Method for regulating spinel type high-entropy oxide by using electrostatic spinning method

Abstract

The invention discloses a method for regulating spinel type high-entropy oxide by using an electrostatic spinning method. The preparation method is characterized by comprising the following steps: fully mixing metal sources with different concentrations, polyacrylonitrile and N, N-dimethylformamide to form a precursor solution, and then preparing the spinel type high-entropy oxide with a nanofiber structure through an electrostatic spinning method. The result shows that compared with a traditional high-entropy oxide preparation method, the electrostatic spinning method is beneficial to lowering the phase change temperature, and formation of the nanoscale high-entropy oxide is promoted. And the formed fiber is greatly influenced by the precursor solution, the final fiber state of the catalyst can be effectively regulated and controlled by changing the amount of the added total metal substance, and great difference is shown in the catalytic oxidation activity of ethyl acetate. The preparation process is simple, and the application value of the high-entropy oxide in the field of heterogeneous catalysis is improved.

Description

Technical Field

[0001] The invention belongs to the field of preparation of spinel high entropy oxides, and specifically relates to a spinel high entropy oxide nanofiber synthesized and regulated by an electrostatic spinning method. Background Art

[0002] Spinel oxides refer to a series of oxides with the general formula of AB2O4 structure, where oxygen ions are cubically densely packed, with A ions located at one-eighth of the tetrahedron and B ions located at one-half of the octahedron. From the perspective of crystal structure, spinel materials are thermodynamically and chemically stable. In industrial applications, they are usually used in the field of catalytic oxidation.

[0003] High entropy oxides (HEOs) are a new type of functional material, usually defined as multi-component oxides with five or more equimolar components forming a single phase. HEOs make it possible for five or more elements to be mixed in a single oxide lattice, which plays a great role in catalysis because multiple metal ions share a lattice site, resulting in a high degree of conformational disorder and inducing lattice distortion. A large number of studies have shown that surface defects formed by metal-metal interactions may help reduce the strength of metal-oxygen bonds, thereby promoting oxygen migration during catalytic oxidation. At the same time, catalytic oxidation technology is mainly affected by the activity of the catalyst, among which transition metals (Co, Mn, Fe, etc.) are low in cost, high in ion valence, and good in toxicity resistance, and are the main components of VOCs degradation catalysts. Selecting transition metals as the metal composition of HEOs is a relatively low-cost, high-efficiency method that provides multiple active sites.

[0004] Common preparation methods for HEOs include coprecipitation, hydrothermal and liquid phase combustion. Coprecipitation and sol-gel methods require complex process and control of parameters such as pH and temperature. In addition, these traditional methods usually require high-temperature calcination to prepare high-entropy oxides. The entropy driving force of the high phase transition temperature (such as 900-1600℃) leads to pore collapse, and agglomeration will inevitably occur, forming large micron-scale low surface area HEOs. In contrast, electrospinning technology allows the precursors of metal salts to be evenly and highly disordered. For polymer solutions, solid fibers will be produced under the action of droplet surface tension and electric field force, which is conducive to the crystallization of structurally disordered high entropy phases at lower temperatures. The properties of the electrospinning precursor solution have a significant impact on the electrospinning process and the properties of the final fiber. For example, viscosity affects the fluidity of the solution and the formation of fibers. Appropriate viscosity can ensure that the solution forms a stable jet in the electric field, thereby forming uniform fibers. Therefore, by changing the total metal concentration in the precursor solution, the ideal nanofibers can be obtained. However, the distribution of the metal on the fibers is chaotic and there are great differences in the fiber states, which affects the catalytic effect of the overall catalyst on ethyl acetate.

[0005] The present invention is based on spinel type (CoMnNiFeZn)O x The lattice distortion is medium to high, and the state of the synthesized fiber is regulated by electrospinning to develop (CoMnNiFeZn)O with excellent oxygen mobility. x The catalyst exhibited high catalytic oxidation performance with ethyl acetate. Summary of the invention

[0006] Based on the above problems, the purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for preparing spinel high entropy oxide by controlling the electrospinning method. This method can promote the formation of a single-phase structure of the catalyst at low temperature, and control the total metal concentration to make it a catalyst with very high catalytic oxidation ability. It has strong operability, low cost, and meets environmental requirements.

