A granular activated carbon composite material loaded with single-atom iron, its preparation method and its application

Abstract

This invention provides a method for preparing a granular activated carbon composite material loaded with monatomic iron, comprising: S1 mixing zinc salt and water to obtain solution A, and impregnating activated carbon particles in solution A; S2 mixing 2-methylimidazole and water to obtain solution B, adding solution B to the mixture obtained in step S1 for reaction, and aging to obtain impregnated activated carbon; S3 calcining the impregnated activated carbon, followed by acid washing, cleaning, and drying to obtain acid-washed and calcined activated carbon; S4 impregnating the acid-washed and calcined activated carbon with an iron salt solution or a ferrous salt solution, followed by calcination to obtain a granular activated carbon composite material loaded with monatomic iron. The granular activated carbon composite material loaded with monatomic iron provided in this application can be used to catalyze the generation of reactive oxygen species from persulfate, and to efficiently degrade and remove recalcitrant organic matter in wastewater through advanced oxidation.

Description

Technical Field

[0001] This invention relates to the fields of environmental functional materials and water treatment technology, and in particular to a granular activated carbon composite material loaded with single-atom iron, its preparation method and its application. Background Technology

[0002] The recalcitrant organic wastewater generated by pharmaceutical, papermaking, and fine chemical industries is characterized by large discharge volumes, high loads, complex compositions, and difficulty in biodegradation. Traditional biological methods have low degradation efficiency for complex organic compounds containing antibiotics and halogenated hydrocarbons, and are easily inhibited by toxicity, hindering the upgrading of the water treatment industry. Activated carbon adsorption is a widely used wastewater treatment technology, but activated carbon still has limited adsorption capacity and is prone to saturation under high loads in treating recalcitrant organic compounds in water; moreover, the adsorption process only involves phase transfer of pollutants, and the resulting saturated activated carbon is difficult to treat as hazardous waste.

[0003] In recent years, advanced oxidation processes based on persulfate (PMS) have attracted widespread attention. Compared to the traditional Fenton system, the PMS advanced oxidation process has a wider applicable pH range, overcoming the Fenton system's dependence on acidic environments; and the sulfate radicals (SO4·) generated during activation... － Its oxidation potential (2.5–3.1 V) is higher than that of hydroxyl radicals, enabling it to efficiently degrade stubborn organic pollutants. Nitrogen-coordinated monatomic iron (Fe-N) x It has significant advantages in activating persulfate: its atomic-level dispersion maximizes the exposure of active sites, Fe-N x The coordination structure can simultaneously activate free radicals (SO4· － / ·OH) and non-free radicals ( 1 The O2 pathway broadens the range of pollutants that can be degraded. Simultaneously, it operates efficiently under neutral conditions, and the nitrogen atom coordination effectively inhibits iron dissolution, avoiding the acid dependence and iron sludge pollution of traditional iron-based catalysts, providing a green and efficient solution for the treatment of complex organic wastewater. However, industrial wastewater treatment typically requires a continuous flow system, and Fe-N... x Catalytic materials are typically nanoparticles, making them difficult to directly fill in fixed-bed reactors. If applied to fluid systems, additional solid-liquid separation equipment is required, increasing energy consumption and cost. Furthermore, when wastewater contains suspended solids or colloids, the powdered catalytic materials may agglomerate and deactivate. These issues limit the application of single-atom iron in large-scale water treatment scenarios.

[0004] To address these issues, researchers have conducted numerous studies. For example, Chinese Patent Publication No. CN111620311A discloses a porous carbon-supported single-atom metal nitrogen coordination composite material and its preparation method. This method utilizes activated carbon to adsorb iron salts and complexes to obtain a precursor. The precursor is then physically ground with an organic nitrogen source and heat-treated in an inert atmosphere to obtain an activated carbon-supported single-atom iron composite material. Chinese Patent Publication No. CN111804301A discloses a method for preparing carbon-supported single-atom metal materials. This method uses activated carbon-supported iron and iron oxide nanoclusters as metal precursors, which are then mixed with an organic nitrogen source. By capturing single atoms generated during the Oswald ripening effect at high temperatures, efficient loading of single-atom iron is achieved. However, the preparation methods provided by these patents are limited to the synthesis of powdered materials and are difficult to apply to fixed-bed reactors. Chinese Patent CN110479249A discloses a method for preparing single-atom catalysts by precursor atomization, which involves spraying an iron salt solution onto the surface of activated carbon, followed by drying and high-temperature calcination to obtain a supported single-atom catalyst. However, the spraying method cannot ensure that the iron salt fully penetrates the nanoscale pores inside the activated carbon, resulting in uneven distribution of active sites and waste of internal space. Chinese Patent CN111420691A provides a metal single-atom catalyst and its preparation method, which uses laser treatment to process a mixed solution of elemental iron and a dispersant, then reacts the activated carbon and the mixed solution under hydrothermal conditions, and finally obtains a supported single-atom iron catalytic material through sintering. This method uses laser irradiation and hydrothermal treatment, which is cumbersome, has a long reaction time, and is not easily industrialized. Chinese patent CN112156752A discloses an adsorbent regenerable modified activated carbon and its application in wastewater treatment. It uses a mixture of iron salt and urea or glycerol to impregnate granular activated carbon, and after drying and high-temperature treatment, obtains activated carbon loaded with single atoms, which has the functions of adsorbing organic matter in water and regenerating in situ with hydrogen peroxide. The urea / glycerol used in this method are both small molecule organic compounds that cannot coordinate with iron or ferrous ions. They are easy to escape during high-temperature processes and it is difficult to form abundant nitrogen / oxygen sites on the surface of activated carbon, thus limiting the anchoring effect on single-atom iron. Chinese patent CN114534780A discloses a supported sulfonium-anchored single-atom catalyst and its preparation method. The method involves synthesizing sulfonium salts on the surface of activated carbon and then loading iron mononuclear halides through sulfonium anchoring. However, the surface modification of activated carbon requires the use of sulfides and halogenated hydrocarbons with high biotoxicity and is carried out under high temperature and high pressure hydrothermal conditions. Iron mononuclear halides are obtained by reacting iron salts with concentrated hydrochloric acid, making the above reaction process difficult to scale up industrially.Chinese Patent CN113600170A discloses a transition metal single-atom active catalyst, its preparation method, and its application. The method involves impregnating activated carbon with an iron phthalocyanine solution, drying it, and then calcining it to obtain a single-atom catalytic material suitable for persulfate activation. While this preparation method is relatively simple, iron phthalocyanine is insoluble in water, necessitating the use of organic solvents such as acetone. Furthermore, to ensure thorough mixing of activated carbon and phthalocyanine, the solvent needs to be evaporated before grinding, leading to the emission of volatile organic compounds. Additionally, the powdered catalytic material cannot be applied to fixed-bed packing, limiting its industrial production and application. Chinese patent CN114177903A discloses a method for preparing microporous materials supported on single-atom and diatomic catalysts. It involves dispersing iron acetylacetonate and powdered activated carbon in supercritical CO2, with the former uniformly dispersed in the micropores of the latter. After high-temperature reduction, a single-atom iron catalyst is obtained. However, this method has requirements on the pore structure of the activated carbon itself, namely, its pore size distribution is within 1 nm, and it is not suitable for all activated carbons. In addition, CO2 only transforms into a supercritical state when the temperature is above 31°C and the pressure is above 72.8 atmospheres. The reaction conditions are harsh, the requirements for the reactor are high, and it is difficult to mass-produce. Chinese patent CN114672838A discloses a method for preparing a carbon-based nitrogen-coordinated metal single-atom or cluster catalyst, as well as its products and applications. The method involves thoroughly grinding nitrogen-containing small organic molecules, volatile metal salts, and activated carbon, followed by high-temperature treatment to obtain activated carbon-supported nitrogen-coordinated single-atom iron catalytic material. However, the material prepared by this method is in powder form, which is not suitable for use in fixed-bed reactors. Furthermore, dry grinding cannot uniformly disperse the single-atom precursor within the pores of the activated carbon, resulting in the active sites being mainly concentrated on the surface of the support. Chinese Patent CN115369427A discloses a molecular hybrid single-atom catalyst for electrocatalytic oxygen reduction to synthesize hydrogen peroxide, its preparation method, and its application. The method involves oxidizing or diazotizing powdered activated carbon with a particle size of 10 nm to 5 μm, and then anchoring porphyrin / phthalocyanine iron with grafted oxygen-containing groups or pyridine groups to obtain a molecular hybrid single-atom iron catalyst. However, this method requires a relatively cumbersome wet oxidation and diazotization process to modify the activated carbon. Furthermore, when the non-polar porphyrin / phthalocyanine iron is anchored on the activated carbon surface, the hydrophilicity of the material decreases sharply, limiting its application in aqueous phases. Chinese patent CN118988250A discloses an adsorbent, its preparation method, and its application. It introduces thiol carboxyl groups on the surface of activated carbon by impregnating and calcining it with thiol. Then, it utilizes the coordination of thiol carboxyl groups with iron ions and obtains an activated carbon adsorbent material loaded with iron single atoms through secondary calcination. The method explicitly mentions that in order to promote the subsequent reaction between the activated carbon source and the thiol, the activated carbon must be ground to a particle size of 200-600 nm. Therefore, the final product cannot be applied to fixed-bed water treatment devices.

