Preparation of an ultrasmall palladium nanoclusters and its application in eliminating nitrate nitrogen in wastewater

Abstract

This invention belongs to the field of environmental protection technology, and discloses the preparation of ultrasmall palladium nanoclusters and their application in eliminating nitrate nitrogen in wastewater. This invention employs a one-step simultaneous nucleation and passivation method, where a large number of palladium nanoclusters are obtained by adding a mild reducing agent during the in-situ reaction of palladium with ligands. The palladium nanoclusters synthesized in this invention have very small and uniform particle sizes, all between 1 and 3 nm. The ultrasmall particle size results in a large number of catalytically active sites on their surface, enabling them to effectively catalyze NO3- at a potential of -0.6 V. ‑ The reduction to NH3 exhibits excellent performance, with a Faraday efficiency of up to 92%. At this potential, the selectivity for NH3 among the products can reach over 97%, while also showing good performance for NO3. ‑ The removal rate is as high as 88%, and after 5 catalytic cycles, the Faraday efficiency and yield of NH3 only decrease slightly.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, and specifically relates to the preparation of ultra-small palladium nanoclusters and their application in eliminating nitrate nitrogen in wastewater. Background Technology

[0002] Nitrogen nitrate is one of the major pollutants in water bodies, with nitrate being the most common form. Ammonia is a widely used and essential chemical in modern society, extensively used as fertilizer, high-value-added chemical raw material, hydrogen carrier, and high-energy-density fuel. Currently, the huge global demand for ammonia relies almost entirely on the Haber process, but this process consumes approximately 1.5% of the world's annual energy consumption and accounts for more than 1.4% of global carbon dioxide emissions. Over the past decade, the synthesis of ammonia via N2 reduction reactions driven by renewable electricity has been extensively studied. However, this process is limited by the low solubility of N2 in water and the highly stable N≡N bond (940.95 kJ / mol). -1 It is very difficult to efficiently generate NH3 directly from N2. Meanwhile, since N = O(204 kJ mol) -1 ) and NO (176kJ mol) -1 The dissociation energy of the NO3 bond is much lower, therefore from NO3... - The preparation of NH3 from compounds is very promising. More importantly, NO3... - Nitrate is one of the main pollutants in industrial wastewater and surface water. Therefore, using renewable electricity to prepare NH3 from nitrate in water provides a way to transform pollutants into high-value-added products, which is to turn waste into treasure and kill two birds with one stone.

[0003] Currently, the development of many high-performance electrochemical nitrate reduction catalysts focuses on copper and copper-containing nanomaterials. Although these materials exhibit high activity, copper is easily oxidized or corroded under environmental conditions, which greatly reduces their catalytic activity and stability. In recent years, palladium-based nanomaterials have been proven to be an ideal catalyst for nitrate reduction, and palladium materials also exhibit high stability. However, the reported palladium-based materials often have relatively large particle sizes. In catalytic reactions, smaller particle sizes generally result in higher performance. Furthermore, due to the quantum confinement effect, particles smaller than 3 nm exhibit drastically different physicochemical properties compared to larger particles, affecting their catalytic performance. Therefore, the synthesis of ultrasmall palladium nanoclusters for electrocatalytic nitrate reduction to eliminate nitrate nitrogen in wastewater has significant application value. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing ultrasmall palladium nanoclusters. This material is prepared via a simple one-step simultaneous nucleation and passivation method. The preparation method is simple to operate, has low substrate loss, and high yield, showing promising prospects for industrial application.

[0005] Another objective of this invention is to provide ultrasmall palladium nanoclusters prepared by the above method. The palladium nanoclusters synthesized by this invention have very small and uniform particle sizes, all between 1 and 3 nm. The ultrasmall particle size results in a large number of catalytically active sites on their surface.

[0006] Another objective of this invention is to provide the application of the aforementioned ultrasmall palladium nanoclusters in the removal of nitrate nitrogen from wastewater. This catalyst possesses a large number of active sites on its surface, exhibiting excellent catalytic performance and stability in the electrocatalytic nitrate reduction reaction.

