High-loading-capacity nitrogen / phosphorus co-coordinated nickel monatomic material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of catalysts for degradation of antibiotics in surface water, in particular to a high-loading-capacity nitrogen / phosphorus co-coordinated nickel monatomic material and a preparation method and application thereof.The high-loading-capacity nitrogen / phosphorus co-coordinated nickel monatomic material is characterized in that a two-step pyrolysis method is adopted, 2-methylimidazole and zinc nitrate are synthesized and pyrolyzed through a hydrothermal method, and then a carbon nitride carrier is prepared; then nickel salt and a phosphorus source are fully absorbed, and secondary pyrolysis is performed under the protection of ammonium halide, so that high dispersion of nickel atoms and common coordination of nitrogen and phosphorus elements are realized. According to the method, the decomposition product of ammonium halide is used for inhibiting agglomeration of metal nickel in the secondary pyrolysis process, environmental pollution and resource and energy waste caused by a traditional acid pickling process are avoided, and the number and stability of monatomic active sites are greatly improved. The prepared monatomic catalyst can efficiently activate persulfate to generate active oxygen, the stability is excellent, the used raw materials are cheap and easy to obtain, the preparation process is green and low-carbon, and the monatomic catalyst has great industrial production value and practical application value.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts for the degradation of antibiotics in surface water, and particularly to a high-loading nitrogen and phosphorus co-coordinated single-atom catalyst for activating persulfate to degrade tetracycline and a low-carbon preparation method thereof. Background Art

[0002] New pollutants in the water environment have posed severe challenges to the production of clean drinking water and the sustainable development of society. The advanced oxidation process based on persulfate has the advantages of strong oxidation ability, wide applicability, and easy storage and transportation, and is one of the most effective water treatment technologies to solve this problem. At present, single-atom catalysts have attracted much attention due to their excellent catalytic performance. Many nitrogen-doped carbon materials containing transition metal single atoms (M-N-C) have shown extremely superior effects in the process of activating persulfate.

[0003] In the process of preparing single-atom catalysts, in order to ensure the monodispersion of metal atoms in the catalyst, it is often necessary to rely on high temperature and strong acid to remove the nanoparticles formed during high-temperature pyrolysis. However, the traditional pickling process requires a large amount of energy to supply heating and stirring equipment. The large amount of acidic waste liquid generated during the production process increases the environmental risk, has high requirements for equipment maintenance and waste liquid disposal, resulting in high production costs, and there are obvious deficiencies in terms of economic and environmental benefits. Moreover, pickling will not only damage the active structures of single-atom sites and supports, leading to a decline in catalytic performance, but also hinder the further improvement of the metal loading of single-atom catalysts. The activity loss and reduced metal utilization rate caused by pickling are contrary to the original intention of the design of single-atom catalysts.

[0004] On the other hand, the planar M-N 4 coordination structure is the most common active center of single-atom catalysts. This symmetric coordination structure leads to a symmetric charge distribution, which is not conducive to the progress of catalytic reactions. Research shows that heteroatoms such as P can regulate the charge distribution of single-atom active sites after co-coordination with N, enhance the adsorption and electron transfer processes of persulfate, and are expected to improve catalytic activity. Usually, a multi-step pyrolysis method is used to gradually introduce one or more heteroatoms into the metal center for co-coordination. However, the increase in pyrolysis steps undoubtedly provides more opportunities for metal aggregation and requires a more complex pickling procedure, which undoubtedly further increases the energy consumption and environmental risk during the production process.

[0005] Therefore, it is more necessary to develop an efficient and reliable single-atom catalyst synthesis strategy to achieve (1) single-atom sites with a stable N and P co-coordinated structure to optimize the electronic structure of the Ni active center; (2) inhibit the aggregation of metals during the multi-step pyrolysis process and improve the purity and loading of single-atom sites; (3) a low-carbon, economical, and sustainable production process. Summary of the Invention

[0006] To solve the above-mentioned defects in the prior art, the purpose of the present invention is to provide a nickel single-atom material with a high loading amount of nitrogen / phosphorus co-coordination and a preparation method thereof. By using stepwise pyrolysis and introducing environmentally friendly chemical vapor deposition (CVD) to replace strong acid pickling, high-loading nickel single-atom sites are formed on the carbon nitride support, and effective doping of nitrogen and phosphorus into the catalyst is achieved. The high density of single-atom active sites and the effective optimization of the charge distribution around nickel atoms by phosphorus enable the material prepared by this method to exhibit excellent performance in activating persulfate to degrade tetracycline.

