Self-supporting nanowire array electrode and preparation method and application thereof

Abstract

The invention provides a self-supporting nanowire array electrode and a preparation method and application thereof.The self-supporting nanowire array electrode comprises a foamy copper substrate and a cuprous oxide / copper nanowire array formed on the surface of the foamy copper substrate in situ, and palladium nanoparticles supported on the array by a replacement reaction with cuprous oxide / copper.

Description

Technical Field

[0001] The present disclosure relates to the technical field of the preparation of nano- and sub-nano materials, and particularly to a self-supporting nanowire array electrode and its preparation method and application, and more specifically to a self-supporting palladium-dispersed cuprous oxide / copper nanowire array electrode and its preparation method, and its application in the electrocatalytic nitrate denitrification reaction. Background Art

[0002] With the rapid development of industrialization and agricultural modernization, nitrate (NO3 - ) pollution has become a global environmental problem, seriously threatening the safety of water environment and public health. Among various nitrate treatment technologies, electrochemical reduction of nitrate (eNO3RR) is regarded as a highly potential green water treatment technology with significant advantages such as mild operating conditions and no secondary pollution, and has become a current research hotspot.

[0003] However, the electrochemical reduction technology faces many technical problems in practical applications. In terms of catalytic efficiency, for the treatment of low-concentration nitrate wastewater, traditional copper-based catalysts have low nitrate reduction efficiency due to mass transfer limitations and the influence of competitive hydrogen evolution reaction (HER), making it difficult to meet the actual treatment requirements. In terms of product selectivity, during the electrocatalytic reaction process, the selectivity of nitrogen is poor, and by-products such as nitrite and ammonia are easily generated, which not only affects the denitrification effect but also may bring new pollution risks. In addition, existing electrodes are prone to inactivation during long-term operation due to reasons such as structural changes and loss of active components, increasing the equipment maintenance cost and operation difficulty. Moreover, the energy consumption of existing electrochemical low-concentration denitrification systems is generally higher than 200 kWh kg -1 N, and the high energy consumption cost greatly limits the large-scale popularization and application of this technology.

[0004] Therefore, developing a new type of electrode with high efficiency, high selectivity, low energy consumption and stability to achieve efficient reduction of nitrate has become a technical problem to be solved urgently at present. Summary of the Invention

[0005] In view of this, the main purpose of the present disclosure is to provide a self-supporting nanowire array electrode and its preparation method and application, in order to at least partially solve at least one of the above-mentioned technical problems.

[0006] To achieve the above purpose, the technical solution of the present disclosure is as follows:

[0007] In one aspect of the present disclosure, a self-supporting nanowire array electrode is provided, including:

[0008] A copper foam substrate, a cuprous oxide / copper nanowire array formed in-situ on the surface of the copper foam substrate, and palladium nanoparticles loaded on the array by a displacement reaction with cuprous oxide / copper.

[0009] In another aspect of the present disclosure, a method for preparing the above-mentioned self-supporting nanowire array electrode is provided, including:

[0010] By means of electrochemical oxidation, calcination and electrochemical reduction treatments, cuprous oxide / copper nanowire arrays are in-situ formed on the surface of copper foam to obtain copper foam with cuprous oxide / copper nanowire arrays;

[0011] The copper foam with cuprous oxide / copper nanowire arrays is subjected to a displacement reaction in a 2 mM - 20 mM soluble palladium salt solution for 3 - 18 h to load palladium nanoparticles on the cuprous oxide / copper nanowire arrays, thereby forming a self-supporting palladium-dispersed cuprous oxide / copper nanowire array electrode.

[0012] In still another aspect of the present disclosure, an application of the above-mentioned self-supporting nanowire array electrode in the electrocatalytic nitrate denitrification reaction is provided.

[0013] According to an embodiment of the present disclosure, a self-supporting nanowire array electrode is provided. Using copper foam as a substrate, cuprous oxide / copper nanowire arrays are in-situ grown on its surface to construct a stable three-dimensional nanowire array structure, which can effectively increase the electrochemical active area of the electrode and expose more active sites, thereby enhancing the adsorption and activation ability of the electrode for nitrates. In addition, palladium nanoparticles are in-situ introduced on the electrode surface through a displacement reaction. The palladium nanoparticles and the cuprous oxide / copper nanowire arrays produce a synergistic effect, jointly optimizing the electronic structure of the electrode surface, significantly enhancing the charge transfer efficiency of the catalytic electrode surface, and thus greatly improving the catalytic performance of the electrode in the electrocatalytic reaction. Description of the Drawings

[0014] Figure 1 It is a scanning electron microscope image of the self-supporting nanowire array electrode in Example 1 of the present disclosure;

[0015] Figure 2 It is a transmission electron microscope image of the self-supporting nanowire array electrode in Example 1 of the present disclosure;

