Preparation method and application of controllable Co-Cu bimetallic oxide nano-catalyst

Abstract

The invention discloses a preparation method of a controllable Co-Cu bimetallic oxide nano-catalyst, and the controllable Co-Cu bimetallic oxide nano-catalyst is applied to electro-catalysis, so that low-concentration nitrate pollutants in high-salinity wastewater can be efficiently removed. According to the preparation method, a constant-voltage electrodeposition method is utilized, the atomic-scale dispersed Co-Cu double-active-site catalyst is constructed on a foamed nickel substrate, and the prepared bimetallic Co-Cu active-site catalyst can remove low-concentration nitrate pollutants efficiently and highly selectively and is suitable for purification of nitrate wastewater with a wide pH range and different concentrations. The method is easy to operate, high in stability and good in electrocatalytic activity, and a reliable solution with practical application potential is provided for green low-carbon electrocatalytic purification of high-salt nitrate wastewater.

Description

Technical Field

[0001] This invention relates to a method for preparing a controllable Co-Cu bimetallic oxide nanocatalyst, and its application in treating low-concentration nitrate pollution, belonging to the field of pollutant treatment technology. Background Technology

[0002] The nitrogen cycle plays an irreplaceable role in maintaining ecosystem balance and biogeochemical processes. In modern agriculture, excessive application of chemical fertilizers, intensive livestock farming, and various human activities such as untreated wastewater discharge from industrial production lead to an increase in nitrate (NO3) levels. - Excessive accumulation of pollutants in water bodies has become one of the most prominent water environment problems.

[0003] Nitrate pollution not only easily leads to eutrophication of water bodies and damages aquatic ecosystems, but it can also be converted into carcinogenic nitrosamines over a long period of time. These substances can enter the human body through various pathways, induce methemoglobinemia, and directly threaten human health.

[0004] Currently, emerging electrocatalytic reduction technology can directly utilize electrical energy to efficiently reduce and purify nitrates in water. However, its application is severely limited by its complex cascade reaction process (specifically involving 8-electron / 9-proton transfer), slow electrode kinetics, and interference from the competitive hydrogen evolution reaction (HER).

[0005] How to achieve highly active, highly selective, and safe purification of low-concentration nitrates remains a key issue that urgently needs to be addressed in the field of pollutant treatment. Breakthroughs in this area will further promote the large-scale application of electrocatalysis technology in the treatment of high-salinity wastewater. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the primary technical problem to be solved by this invention is to provide a method for preparing a controllable Co-Cu bimetallic oxide nanocatalyst.

[0007] Another technical problem to be solved by the present invention is to provide an application of the cobalt-copper bimetallic oxide catalyst obtained by the above method in the electrocatalytic reduction of low-concentration nitrate pollution in high-salt water.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a controllable Co-Cu bimetallic oxide nanocatalyst includes the following steps:

[0010] S1: Under ultrasonic conditions, clean the foamed nickel sequentially with methanol, ethanol and pure water solvent, then vacuum dry and store for later use;

[0011] S2: Construct a three-electrode system, in which the pretreated nickel foam in step S1 is the working electrode, Ag / AgCl (3mol / L KCl) is the reference electrode, and platinum sheet Pt is the counter electrode. In 25mL of a mixed solution of cobalt nitrate (Co(NO3)2·6H2O) and copper nitrate (Cu(NO3)2·3H2O) of a certain concentration, constant potential electrodeposition is performed by chronoamperometry. After electrodeposition for a period of time, the working electrode is removed, washed, and dried to obtain the bimetallic oxide nanocatalyst precursor.

[0012] S3 calcined the prepared bimetallic oxide nanocatalyst precursor in a muffle furnace at high temperature, cooled, washed, and dried to obtain the Co-Cu bimetallic oxide catalyst.

[0013] Furthermore, in step S2, the concentration ratio of cobalt nitrate to copper nitrate is between 0.2 and 5;

[0014] Furthermore, in step S2, the applied voltage is -1.5 to 1.5V (vs. Ag / AgCl), and the electrodeposition time is 3 to 15 minutes.

[0015] Furthermore, in step S3, the calcination temperature is 200–500°C, and the calcination time is 1–5 hours.

