Method for removing organic pollutants in water body by activating persulfate with iron cluster modified manganese monatomic catalyst

Abstract

The invention discloses a method for removing organic pollutants in a water body by activating persulfate by using an iron cluster modified manganese monatomic catalyst, which is characterized in that the iron cluster modified manganese monatomic catalyst is used as a catalyst to activate the persulfate to degrade the organic pollutants in the water body. Wherein the manganese monatomic catalyst modified by the iron cluster comprises a porous nitrogen-doped carbon layered material and manganese monatomic loaded between the surface and the layered structure of the porous nitrogen-doped carbon layered material, the manganese monatomic is modified with the iron cluster, the valence state of iron is divalent, and the valence states of manganese are divalent and trivalent. The method has the advantages of being simple in process, convenient to operate, low in cost, high in practicability, wide in application range, small in catalyst dosage, high in treatment efficiency, good in degradation effect, environmentally friendly and the like, can effectively degrade high-concentration organic pollutants in a water body, particularly has a better removal effect on organic pollutants with the concentration smaller than or equal to 30 mg / L, is high in use value and has a good application prospect. The application prospect is good.

Description

Technical Field

[0001] The present invention belongs to the field of advanced oxidation treatment of organic pollutants, and relates to a method for activating persulfate by using an iron cluster-modified manganese single-atom catalyst to remove organic pollutants in water bodies. Background Art

[0002] With the rapid development of industrial technologies, a large number of organic substances enter water bodies, bringing serious pollution to the water environment and posing potential hazards to humans and aquatic organisms. Taking antibiotics as an example, since antibiotics can be used to treat diseases of humans and livestock and poultry, especially can promote the growth and development of livestock and poultry, they are widely used in the aquaculture industry. However, after use, they cannot be completely decomposed and absorbed by humans or livestock and poultry and enter the water environment. According to relevant research, 94 kinds of antibiotics have been positively detected in the water environment, among which 20 kinds of antibiotics are detected in surface water, and the total detection concentration is 3.61 - 1121 mg / L. For example, the detection frequency and median concentration of ciprofloxacin in surface water are relatively high. Therefore, it is necessary to develop new technologies for removing organic pollutants in water bodies to effectively purify organic pollutants in the water environment.

[0003] Advanced oxidation technologies (AOPs) are one of the most effective methods for treating organic pollutant wastewater at present. By using a large number of reactive oxygen species with high redox potential generated during the catalytic process, macromolecular and refractory organic pollutants can be effectively degraded rapidly, producing low-toxic or non-toxic molecular substances or even completely converted into intermediate substances of hydrated carbon dioxide. And in most cases, the wastewater treated by AOPs contains fewer harmful metabolites. At present, AOPs can be divided into: ozonation, Fenton method, photocatalysis, electrochemical oxidation, and persulfate advanced oxidation method. Persulfates mainly include peroxymonosulfate and peroxydisulfate. The persulfate advanced oxidation method has the following advantages compared with other technologies: a higher achievable free radical generation rate, a greater variety of methods for activating persulfate, a lower dependence of the treatment efficiency on operating parameters (such as pH, initial peroxide load, background components), and lower storage and transportation costs due to the availability of persulfate. Therefore, obtaining a suitable catalyst is very necessary for effectively activating persulfate and achieving effective degradation of organic pollutants.

[0004] Single-atom catalysts (SACs) are catalysts commonly used to activate persulfate. The current research situation is as follows: Due to the low loading rate of metal atoms, the single type of metal atoms, and the easy aggregation in single-atom catalysts, during the treatment process, in order to improve the activation effect of the catalyst on persulfate, excessive metal ions and metal oxides are usually used. At the same time, since metal ions and metal oxides in single-atom catalysts are usually exposed on the surface of the catalyst, they are prone to dissolution and enter the aqueous solution during use. As a result, single-atom catalysts have problems such as a small number of catalytic active sites, low catalytic activity, and easy secondary pollution (such as increased chromaticity), making it difficult to efficiently activate persulfate, and thus resulting in a still poor degradation effect on organic pollutants. Based on this, researchers have proposed a method for activating persulfate using a bimetallic atom nitrogen-doped carbon catalyst. The bimetallic atom nitrogen-doped carbon catalyst used is prepared by the calcination method. Through calcination, more metal atoms can be anchored on the surface of the catalyst, avoiding the aggregation of metal active sites while increasing the number of metal active sites. However, there are still the following defects: (a) The specific surface area of the bimetallic atom nitrogen-doped carbon catalyst is still relatively small, which makes it difficult for more metal active sites to be exposed on the outside of the catalyst, and thus it is difficult to efficiently activate persulfate with a small amount of the catalyst. Increasing the amount of the catalyst will inevitably increase the treatment cost and also increase the potential environmental pollution risk of the catalyst; (b) In the bimetallic atom nitrogen-doped carbon catalyst, different types of metal atoms have high and low valence state complementarity. When used to activate persulfate, the reaction system formed mainly uses the high-valence metal as the active species, and its degradation effect on organic pollutants is not as high as that of singlet oxygen; (c) In the bimetallic atom nitrogen-doped carbon catalyst, by introducing another metal atom with strong catalytic activity on the single-metal atom catalyst, not only is the density of metal active sites low, but also the contact area between these metal atoms is small, resulting in a weak mutual promotion effect between different types of metal atoms and making it difficult to strengthen the activation effect on persulfate; (d) In the bimetallic atom nitrogen-doped carbon catalyst, the introduced metal atoms are directly exposed on the outside of the catalyst and are easily damaged and enter the aqueous solution during use, which will not only weaken the catalytic performance of the catalyst but also easily bring new environmental pollution. The existence of the above defects makes it difficult for the existing bimetallic atom nitrogen-doped carbon catalysts to achieve efficient activation of persulfate under lower usage conditions and to efficiently degrade organic pollutants in water under more environmentally friendly conditions.In addition, most of the existing studies on promoting the performance of metal atoms based on atomic clusters focus on the combination of single-atom active centers and atomic clusters characterized by the same metal. In contrast, there are few studies on exploring the synergistic effects between atomic clusters and single-atom active centers of different metals. At the same time, among the known catalysts composed of atomic clusters and different metal atoms, the metal atoms serving as active centers are completely wrapped by atomic clusters, resulting in a significant reduction in specific surface area and a remarkable decrease in the number of active sites. This makes it difficult for single-atom active centers to contact persulfate, and thus difficult to construct a cyclic reaction system between different metal atoms and persulfate. Moreover, such catalysts still have defects such as small specific surface area, few active sites, and unstable structure, so it is difficult to be applied to the field of advanced oxidation technology for activating persulfate. Therefore, obtaining a metal single-atom nitrogen-doped carbon catalyst with a large specific surface area, a large number of active sites, high catalytic activity, and stable structure plays an important role in efficiently activating persulfate and effectively removing organic pollutants in water bodies. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for activating persulfate with an iron cluster-modified manganese single-atom catalyst to remove organic pollutants in water bodies, which has the advantages of low cost, small catalyst dosage, high treatment efficiency, good degradation effect, and environmental friendliness.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for activating persulfate with an iron cluster-modified manganese single-atom catalyst to remove organic pollutants in water bodies, wherein the method uses the iron cluster-modified manganese single-atom catalyst as a catalyst to activate persulfate for degrading organic pollutants in water bodies; the iron cluster-modified manganese single-atom catalyst uses a porous nitrogen-doped carbon layered material as a carrier, and manganese single atoms are loaded between the surface and the layered structure of the porous nitrogen-doped carbon layered material, and iron clusters are modified on the manganese single atoms; the valence state of iron in the iron cluster-modified manganese single-atom catalyst is divalent, and the valence states of manganese are divalent and trivalent.

[0008] In the above method, further improved, the atomic percentage content of iron in the iron cluster-modified manganese single-atom catalyst is 0.834%, and the atomic percentage content of manganese is 0.016%.

[0009] In the above method, further improved, the specific surface area of the iron cluster-modified manganese single-atom catalyst is 1384.85 m 2 / g.

