A carbon composite cobalt trioxide catalyst for PMS activation, and a preparation method and application thereof

Abstract

The application discloses a carbon-composite cobalt trioxide catalyst for PMS activation and a preparation method and application thereof. The method comprises the following steps: dropping an aqueous solution of 2-methyl imidazole into a mixed aqueous solution of a cobalt salt and a carbon source, stirring and reacting at room temperature, and preparing a composite of the carbon source and a Co-MOF precursor; and placing the composite in an air atmosphere for calcination and in a nitrogen atmosphere for heat treatment in sequence, and preparing the carbon-composite cobalt trioxide catalyst. The Co-MOF precursor is calcined in the air atmosphere to obtain a C-Co3O4 composite material, the addition of the carbon source prevents the agglomeration of the catalyst in the calcination process of the Co-MOF precursor, the heat treatment in the nitrogen atmosphere improves the active center of the catalytic reaction, and the antibiotic degradation efficiency is significantly improved. The preparation method is simple in process, strong in controllability, low in calcination temperature, and stable and good in performance of the obtained catalyst.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment catalyst material development technology, and relates to a carbon composite cobalt tetroxide catalyst for PMS activation, its preparation method and application. Background Technology

[0002] The continued large-scale use and discharge of antibiotics has led to serious water pollution problems. Furthermore, the strong persistence and bioaccumulation of antibiotics pose potential threats to the ecological environment and human health. Therefore, there is an urgent need to develop an economical and effective method for treating antibiotic wastewater. Peroxymonosulfate (PMS) is one such method due to its high SO4 content. ·- Lifespan is longer than HO · Due to its long operating time, wide pH range, and high mineralization, PMS-based advanced oxidation technology is considered an effective method for removing antibiotic wastewater. Among the many PMS activation methods, heterogeneous transition metal catalyst activation has been widely studied due to its low operating cost, lack of additional energy requirements, and mild operating conditions. The core of this approach is to develop a simple, feasible, and highly efficient catalyst for activating PMS.

[0003] Among a series of heterogeneous transition metal catalysts, cobalt-based catalysts are due to Co... 3+ / Co 2+Due to its relatively high standard reduction potential (E0 = 1.92V), Co3O4 is considered one of the most effective PMS activators. Among many heterogeneous cobalt-based catalysts, Co3O4, which is abundant in Earth's resources and inexpensive, has attracted increasing attention. Currently, there are some studies on the synthesis of Co3O4-based catalysts, but traditional synthesis methods have some problems that limit their further application. Liu Jun et al. (Chinese Invention Patent CN103094559B) prepared Co3O4 / C materials using a hydrothermal method followed by calcination. However, the hydrothermal method operates under high temperature and pressure conditions, which is dependent on equipment and poses certain risks. Furthermore, it requires further calcination at 400–500℃ after hydrothermal treatment, resulting in significant energy consumption. Wu Xiaolan et al. (Chinese Invention Patent CN114105217B) prepared carbon-coated cobalt tetroxide anode materials using a calcination method. However, the preparation process requires dissolving the raw materials in an alkaline solution with a pH of 11–13, making the reaction conditions harsh. Li Gang et al. (Chinese Invention Patent CN103736492B) prepared SnO2-Co3O4 / C catalysts using a sol-gel method combined with calcination. However, the sol-gel method has a long preparation cycle, and after the sol-gel method, the precursor needs to be initially carbonized for 10 hours, deeply carbonized for 38 hours, and dried for 12 hours. The entire preparation process is complex and time-consuming. In recent years, using MOF as a precursor and employing calcination has become one of the effective methods for preparing high-catalytic-performance Co3O4 micro- and nanomaterials. Compared with traditional preparation methods, it can precisely and controllably synthesize catalyst materials with specific sizes and morphologies. However, there are still some problems in the related research regarding the synthesis methods and the properties of the synthesized catalysts. Wang Qi et al. (Chinese Invention Patent CN111613787B) prepared TiO2@C-Co3O4 catalyst by calcining TiO2@ZIF-67 precursor, but the calcination temperature of the precursor was as high as 700-800℃, resulting in high energy consumption. Furthermore, in addition to Co and Ti raw materials, they needed to use additional reagents such as hexadecyltrimethylammonium bromide and ammonia during the precursor preparation process. Li Huanhuan et al. (Chinese Invention Patent CN108448071 B) prepared cobalt tetroxide / carbon materials by calcining cobalt-based metal-organic framework precursors, but they used a hydrothermal method with a high-temperature and high-pressure reaction environment when preparing the cobalt-based metal-organic framework precursors, and the material synthesis required 6-9 days, resulting in an excessively long synthesis cycle. Fang Zhen et al. (Chinese Invention Patent CN106229541) B) NC / Co3O4 catalysts were synthesized by calcining ZIF-67 precursor, but the particle size of the synthesized catalyst was still relatively large, reaching 500-600 nm. Large catalyst size is not conducive to the exposure of active centers.In addition to the above, the stability of Co3O4-based catalysts used to activate PMS for pollutant degradation is poor. The tubular Co3O4 prepared by Qin et al. (Qin Q, et al. Environmental Science and Pollution Research, 2022, 29(33): 50135-46.) decreased from 93% to 75% after 5 cycles; the Co3O4@C-900 prepared by OuYang et al. (OuYang CS, et al. Results in Engineering, 2022, 14: 100381.) decreased from 100% to 83% after 5 cycles; and the Co3O4@C-500 prepared by Sheng et al. (Sheng J, et al. Chemical Engineering Journal, 2023: 143945.) decreased from 100% to 64% after 4 cycles. In the existing technology, cobalt ions are released from the catalyst during use, leading to the release of surface active substances (such as active centers Co). 2+ The loss of these substances reduces the reaction rate, resulting in poor cycling performance of the material. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a carbon composite cobalt tetroxide catalyst for PMS activation, its preparation method, and its application, thereby solving the technical problems of easy catalyst deactivation and poor cycle performance in the prior art.

