Preparation method and application of oxygen vacancy-rich manganese dioxide

Abstract

This invention discloses a method for preparing oxygen-vacancy-rich manganese dioxide and its application. The method for preparing oxygen-vacancy-rich manganese dioxide includes the following steps: (1) dissolving divalent manganese salt, divalent ferric salt, and KMnO4 in deionized water and stirring to obtain a precursor solution; (2) transferring the precursor solution to a reaction vessel for hydrothermal reaction; after the reaction, solid and liquid are separated, the obtained solid is dried, ground, and finally calcined to obtain the oxygen-vacancy-rich manganese dioxide. Compared to other iron-doped manganese dioxide or iron-manganese oxides, by adding reducing ferrous sulfate under a high-concentration potassium permanganate hydrothermal atmosphere, the interference of ferric hydroxide precipitate formation when adding ferric sulfate is avoided, making the iron doping more uniform. Simultaneously, the modified manganese dioxide has an increased specific surface area, richer pores, and increased surface oxygen vacancy content, thus enhancing its ability to activate persulfate to degrade phenolic pollutants and exhibiting good cycle stability.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a method for preparing manganese dioxide rich in oxygen vacancies and its application. Background Technology

[0002] Phenol and its derivatives are among the most widely used organic compounds. Phenolic compounds with simple structures can serve as intermediates in chemical products. However, phenolic substances are easily inhaled through the respiratory tract and absorbed through the skin, leading to liver and kidney damage as well as central nervous system disruption. Long-term exposure to phenolic substances may cause respiratory abnormalities, tremors, coma, and even death.

[0003] Advanced oxidation processes (AOPs) in chemical methods treat recalcitrant organic pollutants by generating reactive oxygen species, offering advantages such as environmental friendliness and minimal secondary pollution. Traditional AOPs are based on the Fenton reaction, which involves the generation of reactive oxygen species (ROS) through the production of Fe... 2+ Hydroxyl radicals (·OH) are generated by the reaction with H2O2 to non-selectively degrade pollutants. However, this technology has problems such as the safety of hydrogen peroxide transportation, pH limitations (3-4), and the generation of iron sludge requiring secondary treatment. Compared with H2O2 advanced oxidation technology, persulfate and its related advanced oxidation technologies have the following advantages: (1) Persulfates include permonosulfate (PMS) and perdisulfate (PDS), which can be transported in a stable solid form, overcoming the transportation problems of hydrogen peroxide; (2) Persulfates have a wider pH range (2-9), overcoming the pH limitations of hydrogen peroxide; (3) The activation energy of persulfates is in the form of non-radicals, which can selectively degrade certain target pollutants during the reaction process, reducing the overuse of oxidants. Therefore, persulfates have been favored by researchers as a feasible alternative to H2O2.

[0004] Persulfate activation can be divided into energy activation and electron transfer activation. Compared with energy-based activation methods (such as ultrasound, ultraviolet light and heat), the transition metal activation method in electron transfer activation is relatively simple and inexpensive in terms of reactor / system configuration. Transition metal activation of PMS and PDS can be achieved in homogeneous and heterogeneous systems. Heterogeneous systems are superior to homogeneous systems for the following reasons: (1) Solid heterogeneous catalysts can be easily separated from the treated water and reused without secondary treatment of metal ions; (2) Heterogeneous systems are more tolerant to extreme operating conditions. For example, heterogeneous systems are effective in a wider pH range, including the acidic and alkaline environments (pH = 2-9) commonly found in natural water and wastewater, while transition metal ions dissolved in homogeneous systems will precipitate at neutral and alkaline pH, thereby reducing their performance; (3) Heterogeneous systems can activate persulfate via a non-radical pathway, which can overcome the disadvantage that free radicals are easily quenched by natural organic matter (NOM) in natural water bodies.

[0005] Manganese dioxide (MDC) is a promising persulfate activation catalyst due to its high abundance in nature, low biotoxicity, low cost, easy availability, and strong catalytic activity. Unlike other activation methods (thermal activation, UV activation, ultrasonic activation, and transition metal ion activation) that generate free radicals to non-selectively oxidize pollutants, the MDC-persulfate oxidation water treatment technology can activate persulfate through a non-radical pathway. The catalytic performance of MDC depends on the exposure of manganese atoms, and the presence of oxygen vacancies provides catalytically active sites on the MDC surface. Therefore, the key to the catalytic activity of MDC lies in the construction of these oxygen vacancies.