[0010] In the above method, further improved, the iron cluster-modified manganese single-atom catalyst is prepared by using manganese salt, iron salt, and zinc salt as raw materials, o-phenylenediamine as a template agent, and through impregnation and pyrolysis.

[0011] In the above method, further improved, the preparation method of the iron cluster-modified manganese single-atom catalyst includes the following steps:

[0012] S1. Prepare a zinc-manganese solution from zinc salt and manganese salt, add it to the o-phenylenediamine solution, and stir to obtain a zinc-manganese precursor;

[0013] S2. Pyrolyze the zinc-manganese precursor to obtain a nitrogen-doped carbon layered material with zinc and manganese fixed;

[0014] S3. Mix the nitrogen-doped carbon layered material with zinc and manganese fixed with an iron salt solution, and stir to obtain a nitrogen-doped carbon layered material with zinc, manganese, and iron fixed;

[0015] S4. Pyrolyze the nitrogen-doped carbon layered material with zinc, manganese, and iron fixed to obtain an iron cluster-modified manganese single-atom catalyst.

[0016] In the above method, further improved, the preparation conditions of the iron cluster-modified manganese single-atom catalyst include at least one of (1.1) to (1.9):

[0017] (1.1) In step S1, the zinc-manganese solution is prepared by dissolving zinc salt and manganese salt in methanol; the molar ratio of zinc salt to manganese salt is 5:2; the ratio of zinc salt to methanol is 1 mmol:25 mL; the zinc salt is zinc nitrate hexahydrate; the manganese salt is manganese chloride tetrahydrate;

[0018] (1.2) In step S1, the o-phenylenediamine solution is prepared by dissolving o-phenylenediamine in methanol; the ratio of o-phenylenediamine to methanol is 1 mmol:5 mL;

[0019] (1.3) In step S1, the stirring is carried out at a rotation speed of 600 rpm; the stirring time is 12 h;

[0020] (1.4) After step S1, the following treatment is also included: filter the precipitate after stirring, wash the solid product obtained by filtration with ethanol, the number of washing times is 3 times, dry the washed solid product under vacuum at a temperature of 60 °C, the drying time is 12 h, to obtain a zinc-manganese precursor;

[0021] (1.5) In step S2, the pyrolysis is carried out under a nitrogen atmosphere; the pyrolysis temperature is 500 °C; the pyrolysis time is 2 h;

[0022] (1.6) In step S3, the ratio of the nitrogen-doped carbon layer material fixed with zinc and manganese to the iron salt solution is 1 mg∶1 mL; the iron salt solution is prepared by dissolving an iron salt in isopropanol; the concentration of the iron salt in the iron salt solution is 0.01 mM; the iron salt is ferric nitrate nonahydrate;

[0023] (1.7) In step S3, the stirring time is 24 h;

[0024] (1.8) After the stirring in step S3, the following treatments are further included: centrifuging the stirred product, collecting the solid substance, washing the solid substance with deionized water and ethanol in sequence, the number of times of washing is 3 times, drying the washed solid substance under vacuum at a temperature of 60 °C, the drying time is 24 h, to obtain the nitrogen-doped carbon layer material fixed with zinc, manganese and iron;

[0025] (1.9) In step S4, the pyrolysis is carried out under a nitrogen atmosphere; the heating rate during the pyrolysis process is 5 °C / min; the pyrolysis temperature is 950 °C; the pyrolysis time is 3 h.

[0026] In the above method, further improved, using a manganese single-atom catalyst modified with iron clusters as a catalyst to activate persulfate for degrading organic pollutants in water, including the following steps: mixing the manganese single-atom catalyst modified with iron clusters, persulfate and the water body containing organic pollutants for a degradation reaction to complete the degradation of the organic pollutants in the water body; the initial concentration of the manganese single-atom catalyst modified with iron clusters in the degradation reaction system is ≥0.01 g / L, and the initial concentration of persulfate is ≥0.1 g / L.

[0027] In the above method, further improved, the initial concentration of the manganese single-atom catalyst modified with iron clusters in the degradation reaction system is 0.01 g / L to 0.08 g / L, and the initial concentration of persulfate is 0.1 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is ≥3.

[0028] In the above method, further improved, the initial concentration of the manganese single-atom catalyst modified with iron clusters in the degradation reaction system is 0.015 g / L to 0.06 g / L, and the initial concentration of persulfate is 0.15 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is 3 to 9.

[0029] In the above method, further improved, the initial concentration of the manganese single-atom catalyst modified with iron clusters in the degradation reaction system is 0.02 g / L to 0.055 g / L, and the initial concentration of persulfate is 0.2 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is 3.54 to 9.

[0030] In the above method, further improved, the persulfate is monopersulfate and / or dipersulfate; the monopersulfate is at least one of sodium monopersulfate and potassium monopersulfate; the dipersulfate is at least one of sodium dipersulfate and potassium dipersulfate; the initial concentration of organic pollutants in the water body containing organic pollutants ≤ 30 mg / L; the organic pollutants in the water body containing organic pollutants are antibiotics; the antibiotics are at least one of ciprofloxacin, tetracycline, sulfamethoxazole, and oxytetracycline.

[0031] In the above method, further improved, the degradation reaction is carried out under shaking conditions; the rotation speed of the shaking is 500 rpm to 520 rpm; the temperature of the degradation reaction is 25 °C to 30 °C; the time of the degradation reaction is 0.5 min to 90 min.

[0032] Compared with the prior art, the advantages of the present invention are as follows:

