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

Abstract

The invention provides a pulse preparation method of a cuprous oxide electrocatalyst, a pulse electrochemical denitrification method and application. The pulse preparation method comprises the steps that an electrode pair composed of a copper carrier and an inert electrode is placed in an electrolyte containing chloride ions, and the copper carrier takes a copper elementary substance as a main body; a forward pulse and a reverse pulse are applied to the electrode pair respectively for electrolytic treatment, so that oxidation of copper elementary substances occurs on the surface of the copper carrier during the reverse pulse to form cuprous chloride with chloride ions and then hydrolyze to form cuprous oxide, and reduction of cuprous oxide occurs during the forward pulse to form new copper elementary substances; the forward pulse and the reverse pulse are repeatedly applied to the electrode pair for electrolytic treatment, so that new cuprous oxide is continuously generated on the surface of the copper carrier, the cuprous oxide electrocatalyst is obtained, the copper carrier serves as the cathode of the forward pulse, the inert electrode serves as the anode of the reverse pulse, the copper carrier serves as the anode of the reverse pulse, and the inert electrode serves as the cathode of the reverse pulse.

Description

Technical Field

[0001] The present invention relates to the fields of electrocatalytic reduction, electrode modification, water treatment, sewage denitrification, and more particularly to a pulse preparation method of a cuprous oxide electrocatalyst and a pulse electrochemical denitrification method and application. Background Art

[0002] Nitrate ion (NO3 - ) is an important raw material widely used in industrial production and fertilizer manufacturing. However, with the increase of NO3 - As emissions increase, their negative impact on the environment has gradually become more prominent, especially in terms of water pollution, which has attracted widespread attention. In response to this problem, researchers have been looking for effective NO3 - Removal technology.

[0003] Among the many viable NO3 - In the removal technology, electrochemical NO3 - Removal technology is considered to be one of the most promising technologies due to its excellent controllability and environmental friendliness. In the electrochemical nitrate reduction reaction, copper (Cu) is a - Due to its strong adsorption capacity, copper is often considered to be the most promising electrocatalyst. - Reduction reaction intermediates (such as nitrite NO2 - and nitric oxide (NO) by excessive adsorption, which inhibits the NO3 - The further reduction of NH4+ limits its electrochemical denitrification performance.

[0004] In order to improve the catalytic performance of Cu, the reduction activity is usually improved by forming alloys of precious metals with copper. However, this method is costly and complicated to operate, and is not applicable in actual sewage treatment applications. In addition, researchers have tried to load cuprous oxide (Cu2O) on the copper surface in situ. This loading can not only reduce the interaction between copper and NO3 - The adsorption strength of the reduction reaction intermediates can extend the catalytic life of Cu and reduce NO3 - The reduction energy barrier of NO3 - However, in practical applications, the preparation method of Cu2O and electrochemical reduction are usually two independent steps, which leads to the fact that Cu2O is easily disintegrated in the electroreduction reaction in practical applications and eventually quickly converted into copper, greatly reducing its catalytic activity. Summary of the invention

[0005] In view of this, the main purpose of the present disclosure is to provide a pulse preparation method of cuprous oxide electrocatalyst and a pulse electrochemical denitrification 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 invention is as follows:

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

[0008] Placing an electrode pair consisting of a copper support and an inert electrode in an electrolyte containing chloride ions, wherein the copper support is mainly composed of a single substance of copper;

[0009] Applying a forward pulse and a reverse pulse to the electrode pair respectively to perform an electrolytic treatment, so 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, and during the forward pulse, cuprous oxide is reduced to form new copper;

[0010] Repeating the operation of applying a forward pulse and a reverse pulse to the electrode pair to perform an electrolytic treatment, so that new cuprous oxide is continuously generated on the surface of the copper support to obtain a cuprous oxide electrocatalyst;

[0011] The forward pulse uses the copper carrier as the cathode and the inert electrode as the anode, and the reverse pulse uses the copper carrier as the anode and the inert electrode as the cathode.

[0012] As a second aspect of the present disclosure, a pulse electrochemical denitrification method is provided, comprising:

[0013] Adding chloride ions to nitrate-containing sewage so that the sewage contains both chloride ions and nitrate ions;

[0014] The cuprous oxide electrocatalyst is prepared by using the above-mentioned pulse preparation method using sewage containing chloride ions and nitrate ions as an electrolyte;

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

[0016] As another aspect of the present disclosure, there is provided an application of a cuprous oxide electrocatalyst prepared by the above-mentioned pulse preparation method in the field of electrochemical reduction, especially in the field of electrochemical denitrification.

