Introduction and application of the preparation method of nano ferroferric oxide

wallpapers Industry 2020-09-24
Ferroferric oxide is ferromagnetic. If the particle radius is at the nanometer level, it is called ferromagnetic particles.

Since 2013, a large number of literature on the preparation of nano-Fe3O4 have emerged, and some new preparation processes have also continued to appear. The traditional methods for preparing nano-Fe3O4 mainly include precipitation method, hydrothermal (solvothermal) method, micro emulsification method, and sol-gel method. Emerging preparation methods such as microwave method, pyrolysis of carbonyl precursor method, ultrasonic method, air oxidation method, pyrolysis-reduction method, polyol reduction method, etc. are gradually becoming the research focus of scholars. In the appropriate preparation methods of Fe3O4, new surfactants and preparation systems have also made breakthroughs. Surfactants are not limited to SDS, PEG, CTAB, citric acid, oleic acid, etc., and NSOCMCS, polyacrylamide as modifiers are also reported. The preparation system also successively appeared ethanol-water system, n-propanol-water, propylene glycol-water system and so on.

1. Precipitation method

The precipitation method is the most commonly used method for preparing nanoparticles due to its simple process operation and low cost, high product purity and uniform composition, and is suitable for large-scale production. At the same time, by adding an organic dispersant or complexing agent to the precipitation mixture, the dispersibility of the nanoparticles can be improved, and the shortcomings of easy aggregation of the nanoparticles can be overcome. Commonly used precipitation methods include co-precipitation, hydrolytic precipitation, ultrasonic precipitation, alkoxide hydrolysis, and chelate decomposition.

(1) Co-precipitation method

The co-precipitation method adds a precipitant to a solution containing multiple cations to precipitate all ions ultimately. To obtain uniform precipitation, usually, a salt solution containing multiple cations is slowly added to an excess of precipitant and stirred, so that the concentration of all ions greatly exceeds the equilibrium concentration of the precipitation, and try to make each component separate at the same time in proportion.

The principle is Fe2++2Fe3++8OH-→Fe3O4+4H2O. See the figure on the right.

When preparing nanoparticles by the precipitation method, the molar ratio of Fe2+ and Fe3+ directly affects the crystal structure of the product; the pH value, ion concentration, and reaction temperature of the solution all affect the size of the particles. How to prepare nanoparticles with a single crystal structure and uniform particle size by controlling the reaction conditions is the main problem faced by the precipitation method. The filtration and washing of the external precipitation agent are also issues that must be considered.

The ferroferric oxide nanoparticles obtained by the co-precipitation method mostly have a spherical structure with a small particle size (5-10nm). However, since the reaction temperature is relatively low, the crystallinity of the obtained particles is relatively poor. Moreover, the nano Fe3O4 particles prepared by this method are prone to aggregation between the particles during washing, filtration and drying, which will affect the performance of the nano Fe3O4.

(2) Hydrolysis precipitation method

The hydrolysis precipitation method uses the hydrolysis of alkaline substances to release OH-. Commonly used alkaline substances include urea, hexamethylene diamine, etc., which release OH- at a relatively slow rate. It is beneficial to produce uniform nanoparticles when preparing nano Fe3O4 particles. Particles, usually this method can produce nanoparticles with a particle size of 7nm to 39nm.

(3) Ultrasonic precipitation method

Ultrasound can produce a cavitation effect in the solvent, the generated cavitation bubbles collapse in a short time of 10-11 seconds, and a high temperature of about 5000K is generated in the bubble. Compared with the traditional mixing technology, this series of cavitation is more comfortable to achieve mesoscopic uniform mixing, eliminate local concentration unevenness, increase the reaction speed, stimulate the formation of new phases, and also have a shearing effect on accumulation, which is beneficial to small particles Formation. The application of ultrasonic technology has no special requirements on the nature of the system, as long as there is a liquid medium that transmits energy. Vijayakumar.R et al. used high-intensity ultrasonic radiation to prepare Fe3O4 particles with a particle size of 10nm and superparamagnetism from an aqueous solution of iron acetate salt.

(4) Alkoxide hydrolysis
Using sodium acetate ionization in water to generate acetate reduction, Fe was partially reduced to Fe in an autoclave at about 180°C. Yonghui Deng et al. heated it with FeCl₃ sodium acetate and ethylene glycol in an autoclave at 200°C for 8 hours. Fe3O4 nanoparticles with superparamagnetism.

