Fused salt modified nitrogen-doped biochar supported single-atom iron catalysts, methods of making and using the same

Abstract

The application discloses a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: (1) mixing a biomass material and a bicarbonate, performing pyrolysis and acid washing to obtain a treated molten salt modified biochar; (2) mixing the treated molten salt modified biochar, an iron salt, water and glucose, and performing reaction to obtain a catalyst precursor; and (3) mixing the catalyst precursor and a nitrogen source, and calcining to obtain the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst. The molten salt modified nitrogen-doped biochar supported single-atom iron catalyst has the advantages of rich pore structure, large specific surface area, high active site efficiency, low metal ion leaching, good recyclability and the like, can effectively activate persulfate, and realizes efficient degradation of organic pollutants through a non-radical singlet oxygen dominant and high-valence metal-oxygen species auxiliary combined approach.

Description

Technical Field

[0001] This invention belongs to the field of advanced oxidation water treatment, specifically relating to a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst, its preparation method, and its application. Background Technology

[0002] Persulfate oxidation, as an advanced oxidation process, overcomes the limitations of the Fenton process, which operates within a narrow pH range, and can adapt to a wider pH range. Furthermore, its advantages, including high efficiency, ease of storage and transportation, low cost, and excellent stability, have led to increasing attention and made it a research hotspot in environmental catalysis in recent years. Biochar, with its low cost, non-toxicity, and good adsorption and catalytic performance, is considered a promising persulfate activator. However, the efficiency of raw biochar in activating persulfate is not ideal, requiring further modification to improve its catalytic performance. Therefore, obtaining a highly catalytically active molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst is of practical significance for the remediation and treatment of recalcitrant organic pollutants. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst with rich pore structure, large specific surface area, high active site efficiency, low metal ion leaching, and good recyclability, as well as its preparation method and application.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0005] A method for preparing a molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst includes the following steps:

[0006] (1) The biomass material and bicarbonate are mixed and pyrolyzed at 600℃~800℃ under nitrogen atmosphere. After acid washing, the treated molten salt modified biochar is obtained.

[0007] (2) The treated molten salt modified biochar, iron salt, water and glucose obtained in step (1) are mixed and reacted to obtain the catalyst precursor;

[0008] (3) The catalyst precursor obtained in step (2) is mixed with a nitrogen source and calcined at 900℃~1000℃ under a nitrogen atmosphere to obtain a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst.

[0009] In a further improvement to the above preparation method, in step (1), the mass ratio of the biomass material to bicarbonate is 1:0.1 to 1.

[0010] In a further improvement to the above preparation method, in step (2), the mass ratio of the treated molten salt modified biochar, iron salt, water and glucose is 1:1 to 4:10 to 20:10 to 20.

[0011] In a further improvement to the above preparation method, in step (3), the mass ratio of the catalyst precursor to the nitrogen source is 1:5 to 10.

[0012] The above preparation method is further improved in step (1), where the bicarbonate is sodium bicarbonate, the pyrolysis time is 1h to 2h, the heating rate during pyrolysis is 10℃ / min, and the specific process of acid washing is as follows: the pyrolysis product and acid are mixed, allowed to stand, and then washed and dried; the mass ratio of the pyrolysis product to the acid is 1:100, the acid is hydrochloric acid, the concentration of the hydrochloric acid is 0.5mol / L to 1mol / L, the standing time is 8h, and the washing is performed by washing with water and anhydrous ethanol three times in sequence; the biomass material is further improved by the following steps before use: the biomass material and water are mixed, hydrothermally reacted at 100℃ for 2h, and then dried, pulverized, dried again, and sieved; the biomass material is Salvia miltiorrhiza, the pulverization is pulverized to 0.2mm, the sieving is passed through a 100-200 mesh sieve, and the drying temperature is 60℃.

[0013] The above preparation method is further improved in step (2), where the iron salt is ferric nitrate nonahydrate, the reaction time is 0.5 h to 1 h, the reaction is carried out under ultrasonic conditions, and the catalyst precursor is further treated before use as follows: the reaction product is washed, dried, and ground.

[0014] And / or, in step (3), the nitrogen source is melamine, the calcination time is 1h to 2h, and the heating rate during the calcination process is 10℃ / min.

