Silver-copper nanocluster and application thereof in electro-catalysis nitrate reduction reaction

Abstract

The invention discloses a silver-copper nanocluster and application of the silver-copper nanocluster in an electro-catalysis nitrate reduction reaction. The synthesis method comprises the following synthesis steps: firstly, adding tetra-n-octylammonium bromide into a dichloromethane solution, stirring for five minutes, adding a silver source dissolved in methanol until white flocculent precipitate appears in the solution, adding a copper source until the solution becomes gray, adding triphenylphosphine until the solution becomes cyan clear solution, adding phenethyl mercaptan until the solution becomes orange red, stirring overnight, and filtering to obtain a filtrate; and separating an organic phase from a water phase, carrying out reduced pressure evaporation on the organic phase, and washing the organic phase with methanol for several times to remove residual ligands and by-products. Finally, n-hexane is spread on the upper layer of the dichloromethane solution for liquid diffusion, and orange flaky crystals are obtained. The silver-copper nanocluster disclosed by the invention has the characteristics of novel structure, good stability, easiness in synthesis and high yield, and has excellent catalytic performance in an electro-catalysis nitrate reduction reaction.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial synthesis and catalysis, specifically relating to a silver-copper nanocluster and its application in the electrocatalytic reduction of nitrate. Background Technology

[0002] Electrochemical nitrate reduction reaction (NtrRR) has become an important pathway for water treatment and NH3 synthesis. NH3 is widely considered a promising energy carrier, capable of playing a sustainable role in future energy prospects, and is also a valuable chemical feedstock for agriculture, chemical industry, and other sectors. Currently, the industrial synthesis of ammonia still largely relies on the Haber-Bosch process, which operates under high temperature and pressure, emitting 1%-1.5% of total energy and 1.0%-2.0% of total CO2 worldwide. Nitrogen reduction reaction (NRR) driven by renewable electricity has attracted attention for decades; however, the low solubility of N2 in aqueous solution and the high dissociation energy of N≡N (941 kJ·mol⁻¹) present challenges. -1 The highly competitive hydrogen evolution reaction (HER) makes improving the Faraday efficiency (FE) of ethylene glycol and NH3 in HER extremely difficult. Conversely, NO3... - It exhibits high solubility in aqueous solution, N=O bond (204 kJ·mol⁻¹) -1 The dissociation energy of nitrate reduction (NtrRR) is much lower, making it more energy-efficient than NTRRR for NH3 synthesis. Furthermore, nitrate is a major pollutant in groundwater and industrial wastewater. Therefore, NH3 synthesis via electrochemical nitrate reduction (NtrRR) is a promising pathway for achieving green energy, production, and pollutant removal.

[0003] Developing efficient and durable catalysts is essential for realizing a practical NtrRR method for synthesizing NH3. Among a range of nanocatalysts, copper-based nanomaterials are undoubtedly the most effective for converting NO to NH4. + Copper-based nanomaterials are one of the most effective catalysts for NO3. This is mainly because of their relatively low cost, and more importantly, their strong catalytic ability. - It possesses strong adsorption capacity and exhibits rapid reaction kinetics, which determines the adsorption rate of NO3. - To NO2 - The steps are as follows. However, copper-based NtrRR catalysts also suffer from problems such as high overpotential, poor stability, and accumulation of nitrite intermediates.

[0004] To address these issues, introducing another metal to form a bimetallic catalyst is one of the most effective strategies. This is because the two metals can synergistically interact during catalysis, enabling catalysis, electrochemistry, electrochemical processes, hybridization mechanisms, and hydrogenation reduction processes. Despite the aforementioned progress made in NtrRR using bimetallic nanocatalysts, elucidating the structure-property relationships of catalysts at the atomic level to advance the understanding of the fundamental mechanism remains quite challenging. This is not only because NtrRR is a multi-electron / proton coupled process with a complex reaction pathway, but more importantly, most currently used nanocatalysts lack uniform size, morphology, composition, and chemical coordination environment at the atomic level. The emergence of atomically precise bimetallic nanoclusters can solve this problem because they possess molecular purity, atomically precise crystal structures, and uniform chemical coordination environments. Furthermore, their ultrasmall size endows them with large specific surface areas, abundant active centers, and unique electronic structures. Bimetallic nanoclusters, coupled with their well-defined atomic packing structure, can act as catalysts for the generation of NH4 in NtrRR. + Models for NH3 and effective catalysts. Summary of the Invention