[0007] The objective of this invention is achieved through the following solution:

[0008] A method for preparing ultrasmall palladium nanoclusters includes the following steps:

[0009] (1) Dissolve the palladium salt in a polar organic solvent to obtain a palladium solution;

[0010] (2) Add a reducing agent solution and an alkynyl ligand solution dropwise to the palladium solution obtained in step (1) and stir to obtain a crude product;

[0011] (3) Centrifuge the crude product obtained in step (2) to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash and dry to obtain the final product.

[0012] The palladium salt in step (1) is at least one of palladium acetate, palladium chloride, sodium tetrachloropalladium, potassium tetrachloropalladium, and dichlorotetraamminepalladium, preferably at least one of palladium acetate and palladium chloride.

[0013] The polar organic solvent mentioned in step (1) is any one of toluene, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, and ethyl acetate.

[0014] The amount of polar organic solvent used in step (1) satisfies the following condition: the concentration of palladium salt is 0.0067-0.04 mol / L.

[0015] The palladium salt described in step (1) dissolves in a polar organic solvent at a temperature of -10℃ to 5℃.

[0016] The reducing agent in step (2) is at least one of sodium cyanoborohydride, tert-butylamine borane complex, and diphenylsilane.

[0017] The solvent of the reducing agent solution in step (2) is at least one of methanol, ethanol, and dichloromethane.

[0018] The alkynyl ligand in step (2) is at least one of 2-nitrophenylacetylene, 3,5-bis(trifluoromethyl)phenylacetylene, 2-fluorophenylacetylene, 3-fluorophenylacetylene, 3,5-difluorophenylacetylene, 2-fluorophenylacetylene, methyl 4-alkynylbenzoate, 4-ethylphenylacetylene, 4-ethynyl anisole, 4-cyanophenylacetylene, 4-tert-butylphenylacetylene, phenylacetylene, 3,3-dimethyl-1-butyne, 4-ethynylbenzaldehyde, 4-trifluoromethylphenylacetylene, ferrocene acetylene, and 1-ethynylcyclohexane, preferably at least one of 3,3-dimethyl-1-butyne and phenylacetylene.

[0019] The solvent for the alkynyl ligand solution in step (2) is any one of toluene, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, and ethyl acetate.

[0020] The molar ratio of the reducing agent to the palladium salt in step (2) is 0.06:1-0.6:1, preferably 0.3:1, and the molar ratio of the ligand to the palladium salt is 4.8:1-1.5:1, preferably 2:1.

[0021] The concentration of the reducing agent in the reducing agent solution in step (2) is 0.01 mmol / mL to 2.4 mmol / mL.

[0022] The concentration of alkynyl ligand in the alkynyl ligand solution in step (2) is 0.024 mmol / mL to 2.88 mmol / mL.

[0023] In step (2), the dropping rate of the reducing agent is 10 mL / h-20 mL / h, preferably 12 mL / h-15 mL / h; the dropping rate of the alkynyl ligand is 20 mL / h-40 mL / h, preferably 24 mL / h-30 mL / h.

[0024] The ratio of the alkynyl ligand dropping rate to the reducing agent dropping rate in step (2) satisfies the condition that the alkynyl ligand and the reducing agent are added simultaneously.

[0025] The stirring speed in step (2) is 1200 rpm or higher, preferably 1200-1500 rpm.

[0026] The stirring time in step (2) is 15h-24h, and the stirring temperature is -10℃ to 5℃.

[0027] The centrifugation speed in step (3) is 8000 rpm or higher, preferably 8000-9000 rpm.

[0028] The washing step (3) involves washing the solid with n-hexane at least three times.

[0029] The drying in step (3) is vacuum drying, and the drying temperature is 20℃-40℃, preferably 35℃.

[0030] An ultrasmall palladium nanocluster prepared by the above method has a particle size of 1-3 nm and a uniform particle size.

[0031] The above-mentioned ultra-small palladium nanoclusters are used to eliminate nitrate nitrogen in wastewater.

