Efficient Ni2P nano electrocatalyst for removing nitrate in water body and preparation method of efficient Ni2P nano electrocatalyst

Abstract

The invention provides an efficient Ni2P nano electrocatalyst for removing nitrate in a water body and a preparation method thereof.The preparation method comprises the steps that pretreated foamed nickel is soaked in deionized water to be subjected to a hydrothermal reaction under the closed condition to prepare foamed nickel with Ni (OH) 2 growing on the surface in situ, then the foamed nickel is placed on the downstream portion of a tubular furnace, phosphorus salt is placed on the upstream portion of the tubular furnace, and the high-efficiency Ni2P nano electrocatalyst for removing nitrate in the water body is obtained; and carrying out gas-phase phosphating treatment under an inert atmosphere condition to prepare the high-efficiency Ni2P nano electrocatalyst. Compared with Ni (OH) 2 grown in situ through a traditional hydrothermal method recorded in literature, Ni (OH) 2 grown in situ only by dipping foamed nickel in deionized water under a closed condition is accidentally found, the removal rate of nitrate in a water body is remarkably increased, the nitrate conversion rate can reach 70% or above, and the preparation method is simple and easy to implement. The industrial application of the nickel-based catalyst without noble metal components is expected to be realized, and the nickel-based catalyst is greatly superior to similar products recorded in existing literatures in the field.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalysts for removing nitrates from water bodies, and relates to a high-efficiency Ni2P nano electrocatalyst for removing nitrates from water bodies and a preparation method thereof. Background Art

[0002] With the rapid expansion of industry and agriculture in my country, water pollution has become increasingly serious, especially nitrate pollution, which has become a significant environmental challenge. The widespread presence of nitrates not only affects the self-purification capacity of water bodies, but also poses a potential threat to human health. Nitrates mainly come from agricultural activities, industrial emissions, domestic sewage, etc. Long-term intake of excessive nitrates can cause serious harm to human health, such as blue baby syndrome, gastric cancer and other diseases. Therefore, studying an efficient and environmentally friendly nitrate removal method is of great significance to ensure the safety of people's domestic water.

[0003] At present, the main methods for removing nitrate from water include biological method, physical method, chemical method, etc., but these methods have certain limitations. For example, the treatment effect of biological method is greatly affected by factors such as water quality and temperature; physical methods such as reverse osmosis and ion exchange have high equipment investment and operating costs; chemical methods such as reduction method are prone to secondary pollution. In view of the limitations of the above methods, electrocatalysis, as an emerging nitrate removal technology, has gradually attracted the attention of researchers. The electrocatalytic method uses electrode materials to catalyze the reduction of nitrate by applying current. The electrocatalytic method has significant advantages: it can not only achieve efficient removal of nitrate, but also has a simple operation process and fast reaction speed, and does not require the addition of chemical reagents, avoiding the risk of secondary pollution; at the same time, the electrocatalytic process has low energy consumption, good economic benefits, and is environmentally friendly and does not produce harmful by-products. Therefore, it shows great potential and application value in ensuring water quality safety and environmental protection.

[0004] At present, the commonly used catalysts for electrocatalysis include precious metals (such as platinum and palladium), non-precious metals (such as iron and nickel), carbon materials (such as graphene) and composite materials. Precious metal catalysts are highly active but expensive, non-precious metals are relatively inactive but have low costs, carbon materials have good conductivity but insufficient stability, and composite materials have adjustable performance but are complex to prepare. Nickel-based catalysts have attracted attention due to their high catalytic activity, low cost and good stability. Their advantages are that they can effectively reduce nitrates in a wide potential range and have good corrosion resistance in acidic or alkaline environments, making them suitable for practical water treatment applications.

