Application of nitrogen-doped carbon-loaded iron composite material as catalyst in degradation of organic pollutants in water body

Abstract

The invention discloses an application of a nitrogen-doped carbon-loaded iron composite material as a catalyst in degradation of organic pollutants in a water body, the composite material takes a nitrogen-doped carbon matrix as a carrier, and monatomic iron and iron nanoclusters are dispersed on the carrier; wherein the nanocluster material of iron is coated with a graphene layer, and monatomic iron is uniformly dispersed on the graphene layer; monatomic iron is bonded with nitrogen through an Fe-N bond. When the composite material with a specific structure and specific composition is used as a catalyst to degrade organic pollutants in a water body, on one hand, the cycling stability of the catalyst can be effectively improved (the catalyst has a good degradation effect after being recycled for multiple times); on the other hand, the generated active substances are not influenced by natural organic matters or inorganic ions (such as Cl <-> and HCO3 <->) in the water body to be quenched, so that the oxidation efficiency of the active substances is not reduced, and finally, the catalyst still has good catalytic activity in a relatively large pH range.

Description

Technical Field

[0001] The present invention relates to the application of a nitrogen-doped carbon-supported iron composite material as a catalyst in the degradation of organic pollutants in water bodies. Background Art

[0002] With the acceleration of the industrialization process, the problem of water pollution has become increasingly serious. Water pollution caused by a series of organic pollutants that are difficult to biodegrade (such as antibiotics, dyes, drug residues, etc.) poses a major threat to the ecological environment and human health. Traditional water treatment technologies (biodegradation, adsorption, coagulation, etc.) are difficult to efficiently remove such organic pollutants. Therefore, the development of efficient water treatment technologies to degrade these organic pollutants has become the focus of research. As a key technology for degrading organic pollutants, advanced oxidation technologies (AOPs) have been widely reported. By generating free radicals with strong oxidation ability or non-free radicals with reaction selectivity, the decomposition of organic matter is achieved. Among them, the advanced oxidation technology based on persulfate has attracted more and more attention in the field of wastewater purification. Compared with other peroxides, persulfate has the advantages of low price, high chemical stability, simple storage and transportation, etc., and is widely used as an oxidant in the Fenton-like catalytic reaction. The advanced oxidation technology (AOP) based on persulfate (PMS) has received extensive attention due to its high oxidation ability, broad spectrum and environmental friendliness. After activation, PMS can generate various active substances such as sulfate radicals (SO4 - ·), hydroxyl radicals (·OH), singlet oxygen ( 1 O2) and high-valent metal species. Among them, high-valent iron species exhibit unique advantages in complex water environments due to their strong oxidation ability and selectivity.

[0003] At present, transition metal ions such as Fe, Co, Cu, and Mn can effectively activate PMS to generate active groups through valence conversion, and are the main catalysts for PMS activation. Among them, transition metal iron is widely distributed in the environment, has rich reserves and low toxicity to the ecosystem, and has been widely studied in the Fenton reaction. Iron, iron oxide, iron hydroxide, iron sulfide, iron nitride and iron carbide have been reported as catalysts for the oxidation of refractory organic pollutants. However, traditional iron-based catalysts have many problems: the active sites are easily deactivated (oxides are generated) and easily lost, resulting in insufficient catalytic activity stability; the generated radicals such as SO4 - · and ·OH are easily quenched by natural organic matter or inorganic ions in water bodies (such as Cl - , HCO3 - ), reducing the oxidation efficiency; especially its pH applicable range is narrow, because the traditional Fenton reaction needs to be carried out under acidic conditions (pH = 2.0 - 4.0), which limits its practical application in life. Summary of the Invention

[0004] Objective of the Invention: The objective of the present invention is to provide an application of a nitrogen-doped carbon-supported iron composite material as a catalyst in the degradation of organic pollutants in water. When this composite material with a specific structure and composition is used as a catalyst in the degradation of organic pollutants in water, on the one hand, it can effectively improve the recycling stability of the catalyst (still having good degradation effect after being recycled multiple times), and on the other hand, the active substances generated are not quenched due to the influence of natural organic matter or inorganic ions (such as Cl - 、HCO3 - ) in the water body, thus not reducing the oxidation efficiency of the active substances. Finally, it still has good catalytic activity in a wide pH range.