[0017] The pulse preparation method of the cuprous oxide electrocatalyst provided in the embodiment of the present disclosure utilizes forward pulse and reverse pulse treatment. During the oxidation reverse pulse, cuprous chloride is formed by the stabilizing effect of chloride ions on monovalent copper. During the reduction period, alkalinity is provided based on the hydrogen evolution side reaction, so that cuprous chloride is hydrolyzed to form cuprous oxide. At the same time, the copper element reduced to cuprous oxide can iteratively generate new cuprous oxide in the next pulse cycle. The above preparation method enables the cuprous oxide catalyst to maintain catalytic activity in the electroreduction reaction. In addition, this preparation method is simple and convenient to operate, does not require the addition of protective gas or the control of oxidation conditions, and is safe, green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1A to Figure 1C is a scanning electron microscope (SEM) image of the surface of the copper mesh after the reaction in Example 1 and Comparative Examples 1-2 of the present disclosure;

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

[0020] Figure 2B yes Figure 2A A partial enlarged view of

[0021] Figure 3 It is an X-ray diffraction (XRD) diagram of the deposit on the surface of the copper mesh after the reaction in Example 1 and Comparative Examples 1-2 of the present disclosure. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0023] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. 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 (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0024] In the process of realizing the present disclosure, it was found that when cuprous oxide was loaded in situ on the copper surface to prepare a cuprous oxide catalyst, the cuprous oxide was easily disintegrated in the electroreduction reaction and eventually converted into copper alone. This greatly reduces the catalytic activity of the catalyst and limits its application in the field of electrochemical denitrification. In this regard, the present disclosure proposes a pulse preparation method of a cuprous oxide electrocatalyst and a method and application of pulse electrochemical denitrification. Electrolysis is carried out by forward pulse and reverse pulse electric field, giving full play to the periodic redox switching function, and realizing the directional regulation of the morphology and valence state of the copper oxide layer. Under the action of the pulse electric field, the surface cuprous oxide layer is continuously updated and converted, thereby overcoming the instability of cuprous oxide during the electroreduction process. This method ensures that the cuprous oxide electrocatalyst can continuously and effectively electro-reduce nitrate ions, opening up a new way for the development of electrochemical denitrification technology.

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

[0026] In step S101, 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 a single substance of copper;

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

[0028] In step S103, the operation of applying a forward pulse and a reverse pulse to the electrode pair to perform an electrolytic treatment is repeated, so that new cuprous oxide is continuously generated on the surface of the copper support to obtain a cuprous oxide electrocatalyst;

[0029] The forward pulse uses the copper carrier as the cathode and the inert electrode as the anode, and the reverse pulse uses the copper carrier as the anode and the inert electrode as the cathode.

[0030] According to an embodiment of the present disclosure, electrolysis is performed using a pulsed electric field, and 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 the copper element will be consumed based on the hydrogen evolution side reaction, resulting in an increase in the near-surface pH value, so that the cuprous chloride is hydrolyzed to form cuprous oxide. At the same time, the cuprous oxide is reduced to a new copper element, and in the next pulse cycle, by repeatedly applying forward pulses and reverse pulses to the electrode pair, respectively, new cuprous oxide is iteratively and continuously generated, thereby ensuring the catalytic activity of the cuprous oxide electrocatalyst.

[0031] According to an embodiment of the present disclosure, the pulse preparation method may further include: before placing the copper carrier in the electrolyte, pre-treating the copper carrier to remove surface oil and oxide layer.

[0032] Further, the pretreatment operation may include: soaking the copper carrier with a degreasing agent and ultrasonically vibrating for 10 minutes, for example. The degreasing agent may be a commercial degreasing agent, comprising a surfactant and an organic solvent, to ensure that the surface oil is removed. Then, the copper carrier is placed in a dilute acid solution such as 0.1 M sulfuric acid for 1 minute, or the copper carrier is polished with sandpaper to remove the surface oxide layer. The copper mesh with the oil and oxide layer removed is thoroughly cleaned with ultrapure water to obtain a smooth and pure copper carrier, ensuring the redox reaction, thereby continuously and stably generating cuprous oxide.

