Method for preparing double-phase MnO2 through one-step method and application

Abstract

The invention discloses a method for preparing biphase MnO2 by a one-step method and application, the preparation method comprises the following steps: dispersing a manganese source, an oxidizing agent and inert salt in water, and uniformly mixing to obtain a mixed solution; and carrying out hydrothermal reaction on the mixed solution at 30-170 DEG C for 12-24 hours to obtain the biphase MnO2. The prepared diphase manganese dioxide shows high activity in degradation of non-volatile organic pollutants and denitration of flue gas, when the diphase manganese dioxide is used together with peroxymonosulfate (PMS), the degradation efficiency of phenol and other organic pollutants in a water body can be remarkably improved, and the degradation rate can reach 85%. The preparation method is simple, low in cost, mild in reaction condition, high in product yield, high in purity and suitable for industrial production. The dual-phase manganese dioxide shows excellent catalytic performance in an acidic environment to a neutral environment, has high-efficiency degradation capability on organic pollutants in salt-containing wastewater, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts containing metals or metal oxides, and particularly relates to a one-step method for preparing dual-phase MnO2 and its application. Background Art

[0002] Manganese dioxide (MnO2), as an important transition metal oxide, has a rich crystal structure and diverse physical and chemical properties. It is widely used in electrochemistry, catalysis, environmental governance and other fields. Among them, dual-phase MnO2 exhibits better performance than single-phase MnO2. Single-phase MnO2 has certain limitations in practical applications. For example, in the field of catalysis, its active sites are relatively single, and the catalytic efficiency for certain reactions is limited; in the field of battery materials, there are problems such as low capacity and poor cycle stability. However, due to the synergistic effect of two different crystal phases, dual-phase MnO2 can provide more active sites and enhance electron transfer capabilities, thereby significantly improving its performance in catalytic reactions and battery charging and discharging processes.

[0003] In terms of the preparation method of dual-phase MnO2, although the traditional multi-step synthesis method can produce dual-phase MnO2, it has problems such as complex process, high cost, and long production cycle. The multi-step reaction requires precise control of the reaction conditions of each step, the operation is cumbersome, and impurities are easily introduced, affecting the purity of the product. In contrast, the one-step method for synthesizing dual-phase MnO2 has obvious advantages. It simplifies the preparation process, reduces production costs, improves production efficiency, and also reduces the risk of impurity introduction, which is more conducive to industrial large-scale production. However, the current one-step method for synthesizing dual-phase MnO2 still faces many challenges, such as the difficulty in accurately controlling the reaction conditions, and the difficulty in stably regulating the crystal phase ratio and structure of the product. Therefore, it is of great practical significance to develop a simple, efficient, low-cost method for preparing dual-phase MnO2 that can accurately control the structure and performance of the product.

[0004] Phenol is a common organic pollutant widely found in industrial wastewater, posing a serious threat to the environment and human health. Traditional methods for treating phenol wastewater include adsorption, solvent extraction, chemical oxidation, and biological treatment, but these methods suffer from high costs, complex processes, and secondary pollution. In recent years, studies have found that MnO2 and its composite materials have a good treatment effect on phenol wastewater. However, current preparation methods have problems such as harsh conditions and high costs. Therefore, developing an efficient, green, and low-cost method for preparing manganese dioxide and applying it to the treatment of phenol wastewater is of great practical significance.

