A method for batch preparation of ultrafine iron oxide nanoparticles rich in oxygen vacancies

Abstract

The present invention discloses a method for batch preparation of extremely small iron oxide nanoparticles rich in oxygen vacancies. Based on the magnetothermal loss mechanism of an iron target, the present invention combines water-cooled magneto-induced internal heat and laser ablation in liquid method, and introduces the action of a high-frequency alternating magnetic field during the laser ablation in liquid process, so that iron atoms on the surface of the iron target are in a state of violent oscillation and are more likely to form iron vapor under laser irradiation, thereby increasing the yield of nanoparticles. The beneficial effects generated thereby are as follows: the problem of too low yield of extremely small iron oxide nanoparticles rich in oxygen vacancies prepared by the single laser ablation in liquid method is overcome, and this method is economical, convenient and easy to popularize.

Description

Technical Field

[0001] The present invention relates to a method for batch preparation of ultra-small iron oxide nanoparticles rich in oxygen vacancies. Background Art

[0002] With the intensification of global energy problems, renewable energy technologies, such as fuel cells, metal-air batteries, and water electrolysis technologies, have developed rapidly. To achieve efficient energy conversion, the key lies in the catalytic activity. At present, although noble metals and their alloys are the most excellent catalysts, their high prices and scarcity limit their widespread use in industry. Therefore, it is particularly important to find non-noble metal catalysts that are both active and economical. Currently, transition metal oxides represented by iron oxide nanoparticles are regarded as powerful alternatives to noble metal catalysts due to their economic, abundant, and stable properties.

[0003] To improve the catalytic activity of iron oxide nanoparticles, scholars from various countries have adopted various strategies such as reducing size, doping elements, and surface modification. Among them, reducing size is one of the most direct and effective ways. The advantage of this method is that reducing size can not only increase the specific surface area and the number of catalytic sites, but also create unique exposed sites, thereby enhancing the inherent catalytic activity of iron oxide nanoparticles. Existing research shows that ultra-small iron oxide nanoparticles with a size less than 5 nm can exhibit good catalytic performance and have broad application prospects. However, due to the relatively low inherent catalytic activity of iron oxide catalysts, there is still a certain gap in catalytic performance between ultra-small iron oxide nanoparticles and noble metal catalysts.

[0004] Constructing oxygen vacancies on the catalyst surface is one of the important ways to improve catalytic performance. However, it is very difficult to generate oxygen vacancies in extremely small iron oxide nanoparticles. This is because at extremely small sizes, the bond energy of the Fe-O bond is significantly enhanced due to the surface compression tension. At the same time, at extremely small scales, the "self-purification" effect of iron oxide crystal defects is more significant, making the internal oxygen vacancies unstable, and these oxygen vacancies will disappear through self-repair. Therefore, there is a certain contradiction between constructing oxygen vacancies and reducing the size of iron oxide nanoparticles. Currently, the laser ablation in liquid method is the only method that can prepare extremely small nanoparticles rich in oxygen vacancies. When a short pulse-width (nanosecond, picosecond, femtosecond) laser beam bombards a metal target, the laser beam will quickly vaporize and even ionize the surface of the metal target to form a plasma plume region. Subsequently, the solid vapor or plasma quickly nucleates and grows into extremely small nanoparticles. In a liquid phase environment, the laser ablation effect will cause a strong quenching effect, and the formed nanoparticles cannot be fully oxidized, thus generating a large number of oxygen vacancies. The team of Du Xiwen from Tianjin University successfully prepared cobalt oxide nanoparticles with a size of 2.1 nm and rich in oxygen vacancies, and demonstrated excellent catalytic performance. However, the single liquid-phase laser ablation process is slow, and the yield of the prepared nanoparticles is extremely low. Only 5 mg of nanoparticles can be obtained after one hour of laser treatment, far from meeting the requirements of large-scale production. Currently, there is no method that can mass-produce extremely small iron oxide nanoparticles rich in oxygen vacancies. Summary of the Invention

[0005] Laser ablation of an iron target in water can cause a strong quenching effect, resulting in insufficient oxidation of iron vapor, breaking through the limitation of the "self-purification" effect in iron oxide nanoparticles, and creating a large number of oxygen vacancies in extremely small iron oxide nanoparticles. However, the single liquid-phase laser ablation process is slow, and the yield of the prepared nanoparticles is extremely low, unable to meet the needs of large-scale production. In the process of laser ablation in liquid of the present invention, combined with water-cooled magneto-induced internal heat treatment, while preparing extremely small iron oxide nanoparticles rich in oxygen vacancies, the yield of the nanoparticles is significantly improved. This method is economical, convenient, and easy to promote.