[0033] According to an embodiment of the present disclosure, in step S101, the chloride ions may exist in the water body itself, such as industrial wastewater (especially electroplating wastewater) or tap water, or may be formed by adding inorganic salts containing chloride ions such as potassium chloride, sodium chloride or calcium chloride to the electrolyte. Chloride ions play a key role in stabilizing monovalent copper, and their presence or absence directly affects the change in the valence state of copper. In the subsequent electrolysis process, a stirrer is used for stirring to ensure the uniform distribution of chloride ion concentration in the reaction pool, thereby improving the electrolysis efficiency.

[0034] According to an embodiment of the present disclosure, in step S101, the copper carrier may be a copper plate, a copper mesh, a copper sheet, a copper foam, a copper film, or other copper carriers with porous or smooth surfaces. In the embodiment of the present disclosure, the parameters of the copper mesh may be: the mesh aperture is 50-500 mesh, the mesh area is 1 1~10 10 cm, 0.1~5.0 mm thick, mainly composed of single copper. The inert electrode can be a precious metal such as platinum, palladium, gold, or an inert non-metal electrode such as carbon cloth or carbon felt.

[0035] According to the embodiment of the present disclosure, in step S101, the chloride ion concentration of the electrolyte may 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 may be 3 to 12, for example, the pH may be 3, 5, 7, 11, 12, etc., preferably 5 to 11. Since hydrogen evolution side reaction occurs during reduction, hydrogen ions on the surface of the copper element will be consumed, causing the initial pH value to rise to alkaline, so 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 the embodiment of the present disclosure, in step S102 and step S103, the morphology and valence state of the oxide layer on the surface of the copper carrier are directional regulated through periodic oxidation and reduction reactions. Under the pulsed electric field, the cuprous oxide on the surface is continuously renewed and transformed, which is conducive to the continuous exertion of its electrocatalytic effect.

[0037] According to the embodiment of the present disclosure, the forward pulse and the reverse pulse are constant current pulses or constant voltage pulses, respectively. If the constant current mode is adopted, the forward output current density and time, the reverse output current density and time, and the pulse frequency need to be set. If the constant voltage mode is adopted, the forward output voltage and time, the reverse output voltage and time, and the pulse frequency need to be set.

[0038] According to the embodiment of the present disclosure, taking the case where the forward pulse and the reverse pulse are constant current pulses, the current density of the forward pulse can be 5-30 mA cm -2 , for example, 10 mA cm -2 , 15 mA cm -2 , 20 mA cm -2 , 25mA cm -2 etc., preferably 20 mA cm -2 The time is 2-5 s, for example, 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 -2 , for example, 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 , time 0~3 s, for example, it can be 0.01 s, 0.02s, 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 the embodiments of the present disclosure, the electrochemical catalytic effect of the catalyst can be ensured by adjusting appropriate forward and reverse current density parameters. Too high a forward current will cause the generated cuprous oxide to be quickly reduced to copper element during the nitrate reduction process, resulting in the inability 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 may also cause copper ions to dissolve from the aqueous solution. In addition, the adjustment of pulse parameters also needs to take into account changes in factors such as electrode area, nitrate and chloride ion concentrations, and pH value.

[0040] According to the embodiment of the present disclosure, the generated cuprous oxide can be nanosphere particles of 50 to 500 nm, which are stacked to form a cuprous oxide catalyst layer, for example, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, etc. Since the cuprous oxide nanosphere particles are of moderate size, an ideal contact area is provided, thereby ensuring that the catalyst exhibits a good catalytic effect.

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

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

[0043] According to other embodiments of the present disclosure, a pulse electrochemical denitrification method is also provided, including steps S201 to S203:

[0044] In step S201, chloride ions are added to the nitrate-containing sewage so that the sewage contains both chloride ions and nitrate ions;

[0045] In step S202, wastewater containing chloride ions and nitrate ions is used as an electrolyte, and the cuprous oxide electrocatalyst is prepared by 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 synchronously electrochemically reduce nitrate ions in the electrolyte, so that the nitrate ions are converted into nitrogen.

[0047] According to the embodiments of the present disclosure, during the electrochemical reduction of nitrate ions, the presence or absence of chloride ions will affect the valence of copper. Chloride ions can be quickly adsorbed on the copper surface to form cuprous chloride, stabilize monovalent copper ions, and prevent excessive oxidation from forming divalent copper, which in turn has a significant impact on catalytic performance. In addition, the cuprous oxide obtained based on the pulse preparation method is continuously renewed and converted, so that it can continue to play a catalytic role in reducing NO3 - The effect of this solution solves the problem of instability of cuprous oxide during the electroreduction process.