[0005] Technical Solution: The application of the nitrogen-doped carbon-supported iron composite material as a catalyst in the degradation of organic pollutants in water. The composite material uses a nitrogen-doped carbon matrix as a carrier, and single-atom iron and iron nanoclusters are dispersed on the carrier. Among them, the iron nanoclusters are wrapped with a graphene layer, and single-atom iron is evenly dispersed on the graphene layer. The single-atom iron is bonded to nitrogen through Fe-N bonds.

[0006] In the process of activating PMS in the present invention, SO4· - 、·OH and O2· - free radicals are generated, and non-radical high-valent iron species (Fe(IV) / Fe(V)=O) are also generated. The non-radical path is generated by the reaction of Fe-N x (single-atom iron) active sites with PMS, which can directly oxidize organic pollutants or indirectly mineralize organic pollutants through electron transfer. At the same time, the nitrogen-doped carbon substrate uses its high conductivity to promote the electron transfer between high-valent iron species and pollutants, effectively promoting the rapid degradation of pollutants.

[0007] Among them, in the composite material, the mass percentage of the iron nanoclusters is 50-60%, and the mass percentage of the single-atom iron is 40-50%.

[0008] Among them, the iron nanoclusters include Fe3C nanoparticles and nano-zero-valent iron.

[0009] Among them, the nitrogen-doped carbon matrix has a hierarchical pore structure. The number of micropores (<2μm) accounts for 60-70% of the total number of pores, which provides a high specific surface area and exposes the Fe-N x active sites; the mesopore aperture is concentrated in 2-5nm, and the number of mesopores accounts for about 30-40% of the total number of pores.

[0010] Among them, the above composite material is prepared by the following method. Specifically, first, a ferroporphyrin precursor is synthesized by the coprecipitation method, and then the ferroporphyrin precursor is kept at 700-750 °C for 2-3 h under high-purity N2; finally, the composite material is obtained by pickling.

[0011] Among them, the flow rate of high-purity N2 is 30-50 mL / min.

[0012] Among them, the heating rate is 4-6 °C / min.

[0013] Among them, the calcined powder is dissolved in a sulfuric acid solution and pickled at a water bath temperature of 60-65 °C.

[0014] The composite material of the present invention includes a nitrogen-doped carbon matrix with a hierarchical pore structure, single-atom iron highly dispersed on the carrier, and iron nanoclusters formed after the polymerization of single-atom iron. The iron nanoclusters are iron carbide nanoparticles and a small amount of nano-zero-valent iron. A graphitized carbon layer is wrapped outside the iron nanoclusters, and single-atom iron is dispersed outside the graphitized carbon layer. All single-atom iron is bonded to nitrogen through Fe-N bonds; when the composite material based on the above structure and composition is applied as a catalyst to degrade organic pollutants in water, due to the good conductivity and surface adsorption ability of Fe3C nanoparticles, on the one hand, PMS molecules can be captured by physical adsorption or chemical bonding, accelerating the cleavage of the O-O bond of PMS and promoting the rapid generation of SO4· - 、·OH、O2· - free radicals, thus achieving rapid degradation of pollutants (fast reaction rate); at the same time, since the Fe3C nanoparticles are wrapped with a nitrogen-doped graphitized carbon layer, the Fe3C nanoparticles are not easily oxidized and inactivated, nor are metal ions likely to overflow after oxidation and inactivation; on the other hand, the highly conductive Fe3C nanoparticles and the graphitized carbon layer form a conductive network. The Fe3C nanoparticles transfer electrons to single-atom iron through the graphitized carbon layer, always maintaining the electron cloud density of single-atom iron and improving its Fe III and Fe II cycle efficiency (a high electron cloud density can accelerate the reduction of Fe 3+ and the oxidation of Fe 2+ thereby maintaining an efficient Fe 3+ / Fe 2+ cycle, and further promoting its continuous and efficient PMS activation ability), thereby improving the overall reaction rate and achieving rapid and efficient degradation of pollutants.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: When the composite material with a specific structure and specific composition of the present invention is used as a catalyst for degrading organic pollutants in water, on the one hand, it can effectively improve the cyclic stability of the catalyst (still having a good degradation effect after being recycled multiple times), and on the other hand, the active substances generated are not quenched by natural organic matter or inorganic ions (such as Cl - 、HCO3 - ) in the water body, so as not to reduce the oxidation efficiency of the active substances. Finally, it still has good catalytic activity in a wide pH range. Description of the Drawings

