A preparation method and application of a mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material

Abstract

The present invention discloses a preparation method and application of a mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material. The preparation method first prepares mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres, and then uses these carbon spheres to prepare mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material. The operation is simple, the cost is low, and no complex reactions and reagents are required. The composite material prepared by this method has uniform pore size, symmetrical particles, and a large specific surface area, and has excellent visible light absorption ability and photo-piezoelectric catalytic activity, and can be preferably applied to fields such as photo-piezoelectric catalytic carbon dioxide reduction and pollutant degradation. Such as photo-piezoelectric catalytic reduction of CO2 to CO, degradation of plastics, water splitting for hydrogen production, catalytic generation of H2O2 solution, purification of polluted water, etc.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of a ferroelectric material. Background Art

[0002] The continuous utilization and development of coal, petroleum, and natural gas have disrupted the carbon cycle in nature, causing serious environmental pollution problems. Developing and utilizing efficient and green catalytic technologies to mitigate global warming has become an urgent need. Among numerous catalytic technologies, semiconductor photocatalytic technology has been widely studied due to its green energy and can reduce CO2 to carbon-containing fuels. However, the high recombination rate of photo-generated carriers limits its catalytic ability and cannot meet practical applications. In recent years, it has been reported that the piezoelectric effect is used to improve the separation efficiency of photo-generated charges. By using mechanical energy to induce an internal built-in electric field in the material, the photo-generated carriers are driven to move directionally, promoting the separation of photo-generated carriers and thus improving the catalytic efficiency. However, the low mechanical energy conversion efficiency has become a new problem. Therefore, it is of great significance to explore the synthesis of piezoelectric photocatalysts with high carrier separation efficiency and energy conversion efficiency.

[0003] Many ferroelectric semiconductor materials such as BaTiO3, Bi4Ti3O 12 and LiNbO3, etc. have been reported to exhibit certain photocatalytic activities and also show good piezoelectric properties. To further improve the charge separation efficiency of the catalyst, many modification methods have been proposed by researchers, such as surface engineering, heterojunction strategies, loading of co-catalysts, etc., all of which form a local electric field at the interface to drive the charges to move directionally. At the same time, the reactive sites also greatly affect the photocatalytic reaction activity. It has been reported that the use of a mixture of carbon materials and ferroelectric semiconductors can significantly improve the photo-piezoelectric catalytic ability of the material. However, most of the current reports are simple physical mixtures, which not only have uncontrollable morphologies but also often have the disadvantages of low specific surface area and weak adsorption ability. Therefore, how to design a composite ferroelectric material with a large specific surface area, rich active sites, and high photo-piezoelectric properties and apply it to the field of piezoelectric catalysis is very meaningful for research. Summary of the Invention

[0004] Object of the Invention: Aiming at the above-mentioned existing technologies, a preparation method and application of a mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material are proposed. The prepared ferroelectric material has a large specific surface area, uniform pore size, rich active sites, and high photo-piezoelectric properties.

[0005] Technical Solution: A preparation method of a mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material, comprising:

[0006] S1: Prepare mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres, including: adding a template, an amine source, and a polymerization initiator into deionized water according to a stoichiometric ratio, stirring and mixing them, and carbonizing the obtained sample in a tubular furnace; etching the carbonized product with an alkali solution, and washing, centrifuging, and drying the etched product to obtain mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres;

[0007] S2: Prepare mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric materials, including: dispersing a titanium source and a bismuth source in deionized water according to a stoichiometric ratio, successively adding mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres and an alkali solution, and magnetically stirring evenly, pouring the obtained solution into a hydrothermal autoclave for heating reaction, and washing, centrifuging, and drying the reaction product to obtain the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric materials.

[0008] Further, in the step S1, the stirring rate is 1800 - 2200 r / min, and the heating temperature of the tubular furnace is 800 - 1000 °C.

[0009] Further, in the step S1, the alkali solution is sodium hydroxide solution or calcium hydroxide solution, with a concentration of 4 - 6 mol / L, and the etching time is 12 - 15 h.