[0048] According to the embodiment of the present disclosure, the nitrate ion concentration of the sewage can be 5~2000 mg-N L -1 , for example, 5 mg-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 electro-reduction denitrification method disclosed in the present invention can be used in a wide range of NO3 - The electrochemical reduction time can be adjusted according to the nitrate ion concentration in the sewage. For example, when the nitrate ion concentration in the sewage is 50 mg-N L -1 When the concentration of nitrate ions in the sewage is high, in order to fully realize the electrochemical reduction of nitrates, the electrochemical reduction time needs to be extended accordingly.

[0049] According to another embodiment of the present disclosure, there is provided an application of a cuprous oxide electrocatalyst prepared by the pulse preparation method in the field of electrochemical reduction, for example, it can be used for electrochemical denitrification, hydrogen production, CO2 reduction synthesis of C 2+ The application in the field of electrochemical reduction of products, especially in the field of electrochemical denitrification.

[0050] The technical solution of the present disclosure is described in detail below through preferred embodiments. It should be noted that the specific embodiments below are only used for illustration and are not used to limit the present disclosure.

[0051] Example 1

[0052] Preparation of cuprous oxide electrocatalyst by pulse method under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M and its application in electrochemical denitrification:

[0053] Step S1: Preparation of nitrate simulated wastewater

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

[0055] Step S2: Copper mesh pretreatment

[0056] Soak the copper mesh in degreasing agent and ultrasonically vibrate for 10 minutes to ensure that the surface oil is removed. Then place the copper mesh in 0.1 M sulfuric acid for 1 minute to remove the surface oxide layer. The copper mesh with degreased and oxide layers removed is thoroughly cleaned with ultrapure water.

[0057] Step S3: Setting pulse power supply parameters

[0058] The constant current mode was used and the output current density of the forward pulse was set to 20 mA cm -2 , time 4 s, output current density of reverse pulse 5 mA cm -2 , time 1 s, pulse frequency 0.2 Hz. Connect the copper mesh electrode to the negative pole of the pulse power supply, 2 A 2 cm platinum sheet was connected to the positive electrode of the pulse power supply as a counter electrode.

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

[0060] Step S5: Turn on the pulse power supply, alternately apply forward pulses and reverse pulses to the electrode pair to perform electrolysis treatment, and simultaneously perform cuprous oxide synthesis and nitrate electrochemical removal. After 3 hours, determine the nitrate reduction product. Monitor the concentrations of nitrate, nitrite, and ammonia nitrogen during the nitrate reduction process, and calculate the nitrate removal efficiency and the selectivity of each product.

[0061] Nitrite, ammonia nitrogen, and nitrogen selectivity are calculated by 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 generation rate (%) = 1-C NO2-N / (C0-CNO3-N )-C NH4-N / (C0-C NO3-N )

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

[0067] After sufficient reaction, the nitrate removal rate was measured to be 85.6%, and all the products were nitrogen.

[0068] Comparative Example 1:

[0069] Preparation of copper hydroxide electrocatalyst by pulse method and its application in electrochemical denitrification under wastewater pH=7 and chloride ion-free conditions:

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

[0071] After full reaction, the nitrate removal rate was determined to be 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] Preparation of copper electrocatalyst by direct current electrolysis under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M and its application in electrochemical denitrification:

[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 -2 . Connect the copper mesh electrode to the negative pole of the DC power supply. The 2 cm platinum sheet counter electrode is connected to the positive electrode of the DC power supply. In step S4, the DC power supply is turned on to perform electrochemical removal of nitrate.

[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] Preparation of copper catalyst by direct current electrolysis under the condition of wastewater pH=7 and no chloride ions and its application in electrochemical denitrification:

[0078] The difference from Example 1 is that in step S1, 1.743 g of K2SO4 is added to the nitrate simulated wastewater solution. In step S3, the DC power supply parameters are set, the constant current mode is adopted, and the output current density is 20 mA cm -2 , connect the copper mesh electrode to the negative pole of the DC power supply, 2 The 2 cm platinum sheet counter electrode is connected to the positive electrode of the DC power supply. In step S4, the DC power supply is turned on to perform electrochemical removal of nitrate.

