Nitrogen-doped iron monatomic modified charcoal catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nitrogen-doped iron monatomic modified biochar catalyst and a preparation method and application thereof.The preparation method of the catalyst comprises the steps that sorghum powder is soaked in an iron source solution, carboxymethyl-beta-cyclodextrin and 1-butyl-3-methylimidazolium tetrafluoroborate are added, and after stirring, centrifuging, washing and drying, the nitrogen-doped iron monatomic modified biochar catalyst is obtained; mixing and ball-milling the dried product and melamine to obtain a precursor; and then pyrolyzing and carbonizing the precursor under an anaerobic condition, cooling, grinding and sieving. The prepared catalyst has excellent performance of activating PMS to degrade organic pollutants, meanwhile, the preparation cost is low, the method is simple, and excellent tolerance and use stability are achieved.

Description

Technical Field

[0001] The present invention relates to a nitrogen-doped iron single-atom modified biochar catalyst, a preparation method thereof, and an application thereof, belonging to the technical field of environmental treatment. Background Art

[0002] Advanced oxidation processes (AOPs), also known as deep oxidation processes, are efficient pollutant treatment technologies widely used in fields such as water treatment and air purification. Compared with traditional pollutant treatment methods, AOPs have significant advantages in treating refractory organic pollutants, being able to completely mineralize pollutants into inorganic substances within a relatively short time, thereby achieving a more efficient pollutant removal effect. Therefore, AOPs are particularly suitable for treating complex pollutants and can maintain a stable degradation efficiency under relatively harsh environmental conditions.

[0003] Among many AOPs technologies, the peroxymonosulfate (PMS)-based advanced oxidation technology (PMS-AOP) has become one of the emerging sewage treatment technologies in recent years due to its high cost-effectiveness, wide applicability, and simple operation. As a strong oxidant, PMS can rapidly generate reactive free radicals with strong oxidation ability (such as ·SO 4 ·- and ·OH) under the action of a catalyst, effectively degrading organic pollutants and having good application prospects. However, the activation efficiency of PMS depends on the performance of the catalyst. How to design and prepare an efficient catalyst has become the key to improving the application effect of the PMS-AOP technology.

[0004] Currently, single-metal atom heterogeneous catalysts (SACs), as one of the most advanced PMS-AOP catalysts, have been widely studied in pollutant remediation due to their high atomic utilization rate, unique electronic properties, and low metal leaching. Especially in the application of iron-based catalysts, iron has good catalytic performance and can effectively promote the activation of PMS, thereby improving the degradation efficiency of organic pollutants. However, traditional iron-based catalysts have problems such as low atomic utilization rate and strong metal leaching, resulting in limited catalytic performance. In addition, iron-based catalysts may experience a decline in catalytic performance during long-term reactions, and the stability of the catalytic reaction is poor, affecting their actual application effect.

[0005] In contrast, due to their low cost, environmental friendliness, ease of preparation, and low metal leaching, carbon-based materials have gradually become a research hotspot for PMS-AOP catalysts. Metal-free carbon-based catalysts have certain potential in enhancing the activation efficiency of PMS. However, the catalytic activity of carbon-based materials is generally low, and their catalytic effects are often affected by the unevenness of surface structure and active site distribution, requiring further optimization, such as improving their catalytic performance through heteroatom doping, surface modification, and heat treatment. Although these optimization measures can improve the performance of carbon-based catalysts, due to the high operating costs of carbon-based materials and the limitations in enhancing catalytic efficiency, their promotion in large-scale applications is restricted.

[0006] Therefore, the existing iron-based catalysts and metal-free carbon-based materials each have certain defects and cannot separately meet the requirements of high efficiency, stability, and economy of PMS-AOP in environmental pollution treatment. To improve catalytic efficiency and reduce costs, developing a catalyst that can not only efficiently activate persulfate to rapidly degrade organic pollutants but also has good stability and scalability has become an urgent problem to be solved. Summary of the Invention

[0007] The purpose of the present invention is to provide a nitrogen-doped iron single-atom modified biochar catalyst, its preparation method, and application. This catalyst has excellent performance in activating PMS to degrade organic pollutants, while having low preparation costs, a simple method, and excellent tolerance and use stability.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A preparation method of a nitrogen-doped iron single-atom modified biochar catalyst is to soak sorghum powder in an iron source solution, then add carboxymethyl-β-cyclodextrin and 1-butyl-3-methylimidazolium tetrafluoroborate. After stirring, centrifuging, washing, and drying, take the dried product and mix it with melamine for ball milling to obtain a precursor; then pyrolyze and carbonize the precursor under anaerobic conditions, and grind and sieve it after cooling.