[0016] Figure 3 It is an energy dispersive spectroscopy - elemental distribution map of the self-supporting nanowire array electrode in Example 1 of the present disclosure;

[0017] Figure 4 It is an X-ray diffraction pattern of the electrodes in Examples 1 - 2 and Comparative Examples 1 - 2 of the present disclosure;

[0018] Figure 5 It is a Raman spectrum of the electrodes in Examples 1 - 2 and Comparative Examples 1 - 2 of the present disclosure;

[0019] Figure 6 It is a schematic diagram of the electrocatalytic nitrate denitrification reaction system of the present disclosure;

[0020] Figure 7 Relationship diagram of the running time and nitrogen concentration of the electrocatalytic nitrate denitrification reaction at a flow rate of 22.5 ml / min;

[0021] Figure 8 Relationship diagram of the running time and nitrogen concentration of the electrocatalytic nitrate denitrification reaction at a flow rate of 6 ml / min;

[0022] Figure 9 Nitrogen removal rate diagram of the electrocatalytic nitrate denitrification reaction at flow rates of 22.5 ml / min and 6 ml / min. Detailed implementation manners

[0023] To make the objectives, technical solutions and advantages of the present disclosure clearer and more understandable, the following further describes the present disclosure in detail with reference to specific embodiments.

[0024] In the ranges disclosed in the present disclosure, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present disclosure.

[0025] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations and / or components, but do not exclude the presence or addition of one or more other features, steps, operations or components.

[0026] Nitrate (NO3 - ) pollution is one of the major threats to current water environment safety and public health. Although the electrochemical reduction of nitrate (eNO3RR) technology has become a highly potential treatment method due to its mild operating conditions and no secondary pollution, etc., the existing catalyst and electrode designs still face many problems. In the process of implementing the present disclosure, it is found that the traditional copper-based catalyst is limited by mass transfer and interfered by the competitive hydrogen evolution reaction, resulting in difficulty in improving the nitrate reduction efficiency; the traditional palladium-copper (Pd-Cu) bimetallic catalyst has insufficient synergistic effect of active sites and is difficult to fully exert its catalytic performance; while the traditional flat electrode has a large mass transfer resistance and cannot effectively treat low-concentration nitrate. In addition, the electrocatalytic nitrate denitrification reaction involves a complex process of synergistic electron and proton transfer (2NO3 - + 6H2O + 10e - → N2 + 12OH -, E0 = 0.25 V vs. SHE), higher requirements are put forward for the performance of the counter electrode.

[0027] Based on this, the present disclosure provides a palladium (Pd)-dispersed cuprous oxide / copper (Cu2O / Cu) nanowire array electrode. Using copper foam as the substrate, through a preparation process of in-situ oxidation, constant-temperature calcination, electrochemical reduction, and in-situ replacement, a Cu2O / Cu nanowire array is in-situ grown on the surface of the substrate, and Pd nanoparticles are loaded. The copper foam substrate not only provides stable mechanical support for the electrode but also participates in the reaction as a copper source, enabling the nanowire array to be tightly combined with the substrate, forming a firm and stable three-dimensional structure. This unique structural design significantly increases the specific surface area of the electrode, exposes a large number of active sites, greatly shortens the mass transfer path between the active sites and nitrate, thereby effectively improving the utilization efficiency of active species, accelerating the mass transfer and electron transfer processes, and significantly enhancing the adsorption and activation ability of the electrode for nitrate. In terms of optimizing the catalytic performance, the Pd nanoparticles and the cuprous oxide / copper nanowire array form an efficient synergistic catalytic system. The two act together to optimize the electron distribution and energy band structure on the electrode surface, significantly improving the charge transfer efficiency on the surface of the catalytic electrode.

[0028] Under normal temperature and pressure, using water as the proton source and nitrate as the nitrogen source, when the self-supporting nanowire array electrode is applied to the electrocatalytic nitrate reduction reaction, under specific flow rate conditions, a total nitrogen removal rate of 81.1% can be achieved. After 350 hours of continuous stability testing, the electrode energy consumption is only 158.6 kWh kg -1 -1N, significantly lower than that of the traditional Pd-Cu catalytic system, and there is no phenomenon of electrode shedding, damage, or corrosion during operation, fully demonstrating the comprehensive advantages of high efficiency, high selectivity, low energy consumption, and high stability, providing an innovative and practical solution for the treatment of water body nitrate pollution.

[0029] According to an embodiment of one aspect of the present disclosure, a self-supporting nanowire array electrode is proposed, including:

[0030] A copper foam substrate, a cuprous oxide / copper nanowire array formed in-situ on the surface of the copper foam substrate, and palladium nanoparticles loaded on the array through a displacement reaction with cuprous oxide / copper.