[0015] As a general technical concept, the present invention also provides a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst prepared by the above-mentioned method for preparing molten salt modified nitrogen-doped biochar supported single-atom iron catalyst.

[0016] As a general technical concept, the present invention also provides an application of the above-mentioned molten salt modified nitrogen-doped biochar supported single-atom iron catalyst in the treatment of organic pollutant wastewater.

[0017] Further improvements to the above application include the following steps: mixing molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst and organic pollutant wastewater, and adding persulfate to carry out a degradation reaction to achieve the degradation of organic pollutants in the water; the ratio of the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst to the organic pollutant wastewater is 0.05g~0.2g∶1L.

[0018] In a further improvement to the above application, the amount of persulfate added is 0.75g to 3g per liter of organic pollutant wastewater, wherein the persulfate is potassium persulfate, the concentration of organic pollutants in the wastewater is ≤20mg / L, the organic pollutant in the wastewater is an antibiotic, the antibiotic is tetracycline hydrochloride, the mixing time is 0.5h to 1.5h, and the degradation reaction time is ≥60min.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) This invention provides a method for preparing a single-atom iron catalyst supported on molten salt-modified nitrogen-doped biochar. The single-atom iron catalyst is synthesized through a cascade anchoring strategy. First, biomass materials and bicarbonate are mixed and pyrolyzed, then acid-washed to form porous biochar with high specific surface area and abundant oxygen-containing functional groups. Then, the treated molten salt-modified biochar, iron salt, water, and glucose are mixed and reacted. During the reaction, glucose first chelates with iron atoms and anchors them on the oxygen-rich porous biochar with high surface area. Excess glucose continues to chelate with iron atoms, forming a glucose shell around the iron atoms, isolating them from the outside environment. Finally, the catalyst precursor and nitrogen source are mixed and calcined. During calcination, at low temperatures (<500℃), glucose protects the iron atoms by decomposing the residue. At higher temperatures (>500℃), carbon and nitrogen species (CN-N) are decomposed from the nitrogen source. x It can combine with iron atoms to form Fe-N xThe group acts as a protective mechanism to prevent the aggregation of iron atoms. As the calcination temperature is further increased (≥900℃), the iron atoms are transformed from saturated Fe-N4 coordination to unsaturated Fe-N3 or Fe-N2 coordination, which makes the nitrogen atoms more polar and has a stronger ability to transfer electrons. Ultimately, a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst with excellent catalytic performance is obtained. The preparation method of this invention involves, firstly, molten salt modification and acid washing to give the biochar a loose and porous structure. This is because: at high temperatures (600℃~800℃), bicarbonate flows into the biochar framework in a molten state. After cooling and acid washing, the bicarbonate flowing into the carbon framework is removed, thus filling the biochar with pores. Secondly, iron is loaded onto the biochar in the form of single atoms, giving the carbon material not only the advantages of homogeneous catalyst atomic dispersion and high atomic utilization, but also the advantages of heterogeneous catalyst stability and easy separation. Finally, the nitrogen element doped into the biochar not only generates a large number of defects, but also tightly binds with iron atoms, chelating the iron atoms tightly into the defects, making it difficult for iron atoms to agglomerate and deactivate. The molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst of this invention possesses advantages such as abundant pore structure, large specific surface area, high active site efficiency, low metal ion leaching, and good recyclability. It can effectively activate persulfate and achieve efficient degradation of organic pollutants through a combination of non-radical singlet oxygen-dominant and high-valence metal-oxygen species-assisted pathways. The preparation method of this invention is simple, convenient, low-cost, and environmentally friendly, providing new ideas for the recycling of waste biomass and the green preparation of efficient biochar-based catalysts. It has practical application significance for the remediation and treatment of recalcitrant organic pollutants in wastewater.

[0021] The preparation method of this invention limits the calcination temperature to 900℃~1000℃, which can obtain a nitrogen-doped biochar-supported single-atom iron catalyst with higher catalytic activity. When the calcination temperature is too low, the carbon lattice structure is poor, and the surface area and pore channels are not opened. When the calcination temperature is too high, important oxygen-containing functional groups on the surface of the biochar will volatilize and be lost. At the same time, the structure collapses due to heat, resulting in a reduction in porosity and specific surface area, and it will also increase hydrophobicity, which is not conducive to dispersion. In addition, the biomass material used in this invention is Salvia miltiorrhiza, which contains a lot of cellulose and hemicellulose, and can provide a stable carbon skeleton.