[0033] (1) Aiming at the deficiencies of the existing bimetallic atom nitrogen-doped carbon catalyst, such as small specific surface area, small number of active sites, poor catalytic activity, and poor structural stability, and the resulting defects such as poor activation effect on persulfate, difficulty in efficiently activating persulfate with a small amount of catalyst, poor degradation effect, and risk of secondary pollution, the present invention creatively proposes a method for activating persulfate by an iron cluster-modified manganese single-atom catalyst to remove organic pollutants in water. The iron cluster-modified manganese single-atom catalyst is used as a catalyst to activate persulfate to degrade organic pollutants in water. The iron cluster-modified manganese single-atom catalyst uses a porous nitrogen-doped carbon layered material as a carrier. Manganese single atoms are loaded between the surface and the layered structure of the porous nitrogen-doped carbon layered material, and iron clusters are modified on the manganese single atoms. The valence state of iron in the iron cluster-modified manganese single-atom catalyst is divalent, and the valence state of manganese is divalent and trivalent. Compared with the conventional bimetallic atom nitrogen-doped carbon catalyst, the iron cluster-modified manganese single-atom catalyst adopted in the present invention has the following advantages: (a) Large specific surface area. On the one hand, the specific surface area of the porous nitrogen-doped carbon layered material adopted in the present invention is as high as 1884.85 m 2 / g, and the specific surface area of the conventional nitrogen-doped carbon material is only 605.6 m 2 / g. Therefore, using the porous nitrogen-doped carbon layered material as a carrier is beneficial to increasing the loading amount of metal atoms, and thus beneficial to increasing the number of active sites on the catalyst surface. On the other hand, after fixing the manganese single atoms and iron clusters, the specific surface area of the catalyst is still as high as 1384.85 m 2 / g, which is beneficial to the exposure of more metal atoms on the surface of the catalyst, thereby facilitating the improvement of the catalytic activity and catalytic rate of the catalyst, making the catalyst exhibit very excellent catalytic performance; (b) It has a porous layered structure with a rough surface and rich pore structure. On the one hand, the catalyst exhibits very excellent adsorption capacity, capable of adsorbing a large amount of organic pollutants onto the catalyst surface, which is conducive to shortening the contact distance between the organic pollutants and the active substances, and thus conducive to the efficient degradation of organic pollutants by the active substances. On the other hand, the catalyst exhibits very excellent activation ability, capable of efficiently activating persulfate, which is beneficial to reducing the dosage of the catalyst and can effectively activate persulfate on the premise of using less catalyst; (c) It has good structural stability. The iron clusters and manganese single atoms are sandwiched between the layered structures of the carrier material. On the one hand, since the carrier material is a porous layered structure, these iron clusters and manganese single atoms sandwiched in the carrier can also provide a large number of active sites for activating persulfate. On the other hand, by wrapping the iron clusters and manganese single atoms inside the carrier material, it can also provide effective protection for them, thereby preventing damage during use and effectively preventing metal leaching; (d) It can rapidly form more singlet oxygen ( 1O2) and high-valent metals (FeMn=O). In the iron cluster-modified manganese single-atom catalyst used in the present invention, the valence state of iron is divalent and the valence state of manganese is divalent and trivalent. When they are used as single-atom active sites to activate persulfate, on the one hand, under the combined action of divalent iron, divalent manganese, and trivalent manganese, it can promote the rapid formation of more singlet oxygen and high-valent metals (such as trivalent iron, trivalent manganese, tetravalent manganese) from persulfate. Thus, an active species degradation system mainly composed of singlet oxygen and supplemented by high-valent metals can be constructed. Therefore, under the combined action of singlet oxygen and high-valent metals, organic pollutants in water can be efficiently degraded. On the other hand, under the combined action of trivalent iron, trivalent manganese, tetravalent manganese, and persulfate, it can also promote the formation of divalent iron, divalent manganese, and trivalent manganese. At the same time, under the combined action of divalent iron and trivalent manganese, it can also promote the formation of trivalent iron and divalent manganese. It can be seen that under their combined action, the metal active sites can be quickly restored and the catalytic reaction can be accelerated. Therefore, the catalyst of the present invention can degrade organic pollutants in water more quickly. Taking ciprofloxacin as an example, in the present invention, when the iron cluster-modified manganese single-atom catalyst is used as a catalyst to activate persulfate (peroxymonosulfate) and degrade organic pollutants (ciprofloxacin) in water, the degradation principle is shown in formulas (1)-(11). Specifically: divalent iron ions, divalent manganese ions, and trivalent manganese ions react with peroxymonosulfate to form trivalent iron ions, trivalent manganese ions, tetravalent manganese ions, sulfate ions, and hydroxyl radicals, and at the same time generate sulfate radicals and hydrogen ions. Then, the superoxide radicals generated react with hydroxyl radicals to form singlet oxygen. At the same time, trivalent iron ions, trivalent manganese ions, and tetravalent manganese ions continue to react with peroxymonosulfate to form divalent iron ions, divalent manganese ions, and trivalent manganese ions, and form a cycle of divalent iron ions and trivalent iron ions, divalent manganese ions, trivalent manganese ions and trivalent manganese ions, and tetravalent manganese ions. The generated high-valent metals, furthermore, using the high-valent metals as oxygen species, continue to react with the products of the reaction with peroxymonosulfate to generate a large amount of singlet oxygen to efficiently degrade organic pollutants in water. In particular, when the dosage of the catalyst is 0.05 g / L, the method of the present invention can remove more than 90% of ciprofloxacin within 5 min, and can basically remove ciprofloxacin within 90 min. The degradation effect is very remarkable, and at the same time, ciprofloxacin can be degraded into non-toxic or low-toxic small-molecule substances, realizing the harmless treatment of ciprofloxacin. In addition, compared with liquid H2O2, the persulfate used in the present invention has great advantages in storage and transportation, is more convenient and safer to use, and its reaction products such as CO2 and H2O usually also exist in the natural environment, which is more green and environmentally friendly.The method of the present invention uses an iron-cluster-modified manganese single-atom catalyst to activate persulfate to remove organic pollutants in water, which has the advantages of simple process, convenient operation, low cost, strong practicability, wide adaptability, small catalyst dosage, high treatment efficiency, good degradation effect, green environmental protection, etc. It can effectively degrade high-concentration organic pollutants in water, especially for organic pollutants with a concentration ≤ 30 mg / L, having a better removal effect, high use value, and good application prospects.

[0034] Fe 2+ / Mn 2+ / Mn 3+ + HSO5 - →Fe 3+ / Mn 3+ / Mn 4+ + SO4 2- +·OH (1)

[0035] HSO5 - + H2O→HO2 - + SO4 ·- + H + (2)

[0036] HO2 - + HSO5 - →SO4 ·- + SO4 2- + H + + O2 ·- (3)

[0037] O2 ·- +·OH → 1 O2+ OH - (4)

[0038] Fe 3+ / Mn 3+ / Mn 4+ + HSO5 - →Fe 2+ / Mn 2+ / Mn 3+ +SO5 ·- +H + (5)

[0039] SO5 ·- +H2O →HSO4 - + 1 O2 (6)

[0040] Fe 2+ + Mn 3+ →Mn 2+ + Fe3+ (7)

[0041] Fe 3+ + Mn 3+ →Mn 4+ + Fe 2+ (8)

[0042] FeMn=O (high-valent metal oxygen species) + HSO5 - →FeMn=O (low-valent metal oxygen species) + SO5 ·- + H + (9)

[0043] SO5 ·- + SO5 ·- →2 SO4 2- + 1 O2 (10)

[0044] 1 O2 / FeMn=O (high-valent metal oxygen species) + CIP → intermediate product → CO2 + H2O (11).

[0045] (2) In the present invention, the initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is further optimized to be ≥ 0.01 g / L, and the initial concentration of persulfate is ≥ 0.1 g / L. In particular, when the initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is 0.02 g / L - 0.055 g / L and the initial concentration of persulfate is 0.2 g / L - 0.5 g / L, it makes the degradation system contain a sufficient amount of catalyst and oxidant. Under this condition, activating persulfate with the iron cluster-modified manganese single-atom catalyst can ensure the rapid formation of a large amount of singlet oxygen in the system and promote the redox cycle of each metal active site. Thus, organic pollutants in water can be degraded quickly and thoroughly.

[0046] (3) In the present invention, the initial pH value in the degradation reaction system is further optimized to be ≥ 3. In particular, when the initial pH value is 3 - 9, the removal rate of organic pollutants does not show an obvious decrease, and the removal rate is above 90%. This shows that whether in acidic, neutral or alkaline solutions, the FeMnac-NC / PMS system constructed in the present invention can effectively remove organic pollutants, with better adaptability. Further, it also indicates that the working pH value range of the constructed FeMnac-NC / PMS system is relatively wide and has strong resistance to pH value during the degradation process. Therefore, during the actual treatment process, there is no need to adjust the pH value, which is also beneficial to reducing the treatment cost.

[0047] (4) In the present invention, the iron cluster-modified manganese single-atom catalyst is prepared by using manganese salt, iron salt, and zinc salt as raw materials and o-phenylenediamine as a templating agent through impregnation and pyrolysis. Specifically, first, the zinc salt and manganese salt are made into a solution and mixed with o-phenylenediamine, so that zinc ions and manganese ions are uniformly adsorbed on the surface of o-phenylenediamine, which is not only beneficial to the formation of a layered structure but also beneficial to the dispersion of active sites on the surface of the layered structure. Then, through pyrolysis, o-phenylenediamine is carbonized into a nitrogen-doped carbon layered material with rich defects. At the same time, during the pyrolysis process, manganese atoms and zinc atoms are also firmly fixed in the nitrogen-doped carbon layered material with rich defects to form a nitrogen-doped carbon layered material with zinc and manganese fixed therein. On this basis, the nitrogen-doped carbon layered material with zinc and manganese fixed therein is mixed with an iron salt solution, and through stirring, iron ions are adsorbed between the surface and the layered structure of the carbon material to form a nitrogen-doped carbon layered material with zinc, manganese, and iron fixed therein. Furthermore, the nitrogen-doped carbon layered material with zinc, manganese, and iron fixed therein is pyrolyzed. During the pyrolysis process, iron atom clusters are formed and wrap manganese atoms, making their contact closer. At the same time, by using the reduction effect of the zinc salt, divalent iron ions, divalent manganese ions, and trivalent manganese ions are preserved in a low-valent state, so that higher-valent oxygen species can be better formed during the reaction process. And as the pyrolysis continues, the zinc salt vaporizes and escapes from the interior of the material, which can promote the formation of more porous structures, is beneficial to enriching the pore structure of the material, and finally forms an iron cluster-modified manganese single-atom catalyst with a large surface area, a large number of active sites, high catalytic activity, and stable structure. Description of the Drawings

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.

