Single-atom iron catalyst for degrading organic pollutants by persulfate method, its preparation and application

Abstract

The present invention discloses a single-atom iron catalyst for degrading organic pollutants by the persulfate method. The single-atom iron catalyst is a modified wool protein carbon-supported asymmetric coordination single-atom iron catalyst, which is prepared by dissolving a wool protein solution pretreated by reduction-formic acid method, modifying it with lipoic acid, complexing iron ions, and finally freeze-drying, high-temperature calcination, and pickling. The obtained single-atom iron catalyst has the advantages of high activity, high stability, low cost, and simple operation. It is applied to the reaction of catalytically activating persulfate to degrade organic pollutants, can break the Fe<supgt;3+< / supgt; / Fe<supgt;2+< / supgt; cycle rate limitation existing in the existing iron ion activation process, thereby showing excellent adsorption and catalytic efficiency, and the activation process does not require pH environmental limitation, has good cycle stability, and significantly promotes the application of the persulfate-based advanced oxidation process in wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a single-atom iron catalyst for degrading organic pollutants by the persulfate method, and the preparation and application of the catalyst. Background Art

[0002] Advanced oxidation processes (AOPs) are typical and effective methods for treating refractory organic pollutants in wastewater. They use strong oxidizing free radicals generated in the reaction system to decompose organic pollutants in water into small molecule substances, or even mineralize them into CO2, H2O and corresponding inorganic ions to achieve the purpose of completely removing pollutants. Among them, the advanced oxidation process based on persulfate (i.e., the persulfate-based advanced oxidation process PS-AOPs) has received increasing attention due to its high removal efficiency, simple operation and strong versatility. Persulfate ionizes in water to generate persulfate ions, and its standard redox potential E 0 reaches +2.01V. The molecule contains a peroxy group -O-O-, which is a relatively strong oxidant. However, persulfate is generally relatively stable and the reaction rate is low. It can be activated into sulfate radicals under the condition of transition metal ions (such as iron, silver, cobalt, etc.). In an environment with pH > 8.5, sulfate radicals oxidize water or OH - to produce hydroxyl radicals, and the redox potential E 0 = +2.6V, which is much higher than that of persulfate ions and close to that of hydroxyl radicals, having strong oxidation ability and high removal efficiency for pollutants. Since iron ions are widely present, cheap and easy to obtain, and have less pollution, and also have a high activation efficiency for persulfate, an iron ion-activated persulfate reaction system is mostly used. However, the traditional iron ion-activated persulfate process has always faced application bottlenecks such as pH dependence, the difficult-to-break Fe 3+ / Fe 2+ cycle rate limitation and inability to be recycled. Therefore, developing a catalyst with high activity and high stability for catalytically activating persulfate to improve the effect of degrading organic pollutants is the research focus of such catalysts. Summary of the Invention

[0003] To solve the application bottleneck of the advanced oxidation process using iron ions to activate persulfate in the prior art, the present invention provides a single-atom iron catalyst, which is applied to the reaction of catalytically activating persulfate to degrade organic pollutants, can break the Fe 3+ / Fe 2+ cycle rate limitation existing in the existing iron ion activation process, exhibits excellent adsorption and catalytic efficiency, and does not require a pH environment during the activation process, has good cycle stability, and significantly promotes the application of the persulfate-based advanced oxidation process in wastewater treatment.

[0004] The single-atom iron catalyst for degrading organic pollutants by the persulfate method of the present invention is a single-atom iron catalyst with asymmetric coordination supported on wool protein carbon, which is prepared by complexing iron ions after modifying the wool protein solution dissolved by the reduction pretreatment-formic acid method with lipoic acid, and finally through freeze-drying, high-temperature calcination, and pickling.

