Cobalt-doped manganese oxide octahedral molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention relates to a cobalt-doped manganese oxide octahedral molecular sieve catalyst as well as a preparation method and application thereof, and belongs to the technical field of molecular sieve catalysts. A cobalt-doped manganese oxide octahedral molecular sieve catalyst comprises: a manganese oxide octahedral molecular sieve, the crystal structure of which is K-OMS-2; the cobalt element is introduced into crystal lattices of the manganese oxide octahedral molecular sieve in a doping form; the carbon nano tube is compounded with the manganese oxide octahedral molecular sieve to form a conductive network; the nano titanium dioxide is dispersed in the composite structure; and the carbon coating layer coats the manganese oxide octahedral molecular sieve. Through cobalt doping, construction of a conductive network by a carbon tube, titanium dioxide photoresponse and carbon coating, the problems of low catalytic activity, poor free radical production efficiency, weak electron conduction, unstable structure, poor pH adaptability, single function and the like of conventional K-OMS-2 are systematically solved, and the catalytic oxidation capacity, reaction efficiency, stability and multifunctionality are remarkably improved; the method is suitable for various reaction modes such as Fenton-like, photocatalysis and electro-catalysis.

Description

TECHNICAL FIELD

[0001] The present application relates to a molecular sieve catalyst, in particular to a cobalt-doped manganese oxygen octahedral molecular sieve catalyst and a preparation method and application thereof, and belongs to the technical field of molecular sieve catalysts. BACKGROUND

[0002] Organic pollutants (such as dyes, pesticides, pharmaceutical intermediates, phenolic compounds, antibiotics and plasticizers, etc.) are an important cause of water pollution. These organic pollutants have the characteristics of being difficult to degrade, strong bioaccumulation, high ecological risk, etc. Traditional physical treatment methods (such as sedimentation, adsorption) can only achieve the transfer of pollutants rather than complete degradation, and biological treatment is limited by the low tolerance and low degradation efficiency of the bacterial species to these pollutants. Therefore, developing efficient, green and sustainable organic pollutant degradation technology has become an important research direction in the field of environmental governance.

[0003] Based on advanced oxidation technology (Advanced Oxidation Processes, AOPs), active free radicals with strong oxidizing ability can be efficiently generated to achieve the mineralization or deep degradation of most organic pollutants. Commonly used AOPs include: Fenton-like reaction, photocatalytic oxidation (such as TiO2 / UV), electrochemical oxidation, etc.

[0004] Manganese oxygen octahedral molecular sieve (OMS) is a kind of transition metal manganese oxide material with tunnel or layered structure, and its chemical composition is usually K x Mn8O 16 ·nH2O (such as K-OMS-2) or δ-MnO2, α-MnO2, etc. variants, which have the following structural and performance characteristics: 1. Unique crystal structure The most typical OMS material is K-OMS-2 (manganese potassium mineral type octahedral molecular sieve), which contains a one-dimensional tunnel structure, which is beneficial to the mass transfer and adsorption of reactant molecules. The manganese ions in its structure mainly exist in mixed valence states of Mn(III) / Mn(IV), which have variable valence states and good redox cycling ability, and are the active centers of catalytic reactions.

[0005] 2. Excellent redox performance The Mn³⁺ / Mn 4 ⁺ in the OMS material can change valence during the reaction, thereby effectively activating oxidizing agents (such as H2O2, PMS, PDS) to generate strong oxidizing free radicals and drive the oxidative degradation of organic matter.

[0006] 3. High specific surface area and good stability Some OMS materials have high specific surface area and abundant surface hydroxyl groups, which are helpful for pollutant adsorption and active site exposure, and can improve the efficiency of catalytic reaction. Compared with traditional homogeneous catalysts (such as Fe 2+ ), OMS is usually a solid heterogeneous catalyst, which is easy to separate and recycle, can be used repeatedly, reduces secondary pollution, and meets the concept of green chemistry.

[0007] 4. Catalytic mechanism of OMS in degradation of organic pollutants In Fenton-like or persulfate-like catalytic systems, OMS materials mainly activate hydrogen peroxide or persulfate to generate hydroxyl radicals or sulfate radicals, which have stronger degradation effect on various stubborn organic pollutants. Under certain conditions, OMS can also degrade pollutants by generating singlet oxygen or direct electron transfer, especially in complex water conditions.

