Nitrogen-doped carbon-based cobalt catalyst and use thereof

Abstract

This invention discloses a nitrogen-doped carbon-based supported cobalt catalyst and its application in the degradation of hydroxyl-containing aromatic pollutants. Targeting hydroxyl-containing aromatic pollutants, this invention uses specific conditions to prepare a nitrogen-doped carbon-based supported cobalt catalyst for activating persulfate and degrading specific organic pollutant systems. It establishes a coordination anchoring effect between cobalt and nitrogen-containing sites, improving carbon framework defects and electron transport capabilities, while reducing the risk of metal leaching. This effectively improves catalytic performance and selectivity, achieving efficient activation of persulfate under near-neutral conditions to achieve efficient degradation of hydroxyl-containing aromatic pollutants.

Description

(I) Technical Field

[0001] This invention belongs to the field of advanced oxidation technology for the degradation of novel pollutants, specifically relating to a Co-NC catalyst, its preparation method, and its application in the degradation of hydroxyl-containing aromatic pollutants by activated persulfate. (II) Background Technology

[0002] Currently, advanced oxidation technologies (AORs) are one of the research hotspots for treating organic pollutants both domestically and internationally. The purpose of AORs is to activate / catalyze oxidants through physical, chemical means or catalysts to generate active species with strong oxidizing capabilities, thereby achieving efficient degradation and even complete mineralization of recalcitrant pollutants.

[0003] Among the oxidants used in many advanced oxidation technologies, persulfate has attracted widespread attention due to its low price, good stability, strong oxidizing ability and mineralization efficiency. It can provide hydroxyl and sulfate free radicals with high oxidation potential to effectively oxidize and degrade organic pollutants.

[0004] Because persulfate has limited ability to directly oxidize pollutants and cannot achieve rapid and complete removal of many pollutants, various methods have been developed to effectively activate persulfate in order to improve its efficiency in oxidizing and degrading pollutants. Currently, common persulfate activation methods include heat, ultraviolet light, alkali, carbon materials, photocatalysts, and transition metal ions, all of which can effectively activate persulfate to generate strong oxidizing free radicals or other oxidizing active substances.

[0005] Studies have found that carbon-based activation technology in persulfate activation can effectively degrade organic pollutants. Furthermore, due to its unique nanostructure, excellent conductivity, chemical stability, metal-free nature, high utilization rate, excellent acid and alkali resistance, and economic and environmental friendliness, it exhibits significant advantages. Therefore, the synthesis and modification of carbon materials will become a new research hotspot in persulfate activation research. Biochar, due to its unique porous structure, is easily modified through doping and composite methods, and is economical, environmentally friendly, and easy to prepare, making it an ideal carbon material for use as a catalyst in various chemical processes.

[0006] The excellent properties of biochar make it a suitable substrate material for transition metal catalysts. Potassium bicarbonate-activated biochar has a larger specific surface area and more defect sites, preparing it for the subsequent incorporation of transition metals. Traditional transition metals such as Co, Fe, and Ni can be anchored on biochar, significantly increasing their reactivity. Doping with heteroatoms such as N, S, and P can enhance the catalytic activity of porous carbon. Doping the carbon matrix with heteroatoms typically increases defect sites and electron transfer.

[0007] However, existing catalysts have the following problems when activating persulfate: 1) Insufficient catalytic activity: Some catalysts have limited activation ability for persulfate, resulting in insufficient number of free radicals generated, which cannot effectively degrade organic pollutants; 2) Excessive consumption of chemical reagents: In traditional persulfate activation systems, the typical reaction system has a molar ratio of persulfate to pollutants of 100 to 500:1; 3) Metal ion precipitation: Some catalysts will precipitate metal ions during the reaction, which may not only pollute the treated solution, but also cause harm to human health and the environment; 4) Poor selectivity: Some catalysts may oxidize other components in the solution while degrading organic pollutants, resulting in unsatisfactory degradation effect.