[0022] (2) The present invention also provides a method for preparing a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst for treating organic pollutant wastewater. The molten salt modified nitrogen-doped biochar supported single-atom iron catalyst is mixed with organic pollutant wastewater, and persulfate is added to carry out a degradation reaction, which can effectively remove organic pollutants in water. It has the advantages of simple operation, good degradation effect and low cost, and is suitable for practical application scenarios. Attached Figure Description

[0023] Figure 1 The images show SEM images of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2.

[0024] Figure 2 The X-ray diffraction patterns are those of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2.

[0025] Figure 3 The N2 isotherm adsorption-desorption curves are shown for the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2.

[0026] Figure 4 The images show the pore size distribution of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2.

[0027] Figure 5 The infrared spectra of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2 are shown.

[0028] Figure 6 The images show the Raman spectra of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2.

[0029] Figure 7 The X-ray photoelectron spectroscopy (XPS) spectra of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2 are shown.

[0030] Figure 8 The images show the degradation effects of tetracycline hydrochloride by molten salt modified nitrogen-doped tanshinone biochar supported on single-atom iron catalysts (M / SaFe / N-C900, M / SaFe / N-C600, M / SaFe / N-C700, M / SaFe / N-C800, M / SaFe / N-C1000), treated molten salt modified biochar (MC), molten salt modified nitrogen-doped tanshinone biochar (M / NC), and molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Example 2 of this invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0032] Example 1:

[0033] A method for preparing a molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst according to the present invention includes the following steps:

[0034] (1) Fresh Salvia miltiorrhiza from Shangluo, Shaanxi Province was used. After washing it several times with deionized water, water was added and the mixture was placed in a 100℃ water bath for 2 hours to make Salvia miltiorrhiza Chinese medicine residue. The residue was then dried in a 60℃ drying oven to obtain the pretreated Salvia miltiorrhiza residue.

[0035] (2) The pretreated Salvia miltiorrhiza residue was crushed into 0.2 mm fine powder by a high-speed crusher, dried, and passed through a 200-mesh sieve to obtain Salvia miltiorrhiza residue powder, which was then packed into a self-sealing bag for later use.

[0036] (3) The above-mentioned Salvia miltiorrhiza residue powder and sodium bicarbonate were mixed in a mass ratio of 1:0.1 and placed in a dry crucible. Under a nitrogen atmosphere, the mixture was heated to 800℃ for 1h at a heating rate of 10℃ / min. After grinding, molten salt modified biochar was obtained.

[0037] (4) The molten salt modified biochar and hydrochloric acid were mixed at a mass ratio of 1:100 and the concentration of the hydrochloric acid was 1 mol / L. After standing for 8 hours, the molten salt modified biochar was washed three times by vacuum filtration with ultrapure water and anhydrous ethanol respectively. After vacuum drying at 60°C for 24 hours, the treated molten salt modified biochar was obtained and denoted as MC.

[0038] (5) The above-mentioned molten salt modified biochar, ferric nitrate nonahydrate, water and glucose were mixed in a mass ratio of 1:1:10:10 and reacted under ultrasonic conditions for 1 hour. After washing, drying and grinding, the catalyst precursor was obtained.

[0039] (6) The catalyst precursor and melamine were mixed at a mass ratio of 1:5 and placed in a dry crucible. The mixture was heated to 900°C for 2 hours under a nitrogen atmosphere at a heating rate of 10°C / min to obtain a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst, denoted as M / SaFe / N-C900.

[0040] In the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) prepared in this embodiment, the single-atom iron loading was 0.3 wt% as determined by ICP testing.

[0041] In this embodiment, molten salt modified nitrogen-doped biochar supported single-atom iron catalysts with different calcination temperatures were also prepared. The preparation method was basically the same as that of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900), except that in step (6), the calcination temperatures were 600℃, 700℃, 800℃, and 1000℃, respectively. The molten salt modified nitrogen-doped biochar supported single-atom iron catalysts were named as M / SaFe / N-C600, M / SaFe / N-C700, M / SaFe / N-C800, and M / SaFe / N-C1000, respectively.

