A method for preparing nano platinum metal particles

Abstract

The application provides a preparation method of nano platinum metal particles and belongs to the technical field of nano metal synthesis. In an alkaline environment, in a water-alcohol two-component solvent, sodium citrate is used as a carrier and a platinum salt is used as raw material, the solubility of sodium citrate in the solvent is adjusted, an in-situ template is generated, and the nano platinum metal particles are prepared. The application ingeniously uses the feature that the solubility of sodium citrate is different in different solutions. The sodium citrate is not only used as a reducing agent, but also precipitates as a carrier of the nano platinum particles after the reaction is completed. The carrier is dissolved and washed in water, and solid platinum black is obtained. The application can effectively avoid agglomeration during the drying process of the platinum black and reduce the cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nanometer metal synthesis, and particularly relates to a preparation method of nanometer platinum metal particles. BACKGROUND

[0002] Nanometer platinum particles, also known as platinum black, are a kind of nanometer noble metal particles with unique physical properties and catalytic activity due to surface effect and quantum size effect, and have a high prospect in the development stage of new materials. Nanometer platinum has the advantages of large specific surface area and high catalytic activity, and is widely used in modified electrodes, supported biomolecules, electronic materials, surfactants, catalysts and the like. As a high-performance catalyst, platinum black is often used in the oxidation reaction of hydrogen or alcohol in fuel cells, and has excellent catalytic activity.

[0003] The synthesis methods of nanometer platinum mainly include chemical reduction method, microemulsion method, hydrogen multiple reduction method, polyol method, impregnation method, ion exchange method, electrochemical deposition method, photochemical method and microwave method. At present, the commonly used process for mass production of nanometer platinum is a preparation method based on a liquid phase reduction system to form nanocrystals in a liquid phase. The preparation method has the advantages of mild reaction conditions, simple process operation and advantages in scale-up production. However, the product particles have a high particle size, and the nanometer particles are prone to agglomeration during the solid-liquid separation process, and the yield is low.

[0004] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the background of the present application and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art that is publicly known. SUMMARY

[0005] In order to solve the technical problems of high particle size, easy agglomeration and low yield of nanometer platinum metal particles in the prior art, a new preparation method of nanometer platinum metal particles is provided.

[0006] The present application provides a preparation method of nanometer platinum metal particles. In an alkaline environment, nanometer platinum metal particles are prepared by using excess sodium citrate as a carrier and platinum salt as a raw material in a water-alcohol two-component solvent, and by adjusting the solubility of sodium citrate in the solvent to generate an in-situ template.

[0007] In the presence of sodium citrate, chloroplatinic acid can be reduced to sodium chloroplatinate. The chemical formula of the reaction is as follows:

[0008] H2PtCl6+2Na3C6H5O7+6H2O→Na2PtCl6+2C6H5O7H+4NaOH

[0009] During the reaction, sodium citrate acts as a reducing agent to reduce the platinum (IV) ion in chloroplatinic acid to platinum (II) ion, while itself is oxidized to carbon dioxide and water.

[0010] On the other hand, the excess sodium citrate acts as a template agent to adjust the solubility of sodium citrate in the solvent, so that the reduced platinum nanoparticles are precipitated together with the solid sodium citrate as a carrier.

[0011] In some embodiments, the above preparation method comprises:

[0012] Step (1): adding organic alcohol into the mixed aqueous solution of sodium hydroxide and sodium citrate to form a solution of water-alcohol two-component solvent;

[0013] Step (2): heating the solution and adding platinum salt dispersion to perform platinum reduction reaction to obtain platinum colloid;

[0014] Step (3): adding organic alcohol again into the platinum colloid obtained in step (2) to precipitate the nano platinum metal particles together with sodium citrate to obtain nano platinum metal particle / sodium citrate composite;

[0015] Step (4): adjusting the pH value of the solution to be acidic and aging;

[0016] Step (5): putting the nano platinum metal particle / sodium citrate composite into water, and after post-treatment, obtaining nano platinum metal particles.