[0006] Existing methods for constructing oxygen vacancies in manganese dioxide include H2 heat treatment, electrochemical etching, reduction with elemental metals, and reduction with sodium borohydride. These methods involve significant energy and reducing agent consumption, resulting in high costs. Another method for constructing oxygen vacancies involves doping with low-valence metal ions as precursors (such as Fe). 3+ Oxygen vacancies can be constructed through doping, but this method has low oxygen vacancy construction efficiency. To address these issues, this invention uses a ferrous iron source as a precursor for doping to increase the oxygen vacancy content on the manganese dioxide surface, thereby achieving efficient persulfate-activated degradation of phenolic pollutants. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for preparing manganese dioxide rich in oxygen vacancies. This method utilizes reducing ferrous iron as a dopant, which undergoes a redox reaction with strongly oxidizing potassium permanganate during a hydrothermal process. 2+ Completely converted to Fe 3+ The average valence state of manganese decreases, Mn 3+ The proportion increased, and the adsorbed oxygen O ads Increased exposure ratio leads to a larger specific surface area of ​​the layered structure, thereby constructing a δ-phase layered manganese dioxide rich in oxygen vacancies, which is used for persulfate activation to degrade phenolic pollutants via a non-radical pathway.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of this invention provides a method for preparing manganese dioxide rich in oxygen vacancies, comprising the following steps:

[0010] (1) Dissolve divalent manganese salt, divalent iron salt and KMnO4 in deionized water and stir to obtain a precursor solution;

[0011] (2) The precursor liquid is transferred to a reaction vessel for hydrothermal reaction; after the reaction, the solid and liquid are separated, the obtained solid is dried and ground, and finally calcined to obtain the oxygen-vacancy-rich manganese dioxide.

[0012] In this invention, all raw materials used are of superior purity.

[0013] Preferably, in step (1), the Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is 0%-20%, and it does not contain any endpoints.

[0014] More preferably, the Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is 4-6%.

[0015] Preferably, in step (1), the divalent manganese salt and divalent iron salt are dissolved in deionized water and stirred for 5-15 min; then KMnO4 is added and stirred for 0.5-1.5 min to obtain a precursor solution; more preferably, in step (1), the divalent manganese salt and divalent iron salt are dissolved in deionized water and stirred for 10 min; then KMnO4 is added and stirred for 1 min to obtain a precursor solution.

[0016] Preferably, in step (1), the concentration of KMnO4 in the precursor solution is 85-95 mM.

[0017] Preferably, the divalent manganese salt is at least one of manganese sulfate and its hydrate.

[0018] Preferably, the ferrous salt is at least one of ferrous sulfate and its hydrate.

[0019] Preferably, in step (2), the temperature of the hydrothermal reaction is 150-250℃ and the time is 10-14h; more preferably, in step (2), the temperature of the hydrothermal reaction is 180-220℃ and the time is 11-13h.

[0020] Preferably, in step (2), the solid-liquid separation method is to use a negative pressure filtration device with a 0.22μm aqueous microfiltration membrane, where manganese dioxide solid is retained on the membrane, and the solution containing unreacted metal ions and sulfate anions is separated by passing through the membrane.

[0021] Preferably, in step (2), the grinding method is to grind the dried manganese dioxide solid using an agate mortar and pestle, and then pass it through a 200-mesh sieve.

[0022] Preferably, in step (2), the calcination heating rate is 4-6℃ / min, the calcination temperature is 250-350℃, and the calcination time is 2-4h; more preferably, in step (2), the calcination heating rate is 4-6℃ / min, the calcination temperature is 280-320℃, and the calcination time is 2.5-3.5h.

[0023] A second aspect of the present invention provides a manganese dioxide rich in oxygen vacancies, which is prepared by the aforementioned method for preparing manganese dioxide rich in oxygen vacancies.

[0024] Preferably, the specific surface area of ​​the oxygen-vacancy-rich manganese dioxide is 140-250 m². 2 / g.

[0025] A third aspect of the present invention provides the application of the aforementioned oxygen-vacancy-rich manganese dioxide in the activated persulfate degradation of organic pollutants.

[0026] Preferably, the organic pollutant is a phenolic pollutant.

[0027] The fourth aspect of the present invention provides a method for degrading organic pollutants, comprising the following steps: adding a catalyst to an organic pollutant water body for adsorption, and then adding persulfate to initiate catalytic degradation; wherein the catalyst is manganese dioxide containing oxygen vacancies.

[0028] Preferably, the concentration of organic pollutants in the water body is 5 mg / L-40 mg / L.

[0029] Preferably, the dosage of the catalyst is 2.5-5 g / L.

