Pulse preparation method of cuprous oxide electrocatalyst and method and application of pulse electrochemical denitrification

Abstract

This disclosure provides a pulsed preparation method for a cuprous oxide electrocatalyst, as well as a pulsed electrochemical denitrification method and its application. The pulsed preparation method includes: placing an electrode pair consisting of a copper support and an inert electrode in an electrolyte containing chloride ions, wherein the copper support is primarily composed of elemental copper; applying forward and reverse pulses to the electrode pair for electrolysis, such that during the reverse pulse, oxidation of elemental copper occurs on the surface of the copper support to form cuprous chloride with chloride ions, which subsequently hydrolyzes to form cuprous oxide; during the forward pulse, reduction of cuprous oxide occurs to form new elemental copper; repeating the operation of applying forward and reverse pulses to the electrode pair for electrolysis, thereby continuously generating new cuprous oxide on the surface of the copper support to obtain a cuprous oxide electrocatalyst, wherein the forward pulse uses the copper support as the cathode and the inert electrode as the anode, and the reverse pulse uses the copper support as the anode and the inert electrode as the cathode.

Description

Technical Field

[0001] This disclosure relates to fields such as electrocatalytic reduction, electrode modification, water treatment, and wastewater denitrification, specifically to a pulsed preparation method for a cuprous oxide electrocatalyst and a pulsed electrochemical denitrification method and its application. Background Technology

[0002] Nitrate ions (NO3) - NO3 is an important raw material widely used in industrial production and fertilizer manufacturing; however, with the decline of NO3... - Increased emissions are increasingly revealing their negative environmental impacts, particularly in water pollution, which has garnered widespread attention. To address this issue, researchers have been searching for effective NO3-reducing agents. - Removal technology.

[0003] Among many feasible NO3 - In removal technologies, electrochemical NO3 - Removal technology is considered one of the most promising technologies due to its excellent controllability and environmental friendliness. In the electrochemical reduction reaction of nitrates, copper (Cu) is effective against NO3-. - Copper's strong adsorption capacity for NO3- is often considered a promising electrocatalyst. However, copper's adsorption of NO3-... - Reduction reaction intermediates (e.g., nitrite NO2) - The excessive adsorption of nitric oxide (NO) inhibited NO3. - Further reduction limits its electrochemical denitrification performance.

[0004] To improve the catalytic performance of Cu, alloying noble metals with copper is commonly used to enhance reduction activity. However, this method is costly and complex, making it impractical for real-world wastewater treatment applications. Furthermore, researchers have explored in-situ loading of cuprous oxide (Cu₂O) onto the copper surface. This loading not only mitigates the reaction between copper and NO₃⁻... - The adsorption strength of the reduction reaction intermediates increases, prolonging the catalytic lifetime of Cu and reducing NO3. - The reduction energy barrier is increased, thereby raising NO3 - The reduction efficiency is high. However, in practical applications, the preparation of Cu2O and electrochemical reduction are usually two separate steps. This leads to Cu2O easily disintegrating in the electroreduction reaction and eventually rapidly converting into elemental copper, greatly reducing its catalytic activity. Summary of the Invention

[0005] In view of this, the main objective of this disclosure is to provide a pulsed preparation method for cuprous oxide electrocatalyst and a pulsed electrochemical denitrification method and application, in order to at least partially solve at least one of the aforementioned technical problems.

[0006] To achieve the above objectives, the technical solution disclosed herein is as follows:

[0007] In one aspect of this disclosure, a pulse preparation method for a cuprous oxide electrocatalyst is provided, comprising:

[0008] An electrode pair consisting of a copper carrier and an inert electrode is placed in an electrolyte containing chloride ions, wherein the copper carrier is mainly composed of elemental copper.

[0009] Electrolysis is performed by applying positive and negative pulses to the electrode pair, respectively. During the negative pulse, copper is oxidized on the surface of the copper support to form cuprous chloride with chloride ions, and then hydrolyzed to form cuprous oxide. During the positive pulse, cuprous oxide is reduced to form new copper.

[0010] By repeatedly applying positive and negative pulses to the electrode pair for electrolysis, new cuprous oxide is continuously generated on the surface of the copper support, thus obtaining a cuprous oxide electrocatalyst.

[0011] The positive pulse uses a copper carrier as the cathode and an inert electrode as the anode, while the reverse pulse uses a copper carrier as the anode and an inert electrode as the cathode.

