Sludge-based single-atom catalyst supported on activated carbon and preparation method and application thereof

Abstract

The application discloses a sludge-based activated carbon loaded monatomic catalyst, a preparation method thereof and application thereof in activating peracetic acid to degrade organic pollutants in water. The catalyst comprises a nitrogen-doped sludge activated carbon porous carrier in a graphene appearance and Fe monatomic atoms loaded on the nitrogen-doped sludge activated carbon porous carrier, wherein the Fe monatomic atoms have 2Fe-N4 and Fe2N6 double coordination structures. The preparation method comprises the following steps: S1, after wastewater sludge is dried, crushed, sieved, mixed with a ZnCl2 solution, and then solid-liquid separation is performed to obtain the solid, the solid is dried, first pyrolysis is performed in an inert atmosphere, acid washing purification is performed, and water washing is performed, a sludge-based porous activated carbon is obtained; S2, the sludge-based porous activated carbon, melamine and Fe(NO3)3.9H2O are uniformly mixed in a solvent, and then dried to obtain a precursor solid; and S3, the precursor solid is subjected to second pyrolysis in an inert atmosphere, acid etching, water washing and drying.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment and disposal technology, specifically to a method for preparing a high-performance single-atom catalyst by recycling sewage sludge and its application in advanced oxidation. Background Technology

[0002] With the acceleration of urbanization and the continuous increase in demand for domestic sewage treatment, the construction scale of municipal sewage treatment plants has been expanding. While improving sewage treatment capacity is crucial for ensuring water environment safety, the resulting large amount of sludge has become a key factor restricting the sustainable development of the industry. The massive sludge production brings significant environmental pressure and economic burden during collection, treatment, and final disposal. Currently, sludge treatment and disposal technologies mainly include chemical treatment, thermal treatment, and biological treatment. Although these methods have achieved sludge reduction or harmlessness to some extent, their practical application is often constrained by high energy consumption, high operating costs, and the potential for secondary pollution (such as incomplete solidification of heavy metals and greenhouse gas emissions). Therefore, the development of low-energy, low-cost sludge resource recovery technologies that can achieve high added value is receiving increasing attention.

[0003] Among numerous resource recovery pathways, converting sludge into advanced catalytic materials is a highly promising strategy. Single-atom catalysts refer to a class of supported metal catalysts in which the active metal component is stably dispersed on a support in the form of isolated single atoms. Their microstructure is characterized by the anchoring of the metal single atom to heteroatoms on the support surface, with no aggregation or metal-metal interactions between the metal atoms. Compared to traditional catalysts, single-atom catalysts offer the following advantages: 100% metal atom utilization; highly uniform and well-defined active sites; single and spatially separated active centers effectively suppress side reactions, thus exhibiting excellent catalytic selectivity; and their coordination environment can be precisely controlled through material design to meet the catalytic requirements of specific reactions.

[0004] Wastewater sludge is rich in carbon, making it an excellent carrier for anchoring transition metals. Therefore, recycling and transforming wastewater sludge into single-atom catalysts can not only effectively solve the problems of difficult and costly sludge disposal, turning waste into treasure, but also produce high-value-added functional materials for environmental remediation (such as the degradation of water pollutants), which is in line with the concepts of circular economy and sustainable development.

[0005] The following existing technologies were found through a search:

[0006] The patent specification with publication number CN114349296A discloses a comprehensive recycling method for Fenton iron sludge, comprising the following steps: thoroughly mixing Fenton iron sludge with a carbon source, a nitrogen source, and a template agent, and then grinding the mixture to obtain a powder; calcining the powder mixture under a protective atmosphere at a calcination temperature of 750~900℃ to obtain calcined powder; and subjecting the calcined powder to magnetic separation, wherein the magnetic portion is acid-washed and centrifuged, and the supernatant is rich in Fe. 3+ The solution is an acidic solution, with the lower insoluble layer being a nitrogen-doped carbon-supported Fe single-atom catalyst, FeSAC / NC. The carbon source can be organic sludge, the nitrogen source can be melamine, and the template agent includes at least one of NaCl, Na₂SO₄, and Na₂CO₃. This patented technology utilizes the nitrogen-doped carbon-supported Fe single-atom catalyst, FeSAC / NC, as a coal combustion catalyst. Summary of the Invention

