A ferrite nanocage superstructure material, its preparation method and application

Abstract

The present invention discloses a ferrite nanocage superstructure material, a preparation method thereof and an application thereof. The preparation method comprises the following steps: preparing a zinc-iron Prussian blue nanocubic block precursor material, dispersing the same in deionized water, standing and aging at 15-45 °C for 24-120 h to obtain zinc-iron Prussian blue nanocages; dispersing the same in dilute hydrochloric acid, adding a metal salt, stirring evenly, standing and reacting at 50-120 °C for 6-48 h, filtering, washing, drying, and then annealing at 300-500 °C for 1-5 h. The present invention uses zinc-iron Prussian blue nanocubes as a precursor, obtains zinc-iron Prussian blue nanocages through aging, and prepares a ferrite nanocage superstructure material through ion exchange, which has excellent gas-sensing characteristics.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterials, and particularly relates to a ferrite nanocage superstructure material, a preparation method thereof, and an application thereof. Background Art

[0002] Nanomaterials with complex structures, especially porous or hollow superstructure nanomaterials, have always been widely pursued by scientific researchers. Advantages such as large specific surface area, high porosity, and small grain size often endow these materials with unique physical and chemical properties. The large specific surface area provides abundant active sites for surface-related reactions, including adsorption / desorption, heterogeneous catalysis, and surface redox reactions, etc. The high porosity and open framework structure can better accommodate mechanical strain, load guest substances, and promote mass transfer, which is very helpful for drug loading, cancer targeted therapy, etc. The solid-state diffusion distance (i.e., wall thickness or shell thickness) in porous and hollow nanomaterials is significantly smaller than the size of the corresponding solid materials, breaking through the diffusion limitations in many non-porous materials. The confinement ability of pores and cavities also shows great promise in some applications. More importantly, the special physical and chemical properties related to the spatial structure in open-type superstructure nanomaterials do not exist in their corresponding solid materials.

[0003] Fine and reasonable design of complex nanosuprastructures can endow materials with many properties required for current and emerging applications. Coordination polymers (CPs) have become a rapidly developing research field in the past two decades due to their unique and excellent properties, such as tunable chemical composition, high porosity, and large specific surface area. Prussian blue (PB) and Prussian blue analogues (PBAs) as typical coordination polymers have certain thermal and chemical stabilities, and can be easily converted into corresponding inorganic functional materials by pyrolysis in an inert gas atmosphere or by chemical reaction with required reagents. Especially for metal oxide nanomaterials derived from PBAs, they can not only maintain the morphology of the precursor, but also have adjustable chemical composition, showing obvious advantages in the field of gas sensing. For example, Guo and his colleagues etched PB cubes with sodium hydroxide solution using PVP as a protective agent to obtain PB hollow nanoboxes, and further annealed them in air to obtain Fe2O3 nanoboxes and achieved satisfactory H2S gas sensing performance; Xu et al. synthesized an octahedral structure of Zn-Fe PBAs using PVP as a template agent, and prepared ZnO / ZnFe2O4 hollow nanocages from this as a precursor for the detection of acetone gas; Huang's team used Zn-Fe PBAs nanocubes as a precursor, and prepared a cage-in-cube ZnO / ZnFe2O4 superstructure rich in oxygen vacancies by combining a structure-induced anisotropic etching / anion exchange strategy with an annealing process, and this material can realize the detection of low-temperature trace H2S gas.

[0004] Ferrites (MFe2O4) with a spinel structure have great potential for development in the field of gas sensing due to their unique crystal structure and physical and chemical properties. In ferrites, some or all of the octahedral and tetrahedral coordination positions are occupied by M 2+ and Fe 3 + cations to form a normal spinel or inverse spinel structure. Compared with single metal oxides, the variable multivalent cations and controllable components in spinel ferrites have significant advantages in improving gas sensing performance.

