A method for preparing α-Fe2O3 nanopowder by salt-assisted ultrasonic spray pyrolysis.

Abstract

This invention belongs to the field of inorganic functional material preparation technology, and specifically relates to a method for preparing α-Fe₂O₃ nanopowder by salt-assisted ultrasonic spray pyrolysis. First, an auxiliary salt and a ferric salt are dissolved in deionized water and ultrasonically prepared to form a precursor solution with an iron concentration of 0.01–1 mol / L. Then, the precursor solution is atomized in an ultrasonic atomizer with an ultrasonic frequency of 1.7–3 MHz, and the resulting droplets are collected. After collection, the droplets are ultrasonicated, filtered, and dried to obtain α-Fe₂O₃ nanopowder. This invention, by adding an auxiliary salt as a high-temperature solvent, solves the problems of severe agglomeration, large particle size, and poor uniformity in powders prepared by spray pyrolysis. The α-Fe₂O₃ powder obtained by the above method not only has small particle size, good uniformity and dispersibility, but the added auxiliary salt can also be recycled and reused.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional material preparation technology, and specifically relates to an α-Fe2O3 nanopowder prepared by salt-assisted ultrasonic spray pyrolysis and the method thereof. Background Technology

[0002] α-Fe₂O₃ is a deep red powder, commonly known as iron oxide red, with a hexagonal corundum structure. 2- Fe is arranged in a hexagonal close-packed pattern. 3+ It exists between oxygen ion layers, but only fills two-thirds of the octahedral voids. α-Fe₂O₃ belongs to the rhombohedral crystal system, space group [missing information]. The structure has lattice constants of a = 0.50349 nm and c = 1.3752 nm. α-Fe₂O₃ is the most stable iron oxide phase at room temperature, possessing characteristics such as non-toxicity, environmental friendliness, low cost, and high thermal stability. α-Fe₂O₃ has extremely wide applications in lithium-ion battery anode materials, radar absorbing materials, catalysis, biomedical engineering, gas-sensitive materials, and adsorbents.

[0003] The main methods for preparing α-Fe2O3 include solid-phase method, precipitation method, sol-gel method, spray pyrolysis method, microemulsion method, hydrothermal method, and solvothermal method. However, solid-phase methods suffer from poor uniformity of synthesized powders, severe agglomeration, and irregular morphology; chemical precipitation methods mostly occur in solutions, making it difficult to achieve nanoscale final sample sizes; sol-gel methods, based on the hydrolysis and condensation of metal alkoxides, have high preparation costs; hydrothermal and solvothermal methods allow for the control of the crystal structure and morphology of nanoparticles through changes in experimental conditions, easily yielding products with high purity, good dispersibility, and uniform particle size, making them one of the most widely used methods for synthesizing nano-iron oxide, but they require sophisticated equipment and result in significant batch-to-batch product quality variations; spray pyrolysis utilizes a high-temperature furnace to atomize mixed material solutions (such as metal salt solutions), causing them to undergo instantaneous thermal decomposition, reaction, synthesis, or calcination to obtain ultrafine powders and films using aerosol technology, which is increasingly widely used due to its controllable particle size, uniform composition, and high purity; microemulsion methods show promising application prospects in nanomaterial preparation due to the advantages of controllable particle size, good particle dispersibility, and simple operation, but their industrial application is difficult due to the use and processing of organic matter.

[0004] Patent CN103915217B discloses a method for preparing carbon-coated microcables using α-Fe2O3 nanorods with high specific capacitance. The Fe2O3 preparation method involves a hydrothermal process, where α-Fe2O3 composite nanorods are obtained through hydrothermal calcination. Patent CN103480308B discloses a method for preparing Fe3O4 / α-Fe2O3 core-shell magnetic microspheres. This invention first prepares Fe3O4 nanospheres using a hydrothermal method, then uses a liquid-phase coating method. A certain amount of FeCl3·6H2O is dissolved in deionized water, followed by the sequential addition of PVP and urea. The mixture is stirred until completely dissolved to ensure uniform mixing of the reactants. The prepared Fe3O4 nanospheres are then added, and the reaction is carried out at 80–95°C for 6–24 hours, followed by natural cooling to room temperature. The microspheres are then washed and dried to obtain Fe3O4 / Fe2O3 composite magnetic microspheres. Patent CN110371924B discloses a Fe2O3 porous nanowire electrode material, its preparation method, and its application. This invention involves preparing a ZnO nanoarray via a hydrothermal method, followed by a secondary hydrothermal method to obtain the Fe2O3 porous nanowire electrode material. The resulting Fe2O3 nanowire electrode material is approximately 1 μm long and has a diameter between 20 and 80 nm, exhibiting a porous structure. All of the above methods involve hydrothermal preparation or treatment processes, and all suffer from problems such as complex preparation processes, high equipment requirements, and high costs, making large-scale production difficult. Summary of the Invention

