Nitrogen modified iron-cobalt bimetallic catalyst as well as preparation method and application thereof

Abstract

The invention provides a nitrogen modified iron-cobalt bimetallic catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. The catalyst takes iron and cobalt as active components, and is prepared by adopting a coprecipitation-hydrothermal-step atmosphere heat treatment process: firstly, carrying out coprecipitation reaction on iron salt and cobalt salt, controlling the pH value to be 11 + / -0.5, carrying out aging and hydrothermal treatment, filtering, washing, drying and grinding to obtain a precursor; and calcining the precursor in a hydrogen-containing mixed atmosphere at 400-500 DEG C, and then calcining the precursor in an ammonia-containing mixed atmosphere at 450-600 DEG C to obtain the nitrogen surface modified iron-cobalt bimetallic catalyst. The catalyst is of a carrier-free iron-cobalt bimetallic structure, nitrogen atoms are embedded into alloy lattices or adsorbed on the surface in the form of pyridine nitrogen, pyrrole nitrogen or graphite nitrogen, and a Fe / Co-N high-activity interface is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalysts and organic wastewater treatment, and is a nitrogen surface modified iron-cobalt bimetallic Fenton-like oxidation catalyst and its application in organic wastewater treatment. BACKGROUND

[0002] With the transformation of industrial development mode towards green, circular and low-carbon, the efficient and advanced treatment of industrial wastewater, especially the organic wastewater and organic high-salinity wastewater with complex composition, high toxicity and poor biodegradability, has become a key bottleneck restricting the green and sustainable development of pharmaceutical, pesticide, dyeing and petrochemical industries. For such high-salinity wastewater rich in refractory and toxic organic pollutants such as benzene series, halogenated organic compounds and heterocyclic compounds, and with salinity exceeding 1%, traditional biological treatment methods are often inefficient or even ineffective. Advanced oxidation technology based on the generation of hydroxyl radicals is considered as the most promising deep treatment method, and Fenton-like oxidation technology has attracted much attention due to its ability to overcome the defects of traditional homogeneous Fenton reaction such as secondary pollution and high operation cost.

[0003] Iron-cobalt bimetallic catalysts exhibit good application potential in Fenton-like oxidation due to their excellent synergistic catalytic effect. In the development of iron-cobalt Fenton catalysts, various attempts have been made in the prior art.

[0004] On the one hand, researchers attempt to load active components on carriers to improve the recyclability of the catalyst. Chinese patent application CN201710859772.4 (hereinafter referred to as scheme one) discloses a solid-supported Fenton catalyst and a preparation method thereof. The method uses alumina balls as the carrier, loads aluminum nitrate, copper nitrate and cobalt nitrate on the carrier by impregnation, and then performs alkali treatment, urea soaking and high-temperature calcination to obtain the solid-supported Fenton catalyst. The catalyst can be used in combination with H2O2 to degrade organic pollutants in water.

[0005] However, the technical solution has the following limitations: first, the catalyst needs to be loaded on an alumina carrier, and the preparation process involves multiple impregnation, alkali treatment and urea treatment, which is relatively complicated; second, the introduction of aluminum and copper elements in the active component may affect the exposure efficiency of iron-cobalt active sites and the full play of their synergistic effect; third, the catalyst does not involve surface modification of the active component by nitrogen element, and there is room for further optimization of the efficiency of generating hydroxyl radicals and the mineralization ability of refractory organic matter; fourth, the tolerance and stability of the catalyst in high-salinity complex wastewater systems have not been reported.

[0006] On the other hand, researchers strive to improve the exposure of active sites of the catalyst through structural design. Chinese patent application CN201811555793.8 (hereinafter referred to as scheme two) discloses a low-valence mesoporous iron-cobalt Fenton-like catalyst and a preparation method thereof. The method uses molecular sieve KIT-6 as a hard template, dissolves iron salt and cobalt salt in liquid alcohol, stirs and evaporates by heating to concentrate the solution to precipitate, and then goes through high-temperature calcination, strong-alkali template removal, and hydrogen reduction to prepare a low-valence iron-cobalt Fenton-like catalyst with a mesoporous structure. The catalyst can be used for wastewater treatment, and its mesoporous structure is beneficial to increasing the exposure of active sites.

[0007] However, the technical solution has the following limitations: first, the preparation process needs to use molecular sieve KIT-6 as a hard template to construct a mesoporous structure, and then needs to use a strong alkali solution to dissolve and remove the template, which is complicated and may cause loss of active components during the template removal process; second, although the catalyst is treated by hydrogen reduction to obtain low-valence metal, it does not involve chemical modification of nitrogen elements on the surface of the active component, and the electronic structure and catalytic performance of the surface active center still have room for further optimization; third, the scheme does not explicitly state the tolerance of the catalyst in a high-salt complex wastewater system, and its catalytic activity and stability need to be verified for organic wastewater containing high concentrations of chloride ions or sulfate ions; fourth, the structural stability of the mesoporous structure obtained by the template method needs to be considered in long-term operation.