[0031] According to an embodiment of the present disclosure, copper foam is used as a substrate material, and a cuprous oxide / copper (Cu2O / Cu) nanowire array is constructed on its surface through an in-situ growth technique. The three-dimensional porous framework of copper foam provides stable support for the growth of the nanowire array, enabling the Cu2O / Cu nanowires to adhere tightly to the substrate surface, forming an integrated three-dimensional nanowire array structure. The nanowire array structure significantly increases the specific surface area of the electrode, greatly enhancing the electrochemically active area of the electrode. Compared with traditional planar electrodes, it can provide more reaction sites for electrochemical reactions and expose more active sites. In addition, the array structure significantly shortens the mass transfer distance between the active sites and nitrate, creating favorable conditions for electrochemical reactions.

[0032] Furthermore, Pd nanoparticles are in-situ introduced on the surface of the Cu2O / Cu nanowire array through a displacement reaction, and the Pd nanoparticles and the Cu2O / Cu nanowire array can form an efficient synergistic catalytic system. First, using Pd and Cu bimetals as catalysts, Cu metal has a direct promoting effect on nitrate reduction. Pd nanoparticles have excellent electron capture ability, can activate water molecules to generate atomic hydrogen (H), and at the same time, by regulating the electron transfer path, effectively inhibit the over-reduction of copper oxide and maintain the stable active components of the electrode material. In addition, the Pd nanoparticles can interact with the monovalent copper (Cu(I)) active species in cuprous oxide. The Pd nanoparticles quickly capture the electrons generated by the reaction and promote the charge balance of Cu(I) through interfacial electron transfer, optimizing the electron distribution on the electrode surface, significantly enhancing the charge transfer efficiency, and reducing the charge transfer resistance of the reaction. In addition, the Pd nanoparticles can stabilize the Cu(I) active species, regulate the adsorption of key nitric oxide intermediate products on the electrode surface, promote the conversion of nitric oxide intermediate products to the target product nitrogen, effectively inhibit the generation of by-products such as nitrite and ammonia, and greatly improve the selectivity of the catalytic reaction. The synergistic catalytic system of the self-supporting nanowire array electrode of the present disclosure not only improves the reaction rate but also significantly enhances the stability and durability of the electrode during long-term operation, providing a reliable guarantee for realizing efficient and stable electrocatalytic nitrate denitrification.

[0033] According to an embodiment of the present disclosure, the loading amount of Pd nanoparticles relative to copper foam and the cuprous oxide / copper nanowire array is 11.5 - 13.5 wt%, for example, it can be 11.5 wt%, 12 wt%, 12.5 wt%, 13 wt%, 13.5 wt%, etc. The size of the Pd nanoparticles is 5 - 10 nm, for example, it can be 5 nm, 7 nm, 9 nm, 10 nm, etc. The size of the cuprous oxide / copper nanowire array is 400 - 500 nm, for example, it can be 400 nm, 420 nm, 450 nm, 470 nm, 500 nm, etc.

[0034] According to an embodiment of another aspect of the present disclosure, a method for preparing the above self-supporting nanowire array electrode is provided, including:

[0035] By means of electrochemical oxidation, calcination, and electrochemical reduction treatments, cuprous oxide / copper nanowire arrays are in-situ formed on the surface of copper foam to obtain copper foam with cuprous oxide / copper nanowire arrays.

[0036] The copper foam with cuprous oxide / copper nanowire arrays is subjected to a displacement reaction in a soluble palladium salt solution with a concentration of 2 mM to 20 mM for 3 to 18 hours, and palladium nanoparticles are loaded on the cuprous oxide / copper nanowire arrays to form a self-supporting palladium-dispersed cuprous oxide / copper nanowire array electrode.

[0037] According to an embodiment of the present disclosure, the displacement reaction is as follows:

[0038] Pd 2+ + Cu2O + 2H + → Pd + 2Cu 2+ + H2O; E 0 = 0.78 V

[0039] Pd 2+ + Cu → Pd + Cu 2+ ; E 0 = 0.57 V

[0040] Wherein, the concentration of the soluble palladium salt solution can be, for example, 2 mM, 5 mM, 10 mM, 15 mM, 20 mM, etc. At an appropriate concentration, the progress of the displacement reaction between palladium ions and the surface of the cuprous oxide / copper nanowire arrays is relatively gentle, which is conducive to the uniform nucleation of palladium nanoparticles on the surface of the arrays, forming palladium nanoparticles with smaller sizes and good dispersibility, thereby increasing the number of active sites and enhancing the catalytic activity. Too low a concentration may lead to an overly slow displacement reaction, prolonging the preparation cycle and possibly resulting in insufficient loading. Too high a concentration will cause palladium ions to rapidly aggregate on the surface of the nanowires, leading to particle agglomeration and affecting the mass transfer process.