[0005] This invention is achieved through the following technical solution:

[0006] A method for preparing a carbon-composite cobalt tetroxide catalyst for PMS activation includes the following steps:

[0007] S1: Add an aqueous solution of 2-methylimidazole dropwise to a mixed aqueous solution of cobalt salt and carbon source, stir the reaction at room temperature, centrifuge the reaction product, wash and dry it to obtain a complex of carbon source and Co-MOF precursor.

[0008] S2: The composite of the carbon source and the Co-MOF precursor is calcined in an air atmosphere, and then the calcined product is heat-treated in a nitrogen atmosphere to obtain the carbon composite cobalt tetroxide (C-Co3O4-N2) catalyst.

[0009] Preferably, in step S1, the cobalt salt is any one of cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt hydroxide, and cobalt formate.

[0010] Preferably, in step S1, the carbon source is any one of citric acid, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, carbon nitride, and polyvinyl alcohol.

[0011] Preferably, in step S1, the molar ratio of cobalt salt to carbon source is 1:(0.5-3), and the molar ratio of cobalt salt to 2-methylimidazole is 1:(0.01-0.4).

[0012] Preferably, in step S1, the dropping rate of the aqueous solution of 2-methylimidazole is 5 to 15 mL / min.

[0013] Preferably, in step S1, the stirring reaction time is 4 to 8 hours.

[0014] Preferably, in step S2, the calcination temperature in an air atmosphere is 250–350°C, the calcination time is 4–8 h, and the heating rate is 2–10°C / min.

[0015] Preferably, in step S2, the heat treatment in a nitrogen atmosphere is carried out at a temperature of 200–300°C for 0.5–2 hours, and the heating rate is 2–5°C / min.

[0016] A carbon-composite cobalt tetroxide catalyst for PMS activation was prepared by the method described above.

[0017] The above-mentioned carbon composite cobalt tetroxide catalyst for PMS activation is used in the treatment of antibiotic wastewater.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects:

[0019] This invention discloses a method for preparing a carbon-composite cobalt tetroxide catalyst for PMS activation. The preparation process first involves adding an aqueous solution of 2-methylimidazole dropwise to a mixed aqueous solution of cobalt salt and carbon source, stirring the reaction at room temperature, centrifuging the reaction product, washing and drying it to obtain a composite of carbon source and Co-MOF precursor; calcining the composite of carbon source and Co-MOF precursor in an air atmosphere, and then heat-treating the calcined product in a nitrogen atmosphere to obtain the carbon-composite cobalt tetroxide catalyst.

[0020] (1) This invention obtains a Co3O4-based catalyst derived from a Co-MOF by calcining a Co-MOF precursor. The Co-MOF precursor is prepared by a solution method. The calcination of the Co-MOF precursor is carried out at atmospheric pressure and low temperature. The preparation conditions are mild, energy consumption is low, pH adjustment is not required, the synthesis conditions are relatively safe and mild, and the time consumption is short. Only cobalt salt, carbon source and 2-methylimidazole are required for preparation. In addition, the size of the synthesized Co3O4-based catalyst is precisely controlled by calcining the Co-MOF precursor.

[0021] (2) Calcination in air atmosphere can effectively transform the Co-MOF precursor into Co3O4. Simultaneously, the relatively low calcination temperature allows the carbon source to remain effectively in the catalyst in the form of amorphous C, thus forming C-Co3O4. The residual amorphous C can effectively prevent catalyst agglomeration during subsequent Co-MOF precursor calcination, thereby synthesizing a Co3O4-based catalyst with smaller particle size, significantly increasing the specific surface area of ​​the catalyst. Further heat treatment of the material under a nitrogen atmosphere, in an oxygen-deficient environment, using C as a reducing agent, allows some of the Co in Co3O4 to be converted into Co3O4. 3+ Restored to Co 2+ Co 2+ As an active center for catalytic degradation, it effectively increases the active center of the catalytic reaction and significantly improves the antibiotic degradation efficiency. In this invention, the combined treatment of adding a carbon source during the preparation of the Co-MOF precursor and further heat treatment under a N2 atmosphere effectively improves the catalytic performance of the catalytic material.