[0010] Preferably, the iron source solution is an aqueous solution of Fe(NO 3 ) 3 ·9H 2 O, and the concentration of Fe(NO 3 ) 3 ·9H 2 O is 0.5 - 1 mM;

[0011] The ratio of sorghum powder to the iron source solution is (3 - 10) g : (10 - 50) ml;

[0012] The addition amounts of carboxymethyl-β-cyclodextrin and 1-butyl-3-methylimidazolium tetrafluoroborate are 0.005-0.05 wt% and 0.01-0.07 wt% of the mass of the iron source solution, respectively.

[0013] Preferably, the centrifugation conditions are 5000-10000 rpm for 3-10 min.

[0014] Preferably, the drying conditions are 50-80 °C for 10-30 h.

[0015] Preferably, the mass ratio of the dried product to melamine is 1:(3-8).

[0016] Preferably, the ball milling conditions are: 300-1000 rpm for 0.5-3 h.

[0017] Preferably, the anaerobic condition means in a nitrogen or inert gas atmosphere.

[0018] Preferably, the pyrolysis carbonization conditions are: 400-1000 °C for 1-4 h, and the heating rate is 1-10 °C·min -1 。

[0019] A nitrogen-doped iron single-atom modified biochar catalyst is prepared by any of the above methods.

[0020] Application of the nitrogen-doped iron single-atom modified biochar catalyst prepared by any of the above methods in activating PMS to degrade indole in water, wherein the dosage of the nitrogen-doped iron single-atom modified biochar catalyst is 0.01-0.5 g / L, the dosage of PMS is 0.025-0.5 g / L, and the pH of the water body is 1-11.

[0021] The beneficial effects of the present invention are as follows:

[0022] Using sorghum straw rich in oxygen functional groups as the precursor raw material of biochar can efficiently participate in redox reactions during the catalytic process and improve the catalytic efficiency. At the same time, through nitrogen doping, nitrogen elements are introduced onto the surface of biochar to enhance its electron transfer ability, thereby improving the catalytic activity. By modifying with iron single atoms, through wet impregnation of iron, ball milling mixing, and high-temperature pyrolysis carbonization, the iron single atoms are evenly distributed on the surface of biochar. Introducing an ionic liquid containing an imidazole structure into the impregnation system, its cation inhibits Fe 3+ aggregation through steric hindrance effects; adding carboxymethyl-β-cyclodextrin, using its hydrophobic cavity to encapsulate Fe 3 + to form a host-guest complex, and the carboxylic acid groups form a hydrogen bond network with the hydroxyl groups on the sorghum surface to construct a three-dimensional anchoring structure, further preventing metal migration. Using the ball milling process to strengthen each component (sorghum powder, Fe 3+, the homogeneous mixing of (ionic liquid, cyclodextrin), etc., is ensured to achieve dispersibility at the microscale. And during the carbonization stage, the sorghum powder pyrolyzes to generate a porous biochar substrate, and the residual nitrogen / oxygen functional groups serve as anchoring sites. The imidazole ligand generated by the decomposition of the ionic liquid forms a planar quadrilateral coordination structure with Fe 3+ ; the cyclodextrin dehydrates to generate a conjugated aromatic skeleton, and the iron atoms are fixed through C-O-Fe bonds, ultimately forming a single-atom active center with N / O co-coordination. This can prevent the detachment of iron single atoms from the catalyst surface, solve the problem of insufficient binding degree between nitrogen-doped iron single atoms modified biochar iron and biochar, and further improve the stability and catalytic activity of the catalyst.