[0041] The time of the displacement reaction can be, for example, 3 h, 5 h, 10 h, 15 h, 18 h, etc. A shorter reaction time may result in less palladium loading and the inability to fully exert the catalytic effect of palladium. On the other hand, too long a reaction time will, on the one hand, increase the preparation cost and energy consumption, and on the other hand, the long reaction may cause the formed palladium nanoparticles to agglomerate or dissolve and redeposit, damaging the nanowire array structure and affecting the electrode stability and activity. A displacement reaction time of 3 to 18 h can ensure a reasonable loading of palladium nanoparticles on the cuprous oxide / copper nanowire arrays, taking into account both the preparation efficiency and performance optimization of the electrode.

[0042] According to an embodiment of the present disclosure, through electrochemical oxidation, calcination, and electrochemical reduction treatments, a Cu2O / Cu nanowire array is in-situ formed on the surface of copper foam. The Cu2O / Cu nanowire array electrode material is firmly bonded to the copper foam metal substrate and can maintain a stable nanowire array structure. Subsequently, palladium nanoparticles are loaded on the Cu2O / Cu nanowire array by a displacement reaction to form a self-supported palladium-dispersed cuprous oxide / copper nanowire array electrode, which can provide abundant active sites for electrocatalytic reactions. The method of the present disclosure is simple to prepare and easy to repeat. The prepared self-supported nanowire array electrode exhibits excellent catalytic performance and has good application prospects in the field of electrocatalytic nitrate denitrification.

[0043] According to an embodiment of the present disclosure, the electrochemical oxidation, calcination, and electrochemical reduction treatments include:

[0044] Electrochemical oxidation treatment: Using copper foam as the anode and a noble metal material as the cathode, a solution containing hydroxide ions is used as the electrolyte, and the anode is subjected to electrochemical oxidation treatment to promote the loss of electrons by copper atoms and their combination with hydroxide ions, in-situ growing a cupric hydroxide nanowire array on the surface of copper foam. At this time, the macroscopic color of the electrode is blue. Due to its three-dimensional porous structure and large specific surface area, the cupric hydroxide nanowire array provides sufficient substrate space for the subsequent material growth, can effectively increase the number of active sites. In addition, the porous structure effectively shortens the ion diffusion path, reduces the mass transfer resistance, improves the mass transfer efficiency, and constructs an initial nanostructure conducive to the reaction.

[0045] Calcination treatment: In an oxygen atmosphere, the copper foam with the grown cupric hydroxide nanowire array is calcined to oxidize the cupric hydroxide nanowire array, obtaining copper foam with a cupric oxide nanowire array. At this time, the macroscopic color of the electrode is black. Cupric oxide, as the precursor for the subsequent reduction reaction, can regulate the composition and structure of the nanowire array and provide a stable framework for the subsequent reduction reaction.

[0046] Electrochemical reduction treatment: The copper foam with the grown cupric oxide nanowire array is subjected to electrochemical reduction treatment in an alkaline solution to generate a cuprous oxide / copper nanowire array, obtaining copper foam with a cuprous oxide / copper nanowire array. At this time, the macroscopic color of the electrode is reddish-brown. The cuprous oxide / copper nanowire array can provide more Cu(I) active sites for the electrocatalytic nitrate denitrification reaction, enhancing the adsorption and activation of nitrates.

[0047] According to an embodiment of the present disclosure, the concentration of the solution containing hydroxide ions is 0.1 - 2 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.; the current density of the electrooxidation treatment is 1 - 10 mA cm -2 For example, it can be 1 mA cm-2 、 2 mA cm -2 、 5 mA cm -2 、 7 mA cm -2 、 10 mA cm -2 etc.; the time is 1 - 2 h, for example, it can be 1 h, 1.5 h, 2 h, etc. Appropriate electrochemically oxidative treatment reaction conditions can precisely control the growth process of the cupric hydroxide nanowire array, making it have a uniform morphology and an ideal size distribution. This not only helps to improve the crystallization quality of the cupric oxide nanowire array during the subsequent calcination process, but also can optimize the formation efficiency and structural stability of the cuprous oxide / copper nanowire array during the electrochemically reductive treatment.

[0048] According to the embodiments of the present disclosure, the heating rate of the calcination treatment is 2 - 5 °C / min, for example, it can be 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min, etc.; the calcination temperature is 200 - 300 °C, for example, it can be 200 °C, 220 °C, 250 °C, 270 °C, 300 °C, etc.; the calcination time is 1 - 3 h, for example, it can be 1 h, 2 h, 3 h, etc. Appropriate calcination treatment reaction conditions can precisely control the conversion process of the cupric hydroxide nanowire array to the cupric oxide nanowire array. By controlling the heating rate, calcination temperature, and calcination time, it is ensured that the nanowire array has high crystallinity, a uniform size distribution, and good structural stability. In addition, reasonable calcination conditions can also effectively prevent the agglomeration and sintering of the nanowires, thereby retaining their high specific surface area and excellent catalytic activity.

