CN114471531A

CN114471531A - Nano porous spherical birnessite, preparation method thereof and application thereof in formaldehyde degradation

Info

Publication number: CN114471531A
Application number: CN202110523171.2A
Authority: CN
Inventors: 罗骏; 李光辉; 莽昌烨; 姜涛
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-06-24
Filing date: 2021-06-24
Publication date: 2022-05-13
Anticipated expiration: 2041-06-24
Also published as: CN114471531B

Abstract

The invention belongs to the technical field of formaldehyde catalysis, and particularly discloses a preparation method of nano porous spherical birnessite, which comprises the following steps: step (1): dropwise adding a permanganate A aqueous solution into a bivalent manganese source aqueous solution, and carrying out a first reaction under stirring; wherein the molar ratio of the permanganate A to the divalent manganese source is 0.5-2: 1; step (2): adding permanganate B into a solution system of the first reaction, sealing the mixed solution in a container, heating to perform a second reaction, and separating to obtain a nano porous spherical birnessite product after the reaction is finished; the molar ratio of the permanganate B to the divalent manganese source is 0.5-3.5: 1; the temperature of the second reaction is 160-250 ℃. The material prepared by the invention has excellent formaldehyde catalytic performance.

Description

Nano porous spherical birnessite, preparation method thereof and application thereof in formaldehyde degradation

Technical Field

The invention belongs to the field of nano material manufacturing, and particularly relates to a preparation method of nano porous spherical birnessite capable of efficiently degrading formaldehyde.

Technical Field

With the development of science and technology and the progress of society, the requirement of human beings on indoor decoration is higher and higher, and the problems that follow are more and more. Most interior materials contain a certain amount of formaldehyde, and thus the released formaldehyde gas also pollutes the indoor air and is harmful to human health. Therefore, it is necessary to solve the problem of indoor air pollution. The current means for treating indoor air pollution are adsorption, biological, plasma, photocatalytic and thermal catalytic oxidation. Among them, the thermal catalytic oxidation method is highly preferred for its good formaldehyde removal effect and low operation cost.

The key to the thermal catalytic oxidation process is the choice of catalyst, which is mainly divided into noble metal and transition metal oxides. Wherein, the noble metal catalyst has high catalytic activity and good catalytic effect. However, noble metal catalysts have limited further use due to low reserves, high prices, and the like. Therefore, various researchers have focused on transition metal oxides. Transition metal oxides are mainly classified as manganese oxides, cobalt oxides or composite oxides. Compared with other transition metal oxides, the manganese oxide has the characteristics of low toxicity, high activity, stable structure, various shapes and the like, and attracts various scholars.

Birnessite, a manganese dioxide made of MnO₆The layered manganese oxide ore formed by stacking octahedrons and water molecules of different cations has the characteristics of strong oxidizing capacity, large specific surface area, high ion exchange capacity and the like. The change of the morphology of the birnessite can cause the physical and chemical properties of the birnessite to be greatly changed. Most of birnessite reported in the literature at present is mainly in the shape of a sheet, a petal and a sphere. The specific surface area of the birnessite is changed by changing the micro-morphology of the birnessite, so that the birnessite is promoted to meet the requirements of different fields.

However, the catalytic performance of birnessite on formaldehyde reported in the prior art is still low at room temperature, and the formaldehyde can be removed at a higher temperature. The prior art also lacks a material which can still show good formaldehyde removal performance under the condition of normal temperature.

Disclosure of Invention

The first purpose of the invention is to provide a preparation method of nano porous spherical birnessite, which has low cost, simple operation and convenient treatment. The material has large specific surface area and can efficiently degrade formaldehyde gas in the air.

The second purpose of the invention is to provide the nano-porous spherical birnessite prepared by the preparation method.

The third purpose of the invention is to provide the application of the nano-porous spherical birnessite prepared by the preparation method in the aspect of formaldehyde degradation.