[0032] The specific application involves using ultra-small palladium nanoclusters as a catalyst for electrocatalysis to reduce nitrates to ammonia in wastewater.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] (1) Simple preparation method: The present invention adopts a one-step simultaneous nucleation and passivation method. A large number of palladium nanoclusters can be obtained by adding a mild reducing agent when palladium reacts with ligands in situ, so it is easy to carry out mass production.

[0035] (2) Ultra-small and uniform particle size: The palladium nanoclusters synthesized in this invention have very small and uniform particle size, with particle size ranging from 1 to 3 nm. The ultra-small particle size results in a large number of catalytic active sites on their surface.

[0036] (3) High yield: The yield of the synthesized product by this method exceeds 95%, with very little substrate loss.

[0037] (4) Excellent performance: Resistant to NO3 at a potential of -0.6V - The reduction to NH3 exhibits excellent performance, with a Faraday efficiency of up to 92%. At this potential, the selectivity for NH3 among the products can reach over 97%, while also showing good performance for NO3. - The removal rate is as high as 88%, and after 5 catalytic cycles, the Faraday efficiency and yield of NH3 only decrease slightly. Attached Figure Description

[0038] Figure 1 (a)-(c) are transmission electron microscope (TEM) images of palladium nanoclusters at different magnifications in Example 1.

[0039] Figure 2 This is the elemental mapping distribution of the palladium nanoclusters in Example 1 at the 100 nm scale.

[0040] Figure 3 The full X-ray photoelectron diffraction pattern (a) of the palladium nanoclusters in Example 1 and the high-magnification X-ray photoelectron diffraction pattern (b) of the palladium 3d electron orbitals are shown.

[0041] Figure 4 The palladium nanoclusters in Example 1 were used in a NaNO3 concentration of 0.1 mol / L.-1 1 mol L -1 The Faradaic efficiency and yield of NH3 at different potentials in NaOH solution (a), and the selectivity of the product (b), NO3. - The removal rate (c) and the stability of the catalyst (d).

[0042] Figure 5 In Example 1, palladium nanoclusters were used as catalysts, with Na... 14 NO3 and Na 15 NO3 is a product of nitrate reduction from nitrogen sources. 1 H-NMR spectrum.

[0043] Figure 6 The image shows the SEM image of Comparative Example 1 and its Faraday efficiency and yield for electrocatalytic nitrate reduction at different potentials.

[0044] Figure 7 TEM images of Examples 2, 4, 6, and 8, and their Faraday efficiency and yield at a potential of -0.6V. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0046] Unless otherwise specified, all reagents used in the examples are commercially available.

[0047] Example 1

[0048] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0049] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0050] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the byproducts, and then vacuum dry the solid (35℃) to obtain the final product.

[0051] The final product was placed in a ceramic boat and heated to 500 degrees Celsius in a tube furnace and held at that temperature for 2 hours to ensure the removal of all ligands. The residue was collected and weighed to obtain the mass of palladium in the final product (61.02 mg). This value was divided by the mass of palladium in 0.6 mmol palladium acetate (63.58 mg) to obtain a yield of 95% for Example 1.

[0052] Performance Structure Analysis

[0053] Figure 1 The images are transmission electron microscope (TEM) images of palladium nanoclusters at different magnifications in Example 1. It can be clearly seen from the TEM images that the synthesized palladium nanoclusters have very small particle sizes, basically between 1-2 nm, and the particle sizes are very uniform. There are no palladium nanoparticles that are too large or too small.

[0054] Figure 2 The image shows the elemental mapping distribution of the palladium nanoclusters in Example 1 at the 100 nm scale. It indicates that the synthesized palladium nanoclusters have very good dispersion and no aggregation occurs in a large area. Furthermore, there are a large number of carbon elements around the palladium elements, indicating that the surface of the metal core in the synthesized palladium nanoclusters is protected by ligands.