[0007] This invention provides a sludge-based activated carbon-supported single-atom catalyst, its preparation method, and its application, which can solve the problems of low utilization rate of existing sludge resources and limited activity of traditional catalysts in advanced oxidation technologies. This invention is the first to construct a sludge-based activated carbon-supported single-atom catalyst with both 2Fe-N4 and Fe2N6 dual-coordination structures. This dual-coordination structure, by changing the electronic spin state and electron cloud density of the Fe center, synergistically regulates the electronic structure of the catalytic center, thereby improving the activation efficiency of peracetic acid (PAA), achieving high-value conversion of sludge resources, and significantly enhancing the degradation performance of recalcitrant organic pollutants.

[0008] The specific technical solution is as follows:

[0009] In a first aspect, the present invention provides a sludge-based activated carbon supported single-atom catalyst, comprising a nitrogen-doped sludge activated carbon porous support in the form of graphene and Fe single atoms supported on the nitrogen-doped sludge activated carbon porous support, wherein the Fe single atoms have a 2Fe-N4 and Fe2N6 dual coordination structure.

[0010] In a second aspect, the present invention provides a method for preparing the sludge-based activated carbon supported single-atom catalyst described in the first aspect, comprising the steps of:

[0011] S1, wastewater sludge is dried, crushed and sieved and then mixed with ZnCl2 solution; then solid-liquid separation is performed to obtain solid dried, first pyrolysis under inert atmosphere, acid washing purification, and water washing to obtain sludge-based porous activated carbon;

[0012] S2, sludge-based porous activated carbon, melamine and Fe(NO3)3·9H2O are mixed in a solvent and then dried to obtain a precursor solid; the mass ratio of melamine, sludge-based porous activated carbon and Fe(NO3)3·9H2O is 10:10:(0.5~1); the solvent includes methanol and / or ethanol;

[0013] S3, the precursor solid is subjected to a second pyrolysis under an inert atmosphere, followed by acid etching, water washing, and drying to obtain the sludge-based activated carbon supported single-atom catalyst.

[0014] This invention first uses dewatered sludge as raw material, chemically activates it with ZnCl2, and then performs high-temperature pyrolysis and acid washing to obtain sludge-based porous activated carbon. Subsequently, the sludge-based porous activated carbon is mixed with melamine and Fe(NO3)3·9H2O in methanol and / or ethanol, and subjected to secondary high-temperature pyrolysis and acid etching under an inert atmosphere to obtain a sludge-based activated carbon-supported single-atom catalyst with a 2Fe-N4 and Fe2N6 dual-coordination structure. This dual-coordination catalyst can efficiently activate peracetic acid to degrade organic pollutants in water, and exhibits excellent stability and high oxidant utilization. The preparation method of this invention is simple, and it realizes the waste-to-waste treatment and high-value utilization of sludge waste, providing an economical and efficient approach for sustainable water treatment.

[0015] In step S1, the wastewater sludge can be sludge produced by a regular municipal wastewater treatment plant, without any special restrictions, and it can come from different process units of the wastewater treatment plant.

[0016] Furthermore, in step S1, the drying temperature is 100~105℃.

[0017] Furthermore, in step S1, the sieving refers to passing through a 200-300 mesh sieve.

[0018] In step S1, ZnCl2 not only acts as a pore-forming agent, melting at high temperatures to form micropores and mesopore networks within the carbon matrix, but also functions as a dewatering agent, allowing H and O to escape as H2O during sludge carbonization, thus retaining more carbon skeleton. A suitable mass ratio significantly affects the pore formation of sludge-based porous activated carbon; too low a ratio results in insignificant pore-forming effects, while too high a ratio leads to pore wall collapse and reduced specific surface area. In step S1, the preferred mass ratio of sludge dry weight to ZnCl2 is 1:(1~6), for example, 1:2, 1:4, etc.

