Preparation method and application of Fe-Ni / CN bimetallic monatomic catalyst based on nitrogen-doped carbon

Abstract

The application discloses a Fe-Ni / CN bimetallic site heterogeneous Fenton-like single-atom catalyst, which is a carbon-based precursor of an imidazole-based metal organic framework, and Fe-Ni species is anchored and coordinated with nitrogen; first, a metal organic framework ZIF-8 is used as a carbon precursor, and zinc is sublimated by high-temperature calcination, thereby forming a nitrogen-doped carbon substrate CN with vacancies; nickel nitrate and iron nitrate are used as metal precursors, mixed with the CN, and high-temperature calcination is performed, thereby forming a Fe-Ni-N6 coordinated bimetallic site single-atom catalyst with adjacent iron-nickel sites; and the iron-nickel bimetallic site single-atom catalyst is used as a heterogeneous Fenton-like catalyst to activate peroxymonosulfate and degrade p-nitrophenol.

Description

Technical Field

[0001] This invention belongs to the field of environmental catalysis technology, specifically relating to a method for preparing a nitrogen-doped carbon-based Fe-Ni / CN bimetallic single-atom catalyst and its application. Background Technology

[0002] With the increasing industrialization of the world today, the pollution of large amounts of water bodies by various phenolic pollutants is becoming more and more serious. Recalcitrant phenolic pollutants account for a large portion of many industrial wastewaters, and nitrophenol, as a typical organic phenolic pollutant, urgently requires targeted treatment. Fenton technology is environmentally friendly, simple to operate, and economical, which has led to its increasingly widespread research in the removal of water pollutants. Furthermore, heterogeneous Fenton technology has the advantage of being reusable and reducing resource waste compared to traditional Fenton technology.

[0003] In recent years, single-atom catalysts have shown superior performance compared to traditional transition metal ions due to their near-100% atom utilization efficiency, unique coordination environment, and high stability. Therefore, the catalytic activation of peroxymonosulfate by single-atom catalysts for the degradation of phenolic pollutants has attracted widespread attention. However, high metal loading can lead to the aggregation of isolated metal atoms into less active nanoparticles or clusters, potentially clogging active sites and degrading performance. Clearly, improving catalytic performance by increasing metal loading to obtain highly loaded single-atom catalysts is a significant challenge. Therefore, developing a highly active iron-nickel bimetallic single-atom catalyst for heterogeneous Fenton reactions is highly meaningful. Overcoming the performance degradation limitations of highly loaded metal single-atom catalysts through single-atom catalytic systems would be a feasible method to improve the catalytic performance of Fenton-like catalytic applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of traditional single-metal atom catalyst Fenton technology and to provide a heterogeneous Fenton single-atom catalyst with iron-nickel bimetallic sites and a technology for removing nitrophenol by activating peroxymonosulfate, thereby solving the pollution problem of nitrophenol in wastewater.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a Fe-Ni / CN bimetallic site single-atom catalyst includes the following steps:

[0007] 1) First, zinc nitrate (II) hexahydrate and 2-methylimidazole were dissolved in anhydrous methanol to obtain solution A and solution B, respectively. Then, solution A and solution B were completely solvated by ultrasonic treatment and mixed. The resulting mixed solution was heated at 60°C for 24 hours to obtain a colloidal solution. After centrifugation, drying and calcination, a black powder was obtained, which is the nitrogen-doped porous carbon material, denoted as CN.

[0008] 2) Dissolve Fe(NO3)3·9H2O and Ni(NO3)2·6H2O in isopropanol to obtain solution C. Disperse CN from step 1) in solution C, sonicate for 2-3 hours, stir for 2-3 hours, and centrifuge. Wash the obtained solid 4-5 times with anhydrous methanol and dry at 60-70℃ for 24 hours to obtain CN-Ni. 2+ -Fe 3+ sample;

[0009] 3) The CN-Ni obtained in step 2) 2+ -Fe 3+ Heat treatment was carried out at 900-950℃ for 1 hour under N2 atmosphere with a heating rate of 5℃ / min, followed by natural cooling. The resulting black powder is the target product, denoted as Fe-Ni / CN.