[0008] In summary, the existing iron-cobalt Fenton-like catalysts mainly have the following common technical problems: first, the preparation process is complicated, scheme one involves multiple steps of impregnation and alkali treatment, and scheme two relies on the template method and strong alkali etching, which are not conducive to the simplicity and economy of industrial production; second, there is a lack of chemical modification of the surface active center of the catalyst, and neither scheme one nor scheme two introduces nitrogen elements to regulate the surface of the iron-cobalt active phase, and the intrinsic activity of generating hydroxyl radicals needs to be improved; third, the adaptability to high-salt complex wastewater systems is insufficient, and the existing technologies have not specifically addressed the problem of inhibition of high-concentration chloride ions or sulfate ions on catalytic activity.

[0009] In view of the above deficiencies in the prior art, it is of great significance to develop an iron-cobalt Fenton-like oxidation catalyst with a simple preparation process, clear active center structure, surface chemical modification, and strong salt tolerance, which can promote the practical application of advanced oxidation technology in the field of industrial wastewater deep treatment. SUMMARY

[0010] The purpose of this invention is to provide a nitrogen-modified iron-cobalt bimetallic catalyst, its preparation method, and its application. Through a dual regulation strategy of nitrogen doping modification and synergistic effect of iron-cobalt bimetal, and using a simple process of co-precipitation, hydrothermal treatment, and stepwise atmosphere treatment, nitrogen atoms are used to directly chemically modify the surface of the iron-cobalt bimetallic catalyst, forming a highly active Fe / Co-N interface. This significantly enhances the ability of Fenton-like oxidation catalysts to efficiently generate hydroxyl radicals during the deep treatment of industrial organic wastewater and high-salt organic wastewater.

[0011] The embodiments of the present invention are implemented as follows: A method for preparing a nitrogen-modified iron-cobalt bimetallic catalyst includes the following steps: Step 1: Dissolve iron and cobalt salts in water and stir to form an aqueous solution of iron and cobalt mixed salts, A; dissolve potassium hydroxide in water to form solution B; under heating and stirring, add solution A and solution B dropwise to the reaction vessel in parallel, control the pH of the reaction system to 10.5-11.5, and after precipitation and aging, obtain a suspension containing precipitate; Step 2: The suspension obtained in Step 1 is subjected to hydrothermal treatment, cooled and filtered, and the resulting precipitate is washed until neutral, dried and ground to obtain the catalyst precursor. Step 3: The catalyst precursor obtained in Step 2 is calcined at a first temperature in a hydrogen-containing mixed atmosphere. After cooling, it is calcined at a second temperature in an ammonia-containing mixed atmosphere. After cooling, a nitrogen-surface-modified iron-cobalt bimetallic Fenton oxidation catalyst is obtained.

[0012] In a preferred embodiment of the present invention, the iron salt is at least one hydrate of ferric nitrate, ferric sulfate, or ferric chloride, and the cobalt salt is at least one hydrate of cobalt nitrate, cobalt sulfate, or cobalt chloride; in the iron-cobalt mixed salt aqueous solution A, the concentration of iron ions is 0.33-0.9 mol / L, and the concentration of cobalt ions is 0.33-0.9 mol / L; in solution B, the concentration of potassium ions is 3-7 mol / L.

[0013] In a preferred embodiment of the present invention, in step one, the heating and stirring temperature is 25-75°C and the stirring speed is 300-500 r / min; in step two, the hydrothermal treatment temperature is 120-160°C and the time is 23-25 ​​hours.

[0014] In a preferred embodiment of the present invention, the hydrogen-containing mixed atmosphere is a 5-20% H2 / Ar mixture, and the gas flow rate is 0.33-1.16 cm³ g. - ¹ s - ¹; The ammonia-containing mixed atmosphere is a 50-100% NH3 / Ar mixture, with a gas flow rate of 0.33-1.16 cm³ g. - ¹ s - ¹.

[0015] In a preferred embodiment of the present invention, in step three above, the temperature of the first calcination treatment is 400-500°C and the time is 4.5-5.5 hours; the temperature of the second roasting treatment is 450-600°C and the time is 3.5-4.5 hours.

[0016] The present invention also provides a nitrogen-modified iron-cobalt bimetallic catalyst, which is prepared by any of the aforementioned preparation methods. The catalyst uses iron and cobalt as active components, and nitrogen atoms are incorporated into the structure of the iron-cobalt bimetallic catalyst by heat treatment in a hydrogen / ammonia mixed atmosphere to modify the surface. In the catalyst, iron accounts for 21%-67% of the total mass of the catalyst, and cobalt accounts for 23%-68% of the total mass of the catalyst.

[0017] In a preferred embodiment of the present invention, the above-mentioned iron-cobalt bimetal forms an FeCo alloy phase; nitrogen atoms are embedded in the alloy lattice or adsorbed on the alloy surface in the form of at least one of pyridine nitrogen, pyrrole nitrogen or graphitic nitrogen, forming an Fe / Co-N active interface.