[0016] Figure 1 Comparison of the activities of the composite materials of Example 1 and Comparative Examples 1-2 when used as catalysts;

[0017] Figure 2 Effect of different reaction conditions on the degradation effect of organic pollutants when the composite material (7FNC) prepared in Example 1 is used as a catalyst; among them, a is different pH conditions; b is different PMS concentrations; c is different catalyst concentrations; d is different TC concentrations;

[0018] Figure 3 Electron microscope images of the composite material (7FNC) prepared in Example 1; a, b are TEM; c, d are HRTEM;

[0019] Figure 4 Electron microscope images of the composite material (6FNC) prepared in Comparative Example 1;

[0020] Figure 5 XRD patterns of the materials 6FNC, 7FNC, and 8FNC prepared in Example 1 and Comparative Examples 1-2;

[0021] Figure 6 (a) Effect of different quenchers on the activity of the 7FNC / PMS reaction system for degrading tetracycline; (b) Conversion rate of PMSO to the PMSO2 probe reaction in different catalytic reaction systems. Detailed Embodiments

[0022] Example 1

[0023] The preparation method of the composite material of the present invention includes the following steps:

[0024] (1) Synthesize iron phthalocyanine precursor (FePPc) using the co-precipitation method: Weigh 3 mmol of FeCl3, 35 mmol of urea, 9 mmol of NH4Cl, 0.037 mmol of (NH4)2Mo2O7, and 5 mmol of pyromellitic dianhydride (PMDA); achieve uniform mixing of raw materials through mechanical grinding (grinding time 30 min) to form a blue-green mixture; transfer the mixture to a crucible, place it in a muffle furnace, heat up to 220 °C, and heat for 3 h; after natural cooling, wash it alternately with deionized water, acetone, and methanol 3 times, and then dry it in an oven at 60 °C for 12 h to obtain the iron phthalocyanine precursor;

[0025] (2) Grind 300 mg of FePPc powder and spread it flat in a quartz boat, then place it in a tube furnace; introduce high-purity N2 into it (flow rate 30 mL / min), heat it up to the target temperature of 700 °C at a rate of 4 °C / min, and keep it at this temperature for 3 h; after natural cooling, collect the sample, dissolve 100 mg of the powder in 400 mL of 1 M sulfuric acid solution, place it in a water bath for acid washing, and keep the temperature in the water bath at 60 °C to obtain a composite material, named 7FNC.

[0026] It can be seen from Figure 3 that in the composite material 7FNC of Example 1, there is a nitrogen-doped carbon matrix with a hierarchical pore structure, single-atom iron highly dispersed on the carrier, and nano-clusters of iron formed after the aggregation of single-atom iron. The nano-clusters of iron are iron carbide nanoparticles and a small amount of nano-zero-valent iron. There is a graphitized carbon layer wrapped outside the nano-clusters of iron, and single-atom iron is dispersed outside the graphitized carbon layer. All single-atom iron is bonded to nitrogen through Fe-N bonds; in the composite material 7FNC, the mass percentage of the nano-clusters of iron is 56% (relative to the total mass of single-atom iron and the nano-clusters of iron), and the mass percentage of single-atom iron is 44% (relative to the total mass of single-atom iron and the nano-clusters of iron).

[0027] It can be seen from Figure 6 that during the reaction of the probe compound of the composite material 7FNC in Example 1 with PMSO, a large amount of PMSO2 was generated, and the conversion rate of PMSO to PMSO2 could reach 73%, indicating that the reactive oxygen species in the reaction system mainly consisted of non-free radical high-valent iron species (Fe(IV) / Fe(V)=O). At the same time, DMSO (dimethyl sulfoxide) was used as a high-valent iron species quencher, and the reactive oxygen species quenching experiment also showed that the addition of DMSO effectively inhibited the reaction, verifying the experimental results of the probe compound again.