[0007] Another purpose of the present invention is to provide the application of the nickel single-atom material prepared by this method.

[0008] The present invention is realized through the following technical solutions.

[0009] One aspect of the present invention provides a preparation method of a nickel single-atom material with a high loading amount of nitrogen / phosphorus co-coordination, which is characterized by including:

[0010] (a) Dissolve 1.5 - 2.0% of 2-methylimidazole and 1.0 - 1.5% of zinc nitrate in 96.5 - 97.5% of methanol according to the mass ratio, carry out hydrothermal reaction, and wash and dry the reaction product to obtain a carbon nitride precursor;

[0011] (b) Calcinate the carbon nitride precursor in an inert atmosphere to obtain a carbon nitride support;

[0012] (c) Ultrasonically disperse the carbon nitride support evenly; then, according to the mass ratio of nickel salt: phosphorus source: carbon nitride support = 1:(10 - 50):(20 - 40), add the nickel salt and the phosphorus source to the carbon nitride support, heat, wash and dry to obtain nickel- and phosphorus-loaded carbon nitride;

[0013] (d) Heat and calcinate in an inert atmosphere according to the mass ratio of nickel- and phosphorus-loaded carbon nitride to ammonium halide of (20 - 30):1, naturally cool to room temperature, wash and dry to obtain a high-loading nitrogen / phosphorus co-coordination nickel single-atom catalyst material.

[0014] Preferably, the phosphorus source is one or more of sodium hypophosphite, phytic acid, and phosphoric acid;

[0015] Phytic acid uses a 50% phytic acid solution.

[0016] Preferably, the nickel salt is one or more of nickel chloride hexahydrate, nickel sulfate heptahydrate, and nickel nitrate hexahydrate;

[0017] The nickel salt uses a 10 - 20 mg / ml nickel salt ethanol solution.

[0018] Preferably, the ammonium halide is one or more of ammonium chloride, ammonium bromide, and ammonium iodide.

[0019] Preferably, in step (a), 2-methylimidazole and zinc nitrate are dissolved in methanol and ultrasonically treated for 10 - 30 min, and then hydrothermally reacted by heating at 110 - 130 °C for 1 - 4 h. The product is washed with methanol 3 - 5 times and vacuum dried at 60 - 80 °C for 10 - 14 h.

[0020] Preferably, in step (b), in an atmosphere of nitrogen or argon, the carbon nitride precursor is heated to 950 - 1050 °C at a rate of 5 ± 0.5 °C / min and calcined for 2 - 4 h.

[0021] Preferably, in step (c), the carbon nitride support is rapidly stirred or ultrasonically treated for 20 - 40 min according to the mass ratio of the carbon nitride support to ethanol = 1:(300 - 500);

[0022] A nickel salt and a phosphorus source are added to the carbon nitride support and heated at 70 - 90 °C for 4 - 6 h. The product is washed with ethanol 3 - 5 times and placed in a vacuum at 60 - 80 °C for drying for 10 - 14 h.

[0023] Preferably, in step (d), in an atmosphere of nitrogen or argon, the porcelain boat containing ammonium halide is located upstream and heated from room temperature to 550 °C at a rate of 6 ± 0.5 °C / min, and the porcelain boat of nickel and phosphorus loaded carbon nitride is located downstream and heated from room temperature to 900 °C at a rate of 10 ± 0.5 °C / min in a tube furnace, and maintained for 60 - 90 min. After cooling to room temperature, it is washed with distilled water 3 - 5 times and vacuum dried for 10 - 12 h.

[0024] The present invention adopts a two-step pyrolysis strategy. First, a metal-organic framework is synthesized by a hydrothermal method, and a carbon nitride support is obtained after pyrolysis; then nickel salt and phosphorus source are fully absorbed, and a second pyrolysis is carried out under the protection of ammonium halide, realizing the highly dispersed nickel atoms and the co-coordination of nitrogen and phosphorus elements. The decomposition products of ammonium halide are used to inhibit the aggregation of metallic nickel during the secondary pyrolysis process, avoiding the environmental pollution and the waste of a large amount of resources and energy caused by the traditional pickling process, and greatly improving the number and stability of single-atom active sites. The prepared nickel single-atom material (single-atom catalyst) with a high loading amount of nitrogen / phosphorus co-coordination can efficiently activate persulfate to generate reactive oxygen, and has excellent stability.

