Preparation method of magnetic nanoparticles with high magnetothermal conversion efficiency

Abstract

The invention discloses a preparation method of magnetic nanoparticles with high magnetic-thermal conversion efficiency, the method adopts a jacketed reactor, an interlayer of the jacketed reactor and an external water source form a circulating fluid, the jacketed reactor is fixed in the center of an alternating magnetic field coil, and the method specifically comprises the following steps: (1) adding a NaOH solution into the deoxygenized jacketed reactor, and stirring to obtain a mixed solution; dropwise adding the ferrous salt solution into the NaOH solution under continuous stirring; (2) after dropwise adding, pumping hot water into the interlayer of the jacketed reactor, and keeping the temperature of the water in the interlayer at 80-90 DEG C all the time through the pumping speed; (3) an alternating magnetic field is started, the current is 30-40 A, the frequency is 307 kHz, meanwhile, a NaNO3 solution is dropwise added into the jacketed reactor, curing is conducted after dropwise adding is completed, and the oxidizing agent dropwise adding process and the curing process of a reaction system are both conducted under the alternating magnetic field; and (4) after the reaction, washing and centrifuging the obtained product to obtain the ferroferric oxide magnetic nanoparticles.

Description

Technical Field

[0001] This invention relates to a method for preparing magnetic nanoparticles with high magnetocaloric conversion efficiency. Background Technology

[0002] Magnetothermia is a treatment method that uses an alternating magnetic field to induce heating in magnetic nanoparticles to kill lesion cells, offering advantages such as non-invasiveness and regional selectivity. However, most of the magnetic nanoparticles currently studied are superparamagnetic particles with a diameter of less than 50 nm, resulting in relatively low saturation magnetization, leading to low specific absorption rate (SAR) values ​​and insufficient magnetocaloric conversion efficiency, which fails to meet clinical requirements for thermal effects. Appropriately increasing the particle size of magnetic nanoparticles (>100 nm) can significantly improve their saturation magnetization and magnetocaloric performance.

[0003] Existing water-cooled magnetothermal precipitation methods cannot prepare magnetic nanoparticles with uniform particle sizes greater than 100 nm. For example, the magnetothermal synergistic reaction method proposed by Chen et al., which combines alternating magnetic fields and external water circulation, can improve the crystallinity and uniformity of magnetic nanoparticles, but the resulting magnetic particles have relatively small particle sizes (less than 50 nm), limiting its application in magnetothermal therapy. Conventional coprecipitation methods, in preparing magnetic nanoparticles with particle sizes greater than 100 nm, suffer from problems such as large particle size distribution, easy agglomeration, and difficulty in morphology control, failing to obtain large-particle magnetic nanoparticles with uniform size and good dispersion. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing magnetic nanoparticles with uniform particle size and good dispersibility in the range of 200-300 nm.

[0005] Technical solution: The method for preparing magnetic nanoparticles according to the present invention uses a jacketed reactor, wherein the jacket of the jacketed reactor and an external water source form a circulating fluid, and the jacketed reactor is fixed in the center of an alternating magnetic field coil, specifically including the following steps:

[0006] (1) Add NaOH solution to the deoxygenated jacketed reactor, and add ferrous salt solution dropwise to NaOH solution while stirring continuously;

[0007] (2) After the dripping is completed, hot water is pumped into the jacket of the jacketed reactor. The temperature of the water in the jacket is kept at 80-90℃ by the pumping speed.

[0008] (3) Turn on the alternating magnetic field, with a current of 30-40A and a frequency of 307kHz, and simultaneously add NaNO3 solution or HClO solution to the jacketed reactor. After the addition is completed, the reactor is matured. The reaction system is carried out under the alternating magnetic field during the addition of oxidant and the maturation process.

[0009] (4) After the reaction, the product was washed and centrifuged to obtain magnetic nanoparticles of iron oxide.

[0010] In steps (1) and (3), the NaOH solution, ferrous salt solution, NaNO3 solution, and HClO solution are all prepared using deoxygenated deionized water as the solvent; NaOH and Fe 2+ The molar ratio is 3:2 to 3. If the alkali solution is insufficient, magnetite nanoparticles cannot be produced, and green rust will be produced instead; if the alkali solution is excessive, the pH gradient of the solution will increase during the dropwise addition, the difference in nucleation driving force between particles will increase, and the size distribution will increase, ultimately failing to obtain magnetite nanoparticles with concentrated size and uniform particle size; the dropwise addition rate of the ferrous salt solution is 0.1 to 1 mL / min; if the dropwise addition rate is too fast, it will increase the degree of aggregation of magnetic nanoparticles during the formation process, the slower the better, and in step (1), the reaction system should be stirred at a rate of not less than 500 rpm. Stirring while reacting can also reduce the degree of aggregation of magnetic nanoparticles during the preparation process.

