Preparation method and application of nitrogen-doped alumina-loaded manganese dioxide ozone catalyst based on polydopamine

Abstract

The invention discloses a preparation method of a nitrogen-doped aluminum oxide loaded manganese dioxide ozone catalyst based on polydopamine, which mainly comprises the following steps: S1, immersing aluminum oxide into a Tris-HCl buffer solution in which dopamine is dissolved, adding ferrite for catalytic polymerization, taking out after room-temperature reaction is finished, washing with deionized water, and drying to obtain a nitrogen-doped aluminum oxide loaded manganese dioxide ozone catalyst; drying to obtain a polydopamine modified alumina carrier; s2, adding the polydopamine modified alumina carrier into an aqueous solution containing a manganese salt, dipping for a period of time, then taking out, and carrying out vacuum drying to obtain polydopamine modified alumina complexed with a manganese ion precursor; s3, putting the polydopamine modified aluminum oxide complexed with the manganese ion precursor into a muffle furnace, and calcining for a period of time at high temperature to finally prepare the nitrogen-doped aluminum oxide loaded manganese dioxide ozone catalyst based on the polydopamine. The invention also discloses an application of the ozone catalyst in methylene blue wastewater treatment. Results show that compared with a conventional ozone catalyst, the nitrogen-doped ozone catalyst prepared from polydopamine has the advantages of simple preparation method, high catalytic activity and the like, and shows a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of composite catalysis, and in particular relates to a preparation method of a nitrogen-doped alumina-loaded manganese dioxide ozone catalyst based on polydopamine and an application thereof. Background Art

[0002] In recent years, advanced oxidation treatment technologies (AOPs) have been widely used in industrial wastewater treatment, urban sewage treatment and other fields due to their advantages such as high efficiency, environmental protection and good controllability. Among them, ozone advanced oxidation treatment technology is a technology that uses ozone to treat pollutants in water. Its main principle is to use the oxidizing ability of ozone and the highly active free radicals produced to oxidize and decompose pollutants into harmless substances. However, traditional ozone oxidation technology has the problems of low ozone utilization and incomplete oxidation. In order to solve these problems, ozone catalytic oxidation technology came into being. This technology needs to be carried out in conjunction with an ozone catalyst, which can significantly enhance the utilization rate of ozone, improve the efficiency of the oxidation reaction and reduce the generation of ozonation by-products.

[0003] Ozone catalysts are mainly divided into homogeneous ozone catalysts and heterogeneous ozone catalysts. Among them, homogeneous catalysts exist in the form of aqueous solutions, which are difficult to recover and reuse in actual catalytic reaction systems. In comparison, heterogeneous catalysts exist in solid form, which have the advantages of easy separation and recovery, and convenient reuse. For heterogeneous ozone catalytic technology, commonly used catalysts are mainly transition metal oxides such as Fe3O4, MnO2, and Co3O4. In order to reduce the precipitation of metal ions and improve the mass transfer capacity, it is often necessary to load the active components of the ozone catalyst on the corresponding carrier. Commonly used carriers mainly include activated alumina, activated carbon, and molecular sieves. Kim et al. used two manganese precursors to synthesize mesoporous MnOx / γ-Al2O3 catalysts to remove methyl ethyl ketone by ozone oxidation at room temperature (Materials Letters, 2021, 299: 130105). However, the above catalysts still have the problem of unsatisfactory pollutant removal efficiency, and the catalytic activity needs to be further improved.

[0004] More efficient ozone catalysts can be prepared by doping regulation, mainly because the introduction of different metal or non-metal elements into the catalyst can change the electronic structure, specific surface area, active sites and other physical and chemical properties of the catalyst, thereby improving the activity of the catalyst. Since nitrogen has a lower electronegativity than oxygen, nitrogen doping can enhance the catalytic ozone activity of oxide catalysts, reduce the amount of lattice oxygen in the basic position of the oxide, and thus improve its stability in water. For example, invention patent CN114931963 A prepared a nitrogen-doped magnesium-manganese binary oxide catalyst and applied it to catalytic ozone oxidation to remove acetic acid.