[0018] The present invention also provides an application of nitrogen-modified iron-cobalt bimetallic catalyst, including the application of the aforementioned nitrogen-modified iron-cobalt bimetallic catalyst in the degradation of organic wastewater pollutants.

[0019] In a preferred embodiment of the present invention, the catalyst is contacted with organic wastewater with a pH of 3-11 in a reactor, and the organic matter in the wastewater is degraded at a reaction temperature of 20-50°C.

[0020] In a preferred embodiment of the present invention, the above-mentioned organic wastewater contains chloride ions or sulfate ions, the concentration of which is independently 0-0.513 mol / L; the reactor is a fixed-bed tubular reactor or a batch reactor.

[0021] The beneficial effects of the embodiments of the present invention are: 1. This invention employs a process route of co-precipitation, hydrothermal treatment, and stepwise atmosphere processing. Unlike Scheme 2, it does not rely on molecular sieve KIT-6 as a hard template to construct the mesoporous structure, nor does it require the cumbersome step of dissolving and removing the template with a strong alkaline solution, thus avoiding the loss of active components during template removal. Furthermore, unlike Scheme 1, this invention does not require multiple impregnations and alkaline treatments using alumina microspheres or similar carriers, directly preparing a carrier-free iron-cobalt bimetallic catalyst. This results in more complete exposure of the active components and a higher density of active sites per unit mass of catalyst. 2. This invention employs a stepwise heat treatment process involving calcination in a hydrogen-containing mixed atmosphere and roasting in an ammonia-containing mixed atmosphere for in-situ surface modification of iron-cobalt bimetallic catalysts with nitrogen atoms. Compared to Scheme 2, which only obtains low-valence metals through hydrogenation without nitrogen modification, this invention embeds nitrogen atoms in the iron-cobalt alloy lattice or adsorbs them onto the FeCo alloy surface in the form of pyridine nitrogen, pyrrole nitrogen, or graphitic nitrogen, forming a unique Fe / Co-N highly active interface that enables the efficient generation of highly oxidizing hydroxyl radicals. This interface structure optimizes the electron configuration of the active centers, lowers the reaction energy barrier, and significantly improves the generation efficiency of hydroxyl radicals. 3. This invention uses a small amount of catalyst, exhibits excellent degradation of organic pollutants, and demonstrates superior tolerance to complex high-salt wastewater systems. Particularly in wastewater containing high concentrations of chloride or sulfate ions, the catalyst maintains high catalytic activity, with activity decay significantly lower than that described in Schemes 1 and 2. This is attributed to the stable Fe / Co-N interface structure formed by nitrogen surface modification, which effectively resists the poisoning effect of salt ions on the active sites, making the catalyst a promising candidate for advanced treatment of high-salt organic wastewater. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the preparation method of nitrogen-modified iron-cobalt bimetallic catalyst according to an embodiment of the present invention; Figure 2 The image shows the XRD pattern of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst before reaction in an embodiment of the present invention. Figure 3 The XRD patterns of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst before and after use in this embodiment of the invention are shown. Figure 4 XPS image of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst N1 s in an embodiment of the present invention; Figure 5 This is a diagram showing the effect of different Fe / Co ratios in the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalysts of this invention on the degradation of phenol. Figure 6 The graph shows the performance of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst Fe1Co1 / N in degrading phenol at different temperatures according to an embodiment of the present invention. Figure 7This is a cycle performance diagram of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst Fe1Co1 / N for phenol degradation according to an embodiment of the present invention; Figure 8 The graph shows the performance of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst Fe1Co1 / N in degrading phenol under different sulfate ion concentrations according to embodiments of the present invention. Figure 9 The figures shown are of the performance of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst Fe1Co1 / N in degrading phenol under different chloride ion concentrations according to embodiments of the present invention. Figure 10 The graph shows the performance of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst Fe1Co1 / N in degrading organic matter according to an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be used to limit the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer; reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0025] This embodiment provides a nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst and its preparation method. This type of Fenton oxidation catalyst uses iron and cobalt as active components, and the structure of the iron-cobalt bimetallic catalyst is modified by incorporating nitrogen atoms through heat treatment in a hydrogen / ammonia mixed atmosphere. In the catalyst, iron accounts for 21%-67% of the total catalyst mass, and cobalt accounts for 23%-68% of the total catalyst mass. Please refer to [link to relevant documentation]. Figure 1 It includes the following steps: S1: Coprecipitation reaction Iron and cobalt salts were dissolved together in an aqueous phase and stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. Potassium hydroxide was dissolved in deionized water to form a homogeneous solution B. Solutions A and B were slowly added dropwise to a co-precipitation reactor while continuously heating and stirring, maintaining the pH of the mixed salt solution in the reactor at approximately 11 (pH = 11 ± 0.5). The mixture was then allowed to age for 2 hours, forming a suspension containing the precipitate. The amount of iron salt added was calculated based on an iron content of 21%-67% of the total mass of the catalyst, and the amount of cobalt salt added was calculated based on a cobalt content of 23%-68% of the total mass of the catalyst. The iron salt was ferric nitrate hydrate, ferric sulfate hydrate, or ferric chloride hydrate, and the cobalt salt was cobalt nitrate hydrate, cobalt sulfate hydrate, or cobalt chloride hydrate. The concentrations of iron and cobalt ions in the iron-cobalt aqueous solution were 0.33-0.9 mol / L and 0.33-0.9 mol / L, respectively. The potassium ion concentration in the potassium hydroxide solution was 3-7 mol / L.