[0005] Conventionally, transition metal ions are used to activate persulfate. Since the activation of metal ions will cause changes in the valence states of metal ions, the activity will be reduced; moreover, metal ions are difficult to recover, which will cause water pollution. The single-atom iron catalyst of the present invention uses inexpensive and long-service-life Fe as the catalytic active center. By modifying wool protein with lipoic acid and then complexing iron ions, because lipoic acid and wool protein contain abundant nitrogen and sulfur, they can provide sufficient anchoring sites for iron ions and prevent their aggregation and migration. Finally, through high-temperature calcination, sulfur and nitrogen-anchored carbon-supported single-atom iron with a porous structure is formed. This porous structure can increase the specific surface area and fully contact with persulfate, greatly improving the catalytic efficiency. At the same time, compared with iron ions, when the single-atom iron catalyst is applied, due to the anchoring of iron atoms by the support material, iron atoms will not leach into the solution, and it can be recycled multiple times without causing environmental pollution by iron elements.

[0006] The wool protein solution is prepared by the "reduction pretreatment-formic acid" dissolution method. First, the disulfide bonds in wool are reduced by tris(2-carboxyethyl)phosphine hydrochloride solution with high selectivity for disulfide bonds, so that wool protein dissolves in water; then, lipoic acid is used to graft-modify the wool protein, changing the polypeptide molecular structure and the form of aggregation, making it easier to form parallel or folded arrangements between molecules, providing sufficient sulfur anchoring sites for iron ions; then, most of the formic acid reagent in the wool protein is removed by dialysis, so that the Coulomb force between iron ions and the modified wool protein combines with each other; finally, a protein gel is obtained by freeze-drying, and iron ions are reduced to the atomic level through high-temperature calcination and pickling to obtain a single-atom iron catalyst.

[0007] As a limitation to the above technical solution, the wool protein solution is obtained by adding wool to tris(2-carboxyethyl)phosphine hydrochloride solution and treating it at 70-90°C, and then adding the treated wool fibers to formic acid and fully dissolving them.

[0008] As a limitation to the above technical solution, the lipoic acid-modified wool protein complexing iron ions is obtained by adding lipoic acid powder to the wool protein solution, stirring and reacting at 30-50°C, then undergoing dialysis treatment, and then adding an iron precursor and fully stirring at 30-40°C.

[0009] As a limitation to the above technical solution, the wool dosage is 1 to 2 g, the concentration of tris(2-carboxyethyl)phosphine hydrochloride solution is 80 to 120 g / L, the dosage is 10 to 50 mL, the formic acid dosage is 20 to 50 mL, the lipoic acid dosage is 0.5 to 10 g, and the iron precursor dosage is 0.1 to 0.2 g.

[0010] As a limitation to the above technical solution, the iron precursor is selected from at least one of iron acetylacetonate, ferric chloride, ferrous chloride, ferric nitrate, ferric sulfate, and ferrous sulfate.

[0011] As a limitation to the above technical solution, the freeze-drying temperature is -40 to -60 °C; the high-temperature calcination temperature is 700 to 1000 °C; HCl solution is used for pickling.

[0012] Further limiting the preparation conditions of the catalyst, such as various reaction treatment conditions, raw material dosages, etc., effectively regulates the microstructure of the catalyst, especially the regulation of the size and electronic structure of the active center Fe, realizes the effective control of the substrate reaction kinetics, and thus obtains a high catalytic rate for the activation of persulfate reaction.

[0013] The present invention also provides the preparation of the single-atom iron catalyst for degrading organic pollutants by the persulfate method as described above, including the following preparation steps:

[0014] a. Add 1 to 2 g of wool into 10 to 50 mL of tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 80 to 120 g / L, treat it at 70 to 90 °C for 1 to 3 h to obtain wool fibers, add the wool fibers into 20 to 50 mL of formic acid, stir at 50 to 70 °C for 4 to 6 h to fully dissolve, and centrifuge to obtain the upper clear liquid as wool protein solution;

[0015] b. Add 0.5 to 10 g of lipoic acid powder into the wool protein solution, stir and react at 30 to 50 °C for 1 to 3 h to obtain a modified wool protein solution, put it into a dialysis bag, and perform dialysis treatment with deionized water;

[0016] c. Add 0.1 to 0.2 g of iron precursor into the modified wool protein solution after dialysis treatment, stir at 30 to 40 °C for 1 to 6 h, and freeze-dry the obtained solution at -40 to -60 °C for 12 to 48 h to obtain a protein gel;

[0017] d. Calcinate the protein gel at 700 to 1000 °C for 1 to 4 h, and then perform pickling, washing, and drying of the calcination product with HCl solution to obtain a single-atom iron catalyst.