[0005] For example, the Chinese invention patent application "A new denitrification system for efficiently removing nitrates from water bodies by means of electrocatalytic hydrogen evolution and catalytic hydrogenation and its application" (CN111533220A) discloses a new denitrification system for efficiently removing nitrates from water bodies by means of electrocatalytic hydrogen evolution and catalytic hydrogenation and its application. The denitrification system comprises an electrolytic cell and a three-electrode system inserted into the electrolytic cell. The electrolytic cell contains an electrolyte in which a denitrification catalyst is dispersed and suspended. The three-electrode system comprises a working electrode, a counter electrode and a reference electrode. The counter electrode is a Pt sheet, and the working electrode is a catalyst Ni3S2-NF. The steps for preparing the catalyst Ni3S2-NF are as follows: first, a nickel mesh of a certain size is cut and cleaned; then, the cleaned nickel mesh is added to a thiourea solution and allowed to react under hydrothermal conditions, and then the catalyst Ni3S2-NF is obtained by washing and drying.

[0006] However, in the above-mentioned public technologies and existing technologies, it was found through investigation and summary that when using pure nickel-based catalysts, there is still an objective problem of low nitrate removal efficiency, which invisibly greatly increases the cost of water treatment.

[0007] In summary, there is an urgent need for a nickel-based catalyst that is free of precious metal components and has good electrocatalytic performance to remove nitrate pollutants in water bodies. In order to be more suitable for industrial applications, the preparation process of the electrocatalyst should be relatively simple and reasonable and suitable for industrial production and application. Summary of the invention

[0008] In order to solve the above-mentioned problems in the prior art, the present invention provides a high-efficiency Ni2P nano-electrocatalyst for removing nitrate from water and a preparation method thereof. It is accidentally discovered that under closed conditions, Ni(OH)2 grown in situ by hydrothermal method by immersing nickel foam in deionized water is treated with phosphate by gas phase phosphating method in a tubular furnace to prepare the obtained Ni2P nano-electrocatalyst. Compared with the traditional hydrothermal method for in situ growth of Ni(OH)2 as recorded in the literature, the removal rate of nitrate in water is significantly increased, and the nitrate conversion rate at a voltage of -1.2V (with Ag / AgCl as the reference electrode) can reach more than 70%, which is expected to realize the industrial application of nickel-based catalysts without precious metal components, and is significantly superior to similar products recorded in the existing literature in this field.

[0009] To achieve the above objectives, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0010] The present invention provides a method for preparing a highly efficient Ni2P nano electrocatalyst for removing nitrate from water, which mainly comprises the following steps:

[0011] (1) subjecting the nickel foam to a pretreatment mainly including washing and then putting it into use;

[0012] (2) immersing the nickel foam pretreated in step (1) in deionized water and subjecting it to a hydrothermal reaction at 115-125° C. under closed conditions for 5-7 hours. After the time is up, taking out the solid product and subjecting it to vacuum drying treatment to obtain a nickel foam with Ni(OH)2 grown in situ on the surface;

[0013] (3) placing the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of the tubular furnace, placing the phosphate salt upstream of the tubular furnace, and treating it by gas phase phosphating method under inert atmosphere to prepare a high-efficiency Ni2P nano-electrocatalyst.

[0014] In this article, the nickel foam described in step (1) is conventionally commercially available, and preferably uses nickel foam of common specifications in the technical field (electrocatalyst).

[0015] In this article, the nickel foam in step (1) is usually attached with residual impurities or other impurities / stains, which will affect the catalytic performance of the catalyst prepared subsequently, especially the commercially available nickel foam raw material. Based on this, the nickel foam needs to be pretreated mainly including washing, and the pretreatment mainly including washing can be a pretreatment method known in the art. Those skilled in the art can perform specific operations according to conventional production processes or methods recorded in the prior art.

[0016] In order to better illustrate the present invention and provide a preferred technical solution for reference, the nickel foam is subjected to a pretreatment mainly including washing in step (1), wherein the nickel foam is immersed in acetone and 3 mol / L hydrochloric acid in sequence and ultrasonically treated for 10 to 15 min respectively, and then immersed in ethanol and water in sequence and ultrasonically treated for 2 to 3 min respectively, and finally washed alternately with ethanol and water three times respectively, and then vacuum dried for standby use.