[0007] To achieve the purpose of the present invention, the technical solution specifically comprises the following steps:

[0008] 1) Prepare the precursor solution

[0009] Polyacrylonitrile and metal sources (cobalt nitrate, manganese nitrate, nickel nitrate, iron nitrate and zinc nitrate) are placed in a conical flask, and then dimethylformamide (DMF) solution is added and stirred to form a uniform colloid;

[0010] 2) The solution prepared in step 1) is sucked into a 20 mL syringe, and the solution in the syringe is connected to the electrospinning needle, the flow rate is set, and the nanofibers are prepared by electrospinning;

[0011] 3) The nanofibers prepared in step 2) are placed in a muffle furnace and calcined in an air atmosphere to obtain (CoMnNiFeZn)O x Nanofibers (high entropy oxide nanofibers).

[0012] The molecular weight of polyacrylonitrile in step 1) is 150,000.

[0013] The molar ratio of cobalt nitrate, manganese nitrate, nickel nitrate, iron nitrate and zinc nitrate in step 1) is n1:n2:n3:n4:n5=1:1:1:1:1.

[0014] The ratio of the mass g of polyacrylonitrile in step 1) to the volume mL of the solvent DMF is 0.1:1.

[0015] The stirring time in step 1) is 12 h.

[0016] The flow rate in step 2) was 0.5 mL / h.

[0017] In step 2), the electrospinning conditions are as follows: voltage 25 kV, temperature 40° C., receiving distance 16 cm, and continuous electrospinning time 40 h.

[0018] The calcination conditions in step 3) are: a heating rate of 5°C / min, a calcination constant temperature of 700°C, and a constant temperature calcination time of 2h.

[0019] The fiber structure (CoMnNiFeZn)O prepared by the above method of the present invention x .

[0020] The beneficial effects of the present invention are as follows: (1) the present invention can synthesize high entropy oxide (CoMnNiFeZn)O by electrospinning x .

[0021] (2) The present invention can change the fiber state of the final catalyst by changing the total amount of metal substances in the precursor solution during the synthesis process, and the process is simple.

[0022] (3) The present invention determines that the temperature for forming the spinel phase is 700°C, which promotes the catalyst to maintain a fibrous state, can effectively improve the catalytic oxidation performance of the catalyst and enhance its application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD spectrum of the sample prepared in Example 1.

[0024] Figure 2 These are SEM photos of the samples prepared in Example 1. In the figure, a-1 and a-2 are 1mmol-HEO fiber samples; b-1 and b-2 are 2mmol-HEO fiber samples; c-1 and c-2 are 3mmol-HEO fiber samples.

[0025] Figure 3 This is the TEM image of the 1 mmol-HEO sample prepared in Example 1.

[0026] Figure 4 The sample prepared in Example 1 was heated to 1000 ppm C4H8O2 / Air and the air velocity was 60000 mL h -1 g -1 Catalytic oxidation degradation curve of ethyl acetate under test conditions.

[0027] Figure 5 The sample prepared in Example 1 was heated to 1000 ppm C4H8O2 / Air and the air velocity was 60000 mL h -1 g -1 Cyclic test performance graph under test conditions. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with embodiments, but the scope of protection claimed by the present invention is not limited to the scope represented by the embodiments.

[0029] The syringe of the invention is composed of a syringe with a small hole at the front end and a piston core rod matched therewith.

[0030] Example 1 (Preparation of Precursor Solutions with Different Total Metal Concentrations)

[0031] (1) Weigh 2 g of 150,000 molecular weight polyacrylonitrile (PAN) in a 50 mL conical flask, add 20 mL of DMF under stirring, and then stir and mix at room temperature (25-30° C.) for 10 h.

[0032] (2) Weigh 0.2 mmol, 0.4 mmol and 0.6 mmol of the same substance of five metal sources (cobalt nitrate (Co(NO3)3·6H2O), manganese nitrate (Mn(NO3)2·4H2O), nickel nitrate (Ni(NO3)2·6H2O), iron nitrate (Fe(NO3)3·9H2O) and zinc nitrate (Zn(NO3)2·6H2O)) respectively, and the total amount of metal substances is 1 mmol, 2 mmol and 3 mmol respectively, and dissolve the weighed metals in the conical flask of step (1). Then stir and mix at room temperature (25-30°C) for 2 h.

[0033] (3) The solution prepared in step (2) was sucked into a 20 mL syringe, and the solution in the syringe was connected to the electrospinning needle, the flow rate was set to 0.5 mL / h, and the nanofibers were prepared by electrospinning. The electrospinning conditions were as follows: voltage 25 kV, temperature 40 °C, receiving distance 16 cm, and continuous electrospinning time 40 h.