[0008] While some nitrogen-doped carbon-based cobalt-supported materials have been reported for activating permonosulfate (PMS) and perdisulfate (PDS), PMS and PDS differ in molecular structure, reactivity, and catalytic activation pathways. Previous studies have shown that catalysts do not activate PMS and PDS consistently, potentially corresponding to different active sites and reaction mechanisms. Therefore, new catalysts need to be explored for different substrates. (III) Summary of the Invention

[0009] The purpose of this invention is to provide a nitrogen-doped carbon-based supported cobalt catalyst (Co-NC) and its application in the degradation of hydroxyl-containing aromatic pollutants. This invention targets hydroxyl-containing aromatic pollutants and uses specific conditions to prepare a nitrogen-doped carbon-based supported cobalt catalyst for activating persulfate and degrading specific organic pollutant systems. Specifically, corn steep liquor powder is used as the carbon source, and potassium bicarbonate is used to activate biochar, with the activation time controlled at 50-70 min to balance pore structure construction and carbon skeleton stability, thereby shortening the calcination time. Simultaneously, cobalt chloride hexahydrate, hydroxylamine hydrochloride, 1,10-phenanthroline, and melamine are introduced to jointly promote the formation of Co-Nx active sites. This invention employs a specific process, including three calcination temperatures and metal loading, to construct a coordination anchoring effect between cobalt and nitrogen-containing sites (forming an active structure related to Co-Nx / Co-N interaction), improving carbon skeleton defects and electron transport capacity, while reducing the risk of metal leaching, effectively improving catalytic performance and selectivity. This achieves efficient activation of persulfate under near-neutral conditions, resulting in efficient degradation of hydroxyl-containing aromatic pollutants.

[0010] The technical solution adopted in this invention is:

[0011] This invention provides a nitrogen-doped carbon-based supported cobalt catalyst (denoted as Co-NC catalyst), the preparation method of which includes the following steps:

[0012] (1) The corn steep liquor powder (preferably after passing through a 100-mesh molecular sieve) is transferred into a tube furnace and heated from room temperature to 400-600℃ in a nitrogen atmosphere at a heating rate of 1-5℃ / min. Then, it is heat-treated at this temperature for 100-150 min and cooled to room temperature to obtain biochar.

[0013] (2) Mix the biochar from step (1) with potassium bicarbonate, place it in a tube furnace, and heat it from room temperature to 600-800℃ at a rate of 1-5℃ / min in a nitrogen atmosphere. Then heat it for 50-70 min, cool it naturally to room temperature, wash it once with 0.1mol / L hydrochloric acid, and then wash it three times with deionized water to obtain the pyrolytic activated biochar.

[0014] (3) Dissolve cobalt metal, hydroxylamine hydrochloride, 1,10-phenanthroline and biochar activated in step (2) in ethanol, disperse ultrasonically at room temperature (preferably 30 min), evaporate to dryness by rotary evaporation (preferably 40°C), grind the obtained solid and melamine thoroughly, place in a tube furnace, raise the temperature from room temperature to 500-700°C at a rate of 1-3°C / min in a nitrogen atmosphere, then heat-treat at this temperature for 100-150 min, cool to room temperature, add the obtained sample to a 1 mol / L sulfuric acid aqueous solution, and react with shaking at 20-40°C for 10-15 h (preferably 30°C for 12 h), then wash with deionized water and dry to obtain the catalyst.

[0015] Further, in step (1), the heat treatment conditions are as follows: the temperature is increased from room temperature to 500°C at a heating rate of 5°C / min in a nitrogen atmosphere. This temperature setting is mainly to convert corn steep liquor powder into biochar and does not have a direct impact on the final activity of the catalyst; then the heat treatment is carried out for 120 min and finally cooled to room temperature.

[0016] Further, in step (2), the mass ratio of biochar to potassium bicarbonate is 1:1; the heat treatment conditions are: heating from room temperature to 700℃ at a rate of 5℃ / min in a nitrogen atmosphere, at which point potassium bicarbonate will react with biochar to remove some organic impurities and to pore the carbon material through a chemical reaction. This process will significantly increase the specific surface area of ​​the carbon material and provide more effective sites for metal loading; then heat treatment is carried out for 60 min, and finally cooled to room temperature.

[0017] Further, in step (3), the cobalt metal is cobalt chloride hexahydrate; the mass ratio of the activated biochar to the cobalt metal is 1:0.01-0.15 (preferably 1:0.1), the mass ratio of the activated biochar to hydroxylamine hydrochloride is 1:0.01-0.18 (preferably 1:0.12), and the mass ratio of the activated biochar to 1,10-phenanthroline is 1:0.17-2.52 (preferably 1:1.68); the volume of ethanol used is 50-70 mL / g (preferably 60 mL / g) based on the mass of the activated biochar.

