A biomimetic egg yolk shell structure CuO@Co3O4 nano reactor, a preparation method and application

Abstract

The application belongs to the technical field of nanometer material preparation, and discloses a biomimetic yolk-shell structure CuO@Co3O4 nano reactor, a preparation method and application. Copper salt and cobalt salt are dissolved in a system containing an organic solvent, uniformly mixed, and then a metal organic precursor with a yolk-shell structure is obtained through a solvothermal reaction. Then, the precursor is calcined in an air atmosphere to obtain a biomimetic yolk-shell structure CuO@Co3O4 nano reactor with spatially separated active sites. The biomimetic yolk-shell structure CuO@Co3O4 nano reactor can be used as a catalyst in the electrochemical reduction of nitrate to synthesize ammonia.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, and relates to a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor, its preparation method and application. Background Technology

[0002] Ammonia (NH3) is an important chemical raw material and a potential clean energy carrier, widely used in agriculture and the energy sector. Currently, the Haber-Bosch process is the main industrial method for ammonia synthesis; however, this method requires high temperature and pressure conditions, resulting in high energy consumption and significant carbon emissions, which is detrimental to sustainable development. Therefore, developing green and efficient alternative ammonia production technologies is of great importance.

[0003] Electrochemical nitrate reduction reaction (NO3RR) has attracted widespread attention in recent years. This method can convert nitrates into ammonia under ambient temperature and pressure conditions, while simultaneously realizing the resource utilization of nitrate-containing wastewater. However, this reaction involves multi-electron and multi-proton transfer processes, resulting in a complex reaction pathway and slow kinetics, especially for NO3. - To NO2 - and NO2 - There is a significant kinetic mismatch between the two key steps of further reduction to NH3, which easily leads to the accumulation of intermediate products and the occurrence of side reactions, thereby reducing the selectivity of ammonia.

[0004] Existing research often improves reaction performance by controlling catalyst composition or constructing bimetallic systems, such as introducing multiple metals to achieve a staged tandem catalytic process. Adv. Energy Mater. ,2024, 14, 2401834; Nat. Commun. ,2022, 13, 1129; Adv. Mater. ,2025, 37, 2503291; Small ,2025, 21, e06256), or construct an interface structure to achieve tandem catalysis ( Angew. Chem., Int. Ed. ,2023, 62, e202303327; Angew. Chem., Int. Ed. (2020, 59, 5350-5354). However, most of the above methods are difficult to achieve effective spatial separation of different reaction steps, resulting in insufficient synergy between the reaction processes and making it difficult to fundamentally solve the problem of kinetic mismatch.

[0005] The natural dissimilatory reduction of nitrate to ammonia (DNRA) process provides important insights into this problem. In this process, the reduction of nitrate and nitrite is catalyzed by different enzymes in different regions of the cell, thus achieving efficient cascading and precise control of multi-step reactions. This "spatial separation + functional synergy" catalytic mode helps to avoid intermediate diffusion losses and optimize reaction kinetics. Meanwhile, constructing biomimetic catalytic materials with spatially separated active sites has become an important research direction in recent years. Among them, core-shell nanoreactors, due to their unique hollow structure and tunable internal and external interfaces, are considered ideal platforms for realizing multi-step cascade catalysis. This type of structure not only provides confined reaction space but also promotes the transport of reactants and intermediates through the porous structure of the shell, thereby improving catalytic efficiency. Based on this, referencing the DNRA process and constructing biomimetic catalytic materials with spatially separated active sites holds promise for controlling the reaction pathway and matching kinetics, thereby improving the performance of electrochemical nitrate reduction to ammonia.

[0006] This invention transforms a metal-organic complex precursor into an oxide nanoreactor with an egg yolk shell structure through a one-step calcination process. The spontaneously formed cell-like biomimetic structure during the hydrothermal process provides a confined space for different reaction steps, compensating for the lack of synergy between series reaction processes. This results in a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor electrocatalytic material, which has important reference value for the development of electrocatalytic nitrate reduction catalysts. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing and applying a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor.

[0008] The technical solution of the present invention: A biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor has a cellular egg yolk shell structure, in which Co3O4 is mainly enriched on the outer shell and CuO is confined in the core.