[0010] As a further preferred embodiment of the present invention, in step 1), the mass concentration of solution A is 60-70 g / L and the mass concentration of solution B is 70-80 g / L.

[0011] As a further preferred embodiment of the present invention, in step 1), the mass concentration of solution A is 67.77 g / L (6.777 g of zinc nitrate hexahydrate dissolved in 100 mL of methanol), and the mass concentration of solution B is 78.74 g / L (i.e., 7.874 g of 2-methylimidazole dissolved in 100 mL of methanol).

[0012] As a further preferred embodiment of the present invention, in step 1), centrifugation is performed using ethanol with a purity of 99.5% for 4-5 times, and the drying temperature is 60-70℃ for 24 hours.

[0013] As a further preferred embodiment of the present invention, in step 1), the calcination treatment is carried out by heating at 1000-1100°C for 1 hour in an N2 atmosphere with a flow rate of 5°C / min.

[0014] As a further preferred embodiment of the present invention, in step 2), the ratio of CN to C solution is 150 mg: 15 mL; wherein in C solution, the mass concentration ratio of nickel and iron precursors is 1:1, and the concentration of each is 0.25 mg / mL; 10 mg Fe(NO3)3·9H2O and 10 mg Ni(NO3)2·6H2O are added to 40 mL of isopropanol, and the concentration of each is 0.25 mg / mL.

[0015] The Fe-Ni / CN bimetallic site single-atom catalyst prepared using the method described above.

[0016] Application of the Fe-Ni / CN bimetallic site single-atom catalyst in p-nitrophenol pollutant wastewater.

[0017] The catalyst degrades p-nitrophenol by activating peroxymonosulfate. The amount of Fe-Ni / CN bimetallic single-atom catalyst is 5-10 mg / 100 mL of wastewater, and the amount of peroxymonosulfate is 20-50 mg / 100 mL of wastewater. After 20-30 minutes, the wastewater after the degradation of organic pollutants can be obtained.

[0018] This invention utilizes an imidazole-based metal-organic framework (MOF) as a carbon-based precursor to anchor Fe-Ni species and nitrogen coordination. First, using the MOF ZIF-8 as a carbon precursor, zinc is calcined and sublimated at high temperature to form a nitrogen-doped carbon substrate (CN) with vacancies. Nickel nitrate and iron nitrate are then mixed with CN as metal precursors and calcined at high temperature to form a bimetallic single-atom catalyst with Fe-Ni-N6 coordination at adjacent iron-nickel sites. This iron-nickel bimetallic single-atom catalyst is used as a heterogeneous Fenton-like catalyst to activate peroxymonosulfate for the degradation of p-nitrophenol. By anchoring iron and nickel on a nitrogen-doped carbon support through a two-step calcination defect doping method, this bimetallic single-atom catalyst can efficiently remove p-nitrophenol using oxidation techniques.

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

[0020] 1. This invention provides a method for preparing a Fe-Ni / CN bimetallic site heterogeneous Fenton single-atom catalyst. The operation technique is simple, and the catalyst prepared can better activate peroxymonosulfate degradation of p-nitrophenol compared with single metal atom catalysts. It can also maintain a low metal dissolution rate and avoid secondary pollution.

[0021] 2. This invention improves the activation rate of peroxymonosulfate by synergistic effect of iron and nickel metal sites, and at the same time, improves the degradation rate of p-nitrophenol removal by the Fe-Ni / CN / PMS system.

[0022] 3. This invention uses a two-stage high-temperature calcination method to stably fix metal species on a nitrogen-containing substrate, and only a very small amount of metal elements are lost during the catalytic process.

