Preparation method and application of hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst

Abstract

This invention discloses a method for preparing and applying a hollow tubular carbon nitride-anchored boron-nitrogen co-cobalt single-atom catalyst. The preparation method involves mixing melamine, boric acid, cobalt acetate, and water, stirring to obtain a mixed solution. This solution is then subjected to a hydrothermal reaction at 160℃–180℃ for 12–24 hours. Solid-liquid separation is performed, the solid is washed and dried, and calcined under a nitrogen atmosphere at 450℃–650℃ to obtain the hollow tubular carbon nitride-anchored boron-nitrogen co-cobalt single-atom catalyst. The hollow tubular carbon nitride-anchored boron-nitrogen co-cobalt single-atom catalyst prepared by this invention has advantages such as high specific surface area, numerous reactive sites, good catalytic performance, high metal atom utilization rate, and structural stability. It can be widely used to activate persulfate to degrade organic pollutants, exhibiting good degradation effects and demonstrating significant application value and prospects. Furthermore, the preparation method of this invention is simple, convenient to operate, uses readily available raw materials, is low in cost, and is easily industrialized, showing great application potential in the field of environmental catalysis.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and environmental catalysis technology, specifically relating to a method for preparing and applying a hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst. Background Technology

[0002] Persulfate (PMS) activation technology is a novel advanced oxidation process (AOP) widely used in water treatment. Compared to Fenton, it offers a wider pH range, higher stability, more complete reaction, and is more cost-effective. PMS activation can be categorized based on the activation method, including ultrasonic, electrochemical, transition metal, single-atom catalysts (SCAs), photocatalytic, and thermocatalytic activation of persulfate. Among these, electrochemical, thermal, ultrasonic, and photocatalytic activation methods are energy-intensive and have low efficiency. Transition metal-based activators, however, show great promise due to their high efficiency and mild reaction conditions, requiring no external energy input. However, transition metal-based activators often suffer from metal leaching during use, potentially causing secondary pollution to water bodies, and also incur high operating costs and slow reaction rates. SACs with isolated metal sites have attracted widespread attention in the catalysis field due to their maximum atom utilization, excellent catalytic activity, uniform distribution of active sites, unique electronic structure, and ease of separation and recovery. However, due to their large surface binding energy, SCAs suffer from problems such as agglomeration and coupling during preparation and reaction, forming large clusters, complex preparation, low loading, and ion leaching, which greatly affect the catalytic performance and practical applications of SCAs.

[0003] Currently, methods to improve the catalytic performance and practical applications of Co-SCAs include controlling the coordination environment of their active center atoms, ionic solution coating, anchoring and confining Co atoms on suitable supports, and engineered structures that efficiently expose active sites. In recent years, graphitic carbon nitride has been considered one of the ideal support materials for SCAs, attracting widespread attention due to its excellent chemical and thermal stability, non-toxicity, low cost, and simple preparation. In particular, graphitic carbon nitride possesses abundant NC structures, which can not only anchor single atoms but also improve the electronic structure of the active center. However, existing carbon nitride materials anchoring cobalt single atoms have low specific surface area, few activation sites, and low catalytic efficiency. Currently, the main approach is to modify the coordination environment of Co single atoms by doping with non-metallic elements, but the elemental doping process is currently complex and the doping amount is relatively low. Therefore, overcoming the shortcomings of the existing technologies and developing simple hollow tubular nitrogen-anchored boron-nitrogen co-cobalt single-atom catalysts for persulfate activation under light-free conditions has good prospects. Obtaining hollow tubular nitrogen-anchored boron-nitrogen co-cobalt single-atom catalysts with high metal loading, high catalytic activity, good stability, and high specific area is of great significance for the efficient utilization of persulfate to degrade antibiotics in water. Summary of the Invention

[0004] This invention provides a hollow tubular nitrogen carbide-anchored boron-nitrogen co-cobalt single-atom catalyst with high specific surface area, multiple reactive sites, high single-atom metal loading, fast reaction rate, good stability, and efficient activation of persulfate. It also provides a simple, convenient, low-cost, efficient, and high-yield method for preparing this catalyst. Furthermore, it provides the application of this catalyst in the treatment of antibiotic wastewater.

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

[0006] 1. Mix melamine, boric acid, cobalt acetate, and water, and stir until well mixed to obtain a mixture;

[0007] The mass ratio of melamine to boric acid is 2:0.128 to 0.77, and the concentration of cobalt acetate in the mixture is 2 mmol / L to 55 mmol / L.