[0005] Fe, Co, Ni, Cu, and Zn are elements in the same period with adjacent atomic numbers. However, the five transition cations have different valence states, occupy the central positions of octahedrons / tetrahedrons, and have different gas adsorption and catalytic properties. Therefore, spinel ferrites (MFe2O4) with different M 2+ (M = Co, Ni, Cu, and Zn) exhibit different n / p-type semiconductor properties, different band gaps, and oxygen adsorption capacities. It is necessary to systematically study the relationship between the cation substitution effect and the gas sensing performance of ferrite materials. In addition, traditional ferrites are mostly solid or hollow polyhedron structures, and open superstructure ferrites with a higher specific surface area may provide unexpected advantages for various applications including gas sensing.

[0006] However, the controllable construction of open superstructure ferrites still faces great challenges. To better utilize the inherent properties of these superstructure ferrites and endow them with new functions, more research work is needed to develop new and simple synthesis strategies. Summary of the Invention

[0007] The purpose of the present invention is to provide a ferrite nanocage superstructure material, its preparation method and application; by regulating the micro-nano structure of the composite material, an open cage nanostructure is obtained to improve the gas sensing characteristics.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A preparation method of a ferrite nanocage superstructure material, the preparation method comprising the following steps:

[0010] (1) Dissolve a zinc salt in dilute hydrochloric acid, add an aqueous solution of potassium ferrocyanide thereto, stir until the solution becomes a yellow suspension, stand and age at 10 - 95 °C for 2 - 36 h, filter, wash, and dry to obtain a zinc-iron Prussian blue nanocubic block precursor material, and then disperse it in deionized water, stand and age at 15 - 45 °C for 24 - 120 h, filter, wash, and dry to obtain zinc-iron Prussian blue nanocages;

[0011] (2) Dispersing zinc-iron Prussian blue nanocages in a dilute hydrochloric acid solution, adding metal salt, stirring evenly, standing and reacting at 50-120° C. for 6-48 hours, filtering, washing, and drying, and then annealing at 300-500° C. for 1-5 hours to obtain a Zn-MFe2O4 nanocage superstructure material, wherein M is one of Fe, Co, Ni, Cu, and Zn.

[0012] In step (1), the zinc salt is one or more of zinc chloride, zinc sulfate, zinc acetate and zinc nitrate.

[0013] In step (1), the molar ratio of potassium ferrocyanide to zinc salt is 1:1.

[0014] In step (1), the concentration of the potassium ferrocyanide aqueous solution is 0.1-2.0 mol / L; the concentration of the zinc salt in dilute hydrochloric acid is 0.1-2.0 mol / L; and the concentration of the dilute hydrochloric acid is 0.1-1.2 mol / L.

[0015] In step (2), the metal salt is any one of ferrous sulfate, ferrous chloride, ferrous nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, nickel sulfate, nickel chloride, nickel nitrate, cupric sulfate, cupric chloride, cupric nitrate, zinc sulfate, zinc chloride, and zinc nitrate.

[0016] In step (2), the ratio of the zinc-iron Prussian blue nanocage to the metal salt is 0.1-0.5 g: 0.5-1.5 mmol.

[0017] In step (2), the concentration of the zinc-iron Prussian blue nanocage in dilute hydrochloric acid is 1.0-5.0 mg / mL; the concentration of the dilute hydrochloric acid is 0.1-1.2 M.

[0018] In step (2), the static reaction condition is preferably 50-70° C. for 8-12 h.

[0019] In step (2), the annealing condition is preferably 320-400° C. annealing for 2-3 h.

[0020] In step (2), the heating rate to the specified annealing temperature is 1 to 5°C / min, preferably 1 to 2°C / min.

[0021] The invention also provides a ferrite nano cage superstructure material prepared by the preparation method.

[0022] The present invention also provides the application of the ferrite nanocage superstructure material in a gas sensor, wherein Zn-Fe3O4, Zn-CoFe2O4, and Zn-CuFe2O4 have a high sensitivity response to hydrogen sulfide, and Zn-NiFe2O4 has a high sensitivity response to nitrogen dioxide gas.

[0023] In the preparation method disclosed by the present invention, zinc - iron Prussian blue nanocubes, which are easy to prepare, are used as precursors. Through aging, zinc - iron Prussian blue nanocages are obtained. After ion exchange, zinc - iron Prussian blue analog nanocages are obtained. After high - temperature calcination, ferrite nanocage superstructure materials are obtained.