[0023] Therefore, this invention can accelerate the removal rate of p-nitrophenol, reduce environmental harm, and reduce economic losses because the metal precursors used are relatively inexpensive iron nitrate and nickel nitrate rather than expensive precious metals. This is conducive to large-scale application and provides a new approach for water environment treatment. Attached Figure Description

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 The XRD patterns of CN, Fe / CN, Ni / CN, and Fe-Ni / CN of the catalyst samples prepared in this invention are shown.

[0026] Figure 2 The images show the SEM (a), TEM (b), HR-TEM (c), and spherical aberration electron microscopy (STEM) images (d) of Fe-Ni / CN according to the present invention.

[0027] Figure 3 Dark-field scanning elemental distribution map (a) and EDS energy spectrum and EDS elemental distribution map;

[0028] Figure 4 XPS spectroscopic analysis of the catalyst sample Fe-Ni / CN of this invention;

[0029] Figure 5 A photograph showing the physical process of degrading p-nitrophenol;

[0030] Figure 6 This is a graph showing the degradation activity of p-nitrophenol (4-NP) in this invention. Figure (a) shows the performance of different systems in degrading 4-NP, and Figure (b) shows the UV analysis of the Fe-Ni / CN / PMS system in degrading 4-NP.

[0031] Figure 7 First-order kinetic diagrams for the degradation of 4-NP in different systems. Detailed Implementation

[0032] To make the operational techniques, performance characteristics, and achievement of the objectives of this invention readily understandable, the technical solutions described below are further explained in conjunction with specific embodiments. However, this invention is not limited thereto. The room temperature in this invention refers to 20-30°C.

[0033] Comparative Example 1

[0034] The preparation of CN catalyst includes the following steps:

[0035] 1) Dissolve 6.777 g of zinc nitrate hexahydrate (II) (Zn(NO3)2·6H2O, 99.0%) and 7.874 g of 2-methylimidazole (C4H6N2, 98%) in 100 mL of anhydrous methanol in two round-bottom flasks to obtain solution A and solution B, respectively.

[0036] 2) After complete solvation of solution A and solution B by ultrasound, they were mixed evenly. The resulting mixture was heated at 60°C for 24 hours to obtain a colloidal solution. The solution was washed with ethanol and centrifuged 4 times. The product was dried at 60°C for 24 hours. The solid product was placed in a ceramic boat and calcined in a tube furnace at 1100°C (nitrogen flow rate of 5°C / min) for 60 minutes to obtain a black powder, denoted as CN.

[0037] Comparative Example 2

[0038] The preparation steps of the Fe / CN iron single-atom catalyst are as follows:

[0039] 1) Dissolve 6.777 g of zinc nitrate hexahydrate (II) (Zn(NO3)2·6H2O, 99.0%) and 7.874 g of 2-methylimidazole (C4H6N2, 98%) in 100 mL of anhydrous methanol in two round-bottom flasks to obtain solution A and solution B, respectively.

[0040] 2) The methanol solutions of A and B were completely solvated by ultrasound and then mixed evenly. The resulting mixture was heated at 60°C for 24 hours to obtain a colloidal solution, which was washed with ethanol and centrifuged 4 times. The product was dried at 60°C for 24 hours. The solid product was placed in a ceramic boat and calcined in a tube furnace at 1100°C (nitrogen flow rate of 5°C / min) for 60 minutes to obtain a black powder, denoted as CN.

[0041] 3) Add 20 mg Fe(NO3)3·9H2O to 40 mL of isopropanol and sonicate until a transparent solution is obtained, resulting in mixed solution C; the concentration of each solution is 0.5 mg / mL. Disperse 150 mg of the black powder CN obtained in step 2) in 15 mL of the mixed solution C to obtain a black solution. Sonicate at 60 kHz for 2 h at room temperature, then stir at room temperature for 2 h. Centrifuge the mixture at high speed to obtain the solid. Wash the solid with anhydrous methanol 4-5 times. Dry the washed product at 60 °C for 24 h. Place the solid product in a ceramic boat and place it in a tube furnace under a nitrogen atmosphere with a nitrogen flow rate of 5 °C / min. Calcinate at 900 °C for 60 min to obtain the black powder catalyst, denoted as Fe / CN.