[0009] A method for preparing a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor involves mixing a metal salt solution with an organic ligand, obtaining a CuCo precursor via a hydrothermal method, and then performing a one-step calcination to obtain the biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor (CuO@Co3O4-x). The steps are as follows: (1) Dissolve the organic ligand in isopropanol and sonicate until the solution becomes clear and transparent. Then add the metal salts of Cu and Co to the solution. The mass ratio of the organic ligand to isopropanol is 1:5-1:10, the concentration of the metal salt in isopropanol is 0.025-0.05 mol / L, and the molar ratio of the metal salt of Cu to the metal salt of Co is 1:1-4:1. Then transfer the solution to a hydrothermal reactor and heat it at 100-180 °C for 2-8 hours. After the reaction, wash the product with ethanol several times and dry it to obtain the CuCo precursor. (2) The CuCo precursor was placed in a muffle furnace and calcined at 300~500℃ for 60~180 minutes to obtain a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor (CuO@Co3O4-x). The organic ligand is phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, L-aspartic acid, glycerol, or fumaric acid. The metal salt is a nitrate, chloride, or acetate.

[0010] In step (1), the drying temperature is 50~80℃ and the drying time is 8~24 hours.

[0011] In step (2), the heating rate is 2~5℃ / min.

[0012] The application of a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor in the electrocatalytic reduction of nitrate to ammonia reaction includes the following steps: (1) The biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor was added to water, isopropanol and Nafion in a volume ratio of 50:50:3 and mixed evenly to prepare ink; the ink was evenly coated on carbon paper and dried at room temperature to prepare electrode; (2) The electrodes were placed in the electrolytic cell, with a platinum sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and 1 M KOH and 0.1 M KNO3 as the electrolyte. The electrochemical workstation was used for testing. (3) The ammonia content in the electrolyte was determined by the indophenol blue method; then the amount of indophenol blue generated was quantitatively determined by measuring the absorbance at a wavelength of 655 nm; the method was absolutely calibrated by using a series of ammonium chloride solutions of known concentrations as reference standards; then the ammonia yield was determined according to the standard curve.

[0013] The beneficial effects of this invention are as follows: The CuO@Co3O4-x nanoreactor prepared by this invention exhibits a cell-inspired egg yolk shell structure, and the spatially separated active sites enable better kinetic matching characteristics in the tandem catalytic process. When used as a catalyst, it exhibits good electrocatalytic activity under alkaline conditions. Furthermore, the preparation method is simple, the raw materials are readily available, and it has high practical value, which is of great significance for the design, preparation, and application of catalysts. Attached Figure Description

[0014] Figure 1 This is a scanning electron microscope image of the CuCo-np-2-180 precursor prepared in Example 1.

[0015] Figure 2 This is a scanning electron microscope image of the CuO@Co3O4-2-180 nanoreactor prepared in Example 1.

[0016] Figure 3 The images show transmission electron microscopy (STEM) energy-dispersive X-ray (EDX) elemental mapping images of the CuO@Co3O4-2-180 nanoreactor prepared in Example 1; where (a) is a STEM image of the CuO@Co3O4-2-180 nanoreactor; (b) is the elemental distribution of Cu; (c) is the elemental distribution of Co; and (d) is the elemental distribution of O.

[0017] Figure 4 X-ray diffraction (XRD) tests were performed on the CuO-180, CuO@Co3O4-2-180, and Co3O4-180 nanoreactors prepared in Examples 1-3.

[0018] Figure 5 The image shows a scanning electron microscope (SEM) image of the CuO-N-180 nanomaterials prepared in Comparative Example 3.

[0019] Figure 6 The nitrate reduction catalytic performance of CuO@Co3O4-2-180, CuO-180 and Co3O4-180 tested in Application Example 1 is shown.

[0020] Figure 7 The nitrate reduction catalytic performance of CuO@Co3O4-4-180, CuO@Co3O4-2-180 and CuO@Co3O4-1-180 tested in Application Example 1 is shown. Detailed Implementation

[0021] The specific implementation schemes of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0022] Example 1 Preparation of CuO@Co3O4-2-180 nanoreactor; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 0.5 mmol (145.5 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. The powdered precursor was then dried overnight at 60 °C and named CuCo-np-2-180.

[0023] CuCo-np-2-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The heating rate was maintained at 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO@Co3O4-2-180.

[0024] Transmission electron microscopy (STEM) energy-dispersive X-ray (EDX) elemental mapping image of the CuO@Co3O4-2-180 nanoreactor.

[0025] Figure 3 The elemental distribution image of the CuO@Co3O4-2-180 nanoreactor shows that cobalt is mainly enriched in the outer shell, while copper is confined to the core. The cellular structure indicates that the sample has spatially separated active phases, demonstrating the formation of confined reaction spaces.