[0024] Some of the chemical reaction formulas involved in the reaction process are shown as follows:

[0025] 3Zn 2+ +3[Fe(CN)6] 3- →Zn3[Fe(CN)6]2(1)

[0026] 4Fe 2+ +O2+4H + →4Fe 3+ +2 H2O(2)

[0027] 2Fe 3+ +6Fe 2+ +3Zn3[Fe(CN)6]2→2Fe4[Fe(CN)6]3+9Zn 2+ (3)

[0028] 3Co 2+ +2[Fe(CN)6] 3- +H2O→Co3[Fe(CN)6]2(4)

[0029] 3Ni 2+ +2[Fe(CN)6] 3- +10 H2O→Ni3[Fe(CN)6]2·10 H2O(5)

[0030] 10Cu 2+ +7[Fe(CN)6] 3- +19 H2O→10Cu[Fe(CN)6] 0.7 ·1.9 H2O(6)

[0031] In the present invention, Ostwald ripening strategy is adopted to controllably prepare Zn-Fe PBAs nanocages with special morphological structures without a template agent / protective agent, and a series of M-Fe PBAs (M = Fe, Co, Ni, Cu, Zn) nanocage superstructures are prepared through a cation exchange strategy. Specifically, the density distribution of individual Zn-Fe PBAs nanocubes is changed through the Ostwald ripening mechanism to generate density defects in their central parts, and a passivation layer is formed on their surfaces and edges. By controlling the ripening time, Zn-Fe PBAs nanoboxes and nanocages can be controllably prepared. In addition, combined with the unique structural properties of Zn-Fe PBAs nanocages, a series of M-Fe PBAs (M = Fe, Co, Ni, Cu, Zn) open nanocage superstructures are successfully prepared through a metal cation exchange strategy.

[0032] Compared with the previously reported nanocages, this strategy can simply, greenly and controllably prepare a series of Zn-MFe2O4 nanocages (M = Fe, Co, Ni, Cu, Zn) without complex preparation procedures. After annealing in air, the M-Fe PBAs nanocage superstructures are further transformed into the corresponding metal oxides, and their morphological structures are well maintained. In terms of gas sensing performance, the completely open space structure can generate more defects, which is not only conducive to exposing more active sites, but also conducive to the adsorption and diffusion of target gases on the material surface. The ultra-thin wall thickness also shortens the migration distance of carriers inside the nanocage superstructure. These advantages endow these metal oxide nanocage superstructures with excellent gas sensing performance. Brief Description of the Drawings

[0033] Figure 1 SEM image of the zinc-iron Prussian blue nanocube precursor prepared in Example 1;

[0034] Figure 2 XRD pattern of the zinc-iron Prussian blue nanocube precursor prepared in Example 1;

[0035] Figure 3 SEM image of the zinc-iron Prussian blue nanocage prepared in Example 1;

[0036] Figure 4 SEM image of the Prussian blue analogue nanocage prepared in Example 1;

[0037] Figure 5 SEM image of the Zn-Fe3O4 nanocage superstructure material prepared in Example 1;

[0038] Figure 6 XRD pattern of the Zn-Fe3O4 nanocage superstructure material prepared in Example 1;

[0039] Figure 7 EDS diagram of the Zn-Fe3O4 nanocage superstructure material prepared in Example 1;

[0040] Figure 8 SEM image of the Prussian blue analogue nanocage prepared in Example 2;

[0041] Figure 9 SEM image of the Zn-CoFe2O4 nanocage superstructure material prepared in Example 2;

[0042] Figure 10 XRD pattern of the Zn-CoFe2O4 nanocage superstructure material prepared in Example 2;

[0043] Figure 11 Element distribution map of the Zn-CoFe2O4 nanocage superstructure material prepared in Example 2;

[0044] Figure 12 EDS diagram of the Zn-CoFe2O4 nanocage superstructure material prepared in Example 2;

[0045] Figure 13 SEM image of the Prussian blue analogue nanocage prepared in Example 3;