[0023] The prepared catalyst exhibits remarkable catalytic performance in the indole degradation experiment, superior to traditional biochar catalysts. Moreover, using agricultural waste such as sorghum straw as raw materials is low-cost and environmentally friendly, in line with the concept of green chemistry. The modified catalyst can maintain high activity in complex environments, has good long-term stability, and is suitable for industrial applications.

[0024] In summary, the nitrogen-doped iron single-atom modified biochar catalyst provided by the present invention not only has a significant performance improvement, but also has low production costs and good environmental protection characteristics, providing a new green material choice for catalytic degradation of pollutants. Brief Description of the Drawings

[0025] Figure 1 is the preparation flow chart of nitrogen-doped iron single-atom modified biochar Fe SA -N-BC;

[0026] Figure 2 is the TEM image of the prepared nitrogen-doped iron single-atom modified biochar Fe SA -N-BC;

[0027] Figure 3 is the EDS-Mapping image of the prepared nitrogen-doped iron single-atom modified biochar Fe SA -N-BC;

[0028] Figure 4 is the XRD pattern of the prepared different types of catalysts;

[0029] Figure 5 is the XPS spectrum of the prepared nitrogen-doped iron single-atom modified biochar Fe SA -N-BC (a) total spectrum; (b) C1s spectrum; (c) N1s spectrum;

[0030] Figure 6 is the effect diagram of the degradation of indole by the prepared different types of catalysts activating peroxymonosulfate;

[0031] Figure 7Pseudo-first-order kinetic plots for the degradation of indole by different types of prepared catalysts activating persulfate

[0032] Figure 8 Effect diagrams for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC at different catalyst concentrations

[0033] Figure 9 Effect diagrams for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC at different dosages of oxidant

[0034] Figure 10 Effect diagrams for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC at different pH values

[0035] Figure 11 2D and 3D interaction diagrams of the catalyst concentration and the initial pH of the solution for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC

[0036] Figure 12 2D and 3D interaction diagrams of the oxidant concentration and the initial pH of the solution for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC

[0037] Figure 13 2D and 3D interaction diagrams of the catalyst concentration and the dosage of oxidant for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SA -N-BC

[0038] Figure 14 Effect diagram (left area) and pseudo-first-order kinetic plot (right area) for the degradation of indole by the Fe SA -N-BC catalyst under the optimal operating conditions generated by Design-Expert software (where A: pH = 5.27, catalyst = 0.17 g / L, PMS = 0.26 g / L; B: pH = 5.93, catalyst = 0.1747 g / L, PMS = 0.2725 g / L; C: pH = 7.04, catalyst = 0.2501 g / L, PMS = 0.258 g / L);

[0039] Figure 15 TOC removal rate diagram for the prepared catalyst Fe SA -N-BC under the optimal operating conditions generated by Design-Expert software

[0040] Figure 16 Effect diagrams for the degradation of indole by nitrogen-doped iron single-atom modified biochar Fe SADegradation effect diagram of indole by -N-BC activating peroxymonosulfate under the interference of coexisting anions;

[0041] Figure 17 is nitrogen-doped iron single-atom modified biochar Fe SA Degradation effect diagram of indole by -N-BC catalyst activating peroxymonosulfate in different water qualities;

[0042] Figure 18 is nitrogen-doped iron single-atom modified biochar Fe SA Electron paramagnetic resonance (EPR) spectrogram of -N-BC;

[0043] Figure 19 is nitrogen-doped iron single-atom modified biochar Fe prepared in Comparative Example 4 SA 5-cycle experiment diagram of indole degradation by -N-BC0;

[0044] Figure 20 is nitrogen-doped iron single-atom modified biochar Fe SA 5-cycle experiment diagram of indole degradation by -N-BC catalyst. Detailed implementation method

[0045] Comparative Example 1

[0046] Preparation of BC, the specific steps are as follows:

[0047] Remove the surface dust and other impurities from sorghum straw, crush it into powder with a crusher, and pass through a 60-mesh sieve to obtain sorghum powder. Take 5 g of sorghum powder and place it in a tubular furnace for pyrolytic carbonization under a nitrogen atmosphere (800 °C, heating rate 5 °C·min -1 , hold for 2 h), after natural cooling, grind the obtained black carbon material thoroughly, and pass through a 100-mesh sieve to obtain biochar (BC).