[0042] Comparative Example 3

[0043] The preparation steps of the Ni / CN nickel single-atom catalyst are as follows:

[0044] 1) Dissolve 6.777 g of zinc nitrate hexahydrate (II) (Zn(NO3)2·6H2O, 99.0%) and 7.874 g of 2-methylimidazole (C4H6N2, 98%) in 100 mL of anhydrous methanol in two round-bottom flasks to obtain solution A and solution B, respectively.

[0045] 2) The methanol solutions of A and B were completely solvated by ultrasound and then mixed evenly. The resulting mixture was heated at 60°C for 24 hours to obtain a colloidal solution. The solution was washed with ethanol and centrifuged 4 times. The product was dried at 60°C for 24 hours. The solid product was placed in a ceramic boat and calcined in a tube furnace with a nitrogen flow rate of 5°C / min and a nitrogen atmosphere. The product was heated at 1100°C for 60 minutes to obtain a black powder, denoted as CN.

[0046] 3) 20 mg Ni(NO3)2·6H2O was added to 40 mL of isopropanol and sonicated until a transparent solution was obtained, resulting in a mixed solution with a concentration of 0.5 mg / mL. 150 mg of the obtained black powder CN was dispersed in 15 mL of the obtained mixed solution C to obtain a black solution. The obtained black solution was sonicated at 60 kHz for 2 h at room temperature, and then stirred at room temperature for 2 h. The obtained mixture was centrifuged at high speed to obtain the solid, and the obtained solid was washed 4 times with anhydrous methanol. The obtained product was further dried at 60 °C for 24 h. The obtained solid product was placed in a ceramic boat and calcined in a tube furnace with a nitrogen flow rate of 5 °C / min and a nitrogen atmosphere at 900 °C for 60 min to obtain the black powder catalyst, denoted as Ni / CN.

[0047] Example 1

[0048] The preparation steps of Fe-Ni / CN bimetallic site single-atom catalyst are as follows:

[0049] 1) Zinc nitrate hexahydrate (II) (Zn(NO3)2·6H2O, 99.0%, 6.777g) and 2-methylimidazole (C4H6N2, 98%, 7.874g) were dissolved in 100mL of anhydrous methanol in two separate round-bottom flasks. The methanol solutions of Zn(NO3)2 and dimethylimidazole were solubilized completely by sonication at 60kHz at room temperature, then mixed and heated at 60℃ for 24h. The resulting colloidal solution was centrifuged 4 to 5 times with ethanol (99.5% purity), and the colloidal solution was collected and dried in a vacuum oven at 60℃ for 20h. The collected powder was then heated in a tube furnace at 1100℃ for 1h under a N2 atmosphere at a flow rate of 5℃ / min to obtain a black nitrogen-doped porous carbon powder, denoted as CN; in other embodiments, the calcination temperature can be between 1000-1100℃.

[0050] 2) Add 10 mg Fe(NO3)3·9H2O and 10 mg Ni(NO3)2·6H2O to 40 mL of isopropanol and sonicate until a clear solution is obtained. Then, use a pipette to transfer 15 mL of the prepared solution into a scintillation bottle. Disperse 150 mg CN from step 1) into the above solution. Then, sonicate the resulting mixture for 2 h, stir for 2 h, wash with anhydrous methanol, centrifuge 4 times, and dry at 60 °C overnight (20-24 h) to prepare CN-Ni. 2+ -Fe 3+ sample;

[0051] 3) The obtained CN-Ni 2+ -Fe 3+The catalyst was heat-treated at 900°C for 1 hour under a nitrogen atmosphere with a heating rate of 5°C / min, followed by natural cooling to obtain a black powder catalyst, denoted as Fe-Ni / CN. In other embodiments, the heat treatment temperature in this step can be between 900-950°C.