The birnessite in the prior art is not ideal in shape uniformity and is usually a micron-sized material, the performance of the material in the aspect of formaldehyde catalysis needs to be improved, for example, the formaldehyde degradation performance at normal temperature is poor, and the material is limited in practical application, and aiming at the technical problem, the invention provides the following technical scheme:

a preparation method of nano porous spherical birnessite comprises the following steps:

step (1): dropwise adding a permanganate A aqueous solution into a bivalent manganese source aqueous solution, and carrying out a first reaction under stirring; wherein the molar ratio of the permanganate A to the divalent manganese source is 0.5-2: 1;

step (2): adding permanganate B into a solution system of the first reaction, sealing the mixed solution in a container, heating to perform a second reaction, and separating to obtain a nano porous spherical birnessite product after the reaction is finished;

the molar ratio of the permanganate B to the divalent manganese source is 0.5-3.5: 1;

the temperature of the second reaction is 160-250 ℃.

The invention innovatively discovers that the first reaction is carried out by dripping the permanganate A into the divalent manganese source aqueous solution in advance, then the second reaction is carried out by adding the permanganate B, based on the two-stage reaction thought, the coordination is further matched with the control of all the conditions, the synergy can be realized unexpectedly, the material which is formed by assembling the nanosheets and has the advantages of porosity, sphericity and nanometer size can be obtained, and more importantly, the material obtained by adopting the method has unexpected degradation advantage in the aspect of formaldehyde catalysis.

The research of the invention finds that the step-by-step two-stage reaction idea of permanganate, the combined synergistic control of the adding proportion and the reaction temperature in the reaction idea are the key points for improving the structure and the appearance of the material and the degradation performance of formaldehyde.

In the invention, the divalent manganese source can ionize Mn²⁺The water-soluble compound of (1); preferably at least one of manganese sulfate, manganese nitrate, manganese chloride and manganese acetate, or manganese ore extract. The source of divalent manganese may be a commercial chemical feedstock or may be derived from a mineral smelting feed (e.g. a leach solution).

Preferably, the divalent manganese source is an aqueous solution of Mn²⁺The molar concentration of (A) is 0.1-2M; more preferably 0.1 to 0.5M.

The permanganate A and the permanganate B can ionize to obtain MnO₄The water-soluble salt of (a) is preferably at least one of potassium permanganate, sodium permanganate, and magnesium permanganate.

Aqueous permanganate A solution (with MnO)₄-in) is 0.1-0.5M.

According to the research of the invention, the permanganate A is dripped into the divalent manganese source solution, the dripping speed, the stirring speed in the reaction stage and the reaction time are further controlled, the morphology of the material prepared under the two-stage reaction mechanism can be further improved unexpectedly, and the formaldehyde degradation performance can be further improved.

Preferably, in the step (1), the dropping rate of the permanganate A aqueous solution is 0.001 to 0.005 moL/min.

Preferably, the permanganate A is in aqueous solution (as MnO)₄-in) in a molar ratio of 0.5 to 1:1 with respect to the source of divalent manganese; more preferably 0.5 to 0.6: 1.

Preferably, in the step (1), the stirring speed in the first reaction process is 50-300 r/min.

Preferably, in the step (1), the time of the first reaction process is 0.5-3 h; more preferably 1 to 2 hours.

In the present invention, a permanganate B aqueous solution is added to a first reaction system, and the mixed solution is placed in a pressure-resistant container, which is then closed and heated to carry out a second reaction. Researches find that the control of the addition amount of the permanganate B in the second reaction stage and the reaction temperature is beneficial to obtaining materials with better formaldehyde catalytic degradation performance.

In the present invention, the permanganate B aqueous solution (in MnO)₄-in) is 0.1 to 1.5M; preferably 0.8 to 1M.

Preferably, the molar ratio of the permanganate B to the divalent manganese source is 1-2: 1.

Preferably, the temperature of the second reaction is 180 to 240 ℃.

Preferably, the second reaction time is 12-48 h; further preferably 15 to 24 hours.

In the invention, after the second reaction is finished, the solid-liquid separation is carried out on the product, and the product is obtained after washing and drying.