[0012] As a second aspect of this disclosure, a method for pulsed electrochemical denitrification is provided, comprising:

[0013] Chloride ions are added to wastewater containing nitrates, so that the wastewater contains both chloride ions and nitrate ions.

[0014] Using wastewater containing chloride and nitrate ions as the electrolyte, cuprous oxide electrocatalysts were prepared using the pulse preparation method described above.

[0015] In the preparation of cuprous oxide electrocatalyst, the cuprous oxide electrocatalyst is used to simultaneously electrochemically reduce nitrate ions in the electrolyte during a positive pulse process, so that the nitrate ions are converted into nitrogen gas.

[0016] As another aspect of this disclosure, an application of the cuprous oxide electrocatalyst prepared by the above-described pulse preparation method is provided in the field of electrochemical reduction, particularly in the field of electrochemical denitrification.

[0017] The pulse preparation method for cuprous oxide electrocatalyst provided in this disclosure utilizes forward and reverse pulse processing. During the reverse pulse oxidation, cuprous chloride is formed through the stabilizing effect of chloride ions on monovalent copper. During reduction, alkalinity is provided based on the hydrogen evolution side reaction, allowing cuprous chloride to hydrolyze and form cuprous oxide. Simultaneously, the copper element reduced to cuprous oxide can iteratively generate new cuprous oxide in the next pulse cycle. This preparation method enables the cuprous oxide catalyst to maintain catalytic activity during the electroreduction reaction. Furthermore, this preparation method is simple and convenient to operate, requiring no external protective gas or controlled oxidation conditions, and is safe, green, and environmentally friendly. Attached Figure Description

[0018] Figures 1A-1C These are scanning electron microscope (SEM) images of the copper mesh surface after the reaction in Example 1 and Comparative Examples 1-2 of this disclosure;

[0019] Figure 2A This is a transmission electron microscope (TEM) image of the deposit on the copper mesh surface after the reaction in Example 1 of this disclosure;

[0020] Figure 2B yes Figure 2A A magnified view of a portion of the image;

[0021] Figure 3 These are X-ray diffraction (XRD) patterns of the deposits on the copper mesh surface after the reaction in Example 1 and Comparative Examples 1-2 of this disclosure. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components. All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0024] In the process of developing this disclosure, it was discovered that when preparing cuprous oxide catalysts by in-situ loading cuprous oxide on a copper surface, the cuprous oxide is prone to disintegration during the electroreduction reaction, ultimately transforming into elemental copper. This significantly reduces the catalytic activity of the catalyst, limiting its application in electrochemical denitrification. To address this, this disclosure proposes a pulsed preparation method for cuprous oxide electrocatalysts and a pulsed electrochemical denitrification method and its application. Electrolysis is performed using forward and reverse pulsed electric fields, fully utilizing the periodic redox switching function to achieve targeted control of the morphology and valence state of the copper oxide layer. Under the action of the pulsed electric field, the surface cuprous oxide layer is continuously renewed and transformed, thus overcoming the instability of cuprous oxide during the electroreduction process. This method ensures that the cuprous oxide electrocatalyst can continuously and effectively electroreducte nitrate ions, opening a new avenue for the development of electrochemical denitrification technology.

[0025] According to some embodiments of this disclosure, a pulse preparation method for a cuprous oxide electrocatalyst is provided, comprising steps S101 to S103:

[0026] In step S101, the electrode pair consisting of a copper support and an inert electrode is placed in an electrolyte containing chloride ions, wherein the copper support is mainly composed of elemental copper.

[0027] In step S102, a forward pulse and a reverse pulse are applied to the electrode pair to perform electrolysis, such that during the reverse pulse, copper is oxidized on the surface of the copper support to form cuprous chloride with chloride ions, and then hydrolyzed to form cuprous oxide. During the forward pulse, cuprous oxide is reduced to form new copper.

[0028] In step S103, the operation of applying positive and negative pulses to the electrode pair for electrolysis is repeated to continuously generate new cuprous oxide on the surface of the copper support, thereby obtaining a cuprous oxide electrocatalyst.

[0029] The positive pulse uses a copper carrier as the cathode and an inert electrode as the anode, while the reverse pulse uses a copper carrier as the anode and an inert electrode as the cathode.