[0017] It should be noted that the above-mentioned preferred technical scheme mainly includes the pretreatment of washing, and its main purpose is to remove residual impurities or other impurities / stains attached to the surface of the nickel foam. The specific process steps of the above-mentioned preferred pretreatment are mainly carried out under laboratory conditions. In actual industrial production, the pretreatment method can be improved and replaced according to actual conditions and based on common knowledge.

[0018] In this article, the pretreated nickel foam in step (2) is immersed in deionized water, wherein the amount of deionized water used should be calculated according to the raw material specifications of the nickel foam, and it is preferable that the nickel foam can be completely immersed. In order to better illustrate the present invention and provide a technical solution for reference, under laboratory conditions, the material-liquid ratio of the nickel foam to deionized water is preferably 1g: (100-130)ml.

[0019] In this article, the phosphate salt described in step (3) is a conventional phosphate salt selected based on the phosphating reaction in the gas phase phosphating method. Those skilled in the art can refer to the common knowledge of the gas phase phosphating method to select a suitable phosphate salt. The amount of phosphate salt used should be based on the Ni(OH)2 phosphating reaction to generate Ni2P.

[0020] In order to better illustrate the present invention and provide a technical solution for reference, the phosphate salt selected in step (3) includes any one of sodium hypophosphite and potassium hypophosphite; the mass ratio of the nickel foam with in-situ growth of Ni(OH)2 on the surface to the phosphate salt is preferably 1:(2-4).

[0021] In this article, the gas phase phosphating treatment in step (3) is a conventional process operation based on the common knowledge of gas phase phosphating method, which volatilizes the phosphate salt at high temperature and transports it to the downstream nickel foam surface through gas phase, and reacts with the nickel foam for phosphating.

[0022] In order to better illustrate the present invention and provide a preferred technical solution, the gas phase phosphating treatment in step (3) is to place the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of the tube furnace, place the phosphate salt upstream of the tube furnace, and calcine it in the tube furnace under inert atmosphere to prepare a high-efficiency Ni2P nano electrocatalyst;

[0023] The tube furnace calcination process is carried out according to the following heating method:

[0024] ① Raise the temperature to 28-32°C and maintain the temperature for 55-65 minutes;

[0025] ② Raise the temperature to 250-350℃ at a rate of 1-3℃ / min, maintain this temperature for 50-70min and then cool naturally.

[0026] The inert atmosphere condition may be high purity nitrogen or argon.

[0027] The high-efficiency Ni2P nano-electrocatalyst prepared by gas phase phosphating method can be used after washing and drying according to the common knowledge in the art.

[0028] It should be noted that the inventors of the present invention found in the research summary that there are few pure nickel-based catalysts used for nitrate removal in water bodies in the currently disclosed literature, and most of them are used in conjunction with precious metals such as platinum and palladium. On this basis, in order to explore the efficient industrial preparation of nickel-based catalysts, the conventional hydrothermal method recorded in the literature to grow Ni(OH)2 in situ was restored based on actual experiments, that is, nickel foam or nickel sheet was immersed in a mixed solution of nickel nitrate hexahydrate, ammonium fluoride and urea for hydrothermal reaction, and then Ni2P electrocatalyst was prepared by tubular furnace gas phase phosphating method, but the nitrate removal rate of the catalyst was poor after testing, which is far from meeting the current water treatment needs.

[0029] During the above experiment, it was discovered by chance that the above complex mixed solution system was replaced with simple deionized water and the hydrothermal reaction was carried out under closed conditions. The Ni2P nano-electrocatalyst prepared finally showed a significant enhancement in nitrate removal rate, and after electron microscopy scanning, it was clearly observed that there were dense nano-sheet structures on the catalyst surface. This discovery is expected to realize the industrial application of nickel-based catalysts without precious metal components, and is much better than similar products recorded in existing literature in this field.