[0008] 2. The mixture is subjected to hydrothermal reaction at 160℃~180℃ for 12h~24h, solid-liquid separation is performed, the solid is washed and dried, and calcined at 450℃~650℃ for 1h~5h under nitrogen atmosphere to obtain hollow tubular carbon nitride anchored boron nitrogen co-cobalt single-atom catalyst.

[0009] The washing process uses water or anhydrous ethanol and involves 3 to 5 washing cycles.

[0010] 3. Utilizing hollow tubular nitrogen-anchored boron-nitrogen co-cobalt single-atom catalysts to activate persulfate for the degradation of organic pollutants in water bodies. Specifically, the hollow tubular nitrogen-anchored boron-nitrogen co-cobalt single-atom catalysts are mixed with organic pollutant wastewater, stirred, and then persulfate solution is added to carry out the catalytic degradation reaction, thereby completing the degradation of organic pollutants in the water body.

[0011] The mass-to-volume ratio of the hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst to the organic pollutant wastewater is 3 mg to 18 mg: 30 mL; the concentration of persulfate in the reaction system is 1 mmol / L to 5 mmol / L; the persulfate in the persulfate solution is potassium peroxymonosulfate; the concentration of organic pollutants in the organic pollutant wastewater is 10 mg / L to 50 mg / L; the organic pollutants in the organic pollutant wastewater are antibiotics; the antibiotics are at least one of ciprofloxacin, tetracycline, and norfloxacin.

[0012] The present invention has the following advantages over the prior art:

[0013] (1) This invention addresses the shortcomings of existing methods for preparing nitrogen carbide-anchored cobalt single-atom catalysts, such as complex preparation processes, high costs, low specific surface area, few reactive sites, low metal atom loading and utilization, easy metal agglomeration, low catalytic activity, and poor cycle stability. This invention creatively proposes a method for preparing hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalysts, employing a combination of hydrothermal and calcination methods to prepare high-performance hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalysts. Specifically, a mixed solution of melamine, boric acid, cobalt acetate, and water is prepared and subjected to a hydrothermal reaction. During the hydrothermal reaction, acidic self-assembly influences the formation of carbon nitride, which helps to form a tubular morphology and achieve boron doping. This not only increases the specific surface area of ​​the carbon nitride catalyst but also provides more reaction sites and improves the coordination environment for anchoring cobalt single atoms. Based on this, cobalt single atoms are introduced into the tubular carbon nitride through calcination, thereby obtaining a hollow tubular carbon nitride-anchored boron-nitrogen co-coordinated cobalt single atom catalyst. Compared to conventional preparation methods, the method of this invention utilizes the self-assembly of melamine under acidic conditions, which is more conducive to the formation of tubular structures. This allows cobalt to accumulate on the catalyst surface during subsequent calcination, thereby improving the dispersion and utilization rate of single-atom cobalt in the catalyst and significantly enhancing the catalytic efficiency. Therefore, the preparation method of this invention can produce hollow tubular nitrogen-anchored boron-nitrogen co-coordinated cobalt single-atom catalysts with high single-atom cobalt loading and utilization, good single-atom cobalt dispersion, and high catalytic activity. Compared to conventional nitrogen-anchored cobalt single-atom catalysts, the hollow tubular nitrogen-anchored boron-nitrogen co-coordinated cobalt single-atom catalysts prepared by this invention also have a higher specific surface area and more reactive sites, thus exhibiting better catalytic performance. The hollow tubular nitrogen carbide-anchored boron-nitrogen co-cobalt single-atom catalyst prepared by the method of this invention has advantages such as high specific surface area, multiple reactive sites, good catalytic performance, and high metal atom utilization rate. It can be widely used to activate persulfate to degrade organic pollutants (such as antibiotics) and can achieve good degradation effect, showing great application value and prospects. At the same time, the preparation method of this invention also has the advantages of simple process, convenient operation, readily available raw materials, low cost, easy to realize industrial production, and great application prospects, especially in the field of environmental catalysis.

[0014] (2) The hollow tubular carbon nitride anchored boron-nitrogen co-coordinated cobalt single-atom catalyst prepared by the present invention includes tubular carbon nitride, with single-atom cobalt embedded in the tube wall and internal pore structure of the tubular carbon nitride, and boron is doped in the hollow tubular carbon nitride anchored boron-nitrogen co-coordinated cobalt single-atom catalyst. By simultaneously embedding cobalt single atoms in the tube wall and internal filling network structure of the tubular carbon nitride, the tubular carbon nitride with a large specific surface area is beneficial to suppressing the aggregation of single-atom cobalt. At the same time, the doping of boron enables the tubular carbon nitride and cobalt single atoms to form a stable nitrogen-boron double-coordinated Co-N3B1 configuration.