[0052] In other embodiments, in step 1), solutions A and B can meet the following conditions: the mass concentration of solution A is 60-70 g / L, and the mass concentration of solution B is 70-80 g / L. The ethanol used in the embodiments and comparative examples of this invention is 99.5% pure ethanol. Centrifugation is performed 4-5 times with 99.5% pure ethanol, and drying is carried out at a temperature of 60-70°C for 20-24 hours.

[0053] Performance testing experiments:

[0054] To further illustrate the effects of the invention, Figure 1 The XRD spectra of the catalyst samples CN, Fe / CN, Ni / CN, and Fe-Ni / CN prepared according to the above embodiments are shown. The figures show that the prepared Fe / CN, Ni / CN, Fe-Ni / CN, and CN diffraction peaks are identical, with a broad carbon diffraction peak at 2θ = 26°. No peaks for Fe or Ni nanoparticles were detected, indicating the absence of Fe and Ni nanoparticle aggregation.

[0055] Figure 2 SEM, TEM, HR-TEM, and aberration-corrected transmission electron microscopy images of Fe-Ni / CN are presented. The TEM and SEM images show that Fe-Ni / CN possesses a uniform octahedral structure of ZIF-8. No Fe and Ni nanoparticles were observed in the HR-TEM image. This confirms that iron and nickel exist in atomic form. Figure 3 The SETM and EDS energy dispersive spectroscopy (EDS) spectra and elemental distribution maps of Fe-Ni / CN are presented. In the EDS elemental distribution map, we found the presence of Fe and Ni elements in addition to C and N. Based on the SETM and EDS spectra, we further confirmed the presence of Fe and Ni, and that Fe and Ni are anchored to the carbon-nitrogen-doped substrate in single-atom form.

[0056] Figure 4 (a) shows the XPS spectrum of the Fe-Ni / CN catalyst sample. Analysis revealed that the Fe-Ni / CN catalyst contains four elements: C, N, Fe, and Ni. The O 1s peak comes from O2 adsorbed on the surface in the environment. Since Fe and Ni elements are extremely rare, the signal is very weak. Figure 4(b) is the high-resolution N1s spectrum of the diatomic catalyst Fe-Ni / CN. A porphyrin-like Fe / Ni-N6 coordination structure exists at a binding energy of 399.4 eV. Binding energies of 396.7 eV, 398.3 eV, and 401.1 eV correspond to pyridine N, pyrrole N, and graphite N, respectively. Figure 4 (c) shows the high-resolution C1s spectrum of the diatomic catalyst Fe-Ni / CN. C exists primarily in three forms, corresponding to CC / C=C, C=N, and CN at binding energies of 282.7 eV, 284.2 eV, and 288.1 eV, respectively. This, along with electron microscopy and XRD results, confirms the coordination environment of the metal in the single-atom catalyst. Atomically dispersed iron and nickel are beneficial for the graphitization of carbon, which in turn facilitates PMS activation.

[0057] Application experiments on the degradation performance of p-nitrophenol

[0058] The catalyst prepared above was used to activate the degradation of 4-NP by peroxymonosulfate, such as... Figure 5 As shown, specifically, 10 mg of Fe-Ni / CN catalyst was weighed and dispersed in 100 mL of an aqueous solution containing 20 mg / L p-nitrophenol 4-NP. The mixture was stirred for 20 min to allow for adsorption and desorption equilibrium. After adding 0.3 g / L of potassium persulfate, samples were taken at regular intervals and filtered through a disposable filter. The concentration of residual 4-NP was then detected at 317 nm using a UV spectrophotometer.

[0059] Degradation efficiency such as Figure 6 As shown in Figure a, within 20 min, the adsorption capacities of ZIF-8 and CN for 4-NP were 22% and 21%, respectively, while the adsorption capacities of Fe / CN, Ni / CN, and Fe-Ni / CN for 4-NP were 49%, 38%, and 81%, respectively. The strong adsorption capacity of these catalysts may be attributed to the nitrogen element coordinated with metallic iron and nickel. Different catalysts showed different removal capacities for 4-NP. ZIF-8 and CN could only achieve removal rates of 30% and 38.2% of 4-NP within 5 min, respectively. The single-atom catalysts Fe / CN and Ni / CN, doped with Fe and Ni, respectively, could only remove 80% and 54%, while Fe-Ni / CN could degrade 99.8% of 4-NP within five minutes (6b).

