Preparation method of high-crystal-face manganese-based catalyst for activating peroxymonosulfate through non-free radical way

Abstract

The invention discloses a preparation method of a high-crystal-face manganese-based catalyst for activating peroxymonosulfate through a non-free radical way, and belongs to the field of catalyst preparation. Comprising the following steps: 1) dissolving potassium permanganate in deionized water to obtain a potassium permanganate solution, dissolving ammonium oxalate in deionized water to obtain an ammonium oxalate solution, and mixing the potassium permanganate solution and the ammonium oxalate solution to form a mixed solution; adjusting the pH value of the mixed solution by using an alkaline regulator; the preparation method comprises 1) preparing a mixed solution, 2) transferring the mixed solution into a reaction kettle and carrying out a hydrothermal reaction, 3) naturally cooling the mixed solution to a room temperature after the reaction is finished, collecting a brown product and carrying out alternate centrifugal washing with ultrapure water and absolute ethyl alcohol until a filtrate is neutral, and 4) drying and grinding the washed product to obtain the manganese-based catalyst.

Description

Technical Field

[0001] This invention belongs to the field of environmental functional material preparation and water treatment technology, specifically involving a method for synthesizing manganese-based nanomaterials with high (310) crystal plane exposure and their application in the degradation of organic pollutants in water by activated persulfate (PMS). Background Technology

[0002] Advanced oxidation technologies based on persulfate (PMS) are widely used in the treatment of recalcitrant organic wastewater due to their strong oxidizing power and fast reaction rate. Traditional activation pathways mainly generate sulfate radicals (SO₄•⁻) and hydroxyl radicals (•OH). Although these radicals have high oxidation potentials, they have poor selectivity and are easily interfered with and quenched by background substances in the water (such as natural organic matter, Cl⁻, HCO₃⁻, and other anions), resulting in low oxidant utilization and unstable actual treatment effects.

[0003] In contrast, non-radical pathways (such as generating singlet oxygen 1O2 or direct oxidation via electron transfer complexes) exhibit higher selectivity and resistance to interference, making them more suitable for complex real-world aquatic environments. Manganese-based oxides (MnOx) are a class of environmentally friendly and low-cost PMS activators. Studies have shown that the catalytic activity of manganese oxides is closely related to their crystal structure and exposed crystal faces. However, manganese oxides synthesized by conventional hydrothermal methods often expose thermodynamically stable low-activity crystal faces (such as the (110) crystal face), resulting in insufficient surface active sites and making it difficult to efficiently activate PMS via non-radical pathways. Therefore, developing a manganese-based catalyst with a simple preparation process, the ability to directionally control the exposure of high-energy (310) crystal faces, and a dominant non-radical mechanism is of great significance for improving its practical application potential. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing a high (310) crystal facet manganese-based catalyst for persulfate activation via a non-radical pathway. This method, through specific precursor ratios and an alkaline hydrothermal environment, successfully induces the growth of manganese oxides along a specific direction, achieving directional exposure of the highly active (310) crystal facet, thereby significantly enhancing the catalyst's ability to activate PMS via a non-radical pathway.

[0005] This invention provides a manganese-based catalyst, which is prepared by hydrothermal synthesis, specifically comprising the following steps: 1) Preparation of precursor solution: Dissolve 3.161g of potassium permanganate in 40mL of deionized water, and dissolve 1.241g of ammonium oxalate in 20mL of deionized water. Mix the two solutions to form a mixed solution, and stir magnetically to ensure uniform mixing. Adjust the pH of the mixed solution using an alkaline adjuster, such as potassium hydroxide (KOH) or sodium hydroxide (NaOH) solution.

[0006] 2) Hydrothermal reaction: The above mixed solution was transferred to a 100mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, sealed, and placed in an oven at 160℃ for hydrothermal reaction for 20 hours.

[0007] 3) Product post-processing: After the reaction is completed, allow the reaction vessel to cool naturally to room temperature, collect the brown sample, and wash it several times by alternating centrifugation with ultrapure water and anhydrous ethanol until the filtrate is neutral.