[0011] In step (2), the water pump speed is 200-600 rpm.

[0012] In step (3), the NaNO3 solution is added at a rate of 66–67 μL / s; Fe 2+ The molar ratio of sodium nitrate (NaNO3) to NaNO3 or HClO is 12.5:4-5. Sodium nitrate (NaNO3) acts as an oxidizing agent in the system, oxidizing ferrous salts to ferric iron (Fe3O4), which then forms Fe3O4 nanoparticles. A slower addition rate is better; too rapid an addition will reduce the crystallinity of the particles, resulting in a loose crystal structure. If too much oxidizing agent is added, all ferrous iron will be oxidized to ferric iron, forming ferric hydroxide. If too little oxidizing agent is added, insufficient ferrous iron will be oxidized to ferric iron; a ratio of ferrous to ferric iron of 1:2 is required to form Fe3O4. If the oxidizing agent is too strong, the oxidation reaction will be rapid, increasing the crystallization rate and particle size distribution. If the oxidizing agent is too weak, the particles will grow in one direction and will not form regular spherical shapes.

[0013] In step (3), the dripping time is 55-60 seconds and the maturation time is 38-40 minutes.

[0014] In step (4), the centrifugation speed is 11000-12000 rpm; the centrifugation time is 10-12 min.

[0015] In step (4), the particle size of the magnetite nanoparticles is 200-300 nm.

[0016] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: The method of the present invention can prepare a large and uniform magnetic nanoparticle with high magnetocaloric conversion efficiency, whose particle size range is controlled within ±20 nm, with good dispersibility and monodispersity or weak agglomeration characteristics; based on the mass of Fe element, the specific absorptivity (SAR) of the magnetic nanoparticle dispersion at a concentration of 5 mg / mL can reach 3581.5 W / kg, thus the heating power under the action of an alternating magnetic field is greater than 1.944 × 10⁻⁶ W / kg. 5 W / m 3 This can effectively enhance the therapeutic effect of magnetic nanoparticles in magnetothermal therapy. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the device used in the method of the present invention;

[0018] Figure 2 TEM image of the large-particle-size magnetite nanoparticles generated in Example 1;

[0019] Figure 3 The particle size distribution of the large-diameter magnetite nanoparticles generated in Example 1 is shown in the diagram.

[0020] Figure 4 TEM image of the large-particle-size magnetite nanoparticles generated in Example 2;

[0021] Figure 5 The particle size distribution of the large-particle-size magnetite nanoparticles generated in Example 2 is shown in the diagram.

[0022] Figure 6 TEM image of the large-particle-size magnetite nanoparticles generated in Comparative Example 1;

[0023] Figure 7 The particle size distribution of the large-diameter magnetite nanoparticles generated in Comparative Example 1 is shown in the figure.

[0024] Figure 8 TEM image of the large-particle-size magnetite nanoparticles generated in Comparative Example 2;

[0025] Figure 9 The particle size distribution of the large-particle-size magnetite nanoparticles generated in Comparative Example 2 is shown in the figure.

[0026] Figure 10 TEM image of the large-particle-size magnetite nanoparticles generated in Comparative Example 3;

[0027] Figure 11 TEM image of the large-particle-size magnetite nanoparticles generated in Comparative Example 4.

[0028] Figure 12 The particle size distribution of the large-diameter magnetite nanoparticles generated in Comparative Example 4 is shown in the figure.

[0029] Figure 13 TEM image of the large-particle-size magnetite nanoparticles generated in Comparative Example 5;

[0030] Figure 14 The particle size distribution of the large-diameter magnetite nanoparticles generated in Comparative Example 5 is shown in the figure. Detailed Implementation

[0031] like Figure 1 As shown, the apparatus used in the method of the present invention includes an alternating magnetic field generator and a jacketed reactor fixed in the center of the alternating magnetic field coil. The water in the jacket of the jacketed reactor forms a circulating fluid with the hot water in the external water tank through a water pump. The jacketed reactor is also equipped with a temperature sensor. It also includes a microfluidic device for dripping the solution into the jacketed reactor.