[0010] Further, in the step S2, the temperature of the heating reaction is 160 - 240 °C, and the reaction time is 12 - 48 h.

[0011] The application of the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric materials in photo-piezoelectrocatalysis.

[0012] Further, the photo-piezoelectrocatalysis includes catalyzing the reduction of CO2 to CO, nitrogen fixation for ammonia synthesis, water splitting for hydrogen production, catalyzing the generation of H2O2 solution, and purifying polluted water.

[0013] Beneficial effects: 1. The pomegranate-shaped mesoporous Bi4Ti3O 12 @MNC ferroelectric materials prepared by the present invention have excellent piezo-photocatalytic performance, especially high piezo-reduction performance for CO2.

[0014] 2. The pomegranate-shaped mesoporous Bi4Ti3O 12 @MNC ferroelectric materials synthesized by the present invention through a solvothermal method have low cost, do not require complex reaction processes and reagents, have a large specific surface area of reactants, uniform pore sizes, rich active sites, and high stability.

[0015] 3. The present invention first uses the uniform mesopores of carbon spheres to confine the synthesis and load bismuth titanate nanoparticles to form pomegranate-shaped Bi4Ti3O 12@MNC restricts the agglomeration effect of bismuth titanate during the synthesis process, hinders its formation into flakes, and uniformly disperses it inside and on the surface of carbon spheres.

[0016] 4. The present invention uses an alkaline solution to replace the acidic solution for etching carbon spheres, thereby adjusting the pH to facilitate the formation of the composite material in the second step, so as to achieve the purpose of precisely controlling the synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the flowchart of the preparation method of the present invention;

[0018] Figure 2 is the XRD pattern of the ferroelectric materials obtained in Example 1, Example 8, and Example 9;

[0019] Figure 3 is the XRD pattern of the ferroelectric materials obtained in Example 1 and the comparative example;

[0020] Figure 4 is the SEM image of the ferroelectric materials obtained in Example 1 and the comparative example;

[0021] Figure 5 is the CO2 reduction performance graph of the ferroelectric materials obtained in Example 1 and the comparative example;

[0022] Figure 6 is the morphology diagram of the polyaniline obtained by stirring in step S1 of Example 1, Example 2, and Example 3;

[0023] Figure 7 is the morphology diagram of the carbon spheres obtained by calcination in step S1 of Example 1, Example 4, and Example 5;

[0024] Figure 8 is the morphology diagram of the final composite material obtained in step S2 of Example 1, Example 6, and Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following further explains the present invention with reference to the accompanying drawings.

[0026] The performance evaluation methods of Bi4Ti3O 12 @MNC, Bi4Ti3O 12 +MNC, Bi4Ti3O 12 in the following examples and comparative examples are as follows:

[0027] 1. Phase evaluation method:

[0028] X-ray diffraction (XRD): For the prepared Bi4Ti3O 12 @MNC, Bi4Ti3O 12 +MNC, Bi4Ti3O 12The crystal structure of the material was analyzed on a Bruker D8 Advance series wide-angle X-ray diffractometer in Germany, with a scanning speed of 5° / min and a scanning range of 10° to 80°.

[0029] 2. Microscopic morphology evaluation method:

[0030] Scanning electron microscopy (SEM): The prepared Bi4Ti3O 12 @MNC, Bi4Ti3O 12 +MNC, Bi4Ti3O 12 The material was tested on a JEOL JSM-IT300 series scanning electron microscope in Japan, with an acceleration voltage of 5 - 20 kV.