[0018] As a limitation to the above technical solution, in step a, the centrifugation speed is 10000 r / min and the time is 5 min; and / or;

[0019] In step b, the deionized water is replaced every 30 - 40 min during dialysis treatment, and the treatment lasts for 3 - 4 h; and / or;

[0020] In step d, the calcination temperature is 800 - 900 °C and the time is 1 - 3 h; and / or;

[0021] The calcined product is pickled in a 0.2 - 0.6 mol / L HCl solution for 12 - 24 h, and then washed with deionized water and dried.

[0022] Improve the preparation of the single - atom iron catalyst to significantly enhance the catalytic activity and its application in the advanced oxidation process.

[0023] Meanwhile, the present invention further provides the application of the single - atom iron catalyst for degrading organic pollutants by the persulfate method as described above. The single - atom iron catalyst is used as a catalyst for activating persulfate to replace the soluble iron salt catalyst used in the advanced oxidation process of the persulfate method.

[0024] As a limitation to the above - mentioned technical solution, the single - atom iron catalyst is applicable to acidic or alkaline reaction systems and can be recovered and reused in the advanced oxidation process of the persulfate method.

[0025] The single - atom iron catalyst of the present invention can activate persulfate under normal temperature and pressure and without relying on the pH reaction environment, and then degrade the macromolecular organic matter in industrial wastewater, converting the toxic macromolecular organic matter into non - toxic or low - toxic small - molecule substances. This catalyst not only has high catalytic efficiency and activity, but also has good stability, can be recycled, greatly reduces the cost of wastewater treatment, promotes green development, and plays a protective role in the environment and human health. Brief Description of the Drawings

[0026] Figure 1 is the aberration - corrected electron microscopy image of the single - atom iron catalyst obtained in Example 1 of the present invention;

[0027] Figure 2 is the scanning electron microscopy image of the single - atom iron catalyst obtained in Example 1 of the present invention;

[0028] Figure 3 is the EXAFS spectrum of the single - atom iron catalyst obtained in Example 1 of the present invention;

[0029] Figure 4 is the XANES spectrum of the single - atom iron catalyst obtained in Example 1 of the present invention;

[0030] Figure 5 is the gas chromatogram of the initial solution of p - chlorophenol in Example 1 of the present invention;

[0031] Figure 6, which is the gas chromatogram of the solution after 30 minutes of p-chlorophenol degradation in Example 1 of the present invention. Detailed implementation manners

[0032] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0033] The raw materials involved in the following embodiments and comparative examples are all typical products purchased on the market.

[0034] Example 1

[0035] A kind of iron atom catalyst, and its preparation operation is carried out according to the following steps:

[0036] a. Weigh 1 g of wool and add it to 10 mL of tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 120 g / L, treat it at 70 °C for 2 h. The treated wool fiber is added to 30 mL of formic acid, stirred at 70 °C for 6 h to fully dissolve, centrifuged at 10000 r / min for 5 min, and the obtained supernatant is wool protein solution;

[0037] b. Add 5 g of lipoic acid powder to the wool protein solution obtained in step a, stir and react at 50 °C for 2 h to obtain a modified wool protein solution, then put it into a dialysis bag and perform dialysis treatment with deionized water as the dialysis solution, change the deionized water every 30 min, and complete dialysis for 4 h;

[0038] c. Add 0.15 g of Fe(NO3)3·9H2O to the modified wool protein solution after dialysis in step b, stir for 4 h at 40 °C, and then freeze-dry the obtained solution at -40 °C for 12 h to obtain a protein gel;

[0039] d. Calcinate the protein gel, place it in a tubular furnace and calcine at 900 °C for 2 h, then pickle it in 0.3 mol / L HCl solution for 12 h, and then wash it with deionized water and dry it to obtain a single-atom iron catalyst.

[0040] Perform structural analysis on the obtained single-atom iron catalyst, as shown in Figure 1 the spherical aberration electron microscope image, Figure 2 the scanning electron microscope image, Figure 3 the EXAFS spectrum, and Figure 4The XANES spectrum shows that Fe is an isolated single atom by aberration-corrected electron microscopy. It can be seen by scanning electron microscopy that the overall catalyst has a porous structure. With the help of synchrotron radiation analysis, it can be seen that the catalyst has rich sulfur coordination, forming a Fe1S1N3 structure.