[0026] S2: Hydrothermal treatment The above suspension was subjected to hydrothermal treatment in a co-precipitation reactor for 24 hours, followed by natural cooling of the mixed suspension to room temperature. The heating and stirring temperature was 25-75℃, the hydrothermal temperature rise was 120-160℃, and the stirring speed was 300-500 r / min. The cooled mixed suspension was then filtered to separate the precipitate, and the separated precipitate was washed with deionized water until the pH of the washing solution dropped to 7.0.

[0027] S3: Precursor Preparation The washed precipitate was dried and ground into a uniform powder to obtain a precursor for an iron-cobalt bimetallic advanced oxidation catalyst.

[0028] S4: Step-by-step atmosphere heat treatment The aforementioned precursor was first calcined for 5 hours at a first temperature under a hydrogen-containing mixed atmosphere. After cooling to room temperature, an ammonia-containing mixed gas was introduced, followed by calcination at a second temperature for 4 hours and then cooling to room temperature to obtain a nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst. The hydrogen-containing mixed gas was a 5-20% H2 / Ar mixture, and the flow rate of the hydrogen-containing mixed gas was 0.33-1.16 cm³. 3 g-1 s-1. The ammonia-containing gas mixture is a 50-100% NH3 / Ar mixture, with a flow rate of 0.33-1.16 cm⁻¹. 3 g-1 s-1. The first temperature condition is 400-500℃, and the second temperature condition is 450-600℃.

[0029] This invention also provides the application of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalysts in the degradation of organic wastewater pollutants.

[0030] The specific process is as follows: Sodium hydroxide or hydrochloric acid is added to the organic wastewater to adjust the pH value of the aqueous solution to 3-11; then, the solution is introduced into a reactor to contact the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst at the reaction temperature to degrade the organic matter in the wastewater. In this embodiment, the reactor can be a fixed-bed tubular reactor or a batch reactor. The concentration of chloride or sulfate ions in the organic wastewater is 0-0.513 mol / L, and the reaction temperature is 20-50℃.

[0031] This invention utilizes a co-precipitation-hydrothermal-step atmospheric heat treatment process to prepare a series of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalysts with different iron-cobalt molar ratios, and systematically characterizes their physicochemical structure and catalytic performance. Comparative examples with different iron-cobalt ratios, different ammonia treatment concentrations, and a single-metal control are used to fully verify the superior effectiveness of the technical solution of this invention.

[0032] Example 1 In this embodiment, the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution is 2:1, or the simplest integer ratio of the amounts of iron and cobalt ions is 2:1. 0.06 mol of iron salt and 0.03 mol of cobalt salt (iron nitrate and cobalt nitrate, respectively) are weighed and placed in a glass beaker. 75 mL of deionized water is added, and the mixture is stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. An appropriate amount of potassium hydroxide is weighed and dissolved in deionized water to prepare a 5 mol / L potassium hydroxide solution B.

[0033] During continuous heating and stirring at a speed of 400 r / min and a heating temperature of 50℃, solutions A and B were slowly added dropwise to the co-precipitation reactor. The pH value of the mixed salt solution in the reactor was kept constant at 11±0.5. After the addition was completed, stirring was continued for 2 hours to precipitate and age the solution, forming a suspension containing the precipitate.

[0034] The above suspension was heated to 120°C and hydrothermally reacted in a co-precipitation reactor for 24 hours, then naturally cooled to room temperature. The cooled suspension was filtered and separated, and the separated precipitate was repeatedly washed with deionized water until the pH of the washing solution dropped to 7.0.

[0035] The washed precipitate was dried at 80°C for 12 hours and then ground into a uniform powder to obtain the iron-cobalt bimetallic catalyst precursor.

[0036] The aforementioned precursor was placed in a tube furnace and subjected to a hydrogen-containing mixed atmosphere (5% H2 / Ar mixture, flow rate 0.83 cm³g). - ¹ s - ¹) The mixture was heated to 400℃ at a rate of 5℃ / min and calcined for 5 hours, then cooled to room temperature. The process was then switched to an ammonia-containing mixed gas (80% NH3 / Ar mixture, flow rate 0.83 cm³ g / L). - ¹ s - ¹), calcined at 450℃ for 4 hours at a rate of 5 ℃ / min, and then cooled to room temperature to obtain a nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst, denoted as Fe2Co1 / N.

[0037] Example 2 According to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution being 1:1, 0.045 mol of iron salt and 0.045 mol of cobalt salt were weighed and placed in a glass beaker. 75 mL of deionized water was added, and the mixture was stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. The remaining preparation steps were the same as in the first embodiment, and the resulting catalyst was denoted as Fe1Co1 / N.