[0006] The technical solutions adopted in the present invention are as follows:

[0007] A method for batch preparation of extremely small iron oxide nanoparticles rich in oxygen vacancies, comprising the following steps:

[0008] 1) Use sandpaper to polish the iron metal target to remove the surface oxide layer, and after polishing smoothly, clean it with ethanol and deionized water;

[0009] 2) Prepare a dilute hydrogen peroxide solution with a mass fraction of 0.02 - 0.1%; the hydrogen peroxide content in the solution is controlled between 0.02 - 0.1%. If the hydrogen peroxide content is too low, it is not conducive to the formation of iron oxide nanoparticles; if the hydrogen peroxide content is too high, it is difficult to obtain a high density of oxygen vacancies.

[0010] 3) Immerse the iron target treated in step 1) in the dilute hydrogen peroxide solution, and then place the solution in an alternating magnetic field environment. Use a constant temperature bath to provide a water cooling cycle and keep the solution at a low temperature of 1 - 10 °C; the temperature of the dilute hydrogen peroxide solution will directly affect the particle size of the final product. Therefore, the solution temperature should be below 10 o °C is appropriate. If the temperature is too high, the size of the final product generally exceeds 5 nm, and it is difficult to obtain good catalytic performance.

[0011] 4) After the alternating magnetic field treatment, ablate the iron target in the solution with a laser beam;

[0012] 5) After the iron target is co-treated with the alternating magnetic field and the laser beam, a colloidal solution of extremely small iron oxide nanoparticles rich in oxygen vacancies is obtained;

[0013] 6) Use a high-speed centrifuge to centrifuge and collect the colloidal solution obtained in step 4), and freeze-dry the separated nanoparticles to finally obtain extremely small iron oxide nanoparticles rich in oxygen vacancies.

[0014] Furthermore, if the magnetic field strength and frequency are too low, the oscillation of iron atoms on the surface of the iron target is insufficient, and less iron vapor is formed under the irradiation of the laser, making it difficult to obtain a high yield of nanoparticles; if the magnetic field strength and frequency are too high, it will cause the local solution temperature to be too high, and the size of the final product generally exceeds 5 nm, making it difficult to obtain good catalytic performance. Therefore, in the alternating magnetic field environment of the present invention, the alternating magnetic field strength is 10 - 20 kA / m, and the frequency is 100 - 500 kHz.

[0015] Furthermore, the laser beam is generated by a nanosecond laser pulse generator. If the energy of the laser beam is too low, less iron vapor is generated, making it difficult to obtain a high yield of nanoparticles. Therefore, the energy of the laser beam used in the present invention is greater than 500 mJ, and the frequency is higher than 10 Hz.

[0016] If the laser beam spot diameter is too small, the range of iron vapor generation is small, making it difficult to obtain a high yield of nanoparticles; if the laser beam spot diameter is too large, the particle size of the generated nanoparticles generally exceeds 5 nm, making it difficult to obtain good catalytic performance. Therefore, the laser beam spot diameter in the present invention should be in the range of 1 - 3 mm.

[0017] Furthermore, in step 4), the alternating magnetic field treatment time is at least one minute.

[0018] Further, in step 5), the time for co-processing the iron target with the alternating magnetic field and the laser beam is at least one hour.

[0019] Based on the magnetothermal loss mechanism of the iron target, the present invention combines water-cooled magneto-induced internal heating and laser liquid-phase ablation method, introduces the action of high-frequency alternating magnetic field during the laser liquid-phase ablation process, makes the iron atoms on the surface of the iron target in a violent oscillation state, and is more likely to form iron vapor under laser irradiation, thereby increasing the yield of nanoparticles. The beneficial effects produced thereby are: overcoming the problem of too low yield of extremely small iron oxide nanoparticles rich in oxygen vacancies prepared by the single laser liquid-phase ablation method, and this method is economical, convenient and easy to promote. Description of the Drawings

[0020] Figure 1 is the X-ray diffraction pattern of the sample prepared by the method of the present invention.

[0021] Figure 2 is the transmission electron microscope image and size distribution statistical chart of the sample.