[0005] In the field of flue gas denitrification, commercial vanadium-based (V2O5-WO3 / TiO2) catalysts are widely used, but they have the following bottlenecks: ① The active temperature window is narrow (300-400℃), which makes it difficult to adapt to the medium and low temperature flue gases (150-250℃) in the steel, glass and other industries; ② The vanadium element is biotoxic, and the cost of waste catalyst treatment is high; ③ The sulfur and water resistance are poor, and SO2 and H2O can easily cause the catalyst to be poisoned and deactivated. Although non-vanadium-based catalysts (such as Fe3O4 and CeO2) are environmentally friendly, they have insufficient low-temperature activity (NOx conversion rate <60%). Dual-phase MnO2 has multiple valence states (Mn 3+ / Mn 4+ ) coexistence, which can optimize the NH3-SCR reaction pathway and achieve efficient NOx reduction at low temperatures. Therefore, the development of a dual-phase MnO2 catalyst with both high low-temperature activity and strong resistance to poisoning is the key to breaking through the bottleneck of existing SCR technology. Summary of the Invention

[0006] In order to overcome the problem in the prior art that it is impossible to efficiently and directionally prepare dual-phase manganese dioxide in one step, the purpose of the present invention is to provide a one-step method for preparing dual-phase MnO2 and its application. The method synthesizes dual-phase MnO2 through a one-step hydrothermal reaction and can be applied to the catalytic degradation of organic pollutants in water bodies.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions:

[0008] A one-step method for preparing dual-phase MnO2 comprises the following steps:

[0009] Dispersing a manganese source, an oxidant, and an inert salt in water, and mixing them uniformly to obtain a mixed solution;

[0010] The mixed solution is subjected to a hydrothermal reaction at 30-170° C. for 12-24 hours to obtain biphasic MnO 2 .

[0011] Furthermore, the manganese source is MnSO4·H2O.

[0012] Furthermore, the oxidant is (NH4)2S2O8.

[0013] Furthermore, the inert salt is (NH4)2SO4.

[0014] Furthermore, the ratio of the amount of the oxidizing agent, the inert salt substance and the manganese source is 8-14 mmol: 20-25 mmol: 8-14 mmol.

[0015] A dual-phase MnO2.

[0016] The invention discloses an application of a two-phase MnO2 in the degradation of organic pollutants in water.

[0017] Furthermore, the dual-phase MnO2 is added to the phenol-containing water, stirred and ultrasonically dispersed to make it uniformly dispersed, and then PMS is added to the water and a degradation reaction is carried out under stirring; wherein, the concentration of phenol in the phenol-containing water is 5-30 mg / L, and the mass ratio of PMS:MnO2 is 2:1.

[0018] Application of a two-phase MnO2 in flue gas denitrification.

[0019] Furthermore, the dual-phase MnO2 is set in a fixed bed reactor, and the flue gas containing nitrogen oxides flows through the fixed bed reactor and reacts at 200-600°C, wherein the concentration of nitrogen oxides in the flue gas containing nitrogen oxides is 300-500 ppm, the oxygen content is 5-15%, the water vapor content is 7-15%, and the rest is nitrogen, and the flow rate of the flue gas containing nitrogen oxides is 0.2-1.0 L / min.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The one-step method used in the present invention to prepare dual-phase MnO2 can be completed through a simple hydrothermal reaction, is easy to operate, and does not require special reaction equipment. Compared with traditional multi-step synthesis methods, this method greatly simplifies the preparation process, reduces production costs, reduces the risk of impurity introduction, and is more easily implemented in industrial large-scale production. At the same time, the one-step method can more accurately control the crystal structure and ratio of the product, ensuring the stability of product quality and performance.

[0022] Furthermore, the molar ratio of the oxidant, inert salt, and manganese source in the present invention is 8-14 mmol: 20-25 mmol: 8-14 mmol. This ratio of raw materials controls crystal formation, and ammonium sulfate, as an electrolyte, regulates ionic strength and stabilizes the system. High concentrations of ammonium sulfate inhibit byproduct reactions through the common ion effect, while also affecting the nucleation rate and promoting the formation of a dual-phase structure. Controlling the hydrothermal temperature thermodynamically controls crystal phase stability and prevents the formation of single-phase crystals.