[0008] At present, many researchers at home and abroad have carried out research on the catalytic performance of OMS materials, especially K-OMS-2, in the degradation of dyes (such as methylene blue and rhodamine B), phenols, antibiotics (such as tetracycline and sulfonamides), pesticides, benzene series and other organic pollutants. Although K-OMS-2 shows good catalytic potential, there are still problems such as insufficient catalytic activity, low efficiency of free radical generation, poor pH adaptability, weak electron conduction ability, poor structural stability, single function and the like in practical application (especially industrial or large-scale water treatment). SUMMARY

[0009] The present application aims to solve the above problems and provides a cobalt-doped manganese-oxygen octahedral molecular sieve catalyst.

[0010] The technical scheme for solving the above problems is as follows: A cobalt-doped manganese-oxygen octahedral molecular sieve catalyst suitable for oxidative degradation of organic pollutants, comprising: Manganese-oxygen octahedral molecular sieve with a crystal structure of K-OMS-2; Cobalt element introduced into the crystal lattice of the manganese-oxygen octahedral molecular sieve in a doped form; Carbon nanotubes forming a conductive network with the manganese-oxygen octahedral molecular sieve; Nano-titanium dioxide dispersed in the composite structure in the form of nanoparticles or nanosheets; Carbon coating layer covering the manganese-oxygen octahedral molecular sieve.

[0011] In the above technical scheme of the present application, the manganese-oxygen octahedral molecular sieve is used to provide redox active sites.

[0012] Co 2+ / Co3+ Mn can be optimized as an electronic "modulating agent" 4+ / Mn 3+ oxidation-reduction cycle; enhance the activation ability of active sites to oxidants, promote electron transfer, and increase the yield of hydroxyl radicals, sulfate radicals, and other free radicals; thereby solving the problems of low catalytic activity and insufficient free radical production efficiency of conventional K-OMS-2.

[0013] Carbon nanotubes have strong electrical conductivity and can form efficient electron transport channels, accelerating the migration of electrons from Mn active sites to oxidants. In the case of photocatalysis, carbon nanotubes can rapidly transfer photo-generated electrons through their strong electrical conductivity, inhibiting electron-hole recombination. In addition, carbon nanotubes can also improve the mechanical strength and structural integrity of the catalyst, preventing the collapse of the manganese-oxygen framework under pressure. Thus, the problems of poor electron conductivity and insufficient structural stability of conventional K-OMS-2 are solved.

[0014] Nanometer titanium dioxide, especially anatase, can generate electron-hole pairs (photo-generated carriers) in response to ultraviolet / visible light. Photo-generated electrons, especially in the presence of a carbon nanotube conductive network, can rapidly transfer electrons and participate in the generation of strong oxidizing free radicals. In combination with carbon nanotubes, the problem of no photocatalytic function and inability to utilize light energy of conventional K-OMS-2 is solved.

[0015] Carbon layer coating can protect the manganese-oxygen octahedral molecular sieve framework and reduce potassium ion leaching. It can also improve the structural stability and activity retention rate of the catalyst during multiple cycles. Thus, the problem of activity decline after repeated use of conventional K-OMS-2 is solved.

[0016] As a preferred embodiment of the above technical solution, the manganese-oxygen octahedral molecular sieve has a length of 50-500 nm, a diameter of 10-30 nm, and a specific surface area of 50-150 m 2 / g.

[0017] As a preferred embodiment of the above technical solution, the cobalt element exists in the form of Co 2+ or Co 3+ in the manganese-oxygen octahedral structure or at surface defect sites, with a doping amount of 0.5-5 wt% of the total mass of the molecular sieve catalyst.

[0018] As a preferred embodiment of the above technical solution, the content of carbon nanotubes is 1-10 wt%, and the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a length of 1-10 μm and a diameter of 5-20 nm. They are used to construct electron transport channels and improve the mechanical strength and dispersibility of the material.

[0019] As a preferred solution of the above technical scheme, the nano-titanium dioxide has a content of 1-10 wt%, and is in an anatase type, a rutile type or a mixed crystal type of both.