[0016] Furthermore, the cobalt-copper bimetallic oxide catalyst obtained by the controllable preparation method of Co-Cu bimetallic oxide nanocatalysts.

[0017] Furthermore, the application of cobalt-copper bimetallic oxide catalysts in the electrocatalytic reduction of low-concentration nitrate pollution in high-salt water.

[0018] Furthermore, the nitrate concentration in high-salt water is between 50 and 1000 mg / L, and the chloride ion concentration is between 0.01 and 0.05 mol / L.

[0019] Compared with existing technologies, this invention provides a method for controllably preparing bimetallic active site electrocatalysts, simultaneously optimizing the dual pathways of nitrate adsorption and water splitting to achieve highly efficient and selective electrocatalytic reduction and purification of nitrates. This provides a green, low-carbon, efficient, safe, and low-cost new method for purifying low-concentration nitrate pollutants in high-salt wastewater. The preparation method provided by this invention is simple to operate, low in cost, and suitable for large-scale industrial production. Attached Figure Description

[0020] Figure 1 XRD patterns (10–40°) of Co-Cu / NF-1, Co3O4 / NF, and Cu2O / NF samples.

[0021] Figure 2XRD patterns (40–60°) of Co-Cu / NF-1, Co3O4 / NF, and Cu2O / NF samples.

[0022] Figure 3 XRD patterns (60–80°) of Co-Cu / NF-1, Co3O4 / NF, and Cu2O / NF samples.

[0023] Figure 4 This is a SEM image of the Co3O4 / NF sample.

[0024] Figure 5 This is a SEM image of the Cu2O / NF sample.

[0025] Figure 6 This is a SEM image of the Co-Cu / NF-1 sample.

[0026] Figure 7 Linear voltammetric scan curves of the properties of Co-Cu / NF-1, Co3O4 / NF, and Cu2O / NF samples. Detailed Implementation

[0027] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only used to illustrate the technical solution of the present invention and are not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are still within the protection scope of the present invention.

[0028] Inventive Principles

[0029] Existing traditional catalysts, relying on a single active site, struggle to simultaneously optimize the kinetics of multi-step reaction pathways. In contrast, dual-active-site catalysts, through atomically precise metal pairing, directionally regulate electronic structure, optimize the adsorption energy of reaction intermediates, suppress side reactions, and promote the selective formation of the target product (N2). The electrocatalytic system provided in this invention exhibits high activity, high stability, and high selectivity in N2 formation, making it a core direction for advancing green remediation technologies for nitrate pollution. It is noteworthy that Cl- is prevalent in high-salinity waters. - The distribution of reaction products can be adjusted through redox reactions, which can significantly improve N2 selectivity. This provides a feasibility for in-situ remediation of nitrate pollution in high-salt water bodies.

[0030] Generally, precise control of the d-band center of relative transition metals requires optimization of key intermediates (such as *NO3-, *NO2). - The adsorption energy of *N) dominates the pathway and selectivity of the nitrate reduction reaction (NO3RR). This invention designs a Co-Cu dual-active-site catalyst, utilizing Cu sites to adsorb and drive NO3.- Converted to NO2 - And the Cu site is related to NO2 - The weak adsorption of the copper ions facilitates their desorption and migration to nearby Co sites to complete subsequent deoxygenation and hydrogenation reactions. The Co sites possess excellent H₂O dissociation capabilities, providing a large amount of active hydrogen for the reaction; the synergistic effect of the Co-Cu dual sites achieves a highly efficient hydrogenation and deoxygenation process. Simultaneously with the above reactions, chloride ions are oxidized at the anode to form hypochlorous acid (HClO), ClO₂. - Ions can reduce NO3 - The NH4 formed by the conversion + It is oxidized to N2, forming a closed-loop denitrification pathway that reduces nitrate to N2.

[0031] Example 1: Preparation of Co3O4 / NF catalyst

[0032] S1: Place a 1cm×1cm nickel foam (NF) substrate in methanol, ethanol and deionized water for ultrasonic cleaning for 15 minutes each to remove surface organic contaminants, and then vacuum dry at 60°C for later use.

[0033] S2: Three-electrode system setup: Working electrode was pretreated nickel foam (NF) from S1; reference electrode was Ag / AgCl (3 mol / L KCl); counter electrode was a platinum sheet. Electrodeposition was performed for 10 minutes at a constant potential of -1.0 V (vs. Ag / AgCl) using chronoamperometry in 25 mL of 30 mmol / L Co(NO3)2·6H2O electrolyte.

