Pd-based multi-metal core-shell heterostructured nanocrystals and their preparation methods and applications

Abstract

The present invention discloses a Pd-based multi-metal core-shell heterostructure nanocrystal and a preparation method thereof, including: depositing an Ag thin shell layer on the surface of a Pd seed crystal, and then inducing selective area deposition of metal M with the Ag thin shell layer to form a Pd-based multi-metal core-shell heterostructure nanocrystal. The present invention also discloses the application of the Pd-based multi-metal core-shell heterostructure nanocrystal in the electrocatalytic dechlorination of chlorinated organic pollutants. The electrocatalytic dechlorination activity of the Pd-based multi-metal core-shell heterostructure nanocrystal prepared by the present invention is higher and the persistence is better.

Description

Technical Field

[0001] The present invention relates to the technical field of functional nanomaterials, and particularly to a Pd-based multi-metal core-shell heterostructure nanocrystal, a preparation method thereof, and an application thereof. Background Art

[0002] Pd-based multi-metal nanocrystals with controllable morphology and structure have received extensive attention due to their adjustable electrocatalytic properties. Forming a core-shell structure with Pd as the core is an effective strategy to improve catalytic activity and enhance the structural electrocatalytic durability. For example, the Pd@Au core-shell nanoparticles disclosed in the Chinese patent document with publication number CN112808267A, the palladium cubic nanocrystals with surface-doped phosphorus element Pd@PdP disclosed in the Chinese patent document with publication number CN109355677A, the Pd@Rh nanocatalyst provided by the Chinese patent document with publication number CN110201665A, etc.

[0003] Chlorinated aromatic compounds usually have high toxicity and carcinogenicity due to the presence of Cl atoms, and have strong resistance to biodegradation, which makes it difficult to restore water and soil contaminated by chlorinated aromatic compounds. Among them, chlorophenols, as an important class of chemical products, have extensive applications in the agricultural, pharmaceutical, and polymer industries. In the early days, the annual demand in the world market exceeded 100,000 tons. Even though they have long been included in the blacklists of priority control pollutants and persistent organic pollutants, excessive chlorophenols can still be detected in polluted water and soil all over the world today.

[0004] Electrocatalytic dechlorination can convert chlorophenols into more harmless phenols, which has the advantages of mild reaction conditions, low risk of secondary pollution, simple operation, and high efficiency. However, the cost problem of palladium-based materials with high catalytic activity needs to be considered. Therefore, improving the mass activity and electrocatalytic durability of dechlorination electrocatalysts is the core to promote the application and development of electrocatalytic dechlorination environmental protection technology.

[0005] The Chinese patent document with publication number CN113846342A provides an electrocatalyst in which Pd nanoparticles are loaded on the core-shell skeleton of TiO 2 nanorod arrays - organic dopamine to improve the mass activity per unit of electrocatalytic hydrodechlorination. The combination of multiple metals can often generate higher intrinsic catalytic activity through synergistic effects and electronic effects. For example, the Chinese patent document with publication number CN115323427A uses transition metals Co, Ni, Zn and Pd to form a multi-component metal-organic framework. Among them, PdZn has relatively high initial dechlorination activity, but transition metals are prone to rapid loss during the electrochemical process, so the durability is poor. Summary of the Invention

[0006] The present invention provides a Pd-based multi-metal core-shell heterostructure nanocrystal with higher electrocatalytic dechlorination activity and better durability, and a preparation method thereof.

[0007] The technical solution of the present invention is as follows:

[0008] A preparation method of a Pd-based multi-metal core-shell heterostructure nanocrystal, comprising: depositing a thin Ag shell layer on the surface of Pd seeds, and then inducing selective area deposition of metal M with the Ag thin shell layer to form a Pd-based multi-metal core-shell heterostructure nanocrystal.

[0009] The metal M is Pt and / or Ru.

[0010] The present invention gives full play to the multi-metal synergistic effect to improve the mass activity and electrocatalytic durability of the active metal. Ag, which can be used as a sacrificial metal, is selected to form a wrapped thin shell layer on the surface of Pd, which is used to induce selective area deposition of metal Pt or Ru to form a controllable unique nanostructure. The formation of a heterogeneous shell layer by multiple metals promotes the improvement of the electrocatalytic dechlorination activity of the core active metal. In addition, Ag and Ru have good chlorine resistance and form an electrochemical protection effect on Pd in the same nanocrystal, making it not easy to inactivate. In addition, the nanocrystal plane depression caused by Pt substitution greatly increases the effective electrochemical active surface area of the active metals Pd and Pt, and improves the electrocatalytic activity of the multi-metal nanocrystal.