[0041] Example 2

[0042] An iron atom catalyst is prepared by the following steps:

[0043] a. Weigh 1 g of wool and add it to 20 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 120 g / L. Treat it at 80 °C for 2 h. Add the treated wool fibers to 30 mL of formic acid, stir and dissolve them fully at 60 °C for 6 h, and centrifuge at 10000 r / min for 5 min. The supernatant obtained is the wool protein solution;

[0044] b. Add 3 g of lipoic acid powder to the wool protein solution obtained in step a, stir and react at 50 °C for 2 h to obtain a modified wool protein solution. Then put it into a dialysis bag and perform dialysis treatment with deionized water as the dialysis solution. Replace the deionized water every 40 min and continue for 4 h to complete dialysis;

[0045] c. Add 0.15 g of Fe(NO3)3·9H2O to the modified wool protein solution after dialysis in step b, stir for 4 h at 40 °C, and then freeze-dry the solution at -40 °C for 18 h to obtain a protein gel;

[0046] d. Calcinate the protein gel, place it in a tubular furnace and calcinate at 800 °C for 2 h, then pickle it in a 0.3 mol / L HCl solution for 24 h, wash it with deionized water and dry it to obtain a single-atom iron catalyst.

[0047] Example 3

[0048] An iron atom catalyst is prepared by the following steps:

[0049] a. Weigh 1.5 g of wool and add it to 20 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 100 g / L. Treat it at 70 °C for 2 h. Add the treated wool fibers to 50 mL of formic acid, stir and dissolve them fully at 70 °C for 6 h, and centrifuge at 10000 r / min for 5 min. The supernatant obtained is the wool protein solution;

[0050] b. Add 6 g of lipoic acid powder to the wool protein solution obtained in step a, stir and react at 40 °C for 1 h to obtain a modified wool protein solution. Then put it into a dialysis bag and perform dialysis treatment with deionized water as the dialysis solution. Replace the deionized water every 30 min and continue for 4 h to complete dialysis;

[0051] c. Add 0.2 g of Fe(NO3)3·9H2O to the modified wool protein solution after dialysis in step b, stir at 40 °C for 4 h, and freeze-dry the solution at -50 °C for 12 h to obtain a protein gel.

[0052] d. Calcinate the protein gel, place it in a tube furnace and calcinate at 900 °C for 2 h. After calcination, pickle it in 0.3 mol / L HCl solution for 24 h, then wash it with deionized water and dry it to obtain a single-atom iron catalyst.

[0053] Example 4

[0054] An iron atom catalyst is prepared by the following steps:

[0055] a. Weigh 1 g of wool and add it to 10 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 120 g / L. Treat it at 70 °C for 2 h. Add the treated wool fibers to 40 mL of formic acid, stir at 70 °C for 6 h to fully dissolve, centrifuge at 10000 r / min for 5 min, and the upper clear liquid obtained is the wool protein solution.

[0056] b. Add 3 g of lipoic acid powder to the wool protein solution obtained in step a, stir and react at 50 °C for 2 h to obtain a modified wool protein solution. Then put it into a dialysis bag and perform dialysis treatment with deionized water as the dialysis solution. Replace the deionized water every 30 min and continue dialysis for 4 h to complete dialysis.

[0057] c. Add 0.15 g of FeCl3·6H2O to the modified wool protein solution after dialysis in step b, stir at 40 °C for 4 h, and then freeze-dry the solution at -50 °C for 15 h to obtain a protein gel.

[0058] d. Calcinate the protein gel, place it in a tube furnace and calcinate at 900 °C for 3 h. Then pickle it in 0.3 mol / L HCl solution for 24 h, wash it with deionized water and dry it to obtain a single-atom iron catalyst.

