A copper-containing nanoparticle nitrogen and phosphorus co-doped carbon material, its preparation method and application

Abstract

The present invention discloses a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, as well as its preparation method and application. First, residual sludge from urban domestic sewage treatment plants is cultured and domesticated, followed by hydrochloric acid impregnation and ethanol purification to prepare a microbial flocculant. Subsequently, copper ions are adsorbed and captured by the microbial flocculant, and the resulting Cu@NPC is obtained by high-temperature calcination. The Cu@NPC powder is then coated on a carbon cloth substrate to obtain a Cu@NPC / CC electrode, which is then applied to the electrocatalytic reduction of nitrates in water. The Cu@NPC / CC electrode prepared by the present invention has excellent electrocatalytic nitrate reduction performance and can be used to remove nitrates from surface water, groundwater, and drainage from urban sewage treatment plants, providing a valuable reference for the prevention and control of water pollution caused by nitrogen eutrophication.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical treatment of water pollution, and specifically relates to a method for preparing a nitrogen-phosphorus-doped carbon material containing copper nanoparticles and the application of the material in the field of electrocatalytic reduction of nitrates, especially a technology involving the resource utilization of biochemical sludge. Background Art

[0002] The accelerated pace of modern industrialization and the widespread use of agricultural fertilizers have severely disrupted the natural nitrogen cycle, causing numerous environmental problems, one of which is nitrate contamination of water bodies. Excessive nitrate levels in water bodies accelerate eutrophication; excessive nitrate in drinking water poses a threat to human health, such as methemoglobinemia and even cancer. Consequently, global upper limits on nitrate concentrations in drinking water have been established, and nitrate removal from water is considered a key component of water pollution control. To date, various physical and chemical remediation technologies have been used to remove nitrate from water. Reverse osmosis, ion exchange, and electrodialysis are limited in their applicability due to the generation of secondary concentration waste and high energy costs. Biochemical remediation processes generate sludge and slow nitrogen removal, significantly reducing their effectiveness and making them unsuitable for large-scale application. In comparison, electrocatalytic nitrate reduction is highly attractive and promising due to its simplicity, high catalytic efficiency, and the absence of chemical reducing agents.

[0003] Cathode materials play a vital role in the electrochemical reduction of nitrates. The rate of chemical denitrification can be increased by modifying the electrode by anchoring active components on the cathode surface. Although precious metals such as palladium and platinum have high nitrate removal capabilities, they are difficult to achieve large-scale industrial applications due to their scarcity and high cost. Copper reserves are high and copper nanoparticles have excellent activity in converting nitrates to nitrites, making them highly potentially active metal catalysts in the electrochemical reduction of nitrates. In addition, carbon materials have broad application prospects in the field of heterogeneous catalysis due to their unique physicochemical characteristics, such as high specific surface area, large pore volume, good thermal conductivity and mechanical stability, low density and a wide range of raw materials. Patent CN 113403633 discloses a method for preparing a Cu-CN metal organic framework electrocatalyst for reducing nitrates to ammonia. The Cu-CN metal-organic framework nanomaterial electrocatalyst prepared by this method exhibits high electrocatalytic activity due to the high one-dimensional structure, abundant micropores, and large specific surface area of the core / shell nanoparticles. However, the process is complex, the raw materials present certain risks and hazards, and its engineering applicability needs improvement. Patent CN115652338 discloses a catalyst in which copper-based nanoparticles are filled into the inner cavity of a carbon-based nanocage. This catalyst utilizes the confinement of the carbon nanocage to localize the hydroxide generated during the reaction within the nanocage, increasing the pH around the copper-based nanoparticles within the cage. This copper-based catalyst exhibits excellent electrocatalytic performance for nitrate reduction to ammonia in near-neutral electrolytes. However, the catalyst prepared by this technique has a narrow pH range of application. Patent CN113981481 discloses a method for preparing a one-dimensional carbon-based nanomaterial loaded with copper nanoparticles. The copper-based carbon material prepared by this technique exhibits good nitrate transamination performance, but the synthesis process requires high oil bath temperatures and long times, resulting in low safety. Among these technologies, the main product of nitrate reduction is ammonia nitrogen, and the nitrogen selectivity is low. Therefore, the subsequent disposal process of ammonia nitrogen also needs to be considered. In addition, the generation of carbon components involves high-temperature pyrolysis of chemical reagents, the synthesis conditions are harsh, and the issue of resource recycling is not sufficiently considered.

[0004] The carbonaceous properties of biochemical sludge from urban sewage treatment plants and the presence of special inorganic and organic components have increasingly attracted the interest of scientific and technological workers. Biochemical sludge contains organic components such as sugars and proteins, and is a potential material for biochar preparation. How to use sludge to prepare carbon materials with high disposal efficiency and more practical engineering performance, and then expand the scope of sludge resource utilization to achieve better industrial added value has received great attention. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, a preparation method thereof, and an application thereof, which is applied to the electrocatalytic reduction treatment of nitrates.

[0006] The present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, comprising: obtaining a microbial flocculant by laboratory culturing excess sludge from a sewage treatment plant; adsorbing copper ions with the microbial flocculant to obtain a microbial flocculant that adsorbs copper ions; and calcining the microbial flocculant that adsorbs copper ions as a precursor at high temperature to obtain a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, which is denoted as Cu@NPC.

[0008] Furthermore, in the step of obtaining a microbial flocculant by culturing the wastewater treatment plant surplus sludge in the laboratory, the steps specifically include: (1) sludge immersion treatment: diluting concentrated hydrochloric acid to prepare a hydrochloric acid extraction solution for the sludge microbial flocculant; adding the hydrochloric acid extraction solution to a beaker containing a sludge sample, stirring the extract and the sludge sample at room temperature to mix them evenly, and then placing the solution in a shaker at room temperature and shaking at 150 r / min for 20 min to obtain a sludge mixed solution; (2) microbial flocculant extraction: shaking the sludge mixed solution at 8000 r / min After centrifugation at 8000 r / min for 15 min, the supernatant was taken, and NaOH solution was added dropwise to the supernatant to adjust the pH of the solution to 7.0, thereby obtaining a flocculant mother liquor extracted from the sludge; (3) purification of the microbial flocculant: anhydrous ethanol pre-cooled at 4°C was added to the flocculant mother liquor, and the mixture was soaked at room temperature for 24 h until flocculent precipitates appeared in the solution, thereby obtaining a flocculant mother liquor-ethanol solution; the flocculant mother liquor-ethanol solution was then centrifuged at 8000 r / min for 15 min, and the precipitate was collected to obtain the purified microbial flocculant.