[0030] Preferably, the dosage of persulfate is 0.5-2 mmol / L.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] Compared to hydrogen reduction technology, the preparation method of this invention avoids the safety risks caused by hydrogen; compared to sodium borohydride reduction technology, it reduces the use of explosives; compared to ferric doping technology, it has a higher efficiency in constructing oxygen vacancies and the finished product has better catalytic performance.

[0033] Compared to other iron-doped manganese dioxide or iron-manganese oxides, the addition of reducing ferrous sulfate in a high-concentration potassium permanganate hydrothermal atmosphere avoids the interference of ferric hydroxide precipitation when adding ferric sulfate, resulting in more uniform iron doping. At the same time, the modified manganese dioxide has an increased specific surface area, richer pores, and increased surface oxygen vacancy content, which enhances its ability to activate persulfate to degrade phenolic pollutants and demonstrates good cycle stability. Attached Figure Description

[0034] Figure 1 This is a scanning electron microscope image of δ-MnO2;

[0035] Figure 2 X-ray diffraction pattern of δ-MnO2;

[0036] Figure 3 A comparison chart of degradation effects of different systems;

[0037] Figure 4 A comparative graph showing the effects of different catalysts on the degradation of phenol by persulfate;

[0038] Figure 5 A comparison of PMS consumption rates with and without phenol in the presence of 5% Fe-MnO2 activated PMS;

[0039] Figure 6 The effect of five cycles of the catalyst 5% Fe-MnO2 is shown in the figure. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0042] Example 1

[0043] This embodiment provides a method for preparing manganese dioxide rich in oxygen vacancies. It utilizes ferrous sulfate, which has reducing properties, as a dopant, and reacts it with potassium permanganate, which has strong oxidizing properties, in a hydrothermal process via a redox reaction. During this process, Fe... 2+ Completely converted to Fe 3+ The average valence state of manganese decreases, Mn 3+ The proportion increased, and the adsorbed oxygen O ads Increased exposure ratio leads to the formation of iron-doped δ-phase manganese dioxide rich in oxygen vacancies. Material preparation method:

[0044] (1) Dissolve 120 mg MnSO4·H2O and 80.25 mg FeSO4·7H2O in 56 mL of deionized water and stir at 450 r / min for 10 min to make the solution homogeneous. Add 800 mg KMnO4 to the above mixed solution and stir for 1 min.

[0045] (2) After stirring, the precursor solution was transferred to an 80 mL Teflon-lined autoclave and stored at 200 °C for 12 h.

[0046] (3) After the reactor is cooled to room temperature, it is washed several times with deionized water, and solid-liquid separation is performed by vacuum filtration. The resulting solid is dried overnight at 60°C.

[0047] (4) After the dried material is ground to 200 mesh, it is calcined in an air atmosphere in a muffle furnace at 300℃ for 3 hours to obtain the finished product 5% Fe-MnO2.

[0048] Oxygen vacancies are the active sites of this material, which can activate persulfate to degrade phenolic pollutants via a non-radical pathway, reducing the use of oxidants and showing great application potential.

[0049] Comparative Example 1

[0050] This comparative example provides a method for preparing the catalyst δ-MnO2, specifically including the following steps:

[0051] (1) Dissolve 120 mg MnSO4·H2O in 56 mL of deionized water and stir at 450 r / min for 10 min to make the solution uniform; add 800 mg KMnO4 to the above mixed solution and stir for 1 min.

[0052] (2) After stirring, the precursor solution was transferred to an 80 mL Teflon-lined autoclave and stored at 200 °C for 12 h.

[0053] (3) After the reactor is cooled to room temperature, it is washed several times with deionized water, and solid-liquid separation is performed by vacuum filtration. The resulting solid is dried overnight at 60°C.

[0054] (4) After the dried material is ground to 200 mesh, it is calcined in an air atmosphere in a muffle furnace at 300℃ for 3 hours to obtain the finished product δ-MnO2.

[0055] Scanning electron microscope image of catalyst δ-MnO2 as shown below Figure 1 As shown, the material exhibits a nanoflower structure and possesses abundant active sites.

[0056] The X-ray diffraction pattern of the catalyst δ-MnO2 is as follows Figure 2 As shown, the diffraction peaks of this material match those of PDF#86-0666 (δ-MnO2).

[0057] Comparative Example 2

[0058] This comparative example provides a method for preparing the catalyst 20% Fe-MnO2. The Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is controlled to be 20%, and other conditions are the same as in Example 1. The catalyst 20% Fe-MnO2 is thus prepared.