[0046] Figure 14 SEM image of the Zn-NiFe2O4 nanocage superstructure material prepared in Example 3;

[0047] Figure 15 XRD pattern of the Zn-NiFe2O4 nanocage superstructure material prepared in Example 3;

[0048] Figure 16 EDS diagram of the Zn-NiFe2O4 nanocage superstructure material prepared in Example 3;

[0049] Figure 17 SEM image of the Prussian blue analogue nanocage prepared in Example 4;

[0050] Figure 18 SEM image of the Zn-CuFe2O4 nanocage superstructure material prepared in Example 4;

[0051] Figure 19 XRD pattern of the Zn-CuFe2O4 nanocage superstructure material prepared in Example 4;

[0052] Figure 20 EDS diagram of the Zn-CuFe2O4 nanocage superstructure material prepared in Example 4;

[0053] Figure 21The response sensitivities of the Zn-Fe3O4, Zn-CoFe2O4, Zn-NiFe2O4, and Zn-CuFe2O4 nanocage superstructure materials sensors prepared for the examples to 10 ppm H2S and 100 ppm of different kinds of VOCs (including ethanol, isopropanol, acetone, benzene, toluene, n-butanol, methanol, ammonia, etc.) at a working temperature of 140 °C. Detailed implementation manners

[0054] The present invention will be described in detail below in conjunction with the examples.

[0055] The reaction vessels used in step (2) of each example are all beakers, and the mouths of the beakers are covered with plastic wrap during heating.

[0056] Example 1

[0057] A preparation method of a Zn-Fe3O4 nanocage superstructure material, comprising the following steps:

[0058] (1) Dissolve potassium ferricyanide in deionized water to prepare a 1000 mL, 0.1 M potassium ferricyanide solution; dissolve zinc chloride in dilute hydrochloric acid to prepare a 1000 mL, 0.1 M zinc chloride solution; under magnetic stirring at a rotation speed of 120 rpm, add the above potassium ferricyanide solution to the zinc chloride solution, and then continue to stir at room temperature for 30 min to obtain a mixed suspension. Let it stand and age at 80 °C for 12 h to obtain a yellow precipitate. Filter and wash the yellow precipitate, and dry it at 80 °C for 8 h to obtain a zinc ferroprussiate nanocube precursor; its SEM image is as Figure 1 shown. It can be seen from the figure that it is a uniform cubic block; its XRD pattern is as Figure 2 shown. The diffraction pattern proves that the prepared zinc ferroprussiate has strong peaks and high purity.

[0059] The obtained zinc ferroprussiate nanocubes are left to stand and age in deionized water for 3 days, and then washed thoroughly with absolute ethanol and dried. The obtained product is the zinc ferroprussiate nanocage, and its SEM image is as Figure 3 shown.

[0060] (2) Take 0.2 g of zinc ferroprussiate nanocage and disperse it in 100 mL of 0.1 M dilute hydrochloric acid. Add 1 mmol of FeCl2 and stir vigorously for 30 min, then transfer the beaker to an 80 °C oven and keep it warm for 8 h. Wash the blue precipitate thoroughly with deionized water and ethanol and dry it to obtain a Prussian blue analogue nanocage, and its SEM image is as Figure 4 shown.

[0061] (3) Transfer the obtained Prussian blue analogue nanocage sample to a muffle furnace, heat it to 500 °C at a heating and cooling rate of 1 °C / min and anneal for 1 h to obtain a Zn-Fe3O4 open nanocage superstructure material. Its SEM image is as shown in Figure 5 shown, and its XRD pattern is as shown in Figure 6 shown. It can be seen that the product is zinc-doped Fe3O4. The EDS pattern of the product is as shown in Figure 7 shown. It can be seen that the product contains zinc, iron and oxygen elements, and the silicon element comes from the silicon substrate.

[0062] Example 2

[0063] A preparation method of a Zn-CoFe2O4 open nanocage superstructure composite material includes the following steps:

[0064] (1) The same as step (1) in Example 1.