[0009] Furthermore, in the step of using the microbial flocculant to adsorb copper ions to obtain the microbial flocculant adsorbing copper ions, the method specifically comprises: taking the microbial flocculant in a reaction container, adding Cu 2+ After the solution is added, the reaction container is shaken at a speed of 150 r / min, the shaking temperature is 15-35°C, and the shaking time is 180-420 min to obtain the microbial flocculant that adsorbs copper ions; wherein Cu 2+ The solution is a copper sulfate solution, a copper ammonia solution or a mixture of the two, and the pH range is 3 to 11.

[0010] Furthermore, the step of calcining the microbial flocculant that adsorbs copper ions as a precursor at high temperature to obtain a nitrogen-phosphorus-doped carbon material containing copper nanoparticles specifically includes: centrifuging the microbial flocculant that adsorbs copper ions at 8000 r / min for 15 minutes to collect a first precipitate, first taking the first precipitate and placing it in a sodium borohydride solution, and slowly stirring it at room temperature to obtain a first mixed solution; then placing the first mixed solution in a centrifuge tube and centrifuging it at 8000 r / min for 15 minutes to collect a second precipitate, then placing the second precipitate in a vacuum drying oven at 60°C for 3 hours, with a vacuum degree of -0.1 MPa, to obtain a dried sample; then grinding the dried sample, and calcining the obtained powder under a nitrogen atmosphere, the calcination parameters are heating to 500°C at a heating rate of 2-3°C / min, keeping it at 500°C for 2-4 hours, and then naturally cooling it to room temperature, taking out the calcined powder to obtain the Cu@NPC.

[0011] Furthermore, before the step of obtaining a microbial flocculant by culturing the excess sludge from a sewage treatment plant in the laboratory, the method further includes: taking a dewatered sludge cake from a municipal sewage treatment plant, mixing the dewatered sludge cake and tap water in a container, stirring at room temperature to fully mix the mud and water, and then filtering the mud and water mixture with a 20-mesh sieve to remove solid impurities, and then adding the mud and water mixture into the aeration tank of an SBR intermittent experimental device for uninterrupted air aeration, and adding a carbon source, a nitrogen source, and a phosphorus source as nutrients for microbial growth in a carbon: nitrogen: phosphorus ratio of 100:5:1, wherein the carbon source is glucose, starch, and white sugar; the nitrogen source is peptone or urea; and the phosphorus source is potassium dihydrogen phosphate or sodium dihydrogen phosphate; the COD concentration of the mixed solution is controlled to be 200-300 mg / L, and the mixed solution is aerated every 24 hours. Change the water once. When changing the water, stop aeration and let the mixed liquid stand for 15 minutes. Then pour out 1 / 3 of the volume of the clarified liquid layer on the upper layer of the mixed liquid, and add the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water. The washing treatment includes: first taking the mud-water mixture and letting it stand and settle, and pouring out the supernatant after 30 minutes; then adding deionized water to the beaker at room temperature, slowly stirring the sludge mixture for 3 to 5 minutes, and then letting it stand and settle for 30 minutes, and then pouring out the supernatant. This washing process is repeated 3 times; finally, after the sludge washing is completed, centrifugal dehydration is carried out, the centrifugal speed is 5000r / min, and the centrifugal time is 15 minutes to obtain the pretreated sludge sample.

[0012] The second aspect of the present invention provides a nitrogen and phosphorus doped carbon material containing copper nanoparticles obtained by the above-mentioned method for preparing a nitrogen and phosphorus doped carbon material containing copper nanoparticles.

[0013] A third aspect of the present invention provides the use of the nitrogen-phosphorus-doped carbon material containing copper nanoparticles as described above in the field of electrocatalytic reduction of nitrates.

[0014] Furthermore, the carbon fiber cloth was immersed in a beaker containing anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water for 3 to 5 times to obtain a cleaned carbon cloth; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C and dried for 3 hours to obtain a treated carbon cloth; the Cu@NPC was taken, and deionized water, anhydrous ethanol, and 5wt% Nafion solution were added in sequence, and the Cu@NPC was evenly dispersed by ultrasonic treatment for 20 to 30 minutes to obtain a dispersed solution; the dispersed solution was evenly applied on the treated carbon cloth, placed in a vacuum drying oven at 60°C and dried for 3 hours to prepare a Cu@NPC / CC electrode; an electrochemical standard three-electrode system was used, with the Cu@NPC / CC electrode as the working electrode, the Pt electrode or the Ir-Ru / Ti electrode as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. A mixed solution of sodium sulfate and sodium nitrate was used as the electrolyte, and an electrolysis experiment was carried out in a single-tank electrolytic cell, with an electrolysis current density ranging from 15 to 35 mA / cm 2 , the electrolysis time is 9h; wherein, in the electrolyte, the sodium nitrate concentration range is 10-30mg-N / L, the sodium sulfate concentration range is 0.05-0.2mol / L, the solution pH range is 3-11, Cl - The concentration range is 0.0~2.0g / L, and the coexisting ion K + Mg 2+ , Ca 2+ 、SO4 2- 、HCO3 - The concentration range is 0-300 mg / L, and the COD concentration is 50-300 mg / L. After the electrolysis experiment, the concentration range of nitrate in the electrolyte is 0-6 mg-N / L.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] (1) Extracting organic matter from municipal sludge to prepare microbial flocculants has promoted the development of sludge resource utilization and provided a new path for sludge treatment and disposal;

[0017] (2) Microbial flocculants can achieve the adsorption and capture of copper ions in aqueous solutions, thereby providing technical support for the treatment of copper-containing wastewater and heavy metal pollution control;

[0018] (3) Using a microbial flocculant loaded with copper ions as the raw material, the carbon-based material was modified by nitrogen and phosphorus doping via polysaccharides, proteins, and other substances in the flocculant during the high-temperature carbonization process, resulting in the preparation of a nitrogen-phosphorus-doped carbon material containing copper nanoparticles—Cu@NPC. The Cu@NPC / CC electrode prepared by this method exhibits good catalytic reduction of nitrate, low intermediate product production, high nitrogen gas conversion rate, and long service life. It is expected to be applied in the removal of nitrate from surface water and groundwater, and the reduction of total nitrogen indicators in Class A drainage from urban sewage treatment plants. This invention also provides a new path for the potential resource development and utilization of sludge, a new approach for the design and preparation of electrocatalytic functional electrodes, and technical support for the prevention and control of eutrophication of water bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the X-ray diffraction spectrum of Cu@NPC prepared in Example 1 of the present invention;