[0022] (3) It exhibits good recyclability; after five consecutive cycles, it achieves 100% degradation efficiency of antibiotics within 15 minutes, and the reaction rate constant does not decrease. This invention prepares a Co3O4-based catalyst by calcining a Co-MOF precursor. The strong coordination between the metal cation and the organic ligand results in good stability of the MOF material. Calcination inherits the chemical stability of the MOF material. Simultaneously, the amorphous C in the Co-MOF and the carbon source material present in its porous structure forms a tight contact with Co3O4 during calcination to form C-Co3O4, further enhancing the stability of Co3O4. Based on inheriting the chemical stability of the MOF material, calcination significantly improves the stability of the MOF material, preventing the leaching of cobalt ions from Co3O4 during use and reducing the amount of active Co ions. 2+ The loss of the catalyst yields a highly stable Co3O4-based catalyst.

[0023] Furthermore, in step S1, the molar ratio of cobalt salt to carbon source is 1:(0.5-3), and the molar ratio of cobalt salt to 2-methylimidazole is 1:(0.01-0.4). This allows for effective coordination during the formation of Co-MOF precursor materials, while the carbon source material is combined with it in an appropriate amount. Too much carbon source material will cause it to mask the active metal center, while too little carbon source material will prevent effective carbon residue from being formed during subsequent calcination to exert its function.

[0024] Furthermore, in step S1, the dropping rate of the aqueous solution of 2-methylimidazole is 5-15 mL / min, which allows the carbon source material to effectively recombine with the Co-MOF precursor material while it is being formed.

[0025] Furthermore, in step S1, the stirring reaction time is 4 to 8 hours, which allows the Co-MOF precursor and carbon source material to be mixed more fully and evenly.

[0026] Furthermore, in step S2, the calcination treatment in air atmosphere is carried out at a temperature of 250–350°C for 4–8 hours, with a heating rate of 2–10°C / min. This allows the Co-MOF precursor to be effectively converted into Co3O4. At the same time, the relatively low temperature allows the carbon source material to remain effectively in Co3O4 in the form of amorphous C, thereby forming C-Co3O4.

[0027] Furthermore, in step S2, the heat treatment in a nitrogen atmosphere at a temperature of 200–300°C for 0.5–2 hours with a heating rate of 2–5°C / min allows the amorphous C remaining in C-Co3O4 to act as a reducing agent under oxygen-deficient conditions, thereby reducing some of the Co in Co3O4. 3+ Restored to Co 2+ This enhances the Co content of the active center during PMS activation. 2+ Proportion. Attached Figure Description

[0028] 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.

[0029] Figure 1 This is a schematic flowchart of a method for preparing a carbon composite cobalt tetroxide catalyst for PMS activation according to the present invention.

[0030] Figure 2 The XRD pattern of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention;

[0031] Figure 3 This is a spherical aberration TEM image of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of the present invention;

[0032] Figure 4 The images show SEM images of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention and the comparative catalyst.

[0033] Figure 5 The nitrogen-adsorption-desorption curves of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention and the comparative catalyst are shown.

[0034] Figure 6XPS images of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention and the comparative catalyst;

[0035] Figure 7 This is a comparison diagram showing the effect of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of the present invention on activating PMS to degrade sulfamethoxazole with the comparative catalyst.

[0036] Figure 8 This is a comparison of the effects of the synthesized carbon composite cobalt tetroxide catalyst on the activation of PMS for the degradation of sulfamethoxazole when the molar ratio of cobalt salt to carbon source material changes in this invention.

[0037] Figure 9 This is a comparison chart showing the effect of the synthesized carbon composite cobalt tetroxide catalyst on activating PMS to degrade sulfamethoxazole when the nitrogen atmosphere heat treatment time varies (i.e., the example).

[0038] Figure 10 This is a diagram showing the effect of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of the present invention activating PMS to degrade sulfamethoxazole and being recycled 5 times. Detailed Implementation

[0039] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0041] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0042] In this article, unless otherwise specified, the terms “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of”. For example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a”.

[0043] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0044] like Figure 1 As shown, this invention provides a method for preparing a carbon-composite cobalt tetroxide catalyst for PMS activation, comprising the following steps:

[0045] S1: Add an aqueous solution of 2-methylimidazole dropwise to a mixed aqueous solution of cobalt salt and carbon source, stir the reaction at room temperature for 4-8 h, centrifuge the reaction product at 2000-6000 r / min, wash it alternately with anhydrous ethanol and deionized water 4-6 times, and dry it at 50-80 °C to obtain a complex of carbon source and Co-MOF precursor.

[0046] The molar ratio of cobalt salt to carbon source is 1:(0.5-3), the molar ratio of cobalt salt to 2-methylimidazole is 1:(0.01-0.4), the ratio of cobalt salt to deionized water is (0.5-7) mmol:(5-50) mL, that is, the molar concentration of cobalt salt is 0.01-1.4 mol / L, and the ratio of 2-methylimidazole to deionized water is (0.01-0.08) mol:(20-100) mL, that is, the molar concentration of 2-methylimidazole is 0.1-4 mol / L.