[0026] Example 2 Preparation of CuO@Co3O4-4-180 nanoreactor; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 0.25 mmol (72.8 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named CuCo-np-4-180.

[0027] CuCo-np-4-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The heating rate was maintained at 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO@Co3O4-4-180.

[0028] Example 3 Preparation of CuO@Co3O4-1-180 nanoreactor; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 1 mmol (291 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named CuCo-np-1-180.

[0029] CuCo-np-1-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO@Co3O4-1-180.

[0030] X-ray diffraction (XRD) analysis of CuO-180, CuO@Co3O4-2-180, and Co3O4-180 nanomaterials.

[0031] Characterized by XRD, such as Figure 4 As shown, the CuO@Co3O4-2-180 nanoreactor exhibits two independent phases of CuO and Co3O4, further confirming the phase-separated structural characteristics of the nanoreactor.

[0032] Example 4 Preparation of CuO@Co3O4-2-160 nanoreactor; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 0.5 mmol (145.5 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 160 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. The powdered precursor was then dried overnight at 60 °C and named CuCo-np-2-160.

[0033] CuCo-np-2-160 (200 mg) was heated at 500 °C for 5 °C·min. -1The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO@Co3O4-2-160.

[0034] Example 5 Preparation of CuO@Co3O4-2-140 nanoreactor; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 0.5 mmol (145.5 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 140 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. The powdered precursor was then dried overnight at 60 °C and named CuCo-np-2-140.

[0035] CuCo-np-2-140 (200 mg) was heated at 500 °C for 5 °C·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO@Co3O4-2-140.

[0036] Example 6 Preparation of CuO / Co3O4-T-2-180 nanoreactor; First, 400 mg of trimesic acid was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) of Cu(NO3)2·3H2O and 0.5 mmol (145.5 mg) of Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named CuCo-BTC-2-180.

[0037] CuCo-BTC-2-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The heating rate was maintained at 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO / Co3O4-T-2-180.

[0038] Example 7 Preparation of CuO / Co3O4-D-2-180 nanoreactors; First, 400 mg of isophthalic acid was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) Cu(NO3)2·3H2O and 0.5 mmol (145.5 mg) Co(NO3)2·6H2O were added to the solution, and the mixture was sonicated until the solution became clear and transparent. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named CuCo-BDC-2-180.

[0039] CuCo-BDC-2-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The heating rate was maintained at 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO / Co3O4-D-2-180.

[0040] Comparative Example 1 Preparation of CuO-180 nanomaterials; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) of Cu(NO3)2·3H2O was added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named Cu-np-180.

[0041] Cu-np-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO-180.

[0042] Comparative Example 2 Preparation of Co3O4-180 nanomaterials; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (291 mg) of Co(NO3)2·6H2O was added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named Co-np-180.

[0043] Co-np-180 (200 mg) was heated at 500℃ for 5℃·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named Co3O4-180.

[0044] Comparative Example 3 Preparation of CuO-N-180 nanomaterials; First, 400 mg of diaminoterephthalic acid was dissolved in 40 mL of isopropanol. Then, 1 mmol (241.6 mg) of Cu(NO3)2·3H2O was added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named Cu-BDC-NH2-180.

[0045] Cu-BDC-NH2-180 (200 mg) was heated at 500℃ for 5 °C·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named CuO-N-180.

[0046] Figure 5 The scanning electron microscope morphology of CuO-N-180 was shown, exhibiting an irregular morphology and not showing a unique nanoreactor structure similar to that of Example 1.

[0047] Comparative Example 4 Preparation of NiO-180 nanomaterials; First, 4 mL of glycerol was dissolved in 40 mL of isopropanol. Then, 1 mmol (291 mg) of Ni(NO3)2·6H2O was added to the solution, and the mixture was sonicated until the solution became clear. The solution was then transferred to a hydrothermal reactor and heated at 180 °C for 6 hours. After cooling, the product was separated by centrifugation at 10,000 rpm for 4 minutes. The product was washed several times with ethanol and water. Subsequently, the powdered precursor was dried overnight at 60 °C and named Ni-np-180.

[0048] Ni-np-180 (200 mg) was heated at 500 °C for 5 °C·min. -1 The temperature was increased at a rate of 20°C, and the mixture was calcined in a muffle furnace for 2 hours. The resulting black solid powder was named NiO-180.