[0020] Figure 2 is a scanning electron microscope image of Cu@NPC prepared in Example 1 of the present invention;

[0021] Figure 3a is the carbon element distribution diagram of Cu@NPC prepared in Example 1 of the present invention;

[0022] Figure 3b is the nitrogen element distribution diagram of Cu@NPC prepared in Example 1 of the present invention;

[0023] Figure 3c This is the phosphorus distribution diagram of Cu@NPC prepared in Example 1 of the present invention;

[0024] Figure 3d is the copper element distribution diagram of Cu@NPC prepared in Example 1 of the present invention;

[0025] Figure 4 is a scanning electron microscope image of the Cu@NPC / CC electrode prepared in Example 1 of the present invention;

[0026] Figure 5 This is the nitrate removal effect of the Cu@NPC / CC electrode prepared in Example 1 of the present invention;

[0027] Figure 6a This is a diagram showing the effect of nitrate reduction by Cu@NPC / CC electrodes with different copper loadings prepared in Example 2 of the present invention;

[0028] Figure 6b The copper loading in Example 2 of the present invention is 0.50 mg / cm 2 Product concentration change diagram when ;

[0029] Figure 7aThis is the nitrate reduction effect of the Cu@NPC / CC electrode prepared in Example 3 of the present invention at different pH values;

[0030] Figure 7b The N2 selectivity of the Cu@NPC / CC electrode prepared in Example 3 of the present invention at different pH values;

[0031] Figure 8 This is the treatment effect of the Cu@NPC / CC electrode on simulated wastewater in Example 3 of the present invention;

[0032] Figure 9 This is the cycle stability of the Cu@NPC / CC electrode in Example 3 of the present invention. DETAILED DESCRIPTION

[0033] To address the challenges of the existing technology, the present invention provides a method for preparing a nitrogen-phosphorus-doped carbon material containing copper nanoparticles. The method comprises: obtaining a microbial flocculant by culturing excess sludge from a sewage treatment plant in a laboratory; allowing the microbial flocculant to adsorb copper ions to obtain a microbial flocculant that absorbs copper ions; and calcining the microbial flocculant that absorbs copper ions at high temperature as a precursor to obtain a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, designated as Cu@NPC. The Cu@NPC is then coated onto a conductive support substrate, carbon cloth, to form a Cu@NPC / CC electrode for electrocatalytic nitrate reduction.

[0034] Specifically, the preparation method and application of the nitrogen-phosphorus-doped carbon material containing copper nanoparticles include the following steps:

[0035] S1. Sludge pretreatment

[0036] Take 500-1000g of dewatered sludge cake from a municipal sewage treatment plant, mix the dewatered sludge cake with 10 times its volume of tap water in a container, stir at room temperature to fully mix the mud and water, then use a 20-mesh sieve to filter the mud and water mixture to remove solid impurities such as plastics and branches, and then add the mud and water mixture into the aeration tank of the SBR intermittent experimental device for uninterrupted air aeration, and add carbon source, nitrogen source, phosphorus source, etc. as nutrients for microbial growth according to the carbon: nitrogen: phosphorus ratio of 100:5:1. The carbon source is glucose, starch, white sugar, etc.; the nitrogen source is peptone or urea, etc.; the phosphorus source is potassium dihydrogen phosphate or sodium dihydrogen phosphate, etc.; the COD concentration of the mixed solution is controlled at 200-300mg / L, and the water is changed every 24h. When changing the water, stop aeration and let the mixed solution stand for 1 minute. 5min, then pour out the clarified liquid layer of 1 / 3 volume of the upper layer of the mixed liquid, and add the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water, and the washing process includes the following steps: first, take 2000mL of the mud-water mixture in a beaker and let it settle, and after 30min, pour out the supernatant; then add deionized water 10 times the volume of the sludge to the beaker at room temperature, slowly stir the sludge mixture for 3 to 5min, let it settle for 30min, and then pour out the supernatant, and repeat this washing process 3 times; finally, after the sludge is washed, it is centrifuged and dehydrated, the centrifugal speed is 5000r / min, and the centrifugal time is 15min to obtain the pretreated sludge sample.

[0037] S2. Extraction of microbial flocculants by hydrochloric acid immersion method

[0038] (1) Sludge immersion treatment: dilute 36.5% concentrated hydrochloric acid 10 times to prepare a hydrochloric acid extraction solution for sludge microbial flocculant; add 100 mL of the hydrochloric acid extraction solution to a beaker containing 100 g of sludge sample, stir thoroughly at room temperature to mix the extract and sludge sample, and then place the mixture in a shaker at room temperature and 150 rpm for 20 min to obtain a sludge mixture;

[0039] (2) Extraction of microbial flocculant: The sludge mixture was centrifuged at 8000 r / min for 15 min, and about 200 mL of the supernatant was placed in a 1000 mL beaker. 0.1 mol / L NaOH solution was added dropwise to adjust the pH of the solution to 7.0 to obtain a flocculant mother solution extracted from the sludge;

[0040] (3) Purification of microbial flocculant: 2 to 3 times the volume of anhydrous ethanol pre-cooled at 4°C is added to the flocculant mother liquor, and the mixture is soaked at room temperature for 24 hours. After soaking in anhydrous ethanol, a large amount of flocculent precipitates appear in the solution, and a flocculant mother liquor-ethanol solution is obtained; the flocculant mother liquor-ethanol solution is then centrifuged at 8000 r / min for 15 minutes, and the precipitate is collected to obtain the purified microbial flocculant.

[0041] S3. Preparation of microbial flocculant for adsorbing copper ions

[0042] Take 0.5-2.0g of the microbial flocculant in a 250mL conical flask, add 40-200mL of 50mg / L Cu 2+ The solution is then placed in a constant temperature oscillator and shaken at 150 r / min, the shaking temperature is 15-35°C, and the shaking time is 180-420 min to obtain the microbial flocculant that adsorbs copper ions; wherein Cu 2+ The solution is a copper sulfate solution, a copper ammonia solution or a mixture of the two, and the pH range is 3 to 11.