[0015] (3) This invention utilizes a hollow tubular nitrogen carbide-anchored boron-nitrogen co-cobalt single-atom catalyst to activate persulfate to degrade antibiotics in water. By mixing the hollow tubular nitrogen carbide-anchored boron-nitrogen co-cobalt single-atom catalyst with antibiotic wastewater and then stirring and adding persulfate, the effective degradation of organic pollutants can be achieved. It has the advantages of simple process, convenient operation, low cost, high treatment efficiency and good degradation effect, and it has a good degradation effect on various organic pollutants. Attached Figure Description

[0016] Figure 1 SEM images of the layered carbon nitride (A) prepared in Comparative Example 1, the tubular carbon nitride (B) prepared in Comparative Example 2, the layered nitrogen carbide-anchored cobalt single-atom catalyst (C) prepared in Comparative Example 3, and the hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (D) prepared in Example 1.

[0017] Figure 2 The images show TEM images and EDS images of the hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (Co / B-CN) prepared in Example 1, where image a is the TEM morphology of the catalyst Co / B-CN, image b is the Co atomic distribution of Co / B-CN, image c is the total elemental distribution, image d is the C elemental distribution, image e is the N elemental distribution, image f is the O elemental distribution, image g is the B elemental distribution, and image h is the Co elemental distribution.

[0018] Figure 3 The images show the XRD patterns of the hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (Co / B-CN) prepared in Example 1 of the present invention, the layered carbon nitride (CN) prepared in Comparative Example 1, the tubular carbon nitride (B-CN) prepared in Comparative Example 2, and the layered nitrogen carbide-anchored cobalt single-atom catalyst (Co-CN) prepared in Comparative Example 3.

[0019] Figure 4The time-degradation efficiency graphs are shown for the activation of persulfate to degrade tetracycline hydrochloride solution by hollow tubular nitrogen-anchored boron-nitrogen co-cobalt single-atom catalyst (Co / B-CN), layered carbon nitride (CN), tubular carbon nitride (B-CN), and layered nitrogen-anchored cobalt single-atom catalyst (Co-CN) in Example 2 of the present invention.

[0020] Figure 5 This is a fitting graph of the degradation rate constants corresponding to the activation of persulfate to degrade tetracycline hydrochloride solution by hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (Co / B-CN), layered carbon nitride (CN), tubular carbon nitride (B-CN), and layered nitrogen carbide-anchored cobalt single-atom catalyst (Co-CN) in Example 2 of the present invention.

[0021] Figure 6 This is a graph showing the cycle number versus degradation efficiency of persulfate degrading tetracycline hydrochloride solution using the hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (Co / B-CN) in Example 3 of this invention.

[0022] Figure 7 This is a time-degradation efficiency graph showing the activation of persulfate solutions by a hollow tubular nitrogen-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst (Co / B-CN) in Example 4 of the present invention for the degradation of tetracycline hydrochloride (TC), oxytetracycline (OTC), chlortetracycline (CTC), and ciprofloxacin (CIP) solutions. Detailed Implementation

[0023] It should be understood that the embodiments of the invention shown in the exemplary embodiments are merely illustrative. Although only a few embodiments have been described in detail in this invention, those skilled in the art will readily recognize that various modifications are possible without substantially departing from the teachings of the invention. Accordingly, all such modifications should be included within the scope of the invention. Other substitutions, modifications, variations, and deletions can be made to the design, operating conditions, and parameters of the following exemplary embodiments without departing from the spirit of the invention.

[0024] Example 1: Preparation of hollow tubular nitrogen carbide-anchored boron-nitrogen co-cobalt single-atom catalyst

[0025] 1. Dissolve 2g of melamine, 0.385g of boric acid, and 0.0395g of cobalt acetate in 70mL of deionized water. Stir at 25℃ for 3 hours to obtain a homogeneous mixed solution. Transfer the mixed solution to a 100mL autoclave and keep it at 180℃ for 12 hours. After natural cooling, filter the solution. Wash the solid with water five times and dry it at 60℃ for 4 hours to obtain a supramolecular precursor. Place the supramolecular precursor solid in a crucible, wrap the crucible with tin foil, and place it in a tube furnace under nitrogen protection. Heat the crucible to 550℃ at a heating rate of 2.5℃ / min and keep it at 550℃ for 4 hours. After natural cooling, remove the sample to obtain a black powder sample, which is the tubular nitrogen-anchored boron-nitrogen co-coordinated cobalt single-atom catalyst, named Co / B-CN. The SEM image of the catalyst Co / B-CN ​​is shown below. Figure 1 D, as shown in the figure, has a hollow tubular structure. The TEM and EDS images of the catalyst Co / B-CN ​​are shown below. Figure 2 As can be seen from the figure, the hollow tubular structure and Co single atom were successfully prepared, and the elements were evenly distributed. Its XRD pattern is shown below. Figure 3 As can be seen from the figure, the intensity and position of the peaks changed significantly after doping. Furthermore, the Co (JCPDS No.15-0806) card peak appeared after Co doping, indicating the successful preparation and doping of Co single atoms.