[0005] Therefore, the existing catalyst preparation methods have many limitations, and there is an urgent need to provide a simple, environmentally friendly method for preparing catalysts that can be applied to solid bed reactors for water treatment. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preparing a granular activated carbon composite material supported on single-atom iron. The preparation method provided by this application has the characteristics of simple preparation process, environmental protection, and high catalytic activity of the prepared granular activated carbon composite material supported on single-atom iron, and can be directly used as a catalyst for solid bed reactor.

[0007] In view of this, this application provides a method for preparing a particulate activated carbon composite material loaded with single-atom iron, comprising the following steps:

[0008] S1. Mix zinc salt and water to obtain solution A, and impregnate activated carbon particles in solution A;

[0009] S2. Mix 2-methylimidazole and water to obtain solution B. Add solution B to the mixture obtained in step S1 and react. After aging, impregnated activated carbon is obtained.

[0010] S3. The impregnated activated carbon is calcined to obtain calcined activated carbon;

[0011] The once-calcined activated carbon is acid-washed, then cleaned and dried to obtain acid-washed once-calcined activated carbon.

[0012] S4. Impregnate the acid-washed and calcined activated carbon with an iron salt solution or a ferrous salt solution to obtain iron-loaded acid-washed and calcined activated carbon.

[0013] S5. The iron-loaded acid-washed and calcined activated carbon is calcined to obtain a granular activated carbon composite material loaded with monatomic iron.

[0014] In some specific embodiments, in step S1, the zinc salt includes one or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc gluconate, and zinc lactate; and / or, the particle size of the activated carbon particles is 0.2–5 mm; and / or, the concentration of zinc ions in solution A is 0.10–2.50 mol / L; and / or, the ratio of activated carbon particles to solution A is (0.5–1.5) g: 1 mL; and / or, the impregnation time is 1–5 h.

[0015] In some specific embodiments, in step S2, the molar ratio of the 2-methylimidazole to the zinc ions in the mixed system is (3-10):1; and / or, the reaction time is 2-24 h; and / or, the aging time is 12-36 h.

[0016] In some specific embodiments, step S2, after aging, further includes:

[0017] The obtained impregnated activated carbon is washed, dehydrated, and dried;

[0018] The dehydration method is vacuum filtration and / or centrifugal dehydration, and the drying method is electric heating drying and / or room temperature air drying.

[0019] In some specific embodiments, in step S3, the calcination is carried out under one or more of the following conditions: nitrogen protection, argon protection, and vacuum conditions, and / or the calcination temperature is 800-1000°C, the heating rate is 1-20°C / min, and the time is 0.5-5h.

[0020] In some specific embodiments, in step S3, the pickling reagent is selected from hydrochloric acid, nitric acid or sulfuric acid, the pickling temperature is 10 to 100°C, the pickling time is 1 to 24 hours; and / or, the cleaning reagent is water.

[0021] In some specific embodiments, in step S4, the iron salt includes one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric ammonium sulfate, ferric citrate, and ferric ammonium citrate; the ferrous salt includes one or more of ferrous nitrate, ferrous chloride, and ferrous sulfate; and / or, the impregnation is carried out under stirring or shaking conditions, and the impregnation time is 0.5 to 2 hours.