[0025] In another aspect of the present invention, a nickel single-atom material with a high loading amount of nitrogen / phosphorus co-coordination is provided for degrading tetracycline in antibiotic wastewater. 10 - 100 mg / L of the nickel single-atom material and 0.1 - 0.3 g / L of potassium persulfate or potassium monopersulfate are added to the antibiotic wastewater, and the degradation reaction is carried out at room temperature and pH = 3 - 9.

[0026] Due to the adoption of the above technical solutions, the present invention has the following beneficial effects:

[0027] (1) Preparation of N, P co - coordinated nickel single - atom catalyst with high catalytic performance

[0028] Through a two - step pyrolysis method, the present invention realizes the anchoring of a high content of nickel single atoms and the effective doping of nitrogen and phosphorus into the material, and the amount of phosphorus element in the catalyst can be regulated within a certain range.

[0029] (2) Increasing the loading amount of the single - atom catalyst and avoiding pickling

[0030] Using ammonium halide for etching, the nickel single - atom sites are selectively retained, and the decomposition products of ammonium halide are used to inhibit the agglomeration of metallic nickel during the secondary pyrolysis process; the prepared catalyst has a high loading amount, breaking through the technical problem of low single - atom density caused by "multiple pyrolysis → pickling for impurity removal" in the preparation process of conventional multi - atom - doped single - atom catalysts.

[0031] (3) Dual benefits of environment and economy

[0032] Ammonium chloride in the ammonium halide used in the present invention is a common and low - toxicity chemical. Its decomposition products are mainly ammonia and hydrogen chloride gases, which can be captured and treated by a simple waste gas treatment device. In addition, it is inexpensive and has a small usage amount, does not produce strongly acidic liquid waste, saves production costs, and helps to achieve dual benefits of economy and environment. The etching and impurity removal process is synchronized with and carried out in the same device as pyrolysis, simplifying the process flow, avoiding a large amount of energy consumption and equipment corrosion caused by traditional high - temperature and long - time pickling, and having great cost advantages.

[0033] The present invention provides a green and low - carbon alternative for the preparation of heteroatom - doped single - atom catalysts. The prepared single - atom catalyst has a high loading amount, excellent catalytic activity and catalytic stability; it can efficiently activate persulfate to generate reactive oxygen species, with excellent stability, inexpensive and easily available raw materials, simple and economical preparation process, energy - saving and carbon - reduction, strong universality, and has broad industrial production value and practical application value. Description of the Drawings

[0034] The drawings described herein are used to provide a further understanding of the present invention, form a part of this application, and do not constitute an improper limitation to the present invention. In the drawings:

[0035] Figure 1 is the preparation flow chart of Example 1 of the present invention;

[0036] Figure 2 is the aberration - corrected electron microscopy image (AC - STEM) of Example 1 of the present invention;

[0037] Figure 3 is the X - ray diffraction pattern (XRD) of Example 1 and Comparative Example 1 of the present invention;

[0038] Figure 4 It is the elemental distribution map (EDS) of Example 1 of the present invention;

[0039] Figure 5 It is the effect of the catalysts prepared in Examples 1 and 2 and Comparative Examples 1 and 2 of the present invention in degrading TC. Detailed implementation manners

[0040] The present invention will be described in detail below with reference to the accompanying drawings and specific examples. Here, the illustrative embodiments of the present invention and the descriptions are used to explain the present invention, but do not limit the present invention.

[0041] As Figure 1 shown, the preparation method of the high-loading nitrogen / phosphorus co-coordinated nickel single-atom material provided by the embodiment of the present invention includes the following steps:

[0042] (a) Dissolve 1.5-2.0% of 2-methylimidazole and 1.0-1.5% of zinc nitrate in 96.5-97.5% of methanol according to the mass ratio, and ultrasonically treat for 10-30 min. In a hydrothermal reaction kettle, heat at 110-130 °C for 1-4 h for hydrothermal reaction. The reaction product is washed with methanol 3-5 times and vacuum dried at 60-80 °C for 10-14 h to obtain a carbon nitride precursor;