[0020] As a preferred solution of the above technical scheme, the molecular sieve catalyst exerts catalysis at least based on one of the following mechanisms: 1) under ultraviolet / visible light irradiation, the catalyst reacts with hydrogen peroxide or persulfate to generate hydroxyl radicals or sulfate radicals; and 2) under an applied direct current electric field, the catalyst activates an oxidant to generate radicals.

[0021] Another object of the present application is to provide a preparation method of the above-mentioned cobalt-doped manganese-oxygen octahedral molecular sieve catalyst.

[0022] The preparation method of the cobalt-doped manganese-oxygen octahedral molecular sieve catalyst comprises the following steps: S1, hydrothermal synthesis of K-OMS-2 nanorods: A potassium source, KMnO4 and MnSO4 are subjected to a hydrothermal reaction under an acidic condition to obtain one-dimensional K-OMS-2 nanorods; S2, cobalt doping: The K-OMS-2 nanorods are dispersed in deionized water, an appropriate amount of a cobalt salt solution is added, and stirring is performed for 6-12 hours; centrifugation and washing are performed to remove free cobalt ions, and drying is performed to obtain Co-doped K-OMS-2; S3, carbon nanotube compounding: Carbon nanotubes are dispersed in deionized water by ultrasonic dispersion to form a suspension A; the Co-doped K-OMS-2 is dispersed in deionized water by ultrasonic dispersion to form a suspension B; the suspension A and the suspension B are uniformly mixed under ultrasonic magnetic stirring to obtain a Co-OMS / CNTs composite slurry; S4, introduction of titanium dioxide: Titanium dioxide nanomaterials are uniformly mixed with the Co-OMS / CNTs composite slurry by a sol-gel method, a hydrothermal method or a direct mixing method to obtain a Co-OMS / CNTs / TiO2 composite slurry; S5, carbon coating and heat treatment: An appropriate amount of a carbon source is added to the Co-OMS / CNTs / TiO2 composite slurry, drying treatment is performed, and then carbonization treatment is performed at 600-800 degrees Celsius under an inert atmosphere to form a carbon-coated material; S6, post-treatment: Deionized water or ethanol is used for washing, and then drying is performed, grinding is performed into a fine powder to obtain the molecular sieve catalyst.

[0023] As a preferred technical scheme of the above, the carbon source is selected from one or more of glucose, sucrose, cellulose or polyacrylonitrile, for forming a carbon coating layer during heat treatment to improve the electrical conductivity and structural stability of the material.

[0024] In a third aspect, the present application provides an application of the above-mentioned molecular sieve catalyst.

[0025] The application of the above-mentioned molecular sieve catalyst in the treatment of organic pollutants includes: 1) used in combination with hydrogen peroxide or persulfate in a Fenton-like reaction system; 2) photocatalytic degradation under ultraviolet or visible light irradiation; 3) catalytic reaction promoted by applying an electric field in an electrocatalytic device.

[0026] As a preferred technical scheme of the above, the organic pollutants include dyes, antibiotics, pesticides, pharmaceutical intermediates, phenolic compounds and plasticizers.

[0027] In summary, the present application has the following advantages: 1. By doping cobalt elements, the present application regulates the redox cycle of manganese, optimizes the electronic structure, enhances the activation ability of oxidizing agents, promotes electron transfer, and significantly improves the yield of active oxygen species such as hydroxyl radicals and sulfate radicals; greatly improves the catalytic activity, and more efficiently degrades stubborn organic pollutants such as dyes, antibiotics and phenols; 2. Doping cobalt elements optimizes the valence state cycle of manganese, so that the catalyst can maintain good redox ability in a wider pH range; 3. Conventional K-OMS-2 can only be used for Fenton-like reactions and cannot utilize light or electrical energy, with a single function; the present application introduces nanometer titanium dioxide to generate electron-hole pairs under ultraviolet / visible light and participate in free radical generation; at the same time, carbon nanotubes cooperate to quickly transfer photo-generated electrons, improving the photocatalytic efficiency; in addition, the overall catalyst can also generate free radicals under the action of an electric field (electrocatalytic device); the catalyst has a "Fenton-like + photocatalysis + electrocatalysis" multifunctional synergistic mechanism, and can flexibly select or combine operation modes according to actual needs, greatly improving the processing capacity and scene adaptability; 4. The carbon coating layer of the present application protects the manganese-oxygen skeleton, reduces the dissolution of potassium ions, enhances the corrosion resistance and structural stability, and improves the activity retention rate of the catalyst after multiple cycle reactions; 5. In addition to enhancing the electrical conductivity, carbon nanotubes also improve the mechanical strength and structural integrity of the overall material; preventing the catalyst from breaking or accumulating during the reaction or preparation process; 6、In summary, the present application solves the problems of low catalytic activity, poor free radical generation efficiency, weak electron conduction, unstable structure, poor pH adaptability, and single function of conventional K-OMS-2 by adjusting the electronic structure through cobalt doping, constructing a conductive network through carbon nanotubes, introducing light response through titanium dioxide, and enhancing stability through carbon coating, thereby significantly improving the catalytic oxidation capacity, reaction efficiency, stability, and multifunctionality. The present application is suitable for various reaction modes such as Fenton, photocatalysis, and electrocatalysis, and has efficient, broad-spectrum, and stable degradation effect on organic pollutants such as dyes, antibiotics, and pesticides. DETAILED DESCRIPTION