[0047] The dropping rate of the aqueous solution of 2-methylimidazole is 5–15 mL / min. The volume ratio of the mixed aqueous solution of cobalt salt and carbon source to the aqueous solution of 2-methylimidazole is 1:(0.5–4).

[0048] The cobalt salt is any one of cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt hydroxide, and cobalt formate.

[0049] The carbon source is any one of citric acid, polyvinylpyrrolidone (PVP), hexadecyltrimethylammonium bromide (CTAB), carbon nitride (C3N4), and polyvinyl alcohol (PVA).

[0050] S2: The composite of the carbon source and the Co-MOF precursor is calcined in an air atmosphere, specifically by heating to 250-350°C at a heating rate of 2-10°C / min and holding for 4-8 hours, i.e., calcination for 4-8 hours; then the calcined product is placed in a nitrogen atmosphere and heated to 200-300°C at a heating rate of 2-5°C / min and held for 0.5-2 hours, i.e., heat treatment for 0.5-2 hours, to obtain the carbon composite cobalt tetroxide catalyst.

[0051] This invention discloses a carbon-composite cobalt tetroxide catalyst for PMS activation, its preparation method, and its application. The method involves adding an aqueous solution of 2-methylimidazole dropwise to a mixed aqueous solution of cobalt salt and carbon source, and reacting with stirring at room temperature to obtain a composite of the carbon source and the Co-MOF precursor. This composite is then heat-treated sequentially in air and nitrogen atmospheres to obtain the carbon-composite cobalt tetroxide catalyst. This invention requires only cobalt salt, carbon source, and 2-methylimidazole to obtain a high-performance C-Co3O4 composite material in a relatively short preparation time (10-20 hours for the entire process).

[0052] This invention calcines a Co-MOF precursor in air to obtain a C-Co3O4 composite material. The addition of a carbon source inhibits agglomeration of the Co-MOF precursor during calcination. Further heat treatment under a nitrogen atmosphere, using C as a reducing agent, increases the active sites for the catalytic reaction, significantly improving the antibiotic degradation efficiency. The preparation method of this invention is simple, highly controllable, and involves a low calcination temperature, resulting in a catalyst with stable and good performance.

[0053] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0054] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0055] Example 1

[0056] Synthesis of C-Co3O4-N2 (1:0.5) catalyst (molar ratio of cobalt salt to carbon source is 1:0.5, molar ratio of cobalt salt to 2-methylimidazole is 1:0.01)

[0057] a. Cobalt carbonate and citric acid in a molar ratio of 1:0.5 are added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole is added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt carbonate to 2-methylimidazole is 1:0.01, the ratio of cobalt carbonate to deionized water is 0.5 mmol:50 mL, and the ratio of 2-methylimidazole to deionized water is 0.01 mol:100 mL.

[0058] b. Solution B was added dropwise to solution A at a rate of 5 mL / min, wherein the volume ratio of solution A to solution B was 1:0.5. The mixture was stirred at room temperature for 4 h, and the precipitate was separated by centrifugation at 2000 r / min. The precipitate was washed four times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 50 °C to obtain the complex of carbon source and Co-MOF precursor.

[0059] c. Place the dried composite in an air atmosphere and heat it to 250°C at a rate of 2°C / min, and keep it at that temperature for 4 hours.

[0060] d. The powder obtained by calcination was further heat-treated at 200℃ for 0.5h in a nitrogen atmosphere at a heating rate of 2℃ / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:0.5) catalyst.

[0061] Example 2

[0062] Synthesis of C-Co3O4-N2 (1:1) catalyst (molar ratio of cobalt salt to carbon source is 1:1, ratio of cobalt salt to 2-methylimidazole is 1:0.1)

[0063] a. Cobalt sulfate and polyvinylpyrrolidone (PVP) in a molar ratio of 1:1 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt sulfate to 2-methylimidazole was 1:0.1, the ratio of cobalt sulfate to deionized water was 1 mmol:10 mL, and the ratio of 2-methylimidazole to deionized water was 0.02 mol:30 mL.

[0064] b. Solution B was added dropwise to solution A at a rate of 5 mL / min, wherein the volume ratio of solution A to solution B was 1:1. The mixture was stirred at room temperature for 4 h, and the precipitate was separated by centrifugation at 2000 r / min. The precipitate was washed 4 times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 50 °C to obtain the complex of carbon source and Co-MOF precursor.

[0065] c. Calcine the dried precursor in air at 250°C for 4 hours at a heating rate of 3°C / min;

[0066] d. The powder obtained by calcination is further heat-treated at 200℃ for 1h in a nitrogen atmosphere at a heating rate of 2℃ / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:1) catalyst.