[0022] Figure 3 is the electron paramagnetic resonance spectrum of the sample.

[0023] Figure 4 is the amount of iron oxide nanoparticles prepared by the method of the present invention and the single laser liquid-phase ablation method. Embodiment

[0024] The present invention will be further described below with reference to the accompanying drawings.

[0025] A method for batch preparing extremely small iron oxide nanoparticles rich in oxygen vacancies according to the present invention includes the following steps:

[0026] 1) Use sandpaper to polish the iron target to remove the surface oxide layer, and after polishing smoothly, clean it with ethanol and deionized water.

[0027] [[ID=3�]]2) Take 3 mL of hydrogen peroxide solution with a mass fraction of 30% and dissolve it in 1797 mL of deionized water to prepare a dilute hydrogen peroxide solution with a mass fraction of 0.05%.

[0028] 3) Immerse the iron target processed in step 1) in the dilute hydrogen peroxide solution in step 2), connect a low-temperature constant temperature bath, and keep the solution temperature at 5°C through circulation. Subsequently, use an alternating magnetic field generator to create a high-frequency magnetic field environment acting on the iron target, with the magnetic field intensity set to 14 kA / m and the frequency set to 100 kHz.

[0029] 4) After preheating the iron target for 1 minute using an alternating magnetic field generator, start the nanosecond pulsed laser to ablate the iron target, with the laser beam energy set to 600 mJ, the frequency to 20 Hz, and the spot diameter to 2 mm.

[0030] 5) After the iron target is co-treated with a laser beam and an alternating magnetic field for 1 hour, a colloidal solution of iron oxide nanoparticles can be obtained. The nanoparticles are separated using a high-speed centrifuge with the rotation speed set at 15,000 rpm. The separated nanoparticles are freeze-dried to obtain a powder of extremely small iron oxide nanoparticles rich in oxygen vacancies.

[0031] The X-ray diffraction pattern of the sample prepared by the present invention is as Figure 1 , and it can be seen from Figure 1 that the prepared iron oxide nanoparticles have a spinel structure and there is no substance of other crystal phases.

[0032] The transmission electron microscope image and the size distribution statistical chart of the sample are as Figure 2 , and it can be seen from Figure 2 that the average size of the iron oxide nanoparticles prepared by the method of the present invention is 4.7 nm.

[0033] The electron paramagnetic resonance spectrum of the sample is as Figure 3 , and it can be seen from Figure 3 that the prepared iron oxide nanoparticles contain abundant oxygen vacancies.

[0034] Figure 4 shows the amounts of iron oxide nanoparticles prepared by the method of the present invention and by the single laser ablation in liquid method respectively. It can be seen from Figure 4 that the method of the present invention can prepare 103 mg of extremely small iron oxide nanoparticles rich in oxygen vacancies in 1 hour, which is more than 20 times that prepared by the single laser ablation in liquid method.

[0035] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A method for batch preparation of ultra-small iron oxide nanoparticles rich in oxygen vacancies, characterized in that: It includes the following steps: 1) Remove the oxide layer on the surface of the iron target, and then clean the surface of the iron target with ethanol and deionized water; 2) Prepare a dilute hydrogen peroxide solution with a mass fraction of 0.02 - 0.1%; 3) Immerse the iron target treated in step 1) in the dilute hydrogen peroxide solution, then place the solution in an alternating magnetic field environment, and keep the solution in a low temperature state of 1 - 10 °C; 4) After the alternating magnetic field treatment, ablate the iron target in the solution with a laser beam; 5) After the iron target is co-treated with the alternating magnetic field and the laser beam, a colloidal solution of extremely small iron oxide nanoparticles rich in oxygen vacancies is obtained; 6) Centrifuge and collect the colloidal solution obtained in step 5), freeze-dry the separated nanoparticles, and finally obtain extremely small iron oxide nanoparticles rich in oxygen vacancies; In the alternating magnetic field environment, the alternating magnetic field strength is 10 - 20 kA / m, and the frequency is 100 - 500 kHz; The laser beam is generated by a nanosecond laser pulser, the generated laser beam energy is greater than 500 mJ, the frequency is higher than 10 Hz, and the laser beam spot diameter should be in the range of 1 - 3 mm; In step 4), the alternating magnetic field treatment time is at least one minute; In step 5), the co-treatment time of the iron target with the alternating magnetic field and the laser beam is at least one hour.

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