A defect-rich ε-MnO2 microsphere catalyst, its preparation method and application

Abstract

The application relates to a kind of defect-rich epsilon-MnO2 microspheres catalyst and its preparation method and application, the appearance of the catalyst is round ball with rich scale-shaped protrusions on the surface, the average specific surface area is 79m 2 ·g ‑1 , particle size is 6-9um, the oxygen vacancy content of surface is 12%~14%, the average valence of surface Mn is +3.1~+3.3, the defect-rich epsilon-MnO2 microspheres catalyst for degrading organic pollutants in organic wastewater is prepared quickly and efficiently by using unique reaction raw materials and adjuvants and fine process precise control, the surface of the catalyst is rich in oxygen defects, the main active oxygen group produced after the catalyst participates in the reaction is superoxide free radical, the superoxide free radical can degrade more types of organic matter through various reaction paths, and thus the effective degradation of organic matter in wastewater is realized.

Description

Technical Field

[0001] This invention relates to the field of manganese catalyst preparation technology for wastewater treatment, specifically a defect-rich ε-MnO2 microsphere catalyst, its preparation method, and its application. Background Technology

[0002] With the development of the dye and printing and dyeing industry in modern society, wastewater discharge is constantly increasing. In the printing and dyeing industry, processing one ton of textiles requires 100 to 200 tons of water, of which 80% to 90% becomes wastewater. That is, processing one ton of finished product generates 80 to 180 tons of wastewater. The treatment of printing and dyeing wastewater is quite challenging, mainly because its composition is extremely complex and contains a high concentration of organic matter. Even more problematic is that most of these organic substances are difficult to effectively degrade through biochemical means, greatly increasing the difficulty of wastewater treatment.

[0003] Rhodamine B (RhB), a widely used dye in the printing and dyeing industry, is one of the main pollutants in printing and dyeing wastewater. Its molecular formula is: Rhodamine B is a dibenzo-p-phenylene six-membered oxygen heterocyclic dye, widely used in the manufacture of colored glass and special fireworks. However, Rhodamine B has poor biodegradability; if discharged into water bodies in large quantities without treatment, it will cause the death of aquatic plants and damage the aerobic environment, while also harming human health due to its carcinogenic, teratogenic, and mutagenic effects. The International Agency for Research on Cancer (IARC), a branch of the World Health Organization (WHO), classified RhB as a Group 3 carcinogen on October 27, 2017. Therefore, the treatment of recalcitrant organic matter in wastewater is of great importance.

[0004] Currently, advanced oxidation processes in wastewater treatment technologies show broad application prospects due to their high degradation efficiency and relatively low difficulty in treating degradation byproducts. Catalysts play a crucial role in this technology; therefore, obtaining high-performance catalysts is essential. Among the many available catalysts, manganese-based catalysts have attracted considerable attention due to their low cost and easy availability. They also possess characteristics such as high efficiency, high activity, and good stability, enabling catalytic reactions at relatively low temperatures, and exhibiting long catalyst lifetimes. They demonstrate excellent selectivity and reactivity in many reactions, particularly showing superior performance in selective oxidation reactions, and thus hold great research potential.

[0005] Therefore, in the face of the increasingly serious problem of organic wastewater treatment, providing an effective catalyst to efficiently, conveniently and cost-effectively degrade organic wastewater is of great significance for promoting sustainable industrial development and environmental protection, and is also an important issue that urgently needs to be addressed in the current environmental protection field. Summary of the Invention

[0006] The technical objective of this invention is to rapidly and efficiently prepare a defect-rich ε-MnO2 microsphere catalyst that can be used to degrade organic pollutants in organic wastewater by using unique reaction raw materials and additives, as well as precise process control. The surface of this catalyst is rich in oxygen defects, and the main active oxygen group generated after its participation in the reaction is superoxide radical. This superoxide radical can degrade more types of organic matter through multiple reaction pathways, thereby achieving effective degradation of organic matter in wastewater.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a defect-rich ε-MnO2 microsphere catalyst, which has a spherical appearance with abundant scaly protrusions on its surface and an average specific surface area of ​​79 m². 2 ·g -1 The particle size is 6-9 μm, the oxygen hole content on the surface is 12%~14%, and the average valence state of Mn on the surface is +3.1~+3.3.

