Preparation method and application of small-size and ultra-high dispersion molybdenum phosphide nanoparticles

Abstract

The application discloses a synthesis method and application of small-size and ultra-high dispersion molybdenum phosphide nanoparticles, and belongs to the field of nanometer catalytic materials. The precursor is obtained by simultaneously performing MOF self-assembly and limited wrapping of phosphomolybdic acid, and then is subjected to one-step reaction with sodium hypophosphite under protection of an inert atmosphere to obtain small-size and ultra-high dispersion molybdenum phosphide nanoparticles. The method for preparing molybdenum phosphide nanoparticles by using the MOF assembly-limited synchronous strategy has important advantages, such as small size (average particle size is about 10 nm), uniform dispersion, good monodispersity, no agglomeration, and maximum exposure of active sites, compared with molybdenum phosphide prepared by other methods. The method has the advantages of simple process, mild reaction condition, economy and environmental protection, low cost, and suitability for batch production, and has good application prospect in the fields of electrocatalysis and photocatalysis.

Description

Technical Field

[0001] This invention relates to a method for synthesizing small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles, belonging to the field of nanocatalytic materials. Background Technology

[0002] Platinum group metals, due to their ideal electronic configuration and excellent catalytic activity, are widely used in catalytic processes in petrochemicals, organic synthesis, fuel cells, automotive exhaust treatment, and the electronics industry. However, the scarcity and high price of these precious metals result in high application costs, failing to meet humanity's long-term requirements for sustainable development. Therefore, the scientific community has been actively exploring new catalytic materials that can replace platinum and other precious metals.

[0003] Molybdenum phosphide (MoP), a transition metal phosphide, is considered one of the most promising alternative materials due to its similar electronic structure to platinum, excellent electrical conductivity, and outstanding catalytic stability. In particular, it exhibits highly efficient catalytic ability in the hydrogen evolution reaction and has broad prospects in electrocatalysis, photocatalysis, and battery energy storage.

[0004] In recent years, researchers have developed various methods for synthesizing MoP to control the crystal phase purity, particle size, microstructure, and dispersion state of the products. Common techniques include high-temperature solid-state reactions, temperature-programmed reduction, liquid-phase chemical synthesis, and template methods. Despite significant progress, the preparation of MoP still faces key challenges: due to the high surface energy of MoP nanoparticles, they are prone to agglomeration during preparation or use, leading to a reduction in catalytic active sites and a decrease in overall catalytic performance. While loading them onto carbon-based materials or encapsulating them in a carbon shell can alleviate agglomeration to some extent, achieving uniform dispersion while maintaining fine particle size remains a technical bottleneck. This patent addresses this issue by focusing on preparing molybdenum phosphide nanoparticles with small particle size and excellent dispersibility. Small size means higher specific surface area and more exposed active sites, which helps improve catalytic efficiency; while good dispersibility effectively prevents particle aggregation and ensures the long-term stability of the catalyst. Therefore, progress in achieving efficient and controllable preparation of MoP, improving its dispersibility, developing green synthesis routes, and breaking through large-scale preparation processes is of great significance for promoting the practical application of MoP-based materials in the fields of catalysis and energy. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing molybdenum phosphide nanoparticles with small particle size and excellent dispersibility. A precursor material of ZIF-8 encapsulated phosphomolybdic acid is obtained using a MOF assembly-confined simultaneous strategy, followed by phosphating reduction with sodium hypophosphite to achieve the preparation of small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles. The molybdenum phosphide nanoparticles prepared by this invention are small in size, uniformly dispersed, require no other support, have highly exposed catalyst active sites, and exhibit excellent catalytic activity.

[0006] A method for preparing small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles employs a MOF simultaneous assembly-confinement + phosphating reduction strategy, comprising the following steps: (1) Dissolve 2-methylimidazole in a solvent and stir at room temperature to obtain solution A; (2) Dissolve zinc salt and phosphomolybdic acid hydrate in a solvent, sonicate, then add surfactant and stir at room temperature to obtain solution B; (3) Solution B was quickly added to solution A and the reaction was carried out at room temperature. During the reaction, the self-assembly of ZIF and the encapsulation process of phosphomolybdic acid molecules were carried out simultaneously. The product was centrifuged, washed and dried to obtain the precursor of ZIF-8 encapsulated phosphomolybdic acid. (4) The dried precursor was mixed with a phosphorus source and subjected to a high-temperature phosphating reduction reaction in an inert gas atmosphere. The product was washed and dried to obtain small-sized, ultra-dispersed molybdenum phosphide nanoparticles.