[0038] Example 3 According to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution being 1:2, 0.03 mol of iron salt and 0.06 mol of cobalt salt were weighed and placed in a glass beaker. 75 mL of deionized water was added, and the mixture was stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. The remaining preparation steps were the same as in Example 1, and the resulting catalyst was denoted as Fe1Co2 / N.

[0039] Example 4 According to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution being 1:3, 0.0225 mol of iron salt and 0.0675 mol of cobalt salt were weighed and placed in a glass beaker. 75 mL of deionized water was added, and the mixture was stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. The remaining preparation steps were the same as in Example 1, and the resulting catalyst was denoted as Fe1Co3 / N.

[0040] Comparative Example 1 According to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution being 3:1, 0.0675 mol of iron salt and 0.0225 mol of cobalt salt were weighed and placed in a glass beaker. 75 mL of deionized water was added, and the mixture was stirred at room temperature to form a homogeneous and transparent iron-cobalt mixed salt aqueous solution A. The remaining preparation steps were the same as in Example 1, and the resulting catalyst was denoted as Fe3Co1 / N.

[0041] Comparative Example 2 According to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution being 1:4, 0.018 mol of iron salt and 0.072 mol of cobalt salt were weighed, and the remaining preparation steps were the same as in Example 1. The resulting catalyst was denoted as Fe1Co4 / N.

[0042] Comparative Example 3 (1) Weigh 0.045 mol of iron salt and 0.045 mol of cobalt salt according to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution of 1:1. The precursor preparation steps are the same as in Example 1. After treating the precursor in a hydrogen-containing mixed atmosphere, a 40% NH3 / Ar ammonia-containing mixed gas (flow rate 0.83 cm³ g) is used. - ¹ s - ¹) Perform a second calcination at a temperature, and the remaining steps are the same as in Example 1. The resulting catalyst is denoted as Fe1Co1 / N (40% NH3).

[0043] (2) Weigh 0.045 mol of iron salt and 0.045 mol of cobalt salt according to the molar ratio of iron to cobalt ions in the iron-cobalt aqueous solution of 1:1. The precursor preparation steps are the same as in Example 1. After calcining the precursor in a hydrogen-containing mixed atmosphere, no further roasting treatment in an ammonia-containing mixed atmosphere is performed. The remaining steps are the same as in Example 1. The resulting catalyst without nitrogen modification is denoted as Fe1Co1.

[0044] Comparative Example 4 Weigh 0.09 mol of iron salt and place it in a glass beaker. Add 75 mL of deionized water and stir at room temperature to form a homogeneous and transparent aqueous solution of iron salt, A. The remaining preparation steps, including co-precipitation, hydrothermal treatment, and stepwise atmosphere treatment, are the same as in Example 1. The resulting single-metal catalyst is denoted as Fe / N.

[0045] Comparative Example 5 Weigh 0.09 mol of cobalt salt and place it in a glass beaker. Add 75 mL of deionized water and stir at room temperature to form a homogeneous and transparent aqueous solution of cobalt salt, A. The remaining preparation steps, including co-precipitation, hydrothermal treatment, and stepwise atmosphere treatment, are the same as in Example 1. The resulting single-metal catalyst is denoted as Co / N.

[0046] The physicochemical properties of nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalysts are characterized in the attached figure.

[0047] Figure 2 The image shows the XRD pattern of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst of this invention before the reaction. As can be seen from the image, the catalyst exhibits obvious FeCo alloy phase characteristic diffraction peaks, indicating the formation of a stable iron-cobalt alloy structure.

[0048] Figure 3 The image shows the XRD pattern of the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst of this invention after use. As can be seen from the image, the catalyst retains its original crystal structure after the catalytic reaction, with no significant changes in the position and intensity of the diffraction peaks, demonstrating the excellent reaction stability of this catalyst.

[0049] Figure 4 The image shows the XPS spectrum of the Fe1Co1 / N catalyst N 1s from Example 2 of this invention. Characteristic peaks attributable to pyridine nitrogen, pyrrole nitrogen, and graphitic nitrogen can be observed in the image. Simultaneously, a characteristic peak at the binding energy of 397 eV, attributable to the Fe / Co-N bond, appears, indicating that nitrogen atoms have been successfully doped into the iron-cobalt alloy and formed chemical bonds with the metal, constructing a highly active Fe / Co-N interface.

[0050] Catalyst performance evaluation experiment 1. Comparative Experiment on Phenol Degradation Performance A 100 mg / L phenol solution was placed in a reactor, and NaCl was added to a mass fraction of 2% to simulate high-salt organic wastewater. The pH of the solution was adjusted to 4-5 using hydrochloric acid or sodium hydroxide. 0.025 g / L of catalyst was added to the reactor, and the mixture was sonicated for 5 minutes to ensure uniform catalyst dispersion. The reactor was placed on a magnetic stirrer, heated to 40°C, and stirred at 400 r / min to allow for pre-adsorption equilibrium. Then, H₂O₂ was added to the reactor to an initial concentration of 10 mmol / L to initiate a Fenton-like catalytic degradation reaction. After 10 minutes of reaction, samples were taken to determine the residual phenol concentration, and the degradation rate was calculated. The results are shown in Table 1.