[0065] (2) Take 0.2 g of zinc-iron Prussian blue nanocages and disperse them in 100 mL of dilute hydrochloric acid with a concentration of 0.6 M. Add 1 mmol of CoCl2, stir vigorously for 30 min, and then transfer it to an 80 °C oven and keep it warm for 8 h. Wash the blue precipitate thoroughly with deionized water and ethanol and dry it to obtain Prussian blue analogue nanocages. Its SEM image is as shown in Figure 8 shown.

[0066] (2) Transfer the obtained Prussian blue analogue nanocage sample to a muffle furnace, heat it to 400 °C at a heating and cooling rate of 2 °C / min and anneal for 2 h to obtain a Zn-CoFe2O4 open nanocage superstructure. Its SEM image is as shown in Figure 9 shown, and its XRD pattern is as shown in Figure 10 shown. The element distribution map and EDS results of the prepared Zn-CoFe2O4 nanocage superstructure material are as shown in Figure 11 and Figure 12 shown respectively. It can be seen that the product contains zinc, cobalt, iron and oxygen elements, and the above elements are evenly distributed on the nanocages. The silicon element comes from the silicon substrate.

[0067] Example 3

[0068] A preparation method of a Zn-NiFe2O4 open nanocage superstructure composite material includes the following steps:

[0069] (1) The same as step (1) in Example 1.

[0070] (2) Take 0.2 g of zinc-iron Prussian blue nanocages and disperse them in 100 mL of dilute hydrochloric acid with a concentration of 0.9 M. Add 1 mmol of NiCl2, stir vigorously for 30 min, and then transfer it to an 80 °C oven and keep it warm for 8 h. Wash the blue precipitate thoroughly with deionized water and ethanol and dry it to obtain Prussian blue analogue nanocages. Its SEM image is as shown inFigure 13 as shown

[0071] (3) Transfer the obtained Prussian blue analogue nanocage sample to a muffle furnace, heat it to 350 °C at a heating and cooling rate of 2 °C / min and anneal for 3 h to obtain a product of Zn-NiFe2O4 open nanocage superstructure material. Its SEM image is as Figure 14 shown. The XRD pattern of the product is as Figure 15 shown, and its EDS pattern is as Figure 16 shown. It can be seen that the product contains zinc, iron, nickel and oxygen elements, and the product is zinc-doped NiFe2O4. The silicon element in the EDS pattern comes from the silicon substrate.

[0072] Example 4

[0073] A preparation method of a Zn-CuFe2O4 open nanocage superstructure composite material includes the following steps:

[0074] (1) The same as step (1) in Example 1.

[0075] (2) Take 0.2 g of zinc-iron Prussian blue nanocages and disperse them in 100 mL of dilute hydrochloric acid with a concentration of 1.2 M. Add 1 mmol of CuCl2 and stir vigorously for 30 min, then transfer it to an 80 °C oven and keep it warm for 8 h. Wash the blue precipitate thoroughly with deionized water and ethanol and dry it to obtain Prussian blue analogue nanocages. Its SEM image is as Figure 17 shown.

[0076] (3) Transfer the obtained Prussian blue analogue nanocage sample to a muffle furnace, heat it to 300 °C at a heating and cooling rate of 5 °C / min and anneal for 5 h to obtain a product of Zn-CuFe2O4 open nanocage superstructure material. Its SEM image is as Figure 18 shown. The XRD pattern of the product is as Figure 19 shown, and its EDS pattern is as Figure 20 shown. It can be seen that the product contains zinc, iron, copper and oxygen elements, and it can be seen that the product is zinc-doped CuFe2O4. The silicon element in the EDS pattern comes from the silicon substrate.