[0079] After sufficient reaction, the nitrate removal rate was determined to be 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] Embodiment 2:

[0081] Preparation of cuprous oxide electrocatalyst by pulse method under the conditions of wastewater pH=7 and chloride ion concentration of 0.02 M and its application in electrochemical denitrification:

[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 full reaction, the nitrate removal rate was measured to be 54.7%, the selectivity of nitrite in the product was 10.2%, ammonia nitrogen accounted for 43%, and nitrogen accounted for 46.8%.

[0084] Embodiment 3:

[0085] Preparation of cuprous oxide electrocatalyst by pulse method under the conditions of wastewater pH=7 and chloride ion concentration of 0.06 M and its application in electrochemical denitrification:

[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 full reaction, the nitrate removal rate was measured to be 72.8%, the selectivity of nitrite in the product was 3.5%, ammonia nitrogen accounted for 7.8%, and nitrogen accounted for 88.7%.

[0088] Embodiment 4:

[0089] Preparation of cuprous oxide electrocatalyst by pulse method under the conditions of wastewater pH=3 and chloride ion concentration of 0.1 M and its application in electrochemical denitrification:

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

[0091] After sufficient reaction, the nitrate removal rate was measured to be 17.6%, and all the products were nitrogen.

[0092] Embodiment 5:

[0093] Preparation of cuprous oxide electrocatalyst by pulse method under the conditions of wastewater pH=11 and chloride ion concentration of 0.1 M and its application in electrochemical denitrification:

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

[0095] After sufficient reaction, the nitrate removal rate was determined to be 56.0%, and all the products were nitrogen.

[0096] Example 6

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

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

[0099] After sufficient reaction, the nitrate removal rate was measured to be 51.6%, and all the products were nitrogen.

[0100] Example 7

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

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

[0103] After sufficient reaction, the nitrate removal rate was measured to be 41.7%, and all the products were nitrogen.

[0104] Example 8

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

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

[0107] After sufficient reaction, the nitrate removal rate was determined to be 64.8%, and all the products were nitrogen.

[0108] Example 9

[0109] Under the conditions of wastewater pH=7 and chloride ion concentration of 0.1 M, the pulse frequency was adjusted to prepare cuprous oxide electrocatalyst using the pulse method and its application in electrochemical denitrification:

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

[0111] After sufficient reaction, the nitrate removal rate was determined to be 58.1%, and all the products were nitrogen.

[0112] Figure 1A to Figure 1C It is a scanning electron microscope image of the surface of the copper mesh after the reaction in Example 1 and Comparative Examples 1-2 of the present disclosure is completed.

[0113] like Figure 1A As shown, in Example 1, a cuprous oxide electrocatalyst was prepared by a pulse method in the presence of chloride ions. After a full reaction for 3 hours, a layer of sediment was evenly covered on the surface of the copper mesh. Figure 1B to Figure 1C As shown, when comparative examples 1 and 2 were prepared without chloride ions or without the pulse method, only a small amount or uneven deposits were generated on the surface of the copper mesh.

[0114] Figure 2A is a transmission electron microscope image of the deposit on the surface of the copper mesh after the reaction in Example 1 of the present disclosure is completed; Figure 2B yes Figure 2A A partial enlarged view of .

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

[0116] Figure 3 It is an X-ray diffraction diagram of the deposit on the surface of the copper mesh after the reaction in Example 1 and Comparative Examples 1-2 of the present disclosure.

[0117] like Figure 3As shown, in Example 1, a cuprous oxide electrocatalyst was prepared by a pulse method under the condition of chloride ions. After the reaction, the surface deposits of the copper mesh were mainly cuprous oxide and copper elemental substance, and the cuprous oxide electrocatalyst was successfully prepared. In Comparative Example 1, a copper hydroxide electrocatalyst was prepared by a pulse method under the condition of no chloride ions. After the reaction, the surface deposits of the copper mesh were mainly copper hydroxide and copper elemental substance. This is because the presence of chloride ions has an important influence on the valence state of copper. In the absence of chloride ions, copper is easily over-oxidized to divalent copper. In Comparative Example 2, a copper catalyst was prepared by a direct current electrolysis method under the condition of chloride ions. After the reaction, the surface deposits of the copper mesh were only copper elemental substance. This is because cuprous oxide is easily decomposed in the electroreduction reaction, and copper elemental substance is finally generated.