(5) Chelate decomposition method
The principle of this method is that metal ions and appropriate ligands form a stable complex at room temperature. The complex is destroyed in the proper temperature and pH, and the metal ions are rereleased with the OH- ions in the solution and the addition of precipitating agents. The oxidant acts to generate insoluble metal oxides, hydroxides, salts and other residues of different valences, and further processing can obtain nanoparticles of a specific size or even a particular shape.

2. Hydrothermal (solvothermal) method
The hydrothermal (solvothermal) reaction is a general term for chemical reactions carried out in fluids such as aqueous solutions (organic solvents) or steam under high temperature and pressure. The hydrothermal method is a synthesis of nano-powders developed in the past ten years. The Fe3O4 prepared by this method has small particle size, relatively uniform particle size, does not require high-temperature calcination pretreatment, and can achieve the doping of multivalent ions. Miscellaneous. However, because the hydrothermal method involves the use of high-temperature and high-pressure equipment, the cost of this method is relatively high, and it isn't easy to achieve large-scale production.

The preparation of nano-Fe3O4 by hydrothermal method mostly uses inorganic iron salts (FeCl3·6H2O, FeCl2·4H2O, FeSO4) and organic iron salts (ferrocene Fe(C5H5)2) as precursors, with hydrazine and polyethene glycol, PVP, etc. as surfactants, synthesized under alkaline solution conditions below 200℃.

3. Microemulsification method
The micro emulsification method refers to the formation of an emulsion by two immiscible solvents under the action of surfactants, that is, amphiphilic molecules divide the continuous medium into tiny spaces to form a microreactor, in which the reactants react to form a solid phase. The processes of nucleation, crystal growth, coalescence, and aggregation are restricted by the microreactor, to form nanoparticles that are wrapped with a layer of surfactant and have a specific condensed structure and morphology.

The preparation of nanocatalysts by the microemulsion method has the advantages of simple equipment, mild experimental conditions and controllable particle size, which is unmatched by other methods. Therefore, it has become an exciting technology in the synthesis of nanocatalysts. The research on the preparation of nanocatalysts by microemulsion method mostly focuses on the control of particle size, and there are relatively few researches on the power of particle monodispersity.

4. Sol-gel method (sol-gel)
The method uses the hydrolysis and polymerization of metal alkoxides to prepare a uniform sol of metal oxide or metal hydroxide and then concentrates it into a transparent gel. The gel is dried and heat-treated to obtain superfine oxide powder. The disadvantage of the Sol-gel method is that the use of metal alkoxides as raw materials leads to the high cost and long synthesis cycle of the gelation process. At the same time, the application of the sol-gel method to prepare nanoparticles with a particle size below 100nm has not been reported.

Also, other preparation methods such as microwave method, pyrolysis carbonyl precursor method, ultrasonic method, air oxidation method, pyrolysis-reduction method, polyol reduction method, etc. have been reported successively.

Hai Yanbing etc. used FeSO4 solution to add ammonia solution in a microwave oven for 8 seconds to obtain black Fe3O4 nanoparticles. Alivasatos et al. used the pyrolysis carbonyl precursor method to prepare monodisperse γ-Fe3O4 nanoparticles. Since then, this method has been widely used in the preparation of monodisperse magnetic oxide nanoparticles. Liu et al. used the polyol reduction method to prepare FePt magnetic nanoparticles with a diameter of 3nm by the reduction reaction of ferrous acetylacetonate and platinum acetylacetonate in the high-temperature liquid phase. The particles were monodisperse under the protection of surfactants. Status. Meng Zhe et al. successfully prepared Fe3O4 ultrafine powders with high purity, strong magnetic properties and spherical distribution by using oxidation induction and air oxidation Fe(OH)2 suspension in an environment with pH=10 at room temperature.

application

In new electrification and information society, the application of magnetic materials is pervasive. As a multifunctional magnetic material, ferroferric oxide magnetic material has been widely used in the fields of tumour treatment, microwave absorption materials, catalyst carriers, cell separation, magnetic recording materials, magnetic fluids, and medicine. There are development prospects.

Trunnano is one of the world's largest producers of ferroferric oxide powder. If you have any questions or needs, please contact Dr Leo, email: brad@ihpa.net.