[0028] The present detailed description is merely an explanation of the present application, and is not a limitation of the present application. Any changes made by those skilled in the art after reading the present specification will be within the scope of protection of the patent law.

[0029] This part provides four specific examples, and their general preparation process is as follows: S1: Hydrothermal synthesis of K-OMS-2 nanorods; S2: Cobalt doping; S3: Carbon nanotube composite; S4: Introduction of titanium dioxide; S5: Carbon coating and heat treatment; S6: Post-processing.

[0030] Example 1 This example is a basic preparation example of a catalyst, which is used to verify the basic process feasibility of cobalt doping, carbon nanotube composite, titanium dioxide introduction, and carbon coating. The specific preparation process is as follows: First, K-OMS-2 nanorods were prepared by hydrothermal reaction. K2SO4, KMnO4, and MnSO4 were mixed in deionized water in a certain stoichiometric ratio (molar ratio of raw materials, MnSO4: KMnO4: K2SO4 = 1: 1: 2), under weak acidic conditions adjusted by dilute sulfuric acid (pH = 1.5-2.5), transferred to a hydrothermal reactor, reacted at 120°C for 12 hours, and then naturally cooled to room temperature. The product was separated by centrifugation, washed with deionized water several times until neutral, and then dried in an oven to obtain K-OMS-2 nanorods.

[0031] Then, the obtained K-OMS-2 nanorods are dispersed in deionized water, and a cobalt nitrate solution (in the form of Co (NO3) 2·6H2O) is added, wherein the doping amount of cobalt element is controlled at 0.5 wt% of the total mass of the catalyst, and the reaction is stirred for 6 to 12 hours, so that the cobalt ions fully enter the crystal lattice or surface defect sites of the K-OMS-2. After the reaction is completed, the free cobalt ions that are not adsorbed are removed by centrifugation and washing, and then the catalyst is dried to obtain cobalt-doped K-OMS-2.

[0032] Subsequently, carbon nanotubes (single-walled or multi-walled, length about 1~10 μm, diameter about 5~20 nm) are added to the above-mentioned cobalt-doped K-OMS-2 dispersion liquid at a mass ratio of 1 wt%, and are uniformly dispersed by ultrasonic dispersion to form a suspension; at the same time, the cobalt-doped K-OMS-2 is also ultrasonically dispersed in deionized water to form another suspension, and the two are mixed and continuously ultrasonically dispersed and magnetically stirred to obtain a uniform composite slurry, ensuring that the carbon nanotubes and K-OMS-2 are fully compounded to construct a three-dimensional conductive network.

[0033] After that, nano-titanium dioxide (anatase type, particle size about 10~20 nm) is added to the composite slurry at a proportion of 1 wt% of the total mass of the catalyst, and is uniformly dispersed in the slurry by direct mixing to form a composite slurry containing Co-doped K-OMS-2, CNTs and TiO2.

[0034] Subsequently, an appropriate amount of glucose is added to the composite slurry as a carbon source, and after stirring and drying treatment, the obtained solid mixture is placed in a tube furnace and subjected to carbonization treatment at a temperature of 600°C for 2 hours under a nitrogen protective atmosphere, so that the carbon source is pyrolyzed to form a carbon layer coated on the surface of the catalyst, improving the electrical conductivity and structural stability.