[0022] In some specific embodiments, step S4 further includes washing the obtained activated carbon after impregnation until the washing liquid is colorless;

[0023] And / or, in step S5, the calcination is carried out under one or more of the following conditions: nitrogen protection, argon protection, and vacuum; and / or, the calcination temperature is 400–1000°C, the heating rate is 1–20°C / min, and the time is 0.5–6h.

[0024] This application also provides a particle activated carbon composite material loaded with single-atom iron prepared by the preparation method described above, comprising activated carbon and nitrogen-doped porous carbon loaded in the pores of the activated carbon, wherein the iron atom and the nitrogen atom in the nitrogen-doped porous carbon are coordinated; the nitrogen-doped porous carbon is obtained by calcination of ZIF-L.

[0025] This application also provides the application of the particulate activated carbon composite material with single-atom iron supported by the preparation method described above or the preparation method described above as a catalyst in the degradation of organic matter.

[0026] This application provides a method for preparing a granular activated carbon composite material supported on single-atom iron. First, a nitrogen-rich secondary nano-carbon structure is prepared inside the pores of a granular activated carbon support. Then, based on the anchoring effect of the nitrogen sites within this structure, the granular activated carbon composite material is obtained through impregnation with iron salts and / or ferrous salts, followed by calcination. The raw materials used in this preparation process are environmentally friendly, and the method is simple. The prepared granular activated carbon composite material possesses a well-developed porous structure. The nitrogen atoms in the secondary nano-carbon structure within the activated carbon anchor iron ions and / or ferrous ions through coordination, giving the composite material the advantage of high catalytic activity. Furthermore, the prepared activated carbon composite material is in granular form, making it suitable for use in solid-bed reactors for water treatment, thus avoiding the problems of separation and loss of nanopowder catalysts. Attached Figure Description

[0027] Figure 1 Photograph (a) and scanning electron microscope images (b) to (c) show the appearance of the catalytic material prepared in Example 1 of this invention;

[0028] Figure 2 The images shown are: (a) a high-resolution transmission electron microscope image of the catalytic material prepared in Example 1 of the present invention, (b) a high-angle annular dark-field scanning transmission electron microscope image, and (c) to (d) N and Fe distribution maps in HAADF-STEM mode;

[0029] Figure 3 The X-ray diffraction pattern of the catalytic material prepared in Example 1 of this invention;

[0030] Figure 4 The X-ray photoelectron spectrum of the N1s orbital of the catalytic material prepared in Example 1 of this invention;

[0031] Figure 5 The N2 adsorption-desorption curve and pore parameters of the catalytic material prepared in Example 1 of this invention are shown.

[0032] Figure 6 The bar chart shows the removal rate of Rhodamine B for different experimental schemes in Application Example 1 of this invention.

[0033] Figure 7 This is a bar chart showing the removal rate of Rhodamine B for different experimental schemes in Application Example 2 of the present invention;

[0034] Figure 8 This is a schematic diagram of the continuous flow catalytic experimental apparatus used in Application Example 3 of the present invention;

[0035] Figure 9 This is a graph showing the change in the removal rate of Rhodamine B in Application Example 3 of the present invention. Detailed Implementation

[0036] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0037] In view of the existing requirements for the preparation method and application of activated persulfate catalysts, this application provides a method for preparing a granular activated carbon composite material supported on single-atom iron. First, a nitrogen-rich secondary nano-carbon structure is synthesized inside the pores of a granular activated carbon support. Then, based on the anchoring effect of nitrogen sites, a granular activated carbon composite material containing nitrogen-coordinated single-atom iron sites is prepared through impregnation with iron salts and / or ferrous salts and finally calcination. This composite material has the characteristics of simple and environmentally friendly preparation process and high catalytic activity, and can be directly used as packing material in fixed-bed reactors. Specifically, this invention discloses a method for preparing a granular activated carbon composite material supported on single-atom iron, including the following steps:

[0038] S1. Mix zinc salt and water to obtain solution A, and impregnate activated carbon particles in solution A;

[0039] S2. Mix 2-methylimidazole and water to obtain solution B. Add solution B to the mixture obtained in step S1, react, and after aging, obtain impregnated activated carbon.

[0040] S3. The impregnated activated carbon is calcined to obtain calcined activated carbon;

[0041] The once-calcined activated carbon is acid-washed, then cleaned and dried to obtain acid-washed once-calcined activated carbon.

[0042] S4. Impregnate the acid-washed and calcined activated carbon with an iron salt solution or a ferrous salt solution to obtain iron-loaded acid-washed and calcined activated carbon.

[0043] S5. The iron-loaded acid-washed and calcined activated carbon is calcined to obtain a granular activated carbon composite material loaded with monatomic iron.

[0044] In the preparation of granular activated carbon composite material loaded with monatomic iron, in step S1, zinc salt and water are mixed to obtain solution A, and activated carbon particles are impregnated in solution A. During this process, the zinc salt has good water solubility, and the concentration of the zinc salt solution should not be too low to ensure that zinc ions fully penetrate the interior of the granular activated carbon during impregnation. Specifically, the zinc salt includes one or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc gluconate, and zinc lactate; more specifically, the zinc salt is selected from one or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc gluconate, and zinc lactate; and even more specifically, the zinc salt is selected from zinc sulfate, zinc chloride, zinc nitrate, or zinc acetate. The concentration of zinc ions in solution A is 0.10–2.5 mol / L, specifically 0.125–1.5 mol / L, and even more specifically, 0.25–0.5 mol / L. To ensure the impregnation effect and avoid zinc ion hydrolysis, the impregnation time of the zinc salt was further controlled, ranging from 1 to 5 hours, specifically 2 to 4 hours. Impregnating the activated carbon particles with zinc salt was intended to facilitate the in-situ synthesis of zeolite imidazole ester framework material (ZIF-L) within the activated carbon pores in the next step, through coordination between zinc ions and 2-methylimidazolium ligands. Therefore, the ratio of solution A to activated carbon particles was further controlled to increase the number of zinc ions within the activated carbon. The ratio of activated carbon particles to solution A was (0.5–1.5) g:1 mL, specifically (0.5–1.2) g:1 mL; more specifically, (0.5–0.8) g:1 mL. The activated carbon particles are well known to those skilled in the art, and there are no particular restrictions on their source in this application. In specific embodiments, the activated carbon particles are selected from coconut shell activated carbon, coal-based briquetted and crushed activated carbon, or apricot shell activated carbon; the particle size of the activated carbon particles is 0.2-5 mm, specifically, the particle size of the activated carbon particles is 2-4 mm or 1-3 mm.