[0007] The solvents used in steps (1) and (2) are selected from methanol, ethanol, or deionized water; The surfactant is selected from polyvinylpyrrolidone, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123), F127 or hexadecyltrimethylammonium bromide (CTAB).

[0008] In step (1), the concentration of 2-methylimidazole is 0.5 mol / L to 1 mol / L.

[0009] The zinc salt mentioned in step (2) is selected from zinc nitrate, zinc acetate, or zinc sulfate; The concentration of the zinc salt is 0.04 mol / L to 0.08 mol / L; the molar ratio of the zinc salt to phosphomolybdic acid hydrate is 4 to 8. The concentration of the surfactant is 3 g / L to 9 g / L; the volume ratio of solution A to solution B is 1:0.5 to 1:2.

[0010] In step (4), the phosphorus source is sodium hypophosphite or sodium phosphite; The mass ratio of the precursor to the phosphorus source is 1:6 to 1:10.

[0011] The conditions for the phosphating reduction reaction are as follows: inert gas flow rate of 50~200 sccm, heating rate of 2~10℃ / min, reaction temperature of 500~700℃, and reaction time of 2~5 h.

[0012] A small-sized, ultra-highly dispersed molybdenum phosphide nanoparticle obtained by the preparation method, wherein the molybdenum phosphide nanoparticle has a pure-phase hexagonal structure, an average particle size of 5-15 nm, a particle size distribution deviation of less than 20%, and no agglomeration between particles without carrier support.

[0013] The application of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles in the preparation of catalysts.

[0014] The catalyst is an electrocatalyst or a photocatalyst; the electrocatalyst is used for hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction; The photocatalyst is used for photocatalytic water splitting to produce hydrogen, photocatalytic CO2 reduction, or photocatalytic degradation of organic pollutants.

[0015] The small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles prepared by this invention have the following advantages compared with existing technologies: In this invention, the simultaneous self-assembly and confinement of MOFs ensure the uniform dispersion of phosphomolybdic acid molecules, effectively suppressing problems such as easy agglomeration and uneven dispersion of molybdenum phosphide particles after high-temperature calcination. The process involves fewer parameters, a shorter flow, and lower requirements for the reaction equipment, eliminating the need for harmful or hazardous gases. The resulting small-sized molybdenum phosphide nanoparticles have uniform morphology, higher specific surface area, and more exposed active sites, which helps improve catalytic efficiency. Furthermore, the good dispersibility effectively prevents particle aggregation, ensuring the long-term stability of the catalyst. Attached Figure Description

[0016] Figure 1 The image shows the XRD pattern of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles prepared in Example 1.

[0017] Figure 2 This is a scanning electron microscope image of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles prepared in Example 1.

[0018] Figure 3 This is a TEM image of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles prepared in Example 2.

[0019] Figure 4 The image shows the SEM image of MoP obtained in Comparative Example 1. Detailed Implementation

[0020] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the present invention, any modifications of the present invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0021] Example 1 9.85 g of 2-methylimidazole was dissolved in 180 mL of methanol and stirred continuously for 30 min to obtain solution A. Then, 2.94 g of zinc nitrate hexahydrate and 2.994 g of phosphomolybdic acid hydrate were dissolved in another 180 mL of methanol and sonicated for 10 min. 1.0 g of polyvinylpyrrolidone (PVP) was added, and the mixture was stirred vigorously for 30 min, denoted as solution B. Finally, solution B was rapidly added dropwise to solution A, and the mixture was stirred continuously at room temperature for 24 h. After the reaction was complete, the mixture was washed several times by centrifugation with methanol and ethanol. Then, the precipitate was dried in a vacuum drying oven at 60 °C. After drying, the precursor sample was obtained.