[0048] Comparative Example 2

[0049] Synthesis of Fe-BC, the specific steps are as follows:

[0050] Remove the surface dust and other impurities from sorghum straw, crush it into powder with a crusher, and pass through a 60-mesh sieve to obtain sorghum powder. Soak 5 g of sorghum powder in 25 mL of 0.732 mM Fe(NO 3 ) 3 ·9H 2 O aqueous solution, place it on a magnetic stirrer and stir for 30 min to fully adsorb iron ions, then centrifuge and wash three times with ultrapure water (8000 rpm, 5 min), place it in an oven at 60 °C for drying for 20 h, and then place it in a tubular furnace for pyrolytic carbonization under a nitrogen atmosphere (800 °C, heating rate 5 °C·min -1, keep it for 2 h), after natural cooling, the obtained black carbon material was sufficiently ground and passed through a 100-mesh sieve to obtain iron-loaded biochar (Fe-BC).

[0051] Comparative Example 3

[0052] The synthesis of N-BC was carried out as follows:

[0053] The surface dust and other impurities of sorghum straw were removed, and it was crushed into powder by a crusher and passed through a 60-mesh sieve to obtain sorghum powder. 5 g of sorghum powder was mixed with 25 g of melamine and then ball-milled (480 rpm, 60 min), and then the ball-milled product was placed in a tube furnace and pyrolyzed and carbonized under a nitrogen atmosphere (800 °C, heating rate 5 °C·min -1 , keep it for 2 h), after natural cooling, nitrogen-doped biochar (N-BC) was obtained.

[0054] Comparative Example 4

[0055] Fe SA -N-BC0 was prepared as follows:

[0056] Step 1: The surface dust and other impurities of sorghum straw were removed, and it was crushed into powder by a crusher and passed through a 60-mesh sieve to obtain sorghum powder. Then 5 g of sorghum powder was soaked in 25 mL of 0.732 mM Fe(NO 3 ) 3 ·9H 2 O aqueous solution, placed on a magnetic stirrer and stirred for 30 min to fully adsorb iron ions, then centrifuged (8000 rpm, 5 min), washed 3 times with ultrapure water, and placed in an oven at 60 °C for 20 h of drying.

[0057] Step 2: 5 g of the powder obtained after drying in Step 1 was mixed with 25 g of melamine and then ball-milled (480 rpm, 60 min) for uniform mixing to obtain a precursor.

[0058] Step 3: The precursor obtained after ball-milling in Step 2 was placed in a tube furnace and subjected to high-temperature pyrolysis and carbonization under a nitrogen atmosphere (800 °C, 5 °C·min -1 , keep it for 2 h), after natural cooling, the obtained black carbon material was sufficiently ground and passed through a 100-mesh sieve to obtain iron single-atom biochar (Fe SA -N-BC0).

[0059] Example 1

[0060] Fe SA -N-BC was prepared as follows:

[0061] Step 1: Remove the surface dust and other impurities from sorghum straw, crush it into powder with a crusher, and pass through a 60-mesh sieve to obtain sorghum powder. Then soak 5 g of sorghum powder in 25 mL of 0.732 mM Fe(NO 3 ) 3 ·9H 2 O aqueous solution, add carboxymethyl-β-cyclodextrin at 0.01 wt% of the aqueous solution mass and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) ionic liquid at 0.02 wt%, stir on a magnetic stirrer for 30 min to fully adsorb iron ions, then centrifuge (8000 rpm, 5 min), wash 3 times with ultrapure water, and place in an oven at 60 °C for drying for 20 h.

[0062] Step 2: Mix 5 g of the powder obtained after drying in Step 1 with 25 g of melamine and carry out ball milling (480 rpm, 60 min) for uniform mixing to obtain a precursor.