[0067] Example 3

[0068] Synthesis of C-Co3O4-N2 (1:1.2) catalyst (molar ratio of cobalt salt to carbon source is 1:1.2, and ratio of cobalt salt to 2-methylimidazole is 1:0.15)

[0069] a. Cobalt chloride and hexadecyltrimethylammonium bromide (CTAB) in a molar ratio of 1:1.2 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt chloride to 2-methylimidazole was 1:0.15, the ratio of cobalt chloride to deionized water was 2 mmol:15 mL, and the ratio of 2-methylimidazole to deionized water was 0.03 mol:40 mL.

[0070] b. Solution B was added dropwise to solution A at a rate of 6 mL / min, wherein the volume ratio of solution A to solution B was 1:1.5. The mixture was stirred at room temperature for 5 h, and the precipitate was separated by centrifugation at 3000 r / min. The precipitate was washed four times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 50 °C to obtain the complex of carbon source and Co-MOF precursor.

[0071] c. Calcine the dried precursor in air at 250°C for 6 hours at a heating rate of 4°C / min.

[0072] d. The powder obtained by calcination was further heat-treated at 250°C for 1 h in a nitrogen atmosphere at a heating rate of 2°C / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:1.2) catalyst.

[0073] Example 4

[0074] A catalyst for the synthesis of C-Co3O4 (1:1.5) was prepared (the molar ratio of cobalt salt to carbon source was 1:1.5, and the ratio of cobalt salt to 2-methylimidazole was 1:0.2).

[0075] a. Cobalt nitrate and citric acid in a molar ratio of 1:1.5 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt nitrate to 2-methylimidazole was 1:0.2, the ratio of cobalt nitrate to deionized water was 3 mmol:20 mL, and the ratio of 2-methylimidazole to deionized water was 0.04 mol:50 mL.

[0076] b. Solution B was added dropwise to solution A at a rate of 8 mL / min, wherein the volume ratio of solution A to solution B was 1:2. The mixture was stirred at room temperature for 6 h, and the precipitate was separated by centrifugation at 3000 r / min. The precipitate was washed four times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 60 °C to obtain the complex of carbon source and Co-MOF precursor.

[0077] c. Calcine the dried precursor in air at 250°C for 6 hours at a heating rate of 5°C / min.

[0078] d. The powder obtained by calcination was further heat-treated at 250°C for 2 hours in a nitrogen atmosphere at a heating rate of 5°C / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:1.5) catalyst.

[0079] Example 5

[0080] Synthesis of C-Co3O4-N2 (1:1.8) catalyst (molar ratio of cobalt salt to carbon source is 1:1.8, and ratio of cobalt salt to 2-methylimidazole is 1:0.25)

[0081] a. Cobalt acetate and citric acid in a molar ratio of 1:1.8 are added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole is added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt acetate to 2-methylimidazole is 1:0.25, the ratio of cobalt acetate to deionized water is 4 mmol:25 mL, and the ratio of 2-methylimidazole to deionized water is 0.05 mol:60 mL.

[0082] b. Solution B was added dropwise to solution A at a rate of 10 mL / min, wherein the volume ratio of solution A to solution B was 1:2.5. The mixture was stirred at room temperature for 6 h, and the precipitate was separated by centrifugation at 4000 r / min and washed 4 times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 60 °C to obtain the complex of carbon source and Co-MOF precursor.

[0083] c. Calcine the dried precursor in air at 300°C for 4 hours at a heating rate of 6°C / min;

[0084] d. The powder obtained by calcination was further heat-treated at 250°C for 2 hours in a nitrogen atmosphere at a heating rate of 5°C / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:1.8) catalyst.

[0085] Example 6

[0086] Synthesis of C-Co3O4-N2 (1:2) catalyst (molar ratio of cobalt salt to carbon source is 1:2, and ratio of cobalt salt to 2-methylimidazole is 1:0.3)

[0087] a. Cobalt oxalate and polyvinyl alcohol (PVA) in a molar ratio of 1:2 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt oxalate to 2-methylimidazole was 1:0.3, the ratio of cobalt oxalate to deionized water was 5 mmol:30 mL, and the ratio of 2-methylimidazole to deionized water was 0.06 mol:70 mL.

[0088] b. Solution B was added dropwise to solution A at a rate of 10 mL / min, wherein the volume ratio of solution A to solution B was 1:3. The mixture was stirred at room temperature for 7 h, and the precipitate was separated by centrifugation at 5000 r / min and washed 6 times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 70 °C to obtain the complex of carbon source and Co-MOF precursor.

[0089] c. Calcine the dried precursor in air at 300°C for 6 hours at a heating rate of 7°C / min;

[0090] d. The powder obtained by calcination was further heat-treated at 250°C for 2 hours in a nitrogen atmosphere at a heating rate of 5°C / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:2) catalyst.

[0091] Example 7

[0092] Synthesis of C-Co3O4-N2 (1:2.5) catalyst (molar ratio of cobalt salt to carbon source is 1:2.5, and ratio of cobalt salt to 2-methylimidazole is 1:0.35)

[0093] a. Cobalt hydroxide and carbon nitride (C3N4) in a molar ratio of 1:2.5 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt hydroxide to 2-methylimidazole was 1:0.35, the ratio of cobalt hydroxide to deionized water was 6 mmol:40 mL, and the ratio of 2-methylimidazole to deionized water was 0.07 mol:80 mL.