[0055] Figure 3 The image shows the X-ray photoelectron diffraction (XPS) pattern of the palladium nanoclusters in Example 1. This characterization indicates that palladium 3d 3 / 2 and 3D 5 / 2 The binding energies of the orbitals are 341.98 eV and 336.68 eV, respectively, and their binding energies are located in the Pd region. 2+ and Pd 0 Between (Pd) 2+ 3D 3 / 2 and 3D 5 / 2 The binding energies of the orbitals are 342.9 and 337.7 eV, respectively, for Pd. 0 3D 3 / 2 and 3D 5 / 2 The binding energies of the orbitals are 342.9 eV and 335.3 eV, respectively, indicating that the valence state of palladium in the synthesized palladium nanoclusters is between 0 and +2, which is very different from traditional palladium nanoparticles. This also shows that the particle size of our synthesized clusters is very small, with palladium atoms coordinated with ligands on the surface having a +2 valence and palladium atoms inside having a 0 valence, which is consistent with the characteristics of clusters.

[0056] Figure 4(a) The palladium nanoclusters of Example 1 were subjected to NaNO3 at a concentration of 0.1 mol / L. -1 1 mol L -1 Electrocatalysis of NO3 at different potentials in NaOH solution - The Faraday efficiency and yield of reduced NH3 are shown in the figure. It can be seen that at a low potential of -0.6V, the Faraday efficiency of NH3 reaches a maximum of 92%, and the yield can reach 2.14 mmol / L. -1 mg -1 Figure (b) shows the selectivity of the corresponding products. As can be seen from the figure, NO3 at different potentials... - The only product of reduction is NO2. - The system exhibits high selectivity for NH3, exceeding 90% within a potential range of -0.5 to -0.7V, reaching a peak selectivity of 97% at -0.6V. At this point, the NO2 content in the system... - The content of NO3 is very low. Figure (c) shows the NO3 content at different potentials. - The removal rate of NO3, as shown in the figure, is as follows: at -0.6V... - The removal rate reached a maximum of 88%. Figure (d) shows that after 5 cycles of catalytic experiments, the palladium nanoclusters still have good catalytic activity, and the Faraday efficiency of NH3 is 87.56%, indicating that the catalyst has good stability.

[0057] Figure 5 Using the palladium nanoclusters from Example 1 as a catalyst, Na... 14 NO3 and Na 15 NO3 is a nitrogen source and a product of nitrate reduction. 1 H-NMR spectrum, 15 NH3 has only two peaks in its NMR spectrum, while 14 NH3 shows three peaks at the corresponding chemical shifts. As shown in the graph, when Na... 15 When NO3 is used as the nitrogen source, all products are... 15 NH3, which means that all the NH3 in the reduced system comes from the added NO3. - Rather than other nitrogen sources present in the environment.

[0058] Example 2

[0059] (1) 0.1 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0060] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.03 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 0.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0061] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the byproducts, and then vacuum dry the solid (35℃) to obtain the final product.

[0062] Example 3

[0063] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 10 °C to form a stable solution;

[0064] (2) The obtained stable solution was stirred at 10°C. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0065] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the byproducts, and then vacuum dry the solid (35℃) to obtain the final product.

[0066] Example 4

[0067] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0068] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 2-fluorophenylacetylene ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0069] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the by-products, and then dry the solid under vacuum to obtain the final product.

[0070] Example 5

[0071] (1) 0.6 mmol of palladium chloride was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0072] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0073] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the by-products, and then dry the solid under vacuum to obtain the final product.

[0074] Example 6

[0075] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0076] (2) The stable solution obtained was stirred at 0°C. Simultaneously, 0.18 mmol of tert-butylamine borane complex was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0077] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the byproducts, and then vacuum dry the solid (35℃) to obtain the final product.

[0078] Example 7

[0079] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of toluene at 0 °C to form a stable solution;

[0080] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0081] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the by-products, and then dry the solid under vacuum to obtain the final product.

[0082] Example 8

[0083] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0084] (2) The obtained stable solution was stirred at 0℃. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 15 mL / h, and the dropping rate of the ligand solution was 30 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1500 rpm. After the dropping was completed, the reaction was continued for 18 h to obtain the crude product.