[0059] Example 5

[0060] An iron atom catalyst is prepared by the following steps:

[0061] a. Weigh 1 g of wool and add it to 10 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 120 g / L. Treat it at 70 °C for 2 h. Add the treated wool fibers to 30 mL of formic acid, stir at 60 °C for 6 h to fully dissolve, centrifuge at 10000 r / min for 5 min, and the upper clear liquid obtained is the wool protein solution.

[0062] b. Add 0.5 g of lipoic acid powder to the wool protein solution obtained in step a, stir and react at 50 °C for 2 h to obtain a modified wool protein solution, then put it into a dialysis bag and perform dialysis treatment with deionized water as the dialysis solution, changing the deionized water every 30 min, and complete dialysis after 4 h.

[0063] c. Add 0.15 g of Fe(NO3)3·9H2O to the modified wool protein solution after dialysis in step b, stir for 4 h at 40 °C, and then freeze-dry the solution at -40 °C for 12 h to obtain a protein gel.

[0064] d. Calcinate the protein gel, place it in a tube furnace and calcinate at 900 °C for 2 h, then pickle it in 0.3 mol / L HCl solution for 24 h, wash it with deionized water and dry it to obtain a single-atom catalyst.

[0065] Perform an experiment on the activation of persulfate for the degradation of 4-chlorophenol using the single-atom iron catalysts prepared in Examples 1-5, and reflect the performance of each catalyst through the experimental results.

[0066] Experiment: The reaction temperature is 25 °C, the catalyst dosage is 0.005 g / L (calculated as Fe), the initial mass concentration of 4-chlorophenol is 20 mg / L, the dosage of peroxymonosulfate is 0.2 g / L, and the initial solution pH is 6.8. Take 50 mL of 4-chlorophenol solution in a beaker, add the catalyst, stir for 30 min to reach adsorption-desorption equilibrium, add peroxymonosulfate to start the reaction, and react for a total of 60 min; sample at regular intervals, add 20 μL of sodium thiosulfate solution to the water sample to terminate the reaction, filter it with a 0.22 μm filter membrane and wait for measurement, and analyze the degradation effect of 4-chlorophenol by gas chromatography.

[0067] The degradation effect of 4-chlorophenol is characterized by "removal rate (R, %)". The calculation formula of the removal rate is as follows:

[0068] R = ((C0 - C t ) / C0) × 100%

[0069] In the formula: C0—the initial concentration of the substrate, mg / L; Ct—the concentration of the substrate at time t, mg / L.

[0070] The experimental results are shown in Table 1 below:

[0071] Table 1

[0072] Catalyst Example 1 Example 2 Example 3 Example 4 Example 5 <![CDATA[Initial concentration C0 (mg / L)]]> 20.0 20.0 20.0 20.0 20.0 <![CDATA[Concentration C at time t (30 min) t (mg / L)]]> <0.1 0.4 0.5 0.6 1.6 p - Chlorophenol removal rate (%) >99 98 98 97 92 Reaction time (min) 30 30 30 30 30

[0073] The catalytic result of Example 1 is as Figure 5 and 6As shown, analyzing the initial reaction solution, it can be observed that the peak of p-chlorophenol is relatively high; after reacting for 30 min, it can be observed that the peak of p-chlorophenol basically disappears. This indicates that the catalyst has a high catalytic efficiency, and the activated sulfate radicals have a high removal rate for p-chlorophenol, with an overall high catalytic efficiency.

[0074] In addition, the catalyst of Example 1 was subjected to a recycling experiment. That is, after completing the experiment of activating persulfate to degrade p-chlorophenol, the catalyst was recovered and activated at 300 °C for 1 h under a N2 atmosphere, and then used again for the experiment of catalytically activating persulfate to degrade p-chlorophenol. The recycling experiment was carried out 5 times, and the results are shown in Table 2 below.

[0075] Table 2

[0076]

[0077] As can be seen from the results in the above table, the wool protein-supported single-atom iron catalyst of the present invention has good stability in sequential use.

[0078] Comparative Example 1

[0079] For the single-atom iron catalyst of this comparative example, the modifier lipoic acid was not used, and the pore-forming agent ZnCl2 was added. The specific preparation is as follows.