[0045] In step S2, this application mixes 2-methylimidazole and water to obtain solution B, which is then added to the mixture obtained in step S1. After reaction and aging, impregnated activated carbon is obtained. In the above process, to avoid excess water in the reaction system, the 2-methylimidazole in solution B should be close to saturation to increase the probability of reaction between zinc ions and 2-methylimidazole ligands inside the activated carbon. Theoretically, one zinc ion needs to coordinate with two 2-methylimidazole molecules, so the theoretical molar ratio of zinc salt to 2-methylimidazole should be 1:2. In reality, to ensure complete reaction of zinc ions at room temperature, a higher ligand ratio is needed to drive nucleation and inhibit zinc ion hydrolysis. Furthermore, since the coordination of zinc ions with 2-methylimidazole occurs at room temperature in an aqueous phase, the reaction rate is relatively slow. Therefore, it is necessary to ensure the mass transfer effect and sufficient reaction time during the reaction process. The molar ratio of 2-methylimidazole to zinc ions in the above-mentioned mixed system is (3-10):1. Specifically, the molar ratio of 2-methylimidazole to zinc ions in the above-mentioned mixed system is (4-8):1. More specifically, the molar ratio of 2-methylimidazole to zinc ions in the above-mentioned mixed system is (5-7):1. The reaction time is 2-24 h, and the aging time is 12-36 h. Specifically, the reaction time is 10-18 h, and the aging time is 18-24 h. More specifically, the reaction time is 12-16 h, and the aging time is 20-22 h.

[0046] After the reaction of zinc salt and 2-methylimidazole is completed, the activated carbon is separated from the liquid-phase reaction system, preferably by washing away loosely bonded ZIF-L particles and unreacted raw materials with deionized water. Then, dehydration is performed to prepare for the next drying step. The dehydration method is vacuum filtration and / or centrifugal dehydration, and the drying method is electric heating (65–105°C) and / or air drying at room temperature; specifically, the drying temperature is 70–90°C for 6–18 hours, more specifically, the drying temperature is 70–80°C for 10–12 hours.

[0047] In step S3, the impregnated activated carbon is calcined to obtain calcined activated carbon. During this process, the calcination is carried out under anaerobic conditions. Due to the high thermal stability of the activated carbon itself, its structure remains almost unchanged. However, the organic linkages in the ZIF-L loaded within its pores undergo pyrolysis to generate nitrogen-doped porous carbon, while the zinc metal at the nodes evaporates from the reaction system. In the ZIF-L-derived carbon, the main forms of nitrogen atoms are pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, and a small amount of oxidized nitrogen (NO). Among these nitrogen-containing sites, pyridinic nitrogen has lone pairs of electrons perpendicular to the plane, exhibiting strong coordination ability. High temperatures promote the formation of graphitic nitrogen, whose lone pairs of electrons participate in conjugation, exhibiting the weakest coordination ability. During high-temperature calcination, it is necessary to ensure that the carbonized material contains abundant pyridinic nitrogen structures to provide sites for the anchoring of single-atom iron in subsequent operations; it is also necessary to minimize the evaporation of metallic zinc in the ZIF-L to reduce metal residue. Therefore, this application preferably restricts the calcination conditions; the calcination should be carried out under nitrogen and / or argon protection and / or vacuum conditions; the calcination temperature is 800-1000℃, the heating rate is 1-20℃ / min, and the time is 0.5-5h; specifically, the calcination temperature is 850-950℃, the heating rate is 2-10℃ / min, and the time is 1-3h; more specifically, the calcination temperature is 860-900℃, the heating rate is 2.5-5℃ / min, and the time is 2-3h.

[0048] After calcination, the once-calcined activated carbon is acid-washed, then cleaned and dried to obtain acid-washed once-calcined activated carbon. Even after the above calcination, unvolatile metallic zinc may still exist inside the once-calcined impregnated activated carbon. The acid solution dissolves and removes the metallic zinc, fully exposing the internal pores and nitrogen sites of the once-calcined impregnated activated carbon. The acid washing reagent includes one of hydrochloric acid, nitric acid, and sulfuric acid, and the concentration of hydrogen ions dissociated from the acid washing reagent is 0.5–1 mol / L. The acid washing temperature is 10–100℃, and the time is 1–24 h. Specifically, the acid washing temperature is 45–80℃, and the time is 1.5–12 h; more specifically, the acid washing temperature is 50–60℃, and the time is 2–8 h. The drying temperature is 60–100℃, and the time is 10–24 h. Specifically, the drying temperature is 80–90℃, and the time is 12–18 h.

[0049] The pores of the acid-washed, once-calcined activated carbon are loaded with a large number of secondary nano-carbon structures derived from ZIF-L, and these nano-carbons are rich in pyridine nitrogen sites; Fe 3+ and Fe 2+The empty orbitals can accept lone pairs of electrons from pyridine nitrogen to form coordinate bonds. Therefore, in step S4, the acid-washed once-calcined activated carbon is impregnated with an iron salt solution or a ferrous salt solution to obtain iron-loaded acid-washed once-calcined activated carbon; in this process, the once-calcined activated carbon is impregnated with an iron salt solution and / or a ferrous salt solution to allow Fe to form a coordinate bond. 3+ and / or Fe 2+ The ferric salts are adsorbed onto the nitrogen sites of secondary nano-carbon within the pores of the primary calcined activated carbon through coordination. Furthermore, to prevent hydrolysis of ferric and / or ferrous ions, which could lead to the formation of clusters within the pores of the acid-washed primary calcined activated carbon, the concentration of the ferric salt solution and / or ferrous salt solution should not be too low, and the impregnation time should not be too long. Specifically, the ferric salt includes one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric ammonium sulfate, ferric citrate, and ferric ammonium citrate; the ferrous salt includes one or more of ferrous nitrate, ferrous chloride, and ferrous sulfate; the concentration of ferric ions in the ferric salt solution or the ferrous ion in the ferrous salt solution is 10–100 mmol / L, specifically, the concentration of ferric ions or the ferrous ions is 18.5–60 mmol / L, more specifically, the concentration of ferric ions or the ferrous ions is 20–45 mmol / L, and even more specifically, the concentration of ferric ions or the ferrous ions is 25–30 mmol / L. The impregnation is carried out under stirring or shaking conditions, and the impregnation time is 0.5 to 2 hours, specifically 0.8 to 1.6 hours, and more specifically 1.0 to 1.5 hours.