[0008] Furthermore, the catalyst can synergistically catalyze potassium persulfate through the Mn active sites and oxygen vacancy sites on its surface to generate superoxide radicals as active oxygen groups.

[0009] A method for preparing a defect-rich ε-MnO2 microsphere catalyst includes the following steps: Step 1: Take manganese acetate, trisodium citrate, and urea in a molar ratio of 1:(0.005~2):(3~6), add them to a mixed solvent of water and n-butanol, mix thoroughly, and then place the resulting reaction system in a hydrothermal reactor at 100~160°C. o The reaction was carried out at temperature C for 8-16 hours to obtain the reaction product, which was then set aside for later use. Step 2: Centrifuge the reaction product obtained in Step 1, and wash the resulting solid repeatedly with deionized water and ethanol in sequence. Then, transfer it to a container at 60-150°C. o The product precursor was dried under C conditions for 6-12 hours and then used for later use. Step 3: Place the product precursor obtained in Step 2 into a heating furnace at 400°C. o The product is calcined at C for 3-12 hours to obtain the finished powdered defect-rich ε-MnO2 microsphere catalyst.

[0010] Furthermore, in step one, the concentration of manganese acetate added to the mixed solvent is (5~20) g / L.

[0011] Furthermore, in step one, the volume ratio of water to n-butanol in the mixed solvent is 1:(0.5~2).

[0012] Furthermore, in step three, the heating rate of the calcination treatment is 5~15. o C / min.

[0013] Application of a defect-rich ε-MnO2 microsphere catalyst in the treatment of organic pollutant wastewater.

[0014] Application of a defect-rich ε-MnO2 microsphere catalyst in the treatment of Rhodamine B-containing wastewater.

[0015] A method for applying a defect-rich ε-MnO2 microsphere catalyst includes the following steps: Step (1): Disperse the defect-rich ε-MnO2 microsphere catalyst evenly into the wastewater containing Rhodamine B at an addition amount of 5~100 mg / L, and perform adsorption treatment for 30~120 min. Step (2): Add potassium persulfate, an oxidant, to the wastewater at a dosage of 500-2000 mg / L for 30-120 min to carry out the degradation reaction. Step (3): Filter to remove catalyst.

[0016] Furthermore, in step (1), the content of Rhodamine B in the wastewater is 5~50 mg / L.

[0017] The beneficial effects of this invention are: 1. The average specific surface area of ​​the defect-rich ε-MnO2 microsphere catalyst prepared by the process of the present invention is 79 m². 2 ·g -1 The particles have a diameter of 6-9 μm, good dispersibility, small particle size, large specific surface area, and are rich in oxygen vacancies. Unlike most catalysts that catalyze the generation of sulfate and hydroxyl radicals in PMS, the defect-rich ε-MnO2 microsphere catalyst of this invention has Mn active sites and oxygen vacancies on its surface that can synergistically catalyze the generation of superoxide radicals in PMS. These superoxide radicals have both oxidizing and reducing properties and can degrade more types of organic matter through multiple reaction pathways, thereby endowing the catalyst with excellent Fenton-like catalytic performance.

[0018] 2. The preparation process of this invention uses a solvothermal method with n-butanol aqueous solution to prepare defect-rich ε-MnO2 microsphere catalysts. Compared with existing technologies such as droplet interface drying method, deep eutectic solvent method, self-sacrificing template method, electrodeposition method, one-step redox method, and strong base high-temperature hydrothermal method, this method is simpler and easier to operate, avoiding the use of high-heat processes and complex equipment. Therefore, the equipment cost and raw material cost are relatively low, the process is controllable, and it is suitable for industrial mass production.