[0059] Comparative Example 3

[0060] This comparative example provides a method for preparing the catalyst 5% Fe(III)-MnO2. The divalent iron salt is replaced with trivalent iron salt, the Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is controlled to be 5%, and other conditions are the same as in Example 1, so that the catalyst 5% Fe-MnO2 is prepared.

[0061] The X-ray photoelectron spectroscopy results for different catalysts are shown in Tables 1-3 below. The divalent iron precursor is entirely composed of Fe.2+ Converted to Fe 3+ The average manganese valence state (MnAOS) ranges from 3.394 to 3.525. At the same doping ratio (5%), 5% Fe-MnO2 prepared using divalent iron as a precursor has a lower MnAOS and a higher Mn content than 5% Fe(III)-MnO2 prepared using trivalent iron as a precursor. 3+ Content and higher adsorption oxygen O ads content.

[0062] The results of nitrogen adsorption-desorption experiments with different catalysts are shown in Table 4. 5% Fe 2+ The introduction of MnO2 increased the specific surface area from 68.75 m² / g. 2 / g increased to 210.05m 2 / g, but too much Fe 2+ (20%) The introduction of an oxidizing environment that disrupts the formation of layered manganese dioxide reduces the specific surface area to 142.80 m². 2 / g,

[0063] Table 1. X-ray photoelectron spectroscopy (XPS) results for Fe 2p under different catalysts.

[0064] <![CDATA[Fe 2+ ]]> 0 0 0 0 <![CDATA[Fe 3+ ]]> 0 100 100 100

[0065] Table 2. X-ray photoelectron spectroscopy (XPS) results of Mn 2p atoms for different catalysts.

[0066]

[0067]

[0068] Table 3. X-ray photoelectron spectroscopy (O1s) test results for different catalysts.

[0069] <![CDATA[O -OH ]]> 2.25 4.28 3.25 2.35 <![CDATA[O ads ]]> 10.35 18.98 21.53 15.90 <![CDATA[O latt ]]> 87.40 76.74 75.22 81.75

[0070] Table 4. Test results of nitrogen adsorption-desorption tests for different catalysts.

[0071] <![CDATA[BET result (m 2 / g)]]> 68.75 210.05 142.80 93.32 Average pore diameter (nm) 18.26 13.92 11.55 16.11

[0072] Experimental Example

[0073] To evaluate the catalytic performance of manganese dioxide rich in oxygen vacancies, the following experiment was conducted:

[0074] (1) Weigh 0-10 mg of catalyst into a 50 mL beaker and add 50 mL of phenol aqueous solution with a concentration of 10 mg / L.

[0075] (2) Perform the adsorption reaction for 30 minutes.

[0076] (3) Add 0-0.5 mL of 100 mM PMS to start the catalytic degradation experiment. The sampling time is set to 0 min, 15 min, 30 min, 45 min, 60 min, and 90 min.

[0077] (4) The sampling method is as follows: use a pipette to take 1 mL of sample and mix it with 100 μL of 20 mM sodium thiosulfate solution to stop the reaction. After filtering with a 0.22 μm filter membrane, use a high performance liquid chromatography (HPLC) with a C18 column for testing.

[0078] Figure 3 To compare the degradation effects of different systems, Figure 4 The effects of different catalysts on the degradation of phenol by persulfate were compared. The effects of different catalyst systems or dosages on the degradation of different pollutants by PMS are shown in Table 5-11.

[0079] The test conditions in Table 5 are as follows: catalyst concentration 200 mg / L; in the experiment with added PMS, the PMS concentration was 1 mM and the phenol concentration was 10 mg / L. The test conditions in Table 6 are as follows: catalyst concentration 200 mg / L; PMS concentration 1 mM; phenol concentration 10 mg / L. The test conditions in Table 7 are as follows: 5% Fe-MnO2 catalyst; PMS concentration 1 mM; phenol concentration 10 mg / L. The test conditions in Table 8 are as follows: phenol concentration 10 mg / L. The test conditions in Table 9 are as follows: PMS concentration 1 mM. The test conditions in Tables 10 and 11 are as follows: catalyst concentration 200 mg / L; PMS concentration 1 mM; phenol concentration 10 mg / L.

[0080] Table 5. Degradation effect of different catalyst systems on phenol after 90 min

[0081] Phenol removal rate (%) 27.65 1.52 49.51 13.80 100

[0082] Table 6. Effects of different catalysts on PMS degradation of phenol after 90 min.

[0083]

[0084]

[0085] As shown in Table 6, after 90 min, 5% Fe-MnO2 had the highest removal rate of phenol (100%). The removal rates of phenol in the other control groups were blank group (27.65%), δ-MnO2 (49.51%), 20% Fe-MnO2 (87.54%) and 5% Fe(III)-MnO2 (70.21%).