[0011] Preferably, the preparation method includes the following steps:

[0012] Method A:

[0013] (A-1) After preheating the reaction base liquid at 60-90 °C, adding a Pd precursor, reacting for 10-30 min, then adding an Ag precursor, and subsequently reacting for 2-5 h, centrifuging and washing, and drying the product at room temperature and dissolving it in ethylene glycol to obtain reaction liquid A;

[0014] The reaction base liquid uses water as a solvent and also contains a reducing agent, a surface stabilizer, and a seed stabilizer;

[0015] (A-2) Adding a surface stabilizer to reaction liquid A, adjusting the reaction temperature to 120-180 °C, and then adding a metal M precursor, reacting for 2-5 h and then centrifuging and washing to obtain a Pd-based multi-metal core-shell heterostructure nanocrystal.

[0016] Preferably, the preparation method includes the following steps:

[0017] Method B:

[0018] (B-1) After preheating the reaction base liquid at 60-90 °C, adding a Pd precursor, reacting for 2-5 h, and then centrifuging and washing to obtain Pd seeds;

[0019] The reaction base solution uses water as a solvent and also contains a reducing agent, a surface stabilizer, and a seed stabilizer;

[0020] (B-2) Disperse Pd seeds in ethylene glycol, add the surface stabilizer and the seed stabilizer, heat up to 120 - 150 °C, and dropwise add the Ag precursor under stirring conditions, and react for 10 - 30 min to obtain reaction solution B;

[0021] (B-3) Adjust the temperature of reaction solution B to 120 - 180 °C, then add the metal M precursor, and after reacting for 2 - 5 h, centrifuge and wash to obtain Pd-based multi-metal core-shell heterostructure nanocrystals.

[0022] The reducing agent is ascorbic acid; in the reaction base solution, the concentration of the reducing agent is 3 - 25 g / L.

[0023] The surface stabilizer is polyvinylpyrrolidone; in the reaction base solution, the concentration of the surface stabilizer is 5 - 20 g / L.

[0024] The seed stabilizer is potassium bromide; in the reaction base solution, the concentration of the seed stabilizer is 30 - 100 g / L. The main function of potassium bromide is to adsorb and stabilize the {100} plane of Pd seeds.

[0025] Preferably, the reaction base solution also contains potassium acetate; in the reaction base solution, the concentration of potassium acetate is 0.1 - 18 mmol / L. Potassium acetate mainly acts as a ligand to perform ligand exchange with the Pd precursor, which is the key to regulating the size of Pd seeds, and its concentration can regulate the reaction kinetics of Pd seed growth.

[0026] The Pd precursor is potassium chloropalladate and / or sodium chloropalladate; based on 1 L of the reaction base solution, the dosage of the Pd precursor is 0.01 - 0.1 mol.

[0027] The Ag precursor is silver nitrate and / or silver trifluoroacetate; based on 1 L of the reaction base solution, the dosage of the Ag precursor is 0.001 - 0.015 mol.

[0028] Use a syringe or pipette to dropwise add under rapid magnetic stirring to avoid local high concentration causing nanocrystal aggregation.

[0029] In step (A-1), directly add the Ag precursor to the reaction solution of the Pd precursor, and reduce Ag with the excess ascorbic acid in the solution to deposit an Ag thin shell layer on the surface of the Pd seeds.

[0030] In step (A-1), drying at room temperature results in a high-concentration and high-viscosity black nano-sol of the product instead of complete drying, and nitrogen blowing can be used to accelerate it; centrifugal washing is to wash multiple times with ultrapure water having a volume similar to that of acetone with a volume 2 to 4 times that of the former to remove excess surface stabilizer and excessive potassium bromide.

[0031] In step (A-2), based on 1 L of ethylene glycol, the additional amount of the surface stabilizer is 4 to 16 g.

[0032] In step (B-2), based on 1 L of ethylene glycol, the additional amount of the surface stabilizer is 4 to 16 g; the additional amount of the seed stabilizer is 0.1 to 8 mmol.

[0033] The metal M precursor is platinum acetylacetonate and / or ruthenium(III) chloride anhydrous.