[0017] In some embodiments, the concentration of sodium citrate in the mixed aqueous solution of sodium hydroxide and sodium citrate in step (1) is 0.5-1 mol / L, and the concentration of sodium hydroxide is 0.3-0.7 mol / L.

[0018] In some embodiments, the molar ratio of the organic alcohol added in step (1) to water is 1:(1-0.1).

[0019] And / or, the organic alcohol is one or more of methanol, ethanol, ethylene glycol, and isopropyl alcohol.

[0020] In some embodiments, the platinum salt is one or more of sodium chloroplatinate, ammonium chloroplatinate, potassium hydrogen chloroplatinate, and nitroso platinum ammonium.

[0021] And / or, the platinum salt is dispersed in an organic alcohol solution to obtain a platinum salt dispersion, and the concentration of the platinum salt dispersion is 0.01-0.3 mol / L.

[0022] In some embodiments, the platinum salt dispersion can also be a platinum salt dispersion obtained by dispersing in water.

[0023] In some embodiments, the temperature of the solution heating in step (2) is 30-50℃.

[0024] In some embodiments, the platinum reduction reaction in step (2) comprises: placing the solution in a microwave reactor for reaction, the reaction temperature is 55-70℃, the reaction power is 800-1300W, the reaction time is 0.5-3h, and the temperature is reduced to 10-20℃ after reaction.

[0025] In some embodiments, the molar ratio of the organic alcohol to the water in the sodium hydroxide and sodium citrate mixed aqueous solution in step (3) is (2-5):1.

[0026] In some embodiments, the pH value of the solution in step (4) is adjusted to 2-7.

[0027] In some embodiments, the aging time is 7-10h.

[0028] In some embodiments, the concentration of the dilute sulfuric acid is 2-4mol / L.

[0029] The second aspect of the present application provides a nano platinum metal particle prepared by the above preparation method.

[0030] In some embodiments, a preparation method of a nano platinum metal particle comprises:

[0031] (1) preparing a mixed aqueous solution of sodium hydroxide and sodium citrate, adding an organic alcohol (selected from one or more of methanol, ethanol, ethylene glycol, and isopropyl alcohol) with a molar ratio of 1:1-0.1 to water after stirring and dissolving to form a water-alcohol two-component solvent, and uniformly mixing to obtain a mixed solution; the concentration of sodium citrate in the mixed aqueous solution is 0.5-1mol / L, and the concentration of sodium hydroxide is 0.3-0.7mol / L. The use of sodium hydroxide makes the reaction system alkaline, which is helpful for the reduction of platinum ions. The two-solvent system utilizes the fact that the solubility of sodium citrate in water is high, and the solubility in alcohol is low. Increasing the proportion of water at the beginning of the reaction helps to dissolve sodium citrate, and increasing the proportion of alcohol at the end of the reaction makes sodium citrate precipitate; using more water also helps to reduce the cost of the reaction.

[0032] (2) The mixed solution described in (1) is heated to 30°C-50°C. Preheating the solution helps the platinum ions to heat up quickly, promotes their explosive nucleation, and makes the obtained nano-platinum particles finer in size and better in performance; a platinum salt dispersion is added as a platinum raw material, and after homogeneous dispersion, it is placed in a microwave reactor for reaction, the reaction temperature range is 55°C-70°C, the power is 800-1300W, the reaction time is 0.5-3h, and the temperature is lowered to 10°C-20°C after the reaction to obtain a platinum colloid; lowering the temperature to 10°C-20°C reduces the activity of the nano-platinum particles and reduces the size of the secondary particles formed by agglomeration here; the platinum salt is selected from one or more of sodium chloroplatinate, ammonium chloroplatinate, potassium hydrogen chloroplatinate, and ammonium nitrosoplatinum; the platinum salt dispersion is a platinum salt dispersed in an organic alcohol with a concentration of 0.01-0.3 mol / L.