[0030] In this article, the mechanical stirring, washing and drying all follow the conventional principles in chemical processes, and those skilled in the art can perform specific operations according to common knowledge.

[0031] In the above technical solution, under laboratory conditions, drying is usually performed by vacuum drying, for example, placing the product in a vacuum drying oven at a temperature of 50 to 70° C. for at least 4 hours.

[0032] On the other hand, the efficient Ni2P nano-electrocatalyst for removing nitrate from water provided by the present invention is used to remove nitrate and nitrite from water, and has a better removal effect when the water temperature is 20-30°C, the nitrate concentration is 100-250 mg / L or the nitrite concentration is 100-350 mg / L.

[0033] The present invention has the following beneficial effects:

[0034] 1. The present invention provides a highly efficient Ni2P nano-electrocatalyst for removing nitrate from water and a method for preparing the same. It is accidentally discovered that under closed conditions, Ni(OH)2 grown in situ by hydrothermal method by immersing nickel foam in deionized water is treated with phosphate by gas phase phosphating method in a tubular furnace. Compared with the conventional hydrothermal method for in situ growth of Ni(OH)2 as recorded in the literature, the removal rate of nitrate from water is significantly increased, and the nitrate conversion rate at a voltage of -1.2V (with Ag / AgCl as the reference electrode) can reach more than 70%, which is expected to realize the industrial application of nickel-based catalysts without precious metal components, and is significantly superior to similar products recorded in existing literature in this field.

[0035] 2. The present invention has the characteristics of low cost, simple synthesis and industrial application scale, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a scanning electron microscope image of the surface of the highly efficient Ni2P nano-electrocatalyst prepared in Example 1. It can be clearly observed that there are dense nano-sheet structures on the surface of the sample.

[0037] Figure 2 This is the EDX element mapping of Ni, P and O of the highly efficient Ni2P nano-electrocatalyst prepared in Example 1.

[0038] Figure 3 This is the XRD pattern of the highly efficient Ni2P nano-electrocatalyst prepared in Example 1. It can be seen that the XRD pattern has obvious diffraction peaks in the angle ranges of 39-43°, 45-50° and 53-55°, proving that the highly efficient Ni2P nano-electrocatalyst was successfully synthesized and prepared.

[0039] Figure 4 This is a nitrate removal rate curve diagram of the high-efficiency Ni2P nano-electrocatalyst prepared in Example 1 after testing.

[0040] Figure 5 This is a graph showing the nitrite removal rate of the highly efficient Ni2P nano-electrocatalyst prepared in Example 1 after testing.

[0041] Figure 6 This is a comparison chart of ammonia yield and Faraday efficiency obtained by the high-efficiency Ni2P nano-electrocatalyst prepared in Example 1 under different sodium nitrate concentrations.

[0042] Figure 7 This is a comparison chart of ammonia yield and Faraday efficiency obtained by the high-efficiency Ni2P nano-electrocatalyst prepared in Example 1 under different sodium nitrite concentrations.

[0043] Figure 8The nitrate removal rate comparison curve of the catalyst samples prepared in Example 1 and Comparative Example 1 obtained through testing is shown in FIG. DETAILED DESCRIPTION

[0044] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously change or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0045] The present invention provides a method for preparing a highly efficient Ni2P nano electrocatalyst for removing nitrate from water, which mainly comprises the following steps:

[0046] (1) subjecting the nickel foam to a pretreatment mainly including washing and then putting it into use;

[0047] (2) immersing the nickel foam pretreated in step (1) in deionized water and subjecting it to a hydrothermal reaction at 115-125° C. under closed conditions for 5-7 hours. After the time is up, taking out the solid product and subjecting it to vacuum drying treatment to obtain a nickel foam with Ni(OH)2 grown in situ on the surface;

[0048] (3) placing the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of the tubular furnace, placing the phosphate salt upstream of the tubular furnace, and treating it by gas phase phosphating method under inert atmosphere to prepare a high-efficiency Ni2P nano-electrocatalyst.