[0049] According to the embodiments of the present disclosure, the concentration of the alkaline solution is 0.1 - 2 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, etc.; the current density of the electrochemically reductive reaction is 100 - 500 mAcm -2 , for example, it can be 100 mA cm -2 、 200 mA cm -2 、 300 mA cm -2 、 400 mA cm -2 、 500 mA cm -2 etc.; the reduction reaction time is 1 - 5 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, etc. By optimizing the concentration of the alkaline solution, the current density, and the reduction reaction time, it can be ensured that part of the cupric oxide nanowire array is reduced to cuprous oxide, while part of the copper structure is retained, generating a cuprous oxide / copper nanowire array.

[0050] According to an embodiment of the present disclosure, the soluble palladium salt includes any one of palladium chloride, palladium sulfate, palladium acetate, and potassium tetrachloropalladate. The palladium ions in the soluble palladium salt undergo a replacement reaction with the cuprous oxide and copper in the cuprous oxide / copper nanowires, respectively, to achieve uniform loading of palladium nanoparticles on the cuprous oxide / copper nanowire array.

[0051] According to an embodiment of yet another aspect of the present disclosure, an application of the above-mentioned nanowire array electrode in an electrocatalytic nitrate denitrification reaction is proposed.

[0052] According to an embodiment of the present disclosure, the nanowire array electrode of the present disclosure is applied to the electrocatalytic nitrate denitrification reaction. During the reaction, the Cu(I) active sites on the electrode surface can effectively adsorb nitrate ions and reduce the activation energy of the reduction reaction, thereby accelerating the reduction process of nitrate and converting it into nitrogen or other harmless substances. In addition, the palladium nanoparticles introduced in situ further enhance the catalytic performance of the electrode. Palladium nanoparticles have excellent electrocatalytic activity and can form a synergistic catalytic effect with copper, significantly enhancing the adsorption and activation efficiency of nitrate, improving the selectivity of the reaction, reducing the occurrence of side reactions, and significantly improving the total nitrogen removal rate. In addition, the electrode exhibits good stability and durability during long-term operation.

[0053] According to an embodiment of the present disclosure, the electrocatalytic nitrate denitrification reaction includes:

[0054] Using a nanowire array electrode as the cathode and a precious metal composite material (such as a platinum-coated titanium mesh) as the anode, nitrate denitrification was carried out in nitrate-containing wastewater with a flow rate of 5 to 30 ml / min at a constant current of 10 to 100 mA. The platinum-coated titanium mesh anode, with its excellent stability and durability, can maintain efficient oxidation capacity over long periods of operation, significantly extending the electrode's service life. Furthermore, the flow rate range of 5 to 30 ml / min accommodates electrocatalytic reaction systems of varying scales while addressing the diverse needs of industrial applications. This provides a new, efficient, stable, economical, and environmentally friendly approach for electrocatalytic nitrate denitrification.

[0055] In order to make the purpose, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific examples and drawings. Where specific techniques or conditions are not specified in the examples, they are all conventional methods and can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. It should be noted that the methods provided in the present disclosure are all conventional methods unless otherwise specified, and the reactants and reagents can be obtained from public commercial channels unless otherwise specified.

[0056] Example 1:

[0057] This embodiment provides a self-supporting palladium-dispersed cuprous oxide / copper (Pd@Cu2O / Cu) nanowire array electrode, and the preparation method includes the following steps:

[0058] Take copper foam with a purity of 99.99%, a thickness of 0.8 mm, and a size of 2 2 cm 2 Perform pretreatment on the copper foam: sequentially put it into acetone, 0.1 M hydrochloric acid (HCl) solution, and absolute ethanol for ultrasonic treatment, with each ultrasonic treatment time being 10 minutes. After the ultrasonic treatment is completed, wash it with ultrapure water to obtain the pretreated copper foam.

[0059] Use the pretreated copper foam as the anode, a platinum sheet electrode as the cathode, and 2 M sodium hydroxide (NaOH) solution as the electrolyte. Under room temperature conditions, connect the anode copper foam and the cathode platinum sheet electrode to a power supply, and set the constant current density to 10 mA cm -2 . Perform electrochemical oxidation treatment on the anode for 90 minutes. After the reaction is completed, rinse the electrode surface with ultrapure water and air-dry it naturally to in-situ grow a cuprous oxide nanowire array on the copper foam.

[0060] Put the copper foam with the grown cuprous oxide nanowire array into a quartz boat and transfer it to a tube furnace for calcination treatment. In an oxygen atmosphere, control the oxygen flow rate to be 50 sccm, set the heating rate of the tube furnace to 2 °C / min, heat up to 250 °C and then maintain this temperature, and the calcination time is 2 hours. After the calcination is completed, cool it naturally to room temperature and then take it out to obtain copper foam with a cupric oxide nanowire array.