[0034] S3: Remove the working electrode (nickel foam (NF)), rinse it three times alternately with deionized water and ethanol, and dry it under vacuum at 60°C. A light blue Co(OH)2 / NF flocculent precipitate was observed on the surface of the nickel foam (NF).

[0035] S4: Place the light blue Co(OH)2 / NF in a muffle furnace and heat it to 300°C at 1°C / min in air atmosphere. Then calcine it at a constant temperature for 3 hours, and then let it cool naturally. Clean it with deionized water by ultrasound (3 times, 10 minutes each time), and then dry it under vacuum at 60°C to finally obtain the cobalt metal oxide catalyst.

[0036] The product here is labeled Co3O4 / NF.

[0037] Example 2: Preparation of Cu2O / NF catalyst

[0038] Prepared using the same method as in Example 1; the difference is that the three-electrode system uses Cu(NO3)2·3H2O as the electrolyte solution, and the other reactants and operating steps are the same. The final product here is labeled as Cu2O / NF.

[0039] The final product was a light pink Cu2O / NF catalyst observed on the surface of nickel foam (NF).

[0040] Example 3: Preparation of Co-Cu / NF bimetallic site catalyst

[0041] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 1; the difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution in a volume ratio of 1:1. All other reactants and operating steps were the same. The final product was labeled Co-Cu / NF-1.

[0042] The final product is a light gray Co-Cu / NF bimetallic site catalyst observed on the surface of nickel foam (NF).

[0043] Example 4: Preparation of Co-Cu / NF bimetallic site catalyst

[0044] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution in a volume ratio of 1:2. All other reactants and operating procedures were the same. The final product was labeled Co-Cu / NF-2.

[0045] Example 5: Preparation of Co-Cu / NF bimetallic site catalyst

[0046] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution, with a volume ratio of 2:1. All other reactants and operating procedures were the same. The final product was labeled Co-Cu / NF-3.

[0047] Example 6: Preparation of Co-Cu / NF bimetallic site catalyst

[0048] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution, with a volume ratio of 4:1, and the electrodeposition time was 15 minutes. All other reactants and operating procedures were the same. The final product was labeled Co-Cu / NF-4.

[0049] Example 7: Preparation of Co-Cu / NF bimetallic site catalyst

[0050] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution, with a volume ratio of 1:4, and the electrodeposition time was 3 minutes. All other reactants and operating procedures were the same. The final product was labeled Co-Cu / NF-5.

[0051] Example 8: Preparation of Co-Cu / NF bimetallic site catalyst

[0052] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution, with a volume ratio of 1:3. The electrodeposition time was 8 minutes, and the temperature was increased to 500°C at 1°C / min under air atmosphere, followed by isothermal calcination for 1 hour.

[0053] All other reactants and procedures are the same, and the final product here is labeled Co-Cu / NF-6.

[0054] Example 9: Preparation of Co-Cu / NF bimetallic site catalyst

[0055] The Co-Cu / NF bimetallic site catalyst was prepared using the same method as in Example 3. The difference was that a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O was used as the electrolyte solution, with a volume ratio of 3:1. The electrodeposition time was 15 minutes, and the temperature was increased to 200°C at 1°C / min under air atmosphere, followed by isothermal calcination for 5 hours.

[0056] All other reactants and procedures are the same, and the final product here is labeled Co-Cu / NF-7.

[0057] Example 10: Electrocatalytic nitrate performance test

[0058] Electrochemical tests were performed using a CHI 660 electrochemical workstation: a 1cm × 1cm Co-Cu / NF-1 bimetallic site catalyst was used as the working electrode, a 1cm × 1cm platinum sheet electrode as the counter electrode, and a saturated calomel electrode as the reference electrode. The electrolyte consisted of 0.1 mol / L K₂SO₄ and 140 mg / L NO₃⁻. --N and 0.03 mol / L KCl solution.