[0030] According to embodiments of this disclosure, electrolysis is performed using a pulsed electric field. During the oxidation reverse pulse, cuprous chloride is formed by the stabilizing effect of chloride ions on monovalent copper. During the reduction forward pulse, hydrogen ions on the surface of elemental copper are consumed based on the hydrogen evolution side reaction, leading to an increase in the near-surface pH, which causes cuprous chloride to hydrolyze to form cuprous oxide. Simultaneously, the reduction of cuprous oxide to new elemental copper can be repeated in the next pulse cycle by applying forward and reverse pulses to the electrode pair, iteratively and continuously generating new cuprous oxide, thereby ensuring the catalytic activity of the cuprous oxide electrocatalyst.

[0031] According to embodiments of this disclosure, the pulse preparation method may further include: pretreating the copper carrier before placing it in the electrolyte to remove surface oil and oxide layers.

[0032] Furthermore, the pretreatment process may include: soaking the copper substrate in a degreasing agent and ultrasonically vibrating it for, for example, 10 minutes. The degreasing agent can be a commercially available one containing surfactants and organic solvents to ensure the removal of surface oil. Next, the copper substrate is placed in a dilute acid solution, such as 0.1 M sulfuric acid, for 1 minute, or it is sanded with sandpaper to remove the surface oxide layer. The copper mesh, after removing the oil and oxide layer, is thoroughly rinsed with ultrapure water to obtain a smooth and pure copper substrate, ensuring the redox reaction proceeds and thus continuously and stably generating cuprous oxide.

[0033] According to embodiments of this disclosure, in step S101, chloride ions can be naturally present in the water body, such as industrial wastewater (especially electroplating wastewater) or tap water, or they can be formed by adding chloride-containing inorganic salts such as potassium chloride, sodium chloride, or calcium chloride to the electrolyte. Chloride ions play a crucial role in stabilizing monovalent copper, and their presence or absence directly affects the valence state change of copper. In subsequent electrolysis processes, a stirrer is used to ensure a uniform distribution of chloride ion concentration in the reaction tank, thereby improving electrolysis efficiency.

[0034] According to embodiments of this disclosure, in step S101, the copper carrier can be a copper plate, copper mesh, copper sheet, copper foam, or copper film, etc., with a porous or smooth surface. In embodiments of this disclosure, the parameters of the copper mesh can be: a mesh size of 50-500 mesh, and a mesh area of ​​1... 1~10 It is 10 cm thick and 0.1~5.0 mm thick, with elemental copper as its main component. The inert electrodes can be precious metals such as platinum, palladium, and gold, as well as inert non-metallic electrodes such as carbon cloth or carbon felt.

[0035] According to an embodiment of this disclosure, in step S101, the chloride ion concentration of the electrolyte can be 1 mM to 3 M, for example, 1 mM, 100 mM, 500 mM, 1 M, 2 M, 3 M, etc., and the pH of the electrolyte is 3 to 12, for example, pH can be 3, 5, 7, 11, 12, etc., preferably 5 to 11. Since a hydrogen evolution side reaction occurs during reduction, hydrogen ions on the surface of elemental copper are consumed, causing the initial pH value to rise to alkaline. Therefore, the prepared cuprous oxide electrocatalyst is suitable for a wide range of chloride ion concentrations and pH conditions, and has good repeatability and operability.

[0036] According to embodiments of this disclosure, in steps S102 and S103, the morphology and valence state of the oxide layer on the copper support surface are directionally controlled through periodic oxidation and reduction reactions. Under a pulsed electric field, the cuprous oxide on the surface is continuously renewed and transformed, which is beneficial for maintaining its electrocatalytic effect.

[0037] According to embodiments of this disclosure, the forward pulse and the reverse pulse are either constant current pulses or constant voltage pulses, respectively. If a constant current mode is used, the forward output current density and time, the reverse output current density and time, and the pulse frequency need to be set. If a constant voltage mode is used, the forward output voltage and time, the reverse output voltage and time, and the pulse frequency need to be set.