[0061] Put the copper foam with the cupric oxide nanowire array into 1.0 M NaOH solution and perform an electrochemical reduction reaction at a current of 300 mA for 2 hours to obtain copper foam with a cuprous oxide / copper nanowire array.

[0062] Immerse the copper foam with the cuprous oxide / copper nanowire array into 5 mM palladium chloride (PdCl2) solution for a displacement reaction for 6 hours. Load palladium nanoparticles on the cuprous oxide / copper nanowire array to form a self-supporting Pd@Cu2O / Cu nanowire array electrode 1.

[0063] Example 2

[0064] This embodiment provides a self-supporting palladium-dispersed cuprous oxide / copper (Pd@Cu2O / Cu) nanowire array electrode, and the preparation method is the same as that of Example 1. The only difference is that the displacement reaction time is 12 hours, and a self-supporting Pd@Cu2O / Cu nanowire array electrode 2 is prepared.

[0065] Comparative Example 1

[0066] This comparative example provides a cuprous oxide / copper nanowire array electrode, and the preparation method includes the following steps:

[0067] Take copper foam with a purity of 99.99%, a thickness of 0.8 mm, and a size of 2 2 cm 2 Perform pretreatment on the copper foam: sequentially place it in acetone, 0.1 M HCl solution, and absolute ethanol for ultrasonic treatment, with each ultrasonic treatment time being 10 minutes. After the ultrasonic treatment is completed, wash it with ultrapure water to obtain the pretreated copper foam.

[0068] Use the pretreated copper foam as the anode, a platinum sheet electrode as the cathode, and 2 M sodium hydroxide solution as the electrolyte. Under room temperature conditions, connect the anode copper foam and the cathode platinum sheet electrode to a power supply, and set the constant current density to 10 mA cm -2 Perform electrochemical oxidation treatment on the anode for 90 minutes. After the reaction is completed, rinse the electrode surface with ultrapure water and air-dry it naturally to in-situ grow a cupric hydroxide nanowire array on the copper foam surface.

[0069] Place the copper foam with the grown cupric hydroxide nanowire array in a quartz boat and transfer it to a tube furnace for calcination treatment. In an oxygen atmosphere, control the oxygen flow rate to be 50 sccm, set the heating rate of the tube furnace to 2 °C / min, heat it to 250 °C and then maintain this temperature, and the calcination time is 2 hours. After the calcination is completed, naturally cool it to room temperature and then take it out to obtain copper foam with a copper oxide nanowire array.

[0070] Place the copper foam with the copper oxide nanowire array in 1.0 M NaOH solution and perform an electrochemical reduction reaction at a current of 300 mA for 2 hours to obtain a copper foam electrode with a cuprous oxide / copper nanowire array.

[0071] Comparative Example 2

[0072] This comparative example provides a copper oxide nanowire array electrode, and the preparation method includes the following steps:

[0073] Take copper foam with a purity of 99.99%, a thickness of 0.8 mm, and a size of 2 2 cm 2 Perform pretreatment on the copper foam: sequentially place it in acetone, 0.1 M HCl solution, and absolute ethanol for ultrasonic treatment, with each ultrasonic treatment time being 10 minutes. After the ultrasonic treatment is completed, wash it with ultrapure water to obtain the pretreated copper foam.

[0074] Using the pretreated copper foam as the anode, a platinum sheet electrode as the cathode, and a 2 M sodium hydroxide solution as the electrolyte. At room temperature, connect the anode copper foam and the cathode platinum sheet electrode to a power supply, and set the constant current density to 10 mA cm -2 . Electrochemically oxidize the anode for 90 minutes. After the reaction, rinse the electrode surface with ultrapure water, air dry it, and in-situ grow a copper hydroxide nanowire array on the surface of the copper foam.

[0075] Put the copper foam with the grown copper hydroxide nanowire array into a quartz boat and transfer it to a tube furnace for calcination. In an oxygen atmosphere, control the oxygen flow rate to 50 sccm, set the heating rate of the tube furnace to 2 °C / min, heat up to 250 °C and maintain this temperature, and the calcination time is 2 hours. After the calcination is completed, naturally cool it to room temperature and then take it out to obtain a copper foam electrode with a copper oxide nanowire array.

[0076] Figure 1 This is the scanning electron microscope image of the self-supporting nanowire array electrode in Example 1 of the present disclosure. Figure 1 a is the partially enlarged scanning electron microscope image of the self-supporting nanowire array electrode in Example 1; Figure 1 b is the overall scanning electron microscope image of the self-supporting nanowire array electrode in Example 1.

[0077] As Figure 1 shown, the self-supporting Pd@Cu2O / Cu nanowire array electrode in Example 1 has an obvious nanowire array structure and a large specific surface area.