[0019] In step S1, the temperature of the first pyrolysis also has a significant impact on the formation of pores. If the temperature is too low, it is difficult for porous carbon structures to form, while if the temperature is too high, it will easily lead to the collapse of the carbon framework. In step S1, the preferred temperature for the first pyrolysis is 500~800℃, such as 600℃, 700℃, etc.

[0020] Furthermore, in step S1, the first pyrolysis takes 1 hour.

[0021] In step S1, due to the large amount of inorganic ash in the sludge, conventional acid washing is insufficient to remove the SiO2 encapsulated by the carbon layer. Hydrofluoric acid can completely dissolve the silicate framework, thereby releasing the blocked pores, significantly increasing the specific surface area, and providing abundant anchor sites for subsequent Fe atom loading. In step S1, the acid used for acid washing purification is preferably a mixed solution of hydrochloric acid and hydrofluoric acid. Further, the acid washing purification specifically includes: ultrasonic treatment of the material after the first pyrolysis with a mixed solution of hydrochloric acid and hydrofluoric acid, wherein, even further, the concentrations of hydrochloric acid and hydrofluoric acid are independently 1~3 mol / L, and the ultrasonic treatment time is 3 hours.

[0022] In step S2, the addition of sludge-based porous activated carbon and melamine in equal mass ratios can form a higher proportion of graphite nitrogen, which is beneficial to the formation of the Fe-N coordination structure. The amount of Fe(NO3)3·9H2O added is a key factor in the formation of a dual-coordinate Fe single-atom catalyst. If the amount added is too low, Fe will exist in the catalyst in a single-coordinate form; if the amount added is too high, it is very easy to agglomerate and form iron oxide particles, destroying the single-atom coordination structure and leading to a decrease in catalytic performance. Therefore, in step S2, the mass ratio of melamine, sludge-based porous activated carbon and Fe(NO3)3·9H2O is 10:10:(0.5~1), for example, 10:10:0.75.

[0023] Furthermore, in step S3, the temperature of the second pyrolysis is 700~900℃, for example, 800℃.

[0024] Furthermore, in step S3, the second pyrolysis takes 1 to 3 hours, for example, 2 hours.

[0025] In this invention, the inert atmosphere refers to a gaseous atmosphere that does not participate in the reaction.

[0026] In step S3, acid etching can remove non-single-atom Fe species that are not embedded in the coordination structure.

[0027] Furthermore, in step S3, the acid solution is hydrochloric acid or sulfuric acid.

[0028] Furthermore, in step S3, the acid concentration in the acid solution is 1~3 mol / L.

[0029] Thirdly, the present invention provides the application of the sludge-based activated carbon supported single-atom catalyst described in the first aspect for activating peracetic acid in water to degrade organic pollutants.

[0030] Furthermore, the concentration of the sludge-based activated carbon-supported single-atom catalyst in water is 0.05~0.2 g / L, for example, 0.15 g / L.

[0031] Furthermore, the concentration of the peracetic acid in water is 0.2~0.8 mmol / L, for example 0.6 mmol / L.

[0032] Furthermore, the organic pollutants include one or more of phenol, bisphenol A, 4-chlorophenol, sulfamethoxazole, ofloxacin, norfloxacin, methylene blue, and rhodamine B.

[0033] Compared with the prior art, the beneficial effects of this invention are as follows:

[0034] 1. This invention is the first to construct a stable 2Fe-N4 and Fe2N6 dual coordination structure in a sludge-based activated carbon system, which solves the problems of single iron sites, easy aggregation, and limited activity in traditional sludge-based iron single-atom catalysts.

[0035] 2. This invention overcomes the limitation of traditional single-atom catalysts having a single coordination environment, successfully constructing a 2Fe-N4 and Fe2N6 dual-coordination structure on a sludge-based activated carbon support. Compared to single Fe-N coordination, this unique dual-coordination configuration has superior electronic structure and thermodynamic properties, effectively regulating the electron cloud density of the central metal atom and significantly reducing the energy barrier for peracetic acid activation, thus exhibiting excellent oxidation capacity in catalytic reactions.