[0094] b. Solution B was added dropwise to solution A at a rate of 12 mL / min, wherein the volume ratio of solution A to solution B was 1:3.5. The mixture was stirred at room temperature for 7 h, and the precipitate was separated by centrifugation at 5000 r / min and washed 6 times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 70 °C to obtain the complex of carbon source and Co-MOF precursor.

[0095] c. Calcine the dried precursor in air at 350°C for 6 hours at a heating rate of 8°C / min.

[0096] d. The powder obtained by calcination was further heat-treated at 300℃ for 1.5h in a nitrogen atmosphere at a heating rate of 5℃ / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:2.5) catalyst.

[0097] Example 8

[0098] Synthesis of C-Co3O4-N2 (1:3) catalyst (molar ratio of cobalt salt to carbon source is 1:3, ratio of cobalt salt to 2-methylimidazole is 1:0.4)

[0099] a. Cobalt formate and citric acid in a molar ratio of 1:3 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt formate to 2-methylimidazole was 1:0.4, the ratio of cobalt formate to deionized water was 7 mmol: 5 mL, and the ratio of 2-methylimidazole to deionized water was 0.08 mol: 20 mL.

[0100] b. Solution B was added dropwise to solution A at a rate of 15 mL / min, wherein the volume ratio of solution A to solution B was 1:4. The mixture was stirred at room temperature for 8 h, and the precipitate was separated by centrifugation at 6000 r / min and washed 6 times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 80 °C to obtain the complex of carbon source and Co-MOF precursor.

[0101] c. Calcine the dried precursor in air at 350°C for 8 hours at a heating rate of 10°C / min;

[0102] d. The powder obtained by calcination was further heat-treated in a nitrogen atmosphere at 300℃ for 1.5h at a heating rate of 5℃ / min to obtain a carbon composite cobalt tetroxide catalyst, denoted as C-Co3O4-N2(1:2.5) catalyst.

[0103] The following is a comparative example.

[0104] Comparative Example 1

[0105] Synthetic Co3O4 catalyst (no additional carbon source is added during precursor preparation, the calcination temperature in air is increased to 450℃ and no further heat treatment in nitrogen atmosphere is performed after calcination in air atmosphere)

[0106] a. Cobalt nitrate was added to deionized water and stirred to obtain a homogeneous solution A. 2-Methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt nitrate to 2-methylimidazole was 1:0.2, the ratio of cobalt nitrate to deionized water was 3 mmol:20 mL, and the ratio of 2-methylimidazole to deionized water was 0.04 mol:50 mL.

[0107] b. Add solution B dropwise to solution A at a dropping rate of 20 mL / min, wherein the volume ratio of solution A to solution B is 1:2. Stir at room temperature for 6 h, centrifuge at 1000 r / min to separate the precipitate, and wash it 4 times alternately with anhydrous ethanol and deionized water. After washing, dry the precipitate in an oven at 60 °C to obtain the Co-MOF precursor.

[0108] c. The dried precursor was calcined in air at 450°C for 6 h at a heating rate of 5°C / min to obtain the Co3O4 catalyst.

[0109] Comparative Example 2

[0110] Synthesis of Co3O4-N2 catalyst (no additional carbon source is added during precursor preparation, and the calcination temperature in air is increased to 450℃)

[0111] a. Cobalt nitrate was added to deionized water and stirred to obtain a homogeneous solution A. 2-Methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt nitrate to 2-methylimidazole was 1:0.2, the ratio of cobalt nitrate to deionized water was 3 mmol:20 mL, and the ratio of 2-methylimidazole to deionized water was 0.04 mol:50 mL.

[0112] b. Add solution B dropwise to solution A at a dropping rate of 20 mL / min, wherein the volume ratio of solution A to solution B is 1:2. Stir at room temperature for 6 h, centrifuge at 1000 r / min to separate the precipitate, and wash it 4 times alternately with anhydrous ethanol and deionized water. After washing, dry the precipitate in an oven at 60 °C to obtain the Co-MOF precursor.

[0113] c. Calcine the dried precursor in air at 450°C for 6 hours at a heating rate of 5°C / min.

[0114] d. The powder obtained by calcination was further heat-treated in a nitrogen atmosphere at 450°C for 3 h at a heating rate of 5°C / min to obtain the Co3O4-N2 catalyst.

[0115] Comparative Example 3

[0116] Synthesized C-Co3O4 catalyst (cobalt salt to carbon source molar ratio of 1:1.5, calcined in air atmosphere without further heat treatment in nitrogen atmosphere)

[0117] a. Cobalt nitrate and citric acid in a molar ratio of 1:1.5 were added to deionized water and stirred to obtain a homogeneous solution A. 2-methylimidazole was added to deionized water and stirred to obtain a homogeneous solution B. The molar ratio of cobalt nitrate to 2-methylimidazole was 1:0.2, the ratio of cobalt nitrate to deionized water was 3 mmol:20 mL, and the ratio of 2-methylimidazole to deionized water was 0.04 mol:50 mL.