[0005] This invention provides a silver-copper nanocluster and its application in the electrocatalytic reduction of nitrates. The silver-copper nanocluster of this invention exhibits high yield, good stability, and excellent electrocatalytic performance in the reduction of nitrates. Furthermore, the synthesis method is simple, easy to implement, and operates under mild conditions.

[0006] The silver-copper nanoclusters of this invention have the molecular formula [Ag4Cu]. 34 (PET) 16 (PPh3)6] - TOA + PET is phenylethyl mercaptan, and PPh3 is triphenylphosphine.

[0007] The method for preparing silver-copper nanoclusters of the present invention is a one-pot synthesis, comprising the following steps:

[0008] Step 1: Dissolve 100 mg of tetra-n-octylammonium bromide in 20 mL of dichloromethane solution;

[0009] Step 2: Dissolve 30 mg of silver nitrate in 5 mL of methanol and add it to the solution from Step 1. A white flocculent precipitate will appear in the solution.

[0010] Step 3: Add 60 mg of cuprous chloride powder to the system from Step 2; the solution turns gray.

[0011] Step 4: Add 50 mg of triphenylphosphine to the system from step 3; the solution turns into a clear, blue-green solution.

[0012] Step 5: Add 55 μL of phenylethyl mercaptan to the system from step 4; the solution turns orange-red.

[0013] Step 6: Add sodium borohydride aqueous solution (50 g / 5 mL) to the system from step 5 as a reducing agent, and continue the reaction in the dark for 12 hours;

[0014] Step 7: Separate the aqueous phase and the organic phase, evaporate the organic phase under reduced pressure, and wash the crude product with a large amount of methanol;

[0015] Step 8: Dissolve the crude product in a dichloromethane solution, and finally perform liquid diffusion of n-hexane in the dichloromethane solution for five days to obtain orange flaky crystals, which are the silver-copper nanoclusters [Ag4Cu]. 34 (PET) 16 (PPh3)6] - TOA + .

[0016] In the above preparation process:

[0017] The molar ratio of silver nitrate to cuprous chloride is 1:3.5.

[0018] The molar ratio of silver nitrate to triphenylphosphine is 1:1.

[0019] The molar ratio of silver nitrate to phenylethyl mercaptan is 1:2.5.

[0020] The molar ratio of silver nitrate to sodium borohydride is 1:9.

[0021] The present invention relates to the application of silver-copper nanoclusters in the electrocatalytic nitrate reduction reaction.

[0022] Specifically, a three-electrode system is adopted, with carbon fiber paper coated with the silver-copper nanoclusters as the working electrode, silver chloride electrode as the reference electrode, and platinum as the counter electrode. The cathode and anode regions are separated by a proton exchange membrane. The electrolyte in the cathode region is a K2SO4 solution (0.5M), and the electrolyte in the anode region is a mixed solution of K2SO4 and KNO3 (0.5M K2SO4 + 0.1M KNO3). The nitrate reduction reaction is catalyzed by electrolysis at a constant potential (selectable potential range: -0.6 to -2.1 V vs. RHE).

[0023] Includes the following steps:

[0024] Step 1: Dissolve 2 mg of silver-copper nanoclusters in 100 μL of dichloromethane, then add 40 μL of 5wt% Nafion PFSA;

[0025] Step 2: Drop the above-mentioned rolling liquid onto a 1×1 cm plate. 2 The working electrode for electrocatalytic nitrate testing is used on carbon fiber paper.