[0049] In this article, the nickel foam described in step (1) is conventionally commercially available, and preferably uses nickel foam of common specifications in the technical field (electrocatalyst).

[0050] In this article, the nickel foam in step (1) is usually attached with residual impurities or other impurities / stains, which will affect the catalytic performance of the catalyst prepared subsequently, especially the commercially available nickel foam raw material. Based on this, the nickel foam needs to be pretreated mainly including washing, and the pretreatment mainly including washing can be a pretreatment method known in the art. Those skilled in the art can perform specific operations according to conventional production processes or methods recorded in the prior art.

[0051] In order to better illustrate the present invention and provide a preferred embodiment for reference, the nickel foam is subjected to a pretreatment mainly including washing in step (1), wherein the nickel foam is immersed in acetone and 3 mol / L hydrochloric acid in sequence and ultrasonically treated for 10 to 15 min respectively, and then immersed in ethanol and water in sequence and ultrasonically treated for 2 to 3 min respectively, and finally washed alternately with ethanol and water three times respectively, and then vacuum dried for standby use.

[0052] It should be noted that the above-mentioned preferred technical scheme mainly includes the pretreatment of washing, and its main purpose is to remove residual impurities or other impurities / stains attached to the surface of the nickel foam. The specific process steps of the above-mentioned preferred pretreatment are mainly carried out under laboratory conditions. In actual industrial production, the pretreatment method can be improved and replaced according to actual conditions and based on common knowledge.

[0053] In this article, the pretreated nickel foam in step (2) is immersed in deionized water, wherein the amount of deionized water used should be calculated according to the raw material specifications of the nickel foam, and it is preferable that the nickel foam can be completely immersed. In order to better illustrate the present invention and provide an implementation method for reference, under laboratory conditions, the material-liquid ratio of the nickel foam to deionized water is preferably 1g: (100-130)ml.

[0054] In this article, the phosphate salt described in step (3) is a conventional phosphate salt selected based on the phosphating reaction in the gas phase phosphating method. Those skilled in the art can refer to the common knowledge of the gas phase phosphating method to select a suitable phosphate salt. The amount of phosphate salt used should be based on the Ni(OH)2 phosphating reaction to generate Ni2P.

[0055] In order to better illustrate the present invention and provide an implementation method for reference, the phosphate salt selected in step (3) includes any one of sodium hypophosphite and potassium hypophosphite; the mass ratio of the nickel foam with in-situ growth of Ni(OH)2 on the surface to the phosphate salt is preferably 1:(2-4).

[0056] In this article, the gas phase phosphating treatment in step (3) is a conventional process operation based on the common knowledge of gas phase phosphating method, which volatilizes the phosphate salt at high temperature and transports it to the downstream nickel foam surface through gas phase, and reacts with the nickel foam for phosphating.

[0057] In order to better illustrate the present invention and provide a preferred embodiment, the gas phase phosphating treatment in step (3) is to place the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of the tube furnace, place the phosphate salt upstream of the tube furnace, and calcine it in the tube furnace under inert atmosphere to prepare a high-efficiency Ni2P nano electrocatalyst;

[0058] The tube furnace calcination process is carried out according to the following heating method:

[0059] ① Raise the temperature to 28-32°C and maintain the temperature for 55-65 minutes;

[0060] ② Raise the temperature to 250-350℃ at a rate of 1-3℃ / min, maintain this temperature for 50-70min and then cool naturally.

[0061] The inert atmosphere condition may be high purity nitrogen or argon.

[0062] The high-efficiency Ni2P nano-electrocatalyst prepared by gas phase phosphating method can be used after washing and drying according to the common knowledge in the art.