[0018] Furthermore, in step (3), the mass ratio of the solid after rotary evaporation to melamine is 1:1-5 (preferably 1:1).

[0019] Further, in step (3), the heat treatment conditions are as follows: the temperature is increased from room temperature to 600℃ in a nitrogen atmosphere at a heating rate of 2℃ / min. This temperature is chosen mainly because it avoids excessive adsorption of pollutants by the catalyst, which would lead to saturation of the active sites. It can also promote the synergistic effect of metal and nitrogen, thereby enhancing the catalytic performance and stability. Then, the temperature is kept warm for 120 minutes and finally cooled to room temperature.

[0020] The present invention also provides the application of the nitrogen-doped carbon-based supported cobalt catalyst in the degradation of hydroxyl-containing aromatic pollutants.

[0021] Furthermore, the nitrogen-doped carbon-based supported cobalt catalyst degrades pollutants by activating persulfate; the persulfate is potassium persulfate; and the pollutant is 3-hydroxybenzophenone or rhodamine B (RhB).

[0022] Furthermore, the method of application is as follows: the catalyst is mixed with an aqueous solution of hydroxyl-containing aromatic pollutants, and magnetically stirred at 15-55℃ (preferably 25℃) and 100-300 rpm (preferably 200 rpm) for 20-60 min (preferably 40 min) to reach adsorption saturation. Then potassium persulfate is added, and the reaction is continued for 0-120 min to achieve the degradation of pollutants.

[0023] Furthermore, the catalyst concentration is 0.2-0.8 g / L (preferably 0.5 g / L), the potassium persulfate concentration is 0.1-50 mM (preferably 4 mM), and the pollutant concentration is 10-50 mg / L (preferably 20 mg / L).

[0024] At 25°C, near-neutral conditions, and a PDS of 4 mM, this catalyst can achieve complete removal of 20 mg / L of 3-hydroxybenzophenone within 60 min.

[0025] This invention achieves efficient, stable, and economical catalytic performance by introducing cobalt and the synergistic effect of nitrogen-doped carbon framework, combined with efficient persulfate (PDS) activation under mild reaction conditions and improved cobalt stability. First, the biochar, activated with potassium bicarbonate, increases its specific surface area by approximately 1000 times, providing conditions for subsequent metal loading. Second, nitrogen doping alters the electronic structure of the carbon material, increasing the number of active sites on the catalyst surface. This, combined with cobalt, significantly improves the activation efficiency of PDS, promotes the continuous generation of reactive oxygen species, and enhances the degradation efficiency of organic pollutants, solving the problem of insufficient activity in existing catalysts. Third, the Co-NC activation system constructed in this invention can efficiently utilize persulfate under relatively mild conditions, reducing dependence on excess oxidant and lowering chemical reagent consumption, thus solving the problem of excessive chemical reagent consumption in existing methods. Simultaneously, the coordination between cobalt and nitrogen sites improves the stability of cobalt, inhibiting cobalt ion precipitation during the reaction and avoiding secondary pollution, thus solving the problem of metal ion precipitation in existing methods. Finally, this invention ensures the survival of reactive oxygen species (O2) by regulating the catalyst surface structure and activation pathway. - and 1 O2 plays a dominant role in the activation process of PDS, selectively removing target pollutants through a free radical-non-free radical pathway, reducing ineffective consumption and side reactions of non-target components in solution, and solving the problem of poor selectivity of existing catalysts. In summary, the combined effect of multiple technical solutions makes this invention not only significantly superior in terms of catalytic efficiency and stability, but also capable of removing target pollutants with low dosage and high efficiency, showing good application prospects.

[0026] Compared with existing methods, the beneficial effects of this invention are mainly reflected in:

[0027] 1. Highly efficient degradation

[0028] Using 3-hydroxybenzophenone as a model pollutant, the Co-NC catalyst prepared in this invention achieved a 100% removal rate of 20 mg / L 3-hydroxybenzophenone within 60 min at a low PDS of 4 mM (a molar ratio of sulfate to pollutant of 40:1) (compared to the traditional persulfate activation system, where the typical reaction system has a molar ratio of persulfate to pollutant of 100–500:1). The specific experimental conditions were 25°C and neutral pH. This demonstrates excellent degradation performance, significantly higher than NC, Fe-NC, and Co-C. This is because, compared to NC and Co-C, cobalt and nitrogen doping introduces new active sites, increasing the number of active sites and enhancing the catalytic activity of Co-NC. Compared to Fe-NC, the Co-NC catalyst generates more metal-nitrogen active sites and has a higher graphitic nitrogen content, which is beneficial for electron transfer and activates persulfate to generate more free radicals that oxidize 3-hydroxybenzophenone.