[0032] Example 1

[0033] The method for preparing magnetic nanoparticles of the present invention includes the following steps:

[0034] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0035] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0036] (3) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 4mL of 0.8mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) is slowly added to the jacketed reactor at a rate of 66μL / s. The addition is continued for about 1min. After the addition is completed, the mixture is allowed to mature for 40min. The reaction system is affected by the alternating magnetic field during the addition of NaNO3 solution and the maturation process. The entire process takes 50 minutes.

[0037] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0038] The average particle size of the magnetite nanoparticles prepared in Example 1 was 293.80 nm. Based on the mass of Fe element, the specific absorption rate (SAR) of the magnetite nanoparticle dispersion in Example 1 at a concentration of 5 mg / mL was 3581.5 W / kg. This is because the magnetite nanoparticles prepared in Example 1 had a uniform particle size distribution, and the magnetocaloric conversion performance in all directions on the spherical nanoparticles was consistent. Therefore, the magnetocaloric conversion efficiency was high, which could effectively convert the energy of the alternating magnetic field into heat energy.

[0039] pass Figures 2-3 It can be seen that the product obtained in Example 1 has uniform particle size and is spherical, with the particle size concentrated at 293.80 nm. The improvement in particle size and uniformity enables the product to generate higher heat energy in magnetothermal therapy, thereby improving its therapeutic effect in magnetothermal therapy.

[0040] Example 2

[0041] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0042] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0043] (3) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 4mL of 0.8mol / L HClO solution is slowly added to the jacketed reactor at a rate of 66μL / s. The addition is continued for about 1min. After the addition is completed, the mixture is matured for 40min. The reaction system is affected by the alternating magnetic field during the addition of HClO solution and the maturation process. The entire process takes 50 minutes.

[0044] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0045] The average particle size of the magnetite nanoparticles prepared in Example 2 was 283.37 nm. Based on the mass of Fe element, the specific absorption rate (SAR) of the magnetite magnetic nanoparticle dispersion in Example 2 at a concentration of 5 mg / mL was 3225.8 W / kg. This is because the magnetite magnetic nanoparticles prepared in Example 2 had a relatively uniform particle size distribution, and the magnetocaloric conversion performance in all directions on most of the spherical nanoparticles was basically consistent. Therefore, the magnetocaloric conversion efficiency was high, which could effectively convert the energy of the alternating magnetic field into heat energy.

[0046] pass Figures 4-5 It can be seen that the product obtained in Example 2 has a uniform particle size, is spherical, and has a particle size concentrated at 283.37 nm. The improvement in particle size and uniformity enables the product to generate higher heat energy in magnetothermal therapy, thereby improving its therapeutic effect in magnetothermal therapy.

[0047] Comparative Example 1

[0048] The only difference between Comparative Example 1 and Example 1 is that the amount of NaOH added in step (1) is 0.045 mol, specifically:

[0049] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.045 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 9:2.

[0050] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0051] (3) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 4mL of 0.8mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) is slowly added to the jacketed reactor at a rate of 66μL / s. The addition is continued for about 1min. After the addition is completed, the mixture is allowed to mature for 40min. The reaction system is affected by the alternating magnetic field during the addition of NaNO3 solution and the maturation process, for a total of 50min.

[0052] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0053] The magnetic nanoparticles of iron oxide prepared in Comparative Example 1 had an average particle size of 242.91 nm. Figure 6 It can be seen that the magnetic nanoparticles prepared in Comparative Example 1 exhibit a spherical morphology with uneven particle size and a tendency to aggregate. Figure 7 The particle size dispersion of the intermediate product is much greater than that of Example 1, indicating that the magnetic nanoparticles prepared in Example 1 not only have larger particle size but also more concentrated particle size and better uniformity, thus having a good specific absorption rate (SAR) value. Based on the mass of Fe element, the specific absorption rate (SAR) value of the magnetic nanoparticle dispersion of Comparative Example 1 at a concentration of 5 mg / mL is 965.4 W / kg.

[0054] Comparative Example 2

[0055] The only difference between Comparative Example 2 and Example 1 is that the alternating magnetic field was not activated in step (3). Specifically:

[0056] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0057] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0058] (3) Fix the jacketed reactor in an oil bath at a temperature of 80°C. Add about 4 mL of 0.8 mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) slowly into the jacketed reactor at a rate of 66 μL / s. Continue adding for about 1 min. After the addition is complete, let it mature for 40 min, for a total of 50 min.