[0026] Step 3: Using an electrochemical workstation (Shanghai Chenhua CHI660E), the working electrode was first stabilized in the electrolyte of 0.1 M potassium nitrate and 0.5 M potassium sulfate using a linear sweep voltammetry method within a voltage range of -0.6 to -2.1 V before the electroreduction experiment. Then, LSV was measured at a scan rate of 5 mV / s, and constant potential tests were performed at different potentials for 1 h.

[0027] Step 4: Take a certain amount of electrolyte and dilute it. Detect the concentrations of nitrate, nitrite, and ammonium using a colorimetric method. After diluting the electrolyte to an appropriate concentration within the instrument calibration curve range, determine the ion concentration of the electrolyte after the reaction using a UV-Vis spectrophotometer.

[0028] Variations in KNO3 concentration in the mixed solution have different effects on electrocatalytic performance: excessively low concentrations (<0.01M) result in low reaction rates and low current densities; at higher concentrations (>0.1M), the reaction becomes less concentration-dependent after a certain point, reaching a plateau where mass transfer control takes over. Appropriate concentrations can inhibit the hydrogen evolution reaction (HER) and increase the KNO3 concentration. - The RR selectivity, and the 0.1M concentration is high enough that the incomplete reaction under conventional current density measurements is controlled by mass transfer, making the electrochemical performance more reflective of the intrinsic activity of the catalyst.

[0029] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0030] 1. This invention uses silver nitrate and cuprous chloride as silver and copper sources, respectively, which are readily available; and uses organophosphorus and thiols as ligands, which result in low raw material costs.

[0031] 2. The silver-copper nanoclusters of the present invention have a defined structure, high product purity, and are easy to monitor;

[0032] 3. The synthesis method of this invention is simple and easy to operate, with high yield and high product stability;

[0033] 4. The silver-copper nanoclusters of this invention exhibit excellent electrocatalytic performance in nitrate reduction, achieving a Faraday efficiency of 95% at 1.8 V. Attached Figure Description

[0034] Figure 1 It is [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + After crystallization, single-crystal X-ray diffraction was used to analyze and refine the results of [Ag4Cu]. 34 (PET) 16(PPh3)6] - TOA + Structural diagram of nanoclusters.

[0035] Figure 2 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + The UV-Vis absorption spectrum of nanoclusters. From Figure 2 As can be seen from this, Ag4Cu 34 There are two significant absorption peaks at 280 nm and 405 nm.

[0036] Figure 3 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + Fluorescence spectra of nanoclusters. From Figure 3 As can be seen from this, Ag4Cu 34 There is a visible peak centered at 655 nm and another centered at 705 nm in the dichloromethane solution.

[0037] Figure 4 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + XPS plot of nanoclusters. From Figure 4 It can be seen from Ag4Cu 34 It contains only Ag, Cu, P, S, C, and N elements.

[0038] Figure 5 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + High-resolution XPS spectra of Cu 2p nanoclusters. From Figure 5 As can be seen from this, Cu in Ag4Cu 34 It does not contain Cu ( ).

[0039] Figure 6 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + Auger spectrum of Cu nanoclusters. From Figure 6As can be seen, the peaks of Cu at 571.08 eV and 567.88 eV indicate the presence of Cu ( ) and Cu(0) valence states.

[0040] Figure 7 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + High-resolution XPS spectra of Ag 3d nanoclusters. From Figure 7 As can be seen from this, at 368.4 eV, Ag3d 5 / 2 The peak indicates the price state of silver and Ag( (Very close)

[0041] Figure 8 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + LSV curves of nanoclusters in 0.5 M K₂SO₄ and 0.5 M K₂SO₄ + 0.1 M KNO₃ electrolytes. (See attached image.) Figure 8 As shown, the concentrations of Ag₄Cu were tested and recorded in 0.5M K₂SO₄ electrolytes containing and without 0.1M KNO₃. 34 LSV curves of nanocluster catalysts, at the same potential, contain NO3. - Ag4Cu 34 The current density was significantly higher, indicating that it played a good catalytic role.

