CN102041553B - Preparation method and application of crystalline-state beta-MnOOH nanowire - Google Patents

Abstract

The invention discloses a preparation method and application of crystalline β-MnOOH nanowires. The method is as follows: at normal temperature, the same volume of 0.4-0.6mM divalent manganese salt solution and 0.8-1.0mM alkali solution are mixed under magnetic stirring, and left for 1-2 days to generate crystalline β-MnOOH nanowire precipitates. Crystalline β-MnOOH nanowires are used to prepare mesoporous separation membranes with a thickness of 120-600 nanometers. The nanowires have a fine crystal structure of β-MnOOH with an average diameter of 25 nm. Simply ultrasonically disperse for 5-10 minutes, and filter 2-10ml of the dispersion to form a mesoporous membrane with a thickness of 120-600 nanometers on the porous substrate. This layer of mesoporous membrane can effectively separate 10nm particles from aqueous solution with a flow rate up to 15120L/m ² hbar. The crystalline β-MnOOH nanowires were annealed at 350-450 ^o C for 1 hour in air and then transformed into trimanganese tetraoxide nanowires with a high specific surface area of 70m ² /g, which were used to catalyze the degradation of dye molecules.

Description

A kind of preparation method and application of crystalline β-MnOOH nanowire

technical field

The invention relates to a preparation method and application of crystalline β-MnOOH nanowires.

Background technique

Manganese oxides and their nanostructures have been widely used in catalysis, batteries and other fields. They are usually prepared by several methods: hydrothermal redox method, sol-gel method in organic solvent, salt melting method, etc. These methods are energy-consuming or not very environmentally friendly. Moreover, the specific surface area of the obtained nanostructures is usually relatively small. The invention mainly introduces an environment-friendly method for preparing β-MnOOH nanowires with high specific surface area. This simple synthesis method in aqueous solution at normal temperature can meet the requirements of industrialized large-scale production, and is energy-saving, economical and environmentally friendly. And further expand the application of this nanowire to the separation membrane and catalytic oxidation degradation of organic dye molecules.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a preparation method and application of crystalline β-MnOOH nanowires.

The preparation method of crystalline β-MnOOH nanowires is: at room temperature, mix the same volume of 0.4-0.6 mM divalent manganese salt solution and 0.8-1.0 mM alkali solution under magnetic stirring, and place it for 1-2 days to form crystals. state of β-MnOOH nanowire precipitates.

The divalent manganese salt is manganous nitrate, manganous sulfate or manganous chloride. Described alkali is ethanolamine, sodium hydroxide or potassium hydroxide.

Crystalline β-MnOOH nanowires are used to prepare mesoporous separation membranes with a thickness of 120-600 nm.

The preparation method of the 120-600 nanometer thick mesoporous separation membrane is: ultrasonically disperse the crystalline β-MnOOH nanowire flocculent precipitation for 5 to 10 minutes, and take 2 to 10 ml of crystalline β-MnOOH nanowire The dispersion liquid is filtered to form a mesoporous separation membrane with a thickness of 120-600 nanometers on the porous substrate.

Crystalline β-MnOOH nanowires are used to degrade dye molecules.

The method step of described degradation dye molecule is:

1) Transform the crystalline β-MnOOH nanowires into trimanganese tetraoxide nanowires after annealing at 350-450 ^o C for 1-2 hours in air;

2) Add 20 mg of the manganese tetraoxide nanowire powder prepared above to 100 ml, 25 mg/L methylene blue solution, and then add 15 ml of 30% H ₂ O ₂ to degrade the dye molecules.

The present invention has the beneficial effect compared with prior art:

1) The preparation of β-MnOOH nanowires is carried out in aqueous solution at room temperature, which has low cost, simple process, and easy industrial mass production.

2) The prepared β-MnOOH nanowires not only have good crystallization properties, but also have a high specific surface area of 104 m ² /g.

3) The prepared β-MnOOH nanowires can form a good dispersion, and a mesoporous separation membrane can be obtained by simple filtration, which can be used to separate 10 nanometer particles.

4) The prepared β-MnOOH nanowires can be converted into corresponding manganese oxide nanowires after simple heat treatment, which can be used to catalyze the degradation of organic dye molecules.

5) The β-MnOOH nanowires prepared in the present invention can be used in environmental governance and sewage treatment.

Description of drawings

Figure 1 is the XRD pattern of the prepared β-MnOOH nanowires.

Figure 2 is the SEM photo of the prepared β-MnOOH nanowires.

Fig. 3 is the cross-sectional SEM photo of the β-MnOOH nanowire mesoporous separation membrane with a thickness of 120 nanometers.