[0033] (3) Additional organic alcohol is added to the platinum colloid in step (2) again, with the molar ratio of the additional organic alcohol to the water in the mixed aqueous solution in step (1) being (2-5):1, to adjust the solubility of the inorganic salt sodium citrate in the reaction solution. At this time, sodium citrate is precipitated in situ as a template, and the reduced platinum nanoparticles are precipitated together with the sodium citrate using solid citric acid as a carrier.

[0034] (4) After the sodium citrate-loaded platinum nanoparticles precipitate, the solution changes from a colloid to a suspension. After uniform dispersion, dilute sulfuric acid is added to adjust the pH. After thermal aging, the platinum nanoparticle / sodium citrate complex is separated by filtration and dried to obtain a powder. The dilute sulfuric acid concentration is 2-4 mol / L. After adding the dilute sulfuric acid, the pH of the solution is adjusted to 2-7. The aging time is 7-10 hours. In an acidic environment, the nano-platinum particles are more likely to form aggregates and be loaded on the carrier material.

[0035] (5) Platinum nanoparticles / sodium citrate powder is added to pure water, stirred thoroughly to dissolve the sodium citrate template, and then filtered again, washed, and dried to obtain a pure nano-platinum metal (platinum black) product.

[0036] Compared with the prior art, the present invention achieves the following technical effects:

[0037] (1) The present invention cleverly utilizes the characteristic that sodium citrate has different solubility in different solutions. Sodium citrate not only serves as a reducing agent, but also precipitates the remaining sodium citrate in the mixed solution after the reaction is completed as a carrier of nano-platinum particles. The carrier is dissolved and washed in water to obtain solid platinum black (nano-platinum metal particles). This can effectively avoid agglomeration of platinum black (nano-platinum metal particles) during the drying process, thereby reducing costs.

[0038] (2) In the synthesis process of nano-platinum particle products generated by the in situ template generation method, an innovative approach was proposed to introduce excess sodium citrate, a weakly reducing salt, which can participate in the platinum ion reduction reaction and effectively improve the reaction yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a flow chart of the preparation process of the present invention;

[0040] Figure 2 This is a microscopic morphology image of the platinum nanometal product of Example 1 of the present invention, taken using a transmission electron microscope (TEM);

[0041] Figure 3 This is a microscopic morphology image of the platinum nanometal product in Comparative Example 1 of the present invention taken using a transmission electron microscope (TEM);

[0042] Figure 4 This is a spectrum obtained by X-ray diffraction (XRD) testing of the platinum nanometal product in Example 1 of the present invention;

[0043] Figure 5 These are the electrochemical specific surface area test results of the platinum nanometal products in the examples and comparative examples of the present invention. DETAILED DESCRIPTION

[0044] The technical solutions of the present invention are described below by means of specific embodiments in conjunction with the accompanying drawings. It should be understood that one or more steps mentioned in the present invention do not exclude the presence of other methods and steps before and after the combined steps, or other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and does not limit the order of arrangement of each method or limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships can also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0045] The sources of the raw materials and instruments used in the examples are not particularly limited and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0046] Example 1

[0047] The preparation process described in the present invention is shown in FIG. Figure 1 shown.

[0048] First, take 48.7g sodium citrate and 2.8g sodium hydroxide and be dissolved in 200mL pure water, add 367mL ethylene glycol after dissolving completely, be warming up to 40 ℃ after adding 0.2mol / L chloroplatinic acid-ethylene glycol dispersion 85mL, continue to be warming up to 60 ℃, be placed in microwave reactor 1300W after reaction 1.5h, take out, mixed solution is cooled to 15 ℃, in mixed solution, add organic alcohol (ethylene glycol) 500mL for the second time, now mixed solution has gray solid powder to separate out, and is converted into suspension liquid by colloid, is evenly dispersed and drips 2M H2SO4100mL, after insulation and aging 8h, mixed solution is carried out to solid-liquid separation. The solid particles obtained are dissolved in 600mL pure water after drying, and the mixed solution color gradually darkens after stirring, and solid particles are taken after solid-liquid separation and dried. Repeat this step twice to obtain required nano-platinum metal, and theoretical yield is 3.3g, which is designated as sample 1.