[0078] Figure 2 This is the transmission electron microscope image of the self-supporting nanowire array electrode in Example 1 of the present disclosure. Figure 2 a is the transmission electron microscope image of the surface of the self-supporting nanowire array electrode in Example 1. Figure 2 b is the transmission electron microscope image of the cuprous oxide / copper nanowire array on the self-supporting nanowire array electrode in Example 1.

[0079] Figure 3 This is the energy dispersive spectroscopy - element distribution map of the self-supporting nanowire array electrode in Example 1 of the present disclosure. Figure 3 a is the overall energy dispersive spectroscopy - element distribution map of the self-supporting nanowire array electrode in Example 1; Figure 3 b is the element distribution map of palladium (Pd) on the self-supporting nanowire array electrode in Example 1; Figure 3 c is the element distribution map of copper (Cu) on the self-supporting nanowire array electrode in Example 1; Figure 3 d is the element distribution map of oxygen (O) on the self-supporting nanowire array electrode in Example 1.

[0080] AsFigure 2 and Figure 3 As shown in Figure 3 , obvious Cu2O (111) crystal planes with a lattice spacing of 0.23 nm, Cu (111) crystal planes with a lattice spacing of 0.21 nm, and Pd (111) nanoparticles with a lattice spacing of 0.35 nm can be observed on the self-supporting nanowire array electrode in Example 1 through a transmission electron microscope (TEM) image, indicating the simultaneous presence of Cu2O, Cu, and Pd in the electrode. Through the energy-dispersive spectroscopy - element distribution (EDS-mapping) image, it can be observed that the Pd, Cu, and O elements are evenly distributed in the self-supporting nanowire array electrode in Example 1, and there is no local enrichment or defect.

[0081] Figure 4 This is the X-ray diffraction pattern of the electrodes in Examples 1 - 2 and Comparative Examples 1 - 2 of the present disclosure.

[0082] Figure 5 This is the Raman spectroscopy pattern of the electrodes in Examples 1 - 2 and Comparative Examples 1 - 2 of the present disclosure.

[0083] As Figure 4 and Figure 5 shown, compared with the electrodes in Comparative Examples 1 - 2, Pd characteristic peaks appear in the electrodes in Examples 1 - 2. In Figure 4 , the appearance of the Pd (111) characteristic peak indicates the presence of the Pd phase in the sample; there is also characteristic information related to Pd in Figure 5 . It shows that Pd nanoparticles are successfully loaded on the electrode through a displacement reaction in Examples 1 - 2. Figure 4 Figure 4 , the appearance of the Pd (111) characteristic peak indicates the presence of the Pd phase in the sample; Figure 5 Figure 5 also has characteristic information related to Pd. It shows that Pd nanoparticles are successfully loaded on the electrode through a displacement reaction in Examples 1 - 2.

[0084] The self-supporting Pd@Cu2O / Cu nanowire array electrode 1 prepared in Example 1 is applied to the electrocatalytic nitrate denitrification reaction.

[0085] Using the self-supporting Pd@Cu2O / Cu nanowire array electrode 1 in Example 1 as the cathode and the platinum-coated titanium mesh electrode as the anode, the effective working areas of both the cathode and the anode are 4 cm × 4 cm. The simulated nitrate-contaminated solution formula is: 15 mM NaHCO3, 15 mM Na2SO4, 10 mM NaCl, and 2.5 mM NaNO3. 5 L of the simulated solution in the reservoir is circulated through the cathode and the anode by a peristaltic pump, and a DC power supply provides a constant current of 25 mA. The electrocatalytic nitrate denitrification reaction is carried out on the nitrate-contaminated solution at low and high flow rates of 6 ml / min and 22.5 ml / min, respectively.

[0086] The electrocatalytic nitrate denitrification reaction uses a continuous-flow electrochemical reaction system, Figure 6 This is the schematic diagram of the electrocatalytic nitrate denitrification reaction system of the present disclosure.

[0087] AsFigure 6 As shown in the figure, the electrocatalytic reaction system consists of a reaction cell, a DC power supply, a peristaltic pump, and a pollutant collection cell simulating sodium nitrate (NaNO3, 2.5 mM). The internal chamber volume of the reaction cell is Figure 6 48 mL, and the main material is polytetrafluoroethylene (PTFE) resistant to acid and alkali corrosion. The reaction cell operates in a two-electrode mode with a cathode using a self-supporting palladium-dispersed copper oxide / copper nanowire (Pd@Cu2O / Cu NWs) array electrode and an anode using a platinum-coated titanium mesh (Pt coated Ti mesh).

[0088] Figure 7 It is a graph showing the relationship between the operating time and nitrogen concentration of the electrocatalytic nitrate denitrification reaction at a flow rate of 22.5 ml / min.

[0089] Figure 8 It is a graph showing the relationship between the operating time and nitrogen concentration of the electrocatalytic nitrate denitrification reaction at a flow rate of 6 ml / min.