[0060] Degradation follows pseudo-first-order kinetics, such as Figure 7 As shown, the rate constants (k) of the ZIF-8 / PMS, CN / PMS, Fe / CN / PMS, Ni / CN / PMS, and Fe-Ni / CN / PMS systems are 0.001 min⁻¹, respectively. -1 0.032min -1 0.148min -1 0.053min -10.935min -1 The degradation rates of 4-NP by the Fe-Ni / CN / PMS system were 935, 29.22, 6.32, and 6.54 times higher than those by ZIF-8 / PMS, CN / PMS, Fe / CN / PMS, and Ni / CN / PMS, respectively. The relevant parameters are listed in Table 1. The results indicate that the Fe-Ni bimetallic sites play a coordinating role in the activation of persulfate and are superior to similar single-atom catalysts. These experimental results demonstrate that the Fe-Ni / CN catalyst exhibits highly efficient performance in activating persulfate and degrading 4-NP.

[0061] Table 1 Kinetic parameters of 4-NP catalytic degradation in different experimental systems

[0062]

[0063] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. The application of a Fe-Ni / CN bimetallic site single-atom catalyst in p-nitrophenol pollutant wastewater, wherein the catalyst degrades p-nitrophenol by activating peroxymonosulfate, and the preparation method of the catalyst includes the following steps: 1) First, zinc nitrate hexahydrate and 2-methylimidazole are dissolved in anhydrous methanol to obtain solution A and solution B. Then, solution A and solution B are completely solvated by ultrasonic treatment and mixed. The resulting mixed solution is heated at 60°C for 24 hours to obtain a colloidal solution. After centrifugation, drying and calcination, a black powder is obtained, which is the nitrogen-doped porous carbon material, denoted as CN. 2) Dissolve Fe(NO3)3·9H2O and Ni(NO3)2·6H2O in isopropanol to obtain solution C. Disperse CN from step 1) in solution C, sonicate for 2-3 h, stir for 2-3 h, centrifuge, wash the obtained solid 4-5 times with anhydrous methanol, and dry at 60-70℃ for 20-24 h to obtain CN-Ni. 2+ -Fe 3+ sample; 3) Take the CN-Ni obtained in step 2) 2+ -Fe 3+ Heat treatment was carried out at 900-950℃ for 1 hour under N2 atmosphere with a heating rate of 5℃ / min, followed by natural cooling. The resulting black powder was the target product, denoted as Fe-Ni / CN. In step 1), the calcination treatment is carried out in a tube furnace with a flow rate of 5℃ / min and a nitrogen atmosphere, and heated at 1000-1100℃ for 1 hour.

2. The application according to claim 1, characterized in that: In step 1), the mass concentration of solution A is 60-70 g / L, and the mass concentration of solution B is 70-80 g / L.

3. The application according to claim 1, characterized in that: In step 1), the mass concentration of solution A is 67.77 g / L and the mass concentration of solution B is 78.74 g / L.

4. The application according to claim 1, characterized in that: In step 1), centrifugation is performed using 99.5% pure ethanol 4-5 times, and drying is performed using a vacuum oven at a temperature of 60-70℃ for 20-24 hours.

5. The application according to claim 1, characterized in that: In step 2), the ratio of CN to C solution is 150 mg: 15 mL; in C solution, the mass concentration ratio of nickel and iron precursors is 1:1, and the concentration of each is 0.25 mg / mL.

6. The application according to claim 1, characterized in that: The dosage of Fe-Ni / CN bimetallic single-atom catalyst is 5-10 mg / 100 mL of wastewater, and the dosage of peroxymonosulfate is 20-50 mg / 100 mL of wastewater.

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