[0026] Comparative Example 1: Preparation of Layered Carbon Nitride Catalyst

[0027] 2g of melamine was placed in a crucible and placed in a muffle furnace. The crucible was heated to 550℃ at a heating rate of 2.5℃ / min and held at 550℃ for 4 hours. After natural cooling, the sample was removed, yielding a yellow powder sample, which was layered carbon nitride, named CN. The SEM image of CN is shown below. Figure 1 A. As can be seen from the figure, CN has a layered structure, and its XRD pattern is shown below. Figure 3 As can be seen from the figure, there are two characteristic diffraction peaks at 13.5° and 27.6°, which correspond to the (100) and (002) planes of CN, respectively.

[0028] Comparative Example 2: Preparation of Tubular Carbon Nitride

[0029] 2g of melamine and 0.385g of boric acid were dissolved in 70mL of deionized water and stirred at 25℃ for 3 hours to obtain a homogeneous mixed solution. This mixed solution was transferred to a 100mL autoclave and kept at 180℃ for 12 hours. After natural cooling, it was filtered, and the solid was washed five times with water and dried at 60℃ for 4 hours to obtain the supramolecular precursor. The supramolecular precursor solid was placed in a crucible, wrapped with tin foil, and placed in a tube furnace under nitrogen protection. It was heated to 550℃ at a heating rate of 2.5℃ / min and held at 550℃ for 4 hours. After natural cooling, it was removed to obtain a yellow powder sample, which was tubular carbon nitride, named B-CN. The SEM image of B-CN is shown below. Figure 1 B, as can be seen from the figure, B-CN is a hollow tubular structure, and its XRD pattern is shown below. Figure 3 As can be seen from the figure, the diffraction peak of the (200) crystal plane of B-CN shifts to 27.3°, with a slight blue shift, indicating that the interlayer spacing increases after B doping, because B doping enhances the interlayer interaction.

[0030] Comparative Example 3: Preparation of Layered Nitrogen Carbide Anchored Cobalt Single-Atom Catalyst

[0031] 2g of melamine and 0.395g of cobalt acetate were dissolved in 70mL of deionized water and stirred at 25℃ for 3h to obtain a homogeneous mixed solution. This mixed solution was transferred to a 100mL autoclave and kept at 180℃ for 12h. After natural cooling, it was rinsed 5 times with water and filtered. It was then dried at 60℃ for 4h to obtain the supramolecular precursor. The supramolecular precursor solid was placed in a crucible, wrapped with tin foil, and placed in a tube furnace under nitrogen protection. It was heated to 550℃ at a heating rate of 2.5℃ / min and held at 550℃ for 4h. After natural cooling, it was removed to obtain a black powder sample, which is the layered nitrogen carbide-anchored cobalt single-atom catalyst, named Co-CN. The SEM image of Co-CN is shown below. Figure 1 C. As can be seen from the figure, Co-CN has a blocky structure, and its XRD pattern is shown below. Figure 3 As can be seen from the figure, the Co (JCPDS No.15-0806) card peak appeared after Co doping, indicating the successful preparation of Co single atoms.

[0032] Example 2: Application of the catalysts in Examples 1 and Comparative Examples 1-3 in the treatment of antibiotic wastewater

[0033] Weigh 6 mg each of the catalyst Co / B-CN ​​from Example 1, the layered carbon nitride CN from Comparative Example 1, the hollow tubular carbon nitride B-CN from Comparative Example 2, and the catalyst Co-CN from Comparative Example 3. Place each catalyst in a 30 mL solution of tetracycline hydrochloride with a concentration of 50 mg / L. Then, add 27.6 mg of potassium hydrogen sulfate to the tetracycline hydrochloride solution to carry out the catalytic degradation reaction. During the persulfate activation reaction, take 3 mL of tetracycline hydrochloride solution at 1 min, 2 min, 3 min, 6 min, and 9 min, respectively, and measure the absorbance of tetracycline hydrochloride in the solution using a spectrophotometer. Calculate the degradation efficiency of different catalysts on tetracycline hydrochloride solution under different time conditions.