[0036] 3. The catalyst prepared in this invention exhibits an extremely high catalytic reaction rate. Experiments show that in the PAA system, this catalyst can achieve near-complete removal of phenol (100%) within 2 minutes, and the reaction rate constant is more than 30 times higher than that of ordinary nitrogen-doped carbon materials. Simultaneously, this catalyst has extremely high PAA utilization (>86%), effectively reducing the amount of oxidant added and lowering the operating cost of water treatment.

[0037] 4. This invention transforms residual sludge into a high-performance carrier with a rich microporous structure through chemical activation and high-temperature pyrolysis. This strategy not only solves the environmental pollution and public health risks caused by sludge and significantly reduces the preparation cost of single-atom catalyst carriers, but also achieves waste-to-waste treatment, which is in line with the concepts of circular economy and sustainable development.

[0038] 5. In this invention, the degree of graphitization and defect structure of the material can be optimized by controlling the pyrolysis temperature, thereby further improving the electron transport capacity and the exposure of reactive sites, providing an effective way to regulate the performance of the catalyst. Attached Figure Description

[0039] Figure 1 This is a high-resolution transmission electron microscope (TEM) image of the sludge-based activated carbon-supported single-atom catalyst prepared in Example 1 of the present invention.

[0040] Figure 2This is a high-angle annular dark-field imaging (HAADF) elemental mapping diagram of the sludge-based activated carbon supported single-atom catalyst prepared in Example 1 of the present invention.

[0041] Figure 3 This is an X-ray diffraction (XRD) pattern of the sludge-based activated carbon-supported single-atom catalyst prepared in Example 1 of the present invention.

[0042] Figure 4 This is a high-angle dark-field annular scanning transmission electron microscope image of the sludge-based activated carbon supported single-atom catalyst prepared in Example 1 of the present invention.

[0043] Figure 5 This is a diagram showing the actual distance and theoretical model of the 2Fe-N4 coordination structure of the sludge-based activated carbon supported single-atom catalyst prepared in Example 1 of this invention.

[0044] Figure 6 This is a diagram showing the actual distance and theoretical model of the Fe2N6 coordination structure of the sludge-based activated carbon supported single-atom catalyst prepared in Example 1 of this invention.

[0045] Figure 7 The k of the sludge-based activated carbon supported single-atom catalyst prepared in Example 1 of this invention is... 2 Weighted Fourier transform extended fine structure diagram of X-ray absorption.

[0046] Figure 8 This is a graph showing the effect of sludge-based activated carbon supported on single-atom catalyst catalytic activation of peracetic acid degradation of phenol in Example 2 of the present invention. The vertical axis of the graph is C. t / C0 represents the ratio of the phenol concentration at detection time t to the initial phenol concentration.

[0047] Figure 9 This is a performance comparison chart of the sludge-based activated carbon supported single-atom catalyst SBAC-SAC-900 in Example 2 of the present invention with other reported Fenton-like catalysts. The vertical axis K_value in the figure represents the Fenton-like reaction rate score.

[0048] Figure 10 This is a graph showing the effect of the sludge-based activated carbon-supported single-atom catalyst on the catalytic activation of peracetic acid degradation of phenol under different pH conditions in Example 3 of the present invention. The vertical axis in the graph is C. t / C0 represents the ratio of the phenol concentration at detection time t to the initial phenol concentration.

[0049] Figure 11 This is a graph showing the effect of a sludge-based activated carbon-supported single-atom catalyst on phenol removal in the presence of common anions in Example 3 of this invention. The vertical axis in the graph is C. t / C0 represents the ratio of the phenol concentration at detection time t to the initial phenol concentration.

[0050] Figure 12 This is a graph showing the effect of the sludge-based activated carbon-supported single-atom catalyst on the removal efficiency of phenol in ultrapure water, tap water, and river water in Example 3 of the present invention.