[0043] (b) In an atmosphere of nitrogen or argon, heat the carbon nitride precursor from room temperature to 950-1050 °C at a rate of 5±0.5 °C / min and calcine for 2-4 h to obtain a carbon nitride support;

[0044] (c) According to the mass ratio of carbon nitride support to ethanol = 1:(300-500), add the carbon nitride support to ethanol, and stir rapidly or ultrasonically treat for 20-40 min; then according to the mass ratio of nickel salt:phosphorus source:carbon nitride support = 1:(10-50):(20-40), add the nickel salt and phosphorus source to the carbon nitride support, heat at 70-90 °C for 4-6 h, wash with ethanol 3-5 times, and place in a vacuum at 60-80 °C to dry for 10-14 h to obtain nickel- and phosphorus-loaded carbon nitride;

[0045] The nickel salt is one or more of nickel chloride hexahydrate, nickel sulfate heptahydrate, and nickel nitrate hexahydrate. The nickel salt uses a 10-20 mg / ml nickel salt ethanol solution.

[0046] The phosphorus source is one or more of sodium hypophosphite, phytic acid, and phosphoric acid. Phytic acid uses a 50% phytic acid solution.

[0047] (d) In an atmosphere of nitrogen or argon, heat and calcine according to the mass ratio of nickel and phosphorus-loaded carbon nitride to ammonium halide of (20 - 30):1. Place the porcelain boat containing ammonium halide upstream and heat from room temperature to 550 °C at a rate of 6 ± 0.5 °C / min. Place the porcelain boat of nickel and phosphorus-loaded carbon nitride downstream and heat from room temperature to 900 °C in a tube furnace at a rate of 10 ± 0.5 °C / min, hold for 60 - 90 min, cool naturally to room temperature, wash with distilled water 3 - 5 times, and vacuum dry for 10 - 12 h to obtain a high-loading nitrogen / phosphorus co-coordinated nickel single-atom catalyst material.

[0048] The ammonium halide is one or more of ammonium chloride, ammonium bromide, and ammonium iodide.

[0049] In the present invention, the co-coordination of nitrogen and phosphorus atoms breaks the symmetric coordination structure of nickel atoms, resulting in uneven charge distribution around nickel atoms, reducing the valence state of nickel atoms, enhancing the adsorption of persulfate and accelerating the desorption of activation products during the activation of persulfate. The electron-rich phosphorus element increases the charge density around nickel atoms, facilitating the electron transfer between nickel atoms and persulfate, thereby activating persulfate and enhancing the reaction kinetics of tetracycline degradation. At the same time, the high-purity single-atom sites ensure that the catalyst prepared in the present invention has good stability, and high catalytic performance is still maintained during long-term operation and reuse.

[0050] During the preparation of the single-atom catalyst, the traditional pickling scheme has poor selectivity. Research shows that pickling is prone to damage other active sites and the carrier structure while removing nanoparticles, thereby reducing the overall activity and stability of the catalyst. Moreover, a large amount of metal atoms of the single-atom catalyst is lost after pickling, and it is difficult to form high-density single-atom sites, limiting the improvement space of catalytic activity. The present invention uses ammonium halide for etching, highly selectively retaining nickel single-atom sites and avoiding the generation of clusters.

[0051] The pickling process usually involves strong acids (such as sulfuric acid, hydrochloric acid, etc.), with a large usage amount and a long treatment time (>10 h), requiring a large amount of energy to maintain its operation. At the same time, a large amount of complex liquid waste is generated, increasing the treatment cost and potential environmental risks. The present invention uses ammonium halide and does not produce strong acidic liquid waste.

[0052] The following further elaborates on the present invention through different embodiments.

[0053] Example 1

[0054] Dissolve 1.5% of 2-methylimidazole and 1.5% of zinc nitrate hexahydrate in 97% of methanol according to the mass ratio, ultrasonicate for 30 min, then heat in a hydrothermal reaction kettle at 120 °C for 2 h, wash the product with methanol 3 times, and vacuum dry at 60 °C for 12 h.

[0055] The product was heated from room temperature to 950 °C at a rate of 5 °C / min in a nitrogen atmosphere and held for 3 h to obtain carbon nitride (NC).