[0043] Preparation of S4 and Cu@NPC

[0044] The copper ion-adsorbing microbial flocculant was centrifuged at 8000 r / min for 15 minutes to collect a first precipitate. The first precipitate was first placed in a sodium borohydride solution with a concentration of 1.0 g / L and slowly stirred at room temperature to obtain a first mixed solution. The first mixed solution was then placed in a centrifuge tube and centrifuged at 8000 r / min for 15 minutes to collect a second precipitate. The second precipitate was then placed in a vacuum drying oven at 60°C for 3 hours with a vacuum degree of -0.1 MPa to obtain a dried sample. The dried sample was then ground and the obtained powder was placed in a porcelain boat, which was placed in a tube furnace. Under a nitrogen atmosphere, the temperature of the tube furnace was increased from room temperature to 500°C at a heating rate of 2-3°C / min. After being kept at 500°C for 2-4 hours, the tube furnace was turned off and naturally cooled to room temperature. The calcined powder was taken out to obtain the Cu@NPC.

[0045] Preparation of S5 and Cu@NPC / CC electrodes

[0046] Cut the carbon fiber cloth into 2×2cm size 2The carbon cloth was soaked in a beaker containing anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water for 3 to 5 times to obtain a cleaned carbon cloth; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C and dried for 3 hours to obtain a treated carbon cloth; 20 to 50 mg of the Cu@NPC was taken, and deionized water, anhydrous ethanol, and 5 wt% Nafion solution were added in sequence, and ultrasonicated for 20 to 30 minutes to uniformly disperse the Cu@NPC to obtain a dispersed solution; the dispersed solution was evenly applied on the treated carbon cloth, placed in a vacuum drying oven at 60°C and dried for 3 hours to obtain a Cu@NPC / CC electrode; wherein the volumes of the deionized water, anhydrous ethanol, and Nafion solution were 480 to 1200 μL, 480 to 1200 μL, and 40 to 100 μL, respectively.

[0047] Nitrate removal by S6 and Cu@NPC / CC electrodes

[0048] The electrolysis experiment was carried out in a single-tank electrolytic cell using a standard electrochemical three-electrode system, with the Cu@NPC / CC electrode as the working electrode, the Pt electrode or the Ir-Ru / Ti electrode as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. A mixed solution of sodium sulfate and sodium nitrate was used as the electrolyte. The electrolysis current density ranged from 15 to 35 mA / cm 2 , the electrolysis time is 9h; wherein, in the electrolyte, the sodium nitrate concentration range is 10-30mg-N / L, the sodium sulfate concentration range is 0.05-0.2mol / L, the solution pH range is 3-11, Cl - The concentration range is 0.0~2.0g / L, and the coexisting ion K + Mg 2+ , Ca 2+ 、SO4 2- 、HCO3 - The concentration range is 0-300 mg / L, and the COD concentration is 50-300 mg / L.

[0049] The present invention is described in detail below with reference to specific embodiments.

[0050] Example 1

[0051] 1. Preparation of Cu@NPC / CC electrode

[0052] (1) Sludge pretreatment: Take 500 g of dehydrated sludge cake from a municipal sewage treatment plant, mix the dehydrated sludge cake with 10 times its volume of tap water in a container, stir at room temperature to make the mud and water fully mixed, then use a 20-mesh sieve to filter the mud and water mixture to remove solid impurities such as plastics and branches, and then add the mud and water mixture into the aeration tank of the SBR intermittent experimental device for uninterrupted air aeration, and add glucose, peptone, and potassium dihydrogen phosphate as nutrients for microbial growth in a carbon: nitrogen: phosphorus ratio of 100:5:1, control the COD concentration of the mixed solution to 200 mg / L, and change the water every 24 hours. When changing the water, stop aeration first and let the mixed solution stand for 15 minutes, then pour out 1 / 3 of the upper volume of the mixed solution. The clear liquid layer is added, and the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source is added to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water, and the washing process includes the following steps: first, 2000 mL of the mud-water mixture is taken in a beaker and allowed to settle, and the supernatant liquid is poured out after 30 minutes; then, deionized water 10 times the volume of the sludge is added to the beaker at room temperature, the sludge mixture is slowly stirred for 3 to 5 minutes, and then allowed to settle for 30 minutes, and then the supernatant liquid is poured out, and this washing process is repeated 3 times; finally, after the sludge is washed, it is centrifuged and dehydrated at a centrifugal speed of 5000 r / min and a centrifugal time of 15 minutes. After centrifugal dehydration, the pretreated sludge sample is obtained;

[0053] (2) Extraction of microbial flocculants by hydrochloric acid immersion method

[0054] ① Sludge immersion treatment: dilute 36.5% concentrated hydrochloric acid 10 times to use as the extraction solution for sludge microbial flocculant; add 100 mL of hydrochloric acid extraction solution to a beaker containing 100 g of pretreated sludge, stir thoroughly at room temperature to mix the extract and sludge evenly, then pour the mixed solution into a 150 mL conical flask and place it in a shaker at room temperature and 150 rpm for 20 minutes;

[0055] ② Extraction of microbial flocculant: After the sludge mixture is shaken on a shaker, centrifuge the mixture at 8000r / min for 15min, take about 200mL of the supernatant and place it in a 1000mL beaker. Add 0.1mol / L NaOH solution dropwise to adjust the pH of the solution to 7.0, thus obtaining the flocculant mother solution extracted from the sludge;

[0056] ③ Purification of microbial flocculant: Add 2 to 3 times the volume of 4°C pre-cooled anhydrous ethanol to the flocculant mother liquor obtained in ②, and soak the flocculant mother liquor at room temperature for 24 hours. After soaking in anhydrous ethanol, a large amount of flocculent precipitates will appear in the solution. Then, the flocculant mother liquor-ethanol solution is centrifuged at 8000 r / min for 15 minutes, and the precipitate is collected, which is the purified microbial flocculant;

[0057] (3) Cu adsorption by microbial flocculants 2+ : Take 2.0 microbial flocculant and place it in a 250mL conical flask, add 40mL, 50mg / L CuSO4 and 40mL, 50mg / L Cu(NH3) 2+ The solution was adjusted to pH 7 and placed in a constant temperature oscillator at 25°C for 420 min;

[0058] (4) The solution after the shaking treatment in step (3) was centrifuged at 8000 r / min for 15 minutes to collect the precipitate, and the precipitate was placed in 31.9 mL of a sodium borohydride solution with a concentration of 1.0 g / L and slowly stirred at room temperature; the solution was then placed in a centrifuge tube and centrifuged at 8000 r / min for 15 minutes to collect the precipitate, and then the precipitate was placed in a vacuum drying oven at 60°C for 3 hours with a vacuum degree of -0.1 MPa; the dried sample was then ground; finally, the obtained powder was placed in a porcelain boat, and the porcelain boat was placed in a tube furnace. Under a nitrogen atmosphere, the temperature of the tube furnace was increased from room temperature to 500°C at a heating rate of 2°C / min, and after heat treatment at 500°C for 3 hours, the power of the tube furnace was turned off and it was naturally cooled to room temperature. The calcined powder was taken out, and a nitrogen-phosphorus-doped carbon material containing copper nanoparticles was obtained, which was recorded as Cu@NPC;