[0051] Figure 13 This is a graph showing the recycling performance of the sludge-based activated carbon-supported single-atom catalyst in Example 4 of the present invention. The vertical axis in the graph is C. t / C0 represents the ratio of the phenol concentration at detection time t to the initial phenol concentration. Detailed Implementation

[0052] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the raw materials used in the embodiments are commercially available products.

[0053] Example 1:

[0054] The preparation of single-atom materials supported on sludge-based activated carbon includes the following steps:

[0055] (1) Wastewater sludge from a sewage treatment plant was collected and dried at 105℃ for 24h. The dried sludge was ground into powder and sieved through a 200-mesh sieve. The obtained sludge powder was mixed with ZnCl2 solution at a mass ratio of 1:4 and stirred at room temperature for 24h. The supernatant was filtered and the bottom sludge was dried at 105℃ for 24h. The dried powder was placed in a tube furnace and pyrolyzed at 600℃ for 1h at a heating rate of 10℃ / min under argon atmosphere protection. After cooling to room temperature, the obtained material was ultrasonically treated in a mixed solution of 3 mol / L hydrochloric acid and 3 mol / L hydrofluoric acid for 3h, washed with deionized water until pH=7, and dried to obtain sludge-based porous activated carbon (SBAC).

[0056] (2) 2g of melamine, 2g of the sludge-based porous activated carbon prepared above, and 0.2g of Fe(NO3)3·9H2O were dispersed in 100 mL of methanol and stirred at room temperature for 12 h. The resulting solution was dried at 105 °C to constant weight. The solution was placed in a tube furnace and heated to 900 °C for 3 h under argon atmosphere protection at a heating rate of 5 °C / min. After cooling to room temperature, the resulting powder was etched with 1 mol / L hydrochloric acid for 3 h. Finally, the powder was washed with distilled water until pH=7.0 and dried at 105 °C to obtain the sludge-based activated carbon supported single-atom catalyst, denoted as SBAC-SAC-900.

[0057] Referring to steps (1) to (2) above, only the pyrolysis temperature in step (2) is changed to 700℃ or 800℃, and the corresponding sludge-based activated carbon supported single-atom catalysts are labeled as SBAC-SAC-700 or SBAC-SAC-800 respectively.

[0058] Referring to steps (1) to (2) above, the only difference is that Fe(NO3)3·9H2O is not added, resulting in nitrogen-doped sludge-based porous activated carbon (SBAC-N).

[0059] Depend on Figure 1 , Figure 2 It can be seen that the sludge-based activated carbon-supported single-atom catalyst SBAC-SAC-900 exhibits a typical graphene morphology, and no iron metal clusters were observed, suggesting that iron atoms mainly exist in the form of discrete iron atoms in the material. Simultaneously, the elemental mapping diagram shows that C, N, and Fe are uniformly distributed in the material, further indicating that the material is a CN-Fe coordination structure single-atom catalyst. Figure 3 It can be seen that no peak of elemental iron was found in the single-atom catalyst supported on sludge-based activated carbon. Figure 4 This is a high-angle dark-field annular scanning transmission electron microscope (STEM) image of the SBAC-SAC-900 obtained in Example 1 of this invention. The bright spots in the image are metal atomic points, which visually demonstrates that iron exists in the material in the form of single atoms. However, it can be seen that not all iron atoms are isolated Fe-N4 coordination results; some iron atoms are adjacent to each other. Figure 5 , Figure 6 The actual distance and theoretical model of the coordination structure 2Fe-N4 and Fe2N6 of adjacent Fe atoms in SBAC-SAC-900 prepared in Example 1 of this invention are shown. The Fe-Fe distance in region I is 0.396 nm, which is close to the theoretical Fe-Fe spacing (4.05 Å) of the 2Fe-N4 configuration. The Fe-Fe distance measured in region II is 0.232 nm, which is consistent with the theoretical Fe-Fe spacing (2.53 Å) of the Fe2N6 configuration. Therefore, the material has a dual coordination structure of 2Fe-N4 and Fe2N6. Figure 7 The k of SBAC-SAC-900 prepared in Example 1 of this invention 2 Weighted Fourier transform extended X-ray absorption fine structure diagrams (FTFTs) and fitting results confirmed the absence of Fe-Fe bonds in the synthesized sludge-based activated carbon-supported single-atom catalyst. This further demonstrated that Fe exists as a single atom, successfully synthesizing a sludge-based activated carbon-supported single-atom catalyst and upgrading waste sludge into a high-performance single-atom catalyst. Density functional theory (DFT) calculations showed that the 2Fe-N4 and Fe2N6 dual-coordination structure of this invention exhibits stronger adsorption energy and a lower reaction energy barrier when activating PAA compared to the single-coordination structure, making catalytic reactions more likely.