[0063] Step 3: Place the precursor obtained after ball milling in Step 2 in a tubular furnace and carry out high-temperature pyrolytic carbonization under a nitrogen atmosphere (800 °C, heating program 5 °C·min -1 , hold for 2 h), after natural cooling, fully grind the obtained black carbon material, and pass through a 100-mesh sieve to obtain nitrogen-doped iron single-atom modified biochar (Fe SA -N-BC).

[0064] The nitrogen-doped iron single-atom modified biochar Fe SA -N-BC catalyst prepared in Example 1 above was synthesized through the synergistic effect of wet impregnation, ball milling mixing, and high-temperature pyrolytic carbonization, and the process is as Figure 1 shown. Since the sorghum powder itself has a large specific surface area, rich pore diameters, and is rich in various functional groups on the surface, and the concentration of the soluble metal salt aqueous solution is low, the soluble metal salt has a high dispersion degree on the surface of the soaked sorghum powder.

[0065] Introduce an ionic liquid containing an imidazole structure into the impregnation system, and its cation inhibits the aggregation of Fe 3+ through steric hindrance; add carboxymethyl-β-cyclodextrin, and use its hydrophobic cavity to wrap Fe 3+ to form a host-guest complex, and the carboxylic acid group forms a hydrogen bond network with the hydroxyl group on the sorghum surface to construct a three-dimensional anchoring structure to further prevent metal migration. Adopt the ball milling process to strengthen the homogenization mixing of each component (sorghum powder, Fe 3+ , ionic liquid, cyclodextrin) to ensure the dispersibility at the microscale. And in the carbonization stage, the sorghum powder pyrolyzes to generate a porous biochar substrate, and the residual nitrogen / oxygen functional groups serve as anchoring sites. The imidazole ligand generated by the decomposition of the ionic liquid coordinates with Fe 3+A planar quadrilateral coordination structure is formed; cyclodextrin is dehydrated to generate a conjugated aromatic skeleton, and iron atoms are fixed through C-O-Fe bonds, finally forming a single-atom active center with N / O co-coordination. Both B / F introduced from ionic liquids can be removed during calcination, so no extra elements are introduced.

[0066] The morphology and spatial distribution of the material were observed by transmission electron microscopy (TEM). Figure 2 The TEM image of the nitrogen-doped iron single-atom modified activated carbon catalyst (Fe SA -N-BC) prepared in Example 1 is shown. In the figure, the microscopic morphology of the sample and the spatial structure of the prepared material can be observed. It has an uneven amorphous surface, and a large number of straw wood fiber structures can be seen. Its morphology shows sheet-like folds, and no obvious iron clusters or nanoparticles exist, indicating that Fe atoms do not agglomerate during the pyrolysis synthesis process. To further analyze the elemental composition of the sample, energy-dispersive X-ray spectroscopy (EDS) analysis ( Figure 3 ) was carried out. From the total spectrum in the EDS-mapping image of the sample, it can be seen that various elemental substances are evenly distributed in the catalyst sample. Among them, C, N, and O constitute the basic skeleton, and there are foreign iron and nitrogen atoms in Fe SA -N-BC. From the above results, it can be inferred that during the pyrolysis process, the introduction of foreign nitrogen atoms successfully inhibits the aggregation of iron atoms, and Fe exists in the form of single atoms.

[0067] Figure 4 The XRD patterns of the prepared BC, Fe-BC, N-BC, and Fe SA -N-BC are shown respectively ( Figure 4 , the left region). The XRD pattern shows that the catalyst Fe SA -N-BC observes two broad diffraction peaks at 25.1° and 43.6°, which belong to the 002 crystal plane and 101 crystal plane of carbon respectively. A graphitized carbon peak appears at about 25.1°, which is attributed to the fact that the added Fe can act as a catalyst to generate graphitized carbon in the presence of carbon source conditions. The diffraction peak at 43.6°, that is, the signal of the graphite-like stacking of conjugated aromatic units, becomes significantly weaker and broader, indicating that the catalyst Fe SA -N-BC has rich structural defects. In addition, no obvious peaks corresponding to Fe nanoparticles are found ( Figure 4 , the right region), indicating that neither Fe nanoparticles nor nanoclusters are included, and Fe exists in the form of atoms.