[0042] Figure 9 This invention [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + The Faraday efficiency of nanocluster catalysts at different potentials and NH4 + Yield plot. From Figure 9 As can be seen from this, Ag4Cu 34 The Faraday efficiency reaches its highest level of 96.48% at -1.811V; and the highest NH4 efficiency is achieved at -1.911V. + Yield reached 88.7 mg·h -1 ·g -1 . Detailed Implementation

[0043] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0044] While bimetallic nanocatalysts have made significant progress in NtrRR, elucidating the structure-property relationships of catalysts at the atomic level to advance the understanding of the fundamental mechanism remains quite challenging. This is not only because NtrRR is a multi-electron / proton coupled process with a complex reaction pathway, but more importantly, most currently used nanocatalysts lack uniform size, morphology, composition, and chemical coordination environment at the atomic level. The emergence of atomically precise bimetallic nanoclusters can solve this problem because they possess molecular purity, atomically precise crystal structures, and uniform chemical coordination environments. Furthermore, their ultrasmall size endows them with large specific surface areas, abundant active centers, and unique electronic structures. The coupling of bimetallic nanoclusters with their well-defined atomic packing structure can serve as a model and effective catalyst for the NtrRR formation of NH3. To address the above problems, this invention provides an alloy nanocluster, which is initially reacted with silver and copper salts, followed by the addition of triphenylphosphine and phenylethyl mercaptan, stirring, and the addition of sodium borohydride. The reaction is carried out at room temperature in the dark to obtain a two-phase solution containing an organic phase and an aqueous phase. The organic phase is then crystallized at room temperature to obtain the alloy nanocluster.

[0045] The effects are explained below with reference to the specific experimental process and preparation method.

[0046] experimental drugs

[0047] Tetraoctylammonium bromide (TOAB), silver nitrate (AgNO3, 98%), cuprous chloride (CuCl, 98%), triphenylphosphine (TPP), phenylethyl mercaptan (PET), and sodium borohydride (NaBH4) were purchased from Shanghai Maclean Biochemical Co., Ltd. Solvents including dichloromethane (DCM, C grade), methanol (MeOH, HPLC grade), and n-hexane (n-Hex, HPLC grade) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. The ultrapure water used in this study was purified using a microporous system.

[0048] Example 1: [Ag4Cu] 34 (PET) 16 (PPh3)6] - TOA + Cluster synthesis

[0049] First, 100 mg of tetra-n-octylammonium bromide was dissolved in 20 mL of dichloromethane solution and placed in a 50 mL round-bottom flask. The mixture was stirred at 1000 rpm with a magnetic stirrer at room temperature until fully mixed. Then, 30 mg of silver nitrate dissolved in 5 mL of methanol was added, resulting in a white flocculent precipitate. After reacting for 15 minutes, 60 mg of cuprous chloride was added, turning the solution gray. The mixture was stirred for 20 minutes, followed by the addition of 50 mg of triphenylphosphine. The solution gradually became clear and transparent. Stirring continued for another 20 minutes, then 55 μL of phenylethyl mercaptan was added. After stirring for 30 minutes, the solution turned orange-red. Then, 50 mg of sodium borohydride aqueous solution (dissolved in 5 mL of ice water) was added dropwise to the flask, gradually changing the solution from orange-red to black. After the reaction proceeded for 12 hours, the resulting solution was separated, separating the aqueous phase and retaining the organic phase. The organic phase was evaporated under reduced pressure using a rotary evaporator and then washed several times with a large amount of methanol to remove residual ligands and byproducts. Then, dichloromethane was used for extraction and purification. Finally, dichloromethane and n-hexane (DCM:n-Hex=1:3, v:v) were used as the developing solvent for liquid-phase diffusion. After five days, orange flaky single crystals were formed, yielding [Ag4Cu]. 34 (PET) 16 (PPh3)6] - TOA + Alloy nanoclusters.