[0085] (3) Centrifuge the product obtained in step (2) at more than 8000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the by-products, and then dry the solid under vacuum to obtain the final product.

[0086] Example 9

[0087] (1) 0.6 mmol of palladium acetate was dissolved in 15 mL of dichloromethane at 0 °C to form a stable solution;

[0088] (2) The stable solution obtained was stirred at 0°C. Simultaneously, 0.18 mmol of sodium cyanoborohydride was added to 2 mL of methanol to prepare a reducing agent solution, and 1.2 mmol of 3,3-dimethyl-1-butyne ligand was added to 4 mL of dichloromethane to prepare a ligand solution. The dropping rates of the reducing agent solution and the ligand solution were controlled: the dropping rate of the reducing agent solution was 12 mL / h, and the dropping rate of the ligand solution was 24 mL / h, ensuring that both started and finished dropping simultaneously. During the dropping process, the rotation speed was maintained at 1200 rpm. After the dropping was completed, the reaction was continued for 24 h to obtain the crude product.

[0089] (3) Centrifuge the product obtained in step (2) at more than 9000 rpm to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash the solid three times with 20 mL of n-hexane to remove the by-products, and then dry the solid under vacuum to obtain the final product.

[0090] Comparative Example 1

[0091] Comparative Example 1 is basically the same as Example 1, except that in step (2), the amount of alkynyl ligand in the solution containing alkynyl ligand is not 1.2 mmol, but 0.6 mmol.

[0092] Since the particle size of the synthesized comparative example 1 was too large to be dispersed in conventional solvents, a TEM image could not be obtained; only a SEM image could be obtained. Figure 6(a) is a SEM image of the product of Comparative Example 1. The image shows that it is in an aggregated state, and the particle size has reached the micrometer level, no longer qualifying as nanomaterials. The palladium nanoclusters obtained after the reaction have a particle size much larger than 2 mm or quickly aggregate and cannot be dispersed again. The reason is that when the amount of ligand is relatively small, the ligand cannot bond with palladium in time during the reduction process, ultimately resulting in excessively large palladium cluster particle size, or a large number of unbonded palladium atoms on the surface of the palladium clusters. In this case, although the particle size is less than 2 nm after the reaction, the unbonded palladium atoms have very strong interaction forces during post-processing, leading to irreversible aggregation and ultimately failing to form ultra-small and uniform palladium nanoclusters. (b) shows the product obtained in a reaction with a NaNO3 concentration of 0.1 mol / L. -1 1 mol L -1 Electrocatalysis of NO3 at different potentials in NaOH solution - The Faradaic efficiency and yield of reduced NH3 show that the highest Faradaic efficiency does not exceed 40% and the highest yield is 0.44 mmol / L in the potential range of -0.3 V to -0.7 V. -1 mg -1 The performance is far lower than that of Example 1.

[0093] Figure 7 Figures (a) to (d) show TEM images of Examples 2, 4, 6, and 8. As can be seen from the figures, although the experimental conditions of Examples 2, 4, 6, and 8 differed from those of Example 1, the TEM images show that the synthesized palladium nanoclusters had a particle size of approximately 2-3 nm, which is very similar to that of Example 1. Figure (e) shows the palladium nanoclusters of Examples 2, 4, 6, and 8 in a NaNO3 concentration of 0.1 mol / L. -1 1 mol L -1 Figure (e) shows the electrocatalytic performance of nitrate reduction in NaOH solution at a potential of -0.6 V. It indicates that Examples 2, 4, 6, and 8 exhibit good catalytic performance, with Faradaic efficiencies ranging from 88.9% to 91.5% and yields reaching 1.98 mmol / L. -1 mg -1 -2.09mmol h -1 mg -1 .