[0022] The obtained precursor was mixed with sodium hypophosphite at a mass ratio of 1:9 and thoroughly ground in an agate mortar to ensure a homogeneous mixture. The powder mixture was then transferred to a magnetic boat and placed in the center of a tube furnace. Under an argon (Ar) atmosphere, the mixture was heated to 600°C at a heating rate of 5°C / min and held at that temperature for 3 hours. After the high-temperature reaction was complete, the sample was allowed to cool naturally with the furnace. The resulting black solid product was washed several times with deionized water to remove residual impurity ions. After washing, it was placed in a vacuum drying oven at 60°C and dried to obtain black MoP powder.

[0023] Figure 1 The image shows the XRD pattern of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles obtained in this embodiment. It can be seen from the image that all the characteristic diffraction peaks are consistent with the MoP standard card (PDF#97-064-4086), and the peak intensity is strong, indicating that the MoP obtained in this embodiment has good crystallinity and purity. Figure 2 The image shows the SEM image of the small-sized, ultra-highly dispersed MoP nanoparticles obtained in this embodiment. It can be seen that the obtained product is an ultra-small nanoparticle with uniform size and good dispersion, and its dispersion is better than that of existing carrier-free materials.

[0024] In this embodiment, MoP nanoparticles were used as a photocatalyst for photocatalytic hydrogen production: the prepared MoP nanoparticles and ZnIn2S4 photocatalyst were dispersed in anhydrous ethanol at a mass ratio of 1:9, and a homogeneous suspension was formed by ultrasonic treatment. The solid product was then collected by filtration and vacuum dried to obtain the ZnIn2S4 / MoP photocatalyst. 20 mg of the photocatalyst was weighed and dispersed in an 80 mL solution containing lactic acid (8 mL) and water (72 mL). A xenon lamp (MC-XF300) was used as a visible light source (λ ≥ 420 nm) to horizontally illuminate the reactor. Before illumination, the reactor was evacuated, and a circulating cooling system was used to maintain a stable temperature (7°C) during illumination. Using Ar as the carrier gas, the generated hydrogen was detected by gas chromatography every 1 h. The photocatalytic hydrogen production of ZnIn2S4 / MoP was 343.9 μmol / h / g, which is 2.15 times that of pure ZnIn2S4 (160 μmol / h / g).

[0025] Example 2 The method and steps are the same as in Example 1, except that the phosphating temperature is 700°C. Figure 3 The image shows a TEM image of the small-sized, ultra-highly dispersed MoP nanoparticles obtained in Example 2. It can be seen that the obtained product consists of ultra-small nanoparticles with uniform size and good dispersion. The photocatalytic hydrogen production of ZnIn2S4 / MoP obtained in this example is 543.6 μmol / h / g, which is 3.5 times that of pure ZnIn2S4 (160 μmol / h / g).

[0026] Comparative Example 1: The other steps are the same as in Example 2, except for the precursor synthesis steps. First, 2-methylimidazole is mixed and dissolved with zinc salt to obtain solution A; then, phosphomolybdic acid hydrate and a surfactant are mixed to obtain solution B. Solutions A and B are then mixed and subjected to subsequent reactions to obtain the precursor. SEM images of the MoP prepared by this method are shown below. Figure 4 As shown, the aggregation of MoP under this process condition is very severe, making it difficult to obtain well-dispersed MoP nanoparticles. The photocatalytic hydrogen production of ZnIn2S4 / MoP obtained in this example is 312 μmol / h / g, which is 1.95 times that of pure ZnIn2S4 (160 μmol / h / g).

[0027] Comparative Example 2: The other steps are the same as in Example 2, except that the precursor and sodium hypophosphite are mixed at a mass ratio of 1:4. The resulting product is MoO2 nanomaterials, and MoP particles cannot be obtained.

[0028] Comparative Example 3: The other steps are the same as in Example 2, except that the phosphating temperature is 400°C. The product obtained is MoO2 nanomaterials, and MoP particles cannot be obtained.