[0050] Example 2: [Ag4Cu 34 (PET) 16 (PPh3)6] - TOA + Electrocatalytic nitrate reduction reaction performance test

[0051] Dissolve 2 mg of nanoclusters in 100 μL of dichloromethane, then add 40 μL of 5 wt% Nafion PFSA; drop the above solution onto a 1 × 1 cm plate. 2 Carbon fiber paper was used as the working electrode for the electrocatalytic nitrate assay. An electrochemical workstation (Shanghai Chenhua CHI660E) was used. The working electrode was first stabilized using linear sweep voltammetry within a voltage range of -0.6 to -2.1 V in an electrolyte of 0.1 M potassium nitrate and 0.5 M potassium sulfate before the electroreduction experiment. Then, LSV measurements were performed at a scan rate of 5 mV / s, followed by a 1-hour potentiostatic test at different potentials. A certain amount of electrolyte was diluted, and the concentrations of nitrate, nitrite, and ammonium were determined colorimetrically. After diluting the electrolyte to an appropriate concentration within the instrument calibration curve range, the ion concentration of the electrolyte after the reaction was measured using a UV-Vis spectrophotometer.

[0052] In this invention, there is an Ag4 core, and the periphery is Cu. 34The Ag4 core, with its flattened framework, can activate nitrate ions and contains electron-rich Cu sites, making it easier to donate electrons to reactants, stabilize reaction intermediates, prevent the formation of byproducts, optimize hydrogen adsorption energy, suppress the hydrogen evolution reaction (HER), and improve the selectivity of the target product. The surrounding Cu atoms form the flattened framework, with a large number of Cu atoms in low-coordination states. Low-coordination atoms typically possess higher intrinsic catalytic activity. Furthermore, the potential lattice mismatch between the Ag core and Cu shell introduces a strain effect, altering the d-band centers of the metal atoms and optimizing the adsorption energy for reaction intermediates.

[0053] Activated NO3 - It rapidly gains electrons and protons, loses an oxygen atom, and generates the key intermediate nitrite (NO2). - ), then NO2 - From the Ag site, which is primarily responsible for initial activation, to the Cu site, NO2 - As intermediates continuously gain electrons and protons, and undergo a series of reactions (such as generating NO, NHOH, etc.), the NO bond is eventually broken, forming an NH bond to generate the target product ammonia (NH3, NH4). + ).

[0054] Throughout the process, the adsorption energy of nitrogen-containing intermediates on the catalyst surface was optimized, and the reaction pathway was smooth, while nitrite (NO2) was suppressed. - The desorption and hydrogen evolution reaction (HER) of electrons allow electrons to be used efficiently for ammonia synthesis, resulting in a Faraday efficiency of up to 95%.

[0055] Regarding the [Ag4Cu] prepared above 34 (PET) 16 (PPh3)6] - TOA + The properties of the alloy nanoclusters were tested, and the specific process and results are as follows:

[0056] (1) Single-crystal X-ray diffraction data were recorded on a Rigaku XtaLabSynergy-R diffractometer equipped with a digital camera diffractometer, which included a microfocus rotating anode X-ray source (CuKα, λ=1.54178 Å) and a high-resolution detector [HyPix-6000C] for crystal structure analysis. Diffraction data were processed using CrysAlisPro during data acquisition. The structure was solved and refined during data acquisition using AutoChem. Final structure corrections were performed using SHELXT implemented in Olex2.

[0057] (2) X-ray photoelectron spectroscopy (XPS) measurements were performed using a monochromatic Al Kα (1486.8 eV) 150W X-ray source, a 0.5 mm circular spot size, a floodlight with reverse charging effect, and an S3 analysis chamber with a base voltage below 1×10⁻⁶. -9 The data were collected on a Thermo ESCALAB 250 at mbar; FAT = 20 eV. The sample holder was an aluminum plate used in X-ray photoelectron spectroscopy (XPS) analysis.

[0058] (3) The UV-Vis absorption spectra of the clusters were recorded using an M4 spectrophotometer. The samples were dissolved in dichloromethane solution, and background correction was performed using a dichloromethane blank sample.