[0118] From the comparison between Example 1 and Comparative Examples 1 to 3, it can be seen that the pulse preparation method of the cuprous oxide electrocatalyst disclosed in the present invention can cover a layer of cuprous oxide on the surface of the elemental copper substrate, and this in-situ catalyst modification method has a good nitrate removal effect. If the pulse method is not used to modify the electrocatalyst in situ, the nitrate removal effect is less than 10%, and no cuprous oxide is generated in the process. The continuous reduction action will maintain its original elemental copper form, thereby inhibiting the nitrate reduction effect.

[0119] By comparing Examples 1 to 3 with Comparative Example 1, it can be observed that the removal rate of nitrate and the amount of nitrogen generated will increase accordingly with the increase of chloride ion concentration. At the same time, by comparing Example 1 with Examples 4 to 5, it can be observed that the cuprous oxide electrocatalyst can remove nitrate ions under both acidic and alkaline conditions, and relative to acidic conditions, neutral or alkaline conditions are more conducive to the generation of cuprous oxide, and therefore are more preferred. It shows that the prepared cuprous oxide electrocatalyst has good applicability under a wide range of chloride ion concentrations and pH conditions.

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

[0121] By comparing Example 1 with Examples 7 and 8, as the current density of the forward pulse increases to 25 mA cm-1 of Example 7, -2 When the current density is 20 mA cm, the higher reduction current accelerates the conversion of cuprous oxide to elemental copper, resulting in a higher denitrification effect in Example 7 than in Example 7. -2 Example 1 deteriorates; when the forward current density is reduced to 10 mA cm-1 of Example 8 -2 When the reduction current is reduced, the nitrate reduction reaction is inhibited, which also causes the nitrate removal rate of Example 8 to be slightly lower than that of Example 1.

[0122] By comparing Example 1 and Example 9, as the pulse frequency increases to 1 Hz, due to the faster polarization frequency, the formation of cuprous oxide and the nitrate reduction process are weakened. Therefore, the denitrification effect of Example 9 is 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 the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A pulse preparation method of a cuprous oxide electrocatalyst, comprising: Placing an electrode pair consisting of a copper support and an inert electrode in an electrolyte containing chloride ions, wherein the copper support is mainly composed of a single substance of copper; Applying a forward pulse and a reverse pulse to the electrode pair respectively to perform an electrolytic treatment, so 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, and during the forward pulse, cuprous oxide is reduced to form new copper; Repeating the operation of applying a forward pulse and a reverse pulse to the electrode pair to perform electrolysis treatment, so that new cuprous oxide is continuously generated on the surface of the copper support to obtain the cuprous oxide electrocatalyst; The forward pulse is formed by using the copper support as the cathode and the inert electrode as the anode, and the reverse pulse is formed by using the copper support as the anode and the inert electrode as the cathode.

2. The pulse preparation method according to claim 1, wherein: The generated cuprous oxide is in the form of nanosphere particles of 50 to 500 nm, which are stacked to form a cuprous oxide catalytic layer; The cuprous oxide electrocatalyst comprises the copper carrier and a cuprous oxide catalyst layer formed on the surface of the copper carrier, and the thickness of the cuprous oxide catalyst layer is 10 nm to 100 μm.

3. The pulse preparation 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, preferably 5 to 11.

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

5. The pulse preparation method according to claim 4, 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 0~10 mA cm -2 , time 0~3 s, pulse frequency 0.1~10Hz.

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

7. The pulse preparation 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 layer.

8. A pulse electrochemical denitrification method comprising: Adding chloride ions to the nitrate-containing sewage so that the sewage contains both chloride ions and nitrate ions; Using the sewage containing chloride ions and nitrate ions as an electrolyte, preparing a cuprous oxide electrocatalyst by the pulse preparation method according to any one of claims 1 to 7; In the process of preparing the cuprous oxide electrocatalyst, the cuprous oxide electrocatalyst is used to synchronously electrochemically reduce nitrate ions in the electrolyte during a forward pulse process, so that the nitrate ions are converted into nitrogen.

9. The method according to claim 8, wherein: The nitrate ion concentration of the sewage is 5~2000 mg-N L -1 .

10. Use of a cuprous oxide electrocatalyst prepared by the pulse preparation method according to any one of claims 1 to 7 in the field of electrochemical reduction, especially in the field of electrochemical denitrification.

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