[0042] Comparative Example 1:

[0043] A molten salt modified nitrogen-doped tanshinone biochar is prepared in a manner that is basically the same as the preparation method of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1. The only difference is that in step (5), ferric nitrate nonahydrate is not added. The molten salt modified nitrogen-doped tanshinone biochar obtained is denoted as M / NC.

[0044] Comparative Example 2:

[0045] A molten salt modified iron-supported tanshinone biochar is prepared in a manner that is basically the same as the preparation method of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1. The only difference is that melamine is not added in step (6). The molten salt modified iron-supported tanshinone biochar obtained is denoted as M / Fe-C.

[0046] Figure 1 The images show SEM images of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of the present invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. Figure 1 In the diagram, (a) represents MC, (b) represents M / NC, (c) represents M / Fe-C, and (d) represents M / SaFe / N-C900. From... Figure 1 It can be seen that MC, M / NC, M / Fe-C, and M / SaFe / N-C900 all exhibit irregularly shaped porous structures with wrinkled surfaces, a result of the carbonization of Salvia miltiorrhiza. However, compared to the smooth surface of MC, nitrogen-doped M / NC, iron-loaded M / Fe-C, and nitrogen-doped and iron-loaded M / SaFe / N-C900 develop a rough surface structure. This is because iron atoms loaded into the carbon lattice and nitrogen doping block the pores of the carbon framework, thus forming a rough surface.

[0047] Figure 2 The images show the X-ray diffraction patterns of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. Figure 2As can be seen, MC, M / NC, M / Fe-C, and M / SaFe / N-C900 all exhibit poor crystallinity, indicating that these four materials possess an irregular morphology (SEM characterization also confirms this). Furthermore, MC, M / NC, M / Fe-C, and M / SaFe / N-C900 show broad peaks at 2θ = 22.3° and 43.5°, corresponding to the graphitic carbon (002) plane and the crystalline carbon (100) plane, respectively, indicating that the biochar formed a graphitic structure during carbonization. Compared to MC, the peak morphology of M / Fe-C remained largely unchanged, and XRD failed to detect characteristic iron peaks, indicating the absence of iron-containing complex formation. This also suggests that the iron content on the Tanshinone biochar is low and has no significant impact on the structure of the carbon substrate, indirectly reflecting that the iron in M / Fe-C exists in the form of single atoms. However, compared to MC, the peak intensities of M / NC and M / SaFe / N-C900 at 2θ = 26.57° and 42.07° were reduced. This is because nitrogen doping disrupts the structure of biochar, resulting in more defects and thus reducing the degree of graphitization of the carbon substrate. Furthermore, the XRD pattern of M / SaFe / N-C900 failed to detect the characteristic peaks of iron, confirming the successful preparation of the single-atom iron catalyst.

[0048] Figure 3 The N2 isotherm adsorption-desorption curves are shown for the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. Figure 3 It can be seen that the N2 adsorption-desorption isotherms of MC and M / NC, M / Fe-C, and M / SaFe / N-C900 are all typical Type IV isotherms with a Type H4 hysteresis loop, indicating that all four materials possess a mesoporous structure. The specific surface areas of MC and M / NC, M / Fe-C, and M / SaFe / N-C900 are 966.0, 378.1, 858.2, and 456.7 m², respectively. 2 Compared to MC, the specific surface area of ​​M / NC, M / Fe-C, and M / SaFe / N-C900 all decreased significantly, with M / NC showing the most significant decrease. This is because, at high temperatures, undecomposed melamine flows into the pores of biochar in a molten state, clogging the pores upon cooling and causing a sharp drop in specific surface area. The specific surface area of ​​M / Fe-C decreased less, possibly because the iron loading was lower, only damaging the surface pores and having a smaller impact.