[0005] As a functional polymer, polydopamine can be used for carrier modification and catalyst loading. This patent develops a nitrogen-doped alumina ozone catalyst based on polydopamine, and introduces nitrogen into the alumina ozone catalyst through high-temperature calcination in order to obtain higher ozone catalytic activity and stability. Summary of the invention

[0006] In order to improve the loading efficiency and ozone catalytic activity of heterogeneous ozone catalysts, the purpose of the present invention is to use polydopamine for modification and nitrogen doping to provide a novel method for preparing nitrogen-doped alumina-loaded manganese oxide ozone catalyst. To achieve the above purpose, the method specifically includes the following steps:

[0007] S1, immersing the alumina support in a Tris-HCl buffer solution containing a certain amount of dopamine, adding a ferrous salt solution, reacting at room temperature for a period of time, taking out and washing with deionized water, and drying to obtain a polydopamine-modified alumina support;

[0008] S2, adding the polydopamine-modified alumina support into a manganese salt solution, taking it out after immersion for a period of time, and vacuum drying to obtain the polydopamine-modified alumina support complexed with a metal precursor;

[0009] S3. The polydopamine-modified alumina precursor complexed with manganese ions is placed in a muffle furnace and calcined at high temperature for a period of time to obtain an ozone catalyst of nitrogen-doped alumina loaded with manganese dioxide.

[0010] Furthermore, in step S1, the carrier is γ-Al2O3, and the particle size is 3-5 mm.

[0011] Furthermore, in step S1, the ferrous salt is any one of ferrous chloride, ferrous nitrate and ferrous acetate, and the mass fraction of ferrous ions is 0.5-2%.

[0012] Furthermore, in step S1, the mass fraction of dopamine is 0.1% to 1.0%, the pH value of the reaction solution is 5 to 9, and the polymerization time is 10 to 60 minutes.

[0013] Furthermore, in step S2, the metal precursor is one of manganese chloride, manganese nitrate and manganese acetate, the solution concentration is 0.2-1 mol / L, and the immersion time is 1-3 h.

[0014] Furthermore, in step S3, the calcination temperature is 200-400° C., and the calcination time is 1-3 hours.

[0015] The present invention also provides an application of the ozone catalyst in the treatment of methylene blue wastewater, and the specific steps are: adding the ozone catalyst to a methylene blue solution of a certain concentration, then introducing ozone for catalytic oxidation, taking samples at regular intervals to measure the absorbance, and calculating the ozone catalytic reaction rate according to a standard working curve of the methylene blue solution.

[0016] Furthermore, the concentration of the methylene blue solution is 10 to 40 mg / L.

[0017] Furthermore, the ozone concentration is 1 to 10 mg / L.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] On the one hand, in the Tris-HCl buffer solution, dopamine rapidly undergoes catalytic oxidative polymerization, thereby forming polydopamine on the surface of the alumina carrier with strong adhesion and favorable for the adsorption of metal precursors. On the other hand, the introduction of nitrogen into the alumina ozone catalyst by high-temperature calcination enhances the polarity of the catalyst surface, which is conducive to the close binding of manganese dioxide to the carrier surface. The application study of methylene blue wastewater treatment shows that the nitrogen-doped alumina-supported manganese dioxide catalyst prepared by this method has better ozone catalytic oxidation ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 SEM images of the Al2O3 carriers used in the examples and comparative examples of the present invention;

[0021] Figure 2 This is a SEM image of the polymer-modified Al2O3 / PDA carrier prepared in Example 2 of the present invention;

[0022] Figure 3 This is a SEM image of nitrogen-doped Al2O3 / PDA / MnO2 based on polydopamine prepared in Example 3 of the present invention;