[0049] Figure 1 It is a comparison chart of the removal effects of ciprofloxacin at different concentrations of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) in Example 1 of the present invention.

[0050] Figure 2 It is a comparison chart of the removal effects of ciprofloxacin at different concentrations of potassium monopersulfate in Example 2 of the present invention.

[0051] Figure 3 It is a comparison chart of the removal effects of ciprofloxacin at different concentrations by the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) activating potassium monopersulfate in Example 4 of the present invention.

[0052] Figure 4 It is a comparison chart of the removal effects of ciprofloxacin under different reaction systems in Example 5 of the present invention.

[0053] Figure 5This is a comparison chart of the removal effects of ciprofloxacin under different radical scavengers in Example 6 of the present invention.

[0054] Figure 6 This is a comparison chart of the removal effects of ciprofloxacin under different catalysts in Example 7 of the present invention.

[0055] Figure 7 This is a comparison chart of the removal effects of different pollutants by the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) activating peroxymonosulfate in Example 8 of the present invention.

[0056] Figure 8 This is the XRD pattern of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) prepared in Example 9 of the present invention.

[0057] Figure 9 This is the SEM image of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), zinc-manganese precursor (ZnMn-PPD), and nitrogen-doped carbon layered material with fixed zinc and manganese (Mn-DNC) prepared in Example 9 of the present invention.

[0058] Figure 10 This is the nitrogen adsorption curve of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) prepared in Example 9 of the present invention.

[0059] Figure 11 This is the pore size distribution diagram of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) prepared in Example 9 of the present invention.

[0060] Figure 12 This is the cyclic degradation effect diagram of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) on ciprofloxacin in water in Example 10 of the present invention. Detailed implementation mode

[0061] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0062] In the following embodiments of the present invention, unless otherwise specified, the materials and instruments used are commercially available, the equipment used is conventional equipment, and the data obtained are the averages of more than three repeated experiments.

[0063] Example 1:

[0064] A method for activating persulfate by a manganese single-atom catalyst modified with iron clusters in the present invention to remove organic pollutants in water, specifically, activating peroxymonosulfate (PMS) by a manganese single-atom catalyst modified with iron clusters (FeMnac-NC) and degrading ciprofloxacin (CIP) in water, comprising the following steps:

[0065] (1) Prepare 3 groups of 100 mL of ciprofloxacin aqueous solution with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0066] (2) Add different amounts of the manganese single-atom catalyst modified with iron clusters (FeMnac-NC) to each group of solutions so that the concentration of FeMnac-NC in the solution is 0.01 g / L, 0.02 g / L, 0.05 g / L, and then add potassium peroxymonosulfate so that the concentration of potassium peroxymonosulfate in the solution is 0.2 g / L. Carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in water.

[0067] Control group: Do not add FeMnac-NC, and other conditions are the same.

[0068] In this example, 1 mL of sample solution is taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution is added to a liquid-phase injection bottle containing 20 μL of sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of ciprofloxacin after the reaction is measured using a high-performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and a change curve of the ciprofloxacin concentration under different FeMnac-NC concentrations is plotted. The results are as Figure 1 shown.

[0069] Figure 1 It is a comparison chart of the removal effects of ciprofloxacin under different concentrations of the manganese single-atom catalyst modified with iron clusters (FeMnac-NC) in Example 1 of the present invention. From Figure 1It can be seen that as the concentration of FeMnac-NC increases from 0.01 g / L to 0.05 g / L, the removal rate of CIP increases from 79% to 98.5%. The reason for the accelerated reaction rate may be that 0.05 g / L of FeMnac-NC provides more active sites, which can more effectively activate PMS, thereby accelerating the CIP degradation process. This result indicates that increasing the dosage of the catalyst is an effective strategy to improve the catalytic activity of the FeMnac-NC / PMS system and can significantly enhance the degradation efficiency of CIP. Therefore, when the initial concentration of FeMnac-NC in the degradation reaction system of the present invention is 0.01 g / L to 0.05 g / L, it is beneficial to efficiently and thoroughly remove ciprofloxacin in water. In particular, when the concentration of FeMnac-NC in the degradation reaction system is 0.02 g / L to 0.05 g / L, the best removal effect can be obtained.

[0070] Example 2:

[0071] A method for activating persulfate by an iron cluster-modified manganese single-atom catalyst of the present invention to remove organic pollutants in water, specifically using an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to activate peroxymonosulfate (PMS) and degrade ciprofloxacin (CIP) in water, including the following steps:

[0072] (1) Prepare 3 groups of 100 mL ciprofloxacin aqueous solutions with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0073] (2) Add an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to each group of solutions so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add different amounts of potassium peroxymonosulfate so that the concentration of potassium peroxymonosulfate in the solution is 0.1 g / L, 0.2 g / L, 0.5 g / L; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in water.

[0074] Control group: Do not add potassium peroxymonosulfate, and other conditions are the same.

[0075] In this example, 1 mL of sample solution was taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution was added to a liquid phase injection bottle containing 20 μL of a sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of ciprofloxacin after the reaction was measured using a high performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and a change curve of the ciprofloxacin concentration under different potassium peroxymonosulfate concentrations was plotted. The results are as Figure 2As shown

[0076] Figure 2 This is a comparison chart of the removal effect of ciprofloxacin at different potassium monopersulfate concentrations in Example 2 of the present invention. It can be seen Figure 2 that when the PMS concentrations are set to 0.1 g / L, 0.2 g / L, and 0.5 g / L respectively, the removal rates of CIP reach 95.9%, 98.5%, and 99.3% respectively. When the concentration of PMS increases to 0.5 g / L, the removal rate of CIP reaches 92.3% within 20 min, which is much higher than other concentrations. At the same time, kobs increases from 0.0429 min of 0.1 g / L PMS -1 to 0.0543 min of 0.2 g / L -1 , and when the concentration of PMS increases to 0.5 g / L, the corresponding kobs is 0.1038 min -1 , almost twice that of 0.2 g / L PMS. The reason for the accelerated reaction rate may be that the probability of reaction between a large number of PMS molecules and catalytic active sites increases, thereby increasing the removal rate of CIP. Therefore, when the initial concentration of potassium monopersulfate in the degradation reaction system of the present invention is 0.1 g / L to 0.5 g / L, it is beneficial to efficiently and thoroughly remove ciprofloxacin in water, and the economic benefit is high. In particular, when the concentration of potassium monopersulfate in the degradation reaction system is 0.2 g / L, the best removal effect and economic benefit can be obtained.

[0077] Example 3:

[0078] A method for removing organic pollutants in water by activating persulfate using an iron cluster-modified manganese single-atom catalyst of the present invention, specifically, using an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to activate potassium monopersulfate (PMS) and degrade ciprofloxacin (CIP) in water with different pH values, including the following steps:

[0079] (1) Prepare 5 groups of 100 mL ciprofloxacin aqueous solutions with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0080] (2) Add an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to each group of solutions so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add potassium monopersulfate so that the concentration of potassium monopersulfate in the solution is 0.2 g / L; use 0.1 mol / L HCl or 0.1 mol / L NaOH to adjust the pH values of 4 groups of solutions to 3, 5, 7, and 9, and carry out a degradation reaction for 90 min at 25 °C and 500 rpm to complete the removal of ciprofloxacin in water.

[0081] In this example, at 90 min of the degradation reaction, 1 mL of the sample solution was taken and filtered through a 0.22-μm filter head. The filtered solution was added to a liquid-phase injection vial containing 20 μL of a sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of ciprofloxacin after the reaction was measured using a high-performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin. The change curve of the ciprofloxacin concentration under different pH values was plotted, and the results are shown in Table 1.