[0049] Figure 4The images show the pore size distribution of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. Figure 4 It can be seen that the pore sizes of MC, M / NC, M / Fe-C, and M / SaFe / N-C900 are mainly distributed in the range of 2–5 nm, and the total pore volumes of MC, M / NC, M / Fe-C, and M / SaFe / N-C900 are 0.488, 0.188, 0.437, and 0.233 cm³, respectively. 3 The average pore sizes of MC, M / NC, M / Fe-C, and M / SaFe / N-C900 are 1.980, 1.991, 2.037, and 2.041 nm, respectively. It is evident that these four materials are predominantly mesoporous (this is also confirmed by the isothermal adsorption-desorption curves). Compared to MC, the total pore volume of M / NC and M / SaFe / N-C900 shows a significant decrease, possibly due to the influence of excessive nitrogen doping. The total pore volume of M / Fe-C changes less, possibly because the lower iron loading has a smaller impact on porosity. Compared to MC, the average pore sizes of M / NC, M / Fe-C, and M / SaFe / N-C900 do not change much, possibly because nitrogen doping or iron loading only affects the number of pores in the material, while having a smaller impact on pore size.

[0050] Figure 5 The images show the infrared spectra of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. The vibrations at different locations in the infrared spectra reflect different functional groups. Figure 5 Two characteristic peaks, namely 3450 cm⁻¹, can be clearly observed for MC, M / NC, M / Fe-C, and M / SaFe / N-C900. -1 and 1630cm -1 Due to the stretching vibrations of the -OH functional groups on the surface of the material, at approximately 3450 cm⁻¹ -1 A distinct characteristic peak is formed at approximately 1631 cm⁻¹; this is due to the stretching vibration of the C=O functional group. -1A peak appears at [location missing]. Furthermore, the FT-IR spectra show that with nitrogen doping, the -OH stretching vibration peak gradually weakens and becomes smoother; conversely, iron loading strengthens the -OH stretching vibration, making the peak sharper and more prominent. For the C=O functional group, nitrogen doping does not significantly change the peak, but it shows a gradual strengthening trend; iron loading does not significantly change the peak, but it shows a gradual weakening trend. In summary, compared to MC, the peaks of M / NC, M / Fe-C, and M / SaFe / N-C900 all changed, indicating successful nitrogen doping and iron loading in the catalyst, thus altering the performance of the biochar.

[0051] Figure 6 The images show the Raman spectra of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. A D peak (1350 cm⁻¹) is present in the Raman spectra of the carbon materials. -1 ) and G peak (1585cm) -1 The D peak represents the sp hybridization defect of carbon atoms. 2 Structure (graphene edge structure), G peak represents the sp in-plane stretching vibration of carbon atoms. 2 Structure (planar structure). Typically, it is represented by I. D / I G The value represents the degree of defect in the material; a lower value indicates a higher degree of graphitization, and vice versa. From Figure 6 It can be seen that, compared with MC, M / NC has higher I D / I G The value is significantly increased, possibly because nitrogen doping into the carbon framework generates numerous defects and graphene edges, and the decomposition of melamine at high temperatures also promotes defect formation; while the I of M / Fe-C... D / I G The decrease in the value may be because the iron loading fills the defects on the carbon support, reducing the degree of defects. This also indicates that iron mainly exists in the form of single atoms.

[0052] Figure 7 The images show the full X-ray photoelectron spectroscopy (XPS) spectra of the molten salt modified nitrogen-doped biochar supported on a single-atom iron catalyst (M / SaFe / N-C900) in Example 1 of this invention, the treated molten salt modified biochar (MC), the molten salt modified nitrogen-doped tanshinone biochar (M / NC) in Comparative Example 1, and the molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Comparative Example 2. Figure 7It can be seen that MC, M / NC, M / Fe-C, and M / SaFe / N-C900 are dominated by C, O, and N elements. The C 1s peak appears at 284.80 eV, the O 1s peak at 532.5 eV, and the N 1s peak at 400.63 eV. Among them, the N 1s peak of M / NC and M / SaFe / N-C900 is stronger than that of MC, which is due to nitrogen doping. However, no obvious Fe peak is observed in the XPS of M / Fe-C and M / SaFe / N-C900, which may be because the Fe loading is low and it mainly exists in the form of single atoms.