[0068] Figure 5 The XPS spectrum of the prepared catalyst Fe SA -N-BC is shown. From the total spectrum ( Figure 5 , region a), it can be seen that the catalyst Fe SAThere are four elements, C, N, O, and Fe, in -N-BC. Since the content of Fe element is very low, the signal is weak. Figure 5 Region b in it is the catalyst Fe SA The C-1s spectrum of -N-BC. The peaks located at 284.8, 286.4, and 288.5 eV are attributed to C-C / C═C, N-C═N (sp2 hybridization), and C-N respectively. Among them, the N-C═N structure comes from the polymerization of part of melamine during the calcination process. In addition, the presence of iron carbide was not observed in the C-1s spectrum, which is consistent with the results of XRD and TEM. The high-resolution N-1s spectra of all samples are as Figure 5 shown in region c. The doped carbon materials contain three main characteristic peaks, located at 398.02 eV, 399.24 eV, and 400.64 eV, which are attributed to pyridine N, Fe-N, and pyrrole N respectively. Especially, pyrrolic-N is more obvious. The enhancement of pyrrolidine-N is positively correlated with the adsorption activity of the carbon-based catalyst, thus generating significant catalytic activity. This also makes the catalyst Fe SA -N-BC have good ability to activate PMS to degrade indole.

[0069] In the nitrogen-doped iron single-atom modified biochar obtained in Example 1, the metal single atoms combined with nitrogen and oxygen can serve as active sites to activate peroxymonosulfate to generate sulfate radicals (SO 4 ·- ), hydroxyl radicals (·OH), superoxide anions (O 2 ·- ), as well as singlet oxygen ( 1 O 2 ) and high-valent iron oxide (Fe(IV)═O), which can be used to degrade organic pollutants in the environment.

[0070] The degradation performance of indole (IND) in the application experiment

[0071] The catalysts prepared in Comparative Examples 1-4 and Example 1 were used to activate peroxymonosulfate (PMS) to degrade indole (IND). Specifically: Weigh 25 mg of the catalyst, disperse it in 100 mL of an aqueous solution containing 20 mg / L of IND, stir and adsorb for 30 min to reach the adsorption equilibrium. Then, add 0.02 g / L of potassium peroxymonosulfate. After that, take an appropriate amount of the solution with a disposable syringe at regular intervals, add 0.2 mol / l sodium sulfite solution to terminate the reaction, and filter through a 0.22 μm filter head. Use a high-performance liquid chromatograph to test the change in its peak area and then calculate the removal rate of indole.

[0072] The effect diagram of the prepared catalytic material activating PMS to degrade indole is as Figure 6 shown. The initial BC, Fe-BC, N-BC, Fe SA-N-BC and Fe SA -N-BC has a certain adsorption effect on indole, and can only adsorb 19.7%, 31.6%, 32.9%, 45.2% and 50.6% of indole respectively ( Figure 6 left area in Figure 6 ); PMS alone has a certain degradation effect on IND. After 60 min, the removal rate of indole is only 22.4% ( SA right area in SA ); when PMS is used in combination with these BC-based catalysts, the catalytic degradation effect of indole in the system is significantly improved. Different catalysts have different removal abilities for IND. The initial BC, Fe-BC, N-BC and Fe

[0073] -N-BC can only remove 40.4%, 59.3%, 70.9% and 93.7% of IND within 30 min respectively, while Fe Figure 7 -N-BC can remove 99% of IND within 10 min. SA The degradation follows pseudo-first-order kinetics as SA shown, where the rate constants (k obs ) of the BC / PMS, Fe-BC / PMS, N-BC / PMS, Fe -1 -N-BC / PMS, Fe -1 -N-BC / PMS systems are 0.0305 min -1 , 0.0821 min -1 , 0.16 min -1 , 0.39 min SA , 0.643 min SA respectively; the degradation rate of the Fe