[0008] 4) Drying and calcination: The washed brown precipitate was placed in a 90°C oven and dried overnight. After grinding, a manganese-based catalyst with high (310) crystal face exposure was obtained.

[0009] This invention also provides an application of the aforementioned manganese-based catalyst, namely, a method for degrading recalcitrant organic pollutants in water. The method includes: adding the manganese-based catalyst to wastewater containing organic matter, and simultaneously adding a certain dose of PMS. The manganese-based catalyst, by activating the PMS, can achieve the effect of removing pollutants from the water. The recommended addition amount of the manganese-based catalyst is 0.1 g / L.

[0010] Technical Principle: The manganese-based catalyst (MnO2) with high (310) crystal plane exposure prepared in this invention can serve as a highly efficient heterogeneous catalyst in activating the PMS catalytic oxidation system. The basic principle is that the MnO2 surface has abundant active sites, and the (310) crystal plane is a high-energy crystal plane, typically rich in oxygen vacancies and coordinated unsaturated manganese atoms, which is beneficial for the adsorption and activation of PMS molecules.

[0011] Compared with the prior art, the present invention has the following technical advantages: Precise crystal plane control and abundant active sites: The manganese-based catalyst prepared in this invention is an α-MnO2 nanorod structure, which clearly exposes the (310) crystal plane with a spacing of 0.31 nm. This crystal plane is a high-energy crystal plane, which is usually rich in oxygen vacancies and coordinated unsaturated manganese atoms, which is beneficial to the adsorption and activation of PMS molecules; Non-radical mechanism, strong anti-interference ability: Combined with EPR test results, no obvious free radical (•OH or SO•-4) signal was detected during the activation of PMS by this catalyst, indicating that it follows a non-radical pathway (singlet oxygen or direct electron transfer). This makes the catalytic system highly resistant to interference from inorganic anions and natural organic matter in water, and suitable for the selective oxidation treatment of complex wastewater; The preparation process is simple and reproducible: It adopts a one-step hydrothermal method, the raw materials are cheap and readily available, and the morphology and crystal facets can be controlled by simple redox reactions and pH adjustment, which is easy to prepare on a large scale. Low cost and environmentally friendly: The chemicals used are all common chemical raw materials, resulting in low cost. The catalyst is mainly composed of stable manganese oxides, which are not easily dissolved in water, posing no risk of secondary pollution. Wide range of applications: This catalyst not only has a high efficiency in degrading bisphenol A, but its mechanism of activating PMS to degrade pollutants through a non-radical pathway determines that it can be widely used to treat various types of wastewater containing recalcitrant organic matter, such as pharmaceutical wastewater, dyeing and printing wastewater, and chemical wastewater. Attached Figure Description

[0012] Figure 1 The X-ray diffraction (XRD) pattern of the manganese-based catalyst prepared in the embodiments of the present invention is shown below. Figure 2 These are transmission electron microscope (TEM) and high-resolution transmission electron microscope (HRTEM) images of the manganese-based catalyst prepared in the embodiments of the present invention. Figure 3 The N2 adsorption-desorption isotherm of the manganese-based catalyst prepared in the embodiments of the present invention; Figure 4 The image shows the electron paramagnetic resonance (EPR) spectrum of the PMS system activated by the manganese-based catalyst prepared in the embodiments of the present invention. Figure 5 This is a trend graph showing the effect of the manganese-based catalyst prepared in this embodiment of the invention on the degradation of the model pollutant bisphenol A by PMS. Detailed Implementation

[0013] The present invention will now be described in detail with reference to the accompanying drawings.

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0015] Example 1 1. Catalyst Preparation (1) Weigh 3.161g (20mM) potassium permanganate (KMnO4) and dissolve it in 40mL of deionized water. Stir magnetically until completely dissolved.

[0016] (2) Weigh 1.241g (10mM) ammonium oxalate ((NH4)2C2O4) and dissolve it in 20mL of deionized water. Stir magnetically until completely dissolved.