[0060] Example 2:

[0061] Application of sludge-based activated carbon-supported single-atom materials in the catalytic activation of peracetic acid for the degradation of organic pollutants (pH=7):

[0062] Add 0.15 g / L of the sludge-based activated carbon-supported single-atom catalyst SBAC-SAC-700, SBAC-SAC-800, or SBAC-SAC-900 obtained in Example 1 to 50 mL of a phenol solution with a concentration of 20 mg / L. Stir at 500 rpm for 30 min to establish pollutant adsorption-desorption equilibrium. Then add 0.6 mmol / L of peracetic acid solution to the solution, maintaining the stirring speed at 500 rpm. Start timing. At 0 min, 30 s, 1 min, 2 min, 3 min, 4 min, and 5 min, respectively, take an appropriate amount of solution with a syringe, filter it through a 0.22 μm filter, and add it to a 2 mL liquid chromatography sample vial containing 30 μL of Na2S2O3. Finally, measure the above sample by liquid chromatography, record the corresponding peak area, convert it to phenol concentration according to the standard curve, and calculate the phenol degradation rate.

[0063] Referring to the above application process, without adding a catalyst, it is recorded as the PAA-only group.

[0064] Following the above application process, without adding a catalyst, the peracetic acid solution was replaced with 30wt% hydrogen peroxide, and the dosage was 0.6 mmol / L H2O2 concentration, which was recorded as the H2O2-only group.

[0065] Following the above application process, SBAC-SAC-900 was added at a dosage of 0.15 g / L, and the peracetic acid solution was replaced with 30 wt% hydrogen peroxide at a dosage of 0.6 mmol / L H2O2 concentration. This group was designated as the H2O2+SBAC-SAC group.

[0066] Referring to the above application process, the sludge-based porous activated carbon (SBAC) obtained in step (1) of Example 1 was used to replace the sludge-based activated carbon supported single-atom catalyst. The dosage was 0.15 g / L, and it was designated as SBAC group.

[0067] Referring to the above application process, nitrogen-doped sludge-based porous activated carbon (SBAC-N) obtained in Example 1 was used to replace the sludge-based activated carbon supported on the single-atom catalyst. The dosage was 0.15 g / L, and it was designated as the SBAC-N group.

[0068] Depend on Figure 8It can be seen that the addition of PAA and H2O2 alone has a negligible effect on the degradation of phenol. Notably, SBAC-SAC-900 exhibits excellent catalytic performance at pH 7, achieving 100% removal of 20 mg / L phenol within 3 minutes. This is attributed to the dual-coordination structure 2Fe-N4 and Fe2N6 significantly improving the electronic configuration of the activated carbon in the sludge, thereby enhancing the material's catalytic activity. Meanwhile, due to… Figure 9 It can be seen that, compared with the Fenton-like catalysts reported so far, the sludge-based activated carbon single-atom catalyst SBAC-SAC-900 prepared in Example 1 of this invention exhibits the best performance in Fenton-like reactions.