[0059] The X-ray diffraction pattern (XRD) of the powder is as follows Figure 1 As shown. The "mantou peak" at 24.8° of 2θ belongs to the amorphous carbon material; the diffraction peaks at 2θ = 43.3°, 50.4°, 74.1°, and 89.9° correspond to the (111), (200), (220), and (311) crystal planes of Cu element (PDF#01-1241), respectively; the diffraction peaks at 2θ = 37.1° and 62.5° correspond to the (110) and (220) crystal planes of Cu2O (PDF#34-1354), respectively. This shows that the powder is composed of graphite carbon and copper, and the presence of copper oxide is due to the oxidation of part of the copper element during the preparation process. The scanning electron morphology is shown in FIG. Figure 2 As shown in Figure 3, it further shows that the catalyst powder material obtained is a block structure, and it can be seen that the surface of the material is porous. Figure 3a This is the carbon element distribution diagram of Cu@NPC prepared in Example 1 of the present invention. Figure 3b is the nitrogen element distribution diagram of Cu@NPC prepared in Example 1 of the present invention, Figure 3c This is the phosphorus element distribution diagram of Cu@NPC prepared in Example 1 of the present invention. Figure 3dThis is the copper element distribution diagram of Cu@NPC prepared in Example 1 of the present invention, indicating that the main component of the material is C, and the doping of N and P elements introduces defects on the carbon matrix. In addition, there are nano-copper particles dispersed on the carbon matrix. Therefore, this material is named carbon material containing copper nanoparticles, denoted as Cu@NPC.

[0060] (5) Cut the commercially available carbon fiber cloth into pieces with a size of 2×2 cm 2 The square pieces were immersed in a beaker filled with anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water 3 to 5 times; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C for 3 hours; 20 mg of Cu@NPC powder was added, 480 μL of deionized water, 480 μL of anhydrous ethanol, and 40 μL of 5wt% Nafion solution were added in sequence, and ultrasonicated for 20 minutes to evenly disperse the powder; the dispersed solution was evenly applied on the treated carbon cloth, and placed in a vacuum drying oven at 60°C for 3 hours to obtain a Cu@NPC / CC electrode.

[0061] Figure 4 This is a scanning electron microscope image of the prepared Cu@NPC / CC electrode, showing the successful attachment of Cu@NPC on CC.

[0062] 2. Evaluation of nitrate reduction performance of Cu@NPC / CC electrode

[0063] The electrolysis experiment was carried out in a 300 mL single-tank electrolytic cell using a standard electrochemical three-electrode system with the prepared Cu@NPC / CC electrode as the working electrode, the Pt electrode as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. 250 mL of a mixed solution of sodium sulfate and sodium nitrate was used as the electrolyte. The initial concentration of sodium nitrate was 15 mg-N / L, the concentration of sodium sulfate was 0.05 mol / L, the pH range of the solution was 7, and the electrolysis current density was 25 mA / cm 2 , electrolysis time 15h.

[0064] Figure 5 The figure shows the nitrate removal efficiency of the Cu@NPC / CC electrode. As can be seen from the figure, the nitrate reduction reaction is rapid in the first five hours, with the removal rate rapidly increasing from 0.0% to 87.3%. After five hours, the nitrate concentration in the solution decreases, causing the reaction rate to slow down, and the removal rate reaches 100% by 9 hours.

[0065] Example 2

[0066] 1. Preparation of Cu@NPC / CC electrode

[0067] (1) Sludge pretreatment: Take 500 g of dehydrated sludge cake from a municipal sewage treatment plant, mix the dehydrated sludge cake with 10 volumes of tap water in a container, stir at room temperature to mix the sludge and water thoroughly, then filter the sludge and water mixture with a 20-mesh sieve to remove solid impurities such as plastics and branches, and then add the sludge and water mixture into the aeration tank of an SBR intermittent experimental device for uninterrupted air aeration. Glucose, peptone, and potassium dihydrogen phosphate are added as nutrients for microbial growth in a carbon: nitrogen: phosphorus ratio of 100:5:1. The COD concentration of the mixed solution is controlled at 300 mg / L. The water is changed every 24 hours. When changing the water, aeration is stopped first and the mixed solution is allowed to stand for 15 minutes. Then, 1 / 3 of the upper volume of the mixed solution is poured out to clarify the water. liquid layer, and add the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water, and the washing process includes the following steps: first, take 2000 mL of the mud-water mixture in a beaker and let it settle, and after 30 minutes, pour out the supernatant; then, add deionized water 10 times the volume of the sludge to the beaker at room temperature, slowly stir the sludge mixture for 3 to 5 minutes, let it settle for 30 minutes, and then pour out the supernatant, and repeat this washing process 3 times; finally, after the sludge is washed, it is centrifuged and dehydrated at a centrifugal speed of 5000 r / min and a centrifugal time of 15 minutes. After centrifugal dehydration, the pretreated sludge sample is obtained;

[0068] (2) Extraction of microbial flocculants by hydrochloric acid immersion method

[0069] ① Sludge immersion treatment: dilute 36.5% concentrated hydrochloric acid 10 times to use as the extraction solution for sludge microbial flocculant; add 100 mL of hydrochloric acid extraction solution to a beaker containing 100 g of pretreated sludge, stir thoroughly at room temperature to mix the extract and sludge evenly, then pour the mixed solution into a 150 mL conical flask and place it in a shaker at room temperature and 150 rpm for 20 minutes;

[0070] ② Extraction of microbial flocculant: After the sludge mixture is shaken on a shaker, centrifuge the mixture at 8000r / min for 15min, take about 200mL of the supernatant and place it in a 1000mL beaker. Add 0.1mol / L NaOH solution dropwise to adjust the pH of the solution to 7.0, thus obtaining the flocculant mother solution extracted from the sludge;

[0071] ③ Purification of microbial flocculant: Add 2 to 3 times the volume of 4°C pre-cooled anhydrous ethanol to the flocculant mother liquor obtained in ②, and soak the flocculant mother liquor at room temperature for 24 hours. After soaking in anhydrous ethanol, a large amount of flocculent precipitates will appear in the solution. Then, the flocculant mother liquor-ethanol solution is centrifuged at 8000r / min for 15 minutes, and the precipitate is collected, which is the purified microbial flocculant.