[0056] According to the mass ratio, 1 mg of carbon nitride NC was added to 400 ml of ethanol. After rapid stirring for 30 min, Ni salt: phosphorus source: carbon nitride NC = 1:30:40 was added, and a 20 mg / ml ethanol solution of Ni(NO 3 ) 2 ·6H 2 O and 50% phytic acid solution were added. It was heated at 85 °C for 5 h. The product was washed 3 times with ethanol and dried in vacuo at 60 °C for 14 h to obtain nickel- and phosphorus-loaded carbon nitride (Ni / P@NC).

[0057] Finally, in a nitrogen atmosphere, carbon nitride (Ni / P@NC) and ammonium chloride were mixed and heated and calcined according to a mass ratio of 20:1. The porcelain boat containing ammonium chloride was placed upstream and heated from room temperature to 550 °C at a rate of 6 °C / min. The porcelain boat containing 40 mg of Ni / P@NC was placed downstream and heated from room temperature to 900 °C at a rate of 10 °C / min in a tube furnace and held for 60 min. After cooling to room temperature, it was washed 4 times with distilled water and dried in vacuo for 12 h to obtain a nickel single-atom catalyst Ni-NCP with nitrogen and phosphorus co-coordination 1 .

[0058] The aberration-corrected electron microscopy image of the single-atom catalyst in Example 1 is as shown in Figure 2 . Many isolated bright spots can be seen, indicating that the Ni element is atomically dispersed on the material. The XRD pattern of the single-atom catalyst in Example 1 is as shown in Figure 3 . Two broad peaks are shown, corresponding to the (002) and (101) planes of carbon respectively, and no peaks of nickel and nickel oxides are observed. As shown in Figure 4 , the elemental mapping (EDS) of the catalyst in Example 1 confirmed that nickel, phosphorus, carbon, nitrogen, and oxygen elements were uniformly distributed in the catalyst. According to the test of inductively coupled plasma spectrometer (ICP), the Ni loading in the single-atom catalyst of Example 1 was 1.85 wt%, which was much higher than that of Ni single-atom catalysts reported in many literatures

[0059] Example 2

[0060] 2.0% 2-methylimidazole and 1.5% zinc nitrate hexahydrate were dissolved in 96.5% methanol according to the mass ratio, and ultrasonicated for 20 min. Then it was heated in a hydrothermal reaction kettle at 130 °C for 4 h. The product was washed 4 times with methanol and dried in vacuo at 70 °C for 14 h

[0061] The product was heated from room temperature to 1000 °C at a rate of 4.5 °C / min in a nitrogen atmosphere and held for 4 h to obtain carbon nitride (NC).

[0062] Take 1 mg of carbon nitride NC according to the mass ratio and add it to 300 ml of ethanol. After rapid stirring for 20 min, then add an ethanol solution of Ni(SO 4 ) 2 ·6H 2 O with a concentration of 20 mg / ml and phosphoric acid solution according to the ratio of nickel salt: phosphorus source: carbon nitride NC = 1:10:30. Heat at 90 °C for 4 h, wash the product 4 times with ethanol, and dry it in vacuo at 70 °C for 12 h to obtain nickel- and phosphorus-loaded carbon nitride (Ni / P@NC).

[0063] Finally, in a nitrogen atmosphere, mix and heat and calcine according to the mass ratio of carbon nitride (Ni / P@NC) to ammonium bromide of 30:1. Place the porcelain boat containing ammonium bromide upstream and heat it from room temperature to 550 °C at a rate of 5.5 °C / min. Place the porcelain boat containing Ni / P@NC downstream and heat it from room temperature to 900 °C at a rate of 9.5 °C / min in a tube furnace and hold for 80 min. After cooling to room temperature, wash it 3 times with distilled water and dry it in vacuo for 10 h to obtain a nickel single-atom catalyst Ni-NCP with nitrogen and phosphorus co-coordination 0.5 。

[0064] Example 3

[0065] Dissolve 1.5% 2-methylimidazole and 1.0% zinc nitrate hexahydrate in 97.5% methanol according to the mass ratio, ultrasonicate for 10 min, then heat in a hydrothermal reaction kettle at 110 °C for 1 h. Wash the product 5 times with methanol and dry it in vacuo at 80 °C for 10 h.

[0066] Heat the product from room temperature to 1050 °C at a rate of 5.5 °C / min in a nitrogen atmosphere and hold for 2 h to obtain carbon nitride (NC).