[0034] See results Figure 4 As can be seen from the figure, the B / Co-CN catalyst exhibits the best catalytic activity, degrading 98.3% of tetracycline hydrochloride in 3 minutes and 100% of tetracycline hydrochloride in 6 minutes. This indicates that the B / Co-CN catalyst has the ability to efficiently activate PMS and generate a large amount of active oxygen.

[0035] The fitting results of the degradation rate constant are shown in Figure 5 As can be seen from the figure, the B / Co-CN catalyst has a degradation rate of several times or even hundreds of times that of tetracycline hydrochloride, which more intuitively illustrates the superior performance of the B / Co-CN catalyst.

[0036] Example 3: Stability Experiment of Hollow Tubular Nitrogen Carbide Anchored to Boron-Nitrogen Co-coordinated Cobalt Single Atoms

[0037] 1. Take 6 mg of the catalyst Co / B-CN ​​prepared in Example 1 and place it in 30 mL of tetracycline hydrochloride solution with a concentration of 50 mg / L. Then add 27.6 mg of PMS to carry out catalytic degradation reaction for 9 min. The degradation of organic pollutants in water is completed by activating persulfate, and one cycle is completed.

[0038] 2. The reaction system in step 1 was filtered to obtain the catalyst Co / B-CN. It was washed five times with deionized water, dried at 60℃ for 4 hours, and then used for the degradation of tetracycline hydrochloride for a total of ten cycles.

[0039] The degradation results of tetracycline hydrochloride solution by the catalyst at different cycle numbers are shown in the figure. Figure 6 As can be seen from the figure, the Co / B-CN ​​catalyst can still degrade 97.7% of tetracycline hydrochloride after 10 cycles, indicating that the Co / B-CN ​​catalyst is highly stable and has strong activation performance.

[0040] Example 4: Degradation of different antibiotics by hollow tubular nitrogen carbide-anchored boron-nitrogen co-coordinated cobalt single atoms

[0041] 6 mg of the catalyst Co / B-CN ​​from Example 1 was weighed multiple times and placed in 30 mL of tetracycline hydrochloride (TC), oxytetracycline (OTC), and chlortetracycline (CTC) solutions with a concentration of 50 mg / L, and in 30 mL of ciprofloxacin (CIP) solutions with a concentration of 20 mg / L, respectively. Then, 27.6 mg of potassium hydrogen sulfate was added to each solution to carry out the catalytic degradation reaction. During the persulfate activation reaction, 3 mL of tetracycline hydrochloride, chlortetracycline, oxytetracycline, and ciprofloxacin solutions were taken at 1 min, 2 min, 3 min, 6 min, and 9 min, respectively, and the absorbance values ​​in the solutions were measured using a spectrophotometer. The degradation efficiency of tetracycline hydrochloride, chlortetracycline, oxytetracycline, and ciprofloxacin solutions under different time conditions was calculated.

[0042] The degradation results of tetracycline hydrochloride, chlortetracycline, oxytetracycline, and ciprofloxacin solutions by the catalyst are shown in the figure. Figure 7 As can be seen from the figure, the Co / B-CN ​​catalyst can efficiently degrade a variety of antibiotics within 3 minutes, indicating that it has universality.

[0043] The above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. The application of a hollow tubular carbon nitride-anchored boron-nitrogen co-cobalt single-atom catalyst in the degradation of organic pollutants in water by activated persulfate, characterized in that: The hollow tubular carbon nitride-anchored boron-nitrogen co-cobalt single-atom catalyst is prepared by mixing melamine, boric acid, cobalt acetate, and water, stirring to obtain a mixed solution, subjecting the mixed solution to a hydrothermal reaction at 160℃~180℃ for 12h~24h, separating the solid and liquid, washing and drying the solid, and calcining it at 450℃~650℃ under a nitrogen atmosphere. The boron doping enables the tubular carbon nitride to form a stable nitrogen-boron dual-coordinated Co-N3B1 configuration with the cobalt single atom. The organic pollutant is tetracycline hydrochloride, oxytetracycline, or chlortetracycline.

2. The application according to claim 1, characterized in that: The concentration of cobalt acetate in the mixture was 2 mmol / L to 55 mmol / L, and the mass ratio of melamine to boric acid was 2:0.128 to 0.77.

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