[0072] (3) Cu adsorption by microbial flocculants 2+ : Take 2.0g of microbial flocculant and place it in five 250mL conical flasks, add 40mL of deionized water, 40, 80, 120, and 160mL of 50mg / L CuSO4 solution in sequence, adjust the pH of the solution to 7, and place it in a constant temperature oscillator at 25℃ for 420min;

[0073] (4) The shaken solution was centrifuged at 8000 r / min for 15 min, and the precipitate was placed in 0.0, 10.6, 21.2, 31.9, and 42.5 mL of 1.0 g / L sodium borohydride solution and slowly stirred at room temperature; the solution was then placed in a centrifuge tube and centrifuged at 8000 r / min for 15 min to collect the precipitate, which was then placed in a vacuum drying oven at 60°C for 3 h with a vacuum degree of -0.1 MPa; the dried sample was then ground; finally, the obtained powder was placed in a porcelain boat, and the porcelain boat was placed in a tube furnace. Under a nitrogen atmosphere, the temperature of the tube furnace was increased from room temperature to 500°C at a heating rate of 2°C / min, and after being kept at 500°C for 4 h, the power of the tube furnace was turned off and allowed to cool naturally to room temperature. The calcined powder was taken out, and a nitrogen-phosphorus-doped carbon material containing copper nanoparticles was obtained, which was recorded as Cu@NPC.

[0074] (5) Cut the commercially available carbon fiber cloth into pieces with a size of 2×2 cm 2 The square pieces were immersed in a beaker filled with anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water 3 to 5 times; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C for 3 hours; 20 mg of Cu@NPC powder was taken, 480 μL of deionized water, 480 μL of anhydrous ethanol, and 40 μL of 5wt% Nafion solution were added, and the powder was evenly dispersed by ultrasonication for 20 minutes; the dispersed solution was evenly applied on the treated carbon cloth, and placed in a vacuum drying oven at 60°C for 3 hours to obtain a Cu@NPC / CC electrode.

[0075] 2. Evaluation of nitrate reduction performance of Cu@NPC / CC electrode

[0076] The effect of copper ion doping on nitrate removal was studied using an electrochemical standard three-electrode system. The prepared Cu@NPC / CC electrode was used as the working electrode, the Pt electrode was used as the counter electrode, and the saturated Ag / AgCl electrode was used as the reference electrode. 250 mL of a mixed solution of sodium sulfate and sodium nitrate was used as the electrolyte. Electrolysis experiments were carried out in a 300 mL single-tank electrolytic cell. The nitrate concentration was 15 mg-N / L, the sodium sulfate concentration was 0.05 mol / L, the solution pH was 7, and the electrolysis current density was 25 mA / cm 2 .

[0077] Figure 6a The figure shows the effect of nitrate reduction on Cu@NPC / CC electrodes with different copper loadings. As shown in the figure, compared with the undoped copper electrode, the nitrate reduction efficiency and reduction rate are improved with the increase of copper ion doping. When the doping amount of Cu nanoparticles is greater than 0.25 mg / cm 2 When the doping amount of Cu nanoparticles is 0.50 and 0.75 mg / cm 2 The reduction efficiency can reach 100%. Figure 6b The concentration change of nitrate reduction products of Cu@NPC / CC electrode is shown in Figure 2. When the doping amount of Cu nanoparticles is 0.50 mg / cm 2 As the electrolysis time increases, the concentration of nitrate gradually decreases, the amount of ammonia nitrogen generated gradually increases and finally remains stable, and the concentration of nitrite generated is relatively low. In addition, as can be seen from the TN change curve in the figure, the electrode also shows a high removal effect on total nitrogen.

[0078] Example 3

[0079] 1. Preparation of Cu@NPC / CC electrode:

[0080] (1) Sludge pretreatment: Take 500 g of dehydrated sludge cake from a municipal sewage treatment plant, mix the dehydrated sludge cake with 10 volumes of tap water in a container, stir at room temperature to mix the sludge and water thoroughly, then filter the sludge and water mixture with a 20-mesh sieve to remove solid impurities such as plastics and branches, and then add the sludge and water mixture into the aeration tank of an SBR intermittent experimental device for uninterrupted air aeration. Starch, urea, and sodium dihydrogen phosphate are added as nutrients for microbial growth in a carbon: nitrogen: phosphorus ratio of 100:5:1. The COD concentration of the mixed solution is controlled at 300 mg / L. The water is changed every 24 hours. When changing the water, aeration is stopped first and the mixed solution is allowed to stand for 15 minutes. Then, 1 / 3 of the clarified liquid on the upper layer of the mixed solution is poured out. layer, and add the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water. The washing process includes the following steps: first, take 2000 mL of the mud-water mixture in a beaker and let it settle quietly. After 30 minutes, pour out the supernatant; then, add deionized water 10 times the volume of the sludge to the beaker at room temperature, slowly stir the sludge mixture for 3 to 5 minutes, let it settle quietly for 30 minutes, then pour out the supernatant, and repeat this washing process 3 times; finally, after the sludge is washed, it is centrifuged and dehydrated at a centrifugal speed of 5000 r / min and a centrifugal time of 15 minutes. After centrifugal dehydration, the pretreated sludge sample is obtained.

[0081] (2) Extraction of microbial flocculants by hydrochloric acid immersion method

[0082] ① Sludge immersion treatment: dilute 36.5% concentrated hydrochloric acid 10 times to use as the extraction solution for sludge microbial flocculant; add 100 mL of hydrochloric acid extraction solution to a beaker containing 100 g of pretreated sludge, stir thoroughly at room temperature to mix the extract and sludge evenly, then pour the mixed solution into a 150 mL conical flask and place it in a shaker at room temperature and 150 rpm for 20 minutes;

[0083] ② Extraction of microbial flocculant: After the sludge mixture is shaken on a shaker, centrifuge the mixture at 8000r / min for 15min, take about 200mL of the supernatant and place it in a 1000mL beaker. Add 0.1mol / L NaOH solution dropwise to adjust the pH of the solution to 7.0, thus obtaining the flocculant mother solution extracted from the sludge;