[0023] Figure 4 This is a SEM image of undoped Al2O3 / MnO2 prepared in Comparative Example 2 of the present invention;

[0024] Figure 5 This is a SEM image of Al2O3 / MnO2 after calcination of polydopamine prepared in Comparative Example 3 of the present invention;

[0025] Figure 6 BET diagrams of the Al2O3 carrier of the present invention, the Al2O3 / PDA carrier modified with polydopamine and the nitrogen-doped Al2O3 / PDA / MnO2 in Example 3;

[0026] Figure 7XRD patterns of the Al2O3 carrier of the present invention, the Al2O3 / PDA carrier modified with polydopamine, and the nitrogen-doped Al2O3 / PDA / MnO2 in Example 3;

[0027] Figure 8 This is the UV-Vis spectrum of the ozone-catalyzed degradation of methylene blue by nitrogen-doped Al2O3@PDA@MnO2 based on polydopamine prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described below through specific implementation modes, but the implementation modes of the present invention are not limited thereto.

[0029] Example 1

[0030] 1. Immerse 500g of Al2O3 carrier in 500mL of Tris-HCl buffer solution containing 0.5g dopamine, adjust the solution pH to 7, add 2% ferrous nitrate solution, stir and react at room temperature for 20min, take out and wash three times with deionized water, heat and dry at 110℃ to obtain polydopamine-modified alumina carrier;

[0031] 2. Add 500 g of polydopamine-modified alumina support into 500 mL of manganese chloride solution with a concentration of 0.2 mol / L, immerse at room temperature for 3 h, take out and vacuum dry to obtain polydopamine-modified alumina precursor complexed with manganese ions;

[0032] 3. Put the polydopamine-modified alumina precursor complexed with manganese ions into a muffle furnace and calcine at 200° C. for 3 h to obtain a nitrogen-doped alumina-loaded manganese dioxide ozone catalyst;

[0033] 4. 300g of nitrogen-doped alumina-loaded manganese dioxide ozone catalyst was loaded into the ozone catalytic reaction device, and 500mL of methylene blue solution with a concentration of 20mg / L was added. After adsorption for 30min, 1.6mg / L ozone was introduced from the bottom of the reaction device to carry out the ozone catalytic degradation reaction of methylene blue. 4mL of samples were taken from the sampling port in the middle of the reaction device every 30min, and the concentration change of methylene blue in the solution was measured by UV-Vis spectrophotometer.

[0034] Example 2

[0035] 1. Immerse 500g of Al2O3 carrier in 500mL of Tris-HCl buffer solution dissolved with 1.5g of dopamine, adjust the solution pH to 7, add 2% ferrous nitrate solution, stir and react at room temperature for 20min, take out and wash three times with deionized water, and dry at 110℃ to obtain a polydopamine-modified alumina carrier;

[0036] 2. Add 500g polydopamine-modified alumina carrier into 500mL manganese chloride solution with a concentration of 0.2mol / L, soak at room temperature for 3h, take out and vacuum dry Obtaining an alumina precursor modified with metal polydopamine ;

[0037] 3. Polydopamine modified alumina precursor with metal adsorption The mixture was placed in a muffle furnace and calcined at 300°C for 3 h to obtain a nitrogen-doped alumina-supported manganese dioxide ozone catalyst;

[0038] 4. 300g of nitrogen-doped alumina-loaded manganese dioxide ozone catalyst was loaded into the ozone catalytic reaction device, and 500mL of methylene blue solution with a concentration of 20mg / L was added. After adsorption for 30min, 1.6mg / L ozone was introduced from the bottom of the reaction device to carry out the ozone catalytic degradation reaction of methylene blue. 4mL of samples were taken from the sampling port in the middle of the reaction device every 30min, and the concentration change of methylene blue in the solution was measured by UV-Vis spectrophotometer.