[0005] To address or partially address the aforementioned problems, this invention proposes a method for preparing α-Fe2O3 nanoparticles via salt-assisted ultrasonic spray pyrolysis, comprising the following steps:

[0006] The auxiliary salt and ferric salt were dissolved in deionized water and ultrasonically prepared to form a precursor solution with an iron concentration of 0.01–1 mol / L;

[0007] The precursor solution was atomized in an ultrasonic atomizer with an ultrasonic frequency of 1.7 to 3 MHz, and the atomized droplets were collected. After collection, the droplets were ultrasonicated, filtered and dried to obtain α-Fe2O3 nanopowder.

[0008] Furthermore, the molar ratio of the auxiliary salt to the ferric salt is (1-10):1.

[0009] Furthermore, the auxiliary salt is selected from one or more eutectic mixtures of sodium nitrate, potassium nitrate, sodium acetate, potassium acetate, potassium chloride, and lithium chloride inorganic salts.

[0010] Furthermore, the ferric salt is selected from one of ferric sulfate, ferric chloride, ferric nitrate, and ferric acetate.

[0011] Furthermore, the collection of droplets generated by atomization specifically involves:

[0012] The droplets generated by atomization are carried by a carrier gas through a tubular furnace. The tail end of the tubular furnace is connected to a gas collecting bottle, which contains deionized water for collecting the droplet-like nanoparticles.

[0013] Furthermore, the heating section of the tubular furnace is 400–1000 mm long, and the heating temperature is 700–900 °C.

[0014] Furthermore, the carrier gas is a non-reducing gas, including one of air, nitrogen, and argon;

[0015] The flow rate of the carrier gas is 1 to 10 L / min.

[0016] Furthermore, the collection time of the droplets is 1 hour to 3 hours;

[0017] The ultrasonic time for the droplets is 30 min to 1 h.

[0018] On the other hand, the present invention proposes an α-Fe2O3 nanopowder prepared by the salt-assisted ultrasonic spray pyrolysis method described above.

[0019] Furthermore, the particle size of the α-Fe2O3 nanoparticles is 30–120 nm.

[0020] The beneficial effects of this invention are:

[0021] This invention utilizes an auxiliary salt as a high-temperature solvent during melting in a tube furnace. This prevents the agglomeration, growth, and densification of α-Fe₂O₃ nanoparticles formed in fine droplets. It addresses the problems of severe agglomeration, large particle size, and poor uniformity in powders prepared by spray pyrolysis. The α-Fe₂O₃ powder obtained by this method not only has small particle size, good uniformity, and good dispersibility, but the added auxiliary salt can also be recycled and reused. The entire preparation process is simple, easy to operate, low-cost, and has good repeatability. It can achieve the efficient preparation of monodisperse, high-purity α-Fe₂O₃ nanoparticles, making it suitable for industrial applications.

[0022] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The flowchart of the method for preparing α-Fe2O3 nanopowder by salt-assisted ultrasonic spray pyrolysis proposed in the embodiments of the present invention is shown.

[0025] Figure 2 The XRD pattern of the α-Fe2O3 nanopowder prepared in the embodiments of the present invention is shown;

[0026] Figure 3 The SEM image of the split sample prepared in Example 1 of the present invention is shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] This invention provides a method for preparing α-Fe₂O₃ nanoparticles using a salt-assisted ultrasonic spray pyrolysis method. An inorganic salt is added to a ferric solution to prepare a precursor solution. At a specific ultrasonic frequency, the precursor solution is atomized from the liquid phase into an aerosol via ultrasonic atomization. The aerosol particle size is approximately 1 μm. Driven by a carrier gas, the aerosol undergoes a series of pyrolysis and crystallization reactions in a tube furnace. Finally, the nanoparticles are obtained by washing with deionized water and drying. The main principle of the salt-assisted method is that the added salt acts as a high-temperature solvent, preventing the aggregation, growth, and densification of α-Fe₂O₃ nanoparticles formed in the fine droplets during melting in the tube furnace. After the reaction is complete, the added salt can be washed away and collected again. At this point, each droplet retains several nanoparticles, achieving a process of powder nanoparticle formation.