[0084] ③ Purification of microbial flocculant: Add 2 to 3 times the volume of 4°C pre-cooled anhydrous ethanol to the flocculant mother liquor obtained in ②, and soak the flocculant mother liquor at room temperature for 24 hours. After soaking in anhydrous ethanol, a large amount of flocculent precipitates will appear in the solution. Then, the flocculant mother liquor-ethanol solution is centrifuged at 8000 r / min for 15 minutes, and the precipitate is collected, which is the purified microbial flocculant;

[0085] (3) Cu adsorption by microbial flocculants 2+ : Take 2.0 microbial flocculant and place it in a 250mL conical flask, add 40mL 50mg / L CuSO4 and 40mL 50mg / L Cu(NH3) 2+ The solution was adjusted to pH 7 and placed in a constant temperature oscillator at 25°C for 360 min;

[0086] (4) The solution after the shaking treatment in step (3) was centrifuged at 8000 r / min for 15 minutes to collect the precipitate, and the precipitate was placed in 31.9 mL of a sodium borohydride solution with a concentration of 1.0 g / L and slowly stirred at room temperature; the solution was then placed in a centrifuge tube and centrifuged at 8000 r / min for 15 minutes to collect the precipitate, and then the precipitate was placed in a vacuum drying oven at 60°C for 3 hours with a vacuum degree of -0.1 MPa; the dried sample was then ground; finally, the obtained powder was placed in a porcelain boat, and the porcelain boat was placed in a tube furnace. Under a nitrogen atmosphere, the temperature of the tube furnace was increased from room temperature to 500°C at a heating rate of 2°C / min, and after heat treatment at 500°C for 3 hours, the power of the tube furnace was turned off and it was naturally cooled to room temperature. The calcined powder was taken out, and a nitrogen-phosphorus-doped carbon material containing copper nanoparticles was obtained, which was recorded as Cu@NPC;

[0087] (5) Cut the commercially available carbon fiber cloth into pieces with a size of 2×2 cm 2The square pieces were immersed in a beaker filled with anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water 3 to 5 times; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C for 3 hours; 20 mg of Cu@NPC powder was taken, 480 μL of deionized water, 480 μL of anhydrous ethanol, and 40 μL of 5wt% Nafion solution were added, and the powder was evenly dispersed by ultrasonication for 20 minutes; the dispersed solution was evenly applied on the treated carbon cloth, and placed in a vacuum drying oven at 60°C for 3 hours to obtain a Cu@NPC / CC electrode.

[0088] 2. Analysis of nitrate reduction performance of Cu@NPC / CC electrode

[0089] (1) The study of nitrate removal by the prepared electrode in different pH solutions was conducted using an electrochemical standard three-electrode system. The prepared Cu@NPC / CC electrode was used as the working electrode, the Pt electrode was used as the counter electrode, and the saturated Ag / AgCl electrode was used as the reference electrode. The electrolysis experiment was carried out in a 300 mL single-tank electrolytic cell with 250 mL of a mixed solution of sodium sulfate and sodium nitrate as the electrolyte. The nitrate concentration was 15 mg-N / L, the sodium sulfate concentration was 0.05 mol / L, and the solution pH was adjusted to 3, 5, 7, 9, and 11, respectively. The electrolysis current density was 25 mA / cm 2 , electrolysis time 9h.

[0090] Figure 7a NO3 under different pH conditions - -N removal rate change curve over time, the curve shows that when the pH is in the range of 3-11, NO3 - -N removal rate can be maintained at more than 80%, and by Figure 7b It can be seen that the electrode exhibits good N2 selectivity under different pH conditions, which indicates that the prepared Cu@NPC / CC electrode has a wide pH working range and good nitrogen selectivity.

[0091] (2) The treatment effect of the prepared electrodes on simulated wastewater was studied using an electrochemical standard three-electrode system. The prepared Cu@NPC / CC electrode was used as the working electrode, the Ir-Ru / Ti electrode was used as the counter electrode, and the saturated Ag / AgCl electrode was used as the reference electrode. The electrolysis experiment was carried out in a 300 mL single-tank electrolytic cell with 250 mL of a mixed solution of sodium sulfate and sodium nitrate as the electrolyte. The nitrate concentration was 15 mg-N / L, the sodium sulfate concentration was 0.05 mol / L, the solution pH was 7, and the Cl - The concentration is 1.5g / L, K + Mg 2+ , Ca 2+ 、SO4 2- 、HCO3 -The ion concentration is 250 mg / L, the COD concentration is 250 mg / L, and the electrolysis current density is 25 mA / cm 2 , electrolysis time 9h.

[0092] Figure 8 The curve of TN concentration and TN removal rate in simulated wastewater changes with time. In the simulated wastewater environment, more than 90% of nitrate nitrogen can still be removed. After 9 hours of electrochemical reduction reaction, the TN concentration dropped to 1.94 mg / L, which can meet the Class V limit requirement (<2 mg / L) of the first-level A discharge of urban sewage treatment plants. Most of the nitrate nitrogen is converted into nitrogen gas, achieving harmless treatment of nitrate nitrogen, and Figure 9 After seven cycles of treatment of simulated wastewater using the Cu@NPC / CC electrode, the nitrate reduction efficiency decreased from 100% to 89.4%, and the total nitrogen removal rate decreased from 92.4% to 81.8%. This demonstrates the electrode's excellent stability and durability, maintaining a strong catalytic effect on the electrochemical nitrate reduction process even after approximately 60 hours of use, suggesting promising industrial applications.

[0093] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be subject to the scope defined in the claims.

Claims

1. A method for preparing a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, characterized in that: include: Microbial flocculants are obtained by culturing excess sludge from sewage treatment plants in the laboratory; Adsorbing copper ions with a microbial flocculant to obtain a microbial flocculant that adsorbs copper ions; The microbial flocculant that adsorbs copper ions is used as a precursor and calcined at high temperature to obtain a nitrogen-phosphorus-doped carbon material containing copper nanoparticles, which is denoted as Cu@NPC; The step of calcining the microbial flocculant that adsorbs copper ions as a precursor at high temperature to obtain the nitrogen-phosphorus-doped carbon material containing copper nanoparticles specifically includes: The copper ion-adsorbing microbial flocculant is centrifuged at 8000 r / min for 15 minutes to collect a first precipitate. The first precipitate is first placed in a sodium borohydride solution and slowly stirred at room temperature to obtain a first mixed solution. The first mixed solution is then placed in a centrifuge tube and centrifuged at 8000 r / min for 15 minutes to collect a second precipitate. The second precipitate is then placed in a vacuum drying oven at 60°C for 3 hours with a vacuum degree of -0.1 MPa to obtain a dried sample. The dried sample is then ground and the obtained powder is calcined under a nitrogen atmosphere. The calcination parameters are: heating to 500°C at a heating rate of 2-3°C / min, keeping at 500°C for 2-4 hours, and then naturally cooling to room temperature. The calcined powder is taken out to obtain the Cu@NPC.