[0039] Example 3

[0040] 1. Immerse 500g of Al2O3 carrier in 500mL of Tris-HCl buffer solution dissolved with 2.5g of dopamine, adjust the solution pH to 7, add 2% ferrous nitrate solution, stir and react at room temperature for 20min, take out and wash three times with deionized water, and dry at 110℃ to obtain a polydopamine-modified alumina carrier;

[0041] 2. Add 500 g of polydopamine-modified alumina support into 500 mL of manganese chloride solution with a concentration of 0.2 mol / L, immerse at room temperature for 3 h, take out and vacuum dry to obtain polydopamine-modified alumina adsorbed with metal precursors;

[0042] 3. The polydopamine-modified alumina adsorbed with the metal precursor was placed in a muffle furnace and calcined at 300° C. for 3 h to obtain a nitrogen-doped alumina-loaded manganese dioxide ozone catalyst. Figure 3 The SEM image of the prepared nitrogen-doped Al2O3 / PDA / MnO2 shows that there are many MnO2 nanoparticles on the alumina support. Figure 6 From the BET diagram of the carrier and the ozone catalyst, it can be seen that the specific surface area gradually decreases with the modification of polydopamine and the loading of the catalyst. Figure 7 The XRD patterns of the carrier and the ozone catalyst show that the ozone catalyst prepared by the present invention successfully loads MnO2;

[0043] 4. 300g of nitrogen-doped alumina-loaded manganese dioxide ozone catalyst was loaded into the ozone catalytic reaction device, and 500mL of methylene blue solution with a concentration of 20mg / L was added. After adsorption for 30min, 1.6mg / L ozone was introduced from the bottom of the reaction device to carry out the ozone catalytic degradation reaction of methylene blue. 4mL of samples were taken from the sampling port in the middle of the reaction device every 30min, and the changes in MB concentration in the solution were measured by UV-Vis spectrophotometer. Figure 8 This is the UV-Vis spectrum of the prepared nitrogen-doped Al2O3 / PDA / MnO2 catalyzed by ozone for the degradation of methylene blue. It can be seen from the figure that the concentration of methylene blue gradually decreases and the reaction is basically complete at 120 minutes.

[0044] Comparative Example 1

[0045] Different from Examples 1 to 3, Al2O3 pellets were loaded into the ozone catalytic reaction device, and after the methylene blue solution was added for adsorption equilibrium, ozone was introduced to carry out the catalytic ozone degradation reaction of methylene blue. Samples were taken every 30 minutes, and the concentration change of methylene blue in the solution was measured by UV-Vis spectrophotometer.

[0046] Comparative Example 2

[0047] Different from Examples 1 to 3, the catalyst was directly impregnated and loaded on alumina in this comparative example:

[0048] 1. Immerse 500g of alumina carrier in 500mL of manganese chloride solution with a concentration of 0.2mol / L at room temperature for 4h, take out and vacuum dry to obtain alumina adsorbed with metal precursor;

[0049] 2. The alumina adsorbed with the metal precursor is placed in a muffle furnace and calcined at 300° C. for 3 h to obtain an alumina-supported manganese dioxide ozone catalyst.

[0050] The operation of using alumina-supported manganese dioxide ozone catalyst for catalytic ozone degradation of methylene blue is the same as that of Examples 1 to 3.

[0051] Comparative Example 3

[0052] The difference from Examples 1 to 3 is that in this comparative example, the polydopamine-modified alumina carrier is first calcined and decomposed at 300° C., and then the metal precursor is impregnated and loaded.

