by carbonization reduction with a zinc-containing zeolite imidazolate framework material, carbonization is carried out under the protection of inert gas, the carbonization process comprises the steps of heating the zeolite imidazolate framework material to obtain a carbon layer, reducing zinc ions by the carbon layer to obtain metal zinc, oxidizing the metal zinc while reducing high-valence tungsten in the polyoxometallate into metal tungsten by the metal zinc, reducing the oxidized metal zinc by the carbon layer again, and volatilizing under the heating condition to only leave tungsten nanoparticles loaded in the carbon layer.
2. The method according to claim 1, comprising the steps of dissolving the polyoxometallate and the zinc salt, adding an imidazole ligand solution after dissolving, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
3. The method according to claim 1, comprising the steps of dissolving polyoxometallate in an imidazole ligand solution, adding zinc salt, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
4. The method according to claim 1, comprising the steps of adding the imidazole ligand into a mixed solution of oxometallate and zinc salt, separating, washing, drying and carbonizing to obtain the carbon-supported metal tungsten nanoparticles.
5. The method according to any one of claims 2 to 4, wherein the carbonization temperature is in the range of 800 ℃ and 1200 ℃ to obtain the carbon-supported metal tungsten nanoparticles.
6. The method according to any one of claims 2 to 4, wherein the molar ratio of polyoxometalate to zinc salt is 1: 10 to 200; the concentration range of the polyacid dissolved in water is as follows: 2.525 to 25.25 mmol/L.
7. The method of claim 1, wherein: the tungsten source is a soluble polytungstate of any molecular size consistent with the pore channel size of the zeolitic imidazolate framework material.
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