[0034] (4) The nanofibers prepared in step (3) were placed in a muffle furnace and calcined at a heating rate of 5°C / min, a constant calcination temperature of 700°C, and a constant calcination time of 2h. 1mmol-HEO((CoMnNiFeZn)O was obtained by calcination in air atmosphere. x )、2mmol-HEO((CoMnNiFeZn)O x ) and 3mmol-HEO((CoMnNiFeZn)O x )Three high entropy oxide catalysts.

[0035] Figure 1The XRD spectra of the samples prepared in Example 1 show that strong diffraction lines are observed at 18.5°, 30.4°, 35.9°, 43.6°, 54°, 57.7°, 63.4° and 75° for all three samples, corresponding to the (111), (220), (311), (222), (400), (422), (511), (440) and (531) lattice planes of the face-centered cubic spinel (Fd-3m) phase, respectively. The peaks match well with the standard card Fe3O4 (JCPSD 01-075-0449), the crystallinity is high, the spinel crystal phase is relatively pure, and no diffraction peaks of impurities and other phases are detected.

[0036] Figure 2 This is the SEM photo of the sample prepared in Example 1. 1mmol-HEO, 2mmol-HEO and 3mmol-HEO still maintain the fiber morphology. For the three sample precursors, the metal salt concentration has the greatest influence on the morphology of the polymer. During the electrospinning process of the high-concentration metal salt solution, the fibers are easily stretched unevenly, resulting in a large difference in fiber diameter in the same area. Then, during the calcination process of the precursor, the calcination conditions can further change the morphology of the HEOs nanofibers, resulting in different microstructures of the nanofibers. From a macroscopic point of view, the three samples all maintain their original fiber state after calcination, among which 1mmol-HEO is connected by grain agglomeration to form a fiber; 2mmol-HEO has the same characteristics, growing toward the periphery of the fiber on the basis of the fiber, showing a certain honeycomb shape; 3mmol-HEO is more fibrous than the other three samples. It grows short rod-shaped fibers outward on the basis of fibers with large diameters.

[0037] Figure 3 This is a TEM image of the 1mmol-HEO sample prepared in Example 1. Figure 3 As shown, in the 1mmol-HEO sample, it can be seen that the nanofibers are formed by connecting the grains.

[0038] Obtained by ethyl acetate catalytic oxidation performance test Figure 4 The performance test curve of the samples shows that the 1mmol-HEO catalyst exhibits the best C4H8O2 catalytic oxidation performance (T 50 =235℃, T 90 =266°C), which confirmed that the increase of total metal concentration actually reduced the catalytic oxidation performance of ethyl acetate through electrospinning.

[0039] Figure 5 This is a test diagram of the cyclic performance of 1mmol-HEO catalyzing the oxidation of ethyl acetate. Figure 5It can be observed that after 5 cycles of performance testing, the performance of the 1mmol-HEO catalyst has hardly changed, indicating that the 1mmol-HEO catalyst has good thermal stability.

[0040] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing spinel high entropy oxide by electrospinning, comprising the following steps: 1) Prepare the precursor solution Putting polyacrylonitrile and a metal source in a conical flask, wherein the metal source is cobalt nitrate, manganese nitrate, nickel nitrate, iron nitrate and zinc nitrate, adding dimethylformamide (DMF) solution, stirring to form a uniform colloid, and obtaining a spinning precursor solution; 2) The solution prepared in step 1) is sucked into a 20 mL syringe, and the solution in the syringe is connected to the electrospinning needle, the flow rate is set, and the nanofibers are prepared by electrospinning; 3) placing the nanofibers prepared in step 2) into a muffle furnace and calcining them in an air atmosphere to obtain high entropy oxide nanofibers.

2. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: In the step 1), the molecular weight of polyacrylonitrile is 150,000.

3. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: The molar ratio of the cobalt nitrate n1, manganese nitrate n2, nickel nitrate n3, iron nitrate n4 and zinc nitrate n5 is n1:n2:n3:n4:n5=1:1:1:1:

1.

4. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: In the step 1), the ratio of the mass g of polyacrylonitrile to the volume mL of the solvent DMF is 0.1:

1.

5. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: The stirring time in the step 1) is 12 h.

6. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: The flow rate in step 2) is 0.5 mL / h.

7. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: The electrospinning conditions in the step 2) are as follows: voltage 25 kV, temperature 40°C, receiving distance 16 cm, and continuous electrospinning time 40 h.

8. The method for controlling spinel high entropy oxide by electrospinning as claimed in claim 1, characterized in that: The calcination conditions in step 3) are: a heating rate of 5°C / min, a constant calcination temperature of 700°C, and a constant calcination time of 2 h.

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