[0029] 2. High selectivity

[0030] Under different pH and temperature conditions, the degradation effect of the Co-NC catalyst prepared in this invention on 3-hydroxybenzophenone was essentially unaffected, exhibiting strong selectivity. This indicates that the Co-NC catalyst prepared in this invention can maintain high degradation performance even in complex environments and has broad application prospects.

[0031] 3. Low preparation cost

[0032] The raw materials for preparing the Co-NC catalyst of this invention are readily available, the preparation process is simple, and the requirements for preparation conditions and equipment are low. Compared with the potassium hydroxide activation commonly used in the literature, this invention uses potassium bicarbonate to activate biochar, shortening the calcination time (from 120 min to 60 min) and giving the cobalt source / nitrogen support a high specific surface area and certain chemical stability, providing favorable conditions for the introduction of cobalt and nitrogen doping. This makes the preparation cost of the Co-NC catalyst of this invention relatively low, which is conducive to its industrial application. (iv) Description of the attached drawings

[0033] Figure 1 The XRD patterns are of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2.

[0034] Figure 2 XPS (high resolution N 1s) plots of the catalysts prepared in Examples 1-2 and Comparative Examples 1-2.

[0035] Figure 3The degradation curves of 3-hydroxybenzophenone by different catalyst types under different conditions are shown; a represents the catalyst type; b represents the Co-NC catalyst dosage; c represents the PDS concentration; d represents the 3-hydroxybenzophenone concentration.

[0036] Figure 4 The degradation rate curves of 3-hydroxybenzophenone by persulfate activated by Co-NC catalyst under different pH conditions are shown.

[0037] Figure 5 The degradation rate curves of 3-hydroxybenzophenone were obtained by activating Co-NC catalyst with persulfate at different temperature conditions.

[0038] Figure 6 The degradation rate curves of the Co-NC catalyst after 4 cycles are shown.

[0039] Figure 7 The graph shows the changes in XPS composition before and after one cycle of the Co-NC catalyst. (V) Detailed Implementation Methods

[0040] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto:

[0041] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0042] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0043] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0044] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0045] In the following embodiments and comparative examples of the present invention, the removal rate of 3-HBP is calculated as follows: Removal rate (%) = (1-C t / C0)×100%, where C0 is the initial concentration of pollutants, C t The figures represent the residual concentrations of pollutants at different degradation times. In this embodiment of the invention, the corn steep liquor powder was purchased commercially from Hongrun Baoshun Co., Ltd.

[0046] Example 1: Preparation of NC catalyst

[0047] (1) Weigh an appropriate amount of corn steep liquor powder, pass it through a 100-mesh molecular sieve, and place it in a ceramic boat. In a tube furnace, under a nitrogen atmosphere, heat the powder from room temperature to 500°C at a heating rate of 5°C / min. After heat treatment at 500°C for 120 minutes, allow it to cool naturally to room temperature to obtain the original biochar.

[0048] (2) After grinding the raw biochar and potassium bicarbonate at a mass ratio of 1:1, the mixture was placed in a tube furnace and heated from room temperature to 700℃ at a heating rate of 5℃ / min in a nitrogen atmosphere. After heat treatment at 700℃ for 60 min, the mixture was naturally cooled to room temperature, washed once with 0.1 mol / L hydrochloric acid (100 mL), and then washed three times with deionized water to obtain activated biochar (BC).

[0049] (3) Weigh 0.0062 g of hydroxylamine hydrochloride, 0.0887 g of 1,10-phenanthroline and 0.5 g of BC and dissolve them in 30 mL of ethanol. Sonicate at room temperature for 30 min. Evaporate the resulting dispersant to dryness using a rotary evaporator at 40 °C. Grind the resulting solid and melamine thoroughly at a mass ratio of 1:1. Heat the ground solid to 600 °C at a rate of 2 °C / min in a nitrogen atmosphere. Heat the solid at 600 °C for 120 min and allow it to cool naturally to room temperature to obtain a solid sample. Add the sample to 100 mL of 1 mol / L sulfuric acid aqueous solution and react with shaking at 30 °C for 12 h. Then wash with deionized water and dry at 60 °C to obtain 0.6 g of nitrogen-doped carbon-based catalyst, denoted as NC catalyst.