[0038] According to embodiments of this disclosure, taking a forward pulse and a reverse pulse as constant current pulses as examples, the current density of the forward pulse can be 5~30 mA cm⁻¹. -2 For example, it can be 10 mA cm -2 15 mA cm -2 20 mA cm -2 25mA cm -2 etc., preferably 20 mA cm -2 The duration is 2~5 s, for example, it can be 3 s, 3.5 s, 4 s, 4.5 s, 5 s, etc., preferably 4 s; the current density of the reverse pulse can be 0~10 mA cm⁻¹. -2 For example, it can be 0.1 mA cm -2 0.5 mA cm -2 1 mA cm -2 3mA cm -2 5 mA cm -2 10 mA cm -2 etc., preferably 5 mA cm -2 The duration is 0~3 s, for example, it can be 0.01 s, 0.02 s, 0.1 s, 0.2 s, 1 s, 2 s, 3 s, etc., preferably 1 s, and the pulse frequency is 0.1~10 Hz, for example, it can be 0.1 Hz, 0.2 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, etc., preferably 0.2 Hz.

[0039] According to embodiments of this disclosure, the electrochemical catalytic effect of the catalyst can be ensured by adjusting appropriate forward and reverse current density parameters. Excessive forward current will cause the generated cuprous oxide to be rapidly reduced to elemental copper during nitrate reduction, resulting in the failure to achieve the expected electrochemical catalytic reduction effect within one cycle. If the reverse current is too high, copper will be over-oxidized to form divalent copper, and copper ions may also dissolve from the aqueous solution. Furthermore, the adjustment of pulse parameters also needs to consider changes in factors such as electrode area, nitrate and chloride ion concentrations, and pH value.

[0040] According to embodiments of this disclosure, the generated cuprous oxide can be nanospheres of 50-500 nm, stacked to form a cuprous oxide catalytic layer, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc. Because the cuprous oxide nanospheres are of moderate size, they provide an ideal contact area, thereby ensuring that the catalyst exhibits good catalytic performance.

[0041] According to other embodiments of this disclosure, a cuprous oxide electrocatalyst prepared by the above-described pulse preparation method is also provided.

[0042] The cuprous oxide electrocatalyst comprises a copper support and a cuprous oxide catalytic layer formed on the surface of the copper support. The thickness of the cuprous oxide catalytic layer can range from 10 nm to 100 μm, for example, 10 nm, 100 nm, 500 nm, 1 μm, 10 μm, 100 μm, etc. The thickness of the catalytic layer can be controlled by adjusting pulse parameters such as pulse waveform, current density, time, and pulse frequency, thereby controlling the catalytic effect of the catalyst.

[0043] According to some other embodiments of this disclosure, a method for pulsed electrochemical denitrification is also provided, including steps S201 to S203:

[0044] In step S201, chloride ions are added to the wastewater containing nitrates, so that the wastewater contains both chloride ions and nitrate ions.

[0045] In step S202, using wastewater containing chloride ions and nitrate ions as the electrolyte, cuprous oxide electrocatalyst is prepared using the pulse preparation method described above.

[0046] In step S203, during the preparation of the cuprous oxide electrocatalyst, the cuprous oxide electrocatalyst is used to simultaneously electrochemically reduce nitrate ions in the electrolyte, so that the nitrate ions are converted into nitrogen gas.

[0047] According to embodiments of this disclosure, during the electrochemical reduction of nitrate ions, the presence or absence of chloride ions affects the valence state of copper. Chloride ions can be rapidly adsorbed onto the copper surface to form cuprous chloride, stabilizing monovalent copper ions and preventing excessive oxidation that leads to the formation of divalent copper, thus significantly impacting catalytic performance. Furthermore, the continuous renewal and transformation of cuprous oxide obtained through the pulsed preparation method allows it to continuously perform catalytic reduction of NO3. - This function solves the problem of instability of cuprous oxide during electroreduction.

[0048] According to embodiments of this disclosure, the nitrate ion concentration in wastewater can be 5~2000 mg-N L. -1 For example, it can be 5mg-NL -1 100 mg-N L -1 500 mg-N L -1 1000 mg-N L -1 1500 mg-N L -1 2000 mg-N L -1 The electroreduction denitrification method disclosed herein can be applied over a relatively wide range of NO3-. - It is applicable within a certain concentration range and exhibits good repeatability and operability. The electrochemical reduction time can be adjusted according to the nitrate ion concentration in the wastewater; for example, when the nitrate ion concentration in the wastewater is 50 mg-N / L... -1 At this time, the electrochemical reduction time can be 3 hours. When the concentration of nitrate ions in the wastewater is high, the electrochemical reduction time needs to be extended accordingly in order to fully realize the electrochemical reduction of nitrate.