[0035] Finally, the carbonized product is washed several times with deionized water and ethanol, and then dried and ground to obtain the final catalyst, which is denoted as: Co-0.5 / CNTs-1 / TiO2-1@C-600.

[0036] Example 2 This example is a core optimization example of the catalyst, and the doping and compounding proportions of the components are adjusted to comprehensively improve the catalytic activity, electron conduction, light response and structural stability, which is the optimal catalyst used in the subsequent pollutant degradation experiment. The preparation process is as follows: First, K-OMS-2 nanorods are prepared by hydrothermal reaction (same as in Example 1).

[0037] Subsequently, cobalt doping is performed. In this step, the cobalt element doping amount is increased to 2 wt% of the total mass of the catalyst to more significantly regulate the redox cycle of Mn, enhance the activation ability to oxidants and the efficiency of free radical generation.

[0038] Next, carbon nanotubes are ultrasonically dispersed in deionized water at a mass ratio of 5 wt%, mixed with Co-doped K-OMS-2 that is also ultrasonically dispersed, to form a uniform composite slurry, build a more efficient electron transport network, and at the same time improve the mechanical strength and structural integrity of the catalyst.

[0039] Then, nano-titanium dioxide (anatase type) is added to the slurry at an amount of 3 wt% of the total mass of the catalyst, uniformly dispersed by direct mixing method, and the TiO2 has the characteristics of generating photo-generated carriers under ultraviolet or visible light irradiation, providing active sites for photocatalytic reaction, and improving electron migration efficiency under the synergistic action of CNTs.

[0040] Subsequently, an appropriate amount of glucose is added as a carbon source, dried, and carbonized at a temperature of 700°C for 2 hours under nitrogen protection to form a stable carbon coating layer, further improving the electrical conductivity and corrosion resistance of the catalyst.

[0041] Finally, the carbonized product is washed several times with deionized water and ethanol, then dried and ground to obtain the final catalyst, which is denoted as: Co-2 / CNTs-5 / TiO2-3@C-700. This embodiment is used for subsequent Fenton-like, photocatalytic and electrocatalytic reaction experiments for pollutant degradation.

[0042] Example 3 This embodiment is based on Example 2, further increasing the loading of cobalt, carbon nanotubes and titanium dioxide to explore the influence of higher doping and composite ratio on the performance of the catalyst, and at the same time investigate the structural stability and reaction activity of the catalyst under high loading conditions. The preparation process is as follows: First, K-OMS-2 nanorods are prepared by hydrothermal reaction (same as Example 1).

[0043] Subsequently, cobalt doping is performed. In this step, the cobalt element doping amount is increased to 2 wt% of the total mass of the catalyst to more significantly regulate the redox cycle of Mn, enhance the activation ability to oxidants and the efficiency of free radical generation.

[0044] Next, carbon nanotubes are ultrasonically dispersed in deionized water at a mass ratio of 5 wt%, mixed with Co-doped K-OMS-2 that is also ultrasonically dispersed, to form a uniform composite slurry, build a more efficient electron transport network, and at the same time improve the mechanical strength and structural integrity of the catalyst.

[0045] Subsequently, a proper amount of glucose is added as a carbon source, and after drying, carbonization is performed at a temperature of 750°C for 2 hours under nitrogen protection, to form a stable carbon coating layer, further improving the electrical conductivity and corrosion resistance of the catalyst.

[0046] Subsequently, a proper amount of glucose is added as a carbon source, and after drying, carbonization is performed at a temperature of 750°C for 2 hours under nitrogen protection, to form a stable carbon coating layer, further improving the electrical conductivity and corrosion resistance of the catalyst.

[0047] Finally, the carbonized product is washed several times with deionized water and ethanol, and then dried and ground to obtain the final catalyst, denoted as: Co-3 / CNTs-7 / TiO2-5@C-750.

[0048] Example 4 This example focuses on adjusting the loading ratio of titanium dioxide and the carbonization temperature to investigate the effects of high TiO2 content and higher heat treatment temperature on the photocatalytic performance and structural stability of the catalyst. The preparation process is as follows: First, K-OMS-2 nanorods are prepared by hydrothermal reaction (same as Example 1).