[0019] 3. The preparation process of this invention employs unique and precise process control, using n-butanol for regulation, to prepare defect-rich ε-MnO2 microsphere catalysts with uniform particle size through simple steps. During the preparation process, controlling the volume ratio of water to n-butanol to 1:2~2:1 effectively controls the formation of the unique morphology of the ε-MnO2 microspheres. The addition of n-butanol effectively regulates the polarity and surface tension of the solvent, thereby affecting the nucleation and growth process of the catalyst, preparing the microspherical precursor MnCO3. Subsequently, through specific calcination temperature control, the finished defect-rich ε-MnO2 microsphere catalyst acquires a unique spherical morphology with abundant scaly protrusions on its surface.

[0020] 4. The defect-rich ε-MnO2 microsphere catalyst prepared by this invention has excellent degradation performance on organic matter in organic wastewater. When 100 mL of 10 g / L Rhodamine B solution is used as the degradation target, the catalyst of this invention can achieve a degradation rate of more than 96%. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the catalyst ε-MnO2 prepared in Example 2; Figure 2 This is the X-ray powder diffraction pattern of the catalyst ε-MnO2 prepared in Example 2; Figure 3 This is a scanning electron microscope image of the catalyst Mn2O3 prepared in Comparative Example 1; Figure 4 The X-ray powder diffraction pattern of the catalyst Mn2O3 prepared in Comparative Example 1 is shown. Figure 5 This is a performance comparison chart of the product prepared in Example 2 and the product prepared in Comparative Example 1; Figure 6 This is a capture experiment diagram of the active oxygen groups generated by the product prepared in Example 2 catalyzing PMS. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1: At room temperature, weigh 0.7843 g manganese acetate, 0.015 g trisodium citrate, and 0.9610 g urea, add them to 20 mL of water and 40 mL of n-butanol solution, and place the mixture in a hydrothermal reactor at 100 °C. o The reaction was carried out at C for 16 hours. The resulting solid was centrifuged and washed successively with deionized water and ethanol. o Dry at C for 6 hours, then at 5 o The heating rate is 400 °C / min. oThe catalyst obtained by calcining at C for 12 hours was calculated to be ε-MnO2-1.

[0024] Example 2: At room temperature, weigh 0.7843 g manganese acetate, 0.015 g trisodium citrate, and 0.9610 g urea, add them to 30 mL of water and 30 mL of n-butanol solution, and place the mixture in a hydrothermal reactor at 120°C. o The reaction was carried out at C for 12 hours. The resulting solid was centrifuged and washed successively with deionized water and ethanol. o Dry at C for 10 hours, then at 10 o The heating rate of C / min is 400 o Calcined at C for 4 hours. The resulting catalyst was calculated to be ε-MnO2-2.

[0025] Example 3: At room temperature, weigh 0.7843 g manganese acetate, 0.015 g trisodium citrate, and 1.4423 g urea, add them to 40 mL of water and 20 mL of n-butanol solution, and place the mixture in a hydrothermal reactor at 140°C. o The reaction was carried out at C for 8 hours. The resulting solid was centrifuged and washed successively with deionized water and ethanol. o Dry at C for 12 hours, then at 15 o The heating rate is 400 °C / min. o Calcined at C for 3 hours. The resulting catalyst was calculated to be ε-MnO2-3.

[0026] Comparative Example 1: At room temperature, weigh 0.7843 g manganese acetate, 0.015 g trisodium citrate, and 0.9610 g urea, add them to 30 mL of water and 30 mL of n-butanol solution, and place the mixture in a hydrothermal reactor at 120°C. o The reaction was carried out at C for 12 hours. The resulting solid was centrifuged and washed successively with deionized water and ethanol. o Dry at C for 10 hours, then at 10 o The heating rate of C / min is 800 o The catalyst was calcined at C for 4 hours, and the resulting catalyst had a phase composition of Mn2O3.

[0027] Test measurement 1. Product appearance and performance The finished catalysts obtained in Embodiment 2 and Comparative Example 1 of this invention were characterized by spectral analysis, and the results are shown in the appendix. Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown.

[0028] In the SEM image, ε-MnO2 is spherical in shape with many scale-like protrusions on its surface. This rough structure helps to increase the specific surface area of ​​the material.