[0031] 3. CO2 piezo-photocatalytic reduction performance evaluation method:

[0032] Taking the piezo-photocatalytic reduction of CO2 reaction of Bi4Ti3O 12 @MNC as an example, the specific process is as follows: First, add 100 ml of deionized water to a quartz reactor, and then add 10 mg of Bi4Ti3O 12 @MNC material. The reaction system was evacuated for 30 min by a 2XZ-2B rotary vane vacuum pump and filled with pure CO2 gas to atmospheric pressure, placed in a KQ-400DE digital control ultrasonic cleaner, and irradiated under a UV light source. CO2 reduction experimental conditions: Under ultrasonic conditions of 70 kHz and 260 W, samples were taken by needle every 30 min for a total of 4 times (i.e., the reaction was 2 h), and the temperature was kept at 25 ± 5 °C during the reaction. The obtained gas samples were analyzed by a GC-7920 gas chromatograph for the peak areas of products such as CO to judge the CO2 reduction product situation. The CO2 piezo-photocatalytic reduction performance evaluation methods of Bi4Ti3O 12 +MNC and Bi4Ti3O 12 are the same as above.

[0033] Example 1

[0034] As Figure 1 shown, a preparation method of a mesoporous pomegranate-like Bi4Ti3O 12 @MNC ferroelectric material includes:

[0035] S1: Prepare mesoporous pomegranate-like nitrogen-doped mesoporous carbon spheres.

[0036] At room temperature, silica, aniline, and ammonium persulfate were added to deionized water in a stoichiometric ratio of 2:1:4 and stirred and mixed at a stirring rate of 2000 r / min for 24 h; then the obtained sample was carbonized in a tubular furnace at a heating temperature of 900 °C for 2 h; the carbonized product was etched with a 5 mol / L sodium hydroxide solution for 12 h, and the etched product was washed, centrifuged, and dried to obtain mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres, abbreviated as MNC.

[0037] S2: Using the mesoporous pomegranate-shaped nitrogen-doped mesoporous carbon spheres prepared in step S1 to prepare mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material.

[0038] At room temperature, first, 0.1902 g of Bi(NO3)3·5H2O, 0.1100 g of C 16 H 36 O4Ti, and 0.1000 g of MNC were dispersed in 30 mL of deionized water; secondly, 4.800 g of NaOH was added and magnetically stirred for 1 h; finally, the obtained suspension was transferred to a stainless-steel reaction kettle lined with polytetrafluoroethylene and heated for reaction at a reaction temperature of 160 °C for 30 h; after the reaction, it was washed and centrifuged 3 times with deionized water and dried at 60 °C for 12 h to obtain mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material.

[0039] The pomegranate-shaped mesoporous Bi4Ti3O prepared by the above method 12 @MNC ferroelectric material in the application in the catalytic field, including piezoelectric photocatalytic reduction of CO2 to CO, nitrogen fixation for ammonia synthesis, water splitting for hydrogen production, catalytic production of H2O2 solution, purification of polluted water, etc.

[0040] The mesoporous pomegranate-shaped Bi4Ti3O of the present invention 12 @MNC ferroelectric material's piezoelectric photocatalytic principle is: The crystal structure of the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material is non-centrosymmetric. When subjected to external stress, it can convert mechanical energy into chemical energy. The specific principle is as follows: Under ultrasonic vibration, the quenching of periodic cavitation bubbles will generate 10 8 Pa pressure and act on the material surface. The material surface is prone to bending deformation, and a polarization electric field will be generated inside and a potential difference will be formed. When light irradiates to excite valence band electrons to transition to the conduction band, the photo-generated carriers are driven by the polarization electric field to migrate directionally to the two-pole interface of the material, and are accelerated by the carbon sphere conduction to separate the carriers to the material surface, and thus redox reactions occur with substances such as CO2 adsorbed on the material to achieve the catalytic purpose.

[0041] Comparative Example 1

[0042] Preparation of Bismuth-based Layered Ferroelectric Bi4Ti3O 12 Material and Its Performance Test:

[0043] At room temperature, first disperse 1.9403 g of Bi(NO3)3·5H2O and 1.100 g of C 16 H 36 O4Ti in 30 mL of deionized water. Secondly, add 4.800 g of NaOH and stir magnetically for 1 h. Finally, transfer the obtained suspension to a stainless-steel reactor lined with polytetrafluoroethylene and react at 200 °C for 20 h. After the reaction, wash and centrifuge with deionized water 3 times, and dry at 60 °C for 12 h to obtain Bi4Ti3O 12 material.