[0050] Example 2: Preparation of Co-NC catalyst

[0051] The 0.0062 g hydroxylamine hydrochloride, 0.0887 g 1,10-phenanthroline and 0.5 g BC in step (3) of Example 1 were replaced with 0.202 g cobalt chloride hexahydrate, 0.0591 g hydroxylamine hydrochloride, 0.840 g 1,10-phenanthroline and 0.5 g BC, and the remaining steps were the same as in Example 1, to obtain 1.2 g of nitrogen-doped carbon-based supported cobalt catalyst, denoted as Co-NC catalyst.

[0052] Comparative Example 1: Preparation of Fe-NC Catalyst

[0053] The 0.0062 g hydroxylamine hydrochloride, 0.0887 g 1,10-phenanthroline and 0.5 g BC in step (3) of Example 1 were replaced with 0.249 g ferrous sulfate heptahydrate, 0.062 g hydroxylamine hydrochloride, 0.887 g 1,10-phenanthroline and 0.5 g BC, and the remaining steps were the same as in Example 1, to obtain 1.3 g of Fe-NC catalyst.

[0054] Comparative Example 2: Preparation of Co-C Catalyst

[0055] The 0.0062 g hydroxylamine hydrochloride, 0.0887 g 1,10-phenanthroline and 0.5 g BC in step (3) of Example 1 were replaced with 0.202 g cobalt chloride hexahydrate, 0.0591 g hydroxylamine hydrochloride, 0.840 g 1,10-phenanthroline and 0.5 g BC. The step of adding melamine in step (3) was omitted. All other steps were the same as in Example 1, and 0.8 g of carbon-based supported cobalt catalyst was obtained, which was denoted as Co-C catalyst.

[0056] Example 3: Catalyst Structure Identification

[0057] The catalysts prepared in Examples 1-2 and Comparative Examples 1-2 were detected by XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy), respectively.

[0058] XRD analysis was performed using a Co-Kα radiation source, with the operating voltage and current set to 40 kV and 8 mA, respectively. The scanning range covered 5–90° (2θ), and the scanning rate was 5° / min. Figure 1 As shown, no distinguishable characteristic diffraction peaks of crystalline metal / metal oxide were observed, indicating that there is no high content of highly crystalline metal-based particle phase in the sample.

[0059] XPS detection employed a monochromatic Al-Kα ray source as the excitation source, performing both full-spectrum scanning and high-resolution fine-spectrum scanning. To eliminate charging effects, a dual-beam electron neutralization gun was used for charge compensation, and charge correction was performed based on the C 1s peak (284.80 eV). Gauss-Lorentzian function fitting and semi-quantitative calculations were performed on the characteristic peaks using Advantage 5.99 software. Figure 2 As shown, metal-nitrogen active sites are generated, which participate in the activation of persulfate.

[0060] Example 4: Optimization of conditions for catalyst-activated persulfate degradation of 3-hydroxybenzophenone

[0061] 1. Types of catalysts

[0062] Weigh 0.05 g of NC, Fe-NC, Co-NC, and Co-C prepared in Examples 1-2 and Comparative Examples 1-2 using a balance. Add each to 100 mL of a 20 mg / L (C0) aqueous solution of 3-hydroxybenzophenone (3-HBP). Stir with a magnetic stirrer at 25°C and 200 rpm for 40 min to allow adsorption equilibrium between the catalyst and the pollutants. Then add potassium persulfate (PDS) to a final concentration of 4 mM (1081 mg / L) and start timing for the catalytic reaction. Add 4 mM PDS to 100 mL of a 20 mg / L 3-HBP aqueous solution as a control group (PDS alone).

[0063] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min. One mL of each sample was added to a test tube containing 1 mL of anhydrous methanol, and the mixture was shaken well to terminate the reaction. After standing, the samples were filtered through a 0.22 μm organic filter membrane. The filtrate was then analyzed by high-performance liquid chromatography (HPLC) to determine the residual 3-HBP concentration (denoted as Ct), and the 3-HBP removal rate (Ct / C0) was calculated.