[0053] In summary, the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst of this invention achieves this by using nitrogen doping to create a defect structure in the carbon substrate. This defect structure is then tightly chelated with the supported single-atom iron. Specifically, on the one hand, nitrogen doping results in a fluffy and porous structure on the surface of the biochar. This is because doping the carbon lattice with nitrogen increases the disorder of the carbon lattice, leading to more surface defects at the carbon edges. On the other hand, while the iron supported on the carbon defects in single-atom form reduces the degree of defect in the carbon substrate, it also allows the carbon material to possess the advantages of homogeneous catalysts with atomic dispersion and high atomic utilization, as well as the advantages of heterogeneous catalysts with stability and easy separation. Simultaneously, the tight chelation between the single-atom iron and the defect structure of the biochar prevents iron atoms from agglomerating and deactivating. Furthermore, the surface functional groups of the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst of this invention are mainly -OH and C=O. The peak of the -OH stretching vibration gradually weakens and becomes smoother, while the stretching vibration peak of the C=O functional group shows a gradually strengthening trend, which can better regulate the active sites and activity of the biochar. Therefore, the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst of the present invention has the advantages of rich pore structure, large specific surface area, high utilization rate of active sites, no metal ion leaching, and good recyclability. Thus, it can effectively activate persulfate and achieve efficient degradation of organic pollutants (such as antibiotics) through a combination of non-radical singlet oxygen-dominated and high-valence metal site-assisted pathway.

[0054] Example 2:

[0055] An application of the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst of the present invention in the treatment of organic pollutant wastewater, specifically, the degradation of tetracycline hydrochloride in water using the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst, comprising the following steps:

[0056] The following were taken respectively: molten salt modified nitrogen-doped tanshinone biochar supported single-atom iron catalysts (M / SaFe / N-C900, M / SaFe / N-C600, M / SaFe / N-C700, M / SaFe / N-C800, M / SaFe / N-C1000) prepared in Example 1, treated molten salt modified biochar (MC), molten salt modified nitrogen-doped tanshinone biochar prepared in Comparative Example 1 (M / NC), and molten salt modified iron-supported tanshinone biochar prepared in Comparative Example 2. 15 mg each of biochar (M / Fe-C) were added to 100 mL of tetracycline hydrochloride (TCH) solution with a concentration of 10 mg / L and a pH of 4.86. The mixture was thoroughly mixed and the tetracycline hydrochloride was adsorbed at room temperature and 450 rpm for 30 min to reach adsorption-desorption equilibrium. 0.15 g of potassium persulfate (KHSO5) was then added and the degradation reaction was carried out at room temperature and 450 rpm for 1 h to complete the degradation of tetracycline hydrochloride.

[0057] Figure 8 The images show the degradation effects of tetracycline hydrochloride on molten salt modified nitrogen-doped tanshinone biochar supported with single-atom iron catalysts (M / SaFe / N-C900, M / SaFe / N-C600, M / SaFe / N-C700, M / SaFe / N-C800, M / SaFe / N-C1000), treated molten salt modified biochar (MC), molten salt modified nitrogen-doped tanshinone biochar (M / NC), and molten salt modified iron-supported tanshinone biochar (M / Fe-C) in Example 2 of this invention. Figure 8It can be seen that the biochar catalysts activated by different modification conditions and temperatures exhibit varying effects on the degradation of TCH in PMS water. After 30 min of adsorption and 1 h of degradation, the TCH removal rates of MC, M / NC, M / Fe-C, M / SaFe / N-C600, M / SaFe / N-C700, M / SaFe / N-C800, M / SaFe / N-C900, and M / SaFe / N-C1000 were 69%, 74%, 77%, 76%, 84%, 83%, 90%, and 90%, respectively. This shows that compared to MC, the removal rates of TCH by other materials were all improved, indicating that nitrogen doping and single-atom iron loading can effectively improve the efficiency of molten salt-modified Tanshinone biochar-activated PMS in degrading TCH in water. Furthermore, compared to secondary calcination temperatures of 600℃, 700℃, and 800℃, the molten salt-modified nitrogen-doped tanshinone biochar-supported single-atom iron catalyst with secondary calcination temperatures of 900℃ and 1000℃ exhibits higher removal efficiency. This is because when the secondary calcination temperature reaches 900℃, the coordination structure of Fe and N in the material changes from saturated Fe-N4 coordination to unsaturated Fe-N3 or Fe-N2 coordination, resulting in greater polarity of the N atom and stronger electron transfer ability, thus enhancing catalytic activity. Additionally, to assess the risk of metal leaching and avoid secondary pollution, the concentration of iron ions in the solution after the reaction was determined using ICP. The Fe concentration was found to be 0.3 mg / L, meeting the specific project standard limit (Fe: 0.3 mg / L) for centralized drinking water surface water sources in the Surface Water Environmental Quality Standard (GB 3838-2002). Therefore, the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst of this invention can effectively prevent iron ion leakage and avoid environmental pollution.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for preparing a molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst, characterized in that, Includes the following steps: (1) The biomass material and bicarbonate are mixed and pyrolyzed at 600℃~800℃ under nitrogen atmosphere. After acid washing, the treated molten salt modified biochar is obtained. (2) The treated molten salt modified biochar, iron salt, water and glucose obtained in step (1) are mixed and reacted to obtain a catalyst precursor; the mass ratio of the treated molten salt modified biochar, iron salt, water and glucose is 1:1 to 4:10 to 20:10 to 20. (3) The catalyst precursor obtained in step (2) is mixed with a nitrogen source and calcined at 900℃~1000℃ under a nitrogen atmosphere to obtain a molten salt modified nitrogen-doped biochar supported single-atom iron catalyst.