[0044] Comparative Example 2

[0045] Preparation of Bi4Ti3O 12 and MNC Physical Mixture Material and Its Performance Test:

[0046] Put 100 mg of MNC and 100 mg of Bi4Ti3O from Comparative Example 1 12 into a quartz mortar and grind physically to obtain Bi4Ti3O 12 +MNC physical mixture material.

[0047] As Figure 3 shown, based on the XRD test characterization, Example 1, Comparative Example 1 and Comparative Example 2 all correspond to the standard card PDF﹟35-0795 of Bi4Ti3O 12 , indicating that Bi4Ti3O exists in the material 12 and is a pure phase without other impurities.

[0048] As Figure 4 shown, based on the SEM test characterization, it can be found that both Comparative Example 1 and Comparative Example 2 have nanoflower balls stacked by flaky nanosheets, with a thickness of about 15-50 nm. In addition, mesoporous spheres with a pore size of 18-22 nm are seen in Example 1 and Comparative Example 2. During the catalytic process, more CO2 will be adsorbed, and at the same time, more active sites will be exposed, which is beneficial for CO2 to fully contact the catalyst and undergo reduction reaction.

[0049] As Figure 5 shown, through the performance test of CO2 reduction test on the samples, it can be seen that after 2 h of ultrasonic action, the rate of Bi4Ti3O 12 @MNC for reducing CO2 to CO is 58.79 μmol g -1 h -1 ; the reduction product rate of Bi4Ti3O 12 is 5.41 μmol g -1 h -1 ; Bi4Ti3O12 The reduction product rate of +MNC is 35.06 μmol g -1 h -1 . Compared with Comparative Example 1 and Comparative Example 2, Example 1 of the present invention has excellent piezoelectric photocatalytic CO2 reduction performance.

[0050] Example 2

[0051] The difference from Example 1 is only that in step S1, the stirring rate is 1800 r / min.

[0052] Example 3

[0053] The difference from Example 1 is only that in step S1, the stirring rate is 2200 r / min.

[0054] Example 4

[0055] The difference from Example 1 is only that in step S1, the heating temperature of the tubular furnace is 800 °C.

[0056] Example 5

[0057] The difference from Example 1 is only that in step S1, the heating temperature of the tubular furnace is 1000 °C.

[0058] Example 6

[0059] The difference from Example 1 is only that in step S1, the concentration of the sodium hydroxide solution is 4 mol / L.

[0060] Example 7

[0061] The difference from Example 1 is only that in step S1, the concentration of the sodium hydroxide solution is 6 mol / L.

[0062] Example 8

[0063] The difference from Example 1 is only that in step S2, the heating reaction temperature is 180 °C and the reaction time is 48 h.

[0064] Example 9

[0065] The difference from Example 1 is only that in step S2, the heating reaction temperature is 240 °C and the reaction time is 12 h.

[0066] As Figure 2 shown, based on the XRD test characterization, for the composite materials prepared at different temperatures in Example 1, Example 8, and Example 9, it is found that the crystal form prepared at 200 °C is better, and there are other impurity peaks in Example 10. Therefore, the optimal preparation temperature is 200 °C.

[0067] As Figure 6As shown, only the stirring rate was changed in S1. By comparing Example 1, Example 2, and Example 3, it was found that the morphology of the obtained polyaniline had slight differences. The morphology of the polyaniline synthesized at a stirring rate of 2000 r / min was the best. In Example 2, local dispersion occurred in the spherical polyaniline at a slower stirring rate, and in Example 3, the spherical polyaniline agglomerated at a faster stirring rate. Therefore, the optimal stirring rate was 2000 r / min.

[0068] As Figure 7 shown, only the calcination temperature of the tubular furnace was changed in S1. By comparing Example 1, Example 4, and Example 5, it was found that the morphology of the calcined carbon spheres had slight differences. The morphology of the carbon spheres synthesized at a calcination temperature of 900 °C was the best. There were some impurities in the pomegranate-like carbon spheres in Example 4, and partial template shedding occurred in the pomegranate-like carbon spheres in Example 5. Therefore, the optimal calcination temperature was 900 °C.