[0029] As shown in the XRD pattern above, the diffraction peaks of ε-MnO2-2 at 37.12°, 42.401°, 56.027°, and 66.761° correspond to the (100), (101), (102), and (110) crystal planes of JCPDS#30-0820 ε-MnO2, respectively. The low intensity of these diffraction peaks indicates poor crystallinity and abundant defect structures in the compound.

[0030] The diffraction peaks of Mn2O3 prepared in Comparative Example 1 at 23.131°, 32.951°, 38.234°, 45.178°, 49.347°, 55.189°, and 65.806° correspond to the (211), (222), (400), (332), (431), (440), and (622) crystal planes of JCPDS#41-1442 Mn2O3, respectively. The relatively sharp diffraction peaks indicate good crystallinity.

[0031] Table 1 below shows the XPS oxygen hole concentration analysis of the product ε-MnO2-2 prepared in Example 2 and the product Mn2O3 prepared in Comparative Example 1. Table 1 catalyst Average valence state of Mn Percentage of surface oxygen holes <![CDATA[ε-MnO2]]> 3.2 13.21% <![CDATA[Mn2O3]]> 2.8 9.97% As shown in Table 1, the ε-MnO2 catalyst prepared in this application has a high average valence state of manganese on its surface and has abundant oxygen vacancies.

[0032] 2. Catalytic degradation performance The degradation rate of organic matter was tested using a 100 mL, 10 ppm Rhodamine B (RhB) solution as the degradation target. The reaction conditions were as follows: the initial pH of the solution was approximately 6.4, the amount of catalyst was 10 mg, the initial reaction temperature was room temperature (approximately 24 °C), and the adsorption was carried out at 600 rpm for 1 h to reach adsorption-desorption equilibrium. Then, 750 ppm potassium persulfate (PMS) was added and the reaction was continued for 60 min.

[0033] As attached Figure 5 and Figure 6 As shown, ε-MnO2 exhibits an adsorption removal rate of approximately 9.4% for RhB and a total removal rate of approximately 70.7%, while Mn2O3 shows an adsorption removal rate of approximately 10.2% and a total removal rate of approximately 39.3%, demonstrating that the performance of microsphere-shaped ε-MnO2 is superior to that of Mn2O3. When the PMS dosage is increased to 1500 ppm, the total removal rate of RhB by ε-MnO2 increases to 96% under the same conditions.

[0034] To verify the main reactive oxygen groups of RhB catalyzed by ε-MnO2 in the degradation of RhB by PMS, a capture experiment was conducted. In the capture experiment, 100 mM and 500 mM ethanol, 100 mM and 500 mM tert-butanol, 5 mM p-benzoquinone, and 10 mM furanol were added as capture agents for hydroxyl radicals, sulfate radicals, peroxide radicals, and singlet oxygen. Without a catalyst, RhB showed almost no degradation with only PMS added. With only a catalyst and no PMS added, the catalyst achieved only approximately 11% stable adsorption and removal rate of RhB within 1 hour. After adding the scavenging agents, the catalytic removal rates of RhB under the action of 100mM ethanol, 500mM ethanol, 100mM tert-butanol, 500mM tert-butanol, 5mM p-benzoquinone, and 10mM furanol were 52.87%, 55.46%, 57.48%, 56.06%, 8.38%, and 49.41%, respectively; their total removal rates were 63.05%, 69.42%, 68.88%, 62.70%, 18.26%, and 61.11%, respectively. Compared with the control group without scavenging agents (approximately 70.65%), it can be seen that after capturing hydroxyl radicals, sulfate radicals, and singlet oxygen reactive groups, the removal rate of RhB did not change significantly. The maximum difference between the RhB removal rate of the control group and the control group was within approximately 8%. Therefore, ethanol, tert-butanol, and furanol did not have a significant inhibitory effect on the degradation of RhB, and their concentrations in the reaction can be ignored. The addition of p-benzoquinone had the greatest inhibitory effect on RhB degradation, only about 7% higher than the adsorption removal rate. In the presence of p-benzoquinone, the degradation rate of RhB was significantly reduced. Therefore, it is determined that the active group for the oxidative degradation of RhB should be the peroxide radical (•O2-).