[0050] After the above impregnation is completed, it is further washed with deionized water until the washing solution is colorless, in order to remove iron or ferrous ions that have not coordinated with nitrogen sites and hydrolysis products attached to the surface of the material, so as to prevent them from migrating and agglomerating in the subsequent secondary calcination process and to form a shield for the single-atom iron sites.

[0051] To enhance the coordination between iron atoms and nitrogen atoms on the first-calcined activated carbon, the iron-loaded acid-washed first-calcined activated carbon should be calcined again under an inert gas atmosphere, i.e., step S5, to calcine the iron-loaded acid-washed first-calcined activated carbon to obtain a granular activated carbon composite material loaded with single-atom iron. In the above process, the calcination is achieved by using thermal energy to drive the iron atoms to fully contact the nitrogen sites in the ZIF-L derived carbon, overcoming the reaction energy barrier and forming a more stable Fe-N. x Coordination structure. The calcination temperature is controlled within a reasonable range; if it is too low, a stable Fe-N complex cannot be formed. xExcessive site density can lead to over-graphitization of the carbon matrix (reduced pyridine nitrogen anchoring sites) or sintering of iron atoms; furthermore, the control of the heating rate and time during calcination also affects the uniformity of the structure. Specifically, the calcination treatment is carried out under nitrogen and / or argon purging protection and / or vacuum conditions. The calcination temperature is 400–1000℃, the heating rate is 1–20℃ / min, and the time is 0.5–6h; specifically, the calcination temperature is 500–700℃, the heating rate is 2–5℃ / min, and the time is 1–4h; more specifically, the calcination temperature is 550–600℃, the heating rate is 3–4℃ / min, and the time is 2–2.5h.

[0052] This application also provides a particulate activated carbon composite material loaded with single-atom iron prepared by the above method, comprising activated carbon and nitrogen-doped porous carbon loaded in the pores of the activated carbon, wherein the iron atom and the nitrogen atom in the nitrogen-doped porous carbon are coordinated; the nitrogen-doped porous carbon is obtained by calcination of ZIF-L.

[0053] Furthermore, this application also provides the application of the above-mentioned granular activated carbon composite material supported on single-atom iron as a catalyst in the degradation of organic matter; specifically, the above-mentioned granular activated carbon composite material supported on single-atom iron can be used as a catalyst to catalyze the production of active oxide species from persulfate, effectively degrading organic pollutants (such as Rhodamine B) in water.

[0054] This invention employs a room-temperature liquid-phase method to synthesize ZIF-L within the pores of granular activated carbon, avoiding the use of organic solvents and resulting in a green and simple process. The single-atom iron precursor used in this invention is a common water-soluble ferric salt and / or ferrous salt, avoiding the use of expensive organic iron compounds. The molecular size of 2-methylimidazole is approximately 0.8 nm (major axis) × 0.6 nm (minor axis) × 0.4 nm (thickness), while the pore size of granular activated carbon is typically 1–3 nm. 2-methylimidazole and granular activated carbon can achieve good synergy: on the one hand, 2-methylimidazole, as a ligand, has a molecular size that allows it to smoothly enter the pores of activated carbon and interact with Zn. 2+ Coordination; on the other hand, the confinement effect of activated carbon pores can regulate the nucleation and growth of ZIF-L crystals, optimizing their grain size and pore distribution; in addition, the physical support of the activated carbon skeleton can prevent the structural collapse of ZIF-L during high-temperature carbonization, giving ZIF-L carbides a well-developed porous structure and highly exposed pyridine nitrogen sites.

[0055] This invention innovatively constructs high-density pyridine nitrogen sites in situ inside activated carbon, while iron ions and / or ferrous ions have almost no steric hindrance effect inside the pores of activated carbon. Compared with the method of preparing single-atom iron by pre-preparing Fe-nitrogen-containing organic complexes and then adsorbing them by activated carbon followed by heat treatment, this invention adsorbs iron ions and / or ferrous ions through the coordination of pyridine nitrogen, fundamentally avoiding the adsorption mismatch problem that may exist between activated carbon and Fe-nitrogen-containing organic complexes.

[0056] Furthermore, the preparation method of the granular activated carbon composite material supported on single-atom iron provided by this invention is universal, the process is green and simple, it does not rely on expensive raw materials, and it has significant potential for industrial application. The granular activated carbon composite material can directly replace granular activated carbon and be applied to fixed-bed reactors for water treatment, avoiding the separation and loss problems of nanopowder catalysts. This material can catalyze the generation of active oxygen species from persulfate to achieve the oxidation and removal of organic matter in water, and can be recycled through in-situ advanced oxidation based on persulfate. It is suitable for the treatment of recalcitrant organic wastewater and emergency pollution control scenarios, and has the advantages of recycling and cost reduction.

[0057] To further understand the present invention, the preparation method and application of the granular activated carbon composite material loaded with single-atom iron provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0058] Example 1

[0059] (1) Dissolve 1.0976 g of zinc acetate dihydrate in 20 mL of deionized water to obtain solution A, wherein the zinc ion concentration is 0.25 mol / L;

[0060] Add 10g of coconut shell activated carbon (particle size 2-4mm) to solution A and stir for 1 hour;

[0061] (2) Dissolve 1.6420 g of 2-methylimidazole in 6 mL of deionized water to obtain solution B;

[0062] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 24 hours, and then let it stand for 24 hours to age.

[0063] (3) Use a filter screen to separate the granular activated carbon in the liquid phase reaction system, then rinse off the unfixed particles on its surface with deionized water, then filter it, and dry it at 80°C for 12 hours to obtain impregnated activated carbon.

[0064] (4) Place the impregnated activated carbon in a tubular atmosphere furnace and calcine it under nitrogen purging. The heating rate is 5℃ / min, the calcination temperature is 900℃, and the holding time is 2h to obtain one-time calcined activated carbon.

[0065] (5) The calcined activated carbon was immersed in 1 mol / L hydrochloric acid and soaked at 80°C for 2 hours. After filtration, it was washed with deionized water until neutral and dried at 80°C for 12 hours to obtain acid-washed calcined activated carbon.