[0069] Example 3:

[0070] The effect of sludge-based activated carbon-supported single-atom catalysts on phenol removal efficiency under different influencing factors:

[0071] 1) The effect of a single-atom catalyst supported on sludge-based activated carbon on the degradation of phenol by peracetic acid under different pH conditions was investigated by adjusting the initial pH of the phenol solution with sulfuric acid and sodium hydroxide. Different concentrations of 0.5 mol / L sulfuric acid or 0.5 mol / L sodium hydroxide solution were added to 50 mL of a 20 mg / L phenol solution to adjust the pH to 3, 5, 7, 9, and 11. Then, 0.15 g / L of SBAC-SAC-900 obtained in Example 1 was added, and the mixture was stirred at 500 rpm for 30 min to establish adsorption-desorption equilibrium. Subsequently, 0.6 mmol / L of peracetic acid solution was added to the solution, and the stirring speed was maintained at 500 rpm. Timing was then started. At 0 min, 30 s, 1 min, 2 min, 3 min, 4 min, and 5 min, appropriate amounts of solution were taken using a syringe, filtered through a 0.22 μm filter, and added to a 2 mL liquid chromatography vial containing 30 μL of Na₂S₂O₃. Finally, the samples were measured using liquid chromatography, and the corresponding peak areas were recorded and converted to phenol concentration according to the standard curve to calculate the phenol degradation rate. Figure 10 The figure shows the effect of SBAC-SAC-900 on catalytic activation of peracetic acid to degrade phenol under different pH conditions. It can be seen that the material has a very wide pH adaptation range and can achieve 100% removal of 20 mg / L phenol within 5 min.

[0072] 2) To a 50 mL solution of phenol with a concentration of 20 mg / L, add 10 mmol / L sodium chloride, 10 mmol / L sodium bicarbonate, 10 mmol / L sodium sulfate, 10 mmol / L sodium dihydrogen phosphate, and 10 mg / L humic acid (HA), respectively. Then add 0.15 g / L of SBAC-SAC-900 obtained in Example 1. Stir at 500 rpm for 30 min to establish pollutant adsorption-desorption equilibrium. Subsequently, add 0.6 mmol / L of peracetic acid solution to the solution, maintaining the stirring speed at 500 rpm, and start timing. At 0 min, 30 s, 1 min, 2 min, 3 min, 4 min, and 5 min, appropriate amounts of solution were taken using a syringe, filtered through a 0.22 μm filter, and added to a 2 mL liquid chromatography vial containing 30 μL of Na₂S₂O₃. Finally, the samples were measured using liquid chromatography, and the corresponding peak areas were recorded and converted to phenol concentration according to the standard curve to calculate the phenol degradation rate. Figure 11 The figure shown is a graph illustrating the effect of SBAC-SAC-900 prepared in Example 1 of this invention on the removal effect of phenol in the presence of common anions. It can be seen that the sludge-based activated carbon supported single-atom catalyst of this invention has a strong ability to resist anion interference.

[0073] 3) The solvent (ultrapure water) in a 50 mL solution of 20 mg / L phenol was replaced with tap water and river water, respectively. Then, 0.15 g / L of SBAC-SAC-900 (obtained in Example 1) was added, and the mixture was stirred at 500 rpm for 30 min to establish adsorption-desorption equilibrium. Subsequently, 0.6 mmol / L of peracetic acid solution was added to the solution, and stirring was maintained at 500 rpm. Timing was started. At 0 min, 30 s, 1 min, 2 min, 3 min, 4 min, and 5 min, appropriate amounts of solution were taken using a syringe, filtered through a 0.22 μm filter, and added to a 2 mL liquid chromatography vial containing 30 μL of Na₂S₂O₃. Finally, the samples were measured using liquid chromatography, the corresponding peak areas were recorded, and the concentration was converted to phenol concentration according to the standard curve to calculate the phenol degradation rate. Figure 12 The figure shown is a graph illustrating the effect of SBAC-SAC-900 prepared in Example 1 of this invention on the removal of phenol in ultrapure water, tap water, and river water. It can be seen that the sludge-based activated carbon supported single-atom catalyst of this invention can be adapted to the removal of organic pollutants in natural water bodies and has broad application value.