[0064] The detection method for 3-HBP was as follows: A Water e2695 high-performance liquid chromatograph was used, with an Agilent ZORBAX StableBond C18 column (4.6×250 mm, 5 μm), a mobile phase of water:methanol (v:v = 35:65), a detection wavelength of 290 nm, a flow rate of 1.0 mL / min, a column temperature of 30℃, an injection volume of 20 μL, and an injection time of 8 min.

[0065] The results are as follows Figure 3As shown in Figure a, the adsorption rate of NC reached 99.7% during adsorption, while the adsorption rates of Fe-NC, Co-NC, and Co-C for 3-HBP were around 10%. After adsorption saturation, the degradation rates of Fe-NC, Co-NC, and Co-C for 3-HBP at 120 min were 67%, 100%, and 24.7%, respectively. The degradation of 3-HBP by the PDS system alone was negligible.

[0066] The above results indicate that among the catalysts prepared in Examples 1-2 and Comparative Examples 1-2, the Co-NC catalyst showed the best activation effect in the degradation of 3-HBP by persulfate. The doping of cobalt and nitrogen generated more Co-N active sites, resulting in the best removal effect on pollutants.

[0067] 2. Co-NC catalyst dosage

[0068] Using an analytical balance, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, and 0.08 g of the Co-NC catalyst prepared in Example 2 were weighed and added to 100 mL of a 20 mg / L 3-HBP aqueous solution. The solution was stirred with a magnetic stirrer at 25°C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Then, potassium persulfate with a final concentration of 4 mM was added, and the reaction was started.

[0069] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in step 1, and the removal rate was calculated.

[0070] The results are as follows Figure 3 As shown in Figure b, the removal rate of 3-HBP gradually increases with the increase of Co-NC catalyst dosage. When the catalyst concentration is 0.8 g / L, the degradation rate of pollutants reaches 100% within 30 min.

[0071] 3. PDS concentration

[0072] Weigh 0.05 g of Co-NC catalyst using an analytical balance and add it to 100 mL of 20 mg / L 3-HBP aqueous solution. Stir with a magnetic stirrer at 25 °C and 200 rpm for 40 min to allow the catalyst and pollutant to reach adsorption equilibrium. Then, add potassium persulfate at final concentrations of 0.1, 0.3, 0.5, 1, 2, 3, 4, 5, 10, 25, and 50 mM respectively, and start timing the reaction.

[0073] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in step 1, and the removal rate was calculated.

[0074] The results are as follows Figure 3 As shown in Figure c, when the PDS concentration is 0.1-25 mM, the removal rate of 3-HBP gradually increases with the increase of concentration. When the PDS reaches 50 mM, the reaction rate decreases significantly, indicating that high concentration of PDS will inhibit the reaction rate. The results show that optimizing the PDS concentration in the range of 0.5-4 mM can achieve efficient and economical pollutant degradation.

[0075] 4. 3-HBP concentration

[0076] Weigh 0.05 g of Co-NC catalyst using an analytical balance and add it to 100 mL of 3-HBP aqueous solution with concentrations of 10, 20, 30, 40, and 50 mg / L, respectively. Stir with a magnetic stirrer at 25°C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Then add potassium persulfate with a final concentration of 4 mM and start timing the reaction.

[0077] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in step 1, and the removal rate was calculated.

[0078] The results are as follows Figure 3 As shown in Figure d, the initial pollutant concentration is significantly negatively correlated with the degradation efficiency. Under a fixed PDS / catalyst ratio, the total amount of reactive oxygen species (ROS) generated is limited, which leads to a sharp reduction in the oxidative equivalent available per unit pollutant molecule. Therefore, the degradation efficiency decreases as the pollutant concentration increases.

[0079] 5. pH

[0080] Weigh 0.05 g of Co-NC catalyst using an analytical balance and add it to 100 mL of 20 mg / L 3-HBP aqueous solution. Stir with a magnetic stirrer at 25 °C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Adjust the pH to 2-10 by adding 0.1 M sodium hydroxide aqueous solution and 1 M sulfuric acid aqueous solution, then add potassium persulfate with a final concentration of 4 mM and start timing the reaction.

[0081] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in step 1, and the removal rate was calculated.

[0082] The results are as follows Figure 4 As shown, when the pH is 2-10, the degradation rate of pollutants can reach 100% within 90 minutes. The degradation effect is best when the pH is close to 6. This result indicates that the catalyst has a strong degradation ability under near-neutral conditions and is suitable for use in most natural water bodies or wastewater, especially since strict pH adjustment is usually not required in practical applications.