2. The method for preparing the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst according to claim 1, characterized in that, In step (1), the mass ratio of the biomass material to bicarbonate is 1:0.1 to 1.

3. The method for preparing the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst according to claim 2, characterized in that, In step (3), the mass ratio of the catalyst precursor to the nitrogen source is 1:5 to 10.

4. The method for preparing the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst according to any one of claims 1 to 3, characterized in that, In step (1), the bicarbonate is sodium bicarbonate, the pyrolysis time is 1h to 2h, the heating rate during the pyrolysis process is 10℃ / min, and the specific process of acid washing is as follows: the pyrolysis product and acid are mixed, left to stand, and then washed and dried; the mass ratio of the pyrolysis product to the acid is 1:100, the acid is hydrochloric acid, the concentration of the hydrochloric acid is 0.5mol / L to 1mol / L, the standing time is 8h, and the washing is done by washing with water and anhydrous ethanol three times in sequence; the biomass material also includes the following steps before use: the biomass material and water are mixed, hydrothermally reacted at 100℃ for 2h, and then dried, pulverized, dried again, and sieved; the biomass material is Salvia miltiorrhiza, the pulverization is pulverized to 0.2mm, the sieving is passed through a 100-200 mesh sieve, and the drying temperature is 60℃.

5. The method for preparing the molten salt-modified nitrogen-doped biochar-supported single-atom iron catalyst according to any one of claims 1 to 3, characterized in that, In step (2), the iron salt is ferric nitrate nonahydrate, the reaction time is 0.5h to 1h, the reaction is carried out under ultrasonic conditions, and the catalyst precursor is further treated before use by washing, drying and grinding the reaction product; And / or, in step (3), the nitrogen source is melamine, the calcination time is 1h to 2h, and the heating rate during the calcination process is 10℃ / min.

6. A molten salt modified nitrogen-doped biochar supported single-atom iron catalyst prepared by any one of the methods described in claims 1 to 5.

7. The application of the molten salt modified nitrogen-doped biochar supported single-atom iron catalyst as described in claim 6 in the treatment of organic pollutant wastewater.

8. The application according to claim 7, characterized in that, Includes the following steps: Molten salt-modified nitrogen-doped biochar supported single-atom iron catalyst and organic pollutant wastewater are mixed, and persulfate is added to carry out a degradation reaction to achieve the degradation of organic pollutants in the water body; the ratio of molten salt-modified nitrogen-doped biochar supported single-atom iron catalyst to organic pollutant wastewater is 0.05g~0.2g∶1L.

9. The application according to claim 8, characterized in that, The amount of persulfate added is 0.75g to 3g per liter of organic pollutant wastewater. The persulfate is potassium persulfate. The concentration of organic pollutants in the organic pollutant wastewater is ≤20mg / L. The organic pollutant in the organic pollutant wastewater is an antibiotic, and the antibiotic is tetracycline hydrochloride. The mixing time is 0.5h to 1.5h, and the degradation reaction time is ≥60min.

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