[0074] Example 4:

[0075] Performance evaluation of sludge-based activated carbon-supported single-atom catalyst for recycling:

[0076] Add 0.15 g / L of SBAC-SAC-900 obtained in Example 1 to 50 mL of a phenol solution with a concentration of 20 mg / L. Stir at 500 rpm for 30 min to establish pollutant adsorption-desorption equilibrium. Then add 0.6 mmol / L of peracetic acid solution to the solution, maintaining the stirring speed at 500 rpm. Start timing. At 0 min, 30 s, 1 min, 2 min, 3 min, 4 min, and 5 min, respectively, take appropriate amounts of solution with a syringe, filter through a 0.22 μm filter, and add them to a 2 mL liquid chromatography sample vial containing 30 μL of Na2S2O3. Finally, measure the above sample by liquid chromatography, record the corresponding peak areas, convert them to phenol concentration according to the standard curve, and calculate the phenol degradation rate. After the catalytic reaction is completed, wash the material with ethanol and ultrapure water under vacuum filtration, and then dry it at 105 °C to constant weight. Continue to follow the above phenol degradation test operation procedure. Repeat the above steps 5 times. Figure 13 The diagram shows the recycling performance of SBAC-SAC-900 prepared in Example 1 of this invention. It can be seen that after the sludge-based activated carbon supported on the single-atom catalyst is recycled six times, the degradation efficiency of phenol can still reach more than 90%, which shows excellent stability.

[0077] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A sludge-based activated carbon supported single-atom catalyst, characterized in that, It includes a nitrogen-doped sludge activated carbon porous carrier with a graphene appearance and Fe single atoms loaded on the nitrogen-doped sludge activated carbon porous carrier, wherein the Fe single atoms have a 2Fe-N4 and Fe2N6 dual coordination structure.

2. The method for preparing a sludge-based activated carbon-supported single-atom catalyst according to claim 1, characterized in that, Including the following steps: S1, wastewater sludge is dried, crushed and sieved and then mixed with ZnCl2 solution; then solid-liquid separation is performed to obtain solid dried, first pyrolysis under inert atmosphere, acid washing purification, and water washing to obtain sludge-based porous activated carbon; S2, sludge-based porous activated carbon, melamine and Fe(NO3)3·9H2O are mixed in a solvent and then dried to obtain a precursor solid; the mass ratio of melamine, sludge-based porous activated carbon and Fe(NO3)3·9H2O is 10:10:(0.5~1); the solvent includes methanol and / or ethanol; S3, the precursor solid is subjected to a second pyrolysis under an inert atmosphere, followed by acid etching, water washing, and drying to obtain the sludge-based activated carbon supported single-atom catalyst.

3. The preparation method according to claim 2, characterized in that, In step S1: The drying temperature is 100~105℃; The sieving refers to passing through a 200-300 mesh sieve; The mass ratio of sludge dry weight to ZnCl2 is 1:(1~6); The temperature of the first pyrolysis is 500~800℃; The first pyrolysis lasted for 1 hour. The acid used for the acid washing and purification is a mixed solution of hydrochloric acid and hydrofluoric acid; The acid washing and purification specifically includes: ultrasonic treatment of the material after the first pyrolysis with a mixed solution of hydrochloric acid and hydrofluoric acid, wherein the concentrations of hydrochloric acid and hydrofluoric acid are independently 1~3 mol / L, and the ultrasonic treatment time is 3 hours.

4. The preparation method according to claim 2, characterized in that, In step S3: The temperature of the second pyrolysis is 700~900℃; The second pyrolysis takes 1-3 hours; The acid solution is hydrochloric acid or sulfuric acid; The acid concentration in the acid solution is 1~3 mol / L.

5. The application of the sludge-based activated carbon supported single-atom catalyst according to claim 1 for activating peracetic acid in water to degrade organic pollutants.

6. The application according to claim 5, characterized in that, The concentration of the sludge-based activated carbon-supported single-atom catalyst in water is 0.05~0.2 g / L.

7. The application according to claim 5, characterized in that, The concentration of peracetic acid in water is 0.2~0.8 mmol / L.

8. The application according to claim 5, characterized in that, The organic pollutants include one or more of the following: phenol, bisphenol A, 4-chlorophenol, sulfamethoxazole, ofloxacin, norfloxacin, methylene blue, and rhodamine B.

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