[0028] Comparative Example 1

[0029] A preparation method of a composite material, comprising the following steps:

[0030] (1) Synthesize iron phthalocyanine precursor (FePPc) using the co-precipitation method: Weigh 3 mmol of FeCl3, 35 mmol of urea, 9 mmol of NH4Cl, 0.037 mmol of (NH4)2Mo2O7, and 5 mmol of pyromellitic dianhydride (PMDA); achieve uniform mixing of raw materials through mechanical grinding (grinding time: 30 min) to form a blue-green mixture; transfer the mixture to a crucible, place it in a muffle furnace, heat it to 220 °C, and keep it heated for 3 h; after natural cooling, wash it alternately with deionized water, acetone, and methanol three times, and then dry it in an oven at 60 °C for 12 h to obtain the iron phthalocyanine precursor;

[0031] (2) Grind 300 mg of FePPc powder and spread it evenly in a quartz boat, then place it in a tubular furnace; introduce high-purity N2 into it (flow rate: 30 mL / min), heat it to the target temperature of 600 °C at a rate of 4 °C / min, and keep it at this temperature for 3 h; after natural cooling, collect the sample to obtain a composite material, named 6FNC.

[0032] As Figure 4 can be seen, the composite material 6FNC includes a nitrogen-doped carbon matrix with a hierarchical pore structure, and no agglomerates of iron can be seen on the surface.

[0033] Comparative Example 2

[0034] A method for preparing a composite material, comprising the following steps:

[0035] (1) Synthesize iron phthalocyanine precursor (FePPc) using the co-precipitation method: Weigh 3 mmol of FeCl3, 35 mmol of urea, 9 mmol of NH4Cl, 0.037 mmol of (NH4)2Mo2O7, and 5 mmol of pyromellitic dianhydride (PMDA); achieve uniform mixing of raw materials through mechanical grinding (grinding time: 30 min) to form a blue-green mixture; transfer the mixture to a crucible, place it in a muffle furnace, heat it to 220 °C, and keep it heated for 3 h; after natural cooling, wash it alternately with deionized water, acetone, and methanol three times, and then dry it in an oven at 60 °C for 12 h to obtain the iron phthalocyanine precursor;

[0036] (2) Grind 300 mg of FePPc powder and spread it evenly in a quartz boat, then place it in a tubular furnace; introduce high-purity N2 into it (flow rate: 30 mL / min), heat it to the target temperature of 800 °C at a rate of 4 °C / min, and keep it at this temperature for 3 h; after natural cooling, collect the sample, dissolve 100 mg of the powder in 400 mL of 1 M sulfuric acid solution, place it in a water bath for pickling, and keep the temperature in the water bath at 60 °C to obtain a composite material, named 8FNC.

[0037] In the composite material 8FNC, the mass percentage of iron nanoclusters is 66%, and the mass percentage of single-atom iron is 34%.

[0038] As Figure 5 shown, X-ray diffraction (XRD) characterized the chemical structures of the composite materials obtained in Example 1 and Comparative Examples 1-2. 7FNC showed weak diffraction peaks of Fe3C (JCPDS No. 35-0772) and metallic Fe (JCPDS No. 06-0696) in the XRD pattern (such as in the range of 35-60°), indicating the presence of Fe3C nanoparticles and a small amount of zero-valent iron. Compared with 8FNC synthesized at 800 °C, 7FNC had a lower Fe3C content, while 6FNC (600 °C) only showed a broad peak of graphite carbon (25.3°), indicating that single-atom iron did not agglomerate on the graphite carbon in 6FNC. Scanning electron microscopy and transmission electron microscopy (SEM and TEM) images of 7FNC showed that 7FNC had a porous carbon support layer and a large number of uniformly dispersed nanoparticles on the carbon support layer. High-resolution transmission electron microscopy (HRTEM) showed that 7FNC had a porous carbon substrate and uniformly distributed nanoparticles. The lattice distance of these nanoparticles was about 0.20 nm, which was consistent with the (220) plane of Fe3C; obvious hierarchical pore networks could be seen in the carbon substrate. Micropores (<2 μm) accounted for about 60-70%, which provided a high specific surface area and exposed Fe-N x active sites. Mesopores had pore diameters concentrated in the range of 2-5 nm, accounting for about 30-40%, thus promoting the diffusion of organic pollutant molecules to the active sites; in addition, crystalline graphene layers with a lattice spacing of 0.34 nm wrapped around the Fe3C material, forming a "core-shell" structure that provided strong protection and stabilized the nanocrystals, effectively preventing the oxidation inactivation of Fe3C and enabling it to have good cyclic stability when used as a catalyst.