[0069] As Figure 8 shown, only the concentration of the alkali solution was changed in S1. By comparing Example 1, Example 6, and Example 7, it was found that the morphology of the obtained composite material had significant differences. The bismuth titanate in the composite material was evenly dispersed and had a good morphology under etching with 5 mol / L. The amount of bismuth titanate in the carbon spheres was less in Example 6, and more bismuth titanate nanoparticles agglomerated in Example 7. Therefore, the optimal concentration of the alkali solution was 5 mol / L.

[0070] It should be noted that in step S1 of the preparation method of the present invention, the template is one of silica, mesoporous zeolite, and nanotube, and silica is the best; the amine source is one of aniline, ethylamine, ethylenediamine, and diethylamine, and aniline is the best; the polymerization initiator is one of ammonium persulfate, potassium persulfate, and hydrogen peroxide, and ammonium persulfate is the best; the alkali solution is one of sodium hydroxide and calcium hydroxide. In step S2, the bismuth source is selected from at least one of bismuth oxide, bismuth bromide, bismuth carbonate, bismuth nitrate pentahydrate, and bismuth phosphate, and bismuth nitrate pentahydrate is the best; the titanium source is selected from at least one of titanium dioxide, tetrabutyl titanate, barium metatitanate, and titanium sulfate, and tetrabutyl titanate is the best, and the alkali solution is one of sodium hydroxide and calcium hydroxide.

[0071] The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material, characterized in that, Including: S1: Prepare mesoporous pomegranate-like nitrogen-doped mesoporous carbon spheres, including: adding a template, an amine source, and a polymerization initiator into deionized water according to a stoichiometric ratio, stirring and mixing, and carbonizing the obtained sample in a tube furnace; etching the carbonized product with an alkali solution, and washing, centrifuging, and drying the etched product to obtain mesoporous pomegranate-like nitrogen-doped mesoporous carbon spheres; S2: Prepare mesoporous pomegranate-like Bi4Ti3O using the mesoporous pomegranate-like nitrogen-doped mesoporous carbon spheres 12 @MNC ferroelectric material, comprising: dispersing a titanium source and a bismuth source in deionized water according to a stoichiometric ratio, successively adding mesoporous pomegranate-like nitrogen-doped mesoporous carbon spheres and an alkali solution and stirring magnetically until homogeneous, pouring the resulting solution into a hydrothermal autoclave for heating reaction, and washing, centrifuging, and drying the reaction product to obtain the mesoporous pomegranate-like Bi4Ti3O 12 @MNC ferroelectric material; In S1, the template is silica, the amine source is aniline, and the polymerization initiator is ammonium persulfate.

2. The preparation method of the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material, characterized in that, In step S1, the stirring rate is 1800 - 2200 r / min, and the heating temperature of the tube furnace is 800 - 1000 °C.

3. The preparation method of the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material, characterized in that, In step S1, the alkali solution is a sodium hydroxide solution with a concentration of 4 - 6 mol / L, and the etching time is 12 - 15 h.

4. The preparation method of the mesoporous pomegranate-shaped Bi4Ti3O 12 @MNC ferroelectric material, characterized in that, In step S2, the temperature of the heating reaction is 160 - 240 °C, and the reaction time is 12 - 48 h.

5. Mesoporous pomegranate-shaped Bi4Ti3O prepared by the preparation method according to any one of claims 1-4 12 @MNC ferroelectric material.

6. The mesoporous pomegranate-shaped Bi4Ti3O prepared by the preparation method according to any one of claims 1-4 12 @MNC ferroelectric material for use in photo-piezoelectrocatalysis.

7. The application according to claim 6, wherein The photo-electrocatalysis includes catalyzing the reduction of CO2 to CO, nitrogen fixation for ammonia synthesis, water splitting for hydrogen production, catalyzing the generation of H2O2 solution, and purifying polluted water.

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