[0118] b. Solution B was added dropwise to solution A at a rate of 20 mL / min, wherein the volume ratio of solution A to solution B was 1:2. The mixture was stirred at room temperature for 6 h, and the precipitate was separated by centrifugation at 1000 r / min. The precipitate was washed four times alternately with anhydrous ethanol and deionized water. The precipitate was dried in an oven at 60 °C to obtain the complex of carbon source and Co-MOF precursor.

[0119] c. The dried precursor was calcined in air at 250°C for 6 h at a heating rate of 5°C / min to obtain the C-Co3O4 catalyst.

[0120] Figure 2 The image shows the XRD pattern of the carbon-composite cobalt tetroxide catalyst prepared in Example 4 of this invention; Figure 2 It can be seen that the diffraction peaks of the carbon composite cobalt tetroxide catalyst obtained in this invention are consistent with the diffraction peaks of JSPDS card No. 42-1467 in the database, indicating that the catalyst synthesized by this method is cobalt tetroxide.

[0121] Figure 3 This is a spherical aberration TEM image of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention; (The image is from...) Figure 3 It can be seen that the dark flocculent material appearing at the edge of the catalyst is amorphous carbon, indicating that the catalyst obtained by this invention is carbon composite cobalt tetroxide. The presence of amorphous carbon will prevent the agglomeration of Co3O4 and effectively control the particle size of the final material.

[0122] Figure 4 The images show SEM images of the carbon-composite cobalt tetroxide catalyst prepared in Example 4 of this invention, and the Co3O4, Co3O4-N2, and C-Co3O4 catalysts synthesized in the comparative examples; Figure 4 It can be seen that the particle size of the two C-containing catalysts, carbon composite cobalt tetroxide and C-Co3O4 in the comparative example, obtained by the present invention is 30 nm, which is smaller than the particle size of the C-free catalysts (Co3O4, Co3O4-N2) (60 nm). This is mainly because the presence of C in the C-containing catalysts to a certain extent prevents the aggregation of nanoparticles, thereby producing smaller crystallites.

[0123] Figure 5The nitrogen-adsorption-desorption curves are shown for the carbon composite cobalt tetroxide catalyst prepared in Example 4 of this invention, and for the Co3O4, Co3O4-N2, and C-Co3O4 catalysts synthesized in the comparative examples. Figure 5 As can be seen, the carbon-composite cobalt tetroxide (C-Co3O4-N2) obtained in this invention has a much larger specific surface area than the catalysts (Co3O4, Co3O4-N2) in the comparative examples that do not contain C. This is mainly because the presence of C causes the catalyst to produce smaller particles, thus exhibiting a larger specific surface area. The fact that the C-Co3O4-N2 in this invention has a larger specific surface area than the C-Co3O4 in the comparative examples indicates that heat treatment under an N2 atmosphere also increases the specific surface area of ​​the catalyst.

[0124] Figure 6 XPS plots of the carbon composite cobalt tetroxide (C-Co3O4-N2) catalyst prepared in Example 4 of this invention and the C-Co3O4 catalyst synthesized in the comparative example; Figure 6 It can be seen that the carbon composite cobalt tetroxide (C-Co3O4-N2) obtained in this invention exhibits higher Co content compared to the C-Co3O4 in the comparative example. 2+ / Co 3+ The ratio is mainly because during the additional heat treatment of C-Co3O4 under a nitrogen atmosphere, the oxygen-deficient environment, with C acting as a reducing agent, causes some of the Co in Co3O4 to be reduced. 3+ Restored to Co 2+ This effectively increases the active center Co 2+ The proportion.

[0125] Furthermore, the performance of the carbon-composite cobalt tetroxide catalyst prepared in this invention was evaluated by degrading sulfamethoxazole (SMX). The evaluation process is as follows:

[0126] The reaction was carried out in a 100 mL beaker. 0.005 g of the prepared carbon-composite cobalt tetroxide catalyst was added to an SMX solution with an initial concentration (C0) of 10 mg / L. The catalyst was sonicated for 2 min to ensure uniform dispersion, and then stirred under light-shielded conditions for 20 min to allow for physical adsorption. The pH was controlled by adding boric acid-borax buffer solution. The reaction was triggered by the addition of 1 mM PMS solution. The concentration (C) of the remaining sulfamethoxazole in the reaction solution was measured at certain time intervals. A graph of C / C0 versus reaction time was plotted to obtain the performance test results of the carbon-composite cobalt tetroxide catalyst activating PMS to degrade sulfamethoxazole. The results are shown in [Figure number missing]. Figure 7 ,Depend on Figure 7It can be seen that the C-Co3O4-N2 catalyst obtained in this invention has a good effect on activating PMS to degrade sulfamethoxazole, while the Co3O4, Co3O4-N2, and C-Co3O4 catalysts in the comparative examples all have poor effects on activating PMS to degrade sulfamethoxazole. The higher specific surface area of ​​the C-Co3O4-N2 catalyst provides more reaction sites for PMS activation and sulfamethoxazole degradation. In addition, the higher Co content in the C-Co3O4-N2 catalyst... 2+ / Co 3+ The ratio is beneficial to increasing SO4 ·- The yield and degradation of sulfamethoxazole effectively improved the catalytic performance of C-Co3O4-N2.