The invention discloses a preferable preparation method of porous spherical birnessite for efficiently degrading formaldehyde, which comprises the following steps:

(1) preparing a manganese sulfate aqueous solution for later use:

(2) adding potassium permanganate (MnO 4-relative to the added Mn) into the prepared manganese sulfate aqueous solution²⁺The molar ratio of (a) to (b) is 0.5-2: 1) stirring at room temperature to perform a first stage reaction to obtain a first reaction solution;

(3) adding potassium permanganate (the molar ratio of MnO 4-to the added Mn2+ is 0.5-3.5: 1) into the mixed solution in the step (2), and stirring for reaction for 0.5-3 h to obtain a suspension;

(4) transferring the suspension into a pressure-resistant container, sealing the reactor, and carrying out crystallization reaction at 160-240 ℃ for 12-48 hours;

(5) washing the mixture to be neutral by using absolute ethyl alcohol and deionized water, performing suction filtration by using a vacuum pump, drying at 40-90 ℃, and grinding to obtain birnessite powder.

The invention also provides the nano porous spherical birnessite prepared by the preparation method, and the nano porous spherical birnessite is formed by staggering birnessite nanosheets into a porous nano-sized spherical material.

The invention also provides application of the nano porous spherical birnessite prepared by the preparation method in catalytic degradation of formaldehyde.

Advantageous effects

1. The invention provides a two-stage reaction idea of permanganate, and further discovers that based on the two-stage reaction idea, the two-stage reaction idea is further matched with the combined control of conditions such as material proportion, temperature and the like, the synergy can be realized unexpectedly, the nanometer spherical material with good structure and appearance can be obtained, and more importantly, the material with the appearance structure obtained in the aspect has excellent performance in the aspect of formaldehyde catalysis;

2. the preparation method of the nano porous spherical birnessite capable of efficiently degrading formaldehyde is simple in preparation process, low in cost, free of adding a surfactant or a modifier and environment-friendly. The birnessite prepared by the method has the advantages of rich pore structure, good stability and higher specific surface area, and can have important application value in various fields such as adsorption, catalysis, oxidative degradation materials, air purification materials and the like.

Drawings

FIG. 1 is a scanning electron microscope photograph of example 1, which shows the preparation of nanoporous spherical birnessite having an ability to efficiently degrade formaldehyde;

FIG. 2 is an X-ray diffraction spectrum of nano-porous spherical birnessite prepared in example 1, which has the ability of degrading formaldehyde efficiently;

FIG. 3 is a graph showing the change of formaldehyde conversion rate with temperature of the nanoporous spherical birnessite prepared in example 1, which has the ability to efficiently degrade formaldehyde;

FIG. 4 is a graph of the normal temperature formaldehyde tolerance over time for the preparation of nanoporous spherical birnessite with high formaldehyde degradation capacity in example 1;

FIG. 5 is an SEM photograph of a material prepared in comparative example 1;

FIG. 6 XRD pattern of the material prepared in comparative example 1;

FIG. 7 is a graph of formaldehyde conversion versus temperature for the material prepared in comparative example 1;

FIG. 8 is a scanning electron microscope photograph of a nanoporous spherical birnessite prepared in comparative example 2, which has an ability to efficiently degrade formaldehyde;

FIG. 9 is a graph showing the change of formaldehyde conversion rate with temperature of nano-porous spherical birnessite prepared in comparative example 2, which has the ability to efficiently degrade formaldehyde;

FIG. 10 is a scanning electron microscope photograph of a comparative example 3 preparation material;

FIG. 11 is a graph of formaldehyde conversion versus temperature for the material prepared in comparative example 3;

FIG. 12 scanning electron micrograph of nanoporous spherical birnessite prepared in example 2 with efficient formaldehyde degradation ability;

FIG. 13 is a graph showing the change of formaldehyde conversion rate with temperature of example 2 to prepare nanoporous spherical birnessite having an ability to efficiently degrade formaldehyde;