[0049] Subsequently, cobalt doping is performed. In this step, the cobalt doping amount is increased to 1 wt% of the total mass of the catalyst, to more significantly regulate the redox cycle of Mn, enhance the activation ability of oxidizing agents and the efficiency of free radical generation.

[0050] Next, carbon nanotubes are ultrasonically dispersed in deionized water at a mass ratio of 3 wt%, and mixed with Co-doped K-OMS-2 also ultrasonically dispersed, to form a uniform composite slurry, building a more efficient electron transport network, while improving the mechanical strength and structural integrity of the catalyst.

[0051] Subsequently, a proper amount of glucose is added as a carbon source, and after drying, carbonization is performed at a temperature of 750°C for 2 hours under nitrogen protection, to form a stable carbon coating layer, further improving the electrical conductivity and corrosion resistance of the catalyst.

[0052] Subsequently, a proper amount of glucose is added as a carbon source, and after drying, carbonization is performed at a temperature of 750°C for 2 hours under nitrogen protection, to form a stable carbon coating layer, further improving the electrical conductivity and corrosion resistance of the catalyst.

[0053] Finally, the product after carbonization was washed several times with deionized water and ethanol, and then dried and ground to obtain the final catalyst, denoted as: Co-1 / CNTs-3 / TiO2-7@C-800.

[0054] The catalyst prepared in Example 2, i.e. Co-2 / CNTs-5 / TiO2-3@C-700, was selected as the test product, and the conventional K-OMS-2 without any doping and composite modification was used as the comparative example to carry out the catalytic degradation test of the typical organic pollutant methylene blue, so as to evaluate the difference in catalytic performance of the two types of catalysts under different reaction modes. The selected pollutant methylene blue is a common cationic dye, which is stable in structure and difficult to biodegrade, and is a typical representative for evaluating the oxidative degradation ability of the catalyst in the Fenton-like, photocatalytic and electrocatalytic systems. Three different reaction modes were set up, namely Fenton-like reaction, photocatalytic reaction and electrocatalytic reaction. The catalysts of Example 2 and the comparative example were used for comparison test under each mode, so as to fully investigate the actual effect of composite modification on the activity improvement of the catalyst.

[0055] 1) In the Fenton-like reaction mode, the experimental system was 100 mL of methylene blue aqueous solution with an initial concentration of 10 mg / L, 0.5 g / L of catalyst was added, and 0.1 mmol / L of persulfate PMS was added as an oxidant. The reaction was carried out at room temperature and pressure in a light-proof environment, and the solution was kept uniform by magnetic stirring. The reaction time was 60 minutes, and samples were taken every 10 minutes during the reaction (each time 3 times, and the average value of methylene blue concentration was calculated). The concentration of methylene blue in the solution was determined by ultraviolet visible spectrophotometer at 664 nm wavelength, and the degradation rate at different time points was calculated. The results are shown in Table 1.

[0056] Table 1 Methylene blue (MB) degradation results under Fenton-like reaction conditions The experimental results show that under this mode, the degradation rate of methylene blue using the conventional K-OMS-2 catalyst is only 58% after 60 minutes, indicating that the unmodified K-OMS-2 has low catalytic activity in the Fenton-like system, and the activation ability of PMS is limited, and the active oxygen species such as hydroxyl radicals and sulfate radicals are less, which makes it difficult to effectively degrade the target pollutants. Under the same reaction conditions, the degradation rate of methylene blue using the catalyst of Example 2 reached 95% after 60 minutes of reaction, showing extremely high catalytic activity, which indicates that after cobalt doping, carbon nanotube compounding, titanium dioxide introduction and carbon coating modification, the activation ability of the catalyst to PMS is significantly enhanced, and strong oxidizing free radicals can be efficiently produced, so as to realize the rapid oxidative degradation of methylene blue.

[0057] 2) In the photocatalytic reaction mode, the experiment also uses 100 mL of methylene blue aqueous solution with an initial concentration of 10 mg / L, and 0.5 g / L of catalyst is added, without adding additional oxidants, but using a 300-watt xenon lamp as a light source during the reaction process. The light source is treated with a filter, mainly providing ultraviolet and visible light range irradiation, simulating sunlight irradiation conditions. The reaction system is kept uniform under magnetic stirring, and the reaction time is also 60 minutes. Sampling is taken every 10 minutes for detection (each sampling takes 3 times, and the average value of the methylene blue concentration is calculated). The concentration of methylene blue in the solution is measured at a wavelength of 664 nanometers using a UV-visible spectrophotometer, and the degradation rate at different time points is calculated. The results are shown in Table 2.