[0067] Take 1 mg of carbon nitride NC according to the mass ratio and add it to 500 ml of ethanol. After rapid stirring for 40 min, then add an ethanol solution of NiCl 2 ·6H 2 O with a concentration of 10 mg / ml and sodium phosphate solution according to the ratio of nickel salt: phosphorus source: carbon nitride NC = 1:50:20. Heat at 70 °C for 6 h, wash the product 5 times with ethanol, and dry it in vacuo at 80 °C for 10 h to obtain nickel- and phosphorus-loaded carbon nitride (Ni / P@NC).

[0068] Finally, in a nitrogen atmosphere, carbon nitride (Ni / P@NC) and ammonium iodide were mixed and heated for calcination according to a mass ratio of 25:1. The porcelain boat containing ammonium iodide was placed upstream and heated from room temperature to 550 °C at a rate of 6.5 °C / min, while the porcelain boat containing Ni / P@NC was placed downstream and heated from room temperature to 900 °C at a rate of 10.5 °C / min in a tubular furnace and held for 90 min. After cooling to room temperature, it was washed 5 times with distilled water and vacuum dried for 11 h to obtain a nickel single-atom catalyst Ni-NCP with nitrogen and phosphorus co-coordination. 0.5 。

[0069] Comparative Example 1

[0070] 2-Methylimidazole and zinc nitrate hexahydrate were dissolved in methanol according to the ratio of Example 1, sonicated for 30 min, and then heated in a hydrothermal reaction kettle at 120 °C for 2 h. The product was washed 3 times with methanol and vacuum dried at 60 °C for 12 h.

[0071] The product was heated to 950 °C at a rate of 5 °C / min in a nitrogen atmosphere and held for 3 h to obtain carbon nitride (NC).

[0072] NC was taken according to the ratio of Example 1 and added to ethanol. After rapid stirring for 30 min, an ethanol solution of Ni(NO 3 ) 2 ·6H 2 O (10 mg / ml) and 50% phytic acid solution were added, and heated at 85 °C for 5 h. The product was washed 3 times with ethanol and dried in vacuo at 60 °C for 10 h to obtain carbon nitride supported with nickel and phosphorus (Ni / P@NC).

[0073] Finally, in a nitrogen atmosphere, Ni / P@NC was heated from room temperature to 900 °C at a rate of 10 °C / min and held for 60 min. After cooling to room temperature, it was washed 3 - 5 times with distilled water and vacuum dried for 10 - 12 h to obtain a nickel-based catalyst Ni-NPs with coexistence of single atoms / clusters.

[0074] The catalyst of Comparative Example 1 did not add ammonium chloride as a protection, and its XRD pattern is as Figure 3 shown, showing the presence of crystalline peaks, indicating the presence of Ni nanoparticles in the catalyst.

[0075] Comparative Example 2

[0076] 2-Methylimidazole and zinc nitrate hexahydrate were dissolved in methanol according to the ratio of Example 1, sonicated for 30 min, and then heated in a hydrothermal reaction kettle at 120 °C for 2 h. The product was washed 3 times with methanol and vacuum dried at 60 °C for 12 h.

[0077] The product was heated to 950 °C at a rate of 5 °C / min in an atmosphere of nitrogen and held for 3 h to obtain carbon nitride (NC).

[0078] NC was taken in the proportion of Example 1 and added to ethanol. After rapid stirring for 30 min, 0.3 ml of an ethanol solution of Ni(NO 3 ) 2 ·6H 2 O (10 mg / ml) was added, and the mixture was heated at 85 °C for 5 h. The product was washed 3 times with ethanol and dried in vacuo at 60 °C for 10 h to obtain nickel-loaded carbon nitride (Ni@NC).

[0079] Finally, in an atmosphere of nitrogen, Ni@NC was heated from room temperature to 900 °C at a rate of 10 °C / min and held for 60 min. After cooling to room temperature, it was washed 3 - 5 times with distilled water and dried in vacuo for 10 - 12 h. The nickel single-atom catalyst Ni-NC was obtained.

[0080] Test Example 1

[0081] Comparison of different catalysts:

[0082] 100 mL of an aqueous tetracycline solution with a concentration of 20 mg / L was added to the reactor. At the same time, 0.15 g / L of potassium monopersulfate was added to the reactor, and then 50 mg / L of the catalysts obtained in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were added respectively. Magnetic stirring was carried out in the reactor, and the reaction was carried out at room temperature and pH = 7. After 30 min, the experimental results were tested. The removal rates of tetracycline under different catalyst addition amounts are as Figure 5 shown.