FIG. 14 is a scanning electron microscope photograph of a comparative example 4 preparation material;

FIG. 15 is a graph of formaldehyde conversion versus temperature for the material prepared in comparative example 4;

FIG. 16 scanning electron micrograph of nanoporous spherical birnessite prepared in example 3 with efficient formaldehyde degradation ability;

FIG. 17 is a graph showing the change of formaldehyde conversion rate with temperature of the nanoporous spherical birnessite prepared in example 3, which has the ability of efficiently degrading formaldehyde;

FIG. 18 is a scanning electron microscope photograph of a comparative example 5 preparation material;

FIG. 19 is a plot of formaldehyde conversion as a function of temperature for the material prepared in comparative example 5;

FIG. 20 is a scanning electron microscope photograph of a comparative example 6 preparation material;

FIG. 21 is a graph of formaldehyde conversion versus temperature for the material prepared in comparative example 6;

FIG. 22 is a scanning electron microscope photograph of a comparative example 7 preparation material;

FIG. 23 is a graph of formaldehyde conversion versus temperature for the material prepared in comparative example 7;

FIG. 24 is a scanning electron microscope photograph of a comparative example 8 preparation material;

FIG. 25 is a graph of formaldehyde conversion versus temperature for a material prepared according to comparative example 8;

FIG. 26 is a graph of formaldehyde conversion as a function of temperature for the material prepared in example 4;

FIG. 27 plot of formaldehyde conversion as a function of temperature for the material prepared in example 5;

the specific implementation mode is as follows:

the method for recording the catalytic degradation step of formaldehyde and measuring data comprises the following steps:

determination of the catalytic Activity of the catalyst on HCHO (80 ppm): 0.1g of catalyst powder having a particle size of 200-. The total flow rate was 100ml min-1, corresponding to a Gas Hourly Space Velocity (GHSV) of 60 L.h-1. g-1. Once the given reaction temperature was reached, the catalyst was stable for 1 hour. The reaction products were detected on-line using a gas chromatography-mass spectrometer equipped with a thermal conductivity detector. The catalytic activity of the catalyst was evaluated by conversion of HCHO to CO 2. HCHO conversion of the sample was calculated using the following formula

Wherein [ HCHO ] in and [ CO2] in represent the inlet HCHO and CO2 concentrations [ CO2] out, respectively, for the outlet CO2 concentration.

The room temperature in the invention is, for example, 20 to 35 ℃.

Example 1

(1) Preparing 0.2M manganese sulfate aqueous solution for later use:

(2) dropwise adding 0.4M potassium permanganate solution (the dropwise adding speed is 0.004mol/min, and the dropwise adding molar weight is 0.1mol) into the prepared manganese sulfate aqueous solution (1L), stirring at room temperature (the stirring rotating speed is 80r/min), carrying out a first-stage reaction, and reacting for 60min to obtain a first reaction solution;

(3) continuously adding 0.8M potassium permanganate solution (the adding molar weight is 0.2mol, the dropping speed is the same as that in the step (2)) into the first invention solution, and uniformly stirring to obtain suspension;

(4) transferring the suspension into a pressure-resistant reactor, sealing the reactor, heating to 180 ℃, and carrying out a second-stage reaction for 20 hours;

(5) washing with absolute ethyl alcohol and deionized water to neutrality, vacuum filtering with a vacuum pump, drying at 60 deg.C, and grinding to obtain birnessite powder.

The scanning electron microscope picture of the nano porous spherical birnessite material with the efficient formaldehyde degradation function prepared by the embodiment is shown in an attached figure 1, the X-ray diffraction spectrogram is shown in an attached figure 2, the curve of the change of the conversion rate of formaldehyde along with the temperature is shown in an attached figure 3, and the tolerance of the catalyst to formaldehyde at normal temperature is shown in an attached figure 4.

Comparative example 1

The only difference compared to example 1 is that the potassium permanganate in step (2) is relative to Mn²⁺The adding molar ratio is 0.4;

the obtained material has scanning electron microscope picture shown in figure 5, X-ray diffraction spectrum shown in figure 6, and formaldehyde conversion rate variation curve with temperature shown in figure 7.