[0035] As shown in the SEM images, both ε-MnO2 and Mn2O3 are microspheres, but the specific surface area of ​​ε-MnO2 is 79 m². 2 ·g -1 Much higher than the 4m of Mn2O3 2 ·g -1 A higher specific surface area facilitates the exposure of active sites and their interaction with the substrate, thus promoting the reaction. Furthermore, XPS analysis revealed that the surface oxygen hole concentration of ε-MnO2 was as high as 13%, while that of Mn2O3 was only around 9%. Therefore, the higher surface oxygen hole concentration suggests that ε-MnO2 can synergistically catalyze the formation of •O2- from PMS to degrade RhB.

[0036] The foregoing has shown and described the main features, usage methods, basic principles, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention based on actual circumstances without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A defect-rich ε-MnO2 microsphere catalyst, characterized in that: The catalyst has a spherical appearance with abundant scaly protrusions on its surface, and an average specific surface area of ​​79 m². 2 ·g -1 The particle size is 6-9 μm, the oxygen hole content on the surface is 12%~14%, and the average valence state of Mn on the surface is +3.1~+3.

3.

2. The method for preparing a defect-rich ε-MnO2 microsphere catalyst according to claim 1, characterized in that, Includes the following steps: Step 1: Take manganese acetate, trisodium citrate, and urea in a molar ratio of 1:(0.005~2):(3~6), add them to a mixed solvent of water and n-butanol, mix thoroughly, and then place the resulting reaction system in a hydrothermal reactor at 100~160°C. o The reaction was carried out at temperature C for 8-16 hours to obtain the reaction product, which was then set aside for later use. Step 2: Centrifuge the reaction product obtained in Step 1, and wash the resulting solid repeatedly with deionized water and ethanol in sequence. Then, transfer it to a container at 60-150°C. o The product precursor was dried under C conditions for 6-12 hours and then used for later use. Step 3: Place the product precursor obtained in Step 2 into a heating furnace at 400°C. o The product is calcined at C for 3-12 hours to obtain the finished powdered defect-rich ε-MnO2 microsphere catalyst.

3. The method for preparing a defect-rich ε-MnO2 microsphere catalyst according to claim 2, characterized in that: In step one, the concentration of manganese acetate added to the mixed solvent is (5~20) g / L.

4. The method for preparing a defect-rich ε-MnO2 microsphere catalyst according to claim 2, characterized in that: In step one, the volume ratio of water to n-butanol in the mixed solvent is 1:(0.5~2).

5. The method for preparing a defect-rich ε-MnO2 microsphere catalyst according to claim 2, characterized in that: In step three, the heating rate of the calcination treatment is 5~15. o C / min.

6. The application of the defect-rich ε-MnO2 microsphere catalyst according to claim 1 in the treatment of organic pollutant wastewater.

7. The application of the defect-rich ε-MnO2 microsphere catalyst according to claim 6 in the treatment of organic pollutant wastewater, characterized in that, The organic pollutant is Rhodamine B.

8. The application of the defect-rich ε-MnO2 microsphere catalyst according to claim 7 in the treatment of organic pollutant wastewater, characterized in that, Includes the following steps: Step (1): Disperse the defect-rich ε-MnO2 microsphere catalyst evenly into the wastewater containing Rhodamine B at an addition amount of 5~100 mg / L, and perform adsorption treatment for 30~120 min. Step (2): Add potassium persulfate, an oxidant, to the wastewater at a dosage of 500-2000 mg / L for 30-120 min to carry out the degradation reaction. Step (3): Filter to remove catalyst.

9. The application of the defect-rich ε-MnO2 microsphere catalyst according to claim 8 in the treatment of organic pollutant wastewater, characterized in that: In step (1), the content of Rhodamine B in the wastewater is 5~50 mg / L.

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