[0082] Table 1 Removal effect of FeMnac-NC on ciprofloxacin under different pH conditions

[0083] Removal rate of reaction (90 min) Initial pH = 3.00 90.00％ Initial pH = 3.54 98.5％ Initial pH = 5.00 91.59％ Initial pH = 7.00 90.34％ Initial pH = 9.00 90.25％

[0084] As can be seen from Table 1, the CIP removal rate did not show an obvious decrease under the condition that the initial pH value was 3 - 9, and the removal rate was above 90%. This indicates that whether in acidic, neutral, or alkaline solutions, the FeMnac-NC / PMS system is not affected by it, further showing that the working pH value range of the system is relatively wide and it has strong resistance to pH value during the degradation process. Therefore, during the actual treatment process, it is not necessary to adjust the pH value, which is conducive to reducing the treatment cost.

[0085] Example 4:

[0086] A method for removing organic pollutants in water by activating persulfate using a manganese single-atom catalyst modified with iron clusters according to the present invention, specifically, activating peroxymonosulfate (PMS) using a manganese single-atom catalyst modified with iron clusters (FeMnac-NC) and degrading different concentrations of ciprofloxacin (CIP) in water, including the following steps:

[0087] (1) Prepare 3 groups of 100-mL ciprofloxacin aqueous solutions (the original pH value of this aqueous solution is 3.54), and the concentrations of the ciprofloxacin aqueous solutions are 15 mg / L, 20 mg / L, and 30 mg / L respectively. Two parallel samples are set for each group.

[0088] (2) Add a manganese single-atom catalyst modified with iron clusters (FeMnac-NC) to each group of solutions so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add potassium peroxymonosulfate so that the concentration of potassium peroxymonosulfate in the solution is 0.2 g / L; carry out the degradation reaction for 90 min at 25 °C and 500 rpm to complete the removal of ciprofloxacin in water.

[0089] In this example, 1 mL of sample solution was taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution was added to a liquid phase injection bottle containing 20 μL of sodium thiosulfate quenching agent solution (1 mol / L). Then, the concentration of ciprofloxacin after the reaction was measured using a high-performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and the change curve of the removal rate of ciprofloxacin with different concentrations by the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) was plotted. The results are as follows Figure 3 shown.

[0090] Figure 3 This is a comparative diagram of the removal effect of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) on ciprofloxacin with different concentrations by activating peroxymonosulfate in Example 4 of the present invention. As Figure 3 can be seen, with the increase of the initial concentration of CIP, the degradation effect of the FeMnac-NC / PMS system on CIP decreases significantly. This is because: at a fixed dose of potassium peroxymonosulfate, the amount of reactive species generated is certain. When the initial concentration of CIP increases, it is difficult to generate more reactive species in the system, so only part of CIP can be degraded, resulting in a significant decrease in the removal rate. Therefore, when treating high-concentration organic pollutant wastewater, the dosage of peroxymonosulfate and FeMnac-NC can be increased to achieve efficient removal of organic pollutants in high-concentration wastewater.

[0091] Example 5:

[0092] A method for removing organic pollutants in water by activating persulfate using an iron cluster-modified manganese single-atom catalyst of the present invention, specifically, activating peroxymonosulfate (PMS) using an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) and degrading ciprofloxacin (CIP) in water, including the following steps:

[0093] (1) Prepare 1 group of 100 mL of ciprofloxacin aqueous solution with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0094] (2) Add the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to each group of solutions so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add potassium peroxymonosulfate so that the concentration of potassium peroxymonosulfate in the solution is 0.2 g / L; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in water.

[0095] Control group 1: Do not add FeMnac-NC, and keep other conditions the same.

[0096] Control group 2: No potassium permonosulfate was added, and other conditions were the same.

[0097] In this embodiment, 1 mL of sample solution was taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min of the degradation reaction, respectively, and filtered with a 0.22 μm filter head. The filtered solution was added to a liquid injection bottle containing 20 μL of sodium thiosulfate quencher solution (1 mol / L), and the concentration of ciprofloxacin after the reaction was measured using a high performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin. The change curve of the removal rate of ciprofloxacin under different reaction systems was plotted. The results are as follows: Figure 4 shown.

[0098] Figure 4 The figure is a comparison chart of the removal effect of ciprofloxacin under different reaction systems in Example 5 of the present invention. Figure 4 It can be seen that the addition of potassium persulfate and FeMnac-NC alone can hardly degrade CIP, which indicates that potassium persulfate and FeMnac-NC have a weak ability to decompose CIP. The reason is that the addition of potassium persulfate and FeMnac-NC alone produces fewer active species and has no obvious degradation effect on CIP. When potassium persulfate and FeMnac-NC exist in the reaction system at the same time, CIP will be rapidly degraded, that is, about 80% of CIP is removed within the first 20 minutes, and the removal rate of CIP within 90 minutes is 98.5%, which indicates that FeMnac-NC can effectively activate PMS to produce active species that degrade CIP. This further illustrates the excellent catalytic performance of the system, and also shows that a trace amount of FeMnac-NC has good adsorption capacity and PMS activation ability at the same time. Under the synergistic effect of adsorption and oxidation, it is more conducive to the rapid purification of CIP in wastewater.

[0099] Embodiment 6:

[0100] A method for removing organic pollutants in water by activating persulfate using a manganese single atom catalyst modified with an iron cluster of the present invention, specifically using a manganese single atom catalyst modified with an iron cluster (FeMnac-NC) to activate persulfate (PMS) and degrade ciprofloxacin (CIP) in the water, comprising the following steps:

[0101] (1) Prepare 5 groups of 100 mL of 20 mg / L ciprofloxacin aqueous solution (the original pH value of the aqueous solution is 3.54), with two parallel samples in each group.

[0102] (2) Add the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to each group of solutions respectively, so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add potassium monopersulfate so that the concentration of potassium monopersulfate in the solution is 0.2 g / L; among the 4 groups of solutions, tert-butanol (TBA), methanol (MeOH), furfuryl alcohol (FFA), and p-benzoquinone (p-BQ) are added as radical scavengers, so that the concentration of tert-butanol in the solution is 0.5 M, the concentration of methanol is 0.5 M, the concentration of furfuryl alcohol is 5 mM, and the concentration of p-benzoquinone is 5 mM; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in the water body.

[0103] In this example, 1 mL of sample solution was taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution was added to a liquid-phase injection bottle containing 20 μL of sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of ciprofloxacin after the reaction was measured using a high-performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and a change curve of the removal rate of ciprofloxacin under different radical scavengers was plotted. The results are as Figure 5 shown.

[0104] Figure 5 It is a comparison chart of the removal effects of ciprofloxacin under different radical scavengers in Example 6 of the present invention. From Figure 5 it can be seen that tert-butanol (TBA) is a typical hydroxyl radical scavenger. After adding tert-butanol, the oxidation activity in the FeMnac-NC / PMS system hardly decreases, indicating that there is no hydroxyl radical in the degradation system. Methanol (MeOH) is usually used as a scavenger for hydroxyl radicals and sulfate radicals. When methanol is added, it can be observed that the degradation rate of ciprofloxacin is only slightly inhibited, but the final removal rate is basically the same, confirming that a small amount of sulfate radicals are generated during the degradation reaction. Furfuryl alcohol (FFA) is a selective 1 O2 scavenger. When 5 mM of furfuryl alcohol is added, the removal rate of CIP drops from 98.5% to 52.0%, indicating that singlet oxygen plays a dominant role in the degradation of CIP. p-Benzoquinone (p-BQ), used as a scavenger for O2· – , after adding p-benzoquinone, the removal rate of CIP drops from 98.5% to 86.5%, indicating that the FeMnac-NC / PMS system mainly generates active species mainly 1 O2, as well as a small amount of O2 ·- radicals to oxidatively degrade CIP, and hydroxyl radicals and sulfate radicals may be generated as intermediates in the reaction system to form singlet oxygen.

