A method for regulating spinel high entropy oxide using electrospinning

Abstract

The present invention discloses a method for regulating spinel-type high-entropy oxides using electrospinning. The method is characterized in that metal sources, polyacrylonitrile, and dimethylformamide of varying concentrations are fully mixed to form a precursor solution, followed by preparing a spinel-type high-entropy oxide having a nanofiber structure by electrospinning. Results show that, compared to conventional methods for preparing high-entropy oxides, electrospinning facilitates a lower phase transition temperature and promotes the formation of nanoscale high-entropy oxides. Furthermore, the fibers formed are significantly affected by the precursor solution. By varying the amount of total metal added, the final fiber state of the catalyst can be effectively regulated, exhibiting significant differences in ethyl acetate catalytic oxidation activity. The preparation process is simple, enhancing the application value of high-entropy oxides in the field of heterogeneous catalysis.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of spinel-type high-entropy oxides, and particularly relates to a method for synthesizing and regulating spinel-type high-entropy oxide nanofibers by electrospinning. Background Art

[0002] Spinel oxides refer to a series of oxides with the general formula AB2O4. The oxygen ions are closely packed in a cubic pattern, with the A ions located at the eighth position of the tetrahedron and the B ions at the half position of the octahedron. From a crystal structure perspective, spinel materials are thermodynamically and chemically stable. Industrial applications are typically 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 the metal-oxygen bond, 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 have good toxicity resistance, and are the main components of VOCs degradation catalysts. Selecting transition metals as the metal component of HEOs is a relatively low-cost, high-efficiency method that provides multiple active sites.

[0004] Common methods for preparing HEOs include coprecipitation, hydrothermal methods, and liquid-phase combustion. Coprecipitation and sol-gel methods require complex processes, requiring the regulation of parameters such as pH and temperature. Furthermore, these traditional methods typically require high-temperature calcination to prepare HEOs. The entropic driving force of the high phase transition temperature (e.g., 900-1600°C) leads to pore collapse, inevitably causing agglomeration and forming bulky, micron-sized, low-surface-area HEOs. In contrast, electrospinning allows for a uniform and highly disordered distribution of metal salt precursors. For polymer solutions, the surface tension of the droplets and the electric field create solid fibers, which facilitates the crystallization of the structurally disordered high-entropy phase at relatively low temperatures. The properties of the electrospinning precursor solution significantly influence the electrospinning process and the final fiber properties. For example, viscosity influences the solution's fluidity and fiber formation. Appropriate viscosity ensures a stable jet flow in the electric field, ultimately forming uniform fibers. Therefore, changing the total metal concentration in the precursor solution can obtain ideal nanofibers. However, the distribution of metals 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 exhibits 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 existing technology and provide a preparation method of spinel high entropy oxide by using electrospinning. This method can promote the formation of a single-phase structure of the catalyst at low temperature, regulate the total metal concentration to make it have a catalyst with high catalytic oxidation ability, strong operability, low cost, and meet environmental requirements.

[0007] To achieve the purpose of the present invention, the technical solution specifically includes 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) were placed in a conical flask, and dimethylformamide (DMF) solution was added and stirred to form a uniform colloid;

[0010] 2) The solution prepared in step 1) was drawn into a 20 mL syringe, and the solution in the syringe was then connected to the electrospinning needle. The flow rate was set, and the nanofibers were prepared by electrospinning.

[0011] 3) The nanofibers prepared in step 2) were 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 the 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] The electrospinning conditions in step 2) 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 constant calcination 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: (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 at 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 at 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 will be further described below with reference to the embodiments. However, the scope of protection claimed in the present invention is not limited to the scope shown in the embodiments.

[0029] The syringe of the present 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) into a 50 mL conical flask, add 20 mL of DMF while 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. The weighed metals are dissolved in the conical flask of step (1). Then, the mixture is stirred and mixed 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 then connected to the electrospinning needle. The flow rate was set to 0.5 mL / h, and nanofibers were prepared by electrospinning. The electrospinning conditions were 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 temperature of 700°C, and a constant temperature 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 those of the standard card Fe3O4 (JCPSD 01-075-0449), indicating high crystallinity and a relatively pure spinel phase. No diffraction peaks from impurities or other phases were detected.

[0036] Figure 2 The SEM photos of the samples prepared in Example 1 show that 1mmol-HEO, 2mmol-HEO and 3mmol-HEO still maintain the morphology of fibers. For the three sample precursors, the metal salt concentration has the greatest influence on the morphology of the polymer. During the electrospinning process of high-concentration metal salt solutions, the fibers are easily stretched unevenly, resulting in large differences in fiber diameters in the same area. Then, during the calcination 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 perspective, the three samples all maintain their original fiber state after calcination, among which 1mmol-HEO is connected by grain agglomeration to form a fiber shape; 2mmol-HEO has the same characteristics, growing toward the periphery of the fiber on the basis of the fiber shape, presenting a certain honeycomb shape; 3mmol-HEO is more fibrous than the other three samples, and 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, the 1mmol-HEO sample can be seen to be formed by the connection between the grains to form nanofibers

[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 by electrospinning.

[0039] Figure 5 This is a test chart 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 almost no change, 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. Application of a spinel-type high entropy oxide in catalytic oxidation of ethyl acetate, characterized in that: The method for regulating spinel high entropy oxide by electrospinning specifically comprises the following steps: 1) Prepare the precursor solution Polyacrylonitrile and a metal source are placed in a conical flask, wherein the metal source is cobalt nitrate, manganese nitrate, nickel nitrate, iron nitrate and zinc nitrate, and then a DMF solution is added and stirred to form a uniform colloid to obtain a spinning precursor solution; 2) The solution prepared in step 1) was drawn into a 20 mL syringe, and the solution in the syringe was then connected to the electrospinning needle. The flow rate was set, and the nanofibers were formed 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, wherein the calcination condition is: a constant calcination temperature of 700°C.

2. The use according to claim 1, characterized in that: In the step 1), the molecular weight of polyacrylonitrile is 150,000.

3. The use according to 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 use according to claim 1, wherein: 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 use according to claim 1, characterized in that: The stirring time in the step 1) is 12 h.

6. The use according to claim 1, characterized in that: The flow rate in step 2) is 0.5 mL / h.

7. The use according to claim 1, characterized in that: The electrospinning conditions in step 2) are as follows: voltage 25 kV, temperature 40°C, receiving distance 16 cm, and continuous electrospinning time 40 h.

8. The use according to claim 1, wherein: In the step 3), the heating rate is 5°C / min and the constant temperature calcination time is 2 h.

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