[0066] (6) Dissolve 0.404 g of ferric nitrate nonahydrate in 35 mL of deionized water, and add 5 g of acid-washed and calcined activated carbon to the above ferric nitrate solution. Stir and soak for 90 min, then separate the solid and liquid by filtration, and wash with deionized water until the filtrate is colorless. Dry at 80 °C for 12 h to obtain iron-loaded acid-washed and calcined activated carbon.

[0067] (7) The iron-loaded acid-washed and calcined activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 2℃ / min, the calcination temperature was 500℃, and the holding time was 2h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0068] Optical photographs of the catalytic material prepared in this embodiment are shown below. Figure 1 As shown in (a), the particles are irregular black particles with a size of approximately 2–4 mm. Figure 1 (b) and (c) are scanning electron microscope (SEM) images of the catalytic material at magnifications of 5000x and 100000x, respectively. The surface is relatively rough and covered with nanoscale pores, which can provide reaction space for adsorption and catalysis.

[0069] Figure 2 (a) is a high-resolution transmission electron microscope (HRTEM) image of the catalytic material prepared in this embodiment. The distorted and disordered lattice fringes indicate that the carbon support material exhibits a large-scale amorphous structure, i.e., a typical disordered layer structure. No particulate nanostructures were observed, indicating that iron atoms did not aggregate. Figure 2 (b) is a high-angle annular dark-field scanning transmission electron microscope (HAADF-SREM) image of the catalytic material. Figure 2 (c) and (d) are the distribution diagrams of nitrogen and iron elements in HAADF-STEM mode, respectively. As can be seen from the figure, the material surface contains abundant nitrogen elements, which can provide anchoring points for single-atom iron. The iron elements are uniformly distributed on the material surface, and no agglomeration phenomenon was observed.

[0070] Figure 3 The X-ray diffraction (XRD) pattern of the catalytic material prepared in this embodiment shows that the broad peaks at 25° and 46° correspond to the disordered stacking of graphite layers on the (002) crystal plane and the disordered arrangement of six-membered carbon rings on the (100) crystal plane, respectively. In addition, no diffraction peaks of elemental iron and iron oxide were observed, indicating that the iron element did not aggregate during the reaction process and is more likely distributed in the form of single-atom iron inside the material.

[0071] Figure 4 The X-ray photoelectron spectroscopy (XPS) of the catalytic material prepared in this embodiment shows the presence of pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen in the material. These different forms of single atoms can provide anchoring sites for single-atom iron. The peak at 398.82 eV confirms the presence of Fe-N. x The presence of coordination structures indicates the presence of nitrogen-coordinated single-atom iron on the material surface. Figure 5 The N2 adsorption-desorption curves and pore parameters of the catalytic material prepared according to the present invention 1.

[0072] Example 2

[0073] (1) Dissolve 0.7436g of zinc nitrate hexahydrate in 10mL of deionized water to obtain solution A, wherein the zinc ion concentration is 0.25mol / L;

[0074] Add 5g of coal-based briquetted and crushed activated carbon (particle size 1-3mm) to solution A and stir for 1 hour;

[0075] (2) Dissolve 1.2315g of 2-methylimidazole in 3mL of deionized water to obtain solution B;

[0076] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 12 hours, and then let it stand for 24 hours to age.

[0077] (3) Use a filter screen to separate the granular activated carbon in the liquid phase reaction system, then rinse off the unfixed particles on its surface with deionized water, then clean and dehydrate it with a small centrifugal dryer, and dry it at 70°C for 18 hours to obtain impregnated activated carbon.

[0078] (4) The impregnated activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 2.5℃ / min, the calcination temperature was 850℃, and the holding time was 3h to obtain one-time calcined activated carbon.

[0079] (5) The calcined activated carbon was immersed in 1 mol / L nitric acid and soaked at 60°C for 8 hours. After filtration, it was washed with deionized water until neutral and dried at 90°C for 10 hours to obtain acid-washed calcined activated carbon.

[0080] (6) Dissolve 0.54g of ferric chloride hexahydrate in 100mL of deionized water, and add 4g of acid-washed and calcined activated carbon to the ferric chloride solution. Stir and soak for 60min, then separate the solid and liquid by filtration, and wash with deionized water until the filtrate is colorless. Dry at 80℃ for 12h to obtain iron-loaded acid-washed and calcined activated carbon.

[0081] (7) The iron-loaded acid-washed and calcined activated carbon was placed in a tubular atmosphere furnace and calcined under argon purging. The heating rate was 5℃ / min, the calcination temperature was 600℃, and the holding time was 1h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0082] Example 3

[0083] (1) Dissolve 0.7436g of zinc nitrate hexahydrate in 10mL of deionized water to obtain solution A, wherein the zinc ion concentration is 0.25mol / L;

[0084] Add 5g of apricot shell activated carbon (particle size 2-4mm) to solution A and stir for 2 hours;

[0085] (2) Dissolve 0.8210g of 2-methylimidazole in 3mL of deionized water to obtain solution B;

[0086] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 24 hours, and then let it stand for 24 hours to age.

[0087] (3) Use a filter screen to separate the granular activated carbon in the liquid phase reaction system, then rinse off the unfixed particles on its surface with deionized water, then clean and dehydrate it with a small centrifugal dryer, and dry it at 100℃ for 4 hours to obtain impregnated activated carbon.

[0088] (4) The impregnated activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 2.5℃ / min, the calcination temperature was 950℃, and the holding time was 1h to obtain one-time calcined activated carbon.

[0089] (5) The calcined activated carbon was immersed in 0.5 mol / L sulfuric acid and soaked at 45°C for 12 h. After filtration, it was washed with deionized water until neutral and dried at 100°C for 4 h to obtain acid-washed calcined activated carbon.

[0090] (6) Dissolve 0.5964 g of ferrous chloride tetrahydrate in 50 mL of deionized water, and add 4.5 g of acid-washed and calcined activated carbon to the ferrous chloride solution. Shake the solution at 180 rpm for 100 min in a shaker, then separate the solid and liquid by filtration, and wash the solution with deionized water until the filtrate is colorless. Dry the solution at 80 °C for 12 h to obtain iron-loaded acid-washed and calcined activated carbon.

[0091] (7) The iron-loaded acid-washed and calcined activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 4℃ / min, the calcination temperature was 500℃, and the holding time was 2.5h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0092] Example 4

[0093] (1) 0.7189 g of zinc sulfate heptahydrate was dissolved in 20 mL of deionized water to obtain solution A, in which the zinc ion concentration was 0.125 mol / L;

[0094] Add 10g of coconut shell activated carbon (particle size 1-3mm) to solution A and stir for 1 hour;

[0095] (2) Dissolve 0.8210 g of 2-methylimidazole in 4 mL of deionized water to obtain solution B;

[0096] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 12 hours, and then let it stand for 36 hours to age.