[0049] Example 2

[0050] Take 69.7g sodium citrate, 4.3g sodium hydroxide in 300mL pure water, add 550mL methanol after dissolving completely, add 0.03mol / L chloroplatinic acid-ethylene glycol solution 67mL after the mixed solution is warmed up to 40 ℃, the reaction solution is warmed up to 60 ℃, placed in a microwave reactor 800W after reaction 3h, take out cooling, and be incubated at about 15 ℃. Subsequently, organic alcohol (methanol) 1000mL is added for the second time in the mixed solution. Now, the mixed solution has gray solid powder to separate out, and is converted into suspension by colloid. After being evenly dispersed, 2M H2SO4150mL is added dropwise. After insulation and aging 8h, the mixed solution is carried out to solid-liquid separation. The solid particles obtained are dissolved in 1000mL pure water after drying. After stirring, the mixed solution color gradually darkens. After solid-liquid separation, the solid particles are dried. This step is repeated twice to obtain required nano-platinum particles, which is recorded as sample 2.

[0051] Example 3

[0052] Take 70.96g sodium citrate, 12.1g sodium hydroxide in 500mL pure water, add 550mL ethylene glycol after dissolving completely, add 0.1mol / L chloroplatinic acid-water solution 89mL after mixed solution is warmed up to 40 ℃, reaction solution is warmed up to 60 ℃, after being placed in microwave reactor 900W reaction 3h, take out cooling, and be incubated at about 15 ℃. Subsequently in mixed solution, add organic alcohol (ethanol) 1200mL for the second time, now mixed solution has gray solid powder to separate out, and is converted into suspension liquid by colloid, and 2M H2SO4210mL is added dropwise after being evenly dispersed, after insulation and aging 8h, mixed solution is carried out to solid-liquid separation. The solid particles obtained are dissolved in 1500mL pure water after drying, and the mixed solution color gradually darkens after stirring, and solid particles are taken dry after solid-liquid separation, and this step is repeated twice to obtain required nano platinum particles, which is designated as sample 3.

[0053] Comparative Example 1: The difference from Example 1 is that sodium citrate is not added to the system

[0054] Take 2.8 g of sodium hydroxide and add it to 200 mL of pure water, completely dissolve it, then add 367 mL of ethylene glycol, heat the mixture to 40°C, then add 85 mL of 0.2 mol / L chloroplatinic acid-ethylene glycol solution, continue to heat to 60°C, place it in a microwave reactor at 1300 W for 0.5 h, then take it out, cool the mixture to 15°C, disperse it evenly, then add 100 mL of 2M H2SO4 dropwise, incubate and age for 8 h, then perform solid-liquid separation on the mixture. Disperse the obtained solid particles in 600 mL of pure water, wash, perform solid-liquid separation, then take the solid particles and vacuum dry them to obtain the desired nano platinum particles, which are recorded as Comparative Sample 1.

[0055] Comparative Example 2: The difference from Example 1 is that no organic alcohol is added for the second time after the reaction, causing sodium citrate to precipitate as a carrier

[0056] Take 48.7 g of sodium citrate and 2.8 g of sodium hydroxide and add them to 200 mL of pure water, completely dissolve them, then add 367 mL of ethylene glycol, heat the mixture to 40°C, then add 85 mL of 0.02 mol / L chloroplatinic acid-ethylene glycol dispersion, continue to heat to 60°C, place it in a microwave reactor at 1300 W for 0.5 h, then cool the mixture to 15°C. Subsequently, add 100 mL of 2M H2SO4 dropwise to the mixture, incubate and age for 8 h, then perform solid-liquid separation on the mixture. Dry the obtained solid particles, then dissolve them in 600 mL of pure water, stir evenly, then the color of the mixture gradually darkens, perform solid-liquid separation, then take the solid particles and dry them, repeat this step twice to obtain the desired nano platinum particles, which are recorded as Comparative Sample 2.