[0094] Example 1 exhibits the best catalytic performance, with its structure and performance being the most representative. Structurally, the palladium nanoclusters have uniform particle sizes, all between 1 and 2 nanometers. Generally, smaller particle sizes expose more active sites, resulting in superior performance. This was demonstrated by electrocatalyzing NO3 at different potentials. - Analysis of the reduction products revealed that they exhibited electrocatalytic activity against NO3- at a potential of -0.6V. -The reduction exhibits optimal performance, achieving a Faraday efficiency of 92% and a yield of 2.14 mmol / L at this potential. -1 mg -1 Meanwhile, the selectivity of NH3 can reach over 97%, and NO3... - The removal rate was 88%, and after five cycles of catalytic experiments at this potential, the Faradaic efficiency and yield of NH3 only showed slight decreases, indicating that the palladium nanoclusters have excellent stability. Therefore, they are suitable as a catalyst for removing NO3 from industrial wastewater. - Reducing it to NH3 has significant application prospects and industrialization value.

[0095] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An application of palladium nanoclusters in the removal of nitrate nitrogen from wastewater, characterized in that, Palladium nanoclusters were used as a catalyst for electrocatalysis to reduce nitrates to ammonia in wastewater; The preparation of the palladium nanoclusters includes the following steps: (1) Dissolve the palladium salt in a polar organic solvent to obtain a palladium solution; (2) Add a reducing agent solution and an alkynyl ligand solution dropwise to the palladium solution obtained in step (1) and stir to obtain a crude product; (3) Centrifuge the crude product obtained in step (2) to obtain the supernatant, remove the organic solvent by vacuum evaporation to obtain the solid, wash and dry to obtain the final product; In step (2), the molar ratio of the reducing agent to the palladium salt is 0.06:1-0.6:1; the molar ratio of the ligand to the palladium salt is 4.8:1-1.5:

1. The concentration of the reducing agent in the reducing agent solution in step (2) is 0.01 mmol / mL to 2.4 mmol / mL; The concentration of alkynyl ligand in the alkynyl ligand solution in step (2) is 0.024 mmol / mL to 2.88 mmol / mL.

2. The application according to claim 1, characterized in that: The palladium salt mentioned in step (1) is at least one of palladium acetate, palladium chloride, sodium tetrachloropalladium, potassium tetrachloropalladium, and dichlorotetraamminepalladium. The polar organic solvent in step (1) is any one of toluene, dichloromethane, chloroform, 1,2-dichloroethane, tetrahydrofuran, and ethyl acetate.

3. The application according to claim 1, characterized in that: The amount of polar organic solvent used in step (1) satisfies the following condition: the concentration of palladium salt is 0.0067 - 0.04 mol / L; The palladium salt in step (1) dissolves in a polar organic solvent at a temperature of -10℃ to 5℃.

4. The application according to claim 1, characterized in that: The reducing agent in step (2) is at least one of sodium cyanoborohydride, tert-butylamine borane complex, and diphenylsilane; The alkynyl ligand in step (2) is at least one of 2-nitrophenylacetylene, 3,5-bis(trifluoromethyl)phenylacetylene, 2-fluorophenylacetylene, 3-fluorophenylacetylene, 3,5-difluorophenylacetylene, methyl 4-alkynylbenzoate, 4-ethylphenylacetylene, 4-ethynyl anisole, 4-cyanophenylacetylene, 4-tert-butylphenylacetylene, phenylacetylene, 3,3-dimethyl-1-butyne, 4-ethynylbenzaldehyde, 4-trifluoromethylphenylacetylene, ferrocene acetylene, and 1-ethynylcyclohexane.

5. The application according to claim 1, characterized in that: In step (2), the dropping rate of the reducing agent is 10 mL / h-20 mL / h; the dropping rate of the alkynyl ligand is 20 mL / h-40 mL / h. The ratio of the dropping acceleration rate of the alkynyl ligand to the dropping acceleration rate of the reducing agent in step (2) satisfies the condition that the alkynyl ligand and the reducing agent are added simultaneously.

6. The application according to claim 1, characterized in that: The stirring time in step (2) is 15h-24h, and the stirring temperature is -10℃~5℃; The drying in step (3) is vacuum drying, and the drying temperature is 20℃-40℃.

7. The application according to claim 1, characterized in that, The palladium nanoclusters have a particle size of 1-3 nm and are uniform in size.

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