[0063] It should be noted that the inventors of the present invention found in the research summary that there are few pure nickel-based catalysts used for nitrate removal in water bodies in the currently disclosed literature, and most of them are used in conjunction with precious metals such as platinum and palladium. On this basis, in order to explore the efficient industrial preparation of nickel-based catalysts, the conventional hydrothermal method recorded in the literature to grow Ni(OH)2 in situ was restored based on actual experiments, that is, nickel foam or nickel sheet was immersed in a mixed solution of nickel nitrate hexahydrate, ammonium fluoride and urea for hydrothermal reaction, and then Ni2P electrocatalyst was prepared by tubular furnace gas phase phosphating method, but the nitrate removal rate of the catalyst was poor after testing, which is far from meeting the current water treatment needs.

[0064] During the above experiment, it was discovered by chance that the above complex mixed solution system was replaced with simple deionized water and the hydrothermal reaction was carried out under closed conditions. The Ni2P nano-electrocatalyst prepared finally showed a significant enhancement in nitrate removal rate, and after electron microscopy scanning, it was clearly observed that there were dense nano-sheet structures on the catalyst surface. This discovery is expected to realize the industrial application of nickel-based catalysts without precious metal components, and is much better than similar products recorded in existing literature in this field.

[0065] In this article, the mechanical stirring, washing and drying all follow the conventional principles in chemical processes, and those skilled in the art can perform specific operations according to common knowledge.

[0066] In the above embodiment, under laboratory conditions, the drying is usually performed by vacuum drying, for example, placing the drying chamber in a vacuum drying oven at a temperature of 50 to 70° C. for at least 4 hours.

[0067] On the other hand, the efficient Ni2P nano-electrocatalyst for removing nitrate from water provided by the present invention is used to remove nitrate and nitrite from water, and has a better removal effect when the water temperature is 20-30°C, the nitrate concentration is 100-250 mg / L or the nitrite concentration is 100-350 mg / L.

[0068] The present invention will be further explained in detail with reference to the following examples. However, it should be understood by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0069] Example

[0070] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. The specific conditions not specified in the examples are carried out according to the conditions recommended by normal conditions or manufacturers. The reagents used or the instruments not specified by the manufacturer are all conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0071] 1. Raw materials

[0072] Nickel foam (NF) was purchased from Tianjin Annuohe New Energy Technology Co., Ltd.

[0073] Sodium nitrate (NaNO3), sodium sulfate (Na2SO4), sodium hypophosphite (NaH2PO2·H2O), sodium nitrite (NaNO2), acetone (C3H6O) and hydrochloric acid (HCl) were purchased from Chengdu Kelong Chemical Co., Ltd.

[0074] Deionized water (18.2 MΩ / cm) was used throughout the experiment.

[0075] 2. Test Method

[0076] Electrode Characterization The crystal information of the prepared catalytic electrode was studied using X-ray diffraction (XRD, Rigaku Ultima IV). The morphological characterization was performed using scanning electron microscopy (SEM, sigma300). The elemental composition and concentration were analyzed using energy dispersive X-ray spectroscopy (EDX).

[0077] Electrochemical measurements were performed using a CHI 660E electrochemical analyzer in a standard three-electrode system, with catalyst samples Example 1 and Comparative Example 1 as working electrodes, platinum as counter electrodes, and Ag / AgCl electrodes as reference electrodes. 100 mg / L NaNO3 / NaNO2 was used as the cathode electrolyte, and 0.05 M Na2SO4 (60 mL) was used as the anode electrolyte. In addition, this study explored the effects of nickel phosphide electrode on the performance of the electrochemical reaction at different initial NO3 - -N concentration (20~350mg / L), NO2 --N concentration (20 ~ 350mg / L) and potential (-0.38 ~ -0.78V vs. RHE) activity detection. In each test, 60mL of 0.05MNa2SO4 solution was introduced into the anode chamber, and different amounts of 3g / L sodium nitrate and 0.05M Na2SO4 were added to the cathode chamber. A total of 60mL of mixed solution. During the reaction, all electrolytes in the cathode chamber were magnetically stirred at a speed of 400 revolutions per minute, and all reactions were carried out at a constant temperature of 25 ± 2 ° C. Solution samples were collected regularly for quantitative determination of NO3 - -N, NO2 - -N and NH3-N. In all electrolysis experiments, about 1.5 mL of solution was extracted at fixed intervals to determine the nitrogen concentration.