[0051] Table 1. Comparison of degradation performance of different catalysts on simulated phenol wastewater containing 2% NaCl

[0052] As can be seen from the data in Table 1: (1) The nitrogen-modified iron-cobalt bimetallic catalysts prepared in Examples 1-4 of this invention showed excellent catalytic activity and high salt tolerance. Under high salt conditions containing 2% NaCl, the degradation rate of phenol reached more than 96% within 10 minutes.

[0053] (2) Among them, Example 2 (Fe1Co1 / N) showed the best effect, with a degradation rate of 100%, indicating that the bimetallic synergistic effect was strongest when the iron-cobalt molar ratio was 1:1.

[0054] (3) Comparing Comparative Examples 1 and 2, it can be seen that when the iron-cobalt ratio deviates too far from 1:1, such as 3:1 or 1:4, the catalytic activity decreases significantly.

[0055] (4) Comparison with Example 3 shows that when the ammonia treatment concentration is insufficient (40% NH3) or no nitrogen modification is performed at all, the catalyst activity is significantly lower than that in Example 2, which proves the key role of nitrogen surface modification.

[0056] (5) Comparing Comparative Examples 4 and 5, it can be seen that the single metal catalyst (Fe / N or Co / N) has extremely low activity, indicating that the synergistic effect of iron and cobalt bimetals is a necessary condition for achieving efficient catalysis.

[0057] Furthermore, from Figure 5It can be seen that under the same reaction conditions: initial phenol concentration of 100 mg / L, catalyst dosage of 0.025 g / L, H2O2 concentration of 10 mmol / L, pH 4-5, 2% NaCl content, and reaction temperature of 40℃, the degradation rates of phenol by catalysts with different iron-cobalt molar ratios showed significant differences. Among them, the Fe1Co1 / N catalyst prepared in Example 2 exhibited the fastest degradation rate, rapidly reducing the phenol concentration to a minimum value in the initial stage of the reaction; followed by Fe1Co2 / N in Example 3 and Fe2Co1 / N in Example 1; the Fe1Co3 / N catalyst in Example 4 had a relatively slower degradation rate. However, all catalysts in the examples were able to degrade more than 96% of the phenol within 10 minutes, with Fe1Co1 / N achieving a 100% degradation rate after 10 minutes. Combined with the data in Table 1, it can be seen that Fe1Co1 / N has the best final removal effect, indicating that an iron-cobalt molar ratio of 1:1 is most conducive to achieving deep mineralization of pollutants.

[0058] 2. Effect of reaction temperature on catalytic performance The degradation effect of phenol at an initial concentration of 100 mg / L, catalyst Fe1Co1 / N dosage of 0.025 g / L, H2O2 concentration of 10 mmol / L, pH 4-5, and containing 2% NaCl was investigated at reaction temperatures of 10℃, 20℃, 30℃, 40℃, and 50℃. The results are as follows: Figure 6 As shown, the Fe1Co1 / N catalyst maintains high catalytic activity in the range of 20-50℃, with a slight decrease at 10℃, and the best performance at 40-50℃. This indicates that the catalyst of the present invention is suitable for room temperature or mild heating conditions. The catalyst of the present invention maintains high catalytic activity in a wide temperature range and is suitable for wastewater treatment under different working conditions, and has the potential for energy saving and consumption reduction.

[0059] 3. Catalyst Cyclic Stability Experiment The degradation reaction was carried out under the following conditions: initial phenol concentration of 100 mg / L, catalyst Fe1Co1 / N dosage of 0.2 g / L, H2O2 concentration of 10 mmol / L, pH 4-5, containing 2% NaCl, and reaction temperature of 40℃. After 20 minutes of reaction, the catalyst was separated by a magnet, washed three times with ethanol and deionized water, dried at 70℃ for 12 hours, and then reused. Results from... Figure 7 It can be seen that after five cycles, the Fe1Co1 / N catalyst still maintains excellent degradation activity for phenol-simulated wastewater containing 2% NaCl. The degradation curves of each cycle basically overlap, and the phenol removal rate remains above 90% after 100 minutes of reaction. Figure 3The XRD structure of the catalyst showed no significant change before and after use, which fully demonstrates that the catalyst of this invention has good reaction stability and recycling performance in the treatment of high-salt organic wastewater, and has economic advantages for industrial application.

[0060] 4. Salt ion tolerance test The effects of different concentrations of NaCl and Na2SO4 (chloride ions and sulfate ions) on the degradation efficiency were investigated under the following conditions: initial phenol concentration of 100 mg / L, catalyst Fe1Co1 / N dosage of 0.025 g / L, H2O2 concentration of 10 mmol / L, pH of 4-5, and reaction temperature of 40℃.