[0059] Before each measurement, high-purity argon gas (99.999%) was purged into the electrolyte for 30 minutes to remove dissolved oxygen. Linear scanning voltammetry curves were tested at a scan rate of 10 mV / s under a stirring rate of 500 rpm. Then, a constant potential test was performed for 4 hours. Finally, NO3 in the electrolyte after the test was detected using ultraviolet-visible spectrophotometry. - -N, NO2 - -N,NH4 + -N.

[0060] NO3 - Removal rate c(NO3) - The selectivity s(N2) of N2 and N2 is calculated as follows:

[0061] NO3 - Removal rate c(NO3) - )% = (C0(NO3) - -N)-C t (NO3 - -N)) / C0(NO3 - -N)×100%;

[0062] The selectivity of N2 is s(N2)% = (C0(NO3) - -N)-C t (NO3 - -N)-C t (NO2 - -N)-C t (NH4 + -N) /

[0063] (C0(NO3 - -N)-C t (NO3 - -N))

[0064] In the above formula, C0(NO3) - -N): Initial NO3 in the reaction system - -N concentration (mg / L);

[0065] C t (NO3 - -N): NO3 in the reaction system after reaction time t. - -N concentration (mg / L);

[0066] C t (NO2 - -N): NO2 in the reaction system after reaction time t. --N concentration (mg / L);

[0067] C t (NH4 + -N): NH4 in the reaction system after reaction time t. + -N concentration (mg / L).

[0068] Figures 1-3 The X-ray diffraction (XRD) results show the phase structures of the catalysts prepared in Examples 1 to 3. The diffraction peaks of Co3O4 / NF and Cu2O / NF are consistent with those of Co3O4 (PDF#42-1467) and Cu2O (PDF#03-0898), respectively. Furthermore, diffraction peaks of elemental Cu (PDF#01-1241) were also observed in Cu2O / NF. The XRD pattern of the co-deposited Co-Cu / NF matches well with that of CuCo2O4 (PDF#01-1155).

[0069] Figures 4-6 The scanning electron microscope (SEM) images show the catalysts prepared in Examples 1 through 3. Co3O4 / NF exhibits a loose, porous structure composed of interlocking nanosheets that support each other, forming abundant open channels and a large specific surface area. Cu2O / NF exhibits a uniform and well-dispersed spherical particle morphology. The particle surface has a fine, rough texture, exhibiting a unique "orange peel" morphology, with a relatively uniform particle size distribution and tight packing between particles. The morphology of Co-Cu / NF-1 material differs from both Co3O4 / NF and Cu2O / NF, showing the influence of a bimetallic synergistic effect. The coexistence of Co and Cu alters the crystal growth habit of single metals; its main body consists of spherical particles, but the surface is covered and modified by finer, disordered nanosheets or nanoparticles, forming a rougher, more complex hierarchical structure. This composite microsphere, with its spherical structure as a base, ensures the mechanical strength of the material, while the nanosheet modification on the surface greatly increases the specific surface area and the number of active sites, achieving both high specific surface area and good mass transfer capacity. Cu sites, acting as efficient "activation centers," excel at adsorbing and initially reducing nitrate ions; while adjacent Co sites, acting as "deep reduction centers," tend to further convert intermediate products into N2. Ultimately, this enables the Co-Cu / NF-1 composite material to simultaneously achieve high nitrate removal rates and excellent nitrogen selectivity.

[0070] Figure 7 The linear sweep voltammetry curves shown indicate that the Co-Cu / NF bimetallic site catalyst exhibits the optimal current density. Compared to nitrate-free electrolytes, the addition of nitrate significantly enhances the current density of Co-Cu / NF, demonstrating its excellent nitrate reduction reactivity. Generally, the Cu sites adsorb NO3.- And convert it into NO2 - The Co sites decompose water to produce a large amount of active hydrogen. This dual-active microstructure effectively optimizes the adsorption energy of reaction intermediates on the catalyst surface, lowers the energy barrier of each reaction step, and thus not only significantly increases the current density, but also further guides the reaction to generate NH4. + In ClO - Under oxidation, N2 is generated, thus achieving NO3. - High conversion rate and high selectivity of N2.

[0071] The catalyst products prepared in Examples 1-5 were evaluated for their nitrate removal performance using a chronoamperometry method, mainly comparing the nitrate nitrogen removal rate and N2 selectivity, as shown in Table 1: Electrocatalytic reduction of NO3 by each catalyst. - The performance test results of N2 are shown.