[0039] The applications of the composite materials 6FNC, 7FNC, and 8FNC prepared in Example 1 and Comparative Examples 1-2 as catalysts for degrading organic pollutants in water were as follows:

[0040] The potassium persulfate (PMS) oxidation experiment with tetracycline (TC) as a model organic pollutant was used as a probe reaction, and the 30-min degradation rate η and rate constant (K) were used for comparison. The calculation formula for the degradation rate η was: η = 1 - C t / C0, where C t was the concentration of tetracycline (TC) at the sampling time t, and C0 was the concentration of TC in the solution at the start of the reaction. The higher the degradation rate η, the better its catalytic activity. The rate constant (K) represented the speed of the reaction rate in the reaction. The calculation formula for K was K = -In C t / C0, where C t was the concentration of tetracycline (TC) at the sampling time t, and C0 was the concentration of TC in the solution at the start of the reaction. The larger K was, the faster the reaction rate and the better the catalytic activity.

[0041] The reaction device is a Fenton-like catalytic reactor. The reaction temperature is 298K. The reaction substrate is a 50 mL tetracycline (TC) organic pollutant solution with an initial concentration of 20 mg / L. In the 50 mL organic pollutant solution, the mass concentration of the catalyst is 0.1 g / L. 1.5 mL of a potassium persulfate (PMS) solution with a concentration of 10 mg / mL is added to the 50 mL organic pollutant solution to initiate the reaction. The stirring speed is 600 rpm. The sampling times are 0 min, 1 min, 3 min, 5 min, 7 min, 9 min, 15 min, 20 min, and 30 min respectively. 1 mL of the reaction solution is taken out, and 0.5 mL of a sodium nitrite solution with a concentration of 0.2 mol / L is added to the taken sample as a reaction quencher. The mixture is stirred evenly to quench the reaction. Finally, the concentration of TC is analyzed and detected by high-performance liquid chromatography equipped with a C18 chromatographic column.

[0042] For three parallel reactions, in each reaction system, the same amounts of composite materials 6FNC, 7FNC, and 8FNC are added as catalysts respectively. The catalytic activities of composite materials 6FNC, 7FNC, and 8FNC are as Figure 1 shown in Table 1.

[0043] Table 1

[0044]

[0045] As can be seen from Table 1, composite material 7FNC can rapidly remove 84.2% of TC within 30 min, achieving a large amount of degradation of organic pollutants in a short time. The rate constant (K) of 7FNC is 0.06144 min-1, which is 1.69 times and 1.27 times that of 6FNC (0.03635 min-1) and 8FNC (0.04827 min-1) respectively, indicating that 7FNC has a faster reaction rate. This is related to the formation of a "core-shell" structure (graphene layers wrapped around Fe3C substances) to construct a conductive network. No Fe3C is formed in 6FNC, and the active sites are Fe-Nx, and the material has poor conductivity. The content of Fe3C in 8FNC is too high (76.2% is Fe3C, Fe3O4, etc.), resulting in a reduction of Fe-Nx sites and the coverage of active sites. While 7FNC not only retains the high-activity Fe-Nx configuration but also enhances electron transport through Fe3C, thus greatly improving the reaction rate and catalytic activity of the system.

[0046] The composite material 7FNC prepared in Example 1 is used as a catalyst for multiple cyclic applications. Specifically:

[0047] The reaction temperature was 298 K, and the reaction substrate was a 50 mL tetracycline (TC) organic pollutant solution with an initial concentration of 20 mg / L. In the 50 mL organic pollutant solution, the mass concentration of the catalyst (composite material 7FNC) was 0.1 g / L. 1.5 mL of a potassium persulfate (PMS) solution with a concentration of 10 mg / mL was added to the 50 mL organic pollutant solution to initiate the reaction. The stirring speed was 600 rpm. The sampling times were 0 min, 1 min, 3 min, 5 min, 7 min, 9 min, 15 min, 20 min, and 30 min. 1 mL of the reaction solution was taken out, and 0.5 mL of a sodium nitrite solution with a concentration of 0.2 mol / L was added to the taken sample as a reaction quenching agent. After mixing evenly to quench the reaction, the concentration of TC was finally analyzed and detected by high-performance liquid chromatography equipped with a C18 chromatographic column.