[0057] Comparative Example 3: Blank experiment, the difference from Example 1 is that no platinum salt is added

[0058] First, take 48.7 g of sodium citrate and 2.8 g of sodium hydroxide and dissolve them in 200 mL of pure water, completely dissolve them, then add 367 mL of ethylene glycol, then add 500 mL of ethanol to the mixture, at this time white solid powder precipitates from the mixture, disperse it evenly, then add 100 mL of 2M H2SO4 dropwise, perform solid-liquid separation on the mixture to obtain the exact mass of the precipitated sodium citrate template, weigh the corresponding mass and record it.

[0059] Result analysis

[0060] (1) The mass of the sodium citrate template obtained from the blank sample experiment

[0061] The sodium citrate precipitated in Comparative Example 3 was thoroughly washed with ethanol and then dried. The mass was weighed to 26.6 g, which is the theoretical mass of sodium citrate precipitated as a template in Example 1. Therefore, the content of platinum nanometal in the composite was approximately 11 wt %. The yields of nanoplatinum in both the Example and the Comparative Example were calculated to be greater than 90%, as shown in Table 1.

[0062] The method for preparing platinum nano-metal particles provided by the present invention has a high yield of more than 90%. The obtained nano-platinum metal particles have a small particle size after secondary agglomeration and a high content of active substances per unit area.

[0063] (2) Electron microscopy results

[0064] like Figures 2-3 As shown in the figure, the transmission electron microscope photos of the nano-platinum particles synthesized in Example 1 and Comparative Example 2 are respectively. It can be seen from the figure that the size of the nano-platinum particles obtained in Example 1 is about 5-10nm, and the size of the nano-platinum particles synthesized in Comparative Example 1 and Comparative Example 2 is about 60-80nm. It can be seen from the surface of the photo that there are lattice fringes. The result of the product of Example 1 is significantly lower than that of the comparative example, which will significantly increase the specific surface area of ​​the catalyst. The results of the particle size distribution test are shown in Table 1. The average particle size of the embodiment is lower than that of the commercial sample and the comparative example. The above results show that the introduction of sodium citrate as a carrier in the aging process in the liquid phase synthesis of nano-platinum particles and the removal of it with water after drying to form secondary particles can effectively regulate the assembly pore structure of the nano-platinum metal and improve its specific surface area.

[0065] (3) X-ray diffraction results

[0066] like Figure 4 The X-ray diffraction results of the product synthesized by the method of Example 1 are shown. According to the position of the diffraction peaks, it can be seen that the product only contains pure platinum, without any residual reactants or oxidation reaction.

[0067] (5) Oxygen reduction activity test results

[0068] Further tests on the active surface area of ​​metals were conducted on the samples synthesized in this patent and commercial platinum black, mainly through electrochemical methods, such as Figure 5 The results of cyclic voltammetry (CV) testing the electrochemically active surface area of ​​platinum metal show that the redox peak areas of the curves of Examples 1 and 2 are higher than those of commercial platinum black and significantly higher than those of the comparative example. Therefore, the electrochemically active area (ECSA) of the example samples is also higher than that of commercial platinum black and the comparative example, as shown in Table 1, which is consistent with the results of electron microscopy. These test results fully demonstrate that in this patent, sodium citrate, as an in-situ precipitated template in the liquid phase reaction, can effectively regulate the assembled pore structure of nano-platinum metal, increase its specific surface area, and thus effectively improve its electrochemical performance.