[0072] Table 1 Electrocatalytic reduction of NO3 by various catalysts - Performance test results

[0073] catalyst <![CDATA[Nitrate concentration (mg L -1 )]]> <![CDATA[NO3 - -N removal rate]]> <![CDATA[N2 selectivity]]> <![CDATA[Co3O4 / NF]]> 140 76％ 92％ <![CDATA[Cu2O / NF]]> 140 92％ 58％ Co-Cu / NF-1 140 98％ 99％ Co-Cu / NF-2 140 88％ 67％ Co-Cu / NF-3 140 85％ 79％ Co-Cu / NF-4 140 81％ 88％ Co-Cu / NF-5 140 91％ 60％ Co-Cu / NF-6 140 93％ 58％ Co-Cu / NF-7 140 77％ 90％ FeCo-NPCNFs 100 79％ 85％ FeNi / g-mesoC / NF 50 71％ 29％ CL-Fe@C 100 54％ 98％ PdCu NCs-NOMC 100 90％ 60％ MCS / CNTs 100 75％ 99％

[0074] Table 2. Electrocatalytic removal of NO3 at different concentrations using Co-Cu / NF-1 - Performance test results

[0075]

[0076]

[0077] Based on the results of the electrocatalytic reduction of nitrate to produce nitrogen gas shown in Tables 1 and 2, it can be seen that the controllable bimetallic oxide nanocatalyst prepared in this invention, when applied to the electrocatalytic reduction of nitrate, can efficiently remove low-concentration nitrate pollution and NO3 from high-salt wastewater. - -N removal efficiency reaches up to 98%, with selectivity maintained at 99%. Therefore, it is particularly suitable for electrocatalytic nitrate reduction, and can efficiently remove low-concentration nitrate pollution from high-salt wastewater.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a controllable Co-Cu bimetallic oxide nanocatalyst, characterized in that... Includes the following steps: S1: The nickel foam substrate was sequentially ultrasonically cleaned in methanol, ethanol and deionized water to remove surface organic contaminants, and then vacuum dried for later use. S2: Construct a three-electrode system: The working electrode is the foamed nickel pretreated in step S1; the reference electrode is Ag / AgCl (3 mol / L KCl); the counter electrode is a platinum sheet; electrodeposition is performed using a chronoamperometry method at a constant potential of -1.0 V (vs. Ag / AgCl) in a mixed electrolyte solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O. S3: Remove the working electrode nickel foam, rinse with deionized water and ethanol, and vacuum dry to obtain flocculent precipitate on the surface of the nickel foam; S4: Nickel foam with flocculent precipitate was placed in a muffle furnace and calcined in air atmosphere. After natural cooling, it was ultrasonically cleaned with deionized water and then dried under vacuum to finally obtain the Co-Cu / NF bimetallic site catalyst.

2. The preparation method and application of the controllable Co-Cu bimetallic oxide nanocatalyst as described in claim 1, characterized in that: In step S2, the electrolyte solution is a mixed solution of 30 mmol / L Co(NO3)2·6H2O and 30 mmol / L Cu(NO3)2·3H2O, with a volume ratio between 0.2 and 5.

3. The method for preparing the controllable Co-Cu bimetallic oxide nanocatalyst as described in claim 1, characterized in that: In step S2, the applied voltage is -1.5 to 1.5V (vs. Ag / AgCl), and the electrodeposition time is 3 to 15 minutes.

4. The method for preparing the controllable Co-Cu bimetallic oxide nanocatalyst as described in claim 1, characterized in that: In step S3, the calcination temperature is 200–500°C and the calcination time is 1–5 hours.

5. The cobalt-copper bimetallic oxide catalyst obtained by the method for preparing controllable Co-Cu bimetallic oxide nanocatalyst according to any one of claims 1 to 4.

6. The application of the cobalt-copper bimetallic oxide catalyst as described in claim 5 in the electrocatalytic reduction of low-concentration nitrate pollution in high-salt water.

7. The application of the cobalt-copper bimetallic oxide catalyst as described in claim 6 in the electrocatalytic reduction of nitrate, characterized in that: The nitrate concentration in high-salt water bodies is between 50 and 1000 mg / L, and the chloride ion concentration is between 0.01 and 0.05 mol / L.

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