[0090] Figure 9 It is a graph of the nitrogen removal rate of the electrocatalytic nitrate denitrification reaction at flow rates of 22.5 ml / min and 6 ml / min. Among them, Figure 9 a is the graph of the nitrogen removal rate of the electrocatalytic nitrate denitrification reaction at a flow rate of 22.5 ml / min; Figure 9 b is the graph of the nitrogen removal rate of the electrocatalytic nitrate denitrification reaction at a flow rate of 6 ml / min.

[0091] As Figure 7 , Figure 8 and Figure 9 shown, good nitrate removal effects can be achieved at both higher and lower flow rates. For the electrocatalytic nitrate denitrification reaction at a high flow rate of 22.5 ml / min, the total nitrogen removal rate (TN) is 81.1%, and it can operate stably for 350 h. At a low flow rate of 6 ml / min, the total nitrogen removal rate (TN) is 72.7%, and it can operate stably for 380 h.

[0092] The present disclosure prepares a self-supporting Pd@Cu2O / Cu nanowire array electrode by electrochemical oxidation, calcination, electrochemical reduction, and in-situ replacement methods and applies it to the electrocatalytic nitrate denitrification reaction. The prepared electrode has high stability, good reaction activity, and fast efficiency compared with traditional electrodes.

[0093] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not used to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure should be included within the protection scope of the present disclosure.

Claims

1. A self-supporting nanowire array electrode, characterized in that, Comprising: A copper foam substrate, a cuprous oxide / copper nanowire array formed in-situ on the surface of the copper foam substrate, and palladium nanoparticles loaded on the array through a displacement reaction with cuprous oxide / copper.

2. The self-supporting nanowire array electrode according to claim 1, wherein: The loading amount of the palladium nanoparticles relative to the copper foam and the cuprous oxide / copper nanowire array is 11.5 - 13.5 wt%, The size of the palladium nanoparticles is 5 - 10 nm, The size of the cuprous oxide / copper nanowire array is 400 - 500 nm.

3. A method for preparing a self-supporting nanowire array electrode according to any one of claims 1 to 2, characterized in that, The preparation method comprises: Through electrochemical oxidation, calcination, and electrochemical reduction treatments, a cuprous oxide / copper nanowire array is formed in-situ on the surface of the copper foam to obtain copper foam with a cuprous oxide / copper nanowire array; The copper foam with a cuprous oxide / copper nanowire array is subjected to a displacement reaction in a 2 mM - 20 mM soluble palladium salt solution for 3 - 18 h to load palladium nanoparticles on the cuprous oxide / copper nanowire array, forming a self-supporting palladium-dispersed cuprous oxide / copper nanowire array electrode.

4. The preparation method according to claim 3, wherein: The electrochemical oxidation, calcination, and electrochemical reduction treatments comprise: Using the copper foam as the anode and a noble metal material as the cathode, and using a hydroxide ion-containing solution as the electrolyte, the anode is subjected to electrochemical oxidation treatment to in-situ grow a copper hydroxide nanowire array on the surface of the copper foam; In an oxygen atmosphere, the copper foam with the copper hydroxide nanowire array grown thereon is subjected to calcination treatment to oxidize the copper hydroxide nanowire array, obtaining copper foam with a copper oxide nanowire array; The copper foam with a copper oxide nanowire array is subjected to electrochemical reduction treatment in an alkaline solution to obtain copper foam with a cuprous oxide / copper nanowire array.

5. The preparation method according to claim 4, wherein: The concentration of the hydroxide ion-containing solution is 0.1 - 2 mol / L, The current density of the electro-oxidation treatment is 1~10 mA cm -2 , and the time is 1~2 h.

6. The preparation method according to claim 4, wherein: The heating rate of the calcination treatment is 2 - 5 °C / min, the calcination temperature is 200 - 300 °C, and the calcination time is 1 - 3 h.

7. The preparation method according to claim 4, wherein: The concentration of the alkaline solution is 0.1 - 2 mol / L, The current density of the electrochemically reduction reaction is 100~500 mA cm -2 , and the reduction reaction time is 1~5 h.

8. The preparation method according to claim 3, wherein: The soluble palladium salt includes any one of palladium chloride, palladium sulfate, palladium acetate, and potassium tetrachloropalladate.

9. Application of a self-supporting nanowire array electrode according to any one of claims 1 - 2 in an electrocatalytic nitrate denitrification reaction.

10. The application according to claim 9, wherein: The electrocatalytic nitrate denitrification reaction comprises: Using the self-supporting nanowire array electrode as the cathode and a noble metal composite material as the anode, and under a constant current of 10 - 100 mA, performing a nitrate denitrification reaction on nitrate-containing wastewater with a flow rate of 5 - 30 ml / min.

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