[0029] Specific technical solutions, such as Figure 1 As shown, it includes the following steps:

[0030] S1: Dissolve the auxiliary salt and ferric salt in deionized water and sonicate to prepare a precursor solution with an iron concentration of 0.01–1 mol / L; the sonication time is 15–30 min.

[0031] The molar ratio of the auxiliary salt to the iron salt is (1-10):1, and the purity of both the auxiliary salt and the ferric salt must be ≥99.0%.

[0032] The auxiliary salts include one or a eutectic mixture of sodium nitrate, potassium nitrate, sodium acetate, potassium acetate, potassium chloride, and lithium chloride;

[0033] Ferrous salts can be one of compounds such as ferric sulfate, ferric chloride, ferric nitrate, and ferric acetate.

[0034] S2: The precursor solution is placed in an ultrasonic nebulizer with an ultrasonic frequency of 1.7 to 3 MHz for atomization, and the droplets generated by atomization are collected. After collection, the droplets are ultrasonicated, filtered and dried to obtain α-Fe2O3 nanopowder.

[0035] The specific process for collecting the droplets generated by atomization is as follows: the droplets generated by atomization are driven by a carrier gas through a tubular furnace, the tail end of which is connected to a gas collecting bottle. The gas collecting bottle is filled with deionized water and is used to collect the nanoparticles in droplet form. The collection time is generally greater than or equal to 1 hour, and is generally 1 to 3 hours.

[0036] The tubular furnace used in this process has a heating section of 400–1000 mm and a heating temperature of 700–900 °C. The carrier gas is mainly a non-reducing gas, such as air, nitrogen, or argon, and the carrier gas flow rate is 1–10 L / min.

[0037] To more clearly illustrate the specific application of the method proposed in this invention, the following detailed description is provided in conjunction with specific embodiments.

[0038] Example 1

[0039] (1) Prepare 1000 ml of 0.01 mol / L ferric chloride solution and add 0.1 mol sodium acetate at the same time. The molar ratio is 10. Sonicate for 15 min to obtain a reddish-brown transparent precursor solution.

[0040] (2) The precursor solution prepared in step (1) is placed in an ultrasonic atomizer with an ultrasonic frequency of 3MHz to generate droplets. The droplets are passed through a tube furnace heated to 700℃ by nitrogen gas at a rate of 5L / min. The droplets are collected by a gas collecting bottle containing deionized water. The reaction is carried out for 2 hours. The deionized water containing the powder is ultrasonicated for 1 hour, filtered, and dried to obtain red α-Fe2O3 nanoparticles with a particle size of 30-50nm.

[0041] Comparative Example

[0042] (1) Prepare 1000 ml of 0.01 mol / L ferric chloride solution and sonicate for 15 min to obtain a reddish-brown transparent precursor solution;

[0043] (2) The precursor solution prepared in step (1) was placed in an ultrasonic atomizer with an ultrasonic frequency of 3 MHz to generate droplets. The droplets were passed through a tube furnace heated to 700 ℃ by nitrogen gas at a rate of 5 L / min. The droplets were collected by a gas collecting bottle containing deionized water and reacted for 2 h. The deionized water containing the powder was ultrasonicated for 1 h, filtered, and dried to obtain red α-Fe2O3 nanoparticles with a particle size of 200-500 nm.

[0044] Example 2

[0045] (1) Prepare 1000 ml of 0.1 mol / L ferric sulfate solution and add 0.5 mol potassium chloride at the same time. The molar ratio is 5. Sonicate for 15 min to obtain a reddish-brown transparent precursor solution.

[0046] (2) The precursor solution prepared in step (1) is placed in an ultrasonic atomizer with an ultrasonic frequency of 3MHz to generate droplets. The droplets are passed through a tube furnace heated to 750℃ by nitrogen gas at a rate of 5L / min. The droplets are collected by a gas collecting bottle containing deionized water and reacted for 2 hours. The deionized water containing the powder is ultrasonicated for 1 hour, filtered, and dried to obtain red α-Fe2O3 nanoparticles with a particle size of 40-70nm.

[0047] Example 3

[0048] (1) Prepare 1000 ml of 0.5 mol / L ferric nitrate solution and add 1 mol of sodium nitrate at the same time. The molar ratio is 2. Sonicate for 30 min to obtain a reddish-brown transparent precursor solution.