[0058] Table 2 Methylene blue (MB) degradation results under photocatalytic reaction conditions The experimental results show that the photocatalytic reaction system using the conventional K-OMS-2 catalyst has almost no obvious methylene blue degradation under light conditions, with a 60-minute degradation rate close to zero, indicating no photocatalytic activity. In contrast, the catalyst of Example 2, which is compounded with titanium dioxide nanoparticles with light response ability and forms an efficient electron transport network through carbon nanotubes, can effectively generate photo-generated electrons and holes under light conditions, thereby initiating oxidation reactions. The experiment measured that the degradation rate of methylene blue reached 91% after 60 minutes of reaction, indicating that the catalyst has good photo-generated carrier utilization ability and oxidation degradation efficiency in the photocatalytic system, verifying the positive role of titanium dioxide and carbon nanotube modification.

[0059] 3) In the electrocatalytic reaction mode, the experiment uses a three-electrode system, in which the catalyst of Example 2 or the catalyst of the comparative example is used as the working electrode, platinum is used as the counter electrode, and the saturated mercury electrode or Ag / AgCl electrode is used as the reference electrode. The electrolyte contains 10 mg / L of methylene blue and 0.1 mmol / L of sodium sulfate solution, the reaction is carried out at room temperature, the external voltage is set to 1.0 volts (relative to the reference electrode), the reaction time is 60 minutes, and the mass transfer is uniform during the continuous magnetic stirring. Sampling is taken every 10 minutes for analysis (the sampling method is the same as above). The concentration of methylene blue in the solution is measured at a wavelength of 664 nanometers using a UV-visible spectrophotometer, and the degradation rate at different time points is calculated. The results are shown in Table 3.

[0060] Table 2 Methylene blue (MB) degradation results under photocatalytic reaction conditions The experimental results show that in this mode, when using a conventional K-OMS-2 catalyst, because the catalyst has not been modified for any electrical conductivity or electrical activity, its electrocatalytic activity is weak, and it is difficult to effectively activate dissolved oxygen or oxidants in the solution on the surface of the electrode. The degradation rate of methylene blue is only about 50% after 60 minutes, showing general electrocatalytic performance. When using the catalyst of Example 2, because it has been modified by carbon nanotubes and carbon coating, it has excellent electrical conductivity and electron transfer capacity, and can effectively promote the activation of oxidants and interfacial electron transfer under the condition of an applied electric field, thereby efficiently generating free radicals. The experimental results show that the degradation rate of methylene blue is 89% after 60 minutes of reaction with the catalyst, which is significantly higher than that of the conventional K-OMS-2, indicating that the composite material also has good electron conductivity and oxidation capacity in the electrocatalytic system, further verifying the comprehensive advantages of the composite modification.

[0061] From the experimental results of the three reaction modes, it can be seen that in the Fenton-like reaction, the composite catalyst significantly improves the activation ability of the catalyst for oxidants and the efficiency of free radical generation through the synergistic effect of cobalt doping, carbon nanotubes and titanium dioxide, as well as the carbon coating protection of the structure. In the photocatalytic and electrocatalytic systems, the catalyst of Example 2 also exhibits significantly better degradation performance than the comparative examples, with degradation rates of 91% and 89%, respectively, confirming that the catalyst has excellent catalytic activity and stability in multiple reaction modes, and has strong practical application potential and functional expandability.