[0061] The results are as follows Figure 8 and 9 As shown, even when the concentration of chloride or sulfate ions is as high as 8%, the catalyst can still maintain a phenol degradation rate of over 90% within 14 minutes, proving that the catalyst of this invention has excellent tolerance to high-salt wastewater.

[0062] Under conditions where the sodium chloride mass fraction is 0.05%-8%, the catalyst does not significantly inhibit the degradation efficiency of phenol, and the degradation rate of phenol can reach over 90% within 2 minutes of reaction. Under conditions where the sodium sulfate mass fraction is also 0.05%-8%, the catalyst maintains a similarly high degradation efficiency. Particularly under extreme conditions with a sodium sulfate concentration as high as 8%, the degradation rate of phenol can still reach over 90% after 14 minutes of reaction, and when the sodium sulfate concentration is less than 6%, the degradation rate can reach 90% within 8 minutes. These results indicate that the Fe / Co-N stable interface structure formed by nitrogen surface modification of the catalyst of this invention can effectively resist the poisoning effect of high-concentration salt ions on the active center, making it suitable for the deep treatment of high-salt organic wastewater generated in industries such as chemical, pharmaceutical, and dyeing.

[0063] 5. Broad-spectrum degradation performance experiment The degradation effects of four organic pollutants with different structures—rhodamine B, methylene blue, tetracycline hydrochloride, and malachite green—were investigated under the following conditions: initial pollutant concentration of 100 mg / L, catalyst dosage of Fe1Co1 / N of 0.025 g / L, H2O2 concentration of 10 mmol / L, pH of 4-5, and reaction temperature of 40℃.

[0064] from Figure 10 It can be seen that the Fe1Co1 / N catalyst exhibits significant degradation effects on organic pollutants of various structural types, but the degradation kinetics of different pollutants differ, which provides an important reference for the application of the catalyst of this invention in practical complex wastewater systems.

[0065] The first 20 minutes of the reaction constitute the pre-adsorption stage. During this stage, the catalyst exhibits similar adsorption and removal rates for four pollutants—Rhodamine B, methylene blue, tetracycline hydrochloride, and malachite green—all maintaining a level of 5-8%. This result indicates that the physical adsorption capacity of the catalyst in this invention is limited, and the removal of pollutants mainly relies on the subsequent Fenton-like catalytic oxidation process rather than simple physical adsorption. This is beneficial for the long-term stable operation of the catalyst.

[0066] After 20 minutes, hydrogen peroxide was added to initiate a Fenton-like oxidation reaction, and the degradation curves of each pollutant showed significant differentiation: Methylene blue exhibits the fastest degradation rate after the reaction begins, rapidly reaching 95% after 6 minutes of Fenton-like oxidation, and remaining stable at around 95% for 6-20 minutes. This indicates that the catalyst of this invention possesses excellent catalytic oxidation activity and deep mineralization ability for methylene blue, enabling efficient removal of this type of dye pollutant in a short time.

[0067] The degradation rate of tetracycline hydrochloride reached 85% after 4 minutes of Fenton-like oxidation reaction, and then showed a slow downward trend, finally reaching 94% after 20 minutes of Fenton-like oxidation reaction. This continuously decreasing degradation curve indicates that the catalyst of the present invention has good sustained oxidation ability for antibiotic-like recalcitrant organic compounds, and can gradually break down their stable molecular structure to achieve deep treatment.

[0068] Rhodamine B's degradation rate decreased to 45% after 1 minute of Fenton-like oxidation, then continued to decrease at a relatively rapid rate, finally reaching 85% after 20 minutes of Fenton-like oxidation. Malachite green's degradation rate was 65% after 2 minutes of Fenton-like oxidation, then decreased at a relatively rapid rate, reaching 85% after 20 minutes of Fenton-like oxidation. The degradation curves of these two triphenylmethane dye pollutants exhibited a rapid initial degradation followed by a plateau, indicating that the catalyst of this invention can effectively attack the chromophores of these dyes, achieving rapid decolorization and partial mineralization.

[0069] The significance of the above differences in degradation rates is as follows: First, it proves that the catalyst of this invention has broad-spectrum adaptability and can effectively degrade various types of organic pollutants such as dyes and antibiotics, meeting the wastewater treatment needs of different industries.

[0070] Second, the differences in degradation kinetics reflect the catalyst's ability to recognize and attack different molecular structures. The rapid and complete degradation of methylene blue phenothiazines indicates that the catalyst has a high efficiency in recognizing active sites in their molecular structures; while the degradation processes of rhodamine B and malachite green (triphenylmethanes) are relatively mild, but still achieve a removal rate of 85%, indicating that the catalyst can act continuously and gradually degrade structurally stable organic molecules; the continuous decline curve of tetracycline hydrochloride proves that the catalyst has a deep treatment capability and can achieve efficient removal of recalcitrant emerging pollutants.

[0071] Third, this differentiated degradation behavior provides a basis for process optimization in practical applications. For easily degradable pollutants, a shorter reaction time can be used; for difficult-to-degrade pollutants, the reaction time can be appropriately extended or the amount of catalyst can be increased, so as to achieve graded treatment and precise control of different pollutants.