[0023] When the dual-phase MnO2 prepared by this invention is used in conjunction with peroxymonosulfate (PMS), the dual-phase manganese dioxide promotes charge separation through a heterojunction, optimizes Mn valence state cycling, exposes multiple types of active sites, and forms a highly efficient spark system with PMS. Combined with adsorption and a synergistic free radical / non-free radical mechanism, the catalytic degradation activity for phenol in water is significantly enhanced. Under specific reaction conditions, the phenol contaminant can be removed from wastewater efficiently, cleanly, and at low cost, providing an economical and efficient solution for wastewater treatment.

[0024] In terms of flue gas denitrification, dual-phase MnO2 exhibits high activity and stability due to the electronic interaction between different crystal forms, the easy formation of oxygen vacancies at the phase boundaries, multivalent Mn, and anti-toxicity mechanism. Its denitrification efficiency is higher than that of traditional catalysts, providing a more efficient and economical option for flue gas denitrification, which helps reduce environmental pollution in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The following describes preferred embodiments of the present invention in conjunction with the accompanying drawings. It should be understood that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] Figure 1 The XRD pattern of the product prepared in Example 2 is used to analyze the crystal structure of the product and confirm the formation of a dual-phase structure;

[0027] Figure 2 The phenol degradation curves of the catalyst products prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were measured using the liquid phase at different times, visually demonstrating the change in the phenol degradation ability of the catalyst over time;

[0028] Figure 3 The phenol degradation diagrams of the catalyst products prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at different times were measured using TOC (total organic carbon), reflecting the degree of phenol degradation from the perspective of changes in total organic carbon;

[0029] Figure 4 The prepared catalyst product reflects the degree of flue gas denitrification from the perspective of NO conversion rate at different temperatures. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in a variety of different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present invention.

[0031] The present invention discloses a one-step method for preparing dual-phase MnO2, which comprises dissolving a manganese source, an oxidant, and an inert salt in different proportions to obtain a solution, and then performing a hydrothermal reaction to obtain dual-phase manganese dioxide with different compositions. The method specifically comprises the following steps:

[0032] 1) Dispersing a manganese source, an oxidant, and an inert salt in deionized water and mixing them uniformly to obtain a mixed solution; the molar ratio of the oxidant, the inert salt, and the manganese source is 8-14 mmol: 20-25 mmol: 8-14 mmol.

[0033] The manganese source is MnSO4·H2O, the oxidant is (NH4)2S2O8, and the inert salt is (NH4)2SO4. The ammonium sulfate in the present invention guides the α-γ dual-phase structure through ionic strength regulation and magic plate effect, which cannot be achieved by other sulfates.

[0034] 2) The mixed solution obtained in step 1) is placed in a polytetrafluoroethylene-lined reactor, subjected to a hydrothermal reaction at 30-170° C. for 12-24 hours, and then cooled to room temperature. The mixture is washed with deionized water and alcohol, and dried to obtain dual-phase manganese dioxide with different compositions.

[0035] The dual-phase manganese dioxide obtained in step (2) is α-γ dual-phase manganese dioxide.

[0036] A method for catalytically degrading organic pollutants (phenol) in water using MnO2 prepared according to the method described above. The method comprises the following steps: adding the MnO2 to phenol-containing water, stirring and ultrasonically dispersing the MnO2 to uniformly disperse the phenol; then adding varying amounts of PMS to the water and carrying out a degradation reaction under stirring. The phenol concentration in the phenol-containing water is 5 to 30 mg / L. The PMS:MnO2 mass ratio is 2:1, and the stirring conditions are: a stirring rate of 200 to 500 r / min, a stirring time of 0 to 120 min, and a stirring temperature of 25.0°C.

[0037] An application of MnO2 prepared according to the above method in flue gas denitrification, wherein the flue gas mainly contains nitrogen oxides. The specific method of use is:

[0038] The loaded MnO2 was placed in a flue gas denitrification simulation test. The simulated flue gas was passed through a fixed-bed reactor containing the catalyst at a constant flow rate. The reaction temperature was controlled, and the reactor outlet gas was sampled at regular intervals. The nitrogen oxide concentration was measured using a flue gas analyzer, and the removal rate was calculated. The results showed that after a certain number of minutes of reaction, the dual-phase MnO2 catalyst achieved a nitrogen oxide removal rate that was significantly higher than that of traditional catalysts. As the reaction progressed, the removal rate of the dual-phase MnO2 catalyst reached a stable value, while the removal rate of the traditional catalyst decreased slightly.