[0097] (3) Use a filter screen to separate the granular activated carbon in the liquid phase reaction system, then rinse off the unfixed particles on its surface with deionized water, then filter it, and dry it at 90°C for 6 hours to obtain impregnated activated carbon.

[0098] (4) Place the impregnated activated carbon in a tubular atmosphere furnace and calcine it under nitrogen purging. The heating rate is 10℃ / min, the calcination temperature is 900℃, and the holding time is 3h to obtain one-time calcined activated carbon.

[0099] (5) Soak the once-calcined activated carbon in 1 mol / L nitric acid at 50°C for 7 h, then wash it with deionized water until neutral, and dry it at 80°C for 12 h to obtain acid-washed once-calcined activated carbon.

[0100] (6) Dissolve 0.278g of ferrous sulfate heptahydrate in 40mL of deionized water, and add 8g of acid-washed and calcined activated carbon to the ferrous sulfate solution. Shake the solution at 250 rpm for 50min in a shaker, then separate the solid and liquid by filtration, and wash the solution with deionized water until the filtrate is colorless. Dry the solution at 80℃ for 12h to obtain iron-loaded acid-washed and calcined activated carbon.

[0101] (7) The iron-loaded acid-washed and calcined activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 5℃ / min, the calcination temperature was 700℃, and the holding time was 2h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0102] Example 5

[0103] (1) Dissolve 1.3632g of zinc chloride in 20mL of deionized water to obtain solution A, wherein the zinc ion concentration is 0.5mol / L;

[0104] Add 15g of coconut shell activated carbon (particle size 1-3mm) to solution A and stir for 1 hour;

[0105] (2) Dissolve 3.2840 g of 2-methylimidazole in 20 mL of deionized water to obtain solution B;

[0106] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 10 hours, and then let it stand for 18 hours to age.

[0107] (3) Use a filter screen to separate the granular activated carbon in the liquid phase reaction system, then rinse off the unfixed particles on its surface with deionized water, then filter it, and dry it at 80°C for 10 hours to obtain impregnated activated carbon.

[0108] (4) Place the impregnated activated carbon in a tubular atmosphere furnace and calcine it under nitrogen purging. The heating rate is 5℃ / min, the calcination temperature is 900℃, and the holding time is 2h to obtain one-time calcined activated carbon.

[0109] (5) Immerse the once-calcined activated carbon in 1 mol / L hydrochloric acid, acid wash at 100℃ for 2 h, filter, wash with deionized water until neutral, and dry at 60℃ for 24 h to obtain acid-washed once-calcined activated carbon.

[0110] (6) Dissolve 0.3674 g of ferric citrate in 80 mL of deionized water, and add 10 g of acid-washed and calcined activated carbon to the ferric citrate solution. Shake the solution at 200 rpm for 90 min in a shaker, then separate the solid and liquid by filtration, and wash with deionized water until the filtrate is colorless. Dry at 80 °C for 12 h to obtain iron-loaded acid-washed and calcined activated carbon.

[0111] (7) The iron salt impregnated once-calcined activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 5℃ / min, the calcination temperature was 550℃, and the holding time was 2.5h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0112] Example 6

[0113] (1) 1.0976 g of zinc acetate dihydrate was dissolved in 40 mL of deionized water to obtain solution A, in which the zinc ion concentration was 0.125 mol / L;

[0114] Add 20g of coconut shell activated carbon (particle size 1-3mm) to solution A and stir for 90min;

[0115] (2) Dissolve 1.6420g of 2-methylimidazole in 12mL of deionized water to obtain solution B;

[0116] Add solution B dropwise to the mixture of solution A and activated carbon, continue stirring for 24 hours, and then let it stand for 24 hours to age.

[0117] (3) The granular activated carbon in the liquid phase reaction system is separated by a filter screen, and then the unfixed particles on its surface are rinsed off with deionized water. Then it is filtered and dried at 80°C for 12 hours to obtain impregnated activated carbon.

[0118] (4) Place the impregnated activated carbon in a tubular atmosphere furnace and calcine it under nitrogen purging. The heating rate is 3℃ / min, the calcination temperature is 900℃, and the holding time is 2h to obtain one-time calcined activated carbon.

[0119] (5) Immerse the once-calcined activated carbon in 1 mol / L hydrochloric acid, acid wash at 100℃ for 90 min, filter, wash with deionized water until neutral, and dry at 80℃ for 12 h to obtain acid-washed once-calcined activated carbon.

[0120] (6) Dissolve 0.1443g of ferric nitrate nonahydrate in 35mL of deionized water, and add 5g of acid-washed and calcined activated carbon to the ferric nitrate solution. Shake the solution at 230 rpm for 90min in a shaker, then separate the solid and liquid by filtration, and wash with deionized water until the filtrate is colorless. Dry at 80℃ for 8h to obtain iron-loaded acid-washed and calcined activated carbon.

[0121] (7) The iron salt impregnated once-calcined activated carbon was placed in a tubular atmosphere furnace and calcined under nitrogen purging. The heating rate was 5℃ / min, the calcination temperature was 500℃, and the holding time was 2h to obtain particulate activated carbon catalyst material loaded with nitrogen-coordinated single-atom iron.

[0122] Application Example 1

[0123] Prepare three 35 mL aliquots of 10 mg / L Rhodamine B solution. One aliquot contains 0.0075 g of the catalyst material prepared in Example 1 and 0.015 g of PMS. The other two aliquots contain only 0.0075 g of the catalyst material prepared in Example 1 and 0.015 g of PMS, respectively. After shaking in a shaker at 200 rpm for 10 min, the supernatant is filtered through a 0.22 μm disposable syringe filter. The absorbance of the solution at 554 nm is measured using a UV-Vis spectrophotometer. The concentration of residual Rhodamine B in the solution is calculated using the Rhodamine B absorbance-concentration standard curve to determine the Rhodamine B removal rate for the three experimental batches.