Comparative example 2

The only difference compared with example 1 is that in step (3) (second reaction), the molar ratio of potassium permanganate to manganese sulfate was 4.

The scanning electron microscope picture of the nano porous spherical birnessite material with the efficient formaldehyde degradation function prepared by the embodiment is shown in an attached figure 8, and the curve of the formaldehyde conversion rate along with the temperature change is shown in an attached figure 9.

Comparative example 3

The only difference compared to example 1 is that the potassium permanganate in step (3) is relative to Mn²⁺The adding molar ratio is 0.3;

the scanning electron microscope picture of the material prepared by the comparative example is shown in figure 10, and the curve of the formaldehyde conversion rate along with the temperature is shown in figure 11.

Example 2

The only difference compared to example 1 is that in step (2) the molar ratio of potassium permanganate to manganese sulphate in step (1) is 2: 1.

The scanning electron microscope picture of the nano porous spherical birnessite material with high formaldehyde degradation efficiency prepared by the embodiment is shown in the attached figure 12, and the curve of the formaldehyde conversion rate along with the temperature change is shown in the attached figure 13.

Comparative example 4

The only difference compared with example 1 is that the crystallization temperature in step (4) is 130 ℃.

The scanning electron microscope picture of the material prepared by the comparative example is shown in figure 14, and the curve of the formaldehyde conversion rate along with the temperature is shown in figure 15.

Example 3

The only difference compared to example 1 is that in step (3), the molar ratio of potassium permanganate to manganese sulfate in step (1) is 2: 1.

The scanning electron microscope picture of the nano porous spherical birnessite material with high formaldehyde degradation efficiency prepared by the embodiment is shown in the attached figure 16, and the curve of the formaldehyde conversion rate along with the temperature change is shown in the attached figure 17.

Comparative example 5

Compared with example 1, the only difference is that the first reaction time of step (2) is 20 min;

the scanning electron microscope picture of the material prepared by the comparative example is shown in figure 18, and the curve of the formaldehyde conversion rate along with the temperature is shown in figure 19.

Comparative example 6

Compared with the example 1, the difference is that two-stage range is not adopted, and the total adding molar amount of the potassium permanganate and other processing parameters are the same as those of the example 1;

the scanning electron microscope picture of the comparative example material is shown in figure 20, and the curve of the formaldehyde conversion rate along with the temperature is shown in figure 21.

Comparative example 7

Compared with the example 1, the difference is that in the step (3), the adding molar ratio of the potassium permanganate to the manganese sulfate is 25:1, and the other conditions are the same as the example 1.

The scanning electron microscope picture of the nano porous spherical birnessite material with high formaldehyde degradation efficiency prepared by the comparative example is shown in the attached figure 22, and the curve of the formaldehyde conversion rate along with the temperature change is shown in the attached figure 23.

Comparative example 8

The only difference compared with example 1 is that the treatment temperature (crystallization temperature) in step (4) is 80 ℃.

The scanning electron microscope picture of the material prepared by the comparative example is shown in figure 24, and the curve of the formaldehyde conversion rate along with the temperature is shown in figure 25.

Example 4

(1) Preparing 0.2M manganese sulfate aqueous solution for later use:

(2) dropwise adding 0.5M potassium permanganate solution (the dropwise adding speed is 0.004mol/min and the adding molar ratio relative to manganese sulfate is 0.5) into the prepared manganese sulfate aqueous solution (1L), stirring at room temperature (the stirring speed is 100r/min), carrying out first-stage reaction for 120min, and obtaining a first reaction solution;

(3) continuously adding 0.8M potassium permanganate solution (equivalent to the adding molar ratio of the manganese sulfate in the step (1) being 2, and the dropping speed being the same as that in the step (2)) into the first invention solution, and uniformly stirring to obtain suspension;

(4) transferring the suspension into a pressure-resistant reactor, sealing the reactor, heating to 220 ℃, and carrying out a second-stage reaction for 24 hours;

The curve of the change curve of the conversion rate of formaldehyde along with the temperature of the nano porous spherical birnessite material with the function of efficiently degrading formaldehyde prepared by the embodiment is shown in an attached figure 26.