[0078] All electrochemical tests were performed at room temperature and all measured electrochemical potentials were calibrated with a reversible hydrogen electrode (RHE) using the following formula:

[0079] E(V vs.RHE)=E(Ag / AgCl)+0.197+0.059×pH

[0080] Where E(V vs. RHE) is the conversion potential relative to RHE (V), E(Ag / AgCl) is the experimentally measured potential relative to the Ag / AgCl reference electrode, and 0.197 is the standard potential value of the Ag / AgCl reference electrode (saturated KCl electrolyte) at 25°C.

[0081] Calculate the conversion rate of nitrate:

[0082] Conversion rate = (C0-C t / C0)×100%

[0083] Where C is the nitrate concentration (mg / L);

[0084] Calculate the Faradaic efficiency during the nitrate reaction:

[0085]

[0086] Where F is the Faraday constant (96485 C / mol) and Q is the total charge passing through the electrode.

[0087] Calculate the Faradaic efficiency during the nitrite reaction:

[0088]

[0089] Where F is the Faraday constant (96485 C / mol) and Q is the total charge passing through the electrode.

[0090] The formula for calculating ammonia yield is:

[0091]

[0092] in, represents the concentration of NH3 generated (mg / mL), V represents the volume of the cathode chamber (mL), t represents the reaction time (h), and A represents the effective area of ​​the electrode (cm 2 ).

[0093] 3. Preparation method

[0094] (1) nickel foam (2×3×1.5 cm) was immersed in acetone and 3 mol / L hydrochloric acid for ultrasonic treatment for 10 min, then immersed in ethanol and water for ultrasonic treatment for 3 min, and finally washed with ethanol and water alternately for three times, and then dried in vacuum for use;

[0095] (2) immersing the nickel foam pretreated in step (1) in 35 mL of deionized water and subjecting it to a hydrothermal reaction at 120° C. under closed conditions for 6 h. After the time is up, taking out the solid product and subjecting it to vacuum drying treatment to obtain a nickel foam with Ni(OH)2 in situ grown on the surface;

[0096] (3) placing the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) in the downstream of a tubular furnace, placing 900 mg of sodium hypophosphite in the upstream of the tubular furnace, and calcining the nickel foam in a tubular furnace under a high-purity nitrogen atmosphere (purity ≥ 99.999%) to prepare a highly efficient Ni2P nano-electrocatalyst;

[0097] The tube furnace calcination process is carried out according to the following heating method:

[0098] ① After heating to 30℃, maintain this temperature for 60min;

[0099] ② Raise the temperature to 300℃ at a rate of 2℃ / min, maintain this temperature for 60min and then cool naturally;

[0100] The naturally cooled product was washed with ethanol and water respectively and then vacuum dried to obtain a highly efficient Ni2P nano-electrocatalyst.

[0101] Example 1

[0102] Example 1 follows the steps of “3. Preparation method” above to finally prepare a highly efficient Ni2P nano-electrocatalyst as a sample.

[0103] Comparative Example 1

[0104] Comparative Example 1 is to prepare a Ni2P electrocatalyst as a comparative sample according to the following steps:

[0105] (1) nickel foam (2×3×1.5 cm) was immersed in acetone and 3 mol / L hydrochloric acid for ultrasonic treatment for 10 min, then immersed in ethanol and water for ultrasonic treatment for 3 min, and finally washed with ethanol and water alternately for three times, and then dried in vacuum for use;

[0106] (2) immersing the nickel foam pretreated in step (1) in a mixed solution consisting of 4 mmol nickel nitrate hexahydrate, 8 mmol ammonium fluoride, 20 mmol urea and 35 mL deionized water, and subjecting the mixture to a hydrothermal reaction at 120° C. for 6 h under closed conditions. After the time is up, taking out the solid product and subjecting it to vacuum drying, thereby obtaining a nickel foam with Ni(OH)2 in situ grown on the surface;