[0059] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0060] The average particle size of the magnetite nanoparticles prepared in Comparative Example 2 was 83.92 nm. Based on the mass of Fe element, the specific absorption rate (SAR) of the magnetite nanoparticle dispersion in Comparative Example 2 at a concentration of 5 mg / mL was 1621.9 W / kg.

[0061] pass Figures 8-9 It can be seen that the product of Comparative Example 2 exhibits a relatively irregular morphology. At the same time, the particle size dispersion of the product of Comparative Example 2 is much greater than that of the product of Example 1. However, the particle size of the product of Comparative Example 2 is much smaller than that of the product of Example 2. Therefore, the method of the present invention can improve the particle size and morphological uniformity of the magnetocaloric nanoparticles, thereby effectively improving their magnetocaloric conversion efficiency.

[0062] Comparative Example 3

[0063] The only difference between Comparative Example 3 and Example 1 is that hot water was not introduced into the jacket of the jacketed reactor in step (2); specifically:

[0064] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0065] (2) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 4mL of 0.8mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) is slowly added to the jacketed reactor at a rate of 66μL / s. The addition is continued for about 1min. After the addition is completed, the mixture is allowed to mature for 40min. The reaction system is affected by the alternating magnetic field during the addition of NaNO3 solution and the maturation process. The entire process takes 50 minutes.

[0066] (3) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0067] The magnetic nanoparticles of iron oxide prepared in Comparative Example 3 were needle-shaped, such as... Figure 10 As shown in the figure, the product of Comparative Example 3 exhibits a relatively irregular needle-like morphology. Based on the mass of Fe element, the specific absorbance (SAR) value of the magnetic nanoparticle dispersion of Comparative Example 3 at a concentration of 5 mg / mL is 2525.6 W / kg.

[0068] Since no hot water was introduced into the jacket, the temperature gradient of the reaction system increased, resulting in a large difference in the growth rate of the iron oxide nanoparticles on different crystal planes. That is, the growth rate of iron oxide nanoparticles on specific crystal planes varies. They grow rapidly on crystal planes with high surface energy and grow slowly on crystal planes with low surface energy, which in turn guides the iron oxide nanoparticles to form needle-like structures.

[0069] Comparative Example 4

[0070] The only difference between Comparative Example 4 and Example 1 is that the dropping rate of the NaNO3 solution in step (3) is 500 μL / s; specifically:

[0071] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0072] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0073] (3) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 4mL of 0.8mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) is rapidly added to the jacketed reactor at a rate of 500μL / s. After the addition is completed, the mixture is allowed to mature for 40min. The reaction system is affected by the alternating magnetic field during the addition of NaNO3 solution and the maturation process. The entire process takes 50 minutes.

[0074] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0075] The average particle size of the magnetite nanoparticles prepared in Comparative Example 4 was 212.25 nm. Based on the mass of Fe element, the specific absorption rate (SAR) of the magnetite nanoparticle dispersion in Comparative Example 4 at a concentration of 5 mg / mL was 2627.1 W / kg.

[0076] like Figures 11-12As can be seen, the product of Comparative Example 4 exhibits a relatively irregular morphology, and the particles show a large degree of agglomeration. The particle size dispersion of the product of Comparative Example 4 is much greater than that of the product of Example 1. Therefore, the method of the present invention can ensure the high dispersion and particle size concentration of the large-sized magnetite magnetic nanoparticles, thereby effectively improving their magnetocaloric conversion efficiency.

[0077] Comparative Example 5

[0078] The only difference between Comparative Example 5 and Example 1 is that the NaNO3 solution was added at a rate of 500 μL / s in step (3), and 8 mL of 0.8 mol / L NaNO3 solution was added; specifically:

[0079] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0080] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0081] (3) Turn on the alternating magnetic field with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation. At the same time, about 8mL of 0.8mol / L NaNO3 solution (NaNO3 solution is obtained by dissolving NaNO3 in deoxygenated deionized water) is rapidly added to the jacketed reactor at a rate of 500μL / s. After the addition is completed, the mixture is allowed to mature for 40min. The reaction system is affected by the alternating magnetic field during the addition of NaNO3 solution and the maturation process. The entire process takes 50 minutes.

[0082] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain magnetic nanoparticles of iron oxide.

[0083] The average particle size of the magnetite nanoparticles prepared in Comparative Example 5 was 197.41 nm. Based on the mass of Fe element, the specific absorption rate (SAR) of the magnetite nanoparticle dispersion in Comparative Example 5 at a concentration of 5 mg / mL was 2215.3 W / kg.