[0074] -N-BC / PMS system for IND is 21.43, 8.04, 4.02 and 1.65 times that of BC / PMS, Fe-BC / PMS, N-BC / PMS and Fe Figure 8 and Figure 9 shown, increasing the catalyst dosage can activate more PMS to generate active substances that attack IND. As the dosage of Fe SA -N-BC increases from 0.01 g / L to 0.1 g / L ( Figure 8 ), the degradation rate of IND gradually increases. Further increasing to 0.25 g / L, the degradation rate is as high as 99%, indicating that sufficient catalyst provides sufficient or even saturated active sites for PMS. In terms of the dosage of PMS ( Figure 9 ), Fe SA- The removal rate of IND by the -N-BC / PMS system is positively correlated with the initial concentration of PMS. When the initial concentration of PMS increases from 0.025 g / L to 0.2 g / L, the removal rate of IND increases from 41% to 99%. Higher concentrations of PMS are expected to generate more reactive oxygen species, thus accelerating the oxidative degradation of IND. However, when the PMS concentration is further increased from 0.2 g / L to 0.5 g / L, the removal rate of IND does not change significantly, indicating that increasing the PMS concentration within a certain range is beneficial to promoting the activation of PMS. From the perspective of economy and efficiency, the dosages of the catalyst and oxidant are preferably 0.25 g / L and 0.2 g / L, respectively.

[0075] The prepared catalyst Fe SA -N-BC activates peroxymonosulfate to degrade indole at different pH values as Figure 10 shown. It can be observed that indole can be effectively removed within the pH range of 3 - 9, and there is no significant difference. At pH = 11, the main anionic peroxymonosulfate ion (SO 5 ·- ) is more difficult to activate than the peroxymonosulfuric acid root ion (HSO 5 ·- ), resulting in a decrease in the removal rate of indole in a strong alkaline environment. However, generally speaking, Fe SA -N-BC has a good effect on activating PMS within a wide pH range, indicating that Fe SA -N-BC has a wide pH range tolerance and great potential for practical applications.

[0076] To further optimize the degradation conditions of the Fe SA -N-BC catalyst for IND, with the initial pH of the solution (A), the dosage of the catalyst (B), and the dosage of PMS (C) as independent variables, and the degradation rate of IND as the response variable, a central composite design experiment with 3 factors and 5 levels (-α, -1, 0, +1, +α) including 20 experimental groups was designed using the RSM method based on CCD (Table 1).

[0077] Table 1 Factors, symbols, and levels of CCD design

[0078]

[0079] The individual effects and interaction effects of independent variables on the degradation of IND were analyzed through two-dimensional (2D) contour plots and three-dimensional (3D) surface plots. All two-dimensional contour plots are elliptical contour lines, indicating that there are significant interactions between independent variables. As Figure 11 shown, when the dosage of PMS is 0.2 g / L, with the increase in the dosage of Fe SA -N-BC, the degradation rate of IND gradually increases until 99%.Figure 12 shows Fe SA -N-BC dosage was fixed at 0.25 g / L, the interaction between PMS concentration and solution pH. It can be seen that with the increase of PMS concentration, the degradation rate of IND also increased. Combining Figure 11 and 12 it can be seen that when the optimal PMS concentration and Fe SA -N-BC dosage were selected, the solution pH had no significant effect on the degradation of IND, and high degradation efficiency was shown in a wide range of pH (3 - 9), indicating that the prepared catalyst had strong pH tolerance. Figure 13 Indicates that when the solution (pH = 7) was fixed, with the increase of Fe SA -N-BC dosage and PMS concentration, the degradation rate of IND gradually increased until the optimal degradation efficiency of 99% was reached.

[0080] According to the calculation of this model, when the Fe SA -N-BC dosage was 0.17 g / L, the PMS concentration was 0.26 g / L, and the solution pH was 5.27, the predicted degradation rate of Indole was 97.4%, and the actual degradation rate reached 99.13%. In addition, two groups of conditions were selected for experimental verification of the prediction results of this model. The predicted degradation rates of Indole were 97.86% (under group B conditions) and 96.58% (under group C conditions) respectively, and the actual degradation rates reached 99.21% (under group B conditions) and 99.19% (under group C conditions), indicating that this model could well predict the optimal operating conditions, as Figure 14 shown.