[0069] The nano platinum metal particles prepared in Example 3 have the same properties and structure as those of Examples 1 and 2, and thus are not described here again.

[0070] Table 1: Yield, average particle size and specific surface area of platinum nano metal products in Examples 1, 2 and Comparative Examples 1, 2

[0071]

[0072] In the table: ECSA is electrochemical active area;

[0073] The commercial platinum black sample used is a domestic nano platinum particle powder purchased from Shanghai Hesen Electrical.

[0074] The foregoing description of specific exemplary embodiments of the application has been presented for the purpose of illustration and description. It is not intended to be exhaustive or to limit the application to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. Optional combinations of the described embodiments, and optional substitutions of elements from different embodiments of the application, can be accomplished as would be appreciated by those skilled in the art. The scope of the application is defined by the appended claims, along with the full range of equivalents to which such claims are entitled. The specification is to be considered to be consisting solely of the framed claims, excluding the descriptive and specific embodiments.

Claims

1. A method for preparing nano platinum metal particles, characterized by, In an alkaline environment, in a water-alcohol two-component solvent, with excess sodium citrate as a carrier and platinum salt as a raw material, an in-situ template is generated by adjusting the solubility of sodium citrate in the solvent to prepare nano-platinum metal particles; include: Step (1): adding an organic alcohol to a mixed aqueous solution of sodium hydroxide and sodium citrate to form a water-alcohol two-component solvent solution; Step (2): heating the solution, adding a platinum salt dispersion, and performing a platinum reduction reaction to obtain a platinum colloid; Step (3): adding organic alcohol again to the platinum colloid obtained in step (2), and the nano-platinum metal particles are loaded on the sodium citrate and precipitated together to obtain a suspension containing the nano-platinum metal particles / sodium citrate complex; Step (4): adding dilute sulfuric acid to adjust the pH value of the solution to acidic, keeping warm and aging, performing solid-liquid separation on the mixed solution, and drying the solid particles; Step (5): putting the dried solid particles into water, separating the solid and liquid, and drying the solid particles. Repeat this step twice to obtain nano-platinum metal particles. The molar ratio of the organic alcohol to water added in step (1) is 1:(1-0.1); The platinum salt is dispersed in an organic alcohol solution or water to obtain a platinum salt dispersion; In the step (3), the organic alcohol is added again with a molar ratio of (2-5):1 to the water in the mixed aqueous solution of sodium hydroxide and sodium citrate.

2. The production method according to claim 1, characterized by, In the step (1), the concentration of sodium citrate in the mixed aqueous solution of sodium hydroxide and sodium citrate is 0.5-1 mol / L, and the concentration of sodium hydroxide is 0.3-0.7 mol / L.

3. The method of claim 1, wherein, The organic alcohol is one or more of methanol, ethanol, ethylene glycol, and isopropanol.

4. The method of claim 1, wherein, The platinum salt is one or more of sodium chloroplatinate, ammonium chloroplatinate, potassium hydrogen chloroplatinate, and ammonium nitrosoplatinum; And / or, the concentration of the platinum salt dispersion is 0.01-0.3 mol / L.

5. The preparation method according to claim 1, characterized in that The temperature of the solution heating in step (2) is 30°C-50°C; And / or, the platinum reduction reaction in step (2) comprises: placing the solution in a microwave reactor for reaction at a reaction temperature of 55°C-70°C, a reaction power of 800-1300 W, a reaction time of 0.5-3 h, and cooling to 10°C-20°C after the reaction.

6. The method of claim 1, wherein, In step (4), the pH value of the solution is adjusted to 2-7; And / or, the aging time is 7-10 hours.

7. The preparation method according to claim 1, characterized in that The concentration of the dilute sulfuric acid is 2-4 mol / L.

8. A nano platinum metal particle, characterized by, It is prepared by the preparation method according to any one of claims 1 to 7.

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