[0080] Weigh 1 g of wool and add it to 10 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 120 g / L. Treat it at 70 °C for 2 h. Add the treated wool fibers to 30 mL of formic acid, stir at 70 °C for 6 h to fully dissolve, centrifuge at 10000 r / min for 5 min. The obtained supernatant is the wool protein solution, which is then put into a dialysis bag and dialyzed with deionized water as the dialysis solution. Change the deionized water every 30 min and continue dialysis for 4 h to complete dialysis. Add 0.15 g of Fe(NO3)3·9H2O and 13.6 mg of ZnCl2 to the dialyzed solution. Here, ZnCl2 is the pore-forming agent used to increase the specific surface area of the catalyst. After stirring at 40 °C for 4 h, the solution is freeze-dried at -40 °C for 12 h to obtain a protein gel. The protein gel is calcined, placed in a tubular furnace and calcined at 900 °C for 2 h, then pickled in a 0.3 mol / L HCl solution for 12 h, and then washed with deionized water and dried to obtain the single-atom iron catalyst.

[0081] Comparative Example 2

[0082] For the single-atom iron catalyst of this comparative example, silk fibroin rather than wool protein was used as the carrier, the modifier lipoic acid was not used, and the pore-forming agent ZnCl2 was added. The specific preparation is as follows.

[0083] Boil 1 g of silk fibroin in 100 mL of 0.2 mol / L Na2CO3 aqueous solution for 3 h to fully degum the silk. Then add the degummed silk fibroin to the prepared 100 ml of 9.3 mol / L lithium bromide solution and stir at 65 °C for 2 h. Finally, put the treated silk fibroin solution into a dialysis bag and dialyze for 3 days. Add 0.15 g of Fe(NO3)3·9H2O and 13.6 mg of ZnCl2 to the dialyzed solution. Here, ZnCl2 is a pore-forming agent to increase the specific surface area of the catalyst. After stirring at 40 °C for 4 h, freeze-dry the solution at -40 °C for 12 h to obtain a protein gel. Calcinate the protein gel, place it in a tubular furnace and calcine at 900 °C for 2 h. Then pickle it in 0.3 mol / L HCl for 12 h, wash it with deionized water and dry it to obtain a single-atom iron catalyst.

[0084] Comparative Example 3

[0085] The catalyst in this comparative example is FeCl3·6H2O.

[0086] Respectively conduct the experiment of activating persulfate to degrade 4-chlorophenol with the catalysts of Comparative Examples 1 - 3. The operation of activating persulfate to degrade 4-chlorophenol is the same as above, and the experimental results are shown in Table 3 below:

[0087] Table 3

[0088] Catalyst Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Initial concentration C0 (mg / L)]]> 20 20 20 <![CDATA[Concentration C at time t (30 min) t (mg / L)]]> 3.4 5.6 4.2 p - Chlorophenol removal rate (%) 83 72 79 Reaction time (min) 30 30 30

[0089] As shown in Table 3 above, the removal rate of 4-chlorophenol by activating persulfate in the comparative examples is relatively low. After analysis, the low catalytic efficiency of the catalyst in Comparative Example 1 is because the modifier lipoic acid is not used. Only by using the pore-forming agent zinc chloride to increase the specific surface area of the catalyst, it will reduce the sulfur coordination, lower the activity of Fe, and at the same time, it cannot form a porous structure like that in Example 1, resulting in a small specific surface area and insufficient contact with persulfate. The low catalytic efficiency of the catalyst in Comparative Example 2 is because the sulfur element in silk fibroin is less than that in wool protein, and N, S co-coordination cannot be formed, and its activity is lower than that in Comparative Example 1, reflecting the important role of sulfur coordination in improving catalytic activity. The trivalent iron ions in Comparative Example 3 are directly used to catalyze the activation of persulfate, with low efficiency and cannot be recycled.

[0090] In summary, the lipoic acid-modified wool protein carbon-supported single-atom iron catalyst of the present invention uses the nitrogen and sulfur in wool protein and the sulfur in lipoic acid to complex iron ions, and then prepares a carbon-supported single-atom iron structure anchored by sulfur and nitrogen through high-temperature calcination, making the catalyst have the advantages of high activity, high stability, low cost and simple operation. When applied to catalyze the activation of persulfate to degrade organic pollutants, it can greatly improve the adsorption and catalytic efficiency.