[0127] Figure 8 This is a comparison chart showing the effect of the synthesized carbon-composite cobalt tetroxide catalyst on activating PMS to degrade sulfamethoxazole when the molar ratio of cobalt salt to carbon source material changes in this invention. Figure 8 It can be seen that the C-Co3O4-N2 (1:1, i.e., the product of Example 2), C-Co3O4-N2 (1:1.5, i.e., the product of Example 4), C-Co3O4-N2 (1:2, i.e., the product of Example 6), and C-Co3O4-N2 (1:2.5, i.e., the product of Example 7) catalysts obtained in this invention all have good effects in activating PMS to degrade sulfamethoxazole.

[0128] Figure 9 This is a comparison chart showing the effect of the synthesized carbon composite cobalt tetroxide (C-Co3O4-N2) catalyst on activating PMS to degrade sulfamethoxazole under varying heat treatment time in a nitrogen atmosphere, as described in this invention. Figure 9 It can be seen that the carbon composite cobalt tetroxide (C-Co3O4-N2) catalyst obtained in this invention maintains good activation of PMS to degrade sulfamethoxazole during the N2 treatment time of 0.5 to 2 hours during the synthesis process.

[0129] Figure 10 This is a graph showing the effect of the carbon composite cobalt tetroxide catalyst prepared in Example 4 of the present invention activating PMS to degrade sulfamethoxazole and being recycled 5 times. Figure 10 It can be seen that the carbon composite cobalt tetroxide catalyst obtained in this invention can still achieve 100% activation of PMS within 15 minutes to degrade sulfamethoxazole after 5 cycles, and the reaction rate constant is 0.22958 min. -1 0.28226min -1 0.2459min -1 0.2823min -1 0.24296min -1The efficiency has remained high without any decline. This is mainly because the present invention uses calcined MOF precursors to prepare oxide-based catalysts. While inheriting the chemical stability of MOF materials, the calcination treatment further significantly improves the stability of MOF materials, making it less prone to cobalt ion leaching when degrading antibiotics in a liquid environment. This ensures that the catalyst maintains a relatively sufficient number of active sites throughout the cycle.

[0130] This invention utilizes the calcination of Co-MOF precursors to prepare MOF-derived carbon-composite cobalt tetroxide catalysts. The Co-MOF precursors are prepared using a solution method, and the calcination is carried out at ambient pressure and relatively low temperature. This method offers mild preparation conditions, low energy consumption, and eliminates the need for pH adjustment, resulting in a relatively safe and mild synthesis process with a short preparation time. Only cobalt salts, a carbon source, and 2-methylimidazole are required. The carbon-composite cobalt tetroxide catalyst synthesized in this invention exhibits small grain size, excellent performance in activating PMS to degrade the organic pollutant sulfamethoxazole, and superior cycle stability.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. Use of carbon composite cobalt oxide catalyst for PMS activation in the field of treating antibiotic wastewater, characterized in that, The preparation method of the carbon-composite cobaltosic oxide catalyst for PMS activation comprises the following steps: S1: drop 2-methylimidazole aqueous solution into a mixed aqueous solution of cobalt salt and carbon source, stir the reaction at room temperature, centrifuge and wash the reaction product, and dry to obtain a uniformly dispersed composite of carbon source and Co-MOF precursor; S2: calcine the composite of carbon source and Co-MOF precursor in an air atmosphere, and then heat treat the calcined product in a nitrogen atmosphere to obtain the carbon-composite cobaltosic oxide catalyst.

2. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S1, the cobalt salt is any one of cobalt carbonate, cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt hydroxide, and cobalt formate.

3. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S1, the carbon source is any one of citric acid, polyvinylpyrrolidone, cetyltrimethylammonium bromide, carbon nitride, and polyvinyl alcohol.

4. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S1, the molar ratio of cobalt salt to carbon source is 1:(0.5-3), and the molar ratio of cobalt salt to 2-methylimidazole is 1:(0.01-0.4).

5. The use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S1, the dropwise addition speed of the 2-methylimidazole aqueous solution is 5-15 mL / min.

6. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S1, the stirring reaction time is 4-8 h.

7. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treating antibiotic wastewater, characterized in that, In step S2, the calcination temperature in the air atmosphere is 250-350 ℃, the calcination time is 4-8 h, and the heating rate is 2-10 ℃ / min.

8. Use of a carbon composite cobalt oxide catalyst for PMS activation according to claim 1 in the field of treatment of antibiotic wastewater, characterized in that, In step S2, the heat treatment temperature in the nitrogen atmosphere is 200-300 ℃, the time is 0.5-2 h, and the heating rate is 2-5 ℃ / min.

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