[0049] According to another aspect of this disclosure, an application of the cuprous oxide electrocatalyst prepared by the above-described pulse preparation method in the field of electrochemical reduction is provided, for example, it can be used for electrochemical denitrification, hydrogen production, and CO2 reduction to synthesize C. 2+ Applications in the field of electrochemical reduction of products, especially in the field of electrochemical denitrification.

[0050] The technical solutions of this disclosure will be described in detail below through preferred embodiments. It should be noted that the specific embodiments in the following text are for illustrative purposes only and are not intended to limit this disclosure.

[0051] Example 1

[0052] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, a cuprous oxide electrocatalyst was prepared by a pulse method and its application in electrochemical denitrification was investigated.

[0053] Step S1: Preparation of nitrate-simulated wastewater

[0054] 0.361 g of KNO3 was dispersed in 100 ml of ultrapure water to prepare a nitrate-simulated wastewater with a concentration of 50 mg-N / L. 0.745 g of KCl was added to the above nitrate-simulated wastewater solution to make the chloride ion concentration in the wastewater 0.1 M. The pH of the solution was adjusted to 7 to simulate the treatment of neutral wastewater.

[0055] Step S2: Copper Mesh Pretreatment

[0056] Soak the copper mesh in a degreasing agent and ultrasonically vibrate for 10 minutes to ensure that the surface oil is removed. Then, immerse the copper mesh in 0.1 M sulfuric acid for 1 minute to remove the surface oxide layer. Finally, thoroughly rinse the copper mesh with ultrapure water to remove the oil and oxide layer.

[0057] Step S3: Set pulse power supply parameters

[0058] Using constant current mode, the output current density of the positive pulse is set to 20 mA cm⁻¹. -2 The duration is 4 seconds, and the output current density of the reverse pulse is 5 mA cm⁻¹. -2 The pulse duration is 1 second, and the pulse frequency is 0.2 Hz. The copper mesh electrode is connected to the negative terminal of the pulse power supply. A 2cm platinum sheet is connected as the counter electrode to the positive terminal of the pulse power supply.

[0059] Step S4: Place the electrode pair consisting of copper mesh electrode and platinum sheet in nitrate simulated wastewater, using nitrate simulated wastewater as the electrolyte containing chloride ions.

[0060] Step S5: Turn on the pulsed power supply and alternately apply positive and negative pulses to the electrode pair for electrolysis, simultaneously performing cuprous oxide synthesis and electrochemical removal of nitrate. Measure the nitrate reduction products after 3 hours. Monitor the concentrations of nitrate, nitrite, and ammonia nitrogen during nitrate reduction, and calculate the nitrate removal efficiency and the selectivity of each product.

[0061] The selectivity of nitrite, ammonia nitrogen, and nitrogen gas is calculated using the following formula:

[0062] Nitrate removal rate (%) = (C0 - C) NO3-N ) / C0

[0063] Nitrite selectivity (%) = C NO2-N / (C0-C NO3-N )

[0064] Ammonia nitrogen selectivity (%) = C NH4-N / (C0-C NO3-N )

[0065] Nitrogen formation rate (%) = 1 - C NO2-N / (C0-CNO3-N )-C NH4-N / (C0-C NO3-N )

[0066] Where C0 refers to the initial concentration of nitrate, C NO3-N C NH4-N C NO2-N These refer to the concentrations of nitrate nitrogen, ammonia nitrogen, and nitrite nitrogen in the collected permeate after the reaction is complete.

[0067] After the reaction was complete, the nitrate removal rate was measured to be 85.6%, and the product was entirely nitrogen gas.

[0068] Comparative Example 1:

[0069] A pulse method was used to prepare a copper hydroxide electrocatalyst under wastewater pH=7 and chloride ion-free conditions, and its application in electrochemical denitrification was investigated.

[0070] The difference from Example 1 is that in step S1, 1.743 g of K2SO4 is added to the simulated nitrate wastewater solution.

[0071] After the reaction was complete, the nitrate removal rate was 48.4%, the nitrite selectivity in the product was 8.1%, the ammonia nitrogen selectivity was 44.5%, and the nitrogen generation rate was 47.4%.