[0048] The catalyst after the 30-minute reaction was centrifuged and separated from the solution, washed with deionized water and anhydrous ethanol, and then placed in an oven at 60 °C for drying for 10 - 12 h for the next reaction. The same procedure was followed for each reaction, and it was cycled four times in total. The degradation effect of each reaction process is shown in Table 2.

[0049] Table 2

[0050]

[0051] As can be seen from Table 2, the composite material 7FNC of the present invention still had a degradation rate of 74.1% after multiple cycles, indicating its good catalytic stability. The effective maintenance of the catalytic activity after 4 cycles was mainly due to the fact that the carbon layer effectively protected the iron clusters and prevented their leaching, resulting in a serious decline in catalytic activity. In addition, the single-atom iron and the iron nanocluster rapidly transferred electrons through the carbon substrate, preventing the inactivation of the single-atom iron at the site after the redox reaction with PMS and keeping it always at a high catalytic activity. However, in this process, the competitive adsorption of pollutant intermediate products on the catalytic active sites led to a gradual decrease in the reaction activity with the increase in the number of cycles.

[0052] The composite material 7FNC prepared in Example 1 was used as a catalyst to activate PMS to degrade TC in water, and the influence of different reaction conditions on the catalytic activity of the catalyst was regulated:

[0053] The pH of the reaction system was adjusted to increase by using a 1 mmol / L sodium hydroxide solution and decreased by using a 1 mmol / L hydrochloric acid solution to achieve the regulation of the reaction pH. At the same time, the concentrations of PMS in the reaction system were changed to 0.1 g / L, 0.3 g / L, and 0.7 g / L, the concentrations of the catalyst were changed to 0.1 g / L, 0.2 g / L, and 0.4 g / L, and the initial concentration of TC was changed to 10 mg / L, 20 mg / L, and 80 mg / L respectively to achieve the regulation of the concentrations of PMS, the catalyst, and TC in the reaction system. The obtained degradation effects are as Figure 2 shown in Table 3.

[0054] Table 3 Catalytic activities of the catalyst under different reaction conditions

[0055]

[0056]

[0057] As can be seen from Table 3, as the concentration of PMS increased from 0.1 g / L to 0.3 g / L, the degradation effect was significantly improved, which was mainly due to the increase in the concentration of active free radicals. However, when the concentration of PMS increased from 0.3 g / L to 0.7 g / L, the degradation effect showed a deteriorating trend, which was because too high a concentration of PMS would cause it to react with itself to generate active species with poor reactivity, reducing the concentration of PMS effectively participating in the reaction; the increase in the concentration of the catalyst did not show an obvious promoting effect on the removal rate of TC, which might be because sufficient catalytic sites had been provided when the concentration of the catalytic sites was 0.1 g / L.

[0058] Under different pH reaction conditions, two different reactive oxygen species were generated at the iron single-atom sites and metal iron nanocluster sites, namely non-radical high-valent iron species and radical species. Under acidic conditions, the radicals generated by the metal nanoclusters showed excellent oxidation ability and could quickly remove pollutants. At the same time, its external carbon layer structure also prevented the leaching of metal iron ions, ensuring the stability of the catalytic structure. Under alkaline conditions, it was beneficial to the activation of PMS at the iron single-atom sites, promoting the generation of non-radical high-valent iron species. More importantly, in the catalytic reaction, single-atom iron and metal clusters achieved rapid electron transfer between the two components through the nitrogen-doped graphitic carbon substrate, realizing the cooperation of the two sites, thereby achieving the efficient degradation of pollutants in a wide pH range.