Claims

1. A cobalt-doped manganese-oxygen octahedral molecular sieve catalyst, suitable for oxidative degradation of organic pollutants, comprising: a manganese-oxygen octahedral molecular sieve with a crystal structure of K-OMS-2; cobalt elements doped into the crystal lattice of the manganese-oxygen octahedral molecular sieve; carbon nanotubes forming an electrically conductive network with the manganese-oxygen octahedral molecular sieve; nano-titanium dioxide dispersed in the composite structure in the form of nanoparticles or nanosheets; and a carbon coating layer covering the manganese-oxygen octahedral molecular sieve. The content of the carbon nanotubes is 1-10 wt%, the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a length of 1-10 μm and a diameter of 5-20 nm, and are used to build an electron transport channel and improve the mechanical strength and dispersibility of the material. The content of the nano-titanium dioxide is 1-10 wt%, and the nano-titanium dioxide is in the form of anatase, rutile or a mixed crystal of both. The molecular sieve catalyst exerts a catalytic effect based on at least one of the following mechanisms:

1. under ultraviolet / visible light irradiation, the catalyst reacts with hydrogen peroxide or persulfate to generate hydroxyl radicals or sulfate radicals; and 2. under an applied direct current electric field, the catalyst activates an oxidizing agent to generate radicals. 7.A method for preparing the cobalt-doped manganese-oxygen octahedral molecular sieve catalyst according to any one of claims 1-6, comprising the following steps: S1. hydrothermal synthesis of K-OMS-2 nanorods: a potassium source, KMnO 4 and MnSO 4 are subjected to a hydrothermal reaction under acidic conditions to obtain one-dimensional K-OMS-2 nanorods; S2. cobalt doping: the K-OMS-2 nanorods are dispersed in deionized water, an appropriate amount of a cobalt salt solution is added, and stirring is performed for 6-12 h; centrifugation, washing and drying are performed to remove free cobalt ions, and Co-doped K-OMS-2 is obtained; S3. carbon nanotube compounding: carbon nanotubes are dispersed in deionized water by ultrasonic dispersion to form a suspension A; the Co-doped K-OMS-2 is dispersed in deionized water by ultrasonic dispersion to form a suspension B; the suspension A and the suspension B are mixed uniformly under ultrasonic magnetic stirring to obtain a Co-OMS / CNTs composite slurry; S4. introduction of titanium dioxide: a titanium dioxide nano material is mixed uniformly with the Co-OMS / CNTs composite slurry by a sol-gel method, a hydrothermal method or a direct mixing method to obtain a Co-OMS / CNTs / TiO 2 composite slurry; S5. carbon coating and heat treatment: an appropriate amount of a carbon source is added to the Co-OMS / CNTs / TiO 2 composite slurry, drying treatment is performed, and carbonization treatment is then performed at 600-800 degrees Celsius under an inert atmosphere to form a carbon-coated material; and S6. post-treatment: washing with deionized water or ethanol, followed by drying and grinding into a fine powder to obtain the molecular sieve catalyst. The carbon source is selected from one or more of glucose, sucrose, cellulose or polyacrylonitrile, and is used to form a carbon coating layer during heat treatment to improve the electrical conductivity and structural stability of the material. ​ ​ ​ 2. The cobalt-doped manganese oxygen octahedral molecular sieve catalyst according to claim 1, characterized in that, The manganese-oxygen octahedral molecular sieve has a length of 50-500 nm, a diameter of 10-30 nm, and a specific surface area of 50-150 m 2 / g.

3. The cobalt-doped manganese oxygen octahedral molecular sieve catalyst according to claim 1, characterized in that, The cobalt element is present in the form of Co 2+ or Co 3+ in the manganese-oxygen octahedral structure or at surface defect sites thereof, with a doping amount of 0.5-5 wt% of the total mass of the molecular sieve catalyst.

4. The cobalt-doped manganese oxygen octahedral molecular sieve catalyst according to claim 1, characterized in that, ​ 5. The cobalt-doped manganese oxygen octahedral molecular sieve catalyst according to claim 1, characterized in that, ​ 6. The cobalt-doped manganese-oxygen-octahedral molecular sieve catalyst of claim 1, wherein: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 8. The method of claim 7, wherein, ​ 9. Use of a molecular sieve catalyst as claimed in any one of claims 1 to 6 in the treatment of organic pollutants, characterised in that, The application includes: 1) combined with hydrogen peroxide or persulfate in Fenton-like reaction system; 2) photocatalytic degradation under ultraviolet or visible light irradiation; 3) catalytic reaction is promoted by applying electric field in electrocatalytic device.

10. The use according to claim 9, characterized in that, The organic pollutants include dyes, antibiotics, pesticides, pharmaceutical intermediates, phenolic compounds and plasticizers.

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