[0083] Ni-NCP 1 had the highest removal rate of 93.2%, which was much higher than that of the phosphorus-free nickel single-atom catalyst Ni-NC (83.4%) and the nickel-based catalyst Ni-NPs with coexisting single atoms / clusters (60.3%). It can be seen that after doping with phosphorus, the catalytic activity of the Ni single-atom catalyst was improved; the catalytic effect of Ni-NPs prepared in Comparative Example 1 was inferior to that of the single-atom catalyst, indicating that the etching of ammonium chloride was crucial for the formation of single-atom sites and thus the improvement of catalytic activity.

[0084] Test Example 2

[0085] Different catalyst dosages

[0086] 100 mL of an aqueous tetracycline solution with a concentration of 20 mg / L was added to the reactor. At the same time, 10, 20, 50, 100 mg / L of the nitrogen- and phosphorus-coordinated nickel single-atom catalyst Ni-NCP obtained in Example 1 was added to the reactor 1And 0.15 g / L of potassium monopersulfate were magnetically stirred in a reactor. The reaction was carried out at room temperature and pH = 7, and the experimental results were tested after 30 min.

[0087] The removal rates of tetracycline under different catalyst addition amounts are shown in Table 2.

[0088] Table 2: Degradation effects of different catalyst dosages on tetracycline

[0089] Catalyst dosage 10 mg / L 20 mg / L 50 mg / L 100 mg / L Degradation rate in 30 minutes 79.6％ 86.4％ 93.2％ 95.8％

[0090] With the increase of the catalyst addition amount, the degradation efficiency of tetracycline also increased. However, after the catalyst addition amount exceeded 50 mg / L, the increase in the degradation efficiency of tetracycline was not obvious. Therefore, it can be speculated that for this experiment on the degradation of tetracycline simulated waste liquid, the optimal catalyst dosage is 50 mg / L.

[0091] Test Example 3

[0092] Different persulfate dosages

[0093] 100 mL of an aqueous tetracycline solution with a concentration of 20 mg / L was added to the reactor. At the same time, 0.1, 0.15, 0.3, 0.5 g / L of potassium monopersulfate and 50 mg / L of the nitrogen and phosphorus co-coordinated nickel single-atom catalyst Ni-NCP obtained in Example 1 were added to the reactor 1 , and magnetic stirring was carried out in the reactor. The reaction was carried out at room temperature and pH = 3, and the experimental results were tested after 30 min.

[0094] The removal rates of tetracycline under different potassium monopersulfate addition amounts are shown in Table 3.

[0095] Table 3: Degradation effects of different potassium persulfate dosages on tetracycline

[0096] Dosage of potassium monopersulfate 0.1 g / L 0.15 g / L 0.2 g / L 0.3 g / L Degradation rate in 30 minutes 82.5％ 93.2％ 93.7％ 91.8％

[0097] When the catalyst dosage was 50 mg / L, the tetracycline concentration was 20 mg / L, and pH = 3, the degradation efficiency of tetracycline reached 93.2% at the addition amount of 0.15 g / L of persulfate. Continuing to increase the addition amount of persulfate, the increase in the degradation efficiency was not obvious. Therefore, it can be speculated that for this experiment on the degradation of tetracycline simulated waste liquid, the optimal dosage of potassium monopersulfate is 0.15 g / L.

[0098] Test Example 4

[0099] Different initial TC concentrations

[0100] Add 100 mL of tetracycline aqueous solutions with concentrations of 0.5, 5, 10, and 20 mg / L to the reactor. At the same time, add 0.15 g / L of potassium persulfate and 50 mg / L of the nitrogen and phosphorus co-coordinated nickel single-atom catalyst Ni-NCP obtained in Example 1 to the reactor. 1 , perform magnetic stirring in the reactor, and carry out the reaction at room temperature under the condition of pH = 9. After 30 min, test the experimental results.

[0101] The removal rates of tetracycline under different initial TC concentration conditions are shown in Table 4.