[0086] Examine the oxidant consumption rate, such as Figure 5As shown, without the addition of contaminant (phenol), the oxidant was hardly consumed within 90 min, while after the addition of contaminant, the consumption of PMS reached 50% within 90 min, proving that 5% Fe-MnO2 activates PMS via a non-radical pathway.

[0087] The effects of different catalyst dosages, PMS dosages, and initial phenol concentrations on phenol removal rates were investigated. As shown in Table 7, the phenol removal rate gradually increased (27.65%–100%) with increasing catalyst dosage (0 g / L–10 g / L); as shown in Table 8, the phenol removal rate gradually increased (13.80%–100%) with increasing PMS dosage (0–4 mM); and as shown in Table 9, the phenol removal rate gradually decreased (100%–78.86%) with increasing initial phenol concentration (5 mg / L–40 mg / L).

[0088] Table 7. Effects of different catalyst dosages on the degradation of phenol by PMS after 90 min.

[0089]

[0090] Table 8. Effects of catalyst (5% Fe-MnO2) on the degradation of phenol by PMS at different concentrations after 90 min.

[0091]

[0092] Table 9. Effects of catalyst (5% Fe-MnO2) on the degradation of phenol by PMS at different concentrations after 90 min.

[0093]

[0094] The removal efficiency of 5% Fe-MnO2 activated PMS for different phenolic pollutants was investigated. As shown in Table 10, the removal efficiencies of this system for different pollutants were as follows: o-chlorophenol (100%), m-chlorophenol (65.17%), p-chlorophenol (100%), p-bromophenol (100%), p-fluorophenol (99.38%), 2,4,6-trichlorophenol (63.61%), o-cresol (100%), m-cresol (100%), and p-cresol (100%).

[0095] Table 10. Effect of catalyst (5% Fe-MnO2) on the degradation of different phenolic pollutants in PMS after 90 min.

[0096]

[0097] To assess the stability of the system, a cyclic experiment was conducted. After five cycles, the system maintained a phenol removal rate of over 95%, demonstrating its stability. Figure 6 As shown in Table 11.

[0098] Table 11. Effect of catalyst (5% Fe-MnO2) on the degradation of phenol by PMS after five cycles over 90 min.

[0099] Removal rate (%) 100 100 100 100 95.62

[0100] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing manganese dioxide rich in oxygen vacancies, characterized in that, Includes the following steps: (1) Dissolve divalent manganese salt, divalent iron salt and KMnO4 in deionized water and stir to obtain a precursor solution; the Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is 0%-20%, and there is no end 0%; the concentration of KMnO4 in the precursor solution is 85-95 mM. (2) The precursor liquid is transferred to a reactor for hydrothermal reaction at a temperature of 150-250 °C for 10-14 h. After the reaction, the solid and liquid are separated, the obtained solid is dried and ground, and finally calcined at a temperature of 250-350 °C for 2-4 h to obtain oxygen-vacancy-rich manganese dioxide. The oxygen-vacancy-rich manganese dioxide is iron-doped δ-phase manganese dioxide rich in oxygen vacancies.

2. The method for preparing oxygen-vacancy-rich manganese dioxide according to claim 1, characterized in that, The Fe / Mn molar ratio of total manganese salt and iron salt in the precursor solution is 4-6%.

3. The method for preparing oxygen-vacancy-rich manganese dioxide according to claim 1, characterized in that, In step (1), the divalent manganese salt and divalent iron salt are dissolved in deionized water and stirred for 5-15 min; then KMnO4 is added and stirred for 0.5-1.5 min to obtain the precursor solution.

4. The method for preparing oxygen-vacancy-rich manganese dioxide according to claim 1, characterized in that, In step (2), the heating rate of calcination is 4-6 ℃ / min.

5. A manganese dioxide rich in oxygen vacancies, characterized in that, It is prepared by the method for preparing oxygen-vacancy-rich manganese dioxide according to any one of claims 1-4.

6. The application of oxygen-vacancy-rich manganese dioxide as described in claim 5 in the activated persulfate degradation of organic pollutants, characterized in that, The organic pollutant is a phenolic pollutant.

7. A method for degrading organic pollutants, characterized in that, The process includes the following steps: adding a catalyst to the water body containing organic pollutants for adsorption, followed by the addition of persulfate to initiate catalytic degradation; the organic pollutants are phenolic pollutants. The catalyst is manganese dioxide rich in oxygen vacancies as described in claim 5.

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