[0105] Example 7:

[0106] A method for activating persulfate by an iron cluster-modified manganese single-atom catalyst of the present invention to remove organic pollutants in water, specifically, using an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to activate peroxymonosulfate (PMS) and degrade ciprofloxacin (CIP) in water, including the following steps:

[0107] (1) Prepare 4 groups of 100 mL ciprofloxacin aqueous solutions with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0108] (2) Add potassium peroxymonosulfate to each group of solutions so that the concentration of potassium peroxymonosulfate in the solution is 0.2 g / L; then add an iron cluster-modified manganese single-atom catalyst (FeMnac-NC), an iron single-atom catalyst (Fe-NC), a manganese single-atom catalyst (Mn-NC), and a nitrogen-doped carbon catalyst (NC) as catalysts to each group respectively, so that their concentrations in the solution are all 0.02 g / L; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in water.

[0109] In this example, 1 mL of sample solution was taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution was added to a liquid phase injection bottle containing 20 μL of a sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of ciprofloxacin after the reaction was measured using a high-performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and a change curve of the ciprofloxacin concentration under different catalyst conditions was plotted. The results are as Figure 6 shown.

[0110] Figure 6 is a comparison chart of the removal effects of ciprofloxacin under different catalyst conditions in Example 7 of the present invention. As can be Figure 6 seen, in the reaction systems with Fe-NC, Mn-NC, and NC as catalysts, no obvious degradation of CIP was observed, indicating that Fe-NC, Mn-NC, and NC may not be able to effectively activate potassium peroxymonosulfate to generate effective reactive species to remove CIP under the current conditions. However, the FeMnac-NC / PMS system showed very prominent performance in the degradation of CIP. The reason for the increase in the removal rate may be that the redox cycle between transition metals in the bimetal-loaded catalyst can quickly restore the metal active sites and accelerate the catalytic reaction. Therefore, the bimetal-loaded (Fe, Mn) FeMnac-NC / PMS is superior to the catalysts synthesized by single-metal loading Fe / Mn and the metal-free loading catalyst.

[0111] Example 8:

[0112] A method for activating persulfate by an iron cluster-modified manganese single-atom catalyst of the present invention to remove organic pollutants in water, specifically, an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) is used to activate peroxymonosulfate (PMS), and ciprofloxacin (CIP), tetracycline (TC), sulfamethoxazole (SMX), and oxytetracycline (OTC) in water are degraded respectively, including the following steps:

[0113] (1) Prepare 1 group of 100 mL of ciprofloxacin aqueous solution with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0114] (2) Add the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) to each group of solutions respectively, so that the concentration of FeMnac-NC in the solution is 0.02 g / L; then add potassium peroxymonosulfate, so that the concentration of potassium peroxymonosulfate in the solution is 0.2 g / L; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in water.

[0115] Control group 1: 1 group of 100 mL of tetracycline (TC) aqueous solution with a concentration of 20 mg / L, and other conditions are the same.

[0116] Control group 2: 1 group of 100 mL of sulfamethoxazole (SMX) aqueous solution with a concentration of 20 mg / L, and other conditions are the same.

[0117] Control group 2: 1 group of 100 mL of oxytetracycline (OTC) aqueous solution with a concentration of 20 mg / L, and other conditions are the same.

[0118] In this example, 1 mL of sample solution is taken at 0 min, 2 min, 5 min, 10 min, 20 min, 40 min, 60 min, and 90 min during the degradation reaction, filtered with a 0.22 μm filter head, and the filtered solution is added to a liquid phase injection bottle containing 20 μL of sodium thiosulfate quenching agent solution (1 mol / L), and then the concentration of the pollutant after the reaction is measured using a high performance liquid chromatograph to obtain the corresponding concentration of ciprofloxacin, and a change curve of adding different pollutant concentrations is plotted. The results are as Figure 7 shown.

[0119] Figure 7 is a comparison chart of the removal effects of different pollutants by the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) activating peroxymonosulfate in Example 8 of the present invention. As can be Figure 7 seen, the removal rates of CIP, TC, SMX, and OTC are 98.5% (k obs= 0.0543 min -1 ), 100% (k obs = 0.1629 min -1 ), 54.2% (k obs = 0.0081 min - 1) and 99.2% (k obs = 0.0752 min -1 ), where the removal rates of different organic pollutants are different. The reason may be that TC and OTC contain amide groups and electron-withdrawing groups, which can reduce the ionization potential of organic matter. There are functional groups in the SMX molecule, such as sulfonamide, triazole ring and methyl functional groups, resulting in a relatively high ionization potential of SMX. This indicates that SMX has a relatively strong ionization effect, which may be the reason for the low removal rate compared with TC and OTC. In contrast, CIP containing carboxyl groups produces the opposite effect to the amide group, thereby increasing the ionization potential of CIP. Therefore, the removal rate of CIP by FeMnac-NC / PMS decreases slightly. Therefore, the reaction system has a preferential selectivity for organic pollutants with low ionization potential.

[0120] Example 9:

[0121] A preparation method of an iron cluster-modified manganese single-atom catalyst (FeMnac-NC) used in Examples 1-8, specifically using manganese salt, iron salt, and zinc salt as raw materials, o-phenylenediamine as a template agent, and preparing it by impregnation and pyrolysis, including the following steps:

[0122] (1) Synthesis of the precursor ZnMn-PPD: Dissolve zinc nitrate hexahydrate (20 mmol) and manganese chloride tetrahydrate (8 mmol) in 500 mL of methanol to obtain a zinc-manganese solution, named solution A. Then dissolve o-phenylenediamine (100 mmol) in 500 mL of methanol to obtain an o-phenylenediamine solution, named solution B. Add solution A to solution B and continue to stir at 600 rpm at room temperature for 12 hours. Collect the obtained precipitate by suction filtration, wash it 3 times with ethanol, and dry it in a vacuum oven at 60 °C for 12 h to obtain a zinc-manganese precursor, named ZnMn-PPD.

[0123] (2) Synthesis of FeMnac-NC: Under N2 atmosphere, the obtained ZnMn-PPD precursor was heated to 500 °C and pyrolyzed for 2 h to fix Mn atoms on nitrogen-doped carbon with rich defects, obtaining a nitrogen-doped carbon layered material with zinc and manganese fixed, named Mn-DNC. The obtained Mn-DNC (500 mg) was dispersed into a ferric nitrate solution prepared by dissolving ferric nitrate nonahydrate in 500 mL of isopropanol, and the concentration of ferric nitrate in this ferric nitrate solution was 0.01 mM. After magnetic stirring for 24 h and centrifugation, the centrifuged collected material was washed 3 times with deionized water and ethanol, and dried in a vacuum oven at 60 °C for 24 h to obtain a nitrogen-doped carbon layered material with zinc, manganese and iron fixed. The nitrogen-doped carbon layered material with zinc, manganese and iron fixed was placed in a tube furnace filled with N2. Under N2 atmosphere, it was heated from room temperature to 950 °C at a rate of 5 °C / min and pyrolyzed for 3 h to obtain an iron cluster-modified manganese single-atom catalyst, denoted as FeMnac-NC.

[0124] In this example, the prepared iron cluster-modified manganese single-atom catalyst uses a porous nitrogen-doped carbon layered material as a carrier. Manganese single atoms are loaded between the surface and the layered structure of the porous nitrogen-doped carbon layered material, and iron clusters are modified on the manganese single atoms; in this example, the valence state of iron in the iron cluster-modified manganese single-atom catalyst is divalent, and the valence states of manganese are divalent and trivalent.

[0125] Tested by inductively coupled plasma mass spectrometry (ICP), the atomic percentage content of iron in the iron cluster-modified manganese single-atom catalyst prepared in this example is 0.834%, and the atomic percentage content of manganese is 0.016%. The atomic percentage content of iron in the iron cluster-modified manganese single-atom catalyst prepared by the present invention is all less than 1%, which is beneficial to the formation of a single-atom catalyst.