[0077] Application Example 1

[0078] Application of ferrite open nanocage superstructure composite material in gas sensors

[0079] Disperse the ferrite open nanocage superstructure composites prepared in Examples 1-4 in absolute ethanol, and then evenly coat them on a ceramic tube with electrodes to fabricate a gas sensor. Dry it at 50 °C for 2 h, and then heat-treat it at 200 °C for 2 h. Then, put a small nickel-chromium alloy coil into the tube as a heater to provide the working temperature for the sensor. Age the sensor at 300 °C for 48 h, and then test different volatile organic gases at the working temperature. The specific test operation steps are as follows: Inject a certain amount of organic vapor into the sensor test chamber with a syringe. Wait for about 2 minutes. After the response value output by the sensor stabilizes, then introduce dry air into the test chamber. The response output by the sensor gradually recovers. Use an electrochemical workstation and a computer to test and record the output response values of the sensor in dry air and in the presence of the target gas. The gas response sensitivity of the sensor is defined as S = R a / R g (for reducing gases), where R a is the resistance of the sensor in dry air, and R g is the resistance of the sensor in the test gas.

[0080] Performance test studies show that the prepared ferrite open nanocage superstructure composites have good sensitive responses to common toxic and harmful organic gases in the air. As Figure 21 shown, it can be seen from the figure that compared with different types of VOCs (including ethanol, isopropanol, acetone, benzene, toluene, n-butanol, methanol, and ammonia, etc.), the ferrite open nanocage superstructure materials Zn-Fe3O4, Zn-CoFe2O4, and Zn-CuFe2O4 prepared by this method show good selectivity to hydrogen sulfide, and the Zn-NiFe2O4 prepared by this method shows good selectivity to nitrogen dioxide.

[0081] The above detailed description of a ferrite nanocage superstructure material and its preparation method and application with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be listed within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing a ferrite nanocage superstructure material, characterized in that: The preparation method comprises the following steps: (1) Dissolve zinc salt in dilute hydrochloric acid, add potassium ferrocyanide aqueous solution, stir until the solution becomes a yellow suspension, stand at 10-95 °C for 2-36 h, filter, wash, and dry to obtain zinc iron Prussian blue nanocube precursor material, and then disperse it in deionized water, stand at 15-45 °C for 24-120 h, filter, wash, and dry to obtain zinc iron Prussian blue nanocage; (2) Disperse the zinc iron Prussian blue nanocages in a dilute hydrochloric acid solution, add metal salt, stir evenly, and react at 50-120 °C for 6-48 h. After ion exchange, zinc iron Prussian blue analog nanocages are obtained. After filtering, washing, and drying, and then annealing at 300-500 °C for 1-5 h, Zn-MFe2O4 nanocage superstructure materials are obtained, wherein M is one of Fe, Co, Ni, and Cu.

2. The preparation method according to claim 1, characterized in that: In step (1), the zinc salt is one or more of zinc chloride, zinc sulfate, zinc acetate and zinc nitrate.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the molar ratio of potassium ferrocyanide to zinc salt is 1:

1.

4. The preparation method according to claim 1 or 2, characterized in that: In step (1), the concentration of the potassium ferrocyanide aqueous solution is 0.1-2.0 mol / L; the concentration of the zinc salt in dilute hydrochloric acid is 0.1-2.0 mol / L; and the concentration of the dilute hydrochloric acid is 0.1-1.2 mol / L.

5. The preparation method according to claim 1, characterized in that: In step (2), the metal salt is any one of ferrous sulfate, ferrous chloride, ferrous nitrate, cobalt sulfate, cobalt chloride, cobalt nitrate, nickel sulfate, nickel chloride, nickel nitrate, copper sulfate, copper chloride, copper nitrate, zinc sulfate, zinc chloride, and zinc nitrate.

6. The preparation method according to claim 1, 2 or 5, characterized in that: In step (2), the ratio of the zinc iron Prussian blue nanocage to the metal salt is 0.1-0.5 g: 0.5-1.5 mmol.

7. The preparation method according to claim 1, 2 or 5, characterized in that: In step (2), the concentration of the zinc-iron Prussian blue nanocage in dilute hydrochloric acid is 1.0-5.0 mg / mL; the concentration of the dilute hydrochloric acid is 0.1-1.2 M.

8. The preparation method according to claim 1, 2 or 5, characterized in that: In step (2), the heating rate to the specified annealing temperature is 1-5 °C / min.

9. The ferrite nanocage superstructure material prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the ferrite nanocage superstructure material as claimed in claim 9 in a gas sensor.

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