[0072] Comparative Example 2:

[0073] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, a copper electrocatalyst was prepared by direct current electrolysis and its application in electrochemical denitrification was investigated.

[0074] The difference from Example 1 is that in step S3, the DC power supply parameters are set, a constant current mode is adopted, and the output current density is 20 mA cm⁻¹. -2 Connect the copper mesh electrode to the negative terminal of the DC power supply. A 2 cm platinum plate is connected as the counter electrode to the positive terminal of a DC power supply. In step S4, the DC power supply is turned on to perform electrochemical removal of nitrates.

[0075] After sufficient reaction, the nitrate removal rate was determined to be 7.0%, the nitrite selectivity in the product was 46.7%, the product contained no ammonia nitrogen, and the nitrogen generation rate was 53.3%.

[0076] Comparative Example 3:

[0077] A copper catalyst was prepared by direct current electrolysis under wastewater pH=7 and chloride ion-free conditions, and its application in electrochemical denitrification was investigated.

[0078] The difference from Example 1 is that in step S1, 1.743 g of K₂SO₄ was added to the simulated nitrate wastewater solution. In step S3, the DC power supply parameters were set to constant current mode, with an output current density of 20 mA cm⁻¹. -2 Connect the copper mesh electrode to the negative terminal of the DC power supply. A 2 cm platinum plate is connected as the counter electrode to the positive terminal of a DC power supply. In step S4, the DC power supply is turned on to perform electrochemical removal of nitrates.

[0079] After the reaction was complete, the nitrate removal rate was 2.0%, the nitrite selectivity in the product was 24%, the ammonia nitrogen selectivity was 14.6%, and the nitrogen generation rate was 61.4%.

[0080] Example 2:

[0081] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.02 M, a cuprous oxide electrocatalyst was prepared by a pulse method and its application in electrochemical denitrification was investigated.

[0082] The difference from Example 1 is that in step S1, 1.394 g of K2SO4 and 0.149 g of KCl are added to the above-mentioned nitrate simulated wastewater solution, so that the chloride ion concentration in the wastewater is 0.02 M.

[0083] After sufficient reaction, the nitrate removal rate was determined to be 54.7%, the nitrite selectivity in the product was 10.2%, the ammonia nitrogen content was 43%, and the nitrogen content was 46.8%.

[0084] Example 3:

[0085] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.06 M, a cuprous oxide electrocatalyst was prepared by a pulse method and its application in electrochemical denitrification was investigated.

[0086] The difference from Example 1 is that in step S1, 0.558 g of K2SO4 and 0.447 g of KCl are added to the above-mentioned nitrate simulated wastewater solution, so that the chloride ion concentration in the wastewater is 0.06 M.

[0087] After sufficient reaction, the nitrate removal rate was measured to be 72.8%, the nitrite selectivity in the product was 3.5%, the ammonia nitrogen content was 7.8%, and the nitrogen content was 88.7%.

[0088] Example 4:

[0089] Under the conditions of wastewater pH=3 and chloride ion concentration of 0.1 M, a cuprous oxide electrocatalyst was prepared by a pulse method and its application in electrochemical denitrification was investigated.

[0090] The difference from Example 1 is that in step S1, 0.1 M HCl is used to adjust the pH of the solution to 3 to simulate the treatment of acidic wastewater.

[0091] After the reaction was complete, the nitrate removal rate was measured to be 17.6%, and the product was entirely nitrogen gas.

[0092] Example 5:

[0093] Under the conditions of wastewater pH=11 and chloride ion concentration of 0.1 M, a cuprous oxide electrocatalyst was prepared by a pulse method and its application in electrochemical denitrification was investigated.

[0094] The difference from Example 1 is that in step S1, 0.1 M KOH is used to adjust the pH of the solution to 11 to simulate the treatment of alkaline wastewater.

[0095] After the reaction was complete, the nitrate removal rate was measured to be 56.0%, and the product was entirely nitrogen gas.

[0096] Example 6

[0097] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, cuprous oxide electrocatalyst was prepared by adjusting the reverse current density using a pulse method, and its application in electrochemical denitrification was investigated.

[0098] The difference from Example 1 is that the output current density of the reverse pulse in step S3 is 1 mA cm⁻¹. -2 .

[0099] After the reaction was complete, the nitrate removal rate was measured to be 51.6%, and the product was entirely nitrogen gas.