[0053] 1. Immerse 500g of Al2O3 carrier into 500mL of Tris-HCl buffer solution dissolved with 2.5g of dopamine, adjust the solution pH to 5, add 2% ferrous nitrate solution, stir and react at room temperature for 20min, take out and wash three times with deionized water, and dry at 110℃ to obtain a polydopamine-modified alumina carrier;

[0054] 2. Place the polydopamine-modified alumina support in a muffle furnace and calcine at 300° C. for 3 h to obtain the polydopamine-calcined alumina support;

[0055] 3. Add 500g of alumina carrier calcined with polydopamine into 500mL of manganese chloride solution with a concentration of 0.2mol / L, soak at room temperature for 3h, and take out and vacuum dry. The metal precursor adsorbed Polydopamine calcined alumina;

[0056] 4. The alumina calcined with polydopamine adsorbed with metal precursors was placed in a muffle furnace at 300° C. and calcined for 3 hours to obtain a polydopamine calcined alumina-supported manganese dioxide ozone catalyst;

[0057] The operation of using the alumina-supported manganese dioxide ozone catalyst after calcining polydopamine for catalytic ozone degradation of methylene blue is the same as that of Examples 1 to 3.

[0058] Table 1 Performance comparison of ozone catalysts in different embodiments and comparative examples

[0059]

[0060] As can be seen from the above table, the nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine prepared in the present invention has a higher catalytic reaction rate than the alumina carrier. The catalytic reaction rate of the ozone catalyst prepared by the optimal ratio is dozens of times that of the alumina-based catalyst, and the ozone catalytic oxidation effect can be achieved quickly in a short time. Among them, the catalytic reaction rate of the nitrogen-doped alumina-supported manganese dioxide ozone catalyst prepared in Example 3 reached 0.032min -1 In conclusion, the present invention uses polydopamine to modify the alumina carrier, thereby increasing the loading amount of the Mn element and increasing the active sites on the surface of the ozone catalyst, thereby obtaining higher ozone catalytic activity and stability.

[0061] With the above-mentioned ideal embodiments of the present invention as inspiration, through the above-mentioned description, relevant staff can make various changes and modifications without departing from the technical idea of ​​the present invention. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine, characterized in that the method comprises the following steps: S1, immersing alumina in a Tris-HCl buffer solution containing a certain amount of dopamine, adding ferrous salt to catalyze polymerization of dopamine, reacting at room temperature, taking out and washing with deionized water, and drying to obtain a polydopamine-modified alumina carrier; S2, adding the polydopamine-modified alumina support into an aqueous solution containing a manganese salt, immersing for a period of time, taking out, and vacuum drying to obtain polydopamine-modified alumina complexed with a manganese ion precursor; S3. Put the polydopamine-modified alumina complexed with a manganese ion precursor into a muffle furnace and calcine it at high temperature for a period of time to finally prepare a polydopamine-based nitrogen-doped alumina-loaded manganese dioxide ozone catalyst.

2. The method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine according to claim 1, characterized in that: The alumina carrier in step S1 is γ-Al2O3 pellets with a particle size of 3-5 mm.

3. The method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine according to claim 1, characterized in that: The ferrous salt in step S1 is any one of ferrous chloride, ferrous nitrate and ferrous acetate, and the mass fraction of ferrous ions is 0.5-2%.

4. The method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine according to claim 1, characterized in that: The mass fraction of dopamine in step S1 is 0.1-1.0%, the pH value of the reaction solution is 5-9, and the polymerization time is 10-60 minutes.

5. The method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine according to claim 1, characterized in that: The manganese salt in step S2 is any one of manganese chloride, manganese nitrate and manganese acetate, the solution concentration is 0.2-1.0 mol / L, and the immersion time is 1-3 hours.

6. The method for preparing a nitrogen-doped alumina-supported manganese dioxide ozone catalyst based on polydopamine according to claim 1, characterized in that: The calcination temperature in step S3 is 200-400° C., and the calcination time is 1-3 hours.

7. An application of the ozone catalyst prepared according to claims 1-6 in the treatment of methylene blue wastewater, characterized in that: The concentration of methylene blue solution is 10-40 mg / L, the concentration of ozone is 1-10 mg / L, and the ozone catalytic reaction rate is 0.01-0.05 min -1 .

Images