Claims

1. A single-atom iron catalyst for degrading organic pollutants by the persulfate method, characterized in that: The single-atom iron catalyst is a wool protein carbon-supported asymmetrically coordinated single-atom iron catalyst, which is prepared by complexing iron ions after modifying the wool protein solution dissolved by the reduction pretreatment-formic acid method with lipoic acid, and finally through freeze-drying, high-temperature calcination, and pickling; The wool protein solution is obtained by adding wool to a tris(2-carboxyethyl)phosphine hydrochloride solution, treating it at 70-90 °C, and then adding the treated wool fibers to formic acid to fully dissolve; The lipoic acid-modified wool protein complexed with iron ions is obtained by adding lipoic acid powder to the wool protein solution, stirring and reacting at 30-50 °C, then performing dialysis treatment, and then adding an iron precursor and fully stirring at 30-40 °C.

2. The single-atom iron catalyst for degrading organic pollutants by the persulfate method according to claim 1, wherein: The amount of wool used is 1-2 g, the concentration of the tris(2-carboxyethyl)phosphine hydrochloride solution is 80-120 g / L, the amount used is 10-50 mL, the amount of formic acid used is 20-50 mL, the amount of lipoic acid used is 0.5-10 g, and the amount of iron precursor used is 0.1-0.2 g.

3. The single-atom iron catalyst for degrading organic pollutants by the persulfate method according to claim 1, wherein: The iron precursor is selected from at least one of iron acetylacetonate, ferric chloride, ferrous chloride, ferric nitrate, ferric sulfate, and ferrous sulfate.

4. The single-atom iron catalyst for degrading organic pollutants by the persulfate method according to claim 1, characterized in that: The freeze-drying temperature is -40 to -60 °C; the high-temperature calcination temperature is 700 to 1000 °C; pickling uses an HCl solution.

5. Preparation of the single-atom iron catalyst for degrading organic pollutants by the persulfate method according to any one of claims 1 to 4, characterized in that, It includes the following preparation steps: a. Add 1-2 g of wool to 10-50 mL of a tris(2-carboxyethyl)phosphine hydrochloride solution with a concentration of 80-120 g / L, treat it at 70-90 °C for 1-3 h to obtain wool fibers, add the wool fibers to 20-50 mL of formic acid, and stir at 50-70 °C for 4-6 h to fully dissolve, then centrifuge. The supernatant obtained is the wool protein solution; b. Add 0.5-10 g of lipoic acid powder to the wool protein solution, stir and react at 30-50 °C for 1-3 h to obtain a modified wool protein solution, put it into a dialysis bag, and perform dialysis treatment with deionized water; c. Add 0.1-0.2 g of iron precursor to the modified wool protein solution after dialysis treatment, stir at 30-40 °C for 1-6 h, and freeze-dry the obtained solution at -40 to -60 °C for 12-48 h to obtain a protein gel; d. Calcinate the protein gel at 700-1000 °C for 1-4 h, and then perform pickling, washing, and drying of the calcined product with an HCl solution to obtain the single-atom iron catalyst.

6. The preparation method of the single-atom iron catalyst for degrading organic pollutants by the persulfate method according to claim 5, wherein: In step a, the centrifugation speed is 10000 r / min and the time is 5 min; and / or; In step b, the deionized water is replaced every 30-40 min during dialysis treatment, and it lasts for 3-4 h; and / or; In step d, the calcination temperature is 800-900 °C and the time is 1-3 h; and / or; The calcined product is pickled in a 0.2-0.6 mol / L HCl solution for 12-24 h, then washed with deionized water and dried.

7. Use of the single-atom iron catalyst for degrading organic pollutants by the persulfate method according to any one of claims 1 to 4, characterized in that: The single-atom iron catalyst is used as a catalyst for activating persulfate to replace the soluble iron salt catalyst used in the advanced oxidation process of the persulfate method.

8. Use of the single-atom iron catalyst for degrading organic pollutants by the persulfate method according to claim 7, characterized in that: The single-atom iron catalyst is applicable to acidic or alkaline reaction systems and can be recovered and reused in the advanced oxidation process of the persulfate method.

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