[0100] Example 7

[0101] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, cuprous oxide electrocatalyst was prepared by adjusting the forward current density using a pulse method, and its application in electrochemical denitrification was investigated.

[0102] The difference from Example 1 is that the output current density of the positive pulse is set to 25 mA cm⁻¹ in step S3. -2 .

[0103] After the reaction was complete, the nitrate removal rate was measured to be 41.7%, and the product was entirely nitrogen gas.

[0104] Example 8

[0105] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, cuprous oxide electrocatalyst was prepared by adjusting the forward current density using a pulse method, and its application in electrochemical denitrification was investigated.

[0106] The difference from Example 1 is that the output current density of the positive pulse is set to 10 mA cm⁻¹ in step S3. -2 .

[0107] After the reaction was complete, the nitrate removal rate was measured to be 64.8%, and the product was entirely nitrogen gas.

[0108] Example 9

[0109] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, cuprous oxide electrocatalyst was prepared by adjusting the pulse frequency using a pulse method, and its application in electrochemical denitrification was investigated.

[0110] The difference from Example 1 is that the pulse frequency is 1 Hz.

[0111] After the reaction was complete, the nitrate removal rate was measured to be 58.1%, and the product was entirely nitrogen gas.

[0112] Figures 1A-1C These are scanning electron microscope images of the copper mesh surface after the reaction in Example 1 and Comparative Examples 1-2 of this disclosure.

[0113] like Figure 1A As shown, in Example 1, a cuprous oxide electrocatalyst was prepared using a pulse method under chloride ion conditions. After 3 hours of complete reaction, a layer of deposit was uniformly covered on the surface of the copper mesh. Figures 1B-1C As shown, in Comparative Examples 1 and 2, when prepared under chloride ion-free conditions or without the pulse method, only a small amount or uneven deposits were generated on the surface of the copper mesh.

[0114] Figure 2A This is a transmission electron microscope image of the deposits on the copper mesh surface after the reaction in Example 1 of this disclosure; Figure 2B yes Figure 2A A magnified view of a portion of the image.

[0115] like Figure 2A and Figure 2B As shown, after the reaction in Example 1, a substance with a cuprous oxide crystal structure was deposited on the surface of the copper mesh. The deposited cuprous oxide exists in the form of nanoparticles with a diameter of approximately 250 nm.

[0116] Figure 3 These are X-ray diffraction patterns of the deposits on the copper mesh surface after the reaction in Embodiment 1 and Comparative Examples 1-2 of this disclosure.

[0117] like Figure 3As shown, in Example 1, a cuprous oxide electrocatalyst was prepared using a pulsed method under chloride ion conditions. After the reaction, the deposits on the copper mesh surface were mainly cuprous oxide and elemental copper, successfully preparing the cuprous oxide electrocatalyst. In Comparative Example 1, a copper hydroxide electrocatalyst was prepared using a pulsed method under chloride ion-free conditions. After the reaction, the deposits on the copper mesh surface were mainly copper hydroxide and elemental copper. This is because the presence of chloride ions has a significant impact on the valence state of copper; without chloride ions, copper is easily over-oxidized to divalent copper. In Comparative Example 2, a copper catalyst was prepared using a direct current electrolysis method under chloride ion conditions. After the reaction, the deposits on the copper mesh surface were only elemental copper. This is because cuprous oxide easily decomposes during the electroreduction reaction, ultimately generating elemental copper.

[0118] As can be seen from the comparison of Example 1 and Comparative Examples 1-3, the pulse preparation method of the cuprous oxide electrocatalyst disclosed herein can coat the surface of a copper substrate with a layer of cuprous oxide. This in-situ catalyst modification method has a good nitrate removal effect. If the in-situ modification of the electrocatalyst is not carried out using the pulse method, the nitrate removal effect is below 10%. In this process, no cuprous oxide is generated, and the continuous reduction will maintain its original elemental copper form, thereby inhibiting the nitrate reduction effect.

[0119] By comparing Examples 1-3 and Comparative Example 1, it can be observed that the removal rate of nitrate and the amount of nitrogen generated increase with the increase of chloride ion concentration. Meanwhile, by comparing Example 1 with Examples 4-5, it can be observed that the cuprous oxide electrocatalyst can remove nitrate ions under both acidic and alkaline conditions. Neutral or alkaline conditions are more favorable for cuprous oxide formation than acidic conditions, and are therefore more preferred. This indicates that the prepared cuprous oxide electrocatalyst has good applicability under a wide range of chloride ion concentrations and pH conditions.