[0126] The preparation method of the iron single-atom catalyst (Fe-NC) used in Example 7 includes the following steps:

[0127] (1) Synthesis of the precursor ZnFe-PPD: Zinc nitrate hexahydrate (20 mmol) and ferric nitrate nonahydrate (8 mmol) were dissolved in 500 mL of methanol to obtain a zinc-iron solution, named solution A. Then o-phenylenediamine (100 mmol) was dissolved in 500 mL of methanol to obtain an o-phenylenediamine solution, named solution B. Solution A was added to solution B, and stirring was continued at 600 rpm at room temperature for 12 hours. The obtained precipitate was collected by suction filtration, washed 3 times with ethanol, and dried in a vacuum oven at 60 °C for 12 h to obtain a zinc-iron precursor, named ZnFe-PPD.

[0128] (2) Synthesis of Fe-NC: The obtained ZnFe-PPD precursor was placed in a tubular furnace filled with N2. Under N2 atmosphere, it was heated from room temperature to 950 °C at a rate of 5 °C / min and pyrolyzed for 3 h to obtain an iron single-atom catalyst (Fe-NC), denoted as Fe-NC.

[0129] The preparation method of the manganese single-atom catalyst (Mn-NC) used in Example 7 includes the following steps:

[0130] (1) Synthesis of the precursor ZnMn-PPD: Zinc nitrate hexahydrate (20 mmol) and manganese chloride tetrahydrate (8 mmol) were dissolved in 500 mL of methanol to obtain a zinc-manganese solution, named solution A. Then, o-phenylenediamine (100 mmol) was dissolved in 500 mL of methanol to obtain an o-phenylenediamine solution, named solution B. Solution A was added to solution B, and the mixture was continuously stirred at 600 rpm at room temperature for 12 hours. The obtained precipitate was collected by suction filtration, washed 3 times with ethanol, and dried in a vacuum oven at 60 °C for 12 h to obtain a zinc-manganese precursor, named ZnMn-PPD.

[0131] (2) Synthesis of Mn-NC: The obtained ZnMn-PPD precursor was placed in a tubular furnace filled with N2. Under N2 atmosphere, it was heated from room temperature to 950 °C at a rate of 5 °C / min and pyrolyzed for 3 h to obtain a manganese single-atom catalyst, denoted as Mn-NC.

[0132] The preparation method of the nitrogen-doped carbon catalyst (NC) used in Example 7 includes the following steps:

[0133] (1) Synthesis of the precursor Zn-PPD: Zinc nitrate hexahydrate (20 mmol) was dissolved in 500 mL of methanol and poured into 500 mL of methanol containing 100 mmol of o-phenylenediamine. The mixture was continuously stirred at 600 rpm at room temperature for 12 hours. The obtained precipitate was collected by suction filtration and washed 3 times with ethanol. It was dried in a vacuum oven at 60 °C for 12 h to obtain a zinc precursor, named Zn-PPD.

[0134] (2) Synthesis of NC: The zinc precursor (Zn-PPD) was placed in a tubular furnace filled with N2. Under N2 atmosphere, it was heated from room temperature to 950 °C at a rate of 5 °C / min and pyrolyzed for 3 h to obtain a nitrogen-doped carbon catalyst, denoted as NC.

[0135] Figure 8 XRD patterns of the iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) modified by iron clusters (FeMnac-NC) prepared in Example 9 of the present invention. From Figure 8It can be seen that the crystal structures of FeMnac-NC, Fe-NC, Mn-NC, and NC were studied using an X-ray diffractometer (XRD). The results showed that the XRD patterns of the four materials were almost identical, indicating that FeMnac-NC, Fe-NC, Mn-NC, and NC do not contain any other impurities, and the loading of Fe or Mn metals did not change the crystal structure of the materials, indicating that the metals were mainly deposited on the surface of NC, which shows that the materials were successfully prepared.

[0136] In addition, the surface morphologies of FeMnac-NC, ZnMn-PPD, and Mn-DNC were observed using a scanning electron microscope (SEM), and the internal structural morphology of the FeMnac-NC material was observed using a transmission electron microscope (TEM) and an energy-dispersive spectrometer (EDS). The specific results are as follows:

[0137] Figure 9 SEM images of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), zinc manganese precursor (ZnMn-PPD), and nitrogen-doped carbon layer material with fixed zinc manganese (Mn-DNC) prepared in Example 9 of the present invention. Figure 9 In, a and b are FeMnac-NC; c and d are Mn-DNC; e and f are ZnMn-PPD. From Figure 9 (e) and (f) in, it can be seen that the SEM image of ZnMn-PPD shows that the material has a randomly oriented flaky morphology with a size range between 5 and 100 nm and exhibits a large number of surface cracks. From Figure 9 (c) and (d) in, it can be seen that under the low-temperature carbonization condition of 500 °C, the original morphology of ZnMn-PPD was severely damaged and transformed into a porous structure. The obtained Mn-DNC is an amorphous carbon with a thinner layered structure and rich defects, which can provide more potential anchoring points for subsequent adsorption of Fe 3+ ions and attach metal particles to the surface of the material. From Figure 9 (a) and (b) in, it can be seen that FeMnac-NC was obtained by secondary pyrolytic carbonization of Mn-DNC at 950 °C. Since Zn is easily evaporated above 900 °C, after high-temperature pyrolysis at 950 °C for 3 h, Zn evaporated and separated from the catalyst with N2. At 950 °C, o-phenylenediamine was pyrolyzed thoroughly to form a porous layered structure with a rough surface and rich pore structure.

[0138] The iron cluster-modified manganese single-atom catalyst (FeMnac-NC) prepared in Example 9 of the present invention was tested by TEM and EDS. The results showed that FeMn ac-NC catalyst material has a flaky structure, a rough surface, a rich porous structure, and a metal wrapped by nano-graphite structural layers. In the whole FeMn-NC catalyst, N and Mn are uniformly distributed on carbon, and most of Fe is wrapped and aggregated on carbon. The superimposed graph shows that the nitrogen-doped graphene can well wrap FeMn after annealing, which not only provides a large number of active sites for PMS activation but also prevents metal leaching.

[0139] Figure 10 This is the nitrogen adsorption curve graph of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) prepared in Example 9 of the present invention.

[0140] Figure 11 This is the pore size distribution graph of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), iron single-atom catalyst (Fe-NC), manganese single-atom catalyst (Mn-NC), and nitrogen-doped carbon catalyst (NC) prepared in Example 9 of the present invention.

[0141] From Figure 10 and 11 it can be seen that the specific surface area of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) prepared in this example is 1384.85 m 2 / g. The specific surface area of the nitrogen-doped carbon catalyst (NC) is 1884.85 m 2 / g, the specific surface area of the manganese single-atom catalyst (Mn-NC) is 1029.6062 m 2 / g, and the specific surface area of the iron single-atom catalyst (Fe-NC) is 1089.17 m 2 / g. By comparison, it can be seen that in the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) prepared by the present invention, it still has a very high specific surface area after loading manganese single atoms and iron clusters.

[0142] Example 10:

[0143] Investigate the stability and repeated applicability of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC), including the following steps:

[0144] (1) Prepare 1 group of 1000 mL of ciprofloxacin aqueous solution with a concentration of 20 mg / L (the original pH value of this aqueous solution is 3.54), and set two parallel samples for each group.

[0145] (2) Add the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) prepared in Example 9 to each group of solutions respectively, so that the concentration of FeMnac-NC in the solution is 0.2 g / L; then add potassium monopersulfate so that the concentration of potassium monopersulfate in the solution is 2 g / L; carry out the degradation reaction at 25 °C and 500 rpm for 90 min to complete the removal of ciprofloxacin in the water body.

[0146] After each reaction is completed, filter the remaining mixed solution by suction, dry the remaining solid material, keep it at 60 °C in an oven and dry for 12 h, and then take out the obtained solid material for the next experiment. Repeat steps (1)-(2) four times, and then pyrolyze at 500 °C for 2 h by high-temperature pyrolysis method to pyrolyze the pollutant molecules on the pyrolytic active sites and reactivate the active sites for the 5th cycle.

[0147] Figure 12 This is the cyclic degradation effect diagram of the iron cluster-modified manganese single-atom catalyst (FeMnac-NC) for ciprofloxacin in the water body in Example 10 of the present invention.