Example 5

(1) Preparing 0.2M manganese sulfate aqueous solution for later use:

(2) dropwise adding 0.1M potassium permanganate solution (the dropwise adding speed is 0.004mol/min and the adding molar ratio relative to manganese sulfate is 0.5) into the prepared manganese sulfate aqueous solution (1L), stirring at room temperature (the stirring speed is 80r/min), carrying out first-stage reaction for 60min, and obtaining a first reaction solution;

(3) continuously adding 1M potassium permanganate solution (the adding molar ratio of the potassium permanganate solution to the manganese sulfate is 2, the dropping speed is the same as that in the step (2)) into the first invention solution, and uniformly stirring to obtain a suspension;

(4) transferring the suspension into a pressure-resistant reactor, sealing the reactor, heating to 240 ℃, and carrying out a second-stage reaction for 15 hours;

(5) washing with absolute ethyl alcohol and deionized water to neutrality, vacuum filtering with a vacuum pump, drying at 60 deg.C, and grinding to obtain birnessite powder. The curve of the change curve of the conversion rate of formaldehyde along with the temperature of the nano porous spherical birnessite material with the function of efficiently degrading formaldehyde prepared by the embodiment is shown in an attached figure 27.

The conversion data of formaldehyde of examples 1 to 5 and comparative examples 1 to 8 at different temperatures are shown in Table 1

As can be seen from table 1, the two-stage reaction of the present invention, in combination with the addition of the first-stage reaction and the second-stage reaction and the cooperative control of the crystallization temperature of the second-stage reaction, can unexpectedly improve the performance of the prepared material, and is helpful to further improve the low-temperature and high-temperature catalytic performance, especially can effectively improve the catalytic performance at room temperature, and has a wider practical application prospect.

Claims

1. The preparation method of the nano porous spherical birnessite is characterized by comprising the following steps of:

the temperature of the second reaction is 160-250 ℃.

2. The method of claim 1, wherein the source of manganous is capable of ionizing Mn to form a source of manganous birnessite²⁺The water-soluble compound of (1); preferably at least one of manganese sulfate, manganese nitrate, manganese chloride and manganese acetate, or manganese ore leachate;

preferably, the divalent manganese source is an aqueous solution of Mn²⁺The molar concentration of (A) is 0.1-2M.

3. The method of claim 1, wherein the permanganate A and the permanganate B are capable of ionizing to form MnO₄The water-soluble salt of (a) is preferably at least one of potassium permanganate, sodium permanganate, and magnesium permanganate.

4. The method for preparing the nanoporous spherical birnessite according to claim 1, wherein the molar concentration of the permanganate A aqueous solution is 0.1-0.5M;

the molar concentration of the permanganate B aqueous solution is 0.1-1.5M.

5. The method for preparing the nanoporous spherical birnessite according to claim 1, wherein in the step (1), the dropping rate of the permanganate A aqueous solution is 0.001 to 0.005 moL/min.

6. The method for preparing the nano-porous spherical birnessite according to claim 1, wherein in the step (1), the stirring speed in the first reaction process is 50-300 r/min.

7. The method for preparing the nano-porous spherical birnessite according to claim 1, wherein in the step (1), the reaction time is 0.5-3 hours.

8. The method for preparing the nano-porous spherical birnessite according to claim 1, wherein the reaction time in the step (2) is 12-48 hours.

9. The nano-porous spherical birnessite prepared by the preparation method of any one of claims 1 to 8, which is characterized in that birnessite nanosheets are staggered to form a porous nano-sized spherical material.

10. Application of the nano-porous spherical birnessite prepared by the preparation method according to any one of claims 1 to 8 in catalytic degradation of formaldehyde.