[0034] After adding the metal M precursor, the concentration of metal M in the reaction system is 1 to 5 mmol / L.

[0035] In steps (A-2) and (B-3), the aldehyde alcohol formed by the thermal oxidation of ethylene glycol serves as a reducing agent.

[0036] In steps (A-2) and (B-3), if the metal M precursor is platinum acetylacetonate, the reaction temperature is 120 to 180 °C; if the metal M precursor is ruthenium(III) chloride anhydrous, the reaction temperature is 165 to 180 °C.

[0037] The present invention also provides Pd-based multi-metal core-shell heterostructure nanocrystals prepared by the above preparation method.

[0038] The present invention also provides the application of the Pd-based multi-metal core-shell heterostructure nanocrystals in the electrocatalytic dechlorination of chlorinated organic pollutants.

[0039] The said application includes:

[0040] Loading the Pd-based multi-metal core-shell heterostructure nanocrystals onto a carbon carrier to form a working electrode, using a Pt electrode as the counter electrode, and using a saturated calomel electrode or an Ag / AgCl electrode as the reference electrode to perform electrolytic dechlorination on the chlorinated organic pollutants.

[0041] Preferably, potentiostatic electrolysis is performed, the potential is -0.9 V vs. Ag / AgCl, and the electrolysis temperature is 25 to 30 °C.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] The present invention uses Pd-based multi-metal core-shell heterostructure nanocrystals with a unique core-shell heterostructure as the electrocatalyst for dechlorination and hydrogenation. The multi-metal components produce a synergistic effect, which not only optimizes the electronic structure of Pd and enhances the overall electrocatalytic activity, but also the sacrificial metal in the shell layer has a certain protective effect on the active metal core, improving the electrocatalytic durability of the multi-metal nanocrystals. Description of the Drawings

[0044] Figure 1 Transmission electron microscope images of the Pd@Ag cubic crystals (a) and Pd@AgPt core-shell heterostructure nanocrystals (b) prepared in Example 1.

[0045] Figure 2 Transmission electron microscope image of the Pd@AgPt faceted concave core-shell heterostructure nanocrystals prepared in Example 2.

[0046] Figure 3 Dechlorination performance graph of the metal nanocrystals in Example 2.

[0047] Figure 4 Transmission electron microscope image of the Pd@AgRu metal nanocrystals prepared in Example 3.

[0048] Figure 5 Comparison of the dechlorination efficiency of the metal nanocrystals prepared in Example 3 before and after 10,000 cycles of CV. Detailed Description of the Invention

[0049] Example 1

[0050] Add 25 mL of the reaction base solution that has been fully mixed and dissolved in a 100 mL glass reaction vessel. This base solution is an aqueous solution containing 150 mg of ascorbic acid, 1.5 g of potassium bromide, and 280 mg of polyvinylpyrrolidone. After preheating in an 80 °C oil bath for 5 min, add 5 mL of an aqueous solution of potassium chloropalladate (0.1 mol / L). After the reaction proceeds for 3 h, wash the Pd seeds with ultrapure water with a volume similar to that of the seeds and acetone with a volume 2 - 4 times that of the seeds multiple times. Dry at room temperature and then disperse in 25 mL of ethylene glycol solution to form a high-concentration nanocrystal seed solution. Add 400 mg of polyvinylpyrrolidone and 450 mg of potassium bromide to this seed solution. Heat to 140 °C and preheat for 5 min, and then dropwise add 0.5 mL of an ethylene glycol solution of 0.1 mol / L silver trifluoroacetate with a syringe. After the reaction proceeds for 30 min, the deposition of the Ag thin shell layer is completed, obtaining the Pd@Ag nanocubes as shown in Figure 1 (a) as shown below. Subsequently, the reaction solution can be directly used for the secondary growth of Pt. Adjust the reaction temperature to 140 °C, add 50 mg of platinum precursor platinum acetylacetonate, and use the aldehyde alcohol formed by the thermal oxidation of ethylene glycol as the reducing agent. After the reaction proceeds at the set temperature for 3 h, recover by centrifugation and washing, obtaining as shown in Figure 1In the Pd@AgPt core-shell heterostructure shown in (b), Pt is selectively deposited in the corner regions of the cube.