[0148] As can be seen from Figure 12 the results in, in the 4 cycles, the removal rate of CIP in the first 3 cycles is higher than 90%, and it drops to 77.0% after the 4th cycle. Reactivate the active sites and carry out the 5th cycle. The results show that the CIP removal rate is restored to 90%.

[0149] In addition, detect the metal ion leaching of FeMn ac -NC after the reaction. The results show that after 2 h of reaction, the leaching amount of manganese is only 0.004 mg / L, which is much lower than the surface water standard limit of 0.1 mg / L for domestic drinking water in the GB3838-2002 standard. This indicates that the Mn metal is firmly loaded on the carbon-based material in the form of single atoms. The leaching amount of iron is 0.25 mg / L, which may be because iron exists in the form of clusters in the material and is prone to leaching, but its leaching amount is lower than the surface water standard limit of 0.3 mg / L for domestic drinking water, meeting the domestic drinking water specification.

[0150] Based on the above results, compared with the conventional bimetallic atom nitrogen-doped carbon catalyst, the iron cluster-modified manganese single-atom catalyst used in the present invention has the following advantages: (a) large specific surface area; (b) a porous layered structure with a rough surface and rich pore structure; (c) good structural stability; (d) capable of quickly forming more singlet oxygen ( 1O2) and high-valent metals (FeMn=O). Therefore, when the iron cluster-modified manganese single-atom catalyst of the present invention is used to activate persulfate, it can efficiently activate persulfate and rapidly and continuously generate a large amount of active substances such as singlet oxygen. Furthermore, these active substances can be used to efficiently degrade organic pollutants in water bodies. In particular, for organic pollutants with a concentration ≤ 30 mg / L, it has a better and faster removal effect, and has the advantages of simple process, convenient operation, low cost, strong practicability, wide adaptability, small catalyst dosage, high treatment efficiency, good degradation effect, green environmental protection, etc. It has high use value and good application prospects.

[0151] The above embodiments are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, improvements and refinements made without departing from the principle of the present invention should also be regarded as within the protection scope of the present invention.

Claims

1. A method for activating persulfate by an iron cluster-modified manganese single-atom catalyst to remove organic pollutants in water, characterized in that, The method uses a manganese single-atom catalyst modified with iron clusters as a catalyst to activate persulfate for the degradation of organic pollutants in water; the manganese single-atom catalyst modified with iron clusters uses a porous nitrogen-doped carbon layered material as a carrier, and manganese single atoms are loaded between the surface and the layered structure of the porous nitrogen-doped carbon layered material, and iron clusters are modified on the manganese single atoms; the valence state of iron in the manganese single-atom catalyst modified with iron clusters is divalent, and the valence states of manganese are divalent and trivalent.

2. The method according to claim 1, wherein The atomic percentage content of iron in the iron cluster-modified manganese single-atom catalyst is 0.834%, and the atomic percentage content of manganese is 0.016%; the specific surface area of the iron cluster-modified manganese single-atom catalyst is 1384.85 m 2 / g.

3. The method according to claim 2, wherein The manganese single-atom catalyst modified with iron clusters is prepared by using manganese salt, iron salt, and zinc salt as raw materials and o-phenylenediamine as a template agent through impregnation and pyrolysis; the preparation method of the manganese single-atom catalyst modified with iron clusters includes the following steps: S1. Prepare a zinc-manganese solution from zinc salt and manganese salt, add it to the o-phenylenediamine solution, and stir to obtain a zinc-manganese precursor; S2. Pyrolyze the zinc-manganese precursor to obtain a nitrogen-doped carbon layered material with zinc and manganese fixed; S3. Mix the nitrogen-doped carbon layered material with zinc and manganese fixed with an iron salt solution and stir to obtain a nitrogen-doped carbon layered material with zinc, manganese, and iron fixed; S4. Pyrolyze the nitrogen-doped carbon layered material with zinc, manganese, and iron fixed to obtain a manganese single-atom catalyst modified with iron clusters.

4. The method according to claim 3, wherein The preparation conditions of the manganese single-atom catalyst modified with iron clusters include at least one of (1.1) to (1.9): (1.1) In step S1, the zinc-manganese solution is prepared by dissolving zinc salt and manganese salt in methanol; the molar ratio of zinc salt to manganese salt is 5:2; the ratio of zinc salt to methanol is 1 mmol:25 mL; the zinc salt is zinc nitrate hexahydrate; the manganese salt is manganese chloride tetrahydrate; (1.2) In step S1, the o-phenylenediamine solution is prepared by dissolving o-phenylenediamine in methanol; the ratio of o-phenylenediamine to methanol is 1 mmol:5 mL; (1.3) In step S1, the stirring is carried out under the condition of a rotation speed of 600 rpm; the stirring time is 12 h; (1.4) After step S1 is completed, the following treatment is also included: filter the precipitate after stirring, wash the solid product obtained by filtering with ethanol, the number of washing times is 3 times, dry the washed solid product under vacuum at a temperature of 60 °C, and the drying time is 12 h to obtain a zinc-manganese precursor; (1.5) In step S2, the pyrolysis is carried out in a nitrogen atmosphere; the pyrolysis temperature is 500 °C; the pyrolysis time is 2 h; (1.6) In step S3, the ratio of the nitrogen-doped carbon layered material with zinc and manganese fixed to the iron salt solution is 1 mg:1 mL; the iron salt solution is prepared by dissolving iron salt in isopropanol; the concentration of iron salt in the iron salt solution is 0.01 mM; the iron salt is iron nitrate nonahydrate; (1.7) In step S3, the stirring time is 24 h; (1.8) After the stirring in step S3, the following treatments are further included: centrifuging the stirred product to collect the solid material, washing the solid material with deionized water and ethanol in sequence, the number of times of washing being 3 times, drying the washed solid material under vacuum at a temperature of 60 °C, the drying time being 24 h, to obtain a nitrogen-doped carbon layer material fixed with zinc, manganese and iron; (1.9) In step S4, the pyrolysis is carried out in a nitrogen atmosphere; the heating rate during the pyrolysis is 5 °C / min; the temperature of the pyrolysis is 950 °C; the time of the pyrolysis is 3 h.

5. The method according to any one of claims 1 to 4, characterized in that Degrading organic pollutants in water by activating persulfate with an iron cluster-modified manganese single-atom catalyst, including the following steps: mixing the iron cluster-modified manganese single-atom catalyst, persulfate and water containing organic pollutants for a degradation reaction to complete the degradation of organic pollutants in the water; the initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is ≥ 0.01 g / L, and the initial concentration of persulfate is ≥ 0.1 g / L.

6. The method according to claim 5, wherein The initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is 0.01 g / L to 0.08 g / L, and the initial concentration of persulfate is 0.1 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is ≥ 3.

7. The method according to claim 6, wherein The initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is 0.015 g / L to 0.06 g / L, and the initial concentration of persulfate is 0.15 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is 3 to 9.

8. The method according to claim 7, wherein The initial concentration of the iron cluster-modified manganese single-atom catalyst in the degradation reaction system is 0.02 g / L to 0.055 g / L, and the initial concentration of persulfate is 0.2 g / L to 0.5 g / L; the initial pH value in the degradation reaction system is 3.54 to 9.

9. The method according to claim 5, wherein The persulfate is peroxymonosulfate and / or persulfate; the peroxymonosulfate is at least one of sodium peroxymonosulfate and potassium peroxymonosulfate; the persulfate is at least one of sodium persulfate and potassium persulfate; the initial concentration of organic pollutants in the water containing organic pollutants is ≤ 30 mg / L; the organic pollutants in the water containing organic pollutants are antibiotics; the antibiotics are at least one of ciprofloxacin, tetracycline, sulfamethoxazole and oxytetracycline.

10. The method according to claim 5, characterized in that, The degradation reaction is carried out under shaking conditions; the rotation speed of the shaking is 500 rpm to 520 rpm; the temperature of the degradation reaction is 25 °C to 30 °C; the time of the degradation reaction is 0.5 min to 90 min.

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