[0083] 6. Temperature

[0084] Weigh 0.05 g of Co-NC catalyst using an analytical balance and add it to 100 mL of 20 mg / L 3-HBP aqueous solution. Stir with a magnetic stirrer at 15, 25, 35, 45 and 55 °C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Add potassium persulfate to a final concentration of 4 mM and start timing the reaction.

[0085] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in step 1, and the removal rate was calculated.

[0086] The results are as follows Figure 5 As shown, the degradation efficiency increases significantly as the temperature rises from 15℃ to 55℃.

[0087] Example 4: Cyclic performance of Co-NC catalyst activated for persulfate degradation of 3-hydroxybenzophenone

[0088] Weigh 0.05 g of Co-NC catalyst using an analytical balance and add it to 100 mL of 20 mg / L 3-HBP aqueous solution. Stir with a magnetic stirrer at 25 °C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Add potassium persulfate to a final concentration of 4 mM and start timing the reaction.

[0089] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, and 60 min, respectively. The residual 3-HBP concentration was determined using the method described in Example 3, and the removal rate was calculated. The catalyst used in this experiment was recovered, and the experiment was repeated four times.

[0090] The results are as follows Figure 6 As shown, the degradation rates after four cycles were 100%, 71%, 58%, and 51%, respectively. The cyclic experiment showed that the system had some deactivation; the fourth cycle still maintained 51% of the performance of the first cycle, indicating that the catalyst has a certain degree of reusability, but its stability still needs to be improved.

[0091] The XPS composition changes of the Co-NC catalyst before use and after one cycle are shown in the graph. Figure 7 As shown, the results indicate that Co species did not undergo significant surface loss or enrichment migration during persulfate activation, demonstrating good structural stability. In contrast, the surface N content decreased from 22.9% to 19.2% after the reaction, while the O content increased from 7.9% to 8.7%, indicating that a certain degree of chemical reconstruction occurred on the carbon matrix surface during the reaction. This may be related to partial oxidation of nitrogen-containing sites and nitrogen loss, as well as the introduction of oxygen-containing functional groups. The presence of a small amount of S (0.3%) in the sample after use may be due to the adsorption and residue of sulfate-related species on the surface after persulfate activation. Based on the results of the cycling experiments, it can be inferred that the decrease in catalyst activity is not due to Co loss, but more likely related to the surface active sites being covered by intermediate products or sulfur-containing deposits, and changes in the surface chemical environment, thus leading to a gradual weakening of PDS activation capacity.

[0092] Example 5: Performance of Co-NC catalyst in activating persulfate degradation of different pollutants

[0093] Taking the cobalt-nitrogen composite catalyst prepared in Example 1 as an example, the effect of the cobalt-nitrogen composite catalyst on activating PDS to degrade different pollutants in the presence of different pollutants was tested. The specific steps are as follows:

[0094] Using an analytical balance, 0.05 g of Co-NC catalyst was weighed and added to 100 mL of 20 mg / L solutions of 3-hydroxybenzophenone (3-HBP), rhodamine B (RhB), sulfamethoxazole (SMX), and 4... ， In an aqueous solution of 4-dihydroxydiphenyl sulfone (BPS), the mixture was stirred with a magnetic stirrer at 25°C and 200 rpm for 40 min to allow the catalyst and pollutants to reach adsorption equilibrium. Then, 4 mM potassium persulfate was added, and the reaction was started.

[0095] Samples were taken at reaction times of 0, 5, 10, 15, 20, 30, 40, 50, 60, 90, and 120 min, respectively. The residual 3-HBP concentration was detected using the method in Example 3, and the removal rate was calculated.

[0096] The results are shown in Table 1. RhB was completely degraded within 120 min, SMX was degraded at 55.93%, and although the degradation rate of BPS was only 36.8%, the system still achieved a removal rate of 36.8% under the initial concentration condition of 20 mg / L (far exceeding the actual environmental concentration level). This result indicates that the system not only performs well in the degradation of conventional pollutants, but also has a high efficiency in degrading hydroxyl-containing aromatic pollutants (such as 3-HBP and RhB), making it suitable for the treatment of wastewater containing such pollutants (such as pharmaceutical and dye wastewater), and can effectively cope with high-concentration pollution events, showing broad application prospects.