[0039] The flue gas containing nitrogen oxides has a nitrogen oxide concentration of 300-500 ppm, an oxygen content of 5-15%, a water vapor content of 7-15%, and the remainder is nitrogen simulated flue gas.

[0040] The flow rate of the simulated flue gas is 0.2-1.0 L / min, the reaction temperature is controlled to 200-600°C, and the gas collection time at the reactor outlet is 5-20 min.

[0041] By optimizing and regulating the reaction conditions, the present invention successfully prepares biphasic MnO2. The biphasic MnO2 acts synergistically with peroxymonosulfate to significantly enhance the catalytic degradation activity of organic pollutants such as phenol in water, and is suitable for use in flue gas to improve the flue gas denitrification rate.

[0042] In the present invention, an inert salt is introduced as a crystal form modifier to induce the formation of a dual-phase structure during the hydrothermal process. The mechanism of action of ammonium sulfate is:

[0043] Ionic strength control: SO4 2- With Mn 2+ Forming complexes and slowing down the crystal growth rate;

[0044] pH buffering: NH4 + Hydrolysis produces H + , maintain the pH of the reaction system at 4.5-5.5 to promote the coexistence of two phases.

[0045] Example 1

[0046] 8mmol (NH4)2S2O8, 20mmol (NH4)2SO4, and 8mmol MnSO4·H2O were dissolved in 40ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was poured into the lining of a reactor, and the reactor was placed in an oven for a hydrothermal reaction. The hydrothermal reaction temperature was 90°C and the reaction time was 12 hours. After the resulting reaction solution cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and then dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0047] Example 2

[0048] 8mmol (NH4)2S2O8, 20mmol (NH4)2SO4, and 8mmol MnSO4·H2O were dissolved in 40ml of deionized water and stirred for 8 minutes to obtain a mixed solution. The mixed solution was poured into the lining of the reactor, and the reactor was placed in an oven for hydrothermal reaction. The hydrothermal reaction temperature was 110°C and the hydrothermal reaction time was 12 hours. After the resulting reaction solution was cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at a speed of 11000r / min for 10 minutes, and then washed twice with alcohol at a speed of 11000r / min for 10 minutes. It was then dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0049] By XRD analysis (see Figure 1 ), the obtained diffraction peaks were compared with the MnO2 PDF#72-1982 and MnO2 PDF#82-2169 cards in the Jade standard card, and it was found that the diffraction peaks of the MnO2 prepared in this example were produced by multiple crystalline manganese dioxides, confirming the existence of a dual-phase structure.

[0050] Example 3

[0051] 10 mmol (NH4)2S2O8, 25 mmol (NH4)2SO4, and 14 mmol MnSO4·H2O were dissolved in 40 ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was then poured into the lining of a reactor, which was then placed in an oven for a hydrothermal reaction. The reaction temperature was 30°C and the reaction time was 24 hours. After the resulting reaction solution cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and finally dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0052] Example 4

[0053] 14 mmol (NH4)2S2O8, 22 mmol (NH4)2SO4, and 11 mmol MnSO4·H2O were dissolved in 40 ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was then poured into the lining of a reactor, which was then placed in an oven for a hydrothermal reaction. The reaction temperature was 170°C for 12 hours. After cooling to room temperature, the resulting reaction solution was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and finally dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0054] Example 5

[0055] 12 mmol (NH4)2S2O8, 20 mmol (NH4)2SO4, and 8 mmol MnSO4·H2O were dissolved in 40 ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was then poured into the lining of a reactor, which was then placed in an oven for a hydrothermal reaction. The reaction temperature was 50°C and the reaction time was 24 hours. After the resulting reaction solution cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and finally dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0056] Comparative Example 1