Figure 4 is the Uv-Vis curve of 10 nanometer gold particles separated by a β-MnOOH nanowire mesoporous separation membrane with a thickness of 120 nanometers.

Figure 5 is the XRD pattern of the conversion of β-MnOOH nanowires into Mn ₃ O ₄ nanowires after heat treatment at 400 ⁰ C in air for 1 hour.

Figure 6 is the SEM photo of the β-MnOOH nanowires transformed into Mn ₃ O ₄ nanowires after heat treatment at 400 ⁰ C in air for 1 hour.

Figure 7 is the time-dependent curve of degraded methylene blue and the molecular structure of methylene blue converted from β-MnOOH nanowires to Mn ₃ O ₄ nanowires after heat treatment at 400 ⁰ C in air for 1 hour. .

Detailed ways

Below in conjunction with example further illustrate the present invention.

Example 1

 Preparation and characterization of β-MnOOH nanowires: Add 10 ml of 0.8 mM ethanolamine (NH ₂ CH ₂ CH ₂ OH) aqueous solution to 0.4 mM manganese nitrate (Mn(NO) ₃ ) aqueous solution rapidly at room temperature under magnetic stirring After 1 minute, slow down the stirring speed, and seal the reaction vessel. After one day, a brown flocculent precipitate can be obtained, and XRD proves that the precipitate has a β-MnOOH crystal structure (see Figure 1). SEM morphology analysis shows that these precipitates are nanowires with an average diameter of 25 nm and a length of about 1 micron. High-magnification SEM shows that these nanowires are bundled structures formed by parallel arrangement of thinner 3-5 nm nanowires (see figure 1). BET tests show that the specific surface area of these nanowires is as high as 104 m ² /g.

Example 2

Preparation and characterization of β-MnOOH nanowires: Add 10 ml of 0.8 mM NaOH aqueous solution to 0.4 mM manganese nitrate (Mn(NO) ₃ ) aqueous solution quickly at room temperature under magnetic stirring, and then slow down the stirring speed after 1 minute , and seal the reaction vessel. After one day, a brown flocculent precipitate can be obtained, and XRD proves that the precipitate has a β-MnOOH crystal structure. SEM morphology analysis shows that these precipitates are nanowires with an average diameter of 25 nanometers and a length of about 1 micron. High-magnification SEM shows that these nanowires are bundled structures formed by parallel arrangement of thinner nanowires of 3-5 nanometers.

Example 3

Preparation and characterization of β-MnOOH nanowires: Add 10 ml of 1.0 mM NaOH aqueous solution to 0.6 mM manganous chloride (Mn(NO) ₃ ) aqueous solution quickly at room temperature under magnetic stirring, and then slow down the stirring after 1 minute speed and seal the reaction vessel. After two days, a brown flocculent precipitate can be obtained, and XRD proves that the precipitate has a β-MnOOH crystal structure. SEM morphology analysis shows that these precipitates are nanowires with an average diameter of 25 nanometers and a length of about 1 micron. High-magnification SEM shows that these nanowires are bundled structures formed by parallel arrangement of thinner nanowires of 3-5 nanometers.

Example 4

Preparation and characterization of β-MnOOH nanowires: Add 10 ml of 1.0 mM KOH aqueous solution to 0.6 mM manganese sulfide (Mn(NO) ₃ ) aqueous solution quickly at room temperature under magnetic stirring, and then slow down the stirring speed after 1 minute , and seal the reaction vessel. After two days, a brown flocculent precipitate can be obtained, and XRD proves that the precipitate has a β-MnOOH crystal structure. SEM morphology analysis shows that these precipitates are nanowires with an average diameter of 25 nanometers and a length of about 1 micron. High-magnification SEM shows that these nanowires are bundled structures formed by parallel arrangement of thinner nanowires of 3-5 nanometers.

Example 5

Mesoporous nanowire separation membrane: The above-prepared β-MnOOH nanowire precipitation was dispersed by ultrasonic for 10 minutes, 2 ml of the dispersion was taken, and filtered on a porous polycarbonate membrane (2.5 cm, pore size 200 nm, void rate of 10%) to form a layer of β-MnOOH nanowire filter layer. SEM shows that the filter layer is continuous with a thickness of about 120 nanometers, and the nanowires overlap each other to form a separation layer with many holes, as shown in Figure 2 a-2 c. This membrane can effectively separate 10 nm gold particles from aqueous solution with a rejection rate of 93% (see Figure 2) at a flow rate of 15120 L/m ² hbar.