[0029] Comparative Example 4: The other steps are the same as in Example 2, except that the phosphating temperature is 900°C. The product obtained is Mo metal nanomaterials, and MoP particles cannot be obtained.

[0030] Example 3 The methods and steps are the same as in Example 1, except that the phosphating temperature is 650℃. Linear sweep voltammetry curves of the electrochemical hydrogen evolution reaction (HER) using molybdenum phosphide nanoparticles as an electrocatalyst are shown. In this example, a three-electrode system was used in a 0.5M H₂SO₄ electrolyte, and an overpotential of only 123 mV was required to reach 10 mA·cm⁻¹. -2 The current density and Tafel slope are 52 mV·dec. -1 .

[0031] Example 4 The method and steps are the same as in Example 1, except that the phosphating temperature is 550℃. Using molybdenum phosphide nanoparticles from this example, a photocatalyst was prepared by combining them with C3N4 at a mass percentage of 10%. The photocatalytic reduction of CO2 to CH4 was achieved, with a CH4 yield of 15.45 μmol / h / g and a selectivity of 86% in a pure water system.

Claims

1. A method for preparing small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles, characterized in that, Includes the following steps: (1) Dissolve 2-methylimidazole in a solvent and stir at room temperature to obtain solution A; (2) Dissolve zinc salt and phosphomolybdic acid hydrate in a solvent, sonicate, then add surfactant and stir at room temperature to obtain solution B; (3) Solution B was quickly added to solution A and the reaction was carried out at room temperature. During the reaction, the self-assembly of ZIF and the encapsulation process of phosphomolybdic acid molecules were carried out simultaneously. The product was centrifuged, washed and dried to obtain the precursor of ZIF-8 encapsulated phosphomolybdic acid. (4) The dried precursor was mixed with a phosphorus source and subjected to a high-temperature phosphating reduction reaction in an inert gas atmosphere. The product was washed and dried to obtain small-sized, ultra-dispersed molybdenum phosphide nanoparticles.

2. The preparation method according to claim 1, characterized in that, The solvents used in steps (1) and (2) are selected from methanol, ethanol, or deionized water; The surfactant is selected from polyvinylpyrrolidone, polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer, F127, or hexadecyltrimethylammonium bromide.

3. The preparation method according to claim 1, characterized in that, In step (1), the concentration of 2-methylimidazole is 0.5 mol / L to 1 mol / L; The zinc salt mentioned in step (2) is selected from zinc nitrate, zinc acetate or zinc sulfate.

4. The preparation method according to claim 1, characterized in that, The concentration of the zinc salt is 0.04 mol / L to 0.08 mol / L; the molar ratio of the zinc salt to phosphomolybdic acid hydrate is 4 to 8. The concentration of the surfactant is 3 g / L to 9 g / L; the volume ratio of solution A to solution B is 1:0.5 to 1:

2.

5. The preparation method according to claim 1, characterized in that, In step (4), the phosphorus source is sodium hypophosphite or sodium phosphite; The mass ratio of the precursor to the phosphorus source is 1:6 to 1:

10.

6. The preparation method according to claim 1, characterized in that, The conditions for the phosphating reduction reaction are as follows: inert gas flow rate of 50~200 sccm, heating rate of 2~10℃ / min, reaction temperature of 500~700℃, and reaction time of 2~5 h.

7. A small-sized, ultra-highly dispersed molybdenum phosphide nanoparticle obtained by the preparation method according to any one of claims 1-6, characterized in that, The molybdenum phosphide nanoparticles have a pure hexagonal structure with an average particle size of 5-15 nm and a particle size distribution deviation of less than 20%. They do not aggregate with each other without support.

8. The application of the small-sized, ultra-highly dispersed molybdenum phosphide nanoparticles as described in claim 7 in the preparation of catalysts.

9. The application according to claim 8, characterized in that, The catalyst is an electrocatalyst or a photocatalyst; the electrocatalyst is used for hydrogen evolution reaction, oxygen evolution reaction or oxygen reduction reaction.

10. The application according to claim 8, characterized in that, The photocatalyst is used for photocatalytic water splitting to produce hydrogen, photocatalytic CO2 reduction, or photocatalytic degradation of organic pollutants.

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