[0072] In summary, this invention successfully developed a novel Fenton-like oxidation catalyst with simple preparation process, high catalytic activity, strong salt tolerance, and good stability through a dual regulation strategy of nitrogen surface modification and the synergistic effect of iron-cobalt bimetallic compounds. Compared with existing technologies, this invention eliminates the need for a support and template agent, achieving in-situ chemical modification of the iron-cobalt alloy surface by nitrogen atoms through ammonia-containing atmosphere treatment. This constructs a unique Fe / Co-N highly active interface, significantly improving the efficiency of hydroxyl radical generation and adaptability to high-salt and complex wastewater. It provides an efficient and green advanced oxidation solution for the deep treatment of recalcitrant and high-salt industrial organic wastewater, demonstrating significant technological advancement and broad industrial application prospects.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, several simple deductions, modifications, or substitutions can be made without departing from the technical concept of the present invention, and these should all be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a nitrogen-modified iron-cobalt bimetallic catalyst, characterized in that, Includes the following steps: Step 1: Dissolve iron salt and cobalt salt in water and stir to form a uniform and transparent iron-cobalt mixed salt aqueous solution A; Potassium hydroxide was dissolved in deionized water to form solution B; under heating and stirring, solutions A and B were added dropwise to the reaction vessel in parallel, and the pH of the reaction system was controlled at 10.5-11.

5. After precipitation and aging, a suspension containing precipitate was obtained. Step 2: The suspension obtained in Step 1 is subjected to hydrothermal treatment, cooled and filtered, and the resulting precipitate is washed until neutral, dried and ground to obtain the catalyst precursor. Step 3: The catalyst precursor obtained in Step 2 is calcined at a first temperature in a hydrogen-containing mixed atmosphere, cooled, and then calcined at a second temperature in an ammonia-containing mixed atmosphere. After cooling, the nitrogen-modified iron-cobalt bimetallic Fenton oxidation catalyst is obtained.

2. The method for preparing the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The iron salt is at least one hydrate of ferric nitrate, ferric sulfate, or ferric chloride, and the cobalt salt is at least one hydrate of cobalt nitrate, cobalt sulfate, or cobalt chloride; in the iron-cobalt mixed salt aqueous solution A, the concentration of iron ions is 0.33-0.9 mol / L, and the concentration of cobalt ions is 0.33-0.9 mol / L; in the solution B, the concentration of potassium ions is 3-7 mol / L.

3. The method for preparing the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 1, characterized in that, In step one, the heating and stirring temperature is 25-75℃ and the stirring speed is 300-500 r / min; in step two, the hydrothermal treatment temperature is 120-160℃ and the time is 23-25 ​​hours.

4. The method for preparing the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 1, characterized in that, The hydrogen-containing mixed atmosphere is a 5-20% H2 / Ar mixture with a gas flow rate of 0.33-1.16 cm³ g. - ¹ s - ¹; The ammonia-containing mixed atmosphere is a 50-100% NH3 / Ar mixture with a gas flow rate of 0.33-1.16 cm³ g. - ¹ s - ¹.

5. The method for preparing the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 1, characterized in that, In step three, the first calcination treatment is performed at a temperature of 400-500℃ for 4.5-5.5 hours; the second roasting treatment is performed at a temperature of 450-600℃ for 3.5-4.5 hours.

6. A nitrogen-modified iron-cobalt bimetallic catalyst, characterized in that, The catalyst is prepared by any one of the preparation methods described in claims 1-5. The catalyst uses iron and cobalt as active components, and the surface of the iron-cobalt bimetallic catalyst structure is modified by incorporating nitrogen atoms through heat treatment in a hydrogen / ammonia mixed atmosphere. In the catalyst, iron accounts for 21%-67% of the total mass of the catalyst, and cobalt accounts for 23%-68% of the total mass of the catalyst.

7. The nitrogen-modified iron-cobalt bimetallic catalyst according to claim 6, characterized in that, The iron-cobalt bimetal forms an FeCo alloy phase; the nitrogen atoms are embedded in the alloy lattice or adsorbed on the alloy surface in the form of at least one of pyridine nitrogen, pyrrole nitrogen or graphitic nitrogen, forming an Fe / Co-N active interface.

8. The application of a nitrogen-modified iron-cobalt bimetallic catalyst, characterized in that, This includes the application of the nitrogen-modified iron-cobalt bimetallic catalyst as described in claim 6 or 7 in the degradation of organic wastewater pollutants.

9. The application of the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 8, characterized in that, The catalyst is brought into contact with organic wastewater with a pH of 3-11 in a reactor, and the organic matter in the wastewater is degraded at a reaction temperature of 20-50°C.

10. The application of the nitrogen-modified iron-cobalt bimetallic catalyst according to claim 9, characterized in that, The organic wastewater contains chloride or sulfate ions at a concentration of 0-0.513 mol / L; the reactor is a fixed-bed tubular reactor or a batch reactor.

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