[0049] (2) The precursor solution prepared in step (1) was placed in an ultrasonic atomizer with an ultrasonic frequency of 3 MHz to generate droplets. The droplets were passed through a tube furnace heated to 800 ℃ by nitrogen gas at a rate of 5 L / min. The droplets were collected by a gas collecting bottle containing deionized water and reacted for 1 h. The deionized water containing the powder was ultrasonicated for 30 min, filtered, and dried to obtain red α-Fe2O3 nanoparticles with a particle size of 60-100 nm.

[0050] Example 4

[0051] (1) Prepare 1000 ml of 1 mol / L ferric acetate solution and add 1 mol of potassium acetate at the same time. The molar ratio is 1. Sonicate for 30 min to obtain a reddish-brown transparent precursor solution.

[0052] (2) The precursor solution prepared in step (1) is placed in an ultrasonic atomizer with an ultrasonic frequency of 3MHz to generate droplets. The droplets are passed through a tube furnace heated to 900℃ by nitrogen gas at a rate of 5L / min. The droplets are collected by a gas collecting bottle containing deionized water. After reacting for 1h, the deionized water containing the powder is ultrasonicated for 30min, filtered, and dried to obtain red α-Fe2O3 nanoparticles with a particle size of 80-120nm.

[0053] Test Example 1: X-ray Diffraction Analysis

[0054] The powders prepared from Examples 1-4 and the comparative examples were subjected to X-ray diffraction analysis, and the XRD patterns are shown below. Figure 2 As shown, analysis reveals that the powder is α-Fe2O3 (PDF card number 87-1166), meaning that the nanoparticles prepared in this invention are α-Fe2O3.

[0055] Test Example 2: Scanning Electron Microscopy (SEM) Test

[0056] Electron microscopy scanning tests were performed on the powders prepared in Examples 1-4 and the comparative examples. The scanning results showed that the α-Fe2O3 nanoparticles prepared in the comparative examples had a particle size between 200 and 500 nm, while the α-Fe2O3 nanoparticles prepared by the method of the present invention had a particle size between 30 and 120 nm. The produced separate particles were of uniform size. Figure 3 The SEM image of the α-Fe2O3 nanopowder prepared in Example 1 is shown only as an example.

[0057] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing α-Fe2O3 nanopowder by salt-assisted ultrasonic spray pyrolysis, characterized in that, The method comprises the following steps: ultrasonic preparation of a precursor solution with an iron concentration of 0.01-1 mol / L by dissolving an auxiliary salt and a ferric salt in deionized water; the molar ratio of the auxiliary salt to the ferric salt is (1-10):1; the ferric salt is selected from one of iron sulfate, iron chloride, iron nitrate and iron acetate; ultrasonic atomization of the precursor solution in an ultrasonic atomizer with an ultrasonic frequency of 1.7-3 MHz, and collection of the liquid droplets generated by the atomization, followed by ultrasonic treatment, filtration and drying of the liquid droplets to obtain α-Fe2O3 nanopowder; the collection of the liquid droplets generated by the atomization is specifically that the liquid droplets generated by the atomization are carried by a carrier gas through a tubular furnace, the tail end of the tubular furnace is connected to a gas collection bottle, the gas collection bottle contains deionized water and is used to collect the nanopowder in the form of liquid droplets.

2. The method according to claim 1, wherein the auxiliary salt is a eutectic mixture of one or more of sodium nitrate, potassium nitrate, sodium acetate, potassium acetate, potassium chloride and lithium chloride.

3. The method according to claim 1, wherein the heating section of the tubular furnace is 400-1000 mm, and the heating temperature is 700-900℃.

4. The method according to claim 1, wherein the carrier gas is a non-reducing gas, including one of air, nitrogen and argon; and the flow rate of the carrier gas is 1-10 L / min.

5. The method according to claim 1, wherein the collection time of the liquid droplets is 1-3 h; and the ultrasonic treatment time of the liquid droplets is 30 min-1 h. The α-Fe2O3 nanopowder is prepared by the salt-assisted ultrasonic spray pyrolysis method according to any one of claims 1-5. The particle size of the α-Fe2O3 nanopowder is 30-120 nm. ​ ​ ​ ​ 6. An α-Fe2O3 nanopowder, characterized in that, ​ 7. The a-Fe2O3 nanopowder of claim 6, wherein, ​

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