2. The method for preparing the nitrogen-phosphorus-doped carbon material containing copper nanoparticles according to claim 1, characterized in that: The step of obtaining a microbial flocculant by culturing excess sludge from a sewage treatment plant in a laboratory specifically includes: (1) Sludge immersion treatment: dilute concentrated hydrochloric acid to prepare a hydrochloric acid extraction solution used as a sludge microbial flocculant; add the hydrochloric acid extraction solution to a beaker containing a sludge sample, stir thoroughly at room temperature to mix the extract and the sludge sample evenly, and then place the solution in a shaker at room temperature and oscillate at 150 rpm for 20 minutes to obtain a sludge mixture; (2) Extraction of microbial flocculant: The sludge mixture was centrifuged at 8000 r / min for 15 min, and the supernatant was collected. NaOH solution was added dropwise to the supernatant to adjust the pH of the solution to 7.0, thereby obtaining a flocculant mother solution extracted from the sludge; (3) Purification of microbial flocculant: adding anhydrous ethanol pre-cooled at 4°C to the flocculant mother liquor, soaking at room temperature for 24 hours until flocculent precipitates appear in the solution, thereby obtaining a flocculant mother liquor-ethanol solution; then, the flocculant mother liquor-ethanol solution is centrifuged at 8000 r / min for 15 minutes, and the precipitate is collected to obtain the purified microbial flocculant.

3. The method for preparing the nitrogen-phosphorus-doped carbon material containing copper nanoparticles according to claim 1, characterized in that: The step of using a microbial flocculant to adsorb copper ions to obtain a microbial flocculant that adsorbs copper ions specifically includes: Take the microbial flocculant in a reaction container and add Cu 2+ After the solution is added, the reaction container is shaken at a speed of 150 r / min, the shaking temperature is 15 to 35° C., and the shaking time is 180 to 420 min to obtain the microbial flocculant that adsorbs copper ions; Among them, Cu 2+ The solution is a copper sulfate solution, a copper ammonia solution or a mixture of the two, and the pH range is 3 to 11.

4. The method for preparing the nitrogen-phosphorus-doped carbon material containing copper nanoparticles according to claim 2, characterized in that: Before the step of obtaining microbial flocculants by culturing excess sludge from sewage treatment plants in the laboratory, the process also includes: Take the dewatered sludge cake from the urban domestic sewage treatment plant, mix the dewatered sludge cake and tap water in a container, stir at room temperature to make the mud and water fully mixed, then use a 20-mesh sieve to filter the mud and water mixture to remove solid impurities, and then add the mud and water mixture into the aeration tank of the SBR method intermittent experimental device for uninterrupted air aeration, and add carbon source, nitrogen source and phosphorus source as nutrients for microbial growth according to the carbon: nitrogen: phosphorus ratio of 100:5:

1. The carbon source is glucose, starch and white sugar; the nitrogen source is peptone or urea; the phosphorus source is potassium dihydrogen phosphate or sodium dihydrogen phosphate; the COD concentration of the mixed solution is controlled at 200-300 mg / L, and the water is changed every 24 hours. When changing the water, stop aeration and let the mixed solution stand for 1 minute. 5 minutes, then pour out the clarified liquid layer of 1 / 3 volume of the upper layer of the mixed liquid, and add the same volume of nutrient solution containing carbon source, nitrogen source and phosphorus source to the container. After 7 to 10 days, the activated sludge cultivation and domestication are basically completed; after the sludge properties tend to be stable, it is washed with water, and the washing treatment includes: first, taking the mud-water mixture and letting it settle, and pouring out the supernatant liquid after 30 minutes; then adding deionized water to the beaker at room temperature, slowly stirring the sludge mixture for 3 to 5 minutes, and then letting it settle for 30 minutes, and then pouring out the supernatant liquid, and repeating this washing process 3 times; finally, after the sludge washing is completed, it is centrifuged and dehydrated, the centrifugal speed is 5000r / min, and the centrifugal time is 15 minutes to obtain the pretreated sludge sample. 5 . The nitrogen and phosphorus doped carbon material containing copper nanoparticles obtained by the method for preparing a nitrogen and phosphorus doped carbon material containing copper nanoparticles according to claim 1 .

6. Use of the nitrogen-phosphorus-doped carbon material containing copper nanoparticles as claimed in claim 5 in the field of electrocatalytic reduction of nitrates.

7. The use according to claim 6, characterized in that: The carbon fiber cloth was immersed in a beaker containing anhydrous ethanol, ultrasonically cleaned for 30 minutes, and then rinsed with deionized water for 3 to 5 times to obtain a cleaned carbon cloth; the cleaned carbon cloth was placed in a constant temperature drying oven at 60°C and dried for 3 hours to obtain a treated carbon cloth; the Cu@NPC was taken, deionized water, anhydrous ethanol, and 5wt% Nafion solution were added in sequence, and the Cu@NPC was uniformly dispersed by ultrasonication for 20 to 30 minutes to obtain a dispersed solution; the dispersed solution was evenly applied to the treated carbon cloth, and the carbon cloth was placed in a vacuum drying oven at 60°C and dried for 3 hours to prepare a Cu@NPC / CC electrode; The electrolysis experiment was carried out in a single-tank electrolytic cell using a standard electrochemical three-electrode system, with the Cu@NPC / CC electrode as the working electrode, the Pt electrode or the Ir-Ru / Ti electrode as the counter electrode, and the saturated Ag / AgCl electrode as the reference electrode. A mixed solution of sodium sulfate and sodium nitrate was used as the electrolyte. The electrolysis current density ranged from 15 to 35 mA / cm 2 , electrolysis time is 9h; Among them, in the electrolyte, the sodium nitrate concentration range is 10-30 mg-N / L, the sodium sulfate concentration range is 0.05-0.2 mol / L, the solution pH range is 3-11, and Cl - The concentration range is 0.0~2.0g / L, and the coexisting ion K + Mg 2+ , Ca 2+ 、SO4 2- 、HCO3 - , the concentration range is 0-300 mg / L, and the COD concentration is 50-300 mg / L; after the electrolysis experiment, the concentration range of nitrate in the electrolyte is 0-6 mg-N / L.

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