[0057] A one-step method for preparing single-phase MnO2 is as follows:

[0058] 8 mmol (NH4)2S2O8 and 8 mmol MnSO4·H2O were dissolved in 40 ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was then poured into the lining of a reactor, which was then placed in an oven for a hydrothermal reaction. The reaction temperature was 90°C and the reaction time was 12 hours. After the resulting reaction solution cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and finally dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0059] Comparative Example 2

[0060] A one-step method for preparing single-phase MnO2 is as follows:

[0061] 8 mmol (NH4)2S2O8 and 8 mmol MnSO4·H2O were dissolved in 40 ml of deionized water and stirred for 8 minutes to obtain a uniform mixed solution. The mixed solution was then poured into the lining of a reactor, which was then placed in an oven for a hydrothermal reaction. The reaction temperature was 110°C and the reaction time was 12 hours. After the resulting reaction solution cooled to room temperature, it was centrifuged in a high-speed centrifuge. The solid precipitate was washed twice with deionized water at 11,000 r / min for 10 minutes, then twice with alcohol at 11,000 r / min for 10 minutes, and finally dried at 80°C to obtain a dual-phase MnO2 catalyst.

[0062] The degradation performance of the dual-phase MnO2 catalyst prepared in the test example was tested, and the specific steps were as follows:

[0063] 1) dispersing phenol in water to obtain a phenol solution with a concentration of 20 mg / L;

[0064] 2) 10 mg of the biphasic MnO2 catalyst prepared in Example 1 and Example 2 were added to 100 mL of the phenol solution prepared in step 1), 10 mg of manganese dioxide was added, and the mixture was ultrasonicated for 3 min. The mixture was then placed in a stirred water bath for 30 minutes, and then 20 mg of PMS was added. The concentration of PMS in the solution at different reaction times was tested to evaluate the degradation performance of the biphasic MnO2 catalysts synthesized at different temperatures on phenol in water. The phenol degradation curves of the two MO2 catalysts under stirring were as shown in FIG. Figure 2 and Figure 3 As shown, they are marked as 1-MnO2 and 2-MnO2 respectively. The 1-MnO2 curve in the figure represents the phenol degradation curve measured by adding the dual-phase MnO2 catalyst prepared in Example 1 synthesized at 90°C to the above system, and the 2-MnO2 curve represents the phenol degradation curve measured by adding the dual-phase MnO2 catalyst prepared in Example 2 synthesized at 110°C to the above system. Figure 2 and Figure 3 Comparison shows that the degradation ability of the two-phase MnO2 synthesized at different temperatures to phenol is different, among which the two-phase MnO2 synthesized at 110°C has the strongest degradation ability, and the two-phase MnO2 synthesized at 90°C has the second strongest degradation ability. Under the conditions of a stirring rate of 500r / min and a temperature of 25.0°C in a stirred water bath, after stirring for 60 minutes, the degradation rate of the two-phase MnO2 synthesized at 110°C can reach 85%, achieving efficient degradation of phenol in wastewater. The purpose of adding ammonium sulfate in the present invention is to regulate the ionic strength of the solution and promote the slow growth of γ; SO4 2- Embedded in the MnO2 lattice gap, preferentially stabilizes the γ-MnO2(110) crystal plane, and forms a heterogeneous interface with α-MnO2 (tunnel); pH buffer, NH4 +The release of regulates the pH of the reaction solution, inhibits the formation of δ-MnO2, and promotes the coexistence of α-γ phases.

[0065] The denitration efficiency of the dual-phase MnO2 catalyst prepared in the test example was tested, and the specific steps were as follows:

[0066] Preparation of activated carbon catalyst loaded with dual-phase MnO2 (duplex MnO2 loading of 15%)

[0067] In a simulated flue gas generating device, simulated flue gas with an initial nitrogen oxide concentration of 500 ppm, an oxygen content of 5%, a water vapor content of 10%, and the remainder being nitrogen was prepared.

