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Preparation method of nano ferroferric oxide

wallpapers Industry 2021-04-07
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 carbonyl precursor method, ultrasonic method, air oxidation method, pyrolysis-reduction method, polyol reduction method, etc. are gradually becoming the research hotspots of scholars. In the related preparation methods of Fe3O4, new types of surfactants and preparation systems have also made breakthroughs. Surfactants are not limited to SDS, PEG, CTAB, citric acid, oleic acid, etc., and NSOCMCS and polyacrylamide as modifiers have also been reported. The preparation system also successively appeared ethanol-water system, n-propanol-water, propylene glycol-water system, and so on.
 
Precipitation
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 agglomeration of the nanoparticles can be overcome. Commonly used precipitation methods include co-precipitation, hydrolysis precipitation, ultrasonic precipitation, alkoxide hydrolysis, and chelate decomposition.
(1) Co-precipitation method
The co-precipitation method adds a precipitating agent to a solution containing multiple cations to completely precipitate all ions. In order 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 out at the same time in proportion.
The principle is Fe2++2Fe3++8OH-→Fe3O4+4H2O.
When preparing nanoparticles by 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 agglomeration between the particles during washing, filtering, 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 prepare nanoparticles with a particle size of 7nm to 39nm.
(3) Ultrasonic precipitation method
Ultrasound can produce a cavitation effect in the solvent, and the generated cavitation bubbles collapse in a very 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 easier to achieve mesoscopic uniform mixing, eliminate local concentration unevenness, increase the reaction speed, stimulate the formation of new phases, and can also play a shearing effect on agglomeration, 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 at the appropriate temperature and pH, and the metal ions are released again 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 precipitates of different valences, and further processing can obtain nanoparticles of a certain size or even a certain form.
 
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 a small particle size, relatively uniform particle size, does not require high-temperature calcination pretreatment, and can achieve the doping of multivalent ions. miscellaneous. However, since the hydrothermal method requires the use of high-temperature and high-pressure equipment, the cost of this method is relatively high and it is difficult 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 polyethylene glycol, PVP, etc. as surfactants, synthesized under alkaline solution conditions below 200℃.
Shouheng Sun prepared superparamagnetic Fe3O4 particles with controllable particle size by hydrothermal method. First, Fe(acac)3 was used as the Fe source to prepare Fe3O4 particles with a particle size of 4nm, and then Fe3O4 particles with a particle size of 4nm were used as seeds, and the particle sizes of 6, 8, 12 were prepared by controlling the holding time and other factors. , 16nm Fe3O4 nanoparticles.
Zhen Li et al. reported the use of common FeCl3·H2O instead of expensive Fe(acac)3 as a precursor to prepare Fe3O4 nanoparticles.
Yadong Li et al. reported that FeCl3·6H2O, NaAC, EG, and PEG were used as raw materials to prepare monodisperse Fe3O4 nanoparticles with adjustable particle size.
 
Microemulsification
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 agglomeration are restricted by the microreactor, so as to form nanoparticles with a certain condensed structure and shape wrapped with a layer of surfactant.
The preparation of nano-catalysts by the microemulsion method has the advantages of simple equipment, mild experimental conditions, and controllable particle size, which are unmatched by other methods. Therefore, it has become a very interesting technology in the synthesis of nanocatalysts. Research on the preparation of nano-catalysts by the microemulsion method mostly focuses on the control of particle size, and there are relatively few studies on the control of particle monodispersity.
 
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 disadvantages of the Sol-gel method are that the use of metal alkoxides as raw materials leads to high costs and a long synthesis cycle in the gelation process. At the same time, the application of the sol-gel method to prepare nanoparticles with a particle size of less than 100nm has not been reported yet.
 
In addition, 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 et al. added FeSO4 solution to 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 use the reduction reaction of ferrous acetylacetonate and platinum acetylacetonate in the high-temperature liquid phase to prepare FePt magnetic nanoparticles with a diameter of 3 nm. The particles are monodisperse under the protection of surfactants. status. Meng Zhe et al. successfully prepared Fe3O4 ultrafine powder with high purity, strong magnetism, and spherical distribution by using oxidation induction and air oxidation Fe(OH)2 suspension in an environment with pH=10 at room temperature.

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