[0081] Under the above optimal conditions, the TOC (total organic carbon) removal rate of IND by the prepared Fe SA -N-BC catalyst was studied. After 20 min of reaction, the average TOC removal rate of the Fe SA -N-BC / PMS system (about 55.46%) was higher than that of the initial Pristine BC / PMS system (1.54%), further indicating that the Fe SA -N-BC catalyst had more excellent catalytic performance for the mineralization of IND, as Figure 15 shown.

[0082] Common inorganic anions such as Cl - , NO 3 - , HCO 3 - etc. had little effect on the activation of PMS by Fe SA -N-BC to degrade IND, and the removal rate of IND remained above 98% within 30 min, as Figure 16 shown.

[0083] In addition, the applicability of the Fe SA -N-BC / PMS system in tap water and actual water bodies was evaluated. The results showed that the removal efficiency of indole changed little in different water matrices; this indicates that Fe SA -N-BC / PMS is flexible in more complex matrices, showing great potential for treating actual wastewater with the prepared Fe SA -N-BC catalyst, as Figure 17 shown.

[0084] Using TEMP as a scavenger, electron paramagnetic resonance (EPR) measurements were carried out on the prepared Fe SA -N-BC catalyst. A strong characteristic signal peak of TEMP- 1 O 2 (1:1:1) could be observed, and 1 the characteristic signal of O 2 gradually increased with time, indicating that Fe SA -N-BC activated PMS to generate a large amount of 1 O 2 which then degraded IND, as Figure 18 shown.

[0085] The degraded catalyst material was washed and dried, and the experiment was carried out again according to the above experimental conditions using the cyclic compensation method to verify the cyclic stability of the Fe SA -N-BC catalysts prepared in Comparative Example 4 and Example 1. After five cycles, the removal rate of IND by the Fe SA -N-BC0 catalyst prepared in Comparative Example 4 was about 87%, as Figure 19 shown; however, the removal rate of IND by the Fe SA -N-BC catalyst prepared in Example 1 was about 93%, indicating that the addition of carboxymethyl-β-cyclodextrin and ionic liquid improved the binding strength between iron and biochar, enhancing the stability and catalytic efficiency of the catalyst, as Figure 20 shown.

[0086] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped iron single atom modified biochar catalyst, characterized in that: The method comprises the steps of soaking sorghum powder in an iron source solution, adding carboxymethyl-β-cyclodextrin and 1-butyl-3-methylimidazolium tetrafluoroborate, stirring, centrifuging, washing and drying, mixing the dried product with melamine and ball milling to obtain a precursor; then pyrolyzing and carbonizing the precursor under anaerobic conditions, cooling the precursor, grinding and sieving the precursor.

2. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The iron source solution is an aqueous solution of Fe(NO3)3·9H2O, and the concentration of Fe(NO3)3·9H2O is 0.5-1mM; The ratio of sorghum powder to iron source solution is (3-10) g: (10-50) ml; The added amounts of carboxymethyl-β-cyclodextrin and 1-butyl-3-methylimidazolium tetrafluoroborate are 0.005-0.05wt% and 0.01-0.07wt% of the mass of the iron source solution respectively.

3. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The centrifugal conditions are 5000-10000 rpm, 3-10 min.

4. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The drying conditions are 50-80°C, 10-30h.

5. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The mass ratio of the dried product to melamine is 1:(3-8).

6. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The ball milling conditions are: 300-1000rpm, 0.5-3h.

7. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: Anaerobic conditions refer to conditions under nitrogen or inert gas atmosphere.

8. The method for preparing the nitrogen-doped iron single atom modified biochar catalyst according to claim 1, characterized in that: The conditions for pyrolysis carbonization are: 400-1000℃, 1-4h, heating rate 1-10℃·min -1 .

9. A nitrogen-doped iron single atom modified biochar catalyst, characterized in that: The method is prepared by any one of claims 1 to 8.

10. Application of the nitrogen-doped iron single atom modified biochar catalyst prepared by the method according to any one of claims 1 to 8 in activating PMS to degrade indole in water, characterized in that: The dosage of nitrogen-doped iron single atom modified biochar catalyst is 0.01-0.5 g / L, the dosage of PMS is 0.025-0.5 g / L, and the pH of the water is 1-11.

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