[0068] See also Figure 4 Simulated flue gas was introduced into a fixed-bed reactor containing the catalyst at a flow rate of 0.5 L / min, and the reaction temperature was controlled at 250°C. The reactor outlet gas was collected every 10 minutes, and the nitrogen oxide concentration was detected using a flue gas analyzer to calculate the removal rate. The results showed that after 30 minutes of reaction, the dual-phase MnO2 catalyst prepared in Example 2 achieved a nitrogen oxide removal rate of 95%, while the conventional catalyst had a removal rate of 63%. As the reaction temperature reached 150°C, the removal rate of the dual-phase MnO2 catalyst stabilized at over 90%, while the removal rate of the conventional catalyst dropped slightly to around 60%.

[0069] The present invention uses a manganese source, an oxidant, and an inert salt as raw materials to prepare a dual-phase manganese dioxide through a hydrothermal reaction. The obtained dual-phase manganese dioxide shows high activity in degrading difficult-to-volatile organic pollutants and flue gas denitrification. When used together with peroxymonosulfate (PMS), it can significantly improve the degradation efficiency of organic pollutants such as phenol in water bodies, and its degradation rate can reach 100%. The preparation method of the present invention is simple, low in cost, mild in reaction conditions, and has a large product yield and high purity, making it suitable for industrial production. The dual-phase manganese dioxide shows excellent catalytic performance in acidic to neutral environments, and has a high efficiency in degrading organic pollutants in saline wastewater, and has broad application prospects.

[0070] The above description is merely a description of the preferred embodiment of the present invention and is not to be construed as limiting the claims. The present invention is not limited to the above embodiment, and variations in the specific structure are permitted. Any variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A one-step method for preparing dual-phase MnO2, characterized in that: The following steps are involved: Dispersing a manganese source, an oxidant, and an inert salt in water, and mixing them uniformly to obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction at 30-170° C. for 12-24 hours to obtain biphasic MnO 2 .

2. The method for preparing dual-phase MnO2 in one step according to claim 1, characterized in that: The manganese source is MnSO4·H2O.

3. The method for preparing dual-phase MnO2 in one step according to claim 1, characterized in that: The oxidant is (NH4)2S2O8.

4. The method for preparing dual-phase MnO2 in one step according to claim 1, characterized in that: Inert salts are (NH4)2SO4.

5. The method for preparing dual-phase MnO2 in one step according to claim 1, characterized in that: The ratio of the amount of the oxidizing agent, the inert salt substance and the manganese source is 8 to 14 mmol: 20 to 25 mmol: 8 to 14 mmol.

6. A dual-phase MnO2 prepared by the one-step method according to any one of claims 1 to 5.

7. Use of the dual-phase MnO2 prepared by the one-step method according to any one of claims 1 to 5 in the degradation of organic pollutants in water.

8. The use according to claim 7, characterized in that Dual-phase MnO2 is added to a phenol-containing water body, stirred and ultrasonically dispersed to make it uniformly dispersed, and then PMS is added to the water body and a degradation reaction is carried out under stirring; wherein, the concentration of phenol in the phenol-containing water body is 5-30 mg / L, and the mass ratio of PMS:MnO2 is 2:

1.

9. Use of the dual-phase MnO2 prepared by the one-step method according to any one of claims 1 to 5 in flue gas denitrification.

10. The use according to claim 9, characterized in that The dual-phase MnO2 is set in a fixed bed reactor, and the flue gas containing nitrogen oxides flows through the fixed bed reactor and reacts at 200-600°C, wherein the concentration of nitrogen oxides in the flue gas containing nitrogen oxides is 300-500 ppm, the oxygen content is 5-15%, the water vapor content is 7-15%, and the rest is nitrogen. The flow rate of the flue gas containing nitrogen oxides is 0.2-1.0 L / min.

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