[0107] (3) placing the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) in the downstream of a tubular furnace, placing 900 mg of sodium hypophosphite in the upstream of the tubular furnace, and calcining the nickel foam in a tubular furnace under a high-purity nitrogen atmosphere (purity ≥ 99.999%) to prepare a highly efficient Ni2P nano-electrocatalyst;

[0108] The tube furnace calcination process is carried out according to the following heating method:

[0109] ① After heating to 30℃, maintain this temperature for 60min;

[0110] ② Raise the temperature to 300℃ at a rate of 2℃ / min, maintain this temperature for 60min and then cool naturally;

[0111] The product after natural cooling was washed with ethanol and water respectively and then vacuum dried to obtain the Ni2P electrocatalyst.

[0112] The test results are as follows Figures 1 to 8 As shown, the Ni2P nano-electrocatalyst prepared in Example 1 showed a significant enhancement in nitrate removal rate, and after electron microscopy scanning, it can be clearly observed that there are dense nano-sheet structures on the catalyst surface.

[0113] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a highly efficient Ni2P nano-electrocatalyst for removing nitrate from water, characterized in that The main steps include: (1) subjecting the nickel foam to a pretreatment mainly including washing and then putting it into use; (2) immersing the nickel foam pretreated in step (1) in deionized water and subjecting it to a hydrothermal reaction at 115-125° C. under closed conditions for 5-7 hours. After the time is up, taking out the solid product and subjecting it to vacuum drying treatment to obtain a nickel foam with Ni(OH)2 grown in situ on the surface; (3) placing the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of the tubular furnace, placing the phosphate salt upstream of the tubular furnace, and treating it by gas phase phosphating method under inert atmosphere to prepare a high-efficiency Ni2P nano-electrocatalyst.

2. The preparation method according to claim 1, characterized in that: In step (1), the nickel foam is subjected to a pretreatment mainly including washing, wherein the nickel foam is immersed in acetone and 3 mol / L hydrochloric acid in sequence and ultrasonically treated for 10 to 15 minutes respectively, and then immersed in ethanol and water in sequence and ultrasonically treated for 2 to 3 minutes respectively, and finally washed alternately with ethanol and water three times respectively, and then vacuum dried for standby use.

3. The preparation method according to claim 1, characterized in that: The material-liquid ratio of the nickel foam to deionized water in step (2) is 1 g: (100-130) ml.

4. The preparation method according to claim 1, characterized in that: The phosphate salt selected in step (3) includes any one of sodium hypophosphite and potassium hypophosphite; the mass ratio of the nickel foam with in-situ growth of Ni(OH)2 on the surface to the phosphate salt is 1:(2-4).

5. The preparation method according to claim 1, characterized in that: The gas phase phosphating treatment in step (3) is to place the nickel foam with in-situ growth of Ni(OH)2 on the surface obtained in step (2) downstream of a tubular furnace, place the phosphate salt upstream of the tubular furnace, and perform calcination in the tubular furnace under inert atmosphere to prepare a highly efficient Ni2P nano electrocatalyst; The tube furnace roasting process is carried out according to the following heating method: ① Raise the temperature to 28-32°C and maintain the temperature for 55-65 minutes; ② Raise the temperature to 250-350℃ at a rate of 1-3℃ / min, maintain this temperature for 50-70min and then cool naturally.

6. The high-efficiency Ni2P nano-electrocatalyst prepared by the method for preparing a high-efficiency Ni2P nano-electrocatalyst for removing nitrate from water as claimed in claim 1.

7. Use of the highly efficient Ni2P nano-electrocatalyst as claimed in claim 6 for removing nitrate and nitrite in water.

8. The use according to claim 7, characterized in that: The water temperature is 20-30°C, the nitrate concentration is 100-250 mg / L or the nitrite concentration is 100-350 mg / L.

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