[0051] The multi-metal nanocrystals are loaded on Vulcan C to form an electrocatalyst for modifying hydrophilic carbon paper. The characterization system is a three-electrode system, with Ag / AgCl as the reference electrode, a Pt sheet as the counter electrode, and the modified carbon paper as the working electrode. Using 50 mL of tap water containing 2,4-dichlorophenol as the electrolyte, with a pollutant concentration of 1 mmol / L, constant potential electrolysis is carried out. The set potential for the constant potential electrolysis is -0.9 V vs. Ag / AgCl, at a room temperature of 35 °C. The concentration of 2,4-dichlorophenol before and after is measured using an HPLC high-performance liquid chromatograph. After 6 h of electrolysis using this multi-metal nanocrystal as the electrocatalyst, the dechlorination efficiency of 2,4-dichlorophenol is 92.7%, and more than 99% of the dechlorination products are phenol. The mass activity of the nanocrystals is 13.1 min -1 g -1 Pd+Pt 。

[0052] Example 2

[0053] Add 30 mL of the reaction base solution that has been fully mixed and dissolved in a 100 mL glass reaction vessel. This base solution is an aqueous solution containing 10 mg of potassium acetate, 250 mg of ascorbic acid, 1.8 g of potassium bromide, and 300 mg of polyvinylpyrrolidone. After preheating in an 85 °C oil bath for 5 min, add 5 mL of an aqueous solution of sodium palladium chloride (0.68 mol / L). After the reaction proceeds for 30 min, inject 1 mL of an aqueous solution of silver trifluoroacetate (0.05 mol / L) with a syringe, and continue the reaction for 2.5 h. Wash the Pd@Ag nanocubes with ultrapure water with a similar volume and acetone with a volume 2 - 4 times that of the ultrapure water, dry at room temperature, and then disperse them in 30 mL of an ethylene glycol solution. Add 200 mg of polyvinylpyrrolidone to this solution, heat it to 165 °C, preheat it, and add 60 mg of platinum precursor platinum acetylacetonate. Using the aldehyde alcohol formed by the thermal oxidation of ethylene glycol as the reducing agent, the reaction is carried out at the set temperature for 3 h, and it is recovered by centrifugal washing to obtain as Figure 2 shown in the Pd@AgPt core-shell heterostructure, where Pt is mainly selectively deposited in the region where the cube corners are formed, and due to the galvanic replacement of Pd atoms on the {100} plane with Pt at high temperature, surface depressions of the cube are formed.

[0054] After the multi-metal nanocrystals are supported by graphene to form an electrocatalyst for modifying hydrophilic carbon paper, it is found that the nanocrystal surface depression caused by Pt replacement greatly increases the effective electrochemically active surface area of the active metals Pd and Pt. The characterization system of electrocatalytic activity is still a three-electrode system, with Ag / AgCl as the reference electrode, a Pt sheet as the counter electrode, and the modified carbon paper as the working electrode. Using 50 mL of tap water containing 2-chlorophenol as the electrolyte with a pollutant concentration of 0.5 mmol / L, constant potential electrolysis is carried out. The set potential for constant potential electrolysis is -0.9 V vs. Ag / AgCl, at room temperature of 25 °C. An HPLC high-performance liquid chromatograph is used to measure the concentration changes of 2-chlorophenol and phenol. It is measured that the C t / C 0 concentration change of 2-chlorophenol and the mass of 2-chlorophenol removal are as Figure 3 shown. After electrolysis, the degradation rate of 2-chlorophenol is 95.1%, and the mass activity of the nanocrystals is 16.5 min -1 g -1 Pd+Pt .

[0055] Example 3

[0056] Add 25 mL of the reaction base solution that has been fully mixed and dissolved in a 100 mL glass reaction vessel. This base solution is an aqueous solution containing 15 mg of potassium acetate, 200 mg of ascorbic acid, 1.5 g of potassium bromide, and 290 mg of polyvinylpyrrolidone. After preheating in an oil bath at 75 °C for 5 min, add 5 mL of an aqueous solution of sodium palladium chloride (0.6 mol / L). After the reaction proceeds for 30 min, inject 0.5 mL of an aqueous solution of silver trifluoroacetate (0.1 mol / L) with a syringe, and continue the reaction for 2.5 h. Wash the Pd@Ag nanocubes with ultrapure water with a similar volume and acetone with a volume 2 - 4 times that of the Pd@Ag nanocubes. Dry at room temperature and disperse in 25 mL of ethylene glycol solution. Add 100 mg of polyvinylpyrrolidone to this solution, preheat after raising the temperature to 170 °C, and add 15 mg of ruthenium precursor ruthenium trichloride. Using the aldehyde alcohol formed by the thermal oxidation of ethylene glycol as a reducing agent, the reaction is carried out at the set temperature for 3 h. Recover by centrifugal washing to obtain the Pd@AgRu core-shell heterostructure as Figure 4 shown. Ru is selectively deposited mainly in the vertex region of the cube, and due to the high temperature, there is a certain degree of in-plane depression on the cube surface.