[0059] The composite material 7FNC prepared in Example 1 was used as a catalyst to activate PMS to degrade TC in water, and the influence of different reaction temperatures on the catalytic activity of the catalyst was investigated:

[0060] Table 4 shows the influence of different reaction temperatures on the reaction activity of the catalyst

[0061]

[0062] As can be seen from Table 4, the degradation efficiency of the composite material 7FNC at a low temperature of 277 K is only 69.2%. Due to the insufficient formation of active sites of Fe3C and Fe-N at low temperatures, the oxidation ability of the catalyst is directly reduced. At temperatures of 313 K and 328 K, the catalyst activity also shows a downward trend. This may be because high temperatures cause the inactivation of the catalyst active sites. Under high-temperature reaction conditions, Fe3C nanoparticles may aggregate or oxidize to Fe oxides (such as Fe3O4, Fe2O3) due to thermodynamic instability, resulting in a decrease in the number of active sites. Additionally, high temperatures may damage the Fe-N x coordination structure and reduce the ability to generate high-valent iron species. Therefore, the degradation efficiency of TC decreases. x

[0063] Application of the composite material 7FNC prepared in Example 1 as a catalyst to activate PMS for the degradation of bisphenol A, phenol, and methyl orange in water (at 298 K and pH 6.6). The degradation results are shown in Table 5.

[0064] Table 5

[0065]

[0066] As can be seen from Table 5, the composite material 7FNC exhibits good catalytic degradation performance for various organic pollutants.

[0067] Application of the composite material 7FNC prepared in Example 1 as a catalyst to activate PMS for the degradation of TC in water. By adding different ionic salts to the reaction system to change the water quality conditions, the added ionic salts are sodium chloride, sodium sulfate, sodium bicarbonate, sodium carbonate, and disodium hydrogen phosphate (NaCl, Na2SO4, NaHCO3, Na2CO3, Na2HPO4). The concentration of ionic salts in the reaction system after addition is uniformly controlled at 10 mmol / L (the reaction is carried out at a temperature of 298 K). The degradation effect of TC after adding ionic salts is shown in Table 6.

[0068] Table 6

[0069]

[0070] As can be seen from Table 6, the addition of chloride ions, sulfate ions, bicarbonate ions, and hydrogen phosphate ions has little effect on the reaction, while the addition of carbonate ions slightly inhibits the reaction. The inhibition of carbonate ions on the catalytic performance is mainly due to its tendency to react with free radicals to form carbonate radicals with lower reactivity. Therefore, it shows that the active substances generated by activating PMS with the catalyst of the present invention are not affected by natural organic matter or inorganic ions in water (such as Cl - , HCO3 - ​) is quenched due to the influence, so as not to reduce the oxidation efficiency of the active substance.

Claims

1. Application of a nitrogen-doped carbon-supported iron composite material as a catalyst in degrading organic pollutants in water, characterized in that: The composite material uses a nitrogen-doped carbon matrix as a carrier, on which single-atom iron and iron nanoclusters are dispersed; among them, the iron nanoclusters are wrapped with a graphene layer, and single-atom iron is evenly dispersed on the graphene layer; the single-atom iron is bonded to nitrogen through Fe-N bonds.

2. The application according to claim 1, characterized in that: Among them, In the composite material, the mass percentage of the iron nanoclusters is 50-60%, and the mass percentage of the single-atom iron is 40-50%.

3. The application according to claim 1, wherein: The iron nanoclusters include Fe3C nanoparticles and nano-zero-valent iron.

4. The application according to claim 1, wherein: The nitrogen-doped carbon matrix has a hierarchical pore structure, and the number of micropores accounts for 60-70% of the total number of pores; the number of mesopores accounts for 30-40% of the total number of pores.

5. The application according to claim 4, characterized in that: The pore diameter of the micropores is <2μm; the pore diameter of the mesopores is concentrated in the range of 2-5nm.

6. The application according to claim 1, wherein: The composite material is prepared by the following method: First, a ferric phthalocyanine precursor is synthesized by the co-precipitation method, and then the ferric phthalocyanine precursor is kept at 700-750°C for 2-3h in high-purity N2; finally, the composite material is obtained by pickling.

7. The application according to claim 6, wherein: The flow rate of high-purity N2 is 30-50mL / min.

8. The application according to claim 6, wherein: The heating rate is 4-6°C / min.

9. The application according to claim 6, wherein: The pickling refers to: dissolving the calcined powder in a sulfuric acid solution and pickling at a water bath temperature of 60-65°C.

10. The application according to claim 1, wherein: The specific application process is as follows: in the pollutant solution, the initial concentration of organic pollutants is 20 - 30 mg·L -1 , the mass concentration of the composite material is not higher than 0.1 g / L; the mass concentration of PMS is 0.1 - 0.3 g / L, and the reaction is carried out at a temperature of 25 - 30 °C and a pH value of 3 - 11.

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