[0059] (4) The photoluminescence spectrum was measured using an FL-7000 fluorescence spectrophotometer with the same optical density (OD) of ~0.02.

[0060] (5) Electrochemical measurements were performed on a CHI 660E electrochemical workstation (Shanghai Chenhua). Hydrophilic carbon paper coated with catalyst (TORAY), a silver chloride electrode, and platinum foil were used as the working electrode, reference electrode, and counter electrode, respectively. Electrochemical measurements were performed using this three-electrode system in an H-type cell separated by a proton exchange membrane. The working electrode area was 1 cm². 2 The cathode region contained 30 mL of 0.5 M K₂SO₄ solution. The anode region contained 30 mL of 0.5 M K₂SO₄ + 0.1 M KNO₃ solution. During the reaction, the electrolyte was stirred at 500 rpm. A linear sweep voltammetry method was used to stabilize the polarization curve before the electroreduction experiment. A constant potential test was performed for 1 hour at different applied potentials.

Claims

1. A silver-copper nanocluster, characterized in that: The molecular formula of the silver-copper nanoclusters is [Ag4Cu]. 34 (PET) 16 (PPh3)6] - TOA + PET is phenylethyl mercaptan, and PPh3 is triphenylphosphine.

2. The method for preparing the silver-copper nanoclusters according to claim 1, wherein the synthesis is performed by a one-pot method, characterized in that... Includes the following steps: Step 1: Dissolve tetra-n-octylammonium bromide in a dichloromethane solution; Step 2: Dissolve silver nitrate in methanol and add it to the solution from Step 1. A white flocculent precipitate will appear in the solution. Step 3: Add cuprous chloride powder to the system from Step 2; the solution turns gray. Step 4: Add triphenylphosphine to the system from step 3; the solution turns into a clear, blue-green solution. Step 5: Add phenylethyl mercaptan to the system from step 4; the solution turns orange-red. Step 6: Add sodium borohydride aqueous solution as a reducing agent to the system in step 5, and continue the reaction in the dark for 12 hours; Step 7: Separate the aqueous phase and the organic phase, evaporate the organic phase under reduced pressure, and wash the crude product with a large amount of methanol; Step 8: Dissolve the crude product in a dichloromethane solution, and finally perform liquid diffusion of n-hexane in the dichloromethane solution to obtain orange flaky crystals, which are the silver-copper nanoclusters [Ag4Cu]. 34 (PET) 16 (PPh3)6] - TOA + .

3. The preparation method according to claim 2, characterized in that: The molar ratio of silver nitrate to cuprous chloride is 1:3.

5.

4. The preparation method according to claim 2, characterized in that: The molar ratio of silver nitrate to triphenylphosphine is 1:

1.

5. The preparation method according to claim 2, characterized in that: The molar ratio of silver nitrate to phenylethyl mercaptan is 1:2.

5.

6. The preparation method according to claim 2, characterized in that: The molar ratio of silver nitrate to sodium borohydride is 1:

9.

7. The application of the silver-copper nanoclusters according to claim 1 in the electrocatalytic nitrate reduction reaction.

8. The application according to claim 7, characterized in that: A three-electrode system is adopted, with carbon fiber paper coated with the silver-copper nanoclusters as the working electrode, silver chloride electrode as the reference electrode, and platinum as the counter electrode. The cathode region and the anode region are separated by a proton exchange membrane. The electrolyte in the cathode region is a K2SO4 solution, and the electrolyte in the anode region is a mixed solution of K2SO4 and KNO3. The nitrate reduction reaction is catalyzed by constant potential electrolysis.

9. The application according to claim 8, characterized in that: The concentration of the K2SO4 solution in the cathode region is 0.5M; the concentration of K2SO4 in the mixed solution of K2SO4 and KNO3 in the anode region is 0.5M, and the concentration of KNO3 is 0.1M.

10. The application according to claim 8, characterized in that: Potential range: -0.6 to -2.1 V vs. RHE.

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