[0120] By comparing Examples 1 and 6, it can be observed that in Example 6, when the reverse pulse current density decreases, cuprous oxide cannot be formed as fully as in Example 1, resulting in a decrease in the denitrification effect of Example 6 compared to Example 1.

[0121] By comparing Examples 1 and Examples 7-8, as the current density of the positive pulse increases to 25 mA cm⁻¹ in Example 7, -2 At that time, the higher reduction current accelerated the conversion of cuprous oxide to elemental copper, resulting in a less effective denitrification process in Example 7 compared to the current density of 20 mA cm⁻¹. -2 The performance of Example 1 deteriorated; when the forward current density decreased to 10 mA cm⁻¹ in Example 8, the performance worsened. -2 At that time, due to the weakening of the reduction current, the nitrate reduction reaction was inhibited, which also led to a slight decrease in the nitrate removal rate of Example 8 compared with Example 1.

[0122] By comparing Examples 1 and 9, it was found that as the pulse frequency increased to 1 Hz, the formation of cuprous oxide and the reduction of nitrate were weakened due to the faster polarization frequency. Therefore, the denitrification effect of Example 9 was worse than that of Example 1 with a pulse frequency of 0.2 Hz.

[0123] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for pulsed electrochemical denitrification, comprising: Chloride ions are added to wastewater containing nitrates, so that the wastewater contains both chloride ions and nitrate ions, wherein the wastewater containing chloride ions and nitrate ions is used as the electrolyte. An electrode pair consisting of a copper carrier and an inert electrode is placed in the electrolyte, wherein the copper carrier is mainly composed of elemental copper. Electrolysis is performed by applying a positive pulse and a reverse pulse to the electrode pair, such that during the reverse pulse, copper is oxidized on the surface of the copper support to form cuprous chloride with the chloride ions, and then hydrolyzed to form cuprous oxide. During the positive pulse, cuprous oxide is reduced to form new copper. The operation of applying positive and negative pulses to the electrode pair for electrolysis is repeated to continuously generate new cuprous oxide on the surface of the copper support, thereby obtaining a cuprous oxide electrocatalyst. The positive pulse is wherein the copper support is used as the cathode and the inert electrode is used as the anode, and the negative pulse is wherein the copper support is used as the anode and the inert electrode is used as the cathode. In the process of preparing the cuprous oxide electrocatalyst, the cuprous oxide electrocatalyst is used to simultaneously electrochemically reduce nitrate ions in the electrolyte during the positive pulse process, so that the nitrate ions are converted into nitrogen gas.

2. The method according to claim 1, wherein, The generated cuprous oxide consists of 50-500 nm nanospheres, which stack to form a cuprous oxide catalytic layer; The cuprous oxide electrocatalyst comprises the copper support and a cuprous oxide catalytic layer formed on the surface of the copper support, wherein the thickness of the cuprous oxide catalytic layer is 10 nm to 100 μm.

3. The method according to claim 1, wherein, The chloride ion concentration of the electrolyte is 1 mM to 3 M; the pH of the electrolyte is 3 to 12.

4. The method according to claim 3, wherein, The pH of the electrolyte is 5-11.

5. The method according to claim 1, wherein, The forward pulse and the reverse pulse are constant current pulses, respectively.

6. The method according to claim 5, wherein, The current density of the forward pulse is 5-30 mA cm -2 , time 2-5 s; the current density of the reverse pulse is 0.1-10 mA cm -2 , time 0.01-3 s, pulse frequency is 0.1-10 Hz.

7. The method according to claim 1, wherein: The electrolyte is industrial wastewater containing chloride ions; The copper carrier is a copper plate, copper mesh, copper sheet, copper foam, or copper film; The inert electrode is made of platinum, palladium, gold, carbon cloth, or carbon felt.

8. The method according to claim 1, wherein, The electrolyte is electroplating wastewater.

9. The method according to claim 1, further comprising: Before placing the copper carrier in the electrolyte, the copper carrier is pretreated to remove surface oil and oxide layers.

10. The method according to claim 1, wherein: The nitrate ion concentration in the wastewater is 5~2000 mg-N L. -1 .

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