[0124] Experimental results are as follows Figure 6 As shown, the catalytic material itself has certain adsorption properties and can remove 21.06% of Rhodamine B in the solution. However, PMS alone has a weak oxidation ability and only a 1.7% removal rate for Rhodamine B. When the catalytic material and PMS are used together, a removal rate of 78.71% is achieved in the same time period, which is significantly higher than the sum of the removal rates of the two when used alone. This indicates that a significant synergistic catalytic effect occurs when the two are used together.

[0125] Application Example 2

[0126] Prepare three 35 mL aliquots of 10 mg / L Rhodamine B solution. One aliquot contains 0.0075 g of the catalyst material prepared in Example 6 and 0.015 g of PMS. The other two aliquots contain only 0.0075 g of the catalyst material prepared in Example 6 and 0.015 g of PMS, respectively. After shaking in a shaker at 200 rpm for 10 min, the supernatant is filtered through a 0.22 μm disposable syringe filter. The absorbance of the solution at 554 nm is measured using a UV-Vis spectrophotometer. The concentration of residual Rhodamine B in the solution is calculated using the Rhodamine B absorbance-concentration standard curve to determine the Rhodamine B removal rate for the three experimental batches.

[0127] Experimental results are as follows Figure 7 As shown, the catalytic material itself has certain adsorption properties and can remove 27.53% of Rhodamine B in the solution. However, PMS alone has a weak oxidation ability and only a 1.7% removal rate for Rhodamine B. When the catalytic material and PMS are used together, a removal rate of 83.14% is achieved in the same time period, which is significantly higher than the sum of the removal rates of the two when used alone. This indicates that a significant synergistic catalytic effect occurs when the two are used together.

[0128] Application Example 3

[0129] The catalytic degradation performance of the catalytic material prepared in Example 1 on Rhodamine B in water was verified by continuous flow catalytic experiments, and its practical application potential was evaluated.

[0130] A schematic diagram of the experimental setup is shown below. Figure 8 As shown, the fixed-bed reactor has an inner diameter of 1.5 cm, the solid-bed reactor has a catalyst packing height of 7.5 cm, the concentration of Rhodamine B solution is 2 mg / L, the concentration of PMS solution is 1 mg / L, and the flow rate is 0.4 mL / min. Effluent samples at different time points were collected by an automatic fraction collector, and the absorbance of the solution at 554 nm was measured using a UV-Vis spectrophotometer. The Rhodamine B removal rate was calculated, and the results are shown below. Figure 9 As shown, by Figure 9 It can be seen that the degradation rate of Rhodamine B remained above 95% for nearly 12 hours of operation, indicating that the catalytic material can be applied to fixed-bed dynamic catalytic water treatment scenarios.

[0131] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0132] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a particulate activated carbon composite material supported on single-atom iron, comprising the following steps: S1. Mix zinc salt and water to obtain solution A, and impregnate activated carbon particles in solution A; S2. Mix 2-methylimidazole and water to obtain solution B. Add solution B to the mixture obtained in step S1 and react. After aging, impregnated activated carbon is obtained. S3. The impregnated activated carbon is calcined to obtain calcined activated carbon; the calcination is carried out under one or more of the following conditions: nitrogen protection, argon protection and vacuum conditions; the calcination temperature is 800~1000℃, the heating rate is 1~20℃ / min, and the time is 0.5~5h. The once-calcined activated carbon is acid-washed, then cleaned and dried to obtain acid-washed once-calcined activated carbon; the acid washing is used to dissolve and remove metallic zinc, so that the internal pores and nitrogen sites of the once-calcined impregnated activated carbon are fully exposed. S4. Impregnate the acid-washed and calcined activated carbon with an iron salt solution or a ferrous salt solution to obtain iron-loaded acid-washed and calcined activated carbon. The concentration of ferric ions in the ferric salt solution or the concentration of ferrous ions in the ferrous salt solution is 10~100 mmol / L; S5. The iron-loaded acid-washed and calcined activated carbon is calcined to obtain a granular activated carbon composite material loaded with monatomic iron. The calcination is carried out under one or more of the following conditions: nitrogen protection, argon protection, and vacuum; the calcination temperature is 500~700℃, the heating rate is 1~20℃ / min, and the time is 0.5~6h.

2. The preparation method according to claim 1, characterized in that, In step S1, the zinc salt includes one or more of zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc gluconate, and zinc lactate; and / or, the particle size of the activated carbon particles is 0.2~5 mm; and / or, the concentration of zinc ions in solution A is 0.10~2.50 mol / L; and / or, the ratio of activated carbon particles to solution A is (0.5~1.5) g: 1 mL; and / or, the impregnation time is 1~5 h.

3. The preparation method according to claim 1, characterized in that, In step S2, the molar ratio of the 2-methylimidazole to the zinc ions in the mixed system is (3~10):1; and / or, the reaction time is 2~24h; and / or, the aging time is 12~36h.

4. The preparation method according to claim 1 or 3, characterized in that, In step S2, the aging process further includes: The obtained impregnated activated carbon is washed, dehydrated, and dried; The dehydration method is vacuum filtration and / or centrifugal dehydration, and the drying method is electric heating drying and / or room temperature air drying.

5. The preparation method according to claim 1, characterized in that, In step S3, the pickling reagent is selected from hydrochloric acid, nitric acid or sulfuric acid, the pickling temperature is 10~100℃, the pickling time is 1~24h; and / or, the cleaning reagent is water.

6. The preparation method according to claim 1, characterized in that, In step S4, the iron salt includes one or more of ferric nitrate, ferric chloride, ferric sulfate, ferric ammonium sulfate, ferric citrate, and ferric ammonium citrate; the ferrous salt includes one or more of ferrous nitrate, ferrous chloride, and ferrous sulfate; and / or, the impregnation is carried out under stirring or shaking conditions, and the impregnation time is 0.5 to 2 hours.

7. The preparation method according to claim 1, characterized in that, In step S4, the impregnation process further includes washing the obtained activated carbon until the washing solution is colorless.

8. The particulate activated carbon composite material loaded with single-atom iron prepared by the preparation method according to any one of claims 1 to 7, comprising activated carbon and nitrogen-doped porous carbon loaded in the pores of activated carbon, wherein the iron atom is coordinated with the nitrogen atom in the nitrogen-doped porous carbon; wherein the nitrogen-doped porous carbon is obtained by calcination of ZIF-L.

9. The application of the particulate activated carbon composite material with single-atom iron loading prepared by any one of claims 1 to 7 or as described in claim 8 as a catalyst in the degradation of organic matter.

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