[0049] Figure 5The scanning electron microscopy morphology of Comparative Example 3 shows that the unique nanoreactor structure formed in this invention cannot be produced without the use of the metal salt or ligand mentioned in this invention. Similarly, Comparative Example 4 demonstrates that the unique nanoreactor structure of this invention is formed through the combined action of CuCo bimetal and the ligand glycerol.

[0050] Application Example 1 Catalytic performance tests were conducted on the CuO-180 prepared in Comparative Example 1, CuO@Co3O4-4-180 prepared in Example 2, CuO@Co3O4-2-180 prepared in Example 1, CuO@Co3O4-1-180 prepared in Example 3, and Co3O4-180 nanomaterials prepared in Comparative Example 2.

[0051] The working electrode was prepared as follows: 5 mg of the catalyst prepared in Examples 1-3 and Comparative Examples 1-2 was weighed into a 2 mL centrifuge tube, followed by 250 μL each of H2O and isopropanol, and finally 15 μL of Nafion solution. After mixing thoroughly, the mixture was sonicated for 20 min. 10 μL of the prepared ink was evenly coated onto 0.25 cm × 0.25 cm carbon paper and dried at room temperature. The prepared electrode was placed in an electrolytic cell, with a platinum sheet as the counter electrode, an Ag / AgCl electrode as the reference electrode, and 1 M KOH + 0.1 MKNO3 as the electrolyte. It was tested using an electrochemical workstation, and quantitative analysis was performed using the indophenol blue method for color development.

[0052] like Figure 6 As shown in the graphs, the yield and Faradaic efficiency of ammonia synthesis using CuO-180, CuO@Co3O4-2-180, and Co3O4-180 nanoreactors at a potential of -0.4 V (relative to the reversible hydrogen electrode) can be observed. The yield and Faradaic efficiency of ammonia synthesis using the CuO@Co3O4-2-180 nanoreactor are 44.3 ± 0.6 mg·h⁻¹. -1 ·mg -1 cat The content of 94.8 ± 1.3% is significantly higher than that of pure CuO-180 and Co3O4-180 nanomaterials.

[0053] Figure 7 The catalytic performance comparison charts for different metal salt ratios in the CuO@Co3O4-x nanoreactors obtained in Examples 1-3 are shown. It was tested at -0.4 V (relative to the reversible hydrogen electrode) and quantitatively analyzed using the indophenol blue method. The yield and Faraday efficiency were optimal when the CuCo metal salt was added at a ratio of 2:1.

Claims

1. A biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor, characterized in that, This eggshell-structured CuO@Co3O4 nanoreactor possesses a cell-like confined structure and catalytic function, with Co3O4 mainly enriched on the outer shell and CuO confined within the core.

2. A method for preparing a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor, characterized in that, A CuCo precursor was obtained via hydrothermal method by mixing a metal salt solution with an organic ligand, followed by a one-step calcination process to obtain a biomimetic egg yolk shell structured CuO@Co3O4 nanoreactor; the steps are as follows: (1) Dissolve the organic ligand in isopropanol and sonicate until the solution becomes clear and transparent. Then add the metal salts of Cu and Co to the solution. The mass ratio of the organic ligand to isopropanol is 1:5-1:10, the concentration of the metal salt in isopropanol is 0.025-0.05 mol / L, and the molar ratio of the metal salt of Cu to the metal salt of Co is 1:1-4:

1. Then transfer the solution to a hydrothermal reactor and heat it at 100-180 °C for 2-8 hours. After the reaction, wash the product with ethanol several times and dry it to obtain the CuCo precursor. (2) The CuCo precursor was placed in a muffle furnace and calcined at 300~500℃ for 60~180 minutes to obtain a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor.

3. The preparation method according to claim 2, characterized in that, The organic ligand is phthalic acid, isophthalic acid, terephthalic acid, pyromellitic acid, L-aspartic acid, glycerol, or fumaric acid.

4. The preparation method according to claim 2, characterized in that, The metal salt is a nitrate, chloride, or acetate.

5. The preparation method according to claim 2, characterized in that, In step (1), the drying temperature is 50~80℃ and the drying time is 8~24 hours.

6. The preparation method according to claim 2, characterized in that, In step (2), the heating rate is 2~5℃ / min.

7. Application of a biomimetic egg yolk shell structure CuO@Co3O4 nanoreactor in the electrocatalytic reduction of nitrate to ammonia.

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