[0097] Table 1 Removal performance of different pollutants

[0098]

[0099] In summary, the Co-NC catalyst prepared in this invention exhibits excellent performance in activating potassium persulfate to degrade 3-hydroxybenzophenone, possessing advantages such as high efficiency, strong selectivity, low preparation cost, and significant environmental benefits. The successful preparation and application of this catalyst provides a new approach and method for the efficient treatment of benzophenone-type pollutants, possessing significant scientific and practical value.

Claims

1. A nitrogen-doped carbon-supported cobalt catalyst, characterized in that, The method for preparing the catalyst includes the following steps: (1) The corn steep liquor powder is transferred into a tube furnace and heated from room temperature to 400-600℃ in a nitrogen atmosphere at a heating rate of 1-5℃ / min. Then, it is heat-treated at this temperature for 100-150 min and cooled to room temperature to obtain biochar. (2) Mix the biochar from step (1) with potassium bicarbonate, place it in a tube furnace, and heat it from room temperature to 600-800℃ at a rate of 1-5℃ / min in a nitrogen atmosphere. Then heat it for 50-70 min, cool it naturally to room temperature, wash it once with 0.1 mol / L hydrochloric acid, and then wash it three times with deionized water to obtain the pyrolytic activated biochar. (3) Dissolve cobalt metal, hydroxylamine hydrochloride, 1,10-phenanthroline and biochar activated in step (2) in ethanol, disperse by ultrasonication at room temperature, evaporate by rotary evaporation, grind the obtained solid and melamine thoroughly, place in a tube furnace, heat from room temperature to 500-700℃ at a rate of 1-3℃ / min in a nitrogen atmosphere, then heat-treat at this temperature for 100-150 min, cool to room temperature, add the obtained sample to 1 mol / L sulfuric acid aqueous solution, shake and react at 20-40℃ for 10-15 h, then wash with deionized water and dry to obtain the catalyst.

2. The catalyst of claim 1, wherein In step (1), the heat treatment conditions are as follows: the temperature is increased from room temperature to 500°C at a rate of 5°C / min in a nitrogen atmosphere, then held at that temperature for 120 min, and finally cooled to room temperature.

3. The catalyst of claim 1, wherein In step (2), the mass ratio of biochar to potassium bicarbonate is 1:1; the heat treatment conditions are: heating from room temperature to 700℃ at a heating rate of 5℃ / min in a nitrogen atmosphere, then holding the temperature for 60 min, and finally cooling to room temperature.

4. The catalyst of claim 1, wherein In step (3), the cobalt metal is cobalt chloride hexahydrate; the mass ratio of the activated biochar to the cobalt metal is 1:0.01-0.15, the mass ratio of the activated biochar to hydroxylamine hydrochloride is 1:0.01-0.18, and the mass ratio of the activated biochar to 1,10-phenanthroline is 1:0.17-2.52; the volume of ethanol used is 50-70 mL / g based on the mass of the activated biochar.

5. The catalyst according to claim 1, characterized in that, In step (3), the mass ratio of the solid after rotary evaporation to melamine is 1:1-5.

6. The catalyst according to claim 1, characterized in that, In step (3), the heat treatment conditions are as follows: the temperature is increased from room temperature to 600°C at a rate of 2°C / min in a nitrogen atmosphere, then held at the temperature for 120 min, and finally cooled to room temperature.

7. The application of the nitrogen-doped carbon-based supported cobalt catalyst of claim 1 in the degradation of hydroxyl-containing aromatic pollutants.

8. The application as described in claim 7, characterized in that, The nitrogen-doped carbon-based supported cobalt catalyst degrades pollutants by activating persulfate; the persulfate is potassium persulfate; the pollutant is 3-hydroxybenzophenone or rhodamine B.

9. The application as described in claim 7, characterized in that, The method of application is as follows: the catalyst is mixed with an aqueous solution of hydroxyl-containing aromatic pollutants, and magnetically stirred at 15-55℃ and 100-300 rpm for 20-60 min to reach adsorption saturation. Then potassium persulfate is added, and the reaction is continued for 0-120 min to achieve the degradation of pollutants.

10. The application as described in claim 9, characterized in that, The catalyst concentration is 0.2-0.8 g / L, the potassium persulfate concentration is 0.1-50 mM, and the pollutant concentration is 10-50 mg / L.

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