[0102] Table 4: Degradation effects of different initial TC concentrations on tetracycline

[0103] Initial TC concentration 0.5 5 10 20 Degradation rate in 30 minutes 99.9％ 97.6％ 95.8％ 92.3％

[0104] Thus, it can be seen that when the catalyst dosage is 50 mg / L, the persulfate dosage is 0.15 g / L, and pH = 9, the nitrogen and phosphorus co-coordinated nickel single-atom catalyst Ni-NCP obtained in Example 1 1 has good removal effects on tetracycline simulated wastewater with concentrations of 0.5 - 20 mg / L and has a wide application range.

[0105] The present invention is not limited to the above embodiments. Based on the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and deformations to some technical features without creative labor according to the disclosed technical content, and these substitutions and deformations are all within the protection scope of the present invention.

Claims

1. A method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single atom material, characterized in that: The following steps are involved: (a) dissolving 1.5-2.0% 2-methylimidazole and 1.0-1.5% zinc nitrate in 96.5-97.5% methanol according to a mass ratio, performing a hydrothermal reaction, and washing and drying the reaction product to obtain a carbon nitride precursor; (b) calcining the carbon nitride precursor in an inert atmosphere to obtain a carbon nitride support; (c) uniformly dispersing the carbon nitride carrier by ultrasonication; then adding the nickel salt and the phosphorus source to the carbon nitride carrier in a mass ratio of nickel salt:phosphorus source:carbon nitride carrier=1:(10-50):(20-40), heating, washing and drying to obtain nickel-phosphorus-loaded carbon nitride; (d) heating and calcining in an inert atmosphere according to the mass ratio of nickel and phosphorus-loaded carbon nitride to ammonium halide of (20-30):1, naturally cooling to room temperature, washing and drying to obtain a high-loaded nitrogen / phosphorus co-coordinated nickel single atom catalyst material.

2. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: The phosphorus source is one or more of sodium hypophosphite, phytic acid and phosphoric acid; The phytic acid used was a 50% phytic acid solution.

3. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: The nickel salt is one or more of nickel chloride hexahydrate, nickel sulfate heptahydrate and nickel nitrate hexahydrate; The nickel salt adopts 10-20 mg / ml nickel salt ethanol solution.

4. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: The ammonium halide is one or more of ammonium chloride, ammonium bromide and ammonium iodide.

5. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: In step (a), 2-methylimidazole and zinc nitrate are dissolved in methanol and ultrasonicated for 10 to 30 minutes, and heated at 110 to 130° C. for 1 to 4 hours for hydrothermal reaction. The product is washed with methanol for 3 to 5 times and vacuum dried at 60 to 80° C. for 10 to 14 hours.

6. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: In step (b), in a nitrogen or argon atmosphere, the carbon nitride precursor is heated to 950-1050° C. at a rate of 5±0.5° C. / min and calcined for 2-4 hours.

7. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: In step (c), the carbon nitride support is rapidly stirred or ultrasonically treated for 20-40 minutes at a mass ratio of carbon nitride support to ethanol = 1: (300-500); The nickel salt and the phosphorus source are added to the carbon nitride support and heated at 70-90° C. for 4-6 hours. The product is washed with ethanol for 3-5 times and dried in a vacuum at 60-80° C. for 10-14 hours.

8. The method for preparing a high-load nitrogen / phosphorus co-coordinated nickel single-atom material according to claim 1, characterized in that: In step (d), in a nitrogen or argon atmosphere, a porcelain boat containing ammonium halide is located upstream and heated from room temperature to 550°C at a rate of 6±0.5°C / min, and a porcelain boat containing nickel and phosphorus-loaded carbon nitride is located downstream and heated from room temperature to 900°C at a rate of 10±0.5°C / min in a tubular manner, maintained for 60 to 90 minutes, cooled to room temperature, washed with distilled water for 3 to 5 times, and vacuum dried for 10 to 12 hours.

9. A high-load nitrogen / phosphorus co-coordinated nickel single atom material prepared by the method as described in any one of claims 1 to 8.

10. A high-load nitrogen / phosphorus co-coordinated nickel single atom material as claimed in claim 9 for use in degrading tetracycline in antibiotic wastewater, characterized in that: 10-100 mg / L of nickel single atom material and 0.1-0.3 g / L of potassium persulfate or potassium monopersulfate are added to antibiotic wastewater, and a degradation reaction is carried out at room temperature and pH=3-9.

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