[0084] pass Figures 13-14It can be seen that the product of Comparative Example 5 exhibits a relatively irregular and non-spherical morphology. Although the size is increased, the size distribution is wide, and a large number of particles agglomerate. Similarly, the particle size dispersion of the product of Comparative Example 5 is much greater than that of the product of Example 1.

[0085] Comparative Example 6

[0086] The only difference between Comparative Example 6 and Example 1 is that NaNO3 solution is not added in step (3); specifically:

[0087] (1) Nitrogen gas is introduced into the jacketed reactor to ensure that the reaction system is always carried out in a nitrogen atmosphere; 0.015 mol NaOH is dissolved in 5 mL of deoxygenated deionized water and poured into the jacketed reactor. The reaction system is stirred at 500 rpm. Then, 12.5 mL of 0.8 mol / L FeSO4 solution (the FeSO4 solution is obtained by dissolving FeSO4 in deoxygenated deionized water) is added dropwise to the NaOH solution. The molar ratio of NaOH to FeSO4 is 3:2.

[0088] (2) Turn on the water pump to introduce the hot water in the external water tank into the jacket of the jacketed reactor. The water pump speed is 200-600 rpm to keep the solution temperature of the reaction system at 80℃.

[0089] (3) Turn on the alternating magnetic field, with a current of 30-40A and a frequency of 307kHz. The alternating magnetic field acts on the entire process of particle formation, and the whole process takes 50 minutes.

[0090] (4) After the reaction, the product was washed with deionized water and centrifuged at 11,000 rpm for 10 min to obtain ferrous hydroxide nanoparticles. In Comparative Example 6, since no oxidant (NaNO3) was added, the product could only produce a white flocculent precipitate of ferrous hydroxide, and could not provide ferric iron to form black iron(III) oxide nanoparticles. At the same time, the reaction system was filled with nitrogen gas, so ferrous hydroxide could not be oxidized. The product would remain white ferrous hydroxide for a long time, and iron(III) oxide nanoparticles would not appear.

[0091] Therefore, this invention can prepare magnetic nanoparticles with large and concentrated particle size and uniform morphology, thus exhibiting excellent magnetocaloric conversion efficiency.

Claims

1. A method for preparing magnetic nanoparticles with high magnetocaloric conversion efficiency, characterized in that, The method employs a jacketed reactor, where the jacket of the reactor and an external water source form a circulating fluid. The jacketed reactor is fixed in the center of an alternating magnetic field coil, and specifically includes the following steps: (1) Add NaOH solution to the deoxygenated jacketed reactor, and add ferrous salt solution dropwise to NaOH solution while stirring continuously; (2) After the dripping is completed, hot water is pumped into the jacket of the jacketed reactor, and the water temperature in the jacket is kept at 80-90℃ by the pump speed. (3) Turn on the alternating magnetic field, with a current of 30-40A and a frequency of 307kHz, and simultaneously add NaNO3 solution or HClO solution to the jacketed reactor. After the addition is completed, the reactor is matured. The reaction system is carried out under the alternating magnetic field during the addition of oxidant and the maturation process. (4) After the reaction, the product was washed and centrifuged to obtain magnetic nanoparticles of iron oxide.

2. The preparation method according to claim 1, characterized in that: In steps (1) and (3), the NaOH solution, ferrous salt solution, NaNO3 solution and HClO solution are all prepared using deoxygenated deionized water as the solvent.

3. The preparation method according to claim 1, characterized in that: In step (1), NaOH and Fe 2+ The molar ratio is 3:2 to 3.

4. The preparation method according to claim 1, characterized in that: In step (1), the dropping rate of the ferrous salt solution is 0.1 to 1 mL / min.

5. The preparation method according to claim 1, characterized in that: In step (2), the water pump speed is 200-600 rpm.

6. The preparation method according to claim 1, characterized in that: In step (3), the dropping rate of NaNO3 solution or HClO solution is 30-100 μL / s.

7. The preparation method according to claim 1, characterized in that: In step (3), Fe 2+ The molar ratio with HClO or NaNO3 is 12.5:4-5.

8. The preparation method according to claim 1, characterized in that: In step (3), the dripping time is 55-60 seconds and the maturation time is 38-40 minutes.

9. The preparation method according to claim 1, characterized in that: In step (4), the centrifugation speed is 11000-12000 rpm; the centrifugation time is 10-12 min.

10. The preparation method according to claim 1, characterized in that: In step (4), the particle size of the magnetite nanoparticles is 200-300 nm.

Images