Example 6

Mesoporous nanowire separation membrane: The above-prepared β-MnOOH nanowire precipitation was dispersed by ultrasound for 10 minutes, 10 ml of the dispersion was taken, and filtered on a porous polycarbonate membrane (2.5 cm, pore size 200 nm, void rate of 10%) to form a layer of β-MnOOH nanowire filter layer. SEM shows that the filter layer is continuous, with a thickness of 600 nanometers, and the nanowires overlap each other to form a porous separation layer. This membrane can effectively separate 10 nanometer gold particles from aqueous solution.

Example 7

 The above-prepared β-MnOOH nanowires were collected and dried by centrifugation, and then heat-treated at 350 ^o C in air for 1 hour (the heating rate was 10 ^o C/min), and the trimanganese tetraoxide nanowires were obtained as shown in Figure 3 As shown, the shape of the nanowires remained largely intact. Its specific surface area is 71 m ² /g. Add 20 mg of the manganese tetraoxide nanowire powder prepared above into 100 ml, 25 mg/L methylene blue (molecular structure in Figure 3) solution, and then add 15 ml of 30% H ₂ O ₂ . The concentration of methylene blue in the solution was detected by Uv-Vis spectrometer in the whole catalytic process. It was found that when there were only trimanganese tetraoxide nanowires or only H ₂ O ₂ , no obvious degradation of methylene blue was observed. But when the two were added together, the degradation of methylene blue reached 81% within 5 minutes and 93% after an hour. The main reason is that the trimanganese tetraoxide nanowires catalyze the decomposition of H ₂ O ₂ to form highly active HO ^· , HOO ^· , or O ^{2 ·} -groups. These groups are required to degrade methylene blue. The high specific surface area of manganese tetraoxide nanowires leads to its high catalytic activity.

Example 8

The β-MnOOH nanowires prepared above were collected and dried by centrifugation, and then heat-treated at 450 ^o C in the air for 2 hours (the heating rate was 10 ^o C/min), and the trimanganese tetraoxide nanowires were obtained as shown in Figure 3 As shown, the shape of the nanowires remained largely intact. Add 20 mg of the manganese tetraoxide nanowire powder prepared above into 100 ml, 25 mg/L methylene blue (molecular structure in Figure 3) solution, and then add 15 ml of 30% H ₂ O ₂ . The concentration of methylene blue in the solution was detected by Uv-Vis spectrometer in the whole catalytic process. It was found that when there were only trimanganese tetraoxide nanowires or only H ₂ O ₂ , no obvious degradation of methylene blue was observed. But when the two were added together, the degradation of methylene blue reached 82% within 5 minutes and 95% after an hour. The main reason is that the trimanganese tetraoxide nanowires catalyze the decomposition of H ₂ O ₂ to form highly active HO ^· , HOO ^· , or O ^{2 ·} -groups. These groups are required to degrade methylene blue. The high specific surface area of manganese tetraoxide nanowires leads to its high catalytic activity.

Claims (5)

1. the preparation method of the β of a crystalline state-MnOOH nano wire; It is characterized in that: under the normal temperature; The 0.4-0.6mM manganous salt aqueous solution of equal volume is mixed under magnetic agitation with the 0.8-1.0mM alkali aqueous solution, placed 1-2 days, generate the β-MnOOH nano wire throw out of crystalline state; Described alkali is thanomin, sodium hydroxide or Pottasium Hydroxide.

2. the preparation method of the β of a kind of crystalline state according to claim 1-MnOOH nano wire is characterized in that described manganous salt is Mn nitrate, manganese sulfate or protochloride manganese.

3. the purposes of the β-MnOOH nano wire of the crystalline state of method preparation according to claim 1 is characterized in that: the mesoporous separatory membrane that is used to prepare the 120-600 nanometer thickness.

4. the purposes of the β of a kind of crystalline state according to claim 3-MnOOH nano wire; The preparation method who it is characterized in that the mesoporous separatory membrane of described 120-600 nanometer thickness is: with the β of crystalline state-MnOOH nano wire flocks ultra-sonic dispersion 5～10 minutes, β-MnOOH nano wire dispersion liquid of getting 2～10ml crystalline state filtered the mesoporous separatory membrane that in the porous substrate, forms one deck 120～600 nanometer thickness.

5. the purposes of the β-MnOOH nano wire of the crystalline state of method preparation according to claim 1 is characterized in that: be used for the degradation of dye molecule; The method steps of described degradation of dye molecule is:

1) with the β-MnOOH nano wire of crystalline state in air, 350～450 ℃ of annealing changed into manganic manganous oxide nanometer wire after 1～2 hour;

2) get the manganic manganous oxide nanometer wire powder that makes more than the 20mg and add 100ml, in the methylene blue solution of 25mg/L, add the H of 15ml 30% then ₂O ₂, can the degradation of dye molecule.

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