[0057] After the multi-metal nanocrystals are carbon-supported to form an electrocatalyst for modifying hydrophilic carbon paper, the characterization system is a three-electrode system. Using Ag / AgCl as the reference electrode, a Pt sheet as the counter electrode, and the modified carbon paper as the working electrode, 50 mL of river water added with 4-chlorophenol is used as the electrolyte with a pollutant concentration of 1 mmol / L for potentiostatic electrolysis. The set potential for potentiostatic electrolysis is -0.9 V vs. Ag / AgCl, at room temperature of 25 - 30 °C. After the electrolyte is filtered, a high-performance liquid chromatograph is used to measure the pollutant concentration. Subsequently, the electrocatalyst is subjected to 10,000 CV curve cycles in a high-concentration 4-chlorophenol solution for 24 h, reactivated, and then the electrolysis experiment is carried out. The change in the degradation rate of 4-chlorophenol during the electrolysis process before and after the long-term cycle is as Figure 5 shown. The initial electrolytic degradation rate is 96%, and the degradation rate is 89% after the long-term cycle. The electrocatalytic mass activity can reach 29 min -1 g -1 Pd , which is more than 5 times that of commercial Pd / C. It can be seen that its electrocatalytic activity and durability are far superior to those of commercial Pd / C.

[0058] The above-described embodiments have elaborated on the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, equivalent replacements, etc. made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Application of Pd-based multi-metal core-shell heterostructure nanocrystals in electrocatalytic dechlorination of chlorinated organic pollutants, characterized in that, the preparation method of the Pd-based multi-metal core-shell heterostructure nanocrystals comprises the following steps: (A-1) After preheating the reaction base solution at 60-90 °C, adding a Pd precursor, reacting for 10-30 min, adding an Ag precursor, and then reacting for 2-5 h, centrifuging and washing, and dissolving the product in ethylene glycol after drying at room temperature to obtain reaction solution A; The reaction base solution uses water as a solvent and also contains a reducing agent, a surface stabilizer, and a seed stabilizer; the reaction base solution also contains potassium acetate, and the concentration of potassium acetate in the reaction base solution is 0.1-18 mmol / L; Based on 1 L of the reaction base solution, the dosage of the Pd precursor is 0.01-0.1 mol, and the dosage of the Ag precursor is 0.001-0.015 mol; (A-2) Adding a surface stabilizer to reaction solution A, adjusting the reaction temperature to 120-180 °C, then adding a metal M precursor, using the aldehyde alcohol obtained by the thermal oxidation of ethylene glycol as a reducing agent, reacting for 2-5 h, and then centrifuging and washing to obtain Pd-based multi-metal core-shell heterostructure nanocrystals; The metal M is Pt and / or Ru; The reducing agent is ascorbic acid; the concentration of the reducing agent in the reaction base solution is 3-25 g / L; The surface stabilizer is polyvinylpyrrolidone; the concentration of the surface stabilizer in the reaction base solution is 5-20 g / L; The seed stabilizer is potassium bromide; the concentration of the seed stabilizer in the reaction base solution is 30-100 g / L.

2. The application according to claim 1, characterized in that, the Pd precursor is potassium chloropalladate and / or sodium chloropalladate; the Ag precursor is silver nitrate and / or silver trifluoroacetate; the metal M precursor is platinum acetylacetonate and / or ruthenium trichloride anhydrous; after adding the metal M precursor, the concentration of metal M in the reaction system is 1-5 mmol / L.

3. The application according to claim 1, characterized in that, loading the Pd-based multi-metal core-shell heterostructure nanocrystals onto a carbon carrier to form a working electrode, using a Pt electrode as a counter electrode, and using a saturated calomel electrode or an Ag / AgCl electrode as a reference electrode to perform electrolytic dechlorination on chlorinated organic pollutants.

Images