[0017] (3) Slowly pour the ammonium oxalate solution into the potassium permanganate solution, mix well, and use an alkaline regulator (such as KOH solution) to adjust the pH of the mixed solution to alkaline.

[0018] (4) Transfer the above mixed solution to a 100 mL stainless steel hydrothermal reactor lined with polytetrafluoroethylene and seal it.

[0019] (5) Place the reactor in an oven and keep it at 160°C for 20 hours.

[0020] (6) After the reaction is complete, allow the reactor to cool naturally to room temperature. Remove the product and wash it several times by alternating centrifugation with ultrapure water and anhydrous ethanol until the filtrate is neutral. Collect the brown precipitate, dry it overnight in a 90°C oven, and grind it to obtain black MnO2 catalyst powder.

[0021] 2. Catalytic performance test The reaction was carried out in a 50 mL amber glass bottle. 5 µM / L bisphenol A, 0.1 g / L MnO2 catalyst, and 20 µM / L PMS were added to the system, and the mixture was magnetically stirred to ensure uniform suspension. The reaction was conducted at room temperature (approximately 25 °C) and at natural pH.

[0022] Samples were taken at 0, 6, 12, 18, 24, and 30 minutes after the reaction. 1 mL of the sample was quickly mixed with 0.1 mL of Na2S2O3 solution and then filtered through a 0.22 μM organic filter before analysis.

[0023] Meanwhile, a control experiment was set up without adding MnO2 catalyst, with all other conditions being exactly the same.

Claims

1. A method for preparing a high-crystalline manganese-based catalyst for persulfate activated via a non-radical pathway, characterized in that, Includes the following steps: 1) Dissolve potassium permanganate in deionized water to obtain a potassium permanganate solution, dissolve ammonium oxalate in deionized water to obtain an ammonium oxalate solution, and mix the two to form a mixed solution; adjust the pH value of the mixed solution using an alkaline adjuster; 2) Transfer the mixed solution to a reaction vessel for hydrothermal reaction; 3) After the reaction is complete, allow the mixture to cool naturally to room temperature, collect the brown product, and wash it alternately by centrifugation with ultrapure water and anhydrous ethanol until the filtrate is neutral; 4) The washed product is dried and ground to obtain a manganese-based catalyst.

2. The method for preparing a high-crystalline manganese-based catalyst for persulfate activated via a non-radical pathway according to claim 1, characterized in that, The high-energy crystal plane is a (310) crystal plane, and the resulting MnO2 is a manganese-based catalyst with a high (310) crystal plane exposure.

3. The method for preparing a high-crystalline manganese-based catalyst for persulfate activated via a non-radical pathway according to claim 2, characterized in that, The amount of potassium permanganate used is 3.161g, dissolved in 40mL of deionized water; the amount of ammonium oxalate used is 1.241g, dissolved in 20mL of deionized water.

4. The method for preparing a high-crystalline manganese-based catalyst for persulfate activated via a non-radical pathway according to claim 3, characterized in that, The alkalinity regulator is a potassium hydroxide solution or a sodium hydroxide solution.

5. The method for preparing a high-crystalline manganese-based catalyst for persulfate activated via a non-radical pathway according to any one of claims 1 to 4, characterized in that, The hydrothermal reaction was carried out at a temperature of 160°C for 20 hours.

6. A manganese-based catalyst, characterized in that, The manganese-based catalyst is prepared by the method of preparing a high-crystal-facet manganese-based catalyst for activating persulfate via a non-radical pathway as described in any one of claims 1 to 5. The manganese-based catalyst is MnO2 with exposed high-energy crystal faces and is capable of activating persulfate PMS via a non-radical pathway.

7. A method for degrading recalcitrant organic pollutants in water, characterized in that, include: The manganese-based catalyst of claim 6 is added to the wastewater, and persulfate PMS is added simultaneously, so that PMS is activated by the manganese-based catalyst via a non-radical pathway, thereby achieving the catalytic oxidation degradation of the organic pollutants.

8. The method for degrading recalcitrant organic pollutants in water according to claim 7, characterized in that, The dosage of the manganese-based catalyst is 0.1 g / L.

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